A fiber optic sensor for simultaneous monitoring of temperature and strain

Abstract

An optical fiber sensor capable of simultaneously measuring temperature and strain, belonging to the field of optical fiber sensing technology, is composed of an LD pump source, a wavelength division multiplexer, a Fabry-Perot cavity, a long-period fiber grating, a fixed stage, a translation stage, an erbium-doped fiber, a micro-fiber knot, a 10:90 optical coupler, a random grating, and a spectrum analyzer. The present invention utilizes the erbium-doped fiber to provide optical gain. Through the laser pumping of the pump source, Er<supgt;3+< / supgt; absorbs the pump light and generates stimulated radiation. After reaching the output laser threshold, random laser output is generated; the micro-fiber knot is for temperature sensing, and the long-period fiber grating cascaded with the Fabry-Perot cavity is used for strain sensing. By detecting the wavelength and intensity changes of the output light, the simultaneous measurement of temperature and strain can be achieved. It has the characteristics of simple manufacturing process, low cost, and high sensitivity, and can perform sensing measurements for different environments.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber sensors, and in particular relates to an optical fiber sensor based on a Fabry-Perot structure and a random grating and capable of simultaneously monitoring strain and temperature changes. Background Art

[0002] Fiber optic sensing technology is a new technology that has emerged with the rapid development of optical communications. In optical communication systems, optical fiber is the medium for long-distance transmission of light wave signals. When light waves are transmitted in optical fibers, characteristic parameters such as phase, frequency, amplitude, polarization state, etc. that characterize the light waves will change due to external factors such as temperature, pressure, magnetic field, electric field, etc. Therefore, optical fibers can be used as sensor elements to detect the size of various physical quantities that cause changes in light wave signals. Fiber optic sensors use light as a carrier of sensitive information and optical fiber as a medium for transmitting sensitive information. They have the characteristics of optical fiber and optical measurement.

[0003] Fiber optic sensors have attracted extensive attention due to their advantages such as high sensitivity, light weight, easy manufacturing, corrosion resistance, and anti-electromagnetic interference. However, most fiber optic sensors are based on traditional broadband sensing systems with wide 3dB bandwidth, low light intensity, and low optical signal-to-noise ratio. In addition, most fiber optic sensors cannot measure multiple parameters. Summary of the invention

[0004] 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 monitor temperature and strain simultaneously, and the sensor has the characteristics of simple structure, high sensitivity, stable signal, etc.

[0005] The technical solution adopted by the present invention to solve the technical problem is: an optical fiber sensor capable of simultaneously monitoring temperature and strain, comprising an LD pump source (1), a mobile station (2), a Fabry-Perot cavity (3), a long-period optical fiber grating (4), a fixed station (5), a wavelength division multiplexer (6), an erbium-doped optical fiber (7), a micro-fiber junction (8), a 10:90 optical coupler (9), a random grating (10), and an optical spectrum analyzer (11); the LD pump source (1) is connected to a port (601) of the wavelength division multiplexer (6), the mobile station (2) is connected to the Fabry-Perot cavity (3), and the other end of the Fabry-Perot cavity (3) is connected to the long-period optical fiber grating (4). The optical fiber grating (4) is connected to a long-period optical fiber grating (4), the other end of the long-period optical fiber grating (4) is connected to a fixing platform (5), the other end of the fixing platform (5) is connected to the second port (602) of a wavelength division multiplexer (6), the third port (603) of the wavelength division multiplexer (6) is connected to an erbium-doped optical fiber (7), the other end of the erbium-doped optical fiber (7) is connected to one end of a micro-fiber junction (8), the other end of the micro-fiber junction (8) is connected to the second port (902) of a 10:90 optical coupler (9), the third port (903) of the 10:90 optical coupler (9) is connected to a random grating (10), the second port (902) of the 10:90 optical coupler (9) is connected to an optical spectrum analyzer (11), and the end face is cut at an angle of 8° to suppress Fresnel reflection of the end face.

