Surface plasma resonance annular photonic crystal fiber temperature sensor

Abstract

The invention relates to the technical field of optical fiber sensing, in particular to a surface plasma resonance annular photonic crystal fiber temperature sensor which comprises a photonic crystal fiber and a temperature sensitive layer. Air holes are formed in the photonic crystal fiber, and a gold film is plated on the surface of the photonic crystal fiber; the temperature sensitive layer is composed of a mixed solution of chloroform and ethanol, the volume ratio of the chloroform to the ethanol is 1: 1 to ensure that the refractive index of the temperature sensitive liquid changes rapidly, the temperature sensor is designed to be of an annular structure, the surface of the annular structure is coated with a film, the mode of coating a film in an air hole does not need to be adopted, and the complexity of manufacturing the sensor is simplified; and a mixed liquid of ethanol and chloroform in a volume ratio of 1: 1 is adopted as a temperature-sensitive liquid, chloroform has a large thermosensitive coefficient but a high refractive index, and ethanol is adopted to reduce the refractive index so as to ensure the rapid change of the refractive index of the temperature-sensitive liquid, so that the sensor can detect the temperature in a range of-10 DEG C to 60 DEG C, the temperature sensitivity reaches 15.4 nm / DEG C, and the performance is excellent.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensing, and in particular to a surface plasma resonance annular photonic crystal optical fiber temperature sensor. Background Art

[0002] In today's era of rapid technological development, accurate temperature measurement is of vital importance in many fields. From process control in industrial production to disease diagnosis and monitoring in the biomedical field, accurate temperature information is often one of the key factors to achieve efficient and reliable operation.

[0003] Although traditional temperature sensors can meet the needs of many application scenarios to a certain extent, they also have some limitations. For example, thermocouples and thermal resistor sensors may be limited in accuracy and response speed, and their performance will be greatly affected in some special environments, such as strong electromagnetic fields and corrosive environments. In addition, some traditional temperature sensors are large in size and difficult to meet the needs of miniaturization and integration.

[0004] With the continuous development of optical fiber technology, optical fiber sensors have gradually become a hot topic of research due to their unique advantages. Photonic crystal fiber, as a new type of optical fiber structure, has many excellent properties. It can achieve the regulation of specific transmission characteristics of light by flexibly designing the structural parameters of the optical fiber. At the same time, photonic crystal fiber has the advantages of anti-electromagnetic interference, high temperature resistance, corrosion resistance, small size, and light weight, which is very suitable for temperature measurement in complex and harsh environments.

[0005] Surface plasmon resonance is an optical phenomenon that occurs at the interface between metal and dielectric. When light of a specific wavelength is irradiated onto the metal surface, surface plasmon waves are excited, causing the intensity of the reflected light to change dramatically under certain conditions. This change is very sensitive to the refractive index of the surrounding environment, and changes in temperature will cause changes in the refractive index of the environment. On this basis, the performance of temperature sensing can be further enhanced by adding temperature-sensitive liquid to the photonic crystal fiber. This temperature-sensitive liquid can change its own refractive index as the temperature changes, thereby more sensitively reflecting temperature changes.

[0006] Existing surface plasmon resonance photonic crystal fiber temperature sensors mostly use air hole coating and injection of temperature-sensitive liquid to improve the temperature sensitivity of the sensor, but this method is very difficult to process. Therefore, in order to simplify the manufacturing difficulty of the sensor and improve the performance of the sensor, this paper proposes a ring-shaped surface plasmon resonance photonic crystal fiber temperature sensor with outer cladding coating.

[0007] Therefore, the present application develops a surface plasmon resonance annular photonic crystal fiber temperature sensor to solve the problems existing in the prior art. Summary of the invention

[0008] The purpose of the present invention is to provide a surface plasmon resonance annular photonic crystal fiber temperature sensor to solve the problem in the prior art that the manufacturing difficulty is greatly increased while meeting the high performance of the temperature sensor.

[0009] The technical solution of the present invention is: a surface plasmon resonance annular photonic crystal fiber temperature sensor, comprising: a photonic crystal fiber, a temperature sensitive layer;

[0010] The photonic crystal fiber has air holes inside and the surface of the photonic crystal fiber is plated with a gold film;

[0011] The temperature sensitive layer is composed of a mixed solution of chloroform and ethanol, and the volume ratio of chloroform to ethanol is 1:1, so as to ensure that the refractive index of the temperature sensitive liquid changes rapidly.

