Special optical time domain reflectometer for hollow-core optical cable

Abstract

The invention discloses an optical time domain reflectometer special for a hollow-core optical cable, relates to the technical field of optical communication detection, and aims to solve the problems that an existing optical time domain reflectometer cannot adapt to detection of the hollow-core optical cable, is weak in low backscattering signal capturing capability, poor in operation and maintenance adaptability and the like. The reflectometer comprises a detection module, a light path module, a signal processing module, a fault identification and positioning module, a data interaction module and a power supply module. The detection module is optimally designed based on a photon counting detection principle, the optical path module realizes S + C + L ultra-wideband full coverage and adapts to common wavebands of the air-core optical cable, the signal processing module is internally provided with a special algorithm to improve the detection performance, equipment is convenient to receive after the modules are integrated and optimized, and accurate identification and positioning of various faults of the air-core optical cable can be realized. And data storage, export and remote transmission are supported. According to the invention, on-site mobile operation and maintenance requirements of the hollow-core optical cable are met, the detection efficiency and precision are improved, the industrial operation and maintenance cost is reduced, and technical support is provided for large-scale application of the hollow-core optical cable.

Description

Technical Field

[0001] This invention relates to the technical field of optical communication detection, and more particularly to an optical time domain reflectometer for hollow optical cables. Background Technology

[0002] With the rapid development of optical communication technology, hollow-core optical fiber has completed research and testing. In the future, hollow-core optical cables will be gradually applied to communication networks on a large scale, triggering a major transformation in the field of communication network maintenance. Compared with traditional optical cables, hollow-core optical cables have significant differences in transmission characteristics and structural design, resulting in existing optical time-domain reflectometers being unable to directly adapt to the detection needs of hollow-core optical cables. The main technical pain points are as follows: First, the detection module of existing reflectometers is insufficient in capturing the low backscattered signals generated during the transmission of hollow-core optical cables, failing to meet the requirements for accurate detection. Second, the optical path design of existing equipment is only compatible with the commonly used bands of traditional optical cables, and cannot cover the commonly used bands of hollow-core optical cables such as 1550nm, 1625nm, and 1700nm, resulting in poor detection compatibility. Third, there is a lack of signal processing algorithms specifically for hollow-core optical cables, resulting in low signal-to-noise ratios, weak fault discrimination capabilities, and difficulty in identifying typical faults such as fiber breaks, abnormal splices, and moisture intrusion. Fourth, existing equipment is large and heavy, making it inconvenient for on-site mobile operations, and its data interaction method is singular, making it unsuitable for the field and distributed operation and maintenance scenarios of hollow-core optical cables.

[0003] Currently, the large-scale application of hollow-core optical cables is in the preparatory stage. However, the supporting testing technologies and equipment are not yet perfect. Numerous shortcomings of existing optical time-domain reflectometers (OTDRs) result in high maintenance costs and limited efficiency for hollow-core optical cables, becoming a key bottleneck restricting their widespread application. Therefore, developing a dedicated OTD that meets the testing needs of hollow-core optical cables, boasts superior performance, and is easy to maintain, thereby completing the technological layout in advance, addressing the core pain points of outsourced maintenance in the industry, reducing maintenance costs, and supporting the large-scale application of hollow-core optical cables, has become a pressing technical problem for those skilled in the art. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the prior art and provide a dedicated optical time domain reflectometer for hollow optical cables.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An optical time domain reflectometer for hollow optical cables is provided, comprising a detection module, an optical path module, a signal processing module, a fault identification and location module, a data interaction module, and a power supply module; The detection module is designed based on the photon counting detection principle and is used to capture low backscattering signals generated during the transmission of hollow optical cables. The optical path module is used to realize the transmission, reception and transmission of optical signals; The signal processing module incorporates a pulse regeneration algorithm, a noise suppression algorithm, and a reflection signal recognition algorithm to process the optical signals captured by the detection module, thereby improving the signal-to-noise ratio and fault identification capability. The fault identification and location module is used to identify and locate the fault types of the hollow optical cable. The fault types include at least fiber breakage, abnormal splice, and moisture intrusion. The data interaction module is used to store, export, and remotely transmit optical signal detection data; The detection module, optical path module, signal processing module, fault identification and location module, and data interaction module are integrated and optimized through optical path design and hardware layout to adapt to mobile operations on site. The power module provides a stable power supply to the above modules.

