Optical time domain reflection system based on single photon detection and measurement method

Abstract

The invention provides an optical time domain reflection system based on single photon detection and a measurement method, and relates to the technical field of optical fiber sensing and quantum detection. According to the optical time domain reflection system based on single photon detection, a 1310 nm wave band pulse light source module is selected to provide a high-performance detection light source, a high-sensitivity single photon detector is adapted, and a wave band optical circulator reduces the insertion loss of a device; the single-photon-level detection sensitivity of the single-photon detector greatly improves the capturing capability of the optical time domain reflection system for weak backward Rayleigh scattering signals, and even in a long-distance transmission scene, weak optical signals after attenuation can still be effectively recognized, and the dynamic range of the optical time domain reflection system is remarkably widened; the narrow pulse detection light design is combined with the high time resolution characteristic of the time-to-digital converter, the photon arrival time and the corresponding optical fiber spatial position can be accurately positioned, the inherent contradiction between the dynamic range and the spatial resolution of a traditional OTDR is broken, and collaborative optimization of the two is achieved.

Description

Technical Field

[0001] This application relates to the fields of fiber optic sensing and quantum detection technology, and in particular to an optical time-domain reflectometry system and measurement method based on single-photon detection. Background Technology

[0002] An optical time-domain reflectometer (OTDR) is a core instrument used in the construction and maintenance of fiber optic networks for fault location, loss measurement, and performance evaluation. By analyzing the backscattering and Fresnel reflection signals generated during the transmission of an input optical pulse signal through the fiber, it can locate and evaluate fiber transmission loss, breakage loss, and connector insertion loss. Traditional OTDRs use analog detection technology, which has an inherent contradiction between dynamic range and spatial resolution, making it difficult to detect weak backscattering signals over long distances.

[0003] By replacing the photodetector in a traditional OTDR system with a single-photon detector, a single-photon detection time-domain reflectometry (PC-OTDR) system is constructed. This changes the detection mode from "measuring average power" to "statistically analyzing the photon arrival time distribution." By digitally accumulating extremely low-energy backscattered signals, the performance limitations of the aforementioned system are overcome in principle.

[0004] The 1310nm band, as the low-dispersion window of optical fiber, is widely used in metropolitan area networks and access networks. However, single-photon detectors (such as InGaAs / InP SPADs) suitable for this band suffer from a "dead time" problem during detection. This means that when strong Fresnel reflection points exist in the fiber optic link (such as connectors), the strong reflected signal saturates the SPAD (Single Photon Avalanche Diode) and enters a dead time. During this period, it cannot respond to subsequent photons, resulting in the inability to detect the following scattered signal, creating a dip or distortion on the OTDR curve, i.e., a "dead zone." Here, InGaAs / InP is a material system where the InGaAs layer absorbs photons in specific bands (such as 1310nm, 1550nm, etc.), while the InP layer mainly serves as the region where avalanche multiplication occurs. This material combination makes them particularly suitable for near-infrared applications such as optical fiber communication and lidar.

[0005] Therefore, there is an urgent need for an optical temporal reflectance system and testing scheme that can effectively overcome the dead time limitation of single-photon detectors and achieve high dynamic range and high spatial resolution in the 1310nm band. Summary of the Invention

