Coherence-correlation optical time domain reflection detection method and system

Abstract

According to the coherence-correlation optical time domain reflection detection method and system, a laser signal output by a laser is split into detection light and auxiliary light, and the detection light is injected into a detected optical fiber after being coded and modulated; processing the auxiliary light through an auxiliary light path, and detecting the phase noise of the laser in real time to obtain phase noise information; receiving a reflected signal returned by the detected optical fiber, generating a local reference signal which is homologous with the probe light code, and performing phase adjustment on the local reference signal according to the phase noise information to obtain a phase-compensated local reference signal; and performing sliding window correlation operation on the reflected signal and a local reference signal after phase compensation, realizing optical fiber link reflection characteristic measurement and fault positioning by using a correlation operation result, capturing laser phase noise in real time through an auxiliary optical path, and synchronously completing digital compensation. Related peak broadening and sidelobe lifting caused by phase noise are effectively suppressed, and the signal-to-noise ratio and the dynamic range of long-distance measurement of the system are improved.

Description

Technical Field

[0001] This application relates to the field of distributed optical fiber sensing and coherent detection, specifically to a coherent-correlated optical time-domain reflectometry detection method and system. Background Technology

[0002] Currently, the field of distributed optical fiber sensing and coherent detection technology is developing rapidly, and the integration of communication and sensing has become an important development trend. There is a wide and urgent demand for applications in scenarios such as optical fiber communication monitoring, optical cable fault location, vibration sensing, and structural health diagnosis. The market has a large demand for optical fiber reflection measurement technology that combines high resolution, long detection distance, and strong real-time performance. The market application life of related technologies is long, and the requirements for balancing system performance and cost are increasing.

[0003] In related technologies, traditional optical time domain reflectometers (OTDRs) use pulsed light to detect Rayleigh scattering and Fresnel reflection in optical fibers; correlation-based OTRs achieve energy accumulation through pseudo-random or Gore sequence encoded signals and correlation decoding; and coherent detection-based OTRs can achieve complex field detection by combining dual-polarization orthogonal phase shift keying modulation with local oscillating light to obtain amplitude, phase, and polarization information in the optical fiber link.

[0004] However, in optical time-domain reflectometers based on coherent detection technology, the phase noise introduced by the limited linewidth of the laser can cause correlation peak broadening and sidelobe lifting, thereby limiting the dynamic range and effective ranging of the system. Summary of the Invention

[0005] This application provides a coherent-correlated optical time-domain reflectometry detection method and system, which can solve the technical problem in related technologies where coherent detection optical time-domain reflectometers are affected by laser phase noise, resulting in correlation peak broadening and sidelobe elevation, thus limiting the dynamic range and effective ranging of the system.

[0006] In a first aspect, embodiments of this application provide a coherent-correlated optical temporal reflectance detection method, the coherent-correlated optical temporal reflectance detection method comprising: The laser signal output from the laser is split into a probe beam and an auxiliary beam. The probe beam is encoded and modulated before being injected into the fiber under test. The auxiliary light is processed by the auxiliary optical path to detect the phase noise of the laser in real time and obtain phase noise information. The system receives the reflected signal returned by the fiber under test, generates a local reference signal that is homologous to the probe light code, performs phase adjustment on the local reference signal based on the phase noise information to generate a phase-compensated local reference signal, performs sliding window correlation operation on the reflected signal and the phase-compensated local reference signal, and realizes fiber optic link reflection characteristic measurement and fault location based on the correlation operation result.

[0007] In conjunction with the first aspect, in one embodiment, the coding modulation employs a pseudo-random sequence or a Gray sequence, and the coding modulation method includes orthogonal phase shift keying modulation.

[0008] In conjunction with the first aspect, in one embodiment, the auxiliary optical path processes the auxiliary light in a manner that includes self-heterodyne interferometry or self-zero-difference interferometry.

[0009] In conjunction with the first aspect, in one implementation method, the processing method of the self-heterodyne interferometry includes: The auxiliary light is split into two paths. One path is modulated by an acousto-optic modulator and an RF drive unit, and then interferes with the other path of auxiliary light that has been processed with a fixed delay. The phase noise information is then extracted by coherently detecting the intermediate frequency signal carrying the phase difference information.

[0010] In conjunction with the first aspect, in one implementation method, the processing method of the self-zero difference interferometry includes: The auxiliary light is split into two paths. One path is processed with a fixed delay and then directly interferes with the other unmodulated auxiliary light. The phase noise information is then extracted by coherently detecting the baseband signal carrying the phase difference information.

