CN212539081U - Optical fiber SPR curvature sensor capable of recognizing direction - Google Patents
Optical fiber SPR curvature sensor capable of recognizing direction Download PDFInfo
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- CN212539081U CN212539081U CN202020896383.6U CN202020896383U CN212539081U CN 212539081 U CN212539081 U CN 212539081U CN 202020896383 U CN202020896383 U CN 202020896383U CN 212539081 U CN212539081 U CN 212539081U
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Abstract
The utility model belongs to the field of optical fiber Surface Plasma Resonance (SPR) sensing, and mainly relates to an optical fiber SPR curvature sensor with direction recognition, which can perform curvature measurement, bending direction judgment and multipoint simultaneous measurement based on wavelength division multiplexing technology through two parameters of resonance wavelength and resonance valley depth; the utility model plates a semi-circle surface SPR sensing film on one side of the fiber core of the plastic cladding optical fiber, and remolds and recovers the plastic cladding and the coating layer by using low refractive index coating glue outside; compared with the curvature sensor based on optical fiber interference and grating mechanism, the optical fiber SPR curvature sensor provided by the utility model has the advantages of novel and stable structure, strong bending property, realization of detection only by using a broadband incoherent light source and a visible light band spectrometer, and the like; the method has good application prospect in the fields of geological environment monitoring of landslides, reservoir banks and the like in three gorges reservoir area, building structure health monitoring and the like.
Description
Technical Field
The utility model belongs to fiber Surface Plasmon Resonance (SPR) sensing field relates to a fiber SPR curvature sensor of direction discernment.
Background
The curvature can reflect the characteristics and structural mechanics of materials, is the basis for evaluating the states of machinery, bridges and building structures, and can judge the health state of the structures by acquiring the curvature information of the structures, so the curvature measurement technology is particularly important in the fields of mechanical engineering and structural health monitoring. Compared with an electric sensor, the optical fiber sensor has the advantages of electromagnetic interference resistance, small volume, small transmission loss, easiness in bending, suitability for embedded distribution measurement and the like, so that the optical fiber curvature sensor has a wide research and development prospect and has attracted extensive attention of researchers. In the field of actual engineering sensing, it is sometimes necessary to determine the bending direction of an engineered structure, and therefore, it is highly desirable that a fiber optic curvature sensor be capable of not only measuring curvature, but also determining the bending direction. In addition, in actual engineering measurement, the detection range of the traditional point type optical fiber sensor is limited, and the quasi-distributed optical fiber sensor capable of multi-point detection not only enlarges the detection range of the optical fiber sensor, but also greatly improves the efficiency of structural health detection, so that the quasi-distributed optical fiber sensor capable of realizing detection in a large range has very wide application requirements and great research significance.
Currently, most studied optical fiber curvature sensors are classified into two major types, one is an optical fiber grating type curvature sensor mainly based on an optical fiber bragg grating type and a long-period optical fiber grating, and the other is an optical fiber interferometer type curvature sensor mainly based on a mach-zehnder interferometer.
The common fiber grating curvature sensor mainly realizes curvature measurement by monitoring the offset of the resonant wavelength of the grating, but the common fiber grating curvature sensor cannot identify the bending direction because of the circular symmetry of the optical fiber, so that the fiber grating curvature sensor can identify the bending direction by two methods, one is to cause the refractive index modulation asymmetric distribution of the cross section of the optical fiber in the manufacturing process, and the other is to write special optical fibers such as a D-shaped optical fiber, an eccentric optical fiber and a multi-core optical fiber into the fiber grating, thereby realizing different bending responses in different bending directions. However, specialty fibers are typically not easily fusion spliced to standard single mode fibers and add manufacturing difficulties and costs.
Generally, a mask method is required to be used in a common method for manufacturing an optical fiber grating, wherein a phase mask method is used for manufacturing the optical fiber bragg grating, an amplitude mask method is used for manufacturing the long-period optical fiber grating, the optical fiber grating is required to be placed in a high-pressure hydrogen chamber for a period of time before the optical fiber grating is manufactured by using the mask method, so that the photosensitivity of the optical fiber is increased, the manufacturing of the mask is complex, the manufacturing cost is high, different masks are required to be used for different gratings, and the cost for realizing the simultaneous measurement of the multi-point curvature based on the wavelength division multiplexing technology by using the optical fiber grating sensor is increased. Another method for manufacturing a long-period fiber grating is a point-by-point writing method, which can flexibly control the manufacturing length of the grating, but needs a complex focusing optical system and an accurate displacement moving technology, and can damage the quartz structure of the optical fiber due to the overlarge power of a carbon dioxide laser in the process of writing the long-period fiber grating, thereby reducing the structural strength of the optical fiber, and being easy to break in the process of measuring the curvature, thereby limiting the curvature detection range.
