Large-gain low-phase noise bidirectional amplification system and method

Abstract

The invention belongs to the technical field of optical fiber optical frequency transmission, and provides a large-gain low-phase noise bidirectional amplification system and method.The system comprises a first input unit, a second input unit, a forward amplification unit, a reverse amplification unit and a filtering compensation unit; the input end of the forward amplification unit is connected with the first input unit, the input end of the reverse amplification unit is connected with the second input unit, the output ends of the forward amplification unit and the reverse amplification unit are jointly connected to the filtering compensation unit, and the filtering compensation unit is connected with the reverse amplification unit; the forward amplification unit and the reverse amplification unit are respectively used for generating beat frequency signals, and the filtering compensation unit is used for receiving the beat frequency signals and compensating the reverse amplification unit after filtering. The one-way erbium-doped optical fiber amplifiers are connected through the circulator, and a two-way amplification path is constructed. The gain of each one-way erbium-doped fiber amplifier can be independently controlled, the self-excitation effect is effectively avoided, and therefore the gain of the one-way erbium-doped fiber amplifier is improved.

Description

Technical Field

[0001] The invention belongs to the field of optical fiber optical frequency technology, and particularly relates to a large-gain and low-phase-noise bidirectional amplification system and method. Background Art

[0002] With the progress of optical clock research, the stability and uncertainty of optical clocks are far better than the current reference clock - the cesium fountain clock. This makes optical clocks a strong candidate for redefining the "second". High-precision transmission of optical clock frequency signals can be achieved through optical fibers, which is crucial for high-precision comparison of optical clocks in time and frequency laboratories around the world. In long-distance optical fiber optical frequency transmission systems, as the optical fiber distance increases, the optical fiber loss also increases, resulting in a deterioration of the optical frequency signal-to-noise ratio and a decrease in power. Bidirectional erbium-doped fiber amplifiers are limited by nonlinear phenomena, and the gain is generally controlled at 16dB-18dB, which can no longer meet the amplification requirements.

[0003] In the prior art, Shanghai Jiao Tong University proposed a solution to use a unidirectional erbium-doped fiber amplifier for bidirectional amplification, and used an optical phase-locked loop to lock the phase difference between two unidirectional EDFAs, significantly improving the gain of the amplification system. However, during the transmission process, the transmitted light is affected by the optical fiber link, and when measuring the phase difference, the beat frequency signal is unstable and effective phase detection cannot be performed.

[0004] On this basis, a high-gain bidirectional amplification system based on a unidirectional erbium-doped fiber amplifier is proposed, which ensures the normal operation of the phase noise detection system while ensuring high bidirectional gain. However, the use of an acousto-optic modulator (AOM) in the amplification system causes additional attenuation, and the 1550nm transmission light will enter the noise measurement system, affecting it and deteriorating the signal-to-noise ratio. Summary of the invention

[0005] The purpose of the present invention is to provide a large-gain and low-phase-noise bidirectional amplification system and method to solve the problems in the prior art that the beat frequency is unstable and cannot perform effective phase detection, and the signal to be amplified enters the noise measurement system, affecting it, and the signal-to-noise ratio deteriorates.

[0006] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a large-gain, low-phase-noise bidirectional amplification system, comprising a first input unit, a second input unit, a forward amplification unit, a reverse amplification unit, and a filtering and compensation unit; the input end of the forward amplification unit is connected to the first input unit, the input end of the reverse amplification unit is connected to the second input unit, and the output ends of the forward amplification unit and the reverse amplification unit are commonly connected to the filtering and compensation unit; The forward amplification unit and the reverse amplification unit are used to generate beat frequency signals respectively, and the filtering and compensation unit is used to receive the beat frequency signal and compensate the reverse amplification unit after filtering.

