Photonic crystal fiber and temperature sensor based on sagnac interference principle

Abstract

The application belongs to the technical field of photonic crystal fibers, and particularly discloses a photonic crystal fiber and a temperature sensor based on a Sagnac interference principle. The photonic crystal fiber comprises a base material and an absorption layer outside the base material, the base material is wrapped with a fiber core and air holes, the fiber core is located at the center of the photonic crystal fiber, the air holes are periodically distributed in the form of regular hexagons around the fiber core to form a cladding, the air holes on the upper and lower opposite sides of the regular hexagonal structure of the inner cladding are first air holes, and the rest are third air holes; the air holes of the middle cladding are all first air holes; the air holes of the outer cladding are all second air holes, and the six corners of the outer cladding are missing the second air holes; and the fiber core and all the air holes are filled with a temperature-sensitive liquid material. The temperature sensor comprises the above photonic crystal fiber. The application has the advantages of high sensitivity, low loss, high transmission efficiency and high energy, and can well realize the temperature detection function. The application is suitable for temperature detection.

Description

Technical Field

[0001] This invention belongs to the field of photonic crystal fiber technology, specifically a photonic crystal fiber and temperature sensor based on the Sagnac interference principle. Background Technology

[0002] Photonic crystal fiber (PCF) is a new generation of transmission fiber developed based on photonic crystal technology. PCF enables low loss, nonlinearity, and birefringence, and features single-mode transmission, multi-core transmission, and good dispersion. With the development of fiber optic sensing technology and the maturation of PCF fabrication processes, PCF is increasingly being used in fiber optic sensing fields, such as sensing and measuring parameters like pressure, stress, temperature, bending, and refractive index. PCF development is gradually shifting from single-element photonic crystal fibers to air-hole filled metals and liquid-filled fibers, and significant achievements have been made in these research directions. PCF is a product of rapid scientific development in this new era, and its emergence has a significant impact on both the present and the future.

[0003] In 1996, J.K. Night drew the first photonic crystal fiber, a refractive index-guided photonic crystal fiber. In 2011, BH Kim et al. proposed a high-sensitivity temperature sensor based on indium-filled fiber with side holes and experimentally verified its optical properties; the sensor's temperature sensitivity was estimated at -7.5 nm / ℃. In 2014, Hao Congjing et al. applied a photonic crystal fiber sensor filled with metallic materials to temperature sensing research. Yang Yuanhong et al. proposed a polarization-maintaining photonic crystal fiber hydrogen sensor based on a Sagnac interferometer, measuring hydrogen concentration by measuring changes in the peak value of the Sagnac interferometer's output spectrum. In 2020, Y. Liu et al. proposed a ring-shaped photonic crystal fiber temperature sensor based on a Sagnac interferometer.

[0004] Currently, photonic crystal fiber sensors are used for temperature sensing, primarily by filling air holes with temperature-sensitive liquids that have high thermo-optical coefficients to achieve temperature measurement. One approach involves filling all air holes with temperature-sensitive liquids, achieving an average sensitivity of 18.27 nm / ℃. Another approach involves filling only the larger air holes with temperature-sensitive liquids, yielding average sensitivities of 9.47 nm / ℃ and 8.57 nm / ℃, respectively. Existing photonic crystal fibers still have certain structural limitations, making them susceptible to environmental corrosion, which leads to relatively low sensitivity in photonic crystal fiber temperature sensors. Summary of the Invention

[0005] The purpose of this invention is to provide a photonic crystal fiber and temperature sensor based on the Sagnac interference principle, so as to improve the structure of the photonic crystal fiber and enhance the sensitivity of the photonic crystal fiber temperature sensor.

