High-brightness lasers based on internal focus unstable resonators

We report on the use of etched curved facets to form semiconductor lasers based on unstable resonators with a real internal focus. The lasers which have a cleaved output facet operate to > 1W continuous wave power with a diffraction limited central lobe when corrected for spherical phase. The astigmatism is found to be equal to the geometric calculation and is stable throughout the operating range. Beam degradation is associated with temperature gradients. We have fabricated devices at 1200nm, 980nm and 800nm based on reactive ion etching of GaAs structures demonstrating that the technique can be considered as a platform technology. We discuss the formation of near (facet) fields from the laser and the definition of beam quality for these lasers. The technology has also been used to etch both facets of the resonator to obtain a collimated output beam. In summary, these lasers act both as a high brightness source with reduced power density on the facet as well as a versatile source for designed output and can be scaled into array format.