Long-distance optical fiber transmission phase locking system based on feedback control

Abstract

The invention provides a long-distance optical fiber transmission phase locking system based on feedback control, and the system comprises a signal generation module which is used for generating a first optical signal, and outputting the first optical signal to a signal modulation module through a long-distance link for anti-scattering modulation; the double-path detection module is used for generating a second optical signal, a first distortion signal and a second distortion signal; the feedback control module is used for generating a phase alignment signal and an optimization signal; and the frequency compensation module is used for performing phase alignment and distortion pre-compensation on the second optical signal according to the control of the phase alignment signal and the first optimization signal to generate a third optical signal for real-time compensation to obtain a fourth optical signal for long-distance link output. The invention has the beneficial effects that the user side signal is consistent with the initial optical signal after long-distance transmission, and the high-precision optical frequency transmission requirement is met; various distortion signals are extracted, a comprehensive basis is provided for feedback control, link distortion omission caused by single detection is avoided, and noise suppression pertinence is improved.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber sensing technology, and in particular relates to a long-distance optical fiber transmission phase-locked system based on feedback control. Background Technology

[0002] In scenarios where stringent requirements for optical frequency signal stability exist, such as quantum communication, high-precision clock synchronization, and astronomical observation, the long-distance stable transmission of ultra-stable optical frequency signals is a core support for achieving high-precision applications in these fields. Optical fiber, with its advantages of low loss and high bandwidth, has become the mainstream carrier for optical frequency signal transmission.

[0003] Existing long-distance fiber optic transmission phase-locked loop (PLL) systems mostly adopt a "single-path detection and simple feedback" architecture, which basically achieves long-distance transmission of optical frequency signals. However, in practical applications, there are still many technical limitations: long-distance transmission is susceptible to parasitic reflections and Rayleigh scattering interference. Existing anti-interference technologies are complex and incompletely separate, leading to a decrease in distortion detection accuracy. Relying on single-path photoelectric detection to extract distortion information lacks a secondary comparison between a noise-free reference and the optimized signal, resulting in one-sided feedback control and easy imbalance in compensation. The feedback module only performs simple processing on the distortion signal without fusing dual-path information, resulting in a lot of noise in the control signal and insufficient compensation accuracy. Frequency compensation only targets input-side noise, ignoring potential distortion in the output-side link, leading to significant deviations between the user-end signal and the initial signal.

[0004] Therefore, there is an urgent need for a long-distance optical fiber transmission phase-locked loop system that can comprehensively suppress link interference, accurately extract distortion information, and achieve full-link noise compensation. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a long-distance optical fiber transmission phase-locked loop system based on feedback control, which is particularly suitable for solving the problem of significant deterioration in signal-to-noise ratio caused by attenuation and amplification along the route in thousand-kilometer-level links.

[0006] The technical solution adopted in this invention is: to provide a long-distance optical fiber transmission phase-locked loop system based on feedback control, comprising:

[0007] The signal generation module is used to generate the first optical signal and output it to the signal modulation module through a long-distance link.

[0008] The signal modulation module is used to perform anti-scattering modulation on the first optical signal and output it to the dual-path detection module;

[0009] The dual-path detection module is used to generate a second optical signal and output it to the frequency compensation module. It compares the phase of the first optical signal with the second and third optical signals respectively, extracts the distortion information to obtain the first distortion signal and the second distortion signal, and outputs them to the feedback control module.

[0010] The feedback control module is used to fuse the first distorted signal and the second distorted signal to generate a phase-aligned signal, optimize the second distorted signal to generate a first optimized signal, and output it to the frequency compensation module.

[0011] The frequency compensation module is used to perform phase alignment and distortion pre-compensation on the second optical signal to generate the third optical signal according to the control of the phase alignment signal and the first optimization signal, perform real-time compensation on the third optical signal to obtain the fourth optical signal, send the third optical signal to the dual-path detection module, and output the fourth optical signal for long-distance link.

