A dual-channel isolated large-gain bidirectional fiber amplifier system and method

Abstract

The application discloses a kind of dual-channel isolated large gain bidirectional optical fiber amplification system and method, it is related to optical fiber light frequency technical field, the system includes forward amplification channel, reverse amplification channel and bidirectional phase synchronization unit;Forward amplification channel and reverse amplification channel are independent of each other, respectively for completing the isolated amplification of forward signal light and reverse signal light, and the phase detection of probe light;The input end of bidirectional phase synchronization unit is connected respectively the detection output end of forward amplification channel, reverse amplification channel, and the output end of bidirectional phase synchronization unit is connected respectively in acoustic-optic modulator of forward amplification channel, reverse amplification channel, for extracting the phase error of two-way probe light and simultaneously driving two acoustic-optic modulators by frequency domain layered strategy, realize the phase noise compensation of bidirectional link.Effectively solve the technical bottleneck that present bidirectional amplification gain is limited, self-excitation risk is high, phase compensation is single, bidirectional synchronous compensation is easy to couple oscillation.

Description

Technical Field

[0001] This invention relates to the field of optical fiber and optical frequency technology, specifically to a dual-channel isolated high-gain bidirectional optical fiber amplification system and method. Background Technology

[0002] In long-distance fiber optic frequency transmission systems, fiber transmission loss is one of the core factors limiting system performance. With the continuous increase in transmission distance, especially in practical fiber optic links of hundreds or even thousands of kilometers, accumulated optical power attenuation will lead to a severe deterioration in the signal-to-noise ratio, thus affecting the short-term stability and long-term coherence of the optical frequency transmission. Therefore, it is essential to rationally deploy fiber optic amplifiers in the link to achieve effective compensation for signal power.

[0003] Currently, erbium-doped fiber amplifiers (EDFAs) are widely used in optical frequency transmission systems due to their operating band matching with the C-band of optical fiber communication and their good gain characteristics. However, they have technical defects in the following aspects: the forward and reverse optical paths are not completely isolated, and there is still a strong risk of optical crosstalk and self-oscillation; the probe light and signal light are transmitted on the same fiber, and crosstalk between them leads to a low signal-to-noise ratio of phase detection; phase compensation is only performed on the reverse link, and the noise of the forward link directly affects the stability of the system; there is no automatic gain control, and the gain drifts with temperature and pump power; a large number of shared optical components result in high structural coupling, making fault location difficult and impossible to engineer.

[0004] Specifically, in bidirectional optical frequency transmission structures, the forward and reverse propagating optical signals typically share the same optical fiber and EDFA gain medium. While this saves fiber resources, it easily introduces self-oscillation effects. The mechanism of self-oscillation is as follows: while amplifying the forward signal, the EDFA may also amplify backpropagation noise light generated by fiber end-face reflection, connector back loss, or Rayleigh backscattering. When this backlight is amplified again by the EDFA and forms a closed loop with the original forward signal, satisfying the phase condition and gain threshold, the system will experience self-oscillation, leading to gain lock failure, drastic fluctuations in output power, and even damage to optoelectronic devices. To suppress self-oscillation, traditional bidirectional EDFAs in practical engineering typically strictly control the gain of a single stage or module within the range of 16–18 dB. While this gain limitation can ensure system stability to a certain extent, it significantly weakens the EDFA's ability to compensate for long-distance fiber loss. When the total link loss is much greater than the security gain that EDFA can provide, more amplification nodes must be added, which not only increases the system complexity and cost, but also introduces additional noise accumulation and nonlinear phase disturbances, which is not conducive to achieving high-precision, long-distance fiber optic frequency transmission.

[0005] In summary, how to improve the usable gain of bidirectional EDFA while ensuring its stable operation, or how to explore new optical amplification structures that are resistant to self-oscillation, are the key issues that need to be addressed in current high-precision long-distance fiber optic frequency transmission technology. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a dual-channel isolated high-gain bidirectional fiber optic amplification system and method.

[0007] The objective of this invention is achieved through the following technical solution: In a first aspect, this application discloses a dual-channel isolated high-gain bidirectional fiber optic amplification system, including a forward amplification channel, a reverse amplification channel, and a bidirectional phase synchronization unit. The forward amplification channel and the reverse amplification channel are independent of each other and are used to isolate and amplify the forward signal light and the reverse signal light, respectively, as well as to detect the phase of the probe light. The input end of the bidirectional phase synchronization unit is connected to the detection output end of the forward amplification channel and the reverse amplification channel, respectively, and the output end of the bidirectional phase synchronization unit is connected to the acousto-optic modulator in the forward amplification channel and the reverse amplification channel, respectively, to extract the phase error of the two probe lights and drive the two acousto-optic modulators simultaneously through a frequency domain layering strategy to achieve phase noise compensation of the bidirectional link.

