阅读说明：本技术 色散测量装置、脉冲光源、色散测量方法和色散补偿方法 (Dispersion measuring device, pulse light source, dispersion measuring method, and dispersion compensating method ) 是由 渡边向阳 重松恭平 井上卓 于 2020-03-27 设计创作，主要内容包括：本发明的色散测量装置(1A)具备脉冲形成部(3)、相关光学系统(4)、光检测部(5)和运算部(6)。脉冲形成部(3)根据从脉冲激光光源2输出的被测量光脉冲(Pa),形成包含彼此具有时间差且中心波长彼此不同的多个光脉冲的光脉冲串(Pb)。相关光学系统(4)接收从脉冲形成部(3)输出的光脉冲串(Pb),输出包含光脉冲串(Pb)的互相关或自相关的相关光(Pc)。光检测部(5)检测从相关光学系统(4)输出的相关光(Pc)的时间波形。运算部(6)基于相关光(Pc)的时间波形的特征量,推算脉冲激光光源(2)的波长色散量。由此,实现能够通过简单的结构测量波长色散的色散测量装置、脉冲光源、色散测量方法和色散补偿方法。(A dispersion measuring device (1A) of the present invention is provided with a pulse forming unit (3), a correlation optical system (4), a light detection unit (5), and a calculation unit (6). A pulse forming unit (3) forms an optical pulse train (Pb) including a plurality of optical pulses having time differences and different center wavelengths from each other, on the basis of a measurement optical pulse (Pa) output from a pulse laser light source (2). The correlation optical system (4) receives the optical pulse train (Pb) output from the pulse forming unit (3), and outputs correlated light (Pc) including a cross-correlation or an auto-correlation of the optical pulse train (Pb). A light detection unit (5) detects the time waveform of the correlated light (Pc) output from the correlation optical system (4). A calculation unit (6) estimates the amount of wavelength dispersion of the pulsed laser light source (2) on the basis of the characteristic amount of the time waveform of the correlated light (Pc). Thus, a dispersion measuring device, a pulse light source, a dispersion measuring method, and a dispersion compensating method capable of measuring wavelength dispersion with a simple configuration are realized.)

1. A dispersion measuring apparatus, characterized in that,

the disclosed device is provided with:

a pulse forming unit that forms an optical pulse train including a plurality of 2 nd optical pulses having time differences and center wavelengths different from each other, from the 1 st optical pulse output from the measurement target;

a correlation optical system that receives the optical pulse train output from the pulse forming unit and outputs correlated light including cross-correlation or auto-correlation of the optical pulse train;

a light detection unit that detects a time waveform of the correlated light; and

and a calculation unit that estimates a wavelength dispersion amount of the measurement target based on the characteristic amount of the time waveform.

2. A dispersion measuring apparatus, characterized in that,

the disclosed device is provided with:

a pulse forming unit that forms an optical pulse train including a plurality of 2 nd optical pulses having time differences and center wavelengths different from each other, from the 1 st optical pulse output from the light source;

a correlation optical system that receives the optical pulse train that has passed through the measurement target after being output from the pulse forming unit, and outputs correlation light including a cross-correlation or an auto-correlation of the optical pulse train;

a light detection unit that detects a time waveform of the correlated light; and

and a calculation unit that estimates a wavelength dispersion amount of the measurement target based on the characteristic amount of the time waveform.

3. The dispersion measuring apparatus according to claim 1 or 2,

the calculation unit estimates a wavelength dispersion amount of the measurement target based on a time interval of a plurality of light pulses included in the correlated light.

4. The dispersion measuring apparatus according to any one of claims 1 to 3,

the pulse forming section includes:

a spectroscopic element that spatially separates a plurality of wavelength components included in the 1 st optical pulse for each wavelength; a spatial light modulator that shifts the phases of the plurality of wavelength components output from the spectroscopic element from each other; and a light-condensing optical system that condenses the plurality of wavelength components output from the spatial light modulator.

5. The dispersion measuring apparatus of claim 4,

the spatial light modulator is a polarization-dependent spatial light modulator having a modulating effect in the 1 st polarization direction,

the pulse forming unit inputs the 1 st optical pulse including the 1 st polarization component and a2 nd polarization component orthogonal to the 1 st polarization,

the 1 st polarization component of the 1 st optical pulse is modulated by the spatial light modulator and output as the optical pulse train from the pulse forming unit,

the 2 nd polarization component of the 1 st light pulse is output from the pulse forming unit without being modulated by the spatial light modulator,

the correlation optical system generates the correlation light including the cross-correlation of the optical pulse train from the 1 st polarization component and the 2 nd polarization component.

6. The dispersion measuring apparatus according to any one of claims 1 to 5,

the correlation optical system includes at least one of a nonlinear optical crystal and a phosphor.

7. The dispersion measuring apparatus according to any one of claims 1 to 6,

further provided with:

an optical branching unit that branches the optical pulse train into two branches; and

a delay optical system for giving a time difference to one optical pulse train and the other optical pulse train branched out by the optical branching unit,

the correlation optical system generates the correlation light including autocorrelation from the one optical pulse train and the other optical pulse train after the time delay.

8. The dispersion measuring apparatus according to any one of claims 1 to 7,

the calculation unit compares a feature amount of the time waveform calculated in advance assuming that the wavelength dispersion of the measurement target is zero with the feature amount of the time waveform detected by the light detection unit, and estimates the wavelength dispersion of the measurement target.

9. A pulsed light source is characterized in that,

the disclosed device is provided with:

the dispersion measuring device of claim 1 or 2; and

and a pulse forming device for compensating for the wavelength dispersion amount obtained by the dispersion measuring device for the optical pulse input to or output from the measurement object.

10. A pulsed light source is characterized in that,

the dispersion measuring apparatus according to claim 4 or 5,

the spatial light modulator constitutes a part of a pulse forming apparatus that compensates for a wavelength dispersion amount obtained by the dispersion measuring apparatus for a light pulse input to or output from the measurement object.

11. A dispersion measuring method is characterized in that,

the method comprises the following steps:

a pulse forming step of forming an optical pulse train including a plurality of 2 nd optical pulses having time differences and center wavelengths different from each other, from the 1 st optical pulse output from the measurement target;

a correlated light generation step of generating correlated light including cross-correlation or auto-correlation of the optical pulse train;

a detection step of detecting a time waveform of the correlated light; and

and a calculation step of calculating a wavelength dispersion amount of the measurement target based on the characteristic amount of the time waveform.

12. A dispersion measuring method is characterized in that,

the method comprises the following steps:

a pulse forming step of forming an optical pulse train including a plurality of 2 nd optical pulses having time differences and center wavelengths different from each other, from the 1 st optical pulse output from the light source;

a correlated light generation step of generating correlated light including cross-correlation or auto-correlation of the optical pulse train passing through the measurement target after being output from the pulse formation step;

a detection step of detecting a time waveform of the correlated light; and

and a calculation step of calculating a wavelength dispersion amount of the measurement target based on the characteristic amount of the time waveform.

13. The dispersion measurement method according to claim 11 or 12,

in the calculating step, the wavelength dispersion amount of the measurement target is estimated based on a time interval of a plurality of light pulses included in the correlated light.

14. The dispersion measurement method according to any one of claims 11 to 13,

in the pulse forming step, a plurality of wavelength components included in the 1 st optical pulse are spatially separated for each wavelength, and after the plurality of wavelength components are shifted in phase from each other by using a spatial light modulator, the plurality of wavelength components are condensed.

15. The dispersion measurement method of claim 14,

the spatial light modulator is a polarization-dependent spatial light modulator having a modulating effect in the 1 st polarization direction,

in the pulse forming step, the 1 st optical pulse including the 1 st polarization component and the 2 nd polarization component orthogonal to the 1 st polarization is input, the 1 st polarization component of the 1 st optical pulse is modulated by the spatial optical modulator as the optical pulse train, and the 2 nd polarization component of the 1 st optical pulse is output without being modulated by the spatial optical modulator,

in the correlated light generating step, the correlated light including the cross-correlation of the optical pulse train is generated from the 1 st polarization component and the 2 nd polarization component.

16. The dispersion measurement method according to any one of claims 11 to 15,

in the correlated light generation step, at least one of a nonlinear optical crystal and a phosphor is used.

17. The dispersion measurement method according to any one of claims 11 to 16,

in the correlated light generation step, the optical pulse train is branched into two, one branched optical pulse train is time-delayed with respect to the other optical pulse train, and the correlated light including the autocorrelation of the optical pulse train is generated from the one time-delayed optical pulse train and the other time-delayed optical pulse train.

18. The dispersion measurement method according to any one of claims 11 to 17,

in the calculation step, the wavelength dispersion amount of the measurement target is estimated by comparing a feature amount of the time waveform calculated in advance assuming that the wavelength dispersion of the measurement target is zero with the feature amount of the time waveform detected in the detection step.

19. A dispersion compensation method, characterized in that,

the method comprises the following steps:

a step of estimating a wavelength dispersion amount of the measurement object by using the dispersion measurement method according to claim 11 or 12; and

and forming a pulse for compensating the wavelength dispersion amount for the optical pulse input to or output from the measurement object.

Technical Field

The invention relates to a dispersion measuring apparatus, a pulse light source, a dispersion measuring method and a dispersion compensating method.

Background

Patent document 1 and non-patent document 1 disclose methods of measuring wavelength dispersion of laser pulses. The measurement method described in these documents is called MIIPS (Multiphoton interferometric Phase Scan: Phase scanning by Multiphoton pulse Interference). Fig. 38 is a diagram schematically showing an example of the configuration of a measuring apparatus using MIIPS. The measuring apparatus 100 includes a pulsed light source 101 as a measurement target, a pulse control optical system (pulse shaper) 102 including a spatial light modulator (SLM or the like), an optical system 103 including an SHG crystal 103a, a beam splitter 104, and a calculation unit 105.

First, a sinusoidal phase spectrum modulation is applied to the light pulse output from the pulse light source 101 in the pulse control optical system 102. Then, the light output from the pulse control optical system 102 is input to the SHG crystal 103a, and a Second Harmonic (SHG) corresponding to the modulation pattern is generated in the SHG crystal 103 a. The SHG is input to the spectroscope 104, the emission spectrum of the SHG is acquired in the spectroscope 104, and the calculation unit 105 analyzes the emission spectrum.

In such a configuration, the emission spectrum as a function of the phase shift amount σ of the sinusoidal phase spectrum modulation pattern can be obtained, and the wavelength dispersion amount can be calculated based on the characteristic amount expressed in the two-dimensional data (MIIPS trace). Further, dispersion compensation of the optical pulse can be performed by applying the measured inverse dispersion of the chromatic dispersion to the modulation pattern of the spatial light modulator of the pulse control optical system 102.

Documents of the prior art

Patent document

Patent document 1: japanese Kokai publication No. 2006-502407

Non-patent document

Non-patent document 1: bingwei Xu et al, "Quantitative induction of the multiphoton internal phase method for the multistage phase medium and composition of the interferometric lasers", Journal of the Optical Society of America B, Vol.23, No.4, pp.750-759,2006

Disclosure of Invention

Problems to be solved by the invention

In the measurement apparatus 100 shown in fig. 38, the dispersion is measured based on the change in the emission spectrum according to the amount of phase shift of the phase modulation pattern of the sine wave. For this purpose, the luminescence spectrum must be measured. In general, in the measurement of a light emission spectrum, a combination of a spectroscopic element and a photodetector, or a photodetector (spectroscope) capable of detecting a wavelength-intensity characteristic is required. Therefore, the optical system becomes complicated.

An object of an embodiment is to provide a dispersion measuring apparatus, a pulse light source, a dispersion measuring method, and a dispersion compensating method capable of measuring wavelength dispersion with a simple configuration.

Means for solving the problems

An embodiment is a dispersion measuring device. The dispersion measuring device is provided with: a pulse forming unit that forms an optical pulse train including a plurality of 2 nd optical pulses having time differences and center wavelengths different from each other, from the 1 st optical pulse output from the measurement target; a correlation optical system that receives the optical pulse train output from the pulse forming unit and outputs correlated light including cross-correlation or auto-correlation of the optical pulse train; a light detection unit for detecting a time waveform of the relevant light; and a calculation unit for estimating the wavelength dispersion amount of the measurement object based on the characteristic amount of the time waveform.

An embodiment is a dispersion measuring device. The dispersion measuring device is provided with: a pulse forming unit that forms an optical pulse train including a plurality of 2 nd optical pulses having time differences and center wavelengths different from each other, from the 1 st optical pulse output from the light source; a correlation optical system that receives the optical pulse train that has passed through the measurement target after being output from the pulse forming unit, and outputs correlated light including cross-correlation or auto-correlation of the optical pulse train; a light detection unit for detecting a time waveform of the relevant light; and a calculation unit for estimating the wavelength dispersion amount of the measurement object based on the characteristic amount of the time waveform.

An embodiment is a pulsed light source. The pulse light source includes: the dispersion measuring apparatus of the above-described structure; and a pulse forming device for compensating the wavelength dispersion amount obtained by the dispersion measuring device for the optical pulse input to or output from the measurement object.

An embodiment is a pulsed light source. The pulse light source includes the dispersion measuring device having the above-described configuration, and the spatial light modulator constitutes a part of a pulse forming device that compensates for the wavelength dispersion amount obtained by the dispersion measuring device for the light pulse input to or output from the measurement object.

An embodiment is a dispersion measurement method. The dispersion measurement method comprises the following steps: a pulse forming step of forming an optical pulse train including a plurality of 2 nd optical pulses having time differences and center wavelengths different from each other, from the 1 st optical pulse output from the measurement target; a correlated light generation step of generating correlated light including cross-correlation or auto-correlation of the optical pulse train; a detection step of detecting a time waveform of the correlation light; and a calculation step of calculating a wavelength dispersion amount of the measurement object based on the characteristic amount of the time waveform.

