Full-filling Dirac mode microstructure optical fiber temperature sensor

Abstract

The invention discloses a fully-filled Dirac mode microstructure optical fiber temperature sensor, and belongs to the field of optical fiber temperature sensing, the microstructure optical fiber temperature sensor takes germanium oxide glass as a substrate material, and comprises a fiber core and a cladding; all air holes except the central air hole in the end surface of the optical fiber adopt a periodically arranged triangular lattice structure; the optical fiber center air hole is a large air hole formed by cutting germanium oxide glass in the optical fiber center circular area; the fiber core is a central hole area formed by filling a central air hole with a temperature-sensitive material PDMS; the cladding holes are periodically arranged round holes formed by filling periodically arranged air holes with a temperature-sensitive material polydimethylsiloxane; and the cladding is composed of cladding holes and residual germanium oxide glass. The Dirac mode normalization frequency is in monotonic blue shift along with temperature reduction, so that the temperature sensing function of obtaining the temperature value through the Dirac mode normalization frequency value can be realized.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber temperature sensing, and in particular to a fully filled Dirac mode microstructure optical fiber temperature sensor. Background Art

[0002] Fiber optic temperature sensors offer advantages such as miniaturization, high sensitivity, and strong resistance to interference, corrosion, and high temperatures. They are widely and reliably used in fields such as power systems, chemical engineering, aerospace, environmental monitoring, and building safety monitoring. Currently, fiber optic temperature sensors are generally classified into two types based on the light wave modulation method: intensity modulation and wavelength modulation.

[0003] Light intensity-modulated fiber optic temperature sensors rely on the temperature-dependent variation of light intensity to measure temperature. For example, Meiqi Liu et al. proposed an antiresonant fiber optic temperature sensor based on the surface plasmon resonance effect. This sensor measures temperature by measuring the temperature-dependent variation in limiting loss at a fixed wavelength. However, light intensity measurement is highly susceptible to unstable light source intensity and disturbances in the fiber's external environment.

[0004] Wavelength-modulated fiber optic temperature sensors exhibit characteristic values on their wavelength-dependent curves. The wavelengths corresponding to these characteristic values (i.e., characteristic wavelengths) shift with temperature. Wavelength-modulated fiber optic temperature sensors measure temperature by measuring the shift in characteristic wavelengths. For example, Haoran Wang et al. proposed a seven-core fiber optic temperature sensor coated with gold and PDMS (polydimethylsiloxane). This sensor measures temperature by measuring the shift in the wavelength corresponding to the loss peak in the PDMS layer due to temperature changes in the transmission spectrum. Another example, Wang Wei et al. proposed a microstructured fiber optic temperature sensor that uses torsional distortion to measure temperature. By varying the torsional distortion, the wavelength corresponding to the dispersion valley is shifted, offsetting the wavelength shift caused by temperature changes and maintaining the dispersion valley wavelength constant. The torsional distortion is then used to determine the temperature, enabling temperature measurement. However, temperature measurement based on the shift in wavelength corresponding to characteristic values in the fiber can be affected by intermodal interference or limited by the insensitivity of certain characteristic values to temperature changes, resulting in low overall measurement sensitivity.

[0005] In recent years, a new type of optical fiber has emerged whose light-guiding mechanism is not based on traditional total internal reflection or the photonic bandgap effect, but rather on the unique properties of Dirac points. When the curve corresponding to the normalized frequency versus normalized longitudinal propagation constant at the Dirac point (hereafter referred to as the Dirac spectrum line) and the curve corresponding to the normalized frequency versus normalized longitudinal propagation constant of the core fundamental mode (hereafter referred to as the fundamental mode line) intersect (the normalized frequency corresponding to this intersection is the Dirac mode normalized frequency), the cladding's band structure exhibits a low radiative density of states at the Dirac point, suppressing the radiative loss of light field energy to the cladding and forming a guided mode with narrowband selectivity and low leakage propagation characteristics, namely the Dirac mode. For this type of optical fiber, Kang Xie et al. proposed a photonic crystal fiber that achieves light localization and low-loss transmission through the special band structure of the Dirac point. Yang Zhongmin et al. designed a photonic crystal fiber with a quartz glass matrix and a Dirac point in its cladding band structure. By improving the honeycomb structure, they achieved the appearance of a Dirac point in a Dirac-mode microstructured fiber backed by quartz glass, thereby reducing the refractive index requirements of the matrix glass. However, they did not mention the application of this type of fiber in temperature sensing. Summary of the Invention

[0006] To solve the above technical problems, the present invention proposes a fully filled Dirac mode microstructure optical fiber temperature sensor, which can realize a temperature sensing function of obtaining a temperature value through a Dirac mode normalized frequency value.

[0007] The technical solution adopted in the present invention is:

[0008] A fully filled Dirac mode microstructured optical fiber temperature sensor uses germanium oxide glass as its substrate material, includes a fiber core and a cladding, and includes a central air hole and several periodically arranged air holes from the center outward on the optical fiber end face. The central air hole is formed by cutting the germanium oxide glass inside the circular area at the center of the optical fiber. The periodically arranged air holes are arranged in a triangular lattice structure. The aperture of the central air hole is larger than that of the periodically arranged air holes.

[0009] The central air hole and the periodically arranged air holes are all filled with the temperature-sensitive material polydimethylsiloxane to form a temperature-sensitive area. The fiber core is the central hole area formed by the temperature-sensitive material polydimethylsiloxane filled in the central air hole, and the radius of the circular area in the center of the optical fiber is R; the cladding holes are periodically arranged circular holes filled with the temperature-sensitive material polydimethylsiloxane by the periodic arrangement of air holes, the spacing between adjacent cladding holes is a, and the diameter of the cladding holes is d; the cladding is composed of the cladding holes and the remaining germanium oxide glass.

[0010] A further improvement of the technical solution of the present invention is that the filling rate of the temperature-sensitive material in the cladding is calculated based on the area ratio of the cladding hole and the germanium oxide glass surrounding it, and the formula is:

[0011]

[0012] Where d is the diameter of the cladding hole and a is the lattice constant, that is, the distance between adjacent cladding holes.

[0013] A further improvement of the technical solution of the present invention is that the refractive index of the cladding is the average refractive index of the cladding hole filled with the temperature-sensitive material polydimethylsiloxane and the surrounding germanium oxide glass calculated according to the area ratio, and the formula is:

[0014]

[0015] Among them, n PDMS The refractive index of polydimethylsiloxane is the temperature-sensitive material;

[0016]

[0017] Where T is temperature in degrees Celsius; n si is the refractive index of germanium oxide glass;

[0018] The refractive index of the fiber core is the refractive index of the temperature-sensitive material polydimethylsiloxane, and the formula is:

[0019] n core =n PDMS

[0020] The refractive index difference between the core refractive index and the average refractive index of the cladding is calculated as:

[0021]

[0022] A further improvement of the technical solution of the present invention is that the radius R of the circular area at the center of the optical fiber is in the range of 5.8-5.9 μm.

[0023] A further improvement of the technical solution of the present invention is that the distance a between adjacent cladding holes is in the range of 2.9-3.1 μm.

