A phase type optical frequency domain reflection three-dimensional deformation measurement device and method capable of resisting fading noise

Abstract

The application discloses a kind of phase type optical frequency domain reflection three-dimensional deformation measurement device and method of anti-fading noise, comprising: transmitting detection signal, and be divided into measurement path and reference path;Mode multiplexing is realized by photonic lantern to measurement path signal, generate mode multiplexing multi-mode detection light, and respectively enter different fiber cores of few-mode multicore fiber;The reflected light of three-dimensional deformation information of different fiber cores of few-mode multicore fiber is carried out light domain mixing with reference path signal, obtains the beat frequency signal of different light modes of each fiber core;The beat frequency signal of different light modes in each fiber core is phase-averaged, obtains the strain information of different fiber cores, combines Frenet-Serret framework, reconstructs the three-dimensional deformation of few-mode multicore fiber.The application realizes the effective measurement of spatial three-dimensional shape while compensating coherent fading noise, with the characteristics of high sensitivity, high spatial resolution, is suitable for three-dimensional shape sensing under complex environment.

Description

Technical Field

[0001] This invention belongs to the field of distributed optical fiber sensing technology, specifically, it relates to a phase-type optical frequency domain reflectance three-dimensional deformation measurement device and method that is resistant to fading noise. Background Technology

[0002] Distributed fiber optic sensing (DFOS) technology uses optical fiber as the sensing and transmission medium to acquire environmental information at various locations along the fiber optic cable, representing a significant development direction for fiber optic sensing technology. In recent years, DFOS-based three-dimensional deformation measurement technology has gained significant attention in applications requiring high-precision shape measurement, such as industrial inspection, biomedicine, and aerospace. Among these, distributed sensing technology based on multi-core fiber (MCF) is a representative technology in the field of three-dimensional deformation measurement.

[0003] Currently, mainstream DFOS technologies mainly include optical time-domain reflectometry (OTDR) and optical frequency-domain reflectometry (OFDR). The former struggles to simultaneously achieve optimal spatial resolution and measurement distance, making it difficult to meet the practical application requirements of high-precision, high-resolution strain sensing. The latter, with its comprehensive performance advantages in measurement distance, spatial resolution, and strain accuracy, is currently the core and key technology in the field of distributed fiber optic three-dimensional deformation measurement. Among them, phase-type OFDR, with its optical wave phase-level sensitivity and linear response characteristics, represents an important development direction for DFOS technology in recent years, effectively improving the performance of DFOS-based three-dimensional deformation measurement and expanding its application areas.

[0004] However, during OFDR measurements, the echo signal mainly contains a large number of backscattered Rayleigh (RBS) signals with random phase and amplitude distributions. During coherent mixing at the receiver, the coherent superposition of these numerous RBS signals leads to drastic fluctuations in the beat frequency signal amplitude, exhibiting a coherent fading phenomenon. This coherent fading causes a sharp deterioration in the beat frequency signal signal-to-noise ratio, which is a key factor affecting the accuracy of phase-type OFDR measurements and limiting system reliability.

[0005] To address this problem, researchers have primarily focused on sensing fibers and signal processing. From the perspective of Rayleigh scattering generation mechanisms, gratings can be etched into the fiber to effectively enhance the Rayleigh scattering signal, thereby suppressing the influence of coherent fading noise by improving the RBS signal-to-noise ratio. However, fiber gratings can only achieve quasi-distributed sensing, indirectly degrading spatial resolution and reducing the effective detection distance. Considering the measurement signal, a wide-range swept-frequency light source can be used as the detection signal to improve spatial resolution and reduce the number of random RBS interferences, thus reducing coherent fading. However, current methods for implementing wide-range swept-frequency light sources are structurally complex and costly, and exhibit significant phase frequency noise, limiting their practical application. From a signal processing perspective, multiple independent degrees of freedom with uncorrelated RBS distributions can be measured, and the results of these measurements can be weighted and averaged to effectively solve the coherent fading problem. Common methods for obtaining multiple independent degrees of freedom include frequency division multiplexing, time division multiplexing, and space division multiplexing. These methods often require trade-offs in spatial resolution or response time, leading to a loss in system performance.

