阅读说明：本技术 获得光梳与其光谱范围外连续激光之间拍频信号的方法 (Method for obtaining beat frequency signal between optical comb and continuous laser outside spectral range thereof ) 是由 姚远 李波 杨广 蒋燕义 马龙生 于 2020-04-24 设计创作，主要内容包括：本发明公开了一种获得光梳与其光谱范围外连续激光之间拍频信号的方法,包括以下步骤：飞秒激光与其光谱覆盖范围以外的连续激光同时耦合入光子晶体光纤,利用光子晶体光纤的非线性效应,在飞秒激光光谱展宽获得飞秒光梳的同时,使连续激光产生一系列频率边带,频率边带与连续激光的频率间隔为飞秒光梳重复频率的整数倍,将连续激光及其频率边带记为第二光梳；通过选择合适的探测光谱成分,获得飞秒光梳与第二光梳的拍频信号,该拍频信号即为飞秒光梳与其光谱范围外的连续激光之间的拍频信号。本发明的优点是：解决了由于光梳与其光谱范围外连续激光之间因光谱不重合而无法直接获得拍频信号的难题,该方法结构简单、噪声小、稳定性高。(The invention discloses a method for obtaining beat frequency signals between an optical comb and continuous laser outside the spectral range of the optical comb, which comprises the following steps: the femtosecond laser and the continuous laser outside the spectrum coverage range are simultaneously coupled into the photonic crystal fiber, the nonlinear effect of the photonic crystal fiber is utilized, the femtosecond laser spectrum is broadened to obtain the femtosecond optical comb, the continuous laser generates a series of frequency sidebands, the frequency interval between the frequency sidebands and the continuous laser is integral multiple of the repetition frequency of the femtosecond optical comb, and the continuous laser and the frequency sidebands thereof are marked as a second optical comb; by selecting proper detection spectrum components, beat frequency signals of the femtosecond optical comb and the second optical comb are obtained, and the beat frequency signals are beat frequency signals between the femtosecond optical comb and continuous laser outside the spectrum range of the femtosecond optical comb. The invention has the advantages that: the method solves the problem that beat frequency signals cannot be directly obtained due to the fact that the optical comb and continuous laser outside the spectral range of the optical comb are not overlapped in spectrum, and is simple in structure, low in noise and high in stability.)

1. A method of obtaining a beat signal between an optical comb and a continuous laser outside its spectral range, comprising the steps of: simultaneously coupling femtosecond laser and continuous laser outside the spectrum coverage range of the femtosecond laser into a photonic crystal fiber to realize spectrum broadening of the femtosecond laser to obtain a femtosecond optical comb, generating a frequency sideband by the continuous laser while the spectrum of the femtosecond laser is broadened, wherein the frequency interval between the frequency sideband and the continuous laser is integral multiple of the repetition frequency of the femtosecond optical comb, marking the continuous laser and the frequency sideband as a second optical comb, and selectively detecting spectrum components through a grating and a diaphragm to obtain beat frequency signals of the femtosecond optical comb and the second optical comb.

2. The method of claim 1, wherein the femtosecond laser is generated by a femtosecond laser with power of 500-700 mW, and the continuous laser is generated by a continuous laser with power of 10-30 mW.

3. Between an optical comb and a continuous laser outside its spectral range, obtained according to claim 1The method for beat frequency signal is characterized in that the femtosecond laser adjusts the polarization direction through a first half wave plate, then is coupled into the photonic crystal fiber through a first reflector, a dichroic mirror and a first lens in sequence, the spectrum broadening of the femtosecond laser is realized, the femtosecond optical comb is obtained, and the frequency of comb teeth of the femtosecond optical comb is expressed asf _n= n ×f _r±f ₀(ii) a Wherein n is an integer and is the number of comb teeth of the femtosecond optical comb;f _ris the repetition frequency;f ₀is a carrier phase offset frequency or zero frequency.

4. The method of claim 3, wherein the polarization direction of the continuous laser is adjusted by a second half-wave plate, and then the continuous laser is coupled into the photonic crystal fiber via the dichroic mirror and the first lens, and the femtosecond laser and the photonic crystal fiber generate a frequency off _cw± m ×f _rWherein m is an integer,f _cwis the laser frequency of the continuous laser.

