CN115931021A - Optical fiber sensor, preparation method thereof and sensing device - Google Patents
Optical fiber sensor, preparation method thereof and sensing device Download PDFInfo
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Abstract
The embodiment of the invention discloses an optical fiber sensor, a preparation method thereof and a sensing device. The optical core sensor comprises a first single-mode fiber, a multi-core fiber and a second single-mode fiber which are sequentially connected, wherein the multi-core fiber comprises a central fiber core and at least one peripheral fiber core; the joint of the first single-mode fiber and the multi-core fiber comprises a conical area, the joint of the multi-core fiber and the second single-mode fiber comprises a spherical structure, and the spherical structure forms a Mach-Zehnder interferometer; light is input from a fiber core of the first single-mode fiber and coupled into the fiber core of the multi-core fiber through the tapered region, wherein the central fiber core transmits a fundamental mode, and the peripheral fiber core transmits a high-order mode; light rays in the two modes are diffused and focused in the spherical structure and then coupled into the fiber core of the second single-mode fiber and output from the second single-mode fiber, so that the sensitivity of the optical fiber sensor is improved.
Description
Technical Field
The invention relates to the technical field of sensing, in particular to an optical fiber sensor, a preparation method thereof and a sensing device.
Background
With the continuous development of the optical fiber sensor industry, various optical fiber sensor structures are proposed, such as core-offset welding structures, vase-shaped structures, microcavity structures, optical fiber cascade structures and the like. Although the sensitivity of the eccentric welding structure, the vase-shaped structure and the microcavity structure sensor is high, the mechanical strength of the sensor structure is low, and the sensor structure is not beneficial to practical engineering application; although the optical fiber cascade structure retains the mechanical strength of the optical fiber, the sensitivity of the optical fiber cascade structure is restricted by the structure of the optical fiber cascade structure, and the improvement is difficult.
In recent years, the spherical structure is optimally designed to be a peanut-type structure (consisting of two spherical structures) due to stable structure in the aspect of micro-displacement measurement, and the measured temperature sensitivity of the sensor is 98.65 pm/DEG C at most. The ball-type structure sensor reported above has advantages in the sensing performance, but has large optical loss and low sensitivity in the preparation process.
Disclosure of Invention
The embodiment of the invention provides an optical fiber sensor, a preparation method thereof and a sensing device, wherein a Mach-Zehnder interferometer is formed by a conical region at the joint of a first single-mode optical fiber and a multi-core optical fiber and a spherical structure at the joint of the multi-core optical fiber and a second single-mode optical fiber, light is input from a fiber core of the first single-mode optical fiber and is coupled into a fiber core of the multi-core optical fiber through the conical region, wherein a central fiber core transmits a base mode, and a peripheral fiber core transmits a high-order mode; light rays in the two modes are diffused and focused in the spherical structure and then are coupled into the fiber core of the second single-mode fiber and output from the second single-mode fiber, so that the sensitivity of the optical fiber sensor is improved.
According to an aspect of the present invention, an optical fiber sensor is provided, which specifically includes a first single-mode fiber, a multi-core fiber, and a second single-mode fiber connected in sequence, where the multi-core fiber includes a central fiber core and at least one peripheral fiber core;
the joint of the first single-mode fiber and the multi-core fiber comprises a conical area, the joint of the multi-core fiber and the second single-mode fiber comprises a spherical structure, and the spherical structure forms a Mach-Zehnder interferometer;
light is input from a fiber core of the first single-mode fiber and coupled into a fiber core of the multi-core fiber through the conical area, wherein a central fiber core transmits a fundamental mode, and a peripheral fiber core transmits a high-order mode; light rays of the two modes are diffused and focused in the spherical structure, then are coupled into a fiber core of the second single-mode fiber and are output from the second single-mode fiber.
Optionally, the multi-core fiber of the fiber sensor includes a four-core fiber, a five-core fiber, a seven-core fiber, or a nine-core fiber.
Optionally, the length of the tapered region is greater than or equal to 1.8mm, less than or equal to 5.5mm.
Optionally, the optical fiber sensor specifically further comprises a protective layer, and the protective layer covers at least the tapered region.
Optionally, the protective layer includes an ultraviolet curing glue, a rubber soft body wrapping the ultraviolet curing glue, and an elastic metal groove at least partially wrapping the rubber soft body.
