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High-Efficiency Green Lasers for Microprojectors


The multimedia functionality of small battery-operated mobile devices, such as handsets, is strongly limited by their display sizes. Embedded microprojectors will empower such devices with image sizes larger than that of a typical laptop display. The most efficient projectors scan laser beams with the three fundamental colors, red, green, and blue, rapidly across the projection screen in a similar fashion to the electron beams in a TV tube. The use of laser beams without image-creating light modulators gives these projectors the advantage of high efficiency, near unlimited depth of focus, and small aperture size. Laser light sources for microprojectors must be efficient and compact, allow video frequency modulation for scanners, and demonstrate stable performance when exposed to large temperature changes, shock, and vibration. Whereas red and blue laser diodes are readily available, suitable green laser diodes do not exist yet.

Here, I will present a high-efficiency miniature laser source (<0.7 cm3 volume) that produces green light by optical second harmonic generation of the emission from a high-power distributed Bragg reflector (DBR) laser in a periodically poled lithium niobate (PPLN) waveguide. The device uses adaptive optics to couple the light efficiently into the PPLN over a large range of operating conditions without the submicron alignment tolerances required by fixed optics. The total wall plug efficiency can be as high as 12 % at 140 mW output power. The direct frequency doubling of the DBR laser emission enables modulation with video signals in excess of 100 MHz sufficient for scanning projection of high definition video.