Arbitrarily polarized bound states in the continuum with twisted photonic crystal slabs

Abstract

Arbitrary polarized vortex beam induced by polarization singularity offers a new platform for both classical optics and quantum entanglement applications. Bound states in the continuum (BICs) have been demonstrated to be associated with topological charge and vortex polarization singularities in momentum space. For conventional symmetric photonic crystal slabs (PhCSs), BIC is enclosed by linearly polarized far fields with winding angle of 2π, which is unfavorable for high-capacity and multi-functionality integration-optics applications. Here, we show that by breaking σz-symmetry of the PhCS, asymmetry in upward and downward directions and arbitrarily polarized BIC can be realized with a bilayer-twisted PhCS. It exhibits elliptical polarization states with constant ellipticity angle at every point in momentum space within the vicinity of BIC. The topological nature of BIC reflects on the orientation angle of polarization state, with a topological charge of 1 for any value of ellipticity angle. Full coverage of Poincaré sphere (i.e., $$- {{\pi \over 4}} \le \chi \le {{\pi \over 4}}$$ − π 4 ≤ χ ≤ π 4 and $$- {{\pi \over 2}} \le \psi \le {{\pi \over 2}}$$ − π 2 ≤ ψ ≤ π 2 ) and higher-order Poincaré sphere can be realized by tailoring the twist angles. Our findings may open up new avenues for applications in structured light, quantum optics, and twistronics for photons.

Optical bound states in the continuum in periodic structures: mechanisms, effects, and applications

“…The low-cost and time-saving approaches to fabricating specially designed periodic structures supporting optical BICs are still in demand for easier observation and applications. Besides, with deeper insight into the modulations of optical BICs, more sophisticated three-dimensional periodic structures like tilted gratings requiring special slit angles and multilayered structures requiring precise alignment are needed to achieve special modulation effects [60,61,72,73] . There are still many theoretically proposed optical BICs with novel properties to be experimentally implemented, in which many of them are hindered by the sample preparations.…”

A hierarchical metafabric with dynamically thermochromic property for subambient daytime radiative cooling

“…Therefore, the imminent development of materials and systems that facilitate precise thermal regulation of the human body in an energy-efficient manner is imperative. 7,8 Recently, novel research has yielded diverse designs for radiative cooling that aim to enhance cooling performance, including photon structures, 9,10 aerogel structures, 11 multilayered structures 12,13 and polymer structures. 14,15 Currently, researchers are striving to integrate structural designs into textiles to provide radiative cooling.…”

Modulating Polarization in Second Harmonic Generation through Symmetry Evolution in Plasmonic Lattices

“…In the current era of photonic information, photonic lattices have become increasingly impressive due to their capability for photon confinement and manipulation, which enhances the investigation of light–matter interactions at the nanoscale. In recent years, numerous exceptional studies on photonic lattices have been conducted in the field of topological photonics, , bound states in the continuum (BIC), , terahertz waves generation, nanolasing, and super-resolution imaging. , Additionally, nonlinear optical processes such as harmonic generation and four-wave mixing have been observed in photonic lattices. , Particularly, the nonlinear process of second harmonic generation (SHG), where two photons with the same energy (ℏω) are converted into a photon with double the energy (2ℏω), has garnered significant attention over the past few decades. This interest is due to its narrow nonlinear response, which is enhanced by the lattice resonances and contributes to the development of nanoscale light-driven sources.…”