Optical fiber sensor and sensing device

Abstract

The utility model discloses an optical fiber sensor and a sensing device. The optical fiber sensor comprises a first single-mode optical fiber, a multi-core optical fiber and a second single-mode optical fiber which are connected in sequence; the first single-mode optical fiber and the second single-mode optical fiber are fixed and arranged in parallel, and the multi-core optical fiber is bent into a balloon-shaped structure; light is input from a fiber core of the first single-mode optical fiber, is coupled into a fiber core and a cladding of the multi-core optical fiber through a connection position of the first single-mode optical fiber and the multi-core optical fiber, and emits multiple intermode interferences when being transmitted in the multi-core optical fiber; and the optical fiber is coupled into the fiber core of the second single-mode fiber through the connection position of the multi-core fiber and the second single-mode fiber and is output from the second single-mode fiber. According to the optical fiber sensor provided by the utility model, the balloon-shaped structure is formed by the multi-core optical fiber, so that the balloon-shaped optical fiber sensor is stronger in capability of exciting a high-order mode compared with a traditional single-mode optical fiber, has higher sensitivity, is simpler in structure, smaller in packaging difficulty and stronger in anti-interference capability compared with a grating-type optical fiber sensor, and has a better development prospect.

Description

TECHNICAL FIELD

[0001] The utility model relates to the field of optical fiber sensing technology especially relates to a kind of optical fiber sensor and sensing device. BACKGROUND

[0002] With the development of social productivity and the continuous emergence of new technologies, accurate temperature measurement plays an increasingly important role in industrial production, medical health, aerospace and civil construction fields. Compared with traditional electrical sensors, optical fiber sensors have attracted widespread attention from all sectors of society due to their simple structure, good corrosion resistance, strong anti-electromagnetic interference ability, and low cost. In recent years, people have proposed various high-sensitivity temperature sensors based on optical fibers, including MZI interferometric sensors, fiber Bragg grating sensors, and Michelson reflection fiber sensors.

[0003] Among the reported optical fiber sensors, optical fiber sensors based on grating structures have attracted attention due to their small size, high precision, and large measurement range. Common optical fiber sensors based on grating structures include long-period grating fiber sensors and fiber Bragg grating fiber sensors. Grating-based sensors typically require precise special etching equipment, so grating sensors are expensive and have complex processes, which is not conducive to customization, modification, and mass production. MZI interferometric sensors are commonly used in industrial production due to their simple structure and strong anti-interference ability, but conventional MZI interferometric sensors usually have low sensitivity and are less commonly used in scientific research and precise measurement fields. Therefore, developing high-sensitivity, simple-process optical fiber sensors has become a research hotspot. SUMMARY

[0004] The utility model provides a kind of optical fiber sensor and sensing device, the optical fiber sensor utilizes multi-core optical fiber to form balloon type structure, the ability of high-order mode excited by traditional single-mode optical fiber is stronger, with higher sensitivity, and grating type optical fiber sensor structure is simpler than it, encapsulation difficulty is smaller, anti-interference ability is stronger, with good development prospect.

[0005] According to one aspect of the utility model, an optical fiber sensor is provided, comprising a first single-mode optical fiber, a multi-core optical fiber and a second single-mode optical fiber connected in sequence.

[0006] The first single-mode optical fiber and the second single-mode optical fiber are fixed and parallelly arranged, and the multi-core optical fiber is bent into a balloon type structure.

[0007] Light rays are input from the core of the first single-mode optical fiber, coupled into the core and cladding of the multi-core optical fiber through the connecting position of the first single-mode optical fiber and the multi-core optical fiber, transmitted in the multi-core optical fiber to emit multiple inter-mode interferences, coupled into the core of the second single-mode optical fiber through the connecting position of the multi-core optical fiber and the second single-mode optical fiber and output from the second single-mode optical fiber.

[0008] Optionally, the connecting position of the first single-mode optical fiber and the multi-core optical fiber comprises a first ball-type coupling structure, and the connecting position of the second single-mode optical fiber and the multi-core optical fiber comprises a second ball-type coupling structure.

[0009] Optionally, the first ball-type coupling structure and the second ball-type coupling structure are the same.

[0010] Optionally, the multi-core optical fiber comprises a four-core optical fiber, a five-core optical fiber, a seven-core optical fiber or a nine-core optical fiber.

[0011] Optionally, the diameter of the balloon-type structure is 8±0.5mm.

[0012] Optionally, a protective sleeve is further included, and at least part of the first single-mode optical fiber and the second single-mode optical fiber are fixed in the protective sleeve.

