A handheld multi-beam aligned fiber grating sensing device and method

Abstract

This application discloses a handheld multi-beam alignment fiber optic grating sensing device and method, including a passive sensing grating assembly, a handheld module, and a demodulation control module. The passive sensing grating assembly converts the laser propagating within the fiber into a spatially parallel laser beam and visualizes the invisible passive end optical axis. The handheld module is used to achieve high-speed spatial scanning of multiple beams and complete laser collimation and projection. The demodulation control module is used to generate and distribute multiple sensing lasers and control the synchronous movement of the galvanometer in the handheld module. This application utilizes a hollow ring to visualize the invisible virtual optical axis of the passive end, facilitating rough identification of the passive end's optical axis position by the operator, greatly improving the efficiency of manual alignment. Simultaneously, a two-stage beam-multiplying method is used to split a single laser beam into four beams, which are then scanned through a galvanometer module and an off-axis parabolic mirror to form the effect of hundreds of beams in time, resulting in large spatial coverage and significantly improved alignment efficiency.

Description

Technical Field

[0001] This application belongs to the field of fiber optic grating wireless sensing technology, and more specifically, relates to a handheld multi-beam aligned fiber optic grating sensing device and method. Background Technology

[0002] A grating is created by modulating a periodic refractive index change on the fiber core using ultraviolet laser from the side (one period is several hundred nanometers along the fiber core axis, and the length of a single grating region is approximately 10 millimeters). For example, a grating that reflects a wavelength of 1550 nm can be used to propagate a broadband laser with a wavelength range of 1525 nm to 1565 nm through one end of the fiber. The 1550 nm wavelength light will be reflected back when it encounters the grating, while the other wavelengths of laser light can pass through the grating and continue propagating along the fiber core.

[0003] When changes in external physical quantities alter the refractive index period of a grating, the wavelength reflected by the grating changes accordingly. For example, a grating that normally reflects only 1550nm wavelength laser light might, if its grating region is affected by an external physical change, such as tension or temperature, causing a change in the refractive index period, and the grating then reflects only 1551nm wavelength laser light. Based on this principle, the magnitude of the physical quantity causing the change can be inferred from the change in the reflected laser wavelength. Depending on the packaging design, some grating sensors can be used to measure temperature, while others can be used to measure changes in force.

[0004] Traditional fiber Bragg grating temperature sensing systems, such as Figure 1 As shown, a contact connection scheme is typically used: multiple fiber Bragg grating sensors are connected in series and attached to the point being measured (such as the surface of a high-voltage electrical cabinet), and then physically connected to the demodulator directly via fiber optic patch cords. The demodulator has a built-in broadband light source (wavelength range 1525nm~1565nm), a circulator, and a demodulation module for spectral analysis. It infers temperature changes by monitoring the reflected wavelength shift (e.g., 1550nm→1551nm).

[0005] Figure 1The fiber optic grating sensing system is a common type of grating sensor string used for temperature measurement. Multiple fiber optic grating sensors (shown as 5, 6, and 7 in the figure) are attached to the location where the temperature needs to be measured. One end of fiber optic cable 4 is then connected to demodulator 10. Demodulator 10 includes a broadband light source 1, a circulator 2, and a demodulation module 3. The specific sensing process is as follows: the broadband light source 1 emits broadband laser light in the wavelength range of 1525nm to 1565nm, which enters fiber optic cable 4 through circulator 2 and passes sequentially through temperature sensors 5, 6, and 7. The grating period of each sensor is intentionally set to be different, thus reflecting different wavelengths. For example, sensor 5 reflects a wavelength of 1530nm, sensor 6 reflects a wavelength of 1540nm, and sensor 7 reflects a wavelength of 1550nm. These three wavelengths of laser light are reflected back to circulator 2 and reach demodulation module 3. If a temperature change at a sensor causes a change in the grating spacing, this will result in a change in the wavelength of the laser reflected back from that point. For example, the wavelength reflected from sensor 5 to demodulation module 3 may be 1530nm, but it may become 1531nm. In this case, demodulation module 3 can determine the current temperature value at that point based on the corresponding data that has been calibrated beforehand.

[0006] Existing technology poses a physical connection risk: If this sensing system is deployed in the power industry, fiber optic cables need to be laid from the personnel work area to the high-voltage area, and this connection line will always exist. If there are metal components inside the fiber optic cable, the high-voltage electrodes may be led to the personnel work area along the connection line (and most fiber optic cables on the market have metal components, so workers are very likely to mistakenly use fiber optic cables containing metal components during installation and maintenance), thus bringing the risk of electric shock.

[0007] Some universities and research institutes are now experimenting with fixed, non-contact, single-beam fiber optic sensing solutions within the power industry. For example... Figure 2 As shown, existing non-contact solutions use two fixed fiber optic collimators 8 and 9 to acquire sensing signals. This approach is inflexible and requires stringent alignment precision. For example, due to cost considerations, the outer diameter of fiber optic collimators 8 and 9 is approximately 3 mm, while the emitted laser beam 11 is a single beam with a diameter of 1 mm. Therefore, fiber optic collimators 8 and 9 must be perfectly aligned to establish communication. Consequently, in existing non-contact solutions, the spatial alignment tolerance between the fiber optic collimator at the laser emitter and the fiber optic collimator of the fiber being measured is extremely small. After adjustment by a precision mechanical adjustment mechanism, the collimator must remain fixed in place, making the application extremely inconvenient. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the purpose of this application is to provide a handheld multi-beam alignment fiber grating sensing device, which aims to solve the problem of low alignment efficiency caused by the extremely small spatial alignment tolerance between the fiber collimator at the laser emitter and the fiber collimator of the fiber under test in existing technologies.

