Large Stroke Actuators for Adaptive Optics

In this paper we review the use of a 3- dimensional MEMS fabrication process to prototype long stroke (>10 mum) actuators as are required for use in future adaptive optics systems in astronomy and vision science. The electrochemical fabrication (EFABtrade) process that was used creates metal micro- structures by electroplating multiple, independently patterned layers. The process has the design freedom of rapid prototyping where multiple patterned layers are stacked to build structures with virtually any desired geometry, but in contrast has much greater precision, the capability for batch fabrication and provides parts in engineering materials such as nickel. The design freedom enabled by this process has been used to make both parallel plate and comb drive actuator deformable mirror designs that can have large vertical heights of up to 1 mm. As the thickness of the sacrificial layers used to release the actuator is specified by the designer, rather than by constraints of the fabrication process, the design of large- stroke actuators is straightforward and does not require any new process development. Since the number of material layers in the EFABtrade process is also specified by the designer it has been possible to gang multiple parallel plate actuators together to decrease the voltage required for long-stroke actuators.