The common Mach-Zehnder interferometer optical fiber curvature sensor couples a part of fiber core modes into a single-mode optical fiber cladding through dislocation welding, thick cone welding, fused biconical taper, welded multimode optical fiber and the like so as to excite the optical fiber cladding mode, the optical fiber cladding mode is coupled into the optical fiber core again after being transmitted forward for a certain distance and interfered with the fiber core mode transmitted in the optical fiber core, the optical path difference between the fiber core mode and the cladding mode is changed after the optical fiber is bent, and the measurement of the bending curvature of the optical fiber can be realized by detecting the position of the resonance wavelength. The Mach-Zehnder interferometer optical fiber curvature sensor with the direction identification is manufactured, the asymmetry of the optical fiber is increased through technical means such as dislocation welding, asymmetric thick cone welding and asymmetric fused biconical taper, so that different bending responses in different bending directions are achieved, however, the optical fiber quartz structure is damaged through the mentioned technical means, the structural strength of the optical fiber sensor is reduced, the optical fiber sensor is easy to break in curvature measurement, and the curvature detection range is limited. The asymmetric multi-core optical fiber is used for manufacturing the interferometer optical fiber curvature sensor, so that different bending responses in different bending directions are achieved, but the manufacturing cost of the multi-core optical fiber is high, and the application in practical engineering is not facilitated.
The fiber grating type and fiber interferometer type curvature sensors are also affected by temperature and axial strain during the bending process, resulting in shift of the resonant wavelength. The resonance wavelength is deviated mainly because the elasto-optic effect of axial strain and the thermo-optic effect and the thermal expansion effect of temperature cause the grid distance of the grating to be changed, and the difference between the effective refractive indexes of the fiber cladding and the fiber core is also changed, so that the fiber grating type and the fiber interferometer type curvature sensors are very sensitive to temperature and axial strain, and the measurement accuracy of the two types of fiber curvature sensors is influenced.
The optical fiber type SPR curvature sensor changes the total reflection angle in an optical fiber core by using optical fiber bending, the intensity of an evanescent field of an interface of the fiber core and a cladding is increased, so that resonance wavelength shift and depth change of a resonance valley of an SPR spectral line are caused, and the curvature can be measured by the shift amount of the SPR resonance wavelength or the change amount of the depth of the resonance valley. The resonant wavelength and the resonant valley depth of the fiber SPR are mainly influenced by the total internal reflection angle and the refractive index of the fiber, and the temperature and the axial strain are basically negligible compared with the ultrahigh sensitivity of the SPR sensor. In recent years, curvature measurement using an optical fiber sensor utilizing the SPR effect has been reported, but it has also been reported that the SPR effect is not used to identify the bending direction.
Based on this, the utility model aims to solve the problem, research and realize a new method, can make a simple process, low cost, the preparation time is short, and stable in structure's optic fibre SPR curvature sensor, this curvature sensor not only can measure the camber of monitoring point and judge the crooked direction of monitoring point, can also realize multiple spot camber simultaneous measurement and crooked direction judgement based on wavelength division multiplexing technique, in geological environment monitoring such as three gorges reservoir area landslide, storehouse bank, fields such as building structure health monitoring have good application prospect.
SUMMERY OF THE UTILITY MODEL
In view of this, the present invention provides a fiber SPR curvature sensor with high structural strength and strong bending performance, which solves the problems of high cost, complex process, long manufacturing time and unstable structure in the conventional process of manufacturing fiber SPR curvature sensor. The SPR optical fiber curvature sensor provided by the utility model can measure curvature, judge bending direction and measure multiple points simultaneously based on wavelength division multiplexing technology through two parameters of resonance wavelength and resonance valley depth; the utility model provides an optic fibre SPR camber sensor compares with the camber sensor based on optic fibre is interfered and the grating mechanism, only needs to use broadband incoherent light source and visible light wave band spectrum appearance can realize advantages such as detecting.
