Photonic Crystal Fiber Structure and Fiber Optic Sensor

Abstract

The present invention discloses a photonic crystal fiber structure and an optical fiber sensor, relating to the field of optical fibers. The photonic crystal fiber structure includes an optical fiber matrix, a core, and two reinforcing layers. The optical fiber matrix has a D-shaped structure, the core has an elliptical structure, and the two reinforcing layers are located on both sides of the minor axis of the core. The optical fiber sensor includes the above-mentioned photonic crystal fiber structure. Through the design of the D-shaped geometric optical fiber matrix, the elliptical core, and the air holes, polycarbonate with a high thermo-optic coefficient and a high elasto-optic coefficient is used as the core material for the core. Black phosphorus, which has anisotropic dielectric constant, anisotropic mechanical properties, and a light-enhancing effect to improve the birefringence of the sensor during the process of the core transmitting light, is used as the filling material in the near-core region, resulting in a great improvement in measurement accuracy and anti-interference performance. The pressure sensitivity under different temperature conditions and the temperature sensitivity under different pressure conditions remain unchanged, enabling independent measurement of temperature and pressure.

Description

Technical Field

[0001] The present invention relates to the field of optical fibers, and particularly to a photonic crystal fiber structure and an optical fiber sensor. Background Art

[0002] Photonic devices have significant advantages such as fast transmission rate, low loss, large capacity, and strong anti-interference ability. Compared with electronic devices, they are more in line with the development trend of high efficiency, device integration, and miniaturization. However, the controllability of photons is weaker than that of electrons, which limits the development of all-optical devices. The emergence and development of photonic crystals will break through this limitation: as a new type of material, it can effectively control the transmission of light waves, provide a material basis for various photonic integrated devices, and has great potential in the fields of optical sensing and optical communication. The existing sensors still have the problem that they cannot solve the simultaneous measurement of pressure and temperature. Summary of the Invention

[0003] The object of the present invention is to design a photonic crystal fiber structure and a sensor to solve the above problems.

[0004] The present invention achieves the above object through the following technical solutions:

[0005] A photonic crystal fiber structure includes an optical fiber substrate, a core, and two reinforcing layers for improving the birefringence. The optical fiber substrate is of a D-shaped structure, the core is of an elliptical structure, and the two reinforcing layers are respectively located on both sides of the short axis of the core. The dielectric constant and mechanical properties of the reinforcing layer are both anisotropic, and the reinforcing layer has a light-enhancing effect. A first air layer and multiple second air layers are arranged on the optical fiber substrate. The first air layer wraps around the core and the reinforcing layers, and the second air layers are located outside the first air layer.

[0006] An optical fiber sensor includes the above-mentioned photonic crystal fiber structure.

[0007] The beneficial effects of the present invention are as follows: Through the spatial arrangement design of the D-shaped optical fiber structure, elliptical core structure, first air holes, second air holes, and third air holes, an asymmetric structure will be formed inside the optical fiber, which will greatly improve the sensitivity; in the selection of materials, polycarbonate with a high thermo-optic coefficient and a high elasto-optic coefficient is used as the core, and black phosphorus with anisotropic dielectric constant, anisotropic mechanical properties, and a light-enhancing effect is used as the filling material in the near-core region to improve the birefringence of the sensor during the process of the core transmitting light, resulting in a great improvement in measurement accuracy and anti-interference ability; the pressure sensitivity under different temperature conditions and the temperature sensitivity under different pressure conditions remain unchanged, enabling independent measurement of temperature and pressure. Brief Description of the Drawings

[0008] Figure 1 It is a schematic cross-sectional structure diagram of the photonic crystal fiber structure of the present invention;

[0009] Figure 2 It is a schematic diagram of the structure of the near-core part in the photonic crystal fiber structure of the present invention;

[0010] Figure 3 It is a refractive index simulation diagram of the X-direction polarized light mode simulated by the photonic crystal fiber structure of the present invention in Comsol software;

[0011] Figure 4 It is a refractive index simulation diagram of the Y-direction polarized light mode simulated by the photonic crystal fiber structure of the present invention in Comsol software;

[0012] Figure 5 It is a diagram showing the relationship between temperature and birefringence changes of the fiber optic sensor at three optical window bands of 850 nm, 1310 nm, and 1550 nm when the thickness of black phosphorus is 1 nm;

