Mid-infrared Vernier racetrack resonator tunable filter implemented on a germanium on SOI waveguide platform [Invited]

Currently, most widely tunable lasers rely on an external diffraction grating to tune the laser wavelength. In this paper we present the realization of a chip-scale Vernier tunable racetrack resonator filter on the Ge-on-SOI waveguide platform that allows for wide tuning (108 nm free spectral range) in the 5 mu m wavelength range without any moving parts. The fabricated racetrack resonators have a loaded Q-factor of 20000, resulting in a side-peak suppression of more than 20 dB, which is more than sufficient for wavelength selection in an external cavity laser. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement