Silicon Nitride based Biosensor using Array of Coupled multi slot Waveguide structure

This paper investigates a study concerning the multi-mode multi-slot interference waveguide (MMSI) based on silicon nitride intended for optical biosensor applications for virus detection and compact optical sensing in both the visible and infrared regions. The proposed design consists of five parallel closed slot waveguides exited by launching the fundamental TE mode through the central slot waveguide. The configuration enables strong coupling between the adjacent waveguides and enhances light–analyte interaction. An analytical expression for the self-imaging position is derived using both MMI and coupled-mode theory, and the results are validated using commercial simulation software based on the finite-difference time-domain (FDTD) method. By tuning the geometry, we demonstrate enhanced optical confinement in the slot region, which improves the light-analyte interaction. The structure achieves a maximum sensitivity of 1722 nm/RIU in one of the ports in the visible region and 1898 nm/RIU in one of the ports in the infrared, with a compact device footprint of 170 µm. Compared to previous slot or MMI-based sensors, our design has improved sensitivity, dual-band operation, and CMOS-compatible integration on the SiNOI platform, which makes it a promising candidate for label-free biochemical sensing applications.