Cascaded metasurface for polarization-dependent varifocal vortex beam manipulation.

Area of Science:

• Metasurfaces
• Optical Communications
• Quantum Information Processing

Background:

• Vortex beams with orbital angular momentum (OAM) are crucial for advanced optical applications.
• Current metasurfaces offer limited control, restricting integration of polarization multiplexing and dynamic focal tuning.

Purpose of the Study:

• To develop a tunable, multifunctional cascaded metasurface for advanced OAM beam generation and focal control.
• To overcome limitations of single-degree-of-freedom metasurface designs.

Main Methods:

• Designed a cascaded metasurface utilizing polarization-sensitive phase engineering and interlayer rotational coupling.
• Independently generated distinct OAM states for orthogonal circular polarizations.
• Achieved continuous focal tuning through interlayer rotation.

Main Results:

• Generated distinct OAM states: ℓ = -1 for LCP and ℓ = +1, -1 for RCP.
• Demonstrated focal length modulation from 25.9λ to 9.5λ by rotating the metasurface layers (90° to 240°).
• Experimentally validated the tunable focal properties at the target frequency.

Conclusions:

• The proposed multi-degree-of-freedom metasurface enables independent OAM control and dynamic focal tuning.
• This technology advances high-capacity optical communications, dynamic holography, and quantum state manipulation.
• Paves the way for intelligent metasurfaces in 6G networks and integrated photonics.