[0011] In conjunction with the first aspect, in one implementation, the phase difference signal is integrated and reconstructed to obtain time-series instantaneous phase noise information, which is used for phase adjustment of the local reference signal to perform precise phase compensation for the reflection signal at each reflection point.

[0012] In conjunction with the first aspect, in one embodiment, the step of adjusting the phase of the local reference signal based on the phase noise information to generate a phase-compensated local reference signal includes: The detection is performed in real time on a programmable logic device or digital signal processor platform. The compensated local reference signal and the reflected signal are correlated through a sliding window to achieve full-link coverage detection.

[0013] In conjunction with the first aspect, in one implementation, the laser signal beam splitting is achieved through a coupler, and the beam splitting ratio is adapted to the link detection requirements of the probe light and the noise detection accuracy requirements of the auxiliary light.

[0014] In conjunction with the first aspect, in one embodiment, the reflected signal includes Rayleigh scattered light signal and Fresnel reflected light signal, which is converted into an electrical signal by an avalanche photodiode before being digitized.

[0015] Secondly, embodiments of this application provide a coherent-correlated optical temporal reflectance detection system, the coherent-correlated optical temporal reflectance detection system comprising: The transmitting module is used to generate a stable continuous laser signal and split it into a probe light and an auxiliary light. The probe light is encoded and modulated and then injected directionally into the fiber under test. The auxiliary detection module receives the auxiliary light output from the transmitting module, processes it through self-heterodyne or self-zero difference interference and converts it into an electrical signal, and outputs a phase difference digital signal reflecting the phase noise of the laser after digitization. The receiving module is used to receive the reflected signal returned by the optical fiber under test, amplify it, complete photoelectric conversion and digital processing, and output the reflected digital signal. The signal processing module receives the phase difference digital signal from the auxiliary detection module and the reflected digital signal from the receiving module, generates a local reference signal that is of the same origin as the probe light encoding, reconstructs the time-series instantaneous phase noise information based on the phase difference digital signal, performs phase adjustment on the local reference signal to generate a phase-compensated local reference signal, performs sliding window correlation operation on the reflected digital signal and the phase-compensated local reference signal, extracts the optical fiber link reflection characteristic information, and locates the fault point.

[0016] The beneficial effects of the technical solutions provided in this application include: The laser signal output from the laser is split into a probe beam and an auxiliary beam. The probe beam is encoded and modulated before being injected into the fiber under test. The auxiliary beam is processed through an auxiliary optical path to detect the phase noise of the laser in real time and obtain phase noise information. The reflected signal returned from the fiber under test is received, and a local reference signal with the same encoding as the probe beam is generated. The phase of the local reference signal is adjusted according to the phase noise information to obtain a phase-compensated local reference signal. The reflected signal and the phase-compensated local reference signal are subjected to a sliding window correlation operation. The correlation operation result is used to measure the reflection characteristics of the fiber optic link and locate the fault. This method captures the laser phase noise in real time through an auxiliary optical path and performs digital compensation simultaneously, effectively suppressing the correlation peak broadening and sidelobe rise caused by phase noise. It significantly improves the signal-to-noise ratio and dynamic range of the system for long-distance measurement, ensures real-time detection capability, and does not rely on offline processing and narrow-linewidth lasers, thus reducing the system implementation cost. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of an embodiment of the coherent-correlated optical temporal reflectance detection method of this application; Figure 2 This is a schematic flowchart of another embodiment of the coherent-correlated optical temporal reflectance detection method of this application. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0020] This application provides a coherent-correlated optical time-domain reflectometry detection method and system, which can solve the technical problem in related technologies where coherent detection optical time-domain reflectometers are affected by laser phase noise, resulting in correlation peak broadening and sidelobe elevation, thus limiting the dynamic range and effective ranging of the system.

[0021] In a first aspect, embodiments of this application provide a coherent-correlated optical temporal reflectance detection method.

[0022] In one embodiment, the coherent-correlated optical temporal reflectance detection method includes: S100: Splits the laser signal output from the laser into a probe beam and an auxiliary beam, and injects the probe beam into the fiber under test after encoding and modulation. S200: Processes the auxiliary light through the auxiliary optical path, detects the phase noise of the laser in real time, and obtains phase noise information; S300: Receives the reflected signal returned by the fiber under test, generates a local reference signal that is of the same origin as the probe light code, performs phase adjustment on the local reference signal based on the phase noise information to generate a phase-compensated local reference signal, performs sliding window correlation operation on the reflected signal and the phase-compensated local reference signal, and realizes fiber optic link reflection characteristic measurement and fault location based on the correlation operation result.