[0012] Preferably, the photonic crystal fiber is ring-shaped, and the air holes include a first layer of air holes and a second layer of air holes, and are arranged inside the photonic crystal fiber. The first layer of air holes and the second layer of air holes are arranged sequentially along the radial direction of the photonic crystal fiber to improve the sensitivity of the sensor.

[0013] Preferably, the first layer of air holes is distributed in a hexagon, and the second layer of air holes is distributed in a circle, the first layer of air holes includes a pair of first air holes and a plurality of second air holes, the pair of first air holes is vertically arranged, and the plurality of second air holes are symmetrical relative to the photonic crystal fiber, so that the pair of first air holes and the plurality of second air holes are distributed at the vertices of the hexagon.

[0014] Preferably, when the radius of the photonic crystal fiber is 6.5 μm, the diameter of the first air hole is smaller than the diameter of the second air hole, the diameter of the first air hole d1 = 0.75 μm, the diameter of the second air hole d2 = 1.5 μm, and the diameter of the second layer of air holes d3 = 1.8 μm.

[0015] Preferably, the gold film is in direct contact with the temperature sensitive layer, and the thickness of the gold film is t=37 nm.

[0016] Preferably, the distances between the centers of the first air holes and the second air holes and the center of the photonic crystal fiber are both 2.55 μm, that is, the air hole spacing P=2.55 μm.

[0017] Compared with the prior art, the advantages of the present invention are:

[0018] (1) The temperature sensor is designed as a ring structure, and a film is coated on the surface of the ring structure, which does not require the use of film coating in the air hole or polishing, thereby simplifying the complexity of manufacturing the sensor;

[0019] (2) By reducing the size and number of air holes in the vertical direction of the photonic crystal fiber, the mode coupling between the SPP mode and the core mode is enhanced;

[0020] (3) A mixed liquid of ethanol and chloroform in a volume ratio of 1:1 is used as the temperature sensitive liquid. Chloroform has a large thermal sensitivity coefficient but a high refractive index. Ethanol is used to reduce the refractive index to ensure that the refractive index of the temperature sensitive liquid changes rapidly. The optimized sensor can detect temperatures in the range of -10°C to 60°C, with a temperature sensitivity of 15.4nm / °C, and has excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0022] Figure 1 A cross-sectional view of a surface plasmon resonance annular photonic crystal fiber temperature sensor according to the present invention;

[0023] Figure 2 This is a comparative simulation diagram of different volume ratios of ethanol and chloroform in the temperature sensitive layer of the present invention;

[0024] Figure 3a This is the core mode limitation loss spectrum at different gold film thicknesses according to the present invention;

[0025] Figure 3b It is the sensitivity diagram of the sensor under different gold film thicknesses of the present invention;

[0026] Figure 4a This is the core mode confinement loss spectrum at different air hole spacings according to the present invention;

[0027] Figure 4b It is the sensor sensitivity diagram under different air hole spacings of the present invention;

[0028] Figure 5a This is a core mode limitation loss spectrum diagram under different first pore diameters according to the present invention;

[0029] Figure 5b The core mode limitation loss spectrum under different second pore diameters of the present invention;

[0030] Figure 5c The core mode limitation loss spectrum under different second layer air hole diameters of the present invention;

[0031] Figure 6 The core mode limitation loss spectra at different temperatures described in the present invention;

[0032] Figure 7 It is the corresponding relationship between temperature and resonance wavelength and the fitting curve described in the present invention.

[0033] Wherein: 1. Photonic crystal fiber; 2. Temperature sensitive layer; 3. Air hole; 31. First layer of air holes; 311. First air holes; 312. Second air holes; 32. Second layer of air holes; 4. Gold film. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with specific embodiments:

[0035] like Figure 1 As shown, a surface plasmon resonance annular photonic crystal fiber temperature sensor comprises a photonic crystal fiber 1 and a temperature sensitive layer 2, wherein the cross section of the photonic crystal fiber 1 is annular, and the design of the annular structure can significantly improve the sensitivity and accuracy of the sensor, thereby enhancing the sensing performance, effectively guiding light to propagate inside the photonic crystal fiber 1, and interact with the plasma waves on the surface of the fiber, enhancing the plasma resonance effect, thereby improving the sensitivity of the sensor, and the annular structure can provide a more stable measurement environment, help reduce errors in temperature measurement, and improve measurement accuracy. At the same time, the annular structure is relatively simple and does not require polishing, which simplifies the complexity of manufacturing the sensor, helps reduce the manufacturing cost of the sensor, and improves production efficiency.

