PLASMON RESONANCE BASED MULTICORE PHOTONIC CRYSTAL FIBRE SENSORS FOR ANALYTE DETECTION

Abstract

A dual core SPR based sensor with plasmonic material being silver with an external layer of analyte has been designed. In the structure, there are airholes present to accommodate the plasmonic material with a sufficient amount of the incident light. The presence of airholes has been known for the improvement of sensor performance where the air holes act as microchannels. The diameters of the air holes directly influences the major properties of the sensor, like sensitivity, i.e., larger the diameter of the air holes, the larger the sensitivity. The explicit feature of the SPR method is that it detects even tiny changes in the refractive indices of incident light, with a range of 0.05, we have shown a wide variation in the loss curves of the sensor. There is a phase-matching condition which when satisfied, provides an appropriate resonance condition. So, we have provided a set of parameters and when the suitable factors have been provided, the resonance condition is met. The resonance condition has been represented through a confinement loss versus wavelength curve in which the refractive index is varied with respect to the wavelength. Following this, the loss curves are further plotted at the resonance condition for a dynamic range of refractive indices. The range of refractive indices taken from around 1.25 to 1.34. The sensitivity has also been calculated depending on the change of confinement losses with respect to the wavelength. In addition to this, we have taken a layer of silica at the most outer surface of the sensor with a comparatively thin layer of analyte present inside it. Then, there is a fabricated nanofilm of plasmonic material, with the substrate silica poured in the internal structure with multiple micro sized air holes present inside to selectively vary the refractive index of the analyte. The thickness of the nanofilm taken is 40nm. Through the Finite Element Meshing method, the structure has been fabricated and the parameters like wavelength, refractive index, thickness and diameters of the various air holes have been varied and the confinement losses are thus, calculated. Then, we have plotted the confinement loss curves and thus, the amplitude sensitivity curves are plotted with the main aim of differentiating between Gold, Silver and aluminium based sensors by varying the material and thus, plotting the parameters to get the sensitivities of the different plasmonic materials based sensors and to get an idea which material is the most suitable for the fabrication of biosensors in medical sensing applications. A D-shaped SPR based PCF sensor has been designed with a dual-core structure. As a part of the core, a thin layer of gold has been taken above which, a layer of ZnO has been taken which is acting as the photocatalyst. For the cladding, an analyte of refractive index 1.39 has been taken. There are 14 air holes with varying diameters present with fused silica in order to ensure better coupling between the core and the Surface Plasmon Polaritons mode. The structure has been designed and studied in COMSOL Multiphysics and the operating wavelength has been varied for different refractive indices. The confinement loss curves have been plotted with a variation with wavelength. The wavelength sensitivity of the sensor is 1325nmRIU-1 and the maximum amplitude sensitivity of the sensor is 240.2RIU-1 .