[0023] In this embodiment, the laser signal output from the laser is split into a probe beam and an auxiliary beam. The probe beam is encoded and modulated before being injected into the fiber under test. The auxiliary beam is processed through an auxiliary optical path to detect the phase noise of the laser in real time and obtain phase noise information. The reflected signal returned from the fiber under test is received, and a local reference signal with the same encoding as the probe beam is generated. The phase of the local reference signal is adjusted according to the phase noise information to obtain a phase-compensated local reference signal. The reflected signal and the phase-compensated local reference signal are subjected to a sliding window correlation operation. The correlation operation result is used to measure the reflection characteristics of the fiber optic link and locate the fault. This method captures the laser phase noise in real time through an auxiliary optical path and performs digital compensation simultaneously, effectively suppressing the correlation peak broadening and sidelobe rise caused by phase noise. It significantly improves the signal-to-noise ratio and dynamic range of the system for long-distance measurement, ensures real-time detection capability, and does not rely on offline processing and narrow-linewidth lasers, thus reducing the system implementation cost.

[0024] Furthermore, in one embodiment, S100 includes the following steps: The encoding and modulation employs pseudo-random sequences or Gray sequences, and the encoding and modulation methods include orthogonal phase shift keying modulation.

[0025] In this embodiment, a pseudo-random sequence or Gray sequence is used to encode and modulate the probe light using orthogonal phase shift keying modulation, so that the probe signal can accumulate energy while maintaining high resolution. Combined with real-time detection and digital compensation of phase noise, signal degradation is suppressed more effectively, improving the accuracy of optical fiber link reflection characteristic measurement and the long-distance detection performance of the system.

[0026] Furthermore, in one embodiment, step S200 includes the following steps: The auxiliary optical path processes the auxiliary light using either self-heterodyne interferometry or self-zero-difference interferometry.

[0027] In this embodiment, the auxiliary light is subjected to interference processing using either self-heterodyne interferometry or self-zero-difference interferometry to accurately capture the phase difference signal, thereby supporting the real-time detection of laser phase noise, providing a reliable basis for digital phase compensation of the reflected signal, and optimizing the stability and accuracy of optical fiber link reflection characteristic measurement.

[0028] Furthermore, in one embodiment, the processing method of the self-heterodyne interferometry includes: The auxiliary light is split into two paths. One path is modulated by an acousto-optic modulator and an RF drive unit, and then interferes with the other path of auxiliary light that has been processed with a fixed delay. The phase noise information is then extracted by coherently detecting the intermediate frequency signal carrying the phase difference information.

[0029] In this embodiment, the auxiliary light is split into two paths. One path is modulated by an acousto-optic modulator and a radio frequency driving unit, and the other path is processed with a fixed delay and then interfered with the modulated optical signal. Phase noise information is extracted by coherently detecting the intermediate frequency signal carrying phase difference information, providing accurate support for digital phase compensation of the reflected signal and optimizing the system's measurement effect on the reflection characteristics of the optical fiber link.

[0030] Furthermore, in one embodiment, the processing method of the self-zero difference interferometry includes: The auxiliary light is split into two paths. One path is processed with a fixed delay and then directly interferes with the other unmodulated auxiliary light. The phase noise information is then extracted by coherently detecting the baseband signal carrying the phase difference.

[0031] In this embodiment, one path, after being processed with a fixed delay, directly interferes with another unmodulated auxiliary light. By coherently detecting the baseband signal carrying the phase difference, phase noise information is extracted, providing reliable support for digital phase compensation of the reflected signal and ensuring the accuracy and stability of the optical fiber link reflection characteristic measurement.

[0032] Among them, the self-heterodyne interferometry uses modulation, which introduces a stable frequency difference to form a beat frequency signal that can be accurately demodulated after the two auxiliary lights interfere. It can effectively separate phase difference information from background noise, and is suitable for scenarios with high requirements for phase noise detection sensitivity or relatively smooth laser phase fluctuations, ensuring that phase noise information can be stably extracted even under weak signal conditions. The self-zero difference interferometry does not use modulation. It utilizes the characteristic that the two auxiliary lights are from the same source and have the same frequency, so that the phase difference signal generated by the interference directly corresponds to the change in laser phase noise. Phase noise detection can be achieved without additional modulation devices, simplifying the optical path structure and signal processing flow. It is suitable for scenarios with strict limitations on system complexity and cost, and where the phase noise detection accuracy can meet the compensation requirements.