[0006] To address the aforementioned problems in existing technologies, there is an urgent need to propose a phase-type optical frequency domain reflectance three-dimensional deformation measurement device and method that is resistant to fading noise, effectively compensating for the coherent fading noise of phase-type OFDR. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a phase-type optical frequency domain reflectance three-dimensional deformation measurement device and method resistant to fading noise, thereby resolving the issues present in the prior art.

[0008] To achieve the above objectives, the present invention provides a phase-type optical frequency domain reflectance three-dimensional deformation measurement device resistant to fading noise, comprising:

[0009] The signal transmitting module is used to transmit a detection signal and divide the detection signal into two paths: a measurement path and a reference path for transmission.

[0010] The signal transmission module is used to transmit the measurement path signal and the reference path signal sequentially through a space division multiplexer, a 1-to-3 optical coupler, and an optical circulator.

[0011] The mode multiplexing module is used to receive the measurement path signal, realize mode multiplexing through the photonic lantern, generate multiplexed multimode probe light, and enter different cores of the few-mode multi-core optical fiber respectively.

[0012] The signal mixing module is used to optically mix the reflected light of the three-dimensional deformation information of different cores of a few-mode multi-core optical fiber with the reference path signal to obtain the beat frequency signal of different optical modes of each core.

[0013] The deformation detection module is used to perform phase averaging of the beat frequency signals of different optical modes in each fiber core to obtain strain information of different fiber cores, and, in conjunction with the Frenet-Serret framework, reconstruct the three-dimensional deformation of the few-mode multi-core optical fiber.

[0014] Optionally, the signal transmitting module includes:

[0015] A signal transmitting unit is used to generate a detection signal based on a tunable laser;

[0016] The signal division unit is used to divide the detection signal into two paths, a measurement path and a reference path, through a coupler for transmission.

[0017] Optionally, the signal transmission module includes:

[0018] The measurement path signal transmission unit is used to divide the measurement path signal into several paths based on the space division multiplexer corresponding to the measurement path. Each signal is input to the corresponding 1-to-3 optical coupler and connected to the optical circulator to realize the transmission of the measurement path signal.

[0019] The reference path signal transmission unit is used to divide the reference path signal into several paths based on the space division multiplexer corresponding to the reference path, and each path signal is input to the corresponding 1-to-3 optical coupler for transmission of the reference path signal.

[0020] Optionally, the signal mixing module includes:

[0021] The deformation signal transmission unit is used to transmit reflected light containing three-dimensional deformation information of different cores of a few-mode multi-core optical fiber. The reflected light is demultiplexed through a photonic lantern and then transmitted again through a circulator.

[0022] The optical domain mixing unit is used to perform optical domain mixing between the transmitted reflected light and the reference optical signal of the reference path at the subsequent coupler, and then transmit the optically mixed signal to the photodetector.

[0023] Optionally, the deformation detection module includes:

[0024] The phase averaging unit is used to perform phase averaging on the beat frequency signals of different optical modes in each fiber core to obtain strain information after coherent fading compensation in different fiber cores.

[0025] The deformation acquisition unit is used to calculate the curvature and deflection of the optical fiber based on the strain information of different fiber cores, and to reconstruct the three-dimensional deformation of the few-mode multi-core optical fiber in conjunction with the Frenet-Serret framework.

[0026] This invention also provides a phase-type optical frequency domain reflectance three-dimensional deformation measurement method resistant to fading noise, based on the aforementioned device, comprising the following steps:

[0027] The detection signal is transmitted and split into two paths: a measurement path and a reference path.

[0028] The measurement path signal and the reference path signal are transmitted sequentially through a space division multiplexer, a 1-to-3 optical coupler, and an optical circulator.

[0029] The measurement path signal is multiplexed through a photonic lantern to generate multiplexed multimode probe light, which is then fed into different cores of a few-mode multi-core optical fiber.

[0030] The reflected light from the three-dimensional deformation information of different cores of a few-mode multi-core optical fiber is optically mixed with the reference path signal to obtain the beat frequency signal of different optical modes of each core.

