Optical phase modulation using a refractive lenslet array and microelectromechanical deformable mirror

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Microelectromechanical deformable mirrors (MEM-DMs) are attractive for optical phase modulation applications primarily because of their inherently low cost and low drive voltages. Two problems limiting widespread use of segmented piston MEM-DMs are low optical efficiency (fill factor) and undesired amplitude modulation resulting from interference with the static background structure. Using a lenslet array to focus the incident light onto only the reflective surface of the MEM-DM greatly improves the effective fill factor with a corresponding decrease in interference effects. A refractive lenslet array is used with a very low fill factor MEM-DM (∼7%) to comprise a correcting element that behaves like a 70 to 80% fill factor device. The MEM-DM has 128 active piston micromirror elements. Experiments employing the hybrid correcting element demonstrate single beam steering, dual beam steering, and optical aberration correction. A comprehensive model of the lenslet/MEM-DM geometry is developed. Measured data shows good agreement with model predictions. A thermal circuit model is developed to estimate optical power handling capability of the MEM-DM. A conservative estimate of maximum optical power for this particular MEM-DM is 4 W/element when operated in a helium ambient, suggesting that relatively high power laser control applications are feasible. © 1998 Society of Photo-Optical Instrumentation Engineers.

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Optical Engineering