[0036] A first layer of air holes 31 and a second layer of air holes 32 are sequentially arranged radially in the photonic crystal fiber 1. A gold film 4 is plated on the surface of the photonic crystal fiber 1. The gold film 4 is in direct contact with the temperature sensitive layer 2. The first layer of air holes 31 are distributed in a hexagonal shape, and the second layer of air holes 32 are distributed in a circumferential shape. Figure 1 As shown, the distribution in this way can directly measure the core mode loss in the Y polarization direction, while there is no surface plasmon resonance in the X direction, and the first layer of air holes 31 guides the light wave to be transmitted inside the optical fiber, while reducing the scattering and loss of the optical signal, and further regulating the refractive index distribution of the optical fiber, thereby optimizing the performance of the sensor, and the second layer of air holes 32 helps to optimize the surface plasmon resonance effect, by adjusting the refractive index distribution and the light wave transmission path inside the optical fiber, making the SPR effect more significant and controllable, thereby improving the sensitivity and response speed of the sensor.

[0037] Furthermore, the first layer of air holes 31 includes a pair of first air holes 311 and a plurality of second air holes 312, wherein the pair of first air holes 311 are vertically arranged, and the plurality of second air holes 312 are symmetrical relative to the photonic crystal fiber 1, and the first air holes 311 and the second air holes 312 are distributed on the vertices of a hexagon, and the diameter of the first air holes 311 is smaller than the diameter of the second air holes 312, so that the refractive index distribution inside the optical fiber is more complex and controllable, which helps to guide light waves to propagate in a specific manner inside the optical fiber, while enhancing the sensitivity of the optical fiber to the surrounding environment. Through the different diameters and positions of the first air holes 311 and the second air holes 312, the light waves can be better confined to the core area when transmitted inside the optical fiber, reducing energy leakage and loss, and helping to enhance the surface plasmon resonance effect and the SPR effect.

[0038] like Figure 1-Figure 2 As shown, a temperature sensitive layer 2 is further provided outside the gold film 4, and the temperature sensitive layer 2 is composed of a mixed solution of chloroform and ethanol, and the volume ratio of chloroform to ethanol is 1:1. Different ethanol-chloroform ratios will result in different refractive index ranges. When a mixed liquid of ethanol-chloroform in a ratio of 1:1 is used, a temperature sensitive liquid with a refractive index range of 1.375-1.411 can be obtained. The refractive index difference between the high-refractive-index liquid and the optical fiber material may cause increased scattering and absorption of light during transmission, thereby increasing transmission loss, resulting in reduced signal strength and sensitivity of the sensor, and affecting the accuracy of the measurement result.

[0039] When the refractive index of the temperature-sensitive liquid is too low, the mode coupling efficiency with the optical fiber may be reduced, thereby weakening the intensity of the surface plasmon resonance, making the sensor signal weak, and reducing its sensitivity and detection ability. To ensure the sensitivity and accuracy of the sensor, a volume ratio of chloroform and ethanol of 1:1 is selected.

[0040] In order to reflect the influence of different parameters on the sensitivity of the sensor, this application adopts the control variable method, changes a specified parameter, keeps other parameters unchanged, compares the performance of the sensor, and selects the best parameters. During the optimization process, the sensitivity of the sensor is calculated by calculating the difference in peak wavelength between temperatures of -10°C and 0°C. The three parameters that affect the sensitivity of the sensor are the gold film thickness, the air hole spacing, and the air hole size.

[0041] The limiting loss of the loss spectrum is given by:

[0042]

[0043] Im(n eff ): imaginary part of the effective refractive index;

[0044] α: limiting loss of the core mode;

[0045] Table 1: d in Examples 1-51、 Values ​​of d2, d3, t, and P

[0046]

[0047] As shown in Table 1, in Example 1, the diameter of the first air hole 311 is d1=0.75 μm, the diameter of the second air hole 312 is d2=1.5 μm, the diameter of the second layer of air holes 32 is d3=1.8 μm, the air hole spacing P=2.55 μm, and the thickness of the gold film 4 is t=29 nm. By calculating the limiting loss α at different wavelengths and drawing a loss spectrum, the loss of the core mode is observed, where Im(n eff ) is the imaginary part of the effective refractive index of the optical fiber core mode calculated using COMSOL software.