[0024] A further improvement of the technical solution of the present invention is that the diameter d of the cladding hole is in the range of 1.22-1.42 μm. Due to the adoption of the above technical solution, the technical progress achieved by the present invention is:

[0025] 1. Within the entire temperature sensing range, both the Dirac spectrum line and the fundamental mode line change with temperature and always have an intersection. The optical fiber can transmit a localized Dirac mode at the normalized frequency corresponding to the intersection of the two curves. The present invention has strong localization capabilities at the normalized frequency corresponding to the intersection of the Dirac spectrum line and the fundamental mode line, but lacks localization capabilities at other normalized frequencies, thereby achieving temperature sensing using the Dirac mode normalized frequency value to obtain the temperature value. In the prior art, temperature sensing is performed based on the corresponding relationship between the wavelength and temperature of the dispersion valley and loss peak. The generation of the dispersion valley and loss peak is based on inter-mode coupling at the characteristic wavelength and is not localized.

[0026] 2. The Dirac spectrum line and the fundamental mode line of the present invention move in opposite directions as the temperature decreases, resulting in a significant increase in the movement distance of the Dirac mode normalized frequency per unit temperature change, thereby achieving higher sensing sensitivity.

[0027] 3. The fully filled Dirac mode microstructure optical fiber temperature sensor of the present invention uses the Dirac mode normalized frequency to measure temperature. The temperature sensing range is -10 to 70°C, and its maximum sensitivity can reach 4.75×10-3 (1 / °C). BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic diagram of an optical fiber cross section according to an embodiment;

[0029] Figure 2 Schematic diagram of a curve showing a change in the normalized frequency of a Dirac point corresponding to a normalized longitudinal propagation constant (Dirac spectrum line) and a curve showing a change in the normalized frequency of a fiber core fundamental mode corresponding to a normalized longitudinal propagation constant (fundamental mode line) in an embodiment;

[0030] Figure 3 Schematic diagram of the relationship curve between the normalized frequency of the Dirac mode and temperature in the embodiment. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments;

[0032] The technical solution provided by the present invention solves the following two technical problems simultaneously:

[0033] 1. When both the Dirac spectrum line and the fundamental mode line change with temperature, how can the temperature sensor of the present invention transmit the Dirac mode in the entire temperature sensing range?

[0034] The temperature sensor of the present invention is a normal band gap when two adjacent energy bands in the cladding band structure do not intersect. When the two adjacent energy bands intersect at a point, a Dirac cone exists, with the vertex being the Dirac point. The corresponding normalized frequency varies with the normalized longitudinal propagation constant, namely the Dirac spectrum line. When the sensor has a mathematical model solution that satisfies the Maxwell equations under a certain specific structure and parameters, the normalized frequency corresponding to the mathematical model solution varies with the normalized longitudinal propagation constant, namely the fundamental mode line. However, not all points on the fundamental mode line have the ability to localize the light field and transmit over long distances, that is, the partial solution has only mathematical significance and no physical significance. Only when the Dirac spectrum line and the fundamental mode line have an intersection will a mode with the ability to localize the light field and transmit over long distances, namely the Dirac mode, appear. Therefore, if the Dirac mode is to be transmitted under the premise that both the Dirac spectrum line and the fundamental mode line change with temperature, the temperature sensor of the present invention needs to achieve the following three technical effects:

[0035] (1) At each temperature within the temperature sensing range, a Dirac cone can exist in the cladding band structure, that is, a Dirac spectrum line exists;

[0036] (2) At each temperature within the temperature sensing range, a mathematical model solution that conforms to Maxwell's equations can be formed, that is, a fundamental mode line exists;

[0037] (3) At every temperature within the temperature sensing range, there is always an intersection between the Dirac spectrum line and the fundamental mode line.

[0038] Regarding technical effect (3), the slope of the Dirac spectrum line and the slope of the fundamental mode line are inversely proportional to the cladding equivalent mode refractive index and the core effective mode refractive index, respectively. The cladding equivalent mode refractive index is close to the average refractive index of the cladding calculated according to the area ratio, and the core effective mode refractive index is less than the core refractive index. If only the air hole in the center of the optical fiber is filled with the temperature-sensitive material PDMS as the temperature-sensitive area, only the fundamental mode line will change with the temperature change, and the degree of change is too large, while the Dirac spectrum line does not change with the temperature change, and it is impossible to make the Dirac spectrum line and the fundamental mode line have an intersection within the entire temperature sensing range; if only the cladding hole is filled with the temperature-sensitive material PDMS as the temperature-sensitive area, because the refractive index contrast between the germanium oxide glass and PDMS is less than the refractive index contrast between the germanium oxide glass and the air, the average refractive index of the cladding is too large, making the Dirac spectrum line value too small, that is, the Dirac spectrum line is located below the fundamental mode line, so that the Dirac spectrum line and the fundamental mode line do not have an intersection. Therefore, in the temperature sensor of the present invention, the air hole and the cladding hole in the center of the optical fiber are all filled with the temperature-sensitive material PDMS. The cladding of the present invention is composed of germanium oxide glass and PDMS, while the core is composed only of PDMS, resulting in that within the entire temperature sensing range, the average refractive index of the cladding is greater than the refractive index of the core, making the slope of the Dirac spectrum line smaller than the slope of the fundamental mode line. Therefore, the technical effect (3) of the present invention can be simplified as follows: at each temperature within the temperature sensing range, the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant.

[0039] The following will elaborate on the technical solutions for achieving technical effects (1), (2) and (3).

[0040] (1) A technical solution in which a Dirac cone, i.e., a Dirac spectrum line, exists in the cladding band structure at each temperature within the temperature sensing range:

[0041] The cladding band structure is the result of Bragg scattering of light by the cladding. The specific morphology and characteristics of the cladding band structure are affected by the cladding structure and its parameters. The Dirac cone is a special case that occurs when two adjacent bands in the cladding band structure intersect at a point. Therefore, the existence of the Dirac cone is unrelated to the core structure and its parameters. The refractive index of PDMS, the temperature-sensitive material used to fill the cladding holes, increases with decreasing temperature, while the refractive index of germanium oxide glass, the substrate material, hardly changes with temperature. Therefore, the refractive index contrast between the cladding hole filling material and the substrate material (i.e., the absolute value of the refractive index difference between the two materials) decreases with decreasing temperature, thereby reducing the Bragg scattering intensity, destroying band degeneracy, and suppressing linear dispersion. This causes the previously clear Dirac cone to gradually degenerate, and the Dirac spectral lines to cease to exist stably. Therefore, in order to achieve the technical effect of the presence of a Dirac cone in the cladding band structure at every temperature within the temperature sensing range, the present invention requires a reasonable design of the sensor structure and its parameters, including the cladding hole arrangement, the spacing between adjacent cladding holes, and the cladding hole size, in order to improve the situation where the refractive index contrast between the cladding hole filling material and the substrate material decreases due to temperature drop, causing the Dirac cone to gradually degenerate.