[0012] Furthermore, the signal modulation module includes:

[0013] A first acousto-optic modulator is used to suppress parasitic reflection and Rayleigh scattering of the first optical signal;

[0014] A first radio frequency driving circuit is used to generate a first driving signal to control the adjustment amplitude of the signal frequency of the first acousto-optic modulator.

[0015] A first fiber optic coupler is used to split the first optical signal.

[0016] Furthermore, the dual-path detection module includes:

[0017] A second ultrastable laser is used to generate the second optical signal as a reference.

[0018] The second fiber optic coupler is used to split the second optical signal;

[0019] A third fiber optic coupler is used to combine the first optical signal and the second optical signal;

[0020] A first photodetector is used to perform photoelectric conversion on the combined first optical signal and the second optical signal to generate the first distortion signal;

[0021] A fourth fiber optic coupler is used to combine the first optical signal and the third optical signal;

[0022] The second photodetector is used to perform photoelectric conversion on the combined second optical signal and the third optical signal to generate the second distortion signal.

[0023] Furthermore, the feedback control module includes:

[0024] Intrinsic radio frequency source, used to provide radio frequency reference signal;

[0025] A mixer is used to extract the core error of the second distorted signal using the radio frequency reference signal;

[0026] A first servo feedback circuit is used to perform the optimization processing on the second distorted signal to generate the first optimized signal;

[0027] A first signal adder is used to linearly superimpose the first distorted signal and the optimized signal to generate the phase-aligned signal;

[0028] The second radio frequency driving circuit is used to generate the second driving signal;

[0029] The second signal adder is used to linearly superimpose the first optimized signal and the second driving signal to generate a radio frequency driving signal.

[0030] Furthermore, the frequency compensation module includes:

[0031] A single-sideband modulator is used to perform phase adjustment and noise suppression on the second optical signal according to the phase alignment signal;

[0032] The second acousto-optic modulator is used to adjust the frequency and stabilize the amplitude of the second optical signal according to the radio frequency driving signal, and generate the third optical signal.

[0033] The fifth fiber optic coupler is used to split the third optical signal.

[0034] The third photodetector is used to perform photoelectric conversion on the second optical signal to generate the third distorted signal;

[0035] The second servo feedback circuit is used to perform the optimization processing on the third distorted signal to obtain the second optimized signal.

[0036] The third acousto-optic modulator is used to perform real-time compensation on the third optical signal based on the second optimized signal to obtain the fourth optical signal.

[0037] Furthermore, the signal modulation module also includes a first polarization-maintaining mirror, which is used to perform polarization compensation on the first optical signal from the first fiber coupler.

[0038] Furthermore, the frequency compensation module also includes a second polarization-maintaining mirror, which is used to perform polarization compensation on the third optical signal from the fifth fiber coupler.

[0039] Furthermore, the optimization process includes low-noise filters, signal amplification, and dynamic optimization.

[0040] The advantages and positive effects of this invention are as follows: by adopting the above technical solution, the user-end signal after long-distance transmission is consistent with the initial optical signal, meeting the requirements of high-precision optical frequency transmission; multiple distortion signals are extracted to provide a comprehensive basis for feedback control, avoiding the omission of link distortion by single detection and improving the targeting of noise suppression; by combining phase alignment and distortion pre-compensation, the link noise on the input and output sides is covered, reducing phase shift during signal transmission. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the long-distance optical fiber transmission phase-locked loop system based on feedback control according to the present invention. Detailed Implementation

[0042] The present disclosure will now be described more fully with reference to the accompanying drawings, which illustrate exemplary embodiments of the present disclosure. The technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present disclosure, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without creative effort are within the scope of protection of the present disclosure.

[0043] like Figure 1 As shown, the present invention provides a long-distance optical fiber transmission phase-locked loop system based on feedback control, comprising:

[0044] The signal generation module 10 is used to generate a first optical signal and output it to the signal modulation module 20 through a long-distance link. The signal generation module 10 includes a first ultra-stable laser. The effective linewidth of the first ultra-stable laser is within 3KHz, the output optical power is greater than 10mW, and the transmission is a stable narrow linewidth laser.