An embodiment is a dispersion measurement method. The dispersion measurement method comprises the following steps: a pulse forming step of forming an optical pulse train including a plurality of 2 nd optical pulses having time differences and center wavelengths different from each other, from the 1 st optical pulse output from the light source; a correlated light generation step of generating correlated light including cross-correlation or auto-correlation of the optical pulse train passing through the measurement target after being output from the pulse formation step; a detection step of detecting a time waveform of the correlation light; and a calculation step of calculating a wavelength dispersion amount of the measurement object based on the characteristic amount of the time waveform.

An embodiment is a dispersion compensation method. The dispersion compensation method includes: a step of estimating a wavelength dispersion amount of the measurement object by using the dispersion measurement method having the above-described configuration; and a step of performing pulse formation for compensating the wavelength dispersion amount on the optical pulse input to or output from the measurement object.

Effects of the invention

According to the dispersion measuring device, the pulsed light source, the dispersion measuring method, and the dispersion compensating method of the embodiments, the chromatic dispersion can be measured by a simple structure.

Drawings

Fig. 1 is a diagram schematically showing a configuration of a dispersion measuring apparatus according to an embodiment.

Fig. 2 is a diagram showing an example of the configuration of the pulse forming section.

Fig. 3 is a diagram showing a modulation plane of the SLM.

Fig. 4 (a) to (c) are diagrams showing examples of the multipulses subjected to the bandwidth control.

Fig. 5 (a) to (c) are diagrams showing an example of a multipulse that is a comparative example and is not subjected to bandwidth control.

Fig. 6 is a diagram schematically showing a correlation optical system for generating the correlated light Pc including the autocorrelation of the optical pulse train Pb, as a configuration example of the correlation optical system.

Fig. 7 is a diagram schematically showing a correlation optical system for generating the correlated light Pc including the cross-correlation of the light pulse train Pb, as another configuration example of the correlation optical system.

Fig. 8 is a diagram schematically showing a correlation optical system for generating the correlated light Pc including the cross-correlation of the light pulse train Pb, as still another configuration example of the correlation optical system.

Fig. 9 is a diagram for conceptually explaining the feature amount of the correlated light Pc, and fig. 9 (a) shows an example of the time waveform of the correlated light Pc when the pulse laser light source does not have wavelength dispersion, and fig. 9 (b) shows an example of the time waveform of the correlated light Pc when the pulse laser light source has wavelength dispersion.

Fig. 10 is a diagram schematically showing an example of the hardware configuration of the arithmetic unit.

Fig. 11 is a flowchart showing a dispersion measuring method using the dispersion measuring apparatus.

Fig. 12 (a) is a diagram showing a spectral waveform of the single-pulse measurement optical pulse Pa, and fig. 12 (b) is a diagram showing a temporal intensity waveform of the measurement optical pulse Pa.

Fig. 13 (a) is a diagram showing a spectral waveform of the output light from the pulse forming unit when the SLM is subjected to the phase spectrum modulation in the rectangular waveform, and fig. 13 (b) is a diagram showing a time intensity waveform of the output light from the pulse forming unit.

Fig. 14 is a diagram showing the configuration of a modulation pattern calculation apparatus that calculates the modulation pattern of the SLM.

Fig. 15 is a block diagram showing the internal configuration of the phase spectrum designing section and the intensity spectrum designing section.

Fig. 16 is a diagram showing a flow of calculation of a phase spectrum by the iterative fourier transform method.

Fig. 17 is a diagram showing a flow of calculation of the phase spectrum function in the phase spectrum designing unit.

Fig. 18 is a diagram showing a flow of calculation of the spectral intensity in the intensity spectrum designing section.

Fig. 19 is a diagram showing an example of a flow of generation of a target spectrum map in the target generation unit.

FIG. 20 is a graph showing a calculated intensity spectrum function A_IFTAAn example of the flow of (ω).

FIG. 21 (a) is a spectral chart SG_IFTA(ω, t) and (b) of FIG. 21 is a graph showing a spectrum SG_IFTATarget spectrogram targetSG after (omega, t) change₀Graph of (ω, t).

Fig. 22 (a) is a graph showing a modulation pattern for generating a multipulse subjected to bandwidth control, and fig. 22 (b) is a graph showing an optical pulse train Pb generated by the modulation pattern of fig. 22 (a).

Fig. 23 is a spectrum diagram showing the optical pulse train Pb generated from the modulation pattern in fig. 22 (a).

Fig. 24 (a) is a graph showing a modulation pattern for generating a multi-pulse without performing bandwidth control, and fig. 24 (b) is a graph showing an optical pulse train Pd generated by the modulation pattern of fig. 24 (a).

Fig. 25 is a spectrum diagram showing the optical pulse train Pd generated based on the modulation pattern in fig. 24 (a).

Fig. 26 (a) is a graph plotting a relationship between the average value of the peak time intervals of the optical pulse trains Pb having different center wavelengths and the secondary dispersion amount of the measurement optical pulse Pa, and fig. 26 (b) is a graph plotting a relationship between the average value of the peak time intervals of the optical pulse trains Pd having the same center wavelength and the secondary dispersion amount of the measurement optical pulse Pa.

Fig. 27 is a graph plotting the relationship between the peak intensity of the optical pulse train Pb having mutually different center wavelengths and the secondary dispersion amount of the measurement optical pulse Pa.

Fig. 28 is a graph plotting a relationship between the full width at half maximum of the optical pulse train Pb having mutually different center wavelengths and the secondary dispersion amount of the measurement optical pulse Pa.

Fig. 29 (a) is a graph plotting a relationship between a difference in peak time intervals of the optical pulse trains Pb having different center wavelengths and the third order dispersion amount of the measurement optical pulse Pa, and fig. 29 (b) is a graph plotting a relationship between a difference in peak time intervals of the optical pulse trains Pd having the same center wavelength and the third order dispersion amount of the measurement optical pulse Pa.

Fig. 30 is a graph plotting the relationship between the peak intensity of the optical pulse train Pb having mutually different center wavelengths and the third order dispersion amount of the measurement optical pulse Pa.

Fig. 31 is a graph plotting a relationship between the full width at half maximum of the optical pulse train Pb having mutually different center wavelengths and the third order dispersion amount of the measurement optical pulse Pa.

Fig. 32 is a diagram showing a structure of a pulse forming unit according to modification 1.

Fig. 33 is a diagram showing a configuration of a modification 2.

Fig. 34 is a diagram showing a configuration of a modification example 3.

Fig. 35 is a diagram showing a configuration of a pulse light source according to modification 4.

Fig. 36 is a flowchart showing a dispersion compensation method according to modification 4.

Fig. 37 is a diagram showing a configuration of a pulse light source according to a modification example 5.

Fig. 38 is a view schematically showing an example of the configuration of a measuring apparatus using MIIPS.

Fig. 39 (a) is a graph showing an example of a spectral waveform for generating a multipulse subjected to bandwidth control, and fig. 39 (b) is a graph showing a time waveform of an optical pulse train corresponding to the spectral waveform of fig. 39 (a).

Fig. 40 (a) is a graph showing another example of a spectral waveform for generating a multipulse subjected to bandwidth control, and fig. 40 (b) is a graph showing a time waveform of an optical pulse train corresponding to the spectral waveform of fig. 40 (a).

Detailed Description

Embodiments of a dispersion measuring device, a pulsed light source, a dispersion measuring method, and a dispersion compensating method are described in detail below with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. The present invention is not limited to these examples.

Fig. 1 is a diagram schematically showing a configuration of a dispersion measuring apparatus according to an embodiment. The dispersion measuring apparatus 1A is an apparatus for measuring the wavelength dispersion of a pulsed laser light source 2 to be measured, and includes a pulse forming unit 3, a correlation optical system 4, a light detecting unit 5, and a calculating unit 6.

The optical input end 3a of the pulse forming unit 3 is optically coupled to the pulse laser light source 2 spatially or via an optical waveguide such as an optical fiber. The optical input end 4a of the relevant optical system 4 is optically coupled to the optical output end 3b of the pulse forming unit 3 spatially or via an optical waveguide such as an optical fiber. The light detection unit 5 is optically coupled to the light output end 4b of the relevant optical system 4 spatially or via an optical waveguide such as an optical fiber. The computing unit 6 is electrically connected to the pulse forming unit 3 and the light detecting unit 5.

The pulsed laser light source 2 as a measurement target outputs a coherent measurement light pulse Pa. The pulsed laser light source 2 is, for example, a femtosecond laser, and in one embodiment, is an LD direct excitation type Yb: a solid laser light source such as YAG pulse laser. The measurement optical pulse Pa is an example of the 1 st optical pulse in the present embodiment, and the time waveform thereof is, for example, a gaussian function. The full width at half maximum (FWHM) of the measurement light pulse Pa is, for example, in the range of 10 to 10000fs, in one example 100 fs. The measurement optical pulse Pa is an optical pulse having a certain bandwidth and includes a plurality of continuous wavelength components. In one embodiment, the bandwidth of the measured optical pulse Pa is 10nm, and the center wavelength of the measured optical pulse Pa is 1030 nm.

The pulse forming unit 3 is a part that forms an optical pulse train Pb including a plurality of optical pulses (2 nd optical pulses) from the measurement optical pulse Pa. The optical pulse train Pb is a single pulse group generated by dividing a spectrum constituting the measurement optical pulse Pa into a plurality of wavelength bands and using each wavelength band. In addition, there may be a portion overlapping each other in the boundary of a plurality of bands. In the following description, the optical pulse train Pb may be referred to as "bandwidth-controlled multipulse".

Fig. 2 is a diagram showing an example of the configuration of the pulse forming section 3. The pulse forming section 3 includes a diffraction grating 12, a lens 13, a Spatial Light Modulator (SLM)14, a lens 15, and a diffraction grating 16. The diffraction grating 12 is a spectroscopic element in the present embodiment, and is optically coupled to the pulsed laser light source 2. The SLM14 is optically coupled to the diffraction grating 12 via a lens 13. The diffraction grating 12 spatially separates a plurality of wavelength components included in the measurement optical pulse Pa for each wavelength. As the spectroscopic element, another optical member such as a prism may be used instead of the diffraction grating 12.

The measurement light pulse Pa enters the diffraction grating 12 obliquely, and is split into a plurality of wavelength components. The light P1 including the plurality of wavelength components is condensed for each wavelength component by the lens 13, and is imaged on the modulation surface of the SLM 14. The lens 13 may be a convex lens formed of a light transmitting member, or may be a concave mirror having a concave light reflecting surface.

The SLM14 shifts the phases of the plurality of wavelength components output from the diffraction grating 12 from each other in order to convert the measurement optical pulse Pa into the optical pulse train Pb. Therefore, the SLM14 receives the control signal from the arithmetic unit 6 (see fig. 1), and performs phase modulation and intensity modulation of the light P1 at the same time. Alternatively, SLM14 may be phase modulated only or intensity modulated only. The SLM14 is, for example, a phase modulation type. In one embodiment, SLM14 is a LCOS (liquid crystal on silicon) type. Although the transmission-type SLM14 is shown in the drawing, the SLM14 may be a reflection-type SLM.

Fig. 3 is a diagram showing modulation plane 17 of SLM 14. As shown in fig. 3, a plurality of modulation regions 17a are arranged along a certain direction a on the modulation surface 17, and each modulation region 17a extends in a direction B intersecting the direction a. The direction a is the light splitting direction of the diffraction grating 12. The modulation surface 17 functions as a fourier transform surface, and the respective wavelength components thus dispersed enter the plurality of modulation regions 17 a. The SLM14 modulates the phase and intensity of each incident wavelength component independently of the other wavelength components in each modulation region 17 a. Since the SLM14 of the present embodiment is of a phase modulation type, intensity modulation is realized by a phase pattern (phase image) appearing on the modulation surface 17.

The wavelength components of the modulated light P2 modulated by the SLM14 are focused on one point on the diffraction grating 16 by the lens 15. The lens 15 at this time functions as a condensing optical system for condensing the modulated light P2. The lens 15 may be a convex lens formed of a light transmitting member, or may be a concave mirror having a concave light reflecting surface. The diffraction grating 16 functions as a multiplexing optical system that multiplexes the modulated wavelength components. That is, the plurality of wavelength components of the modulated light P2 are condensed and multiplexed by the lens 15 and the diffraction grating 16, and become a multipulse (light pulse train Pb) whose bandwidth is controlled.

Fig. 4 is a diagram showing an example of a multi-pulse with bandwidth control. In this example, a light pulse Pb of 3 pulses is shown₁～Pb₃The formed optical pulse train Pb. Fig. 4 (a) is a spectral diagram in which the horizontal axis represents time, the vertical axis represents wavelength, and the light intensity is represented by the shade of color. Fig. 4 (b) shows a time waveform of the optical pulse train Pb. Light pulses Pb₁～Pb₃For example, in the form of a Gaussian function。

As shown in fig. 4 (a) and 4 (b), 3 light pulses Pb₁～Pb₃Are separated in time from each other, 3 light pulses Pb₁～Pb₃Are staggered with respect to each other. In other words, Pb with respect to one light pulse₁Another light pulse Pb₂With a time delay with respect to the further light pulse Pb₂Another light pulse Pb₃With a time delay. However, adjacent light pulses Pb₁、Pb₂(or Pb)₂、Pb₃) May also overlap each other. Adjacent light pulse Pb₁、Pb₂(or Pb)₂、Pb₃) The time interval (peak interval) of (c) is, for example, in the range of 10 to 10000fs, and in one example, 2000 fs. In addition, each light pulse Pb₁～Pb₃The FWHM of (A) is, for example, in the range of 10 to 5000fs, and in one example, 300 fs.

