Temperature strain optical fiber sensor based on double-vernier effect

Abstract

The invention discloses a temperature strain optical fiber sensor based on a double-vernier effect, and belongs to the technical field of optical fiber sensing. The sensor is composed of a wide-spectrum light source, a spectrum analyzer, a 2 * 2 coupler, a 1 * 2 coupler, a high-birefringence optical fiber, a single-mode optical fiber and a polarization controller. Two sections of high-birefringence optical fibers are welded with a fast axis at an included angle of 90 degrees and form a Solc-Sagnac interferometer with a polarization controller and a 1 * 2 coupler, a single vernier effect is generated, and fine spectrums in transmitted spectrums are filtered out; meanwhile, a Sagnac interferometer composed of the third-section high-birefringence optical fiber, a polarization controller and a 1 * 2 coupler serves as a reference interferometer, the Sagnac interferometer and the Solc-Sagnac interferometer are connected in parallel through the 2 * 2 coupler to form a Michelson interference structure, and the double-vernier effect is achieved. The free spectral ranges of the two interferometers are close by optimizing the length relation of the high-birefringence optical fibers, so that the sensing sensitivity is further amplified through interference after the two interferometers are connected in parallel.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber sensing, in particular to a temperature and strain optical fiber sensor based on double vernier effect. BACKGROUND

[0002] Optical fiber sensors have shown superior performance and reliability in harsh conditions in the fields of industrial monitoring, environmental detection, and biomedical engineering, due to their high sensitivity, resistance to electromagnetic interference, corrosion resistance, small size, and low cost. In particular, in terms of temperature and strain sensing, optical fiber sensors have become a research hotspot and are widely used in key fields such as structural health monitoring, aerospace, and petrochemical industry.

[0003] Currently, common optical fiber sensors are mainly based on two principles: fiber grating and fiber interferometer. Fiber grating sensors have attracted widespread attention due to their relatively simple fabrication process and ease of integration. However, the sensitivity of fiber grating sensors is usually low, making it difficult to meet the demand for high-precision measurement. On the other hand, fiber interferometer sensors can achieve high sensitivity, but often have complex structures, high process requirements, and are sensitive to environmental disturbances, resulting in poor stability and repeatability.

[0004] To further improve the sensitivity of fiber interferometer sensors, researchers have introduced the vernier effect. The vernier effect amplifies the shift of the sensing signal by superimposing the spectra of two interferometers, thereby significantly improving the sensitivity. However, traditional vernier effects are usually based on single vernier structures, such as single Sagnac or single Mach-Zehnder interferometers, which have limited sensitivity amplification and often have complex spectra, large envelope fitting errors, and other problems.

[0005] Therefore, there is an urgent need in the prior art for a temperature and strain dual-parameter optical fiber sensor with simple structure, low cost, high sensitivity, small size, and good repeatability and stability. SUMMARY

[0006] Based on the deficiencies of the prior art, the present application aims to provide a temperature and strain optical fiber sensor based on double vernier effect, which realizes high-sensitivity temperature and strain dual-parameter measurement.

[0007] To achieve the above-mentioned purpose, the technical solutions adopted by the present application are as follows: A temperature and strain optical fiber sensor based on double vernier effect, the sensor is connected in parallel with a Solc-Sagnac interferometer and a Sagnac interferometer to form a Michelson interference structure, to realize double vernier effect, for amplifying the sensing sensitivity of temperature and strain; The sensor includes a broadband light source, a spectrum analyzer, a 2×2 coupler, a first 1×2 coupler, a second 1×2 coupler, a first section of high birefringence fiber, a second section of high birefringence fiber, a first polarization controller, a second polarization controller, and a third section of high birefringence fiber; The broadband light source is connected to the first input port of the 2×2 coupler, the spectrometer is connected to the second input port of the 2×2 coupler, the first 1×2 coupler input port is connected to the first output port of the 2×2 coupler, and the second 1×2 coupler input port is connected to the second output port of the 2×2 coupler. The first output port of the first 1×2 coupler is connected to one end of the first high birefringence fiber, the other end of the first high birefringence fiber is connected to one end of the second high birefringence fiber, the other end of the second high birefringence fiber is connected to one end of the first polarization controller, and the other end of the first polarization controller is connected to the second output port of the first 1×2 coupler, forming a Solc-Sagnac interferometer. The first output port of the second 1×2 coupler is connected to one end of the second polarization controller, the other end of the second polarization controller is connected to one end of the third high birefringence fiber, and the other end of the third high birefringence fiber is connected to the second output port of the second 1×2 coupler, forming a Sagnac interferometer.

