Multi-core optical fiber multi-channel demodulation system for three-dimensional displacement measurement of mechanical oscillator

Abstract

The invention discloses a multi-core optical fiber multichannel demodulation system for three-dimensional displacement measurement of a mechanical oscillator, which comprises a light source module, a multi-core optical fiber sensing probe, a photoelectric detection module and a signal processing module. A mapping model between multi-channel optical signals and displacement is established, decoupling and high-precision measurement of three-dimensional displacement are realized through a matrix demodulation algorithm, the system takes a multi-core optical fiber as an integrated probe structure, free space optical path alignment is not needed, an optical path is stable, and packaging is simple and convenient; compared with a traditional single-core optical fiber displacement sensing scheme, displacement components of the mechanical oscillator in the three orthogonal directions can be obtained at the same time, and the method has the advantages of being high in measurement precision, high in anti-interference capacity, good in real-time performance, compact in system structure and the like and can be widely applied to the fields of mechanical oscillator displacement measurement, structure health monitoring, precision manufacturing, micro-nano operation positioning and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of precision measurement and optical detection, and particularly relates to a system for three-dimensional displacement measurement of a mechanical oscillator. BACKGROUND

[0002] As a highly sensitive dynamic system, mechanical oscillators (including macroscopic clamping type mechanical oscillators, suspended type mechanical oscillators, etc.) have excellent mechanical properties and exhibit extremely high response sensitivity in many high-precision sensing and measurement fields. Whether based on optical, electromagnetic, mechanical, superconducting or other forms of mechanical oscillator technology, these mechanical oscillators are widely used in fields such as fundamental physics experiments, inertial measurement, mechanical sensing, earthquake monitoring, gravitational wave detection, etc., pushing the boundaries of scientific research and bringing breakthroughs in modern engineering technology. Especially in the fields of precision measurement, weak signal detection and quantum physics, the advantages of mechanical oscillators are particularly prominent.

[0003] However, when different types of mechanical oscillators are applied to different measurement scenarios, their core performance depends on the high-precision detection of small displacements. Therefore, how to achieve accurate and stable displacement measurement is the key to improving the performance of mechanical oscillators. Existing mechanical oscillator displacement reading methods mainly include free-space interference optical path, single-core fiber near-field reading, magnetic / electric reading, etc. The free-space interference optical path has high sensitivity, but its volume is large, its stability is poor, and the optical path alignment is complex, which limits its practical application in precision equipment. The single-core fiber reading method has the advantages of compact structure and easy integration, but it is usually only suitable for single-axis displacement measurement and difficult to achieve multi-dimensional parallel reading. The magnetic / electric reading method relies on the use of low-temperature environment or special materials, which causes a lack of universality and adaptability. SUMMARY

[0004] To overcome the deficiencies of the prior art, the present application provides a multi-core fiber multi-channel demodulation system for three-dimensional displacement measurement of a mechanical oscillator, which aims to solve the problems of large volume, complex alignment, poor stability of free-space optical path and difficulty in achieving three-dimensional parallel measurement of single-core fiber scheme, so as to realize high-precision detection of three-dimensional displacement of a mechanical oscillator.

[0005] To achieve the above-mentioned application purposes, the following technical solutions are adopted: The multi-core fiber multi-channel demodulation system for three-dimensional displacement measurement of a mechanical oscillator is characterized in that it comprises: a light source module, a multi-core fiber sensing probe, a photoelectric detection module, and a signal processing module. The light source module is used to provide a laser beam. The multi-core fiber optic sensing probe includes: one transmitting fiber core and N receiving fiber cores. The transmitting fiber core is optically connected to the light source module and is used to emit laser light towards the object being detected. The N receiving fiber cores are used to receive light signals reflected or scattered by the object being detected. The photoelectric detection module includes: N photodetectors corresponding to the N receiving fiber cores, used to convert the received optical signals into N independent electrical signals respectively; wherein, a single channel is composed of one receiving fiber core and one photodetector; N represents the number of channels, and ; The signal processing module performs multi-channel calculations and demodulation on N independent electrical signals to obtain the three-dimensional displacement of the probe object.

