Study On Large Screen Scanning Laser Display

Compared to other illumination light sources, laser possess several unequaled qualities in its well-orientation, self-colored and high luminance. So laser display can produce much more richful colors, achieve higher pixel resolution and higher image luminance.This paper mainly study on a kind of large screen scanning laser display system which use three solid-state lasers as illumination light sources, the wavelength of the three lasers is 473nm, 532nm, 671nm respectively. The three collimated and focused laser beams are modulated by RGB video signals through three acousto-optic modulators separately. The recombined beams are scanned by a 36- face polygonal mirror rotated at 40000rpm to accomplish horizontal lines and then by a galvanometer controlled by DSP to accomplish vertical lines. The main works in this paper are:1. The parameters in the laser display system are designed and calculated in detail, such as rotating speed and number of faces of the polygon mirror, the optical scanning angle and the frequency of galvanometer. The incident angle of the recombined laser beams and the position between polygon mirror and galvanometer to reduce deformation resulted by scanning display are studied2. The control unit is designed according to the peculiarity of polygon mirror. The analogue video signals are stored in buffer after being transformed from Analog to Digital. The avalanche diode detection system for monitoring the rotary polygon mirror is adopted to use as read clock of the pixels by frequency multipliedtechnology. The horizontal line's counter is also activated by this signal to control galvanometer up and down. This method can insure the horizontal scanning start point in the same position and eliminate the angle division error of the polygon mirror.3. Because of the wavelengths of the RGB tricolor in NTSC or PAL monitor display format is different from that of the laser display format. So the tristimulus values in NTSC format or PAL monitor display format must be transformed to laser format. The transform model and the accomplished method are proposed and discussed in this paper.4. High-speed and broadband acousto-optic modulator (AOM) is widely used in laser display as a light intensity modulator to control the gray scale of pixels. Because the nonlinear of the diffraction efficiency of AOM may lead to tonal distortion, real-time calibration must be put in practice. The nonlinearity modulation characteristic of AOM has been tested and analyzed .An inquiry table established by 6th degree polynomial curve-fitting and interpolation is realized by a real-time inquiry circuit for nonlinear calibration. Laser display experiments have proved its correctness and feasibility.