[0006] In view of the above problems, this application is made to provide an optical time-domain reflectometry system and measurement method based on single-photon detection that overcomes or at least partially solves the above problems. The technical solution is as follows: In the first aspect, an optical time-domain reflectometry system based on single-photon detection is provided, comprising: a pulsed light source module, an optical attenuator, an optical circulator, an optical fiber under test, a delay generator, an acousto-optic modulator, a single-photon detector, a time-to-digital converter, and a host computer; The pulsed light source module is used to generate narrow pulsed light signals in the 1310nm band to provide a detection light source for the optical time-domain reflectometry system. An optical attenuator, connected after the output of the pulse light source module, is used to attenuate narrow pulse optical signals; An optical circulator enables unidirectional low-loss transmission of optical signals, transmitting the backlight signal in the optical fiber under test to the single-photon detector and effectively isolating the backlight signal from entering the pulsed light source module. A delay generator, preceding the acousto-optic modulator, is used to generate pulse signals and apply a delay to the pulse signals; An acousto-optic modulator modulates the backlight signal based on a signal from a delay generator. A single-photon detector is used to convert an optical signal modulated by an acousto-optic modulator into an electrical pulse signal for each photon detected, thereby completing the conversion from optical signal to electrical signal. The time-to-digital converter is used to acquire electrical signals, record the trigger time of the pulse light source module and the cutoff time of the electrical signal of the single-photon detector, and record the number of single photons arriving in a unit time period by statistically analyzing the pulse signals emitted by the single-photon detector in that time period, so as to characterize the intensity of the backlight signal. The host computer is used to process the signals from the time-to-digital converter, calculate the test distance based on the time period and the speed of light propagation in the optical fiber under test, and plot the test distance-light intensity histogram. Combined with the gating system consisting of the delay generator and the acousto-optic modulator, the test distance-light intensity histograms of multiple time periods are reconstructed into signals, which are collectively referred to as the final distortion-free OTDR curve.

[0007] In one possible implementation, a host computer is connected to the pulse light source module, the optical attenuator, the delay generator, and the time-to-digital converter, respectively, to adjust the operating parameters of each device and control the workflow of the optical time-domain reflectometry system.

[0008] In one possible implementation, the pulsed light source module uses gain switching technology to generate light pulses. By loading a pulse with limited pulse width and energy onto it, the pulse width and frequency of the generated light pulses can be flexibly controlled.

[0009] In one possible implementation, the optical circulator can ensure low-loss transmission of the backlight signal and effectively isolate the backlight signal from returning to the pulse light source module, thus preventing damage.

[0010] In one possible implementation, the single-photon detector is an InGaAs / InP APD, where APD stands for avalanche photodiode, operating in free-running or Geiger mode. When the device operates in Geiger mode, it effectively suppresses the afterpulse effect through rapid avalanche quenching. The detection efficiency at 1310nm is 32%, which meets the requirement of not less than 30%.

[0011] In one possible implementation, a delay generator is used to generate a gate control signal to control the opening time of the optical switch and the duration of the gate open state.

[0012] In one possible implementation, when the single-photon detector reaches saturation, it requires a period of recovery and cannot respond to new photons. By using gated signal modulation technology, the limitation of single-photon detector saturation counting can be overcome, enabling the detection of the fiber optic link under test with high dynamic range and strong reflection suppression.

[0013] In one possible implementation, the host computer collects the counting clock cycle information and the corresponding number of photons and plots the OTDR curve of the fiber under test; the host computer is equipped with a graphical display window to display the OTDR curve, and the host computer can be any of a microcontroller, a computer or an embedded processing platform.

[0014] Secondly, a measurement method for an optical time-domain reflectometry system based on single-photon detection is provided, for measuring the optical time-domain reflectometry system based on single-photon detection as described in any of the above claims, the method comprising: Step S1: The pulse light source module injects periodic pulse light signals into the optical fiber under test. When the pulse light signals are transmitted in the optical fiber under test, they generate backlight signals. Step S2: When the pulse light source module outputs a periodic pulse light signal, the synchronous output pulse electrical signal is used as a clock signal and enters the delay generator and the time-to-digital converter respectively. Step S3: The delay generator generates a broadened pulse signal and a delay based on the periodic pulse electrical signal of the pulse light source module, dividing the complete detection cycle into multiple detection segments to form a gating signal, which then enters the acousto-optic modulator. Step S4: The backlight signal is passed through an acousto-optic modulator. The acousto-optic modulator modulates the backlight signal according to the gate signal of the delay generator. A high level signal corresponds to the conduction state, and a low level signal corresponds to the blocking state, so as to control the on and off of the backlight signal. Step S5: The optical signal modulated by the acousto-optic modulator is converted into an electrical pulse signal and counted using a single-photon detector. The counting is performed using a time-to-digital converter, and the counting clock is synchronized with the generation clock of the periodic pulse optical signal in step S1. Step S6: Collect photon count information for each gate cycle, and stitch together the corresponding delay amount based on the photon count information for each gate cycle to draw a complete OTDR curve of the fiber under test.

