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Janus Bound States in the Continuum with Asymmetric Topological Charges
- 发表刊物：Physical Review Letters
- 摘要：We propose a novel topological defect called Janus bound states in the continuum (BICs), featuring asymmetric
topological charges in upward and downward radiation channels. Our approach involves a photonic crystal slab (PCS)
that initially exhibits both out-of-plane and in-plane mirror symmetry, and this PCS possesses one BIC at the Γ point
and two BICs off the Γ point. By introducing certain perturbations that break the out-of-plane mirror symmetry, the
two off-Γ BICs decompose into four circularly polarized states (C points) with identical topological charges (each with
half the topological charge of the original BIC) while the at-Γ BIC is preserved. Then, we selectively manipulate the
four C points associated with the downward radiation channel to converge at the at-Γ BIC, forming a Janus BIC with
distinct topological charges for upward and downward radiation. By further introducing in-plane mirror symmetry
perturbation, we can bring two of the C points with the same handedness and identical topological charges for upward
radiation to merge into the Janus BIC. This process results in a Janus chiral BIC which exhibits large intrinsic chirality
and an infinite Q factor. Janus BICs can induce distinct Pancharatnam–Berry phase singularities in momentum space for
different incident channels, providing a new approach to control orbital angular momentum. Janus chiral BICs hold
promise in enhancing direction-dependent and spin-dependent asymmetric light-matter interaction, opening new
pathways for improving chirality-dependent operation for on-chip devices.
- 卷号：134
- 期号：1
- 页面范围：013805
- 是否译文：否
- 发表时间：2025-01-10
