Double-parameter optical fiber sensor based on conical few-mode fiber grating

Abstract

The utility model discloses a double-parameter optical fiber sensor based on a conical few-mode fiber grating, which belongs to the technical field of optical fiber sensors and comprises a broadband light source (1), a sensing structure (2) and a spectrum analyzer (3). The sensing structure (2) comprises a first single-mode fiber (201), a coreless fiber (202), a conical few-mode fiber grating (203) and a second single-mode fiber (204); more cladding modes are generated through mode field mismatch of the single-mode optical fiber and the coreless optical fiber and bending of a conical area, the double-parameter sensitivity of the sensor is improved, and two transmission characteristic peaks appear on the fiber bragg grating inscribed on the few-mode optical fiber by using different mode numbers in the few-mode optical fiber. The reliability and repeatability of the sensor are greatly improved, the corresponding double-parameter sensitivity can be respectively calculated by observing the position change of an interference spectrum and a transmission characteristic peak, and a sensitivity matrix is further established, so that the simultaneous measurement of double parameters is realized. The sensor has the characteristics of high sensitivity, strong reliability, strong anti-interference capability, small size, simplicity in manufacturing and the like.

Description

Technical Field

[0001] This utility model relates to a dual-parameter fiber optic sensor, and more particularly to a dual-parameter fiber optic sensor based on a tapered few-mode fiber grating, belonging to the field of fiber optic sensor technology. Background Technology

[0002] In fiber optic sensing technology, the simultaneous measurement of dual parameters (such as temperature and strain, temperature and refractive index) has significant application value and is widely used in structural health monitoring, energy transmission, and biomedicine. Traditional methods often employ cascaded designs, connecting or combining two different types of sensing units in series, achieving decoupled measurement of the dual parameters through their respective sensitivities to different parameters. However, such structures have significant drawbacks, including structural complexity, difficulty in fabrication, large size, and difficulty in integration. Furthermore, coupling interference easily occurs between the two sensing units, resulting in poor stability and repeatability during long-term operation, affecting measurement accuracy and reliability. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the purpose of this utility model is to provide a dual-parameter fiber optic sensor based on a tapered few-mode fiber optic grating. This sensor has the characteristics of high sensitivity, high reliability, strong anti-interference ability, small size, and simple manufacturing.

[0004] The technical solution adopted by this utility model to solve the technical problem is as follows:

[0005] A dual-parameter fiber optic sensor based on a tapered few-mode fiber grating is characterized by including a broadband light source SLED (1), a sensing structure (2), and a spectrometer OSA (3); the sensing structure (2) includes a first single-mode fiber (201), a coreless fiber (202), a tapered few-mode fiber grating (203), and a second single-mode fiber (204); the broadband light source SLED (1) is connected to one end of the sensing structure (2), and the other end of the sensing structure (2) is connected to the spectrometer OSA (3); wherein the sensing structure (2) is formed by discharge fusion of one end of the first single-mode fiber (201) and the coreless fiber (202), discharge fusion of the other end of the coreless fiber (202) and one end of the tapered few-mode fiber grating (203), and discharge fusion of the other end of the tapered few-mode fiber grating (203) and one end of the second single-mode fiber (204).

[0006] The beneficial effects of this utility model are:

[0007] 1. By generating more cladding modes through mode field mismatch between single-mode and coreless optical fibers and bending in the conical region, the dual-parameter sensitivity of the sensor is improved.

[0008] 2. By utilizing the different modes in few-mode fibers, two transmission characteristic peaks appear in the fiber Bragg gratings inscribed on them, which greatly improves the reliability and repeatability of the sensor.

[0009] 3. By observing the changes in the position of the interference spectrum and transmission characteristic peaks, the corresponding dual-parameter sensitivities can be calculated, and a sensitivity matrix can be established to achieve simultaneous measurement of the dual parameters. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the structure of a dual-parameter fiber optic sensor based on a tapered few-mode fiber grating according to this utility model. Figure 2 for Figure 1 A schematic diagram of the middle sensing structure (2).