[0006] The multi-core fiber optic multi-channel demodulation system of the present invention is also characterized in that the three-dimensional displacement of the probe object includes: Directional displacement, Directional displacement and Directional displacement, where Directional displacement and The directional displacements are all perpendicular to the optical axis. The direction is parallel to the direction of gravity. The direction is parallel to the orthogonal direction of gravity. The direction is parallel to the optical axis.

[0007] Furthermore, the multi-core fiber optic sensing probe is centered on the transmitting fiber core, with each receiving fiber core evenly distributed around the transmitting fiber core, and the center-to-center distance between adjacent fibers is 8 micrometers to 50 micrometers.

[0008] Furthermore, the detection object is a suspended particle or a displacement feature point on a cantilever beam or a mechanical oscillator, and the size of the detection object is 0.1 mm to 2 mm.

[0009] Furthermore, the signal processing module obtains the three-dimensional displacement of the probe object through the following steps: Step 1: Denote the optical power vector formed by the N independent electrical signals as ,in, Indicates the first Optical power of each channel Indicates transpose; Step 2, Calibrate the first Optical power of each channel For the detection object Directional mapping coefficient , Mapping coefficients on and Directional mapping coefficient Thus, the mapping coefficient matrix A is constructed. ; Step 3, calculating the transfer matrix with dimension ; ; Step 4, calibrating the power deviation vector composed of power deviations of channels , wherein, represents the zero power deviation of the photoelectric detector; Step 5, calculating the three-dimensional displacement vector of the detection object using formula (1) , wherein, represents the displacement in the direction, represents the displacement in the direction, represents the displacement in the direction; (1).

[0010] Compared with the prior art, the present application has the following advantages: 1. Structural integration, avoiding free-space optical path error: The present application realizes the integration of optical path transmission and signal acquisition by integrating a transmitting fiber core and multiple receiving fiber cores inside a multi-core optical fiber, avoiding the problems of optical axis drift and alignment error existing in traditional free-space interference optical paths. This structure does not require external mirrors and spatial collimation components, significantly improving the structural stability and environmental adaptability of the system, reducing the volume, and facilitating packaging and long-term use.

[0011] 2. Realize multi-channel parallel measurement of three-dimensional displacement: The present application sets up a multi-channel signal acquisition system by setting multiple receiving fiber cores and corresponding photoelectric detectors, and uses matrix calibration and demodulation algorithms to simultaneously analyze multiple optical power signals, which can simultaneously obtain the displacement components of the detection object in the X, Y and Z directions. Compared with the traditional single-core fiber readout scheme that can only measure single-axis displacement, the present application realizes multi-dimensional parallel measurement and spatial displacement decoupling, greatly improving the measurement information quantity and real-time response performance.

[0012] 3. Improve measurement accuracy and anti-interference ability: The application adopts a demodulation algorithm based on multi-channel matrix operation to perform weighted inversion and error correction on signals of different channels. The method can effectively eliminate measurement errors caused by single-channel noise and power fluctuation, realize self-calibration and dynamic compensation of the signals, and thus improve the linearity, sensitivity and anti-interference performance of displacement measurement. According to theoretical evaluation, under typical experimental conditions (laser wavelength 1550 nm, optical power 1 mW, and multi-core optical fiber receiving channel number N = 4), the equivalent displacement detection noise density of the system is only 1 fm / Hz, which means that the system has high potential for displacement measurement.

[0013] 4. The light path is easy to align, and the system is easy to package: The probe part of the application adopts a multi-core optical fiber coaxial structure, and all light paths are completed inside the optical fiber, without the need for external optical adjustment. The device structure is compact, and the installation space is small, which is suitable for modular or array packaging. Compared with a free space interference system, the application significantly reduces the assembly difficulty and maintenance cost.

[0014] 5. Strong applicability, easy to engineer: The multi-core optical fiber probe of the system has small volume and high mechanical stability, and can be used for suspended vibrator displacement measurement, real-time displacement detection in micro-nano mechanical systems, structural health monitoring and precision manufacturing. The system has good universality and scalability, meeting the dual needs of high-precision measurement and industrial integration. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Principle diagram of a multi-core optical fiber detecting three-dimensional displacement of a mechanical vibrator; Figure 2 Schematic diagram of an end face of a multi-core optical fiber probe (center illumination, four-channel reception).