[0007] Furthermore, the forward amplification unit includes a first optical coupler, an acousto-optic modulator, a second optical coupler, a first wavelength division multiplexer, a first optical circulator, a first unidirectional erbium-doped fiber amplifier, a second optical circulator and a second wavelength division multiplexer; the input end of the first optical coupler is connected to the first input unit; the output end of the first optical coupler is divided into two paths, one path is connected to the second optical coupler through the acousto-optic modulator, and the other path is connected to the second optical coupler through the first wavelength division multiplexer, the first optical circulator, the first unidirectional erbium-doped fiber amplifier, the second optical circulator and the second wavelength division multiplexer in sequence.

[0008] Furthermore, the second optical coupler is connected to a second photodetector, and the second photodetector is used to detect the two beat frequency signals at the output end of the first optical coupler.

[0009] Furthermore, the reverse amplification unit includes a fiber stretcher and a second unidirectional erbium-doped fiber amplifier; the input end of the second optical coupler is connected to the second input unit, and the output end of the second optical coupler is divided into two paths, one path is connected to the first optical coupler through an acousto-optic modulator, and the other path is connected to the first optical coupler through a second wavelength division multiplexer, a second optical circulator, a fiber stretcher, a second unidirectional erbium-doped fiber amplifier, a first optical circulator and a first wavelength division multiplexer in sequence.

[0010] Furthermore, the first optical coupler is connected to a first photodetector, and the first photodetector is used to detect two beat frequency signals at the output end of the second optical coupler.

[0011] Furthermore, the filtering compensation unit includes a bandpass filter, a mixer, a low-pass filter and a proportional integral differential circuit; the first photodetector and the second photodetector are respectively connected to the mixer MIX through a bandpass filter, the mixer is connected to the proportional integral differential circuit through a low-pass filter, and the proportional integral differential circuit is connected to the optical fiber stretcher.

[0012] Furthermore, the first wavelength division multiplexer and the second wavelength division multiplexer are respectively input with optical signals to be amplified.

[0013] Furthermore, the first input unit is a first laser, and the second input unit is a second laser.

[0014] Furthermore, the first laser and the second laser are both homologous lasers.

[0015] In a second aspect, the present invention provides an amplification method of a large-gain and low-phase-noise bidirectional amplification system, comprising: The laser emitted by the first input unit enters the forward amplification unit to generate optical signals E2 and E3, and the second photodetector detects the beat signal E4 of the optical signals E2 and E3; The laser emitted by the second input unit enters the reverse amplification unit to generate optical signals E5 and E6, and the first photodetector detects the beat signal E7 of the optical signals E5 and E6; The beat signal E4 and the beat signal E7 are taken as the same frequency signals, which are filtered by bandpass filters and then passed through the mixer to obtain the optical signal E8. The optical signal E8 is the phase detection result. According to the phase detection result, the phase difference ΦEDFA1-ΦEDFA2 between the first unidirectional erbium-doped fiber amplifier and the second unidirectional erbium-doped fiber amplifier is obtained, and the phase difference signal is transmitted to the proportional integral differential circuit feedback control optical fiber stretcher, and the laser to be amplified is compensated when passing through the controlled optical fiber stretcher.

[0016] Compared with the prior art, the present invention has the following technical effects: The present invention realizes the amplification of optical signals in the process of bidirectional transmission through the design of forward amplification units and reverse amplification units. This bidirectional amplification capability ensures that the signal maintains sufficient strength during the transmission process, thereby supporting a longer transmission distance or a higher data transmission rate. The forward amplification unit and the reverse amplification unit generate beat frequency signals respectively. By detecting these beat frequency signals, the system can obtain the real-time state of the optical signal during the transmission process, providing a basis for subsequent phase compensation and gain adjustment.

[0017] The design of the filter compensation unit is the key to reducing phase noise. It receives the beat frequency signals from the forward amplification unit and the reverse amplification unit, and extracts useful phase information through filtering. Then, the reverse amplification unit is compensated based on this information to eliminate or reduce the phase noise introduced by the optical fiber link and amplifier.