[0042] In terms of the arrangement of the cladding holes: the temperature sensor of the present invention adopts a triangular lattice structure for the arrangement of the cladding holes. When the refractive index contrast between the cladding hole filling material and the substrate material decreases as the temperature decreases, the band degeneracy in the cladding band structure will be destroyed. The cladding band structure is determined by the geometric symmetry and periodicity of the cladding lattice structure. By rationally designing the geometric symmetry of the cladding lattice structure, the degenerate characteristics of the energy band can be protected to prevent the destruction of the Dirac cone caused by the decrease in the refractive index contrast between the cladding hole filling material and the substrate material due to the decrease in temperature. The six-fold rotational symmetry of the triangular lattice structure constrains the degeneracy of the energy band, forcing two adjacent energy bands to have a Dirac cone with deterministic degeneracy of the energy band and a linear dispersion relationship at the high symmetry point (i.e., K point) in the Brillouin zone, thereby improving the situation where the band degeneracy is destroyed due to the decrease in the refractive index contrast between the cladding hole filling material and the substrate material due to the decrease in temperature. Therefore, the six-fold rotational symmetry of the triangular lattice provides conditions for the stable existence of the Dirac cone, achieving the technical effect of promoting the existence of the Dirac cone in the cladding band structure at every temperature within the temperature sensing range, that is, the existence of the Dirac spectral line.

[0043] In terms of the spacing between adjacent holes in the cladding: In the temperature sensor of the present invention, the spacing between adjacent holes in the cladding is the lattice constant a. When the refractive index contrast between the cladding hole filling material and the substrate material decreases as the temperature decreases, the Bragg scattering intensity will decrease and the linear dispersion in the cladding band structure will be suppressed. The lattice constant a adjusts the band structure of the cladding by affecting the periodicity of the lattice. When the lattice constant a decreases, the periodic structure of the cladding becomes denser, the light wave is subjected to more frequent periodic modulation, the Bragg scattering intensity increases, and the energy band near the K point tends to be flat. However, due to the protection of the Dirac cone by the six-fold rotational symmetry of the triangular lattice, the Dirac cone still exists and the flattening of the energy band near the K point enhances the linear dispersion characteristics of the Dirac cone. At the same time, the reciprocal space basis vector Increasing the lattice constant a broadens the wave vector distribution of the cladding's band structure in momentum space, thereby enhancing the band's dispersion amplitude, resulting in a steeper linear dispersion characteristic. This, in turn, improves the situation where the refractive index contrast between the cladding hole-filling material and the substrate decreases due to lower temperature, leading to a decrease in Bragg scattering intensity and suppressed linear dispersion. Therefore, the technical solution of reducing the lattice constant a promotes the linear dispersion characteristics of the Dirac cone, thereby achieving the technical effect of promoting the existence of a Dirac cone in the cladding band structure at every temperature within the temperature sensing range, that is, the presence of Dirac spectral lines.

[0044] Regarding the cladding hole size: In the temperature sensor of the present invention, the cladding hole size is determined by the cladding hole diameter d, and the cladding hole is filled with the temperature-sensitive material PDMS. When the refractive index contrast between the cladding hole filling material and the substrate material decreases with decreasing temperature, the Bragg scattering intensity decreases and the linear dispersion in the cladding band structure is suppressed. The material filling ratio is calculated as follows: Where d is the cladding hole diameter and a is the lattice constant. Under the conditions of a triangular lattice structure with a constant lattice constant a, increasing the cladding hole diameter d increases the material filling fraction h, the cladding hole volume fraction increases, and the substrate material is divided into smaller, isolated pillars. This strengthens the cladding's periodic structure's ability to modulate light waves, enhancing the Bragg scattering intensity and flattening the energy band near the K point. However, due to the protection of the Dirac cone by the six-fold rotational symmetry of the triangular lattice, the Dirac cone still exists, and the flattening of the energy band near the K point enhances the linear dispersion characteristics of the Dirac cone. This in turn improves the situation in which the Bragg scattering intensity decreases and the linear dispersion is suppressed due to the decrease in refractive index contrast between the cladding hole filling material and the substrate material due to lower temperature. Therefore, increasing the cladding hole diameter d promotes the linear dispersion characteristics of the Dirac cone, thereby achieving the technical effect of promoting the presence of a Dirac cone, that is, the presence of Dirac spectral lines, in the cladding band structure at every temperature within the temperature sensing range.

[0045] In summary, the temperature sensor of the present invention utilizes a triangular lattice structure in its cladding, ensuring the presence of a Dirac cone with a deterministically degenerate energy band and a linear dispersion relation at the K point in the Brillouin zone. By varying the lattice constant a and the cladding hole diameter d, the linear dispersion characteristics of the cladding band structure are regulated. Therefore, the present invention comprehensively adjusts the cladding hole arrangement and parameters a and d to manipulate the cladding band structure, improving the gradual degradation of the previously clear Dirac cone due to the decrease in refractive index contrast between the cladding hole filling material and the substrate material as temperature decreases. This ensures that the cladding band structure exhibits a Dirac cone, i.e., Dirac spectral lines, at every temperature within the temperature sensing range.

[0046] (2) A technical solution that can form a mathematical model solution that conforms to Maxwell's equations at each temperature within the temperature sensing range, that is, a fundamental mode line:

[0047] Only when the core structure and its parameters match those of the cladding can a mathematical model solution that conforms to Maxwell's equations be formed. These mathematical model solutions constitute the fundamental mode line. As the temperature decreases, the refractive index of the temperature-sensitive material, PDMS, increases, while the refractive index of the substrate material, germanium oxide glass, remains almost unchanged. Because the core consists solely of the temperature-sensitive material, PDMS, while the cladding is composed of both the temperature-sensitive material, PDMS, and the substrate material, germanium oxide glass, the increase in the core's refractive index is greater than the increase in the average refractive index of the cladding, calculated based on the area ratio. Furthermore, because the refractive index of the substrate material, germanium oxide glass, is always greater than that of the temperature-sensitive material, PDMS, within the temperature sensing range, the core and cladding's average refractive indices gradually converge, reducing the fiber's mode localization capability. Therefore, in order to achieve the technical effect of being able to form a mathematical model solution that conforms to Maxwell's equations at each temperature within the temperature sensing range, that is, the existence of a fundamental mode line, the present invention needs to reasonably design the structure of the sensor and its parameters, including the cladding hole arrangement, the spacing between adjacent cladding holes, the cladding hole scale, the fiber core morphology and scale, so as to improve the situation where the fiber core structure and its parameters do not match the cladding structure and its parameters due to the temperature drop, so that the mathematical model solution that conforms to Maxwell's equations cannot be formed.

[0048] Only when there is a Dirac cone in the band structure of the cladding can a mathematical model solution that conforms to Maxwell's equations be formed near the normalized frequency corresponding to the Dirac point. In the description of (1), the technical solution for realizing the existence of a Dirac cone in the band structure of the cladding at each temperature within the temperature sensing range has been described in detail. This provides the conditions for forming a mathematical model solution that conforms to Maxwell's equations at each temperature within the temperature sensing range, that is, the existence of a fundamental mode line. The specific numerical control of the cladding structure and its parameters and the core structure and its parameters on the formation of a mathematical model solution that conforms to Maxwell's equations is described in (3). The following will focus on the influence of the core morphology and scale on the formation of a mathematical model solution that conforms to Maxwell's equations.

