Multi-channel optical fiber diagnosis method and system based on single photon counting

Abstract

The embodiment of the invention provides a multi-channel optical fiber diagnosis method and system based on single photon counting, and belongs to the technical field of optical fiber sensing. A multi-channel optical fiber diagnosis method based on single photon counting comprises the following steps: acquiring link identification information of a multi-branch optical fiber link, and distributing a corresponding single photon counting channel and a corresponding channel time delay calibration parameter for each optical fiber link based on the link identification information; injecting a detection pulse into each optical fiber link based on a single photon pulse light source, and starting a counting window of each single photon counting channel to obtain a corresponding photon arrival time sequence; constructing alignment echo data corresponding to each optical fiber link; and performing adaptive counting control on each single photon counting channel based on the alignment echo data, and extracting diagnosis features to output a diagnosis result of the multi-branch optical fiber link. According to the scheme of the invention, multi-channel single-photon echo data which can be aligned and comparable can be obtained, and the method is used for supporting unified diagnosis of a multi-branch optical fiber link.

Description

A multi-channel fiber optic diagnostic method and system for single-photon counting Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and more specifically to a multi-channel fiber optic diagnostic method and a multi-channel fiber optic diagnostic system based on single-photon counting. Background Technology

[0002] Fiber optic links are widely used in communication, sensing, and industrial monitoring, and their operational status is typically determined by backscattered signals. Traditional optical time-domain reflectometry (OTDR) methods are mostly based on analog detection or linear photoelectric counting, which have limited signal dynamic range and struggle to obtain stable echo data under weak scattering conditions. With the development of single-photon level sensitivity detection technology, time-correlated single-photon counting (TCSPC) has gradually become an important means of precise measurement of fiber optic links. TCSPC can record the single-photon trigger time, converting scattering information into a high-precision time series for analyzing attenuation changes and local reflection events in the link.

[0003] In practical deployments, optical cables often have multi-branch structures, requiring simultaneous assessment of the status of multiple fiber optic links under identical operating conditions. Current technologies typically measure each branch independently, resulting in a lack of unified time references among the obtained echo data, making it difficult to align the distance coordinates of different links. Furthermore, differences in loss across branches cause uneven distribution of photon count rates, with count saturation easily occurring at the near end and significant signal sparseness at the far end. This inconsistency in dynamic range further impacts cross-link comparative analysis, making multi-channel joint diagnostics difficult to achieve.

[0004] Furthermore, multi-channel TCSPC hardware typically suffers from inconsistent electronic delays, optical path differences, and trigger clock skew. Without calibration, the photon arrival time series acquired by each channel will not be consistent on the time axis, directly affecting distance conversion accuracy. Since these error characteristics change with temperature, driving method, or aging conditions, a single static calibration is difficult to maintain effectiveness over the long term. Therefore, a fiber optic diagnostic method is needed for multi-channel structures, providing a unified time reference and adapting to count rate variations to improve the reliability of multi-branch link status assessment. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-channel fiber optic diagnostic method and system for single-photon counting, so as to at least solve the problems of inconsistent time coordinates between multi-channel fiber optic links and inconsistent dynamic range of multi-channel photon counting.

[0006] To achieve the above objectives, the first aspect of the present invention provides a multi-channel optical fiber diagnostic method using single-photon counting. The method includes: acquiring link identification information of multiple optical fiber links, and assigning corresponding single-photon counting channels and corresponding channel delay calibration parameters to each optical fiber link based on the link identification information; injecting probe pulses into each optical fiber link based on a single-photon pulse source, and activating the counting window of each single-photon counting channel to obtain the corresponding photon arrival time series; performing delay correction on each photon arrival time series based on the channel delay calibration parameters, and constructing aligned echo data corresponding to each optical fiber link; performing adaptive counting control on each single-photon counting channel based on the aligned echo data, and extracting diagnostic features based on the aligned echo data after adaptive counting control to output the diagnostic results of the multiple optical fiber links.

[0007] Optionally, the link identification information of the multi-branch optical fiber links is obtained, and corresponding single-photon counting channels and corresponding channel delay calibration parameters are assigned to each optical fiber link based on the link identification information. This includes: reading the link identification information of the multi-branch optical fiber links, establishing a mapping table between link numbers and physical connections based on the link identification information, and binding each optical fiber link in the mapping table to a preset single-photon counting channel; after binding, calling the channel delay test pulse corresponding to each single-photon counting channel to obtain the original channel delay data used to characterize the electronic delay, optical path delay, and trigger clock offset of the single-photon counting channel; and constructing corresponding channel delay calibration parameters based on the original channel delay data.

[0008] Optionally, the channel delay test pulse corresponding to each single-photon counting channel is invoked to obtain the raw channel delay data used to characterize the electronic delay, optical path delay, and trigger clock offset of the single-photon counting channel. This includes: injecting a channel delay test pulse corresponding to the single-photon counting channel number into each single-photon counting channel; recording the trigger time, detection time, and waveform response information of the test pulse during the round-trip propagation process between the fiber input end and the single-photon counting channel detection end based on the test pulse; and generating raw channel delay data to characterize the electronic delay, optical path delay, and trigger clock offset based on the trigger time, detection time, and waveform response information during the round-trip propagation process.

