Abstract

A key advantage that semiconductor ring lasers have over Fabry-Pérot (FP) devices for relatively high power applications, is that they do not suffer from Catastrophic Optical Damage (COD) to the cleaved facets of the device bar[l]. However, the directional coupler (DC) section in the ring geometry, equivalent to the facet conditions in a FP laser, cannot be modulated as easily as the FP facets to provide the equivalent to high and low reflectivity coatings, that allow increased quantum efficiency. The symmetric nature of the coupling in ring lasers produces both bidirectional or (fluctuating) bistable directional lasing of the device[2]. In order to produce unidirectional, stable lasing in ring lasers a snail geometry, as shown in Fig.2(a), is considered here. In this case the laser has one cleaved output facet, and the input waveguide is curved until it couples with itself. The benefit is that low coupling between the waveguides in the DC may be easily designed, where the normal ring and bus waveguide geometry equivalent, requiring high coupling values, is more sensitive to fabrication tolerances, and requires long interaction lengths, increasing the device footprint. As a theoretical result, we have calculated the fundamental mode thresholds and output power for Semiconductor Snail Laser (SSL) as a function of device parameters, i.e. coupler efficiency and output facets reflectivities. The coupler efficiency (δ) is the fraction of light transmitted between the waveguides in the DC. We have used a scattering matrix formulation and an analytical approximation to the optical susceptibility for the medium description [3], in order to determine the "optimal" coupling efficiency that maximizes the output power (see Fig.l.) Lasing action and good emission properties were therefore theoretically predicted

© 2009 IEEE