CN117073866A - Temperature sensor based on seven-core optical fiber and bowknot type and preparation method - Google Patents

Abstract

The invention provides a temperature sensor based on a seven-core optical fiber and a bowknot type and a preparation method thereof, and belongs to the technical field of optical fiber sensing. The technical proposal is as follows: a temperature sensor based on a heptacore optical fiber and a bowknot type consists of a broadband light source, a first single-mode optical fiber, a first bending single-mode optical fiber, a heptacore optical fiber, a second bending single-mode optical fiber, a second single-mode optical fiber and a spectrum analyzer. The beneficial effects of the invention are as follows: the temperature sensor is based on a single-mode fiber-spherical structure-seven-core fiber-bent single-mode fiber-single-mode fiber structure; one end of the seven-core optical fiber is welded with a spherical structure, and light can be controlled to propagate in different cores of the seven-core optical fiber by controlling the long diameter and the short diameter of the spherical structure so as to obtain extremely high temperature sensitivity; the sensor has the characteristics of simple structure, convenient manufacture, low cost, high sensitivity and the like.

Description

A temperature sensor based on seven-core optical fiber and bow-tie type and its preparation method

Technical field

The present invention relates to the field of optical fiber sensing technology, and in particular to a temperature sensor based on seven-core optical fiber and bow-tie type and a preparation method.

Background technique

With the rapid development of society, accurate temperature measurement is becoming more and more widely used in industrial production, medical testing, deep-sea exploration and other fields. Compared with traditional electrical sensors, fiber optic sensors have simple structure, corrosion resistance, and anti-electromagnetic interference capabilities. Strong and favored. In recent years, a variety of fiber-based temperature sensors have been proposed, such as MZI interferometric sensors, Bragg grating (FBG) sensors, sagnac ring sensors, and spherical structure sensors based on bent optical fibers. Among them, balloon sensors based on bent single-mode optical fibers have been widely used in temperature, displacement, refractive index, etc. because of their simple production, low cost, and high sensitivity.

Among the currently known fiber optic sensor structures, grating-type fiber optic sensors have the advantages of small size and high precision and are favored by people. However, because long-period gratings and Bragg gratings require the use of special equipment to etch structures in the fiber, resulting in grating The production cost of type sensors is high and the process requirements are high. MZI-based interferometric sensors are currently widely used in the field of optical fiber sensing. Traditional MZI interferometric sensors are usually not sensitive enough and are difficult to promote in the field of precision measurement.

Therefore, sensors based on bent single-mode optical fibers have attracted much attention due to their advantages such as simple fabrication, low cost, high structural strength, and high sensitivity. In order to obtain higher sensitivity, it is necessary to excite the core mode to higher-order modes as much as possible, so an approximately symmetrical bowtie structure is introduced based on a single bent single-mode fiber. In order to improve the physical strength of the sensor and further improve the sensitivity of the sensor, the original coating layer of the single-mode optical fiber is retained.

So far, there are few studies on combining seven-core optical fiber and bow-tie structure for sensing. In recent years, seven-core optical fiber has become an effective way to solve the problem of limited communication capacity due to its spatial division multiplexing characteristics. In addition, the application of the special multi-core structure of seven-core optical fiber in fields such as sensing and medical treatment has also attracted widespread attention from researchers. However, seven-core optical fiber is often used in structures such as MZI/SAGNAC/FP.

How to solve the above technical problems is the subject faced by the present invention.

Contents of the invention

The object of the present invention is to provide a temperature sensor based on seven-core optical fiber and bow-tie type and a preparation method. The sensor is insensitive to the refractive index and has extremely high sensitivity to temperature, avoiding the cross influence of temperature and refractive index. The temperature sensor is based on a single-mode optical fiber-spherical structure-seven-core optical fiber-bent single-mode optical fiber-single-mode optical fiber structure; the spherical structure is welded at one end of the seven-core optical fiber, and the light can be controlled by controlling the long and short diameters of the spherical structure. Propagates in different seven-core optical fiber cores to obtain extremely high temperature sensitivity; the sensor has the characteristics of simple structure, convenient production, low cost, and high sensitivity.

In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is specifically: a temperature sensor based on seven-core optical fiber and bow-tie type, which is composed of a broadband light source, a first single-mode optical fiber, a first bent single-mode optical fiber, a seven-core optical fiber, a second It consists of a bent single-mode optical fiber, a second single-mode optical fiber, and a spectrum analyzer.