[0013] Figure 6 It is a diagram showing the relationship between temperature and birefringence changes of the fiber optic sensor at three optical window bands of 850 nm, 1310 nm, and 1550 nm when the thickness of black phosphorus is 2 nm;

[0014] Figure 7 It is a diagram showing the relationship between temperature and birefringence changes of the fiber optic sensor at three optical window bands of 850 nm, 1310 nm, and 1550 nm when the thickness of black phosphorus is 3 nm;

[0015] Figure 8 It is a diagram showing the relationship between temperature and birefringence changes of the sensor at the optical window with a wavelength of 1550 nm when the thickness of black phosphorus is 1 nm, 2 nm, 3 nm, and without black phosphorus;

[0016] Figure 9 It is a diagram showing the relationship between birefringence changes of the sensor at the optical window with a wavelength of 1550 nm when the width of the black phosphorus layer is 2 μm, 3 μm, 4 μm, 5 μm, and 6 μm;

[0017] Figure 10 It is a diagram showing the relationship between the pressure applied around and the birefringence changes of the fiber optic sensor with and without filling black phosphorus at an external ambient temperature of 293.15 K and at the optical window with a wavelength of 1550 nm;

[0018] Figure 11 It is a diagram showing the relationship between the pressure applied around the sensor and the pressure applied in the Y direction and the birefringence changes at an external ambient temperature of 293.15 K and at the optical window with a wavelength of 1550 nm;

[0019] Figure 12It is a graph showing the relationship between the pressure applied in the Y direction and the birefringence change under the optical window with a wavelength of 1550 nm when the external environmental temperatures are 273.15 K, 283.15 K, 293.15 K, 303.15 K, and 313.15 K;

[0020] Figure 13 It is a graph showing the relationship between the temperature and the birefringence under the conditions that the pressures in the Y direction are 0 MPa, 50 MPa, 100 MPa, 150 MPa, and 200 MPa;

[0021] Among them, the corresponding reference numerals are:

[0022] 1 - optical fiber matrix, 2 - reinforcing layer, 3 - core, 4 - first air hole, 5 - second air hole, 6 - third air hole. Specific embodiments

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and shown in the accompanying drawings here can be arranged and designed in various different configurations.

[0024] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0025] It should be noted that: similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0026] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "upper", "lower", "inner", "outer", "left", "right", etc. are based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationships in which the product of this invention is usually placed during use, or the orientation or positional relationships commonly understood by those skilled in the art. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0027] In addition, the terms "first", "second", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0028] In the description of the present invention, it should also be noted that, unless otherwise clearly specified and defined, terms such as "arrangement" and "connection" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] The following will describe in detail the specific embodiments of the present invention with reference to the accompanying drawings.

[0030] As Figure 1 、 Figure 2 shown, the photonic crystal fiber structure includes a fiber substrate 1, a core 3, and two reinforcing layers 2 for enhancing the birefringence. The fiber substrate 1 has a D-shaped structure, the core 3 has an elliptical structure, and the two reinforcing layers 2 are respectively located on the upper and lower sides of the short axis of the core 3. The dielectric constant and mechanical properties of the reinforcing layer are anisotropic, and the reinforcing layer 2 has the effect of enhancing birefringence. A first air layer and multiple second air layers are arranged on the fiber substrate 1. The first air layer wraps around the core 3 and the reinforcing layers, and the second air layers are located outside the first air layer.

[0031] As Figure 1 、 Figure 2 shown, the first air layer includes two groups of air hole groups. The two groups of air hole groups are respectively located on both sides of the short axis of the core 3. The two groups of air hole groups include two first air holes 4 and two second air holes 5. The two first air holes 4 are located between the two second air holes 5, and the diameter of the second air holes 5 is larger than that of the first air holes 4.

[0032] The core 3 is made of polycarbonate, and the fiber substrate 1 is made of silica.

[0033] The reinforcing layer 2 is a black phosphorus layer, and the black phosphorus layer has the effect of enhancing birefringence.

[0034] As Figure 2 shown, the long axis d5 of the core 3 is 3.3 um, and the short axis d4 is 0.9 um.

[0035] As Figure 2 shown, the length L range of the reinforcing layer is 2 - 6 um, and the thickness range of the reinforcing layer is 1 - 3 nm.

[0036] As Figure 2 shown, the length L of the reinforcing layer is 4 um, the thickness of the reinforcing layer is 2 nm, and the distance d1 between the two reinforcing layers is 1.6 um.

