Thin silicon waveguides for biological and chemical sensing

We show that thin silicon-on-insulator (SOI) microphotonic waveguides offer significant advantages over other material platforms for the applications of biological and chemical sensing. The high index contrast inherent to SOI waveguides allow an extremely large yet highly localized electric field to be supported in the evanescent tail of the waveguide mode, ideal for the probing of thin biological layers. Various sensing geometries including Mach-Zehnder interferometers and high quality factor ring resonators have been designed and fabricated and their performance is presented. SOI sensors are shown to be capable of providing higher intrinsic sensitivity over comparable sensor designs reported in all other lower index contrast planar waveguide material systems. Finally, the device design conditions for optimized sensitivity are examined for the sensing of both bulk solutions and thin adsorbed biomolecular layers.