Dual-parameter sensor based on selective filling of spiral photonic crystal fiber

Abstract

The present invention discloses a dual-parameter sensor based on selective filling of spiral photonic crystal fiber, which includes a core layer, a cladding and toluene liquid. The core layer is located on the central axis of the optical fiber. Six layers of circular air holes are uniformly arranged in the cladding, and the air holes are distributed in an annular array. The toluene liquid is filled in one air hole in the second layer from the inside to the outside of the cladding. The present invention can realize simultaneous sensing and monitoring of twist and temperature, and the two sensing mechanisms do not affect each other. This dual-parameter fiber optic sensor not only has a simple structure, but also has high twist and temperature sensitivities, and has great application value in the fields of mechanical stress strain, twist and temperature warning, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber optic sensing, and in particular to a dual-parameter sensor based on selective filling of helical photonic crystal fiber. Background Art

[0002] In 1977, the United States Naval Research Laboratory began implementing the Foss (Fiber Optic Sensor System) program, which is regarded as the birth date of fiber optic sensors. Since the advent of fiber optic sensors, fiber optic sensing technology has received great attention. Due to its characteristics such as anti-electromagnetic interference, high sensitivity, corrosion resistance, wide frequency band, large dynamic range, and a wide range of measurement objects, and its simple structure, small size, light weight, and low energy consumption, fiber optic sensors have advantages that conventional sensors cannot match and broad development prospects. Its application scope covers almost all important fields of the national economy and people's daily lives. In the current information society, fiber optic sensing technology has been applied in fields such as industry, military, medical, communication, and measurement of physical quantities in harsh environments. "China's Long-Term Plan for 2010" has listed fiber optic sensors as one of the key developing industries. With the development of smart cities and Internet of Things construction in China, the market demand and development potential of fiber optic sensors are huge. In the sensing measurement environment, there are often more than one changing physical quantity. Therefore, multi-parameter sensing has become one of the important research topics in the field of fiber optic sensing. Summary of the Invention

[0003] In order to solve the problem that the existing technology lacks a dual-parameter sensor for simultaneously monitoring twist rate and temperature, the present invention proposes a dual-parameter sensor based on selective filling of helical photonic crystal fiber.

[0004] The dual-parameter sensor based on selective filling of helical photonic crystal fiber includes a core layer, a cladding, and toluene liquid. The core layer is located on the central axis of the optical fiber. Six layers of circular air holes are uniformly arranged in the cladding, and the air holes are distributed in a circular array. The toluene liquid is filled in one air hole in the second layer from the inside to the outside of the cladding.

[0005] Wherein, both the core layer and the cladding are made of silica material, and the filling material is the temperature-sensitive liquid toluene.

[0006] Wherein, the hole pitch of the air holes is 3 μm, the diameter is 1 μm, the range of the twist rate is 13.8 - 14.214 rad / mm, with an interval of 0.138 rad / mm each time. The refractive index of the toluene liquid changes with temperature, and the temperature range is 15 - 30 °C, with an interval of 5 °C each time.

[0007] Wherein, the working wavelength range of the dual-parameter sensor is 450 - 600 nm.

[0008] Among them, the dual-parameter sensor also has a supermode formed by a core mode and a cladding mode. The supermode has a six-layer symmetric single-mode profile and is located between the third and fourth rings of air holes in the cladding.

[0009] Among them, the twist rate range of the dual-parameter sensor is 13.8 - 14.214 rad / mm, and the twist transmission sensitivity of the dual-parameter sensor is not less than 3.623×10 -6 mm 2 / rad.

[0010] Among them, the temperature range of the dual-parameter sensor is 15 - 30 °C, and the temperature sensing sensitivity of the dual-parameter sensor is not less than 2 nm / °C.

[0011] The beneficial effects of the present invention are as follows: For the spiral photonic crystal fiber, the spiral structure causes the energy of the waveguide mode at a specific wavelength to leak into the cladding, manifested as an increase in the loss of the core guided mode and the appearance of a loss peak. By selectively filling the air holes with a liquid having a high thermo-optic coefficient, when the core waveguide mode and the filled waveguide mode match, the energy in the core will strongly couple into the waveguide formed by the filling, manifested as a narrow loss peak, and the mechanisms of these two loss peaks are completely different. By monitoring the drift of the wavelength corresponding to the loss peak, simultaneous measurement of the two parameters of temperature and twist rate is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0013] Figure 1 It is a cross-sectional schematic diagram of the spiral photonic crystal fiber of the dual-parameter sensor based on selective filling of spiral photonic crystal fiber of the present invention.