[0015] In one possible implementation, the host computer is configured to perform the following signal reconstruction process: This causes the spatial positions of the optical fibers corresponding to the gating of different detection pulses to overlap; Based on the measured distance-light intensity histograms of multiple time periods collected by the time-to-digital converter and processed by amplitude reduction, the effective data points of each spatial location under the open door state are extracted. By stitching together all valid data points, a complete optical time-domain reflectometry waveform without dead-time distortion is reconstructed, which is the OTDR curve of the optical fiber under test.

[0016] By employing the above technical solutions, the optical time-domain reflectometry (OTDR) system and measurement method based on single-photon detection provided in this application embodiment utilizes a 1310nm band pulsed light source module to provide a high-performance detection light source, selects a high-sensitivity single-photon detector adapted to the 1310nm band to obtain optimal detection efficiency, and selects a 1310nm band optical circulator to reduce device insertion loss. The single-photon level detection sensitivity of the single-photon detector significantly improves the OTDR system's ability to capture weak backscattered Rayleigh signals. Even in long-distance transmission scenarios, it can still effectively identify attenuated weak light signals, significantly widening the dynamic range of the OTDR system. By adopting a narrow-pulse probe light design combined with the high time resolution characteristics of the time-to-digital converter, it can accurately locate the photon arrival time and the corresponding optical fiber spatial position, achieving centimeter-level spatial positioning accuracy. This breaks the inherent contradiction between the dynamic range and spatial resolution of traditional OTDRs, achieving synergistic optimization of the two.

[0017] Furthermore, through innovative signal reconstruction and external gating collaborative design, the influence of the dead time effect of single-photon detectors is avoided in principle. To address the detector saturation problem caused by strong Fresnel reflection points such as connectors in fiber optic links, the optical time domain reflectometry system can accurately extract effective photon count data that is not affected by dead time interference through gating and delay signals, stitch together a complete test distance-light intensity histogram, and synthesize the final distortion-free OTDR curve, realizing distortion-free signal acquisition across the entire link. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments of this application will be briefly introduced below.

[0019] Figure 1 A structural diagram of an optical temporal reflectance system based on single-photon detection provided in an embodiment of this application is shown. Figure 2 A flowchart is shown below illustrating the measurement method of the optical temporal reflectance system based on single-photon detection provided in an embodiment of this application. Figure 3 A schematic diagram of the dead time defect of a single-photon detector mentioned in an embodiment of this application is shown; Figure 4 This paper shows a schematic diagram of the OTDR curve after gating modulation according to an embodiment of this application; Figure 5 A comparison diagram of gated modulation and non-gated modulation OTDR curves of an embodiment of this application is shown. Detailed Implementation

[0020] Exemplary embodiments of the present application will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this application will be thorough and complete, and will fully convey the scope of the present application to those skilled in the art.

[0021] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such use can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the term "comprising" and its variations should be interpreted as open-ended terms meaning "including but not limited to."