FIG. 4 (c) shows that 3 light pulses Pb are synthesized₁～Pb₃Spectrum of (a). As shown in FIG. 4 (c), 3 light pulses Pb are synthesized₁～Pb₃Has a single peak, but referring to fig. 4 (a), 3 light pulses Pb₁～Pb₃Are staggered from each other. The single peak shown in fig. 4 (c) corresponds approximately to the spectrum of the measurement light pulse Pa.

Adjacent light pulse Pb₁、Pb₂(or Pb)₂、Pb₃) The peak wavelength interval (c) is determined by the spectral bandwidth of the measurement light pulse Pa, and is approximately within a range of 2 times the full width at half maximum. In one example, in the case where the spectral bandwidth of the measured light pulse Pa is 10nm, the peak wavelength interval is 5 nm. Specifically, when the center wavelength of the measurement light pulse Pa is 1030nm, 3 light pulses Pb are generated₁～Pb₃Can be 1025nm, 1030nm and 1035nm, respectively.

Fig. 5 is a diagram showing an example of a multi-pulse without performing bandwidth control as a comparative example. In this example, 3 light pulses Pd are shown₁～Pd₃The formed optical pulse train Pd. FIG. 5 (a) is a light beam in the same manner as FIG. 4 (a)In the spectrum, the horizontal axis represents time, the vertical axis represents wavelength, and the light intensity is represented by the shade of color. Fig. 5 (b) shows a time waveform of the optical pulse train Pd. FIG. 5 (c) shows that 3 optical pulses Pd are combined₁～Pd₃Spectrum of (a).

As shown in (a) to (c) of fig. 5, 3 light pulses Pd₁～Pd₃Are separated in time from each other, but 3 light pulses Pd₁～Pd₃Are identical to each other. The pulse forming unit 3 of the present embodiment generates not such an optical pulse train Pd but an optical pulse train Pb having mutually different center wavelengths as shown in fig. 4.

Reference is again made to fig. 1. The correlation optical system 4 receives the optical pulse train Pb output from the pulse forming unit 3, and outputs the correlated light Pc including the cross-correlation or auto-correlation of the optical pulse train Pb. In the present embodiment, the correlation optical system 4 is configured to include a lens 41, an optical element 42, and a lens 43. The lens 41 is provided on the optical path between the pulse forming unit 3 and the optical element 42, and condenses the optical pulse train Pb output from the pulse forming unit 3 on the optical element 42.

The optical element 42 is, for example, a light-emitting body including at least one of a nonlinear optical crystal that generates a second harmonic wave (SHG) and a phosphor. The nonlinear optical crystal may be, for example, KTP (KTiOPO)₄) Crystal, LBO (LiB)₃O₅) Crystal and BBO (. beta. -BaB)₂O₄) And (4) crystals. Examples of the phosphor include coumarin, stilbene, and rhodamine. The optical element 42 receives the optical pulse train Pb and generates correlated light Pc including cross-correlation or auto-correlation of the optical pulse train Pb. The lens 43 collimates or condenses the correlated light Pc output from the optical element 42.

Here, a configuration example of the relevant optical system 4 will be described in detail. Fig. 6 is a diagram schematically showing a correlation optical system 4A for generating the correlated light Pc including the autocorrelation of the optical pulse train Pb, as a configuration example of the correlation optical system 4. The correlation optical system 4A has a beam splitter 44 as an optical branching means for branching the optical pulse train Pb into two. The beam splitter 44 is optically coupled to the pulse forming unit 3 shown in fig. 1, transmits a part of the optical pulse train Pb input from the pulse forming unit 3, and reflects the remaining part. The branching ratio of the beam splitter 44 is, for example, 1: 1.

One optical pulse train Pba branched by the beam splitter 44 reaches the lens 41 through the optical path 4c including the plurality of mirrors 45. The other optical pulse train Pbb branched by the beam splitter 44 reaches the lens 41 through the optical path 4d including a plurality of mirrors 46. The optical length of the optical path 4c and the optical length of the optical path 4d are different from each other. Therefore, the plurality of mirrors 45 and the plurality of mirrors 46 constitute a delay optical system that gives a time difference to one light pulse train Pba and the other light pulse train Pbb branched in the beam splitter 44. At least a part of the plurality of mirrors 46 is mounted on the movable stage 47, and the optical length of the optical path 4d is variable. Therefore, in this configuration, the time difference between the optical pulse train Pba and the optical pulse train Pbb can be varied.

In this example, the optical element 42 comprises a nonlinear optical crystal. The lens 41 condenses each of the optical pulse trains Pba, Pbb to the optical element 42, and causes the optical axes of the optical pulse trains Pba, Pbb to intersect each other at a predetermined angle in the optical element 42. As a result, in the optical element 42, which is a nonlinear optical crystal, the second harmonic is generated starting from the intersection of the optical pulse trains Pba, Pbb. The second harmonic is the correlated light Pc and includes the autocorrelation of the optical pulse train Pb. The correlated light Pc is collimated or condensed by the lens 43 and then input to the light detection unit 5.

Fig. 7 is a diagram schematically showing a correlation optical system 4B for generating the correlated light Pc including the cross-correlation of the light pulse train Pb, as another configuration example of the correlation optical system 4. In the correlation optical system 4B, the light pulse train Pb reaches the lens 41 through the optical path 4e, and the reference light pulse Pr, which is a single pulse, reaches the lens 41 through the optical path 4 f.

The optical path 4f includes a plurality of mirrors 48 bent in a U shape. At least a part of the plurality of mirrors 48 is mounted on the movable stage 49, and the optical length of the optical path 4f is variable. Therefore, in this configuration, the time difference (difference in time of arrival at the lens 41) between the optical pulse train Pb and the reference optical pulse Pr can be made variable.

In this example, the optical element 42 also comprises a nonlinear optical crystal. The lens 41 condenses the optical pulse train Pb and the reference optical pulse Pr to the optical element 42, and the optical axis of the optical pulse train Pb and the optical axis of the reference optical pulse Pr intersect each other at a predetermined angle in the optical element 42. As a result, in the optical element 42, which is a nonlinear optical crystal, the second harmonic is generated starting from the intersection of the light pulse train Pb and the reference light pulse Pr. The second harmonic is the correlated light Pc and contains the cross-correlation of the optical pulse train Pb. The correlated light Pc is collimated or condensed by the lens 43 and then input to the light detection unit 5.

Fig. 8 is a diagram schematically showing a correlation optical system 4C for generating the correlated light Pc including the cross-correlation of the light pulse train Pb, as still another configuration example of the correlation optical system 4. In this example, the SLM14 of the pulse forming section 3 is a polarization-dependent spatial light modulator having a modulating action in the 1 st polarization direction. On the other hand, the deflection surface of the measurement target light pulse Pa input to the pulse forming unit 3 is inclined with respect to the polarization direction in which the SLM14 has a modulating action, and the measurement target light pulse Pa includes a polarization component in the 1 st polarization direction (arrow Dp in the figure)₁) And a polarization component (symbol Dp in the figure) of the 2 nd polarization direction orthogonal to the 1 st polarization direction₂). The polarization of the measurement light pulse Pa may be not only the above-described polarization (linearly polarized light with an inclination) but also elliptically polarized light.

The polarization component of the 1 st polarization direction in the measurement light pulse Pa is modulated by the SLM14 and output from the pulse forming unit 3 as a light pulse train Pb. On the other hand, the polarization component of the 2 nd polarization direction in the measurement light pulse Pa is not modulated in the SLM14, and is directly output from the pulse forming unit 3. The unmodulated polarization component is supplied as a reference light pulse Pr, which is a single pulse, to the correlation optical system 4 coaxially with the light pulse train Pb.

The correlation optical system 4 generates the correlated light Pc including the cross-correlation of the optical pulse train Pb from the optical pulse train Pb and the reference optical pulse Pr. In this configuration example, by applying a delay to the optical pulse train Pb and varying the delay time (arrow E in the drawing) in the SLM14, the time difference between the optical pulse train Pb and the reference optical pulse Pr (the time difference when the optical pulse train reaches the lens 41) can be varied, and the correlated light Pc including the cross-correlation of the optical pulse Pb can be appropriately generated in the correlation optical system 4.

Fig. 9 is a diagram for conceptually illustrating the feature amount of the correlated light Pc. Fig. 9 (a) shows an example of the time waveform of the correlated light Pc when the pulsed laser light source 2 does not have wavelength dispersion (wavelength dispersion is zero). Fig. 9 (b) shows an example of the time waveform of the correlated light Pc when the pulsed laser light source 2 has wavelength dispersion (wavelength dispersion is not zero).

In addition, these examples show that the optical pulse train Pb input to the correlation optical system 4 includes 3 optical pulses Pb shown in fig. 4 (b)₁～Pb₃The case (1). In this case, the correlated light Pc is configured to include the light pulse Pb₁～Pb₃Respectively corresponding 3 light pulses Pc₁～Pc₃. Here, the light pulse Pc is applied₁～Pc₃Respectively, is set as PE₁～PE₃Light pulse Pc₁～Pc₃Is W in each full width at half maximum (FWHM)₁～W₃Light pulse Pc₁、Pc₂The peak time interval (pulse interval) of (1) is set to G_1,2Light pulse Pc₂、Pc₃Is set to G_2,3。

As shown in fig. 9 (a), when the pulse laser light source 2 does not have wavelength dispersion, the time waveform of the correlated light Pc is substantially the same as the time waveform of the optical pulse train Pb. In this example, for peak intensity, PE₂Bipe (polyethylene)₁And PE₃Large, PE₁And PE₃Are approximately equal. In addition, regarding the full width at half maximum, W₁、W₂And W₃Are substantially equal to each other. With respect to the peak time interval, G_1,2And G_2,3Are approximately equal.

On the other hand, as shown in fig. 9 (b), when the pulse laser light source 2 has wavelength dispersion, the time waveform of the correlated light Pc greatly changes from the time waveform of the optical pulse train Pb. In this example, the light pulse Pc₁～Pc₃Peak intensity PE of₁～PE₃Is greatly reduced as compared with (a) of fig. 9, and the light pulse Pc₁～Pc₃Full width at half maximum W₁～W₃Is greatly enlarged as compared with fig. 9 (a). And, the peak time interval G_1,2Is exceptionally long as compared with fig. 9 (a).

In this way, when the pulsed laser light source 2 has wavelength dispersion, the characteristic amount (peak intensity PE) of the time waveform of the correlated light Pc₁～PE₃Full width at half maximum W₁～W₃Peak time interval G_1,2、G_2,3) Which varies greatly compared to the case where the pulsed laser light source 2 has no wavelength dispersion. Then, the amount of change depends on the amount of wavelength dispersion of the pulsed laser light source 2. Therefore, by observing the change in the characteristic amount of the time waveform of the correlated light Pc, the wavelength dispersion amount of the pulsed laser light source 2 can be known with high accuracy and with ease.

Reference is again made to fig. 1. The light detection unit 5 receives the correlation light Pc output from the correlation optical system 4 and detects a time waveform of the correlation light Pc. The light detection unit 5 includes a photodetector (photodetector) such as a photodiode, for example. The light detection unit 5 converts the intensity of the correlation light Pc into an electric signal, thereby detecting the time waveform of the correlation light Pc. The electric signal as the detection result is supplied to the arithmetic section 6.

The calculation unit 6 estimates the amount of wavelength dispersion of the pulsed laser light source 2 based on the characteristic amount of the time waveform of the correlated light Pc supplied from the light detection unit 5. As described above, according to the findings of the present inventors, when the correlated light Pc including the cross-correlation or the auto-correlation of the optical pulse train Pb is generated, various characteristic amounts (for example, a pulse interval, a peak intensity, a pulse width, and the like) in the time waveform of the correlated light Pc have a significant correlation with the wavelength dispersion amount of the measurement target. Therefore, the calculation unit 6 can estimate the wavelength dispersion amount of the pulsed laser light source 2 to be measured with high accuracy by evaluating the characteristic amount of the time waveform of the correlated light Pc.

Fig. 10 is a diagram schematically showing an example of the hardware configuration of the arithmetic unit 6. As shown in fig. 10, the arithmetic unit 6 can be physically configured as a general computer including a main storage device such as a processor (CPU)61, a ROM62, and a RAM63, an input device 64 such as a keyboard, a mouse, and a touch panel, an output device 65 such as a display (including a touch panel), a communication module 66 such as a network card for transmitting and receiving data to and from other devices, and an auxiliary storage device 67 such as a hard disk.

The processor 61 of the computer can realize the function of the above-described arithmetic unit 6 by a wavelength dispersion amount calculation program. In other words, the wavelength dispersion amount calculation program causes the processor 61 of the computer to operate as the calculation unit 6. The wavelength dispersion amount calculation program is stored in a storage device (storage medium) inside or outside the computer such as the auxiliary storage device 67, for example. The storage device may also be a non-transitory recording medium. Examples of the recording medium include a flexible disk, a recording medium such as a CD or a DVD, a recording medium such as a ROM, a semiconductor memory, and a cloud server.

The auxiliary storage device 67 stores the characteristic amount of the time waveform of the correlated light Pc theoretically calculated in advance assuming that the wavelength dispersion of the pulsed laser light source 2 is zero. If this characteristic amount is compared with the characteristic amount of the time waveform detected by the light detection unit 5, it is known how much the characteristic amount of the correlation light Pc changes due to the wavelength dispersion of the pulse laser light source 2. Therefore, the calculation unit 6 can estimate the wavelength dispersion amount of the measurement target by comparing the characteristic amount stored in the auxiliary storage device 67 with the characteristic amount of the time waveform detected by the light detection unit 5.