[0009] Optionally, a probe pulse is injected into each fiber optic link based on a single-photon pulse source, and the counting window of each single-photon counting channel is activated to obtain the corresponding photon arrival time sequence. This includes: generating probe pulses based on the single-photon pulse source according to the pulse triggering sequence corresponding to the link identification information of each fiber optic link; injecting the probe pulses into the corresponding fiber optic link via an optical coupling structure connected to each fiber optic link; and simultaneously opening the counting window of the single-photon counting channel corresponding to the fiber optic link based on a unified time control signal while injecting the probe pulses, so as to record the photon triggering time information that the probe pulses return to each single-photon counting channel after backscattering or reflection during propagation, thereby forming a photon arrival time sequence.

[0010] Optionally, delay correction is performed on each photon arrival time sequence based on the channel delay calibration parameters, and aligned echo data corresponding to each optical fiber link is constructed. This includes: performing point-by-point time offset compensation on the trigger time of each photon in the photon arrival time sequence corresponding to each single photon counting channel based on the channel delay calibration parameters to obtain a corrected photon arrival time sequence for characterizing the actual round-trip propagation time of the photon; generating distance coordinate scattering data corresponding to each optical fiber link based on the corrected photon arrival time sequence according to a preset time-distance conversion model; and arranging the distance coordinate scattering data in an aligned distance coordinate order according to the link identification information of each optical fiber link to form aligned echo data for each optical fiber link.

[0011] Optionally, distance coordinate scattering data for each fiber optic link is generated based on the corrected photon arrival time series according to a preset time-distance conversion model. This includes: dividing the trigger time of each photon into time intervals based on the corrected photon arrival time series; calculating the photon count value within each time interval in correspondence with the round-trip propagation speed parameter in the preset time-distance conversion model to obtain a set of distance coordinate scattering points characterizing the scattering intensity of each fiber optic link at different distance positions; wherein, the time-distance conversion model consists of a refractive index parameter characterizing the refractive index of the fiber optic medium, a propagation path parameter characterizing the round-trip propagation path of the photon, and a conversion formula for converting the photon trigger time into distance coordinates, wherein the refractive index parameter and the propagation path parameter together define the round-trip propagation speed of the photon in the fiber optic; and aggregating the distance coordinate scattering point set according to the link identification information of the fiber optic link to form distance coordinate scattering data for each fiber optic link.

[0012] Optionally, adaptive counting control is performed on each single-photon counting channel based on the aligned echo data, including: dynamically adjusting the integral time parameter, dead time compensation parameter, and trigger decision threshold parameter of the counting window corresponding to each single-photon counting channel based on the count rate change of each photon trigger time in the aligned echo data, so as to obtain the aligned echo data after adaptive counting control.

[0013] Optionally, the diagnostic features are extracted from the aligned echo data after adaptive counting control to output the diagnostic results of the multi-branch fiber optic links, including: performing distance sequence analysis on the distance coordinate scattering intensity of each fiber optic link based on the aligned echo data after adaptive counting control to obtain a set of diagnostic features to characterize the scattering abrupt change location parameters, attenuation change parameters, and reflection event parameters of each fiber optic link; and generating the corresponding diagnostic results of the multi-branch fiber optic links based on the link identification information of the multi-branch fiber optic links according to the set of diagnostic features.

[0014] A second aspect of the present invention provides a multi-channel fiber optic diagnostic system for single-photon counting. The system includes: an acquisition unit for acquiring link identification information of multiple fiber optic links and allocating corresponding single-photon counting channels and corresponding channel delay calibration parameters to each fiber optic link based on the link identification information; a recording unit for injecting probe pulses into each fiber optic link based on a single-photon pulse source and activating the counting window of each single-photon counting channel to acquire the corresponding photon arrival time sequence; a correction unit for performing delay correction on each photon arrival time sequence based on the channel delay calibration parameters and constructing aligned echo data corresponding to each fiber optic link; and a diagnostic unit for performing adaptive counting control on each single-photon counting channel based on the aligned echo data and extracting diagnostic features based on the aligned echo data after adaptive counting control to output diagnostic results for the multiple fiber optic links.

[0015] On the other hand, the present invention provides a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the above-described multi-channel fiber optic diagnostic method for single-photon counting.

[0016] By acquiring the link identification information of multiple fiber optic links and establishing channel mapping relationships for each fiber optic link, this invention can clarify the physical correspondence structure of multiple channels before the diagnostic process begins, providing a prerequisite for the unified processing of subsequent time data. After injecting probe pulses one by one and recording photon arrival times, the inherent electronic delay, optical path differences, and trigger offset of each single-photon counting channel can be compensated through channel delay calibration parameters, enabling the time series of multiple branches to be expressed in the same reference frame. The aligned echo data constructed based on this is comparable and suitable for joint judgment across links. On this basis, adaptive counting control is introduced, which can adjust the integration time, dead time compensation, and decision threshold according to the count rate change, so that the statistical quality of the near-end high-count segment and the far-end weak-count segment remains consistent. Overall, this invention can obtain echo data that is synchronous across channels, has a consistent dynamic range, and can be directly used for structured analysis, thereby supporting the comprehensive diagnostic process of multiple fiber optic links.

