A quasi-bound band in the continuum in a photonic slab

TL;DR

This paper demonstrates a continuous band of symmetry-protected quasi-bound states in a photonic slab, extending the concept of BICs with long-lived states across a significant portion of the Brillouin zone.

Contribution

It reports the experimental observation of a quasi-bound band in the continuum in a photonic slab, expanding understanding of BICs in photonic systems.

Findings

Support for a continuous quasi-bound state band along Gamma-X

Spectral width remains narrow across half the Brillouin zone

Indicates long lifetime of the quasi-bound states

Abstract

Bound states in the continuum (BIC) are localized waves in electronic, photonic and acoustic systems, which remain decoupled from surrounding propagating waves and hence maintain their oscillation for extraordinary long time [Nat Rev Mater 1, 16048 (2016)]. In photonic crystals, symmetry-protected quasi-BICs (SP-qBIC) have been realized at high symmetry points of the Brillouin zone and utilized in photonic crystal and distributed feedback lasers. In the present work, we measure wavevector-resolved photoluminescence (PL) of monolayer WSe2 weakly coupled to a photonic slab, consisting of a square array of aluminum nanodisks. The results show that the slab supports a continuous band of symmetry-protected quasi-bound states along the Gamma-X direction, extending from the previously reported SP-qBIC at the Gamma point. The spectral width of this quasi-bound band in the continuum remains narrow through at least a half of the Brillouin zone, indicating its long lifetime.