A fiber optic sensor that can measure temperature and strain simultaneously

Abstract

An optical fiber sensor capable of simultaneously measuring temperature and strain belongs to the field of optical fiber sensing technology and is composed of a pump source, a wavelength division multiplexer, a 3-dB coupler, a polarization-maintaining optical fiber, an optical fiber grating, a fixed base, a translation stage, an erbium-doped optical fiber wound between the fixed base and the translation stage, a 10:90 optical coupler, and a random grating. The present invention utilizes erbium-doped optical fiber to provide optical gain, and through laser pumping by a pump source, Er 3+ It absorbs pump light and generates stimulated radiation. After reaching the output laser threshold, it generates random laser output. The Sagnac loop structure and fiber Bragg grating are used as temperature sensors, and the erbium-doped fiber winding device is used as a strain sensor. By detecting the wavelength and intensity changes of the output light, the temperature and strain can be measured simultaneously. It has the characteristics of simple manufacturing process, low cost, high sensitivity, etc., and can perform sensing measurements on different ring mirrors.

Description

Technical Field

[0001] The invention relates to an optical fiber sensor, in particular to an optical fiber sensor based on a Sagnac loop structure and random laser, and belongs to the technical field of optical fiber sensing. Background Art

[0002] The working principle of the fiber optic sensor is that the light emitted by the light source enters the ring mirror to be measured through the optical fiber. Due to changes in the temperature, strain and other factors of the ring mirror, the properties of the transmitted light in the fiber optic sensor change. The correlation between the two is analyzed to obtain the parameters of the ring mirror to be measured. Generally, a broadband light source is used as the light source of the sensor. When sensing changes in the ring mirror parameters, its sensing element is easily interfered by other factors, resulting in low sensor sensitivity and limited range of measurement. In addition, the sensor head of the commonly used stress fiber optic sensor uses a fixed table and a translation table mounted on structures such as optical fibers of different materials, fiber gratings, and special interferometers to apply stress. The sensor head of the commonly used temperature fiber optic sensor uses a combination of fiber gratings and special structures to sense temperature and place it in a temperature control room for temperature adjustment. A fiber optic sensor can only measure specific ring mirror parameters and has a single application range. Summary of the invention

[0003] In order to overcome the above-mentioned deficiencies of the prior art, an object of the present invention is to provide an optical fiber sensor that can simultaneously measure temperature and strain, and the optical fiber sensor has the characteristics of simple structure, high sensitivity, good stability, etc.

[0004] The technical solution adopted by the present invention to solve the technical problem is:

[0005] An optical fiber sensor capable of simultaneously measuring temperature and strain, comprising an LD pump source (1), a wavelength division multiplexer (2), a 3-dB coupler (3), a polarization-maintaining optical fiber (4), an optical fiber grating (5), a fixed base (6), a translation stage (7), an erbium-doped optical fiber (8) wound between the fixed base and the translation stage, a 10:90 optical coupler (9), and a random grating (10); the LD pump source (1) is connected to a port (201) of the wavelength division multiplexer (2), and a second port (202) of the wavelength division multiplexer (2) is connected to a port (201) of the 3-dB coupler (3). (301), the other end of the 3-dB coupler (3) is connected to the two ends of the polarization-maintaining optical fiber (4), the four ports (304) of the 3-dB coupler (3) are connected to the fiber grating (5), the three ports (203) of the wavelength division multiplexer (2) are connected to one end of the erbium-doped optical fiber (8) wound between the fixed base and the translation stage, the other end of the erbium-doped optical fiber (8) wound between the fixed base and the translation stage is connected to the first port (901) of the 10:90 optical coupler (9), and the second port (902) of the 10:90 optical coupler (9) is connected to the random grating (10). The central wavelength of a section of the fiber grating (5) is close to the central wavelength of the random grating (10), and the random grating (10) provides random laser feedback, and the random laser is output from the three ports (903) of the 10:90 optical coupler (9). The fiber end faces at the left and right ends of the entire optical fiber sensor are polished at an angle of 8°.

[0006] Beneficial effects of the present invention:

[0007] 1. Using random laser as the light source, compared with the fiber optic sensor using ordinary broadband light source, it can be well coupled with the optical fiber, has good stability and improves the measurement accuracy;

[0008] 2. The Sagnac loop structure and fiber Bragg grating are used as the temperature sensor head, and the erbium-doped fiber winding device is used as the strain sensor head. The temperature and stress can be sensed and measured at the same time, which effectively improves the temperature sensitivity and stress sensitivity, improves the resolution of the sensor, and runs more stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be further described below in conjunction with the accompanying drawings and embodiments thereof.

[0010] Figure 1 The diagram is a schematic structural diagram of an optical fiber sensor capable of simultaneously measuring temperature and strain according to the present invention.