[0009] This application provides a handheld multi-beam alignment fiber Bragg grating sensing device, including a passive sensing grating assembly at the passive end and a handheld module and demodulation control module at the active end. The passive sensing grating assembly is used to convert the laser propagating in the fiber into a spatial parallel laser beam and visualize the invisible optical axis at the passive end. The handheld module is used to realize high-speed spatial scanning of multiple beams and complete laser collimation and projection, as well as red light indication to assist manual alignment. The demodulation control module is used to generate and distribute multiple sensing lasers, control the synchronous movement of the galvanometer in the handheld module, and integrate visible light guidance and demodulation wavelength offset inversion temperature data.

[0010] Furthermore, the passive sensing grating assembly includes an optical fiber collimator and a hollow metal ring coaxially arranged with the optical fiber collimator; the optical fiber collimator is used to convert the laser propagating in the optical fiber into a spatial parallel laser beam; the hollow metal ring is used to visualize the invisible passive end optical axis, making it easier for the operator to roughly know the position of the passive end optical axis, thereby increasing the probability of handheld alignment.

[0011] Furthermore, the inner diameter of the hollow metal ring is 3 mm to 50 mm, and the outer diameter is 2 mm to 20 mm larger than the inner diameter.

[0012] Furthermore, the spacing between the hollow metal ring and the fiber collimator is proportional to the spacing between the active and passive ends.

[0013] Furthermore, the spacing between the hollow metal ring and the fiber collimator is one-tenth the spacing between the active and passive ends.

[0014] Furthermore, the handheld module includes: an off-axis parabolic reflector, a galvanometer module, an optical fiber collimator, optical fibers, and cables; the galvanometer module reflects the laser beam to various positions of the off-axis parabolic reflector according to a preset scanning path; the off-axis parabolic reflector is used to collimate the diverging laser beam emitted from the galvanometer module into a parallel narrow beam and form a spatial coverage area; the optical fiber collimator is used to collimate the laser in the active-end optical fiber and emit it, and receive the reflected light and couple it back to the active-end optical fiber; the optical fiber is disposed between the optical fiber collimator and the demodulation control module for transmitting the multi-path sensing laser; the cable is disposed between the galvanometer module and the demodulation control module for transmitting galvanometer control signals for galvanometer motion synchronization.

[0015] The galvanometer module is positioned at the focal point of the off-axis parabolic mirror. Since the light emitted from the point light source placed at the focal point becomes a beam strictly parallel to the optical axis of the parent mirror (without divergence) after reflection by the off-axis parabolic mirror, this application places the light-emitting position of the galvanometer module at the focal point of the off-axis parabolic mirror. A beam of light with a diameter of 1 mm emitted from the fiber collimator, after reflection by the two-axis galvanometers in the galvanometer module, can cover the entire surface of the mirror (in sequence) under the scanning of the galvanometer module, achieving 5 coverages per second; as long as one of the thin beams is aligned with the optical axis of the passive end, the sensing signal can be acquired.

[0016] More preferably, the galvanometer module can be set at an optimal offset position with a certain offset from the focal point of the off-axis parabolic mirror; this causes the beam reflected by the off-axis parabolic mirror to converge into a cone shape, reducing the size of the light spot at the far end and further improving the alignment efficiency.

[0017] The preset scanning path can be a zigzag scanning path.

[0018] Furthermore, the demodulation control module includes: a beam splitter, a motion controller, a laser generator, and a wavelength division multiplexer; the beam splitter is used to split a laser beam propagating in one optical fiber into multiple optical fibers, and the multiple laser beams are emitted and reflected by the galvanometer module to the passive end, increasing the number of laser beams emitted from the active end and increasing the probability of alignment; the motion controller is used to control the movement of the galvanometer module; the laser generator is used to generate a red indicator laser of a specific wavelength; the wavelength division multiplexer is used to combine the red indicator laser into the same optical fiber propagating the broadband laser, making it easy for operators to know where the laser is aligned.

[0019] The wavelength of the red indicator laser can be 650nm.

[0020] This application also provides a fiber grating sensing method for multi-beam alignment based on the above-mentioned fiber grating sensing device, comprising the following steps: Align the laser emission direction of the off-axis parabolic mirror with the passive end, and move the handheld module to align the optical axis of the active end with the optical axis of the passive end. The galvanometer module reflects the laser beam to various positions of the off-axis parabolic mirror according to the preset scanning path; The off-axis parabolic mirror collimates the diverging laser beam emitted from the galvanometer into a parallel narrow beam, forming a spatial coverage area; The invisible passive end optical axis is visualized by using a hollow metal ring, which makes it easier for the operator to roughly know the position of the passive end optical axis, thereby increasing the probability of handheld alignment.

[0021] During the handheld module's shaking and alignment process, there is a moment when the optical axes of the active end and the passive end are aligned. The active end can then obtain the wavelength change information of the passive end, thereby knowing the temperature at each sensor.

[0022] Furthermore, the galvanometer module is positioned at the focal point of the off-axis parabolic mirror; or the galvanometer module is positioned at an optimal offset position with a certain offset from the focal point of the off-axis parabolic mirror.

