Room temperature sputtered silicon nitride microcombs and real-time Hz-level tunable laser spectroscopy

Reactively sputtered silicon nitride thin films offer the combination of ultralow optical losses, film thickness above >700nm in a single deposition step, and low processing temperature. Employing this process, we demonstrate microresonators exhibiting Q-factors of 1 million without thermal annealing and 10 million with 800°C thermal annealing in the L-band. Since the waveguides of the ring resonators exhibit anomalous dispersion soliton microcombs can be generated. We will also present a tunable laser spectroscopy scheme where a frequency modulated tunable diode laser is referenced to a fiber cavity. The fiber cavity free-spectral range is determined, in real time, to a sub 10-Hz level over a spectral range of 11 THz at a scanning speed of 1 THz/s. The scheme is applied onto dispersion measurements of integrated microresonators.