GaN vortex metasurface for interference and broadband characteristics.

Area of Science:

• Optics and Photonics
• Materials Science
• Nanotechnology

Background:

• Metasurfaces offer novel ways to manipulate light.
• Optical vortex beams (OVBs) have applications in optical trapping, communication, and imaging.
• Gallium nitride (GaN) is a promising material for nanophotonic devices due to its unique optical and electrical properties.

Purpose of the Study:

• To experimentally demonstrate a highly efficient metasurface for generating OVBs.
• To investigate the performance and characteristics of GaN-based metasurfaces for OVB generation.
• To explore the broadband capabilities and optical phenomena associated with the designed metasurface.

Main Methods:

• Fabrication of high-aspect-ratio GaN meta-structures.
• Experimental characterization of the metasurface's optical performance.
• Mach-Zehnder interferometer analysis to study interference patterns and helicity switching.
• Investigation of the device's response across visible wavelengths.

Main Results:

• Achieved a simulated absolute polarization conversion efficiency (APCE) of up to 98% for OVB generation.
• Observed a flower-like interference pattern at the converging distance, with spiral and dislocation patterns beyond.
• Demonstrated broadband operation across visible wavelengths.
• Confirmed expansion of the annular shape's diameter with increasing incident wavelengths.

Conclusions:

• The developed GaN metasurface is highly efficient for generating OVBs.
• The device exhibits unique optical phenomena, including helicity switching and wavelength-dependent beam expansion.
• The findings highlight the potential of GaN metasurfaces for advanced photonic applications.