[0022] To address the aforementioned technical problems, embodiments of this application provide an optical temporal reflectance system based on single-photon detection, such as... Figure 1 As shown, the optical time-domain reflectometry system based on single-photon detection may include a pulsed light source module, an optical attenuator, an optical circulator, an optical fiber under test, a delay generator, an acousto-optic modulator, a single-photon detector, a time-to-digital converter, and a host computer; Figure 1 In the diagram, dashed lines represent electrical signals, and solid lines represent optical signals. Specifically: The pulsed light source module is used to generate narrow pulsed light signals in the 1310nm band, providing a high-performance detection light source for the optical time-domain reflectometry system. An optical attenuator, connected after the output of the pulse light source module, is used to attenuate narrow pulse optical signals to prevent the intensity of the backlight signal from being too high during detection, which could lead to saturation of the single-photon detector. An optical circulator enables unidirectional low-loss transmission of optical signals, transmitting the backlight signal in the optical fiber under test to the single-photon detector and effectively isolating the backlight signal from entering the pulsed light source module. A delay generator, preceding the acousto-optic modulator, is used to generate pulse signals and apply a delay to the pulse signals; An acousto-optic modulator modulates the backlight signal based on a signal from a delay generator. A single-photon detector is used to convert an optical signal modulated by an acousto-optic modulator into an electrical pulse signal for each photon detected, thereby completing the conversion from optical signal to electrical signal. The time-to-digital converter is used to acquire electrical signals, record the trigger time of the pulse light source module and the cutoff time of the electrical signal of the single-photon detector, and record the number of single photons arriving in a unit time period by statistically analyzing the pulse signals emitted by the single-photon detector in that time period, so as to characterize the intensity of the backlight signal. The host computer is used to process the signals from the time-to-digital converter, calculate the test distance based on the time period and the speed of light propagation in the optical fiber under test, and plot the test distance-light intensity histogram. The gating system, which consists of a delay generator and an acousto-optic modulator, reconstructs the test distance-light intensity histograms from multiple time periods and synthesizes the final distortion-free OTDR curve.

[0023] This embodiment of the optical time-domain reflectometry (OTDR) system based on single-photon detection quantizes the intensity of the optical signal into discrete photon counts. The detection result directly characterizes the number of photons received by the detector within a specific time window, enabling the detection of weak scattered light signals. This single-photon detection-based OTDR system can be simplified to optical pulse injection into the fiber, backlight signal acquisition, signal processing, and analysis, such as... Figure 1As shown, the pulsed light source module generates periodic narrow-pulse optical signals, which are injected into the optical fiber under test through an optical circulator. The backscattered and back-reflected optical signals, collectively referred to as the backlight signal, are transmitted to an acousto-optic modulator through the optical circulator. The acousto-optic modulator applies gated modulation, and the modulated optical signal is detected by a single-photon detector. This single-photon detector responds to a single photon, outputting an electrical pulse for each detected photon, thus completing the conversion from optical to electrical signal. A time-to-digital converter acquires the electrical signal and records the pulsed light source module's response time. The timing of the generated signal and the cutoff time of the electrical signal from the single-photon detector are used to record the number of single photons arriving within a given time period by statistically analyzing the pulse signals emitted by the single-photon detector within that time period, thus characterizing the intensity of the backlight signal. The host computer is used to decode the signal from the time-to-digital converter, calculate the test distance based on the time period and the propagation speed of light in the optical fiber under test, and plot the test distance-light intensity histogram. A gating system composed of a delay generator and an acousto-optic modulator is used to reconstruct the test distance-light intensity histograms from multiple time periods, synthesizing the final distortion-free OTDR curve.

[0024] This application provides a possible implementation method in which a host computer is connected to the pulse light source module, the optical attenuator, the delay generator, and the time-to-digital converter, respectively, to adjust the working parameters of each device and control the workflow of the optical time-domain reflectometry system.

[0025] This application provides a possible implementation method in which a pulsed light source module generates light pulses using gain switching technology. By applying a pulse-width- and energy-limited current pulse to it, the pulse width and frequency of the generated light pulses can be flexibly controlled. Specifically, the pulsed light source module utilizes gain switching technology to achieve stable periodic pulse width light output by applying a narrow pulse current to the laser diode.

[0026] The selection range of pulsed light source modules can cover products that meet the core functional requirement of "generating periodic laser pulses with a specific pulse width," including commercial solid-state lasers, commercial gas lasers, commercial semiconductor lasers, and commercial dye lasers. Furthermore, the output parameters of the pulsed light source module can be further defined, with the center wavelength of the output probe light set to 1310nm, the pulse width controlled to 1ns, and the repetition frequency adjusted to 1kHz to ensure that the detection performance meets the requirements of the solution. In addition, the pulsed light source module outputs a synchronous electrical signal that is fed into the delay generator and the time-to-digital converter, respectively.

