Speckle reduction and image quality improvement in display technologies having laser light sources

Picture quality of a display system is related to its screen quality. There are different display technologies and the qualities of them are related to the used illumination source used inside the device. The popular illumination devices are Cold Cathode Fluorescent Lamp, Ultra High Pressure lamps and Light Emitting Diodes. But due to lasers own special properties if they are used inside the display technologies they come with some advantages, such as more colorful pictures, higher luminance, an improved contrast ratio and also a constant image quality throughout the lasers lifetime, which makes them ideal candidate for display systems. Because lasers are coherent light sources, the mutual interference of wave fronts create a nonuniform intensity pattern which causes unwanted speckle noise in display and projection systems. In this thesis, we propose and experimentally demonstrate results of a new laser drive circuit for laser speckle reduction. By modulating the drive current of the laser diode continuously; we manage to generate independent longitudinal modes that arise from mode hopping. Since these modes have no fixed relationship between each other they act as independent sources which results in speckle reduction in the image. For square wave and triangular wave we experimentally demonstrate a speckle reduction factor of 1.32 and 2.16 respectively, which is in excellent agreement with our theoretical expectations. We conclude that mode hopping in laser systems can be used effectively to suppress speckle noise.