Transmit-receive coupling device of multi-core optical fiber for variable-focus three-dimensional displacement sensing

Abstract

The invention discloses a variable-focus transmitting-receiving coupling device of a multi-core optical fiber for three-dimensional displacement sensing, the variable-focus transmitting-receiving coupling device is composed of a laser source, the multi-core optical fiber and two distance-adjustable lenses, the multi-core optical fiber comprises a central transmitting fiber core and a plurality of receiving fiber cores distributed in the circumferential direction, the transmitting fiber core is coupled with the laser source, and each receiving fiber core is connected with an independent photoelectric detector; the lens group is arranged between the end face of the optical fiber and a measured object and shares an optical axis, the effective focal length is changed by adjusting the distance between the two lenses, and light spots matched with the multiple receiving fiber cores are formed on the end face by reflected / scattered return light of the measured object. According to the invention, stable energy recovery and multi-channel light intensity reading can be realized in a wide distance range, the axial and transverse displacement of a detected body can be inverted conveniently, and the device is compact in structure and suitable for displacement / attitude detection.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement and displacement / attitude detection technology, specifically relating to a transceiver coupling device for a multi-core optical fiber with variable focal length for three-dimensional displacement sensing. Background Technology

[0002] Three-dimensional displacement sensing has wide applications in precision manufacturing, micro-nano manipulation, in-situ detection, and robotic end-effector sensing. Compared with free-space optical systems, fiber optic sensing heads offer advantages such as small size, flexible deployment, resistance to electromagnetic interference, and long-distance signal transmission, making them suitable for deployment in confined or complex environments. Multi-core fiber (MCF) integrates multiple fiber cores within the same cladding, enabling parallel acquisition of multi-channel intensity or phase information at a single probe tip. A structure exemplified by a central transmitting fiber core paired with circumferentially distributed receiving fiber cores can reflect the axial and lateral displacement of the target object through changes in light intensity across each receiving channel, exhibiting compact structure and fast response speed.

[0003] Existing multi-core fiber optic displacement sensing front-ends mostly employ fixed-focal-length optical coupling methods, such as a single spherical lens or a gradient-index (GRIN) lens, to achieve collimation of the emitted light and coupling of the returned light. This type of solution has high coupling efficiency at the nominal working distance, but in practical applications, when the working distance... S′ Deviation from design value, feature size of the measured target R When changes occur, or when optical path shifts due to assembly and adjustment errors, the spot size (bundle waist radius) of the returned light on the fiber end face changes. W ) and the geometric dimensions (circumcircle diameter) of the multi-receiver fiber core D r Mismatches can easily occur between these components. Mismatches will lead to a significant decrease in coupling efficiency and a deterioration in the signal-to-noise ratio, thereby compressing the effective measurement range and increasing the uncertainty of displacement calculation.

[0004] To alleviate the aforementioned problems, existing technologies often employ methods such as external mechanical focusing mechanisms, increasing the aperture of the front-end optical components, or using bulk imaging / interference structures. However, mechanical focusing increases system complexity and response time, which is detrimental to dynamic measurements; increasing the optical aperture, while expanding the depth of field, leads to a larger probe size, making it difficult to apply in confined spaces; and bulk imaging or interferometric solutions are limited by cost, assembly difficulty, vibration resistance, and environmental adaptability, which is not conducive to system miniaturization and field deployment.

