阅读说明：本技术 一种同源双光梳产生的装置与方法 (Device and method for generating homologous double-light comb ) 是由 黄田野 吴志超 魏倩 于 2020-07-19 设计创作，主要内容包括：本发明公开了一种同源双光梳产生的装置与方法,包括泵浦源、波分复用器、保偏掺铒光纤、隔离器、可饱和吸收体、偏振分路合路模块和光纤耦合器依次首尾相连的全保偏光纤谐振腔以及腔外偏振分束器。其中偏振分路合路模块由偏振分束器、可调光延时线和偏振合束器依次连接而成。装置内所有器件偏振不敏感,均可支持产生两个正交的偏振模。通过调节泵浦功率在两个正交的偏振方向上同时实现锁模,从而产生双光梳。装置引入偏振分路合路模块改变光程,从而调节光梳重频差。本发明装置结构简单紧凑、操作方便,产生的双光梳具有很好的相干性和稳定性且重频差可调,具有广泛的工程应用前景。(The invention discloses a device and a method for generating a homologous double-optical comb, which comprises a pumping source, a wavelength division multiplexer, a polarization-maintaining erbium-doped fiber, an isolator, a saturable absorber, a full polarization-maintaining fiber resonant cavity and an extra-cavity polarization beam splitter, wherein the full polarization-maintaining fiber resonant cavity and the extra-cavity polarization beam splitter are sequentially connected end to end through a polarization splitting and combining module and a fiber coupler. The polarization shunting and combining module is formed by sequentially connecting a polarization beam splitter, an adjustable light delay line and a polarization beam combiner. All devices in the device are polarization insensitive and can support the generation of two orthogonal polarization modes. And the mode locking is realized simultaneously in two orthogonal polarization directions by adjusting the pumping power, so that the double-optical comb is generated. The device introduces a polarization shunt and combiner module to change the optical path, thereby adjusting the optical comb frequency difference. The device has simple and compact structure and convenient operation, and the generated double-light comb has good coherence and stability, adjustable repetition frequency difference and wide engineering application prospect.)

1. A device and method for generating a homologous double-light comb are characterized in that: comprises a pump source (1), a fully polarization-maintaining optical fiber resonant cavity (12) and a second polarization beam splitter (10).

The full polarization maintaining fiber resonant cavity (12) is formed by sequentially connecting a wavelength division multiplexer (2), a polarization maintaining erbium-doped fiber (3), an isolator (4), a saturable absorber (5), a polarization shunt combiner module (11) and a fiber coupler (9) end to end. The polarization splitting and combining module (11) is formed by sequentially connecting a first polarization beam splitter (6), an adjustable light delay line (7) and a polarization beam combiner (8).

And the second polarization beam splitter (10) is connected with the optical fiber coupler (9) through a polarization-maintaining single-mode optical fiber.

2. The apparatus and method of claim 1 for homologously dual optical comb generation, wherein: the pumping source (1) is a semiconductor laser coupled by a common single-mode optical fiber, the central wavelength of the pumping source is 976nm, and the pumping source corresponds to a pumping absorption peak of the polarization-maintaining erbium-doped optical fiber (3).

3. The apparatus and method of claim 1 for homologously dual optical comb generation, wherein: all devices in the full polarization-maintaining optical fiber resonant cavity (12) are insensitive to polarization and can support generation of two orthogonal polarization modes, and the tail fibers are polarization-maintaining optical fibers.

4. An apparatus and method for homologously dual optical comb generation as claimed in claim 1 or 3, wherein: the working wavelength of the wavelength division multiplexer (2) is 980/1550nm, the wavelength division multiplexer is provided with three ports of a pumping end (2a), an input end (2b) and an output end (2c), the tail fiber of the pumping end (2a) is a common single-mode optical fiber, and the tail fiber of the input end (2b) and the tail fiber of the output end (2c) are polarization-maintaining single-mode optical fibers.

5. An apparatus and method for homologously dual optical comb generation as claimed in claim 1 or 3, wherein: the polarization-maintaining erbium-doped optical fiber (3) has the model number of Nufern PM-ESF-7/125 and the length of 2.5 m.

6. An apparatus and method for homologously dual optical comb generation as claimed in claim 1 or 3, wherein: the optical isolator (4) adopts an isolator which has the central wavelength of 1550nm and is irrelevant to polarization, and the tail fiber of the isolator is a polarization-maintaining single-mode fiber.

7. An apparatus and method for homologously dual optical comb generation as claimed in claim 1 or 3, wherein: the saturable absorber (5) is made of carbon nano tubes and prepared by a light-driven end face deposition method, and has polarization insensitivity and high damage threshold.

