A photonic crystal optical fiber chemical sensor

Abstract

The present invention discloses a novel photonic crystal fiber chemical sensor. The optical fiber of the present invention includes a cladding and a core, and is characterized in that: the left and right sides of the core of the photonic crystal fiber chemical sensor are provided with four identical elliptical air holes along the x-axis, and the major axis of the elliptical air hole is parallel to the x-axis, and there are three triangular structures composed of air holes of different shapes and sizes above the x-axis, wherein the upper left triangular structure is composed of six layers of elliptical air holes, the upper inverted triangular structure is composed of five layers of large circular air holes, and the upper right triangular structure is composed of six layers of small circular air holes, and the overall structure of the optical fiber is diagonally symmetrically distributed. The photonic crystal fiber chemical sensor of the present invention can realize highly sensitive chemical sensing, and the optical fiber structure has a great reference value in chemical sensing devices for monitoring water, ethanol or benzene.

Description

Technical Field

[0001] The invention relates to the technical field of optical fibers, and in particular to a photonic crystal optical fiber that can be used for chemical sensing. Background Art

[0002] Optical fiber is an important medium in communication systems and is also widely used in the field of sensing. The structural limitations of ordinary optical fibers hinder the improvement of some key characteristics. Photonic crystal fiber (PCF) is a new type of microstructured optical fiber based on the evolution of photonic crystal and optical fiber technology. It has flexible parameter designability and can show characteristics that are difficult to achieve with traditional optical fibers. Since PCF can meet application requirements through structural design, it has important applications in the monitoring of chemical analytes such as gases / liquids, temperature sensing, and pressure sensing. With the development of industrial production, environmental pollution has attracted more and more attention, which has promoted the rapid development of research on sensing and monitoring of chemical analytes such as gases / liquids based on photonic crystal fibers.

[0003] In fact, the sensing and monitoring of chemical analytes such as liquids by photonic crystal fibers is based on the interaction between light (evanescent waves) and analytes (liquids), and then the type and concentration of the substance are monitored based on the results of the interaction. Photonic crystal fibers with high relative sensitivity can be used to monitor environmental quality and detect toxic gases, explosive gases, etc. Summary of the invention

[0004] The purpose of the present invention is to provide a photonic crystal fiber that can be used for chemical sensing to solve the problems existing in the photonic crystal fiber in the prior art.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A photonic crystal fiber that can be used for chemical sensing, wherein the cross section of the fiber includes a cladding and a core. The characteristic of the invention is that: the core of the photonic crystal fiber has four identical elliptical air holes on the left and right sides along the x-axis, and the major axis of the elliptical air holes is parallel to the x-axis; there are three triangular structures composed of air holes of different shapes and sizes above the x-axis, wherein the upper left triangular structure is composed of six layers of elliptical air holes, the inverted triangular structure directly above is composed of five layers of large circular air holes with a diameter of d1, and the upper right triangular structure is composed of six layers of small circular air holes with a diameter of d2; the overall structure of the optical fiber is diagonally symmetrically distributed, that is, there are also three triangular structures composed of air holes of different shapes and sizes below the x-axis, wherein the lower right triangular structure is composed of six layers of elliptical air holes, the lower triangular structure is composed of five layers of large circular air holes with a diameter of d1, and the lower left triangular structure is composed of six layers of small circular air holes with a diameter of d2, and the cladding diameter is d.

[0007] Furthermore, the base material of the optical fiber is silicon dioxide.

[0008] The present invention designs a photonic crystal fiber that can be used for chemical sensing. Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0009] High sensitivity is achieved, and a high relative sensitivity is obtained at a wavelength of 1550nm. The relative sensitivity to water is as high as 56.3%, the relative sensitivity to ethanol is as high as 59.9%, and the relative sensitivity to benzene is as high as 62.5%. This optical fiber structure has great reference value in chemical sensing devices for monitoring water, ethanol or benzene, and has very important application prospects in industrial chemical research and biomedical fields.

