A large frequency difference, tunable, high-stability dual-frequency laser generating device and method

Abstract

The present invention discloses a high-stability dual-frequency laser generating device and method with large frequency difference and tunable properties, which belongs to the field of dual-frequency laser generation, and includes: a light source emission module, which is used to combine the continuous light emitted by two lasers into a dual-frequency laser; a laser phase-locking module, which is used to lock the two lasers on the same reference delay optical fiber, and perform frequency and phase discrimination and filtering conditioning on the dual-frequency laser to obtain a feedback control signal, and output the feedback control signal to the two lasers; a reference delay optical fiber locking module, which is used to lock the length of the reference delay optical fiber; a first optical coupler, which is used to divide the dual-frequency laser into two paths, the first path is connected to the laser phase-locking module, and the second path is connected to the fourth optical coupler; the fourth optical coupler is used to divide the second dual-frequency laser into two paths, the first path is connected to the reference delay optical fiber locking module, and the second path is output. The present invention has low manufacturing cost and can achieve stable control of two lasers and their frequency difference.

Description

Technical Field

[0001] The present invention belongs to the field of dual-frequency laser generation, and in particular relates to a large frequency difference, tunable, highly stable dual-frequency laser generation device and method. Background Art

[0002] Dual-frequency lasers are widely used in laser interferometry, optical sensing, holographic imaging, and photogenerated microwaves, millimeter waves, and terahertz waves. In particular, dual-frequency lasers with high-frequency difference stability can improve the repeatability and stability of measurements, and can be used in long-term, high-precision measurement and sensing, as well as the technical field of ultra-low noise microwave and millimeter wave signal generation. At the same time, dual-frequency lasers with large frequency difference and tunability play an important role in the fields of high-speed target, high-precision absolute distance measurement, and the generation of tunable microwave signals. Taking synthetic wavelength measurement technology as an example, large frequency difference dual-frequency lasers have higher measurement accuracy, and small frequency difference can achieve a larger measurement range (absolute distance measurement). Through dual-frequency laser frequency difference tuning, multi-level synthetic wavelengths can be constructed to achieve high-precision, large dynamic range absolute distance measurement.

[0003] Among the current mainstream dual-frequency laser generation technologies and methods, the Zeeman effect or acousto-optic modulation frequency shift method can only produce a frequency difference output of several MHz or tens of MHz; the common dual longitudinal mode method using gas gain media (such as He-Ne lasers) can produce dual-frequency lasers with a frequency difference range of 600MHz to 1000MHz; lasers based on special solid gain media such as Nd:YAG can achieve frequency difference interval output of several GHz or even several THz, but they all face the problem of difficult precise control. In addition, in order to achieve stable frequency difference output, it is necessary to maintain the stability of the laser optical cavity. On the one hand, this puts higher requirements on the external environment; on the other hand, it also forces it to combine auxiliary technologies such as Pound-Drever-Hall (PDH) frequency stabilization control and cavity vibration isolation / sound insulation control, which increases the cost and complexity of the system. In addition, the dual-light source locking method using PDH frequency stabilization can in principle achieve dual-frequency laser output with a large frequency difference tuning range. However, since the PDH frequency stabilization technology locks the laser frequency on the resonance peak of the high-precision, high-stability Fabry-Perot (FP) reference cavity, in order to achieve the stability of the FP reference cavity itself, it needs to be strictly temperature-controlled, shock-proofed, and sound-insulated, which is difficult to achieve and costly. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a large frequency difference, tunable, highly stable dual-frequency laser generating device and method to solve the problems existing in the prior art.

[0005] To achieve the above object, the present invention provides a large frequency difference, tunable, high-stability dual-frequency laser generating device, comprising:

[0006] A light source emission module is used to combine the continuous light emitted by two lasers into a dual-frequency laser;

[0007] A laser phase-locking module is connected to the light source transmitting module, and is used to lock two lasers on the same reference delay optical fiber, and to perform frequency and phase discrimination and filtering conditioning on the dual-frequency laser to obtain a feedback control signal, and output the feedback control signal to the two lasers;

[0008] A reference delay optical fiber locking module is connected to the light source emission module and the laser phase locking module respectively, and is used to lock the length of the reference delay optical fiber;

[0009] A first optical coupler is used to divide the dual-frequency laser into two paths, the first path is connected to the laser phase-locking module, and the second path is connected to the fourth optical coupler;

[0010] The fourth optical coupler is used to divide the second dual-frequency laser into two paths, the first path is connected to the reference delay fiber locking module, and the second path is output.