[0006] To achieve the above objectives, the present invention employs the following technical methods:

[0007] A photonic crystal fiber based on the Sagnac interference principle includes a substrate material and an absorption layer outside the substrate material. The substrate material encloses a fiber core and air holes. The fiber core is located at the center of the photonic crystal fiber. The air holes are periodically distributed in a regular hexagon around the fiber core to form a cladding. The cladding consists of an inner cladding, an intermediate cladding, and an outer cladding from the inside out. The air holes include a first air hole, a second air hole, and a third air hole with progressively larger diameters. The air holes on the two opposite sides of the regular hexagonal structure of the inner cladding are the first air holes, and the air holes on the remaining sides are the third air holes. All air holes in the intermediate cladding are the first air holes. All air holes in the outer cladding are the second air holes, but the six corners of the regular hexagonal structure of the outer cladding lack the second air holes. The fiber core and all air holes are filled with a temperature-sensitive liquid material.

[0008] As a limitation: the inner cladding, intermediate cladding, and outer cladding are all single-layer air-hole structures; the inner cladding includes two third air holes and four first air holes, with two air holes on each side of the regular hexagonal structure of the inner cladding; the intermediate cladding includes twelve first air holes, with three air holes on each side of the regular hexagonal structure of the intermediate cladding; the outer cladding includes twelve second air holes, with two air holes on each side of the regular hexagonal structure of the outer cladding.

[0009] As further specified: the diameter of the fiber core is 0.6 μm, the diameter of the first air hole is 2.8 μm, the diameter of the second air hole is 3.1 μm, and the diameter of the third air hole is 3.2 μm.

[0010] As a further limitation, the center-to-center distance between adjacent air holes is 3.2 μm.

[0011] As another limitation: the cross-section of the substrate material is a circle with a radius of 10.5 μm.

[0012] As another limitation: the base material is fused silica, and the absorption layer is a perfectly matched layer.

[0013] The present invention also provides a photonic crystal fiber temperature sensor based on the Sagnac interference principle, comprising the aforementioned photonic crystal fiber based on the Sagnac interference principle, and further comprising a broadband light source, a spectrometer, a 3dB coupler, and a polarization controller. The first port of the 3dB coupler is connected to the output end of the broadband light source, the second port of the 3dB coupler is connected to the input end of the spectrometer, the third port of the 3dB coupler is connected to one end of the photonic crystal fiber, the fourth port of the 3dB coupler is connected to one end of the polarization controller, and the other end of the polarization controller is connected to the other end of the photonic crystal fiber; the photonic crystal fiber is placed in a constant temperature room.

[0014] The beneficial effects achieved by this invention, due to the adoption of the above-described solution, compared with the prior art, are as follows:

[0015] (1) The present invention provides a photonic crystal fiber and temperature sensor based on the Sagnac interference principle. By setting a substrate material and an absorption layer, a first air hole and a third air hole are set on the inner cladding, and the air holes in the middle cladding are all first air holes; the air holes in the outer cladding are all second air holes and the six corners of the hexagonal structure of the outer cladding are missing the second air holes. The fiber core and all air holes are filled with a temperature-sensitive liquid material. It has the advantages of low loss, high transmission efficiency, and high energy transmission capacity. It has high temperature sensitivity and can effectively realize the temperature detection function.

[0016] (2) The present invention provides a photonic crystal fiber and temperature sensor based on the Sagnac interference principle. The core diameter is 0.6 μm, the diameter of the first air hole is 2.8 μm, the diameter of the second air hole is 3.1 μm, the diameter of the third air hole is 3.2 μm, the center distance between adjacent air holes is 3.2 μm, the cross section of the substrate material is a circle with a radius of 10.5 μm, the substrate material is fused silica, and the absorption layer is a perfectly matched layer. By controlling the waveguide characteristics and structural flexibility of the photonic crystal fiber, and because the Sagnac interferometer is extremely sensitive to changes in refractive index, it has high linearity and high stability, and can achieve high-sensitivity temperature measurement.

[0017] (3) The photonic crystal fiber and temperature sensor based on the Sagnac interference principle provided by this invention have a sensitivity of 35.14 nm / ℃ and -28.89 nm / ℃ in the range of 25-32℃, and have the characteristics of low loss and high linearity. Compared with the prior art, the structure of this invention is simpler, and the detection performance is optimized, enabling higher precision temperature detection. It has the advantages of high sensitivity, low loss, high transmission efficiency and high energy throughput, and can well realize the temperature detection function. It has broad application prospects in environmental monitoring, mine exploration and medical sensing.

