Optical time domain reflectometer and method for improving accuracy of saturation reflection measurement, storage medium

Abstract

This invention relates to the field of optical time-domain reflectometry (OTDR) technology, specifically to an ORT, a method for improving the measurement accuracy of saturated reflectance, and a storage medium. The method for improving the measurement accuracy of saturated reflectance using an ORT includes: during a single test scan of the ORT, data is acquired from the same optical fiber under test using a first gain level and a second gain level, wherein the gain of the first gain level is higher than the gain of the second gain level; an ORT output curve is generated based on the data acquired using the first gain level; it is determined whether the reflection event acquired using the first gain level is saturated; when the reflection event is determined to be saturated, the reflection value of the reflection event is calculated based on the data acquired using the second gain level to correct the measurement accuracy of the saturated reflectance.

Description

Technical Field

[0001] This invention relates to the field of optical time domain reflectometer technology, and in particular to an optical time domain reflectometer, a method for improving the accuracy of saturated reflectance measurement, and a storage medium. Background Technology

[0002] An optical time domain reflectometer (OTDR) is a core instrument in the field of optical fiber communication used for testing and monitoring the quality of optical fiber links. Its working principle involves injecting optical pulses into the fiber under test and detecting the Rayleigh backscattered light and Fresnel reflected light generated in the fiber to obtain the attenuation characteristic distribution along the fiber's length. This allows for precise analysis of key parameters such as fiber link loss, connector loss, fault location, and reflection event measurement. In an OTDR system, a photodetector converts the received weak optical signal into an electrical signal, which is then amplified by a transimpedance amplifier (TIA) and sampled by an analog-to-digital converter (ADC). To ensure sufficient dynamic range for testing long-distance optical fiber links, a high transimpedance amplification gain is typically required. However, when high-reflection events such as connectors, mechanical joints, or breaks exist in the optical fiber link, the reflected light power may far exceed the linear response range of the detector, causing photodetector saturation and resulting in significant deviations in the measured values ​​of reflection events.

[0003] In existing technologies, two main approaches are used to address the high reflection saturation problem of OTDRs: First, optimizing the fiber optic line connection quality to reduce the reflection coefficient. However, this approach can only prevent, not avoid, the inevitable large reflection events in actual testing scenarios, resulting in poor adaptability. Second, reducing the OTDR test pulse width to decrease the injected optical pulse energy and thus avoid detector saturation. However, this approach sacrifices the OTDR's dynamic range, leading to a shorter effective testing distance and failing to meet the testing requirements of long-distance fiber optic links. Therefore, how to effectively correct the measurement accuracy of saturation reflection events while maintaining the OTDR's dynamic range has become a pressing technical problem to be solved in this field. Summary of the Invention

[0004] This invention provides an optical time-domain reflectometer, a method for improving the accuracy of saturated reflectance measurement, and a storage medium to solve the above-mentioned problems.

[0005] This invention discloses a method for improving the accuracy of saturated reflectance measurement in an optical time-domain reflectometer, comprising:

[0006] During a single test scan of the optical time domain reflectometer, data is acquired from the same fiber under test using a first gain setting and a second gain setting, wherein the gain of the first gain setting is higher than the gain of the second gain setting. The output curve of the optical time domain reflectometer is generated based on the data collected at the first gain level; Determine whether the reflection events collected at the first gain level are saturated; When the reflection event is determined to be saturated, the reflection value of the reflection event is calculated based on the data collected at the second gain setting to correct the measurement accuracy of the saturated reflection.

[0007] Optionally, determining whether the reflection event acquired by the first gain level is saturated includes: Obtain the peak value of the reflection event collected at the first gain level; The peak value of the reflection event is compared with a preset reflection saturation threshold; When the peak value of the reflection event is greater than or equal to the reflection saturation threshold, the reflection event is determined to be saturated.

[0008] Optionally, the method further includes: When it is determined that the reflection event is not saturated, the reflection value of the reflection event is calculated based on the height difference of the reflection event collected by the first gain level.

[0009] Optionally, calculating the reflection value of the reflection event based on the data acquired at the second gain level includes: Determine whether the starting point of the reflection event acquired at the second gain level is greater than a preset noise threshold; When the starting point of the reflection event is greater than the noise threshold, the reflection value of the reflection event is calculated based on the height difference of the reflection event collected by the second gain setting.

[0010] Optionally, the method further includes: When the starting point of the reflection event is less than or equal to the noise threshold, the true reflection height is constructed based on the starting point of the reflection event collected by the first gain level, the peak value of the reflection event collected by the second gain level, and the relative gain coefficient of the first gain level relative to the second gain level. The reflection value of the reflection event is calculated based on the actual reflection height.