[0018] The system of the present invention uses light of a different wavelength from the transmitted light as the measuring light, and detects the phase difference of two unidirectional erbium-doped fiber amplifiers (EDFA) in the amplification system. This design makes the measuring light unaffected by the phase noise of the optical fiber link, thereby improving the signal-to-noise ratio of the detection signal. The transmitted light no longer enters the reference arm of the detection system, reducing the interference to the detection system and further improving the stability and accuracy of the detection. By accurately processing the beat frequency signal through the filter compensation unit, the system can compensate for the phase difference in the reverse amplification unit in real time, thereby effectively reducing the phase noise of the entire system.

[0019] The present invention uses a circulator (CIR) to connect the first unidirectional erbium-doped fiber amplifier and the second unidirectional erbium-doped fiber amplifier to construct a bidirectional amplification path. This design allows the gain of each unidirectional erbium-doped fiber amplifier to be controlled individually, effectively avoiding the self-excitation effect, thereby increasing the gain of the unidirectional erbium-doped fiber amplifier.

[0020] Through the coordinated work of the forward amplification unit and the reverse amplification unit, the system can achieve efficient amplification of optical signals during bidirectional transmission, significantly increasing the transmission distance of optical frequency signals.

[0021] The system structure of the present invention is simple, and the two detection signals are directly phase-compared, and a complex mixing process is no longer required. This design simplifies the signal conditioning process, reduces unnecessary circuit crosstalk, and improves the stability of the system. The filter compensation unit adopts a band-pass filter (Band-Pass Filter, BPF), a mixer (Mixer, MIX), a low-pass filter (Low-Pass Filter, LPF) and a proportional integral differential circuit (Proportion Integral Differential, PID) to achieve accurate filtering, mixing and phase compensation of the beat frequency signal. This design not only improves the compensation accuracy and response speed, but also enhances the system's adaptability and robustness.

[0022] The method of the present invention realizes efficient and stable amplification of optical signals through a unique amplification method. First, the laser emitted by the first input unit enters the forward amplification unit to generate two optical signals; the laser emitted by the second input unit enters the reverse amplification unit to also generate two optical signals. Then, by detecting the beat frequency signals of these optical signals and using the filter compensation unit to perform phase compensation, accurate amplification of the optical signal is achieved. This amplification method not only improves the amplification efficiency, but also reduces phase noise and gain fluctuations, providing strong support for long-distance and high-speed optical signal transmission.

[0023] In summary, the high-gain and low-phase-noise bidirectional amplification system proposed in the present invention realizes efficient and stable bidirectional amplification of optical signals and significantly reduces phase noise. The system has the advantages of simple structure, high stability, high gain, and low phase noise, and has broad application prospects in the fields of long-distance optical communication and optical sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a system structure diagram of the present invention.

[0025] in: The first optical coupler OC1, the acousto-optic modulator AOM, the second optical coupler OC2, the first wavelength division multiplexer WDM1, the first optical circulator CIR1, the first unidirectional erbium-doped fiber amplifier EDFA1, the second optical circulator CIR2, the second wavelength division multiplexer WDM2, the first photodetector PD1, the second photodetector PD2, the fiber stretcher FS, the second unidirectional erbium-doped fiber amplifier EDFA2, the bandpass filter BPF, the mixer MIX, the low-pass filter LPF, and the proportional-integral-differential circuit PID. DETAILED DESCRIPTION

[0026] Explanation of relevant terms: OC: Optical Coupler is an optical device that realizes light splitting and light combining.

[0027] AOM: Acousto-optic modulator (AOM) is a high-speed optical modulation device based on the acousto-optic effect. It changes the refractive index of certain crystals or glass materials (photoelastic effect) through the oscillating mechanical strain of sound waves, thereby achieving modulation and power control of the laser beam.

[0028] WDM: Wavelength Division Multiplexing is a fiber optic communication technology device that allows multiple optical signals of different wavelengths to be transmitted simultaneously in the same optical fiber.

[0029] CIR: Circulator is an optical device with multiple ports in which optical signals can only be transmitted in one direction, that is, after being input from one port, they will be output from the next port in a specific order.

[0030] EDFA: Erbium-Doped Fiber Amplifier is an optical amplifier that uses erbium-doped fiber as the gain medium.

