Multiband OTDR optical path multiplexing switching system and method

Abstract

The embodiment of the invention provides a switching system and method for multiband OTDR optical path multiplexing, and belongs to the technical field of optical fiber testing and optical communication detection. The system comprises a multi-band transmitting unit which is used for switching among a plurality of working bands and outputting OTDR test pulses of corresponding bands; the optical path multiplexing unit is used for respectively introducing the test pulses of the plurality of working wavebands into a measurement optical path and a reference optical path through a unified optical path; the internal reference optical fiber is used for providing reference echo signals for calibration under a plurality of working wavebands; the multi-band echo receiving unit is used for performing band separation on the echo light from the measuring light path and the reference light path and outputting echo signals of corresponding bands; and the control and calibration unit is used for performing normalization processing on the echo signal of each working wave band based on the calibration result. According to the scheme, the test pulse output consistency and the echo data comparability are kept under the multi-band condition, so that a cross-band unified measurement result capable of being used for conjoint analysis is obtained.

Description

A switching system and method for multi-band OTDR optical path multiplexing Technical Field

[0001] This invention relates to the field of optical fiber testing and optical communication detection technology, specifically to a switching system and a switching method for multi-band OTDR optical path multiplexing. Background Technology

[0002] Optical Time Domain Reflectometry (OTDR) is widely used for fiber optic link length measurement, attenuation assessment, and fault location. Traditional OTDRs are typically tested based on a single operating band, and the resulting echo signal reflects the distribution of scattering and reflection points in the fiber. However, with the increasing complexity of fiber optic communication network structures, the attenuation characteristics, scattering intensity, and observability of sensitive events of optical signals in different bands vary significantly. Single-band OTDR testing often struggles to simultaneously address the identification needs of multiple types of faults.

[0003] To improve the applicability of fiber optic testing, multi-band OTDRs have gradually gained attention. By testing at different operating bands, multiple echo curves reflecting different physical characteristics of the fiber can be obtained. However, multi-band testing usually requires an independent optical path structure, and the switching process between different bands depends on multiple light sources or multiple test channels, resulting in a complex overall optical path, high cost, and difficulty in achieving combined measurements of multiple bands in the same test link.

[0004] Furthermore, due to differences in intrinsic loss, beam splitting insertion loss, and detector response across different optical fiber bands, multi-band echo curves often suffer from inconsistent amplitude references and non-uniform time zero points, hindering cross-band result alignment and joint analysis. To address this, existing technologies typically correct these differences through independent calibration, external standard optical fibers, or manual matching. However, these methods are complex, lack automation, and are ill-suited for applications requiring frequent switching of operating bands.

[0005] On the other hand, with the increasing demand for optical communication maintenance, multi-band OTDRs aim to achieve dynamic switching, rapid calibration, and result consistency processing within the same test link, so as to complete multi-band detection without extensive optical path reconstruction. However, existing technologies still lack effective solutions in areas such as optical path multiplexing, internal calibration mechanisms, and cross-band normalization, which limits the application efficiency of multi-band OTDRs in actual network operation and maintenance.

[0006] In summary, existing multi-band OTDR testing processes still suffer from problems such as complex optical path switching, difficulty in unifying differences between bands, and reliance on external structures for calibration methods. A technical solution is needed that can achieve multi-band switching and consistent measurement under a unified optical path structure. Summary of the Invention

[0007] The purpose of this invention is to provide a switching system and method for multi-band OTDR optical path multiplexing, so as to at least solve the problems of complex switching of multi-band OTDR optical paths and inconsistent echo references for different operating bands.

[0008] To achieve the above objectives, a first aspect of the present invention provides a switching system for multi-band OTDR optical path multiplexing, the system comprising: a multi-band transmitting unit for switching between multiple operating bands and outputting OTDR test pulses of corresponding bands; an optical path multiplexing unit connected to the multi-band transmitting unit for introducing OTDR test pulses of multiple operating bands into a measurement optical path and a reference optical path respectively through a unified optical path; an internal reference fiber connected to the reference optical path for providing reference echo signals for calibration in multiple operating bands; a multi-band echo receiving unit for performing band separation on the echo light from the measurement optical path and the reference optical path and outputting echo signals of corresponding bands; and a control and calibration unit for calibrating the reference echo signal of the internal reference fiber during operating band switching and performing normalization processing on the echo signals of each operating band based on the calibration results.

[0009] Optionally, when the multi-band transmitting unit switches between multiple operating bands, it is configured to: obtain a preset output optical power range corresponding to the current operating band; perform power detection on the optical signal to be output in each operating band, and determine the difference between the detection result and the preset output optical power range; adjust the optical power of the optical signal to be output according to the difference, so that the multi-band transmitting unit outputs OTDR test pulses that meet the OTDR test requirements in different operating bands.

[0010] Optionally, when the optical path multiplexing unit introduces test pulses from multiple operating wavelengths into the measurement optical path and the reference optical path respectively, it is configured to: allocate the OTDR test pulses according to a preset optical energy allocation ratio; dynamically adjust the optical energy allocation ratio based on the coupling efficiency and loss characteristics of the reference optical path and the measurement optical path; and ensure that the OTDR test pulses from different operating wavelengths remain within the power range that can be used for calibration when entering the reference optical path, and meet the OTDR ranging dynamic range requirements when entering the measurement optical path.

