Abstract

Recent progress in broad-area semiconductor lasers with nearly 5 W of reported cw output power demonstrates that they represent an attractive alternative to diode-laser arrays for high-power applications. Therefore, understanding the lateral-mode structure of these devices becomes increasingly important. This paper reports on experimental investigations of carrier-guided broadarea lasers with thin GaAs/AlGaAs double-heterostructure active regions. Two types of Sony devices with different active region widths but with otherwise similar structures are used: 50 µm wide SLD-302NT (maximum cw output power P_max = 200 mW) and 200 µm wide SLD-304XT (P_max = 1 W). These devices are known to operate in a superposition of many lateral modes with complicated near-field patterns and broad double-lobe far fields. However, observations of near- and far-field patterns indicate that much simpler modal configurations can exist near threshold. For a 50 µm device at room temperature (threshold current I_th = 119 mA), the near field evolves from three peaks at 121 mA, four at 131 mA, and so on, which corresponds to excitation of a combination of first three, four, etc. lateral modes. Combination of two lowest-order modes was observed at 5°C for a pumping level of 120 mA (I_th = 107 mA). Because of the very small modal gain differences, no single lateral mode can be observed alone. These measurements are interpreted assuming weighted combinations of individual modes, which yields a basis of unperturbed broad-area modes important for studies of perturbed systems, such as thermal effects and spatial redistribution of carriers in high-power broad-area lasers and carrier-guided arrays. Similar measurements performed on one particular 200 µm device reveal four stable peaks from very low current level ( mA) up to the threshold. At some level above the threshold, the device suddenly switches to a combination of many lateral modes.

© 1990 Optical Society of America