[0049] In terms of core morphology and dimensions: The temperature sensor of the present invention defines a circle with a radius R at the center of the optical fiber. The germanium oxide glass within the circle is cut to form a central air hole. This hole is composed of the cut germanium oxide glass boundary and the remaining arc boundary of the cladding hole. The interior of the central air hole is filled with a temperature-sensitive material PDMS as the fiber core. In terms of core morphology, compared with the cores of other microstructured hollow optical fibers composed of circular ring walls, the core of the present invention, composed of the cut germanium oxide glass boundary and the remaining arc boundary of the cladding hole, is less likely to generate surface modes at the junction of the core and cladding, resulting in reduced light energy leakage and enhanced mode localization capability. If the radius R of the circular region in the center of the optical fiber is too large, the overall boundary morphology will approach the circular ring wall, making it easier for surface modes to form at the junction of the core and cladding, thereby reducing the fiber's mode localization capability. In addition, a larger cladding hole diameter d and a narrower germanium oxide glass channel will cause the overall boundary morphology to deviate from the circular ring wall, making it less likely for surface modes to form at the junction of the core and cladding, thereby enhancing the fiber's mode localization capability. In terms of fiber core size, the core size is determined by the radius R of the central circular area of the optical fiber and the diameter d of the cladding hole. When the radius R of the central circular area of the optical fiber is small, the optical fiber mode localization capability is low, and the light energy at the core is small, which is insufficient to support long-distance light transmission. Increasing the radius R of the central circular area of the optical fiber and the diameter d of the cladding hole will increase the core size, which can make the light energy more concentrated in the core area, thereby enhancing the mode localization capability. By reasonably controlling the radius R of the central circular area of the optical fiber or increasing the diameter d of the cladding hole, the energy is concentrated in the core area and the influence of the surface mode is reduced, thereby improving the situation where the optical fiber mode localization capability decreases due to temperature drop, and the optical fiber can form a mathematical mode solution that satisfies Maxwell's equations, achieving the technical effect of the presence of a fundamental mode line at every temperature within the temperature sensing range.

[0050] In summary, the temperature sensor of the present invention achieves the presence of a Dirac cone in the cladding band structure at every temperature within the temperature sensing range by rationally designing and adjusting the cladding hole arrangement, the spacing between adjacent cladding holes, and the cladding hole dimensions. Furthermore, by varying the radius R of the optical fiber's central circular region or the cladding hole diameter d, the fiber core morphology and dimensions are adjusted to match the cladding structure and its parameters, forming a mathematical model solution that satisfies Maxwell's equations and can constitute a fundamental mode line. Therefore, by rationally designing the cladding hole arrangement and comprehensively adjusting the parameters a, d, and R, the present invention achieves a mathematical model solution that satisfies Maxwell's equations, i.e., the presence of a fundamental mode line, at every temperature within the temperature sensing range.

[0051] (3) A technical solution in which, at each temperature within the temperature sensing range, the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant:

[0052] As mentioned above, the technical effect of achieving that the Dirac spectrum line and the fundamental mode line always have an intersection at each temperature within the temperature sensing range can be converted into a technical effect of achieving that the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant at each temperature within the temperature sensing range.

[0053] The temperature sensor of the present invention completely fills the central air hole and cladding holes of the optical fiber with a temperature-sensitive material, PDMS. When the temperature changes, the refractive index of the temperature-sensitive material PDMS filled in the core and cladding holes changes, causing the refractive index of the core and cladding to change, resulting in changes in both the Dirac spectrum line and the fundamental mode line. The present invention requires the rational design of the sensor structure and its parameters to control the following two aspects: increasing the normalized frequency corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line, and reducing the normalized frequency of the fundamental mode line at the same normalized longitudinal propagation constant as the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line. This allows the temperature sensor of the present invention to achieve the technical effect that, at each temperature within the temperature sensing range, the normalized frequency corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is greater than the normalized frequency of the fundamental mode line at the same normalized longitudinal propagation constant.

[0054] Increasing the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line: The normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is the normalized frequency value corresponding to the Dirac point when the Dirac cone first appears in the band structure. The cladding of the present invention adopts a triangular lattice structure, and the cladding holes are filled with a temperature-sensitive material PDMS. As the temperature decreases, the refractive index of the temperature-sensitive material PDMS increases, and the refractive index contrast between the germanium oxide glass and PDMS decreases, resulting in the first appearance of the Dirac cone requiring a larger normalized longitudinal propagation constant, thereby increasing the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line. Moreover, at a certain temperature within the temperature sensing range, the larger the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line, the more likely the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is to be greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant. As can be seen from the above, when the temperature sensor of the present invention is at the upper limit temperature of the temperature sensing range, the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is minimum. Therefore, at the upper limit temperature of the temperature sensing range, the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is ensured to be greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant. This ensures that at every temperature within the temperature sensing range, the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant.

[0055] The cladding holes of the present invention adopt a periodically arranged triangular lattice structure. Since the cladding band structure itself is the result of Bragg scattering of light by the cladding lattice structure, the Bragg scattering is affected by the lattice periodicity. The lattice constant a affects the specific shape and characteristics of the band by adjusting the lattice period. According to Bragg's law: mλ = 2asinθ, where m is an integer representing the reflection order, λ is the wavelength of the incident light wave, a is the distance between adjacent holes in the periodic cladding structure (i.e., the lattice constant), and θ is the angle between the incident wave and the normal to the cladding hole (the normal direction is the direction from the center of the cladding hole to the center of the optical fiber). The relationship between the wavelength and frequency of the light wave is determined by the calculation formula: c = λ × f, where c is the speed of light, which is 3 × 10 8 m / s, f is the frequency of the incident light, it can be seen that the normalized frequency value of the Dirac spectrum line is inversely proportional to the lattice constant a, then the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is inversely proportional to the lattice constant a. When other conditions remain unchanged, the smaller the lattice constant a, the smaller the periodic interval of the lattice, the smaller the wavelength of the light wave that Bragg scattering occurs, and the higher the frequency, the larger the value of the Dirac spectrum line. In addition, the size of the material filling rate will affect the normalized frequency value of the Dirac spectrum line, and the material filling rate is proportional to the normalized frequency value of the Dirac spectrum line. Under the same lattice constant a, the periodic arrangement of the triangular lattice structure makes the material filling rate of the present invention greater than the material filling rate of other lattice structures, so that the normalized frequency value of the Dirac spectrum line increases, thereby increasing the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line. At the same time, the calculation formula of the material filling rate is: Under the condition that the lattice constant a remains constant, a larger cladding hole diameter d leads to a larger material filling rate h, which increases the normalized frequency of the Dirac spectrum line, and thus increases the normalized frequency corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line. Therefore, the three technical solutions of reducing the lattice constant a, adopting a triangular lattice structure, and increasing the cladding hole diameter d will all increase the normalized frequency corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line at the upper limit of the temperature sensing range, thereby achieving the technical effect of promoting the normalized frequency corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line to be greater than the normalized frequency of the fundamental mode line at the same normalized longitudinal propagation constant at each temperature within the temperature sensing range.