[0027] This application provides a possible implementation method in which an optical attenuator is used to precisely control the intensity of optical fiber pulses during transmission. Its core function is to controllably attenuate the pulsed light signal transmitted in the optical fiber to flexibly adjust the power level of the pulsed light, ensuring that the intensity of the output pulsed light can adapt to the needs of the subsequent optical path system (such as matching the sensitivity range of the detection module, avoiding damage to the device by strong light, etc.), thereby ensuring that the entire optical system can achieve the expected signal transmission and detection functions under stable and suitable light intensity conditions.

[0028] This application provides a possible implementation method whereby an optical circulator ensures low-loss transmission of the backscattered light signal and effectively isolates it from returning to the pulsed light source module, preventing damage. Specifically, the optical circulator injects attenuated pulsed light into the fiber under test, while simultaneously sending the backscattered light signal and Fresnel reflected light signal generated on the fiber under test to an acousto-optic modulator. The optical circulator operates at a wavelength of 1310 nm, with a maximum insertion loss of less than 0.8 dB, isolation greater than 30 dB, crosstalk less than -50 dB, and is insensitive to polarization.

[0029] This application provides a possible implementation method in which the single-photon detector is an InGaAs / InP APD, where APD refers to an avalanche photodiode, which operates in free-running or Geiger mode. When the device operates in Geiger mode, it effectively suppresses the after-pulse effect through rapid avalanche quenching. The detection efficiency at 1310nm is 32%, which meets the requirement of not less than 30%.

[0030] For near-infrared light signals in the 1310nm band, single-photon detectors using InGaAs / InP materials with bandwidth matching achieve the best detection efficiency. The detection process of a single-photon detector is as follows: a reverse bias is applied to the device above the breakdown voltage, putting it into Geiger mode to await triggering. When the light signal is incident, photons are captured by the narrow bandgap absorption layer, generating electron-hole pairs. Charge carriers trigger an avalanche effect in the multiplication layer driven by a high-voltage electric field, forming an amplified current pulse. Subsequently, the bias voltage is reduced through a quenching mechanism (active, passive, or gated) to terminate the avalanche and reset the device. After reset, the over-bias state is restored, preparing for the next detection. Each photon detection generates an electrical pulse signal, which is acquired by a time-to-digital converter. The gating signal divides the complete detection cycle into multiple segments. If a segment has a strong reflection signal causing detector saturation, other segments can still operate normally. During data processing, the effective signals are spliced ​​together to avoid the impact of dead time on the entire detection process. Meanwhile, based on the propagation speed of light in optical fiber v=c / n (where c is the propagation speed of light in vacuum and n is the refractive index of optical fiber, calculated to be approximately 2×10^8 m / s), the time axis is converted into the optical fiber length axis, i.e., the test distance, using the formula L=v×t / 2 (t is the round-trip time of photons). Then, by combining the correspondence between photon count intensity and optical signal attenuation, the optical fiber loss distribution and fault location can be realized.

[0031] This application provides a possible implementation method: a delay generator is used to generate a gating signal to control the opening time of the optical switch and the duration of the gate-open state. Specifically, after receiving a synchronous pulse electrical signal from the pulse light source module, the delay generator uses this signal as an external trigger to generate a synchronous and width-adjustable periodic high and low frequency signal, which enters the acousto-optic modulator.

[0032] The acousto-optic modulator modulates the optical signal based on the periodic high and low electrical frequency signals from the delay generator. High electrical frequency corresponds to an open gate, and low electrical frequency corresponds to a closed gate, thus forming a gated modulation of the optical signal.

[0033] This application provides a possible implementation method where a single-photon detector needs time to recover when it reaches saturation and cannot respond to new photons. By using gated signal modulation technology, the limitation of single-photon detector saturation counting can be overcome, and the detection of the fiber optic link under test with high dynamic range and strong reflection suppression can be achieved.

