Wide-Angle Optical Metasurface for Vortex Beam Generation.

Area of Science:

• Optics and Photonics
• Metamaterials
• Beam Shaping

Background:

• Vortex beams carry orbital angular momentum, enabling applications in optical manipulation and communication.
• Metasurfaces offer precise control over light wavefronts with subwavelength structures.
• Achieving wide-angle operation and high topological charges in vortex beams remains a challenge.

Purpose of the Study:

• To develop a metasurface capable of generating wide-angle vortex beams with a high topological charge (TC) of 12.
• To investigate the optical properties and performance of a gallium nitride (GaN) based metasurface.
• To analyze the relationship between metasurface design, helicity, and beam characteristics.

Main Methods:

• Fabrication of a high-aspect-ratio gallium nitride (GaN) metasurface with propagation-phase design.
• Characterization using tilt-view scanning electron microscopy (SEM) for structural analysis.
• Optical performance evaluation via Mach-Zehnder interferometry and direct imaging of beam patterns.

Main Results:

• Demonstrated a metasurface achieving a topological charge of 12 with wide-angle capacity up to 30 degrees.
• Attained a simulated average co-polarization transmission efficiency of up to 97%.
• Observed a unique petal-like interference pattern and manipulated helicity to minimize donut diameter at the focal length.

Conclusions:

• The engineered GaN metasurface successfully integrates wide-angle capability into high-topological-charge vortex beams.
• The device exhibits high efficiency and controllable beam characteristics, with performance degradation beyond 30 degrees incident angle.
• This work advances the development of sophisticated optical components for advanced light manipulation.