[0031] Phase averaging of beat frequency signals of different optical modes within each fiber core is performed to obtain strain information for different fiber cores. Combined with the Frenet-Serret framework, the three-dimensional deformation of a few-mode multi-core fiber is reconstructed.

[0032] Optionally, the process of transmitting a detection signal and splitting it into a measurement path and a reference path includes:

[0033] The detection signal is generated by a tunable laser and then split into two paths, a measurement path and a reference path, by a coupler for transmission.

[0034] Optionally, the process of transmitting the measurement path signal and the reference path signal sequentially through a space-division multiplexer, a 1-to-3 optical coupler, and an optical circulator includes:

[0035] The measurement path signal is divided into several paths by the space division multiplexer corresponding to the measurement path. Each signal is input to the corresponding 1-to-3 optical coupler and connected to the optical circulator to realize the transmission of the measurement path signal.

[0036] The reference path signal is divided into several paths by the space division multiplexer corresponding to the reference path, and each path signal is input to the corresponding 1-to-3 optical coupler for transmission of the reference path signal.

[0037] Optionally, the process of optically mixing the reflected light from the three-dimensional deformation information of different cores of a few-mode multi-core optical fiber with a reference path signal to obtain the beat frequency signal of different optical modes for each core includes:

[0038] Different cores of a few-mode multi-core optical fiber generate reflected light with three-dimensional deformation information. The reflected light is demultiplexed through a photonic lantern and then transmitted through a circulator.

[0039] The transmitted reflected light and the reference light signal of the reference path are optically mixed at the subsequent coupler to obtain the beat frequency signal of different optical modes of each fiber core, which is then transmitted to the photodetector for photoelectric conversion and received by the acquisition card.

[0040] Optionally, phase averaging is performed on the beat frequency signals of different optical modes within each fiber core to obtain strain information for different fiber cores. Combined with the Frenet-Serret framework, the process of reconstructing the three-dimensional deformation of a few-mode multi-core fiber includes:

[0041] Phase averaging of beat frequency signals of different optical modes in each fiber core is performed to obtain strain information after coherent fading compensation in different fiber cores. Based on the strain information of different fiber cores, the curvature and torsion of the optical fiber are calculated, and the three-dimensional deformation of the few-mode multi-core optical fiber is reconstructed by combining the Frenet-Serret framework.

[0042] Compared with the prior art, the present invention has the following advantages and technical effects:

[0043] 1. This invention uses a few-mode multi-core optical fiber for shape sensing, and uses the light of different modes in the fiber core for averaging to achieve the effect of compensating for coherent fading noise.

[0044] 2. The technical solution proposed in this invention does not require trade-offs in spatial resolution or response time, and there is no additional loss of system performance.

[0045] 3. The technical solution proposed in this invention, compared with traditional methods for resisting coherent fading noise, such as special design of optical fibers, use of high-performance light sources, and adoption of complex signal processing techniques, avoids complex optical design and excessive costs. It is an effective method to significantly improve measurement stability with limited increase in system complexity. Attached Figure Description

[0046] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0047] Figure 1 This is a schematic diagram of the basic apparatus of an embodiment of the present invention;

[0048] Figure 2 This is a schematic diagram of the trace distribution of a few-mode multi-core optical fiber after deformation according to an embodiment of the present invention, showing the trace distribution of different cores and different modes; wherein, (a) is a schematic diagram of the trace distribution of core 1 in 3 modes, (b) is a schematic diagram of the trace distribution of core 2 in 3 modes, (c) is a schematic diagram of the trace distribution of core 3 in 3 modes, and (d) is a schematic diagram of the trace distribution of core 1, core 2 and core 3 in different modes on average.

[0049] Figure 3 This is a schematic diagram comparing the shape reconstruction results using single-mode signals and average signals, respectively, according to an embodiment of the present invention. Detailed Implementation

[0050] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0051] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0052] Example 1

[0053] like Figure 1 As shown, this embodiment provides a phase-type optical frequency domain reflectance three-dimensional deformation measurement device resistant to fading noise, comprising:

[0054] The signal transmitting module is used to transmit a detection signal and divide the detection signal into two paths: a measurement path and a reference path for transmission.