[0011] Optionally, the light source emission module includes a first laser, a second laser and a beam combiner;

[0012] The first laser is used to emit continuous light of a first optical frequency;

[0013] The second laser is used to emit continuous light of a second optical frequency;

[0014] The beam combiner is used to combine the continuous light of the first optical frequency and the continuous light of the second optical frequency into a dual-frequency laser.

[0015] Optionally, the laser phase-locking module includes a delayed self-interference structure, a first wavelength division multiplexer, a second wavelength division multiplexer, a first photodetector, a second photodetector, a first loop filter and a second loop filter;

[0016] The delayed self-interference structure is used to convert the frequency fluctuation of the dual-frequency laser into phase fluctuation;

[0017] The first wavelength division multiplexer and the second wavelength division multiplexer are respectively connected to the delayed self-interference structure, and are used to demultiplex the dual-frequency laser after passing through the delayed self-interference structure to obtain the first optical frequency laser and the second optical frequency laser;

[0018] The first photodetector is connected to the first wavelength division multiplexer and the second wavelength division multiplexer respectively, and is used to receive the first optical frequency laser and convert the first optical frequency laser into a first beat frequency signal;

[0019] The second photodetector is connected to the first wavelength division multiplexer and the second wavelength division multiplexer respectively, and is used to receive the second optical frequency laser and convert the second optical frequency laser into a second beat frequency signal;

[0020] The first loop filter is connected to the output of the first photodetector, and is used to perform frequency and phase discrimination on the first beat frequency signal to obtain a first phase error signal, and perform loop filtering and conditioning based on the first phase error signal to output a feedback control signal of the first laser;

[0021] The second loop filter is connected to the output of the second photodetector and is used to perform frequency and phase discrimination on the second beat frequency signal to obtain a second phase error signal, and perform loop filtering and conditioning based on the second phase error signal to output a feedback control signal for the second laser.

[0022] Optionally, the delayed self-interference structure includes a second optical coupler, a reference delayed optical fiber, an optical fiber stretcher, an acousto-optic frequency shifter, and a third optical coupler;

[0023] The second optical coupler is used to split the light wave into two paths, one path is connected to the reference delay optical fiber, and the other path is connected to the acousto-optic frequency shifter;

[0024] The reference delay fiber is used to stabilize the frequency of the laser;

[0025] The optical fiber stretcher is connected to the reference delay optical fiber and is used to compensate for the length change of the reference delay optical fiber;

[0026] The acousto-optic frequency shifter is used to shift the optical frequency;

[0027] The third optical coupler is used to combine the light waves output by the optical fiber stretcher and the acousto-optic frequency shifter for interference.

[0028] Optionally, the reference delay fiber locking module includes an optical frequency comb, a fifth optical coupler, a third photodetector, a mixer, a filter, and a third loop filter;

[0029] The fifth optical coupler is used to perform wave combining interference on the optical frequency comb and the dual-frequency laser to obtain an interference optical signal;

[0030] The third photodetector is connected to the fifth optical coupler and is used to convert the interference light signal into an electrical signal to obtain a third beat frequency signal;

[0031] The mixer is connected to the third photodetector and is used to mix the dual-frequency laser and the beat frequency signal of the adjacent comb teeth of the optical frequency comb;

[0032] The filter is connected to the mixer and is used to filter out the difference of the beat frequency signals from the beat frequency signals;

[0033] The third loop filter is connected to the filter, and is used to perform frequency and phase discrimination on the beat frequency signal of the filtered beat frequency signal difference to obtain a phase error signal of the beat frequency difference, and perform loop filtering and conditioning based on the phase error signal of the beat frequency difference to output a feedback control signal of the optical fiber stretcher in the delayed self-interference structure.