[0033] Furthermore, in one embodiment, by integrating and reconstructing the phase difference signal, time-sequential instantaneous phase noise information is obtained, which is used for phase adjustment of the local reference signal to perform precise phase compensation for the reflection signal at each reflection point.

[0034] In this embodiment, the phase difference signal acquired by the auxiliary optical path is integrated and reconstructed to obtain time-series instantaneous phase noise information, which is used for phase adjustment of the local reference signal. Based on this, precise phase compensation is performed on the reflected signal. Combined with coding modulation and related operations, the accuracy of optical fiber link reflection characteristic measurement and the stability of long-distance detection of the system are further optimized.

[0035] Further, in one embodiment, the step of adjusting the phase of the local reference signal based on the phase noise information to generate a phase-compensated local reference signal includes: The detection is performed in real time on a programmable logic device or digital signal processor platform. The compensated local reference signal and the reflected signal are correlated through a sliding window to achieve full-link coverage detection.

[0036] In this embodiment, after acquiring time-series phase noise information and receiving the reflected signal returned by the fiber under test, the digital phase adjustment of the local reference signal, which is of the same origin as the probe light encoding, is performed in real time on a programmable logic device or digital signal processor platform to generate a phase-compensated local reference signal. By performing sliding window correlation operation between the reflected signal and the phase-compensated local reference signal, full-link coverage detection of the fiber optic link is achieved. This ensures both the real-time performance of the measurement process and the integrity of the full-link detection. Furthermore, precise phase compensation suppresses the correlation peak broadening and sidelobe rise caused by phase noise, further optimizing the system's extraction accuracy of fiber optic link reflection characteristics and fault location accuracy.

[0037] Furthermore, in one embodiment, the laser signal beam splitting is achieved through a coupler, and the beam splitting ratio is adapted to the link detection requirements of the probe light and the noise detection accuracy requirements of the auxiliary light.

[0038] In this embodiment, the laser signal output by the laser is split by a coupler, and the splitting ratio is adapted to the link detection requirements of the probe light and the noise detection accuracy requirements of the auxiliary light. This ensures that the probe light has the energy conditions to meet the link detection requirements, and the auxiliary light can accurately capture phase noise information, providing adaptability support for subsequent digital phase compensation and related calculations, and further ensuring the reliability of fiber optic link reflection characteristic measurement and system adaptability.

[0039] Furthermore, in one embodiment, the reflected signal includes Rayleigh scattering light signal and Fresnel reflected light signal. During reception, the light signal is converted into an electrical signal by an avalanche photodiode and then digitally processed.

[0040] In this embodiment, the Rayleigh scattered light signal and Fresnel reflected light signal returned by the optical fiber under test are received. The optical signal is converted into an electrical signal by an avalanche photodiode and then digitally processed. The digital phase compensation and related calculations are then completed by combining phase noise information to ensure the signal acquisition quality and data reliability of the optical fiber link reflection characteristic measurement.

[0041] In summary, this application addresses the technical challenges of limited dynamic range and effective ranging in coherent detection optical time-domain reflectometry (OTDR) caused by phase noise introduced by the limited linewidth of the laser, leading to correlation peak broadening, sidelobe elevation, and other limitations. It introduces an auxiliary optical path into the traditional coherent-correlated optical time-domain reflectometry (CC-OTDR) architecture to achieve real-time detection and digital compensation of laser phase noise, enabling high-resolution, high signal-to-noise ratio distributed reflectance measurement over long-distance fiber optic links. The complete technical solution is as follows: I. Core Technical Objectives To address the signal degradation problem caused by phase noise in coherent detection OTDRs, real-time measurement of the instantaneous phase noise φPN(t) of the laser is achieved through independent coherent detection in the auxiliary optical path. Phase compensation of the main channel signal is performed on the digital signal processing platform to restore the ideal correlation peak shape and improve the system signal-to-noise ratio and effective detection distance.

[0042] II. Working Principle The working principle of this scheme is based on the accurate estimation of the complex impulse response of the optical fiber link. The core mathematical model and signal characteristics under ideal conditions are as follows: 1. Mathematical model of received signal After coherent detection, the signal x(t) acquired by the receiver is a coherent superposition of the reflected light fields at each scattering point of the optical fiber, and it is superimposed with the laser phase noise and the receiver additive noise. Its expression is:

[0043] The parameters in the formula are defined as follows: : Complex reflection coefficient of the i-th reflection point (including amplitude and phase information); : Round-trip time of the optical signal corresponding to the i-th reflection point; The probe signal of dual polarization orthogonal phase shift keying (DP-QPSK) loaded at the transmitter; The difference in laser phase noise accumulated between the transmitter and receiver during the delay τi, which is usually modeled as a Wiener process; Receiver additive noise.

