Wireless transmission type optical fiber sensor and manufacturing method

Abstract

The invention provides a wireless transmission type optical fiber sensor and a manufacturing method thereof. The wireless transmission type optical fiber sensor comprises a spatial light collimating and beam expanding system, an optical fiber collimator and a sensing unit group which are arranged in sequence, the spatial light collimating and beam expanding system is connected with the optical fiber collimator through an optical path, the optical fiber collimator is connected with the sensing unit group through an optical fiber, and the sensing unit group comprises at least one sensing unit connected in series on the optical fiber; the space light collimation and beam expanding system collimates and expands emitted light received wirelessly and then transmits the emitted light to the sensing unit through the optical fiber collimator, and return light reflected by the sensing unit is collimated and expanded in the space light collimation and beam expanding system through the optical fiber collimator and then is output wirelessly. According to the invention, the optical fiber collimator and the spatial light collimation beam expanding system are additionally arranged at the joint of the sensing unit group and the optical signal, so that wireless transmission of the optical signal is realized, and the system is suitable for a special environment where wired connection is inconvenient at the optical signal transmission position.

Description

Technical Field

[0001] The invention belongs to the field of optical fiber sensing, and in particular relates to a wireless transmission type optical fiber sensor and a manufacturing method thereof. Background Art

[0002] Fiber optic sensing technology has been widely used in various industries and fields. Compared with traditional electrical signal sensors, fiber optic sensors can cope with more complex and harsh environments due to their passivity. For example, in the fields of petrochemicals, nuclear power, transformers, etc., fiber optic sensing can work more stably because it transmits information through photons, which are not easily affected by the environment. Secondly, fiber optic sensors are usually smaller in size, and since fiber gratings are distributed on optical fibers as sensitive units, it is only necessary to increase the number of gratings on one optical fiber to complete multi-point measurements in space. Therefore, in many fields, fiber optic sensing is gradually replacing traditional electrical signal sensors.

[0003] In certain specific environments, wired connections for optical signal transmission can also bring some disadvantages. For example, when monitoring the temperature of the bearing in a compressor, since the fiber Bragg grating temperature sensor is attached to the bearing, and the optical fiber connected to it needs to be connected to an external light source and demodulation unit, when the bearing moves back and forth at high speed, the optical fiber may become entangled or even break inside the machine body. In some harsh working environments, such as construction sites, longer optical fibers are also easily damaged, resulting in the inability to transmit optical signals. In some sealed equipment or environments, the signal pigtail cannot pass through them, making it impossible to use the fiber Bragg grating sensor. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a wireless transmission type optical fiber sensor and a manufacturing method thereof, so as to facilitate the transmission of optical signals under specific environments. The technical solution adopted by the present invention to solve the above technical problems is: As a first aspect of the present invention, the present invention provides a wireless transmission type optical fiber sensor, comprising a spatial light collimation and expansion system, an optical fiber collimator and a sensing unit group which are arranged in sequence; wherein the spatial light collimation and expansion system is connected to the optical fiber collimator via an optical path, the optical fiber collimator is connected to the sensing unit group via an optical fiber, and the sensing unit group comprises at least one sensing unit serially connected to the optical fiber; The spatial light collimation and expansion system collimates and shrinks the transmitted light received wirelessly, and then transmits it to the sensor unit group through the optical fiber collimator. The return light reflected by each sensor unit is collimated and expanded in the spatial light collimation and expansion system through the optical fiber collimator and then output wirelessly.

[0005] According to the above scheme, the spatial light collimation and expansion system and the optical fiber collimator are packaged in a housing, and the housing is provided with a protective lens for the emission light to be injected and the return light to be output.

[0006] According to the above scheme, the spatial light collimation and expansion system includes a lens barrel, and a convex lens and a concave lens respectively located at both ends of the lens barrel; wherein the convex lens is located at one end for receiving the emitted light, and the concave lens is located at one end connected to the optical path of the fiber collimator.

[0007] According to the above scheme, the expansion ratio of the spatial light collimation and expansion system is 5-10 times; the spot diameter of the received emission light and the wireless output is 10-20mm.

[0008] According to the above solution, the lens barrel is fixed in the housing by a clamping ring.

[0009] According to the above scheme, the optical fiber collimator is connected to the spatial light collimation and expansion system through a fixed ferrule, and the optical fiber collimator and the spatial light collimation and expansion system are coaxially assembled.

[0010] According to the above solution, at least one sensor unit of the sensor unit group is encapsulated in the housing.

