Low-stress silicon nitride platform for broadband mid-infrared microphotonics

We experimentally demonstrate a sophisticated mid-IR microphotonics platform adopting engineered Si-rich and low-stress silicon nitride (SiNx) thin films where an extensive infrared transparency up to λ = 8.5 µm is achieved. Furthermore, because of the designed low-stress property, the SiNx deposition is able to reach a thickness > 2 µm that significantly reduces mid-IR waveguide loss to less than 0.2 dB/cm. We show directional couplers functioning over a broad infrared spectrum, thus enabling monolithic mid-IR multiplexing schemes for integrated linear and nonlinear photonics leading to sophisticated label-free sensing technologies.