[0005] Furthermore, although optical coupling technology for multi-core optical fibers has been extensively studied in the field of optical communication, related schemes mainly focus on end-to-end or device-to-device mode field matching, insertion loss, and crosstalk suppression, typically assuming a fixed beam propagation path and stable optical system. These techniques neglect the dynamic characteristics of light reflected or scattered from free-space targets, making it difficult to adapt to the actual needs of displacement sensing applications such as target position changes and fluctuations in the size of the returned light spot. In displacement sensing scenarios, the core challenge lies in ensuring stable and efficient coupling of free-space returned light at the fiber end face under different working distances and target states, and accurately characterizing the variation of coupling efficiency with target displacement. Existing fixed-focal-length schemes are insufficiently adaptable to these dynamic changes, resulting in poor measurement repeatability and limited effective working range, failing to meet the requirements of high-precision, wide-range three-dimensional displacement measurement. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by proposing a variable-focus, multi-core fiber optic transceiver coupling device for three-dimensional displacement sensing. The aim is to dynamically adjust the coupling conditions of the returned light at the fiber end face under different working distances and target conditions, ensuring that the size of the returned light spot matches the geometric dimensions of the multiple receiving fiber cores. This maintains stable coupling efficiency and signal-to-noise ratio over a wide working distance range, expands the effective measurement range, improves the accuracy and repeatability of three-dimensional displacement measurement, and simultaneously retains the advantages of a compact probe structure and ease of deployment in confined spaces.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: The present invention provides a transceiver coupling device for a variable-focus three-dimensional displacement sensing multi-core optical fiber, characterized in that it includes: a laser source, a multi-core optical fiber, and a lens group. The multi-core optical fiber includes: a central transmitting core and multiple receiving cores circumferentially distributed around the transmitting core. The transmitting core is connected to the laser source via an external optical fiber coupler, and the receiving cores are respectively connected to external photodetectors. The lens group is sequentially arranged along a common optical axis between the end face of the multi-core optical fiber and the object under test. The lens group consists of lenses with focal lengths of [missing information]. and It consists of two lenses; wherein, the first lens is located on one side of the end face of the multi-core optical fiber, and the second lens is located on the side of the object being measured; the axial distance between the surface of the first lens facing the multi-core optical fiber and the end face of the multi-core optical fiber is... The axial distance between the surface of the second lens facing the object being measured and the object being measured is... , and as a working distance; The distance between the first lens and the second lens is The effective focal length of the lens group is obtained based on the lens combination principle or ray tracing method. focal length of the first lens The focal length of the second lens and the distance between the two The optical correspondence between them; The emitted light from the transmitting fiber core is focused by the lens group and irradiates the test object. After being reflected or scattered by the test object, the returning light beam is coupled into the multi-receiving fiber core through the lens group, so that the returning light beam forms a light spot distribution that matches the multi-receiving fiber core on the end face of the multi-core fiber. Adjust the spacing To change the effective focal length of the lens group The light spot distribution satisfies ,in, The diameter of the circumscribed circle of the multiple receiving fiber cores at the end face of the multi-core optical fiber. The equivalent beam waist radius of the returning beam at the end face of the multi-core fiber.

[0008] The transceiver coupling device described in this invention is also characterized by using equation (1) to calculate : (1) In equation (1), The beam waist radius of the emitted light from the transmitting fiber core at the end face of the multi-core optical fiber. The operating wavelength; C, D These represent the two optical transmission coefficients corresponding to the optical path originating from the end face of the multi-core fiber, being reflected or scattered by the object under test, and returning to the end face of the multi-core fiber, and are: (2) (3) In equations (2) and (3), R The dimensions of the object being measured.

[0009] Furthermore, the spacing The range is from 0.1 mm to 100 mm to accommodate different working distances. The size of the object being measured R .

[0010] Furthermore, the number of receiving fiber cores is not less than 3.

[0011] Furthermore, the light intensity data output by the photodetector connected to each receiving fiber core is used to analyze the three-dimensional displacement of the measured object.

[0012] Furthermore, the lens surface of the lens group is provided with an anti-reflection coating.

[0013] Furthermore, by selecting a first lens and / or a second lens with different focal lengths to change... and / or The value of is determined and adjusted accordingly. L The spacing is adjusted to achieve the desired result. effective focal length .

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention proposes two lenses + spacing Adjustable zoom lens group (equivalent focal length varies with...) By changing the optical fiber end face and placing it on the coaxial position between the fiber end face and the measured object, continuous focusing capability is fundamentally provided. Therefore, under different working distances and target conditions, the returned light spot can be adjusted back to the matching area, improving coupling efficiency and signal-to-noise ratio and expanding the effective range. This solves the problems of mismatch between the end face light spot and the receiving array, and significant decrease in coupling and signal-to-noise ratio, that commonly occur in multi-core fiber displacement sensors using single lenses or GRIN lenses when the working distance and the size of the measured object change, as well as the problem of poor adaptability of fixed-focus front-ends to changes in working conditions.

[0015] 2. This invention shifts from empirical calibration to verifiable coupled design, and provides a spot-array matching criterion. And in claim 2, an equivalent waist is provided at the end face. The calculation method and the calculation form a closed loop of "design-calculation-acceptance": the design phase can use this to estimate the parameter domain that meets the matching conditions, the assembly and commissioning phase can use this to determine whether it meets the standards, and the mass production phase can use this to control the dispersion. This realizes a coupled design path that is calculable, reproducible, and verifiable, improving the consistency and repeatability of the device across batches and environments, and avoiding the drawbacks of assembly and commissioning uncertainty caused by relying solely on experience-based optimization.