[0008] Furthermore, the polarization rotation angle introduced by controlling the connection between the first high birefringence fiber segment and the first output port of the first 1×2 coupler via the first polarization controller is further adjusted. The polarization rotation angle introduced by connecting the second high-birefringence fiber segment to the first polarization controller sum .

[0009] The first and second segments of highly birefringent optical fibers are fused together at a 90° angle along their fast axes at the first output end of the 1×2 coupler to form a SOlc-type filter structure. The longer first segment serves as the sensing arm, and the shorter second segment serves as the reference arm. The two segments of different lengths produce a single vernier effect, and their transmission spectrum contains only the envelope spectrum, filtering out the fine spectrum.

[0010] The Sagnac interferometer (SI) includes a 1×2 coupler, a polarization controller, and a third segment of highly birefringent fiber (HBF3). The input of the 1×2 coupler is connected to the second output of the 2×2 coupler. The SI serves as a reference interferometer connected in parallel with the SSI to form a Michelson interferometer, generating a double vernier effect.

[0011] The lengths L1 of the first high birefringence fiber, L2 of the second high birefringence fiber, and L3 of the third high birefringence fiber satisfy a specific relationship so that the free spectral range of the envelope spectrum generated by the SSI is similar to the free spectral range of the SI. Thus, after the two are connected in parallel, a double vernier effect is generated through interference, achieving a double amplification of temperature and strain sensitivity.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The two high birefringence optical fibers constituting the SSI are fused together with their fast axes at a 90° angle, which eliminates the fine spectrum in the transmission spectrum and avoids envelope fitting error.

[0013] 2. By connecting the single vernier effect in parallel with the reference interferometer to form a Michelson interferometer, a double vernier effect is generated, thereby achieving a double amplification of the sensing sensitivity.

[0014] 3. The sensor described in this invention has a simple structure, low cost, high sensitivity, and small sensing unit size, while also exhibiting good repeatability and stability. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the temperature strain fiber optic sensor based on the dual vernier effect of the present invention.

[0016] Figure 2 This invention relates to the relationship between the spectral response of a temperature strain fiber optic sensor based on the dual vernier effect and temperature.

[0017] Figure 3 This invention relates to the relationship between the wavelength at the low point of the spectral response envelope spectrum of the single vernier effect and the double vernier effect in a temperature strain fiber optic sensor based on the double vernier effect.

[0018] Figure 4 This invention relates the spectral response of a temperature strain fiber optic sensor based on the dual vernier effect to the stress variation.

[0019] Figure 5 This invention relates to the relationship between the wavelength at the low point of the spectral response envelope spectrum of the single vernier effect and the double vernier effect in a temperature strain fiber optic sensor based on the double vernier effect.