[0031] PD: Photodetector is a photoelectric device that converts light signals into electrical signals.

[0032] FS: A fiber stretcher is a device used to stretch optical fibers. It has important applications in the fields of fiber-optic communications and sensing.

[0033] BPF: A band-pass filter is a filter that allows light signals within a specific frequency range to pass through, but blocks light signals of other frequencies from passing through.

[0034] MIX: A mixer is used to combine two or more signals into one output signal.

[0035] LPF: Low-Pass Filter is used to allow low-frequency signals to pass through while blocking or attenuating high-frequency signals.

[0036] PID: Proportional Integration Differentiation is a control circuit.

[0037] The present invention is further described below in conjunction with the accompanying drawings: Embodiment 1, the present invention provides a large-gain low-phase-noise bidirectional amplification system, comprising a first input unit, a second input unit, a forward amplification unit, a reverse amplification unit and a filtering compensation unit; the input end of the forward amplification unit is connected to the first input unit, the input end of the reverse amplification unit is connected to the second input unit, the output ends of the forward amplification unit and the reverse amplification unit are commonly connected to the filtering compensation unit, and the filtering compensation unit is connected to the reverse amplification unit; The forward amplification unit and the reverse amplification unit are used to generate beat frequency signals respectively, and the filtering and compensation unit is used to receive the beat frequency signal and compensate the reverse amplification unit after filtering.

[0038] The system achieves the amplification of optical signals during bidirectional transmission through the design of forward amplification units and reverse amplification units. This bidirectional amplification capability is crucial for optical fiber communication systems that require bidirectional communication. It ensures that the signal maintains sufficient strength during transmission, thereby supporting longer transmission distances or higher data transmission rates.

[0039] The forward amplification unit and the reverse amplification unit generate beat frequency signals respectively, which are important information reflecting the phase and intensity changes of the optical signal. By detecting these beat frequency signals, the system can obtain the real-time status of the optical signal during transmission, providing a basis for subsequent phase compensation and gain adjustment.

[0040] The design of the filter compensation unit is the key to reducing phase noise. It receives the beat frequency signals from the forward amplification unit and the reverse amplification unit, and extracts useful phase information through filtering. Then, the reverse amplification unit is compensated based on this information to eliminate or reduce the phase noise introduced by the optical fiber link, amplifier, etc. This phase compensation mechanism is crucial to improving the stability and transmission quality of the system.

[0041] In summary, the high-gain low-phase-noise bidirectional amplification system described in this paragraph achieves efficient amplification of optical signals and reduction of phase noise during bidirectional transmission through its unique design and working principle. This system not only has practical application value, but also provides strong support for the development of future optical fiber communication technology.

[0042] Example 2, please refer to Figure 1 The present invention provides a large-gain and low-phase-noise bidirectional amplification system, specifically comprising: The first input unit, the second input unit, the forward amplification unit, the reverse amplification unit and the filter compensation unit. The forward amplification unit is connected to the first input unit and is responsible for processing and amplifying the optical signal from the input; the reverse amplification unit is connected to the second input unit and also performs the amplification task. The output ends of the two amplification units are connected to the filter compensation unit, which performs precise phase compensation on the reverse amplification unit after receiving and processing the beat frequency signals from two directions. This design aims to achieve efficient and stable amplification of optical signals during bidirectional transmission while reducing phase noise.

[0043] The system can process optical signals from two different directions at the same time, realizing a bidirectional amplification function, which is essential for optical fiber networks that require bidirectional communication. By introducing a filter compensation unit, the system can process the received beat frequency signal and perform phase compensation on the reverse amplification unit, thereby significantly reducing phase noise and improving the stability of signal transmission.

[0044] The forward amplification unit integrates the first optical coupler OC1, the acousto-optic modulator AOM, the second optical coupler OC2, the first wavelength division multiplexer WDM1, the first optical circulator CIR1, the first unidirectional erbium-doped fiber amplifier EDFA1, the second optical circulator CIR2 and the second wavelength division multiplexer WDM2. These components are connected through precise optical paths to achieve the branching, modulation, amplification and multiplexing of optical signals. In particular, the first unidirectional erbium-doped fiber amplifier EDFA1 provides a significant gain improvement for the optical signal.