8. An apparatus and method for homologously dual optical comb generation as claimed in claim 1 or 3, wherein: the optical fiber coupler (9) adopts a 20:80 polarization-maintaining optical fiber coupler, and is provided with an input end (9a), an 80% output end (9b) and a 20% output end (9c), and tail fibers of the optical fiber coupler are polarization-maintaining single-mode optical fibers.

9. An apparatus and method for homologously dual optical comb generation as claimed in claim 1 or 3, wherein: the polarization splitting and combining module (11) is formed by connecting a polarization beam splitter (6), an adjustable light delay line (7) and a polarization beam combiner (8) by polarization-maintaining single-mode fibers in sequence. The polarization beam splitter (6) is provided with two output ports, namely an x-axis output port (6a) and a y-axis output port (6 b). The polarization beam combiner (8) is provided with two input ports, namely an x-axis input port (8a) and a y-axis input port (8 b). The x-axis and y-axis are two orthogonal polarization axes, respectively. The x-axis output port (6a) is connected with the x-axis input port (8a), and the y-axis output port (6b) is connected with the y-axis input port (8b), so that two branches are generated. The adjustable light delay line (7) is inserted into any one of the two branches.

Technical Field

The invention relates to the technical field of optical frequency, in particular to a device and a method for generating a homologous double-optical comb.

Background

The femtosecond laser-based optical frequency comb technology has been widely concerned by researchers, and the nobel prize on physics was awarded in 2005. The optical comb is a 'soliton' sequence with equal intervals in the time domain, and the frequency domain is a longitudinal mode comb tooth line with equal intervals. The optical comb provides a 'ruler' for people in a frequency domain, enables optical frequency to be associated with microwave frequency, skillfully solves the problem of direct measurement of optical frequency, is widely applied to the fields of optical atomic clocks, attosecond science, astronomical observation, precise laser spectrum and the like, and particularly brings revolutionary progress in the field of precise laser spectrum measurement.

The double-optical-comb spectrum analysis technology needs to utilize two optical frequency combs with slightly deviated repetition frequencies, one of the two optical frequency combs or a sample passes through the two optical frequency combs together, then a photoelectric detector is used for collecting heterodyne models of the two optical frequency combs, sample spectrum information written on optical frequency comb lines is transferred to a radio frequency domain, and the spectrum information of the sample can be extracted by analyzing the heterodyne models. The double-optical comb spectrum analysis technology can obtain the resolution of kHz magnitude, integrates high-performance indexes such as wide wavelength measurement, high sensitivity and rapid monitoring, and the like, and undoubtedly has milestone significance for the modern precision spectrum analysis technology.

However, any slight pulse time jitter and carrier phase fluctuations between the two sets of optical combs can cause significant distortion of the interferogram. Therefore, the mutual interference characteristic of the double optical comb becomes the key for restricting the technology to be applied. After a lot of efforts, researchers gradually develop three representative techniques to improve the mutual dryness of the dual-optical comb, including coherent dual-optical comb, adaptive dual-optical comb, and homologous dual-optical comb.

The coherent double-optical comb technology needs an ultra-narrow linewidth and ultra-stable laser as reference, has high requirements on locking technology and is complex in device. The self-adaptive double-optical comb technology needs a large amount of collected data to correct the interference pattern, and has high requirements on data processing and complex algorithm. Therefore, the two schemes respectively restrict the double-light comb development to be a high-reliability practical instrument on hardware and software.

The homonymous double-optical comb means that two groups of optical combs are generated from the same light source, so that the optical combs have natural mutual dryness, simple structure and strong environmental interference resistance. Therefore, the research of the homologous double-optical comb will further promote the practical application of the double-optical comb spectrum analysis.

Disclosure of Invention

In order to effectively improve the mutual dryness of the double-optical combs, the invention provides a device and a method for generating the same-source double-optical combs, the device has simple and compact structure and convenient operation, two groups of optical combs with adjustable weight difference are generated from a single full polarization-maintaining optical fiber resonant cavity, and the generated double-optical combs have good coherence and stability.

The invention is realized by the following technical scheme: comprising a pump source 1, a fully polarization maintaining fiber resonator 12 and a second polarization beam splitter 10.

The full polarization maintaining fiber resonant cavity is formed by sequentially connecting a wavelength division multiplexer 2, a polarization maintaining erbium-doped fiber 3, an isolator 4, a saturable absorber 5, a polarization shunt combiner module 11 and an optical fiber coupler 9 end to end. The polarization splitting and combining module 11 is formed by sequentially connecting a first polarization beam splitter 6, an adjustable light delay line 7 and a polarization beam combiner 8.