[0006] Preferably, the detection module includes a photon counting detector, a signal amplification unit, and a signal filtering unit. The photon counting detector is used to receive the backscattered signal from the hollow optical cable, the signal amplification unit is used to amplify the received weak signal, and the signal filtering unit is used to filter out noise in the signal and improve the capture accuracy of low backscattered signals.

[0007] Preferably, the dynamic reference voltage generation circuit is electrically connected to the preset target voltage adjustment module. The commonly used operating wavelengths of the hollow optical cable adapted to the optical path module include 1550nm, 1625nm and 1700nm. The optical path module includes an optical emitting unit, an optical receiving unit and an optical coupling unit. The optical emitting unit selectively emits probe optical signals of the corresponding wavelength band. The optical coupling unit is used to realize the transmission of the probe optical signal and the separation of the backscattered signal. The optical receiving unit is used to receive the separated backscattered signal and transmit it to the detection module.

[0008] Preferably, the pulse regeneration algorithm is used to compensate and regenerate the emitted probe light pulse signal to avoid detection errors caused by pulse signal attenuation; the noise suppression algorithm adopts an adaptive threshold noise reduction mechanism to filter out environmental noise and internal equipment noise; the reflection signal identification algorithm is used to distinguish between normal reflection signals and fault reflection signals of hollow optical cables to improve the accuracy of fault identification.

[0009] Preferably, the fault identification and location module includes a signal feature extraction unit, a fault type matching unit, and a location calculation unit; the signal feature extraction unit is used to extract the amplitude, waveform, and time delay feature parameters of the fault reflection signal; the fault type matching unit matches the extracted feature parameters with a preset fault feature library to determine the fault type; the location calculation unit calculates and determines the specific location of the fault point based on the optical signal transmission speed and reflection time delay.

[0010] Preferably, the data interaction module includes a storage unit, an interface unit, and a remote transmission unit; the storage unit is used to store detection data; the interface unit includes a USB interface and an Ethernet interface for data export; the remote transmission unit supports wireless transmission and is used to transmit detection data to the back-end operation and maintenance management platform in real time.

[0011] Preferably, the optical path design adopts an integrated optical path structure to reduce optical path loss and improve optical signal transmission efficiency; the hardware layout adopts a modular design, with each functional module independently packaged.

[0012] Preferably, the device also includes a display module, which is used to display detection data, fault type, fault location and equipment operating status in real time. The display module adopts a high-definition touch screen and supports operation command input.

[0013] Preferably, the pulse regeneration algorithm is implemented as follows: the FPGA module of the signal processing module acquires the original probe light pulse signal output by the optical transmitting unit, and simultaneously acquires the attenuated pulse signal fed back by the optical receiving unit and establishes the correspondence between the two; the amplitude attenuation, waveform distortion parameters and time delay deviation of the attenuated pulse signal are extracted, and a multinomial fitting algorithm is used to generate a compensation coefficient that is dynamically adjusted in real time. The compensation coefficient is adapted to the pulse attenuation difference under different transmission distances; based on the compensation coefficient, the attenuated pulse signal is subjected to amplitude compensation, waveform correction and time delay calibration with the original probe light pulse signal as a reference to ensure that the waveform similarity between the regenerated pulse and the original probe light pulse signal is greater than a preset threshold; the calibrated regenerated pulse signal is shaped and filtered to remove the noise introduced during the compensation process and output a stable regenerated pulse signal.

[0014] Preferably, the fault identification and location module calculates the fault point using the following formula: L = v × t / 2; where L is the distance to the fault point, v is the optical signal transmission speed, and t is the reflection delay. The distance L calculated from the test point is the location of the fault point.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. Strong adaptability and comprehensive testing coverage: The optical path module has been optimized to adapt to the commonly used wavelengths of hollow optical cables such as 1550nm, 1625nm, and 1700nm, achieving full coverage testing of the S+C+L ultra-wide band. This completely solves the problem that existing reflectors cannot adapt to the wavelength requirements of hollow optical cables and can meet the testing needs of hollow optical cables of different specifications.