[0037] As Figure 2As shown, the diameter d2 of the first air hole 4 ranges from 1.5 to 2 um, the diameter d3 of the second air hole 5 ranges from 1.8 to 2.3 um, the distance Λ2 between two first air holes 4 in the same group is 2.4 um, the distance Λ1 between two second air holes 5 in the same group is 7.2 um, the distance Λ4 between two groups of first air holes 4 is 5 um, and the distance Λ3 between two groups of second air holes 5 ranges from 3.3 to 3.6 um.

[0038] As Figure 1 shown, the second air layer includes a plurality of third air holes 6, the diameter d6 of the third air hole 6 ranges from 5 to 8.5 um, and the distance Λ5 between two adjacent third air holes 6 ranges from 9 to 11 um.

[0039] An optical fiber sensor includes the above-mentioned photonic crystal fiber structure.

[0040] As Figure 1 、 Figure 2 shown, the function of the D-shaped optical fiber substrate 1 in the practical application of the present invention is to improve the birefringence of the optical fiber by introducing an asymmetric structure; the main functions of the first air layer and the second air layer are to reduce the cladding refractive index, limit the energy in the core 3, optimize the optical fiber transmission quality, be more likely to achieve phase matching, and enhance the sensitivity; polycarbonate has a refractive index of 1.586 and a thermo-optic coefficient of 1.04×10 -4 / K. The elliptical core 3 enables the sensor to have a high birefringence. The excellent optical transmission characteristics, high refractive index, and good thermo-optic coefficient of polycarbonate will enhance the temperature sensitivity of the sensor; the excellent optical transmission characteristics, high refractive index, good first stress optical coefficient and second stress optical coefficient of polycarbonate will enhance the pressure sensitivity of the sensor.

[0041] The thermo-optic coefficient expression is: n = n0 + α(T - T0), where α is the thermo-optic coefficient, n0 is the refractive index of the material at room temperature, and T0 is room temperature, i.e., 293.15 K.

[0042] The relative permittivity of black phosphorus has anisotropy and changes with thickness, which lies in the specificity of the crystal cell structure of black phosphorus. The role of black phosphorus in the photonic crystal fiber structure is to improve the birefringence of the optical fiber. Since its permittivity can be regarded as a constant with respect to temperature, the improvement effect of black phosphorus on the birefringence of the optical fiber will not change with temperature. Specifically in production, a probe with a nano-aperture punctures dense pinholes at the above-mentioned position in the near-core 3 region, and then black phosphorus is generated at the pinholes by physical vapor deposition;

[0043] Due to the specificity of the crystal cell structure of black phosphorus crystals, black phosphorus has characteristics such as anisotropy of dielectric constant, anisotropy of mechanical properties, and angular dependence of Raman scattering, which are more obvious in black phosphorus nanosheets. Designing two symmetric black phosphorus layers above and below in the near-core region 3 is to make the optical fiber reflect up and down when hitting the black phosphorus layer 2 to enhance the birefringence; the anisotropy of the dielectric constant of black phosphorus can be expressed as: where ε 33 = ε0, ε0 = 8.854×10 -12 Fm -1 , ε r = 5.76. When filling black phosphorus nanosheets in this position, the positive direction of the Y-axis of the optical fiber plane is used as the positive direction of the Z-axis of black phosphorus nanosheets, the positive direction of the X-axis of the optical fiber plane is used as the positive direction of the X-axis of black phosphorus nanosheets, and the positive direction of the Z-axis of the optical fiber is used as the positive direction of the Y-axis of black phosphorus nanosheets. It can be seen from the formula that the relative dielectric constant of black phosphorus changes with the thickness. When the thickness of black phosphorus nanosheets is 1 - 3 nm, that is, when the thickness of black phosphorus nanosheets is 1 - 3 unit crystal cells, the change of the dielectric constant is more obvious;

[0044] According to the classical Drude model, γ bp can be expressed as η e = 10 -3 eV, n s is the change of electron density with thickness d, which is expressed as: where E f - E c is 0.9 eV at a thickness of 1 nm, 0.6 eV at 2 nm, and 0.4 eV at 3 nm, indicating that the band gap of black phosphorus changes with the thickness, and this characteristic is more obvious in black phosphorus nanosheets. It can be reflected from the formula that the main factor affecting the dielectric constant is the change of the thickness of black phosphorus itself. Similarly, taking the partial derivative of this formula with respect to temperature can show that temperature has no effective influence on the dielectric constant.