[0011] Optionally, the internal reference fiber is provided with multiple reflection feature points along the fiber length direction, and each reflection feature point has different reflection intensity and spacing; under different working bands, by obtaining the echo position and echo amplitude of each reflection feature point, a reference echo sequence for constructing the calibration parameters of the corresponding working band is formed.

[0012] Optionally, when performing band separation, the multi-band echo receiving unit is configured to: distinguish the mixed echo light from the measurement optical path and the reference optical path based on the band separation structure; send the separated echo light of each band into the corresponding signal amplification path, and perform amplitude boosting on the echo signal according to the set gain parameter of the current working band; and perform photoelectric conversion and echo acquisition on the amplitude-boosted echo signals of each band under a unified time reference.

[0013] Optionally, when performing calibration processing, the control and calibration unit is configured to: trigger the acquisition of a reference echo sequence after the switching of each working band is completed; calculate the distance axis correction amount of the corresponding working band based on the time position error of each reflection feature point in the reference echo sequence; calculate the amplitude compensation amount of the corresponding working band according to the amplitude difference of each reflection feature point; and write the distance axis correction amount and the amplitude compensation amount into the calibration parameter set corresponding to the corresponding working band.

[0014] Optionally, when performing normalization processing on the echo signal, the control and calibration unit is configured to: correct the sampling point position of the acquired echo signal based on the distance axis correction amount corresponding to the corresponding working band; adjust the amplitude distribution of the echo signal based on the amplitude compensation amount corresponding to the corresponding working band; and form normalized echo data from the echo signal after distance correction and amplitude adjustment and submit it to the subsequent analysis module for multi-band data alignment and joint discrimination.

[0015] A second aspect of the present invention provides a switching method for multi-band OTDR optical path multiplexing, the method being implemented based on the aforementioned multi-band OTDR optical path multiplexing switching system. The method includes: a multi-band transmitting unit performing switching between multiple operating bands and outputting an OTDR test pulse optical signal for fiber testing at each target operating band; the optical path multiplexing unit introducing the OTDR test pulse optical signal belonging to the target operating band into the measurement optical path and the reference optical path respectively through a unified optical path to form a dual-path test structure for fiber ranging and calibration; and the internal reference fiber aligning the input to the reference optical path at the target operating band. The OTDR test pulse light signal generates a reference echo signal containing multiple reflection feature points. The multi-band echo receiving unit acquires the echo signal belonging to the target operating band under unified acquisition conditions. The control and calibration unit calculates the range axis correction and amplitude compensation based on the reference echo signal of the target operating band and writes the range axis correction and amplitude compensation into the calibration parameter set corresponding to the target operating band. Based on the control and calibration unit calling the calibration parameter set, range axis correction and amplitude correction are performed on the echo signal belonging to the target operating band to generate normalized echo data for multi-band joint analysis.

[0016] Optionally, before acquiring the echo signal belonging to the target operating band, the method further includes: the multi-band echo receiving unit performs amplitude adjustment on the echo optical signal entering the echo signal acquisition process according to the gain parameter set for the target operating band, so that the amplitude value of the echo optical signal falls within a preset amplitude acquisition range, and inputs the amplitude-adjusted echo optical signal into the echo signal acquisition process.

[0017] 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 switching method for multi-band OTDR optical path multiplexing.

[0018] Through the above technical solution, the embodiments of the present invention introduce a multi-band transmitting unit and an optical path multiplexing unit into a unified optical path, enabling OTDR test pulses from multiple working bands to be switched and transmitted without changing the optical path structure, thereby avoiding the structural complexity caused by traditional multi-band testing relying on multiple independent optical paths. Simultaneously, the internal reference fiber in the reference optical path generates reference echo signals that can be used for calibration at different working bands, allowing the system to acquire calibration information reflecting the optical path state and band differences after each band switch. The multi-band echo receiving unit performs band separation between the measurement echo and the reference echo on a unified acquisition link, forming echo data corresponding to each working band. Based on this, the control and calibration unit calculates the distance axis correction and amplitude compensation, and performs normalization processing on the echo signals of each working band, ensuring that the cross-band data remains consistent in distance and amplitude scales. Through the above structural configuration, the problems of complex optical path switching and inconsistent echo references across different bands in multi-band OTDR testing are solved.

[0019] 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

[0020] The accompanying drawings are provided to further illustrate the embodiments of the present invention and constitute a 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 switching method for multi-band OTDR optical path multiplexing provided in one embodiment of the present invention; Figure 2 is a system structure diagram of a switching system for multi-band OTDR optical path multiplexing provided in one embodiment of the present invention. Detailed Implementation

[0021] 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.

[0022] As shown in Figure 1, this embodiment of the invention provides a switching system for multi-band OTDR optical path multiplexing. The system includes: a multi-band transmitting unit for switching between multiple operating bands and outputting OTDR test pulses of corresponding bands; an optical path multiplexing unit connected to the multi-band transmitting unit for introducing OTDR test pulses of multiple operating bands into the measurement optical path and the reference optical path respectively through a unified optical path; an internal reference fiber connected to the reference optical path for providing reference echo signals for calibration in multiple operating bands; a multi-band echo receiving unit for performing band separation on the echo light from the measurement optical path and the reference optical path and outputting echo signals of corresponding bands; and a control and calibration unit for calibrating the reference echo signal of the internal reference fiber during operating band switching and performing normalization processing on the echo signals of each operating band based on the calibration results.