[0056] In terms of reducing the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant as the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line: the temperature sensor of the present invention has a core that is a central hole of a PDMS optical fiber filled with a temperature-sensitive material, a cladding that adopts a triangular lattice structure, and a temperature-sensitive material PDMS filled in the cladding hole, and its fundamental mode line is a curve of the normalized frequency of the core fundamental mode changing with the normalized longitudinal propagation constant, and the calculation formula is: where n eff is the effective refractive index of the propagating mode in the core region of the fully filled Dirac mode microstructured optical fiber, k z is the longitudinal propagation constant (i.e. longitudinal wave vector), is the normalized frequency of the fiber core fundamental mode, is the normalized longitudinal propagation constant. As the temperature decreases, the refractive index n of the thermosensitive material PDMS PDMS increases, resulting in the effective mode refractive index n eff Increase, the slope of the base mode line Decreases, so that the normalized frequency value of the fundamental mode line decreases, and at a certain temperature within the temperature sensing range, the smaller the normalized frequency value of the fundamental mode line is, that is, the smaller the slope of the fundamental mode line is, the easier it is for the starting point of the Dirac spectrum line to be located above the fundamental mode line, and the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is easier to be greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant. As can be seen from the above, when the temperature sensor of the present invention is at the upper limit temperature of the temperature sensing range, the normalized frequency of the fundamental mode line is at its maximum value, and the normalized frequency of the fundamental mode line at the same normalized longitudinal propagation constant as the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is at its maximum value. Therefore, at the upper limit temperature of the temperature sensing range, the normalized frequency of the fundamental mode line at the same normalized longitudinal propagation constant as the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is ensured to be less than the normalized frequency corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line. This ensures that at each temperature within the temperature sensing range, the normalized frequency corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is greater than the normalized frequency of the fundamental mode line at the same normalized longitudinal propagation constant.

[0057] From the perspective of the influence of the core structure and its parameters on the fundamental mode line, the core of the present invention is formed by filling the temperature-sensitive material PDMS in the central air hole formed by the cut germanium oxide glass boundary and the remaining arc boundary of the cladding hole. The core shape and size are determined by the radius R of the central circular area of the optical fiber and the diameter d of the cladding hole, and the core effective mode refractive index n eff The size of R is closely related to the core shape and size. When R is increased, the core size increases, more light energy is concentrated in the core, and the core effective mode refractive index n eff Closer to the refractive index of temperature-sensitive material PDMS Where T is the temperature in degrees Celsius, so that the fiber core effective mode refractive index n eff Increase; when d is increased, the core size increases, more light energy is concentrated in the core, and the overall boundary shape of the core deviates from the circular ring wall, reducing the influence of the surface mode and making the core effective mode refractive index n eff Closer to the refractive index n of the temperature-sensitive material PDMS PDMS , so that the effective mode refractive index of the core neff Increase.

[0058] From the perspective of the influence of the cladding structure and its parameters on the fundamental mode line, the cladding part of the present invention is made of germanium oxide glass as the base material, and the cladding holes thereon adopt a periodically arranged triangular lattice structure, and the cladding holes are filled with temperature-sensitive material PDMS, ε eff It is the equivalent dielectric constant after the periodic cladding structure is equivalent to a uniform medium. Its calculation formula is: In the formula is the transverse characteristic wave vector in the cladding, reflecting the modulation effect of the transverse periodic structure (i.e., cladding) on light, and k0 is the wave vector in free space. By adjusting the lattice constant a, the periodicity of the cladding structure can be changed, affecting the transverse wave vector K in the cladding, and thus affecting the equivalent dielectric constant ε eff , to control the core effective mode refractive index n eff From the above formula, we can see that the smaller the lattice constant a is, the higher the effective mode refractive index n of the core is. eff In addition, the average refractive index of the cladding part calculated according to the area ratio is calculated as follows: where n si is the refractive index of germanium oxide glass, Where λ is the wavelength of light, in micrometers. From the above formula, we can see that under the condition that the lattice constant a remains unchanged, reducing the cladding hole diameter d will increase the average refractive index of the cladding, while the core refractive index n core =n PDMS Does not change with changes in the cladding hole diameter, resulting in a refractive index difference between the core refractive index and the average refractive index of the cladding Increase, thereby improving the mode localization ability of the optical fiber, making the core effective mode refractive index n eff Closer to the refractive index n of the temperature-sensitive material PDMS PDMS , so that the effective mode refractive index of the core n eff Increase.

[0059] Therefore, from the perspective of the influence of the core structure and its parameters on the fundamental mode line, the two technical solutions of increasing the radius R of the circular area in the center of the optical fiber and increasing the diameter d of the cladding hole will both reduce the slope of the fundamental mode line at the upper limit temperature of the temperature sensing range, so that the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant as the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line will decrease; from the perspective of the influence of the cladding structure and its parameters on the fundamental mode line, the two technical solutions of reducing the lattice constant a and reducing the diameter d of the cladding hole will both reduce the slope of the fundamental mode line at the upper limit temperature of the temperature sensing range, so that the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant as the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line will decrease, thereby achieving the technical effect of promoting the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line to be greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant at each temperature within the temperature sensing range.

[0060] In summary, the temperature sensor of the present invention needs to comprehensively consider the impact of changing a and d on the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line and the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant as the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line at the upper limit temperature of the temperature sensing range; and the impact of changing R on the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant as the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line at the upper limit temperature of the temperature sensing range. Therefore, the present invention rationally designs the structure and comprehensively adjusts the parameters a, d, and R so that at the upper limit temperature of the temperature sensing range, the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant, thereby ensuring that at each temperature within the temperature sensing range, the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant.

[0061] 2. How to make the movement of Dirac spectrum lines and fundamental mode lines with decreasing temperature promote the change of Dirac mode normalized frequency monotonically blue shift with decreasing unit temperature.

[0062] The temperature sensor of the present invention can measure temperature only when the Dirac mode normalized frequency changes monotonically with temperature. The greater the change in the Dirac mode normalized frequency per unit temperature change, the higher the sensitivity of the sensor. Therefore, to maximize the change in the Dirac mode normalized frequency of the temperature sensor of the present invention that monotonically blueshifts with decreasing unit temperature, the optimal situation is: (1) the Dirac spectrum line shifts upward with decreasing temperature; (2) at the same time, the fundamental mode line shifts downward with decreasing temperature, so that the two curves show opposite change trends with decreasing temperature.

[0063] (1) Technical solution for the Dirac spectrum line to shift upward as the temperature decreases:

[0064] The temperature sensor of the present invention comprises a base material of germanium oxide glass for the optical fiber cladding, a cladding hole thereon adopting a periodically arranged triangular lattice structure, and a temperature-sensitive material PDMS filled in the cladding hole. The refractive index of the temperature-sensitive material PDMS increases as the temperature decreases, while the refractive index of the base material germanium oxide glass remains almost unchanged as the temperature changes. Therefore, the refractive index contrast between the cladding hole filling material and the base material decreases as the temperature decreases, while the average refractive index of the cladding increases as the temperature decreases. This causes the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line to increase as the temperature decreases, and the Dirac spectrum line moves up; the slope of the Dirac spectrum line decreases as the temperature decreases, and the normalized frequency value of the Dirac spectrum line decreases, and the Dirac spectrum line moves down. Therefore, the present invention needs to increase the amplitude of the increase in the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line as the temperature decreases, and reduce the amount of change in the slope of the Dirac spectrum line as the temperature decreases, so as to achieve the technical effect of the Dirac spectrum line moving up as the temperature decreases.