[0011] 1 is LD pump source, 2 is wavelength division multiplexer; 3 is 3-dB coupler; 4 is polarization-maintaining fiber; 5 is fiber grating; 6 is fixed base; 7 is translation stage; 8 is erbium-doped fiber wound between fixed base and translation stage; 9 is 10:90 optical coupler; 10 is random grating; 201 is the first port of wavelength division multiplexer; 202 is the second port of wavelength division multiplexer; 203 is the third port of wavelength division multiplexer; 301 is the first port of 3-dB coupler; 302 is the second port of 3-dB coupler; 303 is the third port of 3-dB coupler; 404 is the fourth port of 3-dB coupler; 901 is the first port of 10:90 optical coupler; 902 is the second port of 10:90 optical coupler; 903 is the third port of 10:90 optical coupler.

[0012] Specific implementation method

[0013] The following is a detailed description of the structure and working principle of the present invention:

[0014] Figure 1 In the invention, an optical fiber sensor capable of simultaneously measuring temperature and strain comprises an LD pump source 1, a wavelength division multiplexer 2, a 3-dB coupler 3, a polarization-maintaining optical fiber 4, an optical fiber grating 5, a fixed base 6, a translation stage 7, an erbium-doped optical fiber 8 wound between the fixed base and the translation stage, a 10:90 optical coupler 9, and a random grating 10; the LD pump source 1 is connected to a port 201 of the wavelength division multiplexer 2, and a second port 202 of the wavelength division multiplexer 2 is connected to a port 201 of the 3-dB coupler 3. 301, the other end of the 3-dB coupler 3 is connected to the two ends of the polarization-maintaining fiber 4, the four ports 304 of the 3-dB coupler 3 are connected to the fiber grating 5, the three ports 203 of the wavelength division multiplexer 2 are connected to one end of the erbium-doped fiber 8 wound between the fixed base and the translation stage, the other end of the erbium-doped fiber 8 wound between the fixed base and the translation stage is connected to the first port 901 of the 10:90 optical coupler 9, and the second port 902 of the 10:90 optical coupler 9 is connected to the random grating 10. The central wavelength of a section of the fiber grating 5 is close to the central wavelength of the random grating 10, and the random grating 10 provides random laser feedback, and the random laser is output from the third port 903 of the 10:90 optical coupler 9.

[0015] Working principle of a fiber optic sensor that can measure temperature and strain simultaneously:

[0016] A fiber optic sensor that can measure temperature and strain simultaneously Figure 1The components shown are connected well. The 980nm pump light output by the LD pump source 1 enters the wavelength division multiplexer 2 from the first port 201 of the wavelength division multiplexer 2, and enters the erbium-doped optical fiber 8 wound between the fixed base and the translation stage from the third port 203 of the wavelength division multiplexer 2. The laser excites the erbium ions in the erbium-doped optical fiber 8 wound between the fixed base and the translation stage to a high energy level, enters from the first port 901 of the 10:90 optical coupler 9, and oscillates in the random grating 10 after being output from the second port 902 of the 10:90 optical coupler 9. Under the reflection of the random grating 10, part of the light returns to the optical path, passes through the 10:90 optical coupler 9, the erbium-doped optical fiber 8 wound between the fixed base and the translation stage, and enters the first port 301 of the 3-dB coupler 3 from the second port 202 of the wavelength division multiplexer 2. After the input light enters the 3-dB coupler 3, it is divided into two beams of light with the same intensity. One beam is output from the second port 302 of the 3-dB coupler 3 and propagates in the clockwise direction, and the other beam is output from the third port 303 of the 3-dB coupler 3 and propagates in the counterclockwise direction. Due to the birefringence effect of the polarization-maintaining optical fiber 4, the two beams of light An opposite phase difference will be generated. After the two are coupled, an interference spectrum can be formed at the four ports 304 of the 3-dB coupler 3. Changing the temperature of the polarization-maintaining fiber 4 will cause the transmission spectrum of the Sagnac loop structure to shift, thereby realizing temperature sensing. The light output from the four ports 304 of the 3-dB coupler 3 is wavelength-selected in the fiber grating 5. The light is reflected back into the optical path through the fiber grating 5, oscillates back and forth between the optical paths, performs frequency selection and mode selection, and the final random laser is output from the three ports 903 of the 10:90 optical coupler 9. When the translation stage 7 of the erbium-doped fiber winding device is translated for a certain distance, the corresponding laser changes, and the wavelength drift and intensity change are recorded. After multiple experiments, the sensitivity of stress to wavelength and intensity is calculated; when the ring mirror temperature of the Sagnac loop structure area is changed, the output laser changes, and the wavelength drift and intensity change are recorded. After multiple experiments, the sensitivity of stress to wavelength and intensity is calculated. After combining the above experimental data and theoretical analysis, a coefficient matrix can be obtained. When the stress and temperature are changed at the same time, the wavelength drift and intensity change are measured first, and the corresponding stress and temperature to be measured can be calculated through the coefficient matrix. Example

[0017] Figure 1The schematic diagram of the structure of an optical fiber sensor capable of measuring temperature and strain simultaneously is shown in the figure. The laser wavelength of the LD pump source 1 is 980nm, the wavelength division multiplexer 2 is 980nm / 1550nm, the 3-dB coupler 3 is 2×2, the polarization-maintaining optical fiber 4 is 20cm long, the 3-dB coupler 3 and the polarization-maintaining optical fiber 4 form a Sagnac loop structure, the optical fiber grating 5 is 2cm long, the reflectivity is 95% to 99%, and the central wavelength is 1550nm. The length of the erbium-doped optical fiber 8 between the fixed base and the translation stage is 2m, the height of the fixed base 6 and the translation stage 7 are both 10cm, and the distance between the two is 0.22cm. The coupling ratio of the 10:90 optical coupler 9 is 10:90, and the random grating 10 is engraved on the single-mode optical fiber, the length is 1cm, and the reflectivity is 50% to 95%.

