Optically active metasurface with non-chiral plasmonic nanoantennas

Area of Science:

• Optics and Photonics
• Materials Science
• Nanotechnology

Background:

• Metasurfaces offer unique light manipulation capabilities due to their subwavelength structures.
• Achieving optical activity, particularly broadband circular polarization conversion, remains a challenge.
• Existing chiral metasurfaces often rely on complex or inherently chiral building blocks.

Purpose of the Study:

• To design and demonstrate a broadband, optically active metasurface with significant polarization rotation.
• To develop a novel supercell design methodology for creating effective chirality from nonchiral elements.
• To achieve a metasurface with enhanced tolerance to fabrication and temperature variations.

Main Methods:

• Fabrication of a λ/50 thick metasurface composed of a planar array of plasmonic nanoantennas.
• Implementation of a supercell metasurface design strategy utilizing the collective behavior of nonchiral antennas.
• Experimental characterization of the metasurface's polarization rotation capabilities across a broadband near-infrared spectrum.

Main Results:

• Demonstrated a metasurface capable of rotating linearly polarized light by 45° over a broadband wavelength range.
• The optical activity was achieved by generating a fixed phase shift between left and right circular polarized components.
• The supercell design enabled quantitative control over the chiral effect based solely on geometry, simplifying the structure.

Conclusions:

• A novel, ultra-thin optically active metasurface was successfully designed, fabricated, and demonstrated.
• The supercell methodology provides a simplified and robust route to achieving broadband chiral effects using nonchiral components.
• This approach offers improved tolerance to fabrication imperfections and temperature fluctuations, paving the way for practical applications.