[0020] In the diagram: 1-Broadband light source, 2-Spectrum analyzer, 3-2×2 coupler, 4-First 1×2 coupler, 5-Second 1×2 coupler, 6-First high birefringence fiber, 7-Second high birefringence fiber, 8-First polarization controller, 9-Second polarization controller, 10-Third high birefringence fiber, 301-First input port of 2×2 coupler, 302-Second input port of 2×2 coupler, 303-First output port of 2×2 coupler, 304-Second output port of 2×2 coupler, 401-Input port of first 1×2 coupler, 402-First output port of first 1×2 coupler, 403-Second output port of first 1×2 coupler, 501-Input port of second 1×2 coupler, 502-First output port of second 1×2 coupler, 503-Second output port of second 1×2 coupler. Detailed Implementation

[0021] The objectives and technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0022] like Figure 1 This embodiment provides a specific construction method for a temperature strain fiber optic sensor based on the dual vernier effect. The structure includes a broadband light source 1, a spectrum analyzer 2, a 2×2 coupler 3, a first 1×2 coupler 4, a second 1×2 coupler 5, a first high birefringence fiber 6, a second high birefringence fiber 7, a first polarization controller 8, a second polarization controller 9, and a third high birefringence fiber 10.

[0023] The broadband light source 1 is connected to the first input port 301 of the 2×2 coupler, the spectrometer 2 is connected to the second input port 302 of the 2×2 coupler, the first input port 401 of the first 1×2 coupler is connected to the first output port 303 of the 2×2 coupler, the second input port 501 of the second 1×2 coupler is connected to the second output port 304 of the 2×2 coupler, the first output port 402 of the first 1×2 coupler is connected to one end of the first high birefringence fiber 6, the other end of the first high birefringence fiber 6 is connected to one end of the second high birefringence fiber 7, the other end of the second high birefringence fiber 7 is connected to one end of the first polarization controller 8, the other end of the first polarization controller 8 is connected to the second output port 403 of the first 1×2 coupler, the first output port 502 of the second 1×2 coupler is connected to one end of the second polarization controller 9, the other end of the second polarization controller 9 is connected to one end of the third high birefringence fiber 10, and the other end of the third high birefringence fiber 10 is connected to the second output port 503 of the second 1×2 coupler.

[0024] Specifically, broadband light source 1 has a bandwidth of 400 nm.

[0025] In one specific embodiment of the present invention, the first high birefringence fiber 6 has a length of 30 cm, the second high birefringence fiber 7 has a length of 20 cm, and the angle between the fast axis of the first high birefringence fiber 6 and the second high birefringence fiber 7 is 90°.

[0026] Specifically, the first high-birefringence fiber 6 serves as the sensing arm in the temperature and strain sensing process. The Solc-Sagnac interferometer structure, composed of the first 1×2 coupler 4, the first polarization controller 8, the first high-birefringence fiber 6, and the second high-birefringence fiber 7, can generate a single vernier effect, thereby amplifying the sensitivity of temperature and strain sensing.

[0027] Specifically, based on the transmission spectrum formula output by the Solc-Sagnac interferometer, the angle between the fast axis of the first high-birefringence fiber 6 and the second high-birefringence fiber 7 in this invention is 90°, filtering out the fine spectrum corresponding to the high-frequency periodic function; simultaneously, the polarization rotation angle introduced by controlling the connection between the first high-birefringence fiber 6 and the first output port 402 of the first 1×2 coupler 4 via the first polarization controller 8 is... The polarization rotation angle introduced by connecting the second high birefringence fiber 7 to the first polarization controller 8 sum The transmission spectrum output by the Solc-Sagnac interferometer can be expressed as: (1) in, For wavelength, , The birefringence and length of the first high-birefringence fiber 6 are given. , The birefringence and length of the second high birefringence fiber 7 are given.

[0028] In this embodiment of the invention, when the first segment of the high birefringence optical fiber 6 is subjected to external temperature or strain, the single vernier effect output transmission spectrum will shift. The temperature change or strain can be determined by the shift in the envelope spectrum, and the corresponding sensing sensitivity can be expressed as: (2) (3) Among them, S t1 S ε1 Represent the temperature and strain sensitivity of the single vernier effect, respectively, and the resonant wavelength λ. m The condition 2πB1L1 / λ = 2mπ is satisfied (m is an integer).

