SiN strip waveguide design for sensing applications

Abstract

In this work, a highly sensitive sensor made of SiN is proposed that can be used in gas or biological sensing, where the choice depends on whether a marker is used or not. The whole sensor is subjected to water cladding. The proposed device is based on a Mach-Zehnder Interferometer (MZI), while the sensing arm is used for sensing the change in the refractive index of the analyte. Both polarizations (TE, TM) are considered in this study, where a higher sensitivity is achieved for the TE-polarized light. The field confinement in the strip waveguide in the sensing region is investigated and verified with a mode solver, whereas the optimum dimensions are obtained using finite difference eigenmode and finite difference time domain solvers. With a sensing arm length of only 180 μm, the proposed sensor achieves a device sensitivity of about 1942 nm/RIU and a figure-of-merit (FOM) as high as 2284 RIU −1 at the wavelength of 1.55 μm. Higher values of FOM can even be attained by employing a longer sensing arm.