[0017] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation on the embodiments of the present invention. In the drawings: Figure 1 is a flowchart of the steps of a multi-channel fiber optic diagnostic method for single-photon counting provided by an embodiment of the present invention; Figure 2 is a system structure diagram of a multi-channel fiber optic diagnostic system for single-photon counting provided by an embodiment of the present invention. Detailed Implementation

[0019] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0020] As shown in Figure 1, the present invention provides a multi-channel optical fiber diagnostic method for single-photon counting. The method includes: step S10: obtaining link identification information of multiple branch optical fiber links, and assigning corresponding single-photon counting channels and corresponding channel delay calibration parameters to each optical fiber link based on the link identification information.

[0021] Specifically, the link identification information of multiple fiber optic links is read, and a mapping table between link numbers and physical connections is established based on the link identification information. Each fiber optic link in the mapping table is bound to a preset single-photon counting channel. After binding, the channel delay test pulse corresponding to each single-photon counting channel is called to obtain the original channel delay data used to characterize the electronic delay, optical path delay, and trigger clock offset of the single-photon counting channel. The corresponding channel delay calibration parameters are constructed based on the original channel delay data.

[0022] Furthermore, the channel delay test pulses corresponding to each single-photon counting channel are invoked to obtain raw channel delay data characterizing the electronic delay, optical path delay, and trigger clock offset of the single-photon counting channel. This includes: injecting a channel delay test pulse corresponding to the single-photon counting channel number into each single-photon counting channel; recording the trigger time, detection time, and waveform response information of the test pulse during the round-trip propagation process between the fiber input end and the single-photon counting channel detection end based on the test pulse's trigger time, detection time, and waveform response information during the round-trip propagation process; and generating raw channel delay data characterizing the electronic delay, optical path delay, and trigger clock offset based on the test pulse's trigger time, detection time, and waveform response information during the round-trip propagation process.

[0023] In this embodiment of the invention, many multi-branch fiber optic networks are not structurally complex, but in actual access devices, they often contain historical markers, physical splitting structures, and patch records, which are not always accurate. Therefore, it is common practice to start with link identification information, extracting the correspondence between fiber numbers and physical port locations one by one. Link identification information mostly comes from preset files or automatic detection tags, and constructing a mapping table from this information is a common practice. The mapping table undertakes a simple task: describing the relationship between link numbers, port locations, and channel allocation rules. The purpose of this is to maintain a clear attribution for the data generated by each channel in subsequent processing stages, so as not to confuse the data streams of different fiber optic links. After completing this action, the multi-branch structure has a clear basic framework.

[0024] Next, the fiber optic links need to be individually bound to the single-photon counting channels. In most measurement scenarios, the number of single-photon counting channels is not exactly the same as the number of fiber optic links, so fixed or dynamic allocation rules are often used. Fixed allocation is more common in structurally stable scenarios, while dynamic allocation is more common in automated diagnostic equipment. Regardless of the method used, the goal of the binding operation is to assign each fiber optic link to a specific channel and maintain this correspondence in subsequent stages. After binding, the channel delay test has a clear target, and subsequent delay data can be accurately connected to the specific link.

[0025] Channel delay testing is typically performed by injecting test pulses into each single-photon counting channel. The test pulses need to be controllable and distinguishable; therefore, a triggering sequence consistent with the channel number is usually specified. After entering the optical fiber, the test pulse undergoes a round trip propagation, covering the front-end coupling structure, the fiber segment, and the probe input link. Theoretically, the difference between the trigger time and the probe time should reflect the propagation characteristics of the entire optical path. However, in practical devices, electronic delay, switching delay, and differences in probe circuit response often lead to errors. Therefore, recording the trigger and probe times is only one part of obtaining delay information; waveform response information must also be acquired simultaneously. The waveform can reflect subtle differences occurring during the photon response, such as slow drift, rising edge variations, or additional small pulses, all of which may indicate the inherent delay characteristics of the channel.

[0026] After processing this information, the raw time delay data forms a set of parameters that can be directly used for analysis. The raw time delay data does not carry direct interpretive meaning; rather, it constitutes an observational combination of multiple delay factors. For example, electronic delay typically manifests as a fixed offset between trigger and probe; optical path delay depends more on fiber length, refractive index variation, and connection structure; and trigger clock offset reflects minute drifts in the timing reference. When analyzing this information together, it is often necessary to separate errors from different sources. This part of the work usually relies on pre-defined rules or fitting methods and can be completed without complex models. The final result is called the channel time delay calibration parameters.

[0027] After establishing the calibration parameters, a usable benchmark is available for multi-branch data processing. This benchmark does not modify the actual physical behavior of the optical fiber, but rather establishes a unified reference for the timeline. Because the electronic components of different channels have different manufacturing tolerances, even if multiple channels use the same clock source, slight offsets will still occur. Therefore, the calibration parameters serve more as a correction factor to compensate for photon arrival time series during subsequent analysis. The compensation process is not complex; essentially, it involves adding or subtracting a fixed amount to each trigger time to bring all channels back to a consistent position on the timeline. This approach is a common strategy in multi-channel architectures and forms the basis for supporting subsequent distance conversions and event alignment.

