Method and system for measuring rotational speed of a rotating object based on a multi-core optical fiber

Abstract

The application provides a kind of multi-core optical fiber based rotating object rotational speed measurement method and system, the method is by generating the detection light field with specific spatial structure, transmission through multi-core optical fiber and phase modulation obtains the preset structure of the exit light field;The light field is used to irradiate the rotating object, receive the reflected signal and return through the same path, detect the signal intensity change to obtain the time domain signal;Frequency shift information is obtained by frequency domain analysis and the angular velocity is calculated.The method realizes the flexible regulation and control of the light field multi-degree of freedom by the combination of spatial light modulator and multi-core optical fiber, breaks through the limitation of insufficient existing regulation and control degree of freedom;The requirement for optical axis alignment accuracy is reduced by using structured light field;The system miniaturization is realized by using flexible multi-core optical fiber, and the problem of narrow space application is solved;The parallel transmission and anti-interference characteristics of multi-core optical fiber are fully utilized, and the measurement stability and precision in complex environment are significantly improved by digital phase conjugation and transceiver integrated design.

Description

Technical Field

[0001] This invention relates to the field of optical measurement technology, and in particular to a method and system for measuring the rotational speed of a rotating object based on a multi-core optical fiber. Background Technology

[0002] The Doppler effect reveals the physical laws governing frequency changes that occur when light waves interact with moving objects. This phenomenon is of great significance in the field of velocity detection and has been widely applied in astrophysics, aerospace, and advanced manufacturing. Typical Doppler velocimetry techniques involve illuminating a moving object with interference fringes having a specific phase gradient and detecting the frequency shift of the scattered light to measure velocity. In particular, the rotating Doppler effect involves the frequency change characteristics caused by a rotating object, leading researchers to propose various measurement methods. A common method uses the interference of two orbital angular momentum (OAM) vortex beams with the same topological charge but opposite signs to generate a spatial structured light field for measurement. Furthermore, low-speed measurements can also be achieved by utilizing the mode broadening and phase spectrum changes caused by a rotating object truncating a single OAM beam. However, the aforementioned rotating Doppler velocimetry research is mostly applied to macroscopic scenarios, and Doppler signal detection in extreme environments or at microscopic scales still faces significant challenges. Complex environment or endoscopic Doppler detection has important applications in biomedicine and industry, such as detecting the rotational motion of cells or tiny particles in biological samples, and monitoring the rotational state of components in compact spaces.

[0003] To address the aforementioned measurement challenges, optical conductors, especially optical fiber technology, offer a new technological path. Light, as an important optical waveguide element, was initially primarily used in the field of communication. Based on the core size and transmission wavelength, optical fibers can be divided into single-mode fibers and multimode fibers. Single-mode fibers have a smaller core size (approximately 8-10 μm) and can only transmit the fundamental mode, typically used for optical communication transmission. Multimode fibers have a larger core size (usually above 50 μm) and can support multiple modes of transmission. The number of supported modes can be estimated using the fiber's normalized frequency, but dispersion and coupling effects between modes limit their application in imaging and sensing. Multimode fibers consist of thousands to tens of thousands of single-mode cores, with an overall diameter of approximately several hundred micrometers. Each core can independently transmit the light field information at its corresponding location, and because each core is independent, multimode fibers exhibit excellent robustness against external interference and their own deformation. With its advantages of good size, flexibility, and strong anti-interference capabilities, multimode fibers have shown significant application scenarios in endoscopic imaging, fluorescence microscopy, and computational imaging.

[0004] Currently, fiber-optic rotating Doppler velocimetry mainly employs two schemes: one uses a seven-core fiber (i.e., one central core plus six outer cores), selectively exciting the outer cores to generate a specific spatial intensity distribution (such as symmetrical petal-shaped or asymmetrical modes), while the central core collects reflected light signals. The time-domain signals are recorded using photodiodes and oscilloscopes, and then Fourier transform is used to extract frequency information. The magnitude and direction of the rotational speed are determined by combining frequency offset and phase difference. The other scheme involves fusion splicing single-mode and multi-mode fibers to form a mode selector / filter. By selecting the OAM mode of the probe light and signal light, the frequency information of a specific mode is measured, and the measurement is achieved based on the quantitative relationship with the rotational speed.

[0005] However, existing technologies have the following significant problems: First, existing fiber optic field manipulation techniques are difficult to achieve flexible control of multiple degrees of freedom such as amplitude, phase, polarization, and coherence, and lack the ability to generate arbitrary structured light fields; Second, existing methods require the rotation axis of the target object to be strictly aligned with the center of the light source, otherwise it will lead to frequency broadening and a decrease in signal-to-noise ratio, limiting measurement accuracy; Third, existing fiber optic velocimetry systems are large in size and have low integration, making them unsuitable for use in narrow spaces or endoscopic environments; Fourth, existing technologies have not fully utilized the parallel transmission capability and anti-interference characteristics of multi-core optical fibers, resulting in insufficient measurement stability in complex environments. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the problems of insufficient freedom of fiber optic field control, the need for precise alignment of the light source and the object's rotation axis during measurement, large system size and low integration, and poor measurement stability in complex environments in the prior art.

[0007] To address the aforementioned technical problems, this invention provides a method for measuring the rotational speed of a rotating object based on multi-core optical fiber, comprising the following steps:

[0008] S1: Generate a probe light field with a specific spatial structure, transmit the probe light field along a preset path through a multi-core optical fiber, and perform phase modulation on the probe light field during transmission to obtain an output light field with a preset spatial structure.