[0018] This invention is applicable to temperature measurement. Attached Figure Description

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0020] Figure 1 This is a schematic cross-sectional view of a photonic crystal fiber based on the Sagnac interference principle in Embodiment 1 of the present invention;

[0021] Figure 2 This is a schematic diagram of the photonic crystal fiber temperature sensor of Embodiment 2 of the present invention;

[0022] Figure 3 This is a graph showing the relationship between the wavelength, effective refractive index, and confinement loss of the photonic crystal fiber in Embodiment 1 of the present invention.

[0023] Figure 4 This is a graph showing the relationship between the temperature and the resonant wavelength of the photonic crystal fiber in Embodiment 1 of the present invention.

[0024] Figure 5 This is a linear fitting curve of temperature versus resonant wavelength for the photonic crystal fiber in Embodiment 1 of the present invention.

[0025] In the figure: 1. Absorbing layer; 2. Substrate material; 3. Fiber core; 4. First air hole; 5. Second air hole; 6. Third air hole; 7. Broadband light source; 8. 3dB coupler; 9. Polarization controller; 10. Photonic crystal fiber; 11. Spectrometer; 12. Temperature control room. Detailed Implementation

[0026] The present invention will be further described below with reference to the embodiments. However, those skilled in the art should understand that the present invention is not limited to the following embodiments. Any improvements and equivalent changes made based on the specific embodiments of the present invention are within the scope of protection of the claims of the present invention.

[0027] Example 1: A photonic crystal fiber based on the Sagnac interference principle

[0028] A photonic crystal fiber 10 based on the Sagnac interference principle, such as Figure 1As shown, the fiber includes a substrate material 2 and an absorption layer 1 on the outside of the substrate material 2. The substrate material 2 encloses a fiber core 3 and air holes. The fiber core 3 is located at the center of the photonic crystal fiber 10. The air holes are periodically distributed in a regular hexagon around the fiber core 3 to form a cladding. The cladding consists of an inner cladding, an intermediate cladding, and an outer cladding from the inside out. The inner cladding, intermediate cladding, and outer cladding are all single-layer air hole structures. The air holes include a first air hole 4, a second air hole 5, and a third air hole 6 with successively increasing diameters. The air holes on the two opposite sides of the regular hexagonal structure of the inner cladding are the first air holes 4, and the air holes on the remaining sides are the third air holes 6. The inner cladding includes two third air holes 6 and four first air holes 4, with two air holes on each side of the regular hexagonal structure of the inner cladding; the air holes of the middle cladding are all first air holes 4, and the middle cladding includes twelve first air holes 4, with three air holes on each side of the regular hexagonal structure of the middle cladding; the air holes of the outer cladding are all second air holes 5, and the six corners of the regular hexagonal structure of the outer cladding are missing second air holes 5, and the outer cladding includes twelve second air holes 5, with two air holes on each side of the regular hexagonal structure of the outer cladding; the fiber core 3 and all air holes are filled with a temperature-sensitive liquid material.

[0029] In this embodiment, the diameter of the fiber core 3 is 0.6 μm, the diameter of the first air hole 4 is 2.8 μm, the diameter of the second air hole 5 is 3.1 μm, the diameter of the third air hole 6 is 3.2 μm, the center distance between adjacent air holes is 3.2 μm, the cross-section of the substrate material 2 is a circle with a radius of 10.5 μm, the substrate material 2 is fused silica, the absorption layer 1 is a perfect matching layer, and the fiber core 3 and all air holes are filled with a temperature-sensitive liquid material of ethanol.