[0023] In this embodiment of the invention, the solution constructs a well-structured and unified switching system based on the core requirements of optical path multiplexing and cross-band consistency processing in multi-band OTDR testing. The system uses a multi-band transmitting unit as the entry point, achieving switching output of multiple working bands within a single test link, providing a unified pulse source for subsequent measurements.

[0024] Through the optical path multiplexing unit, test pulses from different bands can be rationally allocated to the measurement and reference optical paths on the same physical optical path, avoiding the structural redundancy caused by traditional multi-band testing relying on multiple independent optical paths. The internal reference fiber in the reference optical path generates a reference echo signal with identifiable characteristics in each working band, providing a stable basis for cross-band calibration. The multi-band echo receiving unit distinguishes between measurement echoes and reference echoes within a unified acquisition framework, ensuring the comparability of echo data from different bands. The control and calibration unit further utilizes the reference echoes to construct calibration parameters for each working band and performs normalization processing on the echo signals, ensuring consistency in distance and amplitude dimensions for cross-band data.

[0025] Preferably, when the multi-band transmitting unit switches between multiple operating bands, it is configured to: acquire a preset output optical power range corresponding to the current operating band; perform power detection on the optical signal to be output in each operating band, and determine the difference between the detection result and the preset output optical power range; adjust the optical power of the optical signal to be output according to the difference, so that the multi-band transmitting unit outputs OTDR test pulses that meet the OTDR test requirements in different operating bands.

[0026] In this embodiment of the invention, the configuration logic of the multi-band transmitting unit mainly revolves around energy tuning after switching the operating band. It is important to clarify that OTDR testing has high requirements for pulse energy repeatability, and the loss and coupling conditions of different bands are not consistent. Therefore, an output reference must be re-established after the switching operation. Specifically, the operation typically begins by obtaining the preset output optical power range of the target operating band. This range is often set based on equipment calibration values ​​or optical link models and describes the energy range required to form a qualified test pulse in that band. The subsequent power detection step is more like a rapid scan, detecting the optical signal that is about to enter the subsequent pulse formation process. The detection result shows the offset relationship between the current optical power and the preset range.

[0027] Once the offset is determined, the next step involves the quantitative adjustment of the optical power. Adjustment methods can include variable optical attenuation control or adjustment of the drive current at the source outlet; the choice depends on the characteristics of the light source and the response speed of the control module. The adjustment process does not emphasize continuity, but rather focuses on whether it ultimately falls within the preset range, since OTDR pulse output is a discrete triggering behavior. Once the optical power is adjusted to the target range, the test pulses in the corresponding operating band can maintain a relatively stable energy level, preventing unnecessary amplitude deviations in subsequent scattering sampling due to band differences. This entire process aims to establish cross-band energy consistency, providing a comparable data basis for multi-band testing from the initial stage.

[0028] Preferably, when the optical path multiplexing unit introduces test pulses from multiple operating wavelengths into the measurement optical path and the reference optical path respectively, it is configured to: allocate the OTDR test pulses according to a preset optical energy allocation ratio; dynamically adjust the optical energy allocation ratio based on the coupling efficiency and loss characteristics of the reference optical path and the measurement optical path; so that the OTDR test pulses from different operating wavelengths are all kept within the power range that can be used for calibration when entering the reference optical path, and meet the OTDR ranging dynamic range requirements when entering the measurement optical path.

[0029] In this embodiment of the invention, the core function of the optical path multiplexing unit is to manage the energy allocation of test pulses from different operating bands. This starts with a preset allocation ratio, which is often not a random value but rather set based on previous link calibrations and device parameters. This ratio roughly defines the proportion of energy that the test pulse should be allocated to the measurement optical path and the reference optical path. The existence of this ratio provides an initial anchor point for energy control during complex band switching, but it typically does not remain unchanged for a long time because different bands exhibit significant differences in loss and coupling conditions within the same optical path.

[0030] More specific allocation and adjustment steps often require judgment based on the coupling efficiency between the reference optical path and the measurement optical path. Coupling efficiency is typically a static parameter in design documents, but in actual use, it fluctuates due to fiber interface conditions, insertion loss variations, or device aging. This fluctuation is more pronounced in multi-band testing. The optical path multiplexing unit dynamically updates the allocation ratio based on these changes, ensuring that each working band receives sufficient energy to enter the reference optical path for subsequent calibration, while not compressing the dynamic range required by the measurement optical path. This dynamic update is not a complex optimization algorithm, but rather more like a gradual correction based on detection results; the adjustment process typically involves subtle shifts around the target power range.

[0031] In practice, energy control of the reference optical path is crucial because the amplitude of the calibration signal must avoid being too low or too high. Too low an amplitude makes it difficult to identify reflection feature points, while too high an amplitude may cause saturation in the detection link, affecting the stability of subsequent normalization steps. Therefore, redistributing the input power of the reference optical path after band switching is a necessary means to maintain calibration reliability. The allocation requirements for the measurement optical path are relatively relaxed, but it is still essential to ensure that the energy of the test pulse covers the dynamic range required for OTDR ranging. Since the dynamic range itself varies with band, the optical energy allocation ratio is often periodically adjusted to maintain the continuity and comparability of measurement results.