Fig. 11 is a flowchart showing a dispersion measuring method using the dispersion measuring apparatus 1A including the above configuration. In this method, first, in the pulse forming step S1, design information necessary for forming the optical pulse train Pb is prepared. The design information includes, for example, a peak time interval, a peak intensity, a full width at half maximum, a number of pulses, a bandwidth control amount, and the like, assuming that the wavelength dispersion of the pulsed laser light source 2 is zero.

Then, a pulse laser light source 2 is configured to form a pulse laser including a plurality of light pulses Pb having time differences and different center wavelengths from each other, based on a measurement light pulse Pa output from the pulse laser light source₁～Pb₃The optical pulse train Pb. For example, a plurality of wavelength components included in the measurement optical pulse Pa are spatially separated for each wavelength, and the plurality of wavelength components are condensed after the phases of the plurality of wavelength components are shifted from each other by the SLM 14. Thereby, can easily generateAn optical pulse train Pb is formed.

Next, in the correlated light generation step S2, the correlated light Pc including the cross-correlation or auto-correlation of the light pulse train Pb is generated using the optical element 42 including at least one of the nonlinear optical crystal and the phosphor. For example, as shown in fig. 6, the optical pulse train Pb is branched into two, one branched optical pulse train Pbb is time-delayed with respect to the other optical pulse train Pba, and the autocorrelation correlated light Pc including the optical pulse train Pb is generated from the time-delayed one optical pulse train Pbb and the other optical pulse train Pba.

Next, after the time waveform of the correlated light Pc is detected in the detection step S3, the wavelength dispersion amount of the pulsed laser light source 2 is estimated in the calculation step S4 based on the feature amount of the time waveform. For example, based on the peak intensity E of the correlated light Pc₁～E₃Full width at half maximum W₁～W₃And peak time interval G_1,2、G_2,3At least one of the amounts of wavelength dispersion of the pulsed laser light source 2 is estimated. The amount of wavelength dispersion of the pulsed laser light source 2 is estimated by comparing the amount of characteristic of the time waveform of the correlated light Pc theoretically calculated on the assumption that the wavelength dispersion of the pulsed laser light source 2 is zero with the amount of characteristic of the time waveform detected in the detection step S3. As the feature value of the time waveform of the correlated light Pc assuming that the wavelength dispersion of the pulse laser light source 2 is zero, the feature value used for designing the optical pulse train Pb may be used as it is.

As explained with reference to fig. 8, the SLM14 may also be a polarization dependent SLM14 with a modulating effect in the 1 st polarization direction. In this case, in the pulse forming step S1, the light pulse Pa to be measured including both the component of the 1 st polarization direction and the component of the 2 nd polarization direction orthogonal to the 1 st polarization direction may be input, the component of the 1 st polarization direction in the light pulse Pa to be measured may be modulated into the light pulse train Pb in the SLM14, and the component of the 2 nd polarization direction in the light pulse Pa to be measured may be not modulated into the reference light pulse Pr in the SLM 14. Then, in the correlated light generating step S2, the correlated light Pc including the cross correlation of the optical pulse train Pb may be generated from the optical pulse train Pb having the 1 st polarization direction and the reference optical pulse Pr having the 2 nd polarization direction.

Here, the phase modulation for generating the multi-pulse with the bandwidth controlled in the SLM14 of the pulse forming unit 3 shown in fig. 2 will be described in detail. The region (spectral region) in front of the lens 15 and the region (time domain) behind the diffraction grating 16 are in a fourier transform relationship with each other, and phase modulation in the spectral region affects the time intensity waveform in the time domain. Therefore, the output light from the pulse forming section 3 can have various temporal intensity waveforms different from the measured light pulse Pa in accordance with the modulation pattern of the SLM 14.

As an example, fig. 12 (a) shows a spectral waveform (spectral phase G11 and spectral intensity G12) of a single pulse of the measurement target light pulse Pa, and fig. 12 (b) shows a temporal intensity waveform of the measurement target light pulse Pa. As an example, fig. 13 (a) shows a spectral waveform (spectral phase G21 and spectral intensity G22) of output light from the pulse forming unit 3 when the SLM14 is subjected to rectangular wave-shaped phase spectrum modulation, and fig. 13 (b) shows a temporal intensity waveform of the output light. In fig. 12 (a) and 13 (a), the horizontal axis represents the wavelength (nm), the left vertical axis represents the intensity value (arbitrary unit) of the intensity spectrum, and the right vertical axis represents the phase value (rad) of the phase spectrum. In fig. 12 (b) and 13 (b), the horizontal axis represents time (femtoseconds) and the vertical axis represents light intensity (arbitrary unit).

In this example, by supplying a phase spectrum waveform of a rectangular wave shape to the output light, a single pulse of the measurement light pulse Pa is converted into a double pulse accompanying higher-order light. The spectrum and waveform shown in fig. 13 are examples, and the temporal intensity waveform of the output light from the pulse forming unit 3 can be shaped into various shapes by combining various phase spectra and intensity spectra.

Fig. 14 is a diagram showing a configuration of a modulation pattern calculation apparatus 20 that calculates a modulation pattern of the SLM 14. The modulation pattern calculation device 20 is, for example, a personal computer; smart devices such as smart phones and tablet terminals; or a computer having a processor such as a cloud server. The arithmetic unit 6 shown in fig. 1 may also serve as the modulation pattern calculation device 20.

The modulation pattern calculation device 20 is electrically connected to the SLM14, calculates a phase modulation pattern for making the time intensity waveform of the output light of the pulse forming section 3 close to a desired waveform, and supplies a control signal including the phase modulation pattern to the SLM 14. The modulation pattern is data for controlling the SLM14, and is data of a table containing the intensity of a complex amplitude distribution or the intensity of a phase distribution. The modulation diagrams are, for example, Computer-Generated Holograms (CGH).

The modulation pattern calculation apparatus 20 of the present embodiment causes the SLM14 to exhibit a phase pattern including a phase pattern for phase modulation that gives a phase spectrum for obtaining a desired waveform to the output light and a phase pattern for intensity modulation that gives an intensity spectrum for obtaining a desired waveform to the output light. Therefore, as shown in fig. 14, the modulation pattern calculation device 20 includes an arbitrary waveform input unit 21, a phase spectrum design unit 22, an intensity spectrum design unit 23, and a modulation pattern generation unit 24.

That is, the processor of the computer provided in the modulation pattern calculation device 20 realizes the function of the arbitrary waveform input section 21, the function of the phase spectrum designing section 22, the function of the intensity spectrum designing section 23, and the function of the modulation pattern generating section 24. The respective functions may be implemented by the same processor or by different processors.

The processor of the computer can realize the above-described functions by the modulation pattern calculation program. Therefore, the modulation pattern calculation program causes the processor of the computer to operate as the arbitrary waveform input unit 21, the phase spectrum designing unit 22, the intensity spectrum designing unit 23, and the modulation pattern generating unit 24 in the modulation pattern calculating apparatus 20. The modulation pattern calculation program is stored in a storage device (storage medium) inside or outside the computer. The storage device may also be a non-transitory recording medium. Examples of the recording medium include a flexible disk, a recording medium such as a CD or a DVD, a recording medium such as a ROM, a semiconductor memory, and a cloud server.

The arbitrary waveform input unit 21 receives an input of a desired time intensity waveform from an operator. The operator inputs information on a desired time intensity waveform (e.g., pulse interval, pulse width, number of pulses, etc.) to the arbitrary waveform input section 21. Information on a desired temporal intensity waveform is supplied to the phase spectrum designing section 22 and the intensity spectrum designing section 23. The phase spectrum designing section 22 calculates a phase spectrum of the output light of the pulse forming section 3 suitable for realizing the supplied desired time intensity waveform. The intensity spectrum designing section 23 calculates an intensity spectrum of the output light of the pulse forming section 3 suitable for realizing the supplied desired temporal intensity waveform.

The modulation pattern generating unit 24 calculates a phase modulation pattern (for example, a computer-synthesized hologram) of the output light for supplying the phase spectrum obtained in the phase spectrum designing unit 22 and the intensity spectrum obtained in the intensity spectrum designing unit 23 to the pulse forming unit 3. Then, the control signal SC containing the calculated phase modulation pattern is supplied to the SLM 14. The SLM14 is controlled based on a control signal SC.

Fig. 15 is a block diagram showing the internal configuration of the phase spectrum designing section 22 and the intensity spectrum designing section 23. As shown in fig. 15, the phase spectrum designing section 22 and the intensity spectrum designing section 23 include a fourier transform section 25, a function replacing section 26, a wave function correcting section 27, an inverse fourier transform section 28, and a target generating section 29. The target generation unit 29 includes a fourier transform unit 29a and a spectrogram correction unit 29 b. The functions of these components will be described in detail later.

Here, the desired temporal intensity waveform is represented as a function of the time domain and the phase spectrum is represented as a function of the frequency domain. Thus, a phase spectrum corresponding to the desired temporal intensity waveform is obtained, for example, by an iterative fourier transform based on the desired temporal intensity waveform. Fig. 16 is a diagram showing a flow of calculation of a phase spectrum by the iterative fourier transform method.

First, an initial intensity spectrum function A as a function of frequency ω is prepared₀(ω) and phase spectral function Ψ₀(ω) (process number (1) in the figure). In one example, these intensity spectrum functions A₀(ω) and phase spectral function Ψ₀And (ω) represents the spectral intensity and the spectral phase of the input light, respectively.Next, a spectrum function A including intensity is prepared₀(ω) and phase spectral function Ψ_n(ω) waveform function (a) in the frequency domain (process number (2) in the figure).

[ formula 1]

The subscript n indicates after the nth fourier transform process. The initial phase spectral function Ψ described above was used prior to the initial (1 st) Fourier transform processing₀(ω) as a function of the phase spectrum Ψ_n(ω). i is an imaginary number.

Next, fourier transform from the frequency domain to the time domain is performed on the function (a) (arrow a1 in the figure). Thereby, a waveform function B including the time intensity is obtained_n(t) and time phase waveform function Θ_n(t) waveform function (b) in the frequency domain (process number (3) in the figure).

[ formula 2]

Next, the time intensity waveform function B included in the above function (B) is applied_n(t) substitution to a time intensity waveform function Target based on the desired waveform₀(t) (processing numbers (4) and (5) in the figure).

[ formula 3]

b_n(t)：＝Target₀(t)…(c)

[ formula 4]

Next, the function (d) is subjected to inverse fourier transform from the time domain to the frequency domain (arrow a2 in the figure). Thereby, a spectrum function B containing intensity is obtained_n(ω) and phase spectral function Ψ_n(ω) waveform function (e) of the frequency domain (process number (6) in the figure).

[ formula 5]

Next, in order to constrain the intensity spectrum function B included in the above function (e)_n(ω) replaced by the original intensity Spectrum function A₀(ω) (process number (7) in the figure).

[ formula 6]

B_n(ω)：＝A₀(ω)…(f)

Thereafter, by repeating the above-described processes (2) to (7) a plurality of times, the phase spectrum function Ψ in the waveform function can be made to be_nThe phase spectral shape represented by (ω) approximates the phase spectral shape corresponding to the desired temporal intensity waveform. The resulting phase spectral function Ψ_IFTA(ω) becomes the basis of the modulation pattern for obtaining the desired temporal intensity waveform.

However, the above-described fourier transform method has a problem that although the time intensity waveform can be controlled, the frequency component (wavelength of the frequency band) constituting the time intensity waveform cannot be controlled. Therefore, the modulation pattern calculation device 20 of the present embodiment calculates a phase spectrum function and an intensity spectrum function which are the basis of the modulation pattern by using the calculation method described below. Fig. 17 is a diagram showing a flow of calculation of the phase spectrum function in the phase spectrum designing section 22.

First, an initial intensity spectrum function A as a function of frequency ω is prepared₀(omega) and phase spectral function phi₀(ω) (process number (1) in the figure). In one example, these intensity spectrum functions A₀(omega) and phase spectral function phi₀And (ω) represents the spectral intensity and the spectral phase of the input light, respectively. Next, a spectrum function A including intensity is prepared₀(omega) and phase spectral function phi₀(ω) the 1 st waveform function (g) in the frequency domain (process number (2-a)). Where i is an imaginary number.

[ formula 7]

Next, the fourier transform unit 25 of the phase spectrum designing unit 22 performs fourier transform from the frequency domain to the time domain on the function (g) (arrow a3 in the figure). Thereby, a waveform function a containing time intensity is obtained₀(t) and time phase waveform function phi₀(t) the 2 nd wave function (h) in the time domain (fourier transform step, processing number (3)).

[ formula 8]

Next, the function replacing unit 26 of the phase spectrum designing unit 22 sets the time intensity waveform function Target based on the desired waveform input to the arbitrary waveform input unit 21 as shown in the following expression (i)₀(t) substituting into the time intensity waveform function b₀(t) (Process No. (4-a)).

[ formula 9]

b₀(t)＝Target₀(t)…(i)

Next, the function replacing section 26 of the phase spectrum designing section 22 uses the time intensity waveform function b as shown in the following expression (j)₀(t) substitution time intensity waveform function a₀(t) of (d). That is, the time intensity waveform function a included in the function (h) is used₀(t) substitution to a time intensity waveform function Target based on the desired waveform₀(t) (function replacing step, process number (5)).

