A Photonic Crystal Fiber-Based Biosensor with Quasi-D-shaped Layout and ITO-Graphene Combination

A quasi-D-shaped photonic crystal fiber (PCF) biosensor in the near-infrared region (NIR) is proposed for the purpose of detecting the analytes/liquids of different refractive indices (RIs) ranging from 1.21 to 1.32. In order to realize sensing in the near-infrared region, we use indium tin oxide (ITO) as the plasma material. Then a flake of graphene is deposited on the ITO film. Graphene has excellent molecular adsorption performance, which can improve the detection capability of the PCF sensor. Graphene becomes an ideal dielectric layer for sensing due to its large surface area and rich π-conjugation. To enhance the birefringence, we introduce two elliptical holes around the core. The proposed sensor is designed and numerically analyzed by finite element method. Thickness of the ITO, graphene layer, and the ellipticity of ellipse of PCF are varied so as to study its effect on the sensing characteristics of the proposed sensor. Wavelength sensitivity of the proposed sensor is as high as 12,000 nm/RIU (refractive index unit), and a maximum resolution can be 8.33 × 10−6 RIU. Compared with the traditional D-shaped sensors, the proposed sensor has the advantages of easy manufacturing and high sensitivity.