Auxiliary phase-locking device for adaptation of optical module and phase-locked loop module and use method of auxiliary phase-locking device

Abstract

The invention provides an auxiliary phase-locking device for adaptation of an optical module and a phase-locked loop module and a use method. The auxiliary phase-locking device comprises a frequency-modulated continuous wave generation source, a Mach-Zehnder interferometer, a balanced photoelectric detector, a power divider, an auxiliary phase-locked loop module and an optical phase-locked loop. And the frequency modulation continuous wave generation source is used for generating laser signals. And the Mach-Zehnder interferometer comprises an optical fiber type coupler and an optical fiber delay line, and the optical fiber type coupler receives the laser signals and transmits the laser signals to the balanced photoelectric detector through the optical fiber delay line. And the balanced photoelectric detector receives the laser signal, converts the laser signal into a beat frequency electric signal and outputs the beat frequency electric signal to the power divider. The invention provides an auxiliary phase-locking device for adaptation of an optical module and a phase-locked loop module, which is characterized in that an auxiliary phase-locking module is added in a traditional optical module and a traditional phase-locked loop module; the module adjusts the loop gain of the phase-locked loop by capturing an error or noise characteristic between a current beat frequency signal and a reference frequency signal so as to realize rapid active phase locking.

Description

Technical Field

[0001] The present invention belongs to the technical field of digital signal processing, and in particular relates to an auxiliary phase locking device for adapting an optical module and a phase locked loop module and a use method thereof. Background Art

[0002] The current modulated distributed feedback semiconductor laser generating frequency modulated continuous wave is currently the most economical, convenient and simple laser radar source generation scheme, but this scheme has many problems that need to be solved, such as swept frequency nonlinearity and source phase noise. Sweep frequency nonlinearity refers to the nonlinear mapping between the modulation signal and the output instantaneous frequency due to the competition between the thermal effect and the carrier effect inside the laser, that is, the input linear modulation signal outputs a nonlinear instantaneous frequency. Sweep frequency nonlinearity will affect the ranging accuracy within the coherent distance. If the swept frequency nonlinearity is large, the ranging peak within the coherent distance is not obvious; if the swept frequency nonlinearity is small, the ranging peak within the coherent distance is sharp. Source phase noise mainly affects the coherent measurement distance. The larger the source phase noise, the shorter the coherent distance; conversely, the smaller the source phase noise, the longer the coherent distance.

[0003] Optimizing laser thermal design or external pre-distortion schemes can greatly improve the frequency sweep nonlinearity. In many related studies, the frequency sweep nonlinearity has been reduced to 10 -7 However, the line width of the current distributed feedback semiconductor laser is in the order of hundreds of kHz to MHz. For long-distance measurement applications, this laser cannot meet the needs very well. Therefore, in order to effectively improve the phase noise characteristics of the source, an optical phase-locked loop solution can be used. However, the coordination of the phase-locked loop and the optical module is usually more troublesome. For example, parameters such as loop delay and loop bandwidth need to be redesigned according to different optical modules, which increases the cost of the phase-locked loop and reduces the universality and compatibility of the phase-locked loop technology. Summary of the invention

[0004] The purpose of the present invention is to solve the problem of matching an optical module with a phase-locked loop module, and to provide an auxiliary phase-locking device and a use method for matching an optical module with a phase-locked loop module.

[0005] The present invention adopts the following technical solution:

[0006] An auxiliary phase-locked device for adapting an optical module and a phase-locked loop module comprises a frequency-modulated continuous wave generating source, a Mach-Zehnder interferometer, a balanced photoelectric detector, a power divider, an auxiliary phase-locked loop module, and an optical phase-locked loop.

[0007] A frequency modulated continuous wave generator, used to generate and output a laser signal;

[0008] The Mach-Zehnder interferometer includes an optical fiber coupler and an optical fiber delay line. The optical fiber coupler receives a laser signal and transmits it to a balanced photodetector through the optical fiber delay line.

