Channel-Differentiated Topological Charge Flips and Formation of Janus Bound States in the Continuum in Single-Layer Photonic Lattices
Abstract
The topological charge of a bound state in the continuum (BIC) can flip when the BIC merges with other polarization singularities or, as recently shown, at band flips. Here, using a coupled-mode analysis, we derive an analytical expression for the topological charge of symmetry-protected BICs in one-dimensional single-layer photonic lattices. The expression captures both merging-induced and band-flip-induced charge flips. We find that, during a band flip, the topological charge of the BIC reverses with the formation of lines of circular polarization that cross at the Γ point. In vertically symmetric lattices, each charge flip occurs simultaneously in the upward and downward radiation channels. Breaking vertical symmetry makes both kinds of charge flips channel-differentiated, creating a parameter interval in which the BIC carries opposite topological charges in the two channels and forms a Janus BIC. We show that Janus BICs also emerge in experimentally accessible one- and two-dimensional silicon-based photonic lattices. Our results link the topological charge of a BIC directly to the band structure and the channel-resolved radiation amplitudes and establish a basis for channel-selective control of polarization singularities.
Related
- Photonic Exceptional Topological Bound States in the Continuum
- Polarization-controlled Floquet engineering in twisted photonic lattices
- Continuum Photonic Axion Insulators
- Effects of interface regularity on the bulk-edge correspondence in continuum photonic systems
- Observation of chiral bound states in the continuum in self-biased magneto-optical photonic crystals
BibTeX
@misc{lee2026channeldifferentiated,
title = {{Channel-Differentiated Topological Charge Flips and Formation of Janus Bound States in the Continuum in Single-Layer Photonic Lattices}},
author = {Sun-Goo Lee and Wook-Jae Lee},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.37168},
eprint = {2610.37168},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.37168},
}
RIS
TY - UNPB
TI - Channel-Differentiated Topological Charge Flips and Formation of Janus Bound States in the Continuum in Single-Layer Photonic Lattices
AU - Sun-Goo Lee
AU - Wook-Jae Lee
PY - 2026
DA - 2026/10/27
PB - arXiv
DO - 10.48550/arxiv.2610.37168
UR - https://arxiv.org/abs/2610.37168
AB - The topological charge of a bound state in the continuum (BIC) can flip when the BIC merges with other polarization singularities or, as recently shown, at band flips. Here, using a coupled-mode analysis, we derive an analytical expression for the topological charge of symmetry-protected BICs in one-dimensional single-layer photonic lattices. The expression captures both merging-induced and band-flip-induced charge flips. We find that, during a band flip, the topological charge of the BIC reverses with the formation of lines of circular polarization that cross at the Γ point. In vertically symmetric lattices, each charge flip occurs simultaneously in the upward and downward radiation channels. Breaking vertical symmetry makes both kinds of charge flips channel-differentiated, creating a parameter interval in which the BIC carries opposite topological charges in the two channels and forms a Janus BIC. We show that Janus BICs also emerge in experimentally accessible one- and two-dimensional silicon-based photonic lattices. Our results link the topological charge of a BIC directly to the band structure and the channel-resolved radiation amplitudes and establish a basis for channel-selective control of polarization singularities.
ER -