1.2 - Position Encoding and Phase Control of Resonant 2D-MOEMS-Mirrors

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings OPTO 2011
O1 - Components for Sensing and Detection
A. Tortschanoff, A. Frank, M. Lenzhofer, A. Kenda - Carinthian Tech Research AG, Villach (Austria), M. Wildenhain, T. Sandner - Fraunhofer Institute for Photonic Microsysytems, Dresden (Germany)
22 - 26


Resonant micromechanical scanner mirrors can be fabricated using CMOS compatible technology. They are driven electrostatically with a pulsed driving voltage close to the double of their eigenfrequency and are of high interest for various fields in optics, telecommunications and spectroscopy.

Position encoding of the mirror movement is crucial for most applications. Furthermore for stable oscillation with large amplitude, operation close to resonance must be ensured under varying environmental conditions. For this reason, we have developed a compact device comprising optical position sensing, and driver electronics, with closed loop control, capable of driving resonant 1D- and 2D MOEMS scanner mirrors. Measurement of the mirror motion is is realized with a laser beam reflected from the backside of the mirror. The angular position of the mirror is encoded by an optical trigger signal combined with a harmonic extrapolation function. This approach was successfully implemented for the case of 1D scanner mirrors a while ago and phase stabilization with a precision of <10 ns was demonstrated.

Extending this approach to 2D MOEMS devices adds significant complexity. Cylindrical mirrors are used, in order to suppress the deflection of the orthogonal dimension. In our device the backside of the mirror is hit by two crossed orthogonal laser beams, whose reflections pass a cylindrical mirror before being sent onto the photo-diodes for the timing signals. This rather complex geometry reduces the measurement problem to the control of two independent 1D-oscillations and allows accurate position sensing and closed loop control. Also, for the projection of a stable Lissajou pattern, the phase between the oscillations of the two orthogonal axes must be controlled with high accuracy. Details and charateristics of this key feature of our 2D-device will be presented. Preliminary experiments indicate the abilities of this device and first results will be presented at the conference.