Spatial mode structure of index-guided broad-area quantum-well lasers

The spatial mode characteristics of index-guided ridge-waveguide broad-area (BA) quantum-well lasers grown by organometallic chemical vapor deposition were investigated experimentally. The index-guided BA lasers lase in a high-order lateral mode, and thus emit a double-lobed far-field pattern. This is significantly different from their gain-guided counterparts, which lase in the fundamental mode. For BA lasers with the same width and made on the same or similar material, the index-guided lasers have lower threshold currents, higher quantum efficiencies, and better linearity in the light versus current characteristics. It is observed that the order of the dominant high-order lateral-mode increased with increasing laser width or effective index step of the laser waveguide. In addition, it is found that the mechanism for degradation in the spatial coherence at high pumping levels is the onset of higher order lateral modes