Spin decoupling-based broadband terahertz encoded metalens with multi-focal points

Area of Science:

• Metasurfaces and Nanophotonics
• Electromagnetic Wave Manipulation
• Spin Optics

Background:

• Metasurfaces offer precise control over electromagnetic wavefronts using artificial sub-wavelength structures.
• Controlling electromagnetic waves based on their spin states remains a significant challenge.

Purpose of the Study:

• To propose innovative metalenses capable of spin-decoupled multifocal point generation.
• To demonstrate precise control over electromagnetic waves with different spin states.

Main Methods:

• Design and fabrication of two novel metalenses based on a spin-decoupling principle.
• Characterization of metalens performance under various incident polarizations (linearly, left circularly, and right circularly polarized waves).
• Analysis of focal point generation, intensity distribution, and bandwidth performance.

Main Results:

• The first metalens generates four uniform foci for linearly polarized waves and two foci for circularly polarized waves.
• The second metalens produces one strong and three weak foci for linearly polarized waves, and one strong focus for circularly polarized waves.
• Both metalenses achieve spin-decoupled multifocal points over a wide bandwidth (0.55-0.7 THz) and allow flexible adjustment of focal properties.

Conclusions:

• The developed metalenses enable simultaneous control of orthogonal spin-state electromagnetic waves.
• This technology offers precise spatial energy distribution and opens new avenues for multifunctional optical devices.