A high-sensitivity wedge-shaped SMF-SPR gas sensor with simple structure

Abstract

The application relates to a gas sensor, in particular to a high-sensitivity split-tip-shaped SMF-SPR gas sensor with an extremely simple structure, wherein the high-sensitivity split-tip-shaped SMF-SPR gas sensor is a single-mode optical fiber, the single-mode optical fiber is composed of a fiber core and a cladding, a V-shaped groove is arranged on the cladding, the inner side of the V-shaped groove is coated with a gold film, the gold film is coated with a gas-sensitive film, the top angle of the V-shaped groove is 28-32 DEG, the radius of the fiber core is 3-5 mu m, the radius of the cladding is 18-22 mu m, the thickness of the gold film is 18-22 nm, the thickness of the gas-sensitive film is 280-300 nm, the background material of the fiber core is silicon dioxide, the refractive index of the background material is 1.44, and the V-shaped groove is a split-tip-shaped V-shaped groove polished on the cladding by using femtosecond technology. The sensor has a simple structure and is convenient for actual production and application.

Description

Technical Field

[0001] This invention relates to a gas sensor, specifically to a highly sensitive wedge-shaped SMF-SPR gas sensor with an extremely simple structure. Background Technology

[0002] With the rapid development of nanotechnology, surface plasmon resonance (SPR) technology has become increasingly popular among researchers due to its outstanding advantages, such as fast response speed, online real-time monitoring, and the absence of special labeling requirements. SPR is a unique physical optical phenomenon in which free electrons in a metal absorb the energy of incident photons at the interface between metal and dielectric media, resulting in collective oscillations. Because SPR is highly sensitive to changes in the refractive index of analytes in the external environment, it is frequently used for the identification, detection, and characterization of gaseous or liquid samples in biological, chemical, and environmental analyses.

[0003] In recent years, SPR-based sensing platforms have sprung up like mushrooms after rain, mainly falling into two categories: prism-type and fiber-optic-type. Even though the former's technology is mature, its disadvantages—large system size, high cost, and difficulty in use in specific environments—limit its further development. Among fiber-optic sensing platforms, single-mode fiber and photonic crystal fiber are the most sought-after by researchers. Single-mode fiber (SMF) has no filling air holes in its cladding, resulting in a simple structure and mature actual production technology. Many researchers have invested considerable time and effort in improving the application of SMF, but this has been hampered by generally poor optical properties such as sensitivity. Photonic crystal fiber is a new type of special step-index fiber. Its flexible air hole arrangement design, cutoff-free single-mode transmission, and large mode field area have attracted the attention of researchers. Therefore, various high-performance PCF-SPR sensors have been proposed. However, an undeniable problem is that actual manufacturing remains a barrier, which is difficult to overcome in the short term. Based on the above, there is an urgent need to design a high-performance SPR sensor that is convenient for practical production, using single-mode optical fiber as the carrier. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a highly sensitive wedge-shaped SMF-SPR gas sensor with an extremely simple structure, which is easy to produce and apply in practice.

[0005] The technical solution adopted in this invention is as follows: a highly sensitive wedge-shaped SMF-SPR gas sensor with an extremely simple structure (SMF-SPR is an abbreviation for surface plasmon resonance of single-mode fiber). The highly sensitive wedge-shaped SMF-SPR gas sensor is a single-mode fiber, which consists of a core and a cladding. The cladding has a V-shaped groove, and the inner side of the V-shaped groove is coated with a gold film. A gas-sensitive film is coated on the gold film. The apex angle of the V-shaped groove is 28°-32°, the radius of the core is 3μm-5μm, the radius of the cladding is 18μm-22μm, the thickness of the gold film is 18nm-22nm, and the thickness of the gas-sensitive film is 280nm-300nm.

[0006] Furthermore, the apex angle of the V-groove is 30°, the radius of the fiber core is 4μm, the radius of the cladding is 20μm, the thickness of the gold film is 20nm, and the thickness of the gas-sensitive film is 290nm.

[0007] Furthermore, the background material of the fiber core is silicon dioxide.

[0008] Furthermore, the refractive index of the background material is 1.44.

[0009] Furthermore, the V-groove is a wedge-shaped V-groove formed by polishing the cladding using femtosecond technology.

[0010] Furthermore, the single-mode optical fiber is placed in a gaseous environment.

[0011] The beneficial effects of this invention: This invention provides a highly sensitive wedge-shaped SMF-SPR gas sensor with an extremely simple structure. This sensor has a simple structure, making it easy to manufacture and apply in practice. Its main advantages are as follows:

[0012] (1) The SMF-SPR gas sensor is polished into a wedge-shaped V-groove using femtosecond technology. This design optimizes the energy transmission path and further improves the mode coupling efficiency.

[0013] (2) The SMF-SPR gas sensor is coated with a gold-gas-sensitive composite film, which effectively improves the phase matching between the core guiding mode and the plasma mode.

[0014] (3) The SMF-SPR gas sensor can operate in the mid-infrared region: 1000nm-3500nm;

[0015] (4) The concentration range that the SMF-SPR gas sensor can detect is 0%-3.5%;

[0016] (5) The maximum sensitivity of the SMF-SPR gas sensor output is as high as 12nm / RIU, which far exceeds the maximum threshold of ordinary single-mode fiber and is almost the same as that of photonic crystal fiber.