[0028] Throughout the parameter generation process, the reliability of the test pulses is crucial. To ensure reproducibility, the test pulses need to be stable in waveform, have clear triggering, and consistent amplitude, so that the recorded trigger and probe times are comparable. The waveform response information also needs sufficient resolution to distinguish between true delay and noise disturbances. Typically, channel delay tests are repeated several times, and the actual calibration values ​​are often averaged or subjected to simple statistical processing. This approach avoids the influence of occasional noise on the calibration parameters and better meets the needs of long-term equipment operation.

[0029] Step S20: Inject probe pulses into each fiber optic link based on a single-photon pulse source, and start the counting window of each single-photon counting channel to obtain the corresponding photon arrival time series.

[0030] Specifically, a detection pulse is generated based on a single-photon pulse source according to the pulse triggering sequence corresponding to the link identification information of each optical fiber link; the detection pulse is injected into the corresponding optical fiber link via an optical coupling structure connected to each optical fiber link; at the same time as the detection pulse is injected, the counting window of the single-photon counting channel corresponding to the optical fiber link is opened based on a unified time control signal to record the photon triggering time information of the detection pulse returning to each single-photon counting channel due to backscattering or reflection during propagation, thereby forming a photon arrival time sequence.

[0031] In this embodiment of the invention, in a multi-channel single-photon diagnostic scenario, the organization of the probe pulses essentially determines the clarity of the subsequent data structure. In this embodiment, the single-photon pulse source does not simply repeat the output; instead, the triggering order is arranged according to the link identification information of multiple fiber optic links. Specifically, each fiber optic link's link identifier is associated with a trigger number, and the single-photon pulse source generates a pulse sequence according to this trigger number, ensuring that different links occupy non-overlapping or distinguishable trigger slots on the time axis. This triggering order constraint ensures that the subsequently recorded photon arrival time series naturally carries link attribution information in the time dimension, reducing the burden of additional tags or complex decoding processes.

[0032] When injecting probe pulses into an optical fiber link, energy and path distribution are achieved through an optical coupling structure. In practice, this optical coupling structure can be a controllable optical switch, a programmable optical splitter, or a fixed optical splitter network. The key is to ensure that each pulse corresponding to a trigger number enters the target optical fiber link along the designated optical path. Several parameters are typically monitored during the injection process, such as pulse width, peak power, and polarization state, to obtain sufficient backscattered signal within the single-photon counting operating range. In this way, each optical fiber link receives independent single-photon probe pulse illumination within a predetermined time period, ensuring that subsequent backpropagating scattered photons have distinguishable sources.

[0033] The opening time of the counting window needs to be strictly aligned with the detection pulse; therefore, introducing a unified time control signal is essential. This time control signal serves as a global trigger reference, driving the single-photon pulse source to emit the detection pulse and opening the counting window of the single-photon counting channel bound to the corresponding fiber optic link after a predetermined delay. The width and position of the counting window can be set according to the fiber length, refractive index, and desired monitoring distance range. For example, a longer observation time window is used for long-distance links, while a shorter time window can be used for short-distance links to reduce useless counts. Through this unified control, the time coordinates of different channels can be based on the same clock source, reducing the impact of relative drift between channels.

[0034] During the effective period of the counting window, the single-photon counting channel records the trigger time information of backscattered or reflected photons. Here, the photon trigger time refers to the time interval between the output pulse of the single-photon detector and the unified timing control signal, typically stored as a timestamp. Because the scattering process in optical fibers has statistical properties, a single trigger often corresponds to multiple scattered photons returning at different times; therefore, a single detection pulse will result in a sparse distribution of trigger events on the time axis. The counting channel needs to operate under set dead time and decision threshold conditions to avoid saturation in the strong scattering segment while ensuring that trigger events in the weak scattering segment are reliably recorded. The timetamps accumulated in this way constitute the photon arrival time sequence corresponding to a specific optical fiber link.

[0035] Each time stamp corresponds to a single-photon event, carrying information including channel number, trigger number, and timestamp. Since channel binding was completed earlier using link identification information, and pulse injection and window opening were coordinated using a unified time control signal, the time series generated by each fiber link can be clearly identified in three-dimensional space: channel dimension, pulse number dimension, and time dimension. This structure facilitates subsequent conversion of the time axis to a distance axis and also allows for comparative analysis across multiple channels.

[0036] Step S30: Perform delay correction on the arrival time sequence of each photon based on the channel delay calibration parameters, and construct the aligned echo data corresponding to each optical fiber link.

[0037] Specifically, based on the channel delay calibration parameters, point-by-point time offset compensation is performed on the photon trigger time in the photon arrival time sequence corresponding to each single photon counting channel to obtain a corrected photon arrival time sequence that characterizes the actual round-trip propagation time of the photon; based on the corrected photon arrival time sequence, distance coordinate scattering data corresponding to each optical fiber link is generated according to a preset time-distance conversion model; the distance coordinate scattering data is arranged in an aligned distance coordinate order according to the link identification information of each optical fiber link to form aligned echo data of each optical fiber link.