[0023] When the galvanometer module is set at the optimal offset position with a certain offset from the focal point of the off-axis parabolic mirror 13, the optimal offset position ΔXi (the X-axis offset of the light output center of the galvanometer module relative to the focal point) can be determined by the following method. The core objective is to find the galvanometer X-axis position that minimizes the spot diameter of the beam reflected by the off-axis parabolic mirror at the target sensing distance L (a preset distance between the active end and the passive end, such as 1~5 meters). This can be done by either actual measurement or optical software simulation. As a preferred embodiment of this application, the specific steps of the actual measurement method are as follows: (1) Determine the initial range of the target sensing distance L and the X-axis offset: The initial X-axis offset range of the galvanometer module's light output center relative to the focal point is set by ensuring coverage of the area where the smallest light spot may occur; the target sensing distance L is the preset distance between the active end and the passive end; (2) Select the first position ΔX1: The first test point within the initial range of the X-axis offset is selected as the first position ΔX1; ΔX1 represents the offset of the center of the first light emission from the galvanometer module from the focal point of the off-axis parabolic mirror in the X-axis direction; (3) First light emission test and spot diameter measurement: The galvanometer module is fixed at the first position ΔX1, and a spot measuring instrument is placed at the target sensing distance L to obtain the spot formed after reflection by the off-axis parabolic mirror. The diameter D1 of the spot is measured and recorded. (4) Adjust the X-axis offset by a fixed step size and repeat the test: Along the X-axis offset range, adjust the galvanometer position sequentially according to the preset step size δ, and determine the second position ΔX2=ΔX1+δ, the third position ΔX3=ΔX2+δ... until the offset exceeds the initial range or the spot diameter of the light spot increases more than the previous one in 3 consecutive tests. Repeat step (3) for each position ΔXi, and record the corresponding spot diameters D2, D3...Dn in sequence; (5) Determine the optimal offset position ΔXi: The smallest diameter Dmin is selected from the light spot diameters D1 to Dn; The X-axis offset ΔXi corresponding to the minimum diameter Dmin is taken as the optimal offset position of the galvanometer module.

[0024] Compared with the prior art, the above-described technical solution conceived in this application, by adopting a hollow ring coaxially arranged with the fiber optic collimator, can visualize the virtual optical axis that is invisible at the passive end, making it easier for operators to roughly identify the position of the optical axis at the passive end, and greatly improving the efficiency of manual alignment.

[0025] Meanwhile, a two-stage method for increasing the number of beams is adopted: the first stage splits a single laser beam into four beams using a beam splitter; the second stage uses a galvanometer module and an off-axis parabolic reflector to scan the four laser beams to form the effect of hundreds of beams in time, resulting in a large spatial coverage and significantly improved alignment efficiency compared to the traditional single-beam solution.

[0026] In addition, this application can avoid physical contact of optical fibers under high-voltage environments, and extend the wireless sensing distance to 2-5 meters; the handheld alignment method makes the overall structure more streamlined and lightweight, and the multi-beam scanning greatly improves the alignment efficiency; the active end and the measured end are in wireless contact, which greatly facilitates rapid temperature measurement deployment and flexible reuse of expensive demodulation equipment in multiple locations, making it particularly suitable for the inspection of multiple key sites in the power industry. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a fiber Bragg grating sensing system provided by existing technology; Figure 2 This is a schematic diagram of the structure of a fixed non-contact single-beam fiber optic sensing solution provided by existing technology. Figure 3 This is a schematic diagram of the structure of the handheld multi-beam aligned fiber optic grating sensing device provided in the embodiments of this application; Figure 4(a) is a schematic diagram of the relative position structure of the off-axis parabolic reflector and the galvanometer module in the handheld multi-beam aligned fiber optic grating sensing device provided in the first embodiment of this application. The two-dimensional galvanometer is placed at the focal point of the off-axis parabolic reflector. After each fine beam originating from the two-dimensional galvanometer is reflected, it is parallel to the central axis of the off-axis parabolic reflector. Figure 4(b) is a schematic diagram of the relative position structure of the off-axis parabolic reflector and the galvanometer module in the handheld multi-beam aligned fiber optic grating sensing device provided in the second embodiment of this application. The two-dimensional galvanometer is not placed at the focal point of the off-axis parabolic reflector, but is offset to a certain extent. After each fine beam originating from the two-dimensional galvanometer is reflected, each fine beam will converge in a cone shape. Figure 5(a) is a schematic diagram of the dimensional parameters of the off-axis parabolic reflector provided in the embodiment of this application; Figure 5(b) is a schematic diagram of the relationship between distance L, spot size diameter D and offset ΔX provided in the embodiment of this application; Figure 6This is a flowchart illustrating the implementation of the handheld non-contact multi-beam alignment fiber grating sensing method provided in this application embodiment. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0029] The handheld multi-beam aligned fiber Bragg grating sensing device provided in this application can solve the technical bottlenecks of difficult deployment of sensing systems under high-voltage environments and low single-beam alignment efficiency of existing non-contact solutions; it belongs to the field of fiber Bragg grating wireless sensing technology and is especially suitable for temperature measurement needs of mobile inspection in dangerous environments such as high-voltage electrical cabinets in the power industry.