In order to achieve the above object, the utility model provides a following technical scheme:
an optical fiber SPR curvature sensor with direction identification comprises a plastic cladding multimode optical fiber (1), and a first SPR sensing area (2) and a second SPR sensing area (3) which are sequentially manufactured on the plastic cladding multimode optical fiber; the plastic cladding multimode fiber (1) consists of a first quartz fiber core (1-1), a plastic cladding (1-2) annularly cladding the surface of the first quartz fiber core and a coating layer (1-3) annularly cladding the surface of the plastic cladding; the first SPR sensing area (2) consists of a second quartz fiber core (2-1), a first semicircular surface SPR sensing film (2-2) coated on the surface of the second quartz fiber core and a first low-refractive-index coating layer (2-3) coated on the outermost side in an annular mode; the second SPR sensing area (3) consists of a third quartz fiber core (3-1), a second semicircular surface SPR sensing film (3-2) coated on the surface of the third quartz fiber core and a second low-refractive-index coating layer (3-3) coated on the outermost side in an annular mode; the optical fiber SPR curvature sensor with the direction recognition function can measure curvature and judge the bending direction through two parameters of SPR resonance wavelength and resonance valley depth; the refractive index of the first low-refractive-index coating layer (2-3) is lower than that of the second low-refractive-index coating layer (3-3), the SPR curvature sensing resonance wavelength working range is related to the refractive index of a medium outside the SPR sensing film, the working range of the SPR resonance wavelength can be changed by changing the refractive index of the medium coated outside the SPR sensing film, and the plastic cladding multimode optical fiber coated with mediums with different refractive indexes and the first SPR sensing area are cascaded, so that the simultaneous measurement of multipoint curvature and the judgment of the bending direction based on the wavelength division multiplexing technology can be realized.
Optionally, the plastic-clad multimode fiber (1) has a first quartz fiber core made of pure quartz material with a diameter of 125 μm at the center, a low-refractive-index plastic cladding with a diameter of 150-200 μm is tightly and annularly clad on the outer side of the first quartz fiber core, the low-refractive-index plastic cladding is made of low-refractive-index ultraviolet curing glue, and a common fiber coating layer is tightly and annularly clad on the outer side of the plastic cladding with a diameter of 250 μm.
Optionally, the first semicircular surface SPR sensing film (2-2) is a semicircular film tightly coated on one side of the second quartz fiber core, the thickness of the film is 30nm-60nm, the material is gold, silver, copper and other metals which are easy to generate surface plasma resonance, and the film is plated on one side of the fiber core surface by using a direct current plasma sputtering or magnetron sputtering process to form a semicircle.
Optionally, the optical fiber SPR curvature sensor for direction recognition realizes curvature measurement through two parameters of SPR resonance wavelength and resonance valley depth, and the specific process is as follows: the transmitted light is totally reflected at the interface between the fiber core and the fiber cladding, the included angle between the light and the normal of the interface is called the total reflection angle, according to the condition of exciting surface plasma resonance, the SPR peak is related to the total reflection angle, the total reflection angle changes, the position of the SPR valley on the spectrum shifts, therefore, when the optical fiber sensing area is bent, the total reflection angle in the fiber core changes, the position of the SPR valley on the spectrum shifts, and the larger the change amount of the total reflection angle in the fiber core, the larger the shift amount of the SPR valley on the spectrum, therefore, the fiber bending curvature can be determined by the shift amount of the SPR peak, thereby realizing the wavelength sensing curvature of the SPR valley; as the bending curvature of the optical fiber sensing area is increased, the intensity of an evanescent field at the interface of a fiber core and a cladding layer is increased, the intensity of the evanescent field leaked from the fiber core of the optical fiber is higher, the depth of a resonance valley of the SPR is related to the intensity of the evanescent field, and the depth sensing curvature of the resonance valley of the SPR is further realized.
Optionally, the optical fiber SPR curvature sensor for direction recognition determines the bending direction according to the moving direction of the SPR resonance wavelength, and the specific process is as follows: the optical fiber sensing area is bent, the total reflection angle of transmission light rays on the inner side of the bent portion is increased, the total reflection angle on the outer side of the bent portion is reduced, the resonance wavelength of the SPR is related to the total reflection angle, when the SPR sensing semicircular surface sensing film is on the inner side of the bent portion, the resonance wavelength of the SPR moves towards the long wavelength direction, when the SPR sensing semicircular surface sensing film is on the outer side of the bent portion, the resonance wavelength of the SPR moves towards the short wavelength direction, and therefore the bending direction is judged according to the moving direction of the resonance valley wavelength of the SPR.