5. The method of claim 4, wherein the beat frequency signal is obtained by coupling the femtosecond optical comb and the spectral components filtered out by the second optical comb into the photodetector via a second reflector and a second lensf _b= ( n ×f _r±f ₀) - (f _cw ± m ×f _r) = ( n± m) ×f _r±f ₀-f _cw The beat frequency signalf _bNamely, the beat frequency signal between the continuous laser and the femtosecond optical comb.

Technical Field

The invention belongs to the technical field of photoelectric detection, and particularly relates to a method for obtaining a beat frequency signal between an optical comb and continuous laser outside a spectral range of the optical comb.

Background

The invention of the optical frequency comb solves the problem that the optical frequency comb is high and cannot be directly measured: the frequency of a beat frequency signal between an optical wave to be measured and adjacent comb teeth of an optical comb is measured (generally in a microwave band) and the frequency of the comb teeth of the optical comb, so that the optical frequency measurement is realized. In recent years, the optical frequency comb is also applied to connect light waves with different frequencies to realize frequency ratio measurement between laser lights with different wavelengths; or the frequency precision and coherence of a certain laser are transmitted to other optical wavelengths, for example, an optical clock signal is transmitted to the wavelength of 1.5 um, so that the long-distance high-precision transmission of time/frequency is realized; or transmitting the optical clock signal to the required wavelength to carry out the research on the verification of precise spectrum and basic physical theory; researchers also lock the femtosecond optical comb on a coherent light source with stable frequency to realize frequency control on the femtosecond optical comb, so that applications such as high-precision distance measurement and high-precision optical comb spectrum are developed.

The application of the optical combs is based on obtaining the optical combs with high signal-to-noise ratio and the beat frequency signals of continuous laser, so that the purposes of frequency control of the optical frequency combs, optical frequency measurement, optical coherent transmission and the like are achieved. To obtain the beat frequency signals of the optical comb and the continuous laser, firstly, the frequency spectrum of the optical comb must coincide with the continuous laser, secondly, on the establishment of a light path, the broadened femtosecond laser and the continuous laser are generally coincident in space, the polarization directions are also coincident, and then the broadened femtosecond laser and the continuous laser are incident to a detector to obtain the beat frequency signals of the femtosecond optical comb and the continuous laser.

When the wavelength of the continuous laser happens to fall within the spectral range of the femtosecond optical comb, the continuous laser and the optical comb only need to be superposed in space and polarization and then are incident to a detector to obtain beat frequency signals of the continuous laser and the optical comb. When the wavelength of the continuous laser is outside the spectrum of the broadened femtosecond optical comb, for example, the optical fiber optical comb with the spectral range of 1-2 microns and most of optical clock signals with the wavelength in visible light generally need to firstly perform power amplification and spectral broadening on the optical fiber pulse laser, then frequency doubling is performed to the wavelength of the continuous laser, and then the frequency-doubled femtosecond optical comb and the continuous laser are subjected to beat frequency on a detector to obtain beat frequency signals of the femtosecond optical comb and the continuous laser; the frequency doubling of the near-infrared laser is usually performed to the spectral range of the titanium gemstone femtosecond optical comb in the spectral range of 0.5-1 micron and the laser with the wavelength in the near-infrared band, such as the 1.5 micron optical fiber communication band laser, and then the frequency doubling light and the spectrally broadened femtosecond optical comb are subjected to frequency beating to obtain a beat frequency signal. In some application scenarios, because the wavelengths of the two cannot satisfy the relationship of two times, the spectrum overlapping cannot be realized by the frequency doubling in the above method, and therefore, means such as optical difference frequency are also adopted. However, this method can only be applied to lasers with special wavelengths, such as fiber optical comb and far infrared laser with wavelength of 10 μm.

Disclosure of Invention

The invention aims to provide a method for obtaining a beat frequency signal between an optical comb and continuous laser outside the spectral range of the optical comb according to the defects of the prior art, wherein the femtosecond laser and the continuous laser simultaneously pass through a photonic crystal fiber, the spectrum of the femtosecond laser is broadened, and simultaneously, a new second optical comb which takes the continuous laser frequency as the center and the frequency interval as the repeat frequency of the optical comb is generated, and the second optical comb and the spectrum of the broadened femtosecond optical comb have an overlapping part, so that the beat frequency signal between the continuous laser and the femtosecond optical comb is obtained through beat frequency.

