阅读说明：本技术 基于石墨烯包覆的双芯d型光子晶体光纤spr传感器 (Double-core D-type photonic crystal fiber SPR sensor based on graphene coating ) 是由 肖功利 张开富 杨宏艳 杨秀华 杨寓婷 李海鸥 张法碧 傅涛 邓艳容 孙堂友 陈 于 2019-09-01 设计创作，主要内容包括：本发明提供了一种石墨烯包覆的双芯D型光子晶体光纤SPR折射率传感器。所述光纤SPR传感器包括一具有平面壁和曲面侧壁的折射率引导型光子晶体光纤,所述折射率引导型光子晶体光纤留有左右相互对称的两个纤芯,横截面呈D形,在所述平面壁上具有传感层。本发明在D形光子晶体光纤表面,左右纤芯所对应的传感层分别为石墨烯包覆的金/银纳米柱。利用金/银纳米柱表面产生的等离子体共振对周围的介质环境十分敏感的特性,可以将金属表面临近物质的折射率的微小变化转换成可测量的吸收峰的位移,设计实现高灵敏度的光子晶体光纤SPR传感器。本发明的优点是：双芯结构的设计拓宽了该折射率传感器的检测范围。石墨烯包覆金/银纳米柱的设计既能明显提高传感器的灵敏度,又能有效防止银纳米柱的腐蚀及氧化。该传感器设计新颖,结构简单,体积小,检测范围宽,抗腐蚀能力强,灵敏度高,是一种实用的折射率传感器。(The invention provides a graphene-coated double-core D-type photonic crystal fiber SPR refractive index sensor. The optical fiber SPR sensor comprises a refractive index guide type photonic crystal fiber with a plane wall and a curved side wall, wherein the refractive index guide type photonic crystal fiber is provided with two fiber cores which are symmetrical left and right, the cross section of the two fiber cores is D-shaped, and a sensing layer is arranged on the plane wall. According to the invention, on the surface of the D-shaped photonic crystal fiber, the sensing layers corresponding to the left fiber core and the right fiber core are respectively a graphene-coated gold/silver nano-column. The characteristic that plasma resonance generated on the surface of the gold/silver nano-pillar is very sensitive to the surrounding medium environment is utilized, the tiny change of the refractive index of a substance close to the metal surface can be converted into the displacement of a measurable absorption peak, and the photonic crystal fiber SPR sensor with high sensitivity is designed and realized. The invention has the advantages that: the design of the double-core structure widens the detection range of the refractive index sensor. The design of the graphene-coated gold/silver nano-column can obviously improve the sensitivity of the sensor and can effectively prevent the corrosion and oxidation of the silver nano-column. The sensor has the advantages of novel design, simple structure, small volume, wide detection range, strong corrosion resistance and high sensitivity, and is a practical refractive index sensor.)

1. A double-core D-type photonic crystal fiber SPR sensor based on graphene coating is shown in figure 1 and comprises a fiber sensor body and is characterized in that: the optical fiber sensor body consists of a photonic crystal optical fiber (1), an analyte sensing area (2) and a graphene-coated gold/silver nano-column (3); the diameter D of the photonic crystal fiber cladding is 125um, the length L of the side polished surface is 1mm, and the radius r of the gold/silver nanocolumn is 25 nm.

The two-dimensional structure of the optical fiber sensor is shown in fig. 2 and comprises two fiber cores (5) (6), air holes, gold nanorods (7), graphene (8) and silver nanorods (9) which are reserved before the photonic crystal fiber is laterally polished.

2. The graphene-coated twin-core D-type photonic crystal fiber SPR sensor according to claim 1, wherein: the material of the photonic crystal fiber (1) is polyethylene, and the refractive index is 1.4378.

3. The graphene-clad-based dual-core D-type photonic crystal fiber SPR sensor according to claim 1, wherein: the side polished surface of the photonic crystal fiber (1) is D-shaped, and the two fiber cores (5) and (6) are symmetrical to each other.

4. The graphene-clad-based dual-core D-type photonic crystal fiber SPR sensor according to claim 1, wherein: the radiuses of the gold/silver nano-columns are the same, the distances between the gold/silver nano-columns are the same, and the thicknesses of the coated graphene are the same.

