Improvement of brightness and output power of high-power laser diodes in the visible spectral region

This paper reports on a novel design for a high-brightness quantum-well AlGaInP laser-diode system operating at 635 nm. The spatial coherence of two broad area laser diodes is improved using spatial filtering and optical feedback from a narrow mirror stripe on each laser. To increase power, the outputs from the two systems are passively combined using a polarizing beam splitter. The result is a compact system providing a high-brightness beam. The beam-quality parameter is improved in one direction from M² = 12 and M² = 16 for the two lasers, to M² = 2.1 for the combined beam. The other direction of the beam is left unchanged due to its natural high quality with an M² value around 1.5. A procedure for efficient coupling of the two lasers into a small core-diameter optical fiber is given. This capability facilitates a wide range of applications including interstitial medical therapies, where delivery of the treatment light through thin optical fibers is essential.