[0008] Based on the first aspect, the forward amplification channel includes a first optical circulator CIR1, a first wavelength division multiplexer WDM1, a first acousto-optic modulator AOM1, a first optical isolator ISO1, a first unidirectional erbium-doped fiber amplifier EDFA1, a second optical isolator ISO2, a second wavelength division multiplexer WDM2, a first photodetector PD1, and a first laser. The forward signal light is connected to the signal end of the first wavelength division multiplexer (WDM1) via the first optical circulator (CIR1). The probe light output from the first laser is connected to the probe end of the first wavelength division multiplexer (WDM1) and then combined with the forward signal light. The resulting combined light is then connected to the first acousto-optic modulator (AOM1), the first optical isolator (ISO1), the first erbium-doped fiber amplifier (EDFA1), and the second optical isolator (ISO2) before being input to the second wavelength division multiplexer (WDM2). The first optical isolator ISO1 and the second optical isolator ISO2 are used to ensure the unidirectional transmission of the first combined light in the forward amplification channel and suppress the self-excited oscillation of the first unidirectional erbium-doped fiber amplifier EDFA1. The second wavelength division multiplexer (WDM2) performs wavelength division of the first combined light. The forward signal light is output to the bidirectional transmission fiber via the second optical circulator (CIR2), and the probe light is output to the first photodetector (PD1). The output of the first photodetector (PD1) is connected to the bidirectional phase synchronization unit as the probe output of the forward amplification channel.

[0009] Based on the first aspect, the reverse amplification channel includes a second optical circulator CIR2, a third wavelength division multiplexer WDM3, a second acousto-optic modulator AOM2, a third optical isolator ISO3, a second unidirectional erbium-doped fiber amplifier EDFA2, a fourth optical isolator ISO4, a fourth wavelength division multiplexer WDM4, a second photodetector PD2, and a second laser. The reverse signal light is connected to the signal end of the third wavelength division multiplexer (WDM3) via the second optical circulator (CIR2). The probe light output from the second laser is connected to the probe end of the third wavelength division multiplexer (WDM3) and then combined with the reverse signal light. The resulting combined light is then connected to the second acousto-optic modulator (AOM2), the third optical isolator (ISO3), the second unidirectional erbium-doped fiber amplifier (EDFA2), and the fourth optical isolator (ISO4) before being input to the fourth wavelength division multiplexer (WDM4). The third optical isolator ISO3 and the fourth optical isolator ISO4 are used to ensure the unidirectional transmission of the second combined light in the reverse amplification channel and suppress the self-excited oscillation of the second unidirectional erbium-doped fiber amplifier EDFA2. The fourth wavelength division multiplexer (WDM4) completes the wavelength division of the second combined light. The reverse signal light is output to the bidirectional transmission fiber via the first optical circulator (CIR1), and the probe light is output to the second photodetector (PD2). The output of the second photodetector (PD2) is connected to the bidirectional phase synchronization unit as the probe output of the reverse amplification channel.

[0010] Based on the first aspect, the bidirectional phase synchronization unit includes a first bandpass filter BPF1, a second bandpass filter BPF2, a first mixer MIX1, a third bandpass filter BPF3, a second mixer MIX2, a radio frequency reference signal source RF, a single PID controller, and a frequency domain hierarchical allocation module. The output of the first photodetector PD1 is connected to the first input terminal of the first mixer MIX1 via the first bandpass filter BPF1, and the output of the second photodetector PD2 is connected to the second input terminal of the first mixer MIX1 via the second bandpass filter BPF2. The output of the first mixer MIX1 is connected to the first input terminal of the second mixer MIX2 via the third bandpass filter BPF3, and the RF reference signal source RF is connected to the second input terminal of the second mixer MIX2. The output terminal of the second mixer MIX2 is connected to the input terminal of the single PID controller, and the output terminal of the single PID controller is connected to the input terminal of the frequency domain hierarchical allocation module. The first output terminal of the frequency domain hierarchical allocation module is connected to the control terminal of the first acousto-optic modulator AOM1, and the second output terminal is connected to the control terminal of the second acousto-optic modulator AOM2.

[0011] Based on the first aspect, the frequency domain hierarchical allocation module includes a high-pass filter branch and a low-pass filter branch; the high-pass filter branch extracts high-frequency transient control components and outputs them to a first acousto-optic modulator AOM1 to suppress transient phase noise in the forward link; the low-pass filter branch extracts low-frequency slow-varying control components and outputs them to a second acousto-optic modulator AOM2 to compensate for low-frequency phase drift in the reverse link.

[0012] Based on the first aspect, the bandwidth range of the high-pass filter branch is 100Hz to 1kHz, and the bandwidth range of the low-pass filter branch is 0.01Hz to 0.1Hz.

[0013] Based on the first aspect, the forward signal light and the reverse signal light are 1550nm band optical signals, and the probe light is a 1510nm band optical signal.