[0034] The present invention also provides a method for generating a large frequency difference, tunable, highly stable dual-frequency laser, comprising the following steps:

[0035] Combine the continuous light beams emitted by the two lasers into a dual-frequency laser, and then divide the dual-frequency laser into three parts, the first part is used for output, and the other two parts are used for closed-loop feedback control of the frequencies of the two lasers;

[0036] The second part of the dual-frequency laser converts the frequency fluctuation of the dual-frequency laser into phase fluctuation through the delayed self-interference structure, and then obtains the beat frequency signals containing the phase fluctuation information of the two lasers through the wavelength division multiplexer and the photodetector respectively;

[0037] The beat frequency signal is phase-detected with a low-noise reference signal to obtain an error signal, the error signal is loop-filtered to obtain a feedback signal of the laser, and the output of the laser is controlled by the feedback signal of the laser.

[0038] Optionally, the process of converting the frequency fluctuation of the dual-frequency laser into the phase fluctuation by the delayed self-interference structure also includes calibrating the delayed self-interference structure, and the calibration method includes:

[0039] In the third part, the dual-frequency laser and the optical frequency comb perform interference beat frequency, and then the change of the dual-frequency laser frequency difference is obtained through mixing and filtering;

[0040] A phase error signal is obtained after phase detection between the beat frequency difference and the low-noise reference signal. A loop filter is performed on the phase error signal based on the beat frequency difference to obtain a feedback control signal of the delayed self-interference structure. The delayed self-interference structure is controlled by the feedback control signal of the delayed self-interference structure.

[0041] Compared with the prior art, the present invention has the following advantages and technical effects:

[0042] The present invention uses a delayed interference optical phase-locked loop to lock two independently running lasers on the same reference delay fiber, synchronize the frequency changes of the two lasers, and further realize the delay stability control of the reference delay fiber by using the closed-loop feedback control method through the change of the frequency difference between the two lasers. Thus, stable control of the two lasers and their frequency difference is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0044] Figure 1 Schematic diagram of a highly stable dual-frequency laser generating device according to an embodiment of the present invention;

[0045] In the figure: 1. first laser; 2. second laser; 3. beam combiner; 4. first optical coupler; 5. second optical coupler; 6. reference delay fiber; 7. fiber stretcher; 8. acousto-optic frequency shifter; 9. third optical coupler; 10. first wavelength division multiplexer; 11. second wavelength division multiplexer; 12. first photodetector; 13. second photodetector; 14. first loop filter; 15. second loop filter; 16. fourth optical coupler; 17. optical frequency comb; 18. fifth optical coupler; 19. third photodetector; 20. mixer; 21. filter; 22. third loop filter. DETAILED DESCRIPTION

[0046] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0047] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0048] Embodiment 1

[0049] like Figure 1 As shown, the present invention provides a high-stability dual-frequency laser generating device with large frequency difference and tunable performance, and the specific implementation methods are as follows:

[0050] The first laser 1 and the second laser 2 emit continuous light with frequencies ν1 and ν2 respectively, which are combined by a beam combiner 3. The output of the beam combiner 3 is connected to a first optical coupler 4. The first optical coupler is divided into two paths, the first path is connected to a second optical coupler 5, and the second optical coupler 5 is divided into two paths, one path is connected to a delay optical fiber 6 and an optical fiber stretcher 7 in sequence, and the other path is connected to an acousto-optic frequency shifter 8. The two paths are combined by a third optical coupler 9. The two output ports of the third optical coupler 9 are respectively connected to a first wavelength division multiplexer 10 and a second wavelength division multiplexer 11. The two wavelength division multiplexers separate the continuous light with frequencies ν1 and ν2, and then are respectively connected to a first photodetector 12 and a second photodetector 13. After converting the optical signal into an electrical signal, they are respectively connected to a first loop filter 14 and a second loop filter 15; the first loop filter 14 and the second loop filter 15 are simultaneously connected to a low-noise reference signal, and their outputs are respectively connected to the first laser 1 and the second laser 2. The other output of the first optical coupler 4 is connected to the fourth optical coupler 16. The output of the fourth optical coupler 16 is divided into two paths, one path is used to output the generated dual-frequency laser, and the other path is connected to the two input ports of the fifth optical coupler 18 respectively with the optical frequency comb 17. The output port of the fifth optical coupler 18 is connected to the third photodetector 19. The output of the third photodetector 19 is connected to the mixer 20, the filter 21 and the third loop filter 22. At the same time, the low-noise reference signal is connected to the third loop filter 22. The output of the third loop filter 22 is connected to the optical fiber stretcher 7.