[0011] 1 is a broadband light source (SLED); 2 is a sensing structure; 3 is an OSA (Optical Spectrum Analyzer); 201 is the first single-mode fiber; 202 is a coreless fiber; 203 is a tapered few-mode fiber grating; 204 is the second single-mode fiber.

[0012] Specific implementation methods

[0013] The following is a detailed description of the structure and working principle of this utility model:

[0014] A dual-parameter fiber optic sensor based on a tapered few-mode fiber grating is characterized by comprising a broadband light source SLED (1), a sensing structure (2), and a spectrometer OSA (3); the sensing structure (2) comprises a first single-mode fiber (201), a coreless fiber (202), a tapered few-mode fiber grating (203), and a second single-mode fiber (204); the broadband light source SLED (1) is connected to one end of the sensing structure (2), and the other end of the sensing structure (2) is connected to the spectrometer OSA (3); wherein the sensing structure... Structure (2) consists of a first single-mode fiber (201) and one end of a coreless fiber (202) being fused together by discharge, and the other end of the coreless fiber (202) being fused together by discharge with one end of a tapered few-mode fiber grating (203). The tapered few-mode fiber grating (203) is formed by tapering the few-mode fiber fused with the coreless fiber (202) to form a tapered few-mode fiber, and a fiber Bragg grating is written on the tapered few-mode fiber using a femtosecond laser. The other end of the tapered few-mode fiber grating (203) is fused together by discharge with one end of a second single-mode fiber (204).

[0015] Working principle of a dual-parameter fiber optic sensor based on a tapered few-mode fiber grating:

[0016] A dual-parameter fiber optic sensor based on a tapered few-mode fiber grating Figure 1After connecting all the components shown, the light output from the broadband light source SLED (1) enters the first single-mode fiber (201) and propagates in the form of the fundamental mode. Then, it enters the coreless fiber (202) from the first single-mode fiber (201). Due to mode field mismatch, higher-order modes are excited at the coreless fiber (202). The light of multiple modes continues to propagate and enters the tapered few-mode fiber grating (203) from the coreless fiber (202). Since the few-mode fiber can allow more than one mode to propagate in the fiber core, some modes continue to propagate along the cladding of the tapered few-mode fiber grating (203), and some modes propagate along the fiber core of the tapered few-mode fiber grating (203). Near the front tapered region, due to the deformation of the fiber, some cladding modes continue to propagate along the cladding, and some cladding modes are coupled into the fiber core. This causes Mach-Zehnder interference with the fiber core mode. The interference light and the fiber core mode reflect light of a specific wavelength when passing through the fiber Bragg grating. In a few-mode fiber core, more than one mode is allowed to propagate, so there will be multiple transmission characteristic peaks. After the light continues to propagate, in the back conical region, the interference light and some core modes will be transmitted to the cladding and propagate along the cladding. When the light enters the second single-mode fiber (204) from the conical few-mode fiber grating (203), the interference light and the cladding mode are recoupled into the second single-mode fiber (204), generating composite interference light. Finally, the light is transmitted to the OSA (3) spectrometer. The two physical quantities to be measured are temperature and strain. After different calibration tests of temperature and strain (i.e., selecting two different transmission characteristic peaks that are sensitive to temperature and strain to reflect the temperature and strain responses corresponding to the interference spectrum), the movement of the interference spectrum signal and the transmission characteristic peak signal can be observed by the OSA (3) spectrometer. The temperature and strain sensitivity of the two signals can be calculated. By establishing a sensitivity matrix, the simultaneous measurement of temperature and strain can be realized. Example