[0029] In one specific embodiment of the present invention, the length of the third high-birefringence fiber 10 is 9.4 cm. The Sagnac interferometer structure, consisting of the second 1×2 coupler 5, the second polarization controller 9, and the third high-birefringence fiber 10, is connected in parallel with the Solc-Sagnac interferometer through a 2×2 coupler 3 to form a Michelson interferometer, generating a double vernier effect and achieving a double amplification of temperature and strain sensing sensitivity.

[0030] Specifically, the transmission spectrum formula output by the Sagnac interferometer can be expressed as: (4) Therefore, the output transmission spectrum of the temperature strain fiber optic sensor based on the dual vernier effect implemented in this invention can be expressed as: (5) in, , The birefringence and length of the third high birefringence fiber 10 are given.

[0031] In this embodiment of the invention, when the first segment of the high birefringence optical fiber 6 is subjected to external temperature or strain, the sensor generates a double vernier effect, and the output transmission spectrum will shift. The temperature change or strain is determined by the shift of the envelope spectrum, and the corresponding sensing sensitivity can be expressed as: (6) (7) Among them, S t2 S ε2 These represent the temperature and strain sensitivity of the double vernier effect, respectively.

[0032] To evaluate the actual performance of the developed sensor and verify the double amplification effect of the dual vernier effect, the temperature and strain sensing characteristics of a single Solc-Sagnac interferometer and a complete sensor were experimentally verified. In the temperature response test, the first segment of the high birefringence fiber 6 was placed in a temperature-controlled environment, and the temperature was increased in 1°C increments within the range of 29°C to 35°C, with the transmission spectrum corresponding to each temperature point recorded. The experimental results show that as the temperature increases, the wavelength corresponding to the low point of the spectral response envelope shifts blue, moving towards shorter wavelengths. The relationship between the sensor's temperature and the wavelength of the low point of the envelope spectrum is as follows: Figure 2 As shown. Further linear fitting of the data yielded a temperature sensitivity of −3.61 nm / ℃ for the single Solc-Sagnac interferometer and −61.88 nm / ℃ for the sensor. The amplification factor of the dual vernier effect was 17.14, and its response characteristics are as follows: Figure 3 As shown.

[0033] In the strain response test, the first section of high birefringence fiber 6 was fixed at both ends to two triaxial displacement platforms. Strain was applied by adjusting the displacement platforms, with a minimum adjustment step of 30 μm, equivalent to a stress increment of 100 με. The spectral changes of the sensor under different strain conditions were recorded. The results show that as the strain increases, the wavelength of the spectral trough exhibits a redshift, shifting towards longer wavelengths. The relationship between the strain of the sensor and the wavelength of the low point of the envelope spectrum is as follows: Figure 4 As shown. Linear fitting of the strain response data yielded a strain sensitivity of 47.9 pm / με for the single Solc-Sagnac interferometer and 808.1 pm / με for the sensor. The amplification factor due to the dual vernier effect was 16.87. The fitting curve is shown in Figure 1. Figure 5 As shown. Based on the above temperature and strain sensitivity coefficients, this sensor achieves high-sensitivity measurement of temperature and strain by utilizing the dual vernier effect.

[0034] The temperature strain fiber optic sensor based on the dual vernier effect proposed in this invention introduces parallel Sagnac interferometers to form a Michelson interferometer to generate a dual vernier effect, based on the single vernier effect generated by the Solc-Sagnac interferometer. This achieves a double amplification of temperature and strain sensing sensitivity, and has the advantages of simple structure, low cost, high sensitivity, and small sensing unit size. At the same time, it has good repeatability and stability.

[0035] For the purposes of illustration and description, the foregoing illustrative examples relating to the invention are provided. This is not intended to be an exhaustive description of the invention or to limit it to the precise forms described; modifications and variations can be made based on the foregoing description. The embodiments were chosen and described to explain the principles of the invention and as practical applications thereof, enabling those skilled in the art to use the invention in various embodiments and to make various modifications for specific purposes. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of this invention should be considered within the scope of protection of this invention.