[0009] A balanced photodetector receives the laser signal and converts the laser signal into a beat frequency electrical signal and outputs it to the power divider;

[0010] A power divider receives the electrical signal output by the balanced photodetector and divides the electrical signal into two paths and sends them to the auxiliary phase-locked loop module and the optical phase-locked loop respectively;

[0011] The auxiliary phase-locked loop module is divided into two structures, one of which includes a radio frequency switch, a comparator module, a reciprocal module, a zero-crossing detection module, and an arbitrary function generator I; the other includes a frequency noise power spectrum density statistics module, a comparator module, and an arbitrary function generator I;

[0012] The RF switch is a shared device, one side of which is electrically connected to the power divider, and the other side is connected to the zero-crossing detection module and the frequency noise power spectrum density statistics module, and is used to switch the two structures of the auxiliary phase-locked loop module to turn on or off one structure;

[0013] Among them, in one structure:

[0014] The zero-crossing detection module is used to detect the zero-crossing point of the beat frequency signal, store it, and output it to the inverse calculation module;

[0015] The reciprocal module calculates the frequency of the beat signal according to the difference of the zero-crossing point sequence number and outputs it to the comparator module;

[0016] Arbitrary function generator I, used to generate reference signal;

[0017] The comparator module compares the reference signal frequency of the arbitrary function generator I with the beat frequency signal frequency output by the inverse calculation module, and generates a control voltage for controlling the gain of the adjustable gain module of the optical phase-locked loop;

[0018] In another structure:

[0019] A frequency noise power spectrum density statistics module is used to count the power noise power spectrum density of the beat frequency electrical signal and output the statistical value to the comparator module;

[0020] Arbitrary function generator I, used to generate frequency noise power spectral density statistics of reference signal;

[0021] A comparator module compares the statistical value output by the frequency noise power spectrum density statistical module with the frequency noise power spectrum density statistical value of the reference signal output by the arbitrary function generator I, and generates a control voltage for controlling the gain of the adjustable gain module of the optical phase-locked loop;

[0022] Optical phase-locked loop, including arbitrary function generator II, mixer, adjustable gain module, integrator;

[0023] Arbitrary function generator II, used to generate reference signals;

[0024] The mixer receives the reference signal generated by the arbitrary function generator II and the beat frequency electrical signal input by the power divider, and mixes the two signals to generate an error signal;

[0025] An adjustable gain module receives an error signal, adjusts the error signal gain and outputs it to an integrator;

[0026] The integrator receives the error signal after gain adjustment, and sends the signal to the frequency modulated continuous wave generator after integration processing. In one embodiment, the frequency modulated continuous wave generator is a current modulated distributed feedback semiconductor laser, whose bias current is 200mA, modulation amplitude is 20mA, modulation period is 2.5kHz, and modulation waveform is a triangular wave. The output power of the frequency modulated continuous wave generator is 60mW, and the operating temperature of the entire source is 20°C.

[0027] In one embodiment, the length of the optical fiber delay line is 10 m.

[0028] In one embodiment, the bandwidth of the balanced photodetector is DC-500 MHz, the input optical power of the balanced photodetector is 10 μW, and the fixed gain of the balanced photodetector is 20 dB.

[0029] In one embodiment, the power divider has a distribution ratio of 5:5 and a bandwidth of DC-100 MHz.

[0030] In one embodiment, the bandwidth of the mixer is 40KHz-400MHz. The output amplitude of the arbitrary function generator II is 4.74Vpp. The gain of the adjustable gain module is adjustable within 80dB according to the size of the driving voltage. The integration time of the integrator is 10kHz.

[0031] A method for using an auxiliary phase-locking device for adapting an optical module and a phase-locked loop module, comprising:

[0032] Phase locking based on zero-crossing detection

[0033] Step 1. A frequency modulated continuous wave generator generates a laser light source, which passes through a Mach-Zehnder interferometer and then enters a balanced photodetector;

[0034] Step 2. The beat frequency signal output by the balanced photodetector enters the auxiliary phase-locked loop module;

[0035] Step 3. In the auxiliary phase-locked loop module, the zero point in the output time series is detected by the zero-crossing detection module and the time corresponding to the zero point is recorded. The signal of the zero point time is stored and then sent to the inverse calculation module;

[0036] Step 4. In the inverse module, a frequency-time-varying curve is solved, and the curve is compared with the reference frequency signal generated by the function generator I in the comparator module to generate a voltage signal that varies with time;

[0037] The frequency of the reference frequency signal is:

[0038]

[0039] Among them, f ideal is the frequency value of the reference signal, B is the sweep width of the frequency modulated continuous wave, T period is the frequency modulated continuous wave modulation period. When the modulation signal is a sawtooth wave, T period is the time of a cycle. When the modulation signal is a triangle wave, T period is the time of half a cycle, n is the medium refractive index of the optical fiber delay line in the Mach-Zehnder interferometer, L is the length of the optical fiber delay line in the Mach-Zehnder interferometer, and c is the speed of light in vacuum;

[0040] Step 5. Finally, the voltage signal is fed back to the adjustable gain module in the optical phase-locked loop to adjust the gain and achieve phase locking.