[0030] This application adds a coaxial ring to the front end of the fiber optic collimator at the receiving end, making the virtual optical axis invisible at the passive end more concrete. This facilitates operators in roughly identifying the position of the optical axis at the passive end, greatly improving the efficiency of manual alignment. This application employs a two-stage beam multiplication method. The first stage splits a single laser beam into four beams using a beam splitter. The second stage uses a galvanometer module with an off-axis parabolic reflector to scan the four laser beams, creating the effect of hundreds of beams in time. This results in greater spatial coverage and significantly improved alignment efficiency compared to traditional single-beam solutions.

[0031] Figure 3 The structure of the handheld multi-beam aligned fiber optic grating sensing device provided in this application embodiment is illustrated. The handheld multi-beam aligned fiber optic grating sensing device will now be described in detail with reference to the accompanying drawings. For ease of explanation, only the parts relevant to this application are shown in the figures, which are detailed below: The handheld multi-beam aligned fiber Bragg grating sensing device includes: a passive sensing grating assembly, a handheld module 120, and a demodulation control module 121. The passive sensing grating assembly is located at the passive end and needs to be attached to the high-voltage electrical cabinet where temperature measurement is required during operation. In addition to its fiber Bragg grating sensing function, the passive sensing grating assembly is also used to convert the laser propagating within the fiber into a spatially parallel laser beam and to visualize the invisible optical axis of the passive end. Specifically, the passive sensing grating assembly includes a fiber collimator 22, a hollow metal ring 21 coaxial with the fiber collimator 22, a base 23, and a fiber Bragg grating sensor string located at the rear. The fiber collimator 22 is used to convert the laser propagating within the fiber into a spatially parallel laser beam.

[0032] The fiber collimator 22 can collimate the laser propagating in the fiber into a laser beam with a diameter of 1 mm for transmission in free space, or couple parallel light back into the fiber in the opposite direction. Its core function is to shape the beam through optical lenses (such as self-focusing lenses, aspherical lenses, etc.) to solve the problem of rapid divergence of the output light from the fiber, thereby achieving efficient and low-loss optical signal transmission and coupling in the free space optical path.

[0033] The hollow metal ring 21, coaxial with the fiber optic collimator 22 on the passive end, serves to visualize the invisible optical axis of the passive end, allowing the operator to roughly determine its position and increasing the probability of handheld alignment. Since the hollow metal ring 21 visualizes the optical axis, it is generally made of metal, such as aluminum alloy or steel. Because plastic is more easily deformed than metal, it cannot be used.

[0034] The hollow metal ring 21 has an inner diameter of 3 mm to 50 mm, and an outer diameter that is 2 mm to 20 mm larger than the inner diameter. More preferably, the hollow metal ring 21 can be designed with an inner diameter of 50 mm, an outer diameter of 80 mm, and a thickness of 3 mm, so that it does not obstruct laser communication and can provide position information of the passive end optical axis.

[0035] The commonly used fiber optic collimators are very small optical devices with a diameter of 3 mm and a length of 20 mm. If the passive end fiber optic collimator 22 is placed 5 meters away from the operator at the active end, it is not easy to see such a small passive end fiber optic collimator from the operator's field of vision, let alone obtain the optical axis of such a small passive end fiber optic collimator with the human eye, because the passive end is completely passive and the optical axis is invisible.

[0036] Because the effective optical axis diameter of a fiber optic collimator is only 1 millimeter, and the optical axis of the passive fiber optic collimator is invisible, it is too difficult for operators to manually align the two fiber optic collimators.

[0037] Therefore, if the optical axis of the passive fiber collimator can be visualized, the alignment efficiency can be greatly improved.

[0038] Specifically, during the production of the assembly (including 21, 22, and 23), a visible laser beam is passed through the end of the optical fiber of the fiber collimator 22. The laser beam propagates along the optical fiber and exits from the fiber collimator 22, becoming a visible laser beam with a diameter of 1 mm that exits along the optical axis of the fiber collimator 22. The positions of the hollow metal ring 21 and the fiber collimator 22 are adjusted to ensure that the visible laser is coaxial with 21 (the visible laser is then removed). The line connecting the center of the hollow metal ring 21 and the center of the fiber collimator 22 is the optical axis of the fiber collimator 22. Since these two centers are physically visible to the human eye, the optical axis is thus visualized.

[0039] Obviously, the greater the distance between the hollow metal ring 21 and the fiber optic collimator 22, the higher the accuracy of the optical axis. However, considering the rationality of the structure, it is recommended that the distance between the hollow metal ring 21 and the fiber optic collimator 22 be proportional to the distance between the active end and the passive end, with the former being one-tenth of the latter. For example, if the distance between the active end and the passive end is 5 meters, then the distance between the hollow metal ring 21 and the fiber optic collimator 22 should be 0.5 meters.

[0040] The reason for adding a coaxial ring 21 at the front end of the optical fiber collimator at the receiving end in this application is to visualize the virtual optical axis that is not visible at the passive end, so that the operator can roughly identify the position of the optical axis at the passive end and greatly improve the efficiency of manual alignment.

[0041] In this application, the handheld module 120 and the demodulation control module 121 are located at the active end. The handheld module 120 is used to realize multi-beam high-speed spatial scanning through the galvanometer module (14 and 15), complete laser collimation and projection through the off-axis parabolic reflector 13, and assist manual alignment with red light indication. The demodulation control module 121 is used to generate and distribute multi-channel sensing lasers, control the synchronous movement of the galvanometer, integrate visible light guidance, and demodulate wavelength offset to retrieve temperature data.