[0016] 2. High detection accuracy and accurate fault identification: The detection module has an optimized structure based on the photon counting detection principle, which greatly improves the ability to capture low backscattered signals from hollow optical cables; the signal processing module has built-in dedicated algorithms for pulse regeneration, noise suppression, and reflection signal identification, which effectively improves the signal-to-noise ratio and fault discrimination capability. Combined with the fault identification and positioning module, it can accurately identify various fault types such as fiber breakage, abnormal splice, and water vapor intrusion, with a positioning error of ≤±1m, ensuring detection accuracy.

[0017] 3. Convenient operation and maintenance, suitable for field operations: By optimizing the optical path design and hardware layout, the functional modules are integrated and set up, reducing the size and weight of the equipment, making it easy to move and carry on site, and suitable for field, distributed and other hollow optical cable operation and maintenance scenarios; at the same time, it supports data storage, export and 4G / 5G and WiFi remote transmission, and can realize real-time synchronization of test data to the background operation and maintenance management platform, improving operation and maintenance efficiency.

[0018] 4. Reduced operation and maintenance costs and support for large-scale application: This invention specifically addresses the core pain points of hollow optical cable maintenance, enabling efficient and accurate testing of hollow optical cables without significant adjustments to existing operation and maintenance processes. This reduces manpower and equipment wear and tear, significantly lowering industry operation and maintenance costs. Simultaneously, it provides reliable testing technology support for the large-scale promotion and application of hollow optical cables, filling the technological gap in dedicated testing equipment for hollow optical cables and demonstrating broad application prospects.

[0019] 5. High practicality and good environmental adaptability: The equipment adopts a dual power supply mode of lithium battery and external power supply. It can work continuously for ≥8 hours when fully charged, which is suitable for on-site environments without power supply. The shell is made of waterproof and dustproof material with a protection level of ≥IP65, which can adapt to harsh outdoor working environments and further improve the on-site applicability of the equipment. Attached Figure Description

[0020] Figure 1 This is a frame diagram of a dedicated optical time domain reflectometer for hollow optical cables in a specific embodiment of the present invention; Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0022] refer to Figure 1As shown, the optical time domain reflectometer for hollow optical cables in this embodiment includes a detection module, an optical path module, a signal processing module, a fault identification and location module, a data interaction module, a power supply module, a display module, and a waterproof and dustproof housing. Each functional module adopts a modular integrated design. Through optimized optical path design and hardware layout, the overall volume of the equipment is controlled to 10 cubic decimeters and the weight is controlled to within 4 kg, which meets the needs of on-site mobile operation. The housing is made of waterproof and dustproof ABS material, with a protection level of IP65, which can adapt to harsh working environments such as high temperature, rain, and dust. It includes a detection module, an optical path module, a signal processing module, a fault identification and location module, a data interaction module, and a power supply module. The detection module is designed based on the photon counting detection principle and is used to capture low backscattering signals generated during the transmission of hollow optical cables. The detection module includes a photon counting detector, a signal amplification unit, and a signal filtering unit. The photon counting detector is an avalanche photodiode (APD) with a response wavelength range of 1500-1750nm, which can efficiently receive low backscattered signals generated during hollow optical cable transmission. The signal amplification unit uses a low-noise operational amplifier with an adjustable gain range of 40-60dB, which can amplify weak backscattered signals to a processable range. The signal filtering unit uses a bandpass filter with a center wavelength adapted to the three core bands of 1550nm, 1625nm, and 1700nm, and a bandwidth of ±10nm, which effectively filters out environmental noise and internal equipment noise, improving the capture accuracy of low backscattered signals.

[0023] The optical path module is used to realize the transmission, reception and transmission of optical signals; The optical path module includes an optical transmitting unit, an optical receiving unit, and an optical coupling unit, used to realize the transmission, reception, and transmission of optical signals. It is compatible with the commonly used operating bands of hollow optical cables and achieves full coverage detection of the S+C+L ultra-wideband. The optical transmitting unit adopts a distributed feedback laser (DFB), which can selectively emit probe light pulse signals in three bands: 1550nm, 1625nm, and 1700nm. The pulse width is adjustable from 1ns to 10μs, and the output optical power is 0-10dBm. The optical coupling unit adopts an optical fiber coupler with a coupling ratio of 50:50 and an insertion loss of ≤0.5dB. It is used to realize the transmission of probe light signals to hollow optical cables and the separation of backscattered signals reflected back from hollow optical cables from probe light signals. The optical receiving unit adopts an optical fiber collimator with a receiving efficiency of ≥90%, which accurately transmits the separated backscattered signals to the photon counting detector of the detection module.

