Combining Multimode Emissions from Broad Area Laser Diodes into Single-Mode Spots without Feedback

Broad-area laser diodes are the most efficient coherent light sources and are widely used today. The extraordinary efficiency, modulation easiness, availability to virtually any wavelength and compactness are the principle drives stimulating the development of light sources based on laser diodes. However, due to fundamental limitations of laser diode gain medium, the emission from laser diodes has a major drawback — the emission is not spatially coherent. In other words laser diode light is often seen as a light bulb emission that cannot be focused in a diffraction limited spot of λ/2 or easily transmitted as a narrow beam. Despite the fact that kilowatts of multimode power can be easily extracted from a laser diode array, the resulting single-lobe single-element power from a laser diode is always limited by a value of several watts. Many applications are waiting for a spatially coherent laser diode source offering power from 1 to 100W. The potential substitution of YAG and fiber lasers by a compact, direct single- mode laser diode source would bring significant advancements in a number of applications such as LIDAR/LADAR (Light Intensity Detection and Ranging/Light Amplification Detection and Ranging) systems; high-bit-rate, long-haul free space communication systems; industrial processing applications; and many more.