Sensitization structure of fiber bragg grating temperature sensor

Abstract

The utility model belongs to the field of fiber bragg grating temperature sensors, and relates to a fiber bragg grating temperature sensor sensitization structure which comprises a first metal substrate, a second metal substrate, a first optical fiber, a second optical fiber, a first hollow capillary tube, a second hollow capillary tube and a temperature fiber bragg grating. According to the utility model, the first optical fiber and the second optical fiber are sealed in the second capillary tube and are only influenced by temperature; by adopting the appearance combination of the two metal substrates with larger thermal expansion coefficient difference, the high sensitization of the fiber bragg grating to temperature sensing is realized, and the temperature measurement precision of the fiber bragg grating is effectively improved; the temperature sensor can realize high-sensitivity, high-precision and high-resolution measurement in a large-span temperature interval in cooperation with packaging of the hollow capillary tube.

Description

Technical Field

[0001] The utility model belongs to the field of optical fiber grating temperature sensors and relates to a sensitivity enhancement structure of an optical fiber grating temperature sensor. Background Art

[0002] Fiber Bragg grating temperature sensor uses the change of reflected wavelength with temperature to sense temperature. The temperature change is obtained by calculating the offset of reflected wavelength, and then the ambient temperature is measured. The specific principle is that the fiber Bragg grating temperature sensor is affected by the change of external temperature, the effective refractive index of the fiber core and the grating period change, and the fiber Bragg grating reflection center wavelength shifts. Under normal circumstances, the shift of the reflection center wavelength is fixed with the change of temperature, about 10pm / °C, so by calculating the offset of the reflection center wavelength, the temperature of the environment where the temperature sensor is located can be obtained, and the temperature can be measured. Due to the advantages of fiber Bragg grating temperature sensor such as small size, light weight, strong anti-electromagnetic interference ability, full optical transmission, easy to realize distributed sensing, etc., it is currently widely used in petrochemical, aerospace, health care, power transmission and security systems, and has great development potential.

[0003] Temperature is a factor that directly affects the wavelength change of fiber Bragg grating. People often directly use bare fiber Bragg grating as temperature sensor, but people hope that fiber Bragg grating can have strong mechanical strength and long life. At the same time, they also hope to improve the response sensitivity of fiber Bragg grating to temperature. Therefore, fiber Bragg grating temperature sensor also needs to be packaged. The main function of packaging technology is protection and sensitivity enhancement.

[0004] Before writing the grating in the optical fiber using the phase mask method, it is necessary to remove the organic coating of the optical fiber, and then use the phase mask method to write on the optical fiber. The main component of the optical fiber is SiO 2 , the optical fiber after removing the coating is very fragile and prone to breakage. After the grating is written, the grating needs to be packaged and protected. At the same time, the temperature sensitivity of the bare fiber grating is only 10pm / ℃. Reasonable and effective packaging can not only protect the grating, but also play a certain role in enhancing sensitivity.

[0005] There are two main types of fiber Bragg grating packaging technologies at present: natural bending and stress. The former mainly monitors temperature, while the latter is used in stress, displacement and other fields. However, if the natural bending amplitude is too large, it is difficult to achieve miniaturization of the sensor. If the stress packaging monitors the temperature alone, it is easily interfered by other packaging materials and structures. There are two major types of packaging: chip packaging and tube packaging. Chip packaging uses organic glue and other methods to fix the fiber Bragg grating on a sheet substrate, and transfers the deformation of the substrate caused by the change of the external environment temperature to the fiber Bragg grating, thereby realizing temperature sensing; tube packaging fixes the grating in a capillary tube, protects the grating, and drives the fiber Bragg grating through the deformation of the capillary tube to realize sensing.

