Optical fiber bundle Fabry-Perot sensor based on photothermal effect

Abstract

The invention discloses an optical fiber bundle Fabry-Perot sensor based on a photothermal effect, the sensor comprises an optical fiber bundle (1), a photothermal conversion material (2) and an optical fiber probe (3), the optical fiber bundle (1) comprises an excitation optical fiber (4), a sensing optical fiber (5), an optical fiber sleeve (6) and a filling material (7); a photo-thermal conversion material (2) is inscribed on the end face of an excitation optical fiber (4) through a holographic optical tweezers system, after excitation light (8) is focused on the photo-thermal conversion material (2), a photo-thermal effect is generated, bubbles (9) are generated in liquid, the position or shape of the bubbles (9) is changed due to the change of the flow speed, then the length of the Fabry-Perot interference cavity is changed, and the light intensity of the Fabry-Perot interference cavity is adjusted. The photoelectric detector (11) is used for detecting the change of the reflected signal (20) to realize flow velocity measurement, and the deviation or deformation of the bubble (9) reflects the flow velocity direction; the sensor can be used for multi-parameter real-time monitoring in the fields of industrial production, basic medicine, biological analysis and the like.

Description

(I) Technical field

[0001] The invention relates to an optical fiber bundle Fabry-Perot sensor based on photothermal effect, belonging to the field of optical fiber sensing. (II) Background technology

[0002] The principle of the photothermal effect is to use the phenomenon that a substance absorbs light energy under light, part of which is converted into heat energy and the other part into electrical energy. This phenomenon is due to the fact that after absorbing light energy, the electrons in the substance jump to a higher energy level, and then quickly fall back to the original energy level, while releasing heat and electrical energy. When light shines on an object, the atoms and molecules on the surface of the object absorb photon energy. The absorbed photon energy excites the atoms and molecules on the surface of the object, and the electrons jump from low energy levels to high energy levels, forming a photoexcited state. The photoexcited electrons will release heat energy in the form of heat energy in a very short time and conduct heat energy to the surrounding area. This heat conduction method is similar to heat conduction, but the heat conduction speed of the photothermal effect is faster, usually in the microsecond level. In some substances, the absorbed light energy will cause chemical reactions, such as the combination of oxygen and methane to produce carbon dioxide and water vapor, which will release a lot of heat energy. This phenomenon is also called photochemical reaction.

[0003] Fiber Fabry-Perot sensors are well known in the optical science community and have been used in many research fields such as physics and astrophysics for more than a century. It was first proposed by Cielo et al. and Petuchowski et al. in 1979, and Fabry-Perot interference was realized in 1981. The Fabry-Perot cavity is composed of two parallel lines, completely flat semi-reflecting mirrors, separated by a given gap. After the incident light beam enters the Fabry-Perot cavity, it will be reflected and transmitted at the front and rear end faces of the Fabry-Perot cavity, and the reflected light beams will meet and interfere. Fabry-Perot interference refers to the phenomenon of interference caused by the reflection and refraction of light in the optical fiber due to the uneven distribution of the refractive index of the optical fiber when the light propagates in the optical fiber. When there is a change in the physical quantity in the optical fiber, such as temperature, pressure, strain, etc., the refractive index of the optical fiber will change, thereby changing the characteristics of the Fabry-Perot interference, and then affecting the transmission and interference of the optical signal. The fiber Fabry-Perot sensor is a sensor based on optical principles, which uses the Fabry-Perot interference phenomenon in the optical fiber to achieve the measurement of physical quantities. The sensor has the advantages of high precision, high sensitivity, and strong anti-interference ability, and is widely used in industry, medical care, environmental protection and other fields.

[0004] Photoinitiators, also known as photosensitizers or photocuring agents, are a class of compounds that can absorb energy of a certain wavelength in the ultraviolet region (250-420nm) or visible light region (400-800nm), generate free radicals, cations, etc., and thus initiate monomer polymerization and cross-linking curing. After exposure to light, some monomers absorb photons to form an excited state. The excited active molecules produce free radicals through homolysis, which in turn initiate monomer polymerization to form polymers. Initiator molecules have a certain light absorption ability in the ultraviolet region. After directly or indirectly absorbing light energy, the initiator molecules transition from the ground state to the excited singlet state, and then to the excited triplet state through intersystem crossing; after the excited singlet state or triplet state undergoes unimolecular or bimolecular chemical reactions, active fragments that can initiate monomer polymerization are generated. These active fragments can be free radicals, cations, anions, etc. According to different initiation mechanisms, photoinitiators can be divided into free radical polymerization photoinitiators and cationic photoinitiators.