[0032] In one specific implementation, initial optical energy allocation ratios are set for three commonly used operating wavelengths (1310nm, 1490nm, and 1550nm). For example, the test pulses are allocated to the measurement optical path and the reference optical path in a 7:3 ratio. Taking the 1310nm wavelength as an example, the peak power of the output pulse after being driven by the light source is approximately +4dBm. After coupling into the optical path multiplexing unit, the measurement optical path obtains approximately +2.5dBm, and the reference optical path obtains approximately -1dBm. Under initial conditions, the calibration reflection point of the reference optical path can form an echo amplitude of approximately -35dBm, which meets the calibration requirement of a power window of [-40dBm, -25dBm].

[0033] During the 1490nm test, the insertion loss of the same optical path changed from 2.1dB to approximately 2.8dB, causing the pulse power entering the reference optical path to drop to -3.2dBm. At this point, the optical path multiplexing unit adjusted the allocation ratio from 7:3 to 6:4 based on the detection results, bringing the input power of the reference optical path back to around -1.5dBm. Subsequently, the pulse power of the measurement optical path remained within the effective dynamic range required for OTDR testing (approximately +1dBm to +3dBm).

[0034] In the 1550nm band, due to the low inherent loss of optical fibers, the echo amplitude is often high, and the reference optical path may exhibit a peak value close to -23dBm. To avoid the back-end probe link approaching saturation, the optical energy distribution ratio can be further adjusted to 8:2, controlling the input power of the reference optical path to around -2dBm, thus keeping the calibration structure in a resolvable state.

[0035] Preferably, the internal reference fiber has multiple reflection feature points arranged along the fiber length direction, and each reflection feature point has a different reflection intensity and spacing; under different working bands, by obtaining the echo position and echo amplitude of each reflection feature point, a reference echo sequence for constructing the calibration parameters of the corresponding working band is formed.

[0036] In this embodiment of the invention, the design of the internal reference fiber typically revolves around the layout of reflection feature points. A common approach is to arrange several feature points with different reflection intensities along the length direction. These points are often achieved through micro-bending, refractive index perturbation, or local reflective coatings. The reflection amplitude and spacing parameters of each point are determined during the manufacturing stage. This structure allows the reflection events to exhibit a relatively clear distribution in the echo sequence. The number of points does not need to be excessive, but the spacing needs to cover typical time windows so that identifiable echo curves can still be obtained at different wavelengths.

[0037] When the operating band changes, the reflection characteristics of the reference fiber remain unchanged, but the scattering and insertion loss behaviors will change to some extent. This change is directly reflected in the echo amplitude and echo position at the reflection feature point. The echo position is often sensitive to changes in group velocity; differences in refractive index at different bands will cause small time shifts, which can be used as a reference for subsequent distance axis correction. The echo amplitude is more affected by power distribution, material scattering properties, and optical device response, making it more suitable for constructing amplitude compensation parameters. These data are typically acquired by performing an echo detection at each reflection feature point and extracting the peak time and peak amplitude from the impulse response curve.

[0038] When analyzing these echo data, the intervals between different reflection points provide a natural scaling reference. For example, two feature points with a fixed interval will have different time differences in different bands. This difference reflects the propagation speed of the optical signal in the current band, thus providing a basis for correcting the distance axis model. Similarly, the amplitude ratios between each reflection point can reflect the actual state of the light source energy distribution and link insertion loss, which is suitable for establishing amplitude normalization parameters. By classifying the data of all reflection feature points according to bands, a reference echo sequence (i.e., reference echo signal) is formed, which can be regarded as the input basis for calibration parameters.

[0039] Preferably, when performing band separation, the multi-band echo receiving unit is configured to: distinguish the mixed echo light from the measurement optical path and the reference optical path based on the band separation structure; send the separated echo light of each band into the corresponding signal amplification path, and perform amplitude boosting on the echo signal according to the set gain parameter of the current working band; and perform photoelectric conversion and echo acquisition on the amplitude-boosted echo signals of each band under a unified time reference.

[0040] In this embodiment of the invention, when echo light of different wavelengths propagates in the same optical path, its spectral components are mixed together, requiring separation using a specific wavelength separation structure. Common methods include thin-film filters, arrayed waveguides, or WDM demultiplexers. These structures rely on wavelength selectivity to perform the separation task, causing the mixed echo light to be distributed in groups at the exit, laying the foundation for subsequent processing. After separation, the echo light of each wavelength band is guided into different signal paths, avoiding crosstalk during subsequent amplification.

[0041] The design of the signal amplification path often relies on the gain setting value of the current operating band. This setting value is given before the test begins and describes the amplitude range that the echo signal needs to compensate for before entering the detection link. The amplitude boosting method may be transimpedance amplification or cascaded variable gain amplifiers, with the choice tending to consider noise performance and dynamic range. There is no strict step-by-step rule for amplitude boosting; rather, it is more about performing correction based on the difference between the input amplitude and the target range, so that the signal finally entering the photoelectric conversion stage meets the requirements of the sampling link.

[0042] After amplification, the echo signals from each band are synchronized for photoelectric conversion. Photoelectric conversion relies on a unified time reference, typically determined by a unified trigger clock or sampling sequence, ensuring that signals from different bands are recorded on the same time axis. The significance of a unified time reference lies in the time alignment of the echo curves, providing consistent coordinates for cross-band post-processing; otherwise, asynchronous sampling would lead to distance axis offset. After photoelectric conversion, the echo signals enter the acquisition module, forming a digital sequence directly usable for analysis.