[0034] This application provides a possible implementation method in which the host computer collects the counting clock cycle information and the corresponding number of photons and plots the OTDR curve of the optical fiber under test; the host computer is provided with a graphical display window to display the OTDR curve, and the host computer can be any one of a microcontroller, a computer or an embedded processing platform.

[0035] Based on the optical time-domain reflectometry system based on single-photon detection provided in the above embodiments, and based on the same inventive concept, this application also provides a measurement method for the optical time-domain reflectometry system based on single-photon detection.

[0036] Figure 2 A flowchart of a measurement method for an optical temporal reflectance system based on single-photon detection, as provided in an embodiment of this application, is shown. Figure 2 As shown, the process includes the following steps S1 to S6: Step S1: The pulse light source module injects periodic pulse light signals into the optical fiber under test. When the pulse light signals are transmitted in the optical fiber under test, they generate backlight signals. Step S2: When the pulse light source module outputs a periodic pulse light signal, the synchronous output pulse electrical signal is used as a clock signal and enters the delay generator and the time-to-digital converter respectively. Step S3: The delay generator generates a broadened pulse signal and a delay based on the periodic pulse electrical signal of the pulse light source module, dividing the complete detection cycle into multiple detection segments to form a gating signal, which then enters the acousto-optic modulator. Step S4: The backlight signal is passed through an acousto-optic modulator. The acousto-optic modulator modulates the backlight signal according to the gate signal of the delay generator. A high level signal corresponds to the conduction state, and a low level signal corresponds to the blocking state, so as to control the on and off of the backlight signal. Step S5: The optical signal modulated by the acousto-optic modulator is converted into an electrical pulse signal by a single-photon detector, and counted using a time-to-digital converter. The counting clock is synchronized with the generation clock of the periodic pulse optical signal in step S1. Step S6: Collect photon count information for each gate cycle, and stitch together the corresponding delay amount based on the photon count information for each gate cycle to draw a complete OTDR curve of the fiber under test. Here, the number of photon counts represents the light intensity.

[0037] This application embodiment provides a possible implementation method in which the host computer is configured to execute the following signal reconstruction process: This causes a certain degree of overlap in the spatial positions of the optical fibers corresponding to the gating of different detection pulses; Based on the measured distance-light intensity histograms of multiple time periods collected by the time-to-digital converter and processed by amplitude reduction, the effective data points of each spatial location under the open door state are extracted. By stitching together all valid data points, a complete optical time-domain reflectometry waveform without dead-time distortion is reconstructed, which is the OTDR curve of the optical fiber under test.

[0038] The optical temporal reflectance system based on single-photon detection of this application will be further described below with reference to specific embodiments. In the specific embodiments, according to... Figure 1Connect all components of the optical time-domain reflectometry (OTDR) system and select a 100-meter-long optical fiber for testing. First, set the delay generator's signal output mode to full high-level output, and keep the acousto-optic modulator's gating signal normally open, at which point the five-gated signal is modulated. The host computer controls the pulse light source module to send pulse signals at a frequency of 1kHz to start the test. After a 20-second test period, the test results are as follows: Figure 3 As shown in the curve, after receiving the Fresnel reflection signal, the single-photon detector saturates and can no longer respond to photon signals. A region with no signal appears on the histogram drawn by the system, which is the event blind zone. Another loss event cannot be displayed in this region, causing the system to miss the report.

[0039] Afterwards, the host computer maintains the pulse light source module sending pulse signals at a frequency of 1kHz, sets the output signal of the delay generator to a periodic high and low level signal, and sets the period of the high level to 1 / 6 of the pulse light signal period, and increases the delay sequentially. That is, by applying a gating signal, the entire fiber optic test process is divided into 6 segments, with each segment tested for 10 seconds. The results of splicing the 6 test curves are as follows. Figure 4 As shown in the middle curve, no [symbol] appeared. Figure 3 The event blind zone is shown in the figure. Furthermore, comparing the two curves reveals that, compared to the ungated mode, the dynamic range of the optical temporal reflectometry system based on single-photon detection is improved by approximately 3 dBm, such as... Figure 5 As shown.