[0005] In the field of fiber optic sensing, people have been constantly pursuing and exploring sensing technologies that are highly sensitive, miniaturized, and can achieve multi-parameter measurement. With the development of sensing technology, fiber optic Fabry-Perot sensors with various structures and functions have begun to emerge.

[0006] The invention patent with publication number CN116473634A uses modules such as detection light source, circulator, spectrometer and surgical probe to construct an embedded FP cavity and FBG grating cascade sensor. The invention adopts chemical etching method to prepare fiber Fabry-Perot sensor and femtosecond laser to prepare fiber Bragg grating sensor. The preparation cost is too high and relatively complicated. The invention patent with publication number CN115655447A constructs a fiber Fabry-Perot weak ultrasonic sensor. The sensor includes two parts: a microphone and an ultrasonic sensor; the microphone is in the shape of a horn, and the microphone is connected to the sensor. The preparation process of the sensor is cumbersome and the detection diagram is too simple, which limits its practicality. The invention patent with authorization number CN115096341A uses a conductive optical fiber, a sensing optical fiber and a signal demodulation system to form a side-light composite optical fiber Fabry-Perot sensor. The core of the sensing optical fiber is one or more air channels. The cladding and the core form at least two reflection surfaces with refractive index jumps and parallel to the axis of the optical fiber, forming at least one open-cavity Fabry-Perot cavity located inside the sensing optical fiber. The outer wall of the optical fiber cladding provides at least one reflection surface. The transmission optical fiber and the side are vertically aligned with the sensing optical fiber to form a T-shaped structure. The central axis of the transmission optical fiber core is in the same plane as the normal of the reflection surface formed by the sensing optical fiber axis and the air channel, and is at right angles to the sensing optical fiber axis. The light of the transmission optical fiber core is vertically incident on the sensing optical fiber. Compared with other refractive index detection equipment, the detection cost of this sensor is too high and it is cumbersome to use.

[0007] In order to overcome the above technical deficiencies, the present invention proposes a fiber bundle Fabry-Perot sensor based on the photothermal effect, which has the characteristics of being able to realize multi-parameter sensing, high sensitivity, simple preparation, and high integration. Bubbles are generated on the end face of the optical fiber to construct a composite Fabry-Perot cavity, and the bubbles are acted on by external physical quantities, causing the bubbles to be displaced or deformed, thereby realizing the monitoring of different physical quantities; in addition, the design of photothermal conversion materials, the selection of photothermal conversion materials, etc., can correspond to various wavelengths of lasers, so as to adapt to different external environments and the detection of different physical quantities, thereby further improving the application scenarios and scope of application of the sensor, so the sensor proposed by the present invention has greater advantages over the prior art. (III) Summary of the invention

[0008] In view of the defects of the prior art, the present invention aims to provide a fiber bundle Fabry-Perot sensor based on the photothermal effect. The sensor uses photolithography technology to write or coat a photothermal film on the end face of the optical fiber. The excitation light (8) is transmitted to the photothermal conversion material (2) in the excitation optical fiber (4). The photothermal conversion material (2) generates a photothermal effect in the liquid, thereby generating a bubble (9) on the end face of the optical fiber bundle (1). The end face of the optical fiber bundle (1) and the bubble (9) form a composite Fabry-Perot interference cavity. External physical quantities act on the bubble (9), causing the bubble (9) to deflect or deform, thereby changing the sensor cavity length and the sensing optical fiber (5), thereby achieving the purpose of sensing.

[0009] The object of the present invention is achieved in that:

[0010] like Figure 1As shown, the sensor is a composite Fabry-Perot cavity formed by a sensing optical fiber (5) and an air bubble (9). The air bubble (9) is generated by an excitation light (8) transmitted to the end face of the excitation optical fiber (4) through the excitation optical fiber (4), and the photothermal conversion material (2) on the end face of the excitation optical fiber (4) produces a photothermal effect, thereby generating an air bubble (9) in a liquid environment. A detection light source (12), a photodetector (11) and a sensing optical fiber (5) are connected through a circulator (13). The detection light source (12) is transmitted in the sensing optical fiber (5) to the end face of the sensing optical fiber (5) to generate a first reflected light (14) and a first transmitted light (15). The first transmitted light (15) is transmitted in the liquid to the front surface of the air bubble (9), and a second reflected light (16) and a second transmitted light (17) are generated on the front surface of the air bubble (9). The second transmitted light (17) continues to be transmitted in the air bubble (9) to the rear surface of the air bubble (9) to generate a third reflected light (18). The reflected light (14), the second reflected light (16) and the third reflected light (18) will generate a composite Fabry-Perot interference to generate a reflected signal (20). The reflected signal (20) is received by a photoelectric detector (11). When the external physical quantity changes, the bubble (9) is offset or deformed, and the length of the Fabry-Perot interference cavity changes, causing the intensity information or wavelength information of the reflected signal (20) to change. By analyzing and solving the reflected signal (20) received by each sensing optical fiber (5), a fiber bundle Fabry-Perot sensor based on the photothermal effect is finally realized.

