Concave POF refractive index sensor based on SPR effect

Abstract

The utility model belongs to the technical field of optical fiber sensing, and particularly relates to a concave POF (plastic optical fiber) refractive index sensor based on SPR (surface plasmon resonance) effect. According to the optical fiber sensor, a part of cladding and a fiber core on a plastic optical fiber are removed through a polishing and grinding technology to form a section of concave area; plating a metal nano-film on the concave area to form a sensing area based on the SPR effect; the concave optical fiber sensing area is placed in a medium to be detected, detection light from a broadband light source passes through the optical fiber sensing area from an input optical fiber and then is transmitted to a spectrograph from an output optical fiber, and the spectrograph detects the change of the wavelength of a formant in a transmission spectrum to realize the sensing of the refractive index of the medium; according to the utility model, the structure is simple, the sensitivity is improved, the measurement precision of the sensor is improved, and the sensor has certain practical application value.

Description

Technical Field

[0001] The utility model relates to the technical field of optical fiber sensing, in particular to a concave POF refractive index sensor based on the SPR effect. Background Art

[0002] Surface Plasmon Resonance (SPR) is essentially the collective oscillation of free electrons on the metal surface due to the interaction between incident light and metal, forming an electromagnetic wave that propagates along the metal surface at the metal-medium interface, namely, surface plasmon wave. People have established surface plasmon resonance sensing technology by taking advantage of the sensitivity of the surrounding medium to surface plasmon waves. The combination of SPR technology and fiber optic sensing technology has opened up a new research landscape in the field of sensing. SPR-based fiber optic sensors can be widely used in the detection of trace and dynamic substances and have been widely used in many fields, including life sciences, medical diagnosis, drug development, food analysis, environmental pollution and public safety.

[0003] With the rapid development of optical fiber micromachining technology, optical fiber side polishing technology has opened up a new era in the field of optical fiber sensing. The Chinese invention patent with patent application number 201210067372.7, "Graphene film-sensitized D-type optical fiber SPR sensor and its preparation method", has a D-type structure with a polishing depth that has reached the radius of the optical fiber, and the optical fiber used is a multimode quartz optical fiber. As the polishing depth of the optical fiber increases, the mechanical strength of ordinary quartz optical fiber becomes lower, and the quartz optical fiber is easily damaged, causing the sensor to be easily damaged. The Chinese utility model patent with patent application number 201920571607.3, "A three-layer D-type optical fiber SPR sensor", provides an SPR sensor based on a three-layer structure of a D-type optical fiber. Although this design can improve the sensitivity of the sensor, the three-layer structure is too complex, resulting in multiple variables in the measurement environment, which will affect the accuracy of the measurement results.

[0004] In order to solve the above problems, the utility model designs a concave POF refractive index sensor based on the SPR effect. The special optical fiber used in the utility model is plastic optical fiber. Because plastic optical fiber is light, soft, has a large diameter and a large numerical aperture, it has excellent light transmission ability and tensile strength. Different from the general SPR optical fiber sensor that coats a thin film on a D-shaped structure, the utility model selects a symmetrical concave structure, which increases the contact area between the SPR sensing area and the medium to be measured and improves the sensitivity of the sensor. Coating a single-layer film on the concave structure maintains high sensitivity while eliminating the complex process of coating a multi-layer film, which can better stimulate the SPR effect and improve the refractive index detection range of the sensor, and has certain practical application value. Utility Model Content

[0005] The purpose of the present utility model is to provide a sensor based on SPR for concave POF, aiming to solve the problems of low sensitivity, poor mechanical strength and high cost of existing sensors.

[0006] The above purpose is achieved through the following technical solutions:

[0007] A concave POF refractive index sensor based on SPR effect, which includes a broadband light source 1, an input optical fiber 2, a concave POF sensing module 3 plated with a gold film, an output optical fiber 4, and a spectrometer 5. The light source is connected to the input optical fiber, the input optical fiber is connected to the concave POF sensing module plated with a gold film, and the spectrometer is connected to the concave sensing module through the output optical fiber.

[0008] For the concave POF refractive index sensor based on SPR effect, the light source is an ASE broadband light source.

[0009] For the concave POF refractive index sensor based on SPR effect, the POF includes a core and a cladding. The core is made of a highly transparent polymer polymethyl methacrylate, and the cladding is made of fluoroplastics with a diameter of 500μm, where the diameter of the core is 480μm and the thickness of the cladding is 10μm.

[0010] For the concave POF refractive index sensor based on SPR effect, the concave region removes part of the cladding and the core by polishing. The depths of the polished concave regions are 150μm, 300μm and 150μm respectively. The total length of the concave region is 30mm, and the length of each depth region is 10mm.

[0011] For the concave POF refractive index sensor based on SPR effect, the metal nano-film is plated on the concave region by ion beam sputtering or electron beam deposition technology, and the film thickness is 30nm - 50nm.

[0012] For the concave POF refractive index sensor based on SPR effect, both the input optical fiber and the output optical fiber are optical fibers of the same material and model as the concave POF.

[0013] The beneficial effects achieved by the present utility model are:

[0014] 1. After connecting the broadband light source with the sensing module centered on the concave POF plated with a gold film and the spectrometer, the system has the advantages of high sensitivity, good mechanical strength, low cost, strong anti-electromagnetic interference ability, etc.

[0015] 2. The present utility model uses plastic optical fiber, which is light in weight, flexible and has excellent tensile strength. Due to the large diameter and numerical aperture of the plastic optical fiber, its light conduction ability is great, effectively overcoming the problems of low mechanical strength and easy damage caused by excessive polishing depth of quartz optical fiber.

