High-brightness laser diodes using angular filtering by total reflection

A high power semiconductor laser with a novel lateral design using angular filtering by total reflection for increased brightness is demonstrated. In this so called "Z-Laser" two inner surfaces guide the laser beam by total reflection in a Z shaped path through the laser. Higher order laser modes with larger divergence angles are suppressed because of a smaller reflectivity. This results in a reduced far-field angle. Simulations based on a two-dimensional steady state wave equation solved by using the Pade approximation, an one-dimensional carrier diffusion equation and a logarithmic gain model have been performed to design the device. First prototypes of the laser were fabricated on MBE grown InGaAs/AlGaAs wafers. The inner surfaces providing the refractive index step necessary for total reflection were prepared by chemically assisted ion-beam etching. Single lasers were mounted junction side down on copper heat-sinks. They show lateral far field angles smaller than 2 deg FWHM in excellent agreement with numerical simulations. Output powers of more than 500 mW cw out of a 36 µm facet have been reached. In conclusion, the "Z-Laser" is a promising new design for high power, high brightness semiconductor laser diodes.