[0016] In the figure, 1 is a light source, 2 is a fiber coupler, 3 is a multi-core optical fiber, 4 is a detection object (suspended ball), 5-8 are four photodetectors; DETAILED DESCRIPTION

[0017] In this embodiment, a multi-core optical fiber multi-channel demodulation system for three-dimensional displacement measurement of a mechanical vibrator has a structure as shown in Figure 1 The system includes a laser light source 1, a fiber coupler 2, a multi-core optical fiber 3, a detection object (suspended ball) 4, and photodetectors 5-8 (PD1-PD4) corresponding to each receiving fiber core. The electrical signals output by the photodetectors are real-time calculated by computer algorithms in a signal processing module, and the three-dimensional displacement results of the detection object can be obtained.

[0018] The laser light source 1 can be a spatial laser or a fiber laser. The light source is connected to the multi-core optical fiber 3 through the optical fiber coupler 2, for providing stable and high-coherence laser light beams to the multi-core optical fiber. The light source power and wavelength can be adjusted according to the application scenario to ensure that the reflected light signal has sufficient signal-to-noise ratio.

[0019] The multi-core optical fiber 3 includes one transmitting core and N receiving cores, wherein the transmitting core is located at the geometric center, and the N receiving cores are distributed symmetrically around the circumference. The center-to-center distance between adjacent cores is 8-50 μm, to ensure that each receiving core has distinguishable sensitivity to displacement in different directions. As shown in FIG. 1, it is an example of a typical multi-core optical fiber probe end face structure. The probe is composed of one central transmitting core and four symmetrically distributed receiving cores, forming a multi-channel light signal acquisition array. The symmetric arrangement makes the corresponding light-sensitive directions of each channel not collinear and not coplanar as a whole, thereby ensuring that the system has good spatial resolution and three-dimensional decoupling characteristics. Figure 2

[0020] When the laser light is emitted through the transmitting core and irradiates the detection object surface, the detection object will reflect or scatter the incident light. The reflected or scattered light is received by the N circumferentially distributed receiving cores. Since the small displacement of the detection object in the three-dimensional space will cause a change in the distribution of the reflected light, the light power received by different channels will be different. By analyzing the changes in these multi-channel light power signals, the displacement components of the measured object in the X, Y, and Z directions can be inverted, realizing high-precision three-dimensional displacement measurement. N is the number of receiving cores, and N≥3, to ensure the solvability of the three-dimensional displacement information. When N=3, three-dimensional solution can be realized; when N>3, the system is an over-determined equation set, and the measurement stability and noise resistance can be effectively improved by solving it through the least squares method.

[0021] The detection object 4 can be a suspended particle, a cantilever beam end feature point, or a micro-mechanical vibrator, with a typical size range of 0.1-2 mm.

[0022] The receiving end of the system includes N receiving cores and their corresponding photodetectors. Each receiving core corresponds to one photodetector, forming an independent signal channel, for converting the light signal into an electrical signal. The signal processing module synchronously collects and multi-channel demodulates the N electrical signals, thereby obtaining the three-dimensional displacement information of the detection object.

[0023] The light power received by each photodetector is , and the three-dimensional displacement of the detection object is , which satisfy the mapping relationship shown in equation (1): (1) In equation (1), A is the mapping coefficient matrix,​ is the system bias term. The mapping matrix A reflects the sensitivity coefficients of each receiving channel to displacement components, which is the core parameter of the system solution model; the system bias term represents the static power offset of each channel under the zero position condition, which is derived from the inconsistency of the probe geometry or the difference in the detector gain.