[0042] The handheld module 120 includes: an off-axis parabolic mirror 13, a galvanometer module (14 and 15), an optical fiber collimator 16, an optical fiber 17, and a cable 18; the off-axis parabolic mirror 13 is used to convert the beams reflected by the galvanometer at various angles into parallel beams, achieving a spatial coverage area with a diameter ≥ 50 mm; the galvanometer module is used to perform two-dimensional high-speed scanning (fast axis > 200 Hz, slow axis > 5 Hz), expanding the four laser beams in the time domain to an equivalent of several hundred beams / second, improving alignment efficiency; the optical fiber collimator 16 is used to collimate the laser in the active end optical fiber before emission, and then also receives the reflected light and couples it back to the active end optical fiber; the optical fiber 17 is used to transmit the laser; and the cable 18 is used to transmit galvanometer control signals.

[0043] In this application, the off-axis parabolic mirror 13 can focus parallel light, inheriting the core characteristics of a parabola. Light rays incident parallel to the optical axis of its parent mirror (even for the off-axis portion) will still be precisely converged to its focal point. The focal point is located near the focal point of the parent mirror, but deviates from the optical axis of the parent mirror. Based on this characteristic, in this application, if a laser beam (including broadband lasers of 1525nm~1565nm) emitted from the active end is aligned with the optical axis of the passive end fiber collimator, then the laser beam can enter the passive end fiber collimator, continue to propagate along the fiber, and after encountering the grating, the laser of a specific wavelength will be reflected back, becoming a beam emitted from the passive end fiber collimator. After encountering the off-axis parabolic mirror, the laser beam is reflected to the focal point, that is, reflected to the galvanometer module, and then returns to the active end fiber collimator, continuing to propagate along the fiber, and finally entering the demodulation module. The demodulation module can calculate the change of physical quantity at the sensor based on the wavelength change information.

[0044] The off-axis parabolic reflector 13 in this application can collimate a point light source. The light emitted from the point light source placed at the focal point will become a beam strictly parallel to the optical axis of the parent mirror (without divergence) after reflection by the off-axis parabolic reflector. Based on this characteristic, this application places the light-emitting position of the galvanometer module at the focal point of the off-axis parabolic reflector. A beam of light with a diameter of 1 mm emitted from the fiber collimator, after reflection by the two-axis galvanometer, and scanned by the galvanometer module (fast axis >200 Hz round trip, slow axis >5 Hz round trip), covers the entire reflector surface (in sequence), achieving 5 coverages per second. Using an off-axis parabolic reflector with a diameter of 50.8 mm, hundreds of parallel thin beams covering a diameter of 50 mm can be emitted 5 times per second. As long as one of these thin beams is aligned with the optical axis of the passive end, the sensing signal can be acquired.

[0045] From the perspective of the active end, the operator holds the equipment about 2 to 5 meters away from the high-voltage cabinet, aligns the laser emission direction of the off-axis parabolic reflector 13 with the passive end, and manually moves the handheld module 120. The broadband laser with a wavelength of 1525nm to 1565nm is emitted from the broadband light source, and after passing through the beam splitter 19, it is divided into four laser beams. They advance along their respective optical fibers 17 to four fiber collimators (the actual diameter of the fiber collimator is only 3 mm, and the figure shows an enlarged schematic diagram). The four laser beams are emitted simultaneously and arrive at the galvanometer modules (14 and 15) in the galvanometer module.

[0046] Figure 4(a) shows a schematic diagram of the relative position structure of the off-axis parabolic reflector and the galvanometer module in the handheld multi-beam aligned fiber optic grating sensing device provided in the first embodiment of this application. In this first embodiment, the two-dimensional galvanometer is placed at the focal point of the off-axis parabolic reflector 13. After each fine beam originating from the two-dimensional galvanometer is reflected, it is parallel to the central axis of the off-axis parabolic reflector. The off-axis parabolic reflector 13 can convert the diverging light originating from its focal point into a parallel beam. When the galvanometer module is placed at the focal point of the off-axis parabolic reflector 13, a beam of light with a diameter of 1 mm emitted from the fiber collimator is reflected by the two-axis galvanometer and scanned by the galvanometer module (fast axis > 200 Hz back and forth, slow axis > 5 Hz back and forth) to cover the entire reflector surface (in sequence). It can cover 5 times within one second. Using an off-axis parabolic reflector 13 with a diameter of 50.8 mm, hundreds of parallel fine beams covering a diameter of 50 mm can be emitted 5 times per second. As long as one of the fine beams is aligned with the optical axis of the passive end, the sensing signal can be acquired.

[0047] The galvanometer module is a core optical actuator consisting of two high-speed, precision, orthogonally mounted oscillating mirrors and their closed-loop control system. It can guide a laser beam to any specified position on a two-dimensional plane with extremely fast and precise speed according to computer instructions. It is a key technology for realizing dynamic laser scanning, precise pointing, and complex pattern processing, and has wide and important applications in industrial processing, display and entertainment, scientific research, and medical fields.

[0048] The galvanometer module reflects the laser beam to various positions on the off-axis parabolic reflector 13 according to a preset scanning path. The off-axis parabolic reflector 13 collimates the diverging laser beam emitted from the galvanometer into parallel fine beams, forming a spatial coverage area (diameter ≥ 50 mm; each instant still consists of four 1 mm diameter fine beams, but the galvanometer's scanning frequency is very high, capable of covering the entire off-axis parabolic reflector 5 times per second), significantly improving the alignment probability. Clearly, the more parallel multi-beams there are, the higher the alignment probability.

