Design and development of miniature paraboloidal mirrors that would be deflected magnetically to vary their radii of curvature (and thus their focal lengths) are under study. These mirrors, which belong to the class of microelectromechanical systems (MEMS), are used for compact, robust, focusing optics instruments and imaging systems, and are intended to supplant conventional adjustable optical components (including lenses, curved mirrors, and hinged flat mirrors) for reducing the bulkiness of the associated focusing and zooming mechanisms. The suggested device (see figure) would include a thin paraboloidal diaphragm mounted at a short axial distance from a planar coil; the concave side of the diaphragm would serve as the mirror, and the convex side of the diaphragm would face the planar (concentric) coil and would be coated with a thin layer of magnetic material. Electron-beam binary-optics and low-pressure chemical vapor deposition (LPCVD) processes are used to form the paraboloidal concave surface, and the radio-frequency sputtering process is used to form the thin magnetic layer. At the same time, electroplating is used for the fabrication of the planar coil on silicon wafer. The two wafers would then be bonded together to form the mirror-and-actuator unit.
This approach to miniaturization offers several potential advantages in that the magnetic actuation forms the integral part of the optical sensing mechanism (including beam focusing and steering), thus reducing the overall size of the mirror. Also, the actuation sensitivity would be higher due to the high coefficient of elasticity of the magnetic layer; thus deflections attainable by the proposed approach would be higher than those attainable with electrostatic or piezoelectric actuations.
This work was done by Mary Boghosian and William Tang of Caltech for NASA's Jet Propulsion Laboratory.