[0030] Example 2: A photonic crystal fiber temperature sensor based on the Sagnac interference principle

[0031] A photonic crystal fiber temperature sensor based on the Sagnac interference principle, such as Figure 2 As shown, the photonic crystal fiber 10 based on the Sagnac interference principle in Example 1 also includes a broadband light source 7, a spectrometer 11, a 3dB coupler 8, and a polarization controller 9. The first port of the 3dB coupler 8 is connected to the output of the broadband light source 7, the second port of the 3dB coupler 8 is connected to the input of the spectrometer 11, the third port of the 3dB coupler 8 is connected to one end of the photonic crystal fiber 10, the fourth port of the 3dB coupler 8 is connected to one end of the polarization controller 9, and the other end of the polarization controller 9 is connected to the other end of the photonic crystal fiber 10. The photonic crystal fiber 10 is placed inside a constant temperature chamber 12.

[0032] In this embodiment, the broadband light source 7 outputs laser light to the 3dB coupler 8. The 3dB coupler 8 splits the laser light output by the broadband light source 7 into two beams. One beam passes through the polarization controller 9 and then through the photonic crystal fiber 10 in Embodiment 1 to the 3dB coupler 8. The other beam passes through the photonic crystal fiber 10 in Embodiment 1 and then through the polarization controller 9 to the 3dB coupler 8. The two beams travel in opposite directions within the same loop and finally couple together in the 3dB coupler 8, generating interference. The spectrometer 11 measures the interference spectrum output by the 3dB coupler 8. When there is a rotational angular velocity in the loop plane, the interference fringes measured by the spectrometer 11 will shift. The sensing performance of the temperature sensor of the photonic crystal fiber 10 in this embodiment is detected based on the displacement of the lowest point of the obtained resonance wavelength.

[0033] The optical properties of the photonic crystal fiber 10 of Example 1 were simulated and analyzed using the finite element method combined with a perfectly matched layer and scattering boundary conditions. The relationships between the wavelength, effective refractive index, and confinement loss of the photonic crystal fiber 10 of Example 1 were obtained, such as... Figure 3 As shown. By Figure 3 It can be seen that the effective refractive index decreases with increasing wavelength. As the wavelength increases, the confinement loss of the optical fiber increases. The effective refractive index curves and confinement loss curves in x-polarization mode and y-polarization mode almost overlap.

[0034] When the temperature range is 25-32℃, the relationship between the temperature and the transmission spectrum of the photonic crystal fiber 10 in Example 1 is as follows: Figure 4 As shown, by Figure 4 It can be seen that there are two resonant wavelengths at 26-32℃, namely dipA and dipB. As the temperature increases, dipA shifts towards a shorter wavelength and dipB shifts towards a longer wavelength. The greater the shift of the resonant wavelength, the greater the sensitivity.

[0035] according to Figure 4 A linear fit was performed on the relationship between the two resonant wavelengths dipA and dipB and temperature, resulting in the linear fit curve of temperature versus resonant wavelength for the photonic crystal fiber 10 in Example 1, as shown below. Figure 5 As shown, by Figure 5 It can be seen that the fitting of temperature and resonant wavelength exhibits high linearity. The linear fitting result of the DipA resonant wavelength changing with temperature is y = 35.14x + 1091.61, with a linearity R0. 2 =0.98455, meaning the temperature sensitivity is 35.14 nm / ℃; the linear fitting result of the DipB resonance wavelength with temperature is y = -28.29x + 2519.42, and the linearity R0 is 0.98455. 2=0.98688, meaning the temperature sensitivity is -28.89 nm / ℃. The sensor in this embodiment has the advantages of high sensitivity, low loss, high transmission efficiency, and high energy throughput, enabling it to effectively perform temperature detection.