[0038] Furthermore, based on the corrected photon arrival time series, distance coordinate scattering data corresponding to each optical fiber link is generated according to a preset time-distance conversion model. This includes: dividing the photon triggering time into time intervals based on the corrected photon arrival time series; calculating the photon count value within each time interval in correspondence with the round-trip propagation speed parameter in the preset time-distance conversion model to obtain a set of distance coordinate scattering points characterizing the scattering intensity of each optical fiber link at different distance positions; wherein, the time-distance conversion model consists of a refractive index parameter characterizing the refractive index of the optical fiber medium, a propagation path parameter characterizing the round-trip propagation path of the photon, and a conversion formula for converting the photon triggering time into distance coordinates, wherein the refractive index parameter and the propagation path parameter together limit the round-trip propagation speed of the photon in the optical fiber; and aggregating the distance coordinate scattering point set according to the link identification information of the optical fiber link to form distance coordinate scattering data corresponding to each optical fiber link.

[0039] In this invention embodiment, time delay correction is generally considered a core step in the multi-channel single-photon diagnostic process because the time axis is the sole basis for subsequent distance estimation and event localization. Each single-photon counting channel often has different origins, aging levels, and electron link lengths; therefore, in the initial state, the trigger times of each channel will exhibit a fixed offset or a slow drift. The existence of channel time delay calibration parameters provides a reference framework for correction. By employing point-by-point time offset compensation, the original photon arrival time series can be uniformly pulled back to a single reference coordinate system, making different channels comparable on the time axis.

[0040] The compensation process is relatively straightforward. Each fiber optic link corresponds to a single-photon counting channel, and each time series contains a large number of photon events. Each photon event is recorded as a trigger timestamp, which reflects the moment the detector receives the single-photon event. Channel delay calibration parameters typically include three parts: electronic delay, optical path difference, and clock offset. The compensation process involves adding these quantities to each trigger time to form a new timestamp. The compensated timestamp no longer reflects the device time but rather more closely approximates the physical time of light's actual round-trip propagation in the fiber.

[0041] Once the corrected photon arrival time series is established, the next step is distance conversion. In the field of fiber optic measurement, there is a definite relationship between time and distance. The speed of light propagation in an optical fiber is determined by the refractive index; therefore, a time-distance conversion model can convert a time series into a distance series. This model often uses piecewise or unified expressions, and its basic form is as follows:

[0042] Where: D represents the distance coordinate; v represents the speed of light in the optical fiber; T represents the corrected photon triggering time; T0 represents the reference triggering time offset, used to correspond to the zero-time propagation speed v at the optical fiber inlet, written as:

[0043] Where n represents the refractive index of the optical fiber, and c represents the speed of light in a vacuum. The refractive index n can be obtained from material properties or calibration experiments. The propagation path parameter is often expressed as a multiplier factor, used to describe the double-length structure of the round-trip path. Therefore, the distance in the formula is divided by 2, representing the physical path to the round trip converted to a one-way distance.

[0044] In the actual execution of distance conversion, it is not performed directly on each time tag, but rather by first dividing the time interval. A time interval can be viewed as a time sampling grid, with each interval covering a continuous period of time. Since photon scattering is statistical, exhibiting different count densities at different time intervals, aggregating photon trigger times into time intervals is beneficial for calculating the scattering intensity at different distances. This process is equivalent to dividing the time axis into small segments of fixed width, accumulating the number of photon triggers in each segment, and obtaining the photon count value.

[0045] A one-to-one relationship is established between the photon count value and the distance coordinate at the center of the time interval. The time interval corresponds to a trigger center time t. center After conversion, the distance d is obtained. center This constitutes a set of scattering points with distance coordinates. This set contains two key quantities: distance location and scattering intensity. In fiber optic diagnostics, reflection points, loss sections, or structural disturbances can all cause changes in local scattering intensity; therefore, the distribution of these points directly reflects the link status.

[0046] The time-distance conversion model involves more than just refractive index and path length parameters; it also requires an understanding of the probe link structure. For example, some links have additional connectors, and the delay introduced is not determined by the refractive index but by the geometric path difference. Therefore, propagation path parameters include fiber length, number of connectors, and splice location. The refractive index and path parameters together define the overall propagation characteristics of light within the link. In practical applications, the complete time-distance relationship can be expressed by the following formula:

[0047] Where: n eff (L) represents the equivalent refractive index, which can vary in segments with the link length L to accommodate material differences that may exist in different fiber segments; T represents the corrected photon triggering time; T0 represents the reference triggering time offset; and c is the speed of light in vacuum.

[0048] This model, while maintaining physical accuracy, also allows for adaptation to complex link structures through piecewise refractive index compensation, a common engineering practice. Based on a range-coordinate scattering point set, range-coordinate scattering data can be constructed. When converting the point set into a data structure, all points need to be rearranged according to link identification information, so that the scattering data of each fiber link presents a continuous sequence from near end to far end. This process is equivalent to putting the physical quantities output from multiple channels into a unified format, making the scattering data from different links comparable and complete. The rearranged data, the so-called aligned echo data, is an important foundation for subsequent diagnostic analysis.