As a further optimization solution for a temperature sensor based on seven-core optical fiber and bow-tie type provided by the present invention, one end of the first single-mode optical fiber is connected to the broadband light source through an FC/APC connector, and the first single-mode optical fiber serves as the At the input end of the structure, the other end of the first single-mode optical fiber is connected to the input end of the first bent single-mode optical fiber.

As a further optimization solution for a temperature sensor based on seven-core optical fiber and bow-tie type provided by the present invention, the output end of the first bent single-mode optical fiber is connected to one end of the seven-core optical fiber, and the other end of the seven-core optical fiber is connected to the second Connect the input end of the bent single-mode fiber.

As a further optimization solution for a temperature sensor based on seven-core optical fiber and bow-tie type provided by the present invention, the output end of the second bent single-mode optical fiber is connected to one end of the second single-mode optical fiber as the output end, and the second single-mode optical fiber is connected to one end of the second single-mode optical fiber as the output end. The other end of the optical fiber is connected to the input end of the spectrum analyzer through the FC/APC connector.

In order to better realize the purpose of the present invention, the present invention also provides a curvature sensor temperature measurement method, using the seven-core optical fiber and the bow-tie type temperature sensor, including the following steps:

S1. After the incident light output by the broadband light source enters the input end of the first curved single-mode fiber through the first single-mode fiber, it excites the cladding-coating layer mode in the annular area with a larger curvature of the first curved single-mode fiber, and in After the curvature is reduced, it is coupled back to the fiber core;

S2. The light in the current center then enters the input end of the second curved single-mode fiber through the seven-core fiber. It also excites the cladding-coating layer mode in the annular area with larger curvature. After passing through the annular area, the curvature decreases and the cladding mode The light in the fiber is recoupled back into the fiber core;

S3. Coupling back to the second single-mode fiber. During the whole process, due to the optical path difference between the fundamental mode and the higher-order mode, the phase matching condition is met, and an interference spectrum is generated on the spectrum analyzer. The interference valley wavelength in the spectrum is passed. offset to measure the temperature.

In order to better realize the purpose of the present invention, the present invention also provides a preparation method of a temperature sensor based on seven-core optical fiber and bow-tie type, which includes the following steps:

The first step is to first connect the input end of the first single-mode optical fiber to the broadband light source through the FC/APC optical fiber connector, insert the output end of the first single-mode optical fiber from the first end of the casing and pull it out from the second end. a length, then bend the single-mode optical fiber pulled out from the second end to form a spherical structure, insert the single-mode optical fiber output end from the second end, pull it out from the first end, and tighten the single-mode optical fiber to form the first bent single-mode optical fiber. ;

In the second step, cut the output end of the first bent single-mode optical fiber into a flat shape, and at the same time cut the seven-core optical fiber into a flat shape, place it in a fiber fusion splicer and fuse it with the output end of the cut flattened first bending single-mode optical fiber. The splicing point is the second step. At one fusion splice point, the length of the seven-core optical fiber is 4±0.05mm;

The third step is to cut the input end of another single-mode fiber flat and fuse it with the other end of the seven-core fiber. Then insert the output end of the single-mode fiber into the No. 2 end of the casing and move the casing so that the seven-core The optical fiber is in the middle of the casing;

The fourth step is to tighten the output end of the single-mode fiber in the third part to form a second curved single-mode fiber, and adjust the diameters of the first curved single-mode fiber and the second curved single-mode fiber structure through a precision displacement platform until the The diameter of the first bent single-mode optical fiber is 9±0.05mm, and the diameter of the second bent single-mode optical fiber structure is 9.7mm;

In the fifth step, the two ends of the casing are fixed with ultraviolet curable glue. In the present invention, UV glue is used.

Further, the inner diameter of the casing is 8±0.05mm, and the length is 1.6±0.1cm.

Working principle of the invention:

First, the incident light enters the first curved single-mode fiber. In the large curvature curved structure, the fiber core's ability to bind light decreases, and part of the light escapes to the cladding and is further coupled into the coating layer. Part of the light in the coating layer When the light reaches the boundary of the coating layer air, it is reflected back to the fiber core. Since the effective refractive index and optical path length of the core mode and the coating layer mode are different during propagation, the core mode interferes with the coating layer mode. As the curvature gradually decreases, most of the light in the coating and cladding is coupled back into the fiber core. When the light enters the seven-core fiber from the output end of the first bent single-mode fiber, due to the single-mode fiber and the seven-core fiber The fiber core diameters do not match and the light diverges at the splice point.

