Optical fiber sensor and preparation method thereof

Abstract

The present invention provides an optical fiber sensor and a preparation method thereof. The optical fiber sensor comprises: one end of a first photonic crystal fiber is connected to a broadband light source, and the other end is connected to a first port of a circulator; one end of a second photonic crystal fiber is connected to a second port of the circulator; one end of a third photonic crystal fiber is connected to the other end of the second photonic crystal fiber; the third photonic crystal fiber is provided with a first fiber grating region and a second fiber grating region on the fiber core, and the side surface of the third photonic crystal fiber has a polishing region, and the polishing region is provided between the first grating region and the second grating region; one end of a fourth photonic crystal fiber is connected to the third port of the circulator, and the other end is connected to a spectrum analyzer. The optical fiber sensor disclosed by the present invention has high sensitivity and good environmental adaptability.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to an optical fiber sensor and a preparation method thereof. Background Art

[0002] In the process of ocean development, sound waves, as the only energy field that can be transmitted over long distances in seawater, are currently the most effective form of underwater information perception and processing. Fiber optic hydroacoustic sensors, as a receiving device for underwater sound waves, are extremely important detection instruments for ocean development. Compared with hydroacoustic sensors based on electrical devices, fiber optic hydroacoustic sensors have significant advantages such as anti-electromagnetic interference, low propagation loss, and good compatibility with optical fiber communication networks. They can be used in underwater earthquake monitoring, marine mineral resource exploration, marine fisheries, ocean current monitoring, pollution monitoring and other fields.

[0003] With the continuous decrease in the sound pressure of underwater target signals and the continuous increase in marine environmental noise, the difficulty of detecting underwater acoustic signals has increased rapidly. At the same time, marine oil and gas exploitation has extended from the continental shelf to the deep sea, and the requirements for the resolution of the stratigraphic structure obtained by acoustic detection are getting higher and higher, which puts higher requirements on the sensitivity and environmental adaptability of hydroacoustic sensors. The research and development of fiber-optic hydroacoustic sensors with strong environmental adaptability and high sensitivity plays an important role in improving the exploration and development of deep seabed resources, high-precision marine terrain observation, and silent submarine anti-submarine warfare. However, the sensitivity and environmental adaptability of existing fiber-optic hydroacoustic sensors cannot meet the requirements of practical applications. Summary of the invention

[0004] The object of the present invention is to provide an optical fiber sensor and a method for preparing the same, which can solve at least one of the above-mentioned technical problems. The specific solution is as follows:

[0005] The present invention provides an optical fiber sensor, comprising:

[0006] Broadband light source;

[0007] A first photonic crystal fiber and a second photonic crystal fiber, wherein one end of the first photonic crystal fiber is connected to the broadband light source, and the other end is connected to the first port of the circulator; one end of the second photonic crystal fiber is connected to the second port of the circulator;

[0008] A third photonic crystal fiber, one end of which is connected to the other end of the second photonic crystal fiber; wherein the third photonic crystal fiber is provided with a first fiber grating region and a second fiber grating region on a core, and a side surface of the third photonic crystal fiber has a polishing region, which is provided between the first grating region and the second grating region;

[0009] A fourth photonic crystal fiber, one end of which is connected to the third port of the circulator, and the other end of which is connected to the spectrum analyzer.

[0010] Optionally, the polishing zone includes a polishing plane zone, a first polishing transition zone and a second polishing transition zone, the plane where the polishing plane zone is located is parallel to the core of the third photonic crystal fiber, and the first polishing transition zone and the second polishing transition zone are relatively arranged at two ends of the polishing plane zone.

[0011] Optionally, the total length of the polishing area is 15-70 mm, the length of the polishing plane area is 10-50 mm, and the lengths of the first polishing transition area and the second polishing transition area are respectively in the range of 5-15 mm.

[0012] Optionally, the end surfaces where the first polishing transition zone and the second polishing transition zone are located are curved.

[0013] Optionally, the radial projection lengths of the first polished transition zone and the second polished transition zone on the third photonic crystal fiber are 40-60 um.

[0014] Optionally, the radial projection lengths of the first polished transition zone and the second polished transition zone in the third photonic crystal fiber are 56 um or 58 um.