[0017] (6) The SM F-SPR gas sensor has a simple structure, excellent characteristics, mature manufacturing process, and is convenient for practical application. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the cross-section of the single-mode optical fiber in Example 1;

[0019] Figure 2 This is a graph showing the relationship between the resonant wavelength of the SM F-SPR gas sensor in Example 1 and the concentration of the gas to be measured in the resonant wavelength range of 2.580-2.630μm.

[0020] Figure 3 This is a graph showing the relationship between the resonant wavelength of the SMF-SPR gas sensor in Example 1 and the concentration of the gas to be measured in the resonant wavelength range of 3.215-3.240 μm.

[0021] Figure 4 This is a flowchart of the gas concentration detection process using a single-mode optical fiber in Example 1. Detailed Implementation

[0022] Referring to the figures, a highly sensitive wedge-shaped SMF-SPR gas sensor with a minimal structure is described. The sensor is a single-mode optical fiber, consisting of a core 1 and a cladding 2. A V-groove 4 is provided on the cladding 2, and a gold film 3 is coated on the inner side of the V-groove 4. A gas-sensitive film 5 is coated on the gold film 3. The apex angle of the V-groove 4 is 30°. The radius of the core 1 is 4 μm, the radius of the cladding 2 is 20 μm, the thickness of the gold film 3 is 20 nm, and the thickness of the gas-sensitive film 5 is 290 nm. The background material of the core 1 is silicon dioxide, with a refractive index of 1.44. The V-groove 4 is a wedge-shaped V-groove formed on the cladding 2 using femtosecond polishing technology.

[0023] When light enters a single-mode fiber, different wavelengths of light propagate along the axis of the fiber in specific modes, while surface plasmon waves propagate in a fixed mode within the gold film. When the propagation constant of a certain wavelength of light within the single-mode fiber is the same as that of the surface plasmon wave within the gold film, energy coupling occurs within the gold film. Light energy from the single-mode fiber is coupled into the gold film, reducing the light energy within the single-mode fiber—that is, energy loss occurs within the single-mode fiber. The wavelength corresponding to the maximum energy loss is the resonant wavelength. The energy loss spectrum can be plotted based on the relationship between energy loss and resonant wavelength. The resonant wavelength changes with the concentration of the gas in the gas-sensitive membrane. By placing the single-mode fiber in a specific gas environment and calculating the resonant wavelength, the concentration of the gas to be measured can be detected, thus achieving the purpose of sensing.

[0024] The SMF model of this invention can be established using the finite element method. Its sensing behavior can be simulated using finite element analysis software COMSOL and MATLAB, and then post-processed to obtain the following results: Figure 2 and Figure 3 The graph showing the functional relationship between the resonance wavelength and the concentration of the gas to be measured, and the fitting equations (1) and (2) for the fitted lines are respectively:

[0025] λ(μm)=2.62-0.0112c,0≤c≤3.5 (1)

[0026] λ(μm)=3.24-0.00617c,0≤c≤3.5 (2)

[0027] Where λ is the resonance wavelength in μm and c is the concentration of the gas to be measured in RIU.

[0028] The average wavelength sensitivity of this sensor can be determined by the following formula:

[0029]

[0030] Where Δλ is the displacement of the resonant wavelength, and Δc represents the change in the concentration of the gas to be measured; the slope of the fitting equation is the average wavelength sensitivity of this sensor, which is 11.14 nm / RIU and 6.29 nm / RIU, respectively.

[0031] The gas concentration detection process of this sensor is as follows: Figure 4 As shown, a single-mode optical fiber is placed in the gas environment to be detected. A fiber optic fusion splicer is used to connect the single-mode fiber to both sides of the sensor, with one end connected to a light source and the other end connected to an optical spectroscopy (OSA) analyzer. A data cable is then used to connect the OSA to a PC. After turning on the light source, adjusting it to a suitable wavelength, and exciting the SPR (Spectroradio Resonance) wavelength, the loss curve of the analyte can be obtained, and the corresponding resonance wavelength can be found, thus determining the concentration of the gas to be measured.

Claims

1. A highly sensitive wedge-shaped SMF-SPR gas sensor with an extremely simple structure, characterized in that: The highly sensitive wedge-shaped SMF-SPR gas sensor with a minimal structure is a single-mode fiber, which consists of a core (1) and a cladding (2). The cladding (2) has a V-groove (4), and the inner side of the V-groove (4) is coated with a gold film (3). A gas-sensitive film (5) is coated on the gold film (3). The apex angle of the V-groove (4) is 28°-32°, the radius of the core (1) is 3μm-5μm, the radius of the cladding (2) is 18μm-22μm, the thickness of the gold film (3) is 18nm-22nm, and the thickness of the gas-sensitive film (5) is 280nm-300nm. The background material of the fiber core (1) is silicon dioxide, and the refractive index of the background material is 1.

44.

2. The highly sensitive wedge-shaped SMF-SPR gas sensor with a minimalist structure according to claim 1, characterized in that: The V-groove (4) has a apex angle of 30°, the fiber core (1) has a radius of 4 μm, the cladding (2) has a radius of 20 μm, the gold film (3) has a thickness of 20 nm, and the gas-sensitive film (5) has a thickness of 290 nm.

3. A highly sensitive wedge-shaped SMF-SPR gas sensor with an extremely simple structure according to claim 1 or 2, characterized in that: The V-groove (4) is a wedge-shaped V-groove (4) formed by polishing the cladding (2) using femtosecond technology.

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