[0065] Increasing the amplitude of the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line increases as the temperature decreases: The temperature sensor of the present invention has a cladding with a triangular lattice structure, and the cladding is composed of a base material of germanium oxide glass and a temperature-sensitive material PDMS filled in the cladding holes. The refractive index contrast between the base material of germanium oxide glass and the cladding hole filling material PDMS decreases as the temperature decreases, resulting in the gradual bending of the energy band in the cladding band structure. Increasing the longitudinal propagation constant k z , that is, the momentum component of the photon in the optical fiber axis (i.e. longitudinal direction) is enhanced, resulting in the suppression of the band bending of the transverse plane periodic structure (i.e. cladding triangular lattice structure), that is, the band flattening, providing a larger space for the formation of the Dirac cone, and at the same time, increasing the longitudinal propagation constant k z, which will also lead to an increase in the total momentum of the photon, and increase the corresponding normalized frequency value. Therefore, as the temperature decreases, the first appearance of the Dirac cone needs to be located under a larger normalized longitudinal propagation constant, resulting in an increase in the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line. From the above, it can be seen that the greater the degree of band bending in the cladding band structure as the temperature decreases, the larger the normalized longitudinal propagation constant required to suppress the band bending, resulting in a larger normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line, and a larger increase in the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line as the temperature decreases. From (1), it can be seen that when the lattice constant a is increased and the cladding hole diameter d is reduced, both technical solutions will lead to band bending in the cladding band structure, increase the increase in the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line as the temperature decreases, and thus promote the upward shift of the Dirac spectrum line as the temperature decreases.

[0066] In terms of reducing the amount of change in the slope of the Dirac spectrum line as the temperature decreases: the temperature sensor of the present invention has a cladding part with germanium oxide glass as the substrate, the cladding holes are filled with the temperature-sensitive material PDMS, and the cladding holes adopt a periodically arranged triangular lattice structure. The average refractive index of the cladding part calculated according to the area ratio is calculated as follows: where n PDMS is the refractive index of the temperature-sensitive material PDMS, which increases as the temperature decreases. As mentioned above, the slope of the Dirac spectrum line is inversely proportional to the equivalent mode refractive index. When the temperature decreases, the average refractive index of the cladding n clad As the cladding hole diameter d increases, the cladding equivalent mode refractive index increases, resulting in a decrease in the slope of the Dirac spectrum line. From the above expression, it can be seen that the smaller the ratio of the cladding hole diameter d to the lattice constant a, the smaller the increase in the cladding average refractive index as the temperature decreases, the smaller the increase in the cladding equivalent mode refractive index as the temperature decreases, and the smaller the change in the slope of the Dirac spectrum line as the temperature decreases. Therefore, when increasing the cladding hole diameter d and reducing the lattice constant a, both technical solutions will reduce the change in the slope of the Dirac spectrum line as the temperature decreases, thereby promoting the upward shift of the Dirac spectrum line as the temperature decreases.

[0067] In summary, the temperature sensor of the present invention requires comprehensive consideration of the effects of varying parameters a and d on the magnitude of the increase in the normalized frequency corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line as temperature decreases, as well as the decrease in the slope of the Dirac spectrum line as temperature decreases. Therefore, the present invention utilizes a rationally designed structure and comprehensive adjustments to parameters a and d to shift the Dirac spectrum line upward as temperature decreases.

[0068] (2) At the same time, the technical solution of the base mold line moving downward as the temperature decreases:

[0069] The temperature sensor of the present invention fills the central air hole of the optical fiber with a temperature-sensitive material, PDMS, to form the fiber core. The refractive index of the temperature-sensitive material, PDMS, increases with decreasing temperature, causing the effective mode refractive index of the core to increase as temperature decreases. This decreases the slope of the fundamental mode line, causing the fundamental mode line to shift downward. Therefore, the present invention aims to increase the amount by which the slope of the fundamental mode line decreases with decreasing temperature to promote the technical effect of the downward shift of the fundamental mode line as temperature decreases.

[0070] In terms of increasing the amount of change in the fundamental mode line slope as the temperature decreases: The temperature sensor of the present invention has a core that is a central hole of an optical fiber filled with a temperature-sensitive material PDMS, and a cladding that adopts a triangular lattice structure and fills the cladding holes with the temperature-sensitive material PDMS. As mentioned above, the fundamental mode line calculation formula is: Because the refractive index of the temperature-sensitive PDMS material filling the fiber core increases with decreasing temperature, the effective mode refractive index of the core is always lower than the refractive index of the temperature-sensitive PDMS material, causing the slope of the fundamental mode line to decrease with decreasing temperature. Furthermore, as the temperature decreases, the fiber's localization capability decreases, causing the effective mode refractive index of the core to gradually move away from the refractive index of the temperature-sensitive PDMS material, thus reducing the amount of change in the slope of the fundamental mode line with decreasing temperature. As can be seen from the above, the smaller the decrease in the localization capability of the fiber with decreasing temperature, the closer the effective mode refractive index of the core approaches the refractive index of the temperature-sensitive PDMS material, and the greater the change in the slope of the fundamental mode line with decreasing temperature.

[0071] From the perspective of the influence of the core structure and its parameters on the fundamental mode line, the core of the present invention is formed by filling the temperature-sensitive material PDMS in the central air hole formed by the cut germanium oxide glass boundary and the remaining arc boundary of the cladding hole. The core shape and size are determined by the radius R of the central circular area of the optical fiber and the diameter d of the cladding hole, and the core effective mode refractive index n eff The size of is closely related to the core shape and size. When the radius R of the circular area in the center of the optical fiber increases, the core size increases, and more light energy is concentrated in the core, resulting in the core effective mode refractive index n eff Closer to the refractive index n of the temperature-sensitive material PDMS PDMS At the same time, when the cladding hole diameter d increases, the core size increases, more light energy is concentrated in the core, and the influence of the surface mode is reduced. The localization ability of the optical fiber mode is enhanced, resulting in the effective mode refractive index n of the core. eff Closer to the refractive index n of the temperature-sensitive material PDMS PDMS .

[0072] Considering the influence of the cladding structure and its parameters on the fundamental mode line, the cladding part of the present invention is made of germanium oxide glass as the base material, and the cladding holes thereon adopt a periodically arranged triangular lattice structure, and the cladding holes are filled with the temperature-sensitive material PDMS. As mentioned above, the refractive index difference between the core refractive index and the average refractive index of the cladding is where n PDMS is the refractive index of the temperature-sensitive material PDMS, which increases as the temperature decreases. Under the same other conditions, n clad -n core As the temperature decreases, it decreases, gradually reducing the mode localization ability of the optical fiber, resulting in the effective mode refractive index n eff As the temperature decreases, the refractive index n of the thermosensitive material PDMS moves away PDMS , which reduces the change in the slope of the fundamental mode line as the temperature decreases. From the above, we can see that the smaller the ratio of the cladding hole diameter d to the lattice constant a, the smaller the n clad -n core The decrease in the localization ability of the optical fiber mode with the decrease in temperature becomes smaller, making the effective mode refractive index n eff Closer to the refractive index n of the temperature-sensitive material PDMS PDMS , thereby increasing the amount by which the slope of the fundamental mode line decreases as the temperature decreases.

[0073] Therefore, from the perspective of the influence of the core structure and its parameters on the fundamental mode line, the two technical solutions of increasing the radius R of the circular area in the center of the optical fiber and increasing the diameter d of the cladding hole will both increase the amount of change in the slope of the fundamental mode line as the temperature decreases; from the perspective of the influence of the cladding structure and its parameters on the fundamental mode line, the two technical solutions of increasing the lattice constant a and reducing the diameter d of the cladding hole will both increase the amount of change in the slope of the fundamental mode line as the temperature decreases, thereby promoting the downward shift of the fundamental mode line as the temperature decreases.

