Widely tunable laser diodes with tapered index perturbations for reduced internal reflections and improved wavelength access

The wavelength selectivity of widely tunable laser diodes is usually too weak to enable access to all longitudinal modes. This is because internal reflections may randomly suppress individual modes. The authors show for codirectionally mode coupled lasers, that by tapering the index discontinuities, a marked reduction of the reflections by 2-4 orders of magnitude is possible without affecting the codirectional mode coupling.