According to another aspect of the present invention, a method for manufacturing an optical fiber sensor is provided, which specifically includes:
providing a first single mode fiber, a second single mode fiber and a multi-core fiber;
cutting the tail end of the multi-core optical fiber flat, and fusing the end face of one end of the multi-core optical fiber into a spherical structure by using a fusion splicer;
welding the spherical structure with the second single-mode fiber;
and welding the other end of the multi-core fiber with the first single-mode fiber and tapering the joint to form a tapered region.
Optionally, after welding the other end of the multi-core fiber to the first single-mode fiber and tapering the connection to form a tapered region, the method further includes:
and forming a protective layer, wherein the protective layer at least covers the conical area.
Optionally, forming the protective layer comprises:
placing the optical fiber in a semicircular capillary quartz groove, and injecting ultraviolet curing glue into the capillary quartz groove;
after ultraviolet curing, the optical fiber is placed in the capillary quartz groove of the semicircle at the other side in an inverted mode, and the processes of glue injection and curing are repeated;
wrapping the outer side of the optical fiber with a round rubber soft body;
the sensor is placed in a resilient metal bath.
According to a further aspect of the present invention, a sensing device is provided, which specifically includes a light source, a spectrometer and any one of the above optical fiber sensors, an output end of the light source is connected to a first single mode fiber of the optical fiber sensor, the spectrometer is connected to a second single mode fiber of the optical fiber sensor, and the optical fiber sensor is used for temperature sensing.
According to another aspect of the present invention, a sensing device is provided, which specifically includes a light source, a spectrometer, a first displacement stage, a second displacement stage and any one of the foregoing fiber optic sensors, wherein an output end of the light source is connected to a first single mode fiber of the fiber optic sensor, the spectrometer is connected to a second single mode fiber of the fiber optic sensor, the first single mode fiber is fixed on the first displacement stage, the second single mode fiber is fixed on the second displacement stage, and the fiber optic sensor is used for curvature sensing.
The embodiment of the invention provides an optical fiber sensor, a preparation method thereof and a sensing device, wherein the optical fiber sensor is sequentially connected with a first single-mode optical fiber, a multi-core optical fiber and a second single-mode optical fiber, the multi-core optical fiber comprises a central fiber core and at least one peripheral fiber core, a conical region at the joint of the first single-mode optical fiber and the multi-core optical fiber is combined with a spherical structure at the joint of the multi-core optical fiber and the second single-mode optical fiber, the spherical structure forms a Mach-Zehnder interferometer, light is input from the fiber core of the first single-mode optical fiber and is coupled into the fiber core of the multi-core optical fiber through the conical region, the central fiber core transmits a fundamental mode, and the peripheral fiber core transmits a high-order mode; light rays in two modes are diffused and focused in the spherical structure and then are coupled into a fiber core of the second single-mode fiber and output from the second single-mode fiber, the micro fiber is brought into the spherical structure by adopting a structure formed by connecting the single-mode fiber, the spherical structure and the single-mode fiber, the sensitivity of the sensor is improved by utilizing a strong evanescent field of the fiber, and meanwhile, the optical loss of the device is reduced.
It should be understood that the statements in this section do not necessarily identify key or critical features of the embodiments of the present invention, nor do they necessarily limit the scope of the invention. Other features of the present invention will become apparent from the following description.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the description below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of an optical fiber sensor according to an embodiment of the present invention;
fig. 2 is a flowchart of a method for manufacturing an optical fiber sensor according to an embodiment of the present invention;
fig. 3 is a transmitted light spectrum diagram in the manufacturing process of an optical fiber sensor according to an embodiment of the present invention;
FIG. 4 is a plot obtained after the fast Fourier transform process of FIG. 3;
FIG. 5 is a flow chart of another method for manufacturing an optical fiber sensor according to an embodiment of the present invention;
fig. 6 is a schematic view of a sensing device using an optical fiber sensor according to an embodiment of the present invention;
FIG. 7 is a transmission spectrum using the apparatus shown in FIG. 6;
FIG. 8 is a fitted curve of the transmission spectrum according to FIG. 7;
FIG. 9 is a schematic view of another sensing apparatus using fiber optic sensors according to an embodiment of the present invention;
FIG. 10 is a transmission spectrum using the apparatus shown in FIG. 9;
fig. 11 is a fitted curve of the transmission spectrum according to fig. 10.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
Fig. 1 is a schematic structural diagram of an optical fiber sensor according to an embodiment of the present invention, and referring to fig. 1, the present invention provides an optical fiber sensor, specifically including a first single-mode fiber 10, a multi-core fiber 20, and a second single-mode fiber 30 connected in sequence, where the multi-core fiber 20 includes a central fiber core 21 and at least one peripheral fiber core 22;
the joint of the first single-mode fiber 10 and the multi-core fiber 20 comprises a tapered region 40, the joint of the multi-core fiber 20 and the second single-mode fiber 30 comprises a spherical structure 50, and the spherical structure 50 forms a Mach-Zehnder interferometer;
light is input from the core of the first single mode fiber 10 and coupled into the core of the multi-core fiber 20 through the tapered region 40, wherein the central core 21 transmits a fundamental mode and the peripheral core 22 transmits a high-order mode; the light rays of the two modes are diffused and focused in the spherical structure 50, and then are coupled into the fiber core of the second single-mode fiber 30 and output from the second single-mode fiber 30.
