Closed-loop synchronization scheme of resonant MOEMS-Mirrors with two axes A. Tortschanoff* a , A. Frank a , M. Lenzhofer a , M. Wildenhain b , T. Sandner b , A. Kenda a a Carinthian Tech Research AG, Villach, Austria; b Fraunhofer Institute for Photonic Microsystems, Dresden, Germany ABSTRACT We have developed compact devices comprising optical position sensing and driver electronics, with closed loop control, capable of driving resonant 1D- and 2D-MOEMS scanner mirrors. Position encoding is realized by measuring a laser beam reflected from the backside of the mirror. In the 2D-device we use cylindrical mirrors, in order to suppress the deflection of the orthogonal dimension. This reduces the problem to the control of two independent 1D-oscillations and allows accurate position sensing and closed loop control. In this device the phase between the oscillations of the two orthogonal axes is actively controlled to achieve a stable Lissajous figure. In this contribution we also demonstrate that this approach is scalable for synchronization of separate MEMS mirrors. Keywords: MOEMS, electrostatically driven scanners, synchronization, closed loop control 1. INTRODUCTION Resonantly driven oscillating MOEMS mirrors feature high mirror deflection angles at relatively low driving voltages and minimal energy consumption. Due to their small weight they are shock and vibration resistant and can provide scanning rates of up to 30 kHz. Finally the small device dimensions and possible low production costs are important features with regard to mass production. On the other hand, often there is no inherent position feedback of the movement of the mirror, which is crucial for most applications. For this reason, we have developed compact devices comprising optical position sensing and driver electronics, with closed loop control, capable of driving resonant 1D- and 2D- MOEMS scanner mirrors. Position encoding is realized by measuring 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. The approach is very flexible and especially applicable for high frequency devices, where synchronized excitation 1 is difficult. It was successfully implemented for 1D-device in the past 2,3 . For 2D MOEMS mirrors, we use cylindrical mirrors, in order to suppress the deflection of the orthogonal dimension. The backside of the mirror now 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 reduces the problem to the control of two independent 1D-oscillations and allows accurate position sensing and closed loop control. In this contribution we present in much detail the position encoding and feedback scheme of the novel 2D device, and in addition, demonstrate that this approach is scalable for synchronization of separate MEMS modules. 2. PRINCIPLE AND CONTROL SYSTEM 2.1 MEMS devices Micromechanical scanner mirrors are fabricated at the Fraunhofer IPMS using CMOS compatible technology 4 , 5 . Figure 1 shows a picture of the 2-dimensional Micro Scanning Mirror used in this work. Key feature of these Micro Scanning Mirrors is the patented electrostatic driving principle 6 . Electrodes are placed adjacent to the sides of the mirror. In this way the electrode gap is minimized, capacitance is high and driving voltage can be low. The trade-off is that only resonant oscillation is possible, but at high deflection angles. *andreas.tortschanoff@ctr.at; phone +43 4242 56300 250; fax +43 4242 56300 400