Abstract

In the last few years, semiconductor lasers have become very important systems for theoretical as well as experimental studies of spatio-temporal dynamics in nonlinear optics. In semiconductor lasers, spatiotemporal patterns may occur in both the transverse and the longitudinal direction, i.e. perpendicular and parallel to the direction of beam propagation. These patterns are created by the phenomenon of beam filamentation as well as coexistence and competition of multiple longitudinal and transverse modes. Typically, semiconductor lasers oscillate in several longitudinal inodes, if no single-mode operation is enforced by e.g. distributed feedback structures. Whether one or multiple transverse modes are excited depends primarily on the width of the laser stripe. In addition, however, other parameters such as the phmp current are found to have a major influence. We show that for large pump currents, higher-order transverse modes can be excited even in narrow-stripe lasers which is detrimental to the beam quality in the high-power range [1]. This phenomenon is demonstrated both experimentally and numerically. It is found that the laser, for high pump currents. oscillates in several transverse and longitudinal modes, giving rise to a complex mode-beating behaviour. Numerical simulations are performed on model equations which include spatial resolution of both the transverse and the longitudinal coordinate. Eigenmode analysis is applied to study the modal composition of the complex optical field [2].

© 1998 IEEE