[ formula 10]

Next, the waveform function correction unit 27 of the phase spectrum design unit 22 corrects the 2 nd waveform function so that the spectrum of the 2 nd waveform function (j) after the replacement approaches the target spectrum generated in advance according to the desired wavelength band. First, the 2 nd waveform function (j) is converted into a spectrogram SG by performing time-frequency conversion on the replaced 2 nd waveform function (j)_0,k(ω, t) (process number (5-a) in the figure). The subscript k denotes the k-th conversion process.

Here, the time-frequency conversion is a process of performing frequency filtering processing or numerical operation processing (processing of multiplying a window function while shifting the window function and deriving a spectrum for each time) on a composite signal such as a time waveform to convert the composite signal into three-dimensional information composed of time, frequency, and intensity of a signal component (spectrum intensity). In the present embodiment, the conversion result (time, frequency, spectral intensity) is defined as a "spectrogram".

Examples of the Time-frequency conversion include a Short-Time Fourier Transform (STFT), a wavelet Transform (haar wavelet Transform, Gabor wavelet Transform, mexican hat wavelet Transform, and morale wavelet Transform), and the like.

In addition, a target spectrum map TargetSG generated in advance in accordance with a desired wavelength band is read from the target generation unit 29₀(ω, t). The target spectrogram TargetSG₀The (ω, t) is a value substantially equal to the target time waveform (the time intensity waveform and the frequency components constituting it), and is generated in the target spectrogram function of the processing number (5-b).

Subsequently, the wave function correcting section 27 of the phase spectrum designing section 22 performs the spectrogram SG_0,k(ω, t) and target spectrogram targetSG₀Pattern matching of (ω, t) and investigation of similarity (degree of agreement). In the present embodiment, an evaluation value is calculated as an index indicating the degree of similarity. Then, in the next process number (5-c), it is determined whether or not the obtained evaluation value satisfies a predetermined termination condition. If the condition is satisfied, the process proceeds to the process number (6), and if the condition is not satisfied, the process proceeds to the process number (5-d). In the processing number (5-d), the time phase waveform function Φ included in the 2 nd waveform function is set₀(t) changing to an arbitrary time phase waveform function phi_0,k(t) of (d). The 2 nd waveform function after changing the time phase waveform function is converted again into a spectrogram by time-frequency conversion such as STFT.

Thereafter, the above-mentioned process numbers (5-a) to (5-d) were repeated. Thus, the 2 nd waveform function is corrected so as to make the spectral pattern SG_0,k(ω, t) gradually approaches the target spectrogram, targetSG₀(ω, t) (the wave function correction step).

Then, the inverse fourier transform unit 28 of the phase spectrum designing unit 22 performs inverse fourier transform on the corrected 2 nd waveform function (arrow a4 in the figure), and generates the 3 rd waveform function (k) in the frequency domain (inverse fourier transform step, processing number (6)).

[ formula 11]

The 3 rd waveform function (k) includes a phase spectrum function phi_0,k(ω) becomes the desired phase spectral function Φ to be finally obtained_TWC-TFD(ω). The phase spectral function phi_TWC-TFD(ω) is supplied to the modulation pattern generation section 24.

Fig. 18 is a diagram showing a flow of calculating the spectral intensity in the intensity spectrum designing section 23. Note that the process numbers (1) to (5-c) are the same as the above-described flow of calculating the spectral phase in the phase spectrum designing section 22, and therefore, the description thereof is omitted.

The wave function correcting unit 27 of the intensity spectrum designing unit 23 displays the spectrum graph SG_0,k(ω, t) and target spectrogram targetSG₀When the evaluation value of the similarity of (ω, t) does not satisfy the predetermined termination condition, the time-phase waveform function Φ included in the 2 nd waveform function₀(t) is constrained by an initial value, and the time intensity is a wave function b₀(t) changing to an arbitrary time intensity waveform function b_0,k(t) (Process No. (5-e)). The 2 nd waveform function after the change of the time intensity waveform function is converted into a spectrogram again by time-frequency conversion such as STFT.

Thereafter, the treatment numbers (5-a) to (5-c) were repeated. Thus, the 2 nd waveform function is corrected so as to make the spectral pattern SG_0,k(ω, t) gradually approaches the target spectrogram, targetSG₀(ω, t) (the wave function correction step).

Then, the inverse fourier transform unit 28 of the intensity spectrum designing unit 23 performs inverse fourier transform on the corrected 2 nd waveform function (arrow a4 in the figure), and generates the 3 rd waveform function (m) in the frequency domain (inverse fourier transform step, processing number (6)).

[ formula 12]

Next, in processing number (7-B), the filter processing section of the intensity spectrum designing section 23 applies the intensity spectrum function B included in the 3 rd waveform function (m)_0,k(ω) a filtering process (filtering process step) based on the intensity spectrum of the input light is performed. In particular, in the intensity spectrum function B_0,kIn the intensity spectrum obtained by multiplying (ω) by the coefficient α, a portion exceeding the cutoff intensity of each wavelength determined based on the intensity spectrum of the input light is cut off. This is because, in all wavelength regions, the intensity spectrum function α B_0,k(ω) does not exceed the spectral intensity of the input light.

In one example, the cutoff intensity for each wavelength is set to be equal to the intensity spectrum of the input light (in this embodiment, the initial intensity spectrum function a)₀(ω)) are consistent. In this case, the intensity spectrum function α B is represented by the following formula (n)_0,k(omega) specific intensity spectral function A₀(omega) large frequency as intensity spectrum function A_TWC-TFDThe value of (ω) is taken into the intensity spectrum function A₀The value of (ω). In addition, in the intensity spectrum function α B_0,k(omega) is the intensity spectrum function A₀At frequencies below (ω), as a function of the intensity spectrum A_TWC-TFD(ω) value, taking into the intensity spectrum function α B_0,k(ω) value (process number (7-b) in the figure).

[ formula 13]

The intensity spectrum function A_TWC-TFD(ω) is supplied to the modulation pattern generation unit 24 as a desired spectral intensity to be finally obtained.

The modulation pattern generation unit 24 calculates a phase spectrum function Φ to be calculated by the phase spectrum design unit 22_TWC-TFD(ω) and the intensity spectrum function A calculated by the intensity spectrum designing section 23_TWC-TFDThe spectral intensity represented by (ω) is provided to a phase modulation pattern (e.g., a computer-synthesized hologram) of the output light (data generation step).

Here, fig. 19 shows a target spectrum map TargetSG in the target generation unit 29₀An example of the (ω, t) generation flow is shown. Target spectrogram targetSG₀Since (ω, t) represents a target time waveform (a time intensity waveform and frequency components (band components) constituting the time waveform), generation of a target spectrum diagram is an extremely important step for controlling the frequency components (band components).

As shown in fig. 19, the target generation unit 29 first inputs a spectral waveform (initial intensity spectrum function a)₀(omega) and the initial phase spectral function phi₀(ω)), and a desired time intensity waveform function Target₀(t) of (d). In addition, a time function p containing information of a desired frequency (wavelength) bandwidth is input₀(t) (Process No. 1).

Next, the Target generation unit 29 calculates a waveform function Target for realizing the time intensity by using, for example, an iterative fourier transform method shown in fig. 16₀(t) phase spectral function Φ_IFTA(ω) (process number (2)).

Next, the target generation unit 29 uses the phase spectrum function Φ obtained previously_IFTA(ω) iterative Fourier transform method, calculating for realizing the time intensity waveform function Target₀(t) intensity Spectrum function A_IFTA(ω) (process number (3)). Here, FIG. 20 shows a calculated intensity spectrum function A_IFTAAn example of the flow of (ω).

First, an initial intensity spectrum function A is prepared_k＝0(ω) and phase spectral function Ψ₀(ω) (process number (1) in the figure). Next, a spectrum function A including intensity is prepared_k(ω) and phase spectral function Ψ₀(ω) waveform function (o) of frequency domain (process number in the figure: (ω))2))。

[ formula 14]

The subscript k indicates after the kth fourier transform process. The initial intensity spectrum function A described above is used prior to the initial (1 st) Fourier transform processing_k＝0(omega) as a function of the intensity spectrum A_k(ω). i is an imaginary number.

Next, fourier transform from the frequency domain to the time domain is performed on the function (o) (arrow a5 in the figure). Thereby, a waveform function b containing time intensity is obtained_k(t) waveform function (p) in the frequency domain (processing number (3) in the figure).

[ formula 15]

Then, the time intensity waveform function b included in the above function (p) is used_k(t) substitution to a time intensity waveform function Target based on the desired waveform₀(t) (processing numbers (4) and (5) in the figure).

[ formula 16]

b_k(t)：＝Targrt₀(t)…(q)

[ formula 17]

Next, the function (r) is subjected to inverse fourier transform from the time domain to the frequency domain (arrow a6 in the figure). Thereby, a function C containing an intensity spectrum is obtained_k(ω) and phase spectral function Ψ_k(ω) waveform function(s) in the frequency domain (process number (6) in the figure).

[ formula 18]

Next, in order to constrain the phase spectrum function Ψ included in the above function(s)_k(ω) replacement by the initial phase spectral function Ψ₀(ω) (Process number (7-a) in the figure).

[ formula 19]

Ψ_k(ω)：＝Ψ₀(ω)…(t)

Further, the intensity spectrum function C in the frequency domain after the inverse Fourier transform is applied_k(ω) a filtering process based on the intensity spectrum of the input light is performed. In particular, it will be determined by the intensity spectrum function C_k(ω) is a partial cut-off exceeding the cut-off intensity of each wavelength determined based on the intensity spectrum of the input light in the intensity spectrum.

In one example, the cutoff intensity for each wavelength is set to be related to the intensity spectrum of the input light (e.g., the initial intensity spectrum function A)_k＝0(ω)) are consistent. In this case, as shown in the following equation (u), the intensity spectrum function C_k(omega) specific intensity spectral function A_k＝0(omega) large frequency as intensity spectrum function A_kThe value of (ω) is taken into the intensity spectrum function A_k＝0The value of (ω). In addition, in the intensity spectrum function C_k(omega) is the intensity spectrum function A_k＝0At frequencies below (ω), as a function of the intensity spectrum A_k(ω) value, taking in the intensity spectrum function C_k(ω) value (process number (7-b) in the figure).

[ formula 20]

The intensity spectrum function C included in the above function(s)_k(ω) is replaced with the intensity spectrum function A after the filtering process based on the above-mentioned formula (u)_k(ω)。

Thereafter, by repeating the above-described processes (2) to (7-b), the intensity spectrum function A in the waveform function can be made_k(ω) an intensity spectrum shape close to the intensity light corresponding to the desired temporal intensity waveformThe spectral shape. Finally, an intensity spectrum function A is obtained_IFTA(ω)。

Reference is again made to fig. 19. The phase spectral function Φ in the processing numbers (2) and (3) described above_IFTA(omega) and intensity Spectroscopy function A_IFTAThe calculation of (ω) yields the 3 rd waveform function (v) of the frequency domain including these functions (process number (4)).

[ formula 21]

The fourier transform unit 29a of the target generation unit 29 fourier-transforms the above wave function (v). Thereby, the 4 th wave function (w) in the time domain is obtained (process number (5)).

[ formula 22]

The spectrogram correcting part 29b of the target generating part 29 converts the 4 th wave function (w) into the spectrogram SG by time-frequency conversion_IFTA(ω, t) (process number (6)). Then, in the processing number (7), based on the time function p containing the desired frequency (wavelength) bandwidth information₀(t) to correct the spectrogram SG_IFTA(ω, t), thereby generating a target spectrum map TargetSG₀(ω, t). For example, the spectral pattern SG is partially cut out from two-dimensional data_IFTACharacteristic patterns appearing in (ω, t) based on a function of time p₀(t) performing an operation of the frequency component of the portion. Specific examples thereof will be described in detail below.

For example, consider a triple pulse with a time interval of 2 picoseconds as the desired time intensity waveform function Target₀(t) in the case of (c). At this time, the spectrogram SG_IFTA(ω, t) is the result shown in (a) of FIG. 21. In fig. 21 (a), the horizontal axis represents time (unit: femtosecond) and the vertical axis represents wavelength (unit: nm). The spectral values are represented by the light and shade of the graph, and the brighter the spectral values areIs large. In the spectrogram SG_IFTAIn (ω, t), the triple pulse is taken as a domain D separated on the time axis at intervals of 2 picoseconds₁、D₂And D₃And occurs. Domain D₁、D₂And D₃Has a center (peak) wavelength of 800 nm.

These fields D do not need to be operated assuming that only the temporal intensity waveform of the output light is intended to be controlled (only the triplets are intended to be obtained)₁、D₂And D₃. However, when the frequency (wavelength) band of each pulse is to be controlled, these regions D are required₁、D₂And D₃The operation of (2). That is, as shown in FIG. 21 (b), each domain D is set to₁、D₂And D₃Moving independently of each other in the direction along the wavelength axis (vertical axis) means changing the constituent frequency (band) of each pulse. Such change of the constituent frequency (band) of each pulse is based on a time function p₀(t) is carried out.

For example, in the field D₂Has a peak wavelength fixed at 800nm and is in a domain D₁And D₃The time function p is described in such a manner that the peak wavelengths of (A) are shifted in parallel by-2 nm and +2nm, respectively₀At (t), spectrogram SG_IFTA(ω, t) changes to the target spectrum TargetSG shown in (b) of FIG. 21₀(ω, t). For example, by performing such processing on the spectrogram, a target spectrogram in which the constituent frequency (wavelength band) of each pulse is arbitrarily controlled can be generated without changing the shape of the time intensity waveform.

The effects obtained by the dispersion measuring apparatus 1A and the dispersion measuring method of the present embodiment described above will be described.