[0006] The fiber Bragg grating temperature sensors in the prior art mainly use a single metal or a polymer as a substrate. Usually, the sensitivity of the fiber Bragg grating temperature sensors with a single metal as a substrate is not high enough and the temperature resolution is limited. Although the sensors with polymer as a substrate can significantly improve the sensitivity, it is difficult to measure the temperature in a wide temperature range due to the unstable properties of polymers at high or low temperatures. At the same time, the forward and reverse travel hysteresis of the polymer-based sensors is very large, which will cause a large error in the measurement results and limit the measurement accuracy. Summary of the invention

[0007] In order to solve the above technical problems, the technical problem to be solved by the utility model is to provide a temperature sensor with simple structure, high sensitivity and small size, which can realize accurate measurement of a larger temperature span range through the design of a sensitivity enhancement structure.

[0008] In order to achieve the above purpose, the technical solution of the utility model is as follows:

[0009] A fiber Bragg grating temperature sensor sensitivity enhancement structure comprises a first metal substrate, a second metal substrate, a first optical fiber, a second optical fiber, a first hollow capillary, a second hollow capillary, and a temperature fiber Bragg grating; the first metal substrate and the second metal substrate are both L-shaped, the head end of the first metal substrate is fixedly connected to the tail end of the second metal substrate, the head end of the second metal substrate is fixedly connected to the tail end of the first metal substrate, and the first metal substrate and the second metal substrate are surrounded by an installation space; the first optical fiber, the second optical fiber, the first hollow capillary, the second hollow capillary, and the temperature fiber Bragg grating are all located in the installation space; a first through groove is opened at the short side of the L-shaped first metal substrate, and the L-shaped A second through groove is provided on the short side of the second metal substrate; the first end of the first optical fiber is fixedly connected in the first through groove, and the first end of the second optical fiber is fixedly connected in the second through groove; the second end of the first optical fiber is connected to one end of the temperature fiber grating, and the other end of the temperature fiber grating is connected to the second end of the second optical fiber; the temperature fiber grating is located between the first optical fiber and the second optical fiber, and the center lines of the temperature fiber grating, the first optical fiber, and the second optical fiber coincide with each other; a first hollow capillary is mounted on the first optical fiber, and a second hollow capillary is mounted on the second optical fiber, the outer diameters of the first hollow capillary and the second hollow capillary are the same, and the center lines of the first hollow capillary and the second hollow capillary coincide with each other.

[0010] As a preferred technical solution, the distance between the first hollow capillary and the second hollow capillary is 20 to 40 mm.

[0011] As a preferred technical solution, the grating region length of the temperature fiber grating is 20-25 mm, and the wavelength is 1600-1900 nm.

[0012] As a preferred technical solution, the first optical fiber core has a diameter of 10 to 15 μm and a length of 10 to 15 cm.

[0013] As a preferred technical solution, the second optical fiber core has a diameter of 10 to 15 μm and a length of 10 to 15 cm.

[0014] As a preferred technical solution, the inner diameter of the first hollow capillary is 400-450 μm, and the outer diameter is 500-550 μm.

[0015] As a preferred technical solution, the inner diameter of the second hollow capillary is 400-450 μm, and the outer diameter is 500-550 μm.

[0016] As a preferred technical solution, the thermal expansion coefficient of the first metal substrate between 25-300°C is less than 5×10 -6 / ℃.

[0017] As a preferred technical solution, the thermal expansion coefficient of the second metal substrate between 25-300°C is greater than 18×10 -6 / ℃.

[0018] As a preferred technical solution, the diameters of the first through groove and the second through groove are both 40-45 μm.

[0019] The beneficial effects of the utility model are:

[0020] The utility model seals the first optical fiber and the second optical fiber in the second capillary tube so that they are only affected by temperature; by adopting the shape combination of two metal substrates with large differences in thermal expansion coefficients, the high sensitivity of the fiber Bragg grating to temperature sensing is achieved, and the temperature measurement accuracy of the fiber Bragg grating is effectively improved; with the packaging of the hollow capillary tube, the temperature sensor can achieve high-sensitivity, high-precision, and high-resolution measurement within a large temperature range. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 It is a structural schematic diagram of the utility model.