[0011] Optionally, the actual reflection height is calculated using the following formula: TRH=R_peak_low-R_start_high+Relative_Gain Wherein, TRH is the true reflection height, R_peak_low is the peak value of the reflection event collected by the second gain setting, R_start_high is the starting point of the reflection event collected by the first gain setting, and Relative_Gain is the relative gain coefficient.

[0012] Optionally, the first gain level and the second gain level are configured by different resistance values ​​of the transimpedance amplifier in the optical time domain reflectometer circuit, and the gain level of the transimpedance amplifier is switched by software control.

[0013] Optionally, the output curve of the optical time domain reflectometer is generated entirely based on the data collected at the first gain level, while the data collected at the second gain level is only used to correct the measurement accuracy of saturated reflection and does not participate in the generation of the output curve of the optical time domain reflectometer.

[0014] The present invention also discloses an optical time-domain reflectometer, comprising: Photodetector; A transimpedance amplifier circuit, the transimpedance amplifier circuit including at least two switchable gain levels, wherein the gain of the first gain level is higher than the gain of the second gain level; The control unit is configured to control the transimpedance amplifier circuit to switch to the first gain level and the second gain level respectively during a single test scan of the optical time domain reflectometer, so as to collect data from the same fiber under test respectively. The processing unit is configured to generate an optical time-domain reflectometer output curve based on the data acquired at the first gain level, determine whether the reflection event acquired at the first gain level is saturated, and when the reflection event is determined to be saturated, calculate the reflection value of the reflection event based on the data acquired at the second gain level to correct the measurement accuracy of the saturated reflection.

[0015] The present invention also discloses a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the above-described method for improving the accuracy of saturated reflectance measurement of an optical time-domain reflectometer is implemented.

[0016] The beneficial effects of the optical time domain reflectometer and the method for improving the measurement accuracy of saturated reflectance provided in the embodiments of the present invention are as follows: The present invention adopts a dual-gain acquisition strategy in a single test scan of the optical time domain reflectometer (OTDR). While maintaining the dynamic range and sensitivity at the first gain level (high gain), the data acquired at the second gain level (low gain) is used as a safety backup. When a saturated reflectance event occurs at the first gain level (high gain), the system automatically switches to the corresponding data segment at the low gain level to calculate and replace the reflectance value. Thus, without sacrificing the dynamic range, the measurement deviation of the saturated reflectance event is effectively corrected, which solves the inherent contradiction between reducing the pulse width and sacrificing the dynamic range and high reflectance saturation distortion in the prior art. Attached Figure Description

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a schematic flowchart of an optical time-domain reflectometer and a method for improving the measurement accuracy of saturated reflectance according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the transimpedance amplifier circuit in the OTDR circuit of this invention embodiment; Figure 3 This is the high-gain (G_high) OTDR reflection event acquisition curve of this invention embodiment; Figure 4 This is the low-gain (G_low) OTDR reflection event acquisition curve of an embodiment of the present invention. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0019] This invention provides a method for improving the accuracy of saturated reflectance measurement in an optical time-domain reflectometer, such as... Figure 1 As shown, the method includes: S100: During a single test scan of the optical time domain reflectometer, data is acquired from the same fiber under test using a first gain setting and a second gain setting, wherein the gain of the first gain setting is higher than the gain of the second gain setting. S200: Generate the output curve of the optical time domain reflectometer based on the data acquired at the first gain level; S300: Determine whether the reflection events collected by the first gain level are saturated; S400: When the reflection event is determined to be saturated, the reflection value of the reflection event is calculated based on the data collected by the second gain setting to correct the measurement accuracy of the saturated reflection.

[0020] This invention employs a dual-gain acquisition strategy in a single test scan of an Optical Time Domain Reflectometer (OTDR). While maintaining the first gain level (high gain) to ensure dynamic range and sensitivity, it uses data acquired at the second gain level (low gain) as a safety backup. When a saturation reflection event occurs at the first gain level (high gain), it automatically switches to the corresponding data segment at the low gain level for reflection value calculation and replacement. This effectively corrects the measurement deviation of saturation reflection events without sacrificing dynamic range, thus resolving the inherent contradiction between reducing pulse width at the expense of dynamic range and high reflection saturation distortion in existing technologies.

[0021] Specifically, the acquisition mechanism of the first gain level (high gain) and the second gain level (low gain) ensures that the two acquisitions correspond to the same optical fiber event at the same physical location, avoiding timing deviations introduced by time-division scanning; saturation determination can be automatically identified based on preset thresholds (such as the percentage of the ADC full scale) or reflection peak distortion characteristics (such as flat top, clipping); in the correction calculation stage, the reflection value of the low gain level needs to be converted to an equivalent scale to the high gain level through the gain ratio coefficient.