[0055] The signal transmission module is used to transmit the measurement path signal and the reference path signal sequentially through a space division multiplexer, a 1-to-3 optical coupler, and an optical circulator.

[0056] The mode multiplexing module is used to receive the measurement path signal, realize mode multiplexing through the photonic lantern, generate multiplexed multimode probe light, and enter different cores of the few-mode multi-core optical fiber respectively.

[0057] The signal mixing module is used to optically mix the reflected light of the three-dimensional deformation information of different cores of a few-mode multi-core optical fiber with the reference path signal to obtain the beat frequency signal of different optical modes of each core.

[0058] The deformation detection module is used to perform phase averaging of the beat frequency signals of different optical modes in each fiber core to obtain strain information of different fiber cores, and, in conjunction with the Frenet-Serret framework, reconstruct the three-dimensional deformation of the few-mode multi-core optical fiber.

[0059] Furthermore, the reconstruction framework mentioned in this embodiment can not only use the Frenet-Serret framework, but also the Bishop framework, homogeneous transformation matrix, etc., to realize the process from curvature and torsion to three-dimensional shape.

[0060] Implementable, the signal transmission module includes: a signal transmission unit for generating a detection signal based on a tunable laser; and a signal division unit for dividing the detection signal into a measurement path and a reference path for transmission via a coupler.

[0061] Implementable, the signal transmission module includes: a measurement path signal transmission unit, used to divide the measurement path signal into several paths based on the spatial division multiplexer corresponding to the measurement path, with each signal input to a corresponding 1-to-3 optical coupler and connected to an optical circulator to realize the transmission of the measurement path signal; and a reference path signal transmission unit, used to divide the reference path signal into several paths based on the spatial division multiplexer corresponding to the reference path, with each signal input to a corresponding 1-to-3 optical coupler for the transmission of the reference path signal.

[0062] The feasible signal mixing module includes: a deformation signal transmission unit for transmitting reflected light containing three-dimensional deformation information of different cores of a few-mode multi-core optical fiber, wherein the reflected light is demultiplexed through a photonic lantern and then transmitted again through a circulator; and an optical domain mixing unit for performing optical domain mixing of the transmitted reflected light with the reference light signal of the reference path at a subsequent coupler, and transmitting the optically mixed signal to a photodetector.

[0063] Implementable, the deformation detection module includes: a phase averaging unit, used to perform phase averaging on the beat frequency signals of different optical modes in each fiber core to obtain strain information after coherent fading compensation in different fiber cores; and a deformation acquisition unit, used to calculate the curvature and torsion of the optical fiber based on the strain information of different fiber cores, and reconstruct the three-dimensional deformation of the few-mode multi-core optical fiber in combination with the Frenet-Serret framework.

[0064] On the other hand, based on the same inventive concept as the above embodiments, this embodiment also provides a phase-type optical frequency domain reflectance three-dimensional deformation measurement method resistant to fading noise. This method and the device provided in the above embodiments are mutually referential in effect. The method includes the following steps:

[0065] The detection signal is transmitted and split into two paths: a measurement path and a reference path.

[0066] The measurement path signal and the reference path signal are transmitted sequentially through a space division multiplexer, a 1-to-3 optical coupler, and an optical circulator.

[0067] The measurement path signal is multiplexed through a photonic lantern to generate multiplexed multimode probe light, which is then fed into different cores of a few-mode multi-core optical fiber.

[0068] The reflected light from the three-dimensional deformation information of different cores of a few-mode multi-core optical fiber is optically mixed with the reference path signal to obtain the beat frequency signal of different optical modes of each core.

[0069] Phase averaging of beat frequency signals of different optical modes within each fiber core is performed to obtain strain information for different fiber cores. Combined with the Frenet-Serret framework, the three-dimensional deformation of a few-mode multi-core fiber is reconstructed.

