Patent ID: 7422335

Claim:
A variable-shape mirror comprising: a support base; a mirror portion having a lower surface thereof that is disposed to face the support base and having a mirror surface on a side thereof opposite to the lower surface; a plurality of piezoelectric elements that are sandwiched between an upper surface of the support base and the mirror portion, that have one ends thereof in a direction of expansion and contraction making direct contact with the mirror portion and other ends thereof in the direction of expansion and contraction making direct contact with the upper surface of the support base, and that vary a shape of the mirror surface by expanding and contracting in a direction normal to the upper surface of the support base; a plurality of fixed portions provided in an equal number as the plurality of piezoelectric elements, each of which making a pair with each of the plurality of piezoelectric elements, sandwiched between the support base and the mirror portion, and disposed closer to an outer edge of the mirror portion than is said each of the plurality of piezoelectric elements, wherein the mirror portion is disconnected from the plurality of piezoelectric elements and bonded only to the plurality of fixed portions, wherein a shape of the mirror portion in cross section before being disposed in the variable-shape mirror and lengths of the plurality of fixed portions and of the plurality of piezoelectric elements as measured from the upper surface of the support base to the lower surface of the mirror portion when the plurality of piezoelectric elements are not driven, are so structured and adjusted that the mirror portion is subjected to a force derived from a counterforce thereof so as to act upon the plurality of piezoelectric elements in a direction of contraction when the plurality of piezoelectric elements are not driven, wherein the shape of the mirror portion in cross section before being disposed in the variable-shape mirror is so structured to be identical with a shape of the mirror portion in cross section when the plurality of piezoelectric elements are all driven and fully contracted, and the shape of the mirror portion in cross section is so structured to become convex on a side of the mirror surface and concave on a side of the lower surface when the plurality of piezoelectric elements are all driven and fully expanded.