In the dispersion measuring apparatus 1A and the dispersion measuring method according to the present embodiment, the pulse forming unit 3 (pulse forming step S1) generates a dispersion measuring signal including a plurality of optical pulses Pb including time differences and having different center wavelengths from each other, from the measurement target optical pulse Pa output from the pulse laser light source 2₁～Pb₃The optical pulse train Pb.

In such a case, for example, when the correlated light Pc containing the cross-correlation or auto-correlation of the light pulse train Pb is generated using a nonlinear optical crystal or the like, the phaseVarious characteristic quantities (e.g., peak intensity PE) in the time waveform of the turn-off light Pc₁～PE₃Full width at half maximum W₁～W₃Peak time interval G_1,2、G_2,3Etc.) has a significant correlation with the amount of wavelength dispersion of the pulsed laser light source 2. Therefore, according to the present embodiment, the wavelength dispersion amount of the pulsed laser light source 2 can be accurately estimated in the calculation unit 6.

Further, according to the present embodiment, unlike the measurement device 100 shown in fig. 38, since it is not necessary to measure the emission spectrum, the optical system of the light detection unit 5 can be simplified, and the wavelength dispersion of the pulse laser light source 2 can be measured with a simple configuration. In addition, a combination of a spectrometer and a photodetector that are generally used for measurement of an emission spectrum, or a photodetector that can detect a wavelength-intensity characteristic is generally expensive, and according to the present embodiment, this is not necessary, and therefore, it can contribute to cost reduction of the apparatus.

As in the present embodiment, the calculation unit 6 (in the calculation step S4) may be based on the peak time interval G of the optical pulse train Pb_1,2、G_2,3The wavelength dispersion amount of the measurement optical pulse Pa is obtained. As shown in the following examples, the present inventors have found that, among various features in the time waveform, the peak time interval G is particularly important_1,2、G_2,3There is a significant correlation with the amount of wavelength dispersion of the pulsed laser light source 2. Therefore, by the peak time interval G according to the optical pulse train Pb_1,2、G_2,3By estimating the amount of wavelength dispersion of the measurement optical pulse Pa, the amount of wavelength dispersion of the pulse laser light source 2 can be estimated with higher accuracy.

As shown in fig. 2, the pulse forming section 3 may include: a diffraction grating 12 that spatially separates a plurality of wavelength components included in the measurement optical pulse Pa for each wavelength; an SLM14 that shifts the phases of the plurality of wavelength components output from the diffraction grating 12 from each other; and a lens 15 that condenses the plurality of wavelength components output from the SLM 14. Similarly, in the pulse forming step S1, the plurality of wavelength components included in the measurement optical pulse Pa may be spatially separated for each wavelength, and the phase of the plurality of wavelength components may be phase-phased using the SLM14After being shifted from each other, the plurality of wavelength components are condensed. In this case, it is possible to easily form the optical pulse system including a plurality of optical pulses Pb having time differences and different center wavelengths₁～Pb₃The optical pulse train Pb.

As shown in fig. 8, when the SLM14 is a polarization-dependent SLM having a modulation effect in the 1 st polarization direction, the pulse forming unit 3 may input the measurement target optical pulse Pa including the polarization component in the 1 st polarization direction and the polarization component in the 2 nd polarization direction orthogonal to the 1 st polarization direction (in the pulse forming step S1). In this case, the polarization component of the 1 st polarization direction in the measurement light pulse Pa is modulated by the SLM14 and is output as the light pulse train Pb from the pulse forming unit 3. Further, the polarization component of the 2 nd polarization direction in the measurement light pulse Pa is not modulated in the SLM14 and is output from the pulse forming unit 3. The correlation optical system 4 (in the correlation light generation step S2) can easily generate the correlation light Pc containing the cross-correlation of the optical pulse train Pb from these polarization components.

As in the present embodiment, the correlation optical system 4 may include at least one of a nonlinear optical crystal and a phosphor. Similarly, in the correlated light generation step S2, the correlated light Pc may be generated using at least one of a nonlinear optical crystal and a phosphor. In this case, the correlated light Pc including the cross-correlation or the auto-correlation of the optical pulse train Pb can be easily generated.

As shown in fig. 6, the dispersion measuring apparatus 1A further includes: a beam splitter 44 that branches the optical pulse train Pb into two branches; and a delay optical system that gives a time difference to the one optical pulse train Pbb and the other optical pulse train Pba branched out by the beam splitter 44, the correlation optical system 4 may also generate the correlation light Pc including the autocorrelation from the time-delayed one optical pulse train Pbb and the other optical pulse train Pba. Similarly, in the correlated light generation step S2, the optical pulse train Pb may be branched into two, one branched optical pulse train Pbb may be delayed in time with respect to the other optical pulse train Pba, and the autocorrelation correlated light Pc including the optical pulse train Pb may be generated from the one optical pulse train Pbb and the other optical pulse train Pba after the time delay. For example, by these apparatuses and methods, the autocorrelation correlation light Pc including the optical pulse train Pb can be easily generated.

As in the present embodiment, the calculation unit 6 (in the calculation step S4) may compare the characteristic amount of the time waveform of the correlated light Pc calculated in advance assuming that the wavelength dispersion of the pulse laser light source 2 is zero with the characteristic amount of the time waveform of the correlated light Pc detected by the light detection unit 5 to obtain the wavelength dispersion amount of the measurement light pulse Pa. In this case, the wavelength dispersion amount of the pulsed laser light source 2 can be estimated with higher accuracy.

(examples)

As an example of the above embodiment, the present inventors performed a simulation based on numerical calculation. As the measurement light pulse Pa, a single pulse having a bandwidth of 10nm and a center wavelength of 1030nm is assumed. In order to convert the measured light pulses Pa to include the 3 light pulses Pb shown in FIG. 4₁～Pb₃The optical pulse train Pb in (b) is calculated by the method described in the above embodiment, and the modulation pattern to be presented to the SLM14 is calculated. At this time, the peak time interval G is set_1,2、G_2,3The center wavelengths were set to 2000fs and 1025nm, 1030nm, and 1035nm, respectively.

Fig. 22 (a) is a graph showing the calculated modulation pattern. In the figure, the horizontal axis represents wavelength (unit: nm), the left vertical axis represents light intensity (arbitrary unit), and the right vertical axis represents phase (rad). In the figure, a curve G31 shows a modulation pattern of the spectral phase, and a curve G32 shows a modulation pattern of the spectral intensity.

Fig. 22 (b) is a graph showing the time waveform of the optical pulse train Pb generated by the present simulation. Fig. 23 is a spectrum diagram of the optical pulse train Pb generated by the present simulation. In fig. 22 (b), the horizontal axis represents time (unit: fs) and the vertical axis represents light intensity (arbitrary unit). In fig. 23, the horizontal axis represents time, the vertical axis represents wavelength, and the light intensity is represented by the shade of color. As shown in these figures, the optical pulse Pb including 3 optical pulses Pb having time differences and different center wavelengths was obtained₁～Pb₃The optical pulse train Pb.

In addition, in the present simulationFor comparison, to convert the measured light pulses Pa to include the 3 light pulses Pd shown in fig. 5₁～Pd₃The optical pulse train Pd in (a) is calculated by the method described in the above embodiment, and the modulation pattern to be presented to the SLM14 is calculated. These peak time intervals are set to be equal to the light pulses Pb₁～Pb₃The same applies to each light pulse Pd₁～Pd₃Is 1030 nm.

Fig. 24 (a) is a graph showing the calculated modulation pattern. The graph G41 shows the modulation pattern of the spectral phase, and the graph G42 shows the modulation pattern of the spectral intensity. Fig. 24 (b) is a graph showing the time waveform of the optical pulse train Pd generated by the present simulation. Fig. 25 is a spectrum diagram of the optical pulse train Pd generated by the present simulation. As shown in these figures, 3 optical pulses Pd having time differences and center wavelengths equal to each other are obtained₁～Pd₃The optical pulse train Pd.

[ Change in characteristic quantity of pulse train due to Secondary Dispersion ]

In order to examine the influence of the secondary dispersion of the pulse laser light source 2 on the characteristic amount of the pulse train, the secondary dispersion amount of the measurement optical pulse Pa was changed, and the change in the time waveform of the optical pulse trains Pb and Pd was examined. Fig. 26 (a) and 26 (b) are graphs in which the secondary dispersion amount and the peak time interval G of the measurement light pulse Pa are plotted_1,2、G_2,3Average value of (G)_1,2+G_2,3) Graph of the relationship of/2. Fig. 26 (a) shows a case of the optical pulse train Pb having a center wavelength different for each pulse, and fig. 26 (b) shows a case of the optical pulse train Pd having the center wavelengths of the respective pulses equal to each other. In these figures, the horizontal axis represents the secondary dispersion amount (unit: fs) of the optical pulse Pa to be measured²) The vertical axis represents the peak time interval G_1,2、G_2,3Average value (unit: fs).

Referring to fig. 26 (a), it can be seen that, in the case of the optical pulse train Pb having the center wavelength different for each pulse, the peak time interval G increases with the increase and decrease in the amount of secondary dispersion_1,2、G_2,3The average value of (2) monotonically (approximately linearly) increases and decreases. If it is in more detailBy examining the data finely, the light pulse Pb with respect to the center was confirmed₂Peak time of (b), light pulse Pb of the left and right₁、Pb₃The peak time of (a) tends to move symmetrically with respect to each other according to the dispersion amount. In this example, the peak time interval G_1,2、G_2,3An increase (or decrease) of 50fs of (f) corresponds to 5000fs²Increase (or decrease) in the amount of secondary dispersion.

On the other hand, referring to fig. 26 (b), it can be seen that, in the case of the optical pulse train Pd in which the center wavelengths of the respective pulses are equal to each other, the peak time interval G is not related to the increase or decrease of the secondary dispersion amount_1,2、G_2,3The average value of (a) is approximately constant. From this, it is understood that the peak time interval G of the optical pulse train Pb is different for each pulse based on the center wavelength_1,2、G_2,3The secondary dispersion amount of the pulsed laser light source 2 can be estimated with high accuracy and ease.

FIG. 27 is a graph in which the secondary dispersion amount and the peak intensity E of a measured optical pulse Pa are plotted₁～E₃The graph of the relationship (b) shows the case of the optical pulse train Pb having a center wavelength different for each pulse. The plot of the triangle represents the peak intensity E₁The plotted point of the circle represents the peak intensity E₂The plotted point of the quadrangle represents the peak intensity E₃. In the figure, the horizontal axis represents the secondary dispersion amount (unit: fs) of the measurement light pulse Pa²) The vertical axis represents the peak intensity (arbitrary unit).

Referring to fig. 27, in the optical pulse train Pb having the center wavelength different for each pulse, the peak intensity E increases with the increase and decrease in the amount of secondary dispersion₁～E₃And also increased or decreased. From this, it is found that the peak intensity E of the optical pulse train Pb differs for each pulse based on the center wavelength₁～E₃The secondary dispersion amount of the pulsed laser light source 2 can be estimated with high accuracy and ease.

FIG. 28 is a graph in which the secondary dispersion amount and the full width at half maximum W of a measured optical pulse Pa are plotted₁～W₃The graph of the relationship (b) shows the case of the optical pulse train Pb having a center wavelength different for each pulse. The plotted points of the triangle represent the full width at half maximum W₁Of circular shapePlot points represent full width at half maximum W₂The plotted points of the quadrilateral represent the full width at half maximum W₃. In the figure, the horizontal axis represents the secondary dispersion amount (unit: fs) of the measurement light pulse Pa²) The vertical axis represents the full width at half maximum (unit: fs).

Referring to fig. 28, in the optical pulse train Pb having the center wavelength different for each pulse, the full width at half maximum W increases with the increase and decrease in the amount of the secondary dispersion₁～W₃And also increased or decreased. From this, it is found that the full width at half maximum W of the optical pulse train Pb is different for each pulse based on the center wavelength₁～W₃The secondary dispersion amount of the pulsed laser light source 2 can be estimated with high accuracy and ease.

[ Change in characteristic quantity of pulse train due to third-order Dispersion ]

In order to examine the influence of the third-order dispersion of the pulse laser light source 2 on the characteristic amount of the pulse train, the third-order dispersion amount of the measurement optical pulse Pa was changed, and the change in the time waveform of the optical pulse trains Pb and Pd was examined. Fig. 29 (a) and 29 (b) are graphs in which the third dispersion amount and the peak time interval G of the measurement light pulse Pa are plotted_1,2、G_2,3Difference (G)_1,2-G_2,3) Graph of the relationship of/2. Fig. 29 (a) shows a case of the optical pulse train Pb having a center wavelength different for each pulse, and fig. 29 (b) shows a case of the optical pulse train Pd having the center wavelengths of the respective pulses equal to each other. In these figures, the horizontal axis represents the third-order dispersion amount (unit: fs) of the measurement light pulse Pa³) The vertical axis represents the peak time interval G_1,2、G_2,3The difference (unit: fs).

Referring to fig. 29 (a), it can be seen that, in the case of the optical pulse train Pb having the center wavelength different for each pulse, the peak time interval G increases with the increase and decrease in the amount of the tertiary dispersion_1,2、G_2,3The difference in (c) monotonically increases and decreases. On the other hand, referring to fig. 29 (b), it is understood that in the case of the optical pulse train Pd in which the center wavelengths of the respective pulses are equal to each other, the peak time interval G is not related to the increase or decrease of the third dispersion amount_1,2、G_2,3The difference of (a) is approximately constant. From this, it is understood that the peak time interval G of the optical pulse train Pb is different for each pulse based on the center wavelength_1,2、G_2,3The amount of tertiary dispersion of the pulsed laser light source 2 can be estimated with high accuracy and ease.

