Multi-core optical fiber sensor

Abstract

The invention provides a multi-core optical fiber sensor which comprises a multi-core optical fiber and a deformation sensitive area, the deformation sensitive area is an area where a spiral dislocation long-period grating is located, and the spiral dislocation long-period grating comprises multiple sections of multi-core optical fibers which sequentially rotate by a fixed angle anticlockwise or clockwise in the axial direction of the optical fiber and are sequentially welded; the super-continuum spectrum light source is connected with one end of the multi-core optical fiber through the input single-mode optical fiber and the fan-in device; and the spectrograph is connected with the other end of the multi-core optical fiber through the output single-mode optical fiber and the fan-out device. The optical fiber sensor has the advantages of small size, high integration level and the like, can be applied to complex deformation multi-parameter sensing by demodulating the sensing characteristics of a plurality of fiber cores, can manufacture a long-period grating in a spiral dislocation welding mode, can effectively reduce the cost compared with laser direct writing, phase mask and other modes, and only exists in the optical fiber in a microstructure forming the sensor, so that the cost is reduced. The sensor has high mechanical strength and strong applicability.

Description

Technical Field

[0001] The present invention relates to the technical field of optical sensors, and in particular to a multi-core optical fiber sensor. Background Art

[0002] Deformation refers to the change in shape or size of an object under the action of external force or stress. Detecting object deformation is crucial in structural safety, medical diagnosis, robot perception and virtual reality. It can ensure the safety of engineering structures, assess health conditions, improve the intelligent perception and adaptability of robots, and achieve immersive virtual reality experience. With the increasing requirements for the perception of precision structural deformation, researching high-sensitivity, high-resolution, and high-integration sensor detection technology and developing corresponding sensor detection instruments have become important topics in the current sensor detection field.

[0003] Optical fiber has the advantages of small size, anti-electromagnetic interference, and long-distance transmission. In the field of deformation sensing, its flexibility and bendability enable it to adapt to structural surfaces of various shapes and curvatures. The small size of the optical fiber enables it to be flexibly embedded in tiny structures without causing obvious interference or damage. By inferring the deformation of the structure through non-contact measurement of changes in optical signals, the influence of the sensor itself on the structure can be avoided, ensuring the accuracy and precision of the measurement. In addition, optical fiber sensors have high sensitivity and a wide dynamic range, can detect small deformation changes, and adapt to a wide range of deformations. They have advantages in monitoring small deformations, deformations or stress distributions of precision structures. Deformation sensors based on the principles of optical fiber long-period gratings, Bragg gratings, interferometers, etc. are known.

[0004] The existing Chinese patent application document with publication number CN109839693A discloses a periodic structure deformation type fiber Bragg grating device and its preparation method. The fiber Bragg grating device is composed of an input fiber, a microporous fiber and an output fiber, wherein the input fiber mainly comprises a core and a cladding, the output fiber mainly comprises a core and a cladding, and the microporous fiber mainly comprises a core, an air hole and a cladding. The air hole forms a fiber Bragg grating through periodic deformation, thereby realizing the modulation of the light wave transmitted by the microporous fiber, and realizing the lossy optical filtering or optical sensing function.

[0005] The microporous optical fiber in the prior art can adjust the transmission characteristics of the optical field inside the optical fiber by the number, size and position of the micropores, thereby enhancing the optical filtering or optical sensing capabilities of the periodic structure deformation type fiber grating. However, the sensor cannot monitor and identify multiple deformation parameters at the same time, is easily affected by environmental changes, has poor applicability, and needs to be improved. Summary of the invention

[0006] In view of the defects in the prior art, an object of the present invention is to provide a multi-core optical fiber sensor.

[0007] A multi-core optical fiber sensor provided by the present invention comprises a supercontinuum light source, an input single-mode optical fiber, a fan-in device, a multi-core optical fiber, a spiral dislocation long-period grating, a fan-out device, an output single-mode optical fiber and a spectrometer; the multi-core optical fiber comprises a deformation sensitive region, the deformation sensitive region is the region where the spiral dislocation long-period grating is located, the spiral dislocation long-period grating comprises a plurality of sections of multi-core optical fibers which are rotated counterclockwise or clockwise along the axial direction of the optical fiber by a fixed angle and are fused in sequence; the supercontinuum light source is connected to one end of the multi-core optical fiber through the input single-mode optical fiber and the fan-in device; the spectrometer is connected to the other end of the multi-core optical fiber through the output single-mode optical fiber and the fan-out device.