[0023] In the figure, 1-first metal substrate, 2-second metal substrate, 3-first optical fiber, 4-second optical fiber, 5-temperature fiber grating, 6-first hollow capillary, 7-second hollow capillary. DETAILED DESCRIPTION

[0024] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below with reference to specific illustrations.

[0025] like Figure 1As shown, a fiber Bragg grating temperature sensor sensitivity enhancement structure includes a first metal substrate 1, a second metal substrate 2, a first optical fiber 3, a second optical fiber 4, a first hollow capillary 6, a second hollow capillary 7, and a temperature fiber Bragg grating 5; the first metal substrate 1 and the second metal substrate 2 are both L-shaped, the head end of the first metal substrate 1 is fixedly connected to the tail end of the second metal substrate 2, the head end of the second metal substrate 2 is fixedly connected to the tail end of the first metal substrate 1, and the first metal substrate 1 and the second metal substrate 2 are surrounded by an installation space; the first optical fiber 3, the second optical fiber 4, the first hollow capillary 6, the second hollow capillary 7, and the temperature fiber Bragg grating 5 are all located in the installation space; a first through groove is opened at the short side of the L-shaped first metal substrate, and the L A second through groove is provided at the short side of the second metal substrate of the shape; the first end of the first optical fiber 3 is fixedly connected in the first through groove, and the first end of the second optical fiber 4 is fixedly connected in the second through groove; the second end of the first optical fiber 3 is connected to one end of the temperature fiber grating 5, and the other end of the temperature fiber grating 5 is connected to the second end of the second optical fiber 4; the temperature fiber grating 5 is located between the first optical fiber 3 and the second optical fiber 4, and the center lines of the temperature fiber grating 5, the first optical fiber 3, and the second optical fiber 4 coincide; a first hollow capillary 6 is mounted on the first optical fiber 3, and a second hollow capillary 7 is mounted on the second optical fiber 4, the outer diameters of the first hollow capillary 6 and the second hollow capillary 7 are the same, and the center lines of the first hollow capillary 6 and the second hollow capillary 7 coincide.

[0026] The head end of the first metal substrate 1 and the tail end of the second metal substrate 2 are fixedly connected by welding, and the head end of the second metal substrate 2 and the tail end of the first metal substrate 1 are fixedly connected by welding, and the first metal substrate 1 and the second metal substrate 2 are enclosed to form an installation space. The welding forms include but are not limited to laser welding, ultrasonic welding or argon arc welding.

[0027] The first optical fiber is suspended in the first hollow capillary, and the end of the first hollow capillary is sealed with ceramic glue; similar to the state of the first optical fiber, the second optical fiber is also suspended in the second hollow capillary, and the end of the second hollow capillary is sealed with ceramic glue.

[0028] There is a distance between the first hollow capillary 6 and the second hollow capillary 7, and the temperature fiber grating 5 is located within the distance. According to the size of the temperature fiber grating 5, the distance between the first hollow capillary 6 and the second hollow capillary 7 is 20-40 mm.

[0029] According to the needs of the temperature measurement range, the grating area length of the temperature fiber Bragg grating is 20 to 25 mm and the wavelength is 1600 to 1900 nm.

[0030] To meet the size of the temperature fiber Bragg grating and the temperature measurement requirements, the first optical fiber core diameter is 10-15 μm and the length is 10-15 cm; the second optical fiber core diameter is 10-15 μm and the length is 10-15 cm.

[0031] According to the requirements of packaging the first optical fiber and the second optical fiber, the inner diameter of the first hollow capillary is determined to be 400-450 μm, and the outer diameter is 500-550 μm; the inner diameter of the second hollow capillary is determined to be 400-450 μm, and the outer diameter is 500-550 μm.

[0032] In order to improve the sensitivity of the temperature sensor, the thermal expansion coefficient of the first metal substrate between 25-300°C is less than 5×10 -6 / ℃, the thermal expansion coefficient of the second metal substrate between 25-300℃ is greater than 18×10 -6 / ℃; Generally, the first metal substrate and the second metal substrate can be made of steel containing nickel and chromium. The diameters of the first through groove on the first metal substrate and the second through groove on the second metal substrate are both 40-45 μm.

