Polarization diversity close to the optical bound states in the continuum

Abstract

Bound states in the continuum (BICs) realized in two-dimensional (2D) photonic crystal slabs (PhCSs) have attracted considerable attentions, owing to the advantages in the fabrications and on-chip applications. The polarization vortex centered at BICs in the momentum space displayed by the linear polarization vectors of far-field radiation is a striking property of BICs. Here, by constructing BICs at K point in photonic graphenes, we theoretically demonstrate that the far-field polarization states close to BICs can exhibit remarkable polarization diversity. Interestingly, C-points (circular polarizations) close to BIC at K point are observed. Thus, we propose that, along a closed loop enclosing BICs in the momentum space, the trajectory of the far-field polarization states on the shell of the Poincare sphere could provide a general and straightforward means to characterize the topological natures of BICs. The topological charge carried by the BIC can be defined by the half of the winding number of the trajectory around the S3 axis, which is an integer and half integer for the non-degenerate and double-degenerate BICs at K point, respectively. Our findings could open a gateway towards the applications of BICs in lasers with full polarizations and the generation and manipulation of vector beams of light.

13 pages, 4 figures

References in corpus (6)

• Topological Photonics
• Topological nature of bound states in the radiation continuum
• Topologically Enabled Ultra-high-Q Guided Resonances Robust to Out-of-plane Scattering
• Circularly polarized states spawning from bound states in the continuum
• Observation of optical vortices in momentum space
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• Spin-Orbit-Locking Chiral Bound States in the Continuum
• Evolution and global charge conservation for polarization singularities emerging from nonhermitian degeneracies
• Taming Friedrich-Wintgen interference in resonant metasurface: vortex laser emitting at on-demand tilted-angle
• Topological near fields generated by topological structures
• Polarization Singularities in Light Scattering by Small Particles
• Circularly polarized states and propagating bound states in the continuum in a periodic array of cylinders
• Recovery of topologically robust merging bound states in the continuum in photonic structures with broken symmetry
• Topological photonics in nanoscaled systems with far field radiation and polarization singularities
• Phase fields in momentum space of photonic crystal slabs