[0041] A method for using an auxiliary phase-locking device for adapting an optical module and a phase-locked loop module, comprising:

[0042] Method 2: Phase-locked method based on noise coefficient detection

[0043] Step 1. A frequency modulated continuous wave generator generates a laser light source, which passes through a Mach-Zehnder interferometer and then enters a balanced photodetector;

[0044] Step 2. The beat frequency signal output by the balanced photodetector enters the auxiliary phase-locked loop module;

[0045] Step 3. In the auxiliary phase-locked loop module, the frequency noise power spectrum density statistics module first performs statistics. During the statistics process, the beat frequency signal undergoes five steps of processing: period cutting, polynomial fitting, average value deduction, fast Fourier transform, and bandwidth integration selection, and then outputs the current frequency noise value.

[0046] Step 4. The current frequency noise value output in step 3 is compared with the theoretically designed standard frequency noise value of the same type of optical phase-locked loop in the comparator module, and a dynamic voltage is generated to adjust the loop gain of the optical phase-locked loop to achieve final locking;

[0047] The theoretically designed standard frequency noise value of the optical phase-locked loop is given by the following formula (2):

[0048]

[0049] in, is the square of the frequency noise value of the theoretically designed optical phase-locked loop within a certain loop bandwidth. The integral upper and lower limits DC-BW are the statistical noise bandwidth, f represents the frequency, Δv is the standard frequency width, and G opl l is the theoretically designed closed-loop transfer function of the optical phase-locked loop. During the design process, it is expressed as (3):

[0050]

[0051] i is an imaginary number, F sl Laser transfer function, the cutoff frequency is about 100kHz-10MHz, K is the loop gain, τ is the loop delay, τ1 is the delay time corresponding to the delay line in the Mach-Zehnder interferometer.

[0052] Beneficial effects of the present invention:

[0053] 1. An automated phase-locked loop gain control method is provided, including two achievable module structures.

[0054] 2. The active phase-locking technology can automatically complete the adaptation of the optical module and the phase-locked loop module.

[0055] 3. In the mass production scenario of LiDAR modules, the design difficulty of the phase-locked loop is reduced, saving manual debugging costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a structural schematic diagram of the present invention;

[0057] Figure 2 Flow chart of the steps of two methods of the present invention; (a) is an algorithm flow based on zero-crossing detection as the core of the auxiliary phase-locked loop module; (b) is an algorithm flow based on noise coefficient detection as the core of the auxiliary phase-locked loop module.

[0058] Figure 3 To adopt Figure 2 (a) The result obtained by the algorithm.

[0059] Figure 4 To adopt Figure 2 (b) The result obtained by the algorithm.

[0060] In the figure: 1-frequency modulated continuous wave generation source, 2-Mach-Zehnder interferometer, 3-optical fiber delay line, 4-balanced photodetector, 5-power divider, 6-RF switch, 7-frequency noise power spectrum density statistics module, 8-auxiliary phase-locked loop module, 9-comparator module, 10-reciprocal module, 11-zero-crossing detection module, 12-optical phase-locked loop, 131-arbitrary function generator I, 132-arbitrary function generator II, 14-adjustable gain module, 15-integrator, 16-mixer.

[0061] Note: Frequency-modulated continuous-wave source (FMCW Source) and Mach-Zehnder interferometer (MZI), fiber coupler (FC), fiber delay line (DL), optical phase-locked loop (OPLL), auxiliary phase-locked loop (ALL), balanced photodetector (BPD), power divider (PD), mixer, arbitrary function generator (AFG), adjustable gain module (Variable gain), integrator, RF switch, cross-zero module, reciprocal circuit module (Rec i proca lci rcu it), comparator module (Comparing un it), frequency noise power spectral density statistics module (PSD, Power Spectra l Dens i ty), comparator module (Comparing un it). DETAILED DESCRIPTION

[0062] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0063] like Figure 1As shown, an auxiliary phase-locked device for adapting an optical module and a phase-locked loop module of the present invention includes a frequency-modulated continuous wave generating source 1, a Mach-Zehnder interferometer 2, a balanced photodetector 4, a power divider 5, an auxiliary phase-locked loop module 8, and an optical phase-locked loop 12.