[0024] The signal processing module incorporates a pulse regeneration algorithm, a noise suppression algorithm, and a reflection signal recognition algorithm to process the optical signals captured by the detection module, thereby improving the signal-to-noise ratio and fault identification capability. The signal processing module adopts an FPGA+ARM dual-core architecture and incorporates pulse regeneration, noise suppression, and reflection signal recognition algorithms to process the optical signals captured by the detection module, improving the signal-to-noise ratio and fault discrimination capability. The pulse regeneration algorithm uses an adaptive pulse compensation mechanism to compensate for and regenerate the attenuated detection optical pulse signal during transmission, avoiding detection errors caused by pulse signal attenuation, with a pulse regeneration accuracy ≤0.1ns. The noise suppression algorithm uses an adaptive threshold noise reduction mechanism, which can automatically adjust the noise reduction threshold according to the ambient noise intensity, improving the signal-to-noise ratio to over 30dB. The reflection signal recognition algorithm uses a machine learning model to distinguish between normal reflection signals and fault reflection signals of hollow optical cables through a pre-trained fault signal feature library, with a fault signal recognition accuracy ≥98%.

[0025] (1) Implementation process of pulse regeneration algorithm: First, the original probe light pulse signal output by the optical transmitting unit is acquired through the FPGA module, and the attenuated pulse signal fed back by the optical receiving unit is acquired simultaneously to establish the correspondence between the original pulse and the attenuated pulse. Second, based on the adaptive pulse compensation mechanism, the amplitude attenuation, waveform distortion parameters, and time delay deviation of the attenuated pulse are extracted. Compensation coefficients are generated through a polynomial fitting algorithm, and the compensation coefficients are dynamically adjusted in real time to adapt to the pulse attenuation differences under different transmission distances. Then, the attenuated pulse signal is subjected to amplitude compensation, waveform correction, and time delay calibration according to the compensation coefficients. During the correction process, the original pulse signal is used as the reference to ensure that the waveform similarity between the regenerated pulse and the original pulse is ≥99%. Finally, the regenerated pulse signal is shaped and filtered to remove the noise introduced during the compensation process and output a stable regenerated pulse signal. The pulse regeneration accuracy is required to be ≤0.1ns to avoid detection errors caused by pulse signal attenuation and to provide a reliable pulse reference for subsequent signal processing.

[0026] (2) Implementation process of noise suppression algorithm: The first step involves collecting ambient noise and internal noise from the device during the initialization phase when no detection signal is detected, establishing a noise sample library. This library includes noise characteristics under different environments, such as high temperature, heavy rain, and dust, and is stored in the ARM module's storage unit. The second step involves simultaneously collecting the mixed signal transmitted by the detection module during signal detection. This mixed signal includes backscattered signals, fault reflection signals, and noise. A frequency domain decomposition algorithm is used to decompose the mixed signal into signal and noise frequency bands, with the noise frequency band being matched and identified based on the noise sample library. The third step employs an adaptive threshold noise reduction mechanism. Based on the current ambient noise intensity, the ARM module calculates a dynamic noise reduction threshold in real time, with the threshold adjustment range between 0.1 and 1 dB, avoiding signal distortion or incomplete noise reduction caused by a fixed threshold. The fourth step involves suppressing and filtering the noise frequency band in the mixed signal. A wavelet denoising algorithm is used to further eliminate residual noise while preserving the effective characteristics of the signal frequency band, ultimately improving the signal-to-noise ratio to over 30 dB, ensuring that weak fault reflection signals can be effectively identified.

