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 expansion layers which have a narrow vertical far-field divergence without sacrificing threshold current or threshold current temperature dependence. We have reduced the measured vertical far-field divergence in a 650-nm laser structure from 35 degrees to 24 degrees full-width at half-maximum without changing the threshold current, operating voltage, or threshold current temperature dependence. We have also calculated the tolerances in the thickness and composition necessary to realize this design in practice.