Secondly, at the beginning, light mainly propagates in three forms: central core mode, surrounding core mode and cladding mode. The cladding mode in the seven-core fiber is unstable during the cladding transmission process. With the length of the seven-core fiber increases, the energy of the cladding mode will gradually attenuate and disappear in the seven-core fiber; then, the light propagates in the seven-core fiber in the middle core mode and the surrounding core mode. At the input end of a single-mode fiber, most of the surrounding core modes are coupled into the second curved single-mode fiber to form interference. In the second curved single-mode fiber, the light is transmitted in the same way as the light in the first curved single-mode fiber. The transmission method is roughly the same and is skipped here. During the transmission of incident light, the optical path difference between the core mode and the cladding-coating mode occurs due to the difference in refractive index, thereby producing an interference spectrum on the spectrometer. Changes in temperature will cause the cladding-coating layer pattern to change, causing a wavelength shift in the spectrum, and the temperature can be measured by detecting the wavelength.

Compared with the prior art, the beneficial effects of the present invention are:

1. The present invention is based on bent single-mode-seven-core-bent single-mode optical fiber, and combines the characteristics of bent single-mode optical fiber and seven-core optical fiber to achieve a huge improvement in temperature sensitivity and further improve the practicality of the temperature sensor.

2. The temperature sensor and preparation method of the present invention are not only simple in manufacturing process, but also have low material cost. They only need to use an optical fiber fusion splicer for simple discharge welding. The bow-tie structure based on bent single-mode optical fiber is not only simple in structure, easy to make, but also functional in function. It can replace expensive and complex optical devices and has similar effects. It has huge potential in the popularization and use of fiber optic temperature sensors.

3. The output signal of the temperature sensor of the present invention contains an interference peak formed by mode interference, and the temperature is detected by changing the wavelength of the interference valley with temperature. At the same time, it is very sensitive to temperature and insensitive to refractive index. It is extremely suitable for environments with large differences in refractive index and solves the cross-sensitivity problem of traditional fiber optic temperature sensors and refractive index. It has practical applications in aerospace and food engineering. Broad application space.

4. Instead of the traditional bent single-mode optical fiber, this structure introduces an approximately symmetrical bowtie structure, which increases the curvature of the bent single-mode optical fiber and excites more high-order modes, which makes the temperature sensitivity of the sensor compared to Traditional bent single-mode optical fiber sensors have been qualitatively improved. The high temperature sensitivity and physical strength make the sensor widely practical in precision measurement, aerospace, and deep-sea exploration.

5. Compared with traditional fiber grating sensors, in this structure, only a fiber fusion splicer is needed to complete sensor production. Gratings require special equipment for etching, so the process and precision requirements are strict. In this structure, a bow-tie structure and seven-core optical fiber are used instead of expensive gratings to excite high-order modes, which simplifies the manufacturing process, reduces costs, and improves sensitivity.

6. Compared with traditional pure optical fiber bending single-mode optical fiber sensors, the coating layer of the single-mode optical fiber is retained in this structure. In the large curvature bending structure, part of the light will leak to the coating layer. When the curvature gradually decreases, During the process, the light in the coating couples into the cladding and core and couples with it. The coating layer has a high thermo-optical coefficient and thermal expansion coefficient. When the temperature changes, the sensor can respond in time and has extremely high temperature sensitivity.

7. Due to the introduction of seven-core optical fiber, the distribution of light in space can be changed and some high-order modes can be excited. When light propagates in a seven-core optical fiber, the optical path difference is generated due to the different effective refractive index of the core and cladding, which amplifies the interference effect and achieves a secondary improvement in temperature sensitivity.

Description of the drawings

The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

Figure 1 is a schematic structural diagram of the temperature sensor of the present invention.

Fig. 2 is a schematic diagram of the device when the temperature sensor of the present invention performs temperature measurement.

In Figure 3 (a) is the wavelength (λ) shift diagram as temperature (T) changes, and (b) is the fitting curve diagram of temperature (T) and wavelength (λ) obtained for the trough in (a).