[0049] The preset scanning path can be a zigzag scanning path. By programming the galvanometer control card, the size of the scanning area (generally referring to covering the entire off-axis parabolic reflector 13), as well as the single-step motion increment, motion speed, etc., can be specified.

[0050] Figure 4(b) shows a schematic diagram of the relative position structure of the off-axis parabolic reflector and the galvanometer module in the handheld multi-beam aligned fiber optic grating sensing device provided in the second embodiment of this application. In this second embodiment, the two-dimensional galvanometer is not placed at the focal point of the off-axis parabolic reflector 13, but is offset to a certain extent. After each fine beam originating from the two-dimensional galvanometer is reflected, each fine beam will converge in a cone shape.

[0051] When the galvanometer module is set at the optimal offset position with a certain offset from the focal point of the off-axis parabolic mirror 13, the optimal offset position ΔXi (the X-axis offset of the light output center of the galvanometer module relative to the focal point) can be determined by the following method. The core objective is to find the galvanometer X-axis position that minimizes the spot diameter of the beam reflected by the off-axis parabolic mirror at the target sensing distance L (the preset distance between the active end and the passive end, such as 1~5 meters). This can be done by either actual measurement or optical software simulation. The specific steps of the actual measurement method are as follows: (1) Determine the initial range of the target sensing distance L and the X-axis offset: First, clarify the preset distance (i.e., target sensing distance) L between the active end and the passive end in actual application (e.g., L=1 meter). This distance is fixed by the on-site inspection requirements and is not adjusted with the position of the galvanometer. Set an initial X-axis offset range for the light output center of the galvanometer module relative to the focal point (e.g., ΔX∈[0mm, 35mm], to ensure coverage of the area where the smallest light spot may occur). Here, ΔX represents the offset of the light output center of the galvanometer module from the focal point of the off-axis parabolic mirror in the X-axis direction (positive values ​​are offset along the positive X-axis direction, negative values ​​are offset along the negative X-axis direction). (2) Select the first position ΔX1: Within the initial range of the X-axis offset, the first test point is selected as the first position, for example, ΔX1 = 1mm can be selected; (3) First light emission test and spot diameter measurement: Fix the galvanometer module at the first position ΔX1 and turn on the laser; place the spot measuring instrument at the target sensing distance L to obtain the spot formed after reflection by the off-axis parabolic mirror, and measure and record the diameter D1 of the spot; (4) Adjust the X-axis offset by a fixed step size and repeat the test: Along the X-axis offset range, adjust the galvanometer position sequentially according to the preset step size δ (for example, the step size δ can be set to 1mm) to determine the second position ΔX2=ΔX1+1mm, the third position ΔX3=ΔX2+1mm, and so on, until the offset exceeds the initial range, or the spot diameter of the light spot in 3 consecutive tests is larger than the previous one (indicating that the minimum spot size has been exceeded). Repeat step (3) for each ΔXi position and record the corresponding spot diameters D2, D3...Dn in sequence; (5) Determine the optimal offset position ΔXi: The smallest diameter Dmin is selected from the light spot diameters D1 to Dn; The X-axis offset ΔXi corresponding to the minimum diameter Dmin is taken as the optimal offset position of the galvanometer module.

[0052] Since an off-axis parabolic mirror collimates light emitted from its focal point into parallel light, and the diameter of the fiber optic collimator at the passive end is 3 mm, the alignment efficiency can be further improved by converging the beam reflected from the off-axis parabolic mirror into a cone shape and reducing the size of the spot at the far end.

[0053] Specifically, an off-axis parabolic mirror (with a focal-to-vertex distance of 76.2 mm and a diameter of 50.8 mm) as shown in Figure 5(a) is used, based on the equation of an upward-opening parabola. Where p represents the geometric distance from the focal point to the directrix, the equation of the parabola of the mirror's cross section can be derived as follows: (Define the origin of the coordinate system at the focal point), and place the light output of the two-axis galvanometers off-center from the focal point (0, 0) in the positive X-axis direction.

[0054] As shown in Figure 5(b), the distance from the focal point of the light-emitting position of the galvanometer module in the X-axis direction is ΔX, and the distance from the passive end fiber collimator to the specific intersection point in the direction of the central axis of the off-axis parabolic mirror is L (i.e., the sensing distance from the active end to the passive end). The specific intersection point is the point where the mirror surface of the off-axis parabolic mirror intersects with the central axis of the off-axis parabolic mirror. The diameter of the light spot formed by the light beam obtained after reflection by the off-axis parabolic mirror is D. (As mentioned earlier, the optimal offset position ΔX corresponding to the sensing distance L can be confirmed by either actual measurement or optical software simulation. The following is the method of software simulation.) Using a computer program based on the above parabolic equation, it is possible to simulate the size of the light spot at the far end after 5 light beams are emitted from the offset light-emitting position and reflected by the off-axis parabolic mirror (the reflection normal is the perpendicular line of the tangent at the off-axis parabolic surface of each beam). Figure 5(b) shows the relationship between the offset ΔX and the spot size diameter D when the distance is L=1 meter. It can be seen that when the offset ΔX is 26 mm, the far-end spot diameter is the smallest.