[0022] Further, determining whether the reflection event acquired by the first gain level is saturated includes: Obtain the peak value of the reflection event collected at the first gain level; The peak value of the reflection event is compared with a preset reflection saturation threshold; When the peak value of the reflection event is greater than or equal to the reflection saturation threshold, the reflection event is determined to be saturated.

[0023] By setting a preset reflection saturation threshold, the peak value of the reflection event is quantitatively compared with the threshold, realizing the automated and objective judgment of saturated reflection events. At the same time, the threshold-based judgment mechanism enables the OTDR system to quickly locate saturation events in massive test data, significantly improving data processing efficiency and providing a reliable trigger condition for subsequent automatic switching to low gain mode data for correction. This ensures that the correction strategy is activated only when necessary, avoiding unnecessary intervention in normal unsaturated reflection events.

[0024] The specific value of the reflection saturation threshold can be determined based on the upper limit of the linear response of the photodetector, the full-scale range of the ADC, and the system noise floor. For example, it can be set to 90%-95% of the full-scale range of the ADC or 80%-90% of the electrical signal corresponding to the saturated optical power of the detector. In actual engineering implementation, this threshold can be designed as a factory-fixed value, or it can be customized by the user according to the expected reflection characteristics of the fiber optic link under test. In addition, to avoid saturation judgment oscillation caused by signal jitter, a hysteresis mechanism can be introduced in the threshold comparison stage. That is, two different thresholds are set: the saturation judgment threshold and the desaturation threshold. The saturation flag is officially triggered only after the peak value of the reflection event has been higher than the saturation judgment threshold for a certain period of time or after a certain number of sampling points, thereby enhancing the robustness and stability of the system judgment.

[0025] Furthermore, the method also includes: when the reflection event is determined to be unsaturated, calculating the reflection value of the reflection event based on the height difference of the reflection event acquired at the first gain level. Directly calculating the reflection value using the height difference of the reflection event at the first gain level (high gain) in the unsaturated state fully leverages the advantages of the high gain level in terms of signal-to-noise ratio and dynamic range, ensuring the measurement accuracy for conventional reflection events. Simultaneously, by distinguishing between saturated and unsaturated states and adopting differentiated calculation strategies, optimal allocation of system resources is achieved. The low gain level correction calculation is only activated when necessary, reducing the overall data processing complexity and improving the real-time response performance of the OTDR system.

[0026] Specifically, the height difference of the reflection event can be calculated by locating the starting point of the reflection event (usually the intersection of the reflection front and the backscattering baseline, or the position where the rising edge of the reflection front reaches a certain threshold above the baseline) and the peak value of the reflection event (the highest point of the reflection curve), and then taking the difference between the two on the vertical axis (optical power or level value). To suppress the influence of noise on the height difference calculation, the data near the starting point and peak value can be locally smoothed and filtered (such as moving average or Savitzky-Golay filtering) before calculation. In addition, in the unsaturated state, the system can also synchronously record the height difference data of the reflection event as a reference for subsequent evaluation of the linear working range boundary of the first gain level, providing data support for the dynamic adaptive adjustment of the saturation threshold.

[0027] The calculation of the reflection value of the reflection event based on the data acquired at the second gain level includes: Determine whether the starting point of the reflection event acquired at the second gain level is greater than a preset noise threshold; When the starting point of the reflection event is greater than the noise threshold, the reflection value of the reflection event is calculated based on the height difference of the reflection event collected by the second gain setting.

[0028] Before using the second gain setting data to correct saturated reflection, a noise threshold test is performed on the starting point of the reflection event. This effectively avoids the risk that the reflection event will be submerged by noise due to insufficient gain at the low gain setting, making it impossible to accurately extract the reflection parameters. Only when it is confirmed that the starting point of the reflection event is significantly higher than the noise level is the full height difference calculation at the low gain setting enabled. This ensures the reliability of the correction data and the credibility of the correction results, and prevents secondary measurement errors caused by noise misjudgment.

[0029] The noise threshold can be determined based on the statistical characteristics of the non-reflection event segment in the data collected at the second gain level. For example, 2-3 times the standard deviation or root mean square value of the data segment can be used as the noise threshold, or a fixed empirical value can be used (such as the level value corresponding to -60dBm to -50dBm). When determining whether the starting point of the reflection event is greater than the noise threshold, multiple consecutive sampling points can be required to meet the condition to eliminate the interference of occasional noise spikes. If the starting point of the reflection event does not meet the noise threshold condition, the system can further attempt to perform digital filtering or coherent accumulation processing on the reflection event data at the second gain level to improve the signal-to-noise ratio. If effective reflection parameters still cannot be extracted, an alarm is triggered or the reflection event is marked as uncorrectable, prompting the user to adjust the test parameters or check the fiber optic connection status.