[0043] In one specific implementation, a band separation structure consisting of three wavelength division channels is used to process the mixed echo light from the measurement optical path and the reference optical path. Taking the 1310nm, 1490nm, and 1550nm bands as examples, the mixed echo light enters the corresponding wavelength division ports after passing through the separation structure. The echo light power output from each port is approximately -48dBm, -52dBm, and -45dBm, respectively. To ensure that these signals fall within the input range of the acquisition path, each band is mapped to a separate signal amplification path, and an amplitude boost is performed according to predefined gain parameters. For example, the 1490nm echo signal has a relatively low amplitude at the input end, so the total gain in the amplification path can be set to approximately 28dB to maintain the output signal at around -24dBm; while the 1550nm band, due to its higher initial amplitude, only requires approximately 12dB of gain compensation to enter the sampleable range.

[0044] After amplitude adjustment, the echo signals from each band are synchronously sent to the photoelectric conversion module, with the trigger clock using the same sampling period, such as 20ns, to ensure that the time base remains consistent across the three bands. The digital echo sequence generated after photoelectric conversion contains band-distinguishing labels and can be directly used for subsequent calibration calculations and cross-band analysis.

[0045] Preferably, when performing calibration processing, the control and calibration unit is configured to: trigger the acquisition of a reference echo sequence after the switching of each working band is completed; calculate the distance axis correction amount of the corresponding working band based on the time position error of each reflection feature point in the reference echo sequence; calculate the amplitude compensation amount of the corresponding working band according to the amplitude difference of each reflection feature point; and write the distance axis correction amount and the amplitude compensation amount into the calibration parameter set corresponding to the corresponding working band.

[0046] Furthermore, when performing normalization processing on the echo signal, the control and calibration unit is configured to: correct the sampling point position of the acquired echo signal based on the distance axis correction amount corresponding to the corresponding working band; adjust the amplitude distribution of the echo signal based on the amplitude compensation amount corresponding to the corresponding working band; and form normalized echo data from the echo signal after distance correction and amplitude adjustment and submit it to the subsequent analysis module for multi-band data alignment and joint discrimination.

[0047] In this embodiment of the invention, after the working band is switched, a complete frame of echo data is first acquired for the reference optical path to obtain the reference echo sequence under the current working band. Multiple preset reflection feature points in the reference fiber have theoretical time positions and theoretical amplitudes given during the design phase; these values ​​can be considered as static scales. By comparing the acquired reference echo sequence with this set of scales, the time position deviation and amplitude deviation are obtained, providing input for subsequent distance axis correction and amplitude compensation.

[0048] Time-direction correction typically involves first extracting the arrival time of each reflection feature point, and then constructing an average offset. The current target operating band can be denoted as w, and the theoretical arrival time of the k-th reflection feature point, determined during the design phase, can be denoted as _w_. The arrival time of the same reflection feature point measured in the working band w is denoted as Based on this data, the time offset of the working band w can be calculated. :

[0049] Here, K represents the number of reflection feature points involved in the calibration. This represents the actual sampling time of the k-th reflection feature point under the working band w. This represents the theoretical time position corresponding to the same feature point. Time offset. Give the overall drift of the current working band relative to the scale on the time axis.

[0050] After obtaining the time offset, the original sampling time needs to be mapped to the distance axis. For the i-th sampling point in the working band w, the original sampling time can be denoted as... Let the group velocity of this band in the optical fiber be denoted as . (Time offset) The group speed is (Constitutes the distance axis correction). Corrected distance coordinates. It can be written as:

[0051] In this expression, Typically obtained through a refractive index model or pre-calibration experiment, the distance is divided by 2 to reflect the round-trip propagation path. In this way, the position of each sampling point on the distance axis will be translated around the reflection feature point, and the corresponding spatial coordinates will be given according to the propagation speed of the current band. The distance axis will converge to a unified reference across different working bands.

[0052] Amplitude compensation focuses more on gain difference and zero-point offset. The theoretical amplitude corresponding to the k-th reflection feature point can be denoted as... The measured amplitude under the working band w is recorded as To reduce the impact of random fluctuations, a linear amplitude mapping model can be constructed, introducing a gain coefficient. and bias (These two constitute the amplitude compensation amount), making the mapped amplitude as close as possible to the theoretical amplitude. A feasible solution is given by least squares fitting:

[0053] here, Describe the scaling relationship of the operating band w with respect to the overall gain. Both the amount of shift reflecting the zero point of amplitude are obtained through fitting multi-point data, rather than relying on a single feature point. This process reduces the sensitivity of the calibration parameters to local noise.

[0054] Yes and Then, compensation can be performed on the original amplitude of any sampling point under the working band w. If the original amplitude of the i-th sampling point is... The corrected amplitude writing:

[0055] In this step, the original amplitude distribution is stretched or compressed, accompanied by a uniform bias adjustment, so that the corrected amplitudes of multiple reflection feature points are closer to the theoretical distribution. This results in amplitude data that is comparable across different working bands, laying a foundation for subsequent normalization processing.

