Helicity-dependent continuous varifocal metalens based on bilayer dielectric metasurfaces

Area of Science:

• Optics and Photonics
• Materials Science
• Nanotechnology

Background:

• Metasurfaces enable the development of flat optical components, offering significant size and complexity reductions for imaging systems.
• Dielectric metasurfaces are crucial for efficient light manipulation, paving the way for advanced optical functionalities.
• Helicity-dependent optical elements are essential for applications requiring polarization-sensitive control of light.

Purpose of the Study:

• To design and demonstrate a bilayer, helicity-dependent, continuous varifocal dielectric metalens operating in the near-infrared spectrum.
• To achieve tunable focusing and helicity-dependent dual focal spots using a phase-change material.
• To explore potential applications in miniaturized optical devices and systems.

Main Methods:

• Design of a bilayer metalens comprising silicon nanopillars (half-wave plate) and Sb2S3 nanopillars (phase-change material).
• Utilizing a combination of propagation and geometric phases for helicity-dependent functionality.
• Simulating the metalens performance under circularly and linearly polarized light excitation.

Main Results:

• Demonstrated helicity-dependent longitudinal focal spots for circularly polarized waves.
• Generated helicity-dependent dual foci for linearly polarized light.
• Achieved continuous focal length tuning (32.5–37.2 µm for RCP, 50.5–60.9 µm for LCP) via Sb2S3 crystallization.
• Attained simulated focusing efficiencies exceeding 75% (circularly polarized) and 87% (linearly polarized).

Conclusions:

• The proposed dielectric metalens offers continuous varifocal and helicity-dependent focusing capabilities.
• The design leverages phase-change materials for tunable optical properties.
• This technology holds promise for miniaturized optical communication, imaging, and medical devices.