Observation of stable cylindrical modes in electrically pumped circular grating-coupled surface-emitting lasers

We present the results of a comprehensive experimental study of the modal behavior of electrically pumped circular grating-coupled surface-emitting lasers with resonant second-order gratings. Our results show stable cylindrical mode operation with azimuthal orders m = 1 and m = 52. We have found that, when a passive, unpumped 0.7-microm-deep indentation is included at the center of the circular resonator contact, the modal behavior becomes more stable with respect to increasing current. This result manifests itself in the lasing of two orthogonal m = 1 modes along with one higher-order mode from threshold to 2.2 times threshold or more. The spatial coherence of the cylindrical modes over the area of the resonator leads to better beam quality. Lasers without passive central indentations exhibit mode hopping between quasi-linear modes and higher-order cylindrical modes as the current is increased.