5. The graphene-clad-based dual-core D-type photonic crystal fiber SPR sensor according to claim 1 or 4, wherein: the number of gold/silver nano-pillars is not fixed, so as to just cover the two fiber cores. For example, when d is 50nm, the number of the nanopillars is 720.

6. The graphene-clad-based dual-core D-type photonic crystal fiber SPR sensor according to claim 1, wherein: the diameter of the air hole of the photonic crystal fiber (1) is 9um, and the distance is 9 um.

7. The graphene-clad-based dual-core D-type photonic crystal fiber SPR sensor according to claim 1 or 5, wherein: the distance between the gold/silver nano-columns is 30 nm-70 nm, and the gold/silver nano-columns can be selected according to actual needs.

8. The graphene-clad-based dual-core D-type photonic crystal fiber SPR sensor according to claim 1 or 4, wherein: the number of the graphene layers is preferably 1-5, and the graphene layers can be selected according to actual needs.

Technical Field

The invention relates to an optical fiber SPR sensing technology, in particular to a double-core D-type photonic crystal optical fiber SPR sensor based on graphene coating.

Background

Surface Plasmon Resonance (SPR) is an optical phenomenon in which electrons excited on the surface of a metal or medium oscillate collectively due to P-polarized light or Transverse Magnetic (TM) waves. Electromagnetic waves generated by this optical phenomenon are called Surface Plasmon Polaritons (SPPs), and appear as evanescent waves under certain conditions. SPR is the coupling of a surface plasmon wave to a metal surface when the metal surface is irradiated by Total Internal Reflection (TIR) evanescent waves under certain conditions. By utilizing the property that surface plasmon polariton is extremely sensitive to the change of Refractive Index (RI) of the surrounding medium, SPR has become a promising sensing technology in the fields of chemistry, biomedicine and environmental monitoring. Based on a TIR mechanism, a plurality of operation platforms for exciting SPR by using prisms, optical fibers and Photonic Crystal Fibers (PCF) exist, the prism structure proposed by Kretschmann-Raether in 1968 has the problem of large sensor volume, Jorgenson and Yee of the university of Washington in 1992 in the United states propose that the optical fibers are used as carriers to realize the SPR effect based on the Krestchmann prism structure, and the optical fiber SPR sensor is designed in the next year. Although the optical fiber replaces a prism and has the capability of miniaturization and remote sensing, the traditional optical fiber SPR sensor has the defects of single structure and low sensitivity.

PCF-SPR sensors based on PCF have the advantages that air holes are regularly arranged along the propagation direction, and due to the flexibility of the structural design, the PCF-SPR sensors attract great attention of researchers in recent years. In 2012, an all-solid-state D-type PCF-SPR sensor is designed by Tian M, Lu P, Chen L and the like, and the wavelength sensitivity can reach 7300nm/RIU at the highest within the refractive index range of 1.33-1.38. In 2014, Tan Z, Li X, Chen Y and the like design a liquid core D type PCF-SPR sensor, and the wavelength sensitivity is 6430nm/RIU at most within the refractive index range of 1.32-1.36. DF Santos et al designed a D-type PCF-SPR sensor with a microstructure in 2015, and the maximum wavelength sensitivity of the sensor reaches 10200nm/RIU within the refractive index of 1.36-1.39. Haiwei Fua and Min Zhang in 2019 design a graphene-coated silver nanorod optical fiber sensor, the problem that silver is prone to corrosion and oxidation is effectively solved by application of graphene, and the sensor has the highest sensitivity reaching 8860.93nm/RIU within the refractive index range of 1.33-1.39.

Based on the work, the metal film of the sensor is easy to oxidize, the service life of the sensor is prolonged, the detection range is widened, and the detection precision is improved. The structure of the sensor is improved on the traditional D-type PCF-SPR sensor, two symmetrical fiber cores are reserved on a photonic crystal fiber, and the upper surfaces of the two fiber cores are respectively coated with the graphene-coated gold/silver nanocolumns. The sensor has the advantages of novel design, simple structure, small volume, wide detection range, strong corrosion resistance and high sensitivity, and is a practical refractive index sensor.

Disclosure of Invention

The invention mainly provides a graphene-coated double-core D-shaped optical fiber surface plasmon resonance sensor. The graphene layer is coated on the surface of the gold/silver nano-pillar, so that the sensitivity of the sensor can be obviously improved, and the corrosion and oxidation of the silver nano-pillar can be effectively prevented. The sensor has the characteristic of double resonance peaks due to the design of the double-core structure, so that the detection accuracy is improved, and the detection range of the refractive index sensor is widened.

