Semiconductor laser far-field shaping by means of an angle-selective facet coating

An optical short-wave pass filter, applied as a coating on a semiconductor laser facet, is observed to decrease the far-field width perpendicular to the active layer. The resulting far field has a higher coupling efficiency to circular optics. Combination of this coating with a highly reflective coating on the rear facet gives an improvement of the available external differential efficiency and maintains the threshold current of the uncoated laser. The experimental results obtained can be explained in the framework of a simple model.