[0064] The frequency modulated continuous wave generating source 1 is used to generate and output a laser signal.

[0065] The Mach-Zehnder interferometer 2 includes a 5:5 optical fiber coupler and an optical fiber delay line 3. The optical fiber coupler receives the laser signal and transmits it to the balanced photodetector 4 through the optical fiber delay line 3.

[0066] The balanced photodetector 4 receives the laser signal and converts the laser signal into a beat frequency electrical signal and outputs it to the power divider 5. The main function of the balanced photodetector 4 is to reduce the relative intensity noise of the beat frequency signal and offset the common mode noise, thereby improving the quality of the beat frequency signal.

[0067] The power distributor 5 receives the electrical signal output by the balanced photodetector 4, and divides the electrical signal into two paths and sends them to the auxiliary phase-locked loop module 8 and the optical phase-locked loop 12 respectively. The auxiliary phase-locked loop module 8 is divided into two paths, one of which includes a radio frequency switch 6, a comparator module 9, a reciprocal module 10, a zero-crossing detection module 11, and an arbitrary function generator I 131; the other path includes a radio frequency switch 6, a frequency noise power spectrum density statistics module 7, a comparator module 9, and an arbitrary function generator I 131. The realization of the auxiliary phase-locked loop module 8 relies on a micro central processing unit MCU or a programmable logic gate array FPGA.

[0068] The radio frequency switch 6 is a shared device, one side of which is electrically connected to the power divider 5, and the other side is connected to the zero-crossing detection module 11 and the frequency noise power spectrum density statistics module 7, and is used to switch the two structures of the auxiliary phase-locked loop module 8 to turn on or off one structure;

[0069] Among them, in one structure:

[0070] The zero-crossing detection module 11 is used to detect the zero-crossing point of the beat frequency signal, store it, and output it to the inverse calculation module 10.

[0071] The inverse number calculation module 10 calculates the frequency of the beat signal according to the difference of the zero-crossing point sequence numbers and outputs it to the comparator module 9.

[0072] Arbitrary function generator I131 is used to generate a reference signal.

[0073] The comparator module 9 compares the reference signal frequency of the arbitrary function generator I 131 with the beat signal frequency output by the inverse module 10, and generates a control voltage for controlling the gain of the adjustable gain module 14 of the optical phase-locked loop.

[0074] In another structure:

[0075] The frequency noise power spectrum density statistics module 7 is used to count the power noise power spectrum density of the beat frequency electrical signal and output the statistical value to the comparator module 9.

[0076] Arbitrary function generator I131 is used to generate frequency noise power spectrum density statistics of reference signal.

[0077] The comparator module 9 compares the statistical value output by the frequency noise power spectrum density statistical module 7 with the frequency noise power spectrum density statistical value of the reference signal output by the arbitrary function generator I 131, and generates a control voltage for controlling the gain of the adjustable gain module 14 of the optical phase-locked loop.

[0078] An optical phase-locked loop 12, comprising an arbitrary function generator II 132, a mixer 16, an adjustable gain module 14, and an integrator 15;

[0079] The arbitrary function generator II 132 is used to generate a reference signal. The frequency of the reference signal generated by the arbitrary function generator II 132 is determined by the optical fiber delay length and the frequency sweep rate.

[0080] The mixer 16 receives the reference signal generated by the arbitrary function generator II 132 and the beat frequency electrical signal input by the power divider 5, and mixes the two signals to generate an error signal. The beat frequency electrical signal is input from the local oscillator port of the mixer 16, the reference signal is input from the high frequency port, and the error signal is output from the intermediate frequency port.

[0081] The adjustable gain module 14 receives the error signal, adjusts the gain of the error signal and outputs it to the integrator 15. The adjustable gain module 14 provides a voltage-driven dynamically adjustable output. The gain of the adjustable gain module 14 is controlled by the auxiliary phase-locked loop module 8.

[0082] The integrator 15 receives the error signal after gain adjustment, integrates the signal and sends it to the frequency modulated continuous wave generator 1. The time constant of the integrator 15 is determined by the capacitor and the resistor.