[0014] Based on the first aspect, it also includes an automatic gain control unit, which includes a forward optical power detector, a reverse optical power detector, and a pump drive circuit; the forward optical power detector and the reverse optical power detector detect the output optical power in real time, and the pump drive circuit automatically adjusts the pump current to keep the bidirectional gain symmetrical and stable.

[0015] Secondly, this application discloses a dual-channel isolated high-gain bidirectional fiber amplification method for use in the aforementioned dual-channel isolated high-gain bidirectional fiber amplification system, comprising the following steps: S1. After the forward signal light enters the forward amplification channel, it is combined with the probe light output from the first laser through the first wavelength division multiplexer (WDM1). The resulting first combined light is then sequentially amplified by the first acousto-optic modulator (AOM1), the first optical isolator (ISO1), the first unidirectional erbium-doped fiber amplifier (EDFA1), and the second optical isolator (ISO2). The amplified first combined light is then input to the second wavelength division multiplexer (WDM2). The second wavelength division multiplexer (WDM2) performs wavelength division multiplexing, and the first photodetector (PD1) obtains the forward phase information. S2. After the reverse signal light enters the reverse amplification channel, it is combined with the probe light output from the second laser through the third wavelength division multiplexer (WDM3). The resulting second combined light is then sequentially amplified by the second acousto-optic modulator (AOM2), the third optical isolator (ISO3), the second unidirectional erbium-doped fiber amplifier (EDFA2), and the fourth optical isolator (ISO4). The amplified second combined light is then input to the fourth wavelength division multiplexer (WDM4). The fourth wavelength division multiplexer (WDM4) performs wavelength division multiplexing, and the second photodetector (PD2) obtains the reverse phase information. S3. The bidirectional phase synchronization unit extracts the phase difference between the positive and negative phase information. Based on the control signal generated by the single PID controller, the frequency domain hierarchical allocation module splits the high-frequency control component and the low-frequency control component, respectively driving the first acousto-optic modulator AOM1 and the second acousto-optic modulator AOM2 to perform phase compensation on the bidirectional link. S4: The automatic gain control unit adjusts the pump power of the two unidirectional erbium-doped fiber amplifiers in real time to maintain the consistency and stability of the bidirectional amplification gain.

[0016] The beneficial effects of this invention are: 1) This application sets up two completely independent amplification channels, one for forward and one for reverse, and uses unidirectional EDFA to achieve independent amplification of forward and reverse signal light, avoiding the risk of self-excited oscillation of common cavity bidirectional amplification, breaking through the upper limit of traditional bidirectional amplification gain, achieving stable output with a large gain of ≥30dB, and improving the signal power and signal-to-noise ratio of long-distance optical fiber frequency transmission links.

[0017] 2) This application achieves synchronous compensation of forward and reverse link phase noise by using forward and reverse 1510nm probe light beat frequency phase detection and extracting the phase noise difference between the two EDFAs. This not only suppresses the common-mode phase noise of the link, but also cancels the independent differential-mode phase drift of the two EDFAs, significantly improving the long-term stability of optical frequency transmission.

[0018] 3) This application adopts a single PID controller combined with a frequency domain hierarchical allocation strategy to split the control quantity into high-frequency transient components and ultra-low-frequency slow-changing components, which drive the forward AOM and the reverse AOM respectively; the high bandwidth of the forward loop enables fast power-on locking and high-frequency noise suppression, while the low bandwidth of the reverse loop only compensates for low-frequency drift such as temperature drift and pump slow drift. During the transient process, the reverse loop hardly operates, avoiding the adjustment cancellation, lock-in time extension and oscillation risk caused by the coupling of two control variables, and taking into account both fast locking capability and long-term phase stability.

[0019] 4) This application uses only one PID controller to achieve bidirectional compensation without the need for additional control hardware. Fast and slow loops are decoupled through filtering and frequency division. The circuit and algorithm structure is simple and easy to debug, reducing system complexity and cost, and improving reliability and maintainability.

[0020] 5) This application uses a 1510nm independent probe light for phase detection, which is separated from the 1550nm signal light wavelength to avoid interference of fiber optic link phase noise on the phase detection signal, improve the signal-to-noise ratio of the beat frequency signal and the stability of phase detection, and ensure the accuracy of phase compensation. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a dual-channel isolated high-gain bidirectional fiber optic amplifier system according to an embodiment of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention proposes a dual-channel isolated high-gain bidirectional fiber optic amplification system and method, which realizes independent amplification of forward and reverse links, stable high-gain output, and bidirectional full-phase noise compensation, while ensuring rapid system locking and long-term phase stability. It solves the problems of self-excitation, noise, gain and engineering from the principle, and overcomes the defects of existing technologies such as limited bidirectional amplification gain, high risk of self-excitation, single phase noise compensation, easy coupling oscillation of bidirectional synchronous compensation, and long locking time.