[0006] Beneficial effects of the present invention:

[0007] 1. Compared with the fiber optic sensor using ordinary broadband light source, the use of random laser as the light source has good stability and improves the measurement accuracy;

[0008] 2. The changes of temperature and strain can be monitored simultaneously by using micro-fiber junctions and the cascade of long-period fiber gratings and Fabry-Perot cavities; 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 This is a schematic diagram of the structure of an optical fiber sensor that can monitor strain and temperature changes simultaneously. 1 is an LD pump source; 2 is a mobile station; 3 is a Fabry-Perot cavity; 4 is a long-period fiber grating; 5 is a fixed station; 6 is a wavelength division multiplexer; 7 is an erbium-doped fiber; 8 is a micro-fiber junction; 9 is a 10:90 optical coupler; 10 is a random grating; 11 is a spectrum analyzer; 601 is a wavelength division multiplexer port 1; 602 is a wavelength division multiplexer port 2; 603 is a wavelength division multiplexer port 3; 901 is a 10:90 optical coupler port 1; 902 is a 10:90 optical coupler port 2; 903 is a 10:90 optical coupler port 3. DETAILED DESCRIPTION

[0011] The following is a detailed description of the structure and working principle of the present invention:

[0012] Figure 1 A random laser fiber sensor capable of simultaneously monitoring strain and temperature changes comprises an LD pump source (1), a mobile station (2), a Fabry-Perot cavity (3), a long-period fiber grating (4), a fixed station (5), a wavelength division multiplexer (6), an erbium-doped fiber (7), a micro-fiber junction (8), a 10:90 optical coupler (9), a random grating (10), and a spectrum analyzer (11); the LD pump source (1) is connected to a port (601) of the wavelength division multiplexer (6), the mobile station (2) is connected to the Fabry-Perot cavity (3), and the other end of the Fabry-Perot cavity (3) is connected to the long-period fiber. The optical fiber (7) is connected to a grating (4), the other end of the long-period fiber grating (4) is connected to a fixing platform (5), the other end of the fixing platform (5) is connected to the second port (602) of a wavelength division multiplexer (6), the third port (603) of the wavelength division multiplexer (6) is connected to an erbium-doped optical fiber (7), the other end of the erbium-doped optical fiber (7) is connected to one end of a micro-fiber junction (8), the other end of the micro-fiber junction (8) is connected to the second port (902) of an optical coupler (9), the third port (903) of the optical coupler (9) is connected to a random grating (10), the second port (902) of the optical coupler (9) is connected to an optical spectrum analyzer (11), and the end face is cut at an angle of 8° to suppress Fresnel reflection of the end face.

[0013] Working principle of a fiber optic sensor that can measure temperature and strain simultaneously:

[0014] 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 6 from the first port 601 of the wavelength division multiplexer 6, and enters the erbium-doped optical fiber 7 from the third port 603 of the wavelength division multiplexer 6. The laser excites the erbium ions in the erbium-doped optical fiber 7 to a high energy level, passes through the micro-fiber junction 8, enters from the second port 902 of the 10:90 optical coupler 9, and oscillates in the random grating 10 after being output from the third port 903 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 micro-fiber knot 8, and the erbium-doped fiber 7, and enters the long-period fiber grating 4 through the second port 602 of the wavelength division multiplexer 6. The long-period fiber grating 4 performs wavelength selection, and the light is reflected back to the optical path through the Fabry-Perot cavity 3, oscillates back and forth between the optical paths, performs frequency selection and mode selection, and the random laser finally obtained is output from the third port 901 of the 10:90 optical coupler 9. When the temperature of the micro-fiber knot 8 is changed, the transmission spectrum of the optical fiber will shift, so that the temperature can be sensed. When the mobile platform 2 translates 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 micro-fiber knot 8 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.

[0015] Example

[0016] Figure 1 The schematic diagram of the structure of a fiber optic sensor capable of simultaneously measuring temperature and strain of the present invention. The laser wavelength of the LD pump source 1 is 980nm, the wavelength division multiplexer 2 is 980nm / 1550nm, the total length of the LPFG-FP structure sensor formed by the cascade of the long period fiber grating 4 and the Fabry-Perot cavity 3 is 3.6cm, and the analysis can be selected at 1544.18nm, 1557nm, 1556.27nm and 1566.92nm. The distance between the fixed stage 5 and the translation stage 2 is 5cm. The length of the erbium-doped fiber 7 is 2m, the length of the micro-fiber knot 8 is 2cm, 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, with a length of 1cm and a reflectivity of 50% to 95%.

