A dual-parameter measurement sensor based on FBG and combined structure of capillary glass tube and multimode optical fiber

Abstract

The present application relates to a kind of FBG-based capillary glass tube and multimode optical fiber combination structure's dual-parameter measurement sensor, it is composed of broadband light source, single-mode optical fiber, input multimode optical fiber, capillary glass tube, FBG, silver film, output multimode optical fiber, spectrometer.Input multimode optical fiber makes the light field from single-mode optical fiber to get divergence, the light transmission in capillary glass tube will be divided into two parts in hollow core and glass wall, two beams of light form interference in output multimode optical fiber, silver film on the hollow core of capillary glass tube has high reflectivity, the light transmission in hollow core is very small, interference contrast is enhanced, since FBG is engraved on capillary glass tube, uniform double-beam interference spectrum and FBG transmission spectrum can be seen on spectrometer, change refractive index and temperature, the wavelength moving distance of double-beam interference spectrum and FBG transmission spectrum is obtained by spectrometer, can realize the simultaneous measurement of temperature and refractive index;The sensor has the advantages of high sensitivity, simple structure, low cost and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical fiber sensing, and relates to a dual-parameter measurement sensor based on a combination structure of a FBG-based capillary glass tube and a multimode optical fiber. BACKGROUND

[0002] In the past few decades, optical fiber sensors have been widely studied in sensing measurement due to their unique characteristics, such as good insulation, anti-electromagnetic interference, low cost, light weight, stable chemical performance, compact structure and the ability to work in harsh environments. So far, various optical fiber sensors have been developed based on different sensing principles. In recent years, optical fiber sensors such as Mach-Zehnder interferometer, Michelson interferometer, Fabry-Perot interferometer (FPI) and fiber Bragg grating (FBG) have attracted a lot of attention in the application of monitoring various physical quantities. Among them, the sensor based on fiber grating is one of the most representative and most promising optical fiber sensing technologies due to its mature manufacturing process and multiplexing capability. Integration, miniaturization and multi-parameter measurement are the main directions of the development of optical fiber sensor technology.

[0003] Refractive index and temperature as important sensing parameters have been widely used in industrial production, environmental monitoring, clinical trials and food testing. Refractive index measurement is inevitably affected by temperature changes, so it is of great significance to realize the simultaneous measurement of refractive index and temperature. The dual-parameter measurement sensor disclosed in the patent with the publication number CN205940607U has defects such as complex manufacturing process and low measurement sensitivity, which is limited in actual use. SUMMARY

[0004] The purpose of the present application is to design a dual-parameter measurement sensor based on a combination structure of a FBG-based capillary glass tube and a multimode optical fiber, which can be used for simultaneous measurement of temperature and refractive index, and has the advantages of simple structure, high sensitivity, etc.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] The present application comprises a broadband light source (1), a single-mode optical fiber (2), an input multimode optical fiber (3), a capillary glass tube (4), a FBG (5), a silver film (6), an output multimode optical fiber (7) and a spectrometer (8). The broadband light source (1) is connected to the left end of the single-mode optical fiber (2), the right end of the single-mode optical fiber (2) is connected to the left end of the input multimode optical fiber (3), the right end of the input multimode optical fiber (3) is connected to the left end of the capillary glass tube (4), the capillary glass tube is engraved with the FBG (5), the inner wall of the capillary glass tube is coated with the silver film (6), the right end of the capillary glass tube (4) is connected to the left end of the output multimode optical fiber (7), and the right end of the output multimode optical fiber (7) is connected to the spectrometer (8).

[0007] The broadband light source (1) has a wavelength range of 1500nm-1620nm.

[0008] The input multimode optical fiber (3) has a core diameter of 62.5um, a cladding diameter of 125um and a length of 2-10mm.

[0009] The capillary glass tube (4) has an inner diameter of 20um, an outer diameter of 125um and a length of 10mm.