Figure 4 is a schematic diagram of the device when the temperature sensor in the present invention performs refractive index testing.

In Figure 5, (a) is a wavelength shift diagram as temperature changes; in order to demonstrate the insensitivity of the present invention to the refractive index, the wave trough is partially enlarged;

(b) is the fitted curve of temperature and wavelength obtained for the trough in (a).

Figure 6 is a physical diagram of the temperature sensor of the present invention and a cross-section of the optical fiber.

The left side picture in Figure 7 is a schematic cross-sectional view of a single-mode optical fiber in the present invention; the right side picture is a schematic cross-sectional view of a seven-core optical fiber in the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Of course, the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention.

Example 1

Referring to Figures 1 to 7, the technical solution provided by this embodiment is a temperature sensor based on seven-core optical fiber and bow-tie type. This embodiment is based on two structures: bow-tie type structure and seven-core optical fiber, as shown in Figure 1. It is connected by a broadband light source 1, a first single-mode fiber 2, a first curved single-mode fiber 3, a seven-core fiber 4, a second curved single-mode fiber 5, a second single-mode fiber 6 and a spectrum analyzer 7. Among them, one end of the first single-mode optical fiber 2 is connected to the broadband light source 1 through an FC/APC connector. At the same time, the first single-mode optical fiber 2 serves as the input end of the structure, and the other end of the first single-mode optical fiber 2 is connected to the first bent single-mode optical fiber 2. The input end of the mode fiber is connected. The output end of the first bent single-mode optical fiber is connected to the seven-core optical fiber 4, the other end of the seven-core optical fiber 4 is connected to the input end of the second bent single-mode optical fiber 5, and the other end of the second bent single-mode optical fiber 5 is connected to the output end. The second single-mode optical fiber 6 is connected. Finally, the second single-mode optical fiber 6 is also connected to the spectrum analyzer 7 through the FC/APC connector.

As shown in Figure 2, a diagram of the temperature measurement device, in which the sensor part 3-5 is placed in the platform of the thermostat 8, and the sensor is covered with a thermostat cover. By changing the temperature of the thermostat, the shift diagram of the spectrum with temperature (T) is obtained, as shown in (a) in Figure 3. When the temperature changes, the position of the trough on the spectrometer occurs, and the wavelength (λ) and temperature (T ) shows a linear relationship, as shown in (b) in Figure 3, and the temperature sensitivity is only -3.36nm/℃.

As shown in Figure 4, a diagram of the refractive index measurement device, in which the sensor parts 3-5 are placed in the solution pool 9, and the refractive index sensing experiment is performed by adding solutions with different refractive indexes into the solution pool 9. By changing the refractive index of the solution in the solution pool, the shift diagram of the spectrum as the refractive index (RI) changes is obtained, as shown in (a) in Figure 5. Considering that this embodiment is insensitive to the refractive index, it is not sensitive to the wave trough. We performed partial magnification and observed the position of the wave trough on the spectrometer. There is a linear relationship between wavelength (λ) and refractive index (RI), as shown in (b) in Figure 5. The refractive index sensitivity is only -10.05nm/RIU, which is extremely large. The cross-effect of refractive index on temperature is reduced.

The optical path propagation sequence of the curvature sensor in this embodiment is as follows:

After the incident light output by the broadband light source 1 enters the input end of the first curved single-mode fiber 3 through the first single-mode fiber 2, the cladding-coating layer mode is excited in the annular area with a larger curvature of the first curved single-mode fiber 3, And after the curvature is reduced, it is coupled back to the fiber core. The light in the core then enters the input end of the second curved single-mode fiber 5 through the seven-core fiber 4, and also excites the cladding-coating layer mode in the annular area with larger curvature. , after passing through the annular area, the curvature decreases, and the light in the cladding is re-coupled back to the core, and finally, coupled back to the second single-mode fiber 6. During the whole process, due to the existence of light between the fundamental mode and the higher-order mode The path difference satisfies the phase matching condition, thereby generating an interference spectrum on the spectrum analyzer 7, and measuring the temperature through the shift of the interference valley wavelength in the spectrum.