[0017] Figure 1This is a schematic diagram of the structure of a dual-parameter fiber optic sensor based on a tapered few-mode fiber grating according to this utility model. In the sensing structure (2), the first single-mode fiber (201) and the second single-mode fiber (204) are 4cm long, the coreless fiber (202) is 2cm long, the tapered few-mode fiber grating (203) has an initial length of 5cm, the fiber Bragg grating is written by a femtosecond laser, has a length of 1cm, and a reflectivity of 75%–80%. The broadband light source SLED (1) has a spectral range of 600–1600nm, and the OSA (3) spectrometer is a Yokogawa (AQ6370c). The broadband light source SLED (1) is connected to one end of the sensing structure (2), and the other end of the sensing structure (2) is connected to the other end of the optical fiber grating. One end is connected to the OSA (3) spectrometer; the sensing structure (2) is formed by discharge fusion of one end of the first single-mode fiber (201) and the coreless fiber (202), and discharge fusion of the other end of the coreless fiber (202) and one end of the tapered few-mode fiber grating (203). The tapered few-mode fiber grating (203) is formed by tapering the few-mode fiber after it is fused with the coreless fiber (202) using the flame heating method, and the fiber Bragg grating is written on the tapered few-mode fiber using a femtosecond laser. The other end of the tapered few-mode fiber grating (203) is discharge fused to one end of the second single-mode fiber (204).

[0018] The light output from the broadband light source SLED (1) enters the first single-mode fiber (201) and propagates in the form of the fundamental mode. Then, it enters the coreless fiber (202) from the first single-mode fiber (201). Due to mode field mismatch, higher-order modes are excited at the coreless fiber (202). The light of multiple modes continues to propagate and enters the tapered few-mode fiber grating (203) from the coreless fiber (202). Since the few-mode fiber can allow more than one mode to propagate in the fiber core, some modes continue to propagate along the cladding of the tapered few-mode fiber grating (203), and some modes propagate along the fiber core of the tapered few-mode fiber grating (203). Near the front tapered region, due to the deformation of the fiber, some cladding modes continue to propagate along the cladding, and some cladding modes are coupled into the fiber core. This causes Mach-Zehnder interference with the fiber core mode. When the interference light and the fiber core mode pass through the fiber Bragg grating, they reflect light of a specific wavelength. Due to the few-mode fiber... There is more than one mode that can be propagated in the fiber core, so there will be multiple transmission characteristic peaks. The light continues to propagate. In the back conical region, the interference light and some fiber core modes will be transmitted to the cladding and propagate along the cladding. When the light enters the second single-mode fiber (204) from the conical few-mode fiber grating (203), the interference light and the cladding mode are recoupled into the second single-mode fiber (204), generating composite interference light. Finally, the light is transmitted to the OSA (3) spectrometer. The two physical quantities to be measured are temperature and strain. After different calibration tests of temperature and strain (i.e., selecting two different transmission characteristic peaks that are sensitive to temperature and strain to reflect the temperature and strain response corresponding to the interference spectrum), the movement of the interference spectrum signal and the transmission characteristic peak signal can be observed by the OSA (3) spectrometer. The temperature and strain sensitivity of the two signals can be calculated. By establishing a sensitivity matrix, the simultaneous measurement of temperature and strain can be realized.

[0019] The above embodiments are only one of the preferred embodiments among all the solutions of this utility model. Other simple modifications to a dual-parameter fiber optic sensor based on a tapered few-mode fiber optic grating are all within the scope of protection of this utility model.

Claims

1. A dual-parameter fiber optic sensor based on a tapered few-mode fiber grating, characterized in that: The system includes a broadband light source SLED (1), a sensing structure (2), and a spectrometer OSA (3). The sensing structure (2) includes a first single-mode fiber (201), a coreless fiber (202), a tapered few-mode fiber grating (203), and a second single-mode fiber (204). The broadband light source SLED (1) is connected to one end of the sensing structure (2), and the other end of the sensing structure (2) is connected to the spectrometer OSA (3). The sensing structure (2) is formed by discharge fusion of one end of the first single-mode fiber (201) and the coreless fiber (202), discharge fusion of the other end of the coreless fiber (202) and one end of the tapered few-mode fiber grating (203), and discharge fusion of the other end of the tapered few-mode fiber grating (203) and one end of the second single-mode fiber (204).

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