Claims

1. A temperature strain fiber optic sensor based on the dual-cursor effect, characterized by: The sensor forms a Michelson interference structure by connecting the Solc-Sagnac interferometer and the Sagnac interferometer in parallel, so as to realize a double vernier effect for amplifying the sensing sensitivity of temperature and strain. The sensor comprises a wide-spectrum light source (1), a spectrum analyzer (2), a 2*2 coupler (3), a first 1*2 coupler (4), a second 1*2 coupler (5), a first high-birefringence fiber (6), a second high-birefringence fiber (7), a first polarization controller (8), a second polarization controller (9) and a third high-birefringence fiber (10). The wide-spectrum light source (1) is connected to a first input port (301) of the 2*2 coupler, the spectrum analyzer (2) is connected to a second input port (302) of the 2*2 coupler, an input port (401) of the first 1*2 coupler is connected to a first output port (303) of the 2*2 coupler, and an input port (501) of the second 1*2 coupler is connected to a second output port (304) of the 2*2 coupler. A first output port (402) of the first 1*2 coupler is connected to one end of the first high-birefringence fiber (6), the other end of the first high-birefringence fiber (6) is connected to one end of the second high-birefringence fiber (7), the other end of the second high-birefringence fiber (7) is connected to one end of the first polarization controller (8), and the other end of the first polarization controller (8) is connected to a second output port (403) of the first 1*2 coupler, so as to form a Solc-Sagnac interferometer. A first output port (502) of the second 1*2 coupler is connected to one end of the second polarization controller (9), the other end of the second polarization controller (9) is connected to one end of the third high-birefringence fiber (10), and the other end of the third high-birefringence fiber (10) is connected to a second output port (503) of the second 1*2 coupler, so as to form a Sagnac interferometer.

2. The dual-cursor effect based temperature strain fiber optic sensor of claim 1, wherein: The first high-birefringence fiber (6) and the second high-birefringence fiber (7) are fused at an angle of 90 degrees between the fast axes.

3. The dual-cursor effect based temperature strain fiber optic sensor of claim 1, wherein: the sum of the polarization rotation angle introduced by the first segment of high birefringence fiber (6) connected to the first output port (402) of the first 1x2 coupler (4) through the first polarization controller (8) and the polarization rotation angle introduced by the second segment of high birefringence fiber (7) connected to the first polarization controller (8) .​ 4. The dual-cursor effect based temperature strain fiber optic sensor of claim 1, wherein: When the first high-birefringence fiber (6) is subjected to external temperature or strain, the sensing sensitivity of the sensor is represented by the transmission spectrum offset of the sensor, and is represented as follows: ； wherein the resonance wavelength λ m satisfying the condition 2πB1L1 / λ=2mπ, m being an integer; , is the birefringence and the length of the first segment of high birefringence optical fiber 6, , is the birefringence and the length of the second segment of high birefringence optical fiber 7, , is the birefringence and the length of the third segment of high birefringence optical fiber 10, is the derivative with respect to temperature T, is the temperature sensitivity of the double-bubble effect, is the strain sensitivity of the double-bubble effect.

5. A temperature strain fibre sensor based on the dual-cursor effect according to claim 4, characterised in that: The length L1 of the first high-birefringence fiber (6), the length L2 of the second high-birefringence fiber (7) and the length L3 of the third high-birefringence fiber (10) satisfy the relationship: so that the free spectral range of the envelope spectrum generated by the Solc-Sagnac interferometer is similar to the free spectral range of the Sagnac interferometer, thereby realizing sensitivity amplification through parallel interference.

6. The dual-cursor effect based temperature strain fiber optic sensor of claim 1, wherein: The first high-birefringence fiber (6) serves as a sensing arm, and its length is greater than the length of the second high-birefringence fiber (7) serving as a reference arm.

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