[0056] The above time offset Group speed Gain coefficient and bias Together, these parameters constitute the calibration parameter set for the working band w. During the calibration phase, the control and calibration unit writes this set of parameters into the storage entry for the corresponding working band, for use in subsequent measurements. During the normalization phase, these parameters are no longer repeatedly calculated; instead, distance axis correction and amplitude compensation are directly performed on the newly acquired echo sequence based on the calibration parameter set.

[0057] During normalization, distance correction and amplitude correction are typically performed in a fixed order. First, for each sampling point, according to... and Calculate the corrected distance reuse and Obtain the correction amplitude After the distance and amplitude coordinates are corrected, the normalized echo data corresponding to the working band w is formed. The normalized echo data expresses fiber scattering information under the same distance and amplitude references, which facilitates alignment and joint discrimination with data from other working bands.

[0058] Overall, this set of control and calibration rules, relying on the reflection feature point sequence provided by the internal reference fiber, establishes a repeatable correction model for both the time and amplitude dimensions in multi-band scenarios. Subsequent multi-band event identification, attenuation curve comparison, and fault location comparison can all use normalized echo data as input. The analysis process focuses more on the physical response of the fiber itself, rather than repeatedly dealing with the systematic deviations caused by band switching.

[0059] In another possible implementation, a calibration strategy based on "frequency-domain interference feature mapping" is introduced to replace the traditional time-domain calibration method that relies on reflection feature points. In this approach, the reference optical path no longer relies on discrete reflection points to form a calibration benchmark. Instead, a fiber segment with weakly periodic refractive index modulation is implanted in the reference fiber, causing the echo signal to exhibit a periodic interference envelope in the frequency domain. The period parameter can be set to an equivalent optical path difference within the range of 80cm-120cm, ensuring that the interference fringes at different operating wavelengths have measurable envelope spacing. After the test begins, the measured echo signal is subjected to a Fast Fourier Transform to extract the position f of the main peak of the interference envelope. peak (w), and compared it with the theoretical peak position f. ref By making a comparison, the frequency domain offset Δf is obtained. w Distance axis correction can be based on:

[0060] Perform calculations, where This represents the distance correction amount corresponding to the working band w. At the speed of light, The equivalent refractive index is used. Amplitude compensation is based on the peak-to-valley ratio change of the interference envelope, and the gain correction factor G is obtained by fitting the amplitude attenuation rate of the envelope curve. w This method is used to unify the amplitude distribution across different frequency bands. By employing this strategy, the calibration process does not rely on explicit reflection feature points, maintaining effectiveness even in fiber optic scenarios with a limited number of reflection points or severe damage, thus providing a second calibration path for complex lines.

[0061] As shown in Figure 2, this embodiment of the invention provides a switching method for multi-band OTDR optical path multiplexing. The method is based on the multi-band OTDR optical path multiplexing switching system described above. The method includes: Step S10: The multi-band transmitting unit performs switching between multiple working bands and outputs an OTDR test pulse optical signal for fiber testing under each target working band.

[0062] Specifically, a multi-band transmitter typically needs to perform three actions: determining the operating band, setting the pulse energy, and triggering pulse output. First, when a band switching command arrives, the multi-band transmitter reads the target operating band number and loads the source drive parameters corresponding to that band, such as pulse width, peak power window, and modulation scheme. These drive parameters are often derived from a pre-calibration database to ensure that the output pulses have a convergent energy structure across different bands.

[0063] Furthermore, a power detection is performed on the output optical signal in the target band. If there is a deviation between the detection result and the preset power range of that band, the transmitting unit will perform compensation through an adjustable drive current or a variable optical attenuation component to ensure that the pulse energy falls within the amplitude range that can be used for OTDR scattering measurement. The compensation process does not emphasize continuous dynamics but focuses on matching discrete target ranges. After adjustment, the multi-band transmitting unit outputs test pulses according to the trigger timing sequence, ensuring that each working band enters the optical path multiplexing structure under the required energy state.

[0064] Step S20: Based on the optical path multiplexing unit, the OTDR test pulse optical signal belonging to the target working band is introduced into the measurement optical path and the reference optical path respectively through a unified optical path to form a dual-path test structure for fiber ranging and calibration.

[0065] Specifically, the optical path multiplexing unit first receives test pulses from the multi-band transmitting unit and determines the distribution of the pulses between the measurement optical path and the reference optical path based on the currently set optical energy allocation ratio. Typically, the initial configuration uses a fixed ratio, such as 7:3, but this ratio is dynamically adjusted as optical path loss, coupling efficiency, and band characteristics change.

[0066] Before the pulse enters, the optical path multiplexing unit quickly measures the insertion loss at the coupling port or reads historical compensation values. Using this information, it fine-tunes the energy allocation ratio to ensure that the energy entering the reference optical path remains within the power window required for calibration, while the energy entering the measurement optical path falls within the dynamic range of the OTDR ranging link. The actual energy allocation typically relies on optical splitters, variable couplers, or band-independent optical power control components. Each adjustment is performed on a pulse-level timescale to avoid affecting the overall testing rhythm. Ultimately, the multiplexed dual-path structure forms a complete measurement loop and a reference path for calibration, providing necessary data support for subsequent band difference correction.

[0067] Step S30: Based on the internal reference fiber, a reference echo signal containing multiple reflection feature points is generated for the OTDR test pulse optical signal entering the reference optical path under the target operating band. The echo signal belonging to the target operating band is then acquired by the multi-band echo receiving unit under unified acquisition conditions.

