Sensitivity enhancement in photonic crystal waveguide platform for refractive index sensing applications

Abstract

Listen

Translate article

A photonic crystal (PhC) waveguide platform based on ring-shaped holes in a silicon- on-insulator substrate is proposed in order to realize a refractive index sensor with an improved sensitivity. The three-dimensional finite-difference time domain method is used to analyze the proposed design. The sensitivity is estimated by measuring the shift in the upper band-edge of the output transmission spectrum. Sensitivity analysis of a conventionally designed PhC wave- guide, followed by modification of the structure, has been carried out for improving the sensitivity by introducing a row of holes that forms the line defect. Further improvement in sensitivity is obtained by replacing the defect row of holes by ring-shaped holes, which shows a significantly high sensitivity along with considerable output signal strength. The optimized design shows a wavelength shift of 210 nm for a change in ambient refractive index from air (RI ¼ 1 )t o xylene (RI ¼ 1.5), corresponding to an average sensitivity of420 nm∕RIU.©2014SocietyofPhoto-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JNP.8.083088) of interest in PhC technology for sensing applications due to their compactness and tremendous sensing potential. Holes etched to form the PhC structure in a high dielectric material can be infiltrated with analytes, which change the refractive index (RI) of the holes and thus alter the optical properties of PhC structures. The method of sensing involves the change in the power output and the shifts in the wavelength. The PhCs with line defects formed by altering a row of holes can be designed to obtain highly sensitive photonic crystal waveguide (PhCW)-based RI sensors. 9 The development of a sensor design with high sensitivity is especially important because it enhances the ability of the device to detect low concentrations as well as small changes in the concentration of the analytes. 10 In this article, we proposed a PhCW structure based on ring-shaped holes optimized for RI sensing applications based on three-dimensional finite difference time domain (3-D FDTD) simulations. The device is considered in a silicon-on-insulator (SOI) substrate consisting of a triangular array of holes etched in its silicon device layer to form a PhC structure. The waveguide sensor is formed by replacing the central row of holes in the Γ-X direction and subsequently optimized by incorporating ring-shaped holes in the defect line in order to achieve the best possible improvement in the sensitivity.