[0049] The purpose of aligning echo data is to provide a consistent reference frame across channels. Since the time delay compensation has already eliminated the time differences, and the distance conversion establishes a unified distance scale between links, scattering data from different links can be compared on the same distance coordinate system. Regardless of the location of the reflection event or the variation in the attenuation slope, aligned echo data can be expressed in the same format, making subsequent analysis more intuitive.

[0050] The time series is compensated to become neat, the distance series is converted to become readable, and the scattering point set is organized to become continuous. The resulting aligned echo data is not just a record of a single link, but a structured data block that can be used for simultaneous diagnosis of multiple links. This structured representation can reduce sources of error and enhance the stability and repeatability of the analysis.

[0051] Step S40: Perform adaptive counting control on each single-photon counting channel based on the aligned echo data, and extract diagnostic features based on the aligned echo data after adaptive counting control to output the diagnostic results of the multi-branch fiber optic link.

[0052] Specifically, adaptive counting control is performed on each single-photon counting channel based on the aligned echo data, including: dynamically adjusting the integral time parameter, dead time compensation parameter, and trigger decision threshold parameter of the counting window corresponding to each single-photon counting channel based on the count rate change of each photon trigger time in the aligned echo data, so as to obtain the aligned echo data after adaptive counting control.

[0053] Furthermore, the diagnostic features are extracted from the aligned echo data after adaptive counting control to output the diagnostic results of the multi-branch optical fiber links. This includes: performing distance sequence analysis on the distance coordinate scattering intensity of each optical fiber link based on the aligned echo data after adaptive counting control to obtain a set of diagnostic features to characterize the scattering abrupt change location parameters, attenuation change parameters, and reflection event parameters of each optical fiber link; and generating the corresponding diagnostic results of the multi-branch optical fiber links based on the link identification information of the multi-branch optical fiber links according to the set of diagnostic features.

[0054] In this embodiment of the invention, the loss differences in multi-branch fiber optic links are often significant. The strong scattering region at the near end and the weak scattering region at the far end already show marked differences within the same channel, and these differences are further amplified when multiple channels are superimposed. When using fixed parameters for single-photon counting directly, some channels are prone to saturation at high count intervals, while other channels have almost no effective triggering events at the far end. Adaptive counting control based on aligned echo data aims to reallocate counting resources in this context, ensuring that the statistical quality of different channels and distance segments remains within a comparable range.

[0055] Count rate estimation is a fundamental step in adaptive adjustment. The aligned echo data already contains the distribution of photon trigger times across a uniform distance coordinate system. Therefore, the distance coordinate system can be divided into several intervals, and the ratio of the photon count value within each interval to the corresponding acquisition time can be calculated. The count rate estimation expression is as follows:

[0056] in, Indicates the first Each single-photon counting channel is in the distance range The count rate within, This indicates the cumulative number of photon triggers within this distance range. This indicates the effective observation time for the corresponding distance interval under the current integration settings. By scanning the entire distance range, the count rate distribution curve for each channel can be obtained. This curve directly reflects the high count range, low count range, and near-saturation region.

[0057] After obtaining the count rate distribution, the integration time parameter needs to be adjusted accordingly. For distance ranges with significantly high count rates, the integration time parameter can be shortened to ensure that the count events per unit time fall within the detector's linear response range. This reduces the count loss introduced by the dead-time effect. For distance ranges with low count rates, the integration time is extended to accumulate a sufficient number of photon events through longer observation times, ensuring the stability of subsequent statistical analysis. The update rule for the integration time can be set in conjunction with a preset target count rate range, for example, to bring the count rate closer to a middle value, rather than pursuing some extreme performance.

[0058] The updating of dead-time compensation parameters also depends on the count rate estimation results. Under high count rates, the effect of dead time becomes more pronounced in single-photon counters; without compensation, the scattering intensity at the range coordinates is systematically suppressed near the end. By classifying the count rate ranges, more refined dead-time compensation parameters can be selected in the high count rate range, while maintaining a smaller compensation amount in the low count rate range. In this way, the compensation is no longer a globally fixed value, but a set of range-related parameters used to reduce the nonlinear error caused by dead time.

[0059] The adjustment of the trigger decision threshold parameter mainly considers the balance between noise and weak signals. In the near-end strong signal region, the decision threshold can be appropriately increased to reduce interference from dark counts and scattering tails. In the far-end weak signal region, the threshold needs to be decreased to ensure that weak scattering events can still form effective triggers. Based on the statistical results of the noise floor level in the aligned echo data, different decision thresholds can be configured for each range segment to keep the noise ratio within an acceptable range while not losing key scattering information.

