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Laser display with single-mirror MEMS scanner

: Schreiber, P.; Höfer, B.; Bräuer, A.; Scholles, M.


Journal of the Society for Information Display 17 (2009), No.7, pp.591-595
ISSN: 1071-0922
Journal Article
Fraunhofer IOF ()
projection displays; scanning; MEMS17

While arrayed DMD and LCD microdisplays are well-established approaches for visualization tasks, image-forming laser scanners are an emerging technology used to build miniaturized projection displays. A directly modulated RGB-laser module consisting of diode lasers for red and blue and a frequency-doubled semiconductor laser for green with color combining optics form the light source for the laser scanner have been developed. Subsequent beam-shaping optics suppresses unwanted stray light and enables optimum illumination of the scanning mirror. The MEMS device features a single scanning mirror oscillating in two directions in resonant mode. This requires appropriate data delivery realized by a custom-made driving logic, which converts the pixel stream originally arranged in rows and columns to the Lissajous-like spot trajectory on the screen. Additionally, the increased image brightness at the vertical and horizontal borders of the field of view (FOV) is also compensated by the modulation of laser power. Theoretical investigations of the resulting maximum achievable system transmission are presented. Different systems, such as an extremely miniaturized monochrome projection head with an integrated diode laser and a full-color projector have been realized. Important problems to be tackled are fast analog modulation of the laser power with high resolution and improved suppression of stray light and speckle.