Decoupled-Subspace-Induced Flat Bands in a Photonic Superlattice

Area of Science:

• Photonics
• Condensed Matter Physics
• Materials Science

Background:

• Flat bands in photonic systems are crucial for strong light confinement and enhanced light-matter interactions.
• Achieving flat dispersion across an entire Brillouin zone (BZ) is a significant challenge in photonic research.

Purpose of the Study:

• To propose and demonstrate a practical mechanism for generating BZ-spanning flat bands.
• To explore the coupling between propagating modes and localized resonances for flat band creation.
• To investigate the potential for engineering non-Hermitian degeneracies and their experimental observation.

Main Methods:

• A finite-channel model was employed to theoretically predict the formation of flat bands.
• A plasmonic superlattice was designed and fabricated as a practical implementation.
• Angle-resolved reflection measurements and full-wave simulations were used for characterization and validation.

Main Results:

• A quasi-flat band was experimentally observed across the BZ in the plasmonic superlattice.
• Results showed excellent agreement between experimental measurements and theoretical simulations.
• Suppressed group velocity facilitated the observation of exceptional-point pairs.

Conclusions:

• The study presents a viable strategy for engineering BZ-spanning flat bands using coupled modes and resonances.
• The findings offer a pathway for creating compact photonic devices with enhanced functionalities.
• The mechanism is adaptable to various photonic systems, including dielectric and hybrid platforms.