[0051] Preferably, the first laser 1 and the second laser 2 can be optical fiber lasers, semiconductor lasers, and other lasers whose frequency can be controlled, and their output wavelengths can be in the C band and the L band, and the frequency difference between the two lasers can be spaced from MHz to tens of THz;

[0052] The first optical coupler and the fourth optical coupler may be 99:1 optical couplers; the second optical coupler, the third optical coupler and the fifth optical coupler may be 50:50 optical couplers;

[0053] The reference delay optical fiber 6 can be a single-mode optical fiber or a polarization-maintaining optical fiber, and its length is optimized to be 2 km;

[0054] The first photodetector, the second photodetector and the third photodetector use balanced photodetectors to eliminate common mode noise;

[0055] The spectral range of the optical frequency comb 17 can be appropriately selected according to the frequency difference between the dual-frequency lasers, ranging from tens of nm to hundreds of nm.

[0056] In this embodiment, a method for generating a dual-frequency laser with large frequency difference and tunable high stability is also provided, and the specific implementation steps are as follows:

[0057] Step 1: Two fiber lasers with wavelengths of 1546nm and 1554nm emit continuous photosynthesized beams to become dual-frequency lasers with a frequency difference of about 1THz; then they are divided into two parts through a 99:1 optical coupler, 99% of the dual-frequency laser is used for output, and 1% is used for closed-loop feedback control of the laser frequency;

[0058] Step 2: The dual-frequency laser accounting for 1% is delayed self-interfered through an unbalanced Mach-Zehnder interferometer consisting of a 50:50 optical coupler, a 2km long reference delayed single-mode optical fiber, an optical fiber stretcher, and an acousto-optic frequency shifter that can produce a 40MHz frequency shift, so that the frequency fluctuations of the two lasers are converted into phase fluctuations. After passing through a wavelength division multiplexer and a balanced photodetector, beat frequency signals containing the phase fluctuation information of the two lasers are obtained respectively.

[0059] Step 3: The beat frequency signals of the two lasers generated in step 2 are phase-detected with the low-noise reference signal based on the atomic clock to obtain error signals. After loop filtering and conditioning, feedback signals are obtained to control the output of each laser, so that the laser frequency change is locked on the reference delay fiber. Assume that the frequency of the two lasers is ν i (i=1,2, representing each laser respectively), the frequency fluctuation is δν i , the fiber length is L, the fiber length change caused by environmental changes is δL, and the corresponding delays are τ and δτ respectively. Then, in the locked state, the frequency change of the laser is proportional to the change of the fiber length:

[0060]

[0061] Step 4: Stabilize the reference delayed fiber. Assume that the frequency difference between the two lasers is Δν=ν1-ν2. According to the formula in step 3, after the lasers are phase-locked, the frequency difference change δ(Δν) between the two lasers is also proportional to the reference fiber delay change:

[0062]

[0063] Therefore, the change in the frequency difference of the dual-frequency laser reflects the change in the reference delay length; by interfering with a part of the dual-frequency laser output with the optical frequency comb, and then mixing and filtering to obtain the change in the frequency difference of the dual-frequency laser, the delay jitter information of the reference delay fiber is obtained.

[0064] Step 5: In step 4, the phase error signal is obtained by phase detection between the beat frequency difference and the low noise reference signal, and the phase error signal is output after loop filtering and conditioning to control the optical fiber delay line to compensate for the length change of the reference delay optical fiber caused by the change of the external environment.

[0065] Embodiment 2

[0066] This embodiment provides a large frequency difference, tunable, high-stability dual-frequency laser generating device, including a light source transmitting module, a laser phase locking module and a reference delay fiber 6 phase locking module.

[0067] The light source transmitting module is used to combine the continuous light emitted by two independent lasers into a dual-frequency laser. It includes two lasers and a beam combiner 3. The first laser 1 is used to emit continuous light of a first optical frequency; the second laser 2 is used to emit continuous light of a second optical frequency; the beam combiner 3 is used to combine the continuous light of the first optical frequency with the continuous light of the second optical frequency.