[0045] The reverse amplification unit reuses some key components in the forward amplification unit, and adds a fiber stretcher FS and a second unidirectional erbium-doped fiber amplifier EDFA2 to achieve amplification and phase adjustment of the reverse optical signal. The second photodetector PD2 is used to detect the beat frequency signal of the two optical signals, providing key information for subsequent filtering compensation.

[0046] By integrating a unidirectional erbium-doped fiber amplifier, the optical signal can be efficiently amplified to meet the needs of long-distance, high-capacity optical fiber communications. By using optical couplers, acousto-optic modulators, and optical circulators, the system can flexibly control the transmission path and modulation method of the optical signal, improving the flexibility and configurability of the system. Through photoelectric detectors, the system can detect the beat frequency signals of the two optical signals in real time, providing accurate data support for subsequent filtering compensation.

[0047] The filter compensation unit is the core part of the present invention for reducing phase noise. It consists of two bandpass filters BPF, a mixer MIX, a low-pass filter LPF and a proportional integral differential circuit PID. The unit generates a control signal to drive the fiber stretcher FS by receiving and processing the beat frequency signal from the first photodetector PD1 and the second photodetector PD2, thereby accurately compensating the phase of the optical signal in the reverse amplification unit. In addition, the system uses a homologous laser as the light source of the first input unit and the second input unit, which further reduces the phase noise and gain fluctuation, and improves the overall stability and performance of the system. The first wavelength division multiplexer WDM1 and the second wavelength division multiplexer WDM2 are respectively connected to the optical signal to be amplified, ensuring that the system can process optical signals of multiple wavelengths at the same time, thereby improving the flexibility and scalability of the system.

[0048] The filter compensation unit receives and processes the beat frequency signal, generates a control signal to drive the fiber stretcher for phase adjustment, and realizes accurate phase compensation of the optical signal in the reverse amplifier unit, further reducing the phase noise. The use of a homologous laser as the light source reduces phase noise and gain fluctuations, and improves the overall stability and reliability of the system. By configuring a wavelength division multiplexer, the system can process optical signals of multiple wavelengths at the same time, improving the transmission capacity and spectrum utilization of the system. The introduction of the proportional integral differential circuit enables the system to automatically adjust the phase compensation amount according to the real-time feedback beat frequency signal, realizing intelligent control and improving the automation of the system.

[0049] Embodiment 3, an amplification method of a large-gain and low-phase-noise bidirectional amplification system, comprising: The laser emitted by the first input unit enters the forward amplification unit to generate optical signals E2 and E3, and the second photodetector PD2 detects the beat signal E4 of the optical signals E2 and E3; The laser emitted by the second input unit enters the reverse amplification unit to generate optical signals E5 and E6, and the first photodetector PD1 detects the beat signal E7 of the optical signals E5 and E6. The beat signal E4 and the beat signal E7 are taken as the same frequency signals, which are filtered by the bandpass filter BPF and then passed through the mixer MIX to obtain the optical signal E8. The optical signal E8 is the phase detection result. According to the phase detection result, the phase difference ΦEDFA1-ΦEDFA2 between the first erbium-doped fiber amplifier EDFA1 and the second erbium-doped fiber amplifier EDFA2 is obtained, and the phase difference signal is transmitted to the proportional integral differential circuit PID feedback control optical fiber stretcher FS, and the laser to be amplified is compensated when passing through FS.

[0050] This embodiment takes a 1510nm laser as an example to amplify a 1550nm laser.