[0033] The utility model seals the first optical fiber and the second optical fiber in the second capillary tube so that they are only affected by temperature; by adopting the shape combination of two metal substrates with large differences in thermal expansion coefficients, the high sensitivity of the fiber Bragg grating to temperature sensing is achieved, and the temperature measurement accuracy of the fiber Bragg grating is effectively improved; with the packaging of the hollow capillary tube, the temperature sensor can achieve high-sensitivity, high-precision, and high-resolution measurement within a large temperature range.

[0034] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A fiber Bragg grating temperature sensor sensitivity enhancement structure, characterized in that: The invention comprises a first metal substrate, a second metal substrate, a first optical fiber, a second optical fiber, a first hollow capillary, a second hollow capillary, and a temperature optical fiber grating; the first metal substrate and the second metal substrate are both L-shaped, the head end of the first metal substrate is fixedly connected to the tail end of the second metal substrate, the head end of the second metal substrate is fixedly connected to the tail end of the first metal substrate, and the first metal substrate and the second metal substrate are surrounded by an installation space; the first optical fiber, the second optical fiber, the first hollow capillary, the second hollow capillary, and the temperature optical fiber grating are all located in the installation space; a first through groove is opened at the short side of the L-shaped first metal substrate, and the L-shaped second metal substrate is A second through groove is provided at the short side; the first end of the first optical fiber is fixedly connected in the first through groove, and the first end of the second optical fiber is fixedly connected in the second through groove; the second end of the first optical fiber is connected to one end of the temperature fiber grating, and the other end of the temperature fiber grating is connected to the second end of the second optical fiber; the temperature fiber grating is located between the first optical fiber and the second optical fiber, and the center lines of the temperature fiber grating, the first optical fiber, and the second optical fiber coincide with each other; a first hollow capillary is mounted on the first optical fiber, and a second hollow capillary is mounted on the second optical fiber, the outer diameters of the first hollow capillary and the second hollow capillary are the same, and the center lines of the first hollow capillary and the second hollow capillary coincide with each other.

2. The fiber Bragg grating temperature sensor sensitivity enhancement structure according to claim 1, characterized in that: The distance between the first hollow capillary and the second hollow capillary is 20 to 40 mm.

3. The fiber Bragg grating temperature sensor sensitivity enhancement structure according to claim 1, characterized in that: The grating region length of the temperature fiber Bragg grating is 20 to 25 mm, and the wavelength is 1600 to 1900 nm.

4. The fiber Bragg grating temperature sensor sensitivity enhancement structure according to claim 1, characterized in that: The first optical fiber core has a diameter of 10 to 15 μm and a length of 10 to 15 cm.

5. The fiber Bragg grating temperature sensor sensitivity enhancement structure according to claim 1, characterized in that: The second optical fiber core has a diameter of 10 to 15 μm and a length of 10 to 15 cm.

6. The fiber Bragg grating temperature sensor sensitivity enhancement structure according to claim 1, characterized in that: The first hollow capillary has an inner diameter of 400 to 450 μm and an outer diameter of 500 to 550 μm.

7. The fiber Bragg grating temperature sensor sensitivity enhancement structure according to claim 1, characterized in that: The inner diameter of the second hollow capillary is 400-450 μm, and the outer diameter is 500-550 μm.

8. The fiber Bragg grating temperature sensor sensitivity enhancement structure according to claim 1, characterized in that: The thermal expansion coefficient of the first metal substrate between 25-300°C is less than 5×10 -6 / ℃.

9. The fiber Bragg grating temperature sensor sensitivity enhancement structure according to claim 1, characterized in that: The thermal expansion coefficient of the second metal substrate between 25-300°C is greater than 18×10 -6 / ℃.

10. The fiber Bragg grating temperature sensor sensitivity enhancement structure according to claim 1, characterized in that: The diameters of the first through groove and the second through groove are both 40-45 μm.

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