[0013] Optionally, ultraviolet curing glue is further included in the protective sleeve.

[0014] Optionally, a first optical fiber joint is arranged on the side of the first single-mode optical fiber away from the multi-core optical fiber, and a second optical fiber joint is arranged on the side of the second single-mode optical fiber away from the multi-core optical fiber.

[0015] Optionally, the first optical fiber joint and the second optical fiber joint are the same kind of joint.

[0016] According to another aspect of the present application, a sensing device is provided, comprising a light source, a spectrometer and the above optical fiber sensor, the output end of the light source is connected with the first single-mode optical fiber of the optical fiber sensor, the spectrometer is connected with the second single-mode optical fiber of the optical fiber sensor, and the optical fiber sensor is used for temperature sensing.

[0017] The optical fiber sensor provided by the embodiment of the utility model, through the multi-core optical fiber bending into balloon type structure, light is input from the fiber core of the first single mode optical fiber, is coupled into the fiber core and the cladding of the multi-core optical fiber through the connecting position of the first single mode optical fiber and the multi-core optical fiber, emits multiple mode interference when transmitting in the multi-core optical fiber, is coupled into the fiber core of the second single mode optical fiber and is output from the second single mode optical fiber again through the connecting position of the multi-core optical fiber and the second single mode optical fiber, the ability of exciting high order mode is stronger than traditional single mode optical fiber, has higher sensitivity, and the grating type optical fiber sensor structure is simple, the packaging difficulty is smaller, the anti-interference ability is stronger, has better development prospect.

[0018] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the utility model, and is not used to limit the scope of the utility model. Other features of the utility model will become easy to understand through the following description. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical scheme in the embodiment of the utility model, the drawings needed in the embodiment description will be briefly introduced below, obviously, the drawings in the following description are only some embodiments of the utility model, and for those skilled in the art, other drawings can be obtained according to these drawings without creating labor.

[0020] Figure 1 The structure schematic diagram of the optical fiber sensor provided by the embodiment of the utility model is provided.

[0021] Figure 2 The transmission spectrum diagram obtained for the experiment is provided.

[0022] Figure 3 The spatial spectrum diagram corresponding to Figure 2 is provided.

[0023] Figure 4 The structure schematic diagram of another optical fiber sensor provided by the embodiment of the utility model is provided.

[0024] Figure 5 The structure schematic diagram of a sensing device provided by the embodiment of the utility model is provided.

[0025] Figure 6 The curve diagram of transmission spectrum offset with temperature is provided.

[0026] Figure 7 The wavelength-temperature fitting curve diagram is provided. DETAILED DESCRIPTION

[0027] In order to make the person skilled in the art better understand the technical scheme of the present application, the technical scheme in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by the person skilled in the art without creative labor should belong to the scope of protection of the present application.

[0028] It should be noted that the terms "first", "second" and the like in the description and claims of the present application and the above drawings are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to only those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0029] The currently reported optical fiber sensors include fiber Bragg grating (FBG) type sensors, MZI interference type sensors, etc. For example, in a certain prior art, a temperature displacement sensor based on FBG cascaded multimode optical fiber is proposed, and the temperature sensitivity is -266.25 pm / ℃. In another prior art, an MZI interference type sensor based on multimode optical fiber cascaded seven-core optical fiber for temperature load dual-parameter measurement is proposed, and the temperature sensitivity is 45 pm / ℃, and the transverse load sensitivity is -165 pm / N. However, the FBG sensor has high cost, and the sensitivity of the MZI interference type sensor is not high, which is not conducive to the popularization and application of the optical fiber sensor. At present, the optical fiber sensor based on the balloon type structure is concerned due to its high sensitivity and simple process. In still another prior art, a full optical fiber high-sensitivity mode interferometer formed by a bent commercial single-mode optical fiber (SMF) is proposed, and the temperature sensitivity is 0.418 nm / ℃. In still another prior art, a balloon type structure is cascaded with a long period grating, and a temperature sensitivity of 42.9 pm / ℃ is obtained. In still another prior art, a micro-displacement and temperature simultaneous measurement optical fiber sensor based on two series-connected balloon type bent single-mode optical fibers (BBSMF) and FBG is proposed, and the sensitivities of the interferometer to micro-displacement and temperature are 180 pm / μm and 105 pm / ℃, respectively.