[0045] Signal modulation module 20 is used to perform anti-scattering modulation on the first optical signal and output it to the dual-path detection module 30;

[0046] The dual-path detection module 30 is used to generate a second optical signal and output it to the frequency compensation module 50. It compares the phase of the first optical signal with the second and third optical signals respectively, extracts the distortion information to obtain the first distortion signal and the second distortion signal, and outputs them to the feedback control module 40.

[0047] The feedback control module 40 is used to fuse the first distorted signal and the second distorted signal to generate a phase-aligned signal, optimize the second distorted signal to generate a first optimized signal, and output the signal to the frequency compensation module 50.

[0048] The frequency compensation module 50 is used to perform phase alignment and distortion pre-compensation on the second optical signal according to the control of the phase alignment signal and the first optimization signal to generate a third optical signal, perform real-time compensation on the third optical signal to obtain a fourth optical signal, send the third optical signal to the dual-path detection module 30, and output the fourth optical signal for long-distance link.

[0049] By adopting the above configuration, a complete link of "signal generation, modulation, detection, feedback, and compensation" is constructed to ensure that the user-end signal is consistent with the initial first optical signal after long-distance transmission, meeting the requirements of high-precision optical frequency transmission. Dual-path detection extracts two types of distortion signals, providing a comprehensive basis for feedback control, avoiding the omission of link distortion by single detection, and improving the targeting of noise suppression. The combination of phase alignment and distortion pre-compensation in the frequency compensation module covers link noise on both the input and output sides, reducing phase shift during signal transmission. The third optical signal is fed back to the dual-path detection module, forming a closed-loop optimization, continuously improving the distortion detection accuracy, and ensuring the long-term stable operation of the system.

[0050] To address the problem that the first optical signal is affected by parasitic reflections and Rayleigh scattering interference after traveling long distances, leading to subsequent detection distortion and the inability to transmit the signal in beams, this embodiment provides an implementation method.

[0051] In one embodiment, the signal modulation module includes:

[0052] The first acousto-optic modulator is used to suppress parasitic reflection and Rayleigh scattering of the first optical signal. The frequency shift of the first acousto-optic modulator is no greater than 200MHz and the insertion loss is no greater than 5dB.

[0053] The first radio frequency driving circuit is used to generate a first driving signal and control the adjustment amplitude of the signal frequency of the first acoustic-optic modulator, which is preset according to the driving frequency point of the first acoustic-optic modulator.

[0054] The first fiber optic coupler is used to split the first optical signal.

[0055] With the above configuration, the first acousto-optic modulator specifically suppresses parasitic reflections and Rayleigh scattering, preventing interference signals from mixing into the first optical signal and ensuring the accuracy of subsequent detection; the first radio frequency drive circuit precisely controls the signal frequency adjustment amplitude to ensure stable anti-scattering modulation effect and avoid excessive or insufficient frequency offset; the first fiber optic coupler realizes signal beam splitting, providing a stable first optical signal input for the dual-path detection module and meeting the signal requirements of dual-path comparison detection.

[0056] To address the problem that existing detection modules lack a noise-free reference and cannot separately extract the input side and the optimized distortion signal, resulting in inaccurate feedback control, this embodiment provides an implementation method.

[0057] In one embodiment, the dual-path detection module includes:

[0058] The second ultra-stable laser is used to generate a second optical signal as a reference. The effective linewidth of the second ultra-stable laser is within 3KHz, the output optical power is greater than 10mW, and it transmits a stable narrow-linewidth laser. The first ultra-stable laser and the second ultra-stable laser are preferably fiber lasers or frequency-stabilized lasers.

[0059] The initial calibration of the first and second ultra-stable lasers is achieved through the internal wavelength tuning function of the ultra-stable lasers, using wavelength modulation devices such as temperature and PZT. When the wavelength difference between the two devices is within the locking range of the entire system, frequency locking can be performed through the system.

[0060] The second fiber optic coupler is used to split the second optical signal.

[0061] The third fiber optic coupler is used to combine the first optical signal and the second optical signal;

[0062] The first photodetector is used to perform photoelectric conversion on the first and second optical signals after beam combining to generate the first distortion signal. The bandwidth of the first photodetector is not less than 1 GHz, and the output electrical signal interface is AC coupled.