Optionally, the lengths of the first SPR sensing area (2) and the second SPR sensing area (3) are 10mm-20mm, the plastic clad multimode fiber is mechanically stripped of the coating layer and the plastic clad, the 125 μm fiber core is exposed, one side of the fiber core is coated with a semicircular SPR sensing film, and then an optical fiber coating machine is used for coating a low-refractive-index ultraviolet curing glue on the outermost side to serve as a new low-refractive-index medium coating, so that light can be kept transmitted and a low-refractive-index medium environment for SPR generation can be provided, wherein the refractive index range of the first low-refractive-index coating layer (2-3) on the outermost side of the first SPR sensing area (2) is 1.335-1.355RIU, and the refractive index range of the second low-refractive-index coating layer (3-3) on the outermost side of the second SPR sensing area.
Optionally, the direction-identified optical fiber SPR curvature sensor and the multichannel measurement implementation method thereof are implemented by setting the first low-refractive-index coating layer (2-3) and the second low-refractive-index coating layer (3-3) to have different refractive indexes; or the first low-refractive-index coating layer (2-3) and the second low-refractive-index coating layer (3-3) are set to have the same refractive index, and the first semicircular surface SPR sensing film (2-2) and the second semicircular surface SPR sensing film (3-2) are realized by adopting metal films made of different materials; or the coating layer (2-3) and the second low refractive index coating layer (3-3) are set to have the same refractive index, the first semicircular surface SPR sensing film (2-2) and the second semicircular surface SPR sensing film (3-2) are made of the same metal film, and the first semicircular surface SPR sensing film (2-2) and the second semicircular surface SPR sensing film (3-2) are made of different film thicknesses.
Optionally, after the multichannel measurement of the fiber SPR curvature sensor with direction recognition is implemented by adjusting the refractive index of the coating layer in the sensing region or the metal material of the sensing film, the depths of the resonance valleys in the two sensing regions are adjusted to be consistent by adjusting the thicknesses of the plated metal films in the two sensing regions, so that the measurement based on wavelength division multiplexing is well implemented.
Optionally, the multichannel measurement of the fiber SPR curvature sensor for direction recognition may comprehensively utilize the adjustment of the refractive index of the coating layer in the sensing region, the thickness of the sensing film metal material and the sensing film to precisely adjust the working wavelength range of the SPR valley of resonance in each sensing region, to perform more than two-stage cascade, thereby realizing the detection of more point curvatures and bending directions based on the wavelength division multiplexing technology.
Compared with the prior art, the utility model discloses an optical fiber SPR curvature sensor of direction discernment has following positive effect:
1. the optical fiber SPR curvature sensor has strong bending performance and can realize detection in a larger curvature range. The optical fiber SPR curvature sensor is made of plastic cladding multimode optical fibers, after a cladding and a coating of the plastic cladding optical fibers are removed, an SPR sensing film is plated on the surface of a fiber core of the plastic cladding optical fibers, the plastic cladding and the coating are remolded and restored by low-refractive-index ultraviolet curing glue outside, the physical properties of the sensing optical fibers are the same as those of the optical fibers without the cladding and the coating, the optical fibers are high in flexibility and strong in bendability, and detection can be carried out in a large curvature range;
2. the optical fiber SPR curvature sensor can measure the curvature through two parameters of resonance wavelength and resonance valley depth. When the optical fiber sensing area is bent, the total reflection angle in the optical fiber core is changed, the resonance wavelength of the SPR is related to the total reflection angle, the total reflection angle is changed, the position of the SPR resonance valley on the spectrum is shifted, and the bending curvature of the optical fiber is determined by the shift amount of the SPR resonance peak, so that the measurement curvature of the SPR resonance valley wavelength is realized; when the optical fiber sensing area is bent, the intensity of an evanescent field of a fiber core and a cladding interface is increased, the depth of a resonance valley of SPR is related to the intensity of the evanescent field, and further the curvature can be measured through the depth of the resonance valley;
3. provided is an optical fiber SPR curvature sensor capable of discriminating the bending direction of an optical fiber by the shift direction of the resonance wavelength. The optical fiber is bent, the total reflection angle of the transmission light on the inner side of the bending part is increased, the total reflection angle on the outer side of the bending part is decreased, the resonance wavelength of the SPR is related to the total reflection angle, when the SPR sensing semicircular surface sensing film is on the inner side of the bending part, the resonance wavelength of the SPR moves to the long wavelength direction, when the SPR sensing semicircular surface sensing film is on the outer side of the bending part, the resonance wavelength of the SPR moves to the short wavelength direction, and then the bending direction can be judged through the moving direction of the resonance wavelength of the SPR;
4. provided is an optical fiber SPR curvature sensor capable of simultaneously measuring a plurality of curvatures and judging a bending direction. The refractive index of a medium coated outside the SPR sensing film is changed, the working range of SPR resonance wavelength can be changed, sensors coated with media with different refractive indexes are cascaded, and the simultaneous measurement of the multipoint curvature and the judgment of the bending direction based on the wavelength division multiplexing technology can be realized.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and/or combinations particularly pointed out in the appended claims.
