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Development and characterisation of a miniaturized laser projection display based on MEMS-scanning-mirrors

: Heger, A.; Schreiber, P.; Höfer, B.


Thienpont, H. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Micro-Optics 2010 : 12.-16.4.2010, Brussels, Belgium
Bellingham, WA: SPIE, 2010 (Proceedings of SPIE 7716)
ISBN: 978-0-8194-8189-4
Paper 771619
Conferecne "Micro-Optics" <2010, Brussels>
Fraunhofer IOF ()
MEMS; scanner; laser; speckle; projection; PSF

Biaxial scanning single MEMS-mirrors are a promising approach to build strongly miniaturized laser projectors. This technology enables projection engines with a total height of about 5 mm and integration into slim mobile devices. Further advantages are high overall wall-plug efficiency and high display resolution. Important parameters which determine the optical performance of a laser projection device will be discussed. We studied the influence of mirror flatness errors, occurring during mirror motion, on the point spread function (PSF) and compare the results with optical and mechanical simulations. Based on the analysis of optical design limitations we explain capabilities to optimise the optical performance of such projection devices. Speckle pattern in the projected image are a problem that degrades the picture quality when using laser illumination sources. While speckle suppression is successfully integrated in laser illuminated imagers (like DMD or LCoS), it is still a serious problem for scanning beam applications. We present speckle reduction techniques for a miniaturized projection system and evaluate consequences on the optical performance. We developed a RGB-laser projection module with a total size of 60 × 36 × 10 mm3. It enables VGA resolution with luminous flux of about 10 lumens. All three lasers are coupled into separate multimode fibres. The light that leaves the three fibres is jointly collimated with an achromatic lens and combined with a dispersion prism to illuminate the MEMS-mirror.