Waveguide-coupled, broadband thermal emission enabled by a bulk-micromachined trench undercut

Waveguide-based broadband light sources in photonic integrated circuits are useful for applications ranging from device characterization to chemical sensing to absorption spectroscopy. This work demonstrates a waveguide-coupled optical source capable of broadband light emission and waveguide propagation from visible-to-infrared wavelengths. A foundryprocessed SiN/SiO₂ nanophotonic waveguide has two doped-Si microheater strip lines placed on either side of it. A bulk-micromachining trench undercut etch is performed in which the silicon substrate is isotropically-etched to suspend the Si/SiN/SiO₂ structure enabling exceptional thermal isolation. A bias is applied to both doped-Si microheaters resulting in efficient Joule heating, and the resulting hot lattice thermal emission couples to and propagates down the SiN waveguide. Measurements show a broadband spectrum ranging from 875-1680 nm (limited by our instrumentation) consistent with a blackbody emission. This broadband thermal source has the potential for high efficiency via subsequent waveguide optimization.