Drawings
For the purposes of promoting a better understanding of the objects, features and advantages of the invention, reference will now be made to the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a block diagram of a fiber SPR curvature sensor with direction recognition.
FIG. 2 is a schematic diagram of a system for operating a fiber SPR curvature sensor with direction recognition.
FIG. 3 is a cross-sectional view of the multimode fiber of FIG. 1 corresponding to the AA ', BB', CC 'plane, wherein FIG. (a) is a cross-sectional view of the plastic-clad multimode fiber corresponding to the AA' plane; panel (b) is a cross-sectional view of the first SPR sensing area, corresponding to the BB' plane. FIG. (c) is a cross-sectional view of the second SPR sensing area, corresponding to the CC' plane
FIG. 4 is a diagram of coordinates of a mathematical model of a reflection point of a light beam in a bent optical fiber.
Fig. 5 is a schematic diagram of curves of the transmission light between the reflection angle θ and the projection distance L in different directions of propagation.
Detailed Description
The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will be readily apparent to those skilled in the art from the disclosure herein. The present invention can also be implemented or applied through other different specific embodiments, and various details in the present specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention, and the features in the following embodiments and examples may be combined with each other without conflict.
Wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, and in which there is shown by way of illustration only and not in any way limiting the scope of the invention; for a better understanding of the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc., indicating directions or positional relationships based on the directions or positional relationships shown in the drawings, it is only for convenience of description and simplification of description, but it is not intended to indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore, the terms describing the positional relationships in the drawings are only used for illustrative purposes and are not to be construed as limiting the present invention, and those skilled in the art can understand the specific meanings of the terms according to specific situations.
Referring to FIG. 1, the reference numbers in the drawings denote: the optical fiber sensor comprises a plastic-clad optical fiber 1, a first SPR sensing area 2, a second SPR sensing area 3, a white light source 4, a visible light spectrometer 5 and a computer 6.
The utility model relates to an optical fiber SPR curvature sensor with direction recognition, the cladding diameter of the related plastic cladding multimode optical fiber 1 is 150 μm, the fiber core diameter is 125 μm, the length is about 2m, the optical fiber SPR curvature sensor is used for transmitting the light of a white light source 4 and injecting the light into a first SPR sensing area 2 and a second SPR sensing area 3 in sequence, and the optical fiber SPR curvature sensor is also used for transmitting the light output by the first SPR sensing area 2 and the second SPR sensing area 3 into a visible light spectrometer 5; the first SPR sensing area 2 and the second SPR sensing area 3 are used for measuring the curvature of the structure, the length of the sensing areas is 2cm, and the distance between the two sensing areas is 50 cm; the visible light spectrometer 5 is used for collecting and demodulating optical signals, and the computer 6 is used for analyzing and processing the reflection spectrum data transmitted by the visible light spectrometer 5 by using software. The wavelength range of the white light source 4 is 500-1100nm, the spectrometer 5 is a visible light spectrometer, and the wavelength range is 500-1100 nm.
The concrete connection mode is as follows: the left end of the plastic cladding multimode fiber 1 is connected with a white light source 4, the right end of the plastic cladding multimode fiber 1 is connected with a visible light spectrometer 5, and the visible light spectrometer 5 is connected with a calculator 6.