[0018] A fiber optic sensor that can measure temperature and strain simultaneously Figure 1The components shown are connected well. The 980nm pump light output by the LD pump source 1 enters the wavelength division multiplexer 2 from the first port 201 of the wavelength division multiplexer 2, and enters the erbium-doped optical fiber 8 wound between the fixed base and the translation stage from the third port 203 of the wavelength division multiplexer 2. The laser excites the erbium ions in the erbium-doped optical fiber 8 wound between the fixed base and the translation stage to a high energy level, enters from the first port 901 of the 10:90 optical coupler 9, and oscillates in the random grating 10 after being output from the second port 902 of the 10:90 optical coupler 9. Under the reflection of the random grating 10, part of the light returns to the optical path, passes through the 10:90 optical coupler 9, the erbium-doped optical fiber 8 wound between the fixed base and the translation stage, and enters the first port 301 of the 3-dB coupler 3 from the second port 202 of the wavelength division multiplexer 2. After the input light enters the 3-dB coupler 3, it is divided into two beams of light with the same intensity. One beam is output from the second port 302 of the 3-dB coupler 3 and propagates in the clockwise direction, and the other beam is output from the third port 303 of the 3-dB coupler 3 and propagates in the counterclockwise direction. Due to the birefringence effect of the polarization-maintaining optical fiber 4, the two beams of light An opposite phase difference will be generated. After the two are coupled, an interference spectrum can be formed at the four ports 304 of the 3-dB coupler 3. Changing the temperature of the polarization-maintaining fiber 4 will cause the transmission spectrum of the Sagnac loop structure to shift, thereby realizing temperature sensing. The light output from the four ports 304 of the 3-dB coupler 3 is wavelength-selected in the fiber grating 5. The light is reflected back into the optical path through the fiber grating 5, oscillates back and forth between the optical paths, performs frequency selection and mode selection, and the final random laser is output from the three ports 903 of the 10:90 optical coupler 9. When the translation stage 7 of the erbium-doped fiber winding device is translated for a certain distance, the corresponding laser changes, and the wavelength drift and intensity change are recorded. After multiple experiments, the sensitivity of stress to wavelength and intensity is calculated; when the ring mirror temperature of the Sagnac loop structure area is changed, the output laser changes, and the wavelength drift and intensity change are recorded. After multiple experiments, the sensitivity of stress to wavelength and intensity is calculated. After combining the above experimental data and theoretical analysis, a coefficient matrix can be obtained. When the stress and temperature are changed at the same time, the wavelength drift and intensity change are measured first, and the corresponding stress and temperature to be measured can be calculated through the coefficient matrix.

[0019] The above embodiment is only one of the preferred solutions among all the solutions of the present invention. Other simple changes to an optical fiber sensor that can simultaneously measure temperature and strain fall within the scope of protection of the present invention.

Claims

1. An optical fiber sensor capable of simultaneously measuring temperature and strain, comprising an LD pump source (1), a wavelength division multiplexer (2), a 3-dB coupler (3), a polarization-maintaining optical fiber (4), an optical fiber grating (5), a fixed base (6), a translation stage (7), an erbium-doped optical fiber (8) wound between the fixed base and the translation stage, a 10:90 optical coupler (9), and a random grating (10); the LD pump source (1) is connected to a port (201) of the wavelength division multiplexer (2), a second port (202) of the wavelength division multiplexer (2) is connected to a port (301) of the 3-dB coupler (3), a second port (302) and a third port (303) of the 3-dB coupler (3) are respectively connected to two ends of the polarization-maintaining optical fiber (4), and a 3-dB coupler (3) is connected to a second port (302) and a third port (303) of the 3-dB coupler (3) are respectively connected to two ends of the polarization-maintaining optical fiber (4), and a 3-dB coupler (3) is connected to a second port (303) of the 3-dB coupler (3). The four ports (304) of the dB coupler (3) are connected to the fiber Bragg grating (5), the three ports (203) of the wavelength division multiplexer (2) are connected to one end of the erbium-doped fiber (8) wound between the fixed base and the translation stage, the other end of the erbium-doped fiber (8) wound between the fixed base and the translation stage is connected to the first port (901) of the 10:90 optical coupler (9), and the second port (902) of the 10:90 optical coupler (9) is connected to the random grating (10); the central wavelength of the fiber Bragg grating (5) is close to the central wavelength of the random grating (10), the random grating (10) provides random laser feedback, and the random laser is output from the three ports (903) of the 10:90 optical coupler (9), and the fiber end faces at the left and right ends of the entire optical fiber sensor are polished at an angle of 8°; The laser wavelength of the LD pump source (1) is 980 nm.

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