[0063] The fourth fiber optic coupler is used to combine the first and third optical signals.

[0064] The second photodetector is used to perform photoelectric conversion on the combined second and third optical signals to generate a second distortion signal. The bandwidth of the second photodetector is not less than 10MHz, and the output electrical signal interface is AC coupled. The bandwidth of the first and second photodetectors is more than twice the frequency of the first acousto-optic modulator, and the bandwidth is more than 500MHz.

[0065] With the above setup, the second optical signal generated by the second ultra-stable laser serves as a noise-free reference, providing a reliable comparison basis for distortion detection and avoiding the influence of the reference signal's own deviation on distortion judgment. The second fiber coupler splits the second optical signal, simultaneously meeting the requirements of the frequency compensation module and dual-path beam combining detection, simplifying the system's optical path. The third and fourth fiber couplers respectively complete the beam combining of the two types of optical signals, and combined with the photodetector to achieve photoelectric conversion, accurately extracting the first and second distortion signals, providing comprehensive and pure distortion data for feedback control. Dual-path photodetection distinguishes between the input side and the optimized distortion, avoiding confusion between noise from different link stages by a single detector, and improving the targeting of feedback control.

[0066] To address the problem that distorted signals, without optimization and fusion processing, result in control signals containing clutter, low precision, difficulty in extracting core errors, and inability to accurately drive frequency compensation, this embodiment provides an implementation method.

[0067] In one embodiment, the feedback control module includes:

[0068] Intrinsic radio frequency source, used to provide radio frequency reference signal;

[0069] A mixer is used to extract the core error of a second distorted signal using an RF reference signal;

[0070] The first servo feedback circuit is used to optimize the second distorted signal and generate the first optimized signal.

[0071] The first signal adder is used to linearly superimpose the first distorted signal and the optimized signal to generate a phase-aligned signal;

[0072] The second radio frequency driving circuit is used to generate the second driving signal;

[0073] The second signal adder is used to linearly superimpose the first optimized signal and the second driving signal to generate an RF driving signal. The fusion ratio of the first signal adder and the second signal adder is 1:1.

[0074] With the above setup, the intrinsic RF source provides a stable RF reference, the mixer accurately extracts the core error of the second distortion signal, avoiding the confusion in error judgment caused by the lack of a reference; the first servo feedback circuit optimizes the second distortion signal, reduces noise interference, and improves signal quality; the dual adders respectively realize the fusion of "distortion signal and optimization signal" and "optimization signal and drive signal" to generate phase alignment signal and RF drive signal, which have both precise control logic and drive capability, supporting the efficient operation of the frequency compensation module.

[0075] To address the issues of uncorrected phase deviation of the third optical signal and uncompensated output-side link distortion, which lead to unstable user-end signals and the inability to achieve closed-loop detection, this embodiment provides an implementation method.

[0076] In one embodiment, the frequency compensation module includes:

[0077] A single-sideband modulator (SSB) is used to perform phase adjustment and noise suppression on a second optical signal based on a phase alignment signal. The SSB adopts a three-arm MZM structure. By controlling the DC bias of the three MZMs and the microwave RF signal, a high suppression ratio of 20dB or more and a bandwidth of 0GHz-3GHz can be achieved in the single-sideband suppression.

[0078] The second acousto-optic modulator is used to adjust the frequency and stabilize the amplitude of the second optical signal according to the radio frequency drive signal to generate the third optical signal. The frequency shift of the second acousto-optic modulator is no greater than 200MHz, the insertion loss is no greater than 5dB, the pigtail is a polarization-maintaining pigtail, the polarization extinction ratio is greater than 18dB, and the voltage corresponds to a frequency offset of 100mV / MHz.

[0079] The fifth fiber coupler is used to split the third optical signal. The splitting ratio of the other fiber couplers is 1:1, while the splitting ratio of the fifth fiber coupler is 9:1.

