A hollow-core optical fiber hydrogen sensor

Abstract

The present invention belongs to the field of optical fiber sensing technology, specifically a hollow-core optical fiber hydrogen sensor. The hollow-core optical fiber hydrogen sensor of the present invention comprises a substrate tube, a hydrogen-sensitive film, a dielectric film and a fiber core; wherein the hydrogen-sensitive film is a palladium film, which is coated on the inner wall of the substrate tube, and the dielectric film is plated on the surface of the hydrogen-sensitive film; the fiber core is hollow and is used to load the gas sample to be tested. The present invention obtains the change of hydrogen concentration by detecting the change of the interference peak wavelength in the optical fiber transmission spectrum. It has a simple structure, low cost, strong anti-electromagnetic interference ability, and has good practical value and application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber sensing, and in particular relates to a hollow-core optical fiber hydrogen sensor. Background Art

[0002] As an important clean energy and chemical raw material, hydrogen has a wide range of uses in defense, chemical industry, aerospace and other fields. However, hydrogen is flammable, explosive and easy to leak. At room temperature and standard atmospheric pressure, its explosion limit is 4%~74.5%, which poses certain safety hazards during use and storage. Therefore, it is particularly important to study a fast, sensitive and safe method to monitor the hydrogen concentration in the environment in real time in practical applications.

[0003] Traditional electrochemical hydrogen sensors can provide accurate, fast and stable responses, but their use has certain limitations and it is difficult to work in harsh environments with complex electromagnetic fields and strong corrosion. Moreover, this type of sensor may generate electric sparks during operation and cause explosions, which poses a great safety hazard. Fiber optic sensors have the advantages of good safety, high sensitivity, fast response speed, and strong anti-electromagnetic interference ability, so they have extremely outstanding advantages in hydrogen concentration monitoring. Most of the current fiber optic hydrogen sensors adopt a preparation method of coating a layer of hydrogen-sensitive film on the end face of a solid core optical fiber or on the surface of the core with the cladding removed. Palladium has good selectivity for hydrogen. After absorbing hydrogen, its volume, lattice constant and refractive index will change, and it will restore its original characteristics after analysis. The change in the optical constant of palladium will cause changes in the transmitted light in the optical fiber. By measuring the output intensity, transmission spectrum, phase change and other information of the optical signal, the hydrogen concentration can be detected. However, the manufacturing process of this type of fiber optic hydrogen sensor is relatively complicated, and the hydrogen-sensitive film exposed to the outside is easily contaminated and damaged.

[0004] Hollow-core optical fiber is a circular optical waveguide with air as the core material. It can be used as a natural sample cavity to load gas samples. The sensor prepared by coating the hydrogen-sensitive film in the air optical fiber has low cost, high sensitivity, and long service life, and has important practical application value. Summary of the invention

[0005] In view of the deficiencies in the prior art, an object of the present invention is to provide a hollow-core optical fiber hydrogen sensor which has a simple structure, is easy to manufacture and has a long service life.

[0006] The hollow-core optical fiber hydrogen sensor provided by the present invention comprises a substrate tube, a hydrogen-sensitive film, a dielectric film and a fiber core; wherein the hydrogen-sensitive film is coated on the inner wall of the substrate tube, and the dielectric film is coated on the surface of the hydrogen-sensitive film; the fiber core is hollow and is used to load a gas sample to be tested; wherein the hydrogen-sensitive film is a palladium film, which can be coated on the inner wall of the substrate tube by chemical plating.

[0007] In the present invention, the inner diameter of the hollow fiber core is 100-1000 microns.

[0008] In the present invention, the hydrogen-sensitive film is a palladium film, which is coated on the inner wall of the substrate tube by chemical plating, and the thickness is preferably 50-200 nm.

[0009] In the present invention, the dielectric film material is preferably an ethylene-vinyl acetate copolymer film, which is coated on the surface of the hydrogen-sensitive film by a liquid phase coating method.

[0010] In the present invention, the dielectric film preferably has a thickness of 100-500 nm.

[0011] In the present invention, the substrate tube material is preferably fused quartz, and the inner diameter is about 100-1000 microns.

[0012] In the present invention, the base tube preferably has a length of 1-10 cm.

[0013] The working principle of the present invention is: the optical signal is transmitted in a hollow-core optical fiber coated with a hydrogen-sensitive film and a dielectric film in sequence and produces interference. When the hydrogen concentration changes, the thickness and refractive index of the hydrogen-sensitive film will change, thereby changing the position of the interference peak in the transmission spectrum. The hydrogen concentration in the environment can be detected by detecting the movement of the interference peak wavelength.

