All-Dielectric Metasurface-Enabled Multiple Vortex Emissions.

Abstract

On-chip integrated micro- and nanoscale vortex lasers are key elements for addressing the exponentially growing demand for information capacity. Although tunable vortex microlasers have been reported, each laser pulse still possesses one particular topological charge and requires additional multiplexing. In this study, the simultaneous generation of coherent laser arrays with different topological charges by combining metalenses with semiconductor microlasers is demonstrated. A TiO2 vortex metalens converts two orbital angular momentum beams into the same diffraction-limit spot with opposite circular polarizations through spin-to-orbital conversion. Consequently, the microlaser emission at the focal spot, which can be decomposed into two circularly polarized beams, is collimated into vortex microlaser beams with two different topological charges through a time-reversal process. This concept is extended to a 2 × 2 metalens array by introducing off-axis terms, and eight topological charges are produced simultaneously. This research is a significant step toward the on-chip integration of micro- and nanolasers.