[0011] According to the above scheme, the sensing unit is a fiber Bragg grating or a Fabry-Perot sensor, and each sensing unit is respectively packaged in a packaging fixture or directly attached to the surface of the object to be measured.

[0012] According to the above scheme, the protective lens is an optically coated protective lens for the signal light band.

[0013] As a second aspect of the present invention, the present invention also provides a method for manufacturing the wireless transmission type optical fiber sensor, comprising the following steps: S1. Make a spatial light collimation and beam expansion system; S2, aligning the spatial light collimation and beam expansion system and the optical fiber collimator with the light path and fixing them; S3, connecting the optical fiber collimator and the sensor unit group through optical fiber.

[0014] According to the above method, the step S1 specifically includes: placing the convex lens 4 and the concave lens 7 in the lens barrel 5 and fixing them.

[0015] According to the above method, the S2 specifically includes: S21, placing the optical fiber collimator in the fixed ferrule and fixing the optical fiber collimator; S22, connecting the fixed ferrule to the lens barrel, adjusting the lens barrel and the optical fiber collimator to be coaxial, and then fixing them; S23. Place the lens barrel in the clamping ring and secure it; S24, fixing the protective lens to the window of the housing; S25. Fix the assembled lens barrel and clamping ring to the base of the housing.

[0016] The beneficial effects of the present invention are: 1. By adding a fiber collimator and a spatial light collimation and expansion system at the connection between the sensor unit group and the optical signal, wireless transmission of optical signals is achieved, which is suitable for special environments where wired connection is inconvenient at the optical signal transmission point.

[0017] 2. The spatial light collimation and beam expansion system consists of a convex lens and a concave lens, which is connected to the fiber collimator through an optical path. It has a simple and compact structure. Through the spatial light collimation and beam expansion system, the divergence angle of light transmission can be further reduced, so that the wireless transmission distance of the optical signal can reach the meter level.

[0018] 3. The sensing unit group can be a sensing unit or a string of sensing units. The sensing unit can be packaged together with the optical fiber collimator and the spatial light collimation and expansion system, or it can be packaged separately, or it can be directly mounted on the surface of the object to be measured; that is, only wireless transmission is required between the sensing unit group and the signal transmission end, and the sensing unit group can be combined according to actual needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structural principle of the first embodiment of the present invention.

[0020] Figure 2 It is a schematic cross-sectional view of the package of the first embodiment of the present invention.

[0021] Figure 3 It is a schematic diagram of the structure of the light source demodulation end corresponding to the first embodiment of the present invention.

[0022] Figure 4 It is a schematic cross-sectional view of the package of the second embodiment of the present invention.

[0023] Figure 5 It is a schematic diagram of the structural principle of embodiment 3 of the present invention.

[0024] In the figure: 1-protective lens, 2-housing, 3-top cover, 4-convex lens, 5-lens barrel, 6-holding clamp, 7-concave lens, 8-fixed ferrule, 9-fiber collimator, 10-sensing unit, 11 is a packaging fixture. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] Embodiment 1: This embodiment provides a wireless transmission optical fiber sensor, such as Figure 1As shown, it includes a spatial light collimation and expansion system, a fiber collimator and a sensor unit which are arranged in sequence; wherein the spatial light collimation and expansion system is connected to the fiber collimator through an optical path, the fiber collimator and the sensor unit are connected through an optical fiber, and the sensor unit is serially connected to the optical fiber. The spatial light collimation and expansion system and the fiber collimator ensure that the optical axes are basically in the same straight line, and the light beam can pass through. The sensor unit is set according to the needs of the signal to be measured, for example, it can be a fiber grating temperature sensor, a vibration sensor, etc.

[0027] The spatial light collimation and beam expansion system collimates and shrinks the transmitted light received wirelessly, and then transmits it to the sensing unit through the optical fiber collimator. The return light reflected from the sensing unit is collimated and expanded in the spatial light collimation and beam expansion system through the optical fiber collimator, and then wirelessly output. The transmitted light is emitted by a laser, and the return light is received by a demodulation analyzer. During the transmission of the above light, the spatial light collimation and beam expansion system shrinks the transmitted light received wirelessly, and the spot size is reduced to ensure that the entire light beam can enter the optical fiber collimator, and then the optical fiber collimator is better coupled into the sensing unit. The return light reflected from the sensing unit reduces the divergence angle in the optical fiber collimator, and then further collimates the light beam, reduces the divergent light, and expands the beam in the spatial light collimation and beam expansion system. The spot size is increased and then wirelessly output.

