Anti-resonance optical fiber temperature sensor based on surface plasma resonance

Abstract

The invention provides a hollow-core anti-resonance optical fiber temperature sensor based on surface plasma resonance. The hollow-core anti-resonance optical fiber temperature sensor comprises a cladding region and a fiber core region, the cladding area comprises four cylindrical nested elliptical quartz tubes and two quartz tubes which are uniformly arranged, the quartz tubes intersect with the tube wall of the optical fiber, the inner radius of each cylindrical nested elliptical quartz tube is r1, the inner minor semi-axis of each nested elliptical quartz tube is a, and the tube wall thickness of each cylindrical nested elliptical quartz tube is t1; the inner radius of the quartz tube intersected with the tube wall of the optical fiber is r2, and the thickness of the tube wall is t2; the sensor adopts an anti-resonance optical fiber structure, and a cladding area is formed by uniformly arranging four cylindrical nested elliptical quartz tubes and two quartz tubes intersected with the tube wall of the optical fiber. The two quartz tubes in the x direction are filled with gold threads, and other cladding tube holes are filled with ethanol liquid; the fiber core area is an area enclosed by the six quartz tubes and is filled with ethanol liquid. According to the invention, a surface plasma effect sensing mechanism is realized by filling metal, so that temperature sensing is realized. The detection temperature range of the sensor is-50 DEG C to 50 DEG C, and the sensitivity is 3.16 nm / DEG C. The sensor has the advantages of simple structure and high sensitivity, and has wide application prospects in the fields of biomedicine, environmental science, aerospace and the like.

Description

Technical Field

[0001] The invention relates to the technical field of special optical fiber and optical fiber sensing, and in particular to an anti-resonance optical fiber temperature sensor of surface plasma resonance. Background Art

[0002] With the continuous development of science and technology, optical fiber sensors have been widely used in the field of temperature measurement due to their strong anti-interference ability and high sensitivity. Traditional optical fiber temperature sensors are mainly based on fiber Bragg grating (FBG) technology, but this technology has certain limitations, such as temperature cross-sensitivity and complex demodulation. In order to overcome these problems, optical fiber temperature sensors based on surface plasmon resonance (SPR) effect have gradually attracted attention.

[0003] The SPR effect is caused by collective oscillation of electrons and usually occurs at the interface of two media with opposite dielectric constants. When the wavelength of the incident light meets the phase matching condition, the fiber core mode will couple with the surface plasmon polarization mode, resulting in a sharp increase in the optical energy loss at the resonant wavelength, resulting in a sharp local loss peak. Since the SPR effect is extremely sensitive to the change of the refractive index (RI) of the medium surrounding the metal, this phenomenon can be used to achieve high-sensitivity sensing. Hollow Core Anti-Resonant Fiber (HC-ARF) is a special type of optical fiber that realizes light transmission by utilizing the principle of anti-resonant waveguide. The design of this optical fiber allows it to transmit light in the hollow core instead of in the traditional solid core. This design reduces the light absorption and scattering loss of the material, thereby providing extremely low transmission loss and high transmission bandwidth. At the same time, since the RI of ethanol material is also extremely sensitive to temperature changes, the hollow core anti-resonant fiber can be filled with ethanol liquid and combined with the SPR effect to design a high-sensitivity, high-resolution temperature sensor.

[0004] With the deepening of research on HC-ARF sensors, various high-performance sensors have been proposed. In 2018, Liu et al. proposed a temperature sensing HC-ARF based on all-fiber interferometer, with a sensitivity of 17.45pm / ℃ in the temperature range of 19-108℃. In 2019, Wei et al. proposed a TSL-filled HC-ARF for temperature sensing, with a sensitivity of 1.1nm / ℃ in the temperature range of 15-35℃. However, in practical applications, there is still a lot of room for improvement in the above work, such as insufficient sensitivity and limited detection range. Summary of the invention

[0005] In view of this, the present invention provides a hollow core anti-resonance optical fiber temperature sensor based on surface plasmon resonance

[0006] The invention provides a hollow core anti-resonance optical fiber temperature sensor based on surface plasma resonance. The optical fiber sensor body is composed of a hollow core anti-resonance optical fiber, a cladding tube, a gold wire and ethanol liquid.