The specific manufacturing method comprises the following steps:
(1) prefabricating a bare fiber area, taking a section of plastic cladding multimode fiber with the length of 2m, wherein the fiber core diameter of the plastic cladding multimode fiber is 125 micrometers, the cladding diameter is 140 micrometers, stripping the plastic cladding and a coating layer by using Miller pliers at a position 1m away from one end of the plastic cladding multimode fiber, exposing the fiber core with the length of 2cm, placing the stripped plastic cladding fiber in a U-shaped quartz groove, exposing one half of the outer surface of the fiber core in the air, contacting the outer surface of the fiber core of the other half of the fiber with the inner wall of the U-shaped quartz groove, fixing by using glue, placing the U-shaped quartz groove under a metal target of a small-sized direct current plasma sputtering instrument, and enabling a groove opening of the U-shaped quartz groove to be vertically upward;
(2) gold film was plated at 8X 10 using a small plasma sputter (ETD-2000, with a film thickness monitor connected to the outside)-2Loading 10mA sputtering current under the mbar vacuum stability, vertically descending metal particles from a metal target positioned right above the U-shaped quartz groove, and finally plating a gold film with the thickness of 50nm on the semicircular surface of the optical fiber core exposed in the air;
(3) taking out the coated optical fiber, taking out the U-shaped quartz groove from the small-sized plasma sputtering instrument, immersing the U-shaped quartz groove into a debonding agent, dissolving the debonding agent to remove the glue, taking down the optical fiber coated with the metal semicircular mask, and placing the optical fiber in a clamp of an optical fiber coating machine;
(4) coating and recovering bare fibers, preloading a low-refractive-index ultraviolet curing adhesive with the refractive index of 1.340RIU after curing in an optical fiber coating machine, coating and curing the optical fibers coated with the metal semicircular sensing film with the low refractive index, wherein the cured ultraviolet curing adhesive has the refractive index suitable for being used as a new coating of the sensing area, recovering the diameters of the bare fibers stripped of the optical fiber coating and the coating area to 250 mu m, remolding and recovering the plastic coating and the coating, and finishing the manufacture of the SPR sensing area 2;
(5) the sensing area 3 is manufactured by the same steps on the same section of plastic cladding optical fiber at a distance of 50cm from the sensing area 2, and when the naked fiber is coated and recovered, the optical fiber coating machine uses low-refractive-index ultraviolet curing glue with the refractive index of 1.370 RIU.
The specific using method comprises the following steps: the left end of the whole section of plastic cladding multimode fiber 1 is stripped of a plastic cladding and a coating by a Miller clamp, the end face is cut to be smooth by a fiber cutter, the plastic cladding multimode fiber 1 is inserted into a bare fiber adapter and then is connected with a white light source 4, light emitted by the light source is injected into a first SPR sensing area 2 and a second SPR sensing area 3 of a sensing film coated with media with different refractive indexes through the plastic cladding multimode fiber 1, the plastic cladding and the coating at the right end of the plastic cladding multimode fiber 1 are stripped and the end face is cut to be smooth, the plastic cladding and the coating are inserted into the bare fiber adapter and then are connected with a visible light spectrometer 5, the spectrometer collects spectral data and sends the spectral data into a computer 6 for real-time processing, the first SPR sensing area 2 and the second SPR sensing area 3 are placed in a building structure with deformation, because the refractive index of the first low refractive index coating 2-3 is, the short-wavelength resonance valley represents the first SPR sensing area 2, the long-wavelength resonance valley represents the second SPR sensing area 3, and the curvature simultaneous measurement and the bending direction judgment of two points are realized by two channels through two parameters of resonance wavelength and resonance valley depth.