[0030] The method further includes: when the starting point of the reflection event is less than or equal to the noise threshold, constructing a true reflection height based on the starting point of the reflection event acquired at the first gain setting, the peak value of the reflection event acquired at the second gain setting, and the relative gain coefficient of the first gain setting relative to the second gain setting; and calculating the reflection value of the reflection event based on the true reflection height. When the starting point of the reflection event acquired at the first gain setting is also greater than or equal to the saturation threshold, it is determined that both gain settings are ineffective, and the event is marked as uncorrectable.

[0031] This solution innovatively proposes a hybrid calculation strategy that integrates information from both gain levels to address the extreme case where the starting point of the reflection event at the second gain level is submerged in noise. It utilizes the starting point of the reflection event at the high gain level (which has a sufficient signal-to-noise ratio and accurate positioning due to its high gain) and the peak value of the reflection event at the low gain level (which is not saturated due to its low gain), combined with the relative gain coefficients of the two levels, to construct an equivalent true reflection height. This strategy overcomes the physical limitations of a single gain level, and even when the second gain level cannot independently complete the measurement of a full reflection event, it can still effectively correct for saturated reflection events, greatly expanding the applicability and robustness of the OTDR system.

[0032] Specifically, the starting point of the reflection event at the first gain level can be accurately determined by linear fitting of the reflection front edge in the high-gain data or by the threshold crossing method. Its value corresponds to the starting level above the backscattering baseline on the vertical axis. The peak value of the reflection event at the second gain level needs to be extracted on the premise of confirming that it is not saturated. Usually, the average value of multiple sampling points near the peak of the reflection is taken to suppress random noise. The introduction of the relative gain coefficient is intended to compensate for the inconsistency of the height reference caused by the gain difference between the two levels. Its physical meaning is to convert the peak level of the low gain level to the equivalent scale of the high gain level, or to cancel the influence of the gain difference through difference calculation. In actual implementation, the relative gain coefficient can be calculated by theoretical formula or obtained by actual measurement through calibration process. For example, a standard reflector can be used to test at the two levels respectively, and the peak difference is recorded as the measured relative gain coefficient to eliminate the error caused by device discreteness.

[0033] Specifically, the actual reflection height is calculated using the following formula: TRH=R_peak_low-R_start_high+Relative_Gain (Formula 1) Wherein, TRH is the true reflection height, R_peak_low is the peak value of the reflection event collected by the second gain setting, R_start_high is the starting point of the reflection event collected by the first gain setting, and Relative_Gain is the relative gain coefficient.

[0034] This solution provides a specific formula for calculating the true reflection height. It algebraically combines the peak reflection event value of the second gain level, the starting point of the reflection event of the first gain level, and the relative gain coefficient to achieve quantitative fusion of data from both gain levels. The advantage of this formula is that it requires only three known quantities for calculation, resulting in low computational complexity and facilitating real-time execution in OTDR embedded systems. Furthermore, the formula structure ensures good consistency between the calculated true reflection height and the actual reflection height under unsaturated conditions when the gain difference between the two levels is accurate.

[0035] Specifically, the dimensions of all variables in the formula must be consistent, usually expressed in dB or dBm to represent optical power / level values; R_peak_low is the measured value of the peak point of the reflection event under the second gain setting. This value needs to be extracted after confirming that it is not saturated. If the reflection peak has a slight flat-top distortion (close to but not completely saturated), parabolic fitting can be performed on the peak data to estimate the true peak value; R_start_high is the measured value of the starting point of the reflection event under the first gain setting. Its positioning accuracy directly affects the final calculation result. The linear extrapolation method of the reflection front or the automatic detection algorithm based on the derivative threshold can be used to improve the positioning accuracy; The introduction of Relative_Gain ensures the equivalence of the formula calculation result with the complete height difference under a single gain setting. Its value depends on the dimension convention. When the gain is expressed in dB, if the high gain is greater than the low gain, Relative_Gain is a positive value, reflecting the conversion compensation from the low gain scale to the high gain scale.

[0036] Furthermore, the relative gain coefficient is calculated using the following formula: Relative_Gain=5×log(G_high / G_low) (Formula 2) Wherein, G_high is the transimpedance amplification factor of the first gain level, and G_low is the transimpedance amplification factor of the second gain level.

[0037] Combination Figure 2 The schematic diagram of the transimpedance amplifier circuit in the OTDR circuit shows that the present invention achieves different hardware gains by adjusting different resistor values, and the software can switch the transimpedance gain of the OTDR to perform OTDR test data acquisition respectively.