[0014] The beneficial effects of the present invention are as follows: the sensor of the present invention has a simple structure, low cost, strong anti-interference ability, and can be prepared by a simple liquid phase coating method, providing a convenient, reliable, and sensitive new method for low-concentration hydrogen detection. The structure can also protect the fragile hydrogen-sensitive film and dielectric film inside the hollow-core optical fiber to avoid contamination and damage, which can effectively extend the service life of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the structure of the hollow-core optical fiber hydrogen sensor of the present invention.

[0016] Figure 2 It is the transmission spectrum of the hollow-core optical fiber hydrogen sensor of the present invention at different hydrogen concentrations.

[0017] Figure 3 It is a relationship diagram between the interference peak wavelength and hydrogen concentration of the hollow-core optical fiber hydrogen sensor of the present invention.

[0018] The numbers in the figure are: 1 is the substrate tube, 2 is the hydrogen-sensitive film, 3 is the dielectric film, and 4 is the fiber core. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0020] See attached Figure 1 The hollow-core optical fiber hydrogen sensor is composed of a substrate tube 1, a hydrogen-sensitive film 2, a dielectric film 3 and a core 4. The substrate tube 1 is made of fused quartz; the hydrogen-sensitive film 2 is a palladium film, which is coated on the inner wall of the substrate tube 1 by chemical plating, and has a thickness of 80 nm; the dielectric film 3 is an ethylene-vinyl acetate copolymer film, which has a thickness of 330 nm and is coated on the surface of the hydrogen-sensitive film 2 by liquid phase coating; the core 4 is hollow, with an inner diameter of 700 microns, and is used to load the gas sample to be measured.

[0021] Connect the manufactured hollow-core optical fiber hydrogen sensor to the test system to detect the hydrogen detection characteristics of the sensor of the present invention. Select a halogen tungsten lamp light source with a luminescent wavelength range of 350 to 2500 nm, couple the light drawn from the optical fiber to the core 4 of the hollow-core optical fiber hydrogen sensor of the present invention for transmission, and then output it to the spectrum analyzer through a jumper to record the normalized transmission spectrum of the sensor of the present invention. The optical signal is transmitted in the hollow-core optical fiber and produces interference. When the hydrogen concentration changes, the thickness and refractive index of the hydrogen-sensitive film 2 will change, thereby changing the position of the interference peak in the transmission spectrum. The hydrogen concentration in the environment can be detected by detecting the movement of the interference peak wavelength. Specifically, as the hydrogen concentration increases, the interference peak redshifts; conversely, as the hydrogen concentration decreases, the interference peak blueshifts.

[0022] When the hydrogen concentration is 0% and 4%, the transmission spectrum of the hollow-core optical fiber hydrogen sensor changes as follows: Figure 2 As shown, the interference peak wavelength shifts by about 12 nm. Figure 3 The figure is a relationship diagram between the interference peak wavelength and hydrogen concentration of the hollow core optical fiber hydrogen sensor. As the hydrogen concentration increases, the interference peak gradually redshifts. According to the linear fitting results, the sensitivity of the hollow core optical fiber hydrogen sensor is about 3nm / % when the hydrogen concentration range is 0%-4%.

[0023] In summary, the present invention can detect the hydrogen concentration in the environment by observing the position of the interference peak, and provides a solution for achieving fast, reliable and sensitive low-concentration hydrogen detection.

[0024] Finally, it should be noted that the above specific implementation modes are only used to illustrate the technical solutions of the present invention. However, the present invention is not limited to the specific details in the above implementation modes. Within the technical concept of the present invention, the technical solutions of the present invention can be subjected to various simple modifications, and these simple modifications all belong to the protection scope of the present invention.

Claims

1. A hollow core optical fiber hydrogen sensor, characterized in that: It includes a substrate tube, a hydrogen-sensitive film, a dielectric film and a fiber core; wherein the hydrogen-sensitive film is a palladium film, which is plated on the inner wall of the substrate tube, and the dielectric film is plated on the surface of the hydrogen-sensitive film; the fiber core is hollow and is used to load the gas sample to be tested; The dielectric film is an ethylene-vinyl acetate copolymer film; The substrate material is fused quartz.

2. The hollow core optical fiber hydrogen sensor according to claim 1, characterized in that: The thickness of the hydrogen sensitive film is 50-200nm.

3. The hollow core optical fiber hydrogen sensor according to claim 2, characterized in that: The inner diameter of the hollow fiber core is 100-1000 microns.

4. The hollow core optical fiber hydrogen sensor according to claim 3, characterized in that: The dielectric film has a thickness of 100-500 nm.

5. The hollow core optical fiber hydrogen sensor according to any one of claims 1 to 4, characterized in that: The length of the base tube is 1-10 cm.

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