[0016] 3. The concave structure designed in the present utility model expands the contact area between the metal thin film and the medium to be measured, not only improving the detection range of the refractive index of the sensor, but also greatly enhancing the sensitivity of the sensor.

[0017] 4. The single-layer metal thin film is deposited on the concave structure of the present utility model. To a certain extent, the concave structure can improve the sensitivity of the sensor, eliminating the need to deposit multiple layers of thin films to enhance the sensitivity of the SPR sensing structure, thus saving the complex process of depositing multiple layers of films. At the same time, it avoids excessive variables in the measurement environment caused by multiple layers of thin films interfering with the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The following further describes the present utility model in detail with reference to the drawings, which constitutes a part of the specification and is used together with the embodiments of the present utility model to explain the present utility model, but does not constitute a limitation to the utility model.

[0019] In the drawings:

[0020] Figure 1 is a schematic structural diagram of the sensing system of the present utility model;

[0021] Figure 2 is a schematic structural diagram of the sensing module of the concave POF with a deposited metal thin film of the present utility model;

[0022] Figure 3 is a longitudinal sectional view of the sensing module of the concave POF with a deposited metal thin film of the present utility model;

[0023] In the figure: broadband light source - 1; input optical fiber - 2; sensing module of the concave POF with a deposited gold film - 3; output optical fiber - 4; spectrometer - 5; core - 6; cladding - 7; concave structure - 8; metal nano thin film - 9; DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The following describes the preferred embodiments of the present utility model with reference to the drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present utility model, and are not used to limit the present utility model.

[0025] Embodiment 1:

[0026] A preparation method for a concave POF refractive index sensing system based on the SPR effect.

[0027] A section of the core and the cladding of a plastic optical fiber is removed by polishing to form a concave optical fiber region with a total length of 30 mm, and the obtained concave shape is axisymmetric. A metal nanometer thin film is deposited on the obtained concave region by means of ion beam sputtering or electron beam deposition. The thickness of the thin film is 30 nm - 50 nm, and the material is gold. One end of the optical fiber is connected to a broadband light source, and the other end is connected to a spectrometer. The plastic optical fiber adopted in the utility model has a core made of highly transparent polymer polymethyl methacrylate, a cladding made of fluoroplastics, a diameter of 500 μm, a core diameter of 480 μm, and a cladding thickness of 10 μm. The polishing depths are 150 μm, 300 μm, and 150 μm respectively.

[0028] Example 2:

[0029] In some embodiments of the present utility model, the refractive index measurement includes the following steps:

[0030] The concave POF part coated with a gold film is completely placed in the medium to be measured. The light source 1 is turned on, and the optical signal emitted by the light source 1 enters the sensing module 3 of the concave POF coated with a gold film through the input optical fiber 2. Since the concave region is coated with a metal nanometer thin film, when the evanescent wave transmits to the metal-medium interface and penetrates a certain depth of the metal layer, it will interact with the metal, and the free electrons on the metal surface will oscillate collectively, and the surface plasmon resonance phenomenon, i.e., SPR, will occur. The energy of the incident light is coupled into the surface plasmon wave. When the evanescent wave penetrates the metal thin film and contacts the medium to be measured, due to the different refractive indices of different media to be measured, the conditions for generating surface plasmon resonance are different, resulting in different relevant parameters of the incident light. The optical signal carrying the information of the medium to be measured is transmitted into the spectrometer 5 through the output optical fiber, and the detection of the relevant parameters of the optical signal can realize the detection of the refractive index of the medium. This sensor structure has the advantages of low cost, flexible use, and high sensitivity.

Claims

1. A concave POF refractive index sensor based on the SPR effect, characterized in that: The sensor comprises a broadband light source (1), an input optical fiber (2), a concave POF sensing module coated with a metal nanofilm (3), an output optical fiber (4), and a spectrometer (5), wherein the light source is connected to the input optical fiber, the input optical fiber is connected to the concave POF sensing module coated with a metal nanofilm, and the spectrometer is connected to the concave POF sensing module coated with a metal nanofilm via the output optical fiber.

2. A concave POF refractive index sensor based on the SPR effect according to claim 1, characterized in that: The light source (1) is an ASE broadband light source.

3. A concave POF refractive index sensor based on the SPR effect according to claim 1, characterized in that: The concave POF sensor module (3) coated with a metal nanofilm comprises: a fiber core (6), a cladding (7), a concave region (8) and a metal nanofilm (9), wherein the fiber core (6) is made of highly transparent polymer polymethyl methacrylate, and the cladding (7) is made of fluoroplastic with a diameter of 500 μm, wherein the diameter of the fiber core (6) is 480 μm and the thickness of the cladding (7) is 10 μm.

4. A concave POF refractive index sensor based on the SPR effect according to claim 1, characterized in that: The input optical fiber (2) and the output optical fiber (4) are both optical fibers of the same material and model as the concave POF.

5. The concave POF refractive index sensor based on the SPR effect according to claim 3, characterized in that: The concave region (8) is polished to remove part of the cladding and the core, the depths of the polished concave region are 150 μm, 300 μm and 150 μm respectively, the total length of the concave region is 30 mm, and the length of each depth region is 10 mm.

6. The concave POF refractive index sensor based on the SPR effect according to claim 3, characterized in that: The metal nanofilm (9) is plated on the concave area (8) by ion beam sputtering or electron beam deposition technology, and the film thickness is 30nm-50nm.

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