650-nm lasers with narrow far-field divergence with integrated optical mode expansion layers

By means of numerical simulation of the optical and electrical performance, we have designed 650-nm GaInP-AlGaInP quantum-well lasers with mode expans ion layers which have a narrow vertical far-field divergence without sacrif icing threshold current or threshold current temperature dependence. We hav e reduced the measured vertical far-field divergence in a 650-nm laser stru cture from 35 degrees to 24 degrees full-width at half-maximum without chan ging the threshold current, operating voltage, or threshold current tempera ture dependence. We have also calculated the tolerances in the thickness an d composition necessary to realize this design in practice.