[0015] Optionally, an axial length between the centers of the first fiber grating region and the second fiber grating region is 1-80 mm.

[0016] Optionally, the diameter of the third photonic crystal fiber is 125 um.

[0017] The present invention also provides a method for preparing an optical fiber sensor, comprising the following steps:

[0018] Providing a first photonic crystal fiber, a second photonic crystal fiber, a third photonic crystal fiber and a fourth photonic crystal fiber;

[0019] Polishing the side surface of the third photonic crystal fiber to form a polishing area;

[0020] A first fiber grating region and a second fiber grating region are fabricated on the core of the third photonic crystal fiber, wherein the polishing region is located between the first fiber grating region and the second fiber grating region to form a side-polished fiber grating Fabry-Perot cavity structure;

[0021] The broadband light source, the first photonic crystal fiber, a circulator, the second photonic crystal fiber, the third photonic crystal fiber, the fourth photonic crystal fiber and a spectrum analyzer are sequentially connected to obtain the optical fiber sensor.

[0022] Optionally, polishing the side surface of the third photonic crystal fiber to form a polishing area includes:

[0023] The cladding on the side surface of the third photonic crystal fiber is polished to form a polished plane area, a first polished transition area and a second polished transition area, wherein the plane where the polished plane area is located is parallel to the core of the third photonic crystal fiber, and the first polished transition area and the second polished transition area are relatively arranged at two ends of the polished plane area.

[0024] Compared with the prior art, the above solution of the embodiment of the present invention has at least the following beneficial effects:

[0025] 1. Use photonic crystal fiber as the sensing platform. The sensitivity of optical fiber sensors is closely related to the material and structure of the optical fiber. Photonic crystal fiber introduces air holes in the optical fiber, which greatly reduces its effective Young's modulus. It is more sensitive to pressure than ordinary optical fiber, which can improve the sensitivity of the sensor;

[0026] 2. Adopt fiber grating Fabry-Perot cavity structure (FBG-FP). FBG-FP is a double grating structure that inherits many advantages of FBG, such as easy manufacturing and excellent wavelength division multiplexing capability. Compared with other FP structures, it can greatly reduce the number of couplers and fusion points, thereby simplifying the manufacturing process of the optical fiber sensing system;

[0027] 3. Use side polishing to process the optical fiber. When the FBG-FP cavity is used for sensing, there is inherent cross-interference between the optical fiber in the cavity and the grating optical fiber. The present invention uses side polishing technology to process the optical fiber in the FBG-FP cavity, polishing off a portion of the cladding of the cylindrical optical fiber in the FBG-FP cavity, reducing the effective Young's modulus of the optical fiber in the cavity, making the sensitivity of the optical fiber in the cavity different from that of the grating optical fiber, thereby reducing interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings herein are incorporated into and constitute a part of the specification, showing embodiments consistent with the present invention, and together with the specification, are used to explain the principles of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0029] Figure 1 A schematic structural diagram of an optical fiber sensor provided by the present invention is shown;

[0030] Figure 2 Shows Figure 1 A schematic cross-sectional view of the third photonic crystal fiber in the optical fiber sensor along the axial direction;

[0031] Figure 3The invention shows a method for preparing an optical fiber sensor. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings, and "multiple" generally includes at least two.

[0034] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0035] It should be understood that although the terms first, second, third, etc. may be used to describe the embodiments of the present invention, they should not be limited to these terms.

[0036] It should also be noted that the term "includes", "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, so that a commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprising a ..." do not exclude the existence of other identical elements in the commodity or device including the elements.

[0037] The present invention provides an optical fiber sensor. Figure 1 FIG. 2 shows a schematic diagram of the structure of an optical fiber sensor provided by an embodiment of the present invention. Figure 1 As shown, the optical fiber sensor comprises:

[0038] Broadband light source 1;

[0039] A first photonic crystal fiber 2 and a second photonic crystal fiber 6, wherein one end of the first photonic crystal fiber 2 is connected to the broadband light source 1, and the other end is connected to the first port of the circulator 3; one end of the second photonic crystal fiber 6 is connected to the second port of the circulator 3.

