Coating-free optical fiber needle point reflection type humidity sensor

Abstract

The utility model discloses a coating-free optical fiber needle point reflection type humidity sensor which is of a Mach-Zehnder interference structure formed by a single-mode optical fiber, a coreless optical fiber and a photonic crystal optical fiber, and a layer of gold film is prepared on the end face of the Mach-Zehnder interference structure. Firstly, a single-mode fiber, a coreless fiber and a photonic crystal fiber are welded together in an arc discharge heating mode, and then the end face of the photonic crystal fiber is plated with a gold film. Light emitted by the broadband light source and transmitted in the fiber core passes through the coreless fiber and then enters the photonic crystal fiber, and reflection is formed at the end face. Due to the change of the environmental humidity, water enters through each end hole of the photonic crystal fiber, coupling between a fundamental mode and a high-order mode in the photonic crystal fiber is influenced, the refractive index is changed, and the spectrum of the structure can change along with the change of the environmental humidity. The optical fiber humidity sensor provided by the utility model has the advantages of small volume, simplicity in preparation, high sensitivity and electromagnetic interference resistance.

Description

Technical Field

[0001] The utility model belongs to the technical field of optical fiber sensing, and in particular relates to an uncoated optical fiber needle-tip reflection-type humidity sensor. Background Art

[0002] Humidity, as an important physical parameter, plays an important role in the fields of biomedicine, industrial production, food storage, etc. Accurate and continuous acquisition of environmental humidity has important guiding significance for the production and life process. Traditional electrical humidity sensors are not corrosion-resistant, have poor long-term stability, and are difficult to apply to harsh environments. Fiber optic humidity sensors have the advantages of corrosion resistance, electromagnetic interference resistance, and no need for power supply. They can meet the needs of long-term measurement in harsh environments such as strong electromagnetic interference, flammable and explosive environments, and have irreplaceable advantages.

[0003] Most of the existing humidity sensors have problems such as complex manufacturing process, low sensitivity, and slow response speed. Photonic crystal fiber has a complex refractive index distribution on its cross section, usually containing pores in different arrangements. The scale of these pores is roughly the same order of magnitude as the wavelength of light and runs through the entire length of the device. Water molecules in the air can enter through each end hole, causing the refractive index to change. The entire structure surface does not need to be coated with functional materials to make a highly sensitive fiber optic humidity sensor.

[0004] In the invention patent with publication number CN110873701A applied on October 22, 2019, "An optical fiber humidity sensor based on Mach-Zehnder interferometer", the incident optical fiber, beam splitter, modulation arm, beam combiner and output optical fiber are connected in sequence, wherein the beam splitter and beam combiner are both double-tapered, formed by splicing single-mode optical fiber and thin-core optical fiber and then taper processing, and evenly coating the surface of the tapered area with graphene oxide film, and the minimum diameter of the tapered area is 45μm and the length is 5mm. The above invention method is relatively complicated to operate and requires the coating of functional materials. In contrast, the utility model is relatively simple to operate and easy to prepare. Utility Model Content

[0005] The utility model provides an uncoated optical fiber needle-tip reflection-type humidity sensor for sensing changes in environmental humidity.

[0006] In order to achieve the above purpose, the utility model adopts the following technical solution: an uncoated optical fiber needle tip reflection type humidity sensor, characterized in that it is composed of a single-mode optical fiber, a coreless optical fiber, a photonic crystal optical fiber and a gold film coating; a small section of coreless optical fiber is fused between the single-mode optical fiber and the photonic crystal optical fiber, and the gold film coating is coated on the end face of the photonic crystal optical fiber; an optical fiber needle tip reflection type humidity sensor, one end of the single-mode optical fiber is connected to a coupler, and is connected to a broadband light source and a spectrometer through the coupler. The single-mode optical fiber model is G652D, and the coreless optical fiber model is CL-1010-A, YOFC. The outer diameters of the single-mode optical fiber, the coreless optical fiber and the photonic crystal optical fiber are all 125μm. The length of the coreless optical fiber is between 300μm and 1000μm, and the length of the photonic crystal optical fiber is between 1mm and 10mm, and the coating layer is removed. The thickness of the gold film on the end face is between 150nm and 300nm.