[0080] The third photodetector is used to perform photoelectric conversion on the second optical signal to generate the third distorted signal;

[0081] The second servo feedback circuit is used to optimize the third distorted signal to obtain the second optimized signal;

[0082] The third acousto-optic modulator is used to compensate the third optical signal in real time according to the second optimized signal to obtain the fourth optical signal. The bandwidth of the third photodetector is not less than 10MHz, and the output electrical signal interface is AC coupled.

[0083] With the above setup, the single-sideband modulator adjusts the phase of the second optical signal and suppresses noise based on the phase alignment signal, improving the purity of the optical frequency; the second acousto-optic modulator pre-compensates for distortion to generate the third optical signal, and the third acousto-optic modulator compensates for the noise of the lower-level link in real time based on the optimized signal, forming a dual guarantee of "pre-compensation and real-time compensation" to cover the distortion of the entire link; the third photodetector works with the second servo feedback circuit to capture new noise in the link in real time, ensuring the stable output of the fourth optical signal and meeting the accuracy requirements for long-distance transmission.

[0084] To address the issue of polarization state degradation caused by long-distance transmission or device interference, which affects the accuracy of subsequent modulation and detection, this embodiment provides an implementation method.

[0085] In one embodiment, the signal modulation module further includes a first polarization-maintaining mirror for polarization compensation of the first optical signal from the first fiber coupler.

[0086] With the above settings, the first polarization-maintaining mirror compensates for the polarization change of the first optical signal, avoiding power loss and phase deviation of the optical signal caused by polarization disorder, and ensuring the stability of optical signal polarization. The stable polarization state improves the modulation accuracy of the first acousto-optic modulator and the beam combining efficiency of the subsequent dual-path detection module, reduces the interference of polarization noise on the extraction of distorted signals, and indirectly improves the feedback control and compensation effect.

[0087] To address the issue that the polarization state of the third optical signal easily changes after beam splitting during the frequency compensation stage, affecting the real-time compensation accuracy of the third acousto-optic modulator, this embodiment provides an implementation method.

[0088] In one embodiment, the frequency compensation module further includes a second polarization-maintaining mirror, which is used to perform polarization compensation on the third optical signal from the fifth fiber coupler. The first and second polarization-maintaining mirrors are preferably polarization-maintaining Faraday mirrors (PFMs), and the polarization plane is set at a specific angle, including 90 degrees and 180 degrees.

[0089] With the above settings, the second polarization-maintaining mirror stabilizes the polarization state of the third optical signal, avoids polarization degradation caused by beam splitting or transmission, and ensures the polarization consistency of the optical signal received by the third acousto-optic modulator; it reduces the interference of polarization deviation on real-time compensation, improves the frequency adjustment accuracy of the third acousto-optic modulator, and ensures the polarization purity and frequency stability of the fourth optical signal.

[0090] To address the problem that distorted signals contain clutter, have weak amplitude, and poor stability, leading to unreliable optimized signals and affecting frequency compensation accuracy, this embodiment provides an implementation method.

[0091] In one embodiment, the optimization process includes a low-noise filter, signal amplification, and dynamic optimization.

[0092] With the above settings, low-noise filtering removes noise interference from the second distorted signal, improving signal purity and reducing sources of error in subsequent processing; signal amplification increases the weak second distorted signal to a processable level, avoiding inaccurate optimization due to an excessively weak signal and ensuring the effectiveness of the optimized signal; dynamic optimization adjusts processing parameters according to the signal amplitude, ensuring that second distorted signals of different intensities can be processed appropriately, improving the stability and versatility of the optimized signal, and providing a more reliable control basis for frequency pre-compensation.

[0093] The following description, in conjunction with a preferred embodiment, illustrates the content involved in the above embodiments.