[0083] In one embodiment, the frequency modulated continuous wave generator 1 is a current modulated distributed feedback semiconductor laser, with a bias current of 200mA, a modulation amplitude of 20mA, a modulation period of 2.5kHz, and a modulation waveform of a triangle wave. The output power of the frequency modulated continuous wave generator 1 is 60mW, and the operating temperature of the entire source is 20°C.

[0084] In one embodiment, the length of the optical fiber delay line 3 is 10 m.

[0085] In one embodiment, the bandwidth of the balanced photodetector 4 is DC-500 MHz, the optical power input to the balanced photodetector 4 is 10 μW, and the fixed gain of the balanced photodetector 4 is 20 dB.

[0086] In one embodiment, the power divider 5 has a distribution ratio of 5:5 and a bandwidth of DC-100 MHz.

[0087] In one embodiment, the bandwidth of the mixer 16 is 40KHz-400MHz. The output amplitude of the arbitrary function generator II 132 is 4.74Vpp. The gain of the adjustable gain module 14 is adjustable within 80dB according to the size of the driving voltage. The integration time of the integrator 15 is 10kHz.

[0088] A method for using an auxiliary phase-locking device for adapting an optical module and a phase-locked loop module includes a phase-locking method based on zero-crossing detection and a phase-locking method based on noise coefficient detection.

[0089] Method 1: Phase lock based on zero-crossing detection:

[0090] Step 1. A frequency modulated continuous wave generator 1 generates a laser light source, which passes through a Mach-Zehnder interferometer 2 and then enters a balanced photodetector 4.

[0091] Step 2: The beat frequency signal output by the balanced photodetector 4 enters the auxiliary phase-locked loop module 8 .

[0092] Step 3. In the auxiliary phase-locked loop module 8, the zero point in the output time series is detected by the zero-crossing detection module 11 and the time corresponding to the zero point is recorded. The signal of the zero point time is stored and then sent to the inverse calculation module 10.

[0093] Step 4. In the inverse calculation module 10, a frequency-time-varying curve is calculated, and the curve is compared with the reference frequency signal generated by the arbitrary function generator I 131 in the comparator module 9 to generate a voltage signal that varies with time;

[0094] The frequency of the reference frequency signal is:

[0095]

[0096] Among them, f ideal is the frequency value of the reference signal, B is the sweep width of the frequency modulated continuous wave, T period is the frequency modulated continuous wave modulation period. When the modulation signal is a sawtooth wave, T period is the time of a cycle. When the modulation signal is a triangle wave, T periodis the time of half a cycle, n is the medium refractive index of the additional delay line (optical fiber delay line) in Mach-Zehnder interferometer 2, L is the length of the additional delay line (optical fiber delay line) in Mach-Zehnder interferometer 2, and c is the speed of light in vacuum.

[0097] Step 5. The final voltage signal is fed back to the adjustable gain module in the optical phase-locked loop to adjust the gain and achieve phase locking. Figure 3 As shown, I is the output of the beat signal after zero-crossing detection. The zero-crossing points in each cycle are successfully detected, and the intervals between these zero points can reflect the real-time frequency. II is the output of the inverse module. By taking the inverse of the zero-crossing interval, the denoised beat frequency is successfully decoupled. At this time, the beat signal shows an oscillating trend, indicating that the loop is in an unlocked state. III is the change of the loop gain in the optical phase-locked loop over time. The oscillating beat signal produces an oscillating gain, which can be used to correct the locking performance of the optical phase-locked loop in real time. IV is the time series of the beat signal output after locking and the gain adjustment of the phase-locked loop at this time. The beat signal is stable after locking, and the loop gain is also in a stable state at this time.

[0098] Method 2: Phase-locked method based on noise coefficient detection

[0099] Step 1. A frequency modulated continuous wave generator 1 generates a laser light source, which passes through a Mach-Zehnder interferometer 2 and then enters a balanced photodetector 4.

[0100] Step 2: The beat frequency signal output by the balanced photodetector 4 enters the auxiliary phase-locked loop module 8 .

[0101] Step 3. In the auxiliary phase-locked loop module 8, the frequency noise power spectrum density statistics module 7 first performs statistics. During the statistics process, the beat frequency signal undergoes five steps of period cutting, polynomial fitting, average value deduction, fast Fourier transform, and selection of band integration, and outputs the current frequency noise value.

[0102] Step 4. The current frequency noise value output in step 3 is compared with the theoretically designed standard frequency noise value of the same type of optical phase-locked loop in the comparator module 9, and a dynamic voltage is generated to adjust the loop gain of the optical phase-locked loop 12 to achieve final locking.