[0070] As a specific implementation method, this embodiment uses a few-mode multi-core optical fiber as the sensing carrier. It utilizes phase-type optical frequency domain reflection technology to simultaneously detect optical signals from multiple fiber cores and multiple modes, while applying bending deformation. Taking advantage of the consistency of optical path differences between different modes within the same fiber core and the significant differences in optical path differences between different fiber cores, the vectors of different modes within the core are rotated and summed to compensate for coherent fading. The compensated phase change value is converted into a strain distribution, and the curvature and torsion along the fiber are calculated. Combined with the Frenet-Serret framework, high-precision reconstruction of the fiber's three-dimensional shape is achieved. This method, while compensating for coherent fading noise, achieves effective measurement of spatial three-dimensional shape, exhibiting high sensitivity and high spatial resolution, and is suitable for three-dimensional shape sensing in complex environments.

[0071] In feasible cases where the mode field distributions of both the fundamental mode and higher-order modes are located within the fiber core, the inter-core spacing between different cores in a multi-core fiber is significantly greater than the spatial distance between the intensity field distributions of different modes. Therefore, when the fiber bends, the optical signals of different modes within the same core have a basically consistent optical path difference, while the optical path differences between different cores differ significantly. Thus, it can be considered that the strain difference caused by the different intensity field distributions of different modes within the core during bending is negligible, which is the premise for averaging.

[0072] Considering the averaging effect of multiple degrees of freedom, averaging using three or more optical modes is employed to suppress fading. Specifically, a phase demodulation method is used to process the optical signals of all probe cores and all probe modes. Different modes within the same core are treated as different degrees of freedom of the same parameter, and the phase change value after compensating for coherent fading is obtained by rotating and summing the vectors of different modes. This method optimizes measurement accuracy and dynamic range, overcomes the limitations of existing technologies, and achieves high-precision, high-stability three-dimensional shape measurement in complex environments.

[0073] As a specific implementation method, the method includes the following steps:

[0074] This embodiment employs phase-based optical frequency domain reflectance distributed fiber optic measurement technology. A tunable laser generates a probe signal, which is split into a measurement path and a reference path via a coupler. The measurement path signal is further divided into multiple paths by a spatial multiplexer, with each path input to a 1-to-3 optical coupler and connected to an optical circulator to achieve unidirectional transmission of the optical signal and reception of the reflected signal. The probe light output from the optical circulator undergoes mode multiplexing via a photonic lantern, generating multi-mode optical signals that propagate in a few-mode fiber. These multiplexed multi-mode probe lights then enter different cores of the few-mode multi-core fiber. Similarly, the reference path signal is also split into multiple paths by a spatial multiplexer, with each path input to a 1-to-3 optical coupler as a reference to the measurement path signal.

[0075] In a few-mode multi-core fiber, the signal of each fiber core carries three-dimensional deformation information. The reflected light is demultiplexed through a photonic lantern, then transmitted again through a circulator, and optically mixed with the reference light signal of the reference path at the subsequent coupler (OC). The mixed signal is then photoelectrically converted by a photoelectric balanced detector (BPD) and received by a data acquisition card (DAQ) to obtain the beat frequency signal of the reflected light of different optical modes in each fiber core.

[0076] The phases obtained from different optical modes within the same fiber core are averaged to obtain phase and strain information after compensating for coherent fading. Based on the strain information of different fiber cores, the curvature and torsion of the fiber are calculated, and combined with the Frenet-Serret framework, the three-dimensional deformation of the few-mode multi-core fiber is finally reconstructed.

[0077] The specific process includes:

[0078] Let the averaged phase change of fiber core i be... The center wavelength of the light source is λ, the strain coefficient is κ, the spatial resolution is ΔL, the refractive index of the optical fiber is n, and the strain ε of the fiber core i is... i for:

[0079]

[0080] After obtaining the strain of different cores, the apparent curvature vector of the optical fiber is:

[0081]

[0082] In the formula, N is the total number of fiber cores measured, and θ i Let r be the angle by which fiber core i deviates from the local y-axis. i Let be the distance from fiber core i to the center of the fiber. Let the direction of the curve's movement be the x-axis, then j and k are the unit vectors of the local y-axis and z-axis, respectively.