[0024] Here, the relevant terms used in this application are explained: CIR: An optical circulator is a multi-port optical device with non-reciprocal characteristics. Its non-reciprocity is primarily based on the Faraday magneto-optical effect, achieving unidirectional sequential transmission of optical signals through internal components such as birefringent crystals and Faraday rotators. When an optical signal is input from any port, it can be output from the next port in the numerical order shown in the diagram with very little loss, while the loss to all other ports from that port is very high, making them disconnected ports.

[0025] WDM: Wavelength Division Multiplexing is a technology that combines two or more optical carrier signals of different wavelengths (carrying various information) at the transmitting end using a multiplexer (also called a multiplexer) and couples them into the same optical fiber for transmission. At the receiving end, the optical carriers of various wavelengths are separated by a demultiplexer (also called a demultiplexer), and then further processed by an optical receiver to recover the original signal.

[0026] AOM: Acousto-optic modulator is an external modulation technology device that uses the acousto-optic effect to modulate a laser beam. Its core function is to control the intensity, frequency, or direction of the laser beam through electrical signals.

[0027] ISO: An optical isolator is a passive optical device that allows only unidirectional light to pass through. Its working principle is based on the non-reciprocity of Faraday rotation. Light reflected back from the optical fiber can be effectively isolated by the optical isolator.

[0028] EDFA: Erbium-Doped Fiber Amplifier, is an optical amplifier that uses erbium-doped fiber as the gain medium.

[0029] PD: A photodetector is a core device that converts light signals into electrical signals. Its principle is based on the change in conductivity of the irradiated material caused by radiation.

[0030] BPF: Band-Pass Filter. A band-pass filter is a filter that allows frequency components within a certain frequency range to pass through, but attenuates frequency components in other ranges to a very low level.

[0031] MIX: A mixer is a circuit whose output signal frequency is equal to the sum, difference, or other combination of the frequencies of the two input signals.

[0032] PID: Proportional-Integral-Derivative (PID) circuit is a widely used control circuit in the field of engineering control. It adjusts system error through three control methods: proportional, integral, and derivative, thereby achieving precise control.

[0033] RF: Radio Frequency (RF) refers to high-frequency electromagnetic waves with a frequency higher than 100kHz.

[0034] See Figure 1 This application discloses a dual-channel isolated high-gain bidirectional fiber optic amplification system, including a forward amplification channel, a reverse amplification channel, and a bidirectional phase synchronization unit. The forward amplification channel and the reverse amplification channel are independent of each other and are used to isolate and amplify the forward signal light and the reverse signal light, respectively, as well as to detect the phase of the probe light. The input end of the bidirectional phase synchronization unit is connected to the detection output end of the forward amplification channel and the reverse amplification channel, respectively, and the output end of the bidirectional phase synchronization unit is connected to the acousto-optic modulator in the forward amplification channel and the reverse amplification channel, respectively, to extract the phase error of the two probe lights and drive the two acousto-optic modulators simultaneously through a frequency domain layering strategy to achieve phase noise compensation of the bidirectional link.

[0035] For example, the forward amplification channel and the reverse amplification channel do not share a circulator, optical fiber, or gain medium.

[0036] For example, the forward amplification channel includes a first optical circulator CIR1, a first wavelength division multiplexer WDM1, a first acousto-optic modulator AOM1, a first optical isolator ISO1, a first unidirectional erbium-doped fiber amplifier EDFA1, a second optical isolator ISO2, a second wavelength division multiplexer WDM2, a first photodetector PD1, and a first laser (1510nm). The forward signal light is connected to the signal end of the first wavelength division multiplexer (WDM1) via the first optical circulator (CIR1). The probe light output from the first laser is connected to the probe end of the first wavelength division multiplexer (WDM1) and then combined with the forward signal light. The resulting combined light is then connected to the first acousto-optic modulator (AOM1), the first optical isolator (ISO1), the first erbium-doped fiber amplifier (EDFA1), and the second optical isolator (ISO2) before being input to the second wavelength division multiplexer (WDM2). The first optical isolator ISO1 and the second optical isolator ISO2 are located at the input and output ends of the first unidirectional erbium-doped fiber amplifier EDFA1, respectively. They are used to block the reverse reflected light of the first unidirectional erbium-doped fiber amplifier EDFA1, prevent self-excited oscillation, and ensure the unidirectional transmission of the first combined light in the forward amplification channel. The second wavelength division multiplexer (WDM2) performs wavelength division of the first combined light. The forward signal light is output to the bidirectional transmission fiber via the second optical circulator (CIR2), and the probe light is output to the first photodetector (PD1). The output of the first photodetector (PD1) is connected to the bidirectional phase synchronization unit as the probe output of the forward amplification channel.

