MEMS tuning mechanism for eliminating mode hopping problem in external-cavity lasers

This paper presents a tuning mechanism to provide an adjustable virtual pivot for MEMS tunable lasers, which eliminates the mode hopping problem associated with conventional Littrow lasers. The key idea is to attach the two ends of the blazed grating to two separate translational actuators. The relative displacements of the actuators can be used to translate and/or rotate the blazed grating in a controllable manner. As a result, the wavelength can be continuously tuned ideally over an unlimited range through a simultaneous sweep of the grating angle and cavity length. In the experiments, a MEMS Littrow laser is fabricated by the DRIE process on the SOI wafer and is integrated onto a single chip with the size of 3 mm times 3 mm. It achieves a wide tuning range of 53.2 nm thanks to the introduction of the new tuning mechanism and a 3D optical coupling system.