[0040] This embodiment proposes an optical time-domain reflectometry (OTDR) system and measurement method based on single-photon detection. Leveraging the high sensitivity of single-photon detectors and the high temporal resolution of single-photon counting, this OTDR system features high spatial resolution, high sensitivity, large dynamic range, simple implementation, and integrability. Appropriate types of single-photon detectors can be selected according to different operating wavelength requirements, making it widely applicable in the field of dynamic monitoring of fiber optic link performance. Furthermore, by using a signal delay unit and an acousto-optic modulator to modulate the intensity of the backscattered light signal generated by the optical path system under test, gating of the backscattered signal is achieved. This ensures that only signals within the gating signal's open time can be detected by the single-photon detector, effectively reducing the system's event blind zone while improving its dynamic range.

[0041] Meanwhile, a gated signal modulation method is proposed, which achieves external gate control of the optical signal by applying a delay to the generation clock of periodic pulse light, and concentrates the photon counting from the entire measurement fiber range to the external gate range. The intensity of the counting signal within the gate range is increased by increasing the intensity of the injected probe light. Combined with the synchronous scanning of the gated signal, a large dynamic range measurement of the entire measurement fiber is achieved, which breaks through the bottleneck of limited dynamic range in conventional schemes and signal loss caused by the dead time of single photon detectors.

[0042] Those skilled in the art will understand that the technical solution of this application, or all or part of it, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several program instructions to cause an electronic device (e.g., a personal computer, server, or network device) to execute all or part of the steps of the methods described in the embodiments of this application when running the program instructions. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, portable hard drive, read-only memory (ROM), random access memory (RAM), magnetic disk, or optical disk.

[0043] Alternatively, all or part of the steps of the foregoing method embodiments can be implemented by hardware (such as electronic devices like personal computers, servers, or network devices) related to program instructions. The program instructions can be stored in a computer, and when the program instructions are executed by the processor of the electronic device, the electronic device executes all or part of the steps of the methods described in the embodiments of this application.

[0044] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that within the spirit and principles of this application, modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the corresponding technical solutions to leave the protection scope of this application.

Claims

1. A single-photon-detection-based optical time-domain reflectometry system, characterized by, It comprises: Pulse light source module, optical attenuator, optical circulator, optical fiber to be measured, delay generator, acousto-optic modulator, single photon detector, time-to-digital converter, host computer; The pulse light source module is used for generating a narrow pulse light signal in a 1310 nm wave band, so as to provide a detection light source for an optical time domain reflectometry system. The optical attenuator is connected behind the output end of the pulse light source module, and is used for attenuating the narrow pulse light signal. The optical circulator realizes one-way low-loss transmission of the optical signal, transmits the back light signal in the optical fiber to be measured to the single photon detector, and effectively isolates the back light signal from entering the pulse light source module. The delay generator is used for generating a pulse signal and applying a delay to the pulse signal before the acousto-optic modulator. The acousto-optic modulator modulates the back light signal based on the signal of the delay generator. The single photon detector is used for converting the optical signal modulated by the acousto-optic modulator into an electrical signal. The time-to-digital converter is used for collecting the electrical signal, recording the time of the trigger electrical signal of the pulse light source module and the cutoff time of the electrical signal of the single photon detector, and recording the number of single photons arriving in a time period by counting the pulse signals emitted by the single photon detector in the time period, so as to represent the intensity of the back light signal. The host computer is used for solving the signal of the time-to-digital converter, calculating the test distance according to the time period and the propagation speed of light in the optical fiber to be measured, and drawing a test distance-light intensity histogram. The gating system composed of the delay generator and the acousto-optic modulator reconstructs the test distance-light intensity histograms of multiple time periods to synthesize a final non-distorted OTDR curve.

