Control of slow axis mode behavior with waveguide phase structures in semiconductor broad-area lasers

An increase in the output power of semiconductor waveguide lasers is commonly achieved through broadening the stripe width of the active waveguide region. However, the resulting amplification of high order modes may degrade the beam quality of the laser diode. Further, Filamentation and high peak power densities will limit the lifetime of the device by optical facet damage. We report an approach to control the slow axis mode behaviour by embedding diffractive phase structures directly into the waveguide layers of the active laser region. Using this technique it is possible to enhance the amplification by increasing the overlap with the gain region, whilst additional diffraction losses for higher order modes are generated. By shaping the zero order mode the output beam quality can be increased and a high efficiency of the device maintained. Finally we discuss manufacturing techniques of these monolithic waveguide lasers and show how to integrate phase structures through an additional lithographic step. In our experimental realisation we will demonstrate that micro structured broad area lasers show a smooth transversal mode shape with significantly reduced current dependency.