The purpose of the invention is realized by the following technical scheme:

a method of obtaining a beat signal between an optical comb and a continuous laser outside its spectral range, the method comprising the steps of: simultaneously coupling femtosecond laser and continuous laser outside the spectrum coverage range of the femtosecond laser into a photonic crystal fiber to realize spectrum broadening of the femtosecond laser to obtain a femtosecond optical comb, generating a frequency sideband by the continuous laser while the spectrum of the femtosecond laser is broadened, wherein the frequency interval between the frequency sideband and the continuous laser is integral multiple of the repetition frequency of the femtosecond optical comb, marking the continuous laser and the frequency sideband as a second optical comb, and selectively detecting spectrum components through a grating and a diaphragm to obtain beat frequency signals of the femtosecond optical comb and the second optical comb.

The femtosecond laser is generated by a femtosecond laser with the power of 500-700 mW, and the continuous laser is generated by a continuous laser with the power of 10-30 mW.

The femtosecond laser adjusts the polarization direction through the first half-wave plate, and then is coupled into the photonic crystal fiber through the first reflector, the dichroic mirror and the first lens in sequence to realize the spectral broadening of the femtosecond laser to obtain the femtosecond optical comb, wherein the frequency of comb teeth of the femtosecond optical comb is expressed asf _n= n ×f _r±f ₀(ii) a Wherein n is an integer and is the number of comb teeth of the femtosecond optical comb;f _ris the repetition frequency;f ₀is a carrier phase offset frequency or zero frequency.

The continuous laser adjusts the polarization direction through a second half-wave plate, then is coupled into the photonic crystal fiber through the dichroic mirror and the first lens, and generates the frequency of femtosecond laser and the photonic crystal fiber under the combined action of the femtosecond laser and the photonic crystal fiberf _cw± m ×f _rWherein m is an integer,f _cwis the laser frequency of the continuous laser.

Coupling the femtosecond optical comb and the spectral components filtered out by the second optical comb into the photoelectric detector through a second reflector and a second lens so as to obtain a beat frequency signalf _b= ( n ×f _r±f ₀) - (f _cw ± m ×f _r) = ( n ±m) ×f _r±f ₀-f _cw The beat frequency signalf _bNamely, the beat frequency signal between the continuous laser and the femtosecond optical comb.

The invention has the advantages that: (1) the invention omits the optical frequency doubling and the temperature control and optical coupling device thereof in the prior conventional method, so the system is simpler and the structure is more stable; (2) in the invention, because the continuous laser and the femtosecond optical comb are coaxially transmitted, the detection frequency noise generated by optical path disturbance can be effectively reduced; (3) because the number of the comb teeth of the femtosecond optical comb participating in the beat frequency is increased, the signal-to-noise ratio of the beat frequency signal obtained by the method is higher than that obtained by the conventional method of optically doubling the frequency and then beating the frequency.

Drawings

FIG. 1 is a schematic diagram of a femtosecond optical comb and a continuous laser beat frequency signal outside the optical comb spectrum range obtained in the present invention;

FIG. 2 is a schematic structural diagram of a femtosecond optical comb and a continuous laser beat frequency signal outside the optical comb spectrum range obtained in the present invention.

As shown in fig. 1-2, the respective labels in the figure are: the device comprises a femtosecond laser 1, a first half-wave plate 2, a first reflector 3, a continuous laser 4, a second half-wave plate 5, a dichroic mirror 6, a first lens 7, a photonic crystal fiber 8, a grating 9, a diaphragm 10, a second reflector 11, a second lens 12, a photoelectric detector 13, a third lens 14, a beat frequency devicef _bFemtosecond optical comb frequencyf _nContinuous laser frequencyf _cwRepetition frequency off _r。

Detailed Description

The features of the present invention and other related features are described in further detail below by way of example in conjunction with the following drawings to facilitate understanding by those skilled in the art: