Generalized Geometric Phase for Coupled Meta-Atoms

Area of Science:

• Metasurfaces
• Geometric Phase Optics
• Nanophotonics

Background:

• Geometric phase, including Pancharatnam-Berry (PB) phase, is crucial for metasurface functionalities.
• Conventional metasurface design assumes a linear relationship between PB phase and meta-atom orientation.
• Previous observations of non-linear PB phase behavior lacked a clear mechanistic explanation.

Purpose of the Study:

• To analyze the evolution of PB phases in metasurfaces.
• To investigate the underlying mechanisms responsible for the breakdown of linear PB phase dependence.
• To establish a systematic framework for accurate PB phase analysis in meta-optical devices.

Main Methods:

• Detailed theoretical analysis of PB phase evolution.
• Investigation using quasi-normal modes (QNMs) to understand phase determination.
• Experimental validation using a specifically designed grating structure.

Main Results:

• Identified meta-atom mutual coupling as a critical factor influencing PB phase.
• Demonstrated that PB phase is determined by far-field radiation polarizations of excited QNMs.
• Showcased the combined influence of meta-atom orientation and mutual coupling on PB phase.

Conclusions:

• Meta-atom coupling plays a non-negligible role in determining the PB phase.
• QNMs provide a framework to link meta-atom properties to far-field polarization and PB phase.
• This work enables high-precision characterization and design of meta-optical devices.