Fabrication and characterization of silicon nitride waveguides for mid-infrared applications

This work describes the fabrication and characterization of silicon nitride waveguides for operation in the 2 mu m to 3 mu m range. Fabrication was carried out via PECVD and lithography techniques. Transmission losses were measured, with a tunable laser, to be similar to 20 dB between 2.0 mu m and 2.3 mu m, increasing to mu 30 dB between 2.3 mu m and 2.6 mu m. Beyond 2.8 mu m no transmission was detected, possibly due to the presence of hydrogen in the silicon nitride material (leading to absorption). Losses in the 2.0 mu m to 2.6 mu m range are believed to be a consequence of scattering, as the waveguides presented an RMS roughness of similar to 5 nm. Future work will focus on reducing these sources of absorption and scattering so that operation can be extended to the 4 mu m range.