INTEGRATED OPTICS

Lithographically produced micromirror module uses electrostatic charge to modulate the phase of an incident wavefront by translating the mirror (left) along the vertical axis. When integrated with foreoptics consisting of a diffractive microlens array to concentrate incident light onto the individual mirrors, the micromirror array can act as an adaptive optics system for real-time correction of industrial lasers or as an optically driven spatial light modulator. Each 20-µm2 micromirror of th

INTEGRATED OPTICS

Micromirrors make adaptive optics that could fit on the head of a pin

Kristin Lewotsky

Lithographically produced micromirror module uses electrostatic charge to modulate the phase of an incident wavefront by translating the mirror (left) along the vertical axis. When integrated with foreoptics consisting of a diffractive microlens array to concentrate incident light onto the individual mirrors, the micromirror array can act as an adaptive optics system for real-time correction of industrial lasers or as an optically driven spatial light modulator. Each 20-µm2 micromirror of the 8 ¥ 8 array is mounted on an octagonal pad suspended over a 20-µm-dee¥channel by support members that double as springs. Electrostatic capacitance between the mirror mount and the substrate below causes the mirror to deflect downward by as much as 2 µm; other designs offer deflections as high as 20 µm and significantly larger array sizes.

The micromirrors are on 300-µm centers; the addition of the diffractive microlens array yields an effective fill factor of 100%. In adaptive optics applications, the p-n junction photodiode acts as an interferometric wavefront sensor. For spatial-light-modulator applications, the photodiode receives the optical control signals to vertically reposition the mirror, introducing a wavefront phase shift.

SY Technology Inc. (Huntsville, AL) leads the micromirror development project, which is funded by the US Air Force Phillips Laboratory (Albuquerque, NM). The array shown here was designed by an SY team and produced on a standard CMOS fabrication line at Orbit Semi conductor (Santa Clara, CA); engineers at the Nanotech nology Laboratory (University of California, Los Angeles) performed additional etching procedures. SY Technology is developing other prototype micro-mechanical adaptive optics systems in collaboration with Boston University (Boston, MA), the California Institute of Technology Jet Propulsion Laboratory (Pasadena, CA), and Adaptive Optics Associates (Cambridge, MA). Approaches include a continuous membrane design for high-power systems, a small diaphragm array design, and a segmented mirror design to correct complex atmospheric distortions.

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