Low-cost projection device with a 2D resonant microscanning mirror
This paper presents a demonstrator of a low cost image projection device that has been developed at the Fraunhofer Institute of Photonic Microsystems. The image projection is not based on the common line by line raster scanning of the image. Instead, a resonant 2-dimensional micro scanning mirror is used for the deflection of a modulated laser beam. The mirror is operated at a low ratio of horizontal and vertical oscillation frequency. In particular, a ratio with a small shift from an integer value is used to enable a scan of the whole projection screen with a Lissajous pattern. The control circuit performs an excitation of both mirror axes by driving them with fixed frequency according to the response curves of the actuator. Programmable counters are used to generate the driving frequencies and to determine the actual beam position during the scanning process. That enables a very simple and low cost control circuit. A micro scanning mirror, fabricated at Fraunhofer IPMS, was used in the demonstrator set up. It is operated at oscillation frequencies of 1.4 kHz (slow axis) and 9.4 kHz (fast axis). The control circuit was realized and successfully tested with a FPGA implementation. The image resolution provided by the control circuit is 256 x 256 pixels.