[0010] There is no high-order mode interference. In the wavelength range of 1.2μm-1.8μm, the normalized frequency (V eff ) is less than 2.4048, which satisfies the single-mode transmission condition and effectively avoids the interference introduced by the existence of high-order modes when monitoring chemical analytes, thereby improving the accuracy of chemical sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 The schematic diagram of the cross-section of the photonic crystal fiber structure that can be used for chemical sensing in a specific embodiment. In the figure: 1-base material, 2-elliptical air hole along the x-axis, 3-elliptical air hole in the triangular structure, 4-large circular air hole in the triangular structure, 5-small circular air hole in the triangular structure; a1-long semi-axis of the elliptical air hole along the x-axis, b1-short semi-axis of the elliptical air hole along the x-axis, The hole spacing of the elliptical air holes along the x-axis; a2-the major axis of the elliptical air holes in the triangular structure, b2-the minor axis of the elliptical air holes in the triangular structure, The hole spacing of the elliptical air holes in the triangular structure; d1-the diameter of the large circular air holes in the triangular structure, d2- the diameter of the small circular air holes in the triangular structure, The hole spacing of the small circular air holes in the triangular structure; d - the diameter of the cladding.

[0012] FIG2 is a graph showing the relationship between the relative sensitivity of the photonic crystal fiber that can be used for chemical sensing and the wavelength when the short semi-axis b1 of the elliptical air hole on the x-axis takes different values, wherein:

[0013] Figure 2a is the relative sensitivity when the air holes are filled with water, Figure 2b is the relative sensitivity when the air hole is filled with ethanol, Figure 2c is the relative sensitivity when the air holes are filled with water.

[0014] 3 is a graph showing the relationship between the normalized frequency and the wavelength when the short semi-axis b1 of the elliptical air hole on the x-axis of the photonic crystal fiber that can be used for chemical sensing in a specific embodiment takes different values.

[0015] Figure 3a is the normalized frequency when the air holes are filled with water, Figure 3b is the normalized frequency when the air holes are filled with ethanol, Figure 3c is the normalized frequency when the air pores are filled with benzene. DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and by way of examples. The following examples are intended to explain the present invention but the present invention is not limited to the following examples.

[0017] Figure 1 The figure shows a cross-sectional view of a photonic crystal fiber that can be used for chemical sensing in the present invention, wherein the base material 1 is silicon dioxide. The left and right sides of the core of the photonic crystal fiber have four identical elliptical air holes with a major semi-axis a1 and a minor semi-axis b1 along the x-axis, and the hole spacing is The long axis of the elliptical air hole is parallel to the x-axis. There are three triangular structures composed of air holes of different shapes and sizes above the x-axis. The upper left triangular structure consists of 6 layers of elliptical air holes with a long axis of a2 and a short axis of b2. The hole spacing is The triangular structure directly above is composed of 5 layers of large circular air holes with a diameter of d1 and a hole spacing of The upper right triangle structure consists of 6 layers of small circular air holes with a diameter of d2 and a hole spacing of The overall structure of the optical fiber is diagonally symmetrical, that is, there are also three triangular structures composed of air holes of different shapes and sizes below the x-axis. Among them, the lower right triangular structure is composed of 6 layers of elliptical air holes with a major axis of a2 and a minor axis of b2, and the hole spacing is The triangle structure directly below is composed of 5 layers of large circular air holes with a diameter of d1 and a hole spacing of The triangle structure on the lower left is composed of 6 layers of small circular air holes with a diameter of d2 and a hole spacing of The fiber cladding diameter is d.

[0018] In this embodiment, the photonic crystal fiber structural parameters are: the long semi-axis a1 of the elliptical air holes on the left and right sides of the fiber core along the x-axis is 0.7 μm, and the hole spacing is The major axis of the elliptical air hole in the triangular structure is a2, and the minor axis is b2, which are 1 μm and 0.7 μm respectively. The hole spacing is The diameter d1 of the large circular air hole in the triangular structure is 1 μm, and the hole spacing is The diameter d2 of the small circular air holes in the triangular structure is 0.8 μm, and the hole spacing is Take 0.8μm, the optical fiber cladding diameter d = 13μm.