[0028] It can be seen that there is no line connection between the transmitted light and the wireless transmission type optical fiber sensor, and between the return light of the wireless transmission type optical fiber sensor and the demodulation analyzer. Instead, it is directly transmitted in the form of spatial light, so that it can be deployed in special environments where wired connection is not easy at the transmission end.

[0029] Correspondingly, such as Figure 3 As shown, the demodulation end of the light source also has an identical spatial light collimation and expansion system and a fiber collimator, and the fiber collimator is connected to the circulator through an optical fiber. The other ports of the circulator are connected to the laser and the demodulation device respectively. The light emitted by a small semiconductor laser usually has a large divergence angle and cannot be transmitted over long distances. By using a spatial light collimation and expansion system, after collimation, the transmission distance will be significantly increased, and the order of magnitude can reach the meter level, which is beneficial for long-distance sensing and monitoring; after beam expansion, it will be easier to align with the demodulation device.

[0030] In this embodiment, the specific structure of the wireless transmission optical fiber sensor is as follows: Figure 2 As shown, the spatial light collimation and beam expansion system, the optical fiber collimator and the sensor unit 10 are all packaged in a housing 2, and the housing 2 is provided with a protective lens 1 for the emission light to be injected and the return light to be output.

[0031] More specifically, the spatial light collimation and beam expansion system includes a lens barrel 5, a convex lens 4 and a concave lens 7 respectively located at both ends of the lens barrel 5, and the convex lens 4 and the concave lens 7 are assembled coaxially; among them, the convex lens 4 is located at the end for receiving the emitted light, and the concave lens 7 is located at the end optically connected to the fiber collimator 9. Among them, the focal length of the convex lens f 1 and the focal length of the concave lens f 2 can be freely changed according to the optical path requirements; usually the beam expansion ratio is 5 to 10 times. The beam expansion ratio is related to the focal length of the convex lens f 1 and the focal length of the concave lens f 2 as follows:

[0032] The spot of the spatially transmitted light should not be too large, otherwise it will increase the power loss of the spatial light transmission and needs to be smaller than the diameter of the protective lens; usually the spot diameter of the spatially transmitted light is 10 to 20 mm. In this embodiment, the convex lens is a plano-convex lens with a focal length of 200 mm, the concave lens is a plano-concave lens with a focal length of -25 mm, the beam expansion ratio is 8 times, and the output spot diameter of the fiber collimator is 1.8 mm. According to the beam expansion ratio, the spot diameter of the spatially transmitted light is about 14.4 mm. The wireless transmission distance of this embodiment can reach 3 - 5 meters.

[0033] Furthermore, the lens barrel 5 is fixed in the housing 2 through a clamping ring 6. In this embodiment, the lens barrel 5 is made of aluminum alloy material, and threads need to be machined inside at the lens installation position to fix the lens position with a threaded retaining ring. This method is a conventional method for fixing optical lenses; two planes are milled at the end of the lens barrel, which can be used to position the rotation angle of the lens barrel. Secondly, when the contact surface between the set screw for fixing the ferrule and the lens barrel is a plane, the fastening effect of the screw is the best; the lens barrel is designed to be directly insertable for the fixed ferrule. This structure can not only ensure the coaxiality of each component but also be more convenient for assembly and maintenance; the fiber collimator 9 is connected to the lens barrel 5 through the fixed ferrule 8. The production of the fixed ferrule hole adopts a transitional fit with a basic shaft system. The materials of the fixed ferrule and the lens barrel are selected from aluminum alloy or alloy steel according to actual requirements. The fiber collimator is assembled coaxially with the fixed ferrule, and the fiber collimator is inserted into the fixed ferrule and fixed inside by a set screw. In addition to fixing the fiber collimator, the fixed ferrule also needs to ensure sufficient machining accuracy and the functions of wear resistance and shock absorption; it is necessary to ensure that after the fiber collimator is inserted, it is coaxial with the lenses of the spatial light collimation and beam expansion system.

[0034] The sensing unit is a fiber Bragg grating or a Fabry-Perot sensor. A sensing unit 10 is packaged in a packaging fixture 11 and then fixed in a housing 2. The top of the housing 2 has a top cover 3. The specific packaging method of the sensing unit 10 and the specific form of the packaging fixture 11 are selected according to the sensor type.

[0035] The protective lens is an optical coating protective lens of the signal light band, preferably an optical protective lens coated with a suitable anti-reflection film. The protective lens and the spatial light collimation and expansion system should be coaxially assembled; the protective lens seals the inner cavity of the housing, protects the components in the housing from damage, and ensures the passage of signal light; the surface of the protective lens should be coated with an anti-reflection film of the signal light band to increase the signal light intensity.