When the data were examined in more detail, it was confirmed that the center light pulse Pb was different from the center light pulse Pb in the case of the light pulse train Pb having the center wavelength different for each pulse₂Peak time of (b), light pulse Pb of the left and right₁、Pb₃The peak time of (a) tends to move asymmetrically with respect to each other depending on the dispersion amount. Such a characteristic is different from that of the secondary dispersion amount, and is based on the difference, i.e., the peak time interval G_1,2、G_2,3The relative change tendency of (2) can be distinguished from the dispersion number.

FIG. 30 is a graph in which the amount of tertiary dispersion and the peak intensity E of a measured light pulse Pa are plotted₁～E₃The graph of the relationship (b) shows the case of the optical pulse train Pb having a center wavelength different for each pulse. The plot of the triangle represents the peak intensity E₁The plotted point of the circle represents the peak intensity E₂The plotted point of the quadrangle represents the peak intensity E₃. In the figure, the horizontal axis represents the third-order dispersion amount (unit: fs) of the measurement light pulse Pa³) The vertical axis represents the peak intensity (arbitrary unit).

Referring to fig. 30, in the optical pulse train Pb having the center wavelength different for each pulse, the peak intensity E increases and decreases with the increase and decrease in the amount of the tertiary dispersion₁～E₃And also increased or decreased. From this, it is found that the peak intensity E of the optical pulse train Pb differs for each pulse based on the center wavelength₁～E₃The amount of tertiary dispersion of the pulsed laser light source 2 can be estimated with high accuracy and ease.

FIG. 31 is a graph in which the third-order dispersion amount and the full width at half maximum W of a measured optical pulse Pa are plotted₁～W₃The graph of the relationship (b) shows the case of the optical pulse train Pb having a center wavelength different for each pulse. The plotted points of the triangle represent the full width at half maximum W₁The plotted points of the circle represent the full width at half maximum W₂The plotted points of the quadrilateral represent the full width at half maximum W₃. In the figure, the horizontal axis represents the third-order dispersion amount (unit: fs) of the measurement light pulse Pa³) The vertical axis represents the full width at half maximum (unit: fs).

Referring to fig. 31, in the optical pulse train Pb having the center wavelength different for each pulse, the full width at half maximum W increases with the increase and decrease in the amount of the tertiary dispersion₁～W₃And also increased or decreased. From this, it is found that the full width at half maximum W of the optical pulse train Pb is different for each pulse based on the center wavelength₁～W₃The amount of tertiary dispersion of the pulsed laser light source 2 can be estimated with high accuracy and ease.

(modification 1)

Fig. 32 is a diagram showing a structure of a pulse forming unit 3A as a modification 1 of the above embodiment. The pulse forming unit 3A includes a pulse stretcher 18 and a filter 19 instead of the SLM14 (see fig. 2). The pulse stretcher 18 is provided on the optical path between the pulse laser light source 2 and the diffraction grating 12, and expands the pulse width of the measurement optical pulse Pa. Examples of the pulse stretcher 18 include a glass block, a diffraction grating pair, and a prism.

The filter 19 is an optical intensity filter and is optically coupled to the diffraction grating 12 via the lens 13. The light P1 split by the diffraction grating 12 is condensed by the lens 13 for each wavelength component, and reaches the filter 19. The filter 19 has an optical aperture (or a filter having different absorptance or reflectance from the surroundings) corresponding to each wavelength component, and selectively passes a plurality of wavelength components from the wavelength band constituting the measurement optical pulse Pa. The propagation timings of these multiple wavelength components are shifted from each other by the pulse stretcher 18. The wavelength components having passed through the filter 19 are collected by the lens 15 to one point on the diffraction grating 16. The plurality of wavelength components passing through the filter 19 are condensed and multiplexed by the lens 15 and the diffraction grating 16, and become a multipulse (optical pulse train Pb) whose bandwidth is controlled.

The dispersion measuring apparatus 1A of the above embodiment may include the pulse forming unit 3A of the present modification instead of the pulse forming unit 3. In this case, the same effects as those of the above embodiment can be appropriately obtained.

(modification 2)

Fig. 33 is a diagram showing a configuration of modification 2 of the above embodiment. In the present modification, the optical member 7 to be measured is disposed on the optical path between the pulse laser light source 2 and the pulse forming unit 3, which is a stage before the pulse forming unit 3. In this case, the wavelength dispersion of the pulsed laser light source 2 is zero or close to zero. Alternatively, if the wavelength dispersion of the pulsed laser light source 2 is known, it may not be zero. In the present modification, the optical pulse output from the pulse laser light source 2 is input to the pulse forming unit 3 as a measurement optical pulse Pa via the optical member 7 having wavelength dispersion. In such a configuration, the wavelength dispersion of the optical member 7 can be measured by a simple configuration.

(modification 3)

Fig. 34 is a diagram showing a configuration of modification 3 of the above embodiment. In the present modification, the optical member 7 to be measured is disposed on the optical path between the pulse forming unit 3 and the correlation optical system 4, which is a subsequent stage of the pulse forming unit 3. In the present modification, the optical pulse train Pb is output from the pulse forming unit 3 and then passes through the optical component 7. Then, the correlation optical system 4 receives the optical pulse train Pb passed through the optical unit 7, and outputs the correlated light Pc including the cross-correlation or auto-correlation of the optical pulse train Pb.

The dispersion measurement method of this modification is as follows. First, in the pulse forming step S1 shown in fig. 11, design information necessary for forming the optical pulse train Pb is prepared. Then, a pulse laser including a plurality of light pulses Pb having time differences and different center wavelengths is formed from the light pulse output from the pulse laser light source 2₁～Pb₃The optical pulse train Pb. For example, as shown in fig. 2, a plurality of wavelength components included in an optical pulse output from a pulsed laser light source 2 are spatially separated for each wavelength, and the plurality of wavelength components are condensed after being shifted in phase from each other by using an SLM 14. This makes it possible to easily generate the optical pulse train Pb. After that, the optical pulse train Pb passes through the optical component 7 having wavelength dispersion.

Next, in the correlated light generating step S2, the correlated light Pc including the cross-correlation or auto-correlation of the optical pulse train Pb passed through the optical member 7 is generated using the optical element 42 including at least one of the nonlinear optical crystal and the phosphor. For example, as shown in fig. 6, the optical pulse train Pb is branched into two, one branched optical pulse train Pbb is time-delayed with respect to the other optical pulse train Pba, and the autocorrelation correlated light Pc including the optical pulse train Pb is generated from the time-delayed one optical pulse train Pbb and the other optical pulse train Pba. Thereafter, the detection step S3 and the calculation step S4 are the same as those in the above embodiment.

In the present modification, the optical pulse train Pb output from the pulse forming unit 3 is input to the correlation optical system 4 via the optical component 7 having wavelength dispersion. In such a configuration, the wavelength dispersion of the optical member 7 can also be measured with a simple configuration. That is, the measurement target may be disposed at any one of the front stage and the rear stage of the pulse forming unit 3.

(modification 4)

Fig. 35 is a diagram showing a configuration of a pulsed light source 30A according to a4 th modification of the above embodiment. The pulse light source 30A includes a light source 31, a light branching member 32, a dispersion measuring device 1A, a pulse forming section 33, and a condenser lens 34. The light source 31 includes, for example, the pulse laser light source 2 of the above embodiment or the optical member 7 of modification 1. The optical branching unit 32 is optically coupled to the light source 31, receives the light pulse Pf from the light source 31, and branches the light pulse Pf. The one branched optical pulse Pfa is input to the pulse forming unit 3 of the dispersion measuring apparatus 1A optically coupled to the optical branching unit 32. The other branched light pulse Pfb is input to the pulse forming section 33 optically coupled to the optical branching means 32.

The pulse forming unit 33 is a pulse forming device of the present embodiment, and compensates the optical pulse Pfb output from the light source 31 for the chromatic dispersion (provides inverse dispersion) obtained by the dispersion measuring device 1A. Therefore, the pulse forming unit 33 includes the SLM33a that performs phase modulation, and has the same configuration as the pulse forming unit 3 described above.

The SLM33a is controlled by the arithmetic unit 6 (or other computer) of the dispersion measuring device 1A. The data of the modulation pattern presented on the SLM33a is generated by the arithmetic section 6 (or another computer). The SLM33a is, for example, a phase modulation type. In one embodiment, SLM33a is a LCOS type. Although the transmission type SLM33a is shown in the drawing, the SLM33a may be a reflection type SLM. The dispersion-compensated optical pulse Pfb output from the pulse forming unit 33 is condensed by the condenser lens 34 and is irradiated to the irradiation object 35.

Fig. 36 is a flowchart showing a dispersion compensation method according to this modification. First, the light pulse Pf is output from the light source 31, and the branched light pulse Pfa is input to the pulse forming unit 3 (step S11). Then, the chromatic dispersion amount of the light source 31 is estimated by using the chromatic dispersion measuring apparatus 1A (step S12). Next, the optical pulse Pfb is phase-modulated by the pulse forming unit 33 to compensate for the wavelength dispersion amount (step S13). The dispersion-compensated optical pulse Pfb is irradiated to the irradiation object 35 for use in, for example, laser processing, microscope observation, or the like (step S14).

According to the pulsed light source 30A and the dispersion compensation method of the present modification, since the dispersion measuring device 1A (using the dispersion measuring method) of the above-described embodiment is included, it is possible to measure and compensate the chromatic dispersion by a simple configuration. In this example, the pulse forming unit 33 performs phase modulation for compensating the wavelength dispersion amount on the light pulse Pfb output from the light source 31 to be measured for dispersion, but the present invention is not limited to this. For example, the pulse forming unit 33 may be disposed at a stage before the dispersion measurement target, and the pulse forming unit 33 may perform phase modulation for compensating the wavelength dispersion amount on the optical pulse input to the dispersion measurement target.

(modification 5)

Fig. 37 is a diagram showing a configuration of a pulsed light source 30B as a modification example 5 of the above embodiment. The pulse light source 30B includes a light source 31, a dispersion measuring device 1A, a light branching section 32, and a condenser lens 34. In the present modification, the optical branching member 32 is disposed on the optical path between the pulse forming unit 3 and the correlation optical system 4. After the measurement of the wavelength dispersion amount by the dispersion measuring device 1A, the SLM14 (see fig. 2) of the pulse forming section 3 further performs phase modulation for compensating the wavelength dispersion amount on the optical pulse Pf output from the light source 31. In other words, the pulse forming unit 3 also functions as the pulse forming unit 33 according to modification 4, and the SLM14 constitutes a part of the pulse forming unit for compensating for chromatic dispersion. In this case, as in modification 4, the chromatic dispersion can be measured and compensated for with a simple configuration.

In this example, the pulse forming unit 3 performs phase modulation for compensating the wavelength dispersion amount on the light pulse Pf output from the light source 31 to be measured for dispersion, but the present invention is not limited to this. For example, the pulse forming unit 3 may be disposed at a stage before the dispersion measurement target, and the pulse forming unit 3 may perform phase modulation for compensating the wavelength dispersion amount on the optical pulse input to the dispersion measurement target.

The dispersion measuring apparatus, the pulsed light source, the dispersion measuring method, and the dispersion compensating method are not limited to the above-described embodiments and configuration examples, and various modifications are possible.

In the above-described embodiment, as shown in fig. 2, the mode of forming the optical pulse train Pb using the diffraction grating 12 and the SLM14 is exemplified, and in the modification 1, the mode of forming the optical pulse train Pb using the pulse stretcher 18 and the filter 19 is exemplified, but the mode of forming the optical pulse train Pb in the pulse forming unit 3 and the pulse forming step S1 is not limited to this. For example, a variable mirror may be used instead of the SLM 14. Alternatively, a liquid crystal display, an acousto-optic modulator, or the like capable of electronically controlling the phase may be used instead of the SLM 14.

In the above embodiment, the method of generating the correlated light Pc using the nonlinear optical crystal or the phosphor is exemplified, but the method of generating the correlated light Pc in the correlated optical system 4 and the correlated light generating step S2 is not limited to this.

In addition, the above-described embodiment exemplifies a configuration in which the spectral waveform is calculated using the fourier transform unit 25, the function replacement unit 26, the waveform function correction unit 27, the inverse fourier transform unit 28, and the target generation unit 29 shown in fig. 15, with respect to the method of designing the spectral waveform in the phase spectrum design unit 22 and the intensity spectrum design unit 23 of the modulation pattern calculation device 20 shown in fig. 14, and the method of generating the multipulses for which the bandwidth control is performed thereby.

With this configuration, the time waveform of the multipulses constituting the optical pulse train can be approximated to a desired shape, and the frequency band component of each optical pulse included in the optical pulse train can be controlled with high accuracy. However, the method of generating multipulses by performing bandwidth control is not limited to this method, and for example, as described below, a spectral waveform (spectral modulation pattern) for generating multipulses may be determined by a simpler method without using a complicated optimization algorithm.

Specifically, as a method for generating multi-pulses subjected to bandwidth control, a method of combining linear phase modulation patterns (linear phase patterns) based on information on the number of optical pulses in the multi-pulses to be generated, frequency band components constituting the respective optical pulses, and intervals between the optical pulses can be used. Fig. 39 and 40 shown below are conceptual diagrams for explaining a method of generating such a multi-pulse.

Fig. 39 (a) is a graph showing an example of a spectral waveform for generating a multipulse subjected to bandwidth control. In the graph, the horizontal axis represents wavelength, the left vertical axis represents light intensity, and the right vertical axis represents phase. In the figure, a curve G51 shows the spectral phase, and a curve G52 shows the spectral intensity. In the figure, regions R1, R2, and R3 respectively indicate wavelength regions set for the spectral intensity waveform of the curve G52. In addition, in the spectral phase pattern of the graph G51, the phase pattern X1 represents a phase pattern in the wavelength region R1, the phase pattern X2 represents a phase pattern in the wavelength region R2, and the phase pattern X3 represents a phase pattern in the wavelength region R3. These phase patterns X1, X2, X3 are linear phase patterns having slopes different from each other.