Claims

1. A photonic crystal fiber based on the Sagnac interference principle, characterized in that, The photonic crystal fiber based on the Sagnac interference principle comprises a substrate material and an absorption layer outside the substrate material, a core and air holes are wrapped in the substrate material, the core is located at the center of the photonic crystal fiber, the air holes are periodically distributed around the core in a regular hexagonal structure to form a cladding, the cladding comprises an inner cladding, an intermediate cladding and an outer cladding from inside to outside, the air holes comprise first air holes, second air holes and third air holes with increasing diameters, the air holes on the opposite edges of the upper and lower sides of the regular hexagonal structure of the inner cladding are the first air holes, and the air holes on the remaining edges are the third air holes; the air holes of the intermediate cladding are all the first air holes; the air holes of the outer cladding are all the second air holes, and the second air holes are missing from the six corners of the regular hexagonal structure of the outer cladding; and the core and all the air holes are filled with a temperature-sensitive liquid material. The inner cladding, the intermediate cladding and the outer cladding are all one layer of air hole structure; the inner cladding comprises two third air holes and four first air holes, two air holes are arranged on each side of the regular hexagonal structure of the inner cladding; the intermediate cladding comprises twelve first air holes, three air holes are arranged on each side of the regular hexagonal structure of the intermediate cladding; and the outer cladding comprises twelve second air holes, two air holes are arranged on each side of the regular hexagonal structure of the outer cladding.

2. The photonic crystal fiber based on Sagnac interference principle according to claim 1, characterized in that, The diameter of the core is 0.6 μm, the diameter of the first air hole is 2.8 μm, the diameter of the second air hole is 3.1 μm, and the diameter of the third air hole is 3.2 μm.

3. The photonic crystal fiber based on Sagnac interference principle according to claim 2, characterized in that, The center distance between adjacent air holes is 3.2 μm.

4. The photonic crystal fiber based on Sagnac interference principle according to any one of claims 1-3, characterized in that, The cross section of the substrate material is a circle with a radius of 10.5 μm.

5. The photonic crystal fiber based on Sagnac interference principle according to any one of claims 1-3, characterized in that, The substrate material is fused quartz, and the absorption layer is a perfect matching layer.

6. The photonic crystal fiber based on the Sagnac interference principle according to claim 4 The photonic crystal fiber based on the Sagnac interference principle, characterized in that, The substrate material is fused quartz, and the absorption layer is a perfect matching layer.

7. A photonic crystal fiber temperature sensor based on the Sagnac interference principle, characterized in that, The photonic crystal fiber based on the Sagnac interference principle comprises a substrate material and an absorption layer outside the substrate material, a core and air holes are wrapped in the substrate material, the core is located at the center of the photonic crystal fiber, the air holes are periodically distributed around the core in a regular hexagonal structure to form a cladding, the cladding comprises an inner cladding, an intermediate cladding and an outer cladding from inside to outside, the air holes comprise first air holes, second air holes and third air holes with increasing diameters, the air holes on the opposite edges of the upper and lower sides of the regular hexagonal structure of the inner cladding are the first air holes, and the air holes on the remaining edges are the third air holes; the air holes of the intermediate cladding are all the first air holes; the air holes of the outer cladding are all the second air holes, and the second air holes are missing from the six corners of the regular hexagonal structure of the outer cladding; and the core and all the air holes are filled with a temperature-sensitive liquid material. The inner cladding, the intermediate cladding and the outer cladding are all one layer of air hole structure; the inner cladding comprises two third air holes and four first air holes, two air holes are arranged on each side of the regular hexagonal structure of the inner cladding; the intermediate cladding comprises twelve first air holes, three air holes are arranged on each side of the regular hexagonal structure of the intermediate cladding; and the outer cladding comprises twelve second air holes, two air holes are arranged on each side of the regular hexagonal structure of the outer cladding. The diameter of the core is 0.6 μm, the diameter of the first air hole is 2.8 μm, the diameter of the second air hole is 3.1 μm, and the diameter of the third air hole is 3.2 μm. The center distance between adjacent air holes is 3.2 μm. The cross section of the substrate material is a circle with a radius of 10.5 μm. The substrate material is fused quartz, and the absorption layer is a perfect matching layer.