[0036] The specific process of the application of this embodiment in compressor bearing temperature monitoring is given below: Take this embodiment as Figure 1 The wireless transmission type optical fiber sensor is installed on the bearing bush according to conventional requirements. The spatial light collimation and expansion system and the optical fiber collimator at the light source demodulation end are installed at the fixed end near the bearing bush. The laser light source and the demodulation device at the light source demodulation end are arranged at a farther distance and connected to the optical fiber collimator at the light source demodulation end through an optical fiber. The optical signal is transmitted through space between the wireless transmission type optical fiber sensor and the light source demodulation end. When the bearing bush rotates at high speed, only the wireless transmission type optical fiber sensor rotates with it, thereby avoiding the entanglement of the optical fiber.

[0037] The present invention also provides a method for manufacturing the wireless transmission type optical fiber sensor, comprising the following steps: S1. Make a spatial light collimation and beam expansion system, specifically: place a convex lens 4 and a concave lens 7 in a lens barrel 5, and fix them with a set screw and a threaded clamp ring, wherein one side of the plane of the convex lens 4 and the concave lens 7 is in contact with the threaded clamp ring.

[0038] S2. Align the spatial light collimation and beam expansion system and the optical fiber collimator to the light path and fix them, specifically including: S21, placing the optical fiber collimator 9 in the fixed ferrule 8 and fixing it with a set screw.

[0039] S22, connect the fixed ferrule 8 to the lens barrel 5 and fix them with bolts.

[0040] S23. Place the lens barrel 5 in the two clamping rings 6 and tighten them with bolts. You can also use thread glue to fix them after the bolts are tightened to prevent the bolts from loosening and causing system instability.

[0041] S24, placing the protective lens 1 at the window of the housing 2, and fixing it with glue. The choice of glue can be selected according to actual use.

[0042] S25, fixing the assembled lens barrel 5 and the clamping ring 6 to the base of the housing 2 by means of bolts.

[0043] S3, connecting the optical fiber collimator 9 and the sensor unit 10 through optical fiber. The sensor unit 10 is fixed on the packaging fixture 11, fixed with glue, and then fixed on the base of the housing 2 with bolts.

[0044] Taking the optical grating stress sensor as an example, the grating area must be placed in the middle of the fixture in a suspended position to ensure that the grating area is not subjected to stress during packaging.

[0045] S4. Fix the top cover 3 and the outer shell with bolts.

[0046] It should be noted that: before installing the convex lens, concave lens and protective lens, use acetone to wipe the surface until it is clean and free of dirt to ensure that the signal light can pass through the beam expansion system without obvious optical power loss. After tightening, the bolts fixed on the housing can be fixed with thread glue to prevent the bolts from loosening and causing system instability.

[0047] Embodiment 2: The structure and principle of this embodiment are basically the same as those of the first embodiment, except that: Figure 4 As shown, the spatial light collimation and expansion system and the optical fiber collimator are fixed in the housing 2, and the sensor unit 10 is packaged in a packaging fixture 11 independent of the housing 2. The separately packaged sensor unit can be arranged on the surface of the object to be measured or fixed in the same environment, and can be used to monitor parameters such as vibration and temperature.

[0048] Embodiment three: The structure and principle of this embodiment are basically the same as those of the second embodiment, except that: Figure 5 As shown, the spatial light collimation and beam expansion system and the optical fiber collimator are packaged in a housing, a plurality of sensing units constitute a sensing unit group, and each sensing unit is packaged in an independent grating packaging fixture.

[0049] As a variation of the third embodiment, each sensor unit can also be directly attached to the surface of the object to be measured, which is mainly determined by the physical quantity to be measured and the object. The surface-attached area should be as close as possible to the area to be measured, and the attachment should be firm and can change with the deformation of the object to be measured.

[0050] The sensor of the present invention can transform the light transmitted in the optical fiber into spatial light that can be transmitted in space using an optical collimator and a spatial light collimation and expansion system, which greatly expands the application scenarios of the optical fiber sensor. The optical fiber sensor can be pre-buried separately in the object to be measured. When it is necessary to monitor the information, it is only necessary to use an unmanned aerial vehicle or an unmanned vehicle to align the light source and the demodulator with one end of the spatial light collimation and expansion system of the present invention to achieve bidirectional transmission of the optical signal. In the field of optical fiber sensing in remote wind turbines, nuclear reactors, etc., it has unique scene advantages.