[0007] Furthermore, the sensor has six cladding tubes forming an anti-resonance structure, wherein there are four circular nested elliptical cladding tubes, the internal spaces of which are filled with ethanol liquid, and there are two special cylindrical cladding tubes filled with gold wires.

[0008] Furthermore, two special cladding tubes filled with gold wire are closely connected to the inner wall of the antiresonant optical fiber along the positive and negative directions of the x-axis, respectively, and the remaining four nested cladding tubes are evenly arranged at angles of 60°, 120°, 240°, and 300° to the positive direction of the x-axis and closely connected to the inner wall of the antiresonant optical fiber. The middle area surrounded by these six cladding tubes is the core area of ​​the antiresonant optical fiber for light propagation, and this area is also filled with ethanol liquid.

[0009] Furthermore, the performance of the sensor can be changed by adjusting the radius r1, thickness t1, the minor semi-axis a of the embedded ellipse, the radius r2 of the two cladding tubes in the x direction, the thickness t2 of the cladding tube, the distance d from the center of the cross section of the cladding tube to the center of the fiber core, and the radius R of the anti-resonance fiber. In the range of adjustment parameters, the parameters for the structure to achieve optimal performance are R = 28μm, r1 = 8μm, t1 = 0.5μm, r2 = 12.5μm, t2 = 0.6μm, a = 4μm, d = 25μm.

[0010] Furthermore, the material of the hollow-core anti-resonant optical fiber cladding tube is silicon dioxide.

[0011] Furthermore, ethanol liquid is filled inside the sensor. As the external temperature changes, the refractive index of the ethanol liquid will change, so that the resonant wavelength when the core fundamental mode is coupled with the surface plasma polariton (SPP) mode will also change accordingly. The offset of the Xie Zhenfeng position at the corresponding wavelength can be measured, and then the measured temperature can be obtained through the fitting relationship between temperature and offset. The hollow-core anti-resonant optical fiber temperature sensor based on surface plasma resonance made with the optimal structural parameters can achieve a maximum sensitivity of 3.5nm / ℃ within the temperature range of -50℃ to 50℃, and the maximum quality factor (Figure of merits, FOM) can reach 0.411℃ -1 .

[0012] Compared with the prior art, the above solution provided by the present invention has the following advantages:

[0013] (1) The present invention mainly utilizes the advantages of hollow core anti-resonant optical fiber structure, and realizes high-precision temperature sensing by generating surface plasma effect through the core and cladding tube. The sensor can realize the measurement of temperature range of -50℃~50℃, and has excellent sensitivity and stability.

[0014] (2) The present invention realizes the sensing requirements of this sensor through theoretical simulation, and based on the existing optical fiber drawing technology, the sensor is simple and easy to implement in actual manufacturing and is suitable for temperature measurement under various harsh environmental conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings herein are incorporated in and constitute a part of the specification, illustrate embodiments consistent with the present invention, and together with the description, are used to explain the principles of the present invention. In the drawings:

[0016] Figure 1 A schematic cross-sectional view showing an embodiment of the present invention;

[0017] Figure 2 A schematic diagram showing a mode field of a temperature sensor at a resonant wavelength when the temperature is filled with ethanol liquid at a wavelength of 1.532 μm according to an embodiment of the present invention;

[0018] Figure 3 A schematic diagram showing a curve of the relationship between the temperature and the limiting loss of the sensor according to an embodiment of the present invention;

[0019] Figure 4 A schematic diagram showing the functional relationship between the resonant wavelength and temperature of the sensor according to an embodiment of the present invention;

[0020] Figure 5 A bar diagram showing the relationship between the quality factor and temperature of the sensor according to the embodiment of the present invention;

