arXiv subjects

Guangtai Lu

Publications and source records attributed to Guangtai Lu.

4 recordsLinked to original sources

arXiv2026

Arbitrary Polarization Generation in Magneto-optical Metasurfaces Enabled by Bound States in the Continuum

The generation of arbitrary polarization states of light is essential for optical communication and photonic information processing. Photonic crystal and metasurface platforms supporting bound states in the continuum (BICs) provide a powerful route for polarization engineering through tailoring the radiation from the resonant modes. However, existing approaches typically rely on static structural symmetry breaking or off-normal radiation, which limits continuous polarization tuning of vertical radiation. Here, we demonstrate a magnetooptical metasurface that generates arbitrary polarization states of light at normal radiation. By applying an external magnetic field with variable rientation, a symmetry-protected BIC is transformed into a quasi-BIC whose radiation polarization can be continuously tuned. The magneto-optical perturbation drives the controlled migration of polarization singularities in momentum space, allowing the emitted states to continuously span the entire Poincaré sphere without structural modification. This approach establishes a compact platform for actively tunable polarization sources and polarizationencoded photonic devices.

physics.optics↗

arXiv2025

Experimental realization of wide-mode-area slow light modes in valley photonic crystal heterostructure waveguides

We experimentally realized wide-mode-area slow-light modes in valley photonic crystals (VPhCs) heterostructure waveguides. The waveguides are fabricated on a silicon slab by inserting gapless photonic graphene layers with varying widths and modifying the unit cell spacing near the domain walls. By reducing the spacing between unit cells at the domain boundaries, slow-light guided modes are achieved in VPhCs heterostructure waveguides. The presence of wide-mode-area modes is verified by observing the radiation in light propagation of leaky guided modes above the light line. To characterize guided modes below the light line, we introduce air-slot terminations to induce out-of-plane scattering and measure intensity profiles. The results show that the mode widths are tunable for both fast-light and slow-light modes in VPhCs heterostructure waveguides by adjusting the number of photonic graphene layers. The ability to support wide-mode-area slow-light modes in VPhC heterostructures offers promising opportunities for the development of high-power, on-chip photonic integrated devices.

physics.optics↗

arXiv2025

Topological Corner States in Bilayer and Trilayer Systems with Vertically Stacked Topological Heterostructures

We investigate bilayer and trilayer systems composed of topologically distinct, vertically stacked layers, forming topological heterostructures based on the Benalcazar-Bernevig-Hughes model. We find that a topological phase transition induced by interlayer coupling significantly alters the number of corner states in these topological structures. Furthermore, we find that traditional nested Wilson loop analysis inaccurately classifies certain phases, leading us to evaluate multipole chiral numbers (MCNs) as a more appropriate topological invariant for this scenario. The MCNs not only enable accurate classification of topological phases but also directly correspond to the number of zero-energy corner states, effectively characterizing $\mathbb{Z}$-class HOTI phases. Our study proposes the novel concept of topological heterostructures, providing critical insights into the control of localized corner states within multilayer systems and expanding potential research directions.

cond-mat.mes-hall↗

arXiv2024

Topological Laser in Anomalous Quadrupole Topological Phases

Topological photonics shows considerable promise in revolutionizing photonic devices through the use of topological phases, leading to innovations like topological lasers that enhance light control. One of recent breakthroughs is reducing the size of these systems by utilizing lower-dimensional boundary states, notably via higher-order topological phases. This paper presents the first experimental demonstration of topological laser in anomalous quadrupole topological phase, an instance of higher-order phases. To facilitate this, a topological nanocavity with quality factor near 6,000 is engineered through a twisting operation. The topological nature of our system is validated by calculation of nested Wannier center and the emergency condition of corner states. Our experimental observations reveal the manifestation of corner states and the achievement of single-mode pulsed laser, driven by optical gain from multiple quantum wells at telecommunication wavelengths and at a temperature of 4 K. A lasing threshold of 23 uW and a cold quality factor of 1,500 are deduce through rate equation. Our work gives a new potential in the application of topological principles to advance nanophotonic technologies.

physics.optics↗