[0051] Wireless transmission fiber optic sensor integrates the two advantages of fiber optic sensing and wireless transmission. The fiber itself is insulated, corrosion-resistant, and not subject to electromagnetic interference, making it suitable for special scenarios such as electricity and nuclear radiation; and there is no electrical signal involved, it is inherently explosion-proof and suitable for hazardous environments. Wireless transmission of optical signals can omit the line deployment between the sensing unit and the demodulation device. For example, when monitoring the temperature at the bearing, it is only necessary to arrange the sensing unit at the bearing, without the problem of fiber winding or slip ring connection; the environment in the construction site is responsible, and mechanical operation equipment may break the optical fiber when it presses over the optical fiber. The wireless transmission method only requires the demodulation device to be aligned with the sensing unit during monitoring to complete the information monitoring. There is no line connection between the sensing unit and the demodulation device, and the mechanical operation equipment can pass through without obstacles. In sealed equipment or environment, the channel gap where the optical fiber passes through the shell will affect the airtightness. When using a wireless transmission sensor, it is only necessary to arrange the sensing unit in a sealed environment, and the optical signal can be led out through the optical transmission window, which can greatly reduce the impact on the sealing performance.

[0052] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A wireless transmission optical fiber sensor, characterized in that: It comprises a spatial light collimation and expansion system, a fiber collimator and a sensor unit group which are arranged in sequence; wherein the spatial light collimation and expansion system is connected to the fiber collimator through an optical path, the fiber collimator is connected to the sensor unit group through an optical fiber, and the sensor unit group comprises at least one sensor unit serially connected to the optical fiber; The spatial light collimation and expansion system collimates and shrinks the transmitted light received wirelessly, and then transmits it to the sensor unit group through the optical fiber collimator. The return light reflected by each sensor unit is collimated and expanded in the spatial light collimation and expansion system through the optical fiber collimator and then output wirelessly.

2. The wireless transmission optical fiber sensor according to claim 1, characterized in that: The spatial light collimating and expanding system and the optical fiber collimator are packaged in a shell, and the shell is provided with a protective lens for the emission light to be injected and the return light to be output.

3. The wireless transmission optical fiber sensor according to claim 2, characterized in that: The spatial light collimating and expanding system comprises a lens barrel, and a convex lens and a concave lens respectively located at two ends of the lens barrel; wherein the convex lens is located at one end for receiving emitted light, and the concave lens is located at one end connected to the optical path of the optical fiber collimator.

4. The wireless transmission optical fiber sensor according to claim 3, characterized in that: The beam expansion ratio of the spatial light collimation and beam expansion system is 5-10 times; the diameter of the received emission light and the wireless output light spot is 10-20 mm.

5. The wireless transmission optical fiber sensor according to claim 3, characterized in that: The lens barrel is fixed in the housing by a clamping ring.

6. The wireless transmission optical fiber sensor according to claim 2, characterized in that: The optical fiber collimator is connected to the spatial light collimation and beam expansion system through a fixed ferrule, and the optical fiber collimator and the spatial light collimation and beam expansion system are coaxially assembled.

7. The wireless transmission optical fiber sensor according to claim 2, characterized in that: At least one sensing unit of the sensing unit group is packaged in the housing.

8. The wireless transmission optical fiber sensor according to claim 1, characterized in that: The sensing unit is a fiber grating or Fabry-Perot sensor, and each sensing unit is packaged in a packaging fixture or directly attached to the surface of the object to be measured.

9. The wireless transmission optical fiber sensor according to any one of claims 2 to 6, characterized in that: The protective lens is an optically coated protective lens for the signal light band.

10. The method for manufacturing the wireless transmission optical fiber sensor according to claim 1, characterized in that: The following steps are involved: S1. Make a spatial light collimation and beam expansion system; S2, aligning the spatial light collimation and beam expansion system and the optical fiber collimator with the light path and fixing them; S3, connecting the optical fiber collimator and the sensor unit group through optical fiber.

11. The manufacturing method according to claim 10, characterized in that: The step S1 specifically includes placing the convex lens 4 and the concave lens 7 in the lens barrel 5 and fixing them.

12. The manufacturing method according to claim 11, characterized in that: The S2 specifically includes: S21, placing the optical fiber collimator in the fixed ferrule and fixing the optical fiber collimator; S22, connecting the fixed ferrule to the lens barrel, adjusting the lens barrel and the optical fiber collimator to be coaxial, and then fixing them; S23. Place the lens barrel in the clamping ring and secure it; S24, fixing the protective lens to the window of the housing; S25. Fix the assembled lens barrel and clamping ring to the base of the housing.

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