Range Extension of a Bimorph Varifocal Micromirror Through Actuation by a Peltier Element

A bimorph varifocal micromirror actuated thermoelectrically by a Peltier element is reported. The single-crystal silicon micromirror is 1.2 mm in diameter with a centered 1-mm-diameter gold coating for broadband reflection. The actuation principle is capable of varying the micromirror temperature above and below the ambient temperature, which contributed to a 57% improvement in the addressable curvature range in comparison to previously reported electrothermal and optothermal actuation techniques for the device. Altering the device temperature from 10 °C to 100 °C provided a mirror surface radius of curvature variation from 19.2 to 30.9 mm, respectively. The experimental characterization of the micromirror was used as a basis for accurate finite-element modeling of the device and its actuation. Negligible optical aberrations are observed over the operating range, enabling effectively aberration-free imaging. Demonstration in an optical imaging system illustrated sharp imaging of objects over a focal plane variation of 212 mm.