[0037] For example, the reverse amplification channel includes a second optical circulator CIR2, a third wavelength division multiplexer WDM3, a second acousto-optic modulator AOM2, a third optical isolator ISO3, a second unidirectional erbium-doped fiber amplifier EDFA2, a fourth optical isolator ISO4, a fourth wavelength division multiplexer WDM4, a second photodetector PD2, and a second laser (1510nm). The reverse signal light is connected to the signal end of the third wavelength division multiplexer (WDM3) via the second optical circulator (CIR2). The probe light output from the second laser is connected to the probe end of the third wavelength division multiplexer (WDM3) and then combined with the reverse signal light. The resulting combined light is then connected to the second acousto-optic modulator (AOM2), the third optical isolator (ISO3), the second unidirectional erbium-doped fiber amplifier (EDFA2), and the fourth optical isolator (ISO4) before being input to the fourth wavelength division multiplexer (WDM4). The third optical isolator ISO3 and the fourth optical isolator ISO4 are located at the input and output ends of the second unidirectional erbium-doped fiber amplifier EDFA2, respectively. They are used to block the reverse reflected light of the second unidirectional erbium-doped fiber amplifier EDFA2, prevent self-excited oscillation, and ensure the unidirectional transmission of the first combined light in the forward amplification channel. The fourth wavelength division multiplexer (WDM4) completes the wavelength division of the second combined light. The reverse signal light is output to the bidirectional transmission fiber via the first optical circulator (CIR1), and the probe light is output to the second photodetector (PD2). The output of the second photodetector (PD2) is connected to the bidirectional phase synchronization unit as the probe output of the reverse amplification channel.

[0038] For example, the bidirectional phase synchronization unit includes a first bandpass filter BPF1, a second bandpass filter BPF2, a first mixer MIX1, a third bandpass filter BPF3, a second mixer MIX2, an RF reference signal source RF, a single PID controller, and a frequency domain hierarchical allocation module. The output of the first photodetector PD1 is connected to the first input terminal of the first mixer MIX1 via the first bandpass filter BPF1, and the output of the second photodetector PD2 is connected to the second input terminal of the first mixer MIX1 via the second bandpass filter BPF2. The output of the first mixer MIX1 is connected to the first input terminal of the second mixer MIX2 via the third bandpass filter BPF3, and the RF reference signal source RF is connected to the second input terminal of the second mixer MIX2. The output terminal of the second mixer MIX2 is connected to the input terminal of the single PID controller, and the output terminal of the single PID controller is connected to the input terminal of the frequency domain hierarchical allocation module. The first output terminal of the frequency domain hierarchical allocation module is connected to the control terminal of the first acousto-optic modulator AOM1, and the second output terminal is connected to the control terminal of the second acousto-optic modulator AOM2.

[0039] For example, the frequency domain hierarchical allocation module includes a high-pass filter branch and a low-pass filter branch; the high-pass filter branch extracts high-frequency transient control components and outputs them to a first acousto-optic modulator AOM1 to suppress transient phase noise in the forward link; the low-pass filter branch extracts low-frequency slow-varying control components and outputs them to a second acousto-optic modulator AOM2 to compensate for low-frequency phase drift in the reverse link.

[0040] For example, the bandwidth range of the high-pass filter branch is 100Hz to 1kHz, and the bandwidth range of the low-pass filter branch is 0.01Hz to 0.1Hz.

[0041] For example, the forward and reverse signal lights are 1550nm band optical signals, and the probe light is a 1510nm band optical signal. The probe light is only used for phase difference detection and does not participate in the transmission of the forward and reverse signal lights in the main fiber optic link, thus avoiding phase noise interference in the fiber optic link.

[0042] For example, it also includes an automatic gain control unit, which includes a forward optical power detector, a reverse optical power detector, and a pump drive circuit; the forward optical power detector and the reverse optical power detector detect the output optical power in real time, and the pump drive circuit automatically adjusts the pump current to keep the bidirectional gain symmetrical and stable.

[0043] For example, during system operation, dual-channel isolated amplification and bidirectional phase synchronization detection are used. The forward and reverse amplification channels independently amplify the signal light to avoid self-excited oscillation. The integrated design of single PID frequency domain hierarchical compensation extracts the phase noise difference between the two EDFAs and achieves bidirectional compensation through frequency domain hierarchical control. This effectively solves the technical bottlenecks of existing bidirectional amplification, such as limited gain, high risk of self-excitement, single phase compensation, and easy coupling oscillation in bidirectional synchronization compensation. It achieves high-gain, high-stability, and fast-locking bidirectional fiber amplification, which is suitable for long-distance, high-precision fiber optic frequency transmission systems.

[0044] For example, this embodiment details the working process of the forward amplification channel and the phase detection principle of the 1510nm probe light (the working process of the reverse amplification channel is exactly the same as that of the forward amplification channel, and will not be described in detail here).

