Janus Bound States in the Continuum with Asymmetric Topological Charges
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866916565265416192 |
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| author | Kang, Meng Xiao, Meng Chan, C. T. |
| author_facet | Kang, Meng Xiao, Meng Chan, C. T. |
| contents | 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 Γpoint and two BICs off the Γpoint. By introducing certain perturbations that break the out-of-plane mirror symmetry, the two off-ΓBICs 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-ΓBIC is preserved. Then, we selectively manipulate the four C points associated with the downward radiation channel to converge at the at-ΓBIC, 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. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2402_12689 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Janus Bound States in the Continuum with Asymmetric Topological Charges Kang, Meng Xiao, Meng Chan, C. T. Optics 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 Γpoint and two BICs off the Γpoint. By introducing certain perturbations that break the out-of-plane mirror symmetry, the two off-ΓBICs 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-ΓBIC is preserved. Then, we selectively manipulate the four C points associated with the downward radiation channel to converge at the at-ΓBIC, 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. |
| title | Janus Bound States in the Continuum with Asymmetric Topological Charges |
| topic | Optics |
| url | https://arxiv.org/abs/2402.12689 |