Development of Deformable Mirror Composed of Piezoelectric Thin Films for Adaptive Optics

Abstract

In this paper, we report a piezoelectric deformable mirror composed of piezoelectric thin films for low-voltage adaptive optics (AO). A 2-$\mu$m-thick piezoelectric Pb(Zr,Ti)O$_{3}$ (PZT) film was deposited on a Pt-coated silicon-on-insulator (SOI) substrate, and a diaphragm structure of 15 mm in diameter was fabricated by etching a Si handle wafer. A 19-element unimorph actuator array was produced on the PZT films with an Al reflective layer over the backside of the diaphragm. Measurements of the displacement profile using a laser Doppler vibrometer demonstrated that a large displacement of approximately 1 $\mu$m was obtained by applying a voltage of 10 V$_{\rm pp}$ on one actuator. To examine the application feasibility of the deformable mirror to AO, we reproduced low-order Zernike modes by calculating the voltage on each individual electrode using an influence function matrix. The measurements demonstrated that the deformable mirror could produce the Zernike modes up to the seventh term. Considering the low-voltage actuation as well as the capability for miniaturization of the electrode size, deformable mirrors (DMs) actuated by PZT films are desirable for low-cost AO.