Acoustic energy driven focus-tunable liquid microlens array for Shack-Hartmann wavefront sensor application

This paper presents an innovative simple-structured tunable-focus Shack-Hartmann wavefront sensor. The device of tuning the focal length of liquid micro-lens array by acoustic energy is designed, fabricated, and tested. By vibrating the cylindrical device with a rigid sidewall and a flexible bottom plate, a pumping effect to cause the convex profile of liquid surface and stay the curvature is theoretically described and verified by the experiment, when the device is resonant at an appropriate frequency. We implement the device with the structure of a PDMS made membrane as the bottom flexible plate, a lead zirconium titanium ring transducer as the cylindrical sidewall, and a micromachined SU-8 plate as the top cover. DI water is filled inside the device as the lens material. The fabrication process of PDMS membrane and an array of micro-hole on the SU-8 plate is described. The fabricated device is tested with a collimated laser light setup. Results shows that focused spots arrays at different focal distances are clearly obtained on a CCD camera while tuning the sinusoidal voltage amplitude at a fixed frequency.