[0007] The light emitted by the broadband light source and transmitted in the core enters the photonic crystal fiber after passing through the coreless fiber and forms a reflection at the end face. Due to the change of environmental humidity, water molecules enter through the various end holes of the photonic crystal fiber, and the fundamental mode excites multiple high-order modes to form mode interference, causing the effective refractive index of the fiber to change, so that the spectrum of the structure will change with the change of environmental humidity.

[0008] The beneficial effects of the utility model are:

[0009] 1. This sensor has the advantages of corrosion resistance, anti-electromagnetic interference, compact structure, etc., and can be used in small spaces and harsh environments.

[0010] 2. The manufacturing process of this sensor is simple. It only requires welding the single-mode optical fiber, coreless optical fiber and photonic crystal fiber together in sequence, and then coating the end face of the photonic crystal fiber with a gold film.

[0011] 3. This sensor does not cause damage to the optical fiber during the manufacturing process, ensuring the mechanical strength of the optical fiber structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a structural schematic diagram of the utility model.

[0013] Figure 2 This is the end face structure diagram of the utility model.

[0014] Figure 3 This is a reflection spectrum diagram of the structure described in the utility model.

[0015] In the figure: 1—single-mode optical fiber, 2—coreless optical fiber, 3—photonic crystal fiber, 4—gold film coating, 2(a)—air hole of photonic crystal fiber, 2(b)—gold film coating. DETAILED DESCRIPTION

[0016] The utility model is further described in detail below in conjunction with the accompanying drawings.

[0017] like Figure 1 The figure shows the structure diagram of the sensor of the utility model, and the production includes the following specific steps: the first step is to strip the coating layer of the single-mode optical fiber and the coreless optical fiber in turn and cut the ends flat, and use a fiber fusion splicer to perform fusion connection, and then use a fiber fusion knife to cut the coreless optical fiber into 400μm; the second step is to discharge-fuse the other end of the coreless optical fiber with the photonic crystal optical fiber through a fiber fusion splicer, and then use a fiber fusion knife to cut the photonic crystal optical fiber into 7mm; the third step is to put the single-mode-coreless-photonic crystal optical fiber structure produced in the second step into a vacuum magnetron sputtering coating machine, the substrate rotates at a uniform speed, the sputtering power is 100W, the sputtering time is 5 minutes, and the final gold film coating thickness is about 50nm.

[0018] When performing humidity testing, the fiber optic sensor is connected to a broadband light source and a spectrometer through a circulator, such as Figure 3 The optical fiber sensor is placed in the environment to be tested, and by changing the ambient humidity, water molecules in the air enter through the holes on the end face of the photonic crystal fiber, affecting the coupling between the fundamental mode and the high-order mode in the photonic crystal fiber, causing the refractive index to change, resulting in spectral line drift of the sensor's reflection spectrum.

Claims

1. An uncoated optical fiber needle tip reflective humidity sensor, characterized in that: It consists of single-mode optical fiber, coreless optical fiber, photonic crystal optical fiber and gold film coating; a small section of coreless optical fiber is fused between the single-mode optical fiber and the photonic crystal optical fiber, and the gold film coating is coated on the end face of the photonic crystal optical fiber; the optical fiber needle tip reflection humidity sensor, one end of the single-mode optical fiber is connected to a circulator, and is connected to a broadband light source and a spectrometer through the circulator.

2. The uncoated optical fiber needle tip reflective humidity sensor according to claim 1, characterized in that: The single-mode optical fiber model is G652D, and the core diameter is 9 μm; the coreless optical fiber model is CL-1010-A, YOFC, and the outer diameters of the single-mode optical fiber, coreless optical fiber and photonic crystal optical fiber are all 125 μm.

3. The uncoated optical fiber needle tip reflective humidity sensor according to claim 1, characterized in that: The length of coreless fiber is between 300μm and 1000μm, and the length of photonic crystal fiber is between 1mm and 10mm, and the coating is removed.

4. The uncoated optical fiber needle tip reflective humidity sensor according to claim 1, characterized in that: The thickness of the gold film plated on the end face is between 150nm and 300nm.

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