[0008] Preferably, the multi-core optical fiber comprises at least three cores deviating from the geometric center of the optical fiber, and the cladding diameter of the multi-core optical fiber is 80 to 300 μm.

[0009] Preferably, the spiral dislocation long period grating includes 3 to 10 sections of multi-core optical fiber.

[0010] Preferably, any section of the multi-core optical fiber forming the spiral spliced ​​long-period grating has the same length.

[0011] Preferably, the length of any section of the multi-core optical fiber forming the spiral spliced ​​long-period grating is 300 to 2000 μm.

[0012] Preferably, the fixed rotation angle is 1° to 8°.

[0013] Preferably, a part of the light wave transmitted through the spiral dislocation long-period grating will be transmitted forward in the form of cladding mode, and its resonant wavelength λ can be expressed as:

[0014]

[0015] in, represents the effective mode refractive index of the multi-core optical fiber base film at wavelength λ, represents the effective mode refractive index of the m-order cladding mode of the multi-core fiber at wavelength λ, and Λ is the period of the long-period grating.

[0016] Preferably, when the optical fiber is deformed, the phase matching condition of the optical fiber is:

[0017]

[0018] Where λ represents the resonant wavelength, represents the effective mode refractive index of the multi-core optical fiber base film at wavelength λ, represents the effective mode refractive index of the m-order cladding mode of the multi-core optical fiber at wavelength λ, Λ is the period of the long-period grating, and D represents the deformation.

[0019] Due to the mode dispersion and waveguide dispersion of the optical fiber, the above formula can be further written as:

[0020]

[0021]

[0022] where γ m is the waveguide dispersion coefficient of the m-th order cladding mode, is the deformation sensitivity, η co and η cl is the elastic-optical coefficient of the fiber core and cladding, and the deformation sensitivity of the long-period grating is related to γ m and Related to, where γ m It is related to the period Λ and mode order of the long-period grating.

[0023] Preferably, the length of the spiral dislocation long period grating is 1 to 20 mm. When deformation sensing is performed, the sensing test area is a deformation sensitive area, and the deformation sensitive area needs to cover the spiral dislocation long period grating.

[0024] Preferably, the deformation sensing parameters that can be realized by the multi-core optical fiber sensor include one or more of optical fiber stretching, compression, torsion and bending.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention uses multi-core optical fiber as a sensing element, which has the advantages of small size and high integration. By demodulating the sensing characteristics of multiple cores, it can be applied to complex deformation multi-parameter sensing, and uses spiral staggered welding to make long-period gratings. Compared with laser direct writing and phase mask plates, the cost can be effectively reduced. The microstructure forming the sensor only exists inside the optical fiber. The sensor has high mechanical strength and strong applicability.

[0027] 2. The present invention forms a long-period grating deformation sensor by spirally splicing multiple core optical fibers. This structure is more sensitive to changes in stress and shear force on the optical fiber, and the corresponding sensor has a higher sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0029] Figure 1 This is a schematic diagram of a deformation sensing device based on a multi-core optical fiber spiral splicing type long period grating, which is mainly embodied in the present invention;

[0030] Figure 2The present invention mainly embodies the structure of a multi-core optical fiber spiral splicing long period grating.

[0031] As shown in the figure:

[0032] Supercontinuum light source 1 Fan-out device 6

[0033] Input single mode fiber 2 Output single mode fiber 7

[0034] Fan-in device 3 Spectrometer 8

[0035] Multi-core optical fiber 4 Deformation sensitive area 9

[0036] Spiral staggered long period grating 5 DETAILED DESCRIPTION

[0037] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0038] like Figure 1 and Figure 2 As shown, a multi-core optical fiber sensor provided by the present invention is a long-period grating deformation sensor based on a multi-core optical fiber 4 spirally spliced, comprising a supercontinuum light source 1, an input single-mode optical fiber 2, a fan-in device 3, a multi-core optical fiber 4, a spiral dislocation long-period grating 5, a fan-out device 6, an output single-mode optical fiber 7 and a spectrometer 8. The multi-core optical fiber 4 comprises a deformation sensitive region 9, which is the region where the spiral dislocation long-period grating 5 is located, and the spiral dislocation long-period grating 5 comprises a plurality of sections of multi-core optical fibers 4 which are rotated counterclockwise or clockwise along the axial direction of the optical fiber at a fixed angle and fused in sequence. The supercontinuum light source 1 is connected to one end of the multi-core optical fiber 4 through the input single-mode optical fiber 2 and the fan-in device 3; the spectrometer 8 is connected to the other end of the multi-core optical fiber 4 through the output single-mode optical fiber 7 and the fan-out device 6.