[0038] This scheme provides a theoretical formula for calculating the relative gain coefficient, based on the ratio of the two transimpedance amplification factors and expressed in a logarithmic form of 5, transforming the gain difference at the hardware level into a dB-domain compensation quantity that can be directly involved in the calculation of the actual reflection height. The advantage of this formula is that it can be calculated only by knowing the nominal gain value of the transimpedance amplifier, without the need for additional calibration measurements, thus simplifying the system configuration process.

[0039] Specifically, in the formula, G_high and G_low are the transimpedance amplification factors of the first and second gain levels, respectively, in ohms (Ω). Their ratio, G_high / G_low, reflects the difference in voltage-to-current conversion gain between the two levels. The coefficient 5 is related to the dB definition of the OTDR reflection value. Specifically, there is a non-linear mapping relationship between the reflection height difference and the reflection value (see Equation 3). When deriving the dB compensation amount of the relative gain coefficient, the coefficient transfer in this mapping relationship needs to be considered, ultimately yielding the form 5×log(G_high / G_low). In practical applications, since the actual gain of the transimpedance amplifier may be affected by factors such as temperature drift, power supply fluctuations, and device aging, the actual gain of each level can be measured during the OTDR factory calibration stage, and the measured values ​​can be substituted into the formula for calculation. Alternatively, the measured Relative_Gain can be directly written as a calibration parameter into the system's non-volatile memory to improve the accuracy and stability during long-term use.

[0040] Furthermore, the reflectance value is calculated using the following formula: R = B - 10 × log 10 [(10 H / 5 -1)×W] (Formula 3) Where R is the reflection value, B is the fiber backscattering coefficient, H is the height difference of the reflection event, and W is the pulse width used in the optical time-domain reflectometry test. Combined with... Figure 4 As shown, H_LOW = R peak_low - R start_low. R peak_low is the peak value of the reflection event at the second gain setting (dB), R start_low is the starting value of the reflection event at the second gain setting (dB), and NFT (NoiseFloor Threshold) is the OTDR noise floor at the specified gain setting, a constant related to the hardware design.

[0041] When the unsaturated reflection event start point (R start_low) acquired by the second gain setting is less than the noise floor threshold (NFT), it indicates that the reflection event height is in the noise zone, and H_low cannot be accurately calculated. In this case, the true reflection height TRH (TrueReflectionHeight) can be constructed based on the reflection start point (R start_high) corresponding to the data acquired by the first gain setting, the reflection peak value (R peak_low) corresponding to the data acquired by the second gain setting, and the relative gain (Relative Gain), as shown in Equation 1 above.

[0042] This solution provides the final calculation formula for reflection values. It performs non-linear combination of the reflection event height difference (H), optical fiber backscattering coefficient (B) and test pulse width (W), realizing accurate conversion from original OTDR measurement data to standard reflection values (usually expressed in dB, relative to backscattering level). The advantage of this formula lies in that it comprehensively considers the physical nature of reflection events (the superposition effect of Fresnel reflection and Rayleigh scattering) and the influence of test conditions (pulse width) on reflection peak broadening and height measurement, so that the calculation result has good physical interpretability and industrial universality, which is convenient for benchmarking with international OTDR standards (such as IEC61746) and reflection value specifications in engineering practice.

[0043] Specifically, in the formula, B is the backscattering coefficient of the optical fiber, whose value depends on the optical fiber type (such as G.652, G.655, etc.), operating wavelength (1310nm or 1550nm) and the Rayleigh scattering characteristics of the optical fiber. It can usually be obtained by consulting the technical specification provided by the optical fiber manufacturer, or a B-value database of common optical fiber types can be preset in the OTDR system for users to select, which will not be further elaborated herein. H is the height difference of the reflection event, whose source varies according to different saturation judgment results: it is taken from the first gain gear when there is no saturation; when the signal is saturated and the second gain gear is valid, it is taken from the second gain gear; when the signal is saturated but the second gain gear is invalid, it is taken from the true reflection height TRH calculated by Formula 1. W is the optical pulse width used in OTDR test, with the unit of nanosecond (ns) or microsecond (μs). The larger the pulse width, the more serious the broadening of the reflection peak in the time domain, and the greater the influence on the height difference measurement. The correction term 10×log in the formula 10 [(10 H / 5 -1)×W] is used to compensate for the pulse width broadening effect. In actual implementation, the formula can be simplified for calculation by means of table look-up or polynomial approximation, so as to adapt to the computing power limitation of embedded processors.

[0044] As Figure 3 shown is the acquisition curve of OTDR reflection events in the high gain gear. When the collected reflection R_peak_high obtained by the high gain hardware gear G_high of OTDR is less than the reflection saturation threshold (S_thr), that is R_peak_high<S_thr, the reflection value can be calculated according to the reflection height H_high of the hardware gear itself: R=B-10×log 10 [(10 H_high / 5 -1)×W] B is the backscattering coefficient of the optical fiber, W is the pulse width (in ns) used in OTDR test, and H_high is the height difference of the reflection peak in dB.

