Mode Cooperation in a Two-Dimensional Plasmonic Distributed-Feedback Laser

Plasmonic distributed-feedback lasers based on a two-dimensional periodic array of metallic nanostructures are the main candidate for nanoscale sources of coherent electromagnetic field. In this work we show that, when the pumping spot is smaller than the size of the laser, the nonlinear interaction between the modes of a periodic plasmonic structure via the active medium leads to a new effect, namely, mode cooperation. Mode cooperation is manifested as the lasing of the bright modes in the allowed band with a high generation threshold instead of the dark modes at the edge of the band gap with a low generation threshold. This effect is inherent for two-dimensional distributed-feedback lasers and does not appear in one-dimensional lasers. Mode cooperation arises due to nonorthogonality of the laser modes in the pumped area where the bright modes become synchronized by the phase and their amplitudes interfere constructively. We demonstrate that mode cooperation results in broadening of the radiation pattern above the generation threshold, which has been observed in recent experiments. The obtained results provide new possibilities for effective control and manipulation of the radiation pattern of nanoscale systems.