[0027] (3) Implementation process of the reflected signal recognition algorithm: First, the noise-suppressed net signal is preprocessed by time-domain filtering and amplitude normalization to extract time-domain and frequency-domain features with an extraction accuracy of ≤0.01dB. The preprocessed signal is then transmitted to the ARM module for subsequent identification. Second, a pre-trained machine learning model (using a Support Vector Machine (SVM) model) is invoked. This model is trained based on a large number of normal and fault reflection signals from hollow optical cables. The preset fault feature library includes feature parameters for three typical faults: fiber breakage, abnormal splice points, and moisture intrusion. The feature library can be updated and upgraded via a remote transmission unit. Then, the extracted signal feature parameters are input into the machine learning model and matched with the feature parameters in the preset fault feature library. The matching threshold is set to 95%. When the similarity is ≥95%, the signal is identified as a fault of the corresponding type; when the similarity is <95%, it is identified as a normal reflection signal. Finally, the identification result (normal signal / fault type) is output, and the identified fault signal feature parameters are transmitted to the fault identification and location module to provide data support for fault location. The fault signal identification accuracy is ≥98%.

[0028] The fault identification and location module is used to identify and locate the fault types of the hollow optical cable. The fault types include at least fiber breakage, abnormal splice, and moisture intrusion. The fault identification and location module includes a signal feature extraction unit, a fault type matching unit, and a location calculation unit. The signal feature extraction unit extracts characteristic parameters such as amplitude, waveform, and time delay of the fault reflection signal. The fault type matching unit matches the extracted characteristic parameters with a preset fault feature library, which includes characteristic parameters for three typical faults: fiber breakage, abnormal splice points, and moisture intrusion, enabling rapid fault type determination. The location calculation unit calculates the specific location of the fault point based on the transmission speed and reflection delay of the optical signal in the hollow optical cable using the formula L=v×t / 2 (where L is the distance to the fault point, v is the optical signal transmission speed, and t is the reflection delay). The optical signal transmission speed in the hollow optical cable is calculated as 2.0×10⁻⁶. 8 With a speed of m / s, the positioning error is ≤ ±1m, which can accurately locate the fault point.

[0029] The data interaction module is used to store, export, and remotely transmit optical signal detection data; In this embodiment, the data interaction module includes a storage unit, an interface unit, and a remote transmission unit. The storage unit uses an SD card with a storage capacity of 64GB, capable of storing at least 1000 sets of detection data. It supports cyclic storage, and the data storage format is CSV for easy viewing and analysis later. The interface unit includes a USB 3.0 interface and an Ethernet interface. The USB 3.0 interface is used for data export, and the Ethernet interface is used for wired data transmission. The remote transmission unit supports dual-mode wireless transmission of 4G / 5G and WiFi. The WiFi supports the 802.11b / g / n protocol, which can transmit the detection data to the backend operation and maintenance management platform in real time, realizing remote monitoring and data sharing.

[0030] The detection module, optical path module, signal processing module, fault identification and location module and data interaction module are integrated and set up. Through optical path design and hardware layout optimization, the overall volume of the equipment is controlled to 10 cubic decimeters and the weight is controlled to less than 4 kg, which is convenient for on-site movement and carrying. It is suitable for field, distributed and other hollow optical cable operation and maintenance scenarios, and facilitates on-site mobile operation. The power module provides a stable power supply to the above modules.

[0031] In this embodiment, the power module adopts a dual power supply mode of lithium battery power supply and external power supply. The lithium battery has a capacity of 20000mAh, supports fast charging mode, fast charging power is 20W, full charge time is ≤2 hours, and it can work continuously for ≥8 hours when fully charged. The external power supply interface is DC12V, which is compatible with AC power (220V) and DC power (12V) on site. It can operate normally in the absence of power supply on site, and provide stable power supply for various functional modules such as detection module, optical path module, and signal processing module. The power supply voltage fluctuation is ≤±0.1V.

[0032] The display module is used to display detection data, fault type, fault location and equipment operating status in real time. The display module adopts a high-definition touch screen and supports operation command input.

[0033] In this embodiment, the display module uses a 7-inch high-definition touchscreen with a resolution of 1280×720 and an adjustable brightness range of 200-500 cd / m². 2 It can clearly display detection data, fault type, fault location, and equipment working status under strong light; it supports touch operation, and can input detection parameters, start detection, export data, and other operation commands through the touch screen, making it convenient to operate and suitable for on-site one-handed operation.

[0034] The optical time domain reflectometer for hollow optical cables in this embodiment operates as follows: 1. Equipment Start-up and Parameter Setting: Connect the power supply (either lithium battery power or external power supply can be selected), start the equipment, and input the detection parameters through the display module, including the detection light band. By selecting any one or more of 1550nm, 1625nm, and 1700nm, you can achieve full coverage detection of the S+C+L ultra-wide band, pulse width, detection distance range, etc. After the parameter settings are completed, connect the equipment to the hollow optical cable to be tested through the optical fiber connector to ensure a reliable connection and no optical path loss.