[0009] S2: The emitted light field is used to illuminate the rotating object under test, and the signal light formed after being reflected by the rotating object under test is received. The signal light is transmitted back in the same multi-core optical fiber, and the intensity change of the signal light is detected to obtain the time domain signal.

[0010] S3: Perform frequency domain analysis on the time domain signal to obtain frequency shift information caused by the motion of the rotating object under test, and calculate the angular velocity of the rotating object under test based on the frequency shift information.

[0011] In one embodiment of the present invention, step S1, the method for phase-modulating the probe light field during transmission to obtain an output light field with a preset spatial structure includes the following steps:

[0012] S11: Obtain a hologram formed by the interference of the intermediate outgoing light field and the reference light after transmission through the preset path;

[0013] S12: Perform a Fourier transform on the hologram to obtain the spatial spectrum of the hologram, and extract the first-order term representing the phase information of the light field from the spatial spectrum;

[0014] S13: Perform an inverse Fourier transform on the first-order term to reconstruct the actual phase distribution of the intermediate outgoing light field;

[0015] S14: Based on the actual phase distribution obtained by the above reconstruction, calculate its phase conjugate value as the compensation phase, and load the compensation phase into the detection light field before transmission to obtain the output light field with a preset spatial structure after phase compensation.

[0016] In one embodiment of the present invention, the method for performing frequency domain analysis on the time domain signal to obtain frequency shift information caused by the motion of the rotating object under test in step S3 is as follows: performing Fourier transform on the time domain signal to obtain its frequency domain spectrum, and extracting characteristic peak frequencies from the frequency domain spectrum.

[0017] In one embodiment of the present invention, the method for calculating the angular velocity of the rotating object under test based on the frequency shift information is as follows: the characteristic peak frequency The Doppler frequency shift caused by the rotating object under test, the characteristic peak frequency The angular velocity of the rotating object to be measured satisfies the following relationship:

[0018] ,

[0019] in, This represents the rotational symmetry multiplicity of the probe light field. This represents the rotational symmetry multiplicity of the rotating object under test. express and The least common multiple of, This represents the angular velocity vector of the light source. This represents the angular velocity vector of the rotating object under test.

[0020] In one embodiment of the present invention, the probe light field with a specific spatial structure is a fully coherent structured light field with rotational symmetry, including a Laguerre-Gaussian beam, a perfect vortex beam, or a multi-ring nested beam.

[0021] Based on the same inventive concept, this invention also provides a rotating object rotation speed measurement system based on multi-core optical fiber, used to implement a rotating object rotation speed measurement method based on multi-core optical fiber, including the following modules:

[0022] The light source module is used to generate a probe light field with a specific spatial structure;

[0023] The transmission and phase modulation module is used to transmit the probe light field through a multi-core optical fiber along a preset path, and to perform phase modulation on the probe light field during transmission to obtain an output light field with a preset spatial structure.

[0024] The detection module is used to illuminate the rotating object with the emitted light field and receive the signal light formed after the rotating object under test is reflected, wherein the signal light is transmitted back in the opposite direction through the same multi-core optical fiber.

[0025] The signal acquisition and processing module is used to detect the intensity change of the signal light to obtain a time-domain signal, perform frequency domain analysis on the time-domain signal to obtain frequency shift information caused by the motion of the rotating object, and calculate the angular velocity of the rotating object under test based on the frequency shift information.

[0026] In one embodiment of the present invention, the transmission and phase modulation module includes a multi-core optical fiber, the emitting end of which is a bare fiber end face, for directly irradiating the emitted light field onto the rotating object under test.

[0027] In one embodiment of the present invention, the transmission and phase modulation module includes a spatial light modulator for phase modulation of the probe light field to compensate for the phase difference between the cores in the multi-core optical fiber.

[0028] The present invention also provides an electronic device, which includes a processor, a memory, and a bus system. The processor and the memory are connected through the bus system. The memory is used to store instructions, and the processor is used to execute the instructions stored in the memory to realize the aforementioned method for measuring the rotational speed of a rotating object based on multi-core optical fiber.

[0029] The present invention also provides a computer storage medium storing a computer software product, the computer software product including several instructions for causing a computer device to execute the aforementioned method for measuring the rotational speed of a rotating object based on a multi-core optical fiber.

[0030] The technical solution of the present invention has the following advantages compared with the prior art:

[0031] The rotating object rotation speed measurement method based on multi-core optical fiber described in this invention achieves flexible multi-degree-of-freedom control of the amplitude, phase, polarization, and coherence structure of the optical field by combining a spatial light modulator with multi-core optical fiber. This enables the generation of various complex optical field structures, overcoming the limitations of insufficient control freedom in existing technologies. Utilizing an optical field with a specific spatial structure as the probe light effectively reduces the requirement for precise alignment between the rotation axis and the light source center, improving the robustness and practicality of the measurement.

[0032] This system uses a thin, flexible multi-core optical fiber as its core transmission carrier. Combined with an output end design, it achieves miniaturization and integration of the probe, enabling endoscopic measurements in confined spaces and solving the problem of existing systems' difficulties in application within restricted spaces. The inherent anti-interference characteristics of the multi-core optical fiber, coupled with phase compensation using digital phase conjugation technology and an integrated transceiver optical path design, significantly improve measurement stability and accuracy in complex environments. These features make this invention not only suitable for velocities of macroscopic rotating bodies but also demonstrate application potential in microscopic scale detection and monitoring of extreme industrial environments, effectively expanding the application scope of optical Doppler velocimetry technology. Attached Figure Description

[0033] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0034] Figure 1 This is a flowchart illustrating the method for measuring the rotational speed of a rotating object based on multi-core optical fiber provided in this embodiment of the invention.