[0045] The first laser (1510nm) outputs a probe beam, and its optical signal... Represented as ,in, The initial frequency of the 1510nm laser. For time, This is the initial phase; The forward signal light is connected to the signal terminal of the first wavelength division multiplexer (WDM1) via the first optical circulator (CIR1), and is combined with the 1510nm probe light output from the first laser (1510nm) in the WDM1. The combined light, after being output from the WDM1, sequentially passes through the first acousto-optic modulator (AOM1), the first optical isolator (ISO1), the first erbium-doped fiber amplifier (EDFA1), and the second optical isolator (ISO2) before being input to the second wavelength division multiplexer (WDM2). The first acousto-optic modulator (AOM1) introduces a frequency shift. The first unidirectional erbium-doped fiber amplifier EDFA1 introduces phase noise. The second acousto-optic modulator AOM2 introduces a frequency shift. The second unidirectional erbium-doped fiber amplifier EDFA2 introduces phase noise. .

[0046] After being demultiplexed by the second wavelength division multiplexer WDM2, the 1510nm probe light is detected by the first photodetector PD1 to obtain a forward probe photoelectric signal. , The signal contains phase noise introduced by the first unidirectional erbium-doped fiber amplifier EDFA1. After being filtered by the first bandpass filter BPF1, it is sent to the bidirectional phase synchronization unit to provide a positive detection signal for phase error extraction.

[0047] The first optical isolator ISO1 and the second optical isolator ISO2 ensure unidirectional transmission of optical signals and prevent the first unidirectional erbium-doped fiber amplifier EDFA1 from generating self-excited oscillations; the first acousto-optic modulator AOM1 receives the control signal of the bidirectional phase synchronization unit and is used for forward link phase noise compensation to achieve rapid suppression of high-frequency noise.

[0048] By way of example, this embodiment details the working process of the bidirectional phase synchronization unit and the principle of single PID frequency domain hierarchical compensation.

[0049] The forward detection photoelectric signal output by the first photodetector PD1 After being filtered by the first bandpass filter BPF1, the reverse detection photoelectric signal output by the second photodetector PD2 After being filtered by the second bandpass filter BPF2, the two signals are input to the first mixer MIX1 for beat mixing to generate a difference frequency signal. This difference frequency signal is then filtered by the third bandpass filter BPF3, and its frequency is the same as the frequency output by the RF reference signal source. The reference signal is input to the second mixer MIX2 for mixing and phase detection, and the phase error signal is extracted. , The error signal reflects the phase noise difference between the first unidirectional erbium-doped fiber amplifier EDFA1 and the second unidirectional erbium-doped fiber amplifier EDFA2, and is sent to a single PID controller for calculation and correction. The single PID controller outputs a control signal to a frequency domain hierarchical distribution module, which includes a high-pass filter branch and a low-pass filter branch. The high-pass filter branch, for example, with a bandwidth set to 100Hz to 1kHz, extracts the high-frequency transient control component and outputs it to the first acousto-optic modulator AOM1 to achieve high-bandwidth fast locking of the forward link and suppress transient phase noise such as vibration, acoustic disturbance, and pump high-frequency fluctuations. The low-pass filter branch, for example with a bandwidth of 0.01Hz to 0.1Hz, extracts the ultra-low frequency slow-varying control component and outputs it to the second acousto-optic modulator AOM2. It only slowly compensates for low-frequency phase drift such as temperature drift, slow pump variation, and long-term fiber deformation, and does not participate in transient regulation.

[0050] During the initial power-on phase, only the high-pass filter branch is enabled, and the forward first acousto-optic modulator AOM1 quickly completes phase locking. After the system reaches steady state, the low-pass filter branch is enabled, and the reverse second acousto-optic modulator AOM2 slowly compensates for long-term drift, avoiding coupling oscillations caused by simultaneous bidirectional control actions. Ultimately, the phase noise difference between the first unidirectional erbium-doped fiber amplifier EDFA1 and the second unidirectional erbium-doped fiber amplifier EDFA2 approaches zero, ensuring the phase coherence of the 1550nm signal light after bidirectional amplification.

