Gimbal-less monolithic silicon actuators for tip-tilt-piston micromirror applications

In this paper, fully monolithic silicon,optical scanners are demonstrated with large static optical beam. deflection. The main advantage of the scanners is their high speed of operation for both axes: namely, the actuators allow static two-axis rotation in addition to pistoning of a micromirror without the need for gimbals or specialized isolation technologies. The basic device is actuated by four orthogonally arranged vertical comb-drive rotators etched in the device layer of an silicon-on-insulator wafer, which are coupled by mechanical linkages and mechanical rotation transformers to a central micromirror. The transformers allow larger static rotations of the micromirror from the comb-drive stroke limited rotation of the actuators, with a magnification of up to 3 x angle demonstrated. A variety of one-axis and two-axis devices have been successfully fabricated and tested, in all cases with 600-mum-diameter micromirrors. One-axis micromirrors achieve static optical beam deflections of > 20degrees and peak-to-peak resonant scanning of > 50degrees in one example at a resonant frequency of 4447 Hz. Many two-axis devices utilizing four rotators were tested, and exhibit > 18degrees of static optical deflection at < 150 V, while their lowest resonant frequencies are above 4.5 kHz for both axes. A device which utilizes only three bidirectional rotators for tip-tilt-piston actuation achieves - 10degrees to 10degrees of optical deflection in all axes, and exhibits minimum resonant frequencies of 4096 and 1890 Hz for rotation and pistoning, respectively. Finally, we discuss the preliminary results in scaling tip-tilt-piston devices down to 0.4 x 0.4 mm on a side for high fill-factor optical phased arrays. These array elements include bonded low-inertia micromirrors which fully cover the actuators to achieve high fill-factor.