[0021] The numbers in the figure are: 1, hollow-core antiresonant optical fiber, 2, perfect matching layer, 3, special cylindrical cladding tube, 4, cylindrical nested elliptical cladding tube, 5, ethanol liquid, 6, gold wire, R is the radius of the core of the hollow-core antiresonant optical fiber, r1 and t1 are the inner radius and thickness of the cylindrical nested elliptical cladding tube, a is the short semi-axis of the elliptical nested tube, r2 and t2 are the inner diameter and thickness of the special cylindrical cladding tube intersecting with the inner wall of the optical fiber, and d is the distance between the center of the cross section of the special cylindrical cladding tube and the center of the cross section of the antiresonant optical fiber. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0023] Please refer to Figure 1 The embodiment of the present invention provides a hollow-core anti-resonance optical fiber temperature sensor based on surface plasmon resonance. The optical fiber sensor body is composed of a hollow-core anti-resonance optical fiber, a perfect matching layer, a gold wire, a special cylindrical cladding tube intersecting with the inner wall of the optical fiber, a cylindrical nested elliptical cladding tube, and an ethanol liquid. The hollow-core anti-resonance optical fiber is composed of six cladding tubes, including two special cylindrical cladding tubes intersecting with the inner wall of the optical fiber and four cylindrical nested elliptical cladding tubes, two of which are special cylindrical cladding tubes intersecting with the inner wall of the optical fiber and are tightly connected to the inner wall of the anti-resonance optical fiber along the positive and negative directions of the x-axis, respectively, and the remaining four nested cladding tubes are evenly arranged at angles of 60°, 120°, 240°, and 300° with the positive direction of the x-axis and are tightly connected to the inner wall of the anti-resonance optical fiber. The gold wire is filled inside the two cladding tubes located on the x-axis. The ethanol liquid is filled inside the remaining four cladding tubes and the hollow-core anti-resonance optical fiber.

[0024] In the embodiment of the present invention, the cladding tube material of the hollow core antiresonant optical fiber is silicon dioxide, and its refractive index can be calculated according to the Sellmeier equation. As a commonly used plasma material, the relative dielectric constant of gold wire can be obtained by the Lorentz-Drude model.

[0025] In the embodiment of the present invention, the gold wire is filled inside two cladding tubes located on the x-axis, and the gold wire is used for the anti-resonance optical fiber sensor to excite the SPR effect, and induce the SPP mode to couple with the core fundamental mode to detect the refractive index of the ethanol liquid. The inner diameter of the hollow anti-resonance core is R = 28 μm, the inner diameter of the cylindrical nested elliptical cladding tube is r1 = 8 μm, the short semi-axis of the elliptical nested tube is a = 4 μm, the cladding tube thickness is t1 = 0.5 μm, the inner diameter of the special cylindrical cladding tube intersecting with the inner wall of the optical fiber is r2 = 12.5 μm, the cladding tube thickness is t2 = 0.6 μm, and the distance d between the center of its cross section and the center of the cross section of the anti-resonance optical fiber is 25 μm.

[0026] The sensor of the embodiment of the present invention can realize the sensing of the temperature range of -50℃~50℃, adopts the wavelength modulation method, and uses the finite element method ( Finite element method , FEM) is used to perform mode analysis on the optical fiber sensor of the present invention.

[0027] Figure 2 This is a schematic diagram of the coupling between the fiber core fundamental mode and the SPP mode when the temperature sensor is at a wavelength of 1.532 μm when the external temperature is 50°C in Example 1 of the present invention. From the figure, we can see that energy is transferred from the fundamental mode of the fiber core to the SPP mode on the metal surface, thereby forming a loss peak in the transmission spectrum, and the wavelength of this loss peak corresponds to the resonant wavelength of the sensor at a temperature of 50°C.

[0028] Figure 3 The figure is a schematic diagram of the relationship between the sensor temperature and the limiting loss of the embodiment of the present invention. It can be seen from the figure that as the temperature increases, the loss spectrum red shifts. When the ambient temperature changes from -50°C to 50°C, the resonant wavelength shifts from 1.216μm to 1.532μm.

[0029] Figure 4 and Figure 5 The figure shows the functional relationship between the resonant wavelength and the external temperature and the bar graph of the quality factor and the external temperature of the embodiment 1 of the present invention. The average wavelength sensitivity is usually a physical quantity used to evaluate whether the sensor is sensitive. The sensitivity (S w ) is:

[0030]

[0031] Among them, Δλ peak represents the change in resonant wavelength, and ΔT represents the change in external temperature. The quality factor can also be used to evaluate the performance of the sensor. The FOM formula is:

[0032]

[0033] Where FWHM is half-maximum bandwidth.