[0014] Figure 2 It is a three-dimensional structure schematic diagram of the spiral photonic crystal fiber of the dual-parameter sensor based on selective filling of spiral photonic crystal fiber of the present invention.

[0015] Figure 3 It is the loss characteristic of the core guided mode of the dual-parameter sensor based on selective filling of spiral photonic crystal fiber of the present invention at temperature T = 20 °C and twist rate α = 13.8 rad / mm.

[0016] Figure 4 It is the loss characteristic of the core guided mode of the dual-parameter sensor based on selective filling of spiral photonic crystal fiber of the present invention at different twist rates at temperature T = 20 °C.

[0017] Figure 5 For the dual-parameter sensor based on selective filling of spiral photonic crystal fiber of the present invention, when the twist rate α = 13.8 rad / mm, it shows the loss characteristics of the core guided mode at different temperatures.

[0018] 1 - core layer, 2 - cladding, 3 - toluene liquid. Detailed implementation manners

[0019] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0020] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and 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 thus should not be construed as a limitation to the present invention. In addition, in the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0021] Please refer to Figure 1 , the present invention provides a technical solution: Specific embodiment 1:

[0023] Simplify the spiral waveguide structure using coordinate transformation. The spiral coordinate system is represented by (ξ 1 , ξ 2 , ξ 3 ), and the Cartesian coordinate system is represented by (x, y, z). The relationship expression between the two coordinate systems is:

[0024] x = ξ 1 cos(αξ 3 ) + ξ 2 sin(αξ 3 )

[0025] y = -ξ 1 sin(αξ 3 ) + ξ 2 cos(αξ 3 )

[0026] z = ξ 3

[0027] α represents the twist rate. When α > 0, it corresponds to a left - hand rotation twist rate. When α < 0, it corresponds to a right - hand rotation twist rate. The transmission of the optical fiber exhibits unique transmission losses at certain wavelengths, which is related to the coupling between the core guided mode and the circular orbital angular momentum mode.

[0028] The filling liquid of the photonic crystal fiber is toluene. Since its refractive index is higher than that of the fiber substrate, filling the air holes forms another waveguide core with a high refractive index. At a specific wavelength, the core will have directional coupling with this waveguide, manifested as another narrow loss peak (directional coupling loss peak) appearing in the transmission spectrum of the spiral photonic crystal fiber. Since the wavelength of the directional coupling loss peak is related to the refractive index of the filling liquid, the change in temperature causes a change in the refractive index of the filling liquid, thereby causing a drift in the wavelength corresponding to the directional coupling loss peak. Therefore, the change in temperature can be indirectly measured by measuring the movement of the loss peak position. The refractive index of the toluene liquid 3 can be obtained from the Sellmeier equation and the linear relationship between refractive index and temperature:

[0029]

[0030] where λ is the incident wavelength, T is the ambient temperature in °C, and the temperature - sensitive coefficient α of the toluene liquid 3 is 5.273×10 -4 , and since the temperature - sensitive coefficient of quartz is two orders of magnitude smaller than that of the toluene liquid 3, it can be approximately considered that its refractive index is not affected by temperature.

[0031] Refer to Figure 1 and Figure 2 , the structure of the photonic crystal fiber includes the core layer 1 and the cladding layer 2 from the inside out. The cross - section of the optical fiber is circular. The core layer 1 is located in the innermost layer of the optical fiber. Six layers of circular air holes are evenly arranged in the cladding layer 2. The air holes in the cladding layer 2 are distributed in an annular array, removing the air holes at the six vertices. The hole pitch Λ is 3μm, the air hole diameter d is 1μm, the radius of the optical fiber is 20μm. When measuring the temperature change, the twist rate α = 13.8 rad / mm. When measuring the twist rate change, the temperature T = 20°C. The range of the twist rate α is 13.8 - 14.214 rad / mm, with an interval of 0.138 rad / mm each time. The refractive index of the filling material changes with temperature. The temperature T range is 15 - 30°C, with an interval of 5°C each time.

[0032] The dual - parameter sensor based on the selective filling of spiral photonic crystal fiber is the most common photonic crystal fiber structure. It is simple and easy to implement, has high twist and temperature sensitivities, and has great potential application value in the fields of mechanical stress strain, twist, and temperature warning.

[0033] The working wavelength range of the dual-parameter sensor based on selective filling of spiral photonic crystal fiber in this embodiment is 450 - 600 nm. Through COMSOL Multiphysics simulation calculation, Figure 3 Figure 2 shows the transmission loss characteristics of the dual-parameter sensor based on selective filling of spiral photonic crystal fiber in this embodiment at a fixed temperature T = 20 °C and a twist rate α = 13.8 rad / mm. It can be seen from the figure that the absorption peak caused by twist is at a wavelength of 555 nm, and the absorption peak caused by directional coupling is at a wavelength of 492 nm. Thus, it can be seen that this structure can achieve simultaneous sensing and monitoring of twist and temperature.

