Achromatic Double-Helix Metalens for Broadband Structured Focusing in the Visible Range

Area of Science:

• Optics and Photonics
• Metamaterials
• Nanotechnology

Background:

• Achieving achromatic structured focusing in flat optics for compact depth-resolved imaging and 3D localization is challenging.
• Simultaneously obtaining broadband operation and a depth-encoding focal field remains a significant hurdle.

Purpose of the Study:

• To demonstrate an achromatic double-helix metalens operating across the visible spectrum (600-650 nm).
• To extend achromatic metalenses beyond conventional focusing to broadband structured focusing applications.

Main Methods:

• Designed a metalens combining hyperbolic and double-helix phase profiles using Laguerre-Gaussian modes.
• Optimized phase profile coefficients using particle swarm optimization.
• Developed a meta-atom library considering phase delay, group delay, and group delay dispersion for broadband implementation.

Main Results:

• Fabricated metalens exhibited strong structural fidelity.
• Experimentally reproduced a rotating two-lobe focal field at 625 nm and across the target wavelength range.
• Demonstrated achromatic structured focusing across the visible spectrum.

Conclusions:

• The developed achromatic double-helix metalens successfully achieves broadband structured focusing.
• This compact flat optics platform is suitable for advanced depth-resolved imaging and 3D localization.