[0068] Specifically, after receiving the test pulse, the reference optical path propagates along the internal reference fiber and generates reflection events at multiple preset reflection feature points. The design of these reflection feature points typically employs refractive index perturbations, microbending structures, or local reflective films to ensure that each reflection point exhibits different amplitudes and distinct intervals in the echo. The propagated echo signal contains the reflection peaks from each feature point, forming a reference echo sequence.

[0069] Meanwhile, the pulses in the measurement optical path induce Rayleigh scattering and reflection events in the fiber under test, forming measurement echoes. The multi-band echo receiving unit acquires echoes from both optical paths under a unified acquisition link. The acquisition process uses a unified sampling clock as a reference, ensuring consistent time resolution across different bands. With the aid of a band separation structure, echoes from different bands are prevented from mixing in the receiving link and are separated before entering the amplification path, maintaining a clear data structure for subsequent processing. The final echo sequence contains identifiable peak positions of reference feature points and scattering information from the measurement fiber, providing fundamental input for subsequent calibration calculations.

[0070] Step S40: The control and calibration unit calculates the range axis correction and amplitude compensation based on the reference echo signal of the target working band, and writes the range axis correction and amplitude compensation into the calibration parameter set corresponding to the target working band.

[0071] Specifically, in the calibration process, two types of correction parameters need to be established based on the time position and amplitude distribution of each reflection feature point in the reference echo sequence. The offset of the time position is usually obtained by comparing the actual sampling time and the theoretical set time. This difference can reflect the effective group velocity or sampling reference offset of the optical fiber in the current band. The control and calibration unit constructs the distance axis correction accordingly to align the overall echo curve in spatial coordinates.

[0072] Amplitude compensation relies on the amplitude ratio changes of reflection feature points. By fitting the amplitude deviations of multiple feature points, a unified gain factor and offset parameter are obtained to correct the overall scale differences in echo intensity. After completing the parameter calculations for the time axis and amplitude direction, these data are written into the calibration parameter set according to the working band number. The calibration parameter set typically contains four types of key data: time offset, group velocity parameter, amplitude gain factor, and amplitude offset. Each data point points to a specific working band and serves as a fixed input for normalization processing.

[0073] Step S50: Based on the control and calibration unit calling the calibration parameter set, perform distance axis correction and amplitude correction on the echo signals belonging to the target working band to generate normalized echo data for multi-band joint analysis.

[0074] Specifically, in the normalization process, the control and calibration unit reads the set of calibration parameters corresponding to the target working band and applies these parameters to the newly acquired echo signal. Range axis correction first maps the original sampling time to a unified range reference based on the time offset and the group velocity of the corresponding band, ensuring that the starting point and scale of the echo curve remain consistent on the spatial axis.

[0075] Subsequently, amplitude direction correction is performed. The original amplitude distribution is linearly adjusted using gain factors and bias parameters to ensure comparable dynamic ranges for amplitude curves across different bands. The normalized echo data is constructed from these steps, and its format includes correction distance, correction amplitude, and working band labels, facilitating subsequent modules for cross-band alignment, trend identification, or joint event discrimination. The goal of the normalization process is to eliminate systematic differences introduced by band switching, making the information structure more suitable for multi-band analysis workflows.

[0076] Preferably, before acquiring the echo signal belonging to the target operating band, the method further includes: the multi-band echo receiving unit performs amplitude adjustment on the echo optical signal entering the echo signal acquisition process according to the gain parameter set for the target operating band, so that the amplitude value of the echo optical signal falls within a preset amplitude acquisition range, and inputs the amplitude-adjusted echo optical signal into the echo signal acquisition process.

[0077] In this embodiment of the invention, before entering the formal acquisition stage, the amplitude of the echo light needs to be preprocessed. This step is usually placed in multi-band scenarios to avoid excessive energy differences between different bands. The multi-band echo receiving unit first reads the gain parameters corresponding to the target operating band. These gain parameters have been given a range during the calibration stage to describe the acceptable amplitude range for this echo acquisition. Subsequently, a fast amplitude detection is performed on the echo light that has just entered the receiving link. The detection is generally completed by sampling in the pre-detection stage, extracting only the coarse magnitude of the amplitude without requiring detailed analysis. If the detection result deviates from the preset acquisition range, the receiving link will call the variable gain path to adjust the amplitude so that it moves closer to the target range.

[0078] The amplitude adjustment logic typically employs an discrete stepwise approach rather than a continuous closed-loop method because the amplitude structure of OTDR pulses is inherently a discrete event, making this approach more stable. Typically, if the amplitude falls below the acquisition threshold, the gain of the pre-amplifier stage is increased; if the amplitude approaches saturation, the amplification factor is reduced to bring the signal back into the processable range. The entire process is largely a pre-tuning step, designed to keep subsequent sampling within the detector's linear range and reduce dynamic range edge effects.

[0079] After adjustment, the amplitude has been brought back to a range that is more compatible with different wavelengths. Only then will the echo light be introduced into the formal acquisition process. The acquisition chain operates on this preprocessing foundation, allowing it to focus more on the echo structure itself without being limited by amplitude drift in analysis accuracy. In other words, this preprocessing step establishes closer input conditions for cross-band data, providing a more stable starting point for subsequent calibration and normalization stages.