[0068] The laser phase-locking module is used to lock two lasers on the same reference delay fiber 6 so that their frequency changes are consistent with the fiber delay changes. It includes a second optical coupler 5, a reference delay fiber 6, a fiber stretcher 7, an acousto-optic frequency shifter 8, a third optical coupler 9, a first wavelength division multiplexer 10, a second wavelength division multiplexer 11, a first photodetector 12, a second photodetector 13, a first loop filter 14 and a second loop filter 15. Among them, the second optical coupler 5, the reference delay fiber 6, the fiber stretcher 7, the acousto-optic frequency shifter 8 (for changing the frequency) and the third optical coupler 9 constitute a delayed self-interference structure for converting the frequency fluctuation of the laser into phase fluctuation. The second optical coupler 5 is used to divide the light wave into two paths, one of which is connected to the reference delay fiber 6 and the fiber stretcher 7, and the other is connected to the acousto-optic frequency shifter 8; the reference delay fiber 6 is used as a common reference for the two lasers to stabilize the frequency of the lasers, and the fiber stretcher 7 is used to compensate for the length change of the reference delay fiber 6 so that its delay remains unchanged. The acousto-optic frequency shifter 8 shifts the frequency of the light passing through; the third optical coupler 9 is used to combine two optical waves for interference; the first wavelength division multiplexer 10 and the second wavelength division multiplexer 11 are connected to the third optical coupler 9 for wavelength division multiplexing; the first photodetector 12 is connected to the first wavelength division multiplexer 10 and the second wavelength division multiplexer 11 respectively, and is used to receive the beat signal containing the frequency jitter information of the first optical frequency; the second photodetector 13 is connected to the first wavelength division multiplexer 10 and the second wavelength division multiplexer 11 respectively, and is used to receive the beat signal containing the frequency jitter information of the second optical frequency. The first loop filter 14 is connected to the output of the first photodetector 12, and is connected to the low-noise RF reference signal at the same time. After frequency and phase discrimination, the phase error signal of the first optical frequency is obtained, and the feedback control signal of the first laser 1 is output after loop filtering and conditioning. The second loop filter 15 is connected to the output of the second photodetector 13 and connected to a low-noise RF reference signal. After frequency and phase discrimination, a phase error signal of the second optical frequency is obtained, and then a feedback control signal of the second laser 2 is output through loop filtering.

[0069] The reference delay fiber 6 locking module is used to further lock the length of the reference delay fiber 6 so that its delay remains unchanged. It includes an optical frequency comb 17, a fifth optical coupler 18, a third photodetector 19, a mixer 20, a filter 21, and a third loop filter 22. The optical frequency comb 17 and the dual-frequency laser are combined and interfered in the fifth optical coupler 18, and then connected to the third photodetector 19. The third photodetector 19 converts the interference light signal into an electrical signal to obtain the beat frequency signal of the two lasers and the adjacent teeth of the optical frequency comb 17; the mixer 20 mixes the beat frequency signal of the two lasers and the adjacent teeth of the optical frequency comb 17; the filter 21 filters out the difference of the beat frequency signal from the above beat frequency signal, and the stability of the difference of the beat frequency signal represents the stability of the frequency difference of the two lasers. The third loop filter 22 is connected to the output of the filter 21, and is connected to a low-noise RF reference signal at the same time. After frequency and phase discrimination, a phase error signal of the beat frequency difference is obtained, and after loop filtering conditioning, a feedback signal for controlling the optical fiber delay line is output.

[0070] Accordingly, the present invention provides a method for generating a large frequency difference, tunable, highly stable dual-frequency laser, comprising the following steps:

[0071] Step 1: The continuous photosynthesized beams emitted by two independent lasers become dual-frequency lasers, which are then divided into three parts, one for output and the other two for closed-loop feedback control of the frequencies of the two lasers;

[0072] Step 2, the dual-frequency laser used for feedback control of the laser is transformed into phase fluctuation by forming a delayed self-interference structure composed of an optical coupler, a reference delay fiber 6, a fiber stretcher 7, and an acousto-optic frequency shifter 8, and then the beat frequency signals containing the phase fluctuation information of the two lasers are obtained after passing through a wavelength division multiplexer and a photodetector.

