Surface-emitting, single-lobe operation from second-order distributed-reflector lasers with central grating phaseshift

Surface-emitting diode lasers containing a second-order Bragg grating with a central phaseshift, Delta phi, of values around pi are found to fundamentally favor lasing in a mode of symmetric near-field amplitude profile, which in turn provides emission in a single-lobed beam orthonormal to the surface. Devices of 500 mum long distributed-feedback (DFB) active region (lambda =0.98 mum) and 500 mum long distributed feedback reflector passive regions provide, for Delta phi=pi, a surface-emitted beam pattern with 88% central-lobe power content, and external differential quantum efficiency, eta (D), of 51%. Since the guided field is antisymmetric to start with, and a central pi phaseshift causes two grating-outcoupled beams to be out-of-phase with each other, the net result is a single-lobed far-field pattern. The guided-field peak-to-valley (intensity) ratio, R, in the active (i.e., DFB) region is only 2, which insures single-mode operation to high powers, since the intermodal discrimination is high (greater than or equal to 100 cm(-1)). Over a wide range in Delta phi :60 degrees; eta (D) remains high (> 50%) and the degree of guided-field uniformity remains low (R <2). (C) 2001 American Institute of Physics.