[0083] Assuming the distance from fiber core i to the fiber center is constant and denoted as r, the curvature of the fiber can be calculated using the following formula:

[0084]

[0085] The bending angle of the optical fiber is:

[0086] θ = angle(κ) app ),

[0087] The torsion τ of the optical fiber, which is the change of the bending angle θ with the curve length s, is expressed as:

[0088] τ(s)=θ'(s),

[0089] Following the Frenet-Serret framework, the shape curve is described as the motion of a particle on a continuously differentiable curve in Euclidean space. Three orthogonal vectors are used to represent the state of the curve at each position: the tangent vector T representing the forward direction of the curve, the normal vector N representing the bending direction of the curve, and the subnormal vector B obtained by the cross product of T and N. After setting the initial values ​​of the three vectors, the curvature and torsion are interpolated to fit their values ​​more closely to the differentiable continuous curve. Then, the three vectors are calculated sequentially as the curve length changes using the following formula:

[0090]

[0091] T(j)=sκ(j)N(j)+T(j-1),

[0092] B(j)=-sτ(j)N(j)+B(j-1),

[0093] In the experiment, the shape exists as discrete points, where j represents the j-th point after interpolation. After obtaining the tangent vector along the shape, integrating the tangent vector yields the three-dimensional shape of the optical fiber. The curve r(j) is represented as:

[0094] r(j) = sT(j) + r(j+1).

[0095] refer to Figure 2 and Figure 3 To illustrate the technical effects of this embodiment, Figure 2 This diagram illustrates the trace distribution of different cores and modes in a few-mode multi-core optical fiber after deformation. Different columns represent different cores, and different rows represent different modes. Figure 2 (d) shows the traces after averaging the signals of different modes in the three fiber cores. Figure 3 The results of shape reconstruction using single-mode signals and average signals are shown in comparison.

[0096] As can be clearly seen from the trace diagram, averaging the optical signals of different modes effectively improves the signal-to-noise ratio and suppresses coherent fading, thus resulting in higher accuracy of the demodulation results. In the shape reconstruction result diagram, "trace-1", "trace-2", and "trace-3" represent the shape reconstruction results using modes 1, 2, and 3 from the three fiber cores, respectively; "trace-ave" represents the reconstruction result after averaging the optical signals of different modes and suppressing coherent fading; and "ideal" represents the applied ideal shape. The comparison results show that the shape diagram reconstructed after compensating for coherent fading is closer to the "ideal" ideal shape, fully demonstrating the effectiveness of coherent fading compensation in the shape reconstruction process of this embodiment.

[0097] As the above analysis shows, this embodiment significantly improves the accuracy and reliability of shape reconstruction through multi-mode signal averaging, providing strong technical support for the application of few-mode multi-core optical fibers in the field of three-dimensional shape sensing. Through the above steps, while achieving three-dimensional shape sensing, coherent fading noise is effectively compensated, optimizing measurement accuracy and dynamic range. Therefore, phase-type OFDR three-dimensional shape sensing with resistance to fading noise is realized.

[0098] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A phase-type optical frequency domain reflectance three-dimensional deformation measurement device resistant to fading noise, characterized in that, include: The signal transmitting module is used to transmit a detection signal and divide the detection signal into two paths: a measurement path and a reference path for transmission. The signal transmission module is used to transmit the measurement path signal and the reference path signal sequentially through a space division multiplexer, a 1-to-3 optical coupler, and an optical circulator. The mode multiplexing module is used to receive the measurement path signal, realize mode multiplexing through the photonic lantern, generate multiplexed multimode probe light, and enter different cores of the few-mode multi-core optical fiber respectively. The signal mixing module is used to optically mix the reflected light of the three-dimensional deformation information of different cores of a few-mode multi-core optical fiber with the reference path signal to obtain the beat frequency signal of different optical modes of each core. The deformation detection module is used to perform phase averaging of the beat frequency signals of different optical modes in each fiber core to obtain strain information of different fiber cores, and to reconstruct the three-dimensional deformation of the few-mode multi-core fiber in combination with the Frenet-Serret framework. The signal transmission module includes: The measurement path signal transmission unit is used to divide the measurement path signal into several paths based on the space division multiplexer corresponding to the measurement path. Each signal is input to the corresponding 1-to-3 optical coupler and connected to the optical circulator to realize the transmission of the measurement path signal. The reference path signal transmission unit is used to divide the reference path signal into several paths based on the space division multiplexer corresponding to the reference path, and each path signal is input to the corresponding 1-to-3 optical coupler for transmission of the reference path signal. The signal mixing module includes: The deformation signal transmission unit is used to transmit reflected light containing three-dimensional deformation information of different cores of a few-mode multi-core optical fiber. The reflected light is demultiplexed through a photonic lantern and then transmitted again through a circulator. The optical domain mixing unit is used to perform optical domain mixing between the transmitted reflected light and the reference optical signal of the reference path at the subsequent coupler, and then transmit the optically mixed signal to the photodetector.