[0073] Step 3, the beat frequency signals of the two lasers generated in step 2 are phase-detected with the low-noise reference signal to obtain error signals, which are conditioned by loop filters to obtain feedback signals that are used to control the outputs of the respective lasers so that the laser frequency changes are locked on the reference delay fiber 6.

[0074] Step 4, in order to further stabilize the reference delay fiber 6, a part of the dual-frequency laser output is interfered with the optical frequency comb 17, and then the change of the dual-frequency laser frequency difference is obtained through mixing and filtering. The stability of the frequency difference reflects the stability of the reference delay fiber 6.

[0075] Step 5, in step 4, the phase error signal is obtained after phase detection between the beat frequency difference and the low noise reference signal, and is output after loop filtering and conditioning, and is used to control the optical fiber delay line to compensate for the length change of the reference delay optical fiber 6 caused by the change of the external environment.

[0076] After the above steps, dual-frequency laser output with large frequency difference, tunability and high stability can be achieved.

[0077] In summary, the significant advantages of the present invention compared with the prior art are summarized as follows:

[0078] 1. The present invention uses a delayed interference optical phase-locked loop to lock two independently running lasers on the same reference delay fiber, synchronize the frequency changes of the two lasers, and further use the closed-loop feedback control method to achieve delay stability control of the reference delay fiber through the change of the frequency difference between the two lasers. Compared with most traditional solutions that only stabilize the frequency difference, the technical solution proposed by the present invention can achieve stable control of two lasers and their frequency difference.

[0079] 2. The technical solution proposed in the present invention can arbitrarily select two suitable independent lasers and their frequency intervals according to the needs of actual applications. Under the premise of maintaining high stability, dual-frequency laser output with a frequency difference ranging from MHz to tens of THz can be achieved, which has excellent tunability.

[0080] 3. Compared with frequency stabilization technologies such as PDH that require a high-precision, high-stability FP cavity as a reference, the technical solution proposed in the present invention has lower costs, easier operation, and reduces the stringent requirements for high stability of the external environment.

[0081] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A high-stability dual-frequency laser generator with large frequency difference and tunable performance. It is characterized in that include: A light source emission module is used to combine the continuous light emitted by two lasers into a dual-frequency laser; A laser phase-locking module is connected to the light source transmitting module, and is used to lock two lasers on the same reference delay optical fiber, and to perform frequency and phase discrimination and filtering conditioning on the dual-frequency laser to obtain a feedback control signal, and output the feedback control signal to the two lasers; The laser phase-locking module includes a delayed self-interference structure, a first wavelength division multiplexer, a second wavelength division multiplexer, a first photodetector, a second photodetector, a first loop filter and a second loop filter; The delayed self-interference structure is used to convert the frequency fluctuation of the dual-frequency laser into phase fluctuation; The first wavelength division multiplexer and the second wavelength division multiplexer are respectively connected to the delayed self-interference structure, and are used to demultiplex the dual-frequency laser after passing through the delayed self-interference structure to obtain the first optical frequency laser and the second optical frequency laser; The first photodetector is connected to the first wavelength division multiplexer and the second wavelength division multiplexer respectively, and is used to receive the first optical frequency laser and convert the first optical frequency laser into a first beat frequency signal; The second photodetector is connected to the first wavelength division multiplexer and the second wavelength division multiplexer respectively, and is used to receive the second optical frequency laser and convert the second optical frequency laser into a second beat frequency signal; The first loop filter is connected to the output of the first photodetector, and is used to perform frequency and phase discrimination on the first beat frequency signal to obtain a first phase error signal, and perform loop filtering and conditioning based on the first phase error signal to output a feedback control signal of the first laser; The second loop filter is connected to the output of the second photodetector, and is used to perform frequency and phase discrimination on the second beat frequency signal to obtain a second phase error signal, and perform loop filtering and conditioning based on the second phase error signal to output a feedback control signal of the second laser; The delayed self-interference structure includes a second optical coupler, a reference delayed optical fiber, an optical fiber stretcher, an acousto-optic frequency shifter and a third optical coupler; The second optical coupler is used to split the light wave into two paths, one path is connected to the reference delay optical fiber, and the other path is connected to the acousto-optic frequency shifter; The reference delay fiber is used to stabilize the frequency of the laser; The optical fiber stretcher is connected to the reference delay optical fiber and is used to compensate for the length change of the reference delay optical fiber; The acousto-optic frequency shifter is used to shift the optical frequency; The third optical coupler is used to combine the light waves output by the optical fiber stretcher and the acousto-optic frequency shifter for interference; A reference delay optical fiber locking module is connected to the light source emission module and the laser phase locking module respectively, and is used to lock the length of the reference delay optical fiber; A first optical coupler is used to divide the dual-frequency laser into two paths, the first path is connected to the laser phase-locking module, and the second path is connected to the fourth optical coupler; The fourth optical coupler is used to divide the second dual-frequency laser into two paths, the first path is connected to the reference delay fiber locking module, and the second path is output.

