Planar silicon nitride mid-infrared devices

Integrated mid-infrared devices including (i) straight/bent waveguides and (ii) directional couplers are demonstrated on silicon nitride (SiN) thin films prepared by optimized low-pressure chemical vapor deposition. The deposited SiN film has a broad spectral transparency from visible up to a wavelength of lambda = 8.5 mu m (as seen from Fourier transform infrared spectroscopy). Our SiN waveguide shows a dominant fundamental mode with an optical loss of 2.1 dB/cm at lambda = 3.7 mu m. In addition, we demonstrate an efficient SiN directional coupler between lambda = 3.55 mu m to lambda = 3.75 mu m where an 8 dB extinction ratio is achieved within each channel upon wavelength scanning. With the inherent advantage of complementary metal-oxide-semiconductor compatibility, our SiN platform paves the way to create sophisticated photonic circuits that are desired for mid-infrared nonlinear light generation and chip-scale biochemical sensors. (C) 2013 AIP Publishing LLC.