[0017] 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 6 from the first port 601 of the wavelength division multiplexer 6, and enters the erbium-doped optical fiber 7 from the third port 603 of the wavelength division multiplexer 6. The laser excites the erbium ions in the erbium-doped optical fiber 7 to a high energy level, passes through the micro-fiber junction 8, enters from the second port 902 of the 10:90 optical coupler 9, and oscillates in the random grating 10 after being output from the third port 903 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 micro-fiber knot 8, and the erbium-doped fiber 7, and enters the long-period fiber grating 4 through the second port 602 of the wavelength division multiplexer 6. The long-period fiber grating 4 performs wavelength selection, and the light is reflected back to the optical path through the Fabry-Perot cavity 4, oscillates back and forth between the optical paths, performs frequency selection and mode selection, and the random laser finally obtained is output from the third port 901 of the 10:90 optical coupler 9. When the temperature of the micro-fiber knot 8 is changed, the transmission spectrum of the optical fiber will shift, so that the temperature can be sensed. When the mobile station 2 translates 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 micro-fiber knot 8 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.

[0018] 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. A random optical fiber sensor capable of simultaneously monitoring temperature and strain, characterized in that The invention comprises an LD pump source (1), a mobile station (2), a Fabry-Perot cavity (3), a long-period fiber grating (4), a fixed station (5), a wavelength division multiplexer (6), an erbium-doped fiber (7), a micro-fiber junction (8), a 10:90 optical coupler (9), a random grating (10), and a spectrum analyzer (11); the LD pump source (1) is connected to a port (601) of the wavelength division multiplexer (6), the mobile station (2) is connected to the Fabry-Perot cavity (3), the other end of the Fabry-Perot cavity (3) is connected to the long-period fiber grating (4), and the other end of the long-period fiber grating (4) is connected to the fixed station (5). , the other end of the fixing platform (5) is connected to the second port (602) of the wavelength division multiplexer (6), the third port (603) of the wavelength division multiplexer (6) is connected to the erbium-doped optical fiber (7), the other end of the erbium-doped optical fiber (7) is connected to one end of the micro-fiber junction (8), the other end of the micro-fiber junction (8) is connected to the second port (902) of the 10:90 optical coupler (9), the third port (903) of the 10:90 optical coupler (9) is connected to the random grating (10), the first port (901) of the 10:90 optical coupler (9) is connected to the spectrum analyzer (11), and the end face is cut at an angle of 8° to suppress the Fresnel reflection of the end face; the random grating (10) is engraved on the single-mode optical fiber; The pump light output by the LD pump source (1) enters the wavelength division multiplexer (6) through a port (601) of the wavelength division multiplexer (6), and enters the erbium-doped optical fiber (7) through a port (603) of the wavelength division multiplexer (6). The laser excites the erbium ions in the erbium-doped optical fiber (7) to a high energy level, and enters through a port (902) of a 10:90 optical coupler (9) after passing through a micro-fiber junction (8). After being output from the port (903) of the 10:90 optical coupler (9), the pump light oscillates in a random grating (10). Part of the light is reflected and returns through the original path, and enters a long-period fiber grating (4) through a port (602) of the wavelength division multiplexer (6) for wavelength selection, and then is reflected back to the optical path through a Fabry-Perot cavity (3). The light oscillates back and forth between the optical paths, completing the frequency conversion. The random laser finally obtained is output from a port (901) of a 10:90 optical coupler (9) by selecting a mode. The temperature of the micro-fiber junction (8) is changed to shift the transmission spectrum of the optical fiber, thereby realizing temperature sensing. The mobile stage (2) is translated to change the laser, and the wavelength drift and intensity change are recorded. The sensitivity of stress to wavelength and intensity is calculated through multiple experiments. The ring mirror temperature of the structural area of ​​the micro-fiber junction (8) is changed to change the output laser, and the wavelength drift and intensity change are recorded. The sensitivity of stress to wavelength and intensity is calculated through multiple experiments. After combining the above experimental data and theoretical analysis, a coefficient matrix is ​​obtained. When the stress and temperature are changed at the same time, the wavelength drift and intensity change are first measured, and the stress and temperature to be measured are calculated through the coefficient matrix.

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