[0074] In summary, the temperature sensor of the present invention requires comprehensive consideration of the impact of varying a, d, and R on the decrease in the slope of the fundamental mode line as temperature decreases. Therefore, the present invention utilizes a rationally designed structure and comprehensive adjustments to the parameters a, d, and R to promote the downward shift of the fundamental mode line as temperature decreases.

[0075] like Figure 1As shown, in order to solve the above technical problems, a specific structure of an embodiment of a fully filled Dirac mode microstructure optical fiber temperature sensor proposed by the present invention is given. The present invention uses germanium oxide glass as a base material, including a fiber core and a cladding. Periodic air holes are arranged on the base material, and the germanium oxide glass in the central circular area of the optical fiber is cut to form a central air hole. The radius of the central circular area is R, and the range of the radius R of the central circular area is 5.8-5.9 μm. In this embodiment, R is set as 5.85 μm. The central air hole of the optical fiber and the periodically arranged air holes are all filled with a temperature-sensitive material polydimethylsiloxane (PDMS) as a temperature-sensitive area. The central air hole is filled with the temperature-sensitive material PDMS to form a fiber core. The cladding holes are periodically arranged circular holes formed by filling the periodically arranged air holes with the temperature-sensitive material polydimethylsiloxane. The cladding holes and the remaining germanium oxide glass together constitute a cladding. The adjacent cladding hole spacing of all cladding holes is a, and the adjacent cladding hole spacing a ranges from 2.9 to 3.1 μm. In this embodiment, a is set as 3.0 μm. The cladding hole diameter is d, and the cladding hole diameter d ranges from 1.22 to 1.42 μm. In this embodiment, d is set as 1.32 μm.

[0076] The specific technical solution of this patent can be described as:

[0077] The microstructured optical fiber temperature sensor of the present invention uses germanium oxide glass as a base material and includes a core and a cladding. Periodic air holes are arranged on the base material, and the germanium oxide glass in the central circular area of the optical fiber is cut to form a central air hole. The central air hole and the periodically arranged air holes of the optical fiber are all filled with a temperature-sensitive material, polydimethylsiloxane (PDMS), to serve as a temperature-sensitive area. The central air hole is filled with the temperature-sensitive material PDMS to form a core. The cladding holes are periodically arranged circular holes formed by filling the periodically arranged air holes with the temperature-sensitive material polydimethylsiloxane. The cladding holes and the remaining germanium oxide glass together constitute a cladding. The cladding has the following parameters: a spacing a between adjacent cladding holes; a radius r of the central circular area; and a diameter d of the cladding holes.

[0078] In the present invention, the cladding part is composed of the temperature-sensitive material PDMS filled in the periodically arranged air holes on the remaining germanium oxide glass and the remaining germanium oxide glass. The material filling rate is calculated based on the area ratio of the cladding holes and the surrounding germanium oxide glass. The calculation formula is:

[0079]

[0080] Where d is the cladding hole diameter and a is the lattice constant;

[0081] Its refractive index is the average refractive index of the cladding hole filled with the temperature-sensitive material PDMS and the surrounding germanium oxide glass calculated according to the area ratio. The calculation formula is:

[0082]

[0083] Among them, n PDMS is the refractive index of the temperature-sensitive material PDMS,

[0084]

[0085] Where T is the temperature in degrees Celsius, n si is the refractive index of germanium oxide glass;

[0086] The core part is formed by filling the central air hole with the temperature-sensitive material PDMS. Its refractive index is the refractive index of the temperature-sensitive material PDMS, and the calculation formula is:

[0087] n core =n PDMS

[0088] The refractive index difference between the core refractive index and the average refractive index of the cladding is calculated as:

[0089]

[0090] The above parameters will also affect the reciprocal space basis vector, Bragg's law, and the equivalent dielectric constant after the periodic cladding structure is equivalent to a uniform medium. The reciprocal space basis vector is

[0091] Bragg's law is:

[0092] mλ=2asinθ

[0093] Where m is an integer representing the reflection order, λ is the wavelength of the incident light wave, and θ is the angle between the incident wave and the normal line of the cladding hole (the normal line direction is the direction from the center of the cladding hole to the center of the fiber);

[0094] The equivalent dielectric constant after the periodic cladding structure is equivalent to a uniform medium is:

[0095]

[0096] Where, is the transverse characteristic wave vector in the cladding, reflecting the modulation effect of the transverse periodic structure on light, k z is the longitudinal wave vector, and k0 is the wave vector in free space.

[0097] The impact of the above parameters on the present invention is as follows:

[0098] 1. R is the radius of the circular area at the center of the optical fiber. Increasing R will produce the following technical effects:

[0099] (1) The overall boundary shape of the fiber core will be close to the circular ring wall, and a surface mode will be formed at the junction of the fiber core and the cladding, which is not conducive to the formation of a mathematical model solution that satisfies Maxwell's equations within the entire temperature sensing range;

[0100] (2) It will increase the core size and enhance the localization capability of the optical fiber mode, which is conducive to the formation of a mathematical model solution that satisfies Maxwell's equations within the entire temperature sensing range;

[0101] (3) It will reduce the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant as the starting point of the Dirac spectrum line normalized longitudinal propagation constant, so that in the entire temperature sensing range, the normalized frequency value corresponding to the starting point of the Dirac spectrum line normalized longitudinal propagation constant is greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant;

[0102] (4) It will increase the amount of change in the base mode line slope as the temperature decreases, which is conducive to the base mode line moving downward as the temperature decreases. Conversely, reducing R has the opposite technical effect.

[0103] 2. a is the distance between adjacent cladding holes. Reducing a will produce the following technical effects:

[0104] (1) It will make the light wave be periodically modulated by the cladding more frequently, increase the Bragg scattering intensity, and make the energy band near the K point tend to be flat, which is conducive to the stable existence of the Dirac cone in the cladding band structure within the entire temperature sensing range;

[0105] (2) It will increase the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line, which is beneficial to the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line being greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant within the entire temperature sensing range; it will reduce the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant as the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line, which is beneficial to the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line being greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant within the entire temperature sensing range;

[0106] (3) It will reduce the increase in the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line as the temperature decreases, which is not conducive to the upward shift of the Dirac spectrum line as the temperature decreases; it will reduce the change in the slope of the Dirac spectrum line as the temperature decreases, which is conducive to the upward shift of the Dirac spectrum line as the temperature decreases;

[0107] (4) It will reduce the amount of change in the base mode line slope as the temperature decreases, which is not conducive to the base mode line moving downward as the temperature decreases. Conversely, increasing a has the opposite technical effect.