[0044] 2. Cross-correlation calculation under ideal operating conditions In a Field Programmable Gate Array (FPGA) hardware platform, the received signal x(t) and the locally generated reference signal are compared... Perform cross-correlation operation and output the result. The expression is:

[0045] in, "*" represents complex conjugate calculation.

[0046] In the ideal case where the laser phase noise is 0, As a stability constant, when At that time, the complex amplitude of the cross-correlation output and the complex reflection coefficient of the i-th reflection point It is directly proportional to the local reflection intensity and polarization state of the optical fiber, thus it can simultaneously reveal the local reflection intensity and polarization state of the optical fiber.

[0047] 3. System Spatial Resolution Formula The final spatial resolution of the system is determined by the symbol rate of dual polarization orthogonal phase shift keying (DP-QPSK), and its calculation formula is as follows:

[0048] In the formula, the parameters are defined as follows: c: speed of light in vacuum; n: refractive index of optical fiber; B: DP-QPSK symbol rate.

[0049] 4. The impact of phase noise degradation In actual operation, laser phase noise degrades the ideal autocorrelation characteristics of the signal, causing the main lobe of the correlation peak to broaden and the sidelobe noise floor to rise, directly limiting the signal-to-noise ratio and maximum effective detection distance that the system can obtain. Therefore, it is necessary to use an auxiliary optical path to detect and compensate for phase noise.

[0050] III. Specific Procedures for Auxiliary Optical Path Phase Noise Detection and Digital Compensation Direct measurement and digital compensation of laser phase noise are achieved by using the delayed coherent integration method through an auxiliary optical path. The complete process includes three core steps: phase difference signal acquisition, phase noise reconstruction, and main channel signal compensation, as detailed below: 1. Extraction of Auxiliary Optical Path Interference Signal and Phase Difference There are two methods for extracting phase difference in the auxiliary optical path: one is the self-zero difference interferometry method, and the other is the self-heterodyne interferometry method.

[0051] Since the zero-difference interferometry, after the main laser output is split, one path enters the auxiliary optical path and is divided into two paths: one path is introduced with a fixed time delay through a fixed-delay fiber arm (delay time τd), and the other path serves as a reference beam. Figure 2 The other path of the heterodyne interference law passes through the AOM and the frequency shift drive unit, such as... Figure 1 The two optical signals interfere at the coherent receiver, and the interference signal is obtained by coherent detection. The expression is:

[0052] By performing in-phase quadrature demodulation (I / Q demodulation) on the interference signal, the delayed coherent phase difference signal can be obtained, and its expression is as follows: ; In addition, the phase difference signal can also be measured by frequency shifting one of the optical signals and then using heterodyne demodulation.

[0053] 2. Time-series reconstruction of instantaneous laser phase noise Since the phase is a continuously changing process, the system performs integration and reconstruction on the above phase difference signal in a digital signal processor (DSP) or FPGA digital signal processing platform to obtain the instantaneous phase noise time series of the laser, the expression of which is:

[0054] This process can be implemented through an integration and accumulation module within the FPGA to update the laser phase estimate in real time in a time-series manner.

[0055] 3. Phase compensation and correlation calculation of the main signal channel Using the real-time estimated phase noise sequence, a corresponding phase rotation is applied to the local reference signal of the main signal channel, resulting in a compensated local reference signal. The expression is:

[0056] in, ; Then receive the signal With the compensated local reference sequence Perform cross-correlation operation, the operation expression is:

[0057] After compensation, the main lobe shape of the relevant output is restored, the sidelobe noise is significantly reduced, and the associated degradation effect caused by laser phase drift can be effectively suppressed. Moreover, this process can be executed in parallel in a hardware pipeline manner on the FPGA platform without introducing additional signal delay.

