Strong coupling regime of a quasi-bound state in a continuum in a plasmonic nanohole array with broken symmetry

Area of Science:

• * Condensed matter physics
• * Nanophotonics
• * Quantum optics

Background:

• * Strong coupling regime involves coupling photonic and matter excitations into mixed quasiparticles.
• * Plasmonic bound states in the continuum (BICs) offer unique light confinement properties.
• * Chirality in optical response is crucial for various applications, including sensing and information processing.

Purpose of the Study:

• * To predict and investigate chiral optical response in the strong coupling regime.
• * To explore the formation of chiral plasmonic polariton BICs.
• * To demonstrate the potential for tunable circular dichroism using metasurfaces and active media.

Main Methods:

• * Theoretical modeling of a gold metasurface with oval nanoholes supporting a quasi-BIC.
• * Incorporation of an active medium described by the Lorentz model to achieve strong coupling.
• * Analysis of optical response, including circular dichroism (CD), at finite angles of incidence.

Main Results:

• * Prediction of chiral optical response arising from the strong coupling between quasi-BIC and active medium resonances.
• * Formation of hybrid modes termed plasmonic polariton BICs.
• * Observation of nearly maximum circular dichroism in both absorption and transmission at specific incidence angles.

Conclusions:

• * The study introduces a novel mechanism for achieving chirality via plasmonic polariton BICs in the strong coupling regime.
• * This approach offers a new pathway for studying chiral phenomena using engineered metasurfaces.
• * Potential applications include tunable chiral sensing and optical devices by integrating colloidal quantum dots.