[0051] The 1510nm first laser and the 1510nm second laser are co-source lasers, and the optical signal is expressed as E1=cos(ν0t+Φ0). The laser light emitted by the first 1510nm laser enters the amplification system through the first optical coupler OC1, and is divided into two paths after passing through the first optical coupler OC1. One path passes through the acousto-optic modulator AOM and the second optical coupler OC2 as the reference light to reach the second photodetector PD2, and the optical signal is E2=cos[(ν0+ω)t+Φ0], where ω is the driving frequency of the acousto-optic modulator AOM; the other path passes through the first wavelength division multiplexer WDM1 and the first optical circulator CIR1, and is amplified by the first unidirectional erbium-doped fiber amplifier EDFA1. The amplified optical signal passes through the second optical circulator CIR2 and the second wavelength division multiplexer WDM2, and then passes through the second optical coupler OC2 to reach the second photodetector PD2. The optical signal is E3=cos(ν0t+Φ0+ΦEDFA1), where ΦEDFA1 is the phase noise generated by the optical signal passing through the first unidirectional erbium-doped fiber amplifier EDFA1. The second photodetector PD2 detects the beat frequency signal of the light signal E2 and the light signal E3 as E4=cos(ωt-ΦEDFA1), where: v0 is the initial frequency of the laser, t is the independent variable time, φ0 is the initial phase, and ω is the driving frequency of the AOM.

[0052] The laser light emitted by the second 1510nm laser enters the amplification system through the second optical coupler OC2, and is divided into two paths after passing through the second optical coupler OC2. One path passes through the acousto-optic modulator AOM and the first optical coupler OC1 as the reference light to reach the first photodetector PD1, and the optical signal is E5= cos[(ν0+ω)t+Φ0]; the other path passes through the second wavelength division multiplexer WDM2 and the second optical circulator CIR2, and after passing through the fiber stretcher FS, it is amplified by the second unidirectional erbium-doped fiber amplifier EDFA2. The amplified optical signal passes through the first optical circulator CIR1 and the first wavelength division multiplexer WDM1, and then passes through the first optical coupler OC1 to reach the first photodetector PD1. The optical signal is E6=cos(ν0t+Φ0+ΦEDFA1), and ΦEDFA2 is the phase noise generated by the optical signal passing through the second unidirectional erbium-doped fiber amplifier EDFA2. The first photodetector PD1 detects the beat frequency signal of the two paths of light E5 and E6 as E7=cos(ωt-ΦEDFA2). Where: v0 is the initial frequency of the laser, t is the independent variable time, φ0 is the initial phase, and ω is the driving frequency of the AOM.

[0053] E4 and E7 are co-frequency signals. After the two electrical signals are filtered by the bandpass filter BPF, they are passed through the mixer MIX to obtain the optical signal E8=cos(-ΦEDFA1+ΦEDFA2). Then the optical signal E8 is the phase detection result directly obtained, and the phase difference between EDFA1 and EDFA2, that is, ΦEDFA1-ΦEDFA2, can be obtained. The error signal is passed to the proportional integral differential circuit PID feedback control fiber stretcher FS, and the 1550nm laser is compensated when passing through the fiber stretcher FS.

[0054] When the 1550nm transmission light passes through the amplification system, it enters from the first wavelength division multiplexer WDM1, passes through the first optical circulator CIR1, is amplified by the first unidirectional erbium-doped fiber amplifier EDFA1, and is output by the second optical circulator CIR2 and the second wavelength division multiplexer WDM2; when returning, it enters from the second wavelength division multiplexer WDM2, passes through the second optical circulator CIR2, is amplified by the second unidirectional erbium-doped fiber amplifier EDFA2, and is output by the first optical circulator CIR1 and the first wavelength division multiplexer WDM1.

[0055] In the present invention, the 1550nm laser only passes through the amplification system and does not pass through the reference arm of the measurement system, and will not affect the phase noise measurement result.

[0056] 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 above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high-gain, low-phase-noise bidirectional amplification system, characterized in that: It includes a first input unit, a second input unit, a forward amplification unit, a reverse amplification unit and a filter compensation unit; the input end of the forward amplification unit is connected to the first input unit, the input end of the reverse amplification unit is connected to the second input unit, and the output ends of the forward amplification unit and the reverse amplification unit are connected to the filter compensation unit; The forward amplification unit and the reverse amplification unit are used to generate beat frequency signals respectively, and the filtering and compensation unit is used to receive the beat frequency signal and compensate the reverse amplification unit after filtering.

