Wavelength tunable MEMS VCSELs

MEMS VCSELs are one of the most promising swept source (SS) lasers for optical coherence tomography (OCT) and one of the best candidates for future integration with endoscopes, surgical probes and achieving an integrated OCT system. However, the current MEMS-based SS are solely based on the III-V material system, which
is expensive and challenging to work with. Furthermore, the actuating part, i.e., MEMS, is on the top of the structure which brings a strong dependence on packaging to reduce its sensitivity to the operating environment. This thesis addresses these design drawbacks and proposes a novel design framework. The proposed device
uses a high contrast grating mirror on a MEMS stage as the boom mirror, all of which defined in an SOI wafer. The SOI wafer is then bonded to an InP III-V wafer with the desired active layers, thereby sealing the MEMS. Finally, the top mirror, a dielectric DBR (7 pairs of TiO2 -SiO2), is deposited on top. A systematic study
on the integration of InP to Si using a low-temperature bonding process with Al2O3 as the intermediate layer is presented. The proposed device is based on a silicon substrate with MEMS defined on a silicon membrane in an enclosed cavity. Thus the device is much more robust than the existing MEMS VCSELs. This design also enables either a two-way actuation on the MEMS or a smaller optical cavity (pull-away design), i.e. wider FSR (Free Spectral Range) to increase the wavelength sweep. Fabrication of the proposed device is outlined and the results of device characterization are reported.