[0024] In the calibration stage, in order to obtain the accurate mapping coefficient matrix A and bias vector , a displacement table is used to apply known displacements in X, Y and Z directions , and the optical power responses of each receiving channel are recorded , and a linear regression model is established by using formula (2): (2) Each coefficient is obtained by the least square method , that is: Through the above calibration, the matrix A and the vector can be obtained in the system initialization stage. The coefficients of the mapping matrix reflect the influence degree of displacement in different directions on the change of optical power, and the accuracy directly determines the solution accuracy of the system. After obtaining the mapping matrix , the signal processing module calculates the transfer matrix B by using formula (3): (3) The transfer matrix B is used to realize the inversion of the multi-channel signal to the three-dimensional displacement space. By substituting the actually measured optical power vector P, the displacement vector of the detection object can be calculated by using formula (4): (4) Through the linear inversion model, high-precision demodulation can be realized while ensuring real-time performance.

[0025] Based on the above demodulation algorithm, the COMSOL ray tracing model is used to theoretically calculate the system performance. The results show that under the typical experimental conditions (laser wavelength 1550 nm, optical power 1 mW, multi-core optical fiber receiving channel number N = 4, multi-core optical fiber diameter 150 μm, and center distance between each core 40 μm), the equivalent displacement detection noise density of the system is about 1 fm / √Hz. This result means that the present application can achieve the displacement measurement precision of the traditional free space interference method with a significantly simplified structure.

[0026] The system realizes integrated design of optical structure and algorithm structure, utilizes geometric symmetry of the multi-core optical fiber and linear characteristics of the matrix demodulation algorithm, and realizes high stability three-dimensional displacement measurement without free space optical path. The device structure is compact, the probe is easy to package, and high-precision real-time displacement detection of the mechanical oscillator can be realized in a complex environment.

Claims

1. A multi-core fiber optic multi-channel demodulation system for three-dimensional displacement measurement of a mechanical oscillator, characterized in that, include: Light source module, multi-core fiber optic sensing probe, photoelectric detection module, signal processing module; The light source module is used to provide a laser beam; The multi-core fiber optic sensing probe includes: one transmitting fiber core and N receiving fiber cores. The transmitting fiber core is optically connected to the light source module and is used to emit laser light towards the object being detected. The N receiving fiber cores are used to receive light signals reflected or scattered by the object being detected. The photoelectric detection module includes: N photodetectors corresponding to the N receiving fiber cores, used to convert the received optical signals into N independent electrical signals respectively; wherein, a single channel is composed of one receiving fiber core and one photodetector; N represents the number of channels, and ; The signal processing module performs multi-channel calculations and demodulation on N independent electrical signals to obtain the three-dimensional displacement of the probe object.

2. The multi-core fiber optic multi-channel demodulation system according to claim 1, characterized in that, The three-dimensional displacement of the probe object includes: Directional displacement, Directional displacement and Directional displacement, where Directional displacement and The directional displacements are all perpendicular to the optical axis. The direction is parallel to the direction of gravity. The direction is parallel to the orthogonal direction of gravity. The direction is parallel to the optical axis.

3. The multi-core fiber optic multi-channel demodulation system according to claim 1, characterized in that, The multi-core fiber optic sensing probe has a transmitting fiber core as the center, with each receiving fiber core evenly distributed around the transmitting fiber core, and the center-to-center distance between adjacent fibers is 8 micrometers to 50 micrometers.

4. The multi-core fiber optic multi-channel demodulation system according to claim 1, characterized in that, The detection object is a suspended particle, a displacement feature point on a cantilever beam, or a mechanical oscillator, and the size of the detection object is 0.1 mm to 2 mm.

5. The multi-core fiber multi-channel demodulation according to claim 1, characterized in that, The signal processing module obtains the three-dimensional displacement of the probe object according to the following steps: Step 1: Denote the optical power vector formed by the N independent electrical signals as ,in, Indicates the first Optical power of each channel Indicates transpose; Step 2, Calibrate the first Optical power of each channel For the detection object Directional mapping coefficient , Mapping coefficients on and Directional mapping coefficient Thus, the mapping coefficient matrix A is constructed. ; Step 3, Calculate the dimension as follows transfer matrix ; Step 4, Calibration The power deviation vector formed by the power deviation of each channel ,in, Indicates the first The optical power of the photodetector is zero bias; Step 5: Calculate the three-dimensional displacement vector of the probe object using equation (1). ,in, express Directional displacement, express Directional displacement, express Directional displacement; (1)。

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