Design and Simulation Investigation of Si₃N₄ Photonics Circuits for Wideband On-Chip Optical Gas Sensing around 2 µm Optical Wavelength

We theoretically explore the potential of Si₃N₄ on SiO₂ waveguide platform toward a wideband spectroscopic detection around the optical wavelength of 2 μm. The design of Si₃N₄ on SiO₂ waveguide architectures consisting of a Si₃N₄ slot waveguide for a wideband on-chip spectroscopic sensing around 2 μm, and a Si₃N₄ multi-mode interferometer (MMI)-based coupler for light coupling from classical strip waveguide into the identified Si₃N₄ slot waveguides over a wide spectral range are investigated. We found that a Si₃N₄ on SiO₂ slot waveguide structure can be designed for using as optical interaction part over a spectral range of interest, and the MMI structure can be used to enable broadband optical coupling from a strip to the slot waveguide for wideband multi-gas on-chip spectroscopic sensing. Reasons for the operating spectral range of the system are discussed.