6. The photonic crystal fiber based on the Sagnac interference principle according to claim 4 The substrate material is fused quartz, and the absorption layer is a perfect matching layer. The photonic crystal fiber based on the Sagnac interference principle comprises a substrate material and an absorption layer outside the substrate material, a core and air holes are wrapped in the substrate material, the core is located at the center of the photonic crystal fiber, the air holes are periodically distributed around the core in a regular hexagonal structure to form a cladding, the cladding comprises an inner cladding, an intermediate cladding and an outer cladding from inside to outside, the air holes comprise first air holes, second air holes and third air holes with increasing diameters, the air holes on the opposite edges of the upper and lower sides of the regular hexagonal structure of the inner cladding are the first air holes, and the air holes on the remaining edges are the third air holes; the air holes of the intermediate cladding are all the first air holes; the air holes of the outer cladding are all the second air holes, and the second air holes are missing from the six corners of the regular hexagonal structure of the outer cladding; and the core and all the air holes are filled with a temperature-sensitive liquid material. The inner cladding, the intermediate cladding and the outer cladding are all one layer of air hole structure; the inner cladding comprises two third air holes and four first air holes, two air holes are arranged on each side of the regular hexagonal structure of the inner cladding; the intermediate cladding comprises twelve first air holes, three air holes are arranged on each side of the regular hexagonal structure of the intermediate cladding; and the outer cladding comprises twelve second air holes, two air holes are arranged on each side of the regular hexagonal structure of the outer cladding. The diameter of the core is 0.6 μm, the diameter of the first air hole is 2.8 μm, the diameter of the second air hole is 3.1 μm, and the diameter of the third air hole is 3.2 μm. The center distance between adjacent air holes is 3.2 μm. The cross section of the substrate material is a circle with a radius of 10.5 μm. The substrate material is fused quartz, and the absorption layer is a perfect matching layer.

6. The photonic crystal fiber based on the Sagnac interference principle according to claim 4 The substrate material is fused quartz, and the absorption layer is a perfect matching layer. The photonic crystal fiber based on the Sagnac interference principle comprises a substrate material and an absorption layer outside the substrate material, a core and air holes are wrapped in the substrate material, the core is located at the center of the photonic crystal fiber, the air holes are periodically distributed around the core in a regular hexagonal structure to form a cladding, the cladding comprises an inner cladding, an intermediate cladding and an outer cladding from inside to outside, the air holes comprise first air holes, second air holes and third air holes with increasing diameters, the air holes on the opposite edges of the upper and lower sides of the regular hexagonal structure of the inner cladding are the first air holes, and the air holes on the remaining edges are the third air holes; the air holes of the intermediate cladding are all the first air holes; the air holes of the outer cladding are all the second air holes, and the second air holes are missing from the six corners of the regular hexagonal structure of the outer cladding; and the core and all the air holes are filled with a temperature-sensitive liquid material. The inner cladding, the intermediate cladding and the outer cladding are all one layer of air hole structure; the inner cladding comprises two third air holes and four first air holes, two air holes are arranged on each side of the regular hexagonal structure of the inner cladding; the intermediate cladding comprises twelve first air holes, three air holes are arranged on each side of the regular hexagonal structure of the intermediate cladding; and the outer cladding comprises twelve second air holes, two air holes are arranged on each side of the regular hexagonal structure of the outer cladding. The diameter of the core is 0.6 μm, the diameter of the first air hole is 2.8 μm, the diameter of the second air hole is 3.1 μm, and the diameter of the third air hole is 3.2 μm. The center distance between adjacent air holes is 3.2 μm. The cross section of the substrate material is a circle with a radius of 10.5 μm. The substrate material is fused quartz, and the absorption layer is a perfect matching layer.

6. The photonic crystal fiber based on the Sagnac interference principle according to claim 4 The substrate material is fused quartz, and the absorption layer is a perfect matching layer. The photonic crystal fiber based on the Sagnac interference principle comprises a substrate material and an absorption layer outside the substrate material, a core and air holes are wrapped in the substrate material, the core is located at the center of the photonic crystal fiber,

Images