Mode shaping for enhanced brightness in broad area lasers using monolithically integrated microoptical structures

The brightness of broad area laser diodes is limited by a degradation of the beam quality at high output powers. To overcome this limit, a control of slow axis modes at high injection currents is necessary. In the present publication we show an approach to improve the beam quality with optical microstructures in high-power AlGaAs broad area laser diodes with an operating wavelength of 970 nm. The optical microstructures are monolithically integrated into the waveguide by a lithographical process. Effects of mode competition, the influence of the gain medium on the optical field and the temperature distribution inside the waveguide are considered in the optical design of the micro-structured waveguide. This approach offers the possibility to tailor the phase front of the slow axis modes to reduce filamentation effects and compensate thermal lensing. We show that such optical microstructures deliver a gain of brightness of 65% for a single emitter in continuous wave operation.