[0055] Using the same method, a preset L is established, and then the corresponding ΔXi is found through software simulation. Next time, another preset L' is established, and the ΔXi' corresponding to L' is found using the same method. This allows us to calculate the minimum far-end spot size at each distance, as well as the corresponding offset. Specific data are as follows:

[0056] The data shows that a suitable offset can be found at any location from 1 meter to 5 meters, reducing the original far-end spot size of 50.8 mm (spot size under parallel light) to a small spot size of about 6-7 mm, a reduction of >98% in area. As shown in Figure 4(a), when the active end emits a parallel beam, even if the passive end fiber collimator is within the beam's coverage area, communication cannot be achieved if the optical axis of the passive end fiber collimator deviates slightly from the parallel beam and is not coaxial. However, if the active end beam becomes convergent as shown in the right-hand figure, i.e., the active end laser beam is emitted from multiple angles towards the passive end, the probability of the passive end optical axis coinciding with one of the laser beams is greatly increased, meaning that alignment efficiency can be significantly improved.

[0057] In this application, the demodulation control module 121 includes: a beam splitter 19, a motion controller 20, a laser generator 25, a wavelength division multiplexer 26, a broadband light source, a circulator, and a demodulation module; the broadband light source emits broadband laser light in the wavelength range of 1525nm~1565nm, which enters the optical fiber through the circulator, and the demodulation module can know the current temperature value at that location based on the corresponding data that has been calibrated in advance. Laser generator 25 is used to generate a 650nm red indicator laser (visible to the human eye), because the 1525nm~1565nm broadband laser commonly used for sensing is invisible to the human eye; wavelength division multiplexer 26 is used to combine the 650nm red indicator laser from laser generator 25 into the same optical fiber as the 1525nm~1565nm broadband laser, making it easier for operators to know where the laser is aligned; beam splitter 19 is used to split a laser beam propagating in one optical fiber into four optical fibers, and then the four laser beams are emitted to the galvanometer modules (14 and 15) and reflected towards the passive end, increasing the number of laser beams emitted from the active end and increasing the probability of alignment; motion controller 20 is used to control the movement of galvanometer modules (14 and 15) through cable 18.

[0058] In this application, the demodulation module can use a sampling frequency of up to 5000 Hz. As long as the optical axis of the active end and the optical axis of the passive end are aligned for a moment during the manual shaking alignment process, the active end can obtain the wavelength change information of the passive end, thereby knowing the temperature at each sensor.

[0059] In this application, since the laser emitted by the active end in the 1525nm~1565nm band is invisible light, the system uses wavelength division multiplexer 26 to connect one 650nm red indicator laser emitted by laser generator 25 to the same optical fiber, so that the operator can know where the laser is aimed.

[0060] This application employs a two-stage method to increase the number of beams. Specifically, the first stage splits a laser beam into four beams using a beam splitter 19. The second stage uses a galvanometer module (14 and 15) and an off-axis parabolic reflector 13 to scan the four laser beams to form the effect of hundreds of beams in time, resulting in a large spatial coverage and significantly improved alignment efficiency compared to traditional single-beam solutions.

[0061] like Figure 6 As shown, this application also provides a fiber grating sensing method for multi-beam alignment based on the above-mentioned fiber grating sensing device, comprising the following steps: Align the laser emission direction of the off-axis parabolic mirror with the passive end, and move the handheld module to align the optical axis of the active end with the optical axis of the passive end. The galvanometer module reflects the laser beam to various positions of the off-axis parabolic mirror according to the preset scanning path; The off-axis parabolic mirror collimates the diverging laser beam emitted from the galvanometer into a parallel narrow beam, forming a spatial coverage area; The invisible passive end optical axis is visualized by using a hollow metal ring, which makes it easier for the operator to roughly know the position of the passive end optical axis, thereby increasing the probability of handheld alignment.

[0062] During the handheld module's shaking and alignment process, there is a moment when the optical axes of the active end and the passive end are aligned. The active end can then obtain the wavelength change information of the passive end, thereby knowing the temperature at each sensor.

[0063] This application utilizes a hollow ring to visualize the virtual optical axis that is invisible at the passive end, making it easier for operators to roughly identify the position of the optical axis at the passive end and greatly improving the efficiency of manual alignment. Simultaneously, it employs a two-stage beam multiplication method to split a single laser beam into four beams, which are then scanned through a galvanometer module and an off-axis parabolic reflector to create the effect of hundreds of beams in time, resulting in large spatial coverage and significantly improved alignment efficiency.

[0064] Furthermore, compared to previous solutions that used 3D industrial cameras for visual recognition of passive end positions, this application eliminates the need for expensive 3D industrial cameras, resulting in a simpler overall system and lower costs. Moreover, existing 3D industrial cameras become increasingly expensive and less accurate with increasing sensing distance, limiting their practical applications to a range of 3 meters. This application, however, eliminates the need for 3D industrial cameras, thus extending its application to 5-meter ranges.

