Optimisation of a plasmonic parallel waveguide sensor based on amorphous silicon compounds

This work reports the optimisation of a plasmonic waveguide sensor based on amorphous silicon compounds (a-SiC:H, a-SiN:H or a-SiCN:H) using the FDTD method and modal decomposition. The sensor consists of an array of parallel surface plasmon interferometers with different propagation lengths, each one comprising a thin layer of metal embedded into an amorphous silicon waveguide. In order to reduce the complexity and hardware, we have proposed a structure consisting of an array of parallel surface plasmon interferometers with different propagation lengths, such that at the end of the plasmonic structure the modes can interfere constructively or destructively depending on the refractive index of the sampling medium and the propagation length. The variation of the output intensity at the end of each waveguide element provides a convenient interrogation scheme. In this work we analyse different solutions for splitting the input fundamental mode into the different parallel waveguides, including multi-mode interference structures and directional coupler splitters. By exploring amorphous silicon compounds that can be deposited by Pressure Enhanced Chemical Vapor Deposition (PECVD) at low temperatures, we aim to achieve a low-cost process that is compatible with back-end CMOS processing and wavelengths in the visible to near infrared range.