2. The large frequency difference, tunable, high stability dual-frequency laser generating device according to claim 1, It is characterized in that The light source emission module includes a first laser, a second laser and a beam combiner; The first laser is used to emit continuous light of a first optical frequency; The second laser is used to emit continuous light of a second optical frequency; The beam combiner is used to combine the continuous light of the first optical frequency and the continuous light of the second optical frequency into a dual-frequency laser.

3. The large frequency difference, tunable, high stability dual-frequency laser generating device according to claim 1, It is characterized in that The reference delay fiber locking module includes an optical frequency comb, a fifth optical coupler, a third photodetector, a mixer, a filter, and a third loop filter; The fifth optical coupler is used to perform wave combining interference on the optical frequency comb and the dual-frequency laser to obtain an interference optical signal; The third photodetector is connected to the fifth optical coupler and is used to convert the interference light signal into an electrical signal to obtain a third beat frequency signal; The mixer is connected to the third photodetector and is used to mix the dual-frequency laser and the beat frequency signal of the adjacent comb teeth of the optical frequency comb; The filter is connected to the mixer and is used to filter out the difference of the beat frequency signals from the beat frequency signals; The third loop filter is connected to the filter, and is used to perform frequency and phase discrimination on the beat frequency signal of the filtered beat frequency signal difference to obtain a phase error signal of the beat frequency difference, and perform loop filtering and conditioning based on the phase error signal of the beat frequency difference to output a feedback control signal of the optical fiber stretcher in the delayed self-interference structure.

4. A method for generating a high-stable dual-frequency laser with a large frequency difference and tunability is applied to the high-stable dual-frequency laser generating device according to claim 1, It is characterized in that The following steps are involved: Combine the continuous light beams emitted by the two lasers into a dual-frequency laser, and then divide the dual-frequency laser into three parts, the first part is used for output, and the other two parts are used for closed-loop feedback control of the frequencies of the two lasers; The second part of the dual-frequency laser converts the frequency fluctuation of the dual-frequency laser into phase fluctuation through the delayed self-interference structure, and then obtains the beat frequency signals containing the phase fluctuation information of the two lasers through the wavelength division multiplexer and the photodetector respectively; The beat frequency signal is phase-detected with a low-noise reference signal to obtain an error signal, the error signal is loop-filtered to obtain a feedback signal of the laser, and the output of the laser is controlled by the feedback signal of the laser.

5. The method for generating a large frequency difference, tunable, highly stable dual-frequency laser according to claim 4, It is characterized in that The process of converting the frequency fluctuation of the dual-frequency laser into phase fluctuation by the delayed self-interference structure also includes calibrating the delayed self-interference structure. The calibration method includes: In the third part, the dual-frequency laser and the optical frequency comb perform interference beat frequency, and then the change of the dual-frequency laser frequency difference is obtained through mixing and filtering; A phase error signal is obtained after phase detection between the beat frequency difference and the low-noise reference signal. A loop filter is performed on the phase error signal based on the beat frequency difference to obtain a feedback control signal of the delayed self-interference structure. The delayed self-interference structure is controlled by the feedback control signal of the delayed self-interference structure.

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