Monolithic Piezoelectrically-Actuated MEMS-Tunable VCSEL

Various structures of MEMS tunable VCSEL have been reported. MEMS tunable structures are desirable because they provide a large tuning range and are compatible with current optoelectronic fabrication processes. Several micromechanical tuning elements have been investigated using either electrostatic or thermal actuation mechanisms. Major drawbacks of the capacitive actuation are the large tuning voltages that are needed and the actual allowed movement, which must be less than 1/3 of the gap size. Thermal actuation is another actuation mechanism that provides large displacements for relatively small applied voltages. Such a solution suffers from low actuation speed (thermal transients are generally longer than mechanicals), power constraints, and complications in the fabrication process.

In this report, a novel actuation mechanism utilizing the inherent piezoelectric properties of the AlxGa1-xAs compounds is presented for short-wavelength MEMS tunable VCSEL. Piezoelectric actuation can provide large displacements in bi-directions and linear tuning characteristics with respect to the applied voltage, does not suffer from travel limitations and catastrophic damages, consumes very low power (~1μW), and has a fast response speed. In addition, piezoelectric actuation based on AlxGa1-xAs films offers several benefits, including a large piezoelectric coupling coefficient comparable with that of zinc oxide and the ability to be integrated with high-speed electronic and optoelectronic devices. Furthermore, this novel actuation mechanism allows for improved wavelength control, reduces external and tilt losses and can be easily scaled to long-wavelength VCSEL.