Figure 1.

Schematic sketches of a membrane based focusing device. (a) The device consists of two chips bonded together: the silicon on insulator (SOI) chip containing the mirror membrane suspended with special formed beams at the rigid rim of the chip. The fused silica chip contains the counter electrode within a cavity etched into the fused silica; (b) cross section (not in scale): the membrane chip is bonded upside down to the fused silica chip. By using ring-shaped counter electrodes, the electrostatic force is acting on the outer perimeter of the membrane; (c) parallel incoming light is reflected back to a focal point defined by the parabolic amplitude, w_o, of the electrostatically deformed membrane. In principle, an aluminum coating can be used to enhance reflectivity of the membrane surface [12,14].