The optical fiber SPR curvature sensor with direction identification realizes curvature measurement through two parameters of SPR resonance wavelength and resonance valley depth, transmitted light is totally reflected at the interface between the fiber core and the fiber cladding, the included angle between the light and the normal of the interface is called total reflection angle, according to the condition of exciting surface plasma resonance, the SPR resonance peak is related to the total reflection angle, the total reflection angle is changed, the position of SPR resonance valley on the spectrum is shifted, when the optical fiber sensing area is bent, the total reflection angle in the optical fiber core is changed, the position of an SPR resonance valley on the spectrum is also shifted, and as the bending curvature of the optical fiber increases, the larger the amount of change in the total reflection angle within the core of the optical fiber, the larger the amount of spectral shift of the SPR resonance valley, therefore, the bending curvature of the optical fiber can be determined by the offset of the SPR resonance peak, so that the SPR resonance valley wavelength sensing curvature is realized; as the bending curvature of the optical fiber sensing area is increased, the intensity of an evanescent field at the interface of a fiber core and a cladding layer is increased, the intensity of the evanescent field leaked from the fiber core of the optical fiber is higher, the depth of a resonance valley of the SPR is related to the intensity of the evanescent field, and the depth sensing curvature of the resonance valley of the SPR is further realized.
The optical fiber SPR curvature sensor with direction recognition realizes the judgment of the bending direction through the moving direction of the SPR resonance wavelength, when an optical fiber sensing area is bent, the total reflection angle of transmission light rays at the inner side of a bending part is increased, the total reflection angle at the outer side of the bending part is reduced, the resonance wavelength of SPR is related to the total reflection angle, when an SPR sensing semicircular surface sensing film is arranged at the inner side of the bending part, the SPR resonance wavelength moves towards the long wavelength direction, when the SPR sensing semicircular surface sensing film is arranged at the outer side of the bending part, the SPR resonance wavelength moves towards the short wavelength direction, and then the bending direction is judged through the moving direction of the SPR resonance valley wavelength.
The principle of the using method is that the track equation expression of the point (x, y, z) on the surface of the fiber core of the bent optical fiber is as follows:
wherein R represents the bend radius of the optical fiber and R represents the core radius;
when the transmitted light enters the bent fiber from the point (0, R,0) of the flat fiber, the time tnPoint (x) incident on the surface of the core of the bent optical fibern,yn,zn) The expression of the parameter equation is as follows:
wherein α and β represent
And xoz plane and
the included angle with the xoy plane;
further, substituting expression (2) into expression (1) yields:
the transmitted light is incident on the bent optical fiber from a straight optical fiber for a time tnThe transmission light is incident to the surface of the fiber core of the bent optical fiber for the first time, then the transmission light is totally reflected on the surface of the fiber core of the bent optical fiber and is continuously transmitted forwards along the bent optical fiber until the transmission light is emergent from the bent optical fiber; normal vector of transmission light on plane of first total reflection point on surface of fiber core of bent optical fiber
The expression of (a) is:
the expression of the total reflection angle theta of the transmission light at the first reflection point on the surface of the fiber core of the bent optical fiber is as follows:
the vector characterizing the propagation direction of the transmitted light
With component parallel to normal direction
And a component perpendicular to the normal direction
Expressing, according to the law of reflection, the components after passing through the point of reflection
Constant magnitude, opposite direction, component
The size and direction are not changed; and with the first reflection point as a starting point, transmitting light to continue to propagate forwards in the fiber core of the bent optical fiber, and calculating the reflection angles of other reflection points on the surface of the fiber core of the bent optical fiber by using MATLAB simulation software.
Fig. 1 is a schematic diagram of the system of the present invention. Light emitted by a white light source 4 is sequentially injected into a first SPR sensing area 2 and a second SPR sensing area 3 through a plastic cladding multimode fiber, total reflection and surface plasma resonance occur at the interface of a fiber core of the fiber, a first semicircular surface SPR sensing film 2-2 and a second semicircular surface SPR sensing film 3-2, reflected light signals enter a visible light spectrometer 5 through the plastic cladding multimode fiber 1, the spectrometer 5 transmits transmitted reflection spectra to a computer 6, and MATLAB simulation software is used for processing data in real time, so that reflection spectral curves with different curvatures can be obtained.
Fig. 4 is a schematic diagram of the mathematical model coordinates of the reflection point of the internal beam of the bent optical fiber according to the present invention. The O point is the coordinate axis origin and is the centre of a circle of bent optic fibre, R represents the bending radius of optic fibre, R represents optic fibre core radius, the central axis of optic fibre core is located the xoy plane, the central axis along optic fibre core and the curved surface that is perpendicular to the xoy plane are the neutral plane of bent optic fibre, the neutral plane of bent optic fibre is neither stressed nor receive the pulling force, use neutral plane as the limit, the one side half cylinder that is close to the centre of a circle is the bent optic fibre inboard, the one side half cylinder of keeping away from the centre of a circle is the bent optic fibre outside.