[0045] Due to the anisotropy of the dielectric constant caused by the asymmetry of the crystal cell structure of black phosphorus in the AC(Z) direction and the ZZ(X) direction, according to Maxwell's electromagnetic theory, the relationship between the dielectric constant and the refractive index is as follows: This formula reflects the anisotropy of the refractive index of black phosphorus in the AC(Z) direction and the ZZ(X) direction, which is equivalent to adding a pair of crystals with refractive index asymmetry in the X and Y directions above and below the core 3, thus increasing the overall birefringence of the core 3 region.

[0046] The birefringence enhancement coefficient of black phosphorus for optical fiber sensing is defined by the following formula: In the formula, B0 is the birefringence of the optical fiber without black phosphorus, is the refractive index of the X-direction polarized light mode without black phosphorus, is the refractive index of the Y-direction polarized light mode without black phosphorus, k BP is the amplification coefficient of black phosphorus for birefringence, and B1 is the birefringence of the sensor after black phosphorus is filled into the optical fiber. k BP will change with factors such as the thickness of the filled black phosphorus, the incident light frequency, the filling position in the optical fiber, and the angle formed with the transmitted light. However, during specific measurements, since the internal structure of the sensor has been prepared and fixed, only the incident light frequency of the sensor needs to be considered. Compared with traditional doping materials such as gold, silver, and gallium arsenide, black phosphorus has the advantages of a high resonant light frequency, a large adjustable space for the sensor according to the doping of black phosphorus with different thicknesses, and independent multiplexed measurement.

[0047] Such as Figure 3 、 Figure 4 As shown, it is the refractive index simulation diagram of the X-direction and Y-direction polarized light modes simulated by the comsol software of the photonic crystal fiber structure. Due to the thermo-optic effect, elasto-optic effect, and birefringence characteristics of polycarbonate and silica inside the sensor, a phenomenon occurs where the birefringence inside the sensor changes with temperature and pressure. The sensitivity of this design is characterized by the rate of change of the difference in the refractive indices of the two orthogonal polarized light modes with temperature and pressure. The value of birefringence is expressed by the following formula: In the formula, B represents the magnitude of birefringence, represents the refractive index of the X-direction polarized light mode, represents the refractive index of the Y-direction polarized light mode.

[0048] According to Figure 5 、 Figure 6 、 Figure 7 It can be known that when the thickness of black phosphorus is fixed at any thickness, by comparing the three common optical windows of the sensor at wavelengths of 850 nm, 1310 nm, and 1550 nm, it can be known that when the sensor is in the optical window at a wavelength of 1550 nm, the slope of the curve of birefringence changing with temperature is the largest. From Figure 8 It can be known that at 1550 nm, the slope of the curve of birefringence changing with temperature without black phosphorus is less than that with black phosphorus. When the thickness of black phosphorus decreases, the slope of the curve of birefringence changing with temperature increases. However, since the curve of birefringence changing with temperature when black phosphorus is 1 nm has large fluctuations, it is better to choose a black phosphorus thickness of 2 nm with excellent linear curve effect as the filling thickness.

[0049] According to Figure 6 the relationship between the birefringence and temperature, it can be known that the monitored phase changing with temperature is a straight line. Specifically, there is a temperature sensitivity The temperature range of the sensor is 200 K - 430 K.

[0050] According to Figure 9The birefringence and the change in the width of the black phosphorus layer 2 When the width is 2 μm, 3 μm, 4 μm, 5 μm, and 6 μm, under the change in the width of the black phosphorus, the temperature sensitivity of the photonic crystal fiber structure remains unchanged. When the width is 2 μm, 3 μm, and 4 μm, the curves of the birefringence of the sensor changing with temperature shift up and down. When the width is more than 4 μm, the curves of the birefringence changing with temperature no longer move up and down. At a width of 4 μm, the data curve is smoother and has less data fluctuation compared with other data.

[0051] According to Figure 10 It can be seen that the multiplexed micro-nano structure sensor based on black phosphorus has a better effect of birefringence changing with pressure than that without black phosphorus. The relationship between stress and the refractive index ellipsoid can be specifically expressed as: Where the first stress-optic coefficient is C P1 = 2.45×10 -11 m 2 / N, the second stress-optic coefficient is C P1 = 9.38×10 -11 m 2 / N, and σ x , σ y and σ z are the stresses at a certain point on the cross-section in the X, Y, and Z directions respectively.