[0035] 2. Optical Signal Transmission and Detection: The signal processing module controls the optical transmission unit of the optical path module to transmit a detection optical pulse signal with preset wavelength and parameters. The detection optical pulse signal is transmitted to the hollow optical cable to be tested via the optical coupling unit. When the detection optical signal is transmitted in the hollow optical cable, a backscattered signal will be generated. At the same time, if there are faults such as fiber breakage, abnormal splice, or water vapor intrusion in the hollow optical cable, a fault reflection signal will be generated. After the backscattered signal and the fault reflection signal are separated by the optical coupling unit, they are transmitted to the optical receiving unit, which then transmits the optical signal to the detection module.

[0036] 3. Signal Processing and Fault Identification: The photon counting detector of the detection module receives backscattered signals and fault reflection signals. After being amplified by the signal amplification unit and filtered by the signal filtering unit to remove clutter, the signals are transmitted to the signal processing module. The signal processing module compensates and regenerates the signals using a built-in pulse regeneration algorithm, reduces signal noise and improves the signal-to-noise ratio using a noise suppression algorithm, and extracts signal feature parameters using a reflection signal identification algorithm. These feature parameters are then transmitted to the fault identification and location module. The fault identification and location module matches the extracted feature parameters with a preset fault feature database to determine the fault type, and simultaneously calculates the specific location of the fault point using a location calculation unit.

[0037] 4. Data Display and Interaction: The fault identification and location module transmits the fault type, fault location, and detection data (including backscattered signal waveform, signal-to-noise ratio, transmission loss, etc.) to the display module for real-time display to the operator; at the same time, the data interaction module stores the detection data in the storage unit, and the operator can operate through the display module to export the data (via USB interface or Ethernet interface) or transmit it remotely (via 4G / 5G or WiFi to the back-end operation and maintenance management platform).

[0038] 5. End of inspection: After a single inspection is completed, turn off the probe light emission, disconnect the equipment from the hollow optical cable, turn off the equipment power, and the inspection operation is complete; if multiple hollow optical cable sections need to be inspected, repeat the above steps.

[0039] The optical time-domain reflectometer (OTDR) for hollow optical cables in this embodiment was applied to the maintenance and testing of outdoor hollow optical cables. In one embodiment, the length of the hollow optical cable to be tested was 50km. A 1550nm detection band was used, with a pulse width of 10μs and a detection distance range of 0-50km. During the testing process, the device successfully captured an abnormal signal at the splice point at 32km and a water vapor intrusion signal at 45km. After processing by the fault identification and location module, the device accurately displayed the two fault types: splice point abnormality and water vapor intrusion. The location errors were 0.8m and 0.6m, respectively, both meeting the location requirement of ≤±1m. The test data was remotely transmitted to the back-end maintenance management platform via WiFi, allowing operators to remotely view the test results and arrange for maintenance personnel to go to the fault point for handling. The entire testing process took ≤5 minutes. The device is portable and can work continuously for more than 8 hours outdoors in an environment without power supply, effectively improving the efficiency of hollow optical cable maintenance and testing and reducing maintenance costs.

[0040] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A dedicated optical time-domain reflectometer for hollow optical cables, characterized in that, It includes a detection module, an optical path module, a signal processing module, a fault identification and location module, a data interaction module, and a power supply module; The detection module is designed based on the photon counting detection principle and is used to capture low backscattering signals generated during the transmission of hollow optical cables. The optical path module is used to realize the transmission, reception and transmission of optical signals; The signal processing module incorporates a pulse regeneration algorithm, a noise suppression algorithm, and a reflection signal recognition algorithm to process the optical signals captured by the detection module, thereby improving the signal-to-noise ratio and fault identification capability. The fault identification and location module is used to identify and locate the fault types of the hollow optical cable. The fault types include at least fiber breakage, abnormal splice, and moisture intrusion. The data interaction module is used to store, export, and remotely transmit optical signal detection data; The detection module, optical path module, signal processing module, fault identification and location module, and data interaction module are integrated and optimized through optical path design and hardware layout to adapt to mobile operations on site. The power module provides a stable power supply to the above modules.