The first single-mode fiber 10 may be a single-mode fiber with any dispersion value, and the specific type and model are not limited, the multicore fiber 20 includes a central fiber core 21 and at least one peripheral fiber core 22, for example, the multicore fiber 20 may be a seven-core fiber including a central fiber core and six peripheral fiber cores, the specific type and model of the multicore fiber is not limited, and the number of the peripheral fiber cores 22 is not specifically limited (fig. 1 takes three fiber cores as an example); the tapered region 40 is used to couple light input from the core of the first single mode fiber 10 into the cores of the multi-core fiber 20, and the light is transmitted in the respective modes in the plurality of cores; the spherical structure 50 forms a Mach-Zehnder interferometer structure for outputting the interference, divergence and focusing of the central fiber core 21 and the at least one peripheral fiber core 22 to the second single-mode fiber 30; the first single mode fibre 10 and the second single mode fibre 30 may be the same type of fibre, for example SMF-28 fibre.
It will be appreciated that light first enters the core of the single mode optical fibre 10, the central tapered region formed by the tapered region 40, i.e. the region of minimum cross-sectional area in the tapered region along the direction of light propagation, and is coupled from the single mode optical fibre into the central core 21 and the plurality of peripheral cores 22, it being noted that very little light is coupled into the cladding. Light coupled into a plurality of peripheral cores 22 in the multicore fiber 20 will form high order modes (the specific high order mode of the light corresponds to the type of peripheral fiber compared to the fundamental mode in the central core, the number of high order modes corresponding to the number of types of peripheral fibers); light of the corresponding mode is diffused and focused in the spherical structure 50, then is coupled into the fiber core of the second single-mode fiber 30 and is output, the sensitivity of the sensor is improved by using the strong evanescent field of the fiber, and meanwhile, the optical loss of the device is reduced.
Illustratively, in one embodiment, the length of the central tapered region may be 3.652mm, the diameter of the waist may be 1.9 μm, the length of the multicore fiber 20 may be 2.5cm, and the diameter of the spherical structure 50 may be 346 μm.
The embodiment of the invention discloses an optical fiber sensor, which comprises a first single-mode optical fiber, a multi-core optical fiber and a second single-mode optical fiber which are sequentially connected, wherein the multi-core optical fiber comprises a central fiber core and at least one peripheral fiber core; the joint of the first single-mode fiber and the multi-core fiber comprises a conical area, the joint of the multi-core fiber and the second single-mode fiber comprises a spherical structure, and the spherical structure forms a Mach-Zehnder interferometer; light is input from a fiber core of the first single-mode fiber and coupled into a fiber core of the multi-core fiber through the conical area, wherein a central fiber core transmits a fundamental mode, and a peripheral fiber core transmits a high-order mode; light rays in two modes are diffused and focused in the spherical structure and then are coupled to enter a fiber core of the second single mode fiber and are output from the second single mode fiber, the spherical structure is combined with the fiber, a structure formed by connecting the single mode fiber, the spherical structure and the single mode fiber is adopted, the micro fiber is brought into the spherical structure, the sensitivity of the sensor is improved by utilizing a strong evanescent field of the fiber, when light in the fiber sensor enters the spherical structure from a conical area, core mold interference occurs, signals changing around are converted into electric signals by connecting the standard single mode fiber into a photoelectric detector, and the electric signals are stored, analyzed and displayed, and meanwhile, the light loss of the device is reduced.