[0035] Figure 2 This is a schematic diagram illustrating the principle of iterative compensation optimization in an embodiment of the present invention;

[0036] Figure 3 yes Figure 2 A magnified view of a portion at point A;

[0037] Figure 4 These are schematic diagrams illustrating different experimental results of multi-core optical fibers generating coherent optical fields in embodiments of the present invention.

[0038] Figure 5 This is a schematic diagram of the rotating object rotation speed measurement system based on multi-core optical fiber provided in this embodiment of the invention;

[0039] Figure 6 This is a schematic diagram illustrating the principle of using multi-core optical fibers to control structured light and measure the angular velocity of an object.

[0040] Figure 7(a) is a schematic diagram of the rotational speed measurement results when a quadruple symmetrical positive and negative topological charge superimposed vortex beam is used as the probe beam to illuminate a quadruple symmetrical rotating object in Experiment 1.

[0041] Figure 7(b) is a schematic diagram of the rotational speed measurement results when a six-fold symmetrical positive and negative topological charge superimposed vortex beam is used as the probe beam to illuminate a six-fold symmetrical rotating object in Experiment 1.

[0042] Figure 7(c) is a schematic diagram of the rotational speed measurement results when a six-fold symmetrical positive and negative topological charge superimposed vortex beam is used as the probe beam to illuminate a double-symmetrical rotating rod-shaped object in Experiment 1.

[0043] Explanation of reference numerals in the accompanying drawings: 1. Laser; 2. Beam expander; 3. Spatial light modulator; 4. First lens; 5. Aperture; 6. Second lens; 7. Beam splitter; 8. Multi-core optical fiber; 9. Rotating object under test; 10. Third lens; 11. Photodiode; 12. Computer. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0045] Example 1:

[0046] like Figure 1 As shown, this invention provides a method for measuring the rotational speed of a rotating object based on a multi-core optical fiber, comprising the following steps:

[0047] S1: Generate a probe light field with a specific spatial structure, transmit the probe light field along a preset path through a multi-core optical fiber, and perform phase modulation on the probe light field during transmission to obtain an output light field with a preset spatial structure.

[0048] S2: The emitted light field is used to illuminate the rotating object under test, and the signal light formed after being reflected by the rotating object under test is received. The signal light is transmitted back in the same multi-core optical fiber, and the intensity change of the signal light is detected to obtain the time domain signal.

[0049] S3: Perform frequency domain analysis on the time domain signal to obtain frequency shift information caused by the motion of the rotating object under test, and calculate the angular velocity of the rotating object under test based on the frequency shift information.

[0050] The core process of this invention includes three main steps: First, the generation and transmission of the probe light field are performed. A probe light field with a preset spatial structure is generated using a specific method and transmitted along a predetermined transmission path. During the transmission process, phase modulation is performed to ensure that the output light field has the required specific spatial distribution characteristics. Second, signal acquisition is performed. The modulated output light field is used to illuminate the rotating object under test, and the signal light reflected by the rotating object is collected. After the signal light returns along the original transmission path, the frequency domain signal is obtained by detecting the change in its light intensity over time. Finally, data processing is performed. The frequency domain feature analysis is performed on the acquired time domain signal to extract the characteristic frequency shift information generated by the rotational motion. Based on the quantitative correspondence between the characteristic frequency shift information and the rotational speed, the actual angular velocity of the rotating object is calculated.

[0051] Specifically, in step S1, a probe light field with a specific spatial structure is generated. This is the initial step in achieving the purpose of this invention. In this embodiment, the specific spatial structure includes, but is not limited to: Laguerre-Gaussian beams, perfect vortex beams, multi-ring nested beams, and petal-shaped light fields with rotational symmetry. These structured light fields have a clear angular phase distribution and can generate effective spatial coupling with the surface structure of rotating objects, thereby enhancing the intensity and signal-to-noise ratio of the Doppler signal.

[0052] In this embodiment, the preset path is typically a multi-core optical fiber, with each core considered an independent transmission channel. By precisely controlling the phase of each channel using a spatial light modulator (SLM), arbitrary spatial structure reconstruction of the outgoing light field can be achieved. The core function of this step is to simultaneously detect different positions on the surface of a rotating object through flexible design of the light field's spatial structure, thereby improving the system's spatial sampling rate and anti-migration capability.

[0053] In this embodiment, a fully coherent probe light field with a specific spatial structure is generated. The fully coherent light field corresponds to a single electric field mode, i.e., a single static hologram is loaded by a spatial light modulator.

[0054] Furthermore, such as Figure 2 and Figure 3 As shown, during the transmission of the probe light field through the preset path, the randomly distributed optical path difference between the channels of the transmission medium causes distortion in the emitted light field. To compensate for this distortion and ensure that the emitted light field has a preset spatial structure, digital phase conjugation technology is required for compensation. Specifically, the following steps are included:

[0055] S11: Obtain a hologram formed by the interference of the intermediate outgoing light field and the reference light after transmission through the preset path; in specific implementation, firstly, no modulation is applied to the spatial light modulator, and after the plane wave is generated and coupled into the transmission path through the objective lens, an objective lens is added at the outgoing end to couple the light field out; a path is led from the front of the spatial light modulator as a reference light, and interferes with the target light field at the outgoing end. After interference, an off-axis digital hologram is obtained and recorded by the camera;

[0056] S12: Perform a Fourier transform on the hologram to obtain the spatial spectrum of the hologram, and extract the first-order term representing the phase information of the light field from the spatial spectrum;

[0057] S13: Perform an inverse Fourier transform on the first-order term to reconstruct the actual phase distribution of the intermediate outgoing light field; perform an inverse Fourier transform on the first-order term of the spectrum to recover the electric field information at the transmission path cross section and obtain the phase difference distribution of different transmission channels;

[0058] S14: Based on the actual phase distribution obtained from the above reconstruction, calculate its phase conjugate value as the compensation phase, and load the compensation phase into the probe light field before transmission; in specific implementation, establish a coordinate mapping between the spatial light modulator plane and the transmission path end face, transform the phase distribution conjugate at the cross section according to the coordinate mapping and load it into the corresponding position of the spatial light modulator, and then check the output end face of the transmission path. If a flat field phase is obtained, it means that the phase compensation of the transmission path has been achieved.