[0030] In order to further improve the sensitivity of the MZI interferometric fiber sensor, the utility model discloses a kind of fiber sensors, including sequentially connected first single-mode optical fiber, multicore optical fiber and second single-mode optical fiber;First single-mode optical fiber and second single-mode optical fiber are fixed and parallelly arranged, and multicore optical fiber is curved into balloon type structure;Light is input from the core of first single-mode optical fiber, coupled into the core and cladding of multicore optical fiber through the connecting position of first single-mode optical fiber and multicore optical fiber, emits multiple intermodal interference when transmitting in multicore optical fiber, and then coupled into the core of second single-mode optical fiber through the connecting position of multicore optical fiber and second single-mode optical fiber and output from second single-mode optical fiber.

[0031] Optionally, the multicore optical fiber includes a four-core optical fiber, a five-core optical fiber, a seven-core optical fiber or a nine-core optical fiber.

[0032] For example, the multicore optical fiber is a four-core optical fiber, Figure 1 A structure diagram of the fiber sensor is provided in the embodiments of the utility model, referring to Figure 1 The fiber sensor includes a first single-mode optical fiber 10, a four-core optical fiber 20 and a second single-mode optical fiber 30;The first single-mode optical fiber 10 and the second single-mode optical fiber 30 are fixed and parallelly arranged, and the four-core optical fiber 20 is curved into a balloon type structure.

[0033] In recent years, the four-core optical fiber has become a new hotspot in the field of regional fiber communication due to its space division multiplexing characteristics, and its core spacing is larger, which better avoids crosstalk between different channels. At present, the common commercial four-core optical fiber technology is relatively mature, and researchers gradually expand the application range of the four-core optical fiber to the fields of medical health monitoring, accurate temperature measurement, etc. In another prior art, a high-sensitivity temperature sensor based on a single-mode optical fiber directly connected to a four-core optical fiber is proposed. By directly connecting the single-mode optical fiber to the four-core optical fiber, the light in the core of the single-mode optical fiber is scattered into the four cores of the four-core optical fiber, a high-order mode is excited, and a temperature sensitivity of 209 pm / ℃ is obtained. However, the linear four-core optical fiber sensor has limited ability to excite high-order modes and large loss, so its temperature sensitivity is low, which is not convenient for popularization and application. In order to further improve the sensitivity of the four-core optical fiber sensor, a balloon type structure is introduced in the embodiment. By bending the four-core optical fiber into a balloon type structure, all four cores can excite high-order modes, and the sensitivity is fully improved.

[0034] Compared with the traditional single-mode optical fiber balloon structure, the structure introduces a four-core optical fiber, which can generate high-order modes multiple times. The four-core optical fiber has four cores of the same specification arranged in a square in the cladding, and the distance between the cores is large, which can effectively avoid inter-core crosstalk during propagation. In the balloon structure, as the curvature increases, the binding ability of the core to light decreases, and part of the light leaks from the core to excite high-order modes. In the four-core optical fiber, there are four cores at the same time, so the light leakage occurs in the four cores at the same time, and the ability to excite high-order modes is stronger than that of the traditional single-mode optical fiber balloon structure, and the sensitivity is higher.

[0035] Compared with the traditional grating type optical fiber sensor, the four-core optical fiber balloon structure has a simpler structure and stronger anti-interference ability. The grating structure usually needs high-power precise etching equipment and needs to adjust the process multiple times, which is difficult to design and prepare, and is not conducive to the upgrading and improvement of the sensor. The four-core optical fiber balloon structure only needs to bend the four-core optical fiber to a specific bending radius. Optionally, the diameter of the balloon structure is 8±0.5mm, and the allowable error is ±0.5mm, which only needs to be controlled by a precise displacement platform. The cost of the precise displacement platform is much lower than that of the high-power precise etching equipment. At present, the four-core optical fiber is attracting the attention of researchers, and its manufacturing process is becoming mature. The quality of commercial four-core optical fibers can be guaranteed. In addition, the four-core optical fiber balloon structure has a larger size, smaller packaging difficulty, stronger anti-interference ability, and good development prospects.

[0036] Optionally, with reference to Figure 1 , the connection position of the first single-mode optical fiber 10 and the multi-core optical fiber (four-core optical fiber 20) includes a first fusion ball type coupling structure 11, and the connection position of the second single-mode optical fiber 30 and the multi-core optical fiber includes a second fusion ball type coupling structure 31. Optionally, the first fusion ball type coupling structure 11 and the second fusion ball type coupling structure 31 are the same. In other embodiments, only the first fusion ball type coupling structure can be provided, and the other end of the four-core optical fiber is directly fused with the second single-mode optical fiber. The specific implementation can be selected according to the actual situation.