[0058] Secondly, this application provides a coherent-correlated optical time-domain reflectometry (OTDR) detection system. This system is designed around "real-time phase noise detection of the auxiliary optical path + online digital signal compensation," solving the problems of correlation peak broadening and sidelobe rise caused by laser phase noise in traditional coherent optical time-domain reflectometers (OTDRs). This enables high-resolution reflection characteristic detection and fault location for long-distance fiber optic links. The system is functionally divided into four main units: a transmitting module, an auxiliary detection module, a receiving module, and a signal processing module. It can be flexibly adapted to "self-heterodyne interferometry (SHI)." Figure 1 "Self-zero difference interference ()" Figure 2 Two configurations are available to cover application scenarios with different precision and cost requirements.

[0059] I. Detailed Explanation of Components and Functions of Each Module 1. Transmitting Module: The transmitting module is responsible for generating stable probe light and injecting it into the fiber under test, while also providing a source light signal for auxiliary detection. It includes: Laser: Outputs a continuous and stable laser signal, serving as a source of light for both "probe light" and "auxiliary light", without relying on ultra-narrow linewidth devices, thus balancing performance and cost; Isolator: Connected in series between the laser and coupler 1, it suppresses reflected light from the back-end link from flowing back into the laser, thus preventing interference with the phase and intensity stability of the laser source. Coupler 1: Splits the laser signal into two paths, "probe light (for link detection)" and "auxiliary light (for phase noise detection)", with the splitting ratio adapted to the link energy requirements of the probe light and the noise detection accuracy of the auxiliary light; Encoding and modulation: Pseudo-random sequence (PRBS) or Gray sequence is loaded onto the probe light, and quadrature phase shift keying (DP-QPSK) modulation is used to achieve signal energy accumulation while being compatible with communication transceivers (supporting "communication-sensing integration" applications). Optical circulator: Achieves "transmit-receive" optical path isolation: The probe light is directionally transmitted to the long optical fiber under test, and the reflected signal returned by the optical fiber is directionally transmitted to the receiving module, avoiding mutual interference between the transmitting and receiving optical paths; The long optical fiber under test: the link under test. When the probe light is transmitted in it, it generates two types of reflected signals: Rayleigh scattering light (distributed signal, reflecting link loss) and Fresnel reflection light (concentrated strong reflection, corresponding to fault points such as breakpoints and joints), which are the core basis for measurement.

[0060] 2. Auxiliary Detection Module: The auxiliary detection module captures laser phase noise using interferometry, providing data support for subsequent signal compensation. It consists of "basic common components" and "dedicated configurations for two interferometry modes": (1) Common components of the foundation Coupler 2: Receives the auxiliary light split from Coupler 1 and splits it into two parallel optical signals, providing a dual input source for interferometric detection; Delay fiber: Provides a fixed delay for one of the auxiliary lights, creating a time difference between the two lights to meet the detection conditions for interference phase difference.

[0061] Polarization controller: Adjusts the polarization state of the auxiliary light to ensure that the polarization directions of the two beams are consistent, thus ensuring the interference effect of the coupler (avoiding signal attenuation caused by polarization mismatch). Coupler 3: Combines the two auxiliary beams to achieve optical signal interference and outputs an interference optical signal containing phase difference information (the phase difference directly reflects the phase noise of the laser). Avalanche photodiode: converts weak interference light signals into electrical signals and captures low-amplitude light signals using its internal gain characteristics; Analog-to-digital converter acquisition board: amplifies, filters, and digitizes electrical signals, and outputs "phase difference digital signals" to the signal processing module.

[0062] (2) Dedicated configuration for self-heterodyne interference ( Figure 1 (Unique) Acousto-optic modulator: In conjunction with the radio frequency drive unit, it introduces a stable frequency difference into one of the auxiliary lights, so that the two lights interfere to form a "beat frequency signal", which facilitates the precise demodulation of the phase difference; RF drive unit: provides a stable drive signal for the acousto-optic modulator, controls the frequency difference, and adapts to different signal processing bandwidth requirements.

[0063] (3) Characteristics of self-zero difference interference configuration ( Figure 2 correspond) Without an "acousto-optic modulator and RF drive unit", the two auxiliary lights are processed by "delayed fiber + polarization controller" and then directly interfered in the three-beam coupling at the coupler, simplifying the optical path structure and reducing hardware costs.

[0064] 3. Receiving Module: The receiving module is responsible for collecting the reflected signal returned from the optical fiber and completing the "amplification-photoelectric conversion-digitization" process. Erbium-doped fiber amplifier: Receives reflected signals transmitted by optical circulators, amplifies weak signals that have attenuated after long-distance transmission, and improves the signal-to-noise ratio (to prevent weak signals from being masked by noise). Avalanche photodiode: converts amplified reflected light signals into electrical signals to match the amplitude fluctuation characteristics of the reflected signals; Analog-to-digital converter acquisition board: performs digital processing on electrical signals and outputs "reflected digital signals" to the signal processing module.

