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Miniaturized optical module for projection of arbitrary images based on two-dimensional resonant micro scanning mirrors

: Scholles, M.; Bräuer, A.; Frommhagen, K.; Gerwig, C.; Höfer, B.; Jung, E.; Lakner, H.; Schenk, H.; Schneider, B.; Schreiber, P.; Wolter, A.


Sagan, S.F. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Optical scanning 2005 : 31 July - 1 August 2005, San Diego, California, USA
Bellingham/Wash.: SPIE, 2005 (SPIE Proceedings Series 5873)
ISBN: 0-8194-5878-3
Conference on Optical Scanning <2005, San Diego/Calif.>
Conference Paper
Fraunhofer IPMS ()
image projection; scanning-mirror; MEMS; resonant scanning; micro optic

This contribution presents an optical module for projection of still images and video sequences. It consists of a laser source, miniature collimator optics, and a special MEMS device, a two-dimensional resonant micro scanning mirror. The laser beam is focused onto the micro mirror by the collimator optics. The micro mirror reflects the beam onto the desired projection area with a flare angle of up to 15 degrees for both axes. Given the resonant oscillation of the mirror, the beam follows a Lissajous figure. By choosing appropriate oscillation frequencies, it can be ensured that the laser beam hits every pixel of a pre-defined geometrical image resolution at a given frame rate. Limitations result from mechanical stability of the mirror plate that has a typical diameter of 1 mm and the CMOS-compatible fabrication process of the MEMS device. Projection of images and video sequences is achieved by modulating the laser diode. An external electronics receives data and transforms it into necessary modulation signals. Since frequency and amplitude of oscillation of the micro mirror are highly precise, no electrical feedback from the mirror to the modulation electronics has to be implemented. The system can be operated in open-loop modus. Currently, a monochrome demonstrator with VGA (640 x 480 pixels) resolution and 50 frames per second has been realized. Because of the compact size of the mirror, integration into mobile devices is fairly easy.