[0103] The theoretically designed standard frequency noise value of the optical phase-locked loop can be given by the following formula 2:

[0104]

[0105] in, is the square of the frequency noise value of the theoretically designed optical phase-locked loop within a certain loop bandwidth. The integral upper and lower limits DC-BW are the statistical noise bandwidth, f represents the frequency, Δv is the standard frequency width, and Gopl l is the theoretically designed closed-loop transfer function of the optical phase-locked loop. During the design process, it can be expressed as (3):

[0106]

[0107] i is an imaginary number, F sl The laser transfer function is usually a low-pass function with a cutoff frequency of about 100kHz-10MHz. K is the loop gain, τ is the loop delay, and τ1 is the delay time corresponding to the delay line in the Mach-Zehnder interferometer.

[0108] like Figure 4 As shown in Figure 1, the loop gain of the phase-locked loop changes with the number of iterations after the algorithm is used. The algorithm has good convergence. 14 rad / s, the algorithm only needs 50 iterations to complete the loop gain optimization. Ⅱ is the phase noise diagram of the theoretically designed optical phase-locked loop before and after locking. After locking, the noise within the loop bandwidth is greatly suppressed. When the integration bandwidth is selected as DC-10MHz, the frequency noise value σ φopll =0.728rad 2 Ⅲ is the output result after the phase-locked loop is locked. After locking, the phase noise within the bandwidth is greatly suppressed. When the integration bandwidth is selected as DC-10MHz, the frequency noise value σ φopll =0.731rad 2 , which is almost consistent with the theoretical value, and the subsequent loop gain is stable and the phase-locked loop remains locked.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An auxiliary phase locking device for adapting an optical module and a phase-locked loop module, characterized in that: It includes a frequency modulated continuous wave generator, a Mach-Zehnder interferometer, a balanced photodetector, a power divider, an auxiliary phase-locked loop module, and an optical phase-locked loop; A frequency modulated continuous wave generator, used to generate and output a laser signal; The Mach-Zehnder interferometer includes an optical fiber coupler and an optical fiber delay line. The optical fiber coupler receives a laser signal and transmits it to a balanced photodetector through the optical fiber delay line. A balanced photoelectric detector receives the laser signal and converts the laser signal into a beat frequency electrical signal and outputs it to the power divider; A power divider receives the electrical signal output by the balanced photodetector and divides the electrical signal into two paths and sends them to the auxiliary phase-locked loop module and the optical phase-locked loop respectively; The auxiliary phase-locked loop module is divided into two structures, one of which includes a radio frequency switch, a comparator module, a reciprocal module, a zero-crossing detection module, and an arbitrary function generator I; The other path includes a frequency noise power spectrum density statistics module, a comparator module, and an arbitrary function generator I; The RF switch is a shared device, one side of which is electrically connected to the power divider, and the other side is respectively connected to the zero-crossing detection module and the frequency noise power spectrum density statistics module, and is used to switch the two structures of the auxiliary phase-locked loop module to turn on or off one structure; Among them, in one structure: The zero-crossing detection module is used to detect the zero-crossing point of the beat frequency signal, store it, and output it to the inverse calculation module; The reciprocal module calculates the frequency of the beat signal according to the difference of the zero-crossing point sequence number and outputs it to the comparator module; Arbitrary function generator I, used to generate reference signal; The comparator module compares the reference signal frequency of the arbitrary function generator I with the beat frequency signal frequency output by the inverse calculation module, and generates a control voltage for controlling the gain of the optical phase-locked loop adjustable gain module; In another structure: A frequency noise power spectrum density statistics module is used to count the power noise power spectrum density of the beat frequency electrical signal and output the statistical value to the comparator module; Arbitrary function generator I, used to generate the frequency noise power spectrum density statistics of the reference signal; A comparator module compares the statistical value output by the frequency noise power spectrum density statistical module with the frequency noise power spectrum density statistical value of the reference signal output by the arbitrary function generator I, and generates a control voltage for controlling the gain of the adjustable gain module of the optical phase-locked loop; Optical phase-locked loop, including arbitrary function generator II, mixer, adjustable gain module, integrator; Arbitrary function generator II, used to generate reference signals; The mixer receives the reference signal generated by the arbitrary function generator II and the beat frequency electrical signal input by the power divider, and mixes the two signals to generate an error signal; An adjustable gain module receives an error signal, adjusts the error signal gain and outputs it to an integrator; The integrator receives the error signal after the gain is adjusted, integrates the signal and then sends it to the frequency modulated continuous wave generation source.