[0080] The present invention also provides a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the above-described switching method for multi-band OTDR optical path multiplexing.

[0081] 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.

[0082] 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.

[0083] 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 switching system for multi-band OTDR optical path multiplexing, characterized in that, The system includes: a multi-band transmitting unit for switching between multiple operating bands and outputting OTDR test pulses of corresponding bands; an optical path multiplexing unit connected to the multi-band transmitting unit for introducing OTDR test pulses of multiple operating bands into the measurement optical path and the reference optical path respectively through a unified optical path; an internal reference fiber connected to the reference optical path for providing reference echo signals for calibration in multiple operating bands; a multi-band echo receiving unit for performing band separation on the echo light from the measurement optical path and the reference optical path and outputting echo signals of corresponding bands; and a control and calibration unit for calibrating the reference echo signals of the internal reference fiber when switching operating bands, and performing normalization processing on the echo signals of each operating band based on the calibration results.

2. The system according to claim 1, characterized in that, When the multi-band transmitting unit switches between multiple operating bands, it is configured to: obtain the preset output optical power range corresponding to the current operating band; perform power detection on the optical signal to be output in each operating band, and determine the difference between the signal and the preset output optical power range based on the detection result; The optical power of the output optical signal is adjusted according to the difference, so that the multi-band transmitting unit outputs OTDR test pulses that meet the OTDR test requirements under different operating bands.

3. The system according to claim 1, characterized in that, When the optical path multiplexing unit introduces test pulses from multiple working wavelength bands into the measurement optical path and the reference optical path respectively, it is configured to distribute the OTDR test pulses according to a preset optical energy distribution ratio. Based on the coupling efficiency and loss characteristics of the reference optical path and the measurement optical path, the optical energy distribution ratio is dynamically adjusted so that OTDR test pulses of different operating bands remain within the power range that can be used for calibration when entering the reference optical path, and meet the OTDR ranging dynamic range requirements when entering the measurement optical path.

4. The system according to claim 1, characterized in that, The internal reference fiber has multiple reflection feature points arranged along its length, each with different reflection intensities and spacing. Under different operating bands, by acquiring the echo position and echo amplitude of each reflection feature point, a reference echo sequence is formed to construct the calibration parameters for the corresponding operating band.

5. The system according to claim 1, characterized in that, When performing band separation, the multi-band echo receiving unit is configured to: distinguish the mixed echo light from the measurement optical path and the reference optical path based on the band separation structure; send the separated echo light of each band into the corresponding signal amplification path, and perform amplitude boosting on the echo signal according to the set gain parameter of the current working band; and perform photoelectric conversion and echo acquisition on the amplitude-boosted echo signals of each band under a unified time reference.

6. The system according to claim 4, characterized in that, When performing calibration processing, the control and calibration unit is configured to: trigger the acquisition of a reference echo sequence after the switching of each working band is completed; calculate the distance axis correction amount of the corresponding working band based on the time position error of each reflection feature point in the reference echo sequence; calculate the amplitude compensation amount of the corresponding working band according to the amplitude difference of each reflection feature point; and write the distance axis correction amount and the amplitude compensation amount into the calibration parameter set corresponding to the corresponding working band.

7. The system according to claim 1, characterized in that, When performing normalization processing on the echo signal, the control and calibration unit is configured to: correct the sampling point position of the acquired echo signal based on the distance axis correction amount corresponding to the corresponding working band; adjust the amplitude distribution of the echo signal based on the amplitude compensation amount corresponding to the corresponding working band; and form normalized echo data from the echo signal after distance correction and amplitude adjustment and submit it to the subsequent analysis module for multi-band data alignment and joint discrimination.

8. A switching method for multi-band OTDR optical path multiplexing, characterized in that, The method is implemented based on the multi-band OTDR optical path multiplexing switching system according to any one of claims 1-7. The method includes: a multi-band transmitting unit performing switching between multiple operating bands and outputting an OTDR test pulse optical signal for fiber testing in each target operating band; based on the optical path multiplexing unit, introducing the OTDR test pulse optical signal belonging to the target operating band into the measurement optical path and the reference optical path respectively through a unified optical path to form a dual-path test structure for fiber ranging and calibration; and based on the internal reference fiber, testing the OTDR test pulse optical signal entering the reference optical path in the target operating band. A test pulse optical signal generates a reference echo signal containing multiple reflection feature points. A multi-band echo receiving unit acquires the echo signal belonging to the target operating band under unified acquisition conditions. A control and calibration unit calculates the range axis correction and amplitude compensation based on the reference echo signal of the target operating band and writes these values ​​into a calibration parameter set corresponding to the target operating band. Based on the calibration parameter set, the control and calibration unit performs range axis correction and amplitude correction on the echo signal belonging to the target operating band to generate normalized echo data for multi-band joint analysis.

9. The method according to claim 8, characterized in that, Before acquiring the echo signal belonging to the target operating band, the method further includes: the multi-band echo receiving unit performs amplitude adjustment on the echo optical signal entering the echo signal acquisition process according to the gain parameter set for the target operating band, so that the amplitude value of the echo optical signal falls within the preset amplitude acquisition range, and inputs the amplitude-adjusted echo optical signal into the echo signal acquisition process.

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 switching method for multi-band OTDR optical path multiplexing as described in any one of claims 8 and 9.

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