[0060] After dynamically adjusting the parameters mentioned above, the resulting aligned echo data under adaptive counting control is obtained. The main difference between this dataset and the original aligned echo data lies in statistical quality rather than structural morphology. The saturation risk in the high-count range is mitigated, random fluctuations in the weak-signal range are reduced, and the dynamic range differences between multiple channels are compressed into a narrower range. For subsequent diagnostics, the aligned echo data under adaptive counting control is more suitable for analysis using a unified threshold and algorithm.

[0061] In the diagnostic feature extraction stage, the focus is on distance sequence parsing and feature parameter construction. Based on the aligned echo data after adaptive counting control, a one-dimensional sequence scan of the scattering intensity of the distance coordinates of each fiber link can be performed to identify potential scattering abrupt changes. A common approach is to first calculate the scattering intensity difference between adjacent distance points, then perform thresholding and neighborhood aggregation on the difference sequence to obtain the scattering abrupt change location parameter. This parameter reflects the location of significant structural changes in the link, such as fusion splices, connectors, or localized damage areas.

[0062] The attenuation variation parameter focuses on describing the overall trend. By fitting the scattering intensity of the distance coordinates over a longer distance window, the attenuation slope of the corresponding interval can be obtained. Comparing the attenuation slopes of different intervals can reveal whether there are abnormal dissipation sections or localized additional losses in the link. The fitting method can use simple linear regression, or a piecewise fitting method can be used to apply different models to different intervals. The final attenuation variation parameter constitutes an important basis for judging the overall health status of the link.

[0063] The parameters for reflection events focus on local peak characteristics. By scanning local extrema in the distance sequence and combining indicators such as peak height, peak width, and symmetry, it is possible to determine whether a typical reflection event exists. For example, narrower and higher peaks typically correspond to connector interfaces, while wider, gradually rising peaks may be associated with bending or micro-damage. Organizing these peak characteristics into parameter sets can provide raw features for subsequent fault type classification.

[0064] When the three types of features—scattering abrupt change location parameters, attenuation change parameters, and reflection event parameters—are combined, a diagnostic feature set is formed. This set includes spatial location, intensity variation, and morphological information, making it suitable for multi-level diagnostic assessments. By classifying these features according to the link identification information of multi-branch fiber optic links, a set of diagnostic results corresponding to specific link numbers can be generated. Each link is accompanied by a feature report describing the link's status characteristics at different distance segments.

[0065] As shown in Figure 2, this embodiment of the invention provides a multi-channel fiber optic diagnostic system for single-photon counting. The system includes: an acquisition unit for acquiring link identification information of multiple fiber optic links and assigning corresponding single-photon counting channels and corresponding channel delay calibration parameters to each fiber optic link based on the link identification information; a recording unit for injecting probe pulses into each fiber optic link based on a single-photon pulse source and activating the counting window of each single-photon counting channel to obtain the corresponding photon arrival time sequence; a correction unit for performing delay correction on each photon arrival time sequence based on the channel delay calibration parameters and constructing aligned echo data corresponding to each fiber optic link; and a diagnostic unit for performing adaptive counting control on each single-photon counting channel based on the aligned echo data and extracting diagnostic features based on the aligned echo data after adaptive counting control to output the diagnostic results of the multiple fiber optic links. This embodiment of the invention also provides a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the above-described multi-channel fiber optic diagnostic method for single-photon counting.

[0066] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a microcontroller, chip, or processor to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0067] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details described above. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not further describe the various possible combinations.

[0068] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the embodiments of the present invention, they should also be regarded as the content disclosed by the embodiments of the present invention.

Claims

1. A multi-channel fiber optic diagnostic method for single-photon counting, characterized in that, The method includes: acquiring link identification information of multiple fiber optic links, and assigning corresponding single-photon counting channels and corresponding channel delay calibration parameters to each fiber optic link based on the link identification information; injecting probe pulses into each fiber optic link based on a single-photon pulse source, and activating the counting window of each single-photon counting channel to obtain the corresponding photon arrival time series; performing delay correction on each photon arrival time series based on the channel delay calibration parameters, and constructing aligned echo data corresponding to each fiber optic link; performing adaptive counting control on each single-photon counting channel based on the aligned echo data, and extracting diagnostic features based on the aligned echo data after adaptive counting control to output the diagnostic results of the multiple fiber optic links.

2. The multi-channel fiber optic diagnostic method for single-photon counting according to claim 1, characterized in that, The process involves acquiring link identification information for multiple fiber optic links and assigning corresponding single-photon counting channels and corresponding channel delay calibration parameters to each fiber optic link based on the link identification information. This includes: reading the link identification information of the multiple fiber optic links and establishing a mapping table between link numbers and physical connections based on the link identification information; binding each fiber optic link in the mapping table to a preset single-photon counting channel; after binding, calling the channel delay test pulse corresponding to each single-photon counting channel to obtain the original channel delay data characterizing the electronic delay, optical path delay, and trigger clock offset of the single-photon counting channel; and constructing corresponding channel delay calibration parameters based on the original channel delay data.