[0019] The present invention can use the finite element method and combine the perfect matching layer boundary absorption condition to perform theoretical calculations to obtain the relative sensitivity characteristics and normalized frequency of the present invention.

[0020] In this embodiment, the relative sensitivity characteristics of the photonic crystal fiber when the air holes are filled with water, ethanol, and benzene are respectively obtained when the short semi-axis of the elliptical air hole along the x-axis is 0.3 μm, 0.4 μm, and 0.5 μm. Figure 2a , Figure 2b , Figure 2c As shown, observing Figure 2, we can get:

[0021] The relative sensitivity of the photonic crystal fiber for chemical sensing of the present invention increases with the increase of wavelength. At the commonly used communication wavelength of 1550nm, when b1=0.5μm, the relative sensitivity to water, ethanol and benzene all reach the maximum value, which are 56.3%, 59.9% and 62.5% respectively. It can be seen that the structure has a high relative sensitivity to water, ethanol and benzene, and its sensing accuracy will also be improved accordingly. Therefore, the PCF structure has a great reference value in the chemical sensing device for monitoring water, ethanol or benzene, and has a very important application prospect in the field of industrial chemical research and biomedicine.

[0022] In this embodiment, when the minor axis of the elliptical air hole along the x-axis is 0.3 μm, 0.4 μm, and 0.5 μm, respectively, the normalized frequencies of the air holes of the photonic crystal fiber when filled with water, ethanol, and benzene are respectively as follows: Figure 3a , Figure 3b , Figure 3c As shown, observing Figure 3, we can get:

[0023] The normalized frequency of the photonic crystal fiber that can be used for chemical sensing described in the present invention decreases with the increase of wavelength and increases with the increase of b1, but the photonic crystal fiber satisfies the normalized frequency less than 2.4048 under any parameter value. Therefore, each structure of the photonic crystal fiber satisfies the single-mode transmission condition, effectively avoiding the interference introduced by the existence of high-order modes when monitoring chemical analytes.

[0024] The above is only one embodiment of the present invention, not all or the only embodiment. Any equivalent changes made to the technical solution of the present invention by ordinary technicians in this field after reading the specification of the present invention are covered by the claims of the present invention.

Claims

1. A photonic crystal fiber that can be used for chemical sensing, wherein the cross section of the fiber includes a cladding and a core, and is characterized in that: There are 4 identical elliptical air holes with major semi-axis a1 and minor semi-axis b1 on the left and right sides of the core of the photonic crystal fiber along the x-axis, and the hole spacing is Λ1. The major axis of the elliptical air hole is parallel to the x-axis. There are three triangular structures composed of air holes of different shapes and sizes above the x-axis. Among them, the upper left triangular structure is composed of 6 layers of elliptical air holes with major axis a2 and minor axis b2, and the hole spacing is Λ2. The upper triangular structure is composed of 5 layers of large circular air holes with a diameter of d1, and the hole spacing is Λ3. The upper right triangular structure is composed of 6 layers of small circular air holes with a diameter of d2. The overall structure of the optical fiber is diagonally symmetrical, that is, there are also three triangular structures composed of air holes of different shapes and sizes below the x-axis. Among them, the lower right triangular structure is composed of 6 layers of elliptical air holes with a major axis of a2 and a minor axis of b2, and the hole spacing is Λ2. The triangular structure directly below is composed of 5 layers of large circular air holes with a diameter of d1, and the hole spacing is Λ3. The lower left triangular structure is composed of 6 layers of small circular air holes with a diameter of d2, and the hole spacing is Λ4. The diameter of the optical fiber cladding is d, and the base material of the optical fiber is silica.

2. A photonic crystal fiber for chemical sensing according to claim 1, characterized in that: The elliptical air hole in the triangular structure at the upper left of the x-axis is the same as the elliptical air hole in the triangular structure at the lower right of the x-axis.

3. A photonic crystal fiber for chemical sensing according to claim 1, characterized in that: In the above parameters, the ratio of the diameter of the large circular air hole to the diameter of the small circular air hole in the triangular structure is d1:d2=5:4.

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