The invention is realized by the following technical scheme:

a graphene-coated double-core D-shaped optical fiber surface plasmon resonance sensor adopts a fiber core cladding structure, the material is polyethylene, the fiber core is a symmetrical double solid core, the optical fiber is subjected to side polishing treatment to form a structure with a D-shaped side surface, and the side polishing surface is provided with graphene-coated gold/silver nano columns corresponding to the left and right fiber cores of the optical fiber. The refractive index of the polyethylene material is 1.4378, the diameter D of the photonic crystal fiber is 125 μm, the radius r of the gold/silver nanocolumn is 25nm, the distance D between columns is 50nm, the graphene is a single layer, and the thickness D is₁Is 0.34 nm.

The working mechanism of the invention is as follows:

the sample to be measured is loaded on the side polished surface of the designed photonic crystal fiber SPR sensor, and because the plasma resonance generated on the surface of the gold/silver nano column is very sensitive to the surrounding medium environment, when the refractive index of the sample to be measured changes, the position of a loss absorption peak also changes, so that the small change of the refractive index of a substance adjacent to the surface of the gold/silver nano column can be converted into the displacement of a measurable absorption peak, and the sensing purpose is achieved.

The invention has the advantages that: the double-core D-type photonic crystal fiber SPR sensor is novel in structure, does not need to be internally coated with a metal film, and is easy to realize. The optical fiber SPR sensor manufactured by the model can realize high-sensitivity detection within the refractive index range of 1.32 to 1.41, and the highest detection sensitivity can reach 13100 nm/RIU. In a low refractive index interval (n is 1.32-1.36), the sensor has obvious double-resonance peak characteristics, and sensing results of the characteristics can be used for mutual compensation and correction, so that errors are reduced, and detection accuracy is improved. In addition, the graphene layer is coated on the surface of the gold/silver nano column, so that the sensitivity of the sensor can be obviously improved, and the corrosion and oxidation of the silver nano column can be effectively prevented.

Drawings

FIG. 1 is a schematic three-dimensional structure of the present invention.

Fig. 2 is a cross-sectional view of the present invention and a partially enlarged schematic view of a cross-section of a sensor.

FIG. 3 is a graph of loss spectrum in the low refractive index region (n is 1.32-1.36) according to the present invention.

FIG. 4 is a graph of loss spectrum in the high refractive index region (n is 1.37-1.41) according to the present invention.

Fig. 5 is a graph showing a loss spectrum when the distance between pillars of the au/ag nanopillar of the present invention is changed.

Fig. 6 is a graph of a loss spectrum when the number of graphene layers is changed according to the present invention.

The reference numbers in the figures are: 1. the sensor comprises a photonic crystal fiber, 2, an analyte sensing area, 3, a graphene-coated gold/silver nanorod, 4, an air hole, 5, fiber cores 1 and 6, fiber cores 2 and 7, a gold nanorod, 8, graphene, 9 and a silver nanorod.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings in conjunction with specific examples.

A graphene-coated double-core D-shaped optical fiber surface plasmon resonance sensor is characterized in that as shown in figure 1, a fiber core cladding structure is adopted, polyethylene with the refractive index of 1.4378 is used as a material, the side of a photonic crystal optical fiber is polished to form a D-shaped optical fiber, two solid fiber cores are reserved on the left and the right, and three layers of circular air holes (4) which are arranged in a regular hexagon shape are arranged in a cladding (1). The D-shaped side polished surface is symmetrically distributed with gold/silver nano-columns (3) coated by graphene, the radius r of the nano-columns is 25nm, the inter-column distance D is 50nm, the graphene is single-layer graphene, and the thickness of the graphene is thickDegree d₁0.34 nm. The analyte sensing region (2) of the model is loaded with a sample to be tested, wherein the refractive index of the sample to be tested is in the range of 1.32-1.41.

