Method and apparatus for controllably modulating a laser in a laser projection display
View Patent ↗A laser projection device suitable for displaying full color images is disclosed. The LPD includes a variety of techniques for modulating laser beams produced by one or more lasers with image data to controllably produce the image using a modified raster scan.
1. An arrangement for projecting an image on a viewing screen, comprising:
a laser source including a laser for generating a laser beam having an output power, a main current source for supplying a main bias current to the laser, and another current source for supplying another bias current to the laser;
a feedback circuit including a photodiode for detecting the output power, and for generating and feeding a feedback signal to the main current source to control the main bias current;
a scanner for sweeping the laser beam to form a scan line having pixels arranged along one direction, and for sweeping the scan line along another direction orthogonal to the one direction to form a raster pattern of scan lines on the viewing screen; and
a controller including a modulator for converting input image data into output control signals and for controlling the other current source to modulate the other bias current, both bias currents being combined for modulating the laser beam to illuminate selected pixels on the scan lines to form the image on the viewing screen.
2. The arrangement of claim 1 , wherein the bias currents are added to constitute a drive current for the laser.
3. The arrangement of claim 1 , wherein the bias currents are subtracted to constitute a drive current for the laser.
4. The arrangement of claim 1 , wherein the laser source includes a single laser, and wherein the scanner includes a pair of scan mirrors oscillatable about respective axes extending along both of the directions.
5. The arrangement of claim 4 , wherein the laser emits the laser beam having a green color.
6. The arrangement of claim 1 , wherein the laser source includes a plurality of lasers for emitting respective laser beams, and wherein the controller modulates the laser beam of one of the lasers.
7. A method of projecting an image on a viewing screen, comprising the steps of:
generating a laser beam having an output power by driving a laser, supplying a main bias current to the laser with a main current source, and supplying another bias current to the laser with another current source;
detecting the output power, and generating and feeding a feedback signal to the main current source to control the main bias current;
sweeping the laser beam to form a scan line having pixels arranged along one direction, and sweeping the scan line along another direction orthogonal to the one direction to form a raster pattern of scan lines on the viewing screen; and
converting input image data into output control signals and controlling the other current source with a modulator to modulate the other bias current, both bias currents being combined for modulating the laser beam to illuminate selected pixels on the scan lines to form the image on the viewing screen.
8. The method of claim 7 , and adding the bias currents to constitute a drive current for the laser.
9. The method of claim 7 , and subtracting the bias currents to constitute a drive current for the laser.
10. The method of claim 7 , and oscillating a pair of scan mirrors about respective axes extending along both of the directions.
11. The method of claim 7 , and configuring the laser to emit the laser beam with a green color.
12. The method of claim 7 , and emitting a plurality of laser beams, and wherein the modulating step is performed by modulating one of the laser beams.