Si3N4 grown by low pressure chemical vapor deposition (LPCVD) on thermally oxidized silicon wafers is largely utilized for creating integrated photonic devices due to its ultra-low propagation loss and large transparency window (400 nm to 2350 nm). In this paper, an ultra-low-loss and broadband mode converter for monolithic integration of different materials onto the passive Si3N4 photonic technology platform is presented. The mode size converter is constructed with a vertically tapered Si3N4 waveguide that is then buried by a polymer or an Al2O3 waveguide. The influence of the various design parameters on the converter characteristics are investigated. Optimal designs are proposed, in which the thickness of the Si3N4 waveguide is tapered from 200 nm to ~40 nm. The calculated losses of the mode converters at 976 nm and 1550 nm wavelengths are well below 0.1 dB for the Si3N4-polymer coupler and below 0.3 dB for the Si3N4-Al2O3 coupler. The preliminary experimental results show good agreement with the design values, indicating that the mode converters can be utilized for the low-loss integration of different materials.
Jinfeng Mu, Meindert Dijkstra, Michiel de Goede, Yean-Sheng Yong, and Sonia M. García-Blanco, "Ultra-low-loss and broadband mode converters in Si3N4 technology," Proc. SPIE 10106, Integrated Optics: Devices, Materials, and Technologies XXI, 101060R (Presented at SPIE OPTO: January 31, 2017; Published: 16 February 2017); https://doi.org/10.1117/12.2252706.
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