[0065] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A hand-held multi-beam aligned fiber Bragg grating sensing device, characterized in that, It includes a passive sensing grating assembly located at the passive end and a handheld module (120) and a demodulation control module (121) located at the active end. The passive sensing grating assembly is used to convert laser propagating in the optical fiber into a spatial parallel laser beam and to visualize the invisible passive end optical axis. The handheld module (120) is used to realize multi-beam high-speed spatial scanning and complete laser collimation and projection, as well as red light indication to assist manual alignment; The demodulation control module (121) is used to generate and distribute multiple sensing lasers, control the synchronous movement of the galvanometer in the handheld module (120), and integrate visible light guidance function to retrieve temperature data by demodulating wavelength offset; the passive sensing grating assembly includes an optical fiber collimator (22) and a hollow metal ring (21) coaxially arranged with the optical fiber collimator; the optical fiber collimator (22) is used to convert the laser propagating in the optical fiber into a spatial parallel laser beam; the hollow metal ring (21) is used to visualize the invisible passive end optical axis, so that the operator can roughly know the position of the passive end optical axis and thus improve the probability of handheld alignment; The handheld module (120) includes: an off-axis parabolic mirror (13), a galvanometer module (14, 15), an optical fiber collimator (16), an optical fiber (17), and a cable (18). The galvanometer module reflects the laser beam to various positions of the off-axis parabolic mirror (13) according to a preset scanning path; The off-axis parabolic reflector (13) is used to collimate the diverging laser beam emitted from the galvanometer module into a parallel fine beam and form a spatial coverage area; The fiber collimator (16) is used to collimate the laser in the active end fiber and emit it, and receive the reflected light and couple it back to the active end fiber. The optical fiber (17) is disposed between the optical fiber collimator (16) and the demodulation control module (121) for transmitting the multi-channel sensing laser. The cable (18) is disposed between the galvanometer module and the demodulation control module (121) for transmitting galvanometer control signals for galvanometer motion synchronization; The galvanometer module is located at the focal point of the off-axis parabolic mirror (13); Alternatively, the galvanometer module may be positioned at an optimal offset position that is offset from the focal point of the off-axis parabolic mirror (13).

2. The fiber grating sensor apparatus of claim 1, wherein, The distance between the hollow metal ring (21) and the optical fiber collimator (22) is proportional to the distance between the active end and the passive end; Or the distance between the hollow metal ring (21) and the optical fiber collimator (22) is one-tenth of the distance between the active end and the passive end; Alternatively, the inner diameter of the hollow metal ring (21) may be 3 mm to 50 mm, and the outer diameter may be 2 mm to 20 mm larger than the inner diameter.

3. Fiber grating sensor device according to any of claims 1-2, characterized in that The demodulation control module (121) includes: a beam splitter (19), a motion controller (20), a laser generator (25), and a wavelength division multiplexer (26). The beam splitter (19) is used to split a laser beam propagating in one optical fiber into multiple optical fibers. Multiple laser beams are emitted and reflected to the passive end by the galvanometer module (14, 15), increasing the number of laser beams emitted from the active end and increasing the probability of alignment. The motion controller (20) is used to control the movement of the galvanometer modules (14, 15); The laser generator (25) is used to generate a red indicator laser of a specific wavelength; The wavelength division multiplexer (26) is used to incorporate the red indicator laser into the same optical fiber for broadband laser propagation, so as to know the laser alignment position.

4. A fiber optic grating sensing method for multi-beam alignment based on the fiber optic grating sensing device according to any one of claims 1-3, characterized in that, Includes the following steps: Align the laser emission direction of the off-axis parabolic mirror with the passive end, and move the handheld module to align the optical axis of the active end with the optical axis of the passive end. The galvanometer module reflects the laser beam to various positions of the off-axis parabolic mirror according to the preset scanning path; The off-axis parabolic mirror collimates the diverging laser beam emitted from the galvanometer into a parallel narrow beam, forming a spatial coverage area; The invisible passive end optical axis is visualized by using a hollow metal ring, which makes it easier for the operator to roughly know the position of the passive end optical axis, thereby increasing the probability of handheld alignment. The galvanometer module is located at the focal point of the off-axis parabolic mirror (13); or the galvanometer module is located at an optimal offset position with a certain offset from the focal point of the off-axis parabolic mirror (13).

5. The fiber optic grating sensing method as described in claim 4, characterized in that, During the handheld module's shaking and alignment process, there is a moment when the optical axis of the active end and the optical axis of the passive end are aligned. The active end can then obtain the wavelength change information of the passive end, thereby knowing the temperature at each sensor.

6. The fiber optic grating sensing method as described in claim 4, characterized in that, The optimal offset position ΔXi is determined by the following method: (1) Determine the initial range of the target sensing distance L and the X-axis offset: The initial X-axis offset range of the galvanometer module's light output center relative to the focal point is set by ensuring coverage of the area where the smallest light spot may occur; the target sensing distance L is the preset distance between the active end and the passive end; (2) Select the first position ΔX1: The first test point within the initial range of the X-axis offset is selected as the first position ΔX1; ΔX1 represents the offset of the center of the first light emission from the galvanometer module from the focal point of the off-axis parabolic mirror in the X-axis direction; (3) First light emission test and spot diameter measurement: The galvanometer module is fixed at the first position ΔX1, and a spot measuring instrument is placed at the target sensing distance L to obtain the spot formed after reflection by the off-axis parabolic mirror. The diameter D1 of the spot is measured and recorded. (4) Adjust the X-axis offset by a fixed step size and repeat the test: Along the X-axis offset range, adjust the galvanometer position sequentially according to the preset step size δ, and determine the second position ΔX2=ΔX1+δ, the third position ΔX3=ΔX2+δ... until the offset exceeds the initial range or the spot diameter of the light spot increases more than the previous one in 3 consecutive tests. Repeat step (3) for each position ΔXi, and record the corresponding spot diameters D2, D3...Dn in sequence; (5) Determine the optimal offset position ΔXi: The smallest diameter Dmin is selected from the light spot diameters D1 to Dn; The X-axis offset ΔXi corresponding to the minimum diameter Dmin is taken as the optimal offset position of the galvanometer module.

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