Singlemode tunable VCSELs with integrated MEMS technology

A simple MEMS technology for wafer-scale integration of tunable VCSELs is presented. The tunable VCSEL is composed of a "half-VCSEL", which is a VCSEL without top distributed Bragg reflector (DBR), and an external mirror, which is a micromachined membrane ("MEMS")The GaAs-based half-VCSEL comprises a bottom DBR, an active region with 5 quantum wells (QWs), and an oxide aperture for current confinement. The etched mesa is capped with an antireflection coating (AR-c) and embedded in a low-k dielectric (BCB). Reflown photo-resist droplets are used as sacrificial layer and as preform for making curved micro-mirrors, as shown in the paper. A dielectric DBR (7.5 pairs TiO₂/SiO₂) and an actuation layer (50 nm Ni) are deposited onto the half VCSEL, and then the MEMS structure is etched. Finally, the mirror membrane is released by dissolving the sacrificial layer in acetone and removing the liquid in a critical point dryer.