[0045] H_highR peak_high-R start_high, where H_high is the height difference of the high-gain reflection event (dB), Rpeak_high is the peak value of the high-gain reflection event (dB), Rstart_high is the starting point of the high-gain reflection event (dB), and S_thr is the reflection saturation threshold, which is related to the ADC chip selection of the OTDR and is a constant.

[0046] When the reflection saturation acquired by the OTDR at the high gain setting G_high, i.e., R_peak_high ≥ S_thr, combined with... Figure 4 As shown, perform low-gain G_low data acquisition, and make the following judgments based on the low-gain data acquisition results: When the height starting point (R start_low) of the reflection event acquired by the low-gain hardware mode is greater than the noise floor threshold (NFT), the reflection value R of the reflection event can be directly calculated based on the height difference H_low acquired by the low-gain hardware mode. R = B - 10 × log 10 [(10) H_low / 5 -1)×W] B is the fiber backscattering coefficient, W is the pulse width used in OTDR testing (ns), and H_low is the low-gain reflection peak height difference (dB).

[0047] H_LOW = R peak_low - R start_low. R peak_low is the peak value (dB) of the low-gain reflection event. R start_low is the low-gain reflection event start point (dB), and NFT (Noise Floor Threshold) is the OTDR noise floor at this setting, which is a constant related to hardware design.

[0048] When the starting point (R start_low) of the unsaturated reflection event acquired by the low-gain hardware mode is less than the noise floor threshold (NFT), it indicates that the reflection event height is in the noise zone, and H_low cannot be accurately calculated. In this case, the true reflection height (TRH) can be constructed based on the starting point (R start_high) of the reflection acquired by the high-gain mode, the peak reflection value (R peak_low) of the reflection acquired by the low-gain hardware mode, and the relative gain. The following relationship exists: TRH(dB)=R peak_low(dB)-R start_high(dB)+Relative Gain(dB) Using the OTDR reflection calculation formula, the reflection value R of the saturated reflection event can be obtained as: R = B - 10 × log 10 [(10) TRH / 5 -1)×W] like Figure 2 As shown, the first and second gain levels are implemented by configuring different resistor values ​​in the transimpedance amplifier of the optical time-domain reflectometer circuit, and the gain level of the transimpedance amplifier is switched by software control. This scheme clarifies the hardware implementation of dual gain levels, achieving gain switching through the configuration of different resistor values ​​in the transimpedance amplifier, and controlling the switching timing by software. The resistor switching scheme is simple in structure, low in cost, and highly reliable. Furthermore, the relative gain ratio between the gain levels is precisely determined by the resistor ratio, exhibiting good temperature stability and linearity. Software control provides the system with flexible timing scheduling capabilities, allowing precise control of the acquisition timing and duration of the two levels in a single scan, thus achieving the goal of using two levels for acquisition during a single test scan from a hardware perspective.

[0049] The transimpedance amplifier circuit can use analog switches (such as CMOS multiplexers) in conjunction with multiple sets of precision feedback resistors to achieve gain switching. The resistance values ​​of each set of resistors are configured with logarithmic or linear intervals according to the target gain multiple. For example, a 1MΩ feedback resistor can be used to achieve high gain for the first gain level, and a 100kΩ feedback resistor can be used to achieve low gain (10:1 gain ratio) for the second gain level. Software-controlled switching can be achieved by driving the selection terminal of the analog switch through the GPIO pin of the microcontroller. The switching timing needs to be precisely synchronized with the pulse transmission timing of the OTDR and the sampling timing of the ADC. For example, in each optical pulse transmission cycle, the complete echo data can be acquired first with the first gain level, and then with the second gain level. Alternatively, in a higher-speed implementation, the two levels can be alternately acquired in a single pulse cycle through time-division multiplexing. In addition, to reduce the transient response (such as charge injection and settling time) during level switching, appropriate blanking time can be inserted before and after switching, or the data after switching can be de-glitched.

[0050] Furthermore, the output curve of the optical time-domain reflectometer (OTDR) is generated entirely based on the data acquired at the first gain level. The data acquired at the second gain level is only used to correct the measurement accuracy of saturated reflection and does not participate in the generation of the ODR output curve. The fact that the ODR output curve is generated entirely based on the first gain level (high gain) data, while the second gain level data is only used for local correction of saturated reflection and does not participate in curve generation, ensures that the ODR output curve has excellent characteristics of high dynamic range and high sensitivity overall, avoiding the signal-to-noise ratio degradation problem of far-end signals caused by insufficient gain in low gain level data. Simultaneously, the correction operation only replaces local data points of saturated reflection events, minimizing the impact on the overall continuity and visual consistency of the curve. The OTDR trajectory map obtained by the user maintains the original measurement quality of the high gain level in most sections, obtaining accurate parameter annotations only at the saturated reflection points after correction.