[0016] 3. This invention adjusts the axial spacing between the two lenses. L The lens is set to be continuously adjustable, preferably within a range of 0.1 mm to 100 mm, allowing the equivalent focal length of the lens group to vary continuously within a certain range. It also employs a replaceable lens group structure, allowing for the selection of first and / or second lenses with different focal lengths according to application requirements. (When working distance...) S′ or target feature size R The change in the interval L When within the adjustment range, by adjusting L This allows for waisting of the end face. W Restores the fiber to a state compatible with multiple receiver cores without replacing optical components; when the change exceeds... L When adjusting the lens configuration, try changing to a different lens combination with varying focal lengths and resetting the settings. LThis allows for the acquisition of new focal length coverage. This mechanism overcomes the problem of existing fixed-focal-length solutions requiring the design of multiple device models for different working distances and target sizes. A single device can be adapted to working distances ranging from a few millimeters to hundreds of millimeters and to different sizes of measured targets through simple spacing adjustments or lens replacements. This reduces product model divisions and spare parts types, lowers user configuration costs and inventory pressure, shortens on-site assembly and maintenance cycles, and significantly improves the versatility and practicality of the device in multi-scenario applications. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the multi-core optical fiber transceiver coupling device of the present invention; Figure 2 This is a schematic diagram of the ray tracing simulation of the present invention, showing the simulation results of the coupling effect of the coupling device on the transmission and reception of light; The numbers in the diagram are: 1 for fiber laser, 2 for multi-core fiber, 3 for lens group, 4 for the object under test, and 5 for signal processing module. Detailed Implementation

[0018] To overcome the limitations of existing multi-core fiber optic displacement sensing front-ends that often employ fixed-focus lenses (such as single spherical lenses or GRIN lenses) in terms of working distance... Dimensions of the measured object R To address the issues of poor adaptability to assembly and adjustment errors, and the decrease in coupling efficiency and signal-to-noise ratio due to mismatch between the returned light and the multi-core optical fiber spot, this embodiment proposes a transceiver coupling device for multi-core optical fiber in three-dimensional displacement sensing with variable focus. Its structure is as follows: Figure 1 As shown, the transceiver coupling device of the present invention mainly consists of three core components. A laser source 1 provides a stable coherent beam; a multi-core optical fiber 2 simultaneously performs both transmitting and receiving functions; and a lens group 3 is responsible for focusing and coupling the beam. This integrated design makes the device compact and easy to deploy in confined spaces.

[0019] The multi-core fiber 2 consists of a central transmitting core and multiple receiving cores distributed circumferentially around it. The transmitting core is connected to the laser source 1 via an external fiber coupler to output the laser beam.

[0020] Lens group 3 is sequentially arranged along the common optical axis between the end face of the multi-core optical fiber 2 and the object under test 4, used to focus the emitted light onto the surface of the object under test and efficiently couple the returned light to the multi-receiving fiber cores. For example... Figure 1 As shown, lens group 3 consists of lenses with focal lengths of... and It consists of two lenses. The first lens is located on one side of the end face of the multi-core optical fiber 2, and the second lens is located on the side of the object under test 4. The axial distance between the surface of the first lens facing the multi-core optical fiber 2 and the end face of the optical fiber is... The axial distance between the surface of the second lens facing the test object 4 and the test object 4 is... This distance is the system's working distance. The distance between the first lens and the second lens is... L .

[0021] During the design process, the correspondence between the effective focal length of the lens group and the focal length and spacing of each lens can be determined by the principle of thin lens combination. The theoretical approximate relationship is given by equation (1): (1) It should be noted that the above formula only applies to ideal thin lens combinations. In practical designs, the specific correspondence between lens spacing and the focal length and spacing of each lens can be simulated through ray tracing.

[0022] During operation, the light beam emitted from the transmitting fiber core is focused by lens group 3 and then illuminates the surface of the test object 4. The light is reflected or scattered on the test object 4 and returns. The returned beam is then coupled again to the multi-receiving fiber core by lens group 3, thus forming a light spot distribution on the end face of the multi-core fiber 2 that matches the multi-receiving fiber core. The equivalent bundle waist radius of the light spot on the end face of the multi-core fiber is denoted as [missing information]. The outer diameter of the multi-receiver fiber core is denoted as . .when When the light spot size is too small, the light intensity received by the outer receiving fiber core is weak; when Greater than When the spot size is too large, some energy overflows, leading to a decrease in coupling efficiency. To achieve efficient optical energy coupling, the matching relationship between the spot size and the multiple receiving fiber cores must satisfy equation (2): (2) Equivalent waist radius of light spot The calculation formula is equation (3): (3) In equation (3), The beam waist radius of the emitted light from the transmitting fiber core at the end face of the multi-core optical fiber. is the operating wavelength; C and D are the optical transmission matrix elements from the end face of the multi-core fiber to the equivalent reflecting surface of the test object and back to the end face of the multi-core fiber, and their expressions are Equations (4) and (5), respectively: (4) (5) In equations (4) and (5), Let be the characteristic dimension of the object being measured. The above formula can be used to determine the characteristic dimension of a given object. , , Calculate the required effective focal length under the given conditions And adjust the lens spacing accordingly. To achieve optimal focusing, the spot size is matched to the multi-receiver fiber core.

[0023] To verify the correctness of the design, optical simulation software (such as the COMSOL ray tracing module) was used to analyze the transmission and reception process. Figure 2 As shown, in the parameters Under these conditions, adjust the lens spacing. L to It can focus the light beam on the surface of the object being measured and form a returning light spot, which is then accurately coupled into the receiving fiber core after returning through the lens group.