[0065] 4. Signal Processing Module: The signal processing module is the core of the system's computation. Based on programmable logic devices (such as FPGAs) or digital signal processors (DSPs), it implements real-time processing across multiple stages, specifically including: The local reference sequence unit generates a pseudo-random sequence (PRBS) or Gray sequence that is identical to the "coded modulation" of the transmitting module. This serves as a reference for correlation operations. The synchronization clock ensures timing synchronization with the probe light encoding, laying the foundation for accurate correlation operations. After receiving the reflected signal returned by the fiber under test, the unit calls the pre-set encoding configuration information in the system (which is consistent with the encoding type, sequence length, and modulation rule of the transmitting end's encoding modulation). In a programmable logic device (such as FPGA) or digital signal processor (DSP), a local reference signal identical to the probe light encoding and synchronized with the timing is generated in real time. This encoding configuration information has been synchronized with the transmitting end during system initialization, ensuring that the local reference signal is completely matched with the encoding sequence of the probe light. This provides an accurate reference for subsequent phase adjustment and sliding window correlation operations based on phase noise information. The instantaneous phase noise reconstruction unit receives the phase difference digital signal output by the auxiliary detection module and, based on the integral reconstruction algorithm (implemented through the integral accumulation module in the FPGA), converts the discrete phase difference signal into continuous "time-sequential instantaneous phase noise information" to restore the phase noise characteristics of the laser in real time. Phase compensation sequence generation unit: Based on the reconstructed instantaneous phase noise information, a reverse phase adjustment compensation sequence is generated. This sequence is perfectly matched with the phase noise characteristics of the laser and is used to cancel the interference of phase noise in the correlation calculation. Adjusting the local reference signal unit: superimposing the phase compensation sequence onto the local reference sequence, performing phase rotation adjustment on the local reference signal to generate a phase-compensated local reference signal, ensuring that it is phase-aligned with the effective component in the main probe optical path reflection signal; Sliding window correlation operation unit: Performs sliding window correlation operation on the reflected digital signal output by the receiving module and the phase-compensated local reference signal. The operation is executed in parallel through the FPGA hardware pipeline, and the delay index is processed in batches to achieve full-link coverage detection and extract the reflection intensity distribution at each location of the optical fiber link. The fiber optic fault location unit analyzes relevant calculation results, identifies signal characteristics with abnormal reflection intensity (such as strong reflection peaks corresponding to Fresnel reflection and signal attenuation corresponding to loss points), and accurately locates fault locations such as fiber breaks, joints, and loss points by combining the propagation speed of light in the fiber and round-trip time delay. At the same time, it outputs information on link reflection characteristics (such as amplitude and polarization correlation).

[0066] II. Configuration differences between the two interference modes Self-heterodyne interference ( Figure 1 ): Includes "acoustic-optic modulator and radio frequency drive unit", suitable for long-distance links with "high requirements for phase noise detection sensitivity and smooth laser phase fluctuation" (such as submarine optical cable monitoring). Its advantage is that it can accurately separate phase difference from background noise and is more stable in weak signal conditions. Self-zero interference ( Figure 2 ): No additional components are required. It is suitable for short-distance links (such as indoor fiber optic cabling) where "cost is limited and detection accuracy meets the requirements". Its advantages are simplified optical path and low deployment cost.

[0067] It should be noted that the sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0068] The terms "comprising" and "having," and any variations thereof, in the specification, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus. The terms "first," "second," and "third," etc., are used to distinguish different objects, etc., and do not indicate a sequence, nor do they limit "first," "second," and "third" to different types.

[0069] In the description of the embodiments of this application, terms such as "exemplary," "for example," or "for instance" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as "exemplary," "for example," or "for instance" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary," "for example," or "for instance" is intended to present the relevant concepts in a concrete manner.

[0070] In the description of the embodiments of this application, unless otherwise stated, " / " means "or". For example, A / B can mean A or B. The "and / or" in the text is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, in the description of the embodiments of this application, "multiple" means two or more.

[0071] In some processes described in the embodiments of this application, multiple operations or steps are included in a specific order. However, it should be understood that these operations or steps may not be executed in the order they appear in the embodiments of this application, or they may be executed in parallel. The sequence number of the operation is only used to distinguish different operations, and the sequence number itself does not represent any execution order. In addition, these processes may include more or fewer operations, and these operations or steps may be executed sequentially or in parallel, and these operations or steps may be combined.