[0034] Figure 4 It shows that when the temperature T = 20 °C, the resonance curve based on spiral twist will shift towards the long-wavelength direction as the twist rate increases, while the position of the coupling peak based on the directional coupling effect remains unchanged. It can be found from the inset that within the twist rate range of 13.8 - 14.214 rad / mm for twist sensing, the twist rate and the coupling wavelength satisfy: λ = 36.23α + 55 (λ is in nm and α is in rad / mm), that is, the sensitivity is 3.623×10 -6 mm 2 / rad. Figure 5 It then shows that when the twist rate α = 13.8 rad / mm remains unchanged, the position of the coupling peak based on directional coupling will shift towards the short-wavelength direction as the temperature increases. This is because the change in temperature will affect the refractive index of toluene, thereby affecting the effective refractive index of the directional coupling waveguide mode. It can be found from the inset that the linearity is good within the temperature range of 15 - 30 °C for temperature sensing, and the sensitivity can reach 2 nm / °C.

[0035] In summary, twist-based sensing is not affected by temperature, and temperature sensing based on directional coupling is not affected by the twist rate, that is, these two sensing mechanisms do not affect each other.

[0036] The present invention provides a dual-parameter sensor based on selective filling of spiral photonic crystal fiber, which realizes simultaneous measurement of the twist rate and temperature. For the spiral photonic crystal fiber, the spiral structure causes the energy of the waveguide mode at a specific wavelength to leak into the cladding 2, manifested as an increase in the loss of the core guided mode and the appearance of a loss peak. By selectively filling the air holes with a liquid having a high thermo-optic coefficient, when the core waveguide mode and the filled waveguide mode match, the energy in the core will be strongly coupled into the waveguide formed by the filling, manifested as a narrow loss peak, and the mechanisms for generating these two loss peaks are completely different, enabling simultaneous measurement of dual parameters. The dual-parameter fiber sensor proposed by the present invention has broad application prospects in the monitoring and early warning in fields such as bridges, dams, buildings, mines, robotic arms, and space vehicles.

[0037] The above-disclosed is only a preferred embodiment of the present invention. Of course, it cannot be used to limit the scope of the rights of the present invention. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A dual-parameter sensor based on selective filling of helical photonic crystal fiber, characterized in that, it includes a core layer, a cladding and toluene liquid. The core layer is located on the central axis of the optical fiber. Six layers of circular air holes are uniformly arranged in the cladding. The air holes are distributed in a circular array. The toluene liquid is filled in one air hole in the second layer from the inside to the outside of the cladding; the hole pitch of the air holes is 3 μm, the diameter is 1 μm, the range of the twist rate is 13.8 - 14.214 rad / mm, and the interval is 0.138 rad / mm each time. The refractive index of the toluene liquid changes with temperature, and the temperature range is 15 - 30 °C, with an interval of 5 °C each time; both the core layer and the cladding are made of silica material, and the filling material is the temperature-sensitive liquid toluene; the refractive index of the toluene liquid can be obtained from the Sellmeier equation and the linear relationship between refractive index and temperature: where λ is the incident wavelength, T is the ambient temperature in °C, and the thermosensitivity coefficient of the toluene liquid .

2. The dual-parameter sensor based on selective filling of helical photonic crystal fiber according to claim 1, characterized in that, the working wavelength range of the dual-parameter sensor structure is 450 - 600 nm.

3. The dual-parameter sensor based on selective filling of helical photonic crystal fiber according to claim 2, characterized in that, the dual-parameter sensor also has a supermode formed by the core mode and the cladding mode. The supermode has six layers of symmetric single-mode profiles and is located between the third ring and the fourth ring of the air holes in the cladding.

4. The dual-parameter sensor based on selective filling of helical photonic crystal fiber according to claim 3, characterized in that, The twist rate range of the dual-parameter sensor is 13.8~14.214 rad / mm, and the twist sensing sensitivity of the dual-parameter sensor is not less than 3.623×10 -6 mm 2 / rad.

5. The dual-parameter sensor based on selective filling of helical photonic crystal fiber according to claim 4, characterized in that, the temperature range of the dual-parameter sensor is 15 - 30 °C, and the temperature sensing sensitivity of the dual-parameter sensor is not less than 2 nm / °C.

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