A Numerical Tool for the Analysis and Design of High-Power External-Cavity Semiconductor Lasers

Abstract

The considerable research effort devoted to the development of compact sources of high-power laser radiation for applications such as the optical pumping of solid-state lasers has resulted in the fabrication of semiconductor broad-area and array devices for which output powers of hundreds mW are now commonplace. An efficient use of the available output power requires that the laser device radiates ideally a single lobed far-field pattern close to the diffraction limit. Owing to the wide active region of broad-area devices and to the well-known tendency of laser arrays to favor the out-of-phase supermode, the emission of an output beam of adequate spatial quality is generally difficult to achieve without reducing the maximum output power emitted by the device. Indeed, the lasing emission of broad-area lasers becomes rapidly multiple-lateral-mode as the bias level is increased, owing to their poor lateralmode selectivity. The oscillation of several higher-order lateral modes is accompanied by a broadening of the far-field radiation pattern, together with a degradation of the spatial coherence of the output beam. The modal selectivity of laser arrays is better, but the dominant out-of-phase supermode radiates into a dual-lobe far-field pattern. Controlling the lateral-mode selectivity as well as the characteristics of the favored lateral modes is therefore a key element for achieving high-power lasing emissions of acceptable spatial quality.