[0052] The pressure range of the fiber optic sensor made of the photonic crystal fiber structure of the present invention is 0 - 200 MPa. When there is a black phosphorus layer and pressure is applied around it, the pressure sensitivity of the sensor is When there is no black phosphorus layer and pressure is applied around it, the pressure sensitivity of the sensor is

[0053] According to Figure 11 It can be seen that the effect of the birefringence of the photonic crystal fiber structure of the present invention changing with pressure when pressure is applied in the Y direction is better than that when pressure is applied around it. The pressure sensitivity in the Y direction is

[0054] According to Figure 12 It can be seen that when pressure is applied in the Y direction of the photonic crystal fiber structure of the present invention under the fixed ambient temperature conditions of 273.15 K, 283.15 K, 293.15 K, 303.15 K, and 313.15 K, the pressure sensitivity is a smooth curve with the same magnitude. Specifically, the pressure sensitivity is Under different fixed ambient temperature conditions, temperature only shifts the curve of the relationship between pressure and birefringence as a whole up and down.

[0055] According to Figure 11 , Figure 12It can be seen that the pressure sensitivity improvement of the photonic crystal fiber structure with or without black phosphorus filling does not change with the ambient temperature, reflecting the k BP It does not change with temperature, which confirms that the dielectric constant of black phosphorus does not change with temperature.

[0056] according to Figure 13 It can be seen that when the optical fiber sensor manufactured by the photonic crystal fiber structure of the present invention is subjected to pressure of 0MPa, 50MPa, 100MPa, 150MPa, and 200MPa in the Y direction when measuring temperature, the temperature sensitivity reflected by each curve is the same. Specifically, the temperature sensitivity is The temperature sensitivity curve shifts up and down as a whole under different fixed pressure conditions.

[0057] It can be concluded that: under different fixed ambient temperature conditions, the pressure sensitivity of the sensor will not be affected; under different fixed pressure conditions, the temperature sensitivity of the sensor will not be affected. It can be expressed by the specific formula: B = B0 + S T (T-T0)+S P (P-P0), where B is the birefringence value output by the sensor, the initial temperature and initial pressure are T0 = 293.15K and P0 = 0MPa, respectively, and the pressure sensitivity and temperature sensitivity are S P and S T , B0 = -0.0035 is the birefringence value of the sensor under the conditions of ambient temperature of 293.15K and pressure of 0MPa. When the sensor measures pressure, first measure the birefringence value B1 = B0 + S under any known pressure P1 at ambient temperature. T (T1-T0)+S P (P1-P0), and then measure the birefringence value B2=B0+S when pressure P2 is applied at ambient temperature T (T1-T0)+S P (P2-P0), the pressure value P2 can be obtained according to the above formula = [(B2-B1) / S P ]+P1; When the sensor measures temperature, it first measures the birefringence value B1=B0+S when the temperature is the known temperature T1 under the ambient pressure P1 T (T1-T0)+S P (P1-P0), then measure the birefringence value B2=B0+S when the temperature is the measured temperature T2 under ambient pressure T (T2-T0)+S P (P1-P0), according to the above formula, the temperature value T2 = [(B2-B1) / S T ]+T1.

[0058] Specifically during detection, connect the sensor to the interface corresponding to the birefringence meter, and let the birefringence meter obtain the phase difference between the signals of different modes of the output light to reflect the magnitude of birefringence. The relationship between the specific phase difference and birefringence is expressed by the formula: Φ = (2π / λ)BL, where Φ is the phase difference between modes, λ is the wavelength during monitoring, and L is the length of the sensing unit that the light passes through. Among them, only the birefringence is a variable, so when the temperature and pressure change, the phase changes linearly with the change of birefringence.

[0059] The present invention utilizes the thermo-optic effect and elasto-optic effect of materials, making the birefringence of the sensor change linearly with temperature and pressure. Through the mechanism of generating a large phase difference due to the birefringence difference between polarization modes, it can directly reflect the measured value when light passes through the sensing unit during signal reception and photoelectric conversion. During actual measurement, the device should be pre-measured at the beginning of the measurement to enable the sensor to eliminate the influence of the initial environmental conditions and achieve independent measurement of temperature and pressure.