2. The apparatus according to claim 1, characterized in that, The signal transmitting module includes: A signal transmitting unit is used to generate a detection signal based on a tunable laser; The signal division unit is used to divide the detection signal into two paths, a measurement path and a reference path, through a coupler for transmission.

3. The apparatus according to claim 1, characterized in that, The deformation detection module includes: The phase averaging unit is used to perform phase averaging on the beat frequency signals of different optical modes in each fiber core to obtain strain information after coherent fading compensation in different fiber cores. The deformation acquisition unit is used to calculate the curvature and deflection of the optical fiber based on the strain information of different fiber cores, and in combination with the Frenet-Serret framework, obtain the three-dimensional deformation information of the few-mode multi-core optical fiber.

4. A phase-type optical frequency domain reflectance three-dimensional deformation measurement method resistant to fading noise, characterized in that, The apparatus according to any one of claims 1-3 includes the following steps: The detection signal is transmitted and split into two paths: a measurement path and a reference path. The measurement path signal and the reference path signal are transmitted sequentially through a space division multiplexer, a 1-to-3 optical coupler, and an optical circulator. The measurement path signal is multiplexed through a photonic lantern to generate multiplexed multimode probe light, which is then fed into different cores of a few-mode multi-core optical fiber. The reflected light from the three-dimensional deformation information of different cores of a few-mode multi-core optical fiber is optically mixed with the reference path signal to obtain the beat frequency signal of different optical modes of each core. Phase averaging of beat frequency signals of different optical modes in each fiber core is performed to obtain strain information of different fiber cores. Combined with the Frenet-Serret framework, three-dimensional deformation information of few-mode multi-core optical fiber is obtained. The process of transmitting the measurement path signal and the reference path signal sequentially through a space division multiplexer, a 1-to-3 optical coupler, and an optical circulator includes: The measurement path signal is divided into several paths by the space division multiplexer corresponding to the measurement path. Each signal is input to the corresponding 1-to-3 optical coupler and connected to the optical circulator to realize the transmission of the measurement path signal. The reference path signal is divided into several paths by the space division multiplexer corresponding to the reference path, and each path signal is input to the corresponding 1-to-3 optical coupler for transmission of the reference path signal. The process of optically mixing the reflected light from the three-dimensional deformation information of different cores of a few-mode multi-core optical fiber with a reference path signal to obtain the beat frequency signal of different optical modes of each core includes: Different cores of a few-mode multi-core optical fiber generate reflected light with three-dimensional deformation information. The reflected light is demultiplexed through a photonic lantern and then transmitted through a circulator. The transmitted reflected light and the reference light signal of the reference path are optically mixed at the subsequent coupler to obtain the beat frequency signal of different optical modes of each fiber core, which is then transmitted to the photodetector for photoelectric conversion and received by the acquisition card.

5. The method according to claim 4, characterized in that, The process of transmitting a detection signal and splitting it into a measurement path and a reference path includes: The detection signal is generated by a tunable laser and then split into two paths, a measurement path and a reference path, by a coupler for transmission.

6. The method according to claim 4, characterized in that, Phase averaging of the beat frequency signals of different optical modes within each fiber core yields strain information for each core. Combined with the Frenet-Serret framework, the process of reconstructing the three-dimensional deformation of a few-mode multi-core fiber includes: Phase averaging of beat frequency signals of different optical modes in each fiber core is performed to obtain strain information after coherent fading compensation in different fiber cores. Based on the strain information of different fiber cores, the curvature and torsion of the optical fiber are calculated, and the three-dimensional deformation of the few-mode multi-core optical fiber is reconstructed by combining the Frenet-Serret framework.

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