[0037] The principle of the optical fiber sensor provided in the embodiment is as follows: incident light enters the first balloon-shaped coupling structure 11 through the first single-mode optical fiber 10. Since the first balloon-shaped coupling structure 11 has the function of diverging and refocusing the light, when the light enters the balloon-shaped structure from the core of the first single-mode optical fiber 10, the light diverges and excites high-order modes due to the mismatch of the refractive index. When the light propagates to the center of the first balloon-shaped coupling structure 11, the light is refocused, forming the first mode interference and entering the four-core optical fiber 20. When the light enters the four-core optical fiber 20, part of the light enters the core, and part of the light propagates in the cladding. However, the refractive index of the core and the cladding is not the same, and in long-distance propagation, part of the light is absorbed by the core, forming the second mode interference. A small part of the light propagates in the cladding and gradually disappears. As the degree of bending of the balloon-shaped structure gradually increases, the original transmission condition is destroyed, and the binding ability of the core to the light decreases, and part of the light escapes from the core to the cladding to excite high-order modes. At this time, the high-order modes in the cladding are collectively referred to as cladding modes. When the cladding modes propagate to the cladding-air boundary, most of them are reflected back into the core, interfere with the core modes, and are reflected back again. In the case of large bending, the cladding modes oscillate back and forth between the core and the cladding-air boundary, and constantly interfere with each other. When the curvature gradually decreases, the cladding modes are gradually absorbed by the core and tend to be stable. When the light finally propagates to the second single-mode optical fiber 30 through the second balloon-shaped coupling structure 31, most of the light converges to the core of the second single-mode optical fiber 30 and is transmitted to the optical spectrum analyzer. Due to the excitation of high-order modes multiple times during propagation and the multiple mode interferences, a spectrum with obvious concave-convex can be observed on the optical spectrum analyzer. When the temperature changes, the effective refractive index of the balloon-shaped coupling structure and the four-core optical fiber changes, causing the spectrum to shift. By detecting the shift of the spectrum, the change of the temperature can be reflected. For example, Figure 2 The transmission spectrum obtained by the experiment is shown in FIG. 2, Figure 3 The spatial spectrum corresponding to Figure 2 is shown in FIG. 3.

[0038] The preparation method of the optical fiber sensor comprises the following steps: in the first step A, a fusion splicer is used to discharge and melt the end of the four-core optical fiber multiple times to form a balloon-shaped structure as the balloon-shaped coupling structure of the structure. The manual fusion mode of the fusion splicer is used, the discharge amount is 180, the discharge time is 30 ms, and the discharge times is 6. By controlling the discharge intensity and the discharge times, the balloon-shaped coupling structure with a long radius of 265 μm and a short radius of 170 μm can be repeatedly realized. In the second step B, the balloon-shaped coupling structure and the first single-mode optical fiber are fused by the manual discharge of the fusion splicer, the discharge amount is 150, the discharge time is 20 ms, and the other end of the four-core optical fiber is fused with the second single-mode optical fiber. In the third step C, the four-core optical fiber is passed through the capillary tube, and after the ring is formed, it is passed back through the capillary tube. The two ends are pulled tight to form a balloon-shaped structure of the four-core optical fiber with a diameter of 8 mm. A small amount of ultraviolet curing glue is added to the capillary tube and cured by ultraviolet light.

[0039] Linear fiber sensor has weak ability to excite high-order mode, and often needs to add a taper structure or a multimode fiber as an auxiliary element. Compared with the traditional linear fiber sensor, the balloon type structure can efficiently excite high-order mode due to its special structure, so that the manufacturing process of the sensor is simpler, the physical strength is higher, and the sensor can better adapt to different measurement environments, and has lower dependence on packaging.

[0040] Optionally, the fiber sensor further comprises a protective sleeve, and at least partial regions of the first single-mode fiber and the second single-mode fiber are fixed in the protective sleeve.

[0041] Optionally, the protective sleeve can be a capillary glass tube or a capillary plastic tube, and the embodiments of the present application are not limited in this regard. Optionally, the fiber sensor further comprises ultraviolet curing glue in the protective sleeve, and the first single-mode fiber and the second single-mode fiber are fixed by using the ultraviolet curing glue.

[0042] Figure 4 Another structural schematic diagram of a fiber sensor provided by the embodiments of the present application is shown in FIG. 4. Figure 4 Optionally, the first single-mode fiber 10 is provided with a first fiber joint 50 away from one side of the multi-core fiber (four-core fiber 20), and the second single-mode fiber 30 is provided with a second fiber joint 60 away from one side of the multi-core fiber.