[0059] The loading process includes the following calibration and optimization steps:

[0060] A coarse calibration pattern, such as a cross or grid, is displayed on the spatial light modulator. The optical field distribution corresponding to the output end of the multi-core fiber is recorded by a camera to preliminarily determine the coordinate mapping transformation relationship from the camera plane to the spatial light modulator plane. ;

[0061] The compensation phase is mapped according to coordinates. The transformation is performed and superimposed on the phase of the Fresnel lens to form a composite hologram containing focusing modulation information;

[0062] The composite hologram is loaded into the spatial light modulator, so that the probe light field is transmitted through a multi-core optical fiber and a focused light spot is formed at the output end.

[0063] The peak-to-background ratio (PBR) is used to quantify the quality of the focused spot. The rotation angle, image scaling ratio, and lateral displacement parameters of the spatial light modulator pattern are iteratively optimized until the PBR reaches its maximum value.

[0064] Correct the coordinate mapping relationship based on the optimized parameters. This enables high-precision phase compensation and optical field control, ultimately generating an outgoing optical field with a preset spatial structure.

[0065] Fresnel lenses are phase-type diffractive optical elements that can focus or diverge light beams without introducing additional optical elements by simulating the phase delay distribution of traditional lenses. They are often used in spatial light modulators to achieve dynamic focusing and beam shaping.

[0066] like Figure 4 As shown, when a fully coherent structured light field is generated, multiple fully coherent structured light fields can be produced. A fully coherent light field corresponds to the modulation of a single electric field mode, i.e., a spatial light modulator loading a single static hologram. By designing the corresponding hologram, starting from a Gaussian beam, an elliptical beam with double symmetry is generated, whose electric field distribution is:

[0067] ,

[0068] in and This represents the width of the Gaussian waist in the x and y directions.

[0069] It also produces a Laguerre-Gaussian vortex beam with superposition of positive and negative topological charges, whose electric field distribution is as follows:

[0070] ,

[0071] With topological charges ranging from ±2 to ±5, these beams exhibit a petal-like periodic intensity distribution, providing greater degrees of freedom for rotational sensing. Simultaneously, perfectly nested double-ring vortex beams are generated, featuring concentric ring-shaped intensity distributions with discrete bright spots distributed on the rings. As the topological charge number increases, the number of bright spots on each ring increases, while the ring radius remains constant. Furthermore, by altering the design of the hologram loaded onto the SLM, three or more nested ideal vortex beams can be generated, with the following electric field distribution:

[0072] ,

[0073] Where N represents the total number of rings, and the subscript n indicates the nth ring. The amplitude coefficient of the nth ring is represented by these characteristics, which can be used in sensing applications such as rotational speed detection. The increase in the number of rings and bright spots also reflects the MCF's ability to support higher-order orbital angular momentum modes.

[0074] Furthermore, in step S2, after obtaining the emitted light field with a preset spatial structure, a signal acquisition and detection process is implemented, specifically including the following steps:

[0075] S21: The emitted light field is irradiated onto the surface of the rotating object to be tested, so that the light field interacts with the rotating object;

[0076] S22: Receive the signal light formed after being reflected by the rotating object under test. The signal light carries information about the rotational motion of the object, especially the frequency shift information caused by the rotational Doppler effect.

[0077] S23: The signal light is transmitted back through the same transmission path in reverse to maintain the multiplexing of the optical path and the compactness of the system;

[0078] S24: Detect the change in the intensity of the signal light over time and obtain the corresponding time-domain signal.

[0079] In step S23, the signal light is transmitted back through the same multi-core optical fiber. The multi-core optical fiber adopts a transmit / receive partition design, that is, some fiber cores are dedicated to transmitting the outgoing light field, and other fiber cores are dedicated to receiving the signal light, so as to reduce the interference of the echo signal and maintain the multiplexing of the optical path and the compactness of the system.

[0080] In this step, the signal light, after being reflected by the rotating object's surface, experiences a frequency shift due to the rotational Doppler effect. This shift is proportional to the linear velocity at each point on the object's surface, which in turn is directly related to the angular velocity. Because the outgoing light field has a specific spatial structure, reflected light from different locations will carry different frequency shift information, forming a composite time-domain signal.

[0081] The signal light returns along the original multi-core fiber path, realizing integrated transmission and reception, simplifying the system structure, avoiding phase errors caused by inconsistent paths, and significantly improving the stability and repeatability of the system, making it especially suitable for measurements in endoscopy or confined spaces.

[0082] In practical implementation, the acquisition of time-domain signals requires consideration of the sampling frequency and acquisition time settings. The sampling frequency should be determined based on the expected rotational speed range to ensure that the Nyquist sampling theorem is satisfied and that the frequency changes caused by rotational speed are accurately captured. The acquisition time should be long enough to ensure sufficient frequency resolution for subsequent frequency domain analysis.

[0083] The time-domain signal obtained by the above method contains complete information on the motion characteristics of the rotating object, providing a data foundation for subsequent frequency domain analysis and rotational speed calculation.