Based on the above embodiment scheme, further optimization is performed, the principle and beneficial effects are the same as those of the above embodiment, and no further description is given here, and only the differences are described.
Optionally, the multi-core fiber of the fiber sensor includes a four-core fiber, a five-core fiber, a seven-core fiber, or a nine-core fiber.
The types of the plurality of peripheral fiber cores in the multi-core fiber can be the same or different, and the number, the types and the types are not limited.
Optionally, the length of the tapered region is greater than or equal to 1.8mm, less than or equal to 5.5mm.
Experiments show that the sensitivity of the optical fiber sensor is in positive correlation with the length of the tapered region of the optical fiber sensor, but the length of the tapered region cannot be too long in consideration of subsequent packaging and practical feasibility, and the length of the tapered region is set to be 1.8-5.5 mm in the embodiment.
Optionally, this embodiment provides that the optical fiber sensor further includes a protective layer, and the protective layer covers at least the tapered region.
The protective layer can increase the toughness of the protected optical fiber, prevent signal leakage and external signal interference, and increase the protective layer in the area where the optical fiber is located.
Optionally, the protective layer comprises an ultraviolet curing adhesive, a rubber soft body wrapping the ultraviolet curing adhesive, and an elastic metal groove at least partially wrapping the rubber soft body.
The ultraviolet curing glue, the rubber soft body wrapping the ultraviolet curing glue and the elastic metal groove at least partially wrapping the rubber soft body can further protect the optical fiber area, and the elastic metal groove partially wrapping the rubber soft body can play a supporting role so as to further protect the covered optical fiber and shield external signal interference and internal signal leakage.
Fig. 2 is a flowchart of a method for manufacturing an optical fiber sensor according to an embodiment of the present invention, and referring to fig. 2, the present invention provides a method for manufacturing an optical fiber sensor, which specifically includes:
and S110, providing a first single-mode fiber, a second single-mode fiber and a multi-core fiber.
The relevant parameters of the first single-mode fiber, the second single-mode fiber and the multi-core fiber are matched with each other, and specific types and the number of peripheral fibers in the multi-core fiber are not specifically limited.
And S120, cutting the tail end of the multi-core fiber flat, and fusing the end face of one end of the multi-core fiber into a spherical structure by using a fusion splicer.
The cutting method of the flattening includes, but is not limited to, cutting by an optical fiber cutter, and the mode of fusing the end face of one end of the multicore fiber into a spherical structure is preferably a manual fusion mode using an optical fiber fusion splicer. Illustratively, the discharge intensity may be 35 and the discharge time may be 250ms.
S130, welding the spherical structure with the second single-mode fiber.
Wherein, the fusion process can be fused through the manual fusion mode of the optical fiber fusion splicer.
And S140, welding the other end of the multi-core fiber with the first single-mode fiber, and tapering the joint to form a tapered region.
Wherein the tapering speed can be controlled by setting the flow rates of the oxygen and hydrogen of the oxyhydrogen flame tapering machine, including but not limited to oxyhydrogen flame tapering machines can be used.
It should be noted that, because of the structural and dimensional differences between the ball-type structure and the single-mode fiber, manual fusion splicing is also required.
It is understood that first, a first single mode fiber, a second single mode fiber, and a multi-core fiber are provided; then, the tail end of the multi-core optical fiber can be cut flat by an optical fiber cutter, the multi-core optical fiber is stably placed in an optical fiber fusion splicer, the position of the multi-core optical fiber is adjusted by a stepping displacement table in the fusion splicer, a manual fusion splicing mode is selected, the end face of the optical fiber is fused into a spherical structure through repeated discharge (the discharge intensity is 35, and the discharge time is 250 ms), and the discharge frequency and the discharge amount are determined by the size of the required spherical structure; welding the end surface spherical structure which is welded well with the second single-mode optical fiber, wherein the spherical structure and the second single-mode optical fiber have structural and size differences, so that manual welding is also needed; and finally, the other end of the multi-core optical fiber is welded with the first single-mode optical fiber, the joint is fixed on an oxyhydrogen flame tapering machine, the welding position of the optical fiber is located in a central tapering area of the tapering machine, and the flow rate of oxygen and hydrogen of the oxyhydrogen flame tapering machine is set to control the tapering speed. In the tapering process, the length of the central cone area needs to be concerned, and the state of the comb-shaped peak is observed in real time through a spectrometer, so that the sample can be prepared successfully. Illustratively, fig. 3 is a transmission spectrum of an optical fiber sensor provided by an embodiment of the present invention during a manufacturing process, fig. 4 is a graph obtained after the fast fourier transform processing of fig. 3, and the observation of fig. 3 and fig. 4 is combined during a tapering process to facilitate successful preparation of a sample.
