arXiv subjects

Yingfeng Qi

Publications and source records attributed to Yingfeng Qi.

3 recordsLinked to original sources

arXiv2026

Observation of fractality-induced topology in photonic crystals

Fractal topology--achieved by integrating nontrivial topology into fractal geometries with self-similarity and non-integer dimensions--has opened new avenues for exploring topological phases of matter. Recent theoretical advances revealed a counterintuitive fractal topology: fractality itself can induce nontrivial topology in an otherwise trivial system. Here, we report the first experimental observation of fractality-induced topology in a tight-binding-like photonic crystal, without relying on traditional driving mechanisms such as magnetic fields, staggered hopping, or spin-orbit coupling. We demonstrate that fractality alone is sufficient to lift the degeneracy of Kagome lattice band structure and induce topological corner states within the bandgap of the resulting fractal Kagome photonic crystal, which is a photonic higher-order topological insulator. This work experimentally reveals a novel mechanism for realizing nontrivial topological states, expanding both the fundamental frontier and potential application of topological physics.

physics.optics↗

arXiv2026

Crosstalk-free Chiral Anomaly Bulk States in Photonic Crystals

Ultracompact cladding-free waveguide arrays with zero inter-channel spacing and negligible crosstalk open a new avenue for high-density integrated photonic circuits. However, existing cladding-free waveguide arrays typically rely on conventional trivial bulk modes, making them highly susceptible to scattering losses at sharp bends or in the presence of obstacles and defects. To overcome this limitation, we theoretically propose and experimentally demonstrate a robust, crosstalk-free, and cladding-free photonic waveguide array based on chiral anomaly bulk states (CABSs) in photonic crystals. By interfacing distinct Dirac photonic crystals that host Dirac cones at different high-symmetry points ({\Gamma} and K) in the Brillouin zone and carefully engineering the boundary conditions, the boundary-induced CABSs in adjacent channels become effectively decoupled due to a large momentum separation, thereby eliminating inter-channel crosstalk. More importantly, we experimentally demonstrate that these crosstalk-free CABSs are robust to perturbations, including metallic obstacles, air defects, and sharp bends. We further extend the CABS-based waveguide array to two dimensions and demonstrate a cladding-free triangular resonator and a crosstalk-free waveguide crossing, both of which are previously unattainable. Our work establishes a new design paradigm for cladding-free, crosstalk-free, and ultracompact topological photonic devices, paving the way for robust, highly integrated photonic circuits.

physics.optics↗

arXiv2024

Topological Dirac-vortex modes in a three-dimensional photonic topological insulator

Recently, topological Dirac-vortex modes in Kekul\'e-distorted photonic lattices have attracted broad interest and exhibited promising applications in robust photonic devices such as topological cavities, lasers, and fibers. However, due to the vectorial nature of electromagnetic waves that results in complicated band dispersions and fails the tight-binding model predictions, it is challenging to construct three-dimensional (3D) topological photonic structures with Kekul\'e distortion and the photonic topological Dirac-vortex modes have thus far been limited to two-dimensional (2D) systems. Here, by directly mapping a 3D Kekul\'e-distorted tight-binding model in a 3D tight-binding-like photonic crystal exhibiting scalar-wave-like band structures, we theoretically propose and experimentally demonstrate topological Dirac-vortex modes in a 3D photonic topological insulator for the first time. Using microwave near-field measurements, we directly observe robust photonic topological Dirac-vortex modes bound to and propagate along a one-dimensional (1D) Dirac-vortex line defect, matching well with the tight-binding and simulation results. Our work offers an ideal platform to map tight-binding models in 3D topological photonic crystals directly and opens a new avenue for exploiting topological lattice defects to manipulate light in 3D space.

physics.optics↗