Lateral mode discrimination and self-stabilization in ridge waveguide laser diodes

Lateral mode discrimination and output stability is experimentally investigated in ridge waveguide laser diodes, having various residual guide thicknesses outside the ridge region. It is found that a critical residual thickness exists below which the lasers emit in a single mode, with a low threshold current. Above this critical value, the threshold current rises rapidly with the residual guide thickness, and the lasers oscillate simultaneously in the two lowest order lateral modes. Increasing the injected current intensity, in this regime, results in nonlinear light output-current curves, but also improves mode discrimination in favor of the fundamental mode, until single-mode operation is re-established. A simple mechanism is suggested to explain this phenomenon