2. The optical time-domain reflectometer for hollow optical cables according to claim 1, characterized in that, The detection module includes a photon counting detector, a signal amplification unit, and a signal filtering unit. The photon counting detector is used to receive the backscattered signal from the hollow optical cable. The signal amplification unit is used to amplify the received weak signal. The signal filtering unit is used to filter out noise in the signal and improve the capture accuracy of low backscattered signals.

3. The optical time-domain reflectometer for hollow optical cables according to claim 1, characterized in that, The commonly used operating wavelengths of the hollow optical cables adapted to the optical path module include 1550nm, 1625nm, and 1700nm. The optical path module includes an optical emitting unit, an optical receiving unit, and an optical coupling unit. The optical emitting unit selectively emits probe optical signals of the corresponding wavelength band. The optical coupling unit is used to realize the transmission of the probe optical signal and the separation of the backscattered signal. The optical receiving unit is used to receive the separated backscattered signal and transmit it to the detection module.

4. The optical time-domain reflectometer for hollow optical cables according to claim 1, characterized in that, The pulse regeneration algorithm is used to compensate and regenerate the emitted probe light pulse signal to avoid detection errors caused by pulse signal attenuation; the noise suppression algorithm adopts an adaptive threshold noise reduction mechanism to filter out environmental noise and internal equipment noise; the reflection signal identification algorithm is used to distinguish between normal reflection signals and fault reflection signals of hollow optical cables to improve the accuracy of fault identification.

5. The optical time-domain reflectometer for hollow optical cables according to claim 1, characterized in that, The fault identification and location module includes a signal feature extraction unit, a fault type matching unit, and a location calculation unit; the signal feature extraction unit is used to extract the amplitude, waveform, and time delay characteristic parameters of the fault reflection signal; The fault type matching unit matches the extracted feature parameters with a preset fault feature library to determine the fault type; the positioning calculation unit calculates and determines the specific location of the fault point based on the optical signal transmission speed and reflection delay.

6. The optical time-domain reflectometer for hollow optical cables according to claim 1, characterized in that, The data interaction module includes a storage unit, an interface unit, and a remote transmission unit; the storage unit is used to store detection data; the interface unit includes a USB interface and an Ethernet interface for data export; the remote transmission unit supports wireless transmission and is used to transmit detection data to the back-end operation and maintenance management platform in real time.

7. The optical time-domain reflectometer for hollow optical cables according to claim 1, characterized in that, The optical path design adopts an integrated optical path structure to reduce optical path loss and improve optical signal transmission efficiency; the hardware layout adopts a modular design, with each functional module independently packaged.

8. The optical time-domain reflectometer for hollow optical cables according to claim 1, characterized in that, It also includes a display module, which is used to display detection data, fault type, fault location and equipment working status in real time. The display module adopts a high-definition touch screen and supports operation command input.

9. The optical time-domain reflectometer for hollow optical cables according to claim 1, characterized in that, The system also includes a display module. The pulse regeneration algorithm is implemented as follows: the FPGA module of the signal processing module acquires the original probe light pulse signal output by the optical transmitting unit, and simultaneously acquires the attenuated pulse signal fed back by the optical receiving unit and establishes the correspondence between the two; the amplitude attenuation, waveform distortion parameters and time delay deviation of the attenuated pulse signal are extracted, and a multinomial fitting algorithm is used to generate a compensation coefficient that is dynamically adjusted in real time. The compensation coefficient is adapted to the pulse attenuation difference under different transmission distances; based on the compensation coefficient, the attenuated pulse signal is compensated for amplitude, corrected for waveform and calibrated for time delay, with the original probe light pulse signal as the reference, to ensure that the waveform similarity between the regenerated pulse and the original probe light pulse signal is greater than a preset threshold. The calibrated regenerated pulse signal is shaped and filtered to remove noise introduced during the compensation process, and a stable regenerated pulse signal is output.

10. The optical time-domain reflectometer for hollow optical cables according to claim 1, characterized in that, It also includes a display module, and the fault identification and location module calculates the fault point using the following formula: L = v × t / 2; where L is the distance to the fault point, v is the optical signal transmission speed, and t is the reflection delay. The distance L calculated from the test point is the location of the fault point.

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