[0039] Specifically, each section of multi-core optical fiber 4 has the same geometric parameters, the multi-core optical fiber 4 includes at least three cores that deviate from the geometric center of the optical fiber, and the cladding diameter of the multi-core optical fiber 4 is 80 to 300 μm. The spiral dislocation long period grating 5 includes 3 to 10 sections of multi-core optical fiber 4, and the length of any section of multi-core optical fiber 4 forming the spiral splicing type long period grating is the same, and the length of any section of multi-core optical fiber 4 forming the spiral splicing type long period grating is 300 to 2000 μm, and the rotation fixed angle is 1° to 8°. The optical fiber fusion splicer can select 100P, 100P+ or other fusion splicing equipment with a spiral program.

[0040] Furthermore, the length of the spiral dislocation long period grating 5 is 1 to 20 mm. When deformation sensing is performed, the sensing test area is the deformation sensitive area 9, and the deformation sensitive area 9 needs to cover the spiral dislocation long period grating 5. The deformation sensing parameters that can be achieved based on the multi-core optical fiber 4 spiral splicing type long period grating deformation sensor include one or more of optical fiber stretching, compression, torsion and bending.

[0041] The deformation sensitive area 9 of the multi-core optical fiber 4 is the area where the spiral dislocation long-period grating 5 of the multi-core optical fiber 4 is located. The sensor is mainly used for microstructure deformation sensing. Its working principle is: the mode field mismatch generated when the multi-core optical fiber 4 is dislocated causes a part of the light transmitted in the core to enter the cladding. The dislocation fusion of multiple sections of the multi-core optical fiber 4 produces periodic refractive index modulation, so that light with a specific wavelength enters the cladding and is transmitted forward in the form of a high-order cladding mode. Its wavelength meets the phase matching condition, while the rest of the light is still transmitted in the form of the core base film to form a long-period grating. Due to the different elastic-optical coefficients of the core and the cladding, when the optical fiber is deformed, the change in the difference in the mode effective refractive index between the core base film and the cladding high-order mode causes the resonance trough of the long-period grating to drift. By monitoring the changes in the resonance trough, the deformation can be perceived and measured. Since the geometric distributions of different cores of the multi-core optical fiber 4 are different, the corresponding optical fibers have differentiated spectral change characteristics due to different deformation degrees under shear force or stress. By monitoring and recording the response functions of different cores of the optical fiber under various deformation states and solving each response function, the fitting function of the spectral change of the optical fiber under different deformation states can be obtained, thereby realizing multi-parameter deformation sensing.

[0042] This application uses bending and torsion sensing as an example for explanation: when the optical fiber is bent, the core close to the bending direction and the core far from the bending direction have different deformation amounts when the curvature of the optical fiber changes at the same time, and the corresponding transmission spectrum of the spiral dislocation long period grating 5 of each core is different; similarly, when the optical fiber is twisted, the core close to the geometric center of the optical fiber and the core far from the geometric center of the optical fiber have different deformation amounts when the torsion of the optical fiber changes at the same time, and the corresponding transmission spectrum of the spiral dislocation long period grating 5 of each core is different. By measuring the transmission spectrum of each core of the multi-core optical fiber 4 with the change of torsion and curvature, the response function of each core with respect to torsion and curvature is obtained, and the characteristic spectrum of each core of the optical fiber under different torsion and bending conditions can be obtained by solving each group of response functions. Conversely, the size and direction of the torsion and curvature of the optical fiber can be judged according to the transmission spectrum of each core, thereby realizing the simultaneous measurement of torsion and bending.

[0043] The sensing area of ​​the deformation sensor based on the multi-core optical fiber 4 helical dislocation long period grating 5 of this embodiment is the area where the long period grating is located. A part of the light wave transmitted through the long period fiber grating will be transmitted forward in the form of cladding mode, and its resonant wavelength λ can be expressed as:

[0044]

[0045] in, represents the effective mode refractive index of the 4-base coating of the multi-core optical fiber at wavelength λ, represents the effective mode refractive index of the 4m-order cladding mode of the multi-core fiber at wavelength λ, and Λ is the period of the long-period grating.