[0043] In specific implementation, the fiber joint can be selected from ST, SC, FC, LC, etc., and can be selected according to actual conditions in specific implementation. Optionally, the first fiber joint 50 and the second fiber joint 60 are the same type of joint. For example, the first fiber joint and the second fiber joint can both be FC / APC joints.

[0044] Figure 5 A structural schematic diagram of a sensing device provided by the embodiments of the present application is shown in FIG. 5. Figure 5 The sensing device comprises a light source 200, a spectrometer 300, and any one of the fiber sensors 100 provided by the above embodiments, the output end of the light source 200 is connected with the first single-mode fiber of the fiber sensor 100, the spectrometer 300 is connected with the second single-mode fiber of the fiber sensor 100, and the fiber sensor 100 is used for temperature sensing.

[0045] For example, the fiber sensor 100 is placed in a thermostat 400, the input end is connected to a wide-spectrum light source by a commercial single-mode fiber, and the output end is also connected to a spectrum analyzer by a commercial single-mode fiber. The temperature in the thermostat 400 is increased by 1℃ every 2 minutes, and the temperature is maintained for 5 minutes after the temperature is increased, and the data is recorded after the transmission spectrum is stabilized. Figure 6 A curve diagram of the transmission spectrum offset with temperature is shown in FIG. 6.Figure 7 The wavelength-temperature fitting curve is provided by analyzing the experimental data, the temperature sensitivity of the optical fiber sensor provided by the embodiment of the utility model is 2.02nm / ℃, the temperature measurement range is 33℃-46℃, the temperature sensitivity of the optical fiber sensor is higher in the temperature interval, and the stability is better, and has higher engineering value.

[0046] The above specific embodiments do not constitute a limitation on the protection scope of the utility model. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement within the spirit and principle of the utility model should be included in the protection scope of the utility model.

Claims

1. An optical fiber sensor, characterized by, The optical fiber sensor comprises a first single-mode optical fiber, a multi-core optical fiber and a second single-mode optical fiber connected in sequence. The first single-mode optical fiber and the second single-mode optical fiber are fixed and parallel, and the multi-core optical fiber is curved into a balloon-shaped structure. Light is input from the core of the first single-mode optical fiber, coupled into the core and cladding of the multi-core optical fiber at the connecting position of the first single-mode optical fiber and the multi-core optical fiber, transmitted in the multi-core optical fiber to emit multiple intermodal interference, coupled into the core of the second single-mode optical fiber at the connecting position of the multi-core optical fiber and the second single-mode optical fiber and output from the second single-mode optical fiber.

2. The fiber optic sensor of claim 1, wherein, The connecting position of the first single-mode optical fiber and the multi-core optical fiber comprises a first fused ball-shaped coupling structure, and the connecting position of the second single-mode optical fiber and the multi-core optical fiber comprises a second fused ball-shaped coupling structure.

3. The fiber optic sensor of claim 2, wherein, The first fused ball-shaped coupling structure and the second fused ball-shaped coupling structure are the same.

4. The fiber optic sensor of claim 1, wherein, The multi-core optical fiber comprises a four-core optical fiber, a five-core optical fiber, a seven-core optical fiber or a nine-core optical fiber.

5. The fiber optic sensor of claim 1, wherein, The diameter of the balloon-shaped structure is 8±0.5mm.

6. The fiber optic sensor of claim 1, wherein, A protective sleeve is further included, and at least part of the first single-mode optical fiber and the second single-mode optical fiber are fixed in the protective sleeve.

7. The fiber optic sensor of claim 6, wherein, An ultraviolet curing glue is further included in the protective sleeve.

8. The fiber optic sensor of claim 1, wherein, A first optical fiber connector is arranged on the side of the first single-mode optical fiber away from the multi-core optical fiber, and a second optical fiber connector is arranged on the side of the second single-mode optical fiber away from the multi-core optical fiber.

9. The fiber optic sensor of claim 8, wherein, The first optical fiber connector and the second optical fiber connector are the same type of connector.

10. A sensing device, characterized by The optical fiber sensor according to any one of claims 1-9, a light source and a spectrometer, the output end of the light source is connected with the first single-mode optical fiber of the optical fiber sensor, and the spectrometer is connected with the second single-mode optical fiber of the optical fiber sensor, and the optical fiber sensor is used for temperature sensing.

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