The second polarization beam splitter 10 is connected with the fiber coupler 9 through a polarization-maintaining single-mode fiber.

Further, the pump source 1 is a semiconductor laser coupled by a common single-mode fiber, the center wavelength of the pump source is 976nm, and the pump source corresponds to a pump absorption peak of the polarization-maintaining erbium-doped fiber 3.

Further, the wavelength division multiplexer 2 has an operating wavelength of 980/1550nm, and has three ports, i.e., a pumping end 2a, an input end 2b, and an output end 2c, wherein a pigtail of the pumping end (2a) is a common single-mode fiber, and pigtails of the input end 2b and the output end 2c are polarization-maintaining single-mode fibers.

Further, the polarization-maintaining erbium-doped fiber 3 is of a Nufern PM-ESF-7/125 model and has a length of 2.5 m.

Further, the optical isolator 4 uses a polarization-independent isolator with a center wavelength of 1550nm, and its pigtail is a polarization-maintaining single-mode fiber.

Furthermore, the saturable absorber 5 is made of carbon nanotubes and prepared by a light-driven end face deposition method, and has polarization insensitivity and high damage threshold.

Further, the optical fiber coupler 9 adopts a 20:80 polarization maintaining optical fiber coupler, and has an input end 9a, an 80% output end 9b and a 20% output end 9c, and the pigtails thereof are polarization maintaining single mode fibers.

Further, the polarization splitting and combining module 11 is formed by connecting a polarization beam splitter 6, an adjustable light delay line 7 and a polarization beam combiner 8 in sequence through a polarization-maintaining single-mode fiber. The polarization beam splitter 6 has two output ports, namely an x-axis output port 6a and a y-axis output port 6 b. The polarization beam combiner 8 has two input ports, namely an x-axis input port 8a and a y-axis input port 8 b. The x-axis and y-axis are two orthogonal polarization axes, respectively. The x-axis output port 6a is connected to the x-axis input port 8a and the y-axis output port 6b is connected to the y-axis input port 8b, resulting in two branches. The adjustable light delay line 7 is inserted into any one of the two branches.

Further, all devices in the device are polarization insensitive and can support the generation of two orthogonal polarization modes. And the mode locking is realized simultaneously in two orthogonal polarization directions by adjusting the pumping power, so that the double-optical comb is generated.

Further, the optical path length is changed by adjusting the adjustable optical delay line 7, so that the optical comb repetition frequency difference is adjusted.

Further, the second polarization beam splitter 10 splits the output of the fully-polarization maintaining fiber resonator 12 into the optical comb 1 and the optical comb 2 with slightly different repetition frequencies.

The technical scheme provided by the invention has the beneficial effects that: 1. the device adopts an all-fiber full polarization maintaining structure, has high beam quality and good stability, is convenient for welding coupling and is convenient to maintain. 2. The invention realizes the generation of the double-optical comb from the single resonant cavity and ensures the good coherence of the double-optical comb. 3. The invention realizes the flexibility and adjustability of the double optical comb frequency difference by introducing the polarization shunt and combiner module.

Drawings

In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the technical description of the present invention will be briefly introduced below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive labor.

FIG. 1 is a schematic diagram of a homological dual optical comb generating device according to the present invention;

fig. 2 shows an experimental dual-optical comb pulse sequence generated by a homologous dual-optical comb generating device according to the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Fig. 1 shows a schematic structural diagram of a homologous dual-optical-comb generating device of the present invention, which includes three parts, namely a pump source 1, a fully-polarization-maintaining fiber resonator 12, and a second polarization beam splitter 10.

The full polarization maintaining fiber resonant cavity is formed by sequentially connecting a wavelength division multiplexer 2, a polarization maintaining erbium-doped fiber 3, an isolator 4, a saturable absorber 5, a polarization shunt combiner module 11 and an optical fiber coupler 9 end to end. The polarization splitting and combining module 11 is formed by sequentially connecting a first polarization beam splitter 6, an adjustable light delay line 7 and a polarization beam combiner 8.

The pumping source 1 is a semiconductor laser coupled by a polarization maintaining single mode fiber, the central wavelength of the semiconductor laser is 976nm, and the pumping source corresponds to a pumping absorption peak of the erbium-doped fiber. Coupled into the polarization maintaining fiber cavity by an 980/1550nm wavelength division multiplexer 2.