[0084] Further, in step S3, after obtaining the time-domain signal, frequency-domain analysis is performed on it to extract the frequency shift information caused by the motion of the rotating object. Specifically, the Fast Fourier Transform (FFT) algorithm is used to process the acquired time-domain signal, transforming it from the time domain to the frequency domain to obtain the corresponding frequency spectrum.

[0085] By analyzing the frequency domain spectrum, characteristic peak frequencies generated by the rotational Doppler effect can be observed. These peak frequencies correspond to the frequency shift caused by the rotating object and are key parameters for calculating the rotational speed. In practice, characteristic peak frequencies can be extracted by identifying significant peaks in the frequency domain spectrum. .

[0086] The characteristic peak frequency The Doppler frequency shift caused by the rotating object under test, the characteristic peak frequency The angular velocity of the rotating object to be measured satisfies the following relationship:

[0087] ,

[0088] in, This represents the rotational symmetry multiplicity of the probe light field. This represents the rotational symmetry multiplicity of the rotating object under test. express and The least common multiple of, This represents the angular velocity vector of the light source. This represents the angular velocity vector of the rotating object under test.

[0089] In summary, the rotating object rotation speed measurement method based on multi-core optical fiber provided in this embodiment effectively solves the problems of low degree of freedom in optical field manipulation, stringent system alignment requirements, large probe size, and insufficient stability in complex environments in traditional optical fiber velocimetry technology. By using a spatial light modulator in conjunction with multi-core optical fiber, flexible multi-degree-of-freedom control of optical field amplitude, phase, polarization, and coherence structure is achieved, enabling the generation of various complex optical field structures and overcoming the limitations of existing technologies in optical field construction. The use of digital phase conjugation technology to compensate for phase distortion during transmission in real time ensures that the output optical field possesses a preset spatial structure, thereby significantly reducing the dependence on strict alignment between the rotation axis and the center of the light source, and improving the robustness and practicality of the measurement system.

[0090] This method employs a thin, flexible multi-core optical fiber as the optical field transmission carrier. Combined with an integrated transceiver optical path design, it achieves miniaturization and integration of the system probe, enabling endoscopic measurements in confined spaces and effectively expanding the applicable scenarios of optical velocimetry technology. The inherent anti-interference characteristics of multi-core optical fiber, combined with a fully coherent optical field of a specific structure, effectively suppresses signal degradation caused by speckle noise and mode coupling, improving the signal-to-noise ratio and stability of measurements in complex environments.

[0091] Therefore, this method not only has important application value in the industrial field for the condition monitoring and fault diagnosis of rotating parts, but also provides a new technical path for microscale motion detection in the biomedical field, such as cell rotation behavior analysis and particle motion monitoring in microfluidic systems, fully demonstrating its broad application potential in multi-scale and multi-scenario rotation speed measurement.

[0092] Example 2:

[0093] like Figure 5 As shown, this invention provides a rotating object rotation speed measurement system based on multi-core optical fiber, used to implement the rotating object rotation speed measurement method based on multi-core optical fiber described in Embodiment 1, including:

[0094] The light source module is used to generate a probe light field with a specific spatial structure;

[0095] The transmission and phase modulation module is used to transmit the probe light field through a multi-core optical fiber along a preset path, and to perform phase modulation on the probe light field during transmission to obtain an output light field with a preset spatial structure.

[0096] The detection module is used to illuminate the rotating object with the emitted light field and receive the signal light formed after the rotating object under test is reflected, wherein the signal light is transmitted back in the opposite direction through the same multi-core optical fiber.

[0097] The signal acquisition and processing module is used to detect the intensity change of the signal light to obtain a time-domain signal, perform frequency domain analysis on the time-domain signal to obtain frequency shift information caused by the motion of the rotating object, and calculate the angular velocity of the rotating object under test based on the frequency shift information.

[0098] The system includes a light source module, a transmission and phase modulation module, a detection module, and a signal acquisition and processing module. The modules are connected optically and electrically to form a complete measurement system.

[0099] like Figure 6 As shown, specifically, the light source module is used to generate a probe light field with a specific spatial structure, providing a high-quality optical probe foundation for measuring the rotational speed of a rotating object. This module sequentially comprises six core optical components along the optical path transmission direction: laser 1, beam expander 2, spatial light modulator 3, first lens 4, aperture 5, and second lens 6.

[0100] Laser 1 serves as the light source of the system, generating an initial coherent Gaussian beam. Its output wavelength can be optimized in the visible to near-infrared band (including typical wavelengths such as 532nm, 635nm, and 1550nm) according to the surface reflection characteristics of the rotating object 9 under test and the environmental measurement requirements, in order to ensure the best signal reflection intensity and environmental adaptability.

[0101] The laser beam output from laser 1 is processed by beam expander 2, which expands the originally narrow laser beam into a collimated beam with a larger aperture. This process not only effectively corrects the divergence angle of the beam, but more importantly, it enables the beam aperture to be precisely matched with the effective modulation region of the subsequent spatial light modulator 3, providing the necessary optical conditions for the generation of a high-quality structured light field.

[0102] The collimated beam, after beam expansion, is then incident on the spatial light modulator 3. As the core component of the light source module, the spatial light modulator 3 precisely controls the phase and amplitude of the incident wavefront by loading a pre-designed computational hologram. The spatial light modulator 3 can convert a simple Gaussian beam into a Laguerre-Gaussian beam with a complex phase distribution, a perfect vortex beam, or a structured light field with specific rotational symmetry. This flexible light field construction capability is a key technological foundation for achieving precise measurements of objects with different rotational symmetries.