According to the preparation method of the optical fiber sensor provided by the embodiment of the invention, the first single-mode optical fiber, the second single-mode optical fiber and the multi-core optical fiber are provided; then, the tail end of the multi-core optical fiber is cut flat, and the end face of one end of the multi-core optical fiber is fused into a spherical structure by using a fusion splicer; then the spherical structure is welded with the second single-mode fiber; and finally, welding the other end of the multi-core fiber with the first single-mode fiber, and tapering the joint to form a tapered region, so as to obtain the fiber sensor in the embodiment. The optical fiber sensor which utilizes the strong evanescent field of the optical fiber to improve the sensitivity of the sensor and simultaneously reduces the optical loss of the device is prepared by effectively welding through the real-time observation of the transmitted light spectrogram and the curve obtained after the fast Fourier transform processing.
Based on the above embodiment, further optimization, optionally after the other end of the multi-core fiber is fusion-spliced with the first single-mode fiber and the joint is tapered to form a tapered region, the method may further include: and forming a protective layer, wherein the protective layer at least covers the conical area.
Fig. 5 is a flowchart of a method for manufacturing another optical fiber sensor according to an embodiment of the present invention, and referring to fig. 5, the method for manufacturing another optical fiber sensor according to an embodiment of the present invention specifically includes the following steps:
s210, providing a first single-mode fiber, a second single-mode fiber and a multi-core fiber.
And S220, flattening the tail end of the multi-core fiber, and fusing the end face of one end of the multi-core fiber into a spherical structure by using a fusion splicer.
And S230, welding the spherical structure with the second single-mode fiber.
And S240, welding the other end of the multi-core fiber with the first single-mode fiber, and tapering the joint to form a tapered region.
And S250, forming a protective layer, wherein the protective layer at least covers the conical area.
The protective layer may include an ultraviolet curing adhesive, and the specific thickness, the coverage area, and the like of the protective layer may be designed according to actual situations.
Optionally, forming the protective layer comprises: placing the optical fiber in a semicircular capillary quartz groove, and injecting ultraviolet curing glue into the capillary quartz groove; after ultraviolet curing, the optical fiber is placed in the capillary quartz groove of the semicircle at the other side in an inverted mode, and the processes of glue injection and curing are repeated; wrapping the outer side of the optical fiber with a round rubber soft body; the sensor is placed in a resilient metal bath.
It is understood that first, a first single mode fiber, a second single mode fiber, and a multi-core fiber are provided; then, the tail end of the multi-core optical fiber can be cut flat by an optical fiber cutter, the multi-core optical fiber is stably placed in an optical fiber fusion splicer, the position of the multi-core optical fiber is adjusted by a stepping displacement table in the fusion splicer, a manual fusion splicing mode is selected, the end face of the optical fiber is fused into a spherical structure by repeated discharge, and the discharge frequency and the discharge capacity are determined by the size of the required spherical structure; welding the end surface spherical structure which is welded well with the second single-mode optical fiber, wherein the spherical structure and the second single-mode optical fiber have structural and size differences, so that manual welding is also needed; and then, the other end of the multi-core optical fiber is welded with the first single-mode optical fiber, the joint is fixed on an oxyhydrogen flame tapering machine, the welding position of the optical fiber is positioned in a central tapering area of the tapering machine, and the flow rate of oxygen and hydrogen of the oxyhydrogen flame tapering machine is set to control the tapering speed. And finally, placing the optical fiber in a semicircular capillary quartz groove, slowly injecting ultraviolet curing glue into the quartz groove, and taking care that the inner wall of the quartz groove needs to be coated with an anti-sticking agent in advance to prevent the ultraviolet glue from sticking to the inner wall of the quartz groove in the ultraviolet curing process to cause the optical fiber to be incapable of being taken out. And after ultraviolet curing, the optical fiber is placed in the semicircular quartz groove on the other side in an inverted mode, and the processes of glue injection and curing are repeated, so that the outer layer of the whole optical fiber is wrapped with a coating layer formed by ultraviolet glue. And then, wrapping the outer side of the optical fiber by using a round rubber soft body to further increase the mechanical property of the sensor, then placing the sensor in an elastic metal groove, and marking a scale on the outer part of the metal groove so as to calculate the bending curvature of the sensor in an actual curvature test, so as to obtain the optical fiber sensor with a protective layer.