Fig. 39 (b) is a graph showing a time waveform of the optical pulse train corresponding to the spectral waveform shown in fig. 39 (a). In the graph, the horizontal axis represents time, and the vertical axis represents light intensity. In this method, an optical pulse is generated from the number of linear phase patterns having different slopes included in the spectral phase in the time waveform of the optical pulse train. In the example shown in fig. 39, the linear phase patterns X1, X2, and X3 described above are provided in the wavelength regions R1, R2, and R3, thereby generating multi-pulses with bandwidth control, each of which is composed of 3 optical pulses Y1, Y2, and Y3.

In such a method, the magnitude of the slope of the linear phase pattern Xi corresponds to the amount of shift in the time waveform of the corresponding optical pulse Yi. The band components constituting each optical pulse Yi can be controlled by setting the division of the wavelength region Ri with respect to the spectral waveform. In the example shown in fig. 39, the optical pulse Y1 is generated from the spectral intensity component of the wavelength region R1, the optical pulse Y2 is generated from the spectral intensity component of the wavelength region R2, and the optical pulse Y3 is generated from the spectral intensity component of the wavelength region R3.

In the above method, for example, the control of the spectral intensity component may be performed by performing a filtering process (intensity cutoff by intensity modulation) on the unnecessary intensity component in advance. In addition, when the difference between the slopes of the phase patterns X1, X2, and X3 is small, the light pulses may not be sufficiently separated in the obtained time waveform, and therefore, it is preferable to set the phase patterns in consideration of such a point. In the example shown in fig. 39, the phase pattern in the spectral phase is a continuous pattern, but may be a discontinuous pattern.

Fig. 40 (a) is a graph showing another example of a spectral waveform for generating a multipulse whose bandwidth is controlled. In the figure, a curve G61 represents the spectral phase, and a curve G62 represents the spectral intensity. In the figure, regions R4, R5, and R6 respectively indicate wavelength regions set for the spectral intensity waveform of graph G62. In addition, in the spectral phase pattern of the graph G61, the phase pattern X4 represents a phase pattern in the wavelength region R4, the phase pattern X5 represents a phase pattern in the wavelength region R5, and the phase pattern X6 represents a phase pattern in the wavelength region R6. These phase patterns X4, X5, and X6 are linear phase patterns having different slopes, and are discontinuous at the boundary between the phase patterns X5 and X6.

Fig. 40 (b) is a graph showing a time waveform of the optical pulse train corresponding to the spectral waveform shown in fig. 40 (a). In the example shown in fig. 40, by setting the discontinuous phase pattern in the spectral phase, the optical pulse Y4 is generated from the spectral intensity component of the wavelength region R4, the optical pulse Y6 is generated from the spectral intensity component of the wavelength region R5, and the optical pulse Y5 is generated from the spectral intensity component of the wavelength region R6. By setting the phase pattern in the spectral phase in this manner, the frequency band components constituting each optical pulse can be arbitrarily replaced and set in the time waveform.

The dispersion measuring apparatus of the above embodiment includes: a pulse forming unit that forms an optical pulse train including a plurality of 2 nd optical pulses having time differences and center wavelengths different from each other, from the 1 st optical pulse output from the measurement target; a correlation optical system that receives the optical pulse train output from the pulse forming unit and outputs correlated light including cross-correlation or auto-correlation of the optical pulse train; a light detection unit for detecting a time waveform of the relevant light; and a calculation unit for estimating the wavelength dispersion amount of the measurement object based on the characteristic amount of the time waveform.

The dispersion measuring apparatus according to the above embodiment includes: a pulse forming unit that forms an optical pulse train including a plurality of 2 nd optical pulses having time differences and center wavelengths different from each other, from the 1 st optical pulse output from the light source; a correlation optical system that receives the optical pulse train that has passed through the measurement target after being output from the pulse forming unit, and outputs correlated light including cross-correlation or auto-correlation of the optical pulse train; a light detection unit for detecting a time waveform of the relevant light; and a calculation unit for estimating the wavelength dispersion amount of the measurement object based on the characteristic amount of the time waveform.

The dispersion measurement method according to the above embodiment includes: a pulse forming step of forming an optical pulse train including a plurality of 2 nd optical pulses having time differences and center wavelengths different from each other, from the 1 st optical pulse output from the measurement target; a correlated light generation step of generating correlated light including cross-correlation or auto-correlation of the optical pulse train; a detection step of detecting a time waveform of the correlation light; and a calculation step of calculating a wavelength dispersion amount of the measurement object based on the characteristic amount of the time waveform.

The dispersion measurement method according to the above embodiment includes: a pulse forming step of forming an optical pulse train including a plurality of 2 nd optical pulses having time differences and center wavelengths different from each other, from the 1 st optical pulse output from the light source; a correlated light generation step of generating correlated light including cross-correlation or auto-correlation of the optical pulse train that has passed through the measurement target after being output from the pulse formation step; a detection step of detecting a time waveform of the correlation light; and a calculation step of calculating a wavelength dispersion amount of the measurement object based on the characteristic amount of the time waveform.

In these apparatuses and methods, an optical pulse train including a plurality of 2 nd optical pulses having time differences from each other and center wavelengths different from each other is generated from the 1 st optical pulse in a pulse forming unit (pulse forming step). Then, the 1 st light pulse is output from the measurement object, or the light pulse train passes through the measurement object.

In such a case, according to the findings of the present inventors, when correlated light including cross-correlation or auto-correlation of an optical pulse train is generated using, for example, a nonlinear optical crystal or the like, various characteristic amounts (e.g., pulse interval, peak intensity, pulse width, and the like) in a time waveform of the correlated light have a significant correlation with a wavelength dispersion amount of a measurement object. Therefore, according to the above-described apparatus and method, the wavelength dispersion amount of the measurement target can be accurately estimated in the calculation unit (calculation step).

Further, according to the above-described apparatus and method, unlike the measuring apparatus 100 shown in fig. 38, since it is not necessary to measure the emission spectrum, the optical system of the light detection section (detection step) can be simplified, and the chromatic dispersion of the measurement object can be measured with a simple configuration.

In the above-described measuring apparatus, the calculation unit may be configured to estimate the wavelength dispersion amount of the measurement target based on a time interval between the plurality of light pulses included in the correlated light. In the above-described measurement method, the wavelength dispersion amount of the measurement target may be estimated from the time intervals of the plurality of light pulses included in the correlated light in the calculation step.

The present inventors found that, among various characteristic quantities in a time waveform, particularly, a pulse interval has a significant correlation with a wavelength dispersion quantity of a measurement object. Therefore, according to these apparatus and method, the wavelength dispersion amount of the measurement target can be estimated with higher accuracy.

In the above-described measuring device, the pulse forming unit may include: a spectroscopic element that spatially separates a plurality of wavelength components included in the 1 st optical pulse for each wavelength; a spatial light modulator which shifts the phases of the plurality of wavelength components output from the spectroscopic element from each other; and a light-condensing optical system that condenses the plurality of wavelength components output from the spatial light modulator. In the above-described measurement method, in the pulse forming step, the plurality of wavelength components included in the 1 st optical pulse may be spatially separated for each wavelength, the phases of the plurality of wavelength components may be shifted from each other by using a spatial light modulator, and then the plurality of wavelength components may be condensed.

For example, with these apparatuses and methods, an optical pulse train including a plurality of 2 nd optical pulses having time differences and center wavelengths different from each other can be easily formed.

In the above-described measuring apparatus, the spatial light modulator may be a polarization-dependent spatial light modulator having a modulation effect in a1 st polarization direction, the pulse forming unit may input a1 st light pulse including a1 st polarization direction component and a2 nd polarization direction component orthogonal to the 1 st polarization direction, the 1 st polarization direction component of the 1 st light pulse may be modulated by the spatial light modulator and output as the light pulse train from the pulse forming unit, the 2 nd polarization direction component of the 1 st light pulse may be output from the pulse forming unit without being modulated by the spatial light modulator, and the correlation optical system may generate the correlation light including the cross correlation of the light pulse train from the 1 st polarization direction component and the 2 nd polarization direction component.

In the above-described measuring method, the spatial light modulator may be a polarization-dependent spatial light modulator having a modulating action in a1 st polarization direction, the 1 st optical pulse including a component in the 1 st polarization direction and a component in a2 nd polarization direction orthogonal to the 1 st polarization direction may be input in the pulse forming step, the component in the 1 st polarization direction in the 1 st optical pulse may be modulated in the spatial light modulator to form an optical pulse train, the component in the 2 nd polarization direction in the 1 st optical pulse may not be modulated in the spatial light modulator and may be output, and the correlated light including cross-correlation of the optical pulse train may be generated from the component in the 1 st polarization direction and the component in the 2 nd polarization direction in the correlated light generating step.

For example, by these apparatuses and methods, correlated light including the cross-correlation of optical pulse trains can be easily generated.

In the above-described measuring apparatus, the correlation optical system may be configured to include at least one of a nonlinear optical crystal and a phosphor. In the above-described measuring method, at least one of the nonlinear optical crystal and the fluorescent material may be used in the correlated light generation step.

For example, by these apparatuses and methods, correlated light including cross-correlation or auto-correlation of an optical pulse train can be easily generated.

The above-described measuring apparatus may further include: an optical branching unit that branches the optical pulse train into two branches; and a delay optical system that gives a time difference to the one optical pulse train and the other optical pulse train branched by the optical branching unit, wherein the correlation optical system generates correlation light including autocorrelation from the one optical pulse train and the other optical pulse train after the time delay. In the above-described measuring method, the correlation light generating step may be configured to branch the optical pulse train into two branches, time-delay one of the branched optical pulse trains relative to the other optical pulse train, and generate the correlation light including the autocorrelation of the optical pulse train from the time-delayed one of the optical pulse trains and the other optical pulse train.

For example, such an apparatus and method can easily generate correlated light including autocorrelation of an optical pulse train.

In the above-described measuring apparatus, the calculation unit may be configured to estimate the wavelength dispersion amount of the measurement target by comparing a feature amount of a time waveform calculated in advance assuming that the wavelength dispersion of the measurement target is zero with a feature amount of a time waveform detected by the light detection unit. In the above-described measurement method, the calculation step may be configured to estimate the wavelength dispersion amount of the measurement target by comparing a feature amount of a time waveform calculated in advance on the assumption that the wavelength dispersion of the measurement target is zero with a feature amount of a time waveform detected in the detection step.

According to these apparatus and method, the wavelength dispersion amount of the measurement object can be estimated with higher accuracy.

The pulsed light source of the above embodiment includes: the dispersion measuring apparatus of the above-described structure; and a pulse forming device for compensating the wavelength dispersion amount obtained by the dispersion measuring device for the optical pulse input to or output from the measurement object.

The pulse light source of the above embodiment includes the dispersion measuring device having the above configuration, and the spatial light modulator of the dispersion measuring device constitutes a part of a pulse forming device that compensates for the wavelength dispersion amount obtained by the dispersion measuring device for the light pulse input to or output from the measurement object.

The dispersion compensation method of the above embodiment includes: a step of estimating a wavelength dispersion amount of the measurement object by using the dispersion measurement method having the above-described configuration; and a step of performing pulse formation for compensating the wavelength dispersion amount on the optical pulse input to or output from the measurement object.

In these pulsed light sources and dispersion compensation methods, since the dispersion measuring device or dispersion measuring method described above is included, it is possible to measure and compensate for chromatic dispersion with a simple structure.

Industrial applicability of the invention

The embodiments can be used as a dispersion measuring apparatus, a pulsed light source, a dispersion measuring method, and a dispersion compensating method capable of measuring wavelength dispersion with a simple structure.

Description of the symbols

1A … … dispersion measuring device

2 … … pulse laser light source

3. 3A … … pulse forming part

3a … … light input end

3b … … light output end

4. 4A, 4B, 4C … … related optical system

4a … … light input end

4b … … light output end

4 c-4 f … … light path

5 … … light detection unit

6 … … arithmetic unit

7 … … optical component

12 … … diffraction grating

13. 15 … … lens

14 … … Spatial Light Modulator (SLM)

16 … … diffraction grating

17 … … modulation surface

17a … … modulation region

18 … … pulse stretcher

19 … … filter

20 … … modulation pattern calculation device

21 … … arbitrary waveform input part

22 … … phase spectrum design part

23 … … intensity Spectrum design section

24 … … modulation pattern generating section

25 … … Fourier transform unit

26 … … function replacement part

27 … … wave form function correcting part

28 … … inverse Fourier transform unit

29 … … target generation part

29a … … Fourier transform unit

29b … … spectrogram correcting part

30 … … pulse light source

31 … … light source

32 … … optical branching unit

33 … … pulse forming part

34 … … condenser lens

41. 43 … … lens

42 … … optical element

44 … … beam splitter

45. 46, 48 … … reflector

47. 49 … … mobile station

61 … … processor

64 … … input device

65 … … output device

66 … … communication module

67 … … auxiliary storage device

100 … … measuring device

101 … … pulse light source

102 … … pulse control optical system

103 … … optical system

103a … … SHG crystal

104 … … light splitter

105 … … arithmetic unit

Pa … … measured light pulse

Pb and Pd … … optical pulse train

Pb₁～Pb₃，Pd₁～Pd₃… … light pulse

Pba, Pbb … … optical pulse train

Pc … … correlated light

Pc₁～Pc₃… … light pulse

Pf … … light pulse

Pr … … reference light pulse

SC … … controls the signal.