Numerical procedure for the lateral-mode analysis of broad-area semiconductor lasers with an external cavity

A numerical procedure for the investigation of the lateral modes of semiconductor lasers with an external cavity is described. The propagation of the optical field inside the semiconductor laser is carried out via a standard beam-propagation scheme, while the method of coordinate scaling with the generalized Huygens-Fresnel integral allows for a computationally efficient propagation of the field in the external cavity. Using an eigenfunction solver based on the Prony method, it is shown that a simple external-cavity configuration comprising a broad area laser, a collimation lens, and a uniform end reflector can exhibit a complex modal behavior. Compared to a solitary broad area laser, optimized external cavities can yield enhanced modal discriminations, resulting in a single-lateral-mode operation with output power in excess of 100 mW along with a clean, single-lobed far-field pattern. The spatial-filtering action of the broad-area laser is highlighted, and we also discuss of the role played by the wavefront curvature of the beam incident upon the broad-area laser for achieving an efficient suppression of the higher order modes along with minimum increase of the threshold current