According to the preparation method of the optical fiber sensor provided by the embodiment of the invention, the first single-mode optical fiber, the second single-mode optical fiber and the multi-core optical fiber are provided; then, the tail end of the multi-core optical fiber is cut flat, and the end face of one end of the multi-core optical fiber is fused into a spherical structure by using a fusion splicer; then the spherical structure is welded with the second single-mode fiber; then, the other end of the multi-core fiber is fusion-spliced with the first single-mode fiber, the joint is tapered to form a tapered region, and finally, a protective layer is formed, and the protective layer at least covers the tapered region, so that the optical fiber sensor in the above embodiment can be obtained. The optical fiber sensor after the protective layer is added can effectively protect an optical fiber area, the elastic metal groove partially wrapping the rubber soft body can play a supporting role to further protect the covered optical fiber, and meanwhile, the mechanical strength of the optical fiber sensor can be improved to prevent the optical fiber sensor from being damaged in the using process by shielding external signal interference and internal signal leakage.
Fig. 6 is a schematic view of a sensing device using an optical fiber sensor according to an embodiment of the present invention, and referring to fig. 6, the present invention further provides a sensing device, which specifically includes a light source 1, a spectrometer 2, and any one of the optical fiber sensors 3 according to the above embodiments. The output end of the light source 1 is connected with a first single-mode optical fiber of the optical fiber sensor 3, the spectrometer 2 is connected with a second single-mode optical fiber of the optical fiber sensor 3, and the optical fiber sensor 3 is used for temperature sensing.
The light source 1 includes but is not limited to a broadband light source, and the light source 1, the spectrometer 2 and any of the above optical fiber sensors 3 should be matched with each other, for example, the range and precision tested by the spectrometer are adapted to the output range of the light source and the sensing range and precision of the optical fiber sensor. The sensor can be applied to temperature sensing test, and is characterized in that an optical fiber sensor is placed in a thermostat, one side of the sensor is connected with a broadband light source, and the other side of the sensor records the transmission spectrum change of the sensor at different temperatures through a spectrometer.
Illustratively, FIG. 7 is a transmission spectrum using the apparatus shown in FIG. 6, FIG. 8 is a fitted curve based on the transmission spectrum of FIG. 7, and the experimentally measured detectable interval of the sensor is 30 deg.C-75 deg.C. Referring to fig. 7 and 8, the optimum detection temperature range is 30-40 deg.c, in which the sensor temperature sensitivity is at most 0.45 nm/deg.c.
Fig. 9 is a schematic view of another sensing device using an optical fiber sensor according to an embodiment of the present invention, where a first displacement stage and a second displacement stage may be arranged to perform a curvature sensing test using any one of the optical fiber sensors, and referring to fig. 9, optionally, the sensing device includes a light source 1, a spectrometer 2, a first displacement stage 4, a second displacement stage 5, and any one of the optical fiber sensors 3, an output end of the light source 1 is connected to a first single-mode fiber of the optical fiber sensor 3, the spectrometer 2 is connected to a second single-mode fiber of the optical fiber sensor 3, the first single-mode fiber is fixed on the first displacement stage 4, the second single-mode fiber is fixed on the second displacement stage 5, and the optical fiber sensor 3 is used for curvature sensing.
Wherein, the first displacement table 4 and the second displacement table 5 are used for fixing the optical fiber sensor 3, and the curvature sensing test is carried out by adjusting the relative position of the first displacement table 4 and the second displacement table 5 to change the curvature radius of the optical fiber. The first and second displacement stations 4, 5 include, but are not limited to, any mechanical displacement platform that meets the needs, and are not limited to a particular type or model.
It can be understood that the curvature sensing test of the sensor is to fix the optical fiber sensor between two displacement tables, change the curvature radius of the optical fiber by adjusting the position of the left displacement table, and calculate the curvature by formula. One side of the sensor is connected with a broadband light source, and the other side of the sensor records the transmission spectrum change of the sensor under different curvatures through a spectrometer. The curvature calculation formula is as follows:
where L is the distance between the two translation stages, R is the radius of curvature, x is the displacement of the left displacement stage, and C is the curvature.