[0010] The FBG (5) is written on the capillary glass tube (4) by femtosecond laser and phase mask method, and has a length of 10mm.

[0011] The output multimode optical fiber (7) has a core diameter of 62.5um and a cladding diameter of 125um.

[0012] A dual-parameter measurement sensor based on a capillary glass tube and a multimode optical fiber combined structure, which works in the following way: the light emitted by the broadband light source (1) enters the input multimode optical fiber (3) through the single-mode optical fiber (2), and due to the large mode field diameter of the multimode optical fiber, the light field is divergent in the input multimode optical fiber (3), and due to the inner diameter of 20um and the outer diameter of 125um of the capillary glass tube (4), a part of the light will be transmitted in the hollow core of the capillary glass tube (4), and another part of the light will be transmitted in the glass wall, when the light beam reaches the output multimode optical fiber (7), due to the different optical path differences of the two beams, the two beams will form interference in the output multimode optical fiber (7), and because the inner wall of the capillary glass tube is coated with a silver film, due to the high reflectivity of the silver film, the light transmitted in the hollow core has very small loss, and a high reflection is formed in the hollow core, which makes the contrast of the interference better, and on the spectrometer (8), a uniform double-beam interference spectrum and a FBG transmission spectrum can be seen. When the refractive index of the external liquid changes, the double-beam interference spectrum will move, and the position of the FBG transmission spectrum will not change; when the external temperature changes, the double-beam interference spectrum and the FBG transmission spectrum will move, and the different wavelength changes of the double-beam interference spectrum and the FBG transmission spectrum are recorded, and according to the following formula, the temperature and the refractive index can be measured at the same time:

[0013]

[0014]

[0015] Δλ1 represents the wavelength change of the double-beam interference spectrum, and Δλ2 represents the wavelength change of the FBG transmission spectrum, represents the temperature sensitivity coefficient of the double-beam interference, represents the temperature sensitivity coefficient of the FBG, represents the refractive index sensitivity coefficient of the double-beam interference, where n represents the refractive index of the FBG, ΔT represents the temperature change, and Δn represents the refractive index change.

[0016] The above two equations can be written in matrix form as follows: Thus, the temperature and the refractive index are obtained as follows: Through pre-calibration of the sensitivity coefficient matrix, the wavelength changes of the double-beam interference spectrum and the FBG transmission spectrum obtained from the spectrometer can realize simultaneous measurement of the temperature and the refractive index.

[0017] The present application has the advantages that the sensing structure only needs to be made on a fiber fusion machine, and has simple structure and low cost; the combination structure of the capillary glass tube and the multimode optical fiber constitutes a double-beam interferometer, so the sensitivity of the measurement is high. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Fig. 1 is a schematic diagram of the system structure of the present application.

[0019] 1 is a broadband light source, 2 is a single-mode optical fiber, 3 is an input multimode optical fiber, 4 is a capillary glass tube, 5 is an FBG, 6 is a silver film, 7 is an output multimode optical fiber, and 8 is a spectrometer. DETAILED DESCRIPTION

[0020] The specific embodiments of the present application will be further described below. Figure 1