[0011] The excitation optical fiber (4) used in the optical fiber Fabry-Perot sensor based on the photothermal effect is a single-mode optical fiber, a multi-mode optical fiber, or other optical fibers.

[0012] The sensing optical fiber (5) used in the optical fiber Fabry-Perot sensor based on the photothermal effect is a single-mode optical fiber, a multi-mode optical fiber, or other optical fibers.

[0013] The sensing optical fibers (5) used in the optical fiber Fabry-Perot sensor based on the photothermal effect are three optical fibers, four optical fibers, five optical fibers or other multiple optical fibers.

[0014] The sensing optical fibers (5) used in the optical fiber Fabry-Perot sensor based on the photothermal effect are arranged in a triangle, a quadrilateral, a pentagon or other polygons.

[0015] The photothermal conversion material (2) in the optical fiber Fabry-Perot sensor based on the photothermal effect is a photolithographic material, a metal material, a metal-medium composite material or other materials with photothermal conversion performance.

[0016] In the optical fiber Fabry-Perot sensor based on the photothermal effect, the photothermal conversion material (2) completely covers the middle optical fiber end face or only covers the middle optical fiber core.

[0017] The photolithography material used in the optical fiber Fabry-Perot sensor based on the photothermal effect is a free radical photoinitiator, a cationic photoinitiator or other photolithography materials such as metal oxoate.

[0018] The photothermal conversion material (2) in the optical fiber Fabry-Perot sensor based on the photothermal effect is a dot array, a strip array, a dot and strip combination array or other patterned array.

[0019] The holographic optical tweezers platform is used to focus the laser onto the fiber end, and the writing method adopted can use a spatial light modulator to achieve single-channel writing, dual-channel writing, or multi-channel writing.

[0020] When an air bubble (9) is generated on the end face of an optical fiber bundle (1) by using an excitation light (8), the position where the air bubble (9) is attached is on the photothermal conversion material (2) or on the end face of the optical fiber bundle (1). When the air bubble (9) is attached to the photothermal conversion material (2), the sensor is a composite Fabry-Perot interference cavity composed of three reflection surfaces, namely, the end face of the optical fiber bundle (1), the front surface of the air bubble (9) and the rear surface of the air bubble (9). When the air bubble (9) is attached to the end face of the optical fiber bundle (1), the sensor is a Fabry-Perot interference cavity composed of two reflection surfaces, namely, the end face of the optical fiber bundle (1) and the rear surface of the air bubble (9).

[0021] By simplifying the optical fiber bundle Fabry-Perot sensor based on the photothermal effect into a three-layer high-reflection film structure of "optical fiber end face and front and rear surfaces of the bubble", the three layers of high-reflection films constitute a composite Fabry-Perot interference cavity. The optical path distribution of the three-layer film structure is analyzed, and the corresponding mathematical description is given below.

[0022] The fiber Fabry-Perot sensor is an optical resonant cavity composed of two optical parallel plates with highly reflective films on the end faces, a spacing of d, and strictly parallel to each other.

[0023] Assume that the reflectivity and transmittance of the mirror are R and T respectively, and T+R=1. Other losses, such as absorption or scattering of light by the reflector, are ignored, so the reflectivity R FP and refractive index T FP They are:

[0024]

[0025]

[0026] The phase shift caused by one round trip in the FP cavity is:

[0027]

[0028] Because the mirror is a dielectric, a phase shift of π / 2 is added.

[0029] When the reflectivity is R, according to the classical multi-beam interference, the reflected light intensity and transmitted light intensity are:

[0030]

[0031]

[0032] From the above formula, we can know that the maximum value of the interference intensity of the transmitted light is I r , the minimum value is:

[0033]

[0034] Courseware, the larger the reflectivity R is, the more significant the change in interference light intensity is, that is, the higher the resolution is.