Illustratively, fig. 10 is a transmission spectrum using the apparatus shown in fig. 9, fig. 11 is a fitted curve based on the transmission spectrum of fig. 10, and referring to fig. 10 and 11, it is experimentally determined that the maximum curvature sensitivity of the sensor can be up to 66.96nm/m -1 。
According to the sensing device of the optical fiber sensor in temperature and curvature sensing, light output by a light source enters any one of the optical fiber sensors in the embodiments, the light sequentially passes through a first single-mode fiber, a multi-core fiber and a second single-mode fiber, core-mode interference occurs when light in the optical fiber sensor enters a spherical structure from a conical region according to collection of a spectrometer, and signals changing due to changes of ambient temperature or curvature are generated.
The above-described embodiments should not be construed as limiting the scope of the invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions may be made in accordance with design requirements and other factors. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. An optical fiber sensor is characterized by comprising a first single-mode optical fiber, a multi-core optical fiber and a second single-mode optical fiber which are sequentially connected, wherein the multi-core optical fiber comprises a central fiber core and at least one peripheral fiber core;
the joint of the first single-mode fiber and the multi-core fiber comprises a conical region, the joint of the multi-core fiber and the second single-mode fiber comprises a spherical structure, and the spherical structure forms a Mach-Zehnder interferometer;
light is input from the fiber core of the first single-mode optical fiber and coupled into the fiber core of the multi-core optical fiber through the tapered region, wherein the central fiber core transmits a fundamental mode, and the peripheral fiber core transmits a high-order mode; and light rays of the two modes are diffused and focused in the spherical structure and then are coupled into the fiber core of the second single-mode fiber and output from the second single-mode fiber.
2. The fiber sensor of claim 1, wherein the multi-core fiber comprises a four-core fiber, a five-core fiber, a seven-core fiber, or a nine-core fiber.
3. The fiber optic sensor of claim 1, wherein the tapered region has a length greater than or equal to 1.8mm and less than or equal to 5.5mm.
4. The fiber optic sensor of claim 1, further comprising a protective layer covering at least the tapered region.
5. The fiber sensor of claim 4, wherein the protective layer comprises an ultraviolet-curable glue, a rubber soft body wrapping the ultraviolet-curable glue, and an elastic metal groove at least partially wrapping the rubber soft body.
6. A method of making an optical fiber sensor, comprising:
providing a first single mode fiber, a second single mode fiber and a multi-core fiber;
cutting the tail end of the multi-core optical fiber flat, and fusing the end face of one end of the multi-core optical fiber into a spherical structure by using a fusion splicer;
welding the spherical structure with the second single-mode optical fiber;
and welding the other end of the multi-core fiber with the first single-mode fiber and tapering the joint to form a tapered region.
7. The method for preparing according to claim 6, further comprising, after fusing the other end of the multi-core optical fiber to the first single-mode optical fiber and tapering a junction to form a tapered region:
forming a protective layer covering at least the tapered region.
8. The production method according to claim 7, wherein the forming of the protective layer includes:
placing the optical fiber in a semicircular capillary quartz groove, and injecting ultraviolet curing glue into the capillary quartz groove;
after ultraviolet curing, the optical fiber is placed in a capillary quartz groove of the semicircle at the other side in an inverted mode, and the processes of glue injection and curing are repeated;
wrapping the outer side of the optical fiber with a round rubber soft body;
the sensor is placed in a resilient metal bath.
9. A sensing device, comprising a light source, a spectrometer and the optical fiber sensor of any one of claims 1 to 5, wherein an output end of the light source is connected to a first single mode fiber of the optical fiber sensor, the spectrometer is connected to a second single mode fiber of the optical fiber sensor, and the optical fiber sensor is used for temperature sensing.
10. A sensing device, comprising a light source, a spectrometer, a first displacement table, a second displacement table and the optical fiber sensor of any one of claims 1 to 5, wherein an output end of the light source is connected with a first single mode fiber of the optical fiber sensor, the spectrometer is connected with a second single mode fiber of the optical fiber sensor, the first single mode fiber is fixed on the first displacement table, the second single mode fiber is fixed on the second displacement table, and the optical fiber sensor is used for curvature sensing.
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