[0051] For example, this application discloses a dual-channel isolated high-gain bidirectional fiber amplification method for use in the aforementioned dual-channel isolated high-gain bidirectional fiber amplification system, comprising the following steps: S1. After the forward signal light enters the forward amplification channel, it is combined with the probe light output from the first laser through the first wavelength division multiplexer (WDM1). The resulting first combined light is then sequentially amplified by the first acousto-optic modulator (AOM1), the first optical isolator (ISO1), the first unidirectional erbium-doped fiber amplifier (EDFA1), and the second optical isolator (ISO2). The amplified first combined light is then input to the second wavelength division multiplexer (WDM2). The second wavelength division multiplexer (WDM2) performs wavelength division multiplexing, and the first photodetector (PD1) obtains the forward phase information. S2. After the reverse signal light enters the reverse amplification channel, it is combined with the probe light output from the second laser through the third wavelength division multiplexer (WDM3). The resulting second combined light is then sequentially amplified by the second acousto-optic modulator (AOM2), the third optical isolator (ISO3), the second unidirectional erbium-doped fiber amplifier (EDFA2), and the fourth optical isolator (ISO4). The amplified second combined light is then input to the fourth wavelength division multiplexer (WDM4). The fourth wavelength division multiplexer (WDM4) performs wavelength division multiplexing, and the second photodetector (PD2) obtains the reverse phase information. S3. The bidirectional phase synchronization unit extracts the phase difference between the positive and negative phase information. Based on the control signal generated by the single PID controller, the frequency domain hierarchical allocation module splits the high-frequency control component and the low-frequency control component, respectively driving the first acousto-optic modulator AOM1 and the second acousto-optic modulator AOM2 to perform phase compensation on the bidirectional link. S4, the automatic gain control unit adjusts the pump power of the two unidirectional erbium-doped fiber amplifiers in real time to maintain the consistency and stability of the bidirectional amplification gain. Complete physical isolation between the forward and reverse channels eliminates the EDFA self-excitation effect; independent transmission of probes at different wavelengths improves the phase detection signal-to-noise ratio; bidirectional phase synchronization compensation ensures phase coherence of the bidirectional amplification link; and automatic gain closed-loop achieves high gain and high stability (≥30dB).

[0052] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A dual-channel isolated high-gain bidirectional fiber optic amplification system, characterized in that: It includes a forward amplification channel, a reverse amplification channel, and a bidirectional phase synchronization unit. The forward amplification channel and the reverse amplification channel are independent of each other and are used to isolate and amplify the forward signal light and the reverse signal light, respectively, as well as to detect the phase of the probe light. The input of the bidirectional phase synchronization unit is connected to the detection output of the forward amplification channel and the reverse amplification channel, respectively, and the output of the bidirectional phase synchronization unit is connected to the acousto-optic modulator in the forward amplification channel and the reverse amplification channel, respectively. It is used to extract the phase error of the two probe lights and drive the two acousto-optic modulators simultaneously through a frequency domain layering strategy to achieve phase noise compensation of the bidirectional link. The bidirectional phase synchronization unit includes a first bandpass filter BPF1, a second bandpass filter BPF2, a first mixer MIX1, a third bandpass filter BPF3, a second mixer MIX2, an RF reference signal source RF, a single PID controller, and a frequency domain hierarchical allocation module. The output of the first photodetector PD1 is connected to the first input terminal of the first mixer MIX1 via the first bandpass filter BPF1, and the output of the second photodetector PD2 is connected to the second input terminal of the first mixer MIX1 via the second bandpass filter BPF2. The output of the first mixer MIX1 is connected to the first input of the second mixer MIX2 via the third bandpass filter BPF3, and the RF reference signal source RF is connected to the second input of the second mixer MIX2; the output of the second mixer MIX2 is connected to the input of a single PID controller, and the output of the single PID controller is connected to the input of a frequency domain hierarchical allocation module; the first output of the frequency domain hierarchical allocation module is connected to the control of the first acousto-optic modulator AOM1, and the second output is connected to the control of the second acousto-optic modulator AOM2. The frequency domain hierarchical allocation module includes a high-pass filter branch and a low-pass filter branch; the high-pass filter branch extracts high-frequency transient control components and outputs them to the first acousto-optic modulator AOM1 to suppress transient phase noise in the forward link; the low-pass filter branch extracts low-frequency slow-varying control components and outputs them to the second acousto-optic modulator AOM2 to compensate for low-frequency phase drift in the reverse link.

2. The dual-channel isolated high-gain bidirectional fiber optic amplification system according to claim 1, characterized in that: The forward amplification channel includes a first optical circulator CIR1, a first wavelength division multiplexer WDM1, a first acousto-optic modulator AOM1, a first optical isolator ISO1, a first unidirectional erbium-doped fiber amplifier EDFA1, a second optical isolator ISO2, a second wavelength division multiplexer WDM2, a first photodetector PD1, and a first laser. The forward signal light is connected to the signal end of the first wavelength division multiplexer (WDM1) via the first optical circulator (CIR1). The probe light output from the first laser is connected to the probe end of the first wavelength division multiplexer (WDM1) and then combined with the forward signal light. The resulting combined light is then connected to the first acousto-optic modulator (AOM1), the first optical isolator (ISO1), the first erbium-doped fiber amplifier (EDFA1), and the second optical isolator (ISO2) before being input to the second wavelength division multiplexer (WDM2). The first optical isolator ISO1 and the second optical isolator ISO2 are used to ensure the unidirectional transmission of the first combined light in the forward amplification channel and suppress the self-excited oscillation of the first unidirectional erbium-doped fiber amplifier EDFA1. The second wavelength division multiplexer (WDM2) performs wavelength division of the first combined light. The forward signal light is output to the bidirectional transmission fiber via the second optical circulator (CIR2), and the probe light is output to the first photodetector (PD1). The output of the first photodetector (PD1) is connected to the bidirectional phase synchronization unit as the probe output of the forward amplification channel.

