Refractive Index Sensing Using Silicon-on-Insulator Waveguide Based Directional Coupler

We propose a refractive index (RI) sensor based on a vertical directional coupling between two silicon-on-insulator (SOI) waveguides. It is shown that by optimizing the SOI waveguide parameters, high-bulk and adlayer sensitivities can be achieved. Using the optimized waveguide parameters for the aqueous cover, we report the bulk sensitivity ∼7000 (3400) nm/RIU for RI∼1.33, and the adlayer sensitivity ∼9 (5) nm/nm for an adsorbed bio layer of RI 1.45, for the transverse electric (TE) (transverse magnetic (TM)) mode propagation in the optical communication wavelength band. The proposed sensor has the potential for bio sensing applications due to high-bulk and adlayer sensitivities.