[0094] In long-distance fiber-optic frequency transmission scenarios of 1000km and above, a fiber laser (first ultra-stable laser) is selected as the generator for the far-end ultra-stable narrow-linewidth optical frequency signal (first optical signal). This signal is output through a 1000km single-mode polarization-maintaining fiber to an AOM (first acousto-optic modulator) to suppress parasitic reflections and Rayleigh scattering interference. The modulated first optical signal then enters a polarization-maintaining fiber coupler (first fiber coupler), which splits the single-path optical signal into two paths. One path is used for signal comparison in subsequent dual-path detection modules, while the other path is retained as a backup signal. A polarization-maintaining mirror (first polarization-maintaining mirror) is placed between the first and fourth fiber couplers to compensate and calibrate the polarization state of the optical signal, ensuring the polarization stability of the optical signal input to the fourth fiber coupler.

[0095] A frequency-stabilized laser (second ultra-stable laser) is selected to generate an ultra-stable narrow-linewidth reference optical signal (second optical signal). This signal serves as the reference for optical frequency transmission. After being split by another polarization-maintaining fiber coupler (second fiber coupler), the signals are sent to two different polarization-maintaining fiber couplers (third fiber coupler and fourth fiber coupler). The third fiber coupler combines the first and second optical signals, and the combined optical signal is sent to a photodetector (first photodetector). The first photodetector converts the combined optical signal into an electrical signal and extracts distortion information reflecting input-side link noise (first distortion signal). The fourth fiber coupler receives the optical signal (third optical signal) output from the subsequent frequency compensation module. After being calibrated by the first polarization-maintaining mirror, the first and third optical signals are combined and sent to another photodetector (second photodetector) to extract distortion information reflecting residual noise after output-side pre-compensation (second distortion signal).

[0096] The intrinsic RF source provides a stable RF reference signal, serving as a benchmark for error extraction from the distorted signal. The second distorted signal and the RF reference signal are processed by a frequency divider and a low-pass filter, respectively, before entering the mixer. Mixing extracts the core error information from the second distorted signal. To optimize the error signal quality, a servo feedback circuit (first servo feedback circuit) filters and amplifies the second distorted signal (the mixer output signal cannot be automatically split; here, a power divider outputs it to two identical servo feedback circuits), generating an optimized signal (first optimized signal). The first distorted signal is then processed by an RF amplifier and fused with the first optimized signal by a signal adder (first signal adder) to generate a control signal (phase alignment signal) for phase adjustment. Simultaneously, another RF drive circuit (second RF drive circuit) generates a basic drive signal, which is then fused with the first optimized signal by another signal adder (second signal adder) to generate an RF drive signal for frequency compensation.

[0097] A single-sideband modulator receives the phase alignment signal and performs phase adjustment and noise suppression on the second optical signal output from the second ultra-stable laser, achieving initial phase-locking of the optical signal. The phase-locked optical signal enters another AOM (second acousto-optic modulator), which receives the RF drive signal output from the feedback control module to adjust the frequency and stabilize the amplitude of the optical signal, generating a pre-compensated optical signal (third optical signal). The third optical signal then enters a polarization-maintaining fiber coupler (fifth fiber coupler), which proportionally splits the optical signal into two paths. Most of the optical signal is used for subsequent real-time compensation processing, while a small portion is sent to a photodetector (third photodetector) to detect dynamic noise generated in the downstream link and convert the noise information into an electrical signal (third distortion signal).

[0098] The third distorted signal, after being processed by a bandpass filter and an RF amplifier, is sent to another servo feedback circuit (the second servo feedback circuit). After optimization processing, a real-time compensation command (the second optimized signal) is generated, which is then sent to the third AOM (the third acousto-optic modulator). The third acousto-optic modulator receives most of the third optical signal output from the fifth fiber coupler and performs real-time noise compensation on the optical signal according to the second optimized signal, generating the final stable optical signal (the fourth optical signal). To ensure that the polarization state of the fourth optical signal meets the requirements for long-distance transmission, another polarization-maintaining mirror (the second polarization-maintaining mirror) is set before the output to perform final calibration of its polarization state. The calibrated fourth optical signal is then sent to the user end through a 1000km single-mode polarization-maintaining fiber, completing the entire long-distance fiber optic frequency transmission process.

