Active Quasi-BIC Enabled Optical Vortex Generation

Electromagnetic beams that carry orbital angular momentum (OAM) have enormous potential in various applications. By exploiting the winding topology of quasi-BIC modes around the polarization singularity in k-space, a novel optical vortex (OV) generation method has been recently proposed. Compared with the conventional approaches, this method can lead to robust OV generators which are feasible and easy to fabricate. Here, by leveraging the nonlinear dynamics of silicon, we demonstrate a silicon-based quasi-BIC platform supporting optically switchable OV generation. A Huygens sources-based model extends the near-field (NF) spatial modal analysis to the far-field (FF) region. Meanwhile, the OV switching effects in the picosecond scale are studied using nonlinear modeling at near-infrared wavelengths. The demonstrated nontrivial topological nature can expand the applications of BIC-based devices in many areas including high-capacity optical communication and mode-division multiplexing.