[0060] The sensor manufactured by the design of this photonic crystal fiber structure can achieve the composite functions of measuring temperature and pressure, and can achieve higher-precision measurement when measuring pressure unidirectionally. When facing different temperatures and pressures, the sensor can operate independently without interference. The sensor has the advantages of being resistant to external environmental refractive index and electromagnetic field interference. By introducing the fiber asymmetry structure and filling the micro-nano structure with black phosphorus with anisotropic dielectric constant, anisotropic mechanical properties and enhanced birefringence effect, the birefringence of the fiber output is increased; when the wavelength of the incident light is selected as 1550 nm, the pressure sensitivity and temperature sensitivity of the sensor are relatively high. At this time, the temperature sensitivity reaches 2.04×10 -5 / K when the thickness of black phosphorus is 2 nm. At this time, the pressure sensitivity under omnidirectional pressure is 2×10 -5 / MPa, and the pressure sensitivity when compressed in the Y direction is 5.95×10 -5 / MPa. The pressure sensitivity under different temperature conditions and the temperature sensitivity under different pressure conditions remain unchanged, enabling independent measurement of temperature and pressure.

[0061] Structurally: Through the spatial arrangement design of the D-type fiber structure, elliptical core 3 structure, first air hole 4, second air hole 5 and third air hole 6, an asymmetric structure will be formed inside the fiber, effectively improving the sensitivity;

[0062] In terms of materials: Silica is used as the optical fiber matrix 1, and polycarbonate is used as the optical plastic with excellent optical fiber coupling characteristics. On this basis, when polycarbonate is used as the single-mode optical fiber core 3, the size of the core 3 can be further reduced. Polycarbonate has a relatively high thermo-optic coefficient and high birefringence, which can improve the temperature sensitivity of this sensor when used as the optical fiber core 3. Polycarbonate has a good elasto-optic coefficient and high birefringence, which can improve the pressure sensitivity of this sensor when used as the core 3 material; Black phosphorus is mainly used for its anisotropy in dielectric constant, anisotropy in mechanical properties, and optical enhancement effect, which endows black phosphorus with the characteristic of birefringence amplification coefficient, greatly improving the measurement accuracy and anti-interference ability of the sensor.

[0063] The technical solutions of the present invention are not limited to the limitations of the above specific embodiments. Any technical deformation made according to the technical solutions of the present invention falls within the protection scope of the present invention.

Claims

1. Photonic crystal fiber structure, characterized in that: It includes an optical fiber substrate, a core, and two reinforcing layers for enhancing the birefringence. The optical fiber substrate has a D-shaped structure, the core has an elliptical structure, and the two reinforcing layers are respectively located on both sides of the short axis of the core. The dielectric constant and mechanical properties of the reinforcing layers are anisotropic, and the reinforcing layers have an optical enhancement effect. There is a first air layer and multiple second air layers arranged on the optical fiber substrate. The first air layer wraps around the core and the reinforcing layers, and the second air layers are located outside the first air layer; the long axis of the core is 3.3 um, the short axis is 0.9 um, the reinforcing layer is a black phosphorus layer, the length range of the reinforcing layer is 2 - 6 um, the thickness range of the reinforcing layer is 1 - 3 nm, the core is made of polycarbonate, and the optical fiber substrate is made of silica; The first air layer includes two groups of air hole groups, which are respectively located on both sides of the short axis of the core. The two groups of air hole groups include two first air holes and two second air holes. The two first air holes are located between the two second air holes. The diameter of the second air holes is larger than that of the first air holes. The diameter range of the first air holes is 1.5 - 2 um, the diameter range of the second air holes is 1.8 - 2.3 um, the distance between the two first air holes in the same group is 2.4 um, the distance between the two second air holes in the same group is 7.2 um, the distance between the two groups of first air holes is 5 um, and the distance range between the two groups of second air holes is 3.3 - 3.6 um.

2. The photonic crystal fiber structure according to claim 1, wherein: The length of the reinforcing layer is 4 um, and the thickness of the reinforcing layer is 2 nm.

3. The photonic crystal fiber structure according to any one of claims 1-2, characterized in that: The second air layer includes multiple third air holes. The diameter range of the third air holes is 5 - 8.5 um, and the distance range between adjacent two third air holes is 9 - 11 um.

4. Fiber optic sensor, characterized in that: It includes the photonic crystal fiber structure according to any one of claims 1 to 3.

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