[0035] When the reflectivity is much less than 1:

[0036]

[0037] It can be seen that when the incident light intensity is constant, the cavity length of the sensor is a function of the wavelength and the output light intensity. This means that if the cavity length changes, the output light intensity and wavelength distribution will change.

[0038] The beneficial effects of the present invention are:

[0039] The present invention proposes a fiber bundle Fabry-Perot sensor based on the photothermal effect according to the needs of the modern sensing field and inherits the advantages of existing sensors. Thanks to the composite Fabry-Perot interference cavity composed of the "fiber end face, bubble front surface and bubble rear surface" structure, the bubble (9) is deformed or its position is changed by the action of different external physical quantities on the bubble (9), and the cavity length of the Fabry-Perot cavity will change, and the intensity information or wavelength information of the reflected signal (20) received by the photodetector (11) will change, thereby achieving the purpose of sensing. The present invention is simple to prepare, has a high degree of integration, and can realize the detection and analysis of different environments and different physical quantities, overcoming the shortcomings of complex detection technology, low detection efficiency, and limited application range. Therefore, the sensor proposed by the present invention has greater advantages than the prior art. (IV) Description of the drawings

[0040] Figure 1The invention relates to a fiber bundle Fabry-Perot sensor based on the photothermal effect. The sensor comprises a fiber bundle (1), a photothermal conversion material (2) and a fiber probe (3), wherein the fiber bundle (1) comprises an excitation fiber (4), a sensing fiber (5), an optical fiber sleeve (6) and a filling material (7), the excitation fiber (4) comprises an excitation fiber cladding (401) and an excitation fiber core (402), and the sensing fiber (5) comprises a sensing fiber cladding (501) and a sensing fiber core (502).

[0041] Figure 2 is the coverage of the photothermal conversion material (2), Figure 2 (a) is the full coverage of the end of the excitation optical fiber (4), Figure 2 (b) only covers the excitation optical fiber core (402).

[0042] Figure 3 The figure is a schematic diagram of the cutting process of an optical fiber (1). In the figure, (1) is an optical fiber, (203) is an optical fiber clamping tool, and (204) is an optical fiber cutting knife.

[0043] Figure 4 This is a diagram of the optical fiber sleeve fixing, and (6) is the optical fiber sleeve.

[0044] Figure 5 is a schematic diagram of the photothermal conversion material (2) processing process. Figure 5 (a) is a holographic optical tweezers platform structure, which includes an excitation light (8), a microchannel (10), an LED (301), an objective lens (302) and a reflector (303); Figure 5 (b) is a process of writing the photothermal conversion material (2) on the end face of the excitation optical fiber (4) by the excitation light (8).

[0045] Figure 6 is a schematic diagram of the number of optical fiber bundles (1). Figure 6 (a) Four optical fibers; Figure 6 (b) five optical fibers; Figure 6 (c) six optical fibers; Figure 6 (d) is seven optical fibers, among which (4) is the optical fiber, (401) is the excitation fiber cladding, (402) is the excitation fiber core, (5) is the sensing fiber, (501) is the sensing fiber cladding, (502) is the sensing fiber core, (6) is the optical fiber sleeve, and (7) is the filling material.

[0046] Figure 7 It is a schematic diagram of the shape of the photothermal conversion material (2). Figure 7 (a) is circular; Figure 7 (b) is a triangle; Figure 7 (c) is a quadrilateral; Figure 7(d) is a pentagon, wherein (2) is the photothermal conversion material, (4) is the optical laser fiber, (401) is the excitation fiber cladding, (402) is the excitation fiber core, (5) is the sensing fiber, (501) is the sensing fiber cladding, (502) is the sensing fiber core, (6) is the fiber sleeve, and (7) is the filling material.

[0047] Figure 8 Schematic diagram of the position of the bubble (9), wherein (1) is the optical fiber bundle, (2) is the photothermal conversion material, and (9) is the bubble. Figure 8 (a) is a schematic diagram of bubbles (9) attached to the photothermal conversion material (2); Figure 8 (b) is a schematic diagram of the bubble (9) attached to the end face of the optical fiber bundle (1).