[0040] A third photonic crystal fiber 7, one end of which is connected to the other end of the second photonic crystal fiber 6; wherein the third photonic crystal fiber 7 is provided with a first fiber grating region 71 and a second fiber grating region 72 on a core 70, and a side surface of the third photonic crystal fiber 7 has a polishing region 73, and the polishing region 73 is arranged between the first grating region 71 and the second grating region 72;

[0041] A fourth photonic crystal fiber 4 , one end of which is connected to the third port of the circulator 3 , and the other end of which is connected to the spectrum analyzer 5 .

[0042] In the present invention, the first photonic crystal fiber 2, the second photonic crystal fiber 6, the third photonic crystal fiber 7, and the fourth photonic crystal fiber 4 can be photonic crystal fibers with the same characteristics, such as the same core diameter, or photonic crystal fibers with different characteristics. The diameter D2 of the third photonic crystal fiber ranges from 110 to 135 um. Optionally, the diameter D2 of the third photonic crystal fiber is 125 um.

[0043] The first photonic crystal fiber 2, the second photonic crystal fiber 6, the third photonic crystal fiber 7, and the fourth photonic crystal fiber 4 all have air holes 75, so that the core has a two-dimensional crystal structure arranged periodically. By changing the structure of the photonic crystal fiber and introducing air holes in the fiber, the effective Young's modulus of the fiber is greatly reduced, and the axial strain is increased, so that the sensitivity of the photonic crystal fiber to sound pressure is higher than that of ordinary optical fiber, and its core and cladding have the same thermal expansion coefficient, and have lower temperature sensitivity than ordinary optical fiber. Therefore, replacing ordinary optical fiber with photonic crystal fiber and applying it to underwater acoustic detection can improve the sensitivity and temperature stability of underwater acoustic sensors.

[0044] The first fiber grating region 71 and the second fiber grating region 72 are arranged on the core of the third photonic crystal fiber. Figure 2 As shown, a fiber grating Fabry-Perot cavity structure (FBG-FP) is formed. The present invention can achieve a full fiber sensing system by directly arranging the fiber grating on the optical fiber and forming a double grating structure, so that the underwater acoustic sensor probe encapsulated by this structure is small in size, has high reliability in complex environments, can reduce application costs, and is easy to achieve large-scale array multiplexing through wavelength division multiplexing and other methods. Compared with other Fabry-Perot structures, it avoids difficult welding, thereby simplifying the manufacturing of the sensing system.

[0045] The distance between the center of the first fiber grating area 71 and the center of the second fiber grating area 72 is greater than or less than or equal to the total length of the polishing area 73. In an embodiment of the present invention, the axial length L3 between the center of the first fiber grating area 71 and the center of the second fiber grating area 72 is 1-80 mm. Optionally, the length of L3 is 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 60 mm. The shortest distance L4 from the center of the first fiber grating area 71 to the edge of the polishing area is 0-10 mm; similarly, the shortest distance L4 from the center of the second fiber grating area 72 to the edge of the polishing area is 0-10 mm.

[0046] The polishing area 73 includes a polishing plane area 730, a first polishing transition area 731 and a second polishing transition area 732. The plane where the polishing plane area 730 is located is parallel to the core 70 of the third photonic crystal fiber 7. The first polishing transition area 731 and the second polishing transition area 732 are relatively arranged at the two ends of the polishing plane area. Optionally, the end faces where the first polishing transition area 731 and the second polishing transition area 732 are located are curved surfaces. Of course, in other optional embodiments, they can also be planes. The present invention uses side polishing technology to process the optical fiber in the fiber grating Fabry-Perot cavity structure and maintains the remaining part of the optical fiber unchanged. Under the same sound pressure, the polished part has a greater deformation than the unpolished part, thereby improving the sensitivity of the sensing system; in addition, side polishing makes the sensitivity of the optical fiber in the cavity and the grating optical fiber different, reducing the cross-interference between the optical fiber and the grating in the cavity inherent in the fiber grating Fabry-Perot cavity structure.

[0047] In the present invention, the depth D1 of the polishing zone is 40-60um. The depth of the polishing zone refers to the radial projection length of the first polishing transition zone 731 and the second polishing transition zone 732 in the third photonic crystal fiber. Optionally, the depth D1 is 56um or 58um.