2. The single-photon-detection-based optical time-domain reflection system according to claim 1, wherein, The host computer is connected with the pulse light source module, the optical attenuator, the delay generator and the time-to-digital converter respectively, adjusts the working parameters of the devices, and controls the working process of the optical time domain reflectometry system.

3. The single-photon-detection-based optical time-domain reflection system of claim 1, wherein, The pulse light source module generates optical pulses by using gain switching technology, and can flexibly control the pulse width and frequency of the generated optical pulses by loading current pulses with limited pulse width and energy on the pulse light source module.

4. The single-photon-detection-based optical time-domain reflection system of claim 1, wherein, The optical circulator can ensure low-loss transmission of the back light signal and effectively isolate the back light signal from returning to the pulse light source module, thereby avoiding damage.

5. The single-photon-detection-based optical time-domain reflection system of claim 1, wherein, The single photon detector is an InGaAs / InP APD, where APD refers to an avalanche photodiode, which works in a free-running or Geiger mode; the device works in the Geiger mode, effectively suppresses the after-pulse effect through fast avalanche quenching, and has a detection efficiency of 32% in the 1310 nm wave band, which meets the requirement of not less than 30%.

6. The single-photon-detection-based optical time-domain reflection system of claim 1, wherein, The delay generator is used for generating a gating signal to control the opening time of the optical switch and the duration of the gate opening state.

7. The single-photon-detection-based optical time-domain reflection system of claim 1, wherein, The single photon detector needs a period of time to recover when its technology reaches saturation, and cannot respond to new photons. The gating signal modulation technology is used to overcome the limitation of saturated counting of the single photon detector.

8. The single-photon-detection-based optical time-domain reflection system of claim 1, wherein, The host computer collects clock period information and corresponding photon numbers and draws an OTDR curve of the optical fiber to be measured; the host computer has a graphic display window to display the OTDR curve, and the host computer is any one of a single chip microcomputer, a computer or an embedded processing platform.

9. A measurement method of a single-photon-detection-based optical time domain reflection system, for measuring the single-photon-detection-based optical time domain reflection system according to any one of claims 1 to 8, characterized in that, The method comprises: Step S1, the pulsed light source module injects a periodic pulsed light signal into the optical fiber to be measured, and the pulsed light signal generates a backscattered light signal when it is transmitted in the optical fiber to be measured; Step S2, when the pulsed light source module outputs the periodic pulsed light signal, a synchronous output pulsed electrical signal is output as a clock signal, which enters the delay generator and the time-to-digital converter respectively; Step S3, the delay generator generates a stretched pulse signal and a delay according to the periodic pulsed electrical signal of the pulsed light source module, divides the complete detection period into multiple detection periods, forms a gating signal, and the gating signal enters the acousto-optic modulator; Step S4, the backscattered light signal passes through the acousto-optic modulator, and the acousto-optic modulator modulates the backscattered light signal according to the gating signal of the delay generator, the high-level signal corresponds to the on state, and the low-level signal corresponds to the blocking state, so as to control the on-off of the backscattered light signal; Step S5, the single-photon detector converts the light signal modulated by the acousto-optic modulator into an electrical pulse signal and counts, and the time-to-digital converter is used for counting, and the counting clock is synchronized with the generation clock of the periodic pulsed light signal in step S1; Step S6, collect the photon counting information of each gating period, splice the corresponding delay amount according to the photon counting information of each gating period, and draw the OTDR curve of the optical fiber to be measured.

10. The measurement method of a single-photon-detection-based optical time domain reflection system according to claim 9, wherein, The upper computer is configured to perform the following signal reconstruction process: Make the gating of different detection pulses corresponding to the spatial position of the optical fiber have overlap; Based on the test distance-intensity histogram of the multiple time periods processed by the amplitude reduction collected by the time-to-digital converter, extract the effective data points in the open state of each spatial position; Splice all effective data points to reconstruct a complete and dead-time distortion-free optical time domain reflectometry waveform diagram, i.e. the OTDR curve of the optical fiber to be measured.

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