The polarization-maintaining erbium-doped fiber 3 is used as a gain fiber to provide gain for the resonant cavity, has the model number of NufernPM-ESF-7/125, and has the length of 2.5 m.

The optical isolator 4 adopts an isolator which has a central wavelength of 1550nm and is irrelevant to polarization, and is used for ensuring unidirectional laser transmission and eliminating harmful reflection. The tail fiber is a polarization-maintaining single-mode fiber.

The saturable absorber 5 is a core device for realizing mode locking, is made of carbon nano tubes and is prepared by a light-driven end face deposition method: the scattering force generated by the light radiation pushes the carbon nanotube molecules to move towards the light propagation direction. When the scattering force and the gradient force reach a certain balance, the carbon nano tube forms annular deposition on the end face of the optical fiber, and the structure has the characteristics of high damage threshold and polarization insensitivity and is suitable for a polarization multiplexing optical fiber resonant cavity.

The optical fiber coupler 9 adopts a 20:80 polarization maintaining optical fiber coupler, the output end 9c is used as an output port of the laser resonant cavity, and the tail fiber is a polarization maintaining single-mode optical fiber.

The second polarization beam splitter 10 is connected to the output end 9c of the fiber coupler 9d through a polarization-maintaining single-mode fiber, and is configured to separate a dual-optical comb generated by the fully polarization-maintaining fiber resonator 12.

All devices in the device are polarization insensitive and can support the generation of two orthogonal polarization modes. And the mode locking is realized simultaneously in two orthogonal polarization directions by adjusting the pumping power, so that the double-optical comb is generated.

The device of the invention adjusts the optical comb frequency difference by introducing the polarization shunt and combiner module 11. In the polarization splitting and combining module 11, the polarization beam splitter 6 first splits laser light into two linearly polarized light beams along x and y axes (two orthogonal polarization axes), which are output by an x-axis output port 6a and a y-axis output port 6b, respectively, and are transmitted to an x-axis input port 8a and a y-axis input port 8b through two branch polarization-maintaining fibers, and are recombined into one path through the polarization beam combiner 9. Because the paths of the two beams of light transmitted along the x axis and the y axis are different, the time required for one circle of movement in the cavity is different, and a double-light comb is formed. The lengths of the two branches of the x axis and the y axis are respectively marked as L_xAnd L_yAnd the length of the trunk optical fiber is recorded as L₀. The time required for two groups of pulses to travel one revolution in the resonant cavity is then expressed as:

T_x＝c(L₀+L_x)/n_x(1)

T_y＝c(L₀+L_y)/n_y(2)

wherein n is_xAnd n_yThe refractive indices of the two polarization axes of the fiber are shown, and c is the speed of light in vacuum. Therefore, the repetition frequencies of the two groups of optical combs are respectively 1/T_xAnd 1/T_yDouble light comb repetition frequencyThe difference can be expressed as:

if the length of the optical fiber introduced by the adjustable optical delay line 7 is continuously adjustable within the range of 0-delta l, the adjustment range of the repetition frequency difference is cn_xΔl/n²L². If the repetition frequency of the optical comb is 20MHz, the time delay of the adjustable optical delay line 7 is 0-500 ps, and the adjusting step length is 10fs, the optical comb repetition frequency difference can be adjusted within the range of 0-200 kHz, and the adjusting precision is 4 Hz. The adjusting range can improve the adjusting range of the kHz magnitude in the current polarization multiplexing scheme by 2 magnitude.

A double optical comb was created from a single fully-polarization-maintaining fiber resonator 12 at a pump power of 110mW, a cavity length of 13.2m, and a tunable optical delay line 7 delay of 0ps, as measured by an oscilloscope (OSC, Tektronix DPO4104), as shown in the first trace of fig. 2. Because the oscilloscope cannot trigger two pulse sequences with different repetition frequencies, a fixed pulse sequence and a fast drifting pulse sequence exist in a trace line, and the difference of the repetition frequencies of the double optical combs generated by the invention is further verified. The pulse sequence of the double optical comb output from the fully polarization maintaining fiber resonator 12 after being separated by the second polarization beam splitter 10 is shown in the second and third traces of fig. 2, and the pulse period T of the optical comb 1 and the optical comb 2 is shown in the second and third traces_xAnd T_yThe frequency difference of the two groups of optical combs generated by the invention is further verified to be very small, and the condition of double-optical comb spectrum analysis is met.

In conclusion, the device and the method for generating the homologous double optical combs provided by the invention realize that two groups of optical combs with adjustable repetition frequency difference are generated from a single full polarization maintaining fiber resonant cavity.

While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.