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

Abstract

Surface-emitting diode lasers containing a second-order Bragg grating with a central phaseshift, Δφ, of values around π 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 μm long distributed-feedback (DFB) active region (λ=0.98 μm) and 500 μm long distributed feedback reflector passive regions provide, for Δφ=π, a surface-emitted beam pattern with 88% central-lobe power content, and external differential quantum efficiency, ηD, of 51%. Since the guided field is antisymmetric to start with, and a central π 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 (⩾100 cm−1). Over a wide range in Δφ:60°; ηD remains high (>50%) and the degree of guided-field uniformity remains low (R<2).