[0021] Figure 1 ​The application discloses a two-parameter measurement sensor based on a FBG and a capillary glass tube and a multimode optical fiber combined structure, which is characterized by comprising a broadband light source (1), a single-mode optical fiber (2), an input multimode optical fiber (3), a capillary glass tube (4), an FBG (5), a silver film (6), an output multimode optical fiber (7) and a spectrometer (8). The broadband light source (1) is connected with the left end of the single-mode optical fiber (2), the right end of the single-mode optical fiber (2) is connected with the left end of the input multimode optical fiber (3), the right end of the input multimode optical fiber (3) is connected with the left end of the capillary glass tube (4), the FBG (5) is engraved on the capillary glass tube (4) and has a length of 10 mm, the silver film (6) is plated on the inner wall of the capillary glass tube (4), the right end of the capillary glass tube (4) is connected with the left end of the output multimode optical fiber (7), and the right end of the output multimode optical fiber (7) is connected with the spectrometer (8). The input multimode optical fiber diverges the light field from the single-mode optical fiber, when the light is transmitted into the capillary glass tube, the light transmitted in the capillary glass tube is divided into two parts transmitted in the hollow core and the glass wall, the light path difference of the two beams of light is different, and interference can be formed in the output multimode optical fiber. Because the silver film plated on the hollow core of the capillary glass tube has high reflectivity, the light transmitted in the hollow core can form high reflection in the hollow core, the transmission loss is very small, and therefore the contrast of the interference is better. In addition, the FBG is engraved on the capillary glass tube, and uniform double-beam interference spectrum and FBG transmission spectrum can be seen on the spectrometer. When the refractive index of the external liquid changes, the double-beam interference spectrum moves, and the position of the FBG transmission spectrum remains unchanged. When the external temperature changes, the double-beam interference spectrum and the FBG transmission spectrum both move, the wavelength change of the double-beam interference spectrum and the FBG transmission spectrum is recorded, and the simultaneous measurement of the temperature and the refractive index can be realized.

[0022] In a specific experiment of the application: the position of a wave peak of the double-beam interference spectrum is 1550 nm, and the position of the FBG transmission spectrum is 1552.5 nm; first, the temperature is kept unchanged, and the liquid with a refractive index of 1.33-1.38 is dropped on the capillary glass tube to obtain the wavelength moving distance of the double-beam interference spectrum and the FBG transmission spectrum under different refractive indexes, and the refractive index sensitivity coefficient of the double-beam interference is obtained through data fitting. The refractive index sensitivity coefficient of the FBG is 10 nm / RIU. Then, the refractive index is kept unchanged, and only the temperature is changed, the wavelength moving distance of the double-beam interference spectrum and the FBG transmission spectrum under different temperatures is measured in the range of 30-70 DEG C, and the temperature sensitivity coefficient of the double-beam interference is obtained through data fitting. The temperature sensitivity coefficient of the FBG is 0.01 nm / DEG C. The sensitivity coefficient matrix can be obtained, and then the relationship between the temperature and the refractive index and the wavelength change can be obtained according to the above formula. When the temperature change and the refractive index change are both unknown, the wavelength change Δλ1 is 10 nm by observing the peak position of the double-beam interference spectrum on the optical spectrum analyzer as 1560 nm; the wavelength change Δλ2 is 0.5 nm by observing the position of the FBG transmission spectrum on the optical spectrum analyzer as 1553 nm; the temperature change ΔT is 40 ℃ and the refractive index change Δn is 0.01 by substituting the values of Δλ1 and Δλ2 into the above formula.

Claims

1. A dual-parameter measurement sensor based on a combination structure of FBG capillary glass tube and multimode optical fiber, characterized in that, The system includes a broadband light source (1), a single-mode fiber (2), an input multimode fiber (3), a capillary glass tube (4), an FBG (5), a silver film (6), an output multimode fiber (7), and a spectrometer (8). The broadband light source (1) is connected to the left end of the single-mode fiber (2), the right end of the single-mode fiber (2) is connected to the left end of the input multimode fiber (3), the right end of the input multimode fiber (3) is connected to the left end of the capillary glass tube (4), the capillary glass tube (4) is engraved with an FBG (5) and is 10 mm long, the inner wall of the capillary glass tube (4) is coated with a silver film (6), the right end of the capillary glass tube (4) is connected to the left end of the output multimode fiber (7), and the right end of the output multimode fiber (7) is connected to the spectrometer (8).

2. The dual-parameter measurement sensor based on a combination structure of FBG capillary glass tube and multimode optical fiber according to claim 1, characterized in that, The capillary glass tube (4) is 10 mm long, has an inner diameter of 20 μm, and an outer diameter of 125 μm.

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