[0051] During the curve generation stage, the data acquired at the first gain level is digitized by the ADC and then sequentially undergoes dark current subtraction, average noise reduction (e.g., averaging across multiple scans), logarithmic transformation (converting linear power values ​​to dB scales), and distance calibration (converting the time axis to the fiber length axis) to form a standard OTDR trajectory curve. When a saturation reflection event is detected and correction calculations are completed, the correction results are presented in several ways: the reflection point can be marked with special markers (e.g., different colors or icons) on the OTDR display interface as the corrected data, while the original saturation value and the corrected reflection value are listed in a data table for user comparison. At the data storage level, the original dual-gain level data can be stored separately in different areas of the internal memory. The corrected curve is stored separately as derived data, or it can overwrite the saturation data segment in the original curve, but retains the metadata of the correction markers and correction parameters (e.g., the gain level used, relative gain coefficient, etc.) for subsequent traceability and verification. Furthermore, the corrected reflection value can also be used to recalculate the link loss near that point, correcting pseudo-loss anomalies caused by saturation.

[0052] This invention also discloses an optical time-domain reflectometer, which includes a photodetector, a transimpedance amplifier circuit, and a control unit. Combined with... Figure 2As shown, the transimpedance amplifier circuit includes at least two switchable gain levels, wherein the gain of the first gain level is higher than that of the second gain level. The control unit is configured to control the transimpedance amplifier circuit to switch to the first gain level and the second gain level respectively during a single test scan of the optical time-domain reflectometer (OTDR) to acquire data from the same fiber under test. The processing unit is configured to generate an ODR output curve based on the data acquired at the first gain level, determine whether the reflection event acquired at the first gain level is saturated, and when the reflection event is determined to be saturated, calculate the reflection value of the reflection event based on the data acquired at the second gain level to correct the measurement accuracy of the saturated reflection.

[0053] Optical time domain reflectometers (OTDRs) achieve full automation of the entire process, from optical signal reception and electrical signal amplification to dual-gain switching control and saturation detection and correction calculation, through a modular architecture design of photodetectors, transimpedance amplifier circuits with switchable gain levels, control units, and processing units. With a compact hardware architecture and integrated software algorithms, complex dual-gain measurement and saturation correction functions are built into standard OTDR devices. Users can obtain high-precision saturation reflectance measurement results without external auxiliary equipment or cumbersome manual operations, significantly improving the engineering practicality and market competitiveness of OTDR products.

[0054] The photodetector can be an avalanche photodiode (APD) or a PIN photodiode. The APD, due to its internal gain characteristics, can further improve the receiving sensitivity, but it needs to be used in conjunction with a bias control circuit. In addition to the resistor switching scheme described in claim 9, the transimpedance amplifier circuit can also use a programmable gain amplifier (PGA) or a digital potentiometer to achieve continuous or discrete gain adjustment, supporting more ranges. The control unit can be an FPGA, DSP, or a high-performance ARM processor, responsible for generating the light pulse trigger signal, gain switching control signal, and ADC sampling clock signal, and ensuring the precise timing relationship between the three (e.g., delaying the extinction time after light pulse emission before starting sampling to avoid crosstalk at the transmitter). The processing unit can be integrated with the control unit in the same processor, or a dedicated digital signal processor can be used. Its software functional modules include: a dual-gain data acquisition and buffer management module, an automatic reflection event detection and location module, a saturation judgment and correction strategy decision module, a reflection value calculation and curve correction module, and a human-computer interaction and result display module, which will not be detailed here. In addition, this product can also integrate temperature compensation function, which adjusts the relative gain coefficient in real time according to the operating temperature of the transimpedance amplifier circuit to offset the impact of temperature drift on the correction accuracy. Details will not be elaborated here.

[0055] The present invention also discloses a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, it implements the method described above for improving the accuracy of saturated reflectance measurement of an optical time-domain reflectometer.

[0056] The aforementioned method is embedded in a computer-readable storage medium in the form of a computer program, which allows the method to be flexibly deployed and executed on general computing platforms or embedded systems. This breaks through the limitations of specific hardware devices and provides legal and technical protection for the software-based, standardized, and cross-platform application of OTDR saturation reflection correction technology. It also facilitates the functional expansion of the technology on existing OTDR devices through firmware upgrades, software licensing, and other means, reducing the cost threshold for technology promotion and application. At the same time, it is also conducive to the formation of an independent software product line.