Fig. 5 is a schematic diagram of curves between the reflection angle θ and the projection distance L of the transmission light of the present invention in different propagation directions. The projection distance L is the projection of the shortest distance r between the reflection point P of the transmission light on the surface of the fiber core and the central axis of the fiber core of the optical fiber on the xoy plane. In the figure, (a) is an angle α of 0 ° when the light is transmitted; the beta is 9 degrees of propagation direction and enters the bent optical fiber, and the reflection angle theta and the projection distance L are curves under different bending curvatures; in the figure, (b) is an angle α of 9 ° when the light is transmitted; a curve of a reflection angle theta and a projection distance L under different bending curvatures enters the bent optical fiber along a propagation direction of 27 degrees; the curves under different curvatures are intersected at the position where L is 0, and the reflection point is positioned at the junction of the surface of the fiber core and a neutral plane; l <0 means that the angle of total reflection is inside the bent fiber, which increases with increasing curvature; l >0 indicates that the angle of total reflection is outside the bent fiber, which decreases with increasing curvature.
Finally, the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the scope of the claims of the present invention.
Claims (4)
1. A fiber SPR curvature sensor with direction discrimination, comprising:
the optical fiber sensor comprises a plastic cladding multimode optical fiber (1), and a first SPR sensing area (2) and a second SPR sensing area (3) which are sequentially manufactured on the plastic cladding multimode optical fiber;
the plastic cladding multimode fiber (1) consists of a first quartz fiber core (1-1), a plastic cladding (1-2) annularly cladding the surface of the first quartz fiber core and a coating layer (1-3) annularly cladding the surface of the plastic cladding;
the first SPR sensing area (2) consists of a second quartz fiber core (2-1), a first semicircular surface SPR sensing film (2-2) coated on the surface of the second quartz fiber core and a first low-refractive-index coating layer (2-3) coated on the outermost side in an annular mode;
the second SPR sensing area (3) consists of a third quartz fiber core (3-1), a second semicircular surface SPR sensing film (3-2) coated on the surface of the third quartz fiber core and a second low-refractive-index coating layer (3-3) coated on the outermost side in an annular mode;
the optical fiber SPR curvature sensor with the direction recognition function can measure curvature and judge the bending direction through two parameters of SPR resonance wavelength and resonance valley depth;
the refractive index of the first low-refractive-index coating layer (2-3) is lower than that of the second low-refractive-index coating layer (3-3).
2. A direction-discriminating fiber SPR curvature sensor as claimed in claim 1, wherein: the plastic cladding multimode fiber (1) is characterized in that the center of the plastic cladding multimode fiber is a first quartz fiber core made of pure quartz material with the diameter of 125 mu m, the outer side of the first quartz fiber core is annularly and tightly wrapped with a low-refractive-index plastic cladding to the diameter of 150 mu m and 200 mu m, the low-refractive-index plastic cladding is made of low-refractive-index ultraviolet curing glue, and the outer side of the plastic cladding is annularly and tightly wrapped with a common fiber coating to the diameter of 250 mu m.
3. A direction-discriminating fiber SPR curvature sensor as claimed in claim 1, wherein: the first semicircular surface SPR sensing film (2-2) is a semicircular film which is tightly coated on one side of the second quartz fiber core, is 30-60 nm thick and is made of gold, silver or copper, and is plated on one side of the surface of the fiber core by utilizing a direct current plasma sputtering or magnetron sputtering process to form a semicircle.
4. A direction-discriminating fiber SPR curvature sensor as claimed in claim 1, wherein: the first SPR sensing area (2) and the second SPR sensing area (3) are 10mm-20mm in length, wherein the refractive index of the first low-refractive-index coating layer (2-3) on the outermost side of the first SPR sensing area (2) is 1.335-1.355RIU, and the refractive index of the second low-refractive-index coating layer (3-3) on the outermost side of the second SPR sensing area (3) is 1.365-1.385 RIU.
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| CN114608636A (en) * | 2022-03-11 | 2022-06-10 | 重庆三峡学院 | S-shaped optical fiber cladding SPR sensor and manufacturing and using methods thereof |
| CN114608636B (en) * | 2022-03-11 | 2023-08-04 | 重庆三峡学院 | S-shaped optical fiber cladding SPR sensor and manufacturing and using methods thereof |
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