[0048] The total length L0 of the polishing area is 15-70 mm, that is, the maximum distance between the first polishing transition area L2 and the second polishing transition area L2. The length L1 of the polishing plane area is 10-50 mm, and the lengths of the first polishing transition area L2 and the second polishing transition area L2 are 5-15 mm respectively. In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 15 mm, 5 mm, and 5 mm respectively.

[0049] In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 20 mm, 10 mm, and 5 mm, respectively.

[0050] In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 30 mm, 10 mm, and 10 mm, respectively.

[0051] In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 30 mm, 20 mm, and 5 mm, respectively.

[0052] In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 50 mm, 30 mm, and 10 mm, respectively.

[0053] In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 70 mm, 40 mm, and 15 mm, respectively.

[0054] In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 70 mm, 50 mm, and 10 mm, respectively.

[0055] In practical applications, the light emitted by the broadband light source 1 is coupled into the first photonic crystal fiber 2, the light in the first photonic crystal fiber 2 is output to the second photonic crystal fiber 6 through the circulator 3, the second photonic crystal fiber 6 inputs the light into the side-thrown fiber grating Fabry-Perot cavity structure, the reflected light passes through the circulator 3 and enters the fourth photonic crystal fiber 4, and is finally received and processed by the spectrum analyzer 5.

[0056] The optical fiber sensor provided by the present invention uses a photonic crystal fiber with higher sound pressure sensitivity than ordinary optical fiber as a sensing platform, and constructs a high-sensitivity FBG-FP cavity on the photonic crystal fiber to realize weak sound signal detection; in order to further enhance the sensitivity and reduce the cross-interference between the optical fiber in the cavity and the grating optical fiber, the optical fiber in the FBG-FP cavity is processed by side polishing technology to enhance the change of the optical fiber in the cavity under the same sound pressure. The optical fiber sensor of the present invention has the advantages of high sensitivity, low cost, good stability and environmental adaptability, easy miniaturization, etc., and is a feasible way to realize underwater acoustic detection in complex environments.

[0057] According to the above optical fiber sensor, the present invention also provides a method for preparing the optical fiber sensor, such as Figure 3 As shown, the method comprises the following steps:

[0058] S102, providing a first photonic crystal fiber, a second photonic crystal fiber, a third photonic crystal fiber and a fourth photonic crystal fiber;

[0059] In this step, the first photonic crystal fiber 2, the second photonic crystal fiber 6, the third photonic crystal fiber 7, and the fourth photonic crystal fiber 4 can be photonic crystal fibers with the same characteristics, such as the same core diameter, or photonic crystal fibers with different characteristics. The diameter D2 of the third photonic crystal fiber is 110-135um. Optionally, the diameter D2 of the third photonic crystal fiber is 125um.

[0060] The first photonic crystal fiber 2, the second photonic crystal fiber 6, the third photonic crystal fiber 7, and the fourth photonic crystal fiber 4 all have air holes 75, so that the core has a two-dimensional crystal structure arranged periodically. By changing the structure of the photonic crystal fiber and introducing air holes in the fiber, the effective Young's modulus of the fiber is greatly reduced, and the axial strain is increased, so that the sensitivity of the photonic crystal fiber to sound pressure is higher than that of ordinary optical fiber, and its core and cladding have the same thermal expansion coefficient, and have lower temperature sensitivity than ordinary optical fiber. Therefore, replacing ordinary optical fiber with photonic crystal fiber and applying it to underwater acoustic detection can improve the sensitivity and temperature stability of underwater acoustic sensors.

[0061] S104, performing polishing treatment on the side surface of the third photonic crystal fiber to form a polishing area;

[0062] In this step, a section of photonic crystal fiber is polished on the side to remove part of the cladding to form a polished area. In this embodiment, the side surface of the third photonic crystal fiber is polished to form a polished area, specifically including:

[0063] The cladding of the side surface of the third photonic crystal fiber is polished to form a polished plane area, a first polished transition area and a second polished transition area. The plane where the polished plane area is located is parallel to the core of the third photonic crystal fiber. The first polished transition area and the second polished transition area are relatively arranged at the two ends of the polished plane area. Optionally, the end faces where the first polished transition area 731 and the second polished transition area 732 are located are curved surfaces. Of course, in other optional implementations, they can also be planes.