[0103] The modulated light field undergoes preliminary wavefront transformation through the first lens 4. This lens collects and initially focuses the diffracted light field emitted from the spatial light modulator 3.

[0104] Furthermore, the spatial light modulator 3 can also be loaded with a Fresnel lens phase pattern to achieve dynamic focusing of the outgoing light field. A Fresnel lens is a phase modulation element based on the principle of diffraction. By simulating the phase distribution of a traditional lens, it can achieve beam focusing without introducing a physical lens, making it suitable for integrated control of complex light fields.

[0105] The aperture 5 is positioned after the first lens 4. Through a precisely set aperture, it effectively selects the desired first-order diffracted light or target modulated light field to pass through, while filtering out stray light components generated during the modulation process. This spatial filtering process significantly improves the spatial purity and signal-to-noise ratio characteristics of the emitted probe light field.

[0106] The second lens 6 is located after the aperture stop 5. Its main function is to re-collimate the spatially filtered light field and optimize its wavefront characteristics, ensuring that the probe light field can enter the subsequent transmission and phase modulation modules with the best phase and intensity distribution. The second lens 6 and the first lens 4 together form a complete optical processing system, realizing the effective shaping and transmission preparation of the modulated light field.

[0107] Furthermore, the transmission and phase modulation module is used to transmit the probe light field along a preset path and to perform phase modulation on the probe light field during transmission to compensate for phase distortion during transmission, thereby obtaining an output light field with a preset spatial structure at the output end. This module mainly includes a multi-core optical fiber 8, a spatial light modulator 3, and a beam splitter 7.

[0108] Multi-core fiber 8 serves as the core transmission medium, composed of thousands to tens of thousands of single-mode fiber cores. Due to manufacturing limitations, randomized optical path differences exist between the fiber cores, resulting in random speckle patterns at the far-end output when a plane wave is incident, making it impossible to directly form the preset optical field structure. Therefore, a spatial light modulator 3 is needed to achieve precise control of the input phase of each fiber core, constructing a phase control array to customize the transmission characteristics of the optical field.

[0109] To achieve phase compensation, the system employs digital phase conjugation technology. During the calibration phase, a modulation pattern is loaded onto the spatial light modulator 3, generating a plane wave that couples into the multi-core fiber 8 through the objective lens. A camera is positioned at the output end to record the light intensity distribution. Simultaneously, a reference beam is split from the spatial light modulator 3 and interferes with the target light field at the output end to form an off-axis digital hologram. By performing a two-dimensional Fourier transform on the hologram, the first-order term representing phase information is extracted from the spatial spectrum. Then, an inverse Fourier transform is performed to reconstruct the electric field distribution at the fiber cross-section, thereby obtaining the phase difference distribution of each fiber core.

[0110] Based on the reconstructed phase distribution, its phase conjugate value is calculated, and a precise coordinate mapping is established between the plane of the spatial light modulator 3 and the end face of the multi-core fiber 8. By loading the phase conjugate distribution onto the corresponding position of the spatial light modulator 3 according to the coordinate mapping, the random phase difference between each fiber core can be compensated. During the verification phase, the effectiveness of the phase compensation is confirmed by checking whether a flat-field phase is obtained at the fiber output end face.

[0111] In actual measurement, the spatial light modulator 3 performs a dual function: on the one hand, it loads a computational hologram to generate a light field with a specific spatial structure; on the other hand, it superimposes a phase conjugate compensation pattern to form complete modulation information. The modulated light field is coupled into the multi-core fiber 8 after being optimized by a lens group. Under the effect of phase compensation, even after long-distance transmission, the preset spatial structure can still be maintained at the output end, providing high-quality light field conditions for subsequent rotational speed measurement.

[0112] This module effectively overcomes the inherent phase inconsistency problem of multi-core optical fiber 8 by organically combining digital phase conjugation technology with spatial light modulator 3, and realizes the high-fidelity transmission of complex optical fields in the optical fiber transmission process, providing key technical support for the stable operation of the system in complex environments.

[0113] Furthermore, the detection module is used to illuminate the rotating object with the emitted light field and receive the signal light reflected by the object. The core of this module lies in utilizing the same multi-core optical fiber 8 to achieve both transmission and reception of the optical signal, constructing a compact optical path structure integrating transmission and reception. In specific implementation, the emitted light field, processed by the transmission and phase modulation module and possessing a preset spatial structure, is directly emitted from the bare fiber end face of the multi-core optical fiber 8 and illuminates the surface of the rotating object 9 under test. To achieve effective illumination and signal collection, a third lens 10 can be placed between the fiber optic output end and the object. The numerical aperture of the third lens 10 must match that of the multi-core optical fiber 8. Its function is twofold: firstly, to focus the emitted light field to increase the energy density of the illumination spot; secondly, the third lens 10 simultaneously collects the signal light reflected or scattered by the surface of the rotating object. Due to the interaction with the rotating object, the frequency of the signal light undergoes a corresponding frequency shift due to the rotational Doppler effect, carrying key information about the object's motion. The collected signal light is coupled back to the multi-core optical fiber 8 via the same lens and then transmitted back along the original transmission path. This common-path design not only greatly simplifies the system structure and reduces the difficulty of assembly and adjustment, but more importantly, it effectively avoids the additional phase noise and optical path difference that may be introduced by optical path separation, significantly improving the stability and measurement repeatability of the system, and is especially suitable for space-constrained endoscopic inspection environments.