2. The device according to claim 1, characterized in that The frequency modulated continuous wave generator is a current modulated distributed feedback semiconductor laser, with a bias current of 200mA, a modulation amplitude of 20mA, a modulation period of 2.5kHz, a modulation waveform of a triangle wave, an output power of 60mW, and an operating temperature of 20°C.

3. The device according to claim 1, characterized in that The length of the optical fiber delay line is 10m.

4. The device according to claim 1, characterized in that The bandwidth of the balanced photodetector is DC-500MHz, the input optical power of the balanced photodetector is 10μW, and the fixed gain of the balanced photodetector is 20dB.

5. The device according to claim 1, characterized in that The power divider has a distribution ratio of 5:5 and a bandwidth of DC-100MHz.

6. The device according to claim 1, characterized in that The bandwidth of the mixer is 40KHz-400MHz, the output amplitude of the arbitrary function generator II is 4.74Vpp, the adjustable gain module, the gain is adjustable within 80dB according to the size of the driving voltage, the integrator, the integration time is 1 / 10kHz.

7. A method for using an auxiliary phase-locking device for adapting an optical module and a phase-locked loop module, characterized in that: Phase locking based on zero-crossing detection, including: Step 1. A frequency modulated continuous wave generator generates a laser light source, which passes through a Mach-Zehnder interferometer and then enters a balanced photodetector; Step 2. The beat frequency signal output by the balanced photodetector enters the auxiliary phase-locked loop module; Step 3. In the auxiliary phase-locked loop module, the zero point in the output time series is detected by the zero-crossing detection module and the time corresponding to the zero point is recorded. The signal of the zero point time is stored and then sent to the inverse calculation module; Step 4. In the inverse module, a frequency-time-varying curve is solved, and the curve is compared with the reference frequency signal generated by the function generator I in the comparator module to generate a voltage signal that varies with time; The frequency of the reference frequency signal is: Among them, f ideal is the frequency value of the reference signal, B is the sweep width of the frequency modulated continuous wave, T period is the frequency modulated continuous wave modulation period. When the modulation signal is a sawtooth wave, T period is the time of a cycle. When the modulation signal is a triangle wave, T period is the time of half a cycle, n is the medium refractive index of the optical fiber delay line in the Mach-Zehnder interferometer, L is the length of the optical fiber delay line in the Mach-Zehnder interferometer, and c is the speed of light in vacuum; Step 5. Finally, the voltage signal is fed back to the adjustable gain module in the optical phase-locked loop to adjust the gain and achieve phase locking.

8. A method for using an auxiliary phase-locking device for adapting an optical module and a phase-locked loop module, characterized in that: Phase lock method based on noise figure detection, including: Step 1. A frequency modulated continuous wave generator generates a laser light source, which passes through a Mach-Zehnder interferometer and then enters a balanced photodetector; Step 2. The beat frequency signal output by the balanced photodetector enters the auxiliary phase-locked loop module; Step 3. In the auxiliary phase-locked loop module, the frequency noise power spectrum density statistics module first performs statistics. During the statistics process, the beat frequency signal undergoes five steps of processing: period cutting, polynomial fitting, average value deduction, fast Fourier transform, and bandwidth integration selection, and then outputs the current frequency noise value. Step 4. The current frequency noise value output in step 3 is compared with the theoretically designed standard frequency noise value of the same type of optical phase-locked loop in the comparator module, and a dynamic voltage is generated to adjust the loop gain of the optical phase-locked loop to achieve final locking; The theoretically designed standard frequency noise value of the optical phase-locked loop is given by the following formula (2): in, is the square of the frequency noise value of the theoretically designed optical phase-locked loop within a certain loop bandwidth. The integral upper and lower limits DC-BW are the statistical noise bandwidth, f represents the frequency, Δv is the standard frequency width, and G opll is the theoretically designed closed-loop transfer function of the optical phase-locked loop. During the design process, it is expressed as (3): i is an imaginary number, F sl Laser transfer function, the cutoff frequency is about 100kHz-10MHz, K is the loop gain, τ is the loop delay, τ1 is the delay time corresponding to the delay line in the Mach-Zehnder interferometer.

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