3. The multi-channel fiber optic diagnostic method for single-photon counting according to claim 2, characterized in that, The process involves calling the channel delay test pulse corresponding to each single-photon counting channel to obtain raw channel delay data characterizing the electronic delay, optical path delay, and trigger clock offset of that single-photon counting channel. This includes: injecting a channel delay test pulse corresponding to the single-photon counting channel number into each single-photon counting channel; recording the trigger time, detection time, and waveform response information of the test pulse during its round-trip propagation between the fiber input end and the single-photon counting channel detection end based on the test pulse's trigger time, detection time, and waveform response information during the round-trip propagation; and generating raw channel delay data characterizing the electronic delay, optical path delay, and trigger clock offset, respectively, based on the test pulse's trigger time, detection time, and waveform response information during the round-trip propagation.

4. The multi-channel fiber optic diagnostic method for single-photon counting according to claim 1, characterized in that, The process involves injecting probe pulses into each fiber optic link using a single-photon pulse source and activating the counting window of each single-photon counting channel to obtain the corresponding photon arrival time sequence. This includes: generating probe pulses based on the single-photon pulse source according to the pulse triggering sequence corresponding to the link identification information of each fiber optic link; injecting the probe pulses into the corresponding fiber optic link via an optical coupling structure connected to each fiber optic link; and simultaneously opening the counting window of the single-photon counting channel corresponding to the fiber optic link based on a unified time control signal to record the photon triggering time information of the probe pulses returning to each single-photon counting channel due to backscattering or reflection during propagation, thereby forming the photon arrival time sequence.

5. The multi-channel fiber optic diagnostic method for single-photon counting according to claim 1, characterized in that, Based on the channel delay calibration parameters, delay correction is performed on the arrival time series of each photon, and aligned echo data corresponding to each optical fiber link is constructed. This includes: performing point-by-point time offset compensation on the trigger time of each photon in the arrival time series corresponding to each single photon counting channel based on the channel delay calibration parameters to obtain a corrected photon arrival time series that characterizes the actual round-trip propagation time of the photon; generating distance coordinate scattering data corresponding to each optical fiber link based on the corrected photon arrival time series according to a preset time-distance conversion model; and arranging the distance coordinate scattering data in an aligned distance coordinate order according to the link identification information of each optical fiber link to form aligned echo data for each optical fiber link.

6. The multi-channel fiber optic diagnostic method for single-photon counting according to claim 5, characterized in that, Based on the corrected photon arrival time series, distance coordinate scattering data corresponding to each optical fiber link is generated according to a preset time-distance conversion model. This includes: dividing the photon trigger time into time intervals based on the corrected photon arrival time series; calculating the photon count value within each time interval in correspondence with the round-trip propagation speed parameter in the preset time-distance conversion model to obtain a set of distance coordinate scattering points characterizing the scattering intensity of each optical fiber link at different distance positions; wherein, the time-distance conversion model consists of a refractive index parameter characterizing the refractive index of the optical fiber medium, a propagation path parameter characterizing the round-trip propagation path of the photon, and a conversion formula for converting the photon trigger time into distance coordinates, the refractive index parameter and the propagation path parameter jointly defining the round-trip propagation speed of the photon in the optical fiber; and aggregating the distance coordinate scattering point set according to the link identification information of the optical fiber link to form distance coordinate scattering data corresponding to each optical fiber link.

7. The multi-channel fiber optic diagnostic method for single-photon counting according to claim 1, characterized in that, Adaptive counting control is performed on each single-photon counting channel based on the aligned echo data, including: dynamically adjusting the integral time parameter, dead time compensation parameter, and trigger decision threshold parameter of the counting window corresponding to each single-photon counting channel based on the count rate change of each photon trigger time in the aligned echo data, so as to obtain the aligned echo data after adaptive counting control.

8. The multi-channel fiber optic diagnostic method for single-photon counting according to claim 7, characterized in that, The diagnostic features extracted from the aligned echo data after adaptive counting control are used to output diagnostic results for multi-branch fiber optic links. This includes: performing distance sequence analysis on the distance coordinate scattering intensity of each fiber optic link based on the aligned echo data after adaptive counting control to obtain a set of diagnostic features to characterize the scattering abrupt change location parameters, attenuation change parameters, and reflection event parameters of each fiber optic link; and generating corresponding diagnostic results for the multi-branch fiber optic links based on the link identification information of the multi-branch fiber optic links according to the set of diagnostic features.

9. A multi-channel fiber optic diagnostic system for single-photon counting, characterized in that, The system includes: an acquisition unit for acquiring link identification information of multiple fiber optic links and assigning corresponding single-photon counting channels and corresponding channel delay calibration parameters to each fiber optic link based on the link identification information; a recording unit for injecting probe pulses into each fiber optic link based on a single-photon pulse source and activating the counting window of each single-photon counting channel to acquire the corresponding photon arrival time series; a correction unit for performing delay correction on each photon arrival time series based on the channel delay calibration parameters and constructing aligned echo data corresponding to each fiber optic link; and a diagnostic unit for performing adaptive counting control on each single-photon counting channel based on the aligned echo data and extracting diagnostic features based on the aligned echo data after adaptive counting control to output diagnostic results for the multiple fiber optic links.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores instructions that, when executed on a computer, cause the computer to perform the multi-channel fiber optic diagnostic method for single-photon counting as described in any one of claims 1-8.

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