[0099] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A long-distance optical fiber transmission phase-locked system based on feedback control, characterized in that, include: The signal generation module is used to generate the first optical signal and output it to the signal modulation module through a long-distance link. The signal modulation module is used to perform anti-scattering modulation on the first optical signal and output it to the dual-path detection module; The dual-path detection module is used to generate a second optical signal and output it to the frequency compensation module. It compares the phase of the first optical signal with the second and third optical signals respectively, extracts the distortion information to obtain the first distortion signal and the second distortion signal, and outputs them to the feedback control module. The feedback control module is used to fuse the first distorted signal and the second distorted signal to generate a phase-aligned signal, optimize the second distorted signal to generate a first optimized signal, and output it to the frequency compensation module. The frequency compensation module is used to perform phase alignment and distortion pre-compensation on the second optical signal to generate the third optical signal according to the control of the phase alignment signal and the first optimization signal, perform real-time compensation on the third optical signal to obtain the fourth optical signal, send the third optical signal to the dual-path detection module, and output the fourth optical signal for long-distance link.

2. The long-distance optical fiber transmission phase-locked system based on feedback control according to claim 1, characterized in that, The signal modulation module includes: A first acousto-optic modulator is used to suppress parasitic reflection and Rayleigh scattering of the first optical signal; A first radio frequency driving circuit is used to generate a first driving signal to control the adjustment amplitude of the signal frequency of the first acousto-optic modulator. A first fiber optic coupler is used to split the first optical signal.

3. The long-distance optical fiber transmission phase-locked system based on feedback control according to claim 1, characterized in that, The dual-path detection module includes: A second ultrastable laser is used to generate the second optical signal as a reference. The second fiber optic coupler is used to split the second optical signal; A third fiber optic coupler is used to combine the first optical signal and the second optical signal; A first photodetector is used to perform photoelectric conversion on the combined first optical signal and the second optical signal to generate the first distortion signal; A fourth fiber optic coupler is used to combine the first optical signal and the third optical signal; The second photodetector is used to perform photoelectric conversion on the combined second optical signal and the third optical signal to generate the second distortion signal.

4. The long-distance optical fiber transmission phase-locked system based on feedback control according to claim 1, characterized in that, The feedback control module includes: Intrinsic radio frequency source, used to provide radio frequency reference signal; A mixer is used to extract the core error of the second distorted signal using the radio frequency reference signal; A first servo feedback circuit is used to perform the optimization processing on the second distorted signal to generate the first optimized signal; A first signal adder is used to linearly superimpose the first distorted signal and the optimized signal to generate the phase-aligned signal; The second radio frequency driving circuit is used to generate the second driving signal; The second signal adder is used to linearly superimpose the first optimized signal and the second driving signal to generate a radio frequency driving signal.

5. The long-distance optical fiber transmission phase-locked system based on feedback control according to claim 1, characterized in that, The frequency compensation module includes: A single-sideband modulator is used to perform phase adjustment and noise suppression on the second optical signal according to the phase alignment signal; The second acousto-optic modulator is used to adjust the frequency and stabilize the amplitude of the second optical signal according to the radio frequency driving signal, and generate the third optical signal. The fifth fiber optic coupler is used to split the third optical signal. The third photodetector is used to perform photoelectric conversion on the second optical signal to generate the third distorted signal; The second servo feedback circuit is used to perform the optimization processing on the third distorted signal to obtain the second optimized signal. The third acousto-optic modulator is used to perform real-time compensation on the third optical signal based on the second optimized signal to obtain the fourth optical signal.

6. The long-distance optical fiber transmission phase-locked system based on feedback control according to claim 2, characterized in that: The signal modulation module further includes a first polarization-maintaining mirror, which is used to perform polarization compensation on the first optical signal from the first fiber coupler.

7. The long-distance optical fiber transmission phase-locked system based on feedback control according to claim 5, characterized in that: The frequency compensation module further includes a second polarization-maintaining mirror, which is used to perform polarization compensation on the third optical signal from the fifth fiber coupler.

8. The long-distance optical fiber transmission phase-locked system based on feedback control according to claim 4 or 5, characterized in that: The optimization process includes low-noise filters, signal amplification, and dynamic optimization.

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