Circular grating-coupled surface-emitter with high-quality focused output beam

We have investigated the effect of resonator size and geometry on the performance of focusing circular grating-coupled surface-emitting lasers. Both the effects of reducing the resonator diameter and introducing an unpumped indentation in the center of the resonator have been studied. We have found that inclusion of such an unpumped central indentation can greatly improve the spatial-mode behavior, resulting in a very uniform near-field intensity, single wavelength emission, and a focused spot size only 1.5 times the diffraction limit for a laser oscillating in the fundamental circular mode. Reducing the resonator diameter of lasers without an unpumped central indentation does not offer similar improvement.