[0048] In Examples 2-5, only the thickness of the gold film 44 is changed. While keeping the diameter of the first air hole 311, the diameter of the second air hole 312, the diameter of the second layer of air holes 32, and the air hole spacing unchanged, the limiting loss is calculated and the loss spectrum of different gold film 4 thicknesses is plotted.

[0049] In summary, in combination with Examples 1-5 and Figure 3a and Figure 3b As shown, with the increase of the thickness t of the gold film 4, the peak loss first increases and then decreases, the loss spectrum red-shifts, and the FWHM first decreases and then increases. With the increase of the thickness t of the gold film 4, the sensitivity of the sensor first increases and then decreases. Therefore, the core mode limits the half-wave full width (FWHM) of the loss spectrum and the sensor sensitivity, and the selected gold film 4 thickness is t=37nm.

[0050] Table 2: Values ​​of d1, d2, d3, t, and P in Examples 6-10

[0051]

[0052] As shown in Table 2, in Example 6, the diameter of the first air hole 311 is d1 = 0.75 μm, the diameter of the second air hole 312 is d2 = 1.5 μm, the diameter of the second layer of air holes 32 is d3 = 1.8 μm, the air hole spacing P = 2.51 μm, and the thickness of the gold film 4 is t = 37 nm. The loss of the core mode is observed by calculating the limiting loss α at different wavelengths and drawing a loss spectrum.

[0053] In Examples 7-10, only the air hole spacing P is changed, and the limiting loss α is calculated while keeping the diameter of the first air hole 311, the diameter of the second air hole 312, the diameter of the second layer of air holes 32 and the thickness of the gold film 4 unchanged, and the loss spectrum of different air hole spacings is plotted.

[0054] In summary, in combination with Examples 6-10 and Figure 4a and Figure 4bAs shown in the figure, with the increase of the air hole spacing P, the peak loss gradually decreases, and the lower peak loss will affect the surface plasma resonance effect, thereby affecting the final result analysis, and increasing the air hole spacing P will cause the sensitivity of the sensor to decrease. Therefore, considering the effect of the air hole spacing P on the loss spectrum and sensitivity, the selected air hole spacing P is 2.55μm.

[0055] Table 3: Values ​​of d1, d2, d3, t, and P in Examples 11-23

[0056]

[0057] As shown in Table 3, in Example 11, the diameter of the second pore 312 is d2=1.5μm, the diameter of the second layer of air pores 32 is d3=1.8μm, the air pore spacing is P=2.55μm, the thickness of the gold film 4 is t=37nm, and the diameter of the first pore 311 is d1=0.73μm. The loss of the core mode is observed by calculating the limiting loss α at different wavelengths and drawing a loss spectrum. In Examples 12-14, only the diameter of the first pore 311 is changed. While keeping the diameter of the second pore 312, the diameter of the second layer of air pores 32, the air pore spacing and the thickness of the gold film 4 unchanged, the limiting loss is calculated, and the loss spectrum of different first pore 311 diameters is drawn.

[0058] In Example 15, the diameter of the first pore 311 is d1=0.75μm, the diameter of the second layer of air holes 32 is d3=1.8μm, the air hole spacing P=2.55μm, the thickness of the gold film 4 is t=37nm, and the diameter of the second pore 312 is d2=1.4μm. The loss of the core mode is observed by calculating the limiting loss α at different wavelengths and drawing a loss spectrum. In Examples 16-19, only the diameter of the second pore 312 is changed. While keeping the diameter of the first pore 311, the diameter of the second layer of air holes 32, the air hole spacing and the thickness of the gold film 4 unchanged, the limiting loss is calculated, and the loss spectrum of the second pore 312 with different diameters is drawn.

[0059] In Example 20, the diameter of the first pore 311 is d1=0.75μm, the diameter of the second pore 312 is d2=1.5μm, the air hole spacing is P=2.55μm, the thickness of the gold film 4 is t=37nm, and the diameter of the second layer of air holes 32 is d3=1.7μm. The loss of the core mode is observed by calculating the limiting loss α at different wavelengths and drawing a loss spectrum. In Examples 21-23, only the diameter of the second layer of air holes 32 is changed. While keeping the diameter of the first pore 311, the diameter of the second pore 312, the air hole spacing and the thickness of the gold film 4 unchanged, the limiting loss is calculated, and the loss spectrum of the second layer of air holes 32 with different diameters is drawn.