[0064] The present invention uses the side polishing technology to process the optical fiber in the fiber Bragg Fabry-Perot cavity structure, and maintains the remaining part of the optical fiber unchanged. Under the same sound pressure, the polished part has a larger deformation than the unpolished part, thereby improving the sensitivity of the sensing system; in addition, the side polishing makes the sensitivity of the optical fiber in the cavity and the grating optical fiber different, reducing the cross-interference between the optical fiber and the grating in the cavity inherent in the fiber Bragg Fabry-Perot cavity structure.

[0065] In the present invention, the depth D1 of the polishing zone is 40-60um. The depth of the polishing zone refers to the radial projection length of the first polishing transition zone 731 and the second polishing transition zone 732 in the third photonic crystal fiber. Optionally, the depth D1 is 56um or 58um.

[0066] The total length L0 of the polishing area is 15-70 mm, that is, the maximum distance between the first polishing transition area L2 and the second polishing transition area L2. The length L1 of the polishing plane area is 10-50 mm, and the lengths of the first polishing transition area L2 and the second polishing transition area L2 are 5-15 mm respectively. In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 15 mm, 5 mm, and 5 mm respectively.

[0067] In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 20 mm, 10 mm, and 5 mm, respectively.

[0068] In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 30 mm, 10 mm, and 10 mm, respectively.

[0069] In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 30 mm, 20 mm, and 5 mm, respectively.

[0070] In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 50 mm, 30 mm, and 10 mm, respectively.

[0071] In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 70 mm, 40 mm, and 15 mm, respectively.

[0072] In an optional embodiment of the present invention, the lengths L0, L1, and L2 are 70 mm, 50 mm, and 10 mm, respectively.

[0073] S106, manufacturing a first fiber grating region and a second fiber grating region on the core of the third photonic crystal fiber, wherein the polishing region is located between the first fiber grating region and the second fiber grating region, to form a side-polished fiber grating Fabry-Perot cavity structure;

[0074] In this step, two first fiber grating regions and second fiber grating regions at a certain distance are formed in the side-cast region of the third photonic crystal fiber after side-casting by ultraviolet exposure, and a Fabry-Perot cavity is formed. The present invention can achieve a full-fiber sensing system by directly arranging the fiber grating on the optical fiber and forming a double grating structure, so that the underwater acoustic sensor probe encapsulated by this structure is small in size, has high reliability in complex environments, can reduce application costs, and is easy to realize large-scale array multiplexing through wavelength division multiplexing and other methods. Compared with other Fabry-Perot structures, it avoids difficult welding, thereby simplifying the manufacturing of the sensing system.

[0075] Wherein, the first fiber grating area 71 and the second fiber grating area 72 are arranged on the core of the third photonic crystal fiber. The distance between the center of the first fiber grating area 71 and the center of the second fiber grating area 72 is greater than or less than or equal to the total length of the polishing area 73. In an embodiment of the present invention, the axial length L3 between the center of the first fiber grating area 71 and the center of the second fiber grating area 72 is 1-80mm. Optionally, the length of L3 is 10mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, 60mm. The shortest distance L4 from the center of the first fiber grating area 71 to the edge of the polishing area is 0-10mm; similarly, the shortest distance L4 from the center of the second fiber grating area 72 to the edge of the polishing area is 0-10mm.

[0076] S108, sequentially connect a broadband light source, the first photonic crystal fiber, a circulator, a second photonic crystal fiber, a third photonic crystal fiber, a fourth photonic crystal fiber and a spectrum analyzer to obtain the optical fiber sensor.

[0077] In this step, the light emitted by the broadband light source is coupled into the first photonic crystal fiber, the light in the first photonic crystal fiber is output to the second photonic crystal fiber through the circulator, the second photonic crystal fiber inputs the light into the side-thrown fiber grating Fabry-Perot cavity structure, the reflected light passes through the circulator into the fourth photonic crystal fiber, and is finally received and processed by the spectrum analyzer.

