Spatial mode structure of broad-area semiconductor quantum well lasers

The spatial mode characteristics of gain-guided broad-area quantum well lasers grown by organometallic chemical vapor deposition were investigated experimentally. GaAs/AlGaAs quantum well lasers grown on 6°-off (100) oriented substrates exhibit excellent material uniformity, which allows study of their modal behavior. Gain-guided broad-area lasers fabricated on such uniform material demonstrate nearly ideal gain-guiding modal behavior. These lasers tend to lase in the fundamental mode near threshold and emit single-lobed far-field patterns. In these well-behaved broad-area lasers, we have identified the mechanism for degradation in the spatial coherence at high pumping levels as the onset of higher order lateral modes.