[0060] In summary, in combination with Examples 11-23 and Figure 5a, Figure 5b and Figure 5c As shown, the diameters of the first air hole 311, the second air hole 312 and the second layer of air holes 32 will directly affect the FWHM and peak loss of the sensor limiting loss spectrum. In order to obtain a narrower FWHM and a higher peak loss, the diameters of the first air hole 311, the second air hole 312 and the second layer of air holes 32 are selected to be 0.75 μm, 1.5 μm and 1.8 μm, respectively.

[0061] Table 4: Values ​​of d1, d2, d3, t, P, and T in Examples 24-31

[0062]

[0063] As shown in Table 4, in Example 24, the diameter of the first pore 311 is d1=0.75μm, the diameter of the second pore 312 is d2=1.5μm, the diameter of the second layer of air holes 32 is d3=1.8μm, the air hole spacing P=2.55μm, the thickness of the gold film 4 is t=37nm, and T=-10°C. The loss of the core mode is observed by calculating the limiting loss α at different wavelengths and drawing a loss spectrum. In Examples 25-31, only the temperature is changed. While keeping the diameter of the first pore 311, the diameter of the second pore 312, the diameter of the second layer of air holes 32, the air hole spacing and the thickness of the gold film 4 unchanged, the limiting loss α is calculated and the loss spectrum at different temperatures is drawn.

[0064] In summary, after setting all the parameters, combined with Figure 6 , and a polynomial fitting was performed on the resonance wavelength and the refractive index of the analyte, and the following was obtained: Figure 7 The fitting curve shown has a fitting degree of 0.99805. Compared with existing sensors, it has high sensitivity and high nonlinear fitting degree.

[0065] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the scope of protection of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is limited by the attached claims rather than the above description, and it is intended to include all changes within the meaning and scope of the equivalent elements of the claims in the present invention.

Claims

1. A surface plasmon resonance ring photonic crystal fiber temperature sensor, characterized in that: include: Photonic crystal fiber (1), temperature sensitive layer (2); The photonic crystal optical fiber (1) has an air hole (3) inside, and the surface of the photonic crystal optical fiber (1) is plated with a gold film (4); The temperature sensitive layer (2) is composed of a mixed solution of chloroform and ethanol, and the volume ratio of chloroform to ethanol is 1:1, so as to ensure that the refractive index of the temperature sensitive liquid changes rapidly.

2. The surface plasmon resonance ring photonic crystal fiber temperature sensor according to claim 1, characterized in that: The photonic crystal fiber (1) is annular in shape, and the air holes (3) comprise a first layer of air holes (31) and a second layer of air holes (32), and are arranged inside the photonic crystal fiber (1); the first layer of air holes (31) and the second layer of air holes (32) are arranged in sequence along the radial direction of the photonic crystal fiber (1), so as to improve the sensitivity of a sensor.

3. A surface plasmon resonance annular photonic crystal fiber temperature sensor according to claim 2, characterized in that: The first layer of air holes (31) is distributed in a hexagonal shape, and the second layer of air holes (32) is distributed in a circumferential shape. The first layer of air holes (31) comprises a pair of first air holes (311) and a plurality of second air holes (312). The pair of first air holes (311) are vertically arranged, and the plurality of second air holes (312) are symmetrical relative to the photonic crystal optical fiber (1), so that the pair of first air holes (311) and the plurality of second air holes (312) are distributed at the vertices of the hexagon.

4. A surface plasmon resonance annular photonic crystal fiber temperature sensor according to claim 3, characterized in that: When the radius of the photonic crystal optical fiber (1) is 6.5 μm, the diameter of the first air hole (311) is smaller than the diameter of the second air hole (312), the diameter d1 of the first air hole (311) is 0.75 μm, the diameter d2 of the second air hole (312) is 1.5 μm, and the diameter d3 of the second layer of air holes (32) is 1.8 μm.

5. The surface plasmon resonance ring photonic crystal fiber temperature sensor according to claim 1, characterized in that: The gold film (4) is in direct contact with the temperature sensitive layer (2), and the thickness of the gold film (4) is t=37 nm.

6. The surface plasmon resonance annular photonic crystal fiber temperature sensor according to claim 3, characterized in that: The distances between the centers of the first air holes (311) and the second air holes (312) and the center of the photonic crystal optical fiber (1) are both 2.55 μm, that is, the spacing P of the air holes is 2.55 μm.

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