The method comprises the steps of adopting a wavelength modulation method, enabling the wavelength variation range to be 500-800 nm, carrying out numerical simulation on the designed experimental model by utilizing COMSOL Multiphysics calculation software based on a full vector Finite Element Method (FEM), solving the effective refractive index of a mode field under the coordination of boundary conditions of an anisotropic Perfect Matching Layer (PML), calculating the mode field loss according to a mode field loss formula, and drawing a loss spectrum of the optical fiber by utilizing Origin software. As shown in fig. 3, in the low refractive index region (n ═ 1.32 to 1.36), it can be seen that the optical fiber loss spectrum has two sets of loss absorption peaks, and the positions of the loss absorption peaks indicate that the surface plasmon resonance phenomenon occurs at the wavelength. The simulation is carried out in the wave band range of 500 nm-800 nm, and the sensitivity and the resolution of the model are calculated. It can be seen that the absorption peak is red-shifted with the increase of the refractive index of the sample to be measured, and the change of the refractive index is measured to be delta n_aOffset amount of time absorption peak DeltaLambda_peakUsing the formula S_λ(λ)＝Δλ_peak/Δn_a(nm/RIU) the sensitivity S of the sensor can be calculated_λ(lambda). When refractive index n_aThe first set of loss peaks varied from 1.32 to 1.33, 1.34, 1.35 and 1.36 with peak offsets of 20, 21, 25 and 30nm, respectively. The sensitivity was 2000, 2100, 2500 and 3000nm/RIU, respectively, with an average sensitivity of 2400 nm/RIU. The second set of loss peaks had peak offsets of 15, 18, 22 and 28nm, respectively, corresponding sensitivities of 1500, 1800, 2200 and 2800nm/RIU, respectively, and an average sensitivity of 2075 nm/RIU. Using a high-precision spectrometer with the resolution of 0.01nm, the average minimum resolution of the sensors corresponding to the two groups of loss peaks is respectively 4.21 multiplied by 10^-6RIU and 4.94X 10^-6RIU。

As shown in fig. 4, in the high refractive index section (n is 1.37 to 1.41), the wavelength ranges from 700nm to 1100nm, and the absorption peak is red-shifted with the increase of the refractive index of the sample to be measured. Also by measuring when the refractive index changes by an_aOffset amount of time absorption peak DeltaLambda_peakAnd calculating the sensitivity. When refractingRate n_aThe peak shift of the loss peak was 42, 53, 76 and 131nm when changing from 1.37 to 1.38, 1.39, 1.40 and 1.41, respectively. The sensitivities were 4200, 5300, 7600 and 13100nm/RIU, respectively, the average sensitivity was 7550nm/RIU, and the average minimum resolution was 1.32X 10^-6RIU. It can be seen that the measurement range of the photonic crystal fiber SPR sensor made by the model is much wider than that of the existing general sensor, and the resolution is improved by one order of magnitude.

In order to make the optical fiber sensor more flexibly select parameters when being manufactured, and the optical fiber sensor is applied to different use environments and detection ranges, the invention researches two important parameters, namely the distance d between the nano-columns and the number N of the graphene layers.

As shown in fig. 5, d is taken to be in the range of 30-70 nm, two groups of loss peaks of the loss spectrum curve are subjected to blue shift along with the increase of d, and d is taken to be 50nm in the invention, so that the purpose of detecting by using spectra with different wavelengths can be further selected according to the rule.

As shown in fig. 6, the graphene thickness d was investigated₁Influence on the loss spectrum of the SPR sensor from d₁Since 0.34 × N (nm) is the thickness of single-layer graphene and N is the number of graphene layers, studies can be made by selecting different N values. When the refractive index n of the sample is_aWhen the width d between the columns is 50nm and 1.33, the loss spectrum curve of the optical fiber sensor is as shown in fig. 6, and two groups of loss peaks of the loss spectrum curve are blue-shifted and the peak value of the loss peak is reduced along with the increase of N. The method takes N as 1, and can also balance the cost of the graphene coating, and the like, and can be selected according to the above rules.

The sensor structure of the invention has the characteristics of double transmission peaks with high quality factor and high sensitivity in visible light and near infrared frequency bands, and can achieve the purposes of adjusting detection spectrum and controlling cost by modifying related structure parameters, thereby realizing the optical fiber sensor with long service life, wide detection range, high detection precision and miniaturization.

It should be noted that, although the above-mentioned embodiments of the present invention are illustrative, the present invention is not limited thereto, and thus the present invention is not limited to the above-mentioned embodiments. Other embodiments, which can be made by those skilled in the art in light of the teachings of the present invention, are considered to be within the scope of the present invention without departing from its principles.