[0114] Furthermore, the signal acquisition and processing module is responsible for converting the reflected light signal carrying motion information into an electrical signal, and extracting the angular velocity of the rotating object through signal processing. The core hardware of this module consists of a high-speed photodiode 11 and a data acquisition system based on a computer 12. In specific implementation, the signal light transmitted back from the multi-core optical fiber 8 is first detected by the high-speed photodiode 11, and its intensity change over time is converted into a corresponding time-domain electrical signal. The response bandwidth of the photodiode 11 must be significantly higher than the highest frequency of the Doppler shift signal under test to ensure distortion-free signal acquisition. The generated time-domain analog electrical signal is digitally sampled by a high-speed data acquisition card. The sampling frequency is strictly set according to the Nyquist sampling theorem, typically more than 2.5 times the expected highest signal frequency to prevent spectral aliasing; at the same time, the acquisition time must be long enough to ensure sufficient frequency resolution for frequency domain analysis to distinguish subtle differences in rotational speed.

[0115] The digitized time-domain signal is transmitted to a computer I2 or an embedded processor for analysis using a built-in dedicated signal processing algorithm. The core of the processing is to perform a Fast Fourier Transform (FFT) on the time-domain signal, transforming it from the time domain to the frequency domain to obtain the signal's power spectral density distribution. Subsequently, the algorithm automatically searches for and extracts the characteristic peak frequency caused by the rotating Doppler effect in the frequency spectrum. According to a pre-established physical model, this characteristic peak frequency has a clear quantitative relationship with the angular velocity of the rotating object.

[0116] ,

[0117] in, This represents the rotational symmetry multiplicity of the probe light field. This represents the rotational symmetry multiplicity of the rotating object 9 under test. express and The least common multiple of, This represents the angular velocity vector of the light source. This represents the angular velocity vector of the rotating object 9 to be measured.

[0118] Based on this relationship and combined with the known parameters, the processing software automatically calculates the magnitude of the angular velocity of the rotating object 9 to be tested.

[0119] Experiment 1:

[0120] To verify the effectiveness of the method for measuring the rotational speed of rotating objects based on multi-core optical fibers, this experiment used multi-core optical fibers as the core transmission medium and placed a digital micromirror device (DMD) at its output end to simulate target objects with different rotational symmetry characteristics. In the experiment, the DMD was loaded with four-fold symmetry, six-fold symmetry, and two-fold symmetry rotational modes to simulate the reflection characteristics of different types of rotating objects. The reflected signals were transmitted back to the detection end through the same multi-core optical fiber, realizing a compact optical path design integrating transmission and reception.

[0121] During the experiment, the rotational speeds of the rotating object were set to 0.05Hz, 0.1Hz, and 0.2Hz. The detector recorded the time-domain signal reflected by the rotating object, and the corresponding frequency domain spectrum was obtained by performing a Fourier transform on the time-domain signal. The experimental results are shown in Figures 7(a), 7(b), and 7(c). When a quadruple-symmetric vortex beam with superimposed positive and negative topological charges was used as the probe light to illuminate the quadruple-symmetric rotating object, the frequency domain spectra of the signal at rotational speeds of 0.05Hz, 0.1Hz, and 0.2Hz showed that the spectral characteristic peaks appeared at 0.2Hz, 0.4Hz, and 0.8Hz, respectively, exhibiting a clear fourth harmonic relationship, which verified the quantitative relationship between the rotational symmetry multiplicity and the characteristic frequency of the probe light field. When a six-fold symmetric vortex beam with superimposed positive and negative topological charges was used as the probe light to illuminate the six-fold symmetric rotating object, the frequency domain spectra of the signal at rotational speeds of 0.05Hz, 0.1Hz, and 0.2Hz showed that the characteristic peaks appeared at 0.2Hz, 0.4Hz, and 0.8Hz, respectively, exhibiting a clear fourth harmonic relationship, thus verifying the quantitative relationship between the rotational symmetry multiplicity and the characteristic frequency of the probe light field. When a doubly symmetrical rotating object is irradiated, the frequency domain spectra of the signal at rotational speeds of 0.05Hz, 0.1Hz, and 0.2Hz show spectral characteristic peaks around 0.3Hz, 0.6Hz, and 1.2Hz, respectively, exhibiting a clear sixth harmonic relationship. This further verifies the influence of the rotational symmetry multiplicity of the probe light field on the measurement results. When a doubly symmetrical vortex beam with superimposed positive and negative topological charges is used as the probe light to irradiate a doubly symmetrical rotating object (such as a rod-shaped object), the frequency domain spectra of the signal at rotational speeds of 0.05Hz, 0.1Hz, and 0.2Hz are obtained. Since the rotational symmetry multiplicity of the probe light and the object are different, their spectral characteristics reflect the harmonic relationship corresponding to their least common multiple. That is, the interaction between the doubly symmetrical probe light and the doubly symmetrical object generates a sixth harmonic characteristic signal, verifying the universal measurement capability of the method of this invention for rotating objects with different symmetries.

[0122] Experimental results show that the proposed measurement system is effective for measuring the rotational speed of rotating objects with different symmetries. By analyzing the characteristic peak frequencies in the spectrum, the actual angular velocity of the rotating object can be accurately determined. This rotational speed measurement method based on multi-core optical fibers not only verifies the correctness of the theoretical model but also demonstrates its potential for accurate measurement of different types of rotating targets in practical applications, providing a reliable technical solution for optical measurement of rotational speed in complex environments.

[0123] Example 3:

[0124] The present invention also provides an electronic device, which includes a processor, a memory, and a bus system. The processor and the memory are connected through the bus system. The memory is used to store instructions, and the processor is used to execute the instructions stored in the memory to implement the rotating object rotation speed measurement method based on multi-core optical fiber described in Embodiment 1.