[0057] The computer-readable storage media include, but are not limited to: flash memory (such as NOR Flash or NAND Flash), electrically erasable programmable read-only memory (EEPROM), hard disk drive (HDD), solid-state drive (SSD), optical disc (CD-ROM, DVD-ROM), and removable storage media (such as USB flash drives, SD cards, etc.). The computer program can be written in programming languages ​​such as C / C++, Python, and MATLAB, and compiled into binary code or intermediate code executable on the target processor. In embedded OTDR systems, the program is typically burned into the device's program memory and executed in conjunction with the operating system or bare-metal runtime environment. At the implementation level, the program can be designed as a standalone application or integrated into the existing software architecture as a functional module (such as a plugin or dynamic link library) of the OTDR system software. Furthermore, the program can be deployed to sold OTDR devices via network distribution (such as OTA online upgrades) to achieve remote function updates and performance optimization. Its version management and authorization control can be guaranteed through digital signatures and encrypted license mechanisms.

[0058] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Those skilled in the art can modify the technical solutions described in the above embodiments, or make equivalent substitutions for some of the technical features; and all such modifications and substitutions should fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for improving the accuracy of saturated reflectance measurement in an optical time-domain reflectometer, characterized in that, include: During a single test scan of the optical time domain reflectometer, data is acquired from the same fiber under test using a first gain setting and a second gain setting, wherein the gain of the first gain setting is higher than the gain of the second gain setting. The output curve of the optical time domain reflectometer is generated based on the data collected at the first gain level; Determine whether the reflection events collected at the first gain level are saturated; When the reflection event is determined to be saturated, the reflection value of the reflection event is calculated based on the data collected at the second gain setting to correct the measurement accuracy of the saturated reflection.

2. The method according to claim 1, characterized in that, The step of determining whether the reflection event collected by the first gain level is saturated includes: Obtain the peak value of the reflection event collected at the first gain level; The peak value of the reflection event is compared with a preset reflection saturation threshold; When the peak value of the reflection event is greater than or equal to the reflection saturation threshold, the reflection event is determined to be saturated.

3. The method according to claim 1, characterized in that, The method further includes: When it is determined that the reflection event is not saturated, the reflection value of the reflection event is calculated based on the height difference of the reflection event collected by the first gain level.

4. The method according to claim 1, characterized in that, The calculation of the reflection value of the reflection event based on the data acquired at the second gain level includes: Determine whether the starting point of the reflection event acquired at the second gain level is greater than a preset noise threshold; When the starting point of the reflection event is greater than the noise threshold, the reflection value of the reflection event is calculated based on the height difference of the reflection event collected by the second gain setting.

5. The method according to claim 4, characterized in that, The method further includes: When the starting point of the reflection event is less than or equal to the noise threshold, the true reflection height is constructed based on the starting point of the reflection event collected by the first gain level, the peak value of the reflection event collected by the second gain level, and the relative gain coefficient of the first gain level relative to the second gain level. The reflection value of the reflection event is calculated based on the actual reflection height.

6. The method according to claim 5, characterized in that, The actual reflection height is calculated using the following formula: TRH=R_peak_low-R_start_high+Relative_Gain Wherein, TRH is the true reflection height, R_peak_low is the peak value of the reflection event collected by the second gain setting, R_start_high is the starting point of the reflection event collected by the first gain setting, and Relative_Gain is the relative gain coefficient.

7. The method according to any one of claims 1-6, characterized in that, The first gain level and the second gain level are achieved by configuring different resistance values ​​of the transimpedance amplifier in the optical time domain reflectometer circuit, and the gain level of the transimpedance amplifier is switched by software control.

8. The method according to any one of claims 1-6, characterized in that, The output curve of the optical time domain reflectometer is generated entirely based on the data collected at the first gain level. The data collected at the second gain level is only used to correct the measurement accuracy of saturated reflection and does not participate in the generation of the output curve of the optical time domain reflectometer.

9. An optical time-domain reflectometer, characterized in that, include: Photodetector; A transimpedance amplifier circuit, the transimpedance amplifier circuit including at least two switchable gain levels, wherein the gain of the first gain level is higher than the gain of the second gain level; The control unit is configured to control the transimpedance amplifier circuit to switch to the first gain level and the second gain level respectively during a single test scan of the optical time domain reflectometer, so as to collect data from the same fiber under test respectively. The processing unit is configured to generate an optical time-domain reflectometer output curve based on the data acquired at the first gain level, determine whether the reflection event acquired at the first gain level is saturated, and when the reflection event is determined to be saturated, calculate the reflection value of the reflection event based on the data acquired at the second gain level to correct the measurement accuracy of the saturated reflection.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the method for improving the accuracy of saturated reflectance measurement of an optical time-domain reflectometer as described in any one of claims 1-8.

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