[0072] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) as described above, and includes several instructions to cause a terminal device to execute the methods described in the various embodiments of this application.

[0073] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A coherent-correlated optical temporal reflectance detection method, characterized in that, The coherent-correlated optical temporal reflectance detection method includes: The laser signal output from the laser is split into a probe beam and an auxiliary beam. The probe beam is encoded and modulated before being injected into the fiber under test. The auxiliary light is processed by the auxiliary optical path to detect the phase noise of the laser in real time and obtain phase noise information. The system receives the reflected signal returned by the fiber under test, generates a local reference signal that is homologous to the probe light code, performs phase adjustment on the local reference signal based on the phase noise information to generate a phase-compensated local reference signal, performs sliding window correlation operation on the reflected signal and the phase-compensated local reference signal, and realizes fiber optic link reflection characteristic measurement and fault location based on the correlation operation result.

2. The coherent-correlated optical temporal reflectance detection method as described in claim 1, characterized in that, The encoding and modulation employs pseudo-random sequences or Gray sequences, and the encoding and modulation methods include orthogonal phase shift keying modulation.

3. The coherent-correlated optical temporal reflectance detection method as described in claim 1, characterized in that, The auxiliary optical path processes the auxiliary light using either self-heterodyne interferometry or self-zero-difference interferometry.

4. The coherent-correlated optical temporal reflectance detection method as described in claim 3, characterized in that, The processing methods of the self-heterodyne interferometry include: The auxiliary light is split into two paths. One path is modulated by an acousto-optic modulator and an RF drive unit, and then interferes with the other path of auxiliary light that has been processed with a fixed delay. The phase noise information is then extracted by coherently detecting the intermediate frequency signal carrying the phase difference information.

5. The coherent-correlated optical temporal reflectance detection method as described in claim 3, characterized in that, The processing methods of the self-zero difference interferometry method include: The auxiliary light is split into two paths. One path is processed with a fixed delay and then directly interferes with the other unmodulated auxiliary light. The phase noise information is then extracted by coherently detecting the baseband signal carrying the phase difference.

6. The coherent-correlated optical temporal reflectance detection method as described in claim 4 or 5, characterized in that, By integrating and reconstructing the phase difference signal, time-sequential instantaneous phase noise information is obtained, which is used for phase adjustment of the local reference signal to accurately compensate the reflected signal at each reflection point.

7. The coherent-correlated optical temporal reflectance detection method as described in claim 1, characterized in that, The step of adjusting the phase of the local reference signal based on the phase noise information to generate a phase-compensated local reference signal includes: The detection is performed in real time on a programmable logic device or digital signal processor platform. The compensated local reference signal and the reflected signal are correlated through a sliding window to achieve full-link coverage detection.

8. The coherent-correlated optical temporal reflectance detection method as described in claim 1, characterized in that, The laser signal beam splitting is achieved through a coupler, and the beam splitting ratio is adapted to the link detection requirements of the probe light and the noise detection accuracy requirements of the auxiliary light.

9. The coherent-correlated optical temporal reflectance detection method as described in claim 1, characterized in that, The reflected signals include Rayleigh scattered light signals and Fresnel reflected light signals. When received, the light signals are converted into electrical signals by avalanche photodiodes and then digitally processed.

10. A coherent-correlated optical temporal reflectance detection system, characterized in that, The coherent-correlated optical temporal reflectance detection system includes: The transmitting module is used to generate a stable continuous laser signal and split it into a probe light and an auxiliary light. The probe light is encoded and modulated and then injected directionally into the fiber under test. The auxiliary detection module receives the auxiliary light output from the transmitting module, processes it through self-heterodyne or self-zero difference interference and converts it into an electrical signal, and outputs a phase difference digital signal reflecting the phase noise of the laser after digitization. The receiving module is used to receive the reflected signal returned by the optical fiber under test, amplify it, complete photoelectric conversion and digital processing, and output the reflected digital signal. The signal processing module receives the phase difference digital signal from the auxiliary detection module and the reflected digital signal from the receiving module, generates a local reference signal that is of the same origin as the probe light encoding, reconstructs the time-series instantaneous phase noise information based on the phase difference digital signal, performs phase adjustment on the local reference signal to generate a phase-compensated local reference signal, performs sliding window correlation operation on the reflected digital signal and the phase-compensated local reference signal, extracts the optical fiber link reflection characteristic information, and locates the fault point.

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