Current-controlled curvature of coated micromirrors

Precise control of micromirror curvature is critical in many optical microsystems. Micromirrors with current-controlled curvature are demonstrated. The working principle is that resistive heating changes the temperature of the micromirrors and thermal expansion induces a controlled curvature whose magnitude is determined by coating design. For example, for wide focal-length tuning, the radius of curvature of a gold-coated mirror was tuned from 2.5 to 8.2 mm over a current-induced temperature range from 22 degrees to 72 degrees C. For fine focal-length tuning, the radius of curvature of a dielectric-coated (SiO2/Y2O3 lambda/4 pairs) mirror was tuned from -0.68 to -0.64 mm over a current-induced temperature range from 22 to 84 degrees C. These results should be readily extendable to mirror flattening or real-time adaptive shape control.