CW Operation of a Tunable 1550-nm VCSEL Integrating Liquid-Crystal Microcells

An InP-based Vertical-Cavity Surface-Emitting Laser (VCSEL) with a liquid crystal (LC) microcell monolithically integrated on its surface for spectral tuning is investigated. Unlike tunable VCSELs integrating a movable membrane, here the physical length of the cavity remains unchanged and only the voltage applied on the LC ensures a refractive index modification for a particular polarization emitted by the VCSEL. This tunable VCSEL operates in CW at room temperature and exhibits more than 23 nm wavelength tuning around $1.55~\mu \text{m}$ at a maximum applied voltage of 20 V. The measured laser threshold around 6.5 mW is still comparable to VCSEL without LC microcell, a clear indication that the optical losses related the LC are very low. On the other hand, for this first optically pumped device, the lasing characteristics suggest that the LC birefringence is lower than expected. To assess this hypothesis, thermo-optical simulations have been conducted.