[0046] According to elastic mechanics and the elasto-optic effect, when the optical fiber is deformed, the long-period grating is stretched or compressed under the action of stress or shear force, resulting in a change in the grating period. At the same time, due to the different elasto-optic coefficients of the core and cladding materials of the multi-core optical fiber 4, the effective refractive index difference of the core-cladding mode will change with the deformation of the optical fiber. At this time, the phase matching condition of the optical fiber can be written as:

[0047]

[0048] Where D is the deformation amount. When the optical fiber is deformed, the effective refractive index of the core and cladding modes changes due to the elasto-optical effect of the quartz material. Due to the mode dispersion and waveguide dispersion of the optical fiber, the above formula can be further written as:

[0049]

[0050]

[0051] where γ m is the waveguide dispersion coefficient of the m-th order cladding mode, is the deformation sensitivity, η co and η cl is the elastic-optical coefficient of the fiber core and cladding, and the deformation sensitivity of the long-period grating is related to γ m and Related to, where γ m It is related to the period Λ and mode order of the long-period grating.

[0052] In the description of the present application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0053] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A multi-core optical fiber sensor, characterized in that: It comprises a supercontinuum light source (1), an input single-mode optical fiber (2), a fan-in device (3), a multi-core optical fiber (4), a spiral dislocation long-period grating (5), a fan-out device (6), an output single-mode optical fiber (7) and a spectrometer (8); The multi-core optical fiber (4) comprises a deformation sensitive region (9), wherein the deformation sensitive region (9) is a region where a spiral dislocation long period grating (5) is located, wherein the spiral dislocation long period grating (5) comprises a plurality of sections of multi-core optical fibers (4) which are rotated counterclockwise or clockwise at a fixed angle in sequence along the axial direction of the optical fiber and are fused in sequence; The supercontinuum light source (1) is connected to one end of a multi-core optical fiber (4) via an input single-mode optical fiber (2) and a fan-in device (3); The spectrometer (8) is connected to the other end of the multi-core optical fiber (4) via an output single-mode optical fiber (7) and a fan-out device (6).

2. The multi-core optical fiber sensor according to claim 1, characterized in that: The multi-core optical fiber (4) comprises at least three fiber cores that are offset from the geometric center of the optical fiber, and the cladding diameter of the multi-core optical fiber (4) is 80 to 300 μm.

3. The multi-core optical fiber sensor according to claim 1, characterized in that: The spiral dislocation long-period grating (5) comprises 3 to 10 sections of multi-core optical fiber (4).

4. The multi-core optical fiber sensor according to claim 3, characterized in that: The lengths of any section of the multi-core optical fiber (4) forming the spiral spliced ​​long-period grating are the same.

5. The multi-core optical fiber sensor according to claim 3, characterized in that: The length of any section of the multi-core optical fiber (4) forming the spiral spliced ​​long-period grating is 300 to 2000 μm.

6. The multi-core optical fiber sensor according to claim 1, characterized in that: The fixed rotation angle is 1° to 8°.

7. The multi-core optical fiber sensor according to claim 1, characterized in that: A part of the light wave transmitted through the spiral dislocation long period grating (5) will be transmitted forward in the form of cladding mode, and its resonant wavelength λ can be expressed as: in, represents the effective mode refractive index of the base film of the multi-core optical fiber (4) at wavelength λ, represents the effective mode refractive index of the m-order cladding mode of the multi-core optical fiber (4) at wavelength λ, and Λ is the period of the long-period grating.

8. The multi-core optical fiber sensor according to claim 7, characterized in that: When the optical fiber is deformed, the phase matching condition of the optical fiber is: Where λ represents the resonant wavelength, represents the effective mode refractive index of the base film of the multi-core optical fiber (4) at wavelength λ, represents the effective mode refractive index of the m-order cladding mode of the multi-core optical fiber (4) at wavelength λ, Λ is the period of the long-period grating, and D represents the deformation amount. Due to the mode dispersion and waveguide dispersion of the optical fiber, the above formula can be further written as: where γ m is the waveguide dispersion coefficient of the m-th order cladding mode, is the deformation sensitivity, η co and η cl is the elastic-optical coefficient of the fiber core and cladding, and the deformation sensitivity of the long-period grating is related to γ m and Related to, where γ m It is related to the period Λ and mode order of the long-period grating.

9. The multi-core optical fiber sensor according to claim 1, characterized in that: The length of the spiral dislocation long period grating (5) is 1 to 20 mm. When deformation sensing is performed, the sensing test area is the deformation sensitive area (9), and the deformation sensitive area (9) needs to cover the spiral dislocation long period grating (5).

10. The multi-core optical fiber sensor according to claim 1, characterized in that: The deformation sensing parameters that can be realized by the spirally spliced ​​long-period grating deformation sensor based on the multi-core optical fiber (4) include one or more of the optical fiber stretching, compression, torsion and bending.

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