2. A high-gain, low-phase-noise bidirectional amplification system according to claim 1, characterized in that: The forward amplification unit comprises a first optical coupler, an acousto-optic modulator, a second optical coupler, a first wavelength division multiplexer, a first optical circulator, a first unidirectional erbium-doped fiber amplifier, a second optical circulator and a second wavelength division multiplexer; the input end of the first optical coupler is connected to the first input unit; the output end of the first optical coupler is divided into two paths, one path is connected to the second optical coupler through the acousto-optic modulator, and the other path is connected to the second optical coupler through the first wavelength division multiplexer, the first optical circulator, the first unidirectional erbium-doped fiber amplifier, the second optical circulator and the second wavelength division multiplexer in sequence.

3. A high-gain, low-phase-noise bidirectional amplification system according to claim 2, characterized in that: The second optical coupler is connected to a second photodetector, and the second photodetector is used to detect the two-way beat frequency signals at the output end of the first optical coupler.

4. A high-gain, low-phase-noise bidirectional amplification system according to claim 3, characterized in that: The reverse amplification unit includes a fiber stretcher and a second unidirectional erbium-doped fiber amplifier; the input end of the second optical coupler is connected to the second input unit, and the output end of the second optical coupler is divided into two paths, one path is connected to the first optical coupler through an acousto-optic modulator, and the other path is connected to the first optical coupler through a second wavelength division multiplexer, a second optical circulator, a fiber stretcher, a second unidirectional erbium-doped fiber amplifier, a first optical circulator and a first wavelength division multiplexer in sequence.

5. A high-gain, low-phase-noise bidirectional amplification system according to claim 4, characterized in that: The first optical coupler is connected to a first photodetector, and the first photodetector is used to detect two beat frequency signals at the output end of the second optical coupler.

6. A high-gain, low-phase-noise bidirectional amplification system according to claim 5, characterized in that: The filtering compensation unit includes a bandpass filter, a mixer, a low-pass filter and a proportional-integral-differential circuit; the first photodetector and the second photodetector are connected to the mixer MIX through a bandpass filter respectively, the mixer is connected to the proportional-integral-differential circuit through a low-pass filter, and the proportional-integral-differential circuit is connected to the optical fiber stretcher.

7. A high-gain, low-phase-noise bidirectional amplification system according to claim 5, characterized in that: The first wavelength division multiplexer and the second wavelength division multiplexer respectively input optical signals to be amplified.

8. A high-gain, low-phase-noise bidirectional amplification system according to claim 1, characterized in that: The first input unit is a first laser, and the second input unit is a second laser.

9. A high-gain, low-phase-noise bidirectional amplification system according to claim 8, characterized in that: The first laser and the second laser are both co-source lasers.

10. An amplification method for a high-gain, low-phase-noise bidirectional amplification system according to any one of claims 1 to 9, characterized in that: include: The laser emitted by the first input unit enters the forward amplification unit to generate optical signals E2 and E3, and the second photodetector detects the beat signal E4 of the optical signals E2 and E3; The laser emitted by the second input unit enters the reverse amplification unit to generate optical signals E5 and E6, and the first photodetector detects the beat signal E7 of the optical signals E5 and E6; The beat signal E4 and the beat signal E7 are taken as the same frequency signals, which are filtered by bandpass filters and then passed through the mixer to obtain the optical signal E8. The optical signal E8 is the phase detection result. According to the phase detection result, the phase difference ΦEDFA1-ΦEDFA2 between the first unidirectional erbium-doped fiber amplifier and the second unidirectional erbium-doped fiber amplifier is obtained, and the phase difference signal is transmitted to the proportional integral differential circuit feedback control optical fiber stretcher, and the laser to be amplified is compensated when passing through the controlled optical fiber stretcher.

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