[0034] like Figure 4 and Figure 5 As shown, using Figure 3 The calculation of the resonance wavelength can be used to obtain the function relationship of the external temperature, that is, y = 3.15714x + 1379.33, and the corresponding fitting coefficient is 0.998. We can use the sensitivity formula to obtain that when the temperature is between -50℃ and -30℃, the sensitivity reaches a maximum value of 3.5nm / ℃. At the same time, we can obtain the maximum quality factor of 0.411℃ -1 Therefore, we can conclude that the present invention has good sensing performance.

[0035] During the use of the sensor, when the temperature to be tested is within the range of -50°C to 50°C, the wavelength position corresponding to the valley due to loss in the spectrum obtained by real-time measurement will correspond to the loss peak position of the optical fiber core mode in the following analysis. Combined with the analysis in Example 1, the value of the measured temperature can be obtained more accurately based on the position of the resonant wavelength where the loss peak is located.

[0036] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An anti-resonance optical fiber temperature sensor based on surface plasmon resonance, as shown in FIG1 , characterized in that: The optical fiber sensor body is composed of a hollow core anti-resonance optical fiber (1), a perfect matching layer (2), a special cylindrical quartz tube (3) intersecting with the inner wall of the optical fiber, a cylindrical nested elliptical quartz tube (4), ethanol liquid (5), and a gold wire (6). Each cladding tube (4) of the anti-resonance optical fiber (1) has three air holes, and all the air holes are filled with ethanol liquid (5). The air holes inside the special cylindrical quartz tube (3) are filled with gold wire (6). The ethanol liquid (5) is distributed in the core area of ​​the anti-resonance optical fiber (1) and in the holes of the four cladding cylindrical nested elliptical quartz tubes (4).

2. The anti-resonance optical fiber temperature sensor based on surface plasmon resonance according to claim 1, as shown in FIG1, is characterized in that: The antiresonant optical fiber (1) comprises two special cylindrical quartz tubes (3) filled with gold wires (6) and four cylindrical nested elliptical quartz tubes (4). The performance of the antiresonant optical fiber (1) can be changed by adjusting the thickness t2, radius r2 and distance r3 between the center of the quartz tube and the center of the fiber core of the special cylindrical quartz tube (3) formed by the intersection of the inner walls of the optical fibers, as well as the thickness t1, radius r1 and the inner elliptical minor semi-axis a of the cylindrical nested elliptical quartz tube (4).

3. The anti-resonance optical fiber temperature sensor based on surface plasmon resonance according to claims 1 and 2, as shown in FIG1, is characterized in that: The radius R of the antiresonance optical fiber varies in the range of 26 to 30 μm.

4. The anti-resonance optical fiber temperature sensor based on surface plasmon resonance according to claims 1 and 2, as shown in FIG1, is characterized in that: The two special cylindrical quartz tubes (3) are arranged horizontally opposite to each other along the x-axis direction, the distance d between the center of their cross section and the center of the cross section of the antiresonance optical fiber varies in the range of 23 to 26 μm, and the thickness t2 of the quartz tube varies in the range of 0.4 to 0.8 μm.

5. The anti-resonance optical fiber temperature sensor based on surface plasmon resonance according to claims 1 and 2, as shown in FIG1, is characterized in that: The four cylindrical nested elliptical quartz tubes (4) are respectively arranged at 60°, 120°, 240°, and 300° are evenly arranged and connected to the inner wall of the antiresonant optical fiber. The short semi-axis of the inner elliptical nested tube always points to the center of the antiresonant optical fiber core. The inner nested tube and the outer quartz tube have the same thickness of t1. The radius r1 of the outer quartz tube varies in the range of 6 to 9 μm, the short semi-axis a of the inner elliptical nested tube varies in the range of 3 to 5 μm, and the thickness t1 of the inner and outer nested tubes varies in the range of 0.4 to 0.8 μm.

6. The anti-resonance optical fiber temperature sensor based on surface plasmon resonance according to claims 1 to 5, characterized in that: The sensor can realize sensing when the structural parameters change. Under the optimal parameters, when the temperature to be measured is within the range of -50°C to 50°C, the maximum sensitivity can reach 3.5nm / °C.

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