[0125] Example 4:

[0126] The present invention also provides a computer storage medium storing a computer software product, the computer software product including several instructions for causing a computer device to execute the rotating object rotation speed measurement method based on multi-core optical fiber described in Embodiment 1.

[0127] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0128] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0129] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0130] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0131] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for measuring the rotational speed of a rotating object based on multi-core optical fiber, characterized in that, Includes the following steps: S1: Generate a probe light field with a specific spatial structure, transmit the probe light field along a preset path through a multi-core optical fiber, and perform phase modulation on the probe light field during transmission to obtain an output light field with a preset spatial structure. The method is as follows: S11: Obtain a hologram formed by the interference of the intermediate outgoing light field and the reference light after transmission through the preset path; S12: Perform a Fourier transform on the hologram to obtain the spatial spectrum of the hologram, and extract the first-order term representing the phase information of the light field from the spatial spectrum; S13: Perform an inverse Fourier transform on the first-order term to reconstruct the actual phase distribution of the intermediate outgoing light field; S14: Based on the actual phase distribution obtained by the above reconstruction, calculate its phase conjugate value as the compensation phase, and load the compensation phase into the probe light field before transmission to obtain the output light field with a preset spatial structure after phase compensation. S2: The emitted light field is used to illuminate the rotating object under test, and the signal light formed after being reflected by the rotating object under test is received. The signal light is transmitted back in the same multi-core optical fiber, and the intensity change of the signal light is detected to obtain the time domain signal. S3: Perform frequency domain analysis on the time domain signal to obtain frequency shift information caused by the motion of the rotating object under test. The method is as follows: perform Fourier transform on the time domain signal to obtain its frequency domain spectrum, and extract the characteristic peak frequency from the frequency domain spectrum. The angular velocity of the rotating object under test is calculated based on the frequency shift information, using the characteristic peak frequency. The Doppler frequency shift caused by the rotating object under test, the characteristic peak frequency The angular velocity of the rotating object to be measured satisfies the following relationship: ， in, This represents the rotational symmetry multiplicity of the probe light field. This represents the rotational symmetry multiplicity of the rotating object under test. express and The least common multiple of, This represents the angular velocity vector of the light source. This represents the angular velocity vector of the rotating object under test.

2. The method for measuring the rotational speed of a rotating object based on multi-core optical fiber according to claim 1, characterized in that: The probe light field with a specific spatial structure is a fully coherent structured light field with rotational symmetry, including a Laguerre-Gaussian beam, a perfect vortex beam, or a multi-ring nested beam.

3. A rotating object rotation speed measurement system based on multi-core optical fiber, used to implement the rotating object rotation speed measurement method based on multi-core optical fiber as described in any one of claims 1 to 2, characterized in that, Includes the following modules: The light source module is used to generate a probe light field with a specific spatial structure; The transmission and phase modulation module is used to transmit the probe light field through a multi-core optical fiber along a preset path, and to perform phase modulation on the probe light field during transmission to obtain an output light field with a preset spatial structure. The method is as follows: S11: Obtain a hologram formed by the interference of the intermediate outgoing light field and the reference light after transmission through the preset path; S12: Perform a Fourier transform on the hologram to obtain the spatial spectrum of the hologram, and extract the first-order term representing the phase information of the light field from the spatial spectrum; S13: Perform an inverse Fourier transform on the first-order term to reconstruct the actual phase distribution of the intermediate outgoing light field; S14: Based on the actual phase distribution obtained by the above reconstruction, calculate its phase conjugate value as the compensation phase, and load the compensation phase into the probe light field before transmission to obtain the output light field with a preset spatial structure after phase compensation. The detection module is used to illuminate the rotating object with the emitted light field and receive the signal light formed after the rotating object under test is reflected, wherein the signal light is transmitted back in the opposite direction through the same multi-core optical fiber. The signal acquisition and processing module is used to detect the intensity change of the signal light to obtain a time-domain signal, and to perform frequency domain analysis on the time-domain signal to obtain frequency shift information caused by the motion of the rotating object. The method is as follows: perform Fourier transform on the time-domain signal to obtain its frequency domain spectrum, and extract the characteristic peak frequency from the frequency domain spectrum. The angular velocity of the rotating object under test is calculated based on the frequency shift information, using the characteristic peak frequency. The Doppler frequency shift caused by the rotating object under test, the characteristic peak frequency The angular velocity of the rotating object to be measured satisfies the following relationship: ， in, This represents the rotational symmetry multiplicity of the probe light field. This represents the rotational symmetry multiplicity of the rotating object under test. express and The least common multiple of, This represents the angular velocity vector of the light source. This represents the angular velocity vector of the rotating object under test.

4. The rotating object rotation speed measurement system based on multi-core optical fiber according to claim 3, characterized in that: The transmission and phase modulation module includes a multi-core optical fiber, the output end of which is a bare fiber end face, used to directly irradiate the rotating object under test with the output light field.

5. The rotating object rotation speed measurement system based on multi-core optical fiber according to claim 4, characterized in that: The transmission and phase modulation module includes a spatial light modulator for phase modulation of the probe light field to compensate for the phase difference between the cores in the multi-core optical fiber.

6. An electronic device, characterized in that, The electronic device includes a processor, a memory, and a bus system. The processor and the memory are connected through the bus system. The memory is used to store instructions, and the processor is used to execute the instructions stored in the memory to implement the rotating object rotation speed measurement method based on multi-core optical fiber as described in any one of claims 1 to 2.

7. A computer storage medium, characterized in that, The computer storage medium stores a computer software product, which includes several instructions for causing a computer device to execute the rotating object rotation speed measurement method based on multi-core optical fiber as described in any one of claims 1 to 2.

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