[0048] Fig. 9 The invention relates to a fiber bundle Fabry-Perot sensor based on the photothermal effect, comprising a fiber bundle (1), a photothermal conversion material (2) and a fiber probe (3), wherein the fiber bundle (1) comprises an excitation fiber (4), a sensing fiber (5), an optical fiber sleeve (6) and a filling material (7), the excitation fiber (4) comprises an excitation fiber cladding (401) and an excitation fiber core (402), and the sensing fiber (5) comprises a sensing fiber cladding (501) and a sensing fiber core (502). (V) Specific implementation methods

[0049] The present invention will be further described below with reference to the accompanying drawings and examples.

[0050] The preparation process of the fiber bundle Fabry-Perot sensor based on the photothermal effect is mainly divided into the following three steps:

[0051] Step 1: Microchannel processing: Prepare a glass substrate of suitable size, and use femtosecond processing technology to write a microchannel (10) on one of the glass substrates.

[0052] Step 2: Fiber processing. Figure 3 As shown, the prepared excitation optical fiber (4) and sensing optical fiber (5) are stripped of their outer coatings with wire strippers, wiped clean with alcohol, fixed with an optical fiber clamp (203), and the optical fiber end faces are cut flat with a cutting knife (204). Figure 4 As shown, the cleaned excitation optical fiber (4) and the sensing optical fiber (5) are fixed together using an optical fiber sleeve (6), and the remaining gap is filled with a filling material (7), and the processed optical fiber bundle is inserted into the optical fiber probe (3).

[0053] Step 3: Photothermal structure writing. As shown in FIG5 , the prepared photoinitiator solution is dropped on the end face of the optical fiber, and the excitation light (8) is focused on the end face of the excitation optical fiber (4) through the holographic optical tweezers platform. By changing the focus position of the excitation light (8), the required photothermal conversion structure (2) is written.

[0054] The present invention will be further described below in conjunction with specific embodiments.

[0055] Embodiment 1: A fiber bundle Fabry-Perot sensor based on photothermal effect is used to detect the magnitude and direction of external flow velocity.

[0056] like Fig. 9As shown, the optical fiber bundle Fabry-Perot sensor based on the photothermal effect comprises an optical fiber bundle (1), a photothermal conversion material (2) and an optical fiber probe (3), wherein the optical fiber bundle (1) comprises an excitation optical fiber (4), a sensing optical fiber (5), an optical fiber sleeve (6) and a filling material (7), the excitation optical fiber (4) comprises an excitation optical fiber cladding (401) and an excitation optical fiber core (402), and the sensing optical fiber (5) comprises a sensing optical fiber cladding (501) and a sensing optical fiber core (502). Referring to the above-mentioned preparation process steps 1 to 3, after the microchannel (10) is processed by femtosecond, the processed excitation optical fiber (4) and the sensing optical fiber (5) are fixed by the optical fiber sleeve (6) and the filling material (7) and then inserted into the optical fiber probe (3). When the excitation light (8) is transmitted to the photothermal conversion material (2) through the excitation optical fiber (4), the photothermal conversion material (2) will produce a photothermal effect and generate a bubble (9). The three reflection surfaces of "optical fiber end face, bubble front surface and bubble rear surface" constitute a composite Fabry-Perot interference cavity. When the detection light source (12) is injected into the sensing optical fiber (5) through the circulator (13) and transmitted to the optical fiber end face, the light source will be in the light The fiber end face generates a first reflected light (14) and a first transmitted light (15), and then the first transmitted light (15) is transmitted in the liquid to reach the front surface of the bubble (9), and generates a second reflected light (16) and a second transmitted light (17) on the front surface of the bubble (9). The second transmitted light (17) continues to be transmitted in the bubble (9) to the rear surface of the bubble (9) to generate a third reflected light (18). The first reflected light (14), the second reflected light (16) and the third reflected light (18) will generate a composite Fabry-Perot interference to generate a reflected signal (20), and the reflected signal (20) in the sensing optical fiber (5) is transmitted to the photodetector (11) through the circulator (13). The microflow (19) is injected along the microchannel (10). Due to the different magnitudes and directions of the flow velocity injected into the microchannel (10), the size and direction of the displacement or deformation of the bubble (9) on the end face of the optical fiber bundle are also different, so that the intensity information or wavelength information of the reflection signal (20) of different sensing optical fibers (5) received by the photoelectric detector (11) will also be different. The impact force of the microflow (19) causes the bubble (9) to change to the same position as the microflow direction, so that the reflection signal (20) received by the sensing optical fiber (5) in the displacement direction of the bubble (9) is enhanced, and the reflection signal (20) received by the sensing optical fiber (5) in the opposite direction is weakened, so as to judge the magnitude and direction of the flow velocity, and finally realize a fiber bundle Fabry-Perot flow rate sensor based on the photothermal effect.