[0024] The simulation results were then verified through optical experiments. In the experiments, an optical power meter and a beam analyzer were used to measure the distribution of the returned light beam and to evaluate the matching degree between the beam size and the multiple receiver fiber cores. The lens group spacing was adjusted... L Ensure the spot size meets 2 W ≈ D The design conditions of ᵣ enable efficient coupling and high signal-to-noise ratio detection.

[0025] In this embodiment, the adjustable spacing of lens group 3 The range is from 0.1 mm to 100 mm to accommodate different working distances. and the dimensions of the object being measured This adjustable range ensures the device has good flexibility and adaptability in different application scenarios, and can meet a variety of measurement needs.

[0026] In addition, the device contains at least three receiving fiber cores. Increasing the number of receiving fiber cores enhances the ability to capture reflected or scattered light and improves measurement accuracy. The number and distribution of receiving fiber cores can be flexibly configured according to specific applications; common arrangements include six or eight receiving fiber cores, acquiring signals from different directions. Each receiving fiber core is connected to an independent photodetector via a fiber bundle fan-out. The signals output by each detector are demodulated by the signal processing module 5 to obtain the three-dimensional displacement information of the target being measured.

[0027] To improve the system's optical performance and transmission efficiency, each lens in the lens group is coated with a high-performance multilayer dielectric anti-reflection film to reduce reflection loss in the transmission and return paths. Lens group 3 adopts a replaceable structure, allowing for the replacement of lenses with different focal lengths according to different measurement requirements, and is optimized in conjunction with the lens spacing. Adjustment to achieve the target effective focal length Thus maintaining under different working conditions The optimal coupling state.

[0028] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention.

Claims

1. A transceiver coupling device for a multi-core optical fiber with variable focus for three-dimensional displacement sensing, characterized in that, include: Laser source, multi-core optical fiber, and lens assembly; The multi-core optical fiber includes: a central transmitting core and multiple receiving cores circumferentially distributed around the transmitting core. The transmitting core is connected to the laser source via an external optical fiber coupler, and the receiving cores are respectively connected to external photodetectors. The lens group is sequentially arranged along a common optical axis between the end face of the multi-core optical fiber and the object under test. The lens group consists of lenses with focal lengths of [missing information]. and It consists of two lenses; wherein, the first lens is located on one side of the end face of the multi-core optical fiber, and the second lens is located on the side of the object being measured; the axial distance between the surface of the first lens facing the multi-core optical fiber and the end face of the multi-core optical fiber is... The axial distance between the surface of the second lens facing the object being measured and the object being measured is... , and as a working distance; The distance between the first lens and the second lens is The effective focal length of the lens group is obtained based on the lens combination principle or ray tracing method. focal length of the first lens The focal length of the second lens and the distance between the two The optical correspondence between them; The emitted light from the transmitting fiber core is focused by the lens group and irradiates the test object. After being reflected or scattered by the test object, the returning light beam is coupled into the multi-receiving fiber core through the lens group, so that the returning light beam forms a light spot distribution that matches the multi-receiving fiber core on the end face of the multi-core fiber. Adjust the spacing To change the effective focal length of the lens group The light spot distribution satisfies ,in, The diameter of the circumscribed circle of the multiple receiving fiber cores at the end face of the multi-core optical fiber. The equivalent beam waist radius of the returning beam at the end face of the multi-core fiber.

2. The transceiver coupling device according to claim 1, characterized in that, Calculate using formula (1) : (1) In equation (1), The beam waist radius of the emitted light from the transmitting fiber core at the end face of the multi-core optical fiber. C is the operating wavelength. 、 D represents the two optical transmission coefficients corresponding to the optical path originating from the end face of the multi-core fiber, being reflected or scattered by the object under test, and returning to the end face of the multi-core fiber, and has the following: (2) (3) In equations (2) and (3), R The dimensions of the object being measured.

3. The transceiver coupling device according to claim 1, characterized in that, The spacing The range is from 0.1 mm to 100 mm to accommodate different working distances. The size of the object being measured R .

4. The transceiver coupling device according to claim 1, characterized in that, The number of receiving fiber cores is no less than 3.

5. The transceiver coupling device according to claim 1, characterized in that, The light intensity data output by the photodetector connected to each receiving fiber core is used to analyze the three-dimensional displacement of the measured object.

6. The transceiver coupling device according to claim 1, characterized in that, The lens surface of the lens group is provided with an anti-reflection coating.

7. The transceiver coupling device according to claim 1, characterized in that, By selecting a first lens and / or a second lens with different focal lengths to change and / or The value of is determined and adjusted accordingly. L The spacing is adjusted to achieve the desired result. effective focal length .

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