Double-sided asymmetric metasurfaces achieving sub-microscale focusing from a GaN green laser diode

We proposed and demonstrated a highly efficient sub-microscale focusing from a GaN green laser diode (LD) integrated with double-sided asymmetric metasurfaces. The metasurfaces consist of two nanostructures in a GaN substrate: nanogratings on one side and a geometric phase based metalens on the other side. When it was integrated on the edge emission facet of a GaN green LD, linearly polarized emission was firstly converted to the circularly polarized state by the nanogratings functioning as a quarter-wave plate, the phase gradient was then controlled by the metalens on the exit side. In the end, the double-sided asymmetric metasurfaces achieve a sub micro-focusing from linearly polarized states. Experimental results show the full width at half maximum of the focused spot size is about 738 nm at the wavelength 520 nm and the focusing efficiency is about 72.8%. Our results lay a foundation for the multi-functional applications in optical tweezers, laser direct writing, visible light communication, and biological chip.& COPY; 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

We propose and demonstrate a highly efficient sub-microscale focusing technique by integrating double-sided asymmetric metasurfaces onto a GaN green laser diode. The metasurfaces consist of nanogratings on one side and a geometric phase based metalens on the other side. When integrated on the edge emission facet of the LD, linearly polarized emission is converted to circularly polarized state by the nanogratings, and the phase gradient is controlled by the metalens on the exit side. Experimental results show a sub micro-focusing from linearly polarized states with a focused spot size of about 738 nm at 520 nm wavelength and a focusing efficiency of approximately 72.8%. This research lays a foundation for various applications in optical tweezers, laser direct writing, visible light communication, and biological chip.