[0078] The preparation method of the optical fiber sensor and the optical fiber sensor provided by the present invention have at least the following beneficial effects:

[0079] 1. Use photonic crystal fiber as the sensing platform. The sensitivity of optical fiber sensors is closely related to the material and structure of the optical fiber. Photonic crystal fiber introduces air holes in the optical fiber, which greatly reduces its effective Young's modulus. It is more sensitive to pressure than ordinary optical fiber, which can improve the sensitivity of the sensor;

[0080] 2. Use fiber grating Fabry-Perot cavity structure (FBG-FP). FBG-FP is a dual grating structure that inherits many advantages of FBG, such as easy manufacturing and excellent wavelength division multiplexing capability. Compared with other FP structures, it can greatly reduce the number of couplers and fusion points, thereby simplifying the manufacturing process of the optical fiber sensing system.

[0081] 3. Use side polishing to process the optical fiber. When the FBG-FP cavity is used for sensing, there is inherent cross-interference between the optical fiber in the cavity and the grating optical fiber. The present invention uses side polishing technology to process the optical fiber in the FBG-FP cavity, polishing off a portion of the cladding of the cylindrical optical fiber in the FBG-FP cavity, reducing the effective Young's modulus of the optical fiber in the cavity, making the sensitivity of the optical fiber in the cavity different from that of the grating optical fiber, thereby reducing interference.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An optical fiber sensor, characterized in that: include: Broadband light source; A first photonic crystal fiber and a second photonic crystal fiber, wherein one end of the first photonic crystal fiber is connected to the broadband light source, and the other end is connected to the first port of the circulator; one end of the second photonic crystal fiber is connected to the second port of the circulator; a third photonic crystal fiber, one end of which is connected to the other end of the second photonic crystal fiber; wherein the third photonic crystal fiber is provided with a first fiber grating region and a second fiber grating region on a core, and a side surface of the third photonic crystal fiber has a polishing region, The polishing area is arranged between the first fiber grating area and the second fiber grating area; a fourth photonic crystal fiber, one end of which is connected to the third port of the circulator, and the other end of which is connected to the spectrum analyzer; The polishing area includes a polishing plane area, a first polishing transition area and a second polishing transition area, the plane where the polishing plane area is located is parallel to the core of the third photonic crystal fiber, and the first polishing transition area and the second polishing transition area are relatively arranged at two ends of the polishing plane area; The end surfaces where the first polishing transition zone and the second polishing transition zone are located are curved surfaces; The total length of the polishing area is 15-70 mm, the length of the polishing plane area is 10-50 mm, and the lengths of the first polishing transition area and the second polishing transition area are 5-15 mm respectively; The radial projection length of the first polishing transition zone and the second polishing transition zone in the third photonic crystal fiber is 40-60um; The radial projection length of the first polishing transition zone and the second polishing transition zone in the third photonic crystal fiber is 56um or 58um; The axial length between the centers of the first fiber grating region and the second fiber grating region is 1-80 mm.

2. A method for preparing an optical fiber sensor, characterized in that: The method is used to prepare the optical fiber sensor as claimed in claim 1, comprising the following steps: Providing a first photonic crystal fiber, a second photonic crystal fiber, a third photonic crystal fiber and a fourth photonic crystal fiber; Polishing the side surface of the third photonic crystal fiber to form a polishing area; A first fiber grating region and a second fiber grating region are fabricated on the core of the third photonic crystal fiber, wherein the polishing region is located between the first fiber grating region and the second fiber grating region to form a side-polished fiber grating Fabry-Perot cavity structure; The broadband light source, the first photonic crystal fiber, a circulator, the second photonic crystal fiber, the third photonic crystal fiber, the fourth photonic crystal fiber and a spectrum analyzer are sequentially connected to obtain the optical fiber sensor.

3. The method according to claim 2, characterized in that The side surface of the third photonic crystal fiber is polished to form a polishing area, comprising: The cladding on the side surface of the third photonic crystal fiber is polished to form a polished plane area, a first polished transition area and a second polished transition area, wherein the plane where the polished plane area is located is parallel to the core of the third photonic crystal fiber, and the first polished transition area and the second polished transition area are relatively arranged at two ends of the polished plane area.

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