Refractive index sensing using silicon-on-insulator waveguide based modal interferometer

Abstract

We propose a refractive index sensor based on modal interference between the first two TE modes in a silicon-on-insulator dual-mode waveguide. It is shown that by appropriately choosing the waveguide dimensions one can achieve a large variation of the modal effective index difference with the ambient refractive index (ARI) as well as a smaller group effective index difference between the two modes, resulting in an extremely high RI sensitivity in the wavelength interrogation scheme. The RI sensitivity of the proposed sensor is found to be ∼ 9100 nm/RIU for the ARI∼1.33, which is the highest reported RI sensitivity achieved in the integrated optic modal interferometers till date. The figure of merit is also found to be extremely high and is more than 2800.