This embodiment achieves an improvement in temperature sensitivity by stimulating a high-order mode with extremely high temperature sensitivity, which not only solves the problem of cross-influence of temperature and refractive index, but also has the advantages of low cost, easy production, and small size, which greatly It improves the practicality of optical fiber temperature sensors and has great application prospects in production.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (7)

1. A temperature sensor based on seven-core optical fiber and bow-tie type, characterized in that it consists of a broadband light source (1), a first single-mode optical fiber (2), a first bent single-mode optical fiber (3), a seven-core optical fiber (4 ), a second bent single-mode optical fiber (5), a second single-mode optical fiber (6), and a spectrum analyzer (7). 2. The temperature sensor based on seven-core optical fiber and bow-tie type according to claim 1, characterized in that one end of the first single-mode optical fiber (2) is connected to the broadband light source (1) through an FC/APC connector. The first single-mode optical fiber (2) is connected as the input end of the structure, and the other end of the first single-mode optical fiber (2) is connected to the input end of the first bent single-mode optical fiber (3). 3. The temperature sensor based on seven-core optical fiber and bow-tie type according to claim 2, characterized in that the output end of the first bent single-mode optical fiber (3) is connected to one end of the seven-core optical fiber (4), and the seven-core optical fiber (4) The other end of the optical fiber (4) is connected to the input end of the second bent single-mode optical fiber (5). 4. The temperature sensor based on seven-core optical fiber and bow-tie type according to claim 3, characterized in that the output end of the second bent single-mode optical fiber (5) and the second single-mode optical fiber (6) as the output end One end is connected, and the other end of the second single-mode optical fiber (6) is connected to the input end of the spectrum analyzer (7) through an FC/APC connector. 5. A curvature sensor temperature measurement method, characterized in that using the seven-core optical fiber and a bowtie-type temperature sensor according to any one of claims 1-4, including the following steps: S1. After the incident light output by the broadband light source (1) enters the input end of the first curved single-mode fiber (3) through the first single-mode fiber (2), it passes through the ring with a larger curvature of the first curved single-mode fiber (3). The cladding-coating mode is excited in the zone and coupled back to the core after the curvature is reduced; S2. The light in the current center then enters the input end of the second curved single-mode fiber (5) through the seven-core optical fiber (4), and also excites the cladding-coating layer mode in the annular area with larger curvature. After passing through the annular area, The curvature is reduced and light in the cladding is recoupled back into the core; S3. Coupling back to the second single-mode fiber (6). During the whole process, due to the optical path difference between the fundamental mode and the higher-order mode, the phase matching condition is met, and an interference spectrum is generated on the spectrum analyzer (7). The temperature is measured through the shift of the interference valley wavelength in the spectrum. 6. A method for preparing a temperature sensor based on seven-core optical fiber and bow-tie type according to any one of claims 1-4, characterized in that it includes the following steps: In the first step, first connect the input end of the first single-mode optical fiber (2) to the broadband light source (1) through the FC/APC optical fiber connector, and connect the first single-mode optical fiber (2) output end from No. 1 of the casing. After inserting the end, pull out a length from end No. 2, then bend the single-mode optical fiber pulled out from end No. 2 to form a spherical structure, insert the output end of the single-mode optical fiber from end No. 2, pull it out from end No. 1, and tighten the single-mode optical fiber. mode optical fiber to form a first curved single-mode optical fiber; In the second step, cut the output end of the first bent single-mode optical fiber into a flat shape, and at the same time cut the seven-core optical fiber into a flat shape, place it in a fiber fusion splicer and fuse it with the output end of the cut flattened first bending single-mode optical fiber. The splicing point is the second step. At one fusion splice point, the length of the seven-core optical fiber is 4±0.05mm; The third step is to cut the input end of another single-mode fiber flat and fuse it with the other end of the seven-core fiber. Then insert the output end of the single-mode fiber into the No. 2 end of the casing and move the casing so that the seven-core The optical fiber is in the middle of the casing; The fourth step is to tighten the output end of the single-mode fiber in the third part to form a second curved single-mode fiber, and adjust the diameters of the first curved single-mode fiber and the second curved single-mode fiber structure through a precision displacement platform until the The diameter of the first bent single-mode optical fiber is 9±0.05mm, and the diameter of the second bent single-mode optical fiber structure is 9.7±0.05mm; Step 5: Use UV curing glue to fix both ends of the casing. 7. The method for preparing a temperature sensor based on seven-core optical fiber and bow-tie type according to claim 7, characterized in that the inner diameter of the casing is 8±0.05mm and the length is 1.6±0.1cm.