[0108] 3. d is the diameter of the cladding hole. Increasing d will produce the following technical effects:

[0109] (1) It will increase the material filling rate, enhance the modulation ability of the cladding periodic structure on light waves, increase the Bragg scattering intensity, and make the energy band near the K point tend to be flat, which is conducive to the stable existence of the Dirac cone in the cladding band structure within the entire temperature sensing range;

[0110] (2) It will cause the overall boundary morphology of the fiber core to deviate from the circular ring wall, and it will be difficult for the surface mode to form at the junction of the fiber core and the cladding, which is conducive to the formation of a mathematical model solution that satisfies Maxwell's equations within the entire temperature sensing range; it will increase the fiber core size and enhance the fiber mode localization capability, which is conducive to the formation of a mathematical model solution that satisfies Maxwell's equations within the entire temperature sensing range;

[0111] (3) It will increase the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line, which is beneficial to the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line is greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant within the entire temperature sensing range; from the perspective of the influence of the core structure and its parameters on the fundamental mode line, it will reduce the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant as the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line, which is beneficial to the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant as the starting point of the Dirac spectrum line within the entire temperature sensing range. The normalized frequency value corresponding to the starting point of the Dirac spectrum line normalized longitudinal propagation constant is greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant. Considering the influence of the cladding structure and its parameters on the fundamental mode line, the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant as the starting point of the Dirac spectrum line normalized longitudinal propagation constant will be increased, which is not conducive to the normalized frequency value corresponding to the starting point of the Dirac spectrum line normalized longitudinal propagation constant being greater than the normalized frequency value of the fundamental mode line under the same normalized longitudinal propagation constant within the entire temperature sensing range.

[0112] (4) It will increase the amplitude of the increase of the normalized frequency value corresponding to the starting point of the normalized longitudinal propagation constant of the Dirac spectrum line as the temperature decreases, which is conducive to the upward shift of the Dirac spectrum line as the temperature decreases; it will reduce the change of the slope of the Dirac spectrum line as the temperature decreases, which is conducive to the upward shift of the Dirac spectrum line as the temperature decreases;

[0113] (5) Considering the influence of the core structure and its parameters on the fundamental mode line, the amount of change in the fundamental mode line slope as the temperature decreases will increase, which is conducive to the downward shift of the fundamental mode line as the temperature decreases. Considering the influence of the cladding structure and its parameters on the fundamental mode line, the amount of change in the fundamental mode line slope as the temperature decreases will decrease, which is not conducive to the downward shift of the fundamental mode line as the temperature decreases. Conversely, reducing d has the opposite technical effect.

[0114] In the solution of the present invention, by designing the structure and its parameters, it is achieved that at each temperature within the temperature sensing range, a Dirac cone can exist in the cladding band structure, that is, a Dirac spectrum line exists, and a mathematical model solution that conforms to the Maxwell equations can be formed, that is, a fundamental mode line exists, and the Dirac spectrum line and the fundamental mode line always have an intersection. At the same time, it is achieved that the Dirac spectrum line moves up as the temperature decreases and the fundamental mode line moves down as the temperature decreases, thereby maximizing the technical effect of the change in the monotonically blue shifted amount of the Dirac mode normalized frequency of the temperature sensor of the present invention as the unit temperature decreases. Ultimately, temperature sensing is achieved by utilizing the corresponding relationship between the Dirac mode normalized frequency and temperature, and obtaining the temperature value through the Dirac mode normalized frequency value, thereby obtaining a fully filled Dirac mode microstructure optical fiber temperature sensor that uses the Dirac mode normalized frequency for temperature measurement.

[0115] See attached Figure 2 When the temperature ranges from -10℃ to 70℃, the normalized frequency value of the Dirac point corresponding to the curve of the change with the normalized longitudinal propagation constant (Dirac spectrum line) and the normalized frequency value of the fiber core fundamental mode corresponding to the curve of the change with the normalized longitudinal propagation constant (fundamental mode line) are equal at a certain normalized longitudinal propagation constant.

[0116] See attached Figure 3 , the temperature ranges from -10℃ to 70℃, and the temperature is determined by using the corresponding relationship between the Dirac mode normalized frequency and temperature. When the temperature changes from -10℃ to 10℃, the change in the Dirac mode normalized frequency is the largest and is 0.095, so the maximum sensitivity of the sensor can reach 4.75×10 -3 (1 / ℃).

[0117] In summary, the present invention achieves the following technical effects:

[0118] 1. Within the entire temperature measurement range, the curve of the normalized frequency corresponding to the Dirac point versus the normalized longitudinal propagation constant (i.e., the Dirac spectrum line) and the curve of the normalized frequency of the fiber core fundamental mode versus the normalized longitudinal propagation constant (i.e., the fundamental mode line) both change with temperature, and there is always an intersection point (the normalized frequency corresponding to the intersection point is the Dirac mode normalized frequency), ensuring that the optical fiber can transmit the Dirac mode at every temperature within the temperature sensing range.

[0119] 2. The Dirac mode normalized frequency monotonically redshifts (or blueshifts) with increasing (or decreasing) temperature, and the shifts of the Dirac spectrum lines and fundamental mode lines with temperature both contribute to the change in the Dirac mode normalized frequency per unit temperature change. Based on the above two technical effects, the fully filled microstructured optical fiber temperature sensor of the present invention can utilize the corresponding relationship between the Dirac mode normalized frequency and temperature for temperature sensing.

Claims

1. A fully filled Dirac mode microstructure optical fiber temperature sensor, using germanium oxide glass as a substrate material, including a core and a cladding, characterized by: The optical fiber end face includes a central air hole and a plurality of periodically arranged air holes from the center outward; the central air hole is an air hole formed by cutting the germanium oxide glass inside the circular area in the center of the optical fiber; the periodically arranged air holes are arranged in a triangular lattice structure; the aperture of the central air hole is larger than the aperture of the periodically arranged air holes; The central air hole and the periodically arranged air holes are all filled with the temperature-sensitive material polydimethylsiloxane to form a temperature-sensitive area. The fiber core is the central hole area formed by the temperature-sensitive material polydimethylsiloxane filled in the central air hole, and the radius of the circular area in the center of the optical fiber is R; the cladding holes are periodically arranged circular holes formed by the periodically arranged air holes filled with the temperature-sensitive material polydimethylsiloxane, the distance between adjacent cladding holes is a, and the diameter of the cladding holes is d; the cladding is composed of the cladding holes and the remaining germanium oxide glass.

2. The fully filled Dirac mode microstructure optical fiber temperature sensor according to claim 1, characterized in that: In the cladding, the filling rate of the temperature-sensitive material is calculated based on the area ratio of the cladding hole and the germanium oxide glass surrounding it, and the formula is: Where d is the diameter of the cladding hole and a is the lattice constant, that is, the distance between adjacent cladding holes.

3. The fully filled Dirac mode microstructure optical fiber temperature sensor according to claim 1, characterized in that: The refractive index of the cladding is the average refractive index of the cladding hole filled with the temperature-sensitive material polydimethylsiloxane and the surrounding germanium oxide glass calculated according to the area ratio, and the formula is: Among them, n PDMS The refractive index of polydimethylsiloxane is the temperature-sensitive material; Where T is temperature in degrees Celsius; n si is the refractive index of germanium oxide glass; The refractive index of the fiber core is the refractive index of the temperature-sensitive material polydimethylsiloxane, and the formula is: n core =n PDMS The refractive index difference between the core refractive index and the average refractive index of the cladding is calculated as:

4. The fully filled Dirac mode microstructure optical fiber temperature sensor according to claim 1, characterized in that: The radius R of the circular area in the center of the optical fiber is in the range of 5.8-5.9 μm.

5. The fully filled Dirac mode microstructure optical fiber temperature sensor according to claim 1, characterized in that: The distance a between adjacent cladding holes is in the range of 2.9-3.1 μm.

6. The fully filled Dirac mode microstructure optical fiber temperature sensor according to claim 1, characterized in that: The cladding hole diameter d ranges from 1.22 to 1.42 μm.

Images