3. The dual-channel isolated high-gain bidirectional fiber optic amplification system according to claim 2, characterized in that: The reverse amplification channel includes a second optical circulator CIR2, a third wavelength division multiplexer WDM3, a second acousto-optic modulator AOM2, a third optical isolator ISO3, a second unidirectional erbium-doped fiber amplifier EDFA2, a fourth optical isolator ISO4, a fourth wavelength division multiplexer WDM4, a second photodetector PD2, and a second laser. The reverse signal light is connected to the signal end of the third wavelength division multiplexer (WDM3) via the second optical circulator (CIR2). The probe light output from the second laser is connected to the probe end of the third wavelength division multiplexer (WDM3) and then combined with the reverse signal light. The resulting combined light is then connected to the second acousto-optic modulator (AOM2), the third optical isolator (ISO3), the second unidirectional erbium-doped fiber amplifier (EDFA2), and the fourth optical isolator (ISO4) before being input to the fourth wavelength division multiplexer (WDM4). The third optical isolator ISO3 and the fourth optical isolator ISO4 are used to ensure the unidirectional transmission of the second combined light in the reverse amplification channel and suppress the self-excited oscillation of the second unidirectional erbium-doped fiber amplifier EDFA2. The fourth wavelength division multiplexer (WDM4) completes the wavelength division of the second combined light. The reverse signal light is output to the bidirectional transmission fiber via the first optical circulator (CIR1), and the probe light is output to the second photodetector (PD2). The output of the second photodetector (PD2) is connected to the bidirectional phase synchronization unit as the probe output of the reverse amplification channel.

4. A dual-channel isolated high-gain bidirectional fiber optic amplification system according to claim 3, characterized in that: The bandwidth range of the high-pass filter branch is 100Hz to 1kHz, and the bandwidth range of the low-pass filter branch is 0.01Hz to 0.1Hz.

5. A dual-channel isolated high-gain bidirectional fiber optic amplification system according to claim 4, characterized in that: The forward and reverse signal lights are 1550nm wavelength optical signals, and the probe light is a 1510nm wavelength optical signal.

6. The dual-channel isolated high-gain bidirectional fiber optic amplification system according to claim 1, characterized in that: It also includes an automatic gain control unit, which includes a forward optical power detector, a reverse optical power detector, and a pump drive circuit; the forward optical power detector and the reverse optical power detector detect the output optical power in real time, and the pump drive circuit automatically adjusts the pump current to keep the bidirectional gain symmetrical and stable.

7. A dual-channel isolated high-gain bidirectional fiber amplification method, used in the dual-channel isolated high-gain bidirectional fiber amplification system according to any one of claims 1-6, characterized in that, Includes the following steps: S1. After the forward signal light enters the forward amplification channel, it is combined with the probe light output from the first laser through the first wavelength division multiplexer (WDM1). The resulting first combined light is then sequentially amplified by the first acousto-optic modulator (AOM1), the first optical isolator (ISO1), the first unidirectional erbium-doped fiber amplifier (EDFA1), and the second optical isolator (ISO2). The amplified first combined light is then input to the second wavelength division multiplexer (WDM2). The second wavelength division multiplexer (WDM2) performs wavelength division multiplexing, and the first photodetector (PD1) obtains the forward phase information. S2. After the reverse signal light enters the reverse amplification channel, it is combined with the probe light output from the second laser through the third wavelength division multiplexer (WDM3). The resulting second combined light is then sequentially amplified by the second acousto-optic modulator (AOM2), the third optical isolator (ISO3), the second unidirectional erbium-doped fiber amplifier (EDFA2), and the fourth optical isolator (ISO4). The amplified second combined light is then input to the fourth wavelength division multiplexer (WDM4). The fourth wavelength division multiplexer (WDM4) performs wavelength division multiplexing, and the second photodetector (PD2) obtains the reverse phase information. S3. The bidirectional phase synchronization unit extracts the phase difference between the positive and negative phase information. Based on the control signal generated by the single PID controller, the frequency domain hierarchical allocation module splits the high-frequency control component and the low-frequency control component, respectively driving the first acousto-optic modulator AOM1 and the second acousto-optic modulator AOM2 to perform phase compensation on the bidirectional link. S4: The automatic gain control unit adjusts the pump power of the two unidirectional erbium-doped fiber amplifiers in real time to maintain the consistency and stability of the bidirectional amplification gain.

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