Silicon nitride based mid-infrared microphotonics for sensor applications

Integrated mid-infrared waveguides and directional couplers are demonstrated on silicon nitride (SiN) thin films by low-pressure chemical vapor deposition. The prepared SiN film has a broad spectral transparency from visible up to mid-infrared (mid-IR). The SiN waveguide shows a dominant fundamental mode with an optical loss of 2.1 dB/cm at λ = 3.7 μm. In addition, we demonstrate an efficient SiN directional coupler with an 8 dB extinction ratio upon wavelength sweep between λ = 3.55 μm to λ = 3.75 μm. With the inherent advantage of complementary metal-oxide-semiconductor (CMOS) compatibility, our SiN platform paves the way to create sophisticated photonic circuits that are desired for chip-scale mid-IR biochemical sensors.