Claims

1. The present invention provides an optical fiber bundle Fabry-Perot sensor based on photothermal effect, which is characterized by: The sensor comprises an optical fiber bundle (1), a photothermal conversion material (2) and an optical fiber probe (3), wherein the optical fiber bundle (1) comprises an excitation optical fiber (4), a sensing optical fiber (5), an optical fiber sleeve (6) and a filling material (7), the excitation optical fiber (4) comprises an excitation optical fiber cladding (401) and an excitation optical fiber core (402), and the sensing optical fiber (5) comprises a sensing optical fiber cladding (501) and a sensing optical fiber core (502); when the excitation light (8) is transmitted to the photothermal conversion material (2) at the end face of the optical fiber bundle (1) through the excitation optical fiber (4), the photothermal conversion material (2) A photothermal effect is generated, and a bubble (9) is generated on the end face of the exciting optical fiber (4). The three reflection surfaces of the end face of the optical fiber bundle (1), the front surface of the bubble (9), and the rear surface of the bubble (9) constitute a composite Fabry-Perot interferometer cavity. The photodetector (11) and the detection light source (12) are connected to the sensing optical fiber (5) through a circulator (13) and transmitted to the end face of the optical fiber. The light source generates a first reflected light (14) and a first transmitted light (15) on the end face of the optical fiber. Then, the first transmitted light (15) is transmitted in the liquid to reach the front surface of the bubble (9). The second reflected light (16) and the second transmitted light (17) are generated on the surface of the bubble (9), and the second transmitted light (17) will continue to be transmitted in the bubble (9) to the rear surface of the bubble (9) to generate the third reflected light (18). The first reflected light (14), the second reflected light (16) and the third reflected light (18) will generate a composite Fabry-Perot interference to generate a reflection signal (20). The reflection signal (20) in the sensing optical fiber (5) is transmitted to the photodetector (11) through the circulator (13); the optical fiber probe (3) is inserted into the microchannel (10). Due to the microchannel (10) The flow rate of the liquid injected into the air bubble (9) is different, resulting in different displacement or deformation sizes of the bubble (9), so that the intensity information or wavelength information of the reflection signal (20) of the sensing optical fiber (5) received by the photodetector (11) will also change accordingly. The direction of the microflow is different, and the reflection signals (20) received from different sensing optical fibers (5) will also change. By analyzing the reflection signals (20) received by different surrounding sensing optical fibers (5), the flow direction and flow size of the microflow can be analyzed and determined, and finally a fiber bundle Fabry-Perot sensor based on the photothermal effect is realized.

2. The optical fiber bundle Fabry-Perot sensor based on photothermal effect according to claim 1, characterized in that: The sensing optical fiber (5) used is three optical fibers, four optical fibers, five optical fibers or other multiple optical fibers.

3. The optical fiber bundle Fabry-Perot sensor based on photothermal effect according to claim 1, characterized in that: The excitation optical fiber (4) used is a single-mode optical fiber, a multi-mode optical fiber or other optical fibers.

4. The optical fiber bundle Fabry-Perot sensor based on photothermal effect according to claim 1, characterized in that: The sensing optical fiber (5) used is a single-mode optical fiber, a multi-mode optical fiber or other optical fibers.

5. The optical fiber bundle Fabry-Perot sensor based on photothermal effect according to claim 1, characterized in that: The sensing optical fibers (5) used are arranged in a triangle, a quadrilateral, a pentagon or other polygons.

6. The optical fiber bundle Fabry-Perot sensor based on photothermal effect according to claim 1, characterized in that: The photothermal conversion material (2) is a photolithographic material, a metal material, a metal-medium composite material or other material with photothermal conversion performance.

7. The optical fiber bundle Fabry-Perot sensor based on photothermal effect according to claim 1, characterized in that: The photothermal conversion material (2) completely covers the end face of the middle optical fiber or only covers the core of the middle optical fiber.

8. The optical fiber bundle Fabry-Perot sensor based on photothermal effect according to claim 1, characterized in that: The photolithographic material used is a free radical photoinitiator, a cationic photoinitiator or other photolithographic materials such as metal oxo salts.

9. The optical fiber bundle Fabry-Perot sensor based on photothermal effect according to claim 1, characterized in that: The photothermal conversion material (2) is a dot array, a stripe array, a dot and stripe combination array or other patterned array.

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