Floquet topological physics, an area exploring periodically driven systems and leveraging degrees of freedom in the temporal dimension, has opened new avenues in photonics by enabling the creation of novel topological phases, new control mechanisms, and intriguing phenomena that are inaccessible or challenging to realize in static systems. These include anomalous Floquet topological insulators, anomalous Floquet Anderson insulators, and topological phases with broken time-reversal symmetry without the need for magnetic fields. Unlike conventional topological photonics, which relies on fixed structural or material properties to induce topological states, Floquet topological photonics leverages time-periodic modulation to access a broader range of topological effects, introducing flexibility in tuning topological transitions and wave dynamics. This review aims to provide a comprehensive overview of Floquet topological phases in photonic systems, explaining the theoretical basics, highlighting experimental platforms, the interplay with disorder, as well as the latest advancements beyond linear, Hermitian, Euclidean-geometry photonic systems, and recent progress in applications.

Vanadium dioxide (VO2) is a popular phase-transition material with broad applications ranging from thermal management in smart windows to neuromorphic computing. Currently, VO2 thin films are usually fabricated at high temperatures, making them incompatible in forming on top of CMOS and flexible polyimide substrates. This study explores a low-temperature VO2 thin film formation approach that combines atomic layer deposition (ALD) with a post-deposition anneal. With systematic material characterizations, we clearly demonstrate high-quality VO2 film formation on Si substrates at a significantly reduced annealing temperature of 300 °C. Further reducing the annealing temperature to 250 oC is shown to lead to insufficient VO2 crystallization whilst elevating the temperature to 400 oC results in overoxidation into V2O5. We implement our method on polyimide substrates and demonstrate that the high-quality phase transition is indeed preserved. This work demonstrates the ability of low-temperature formation of VO2 thin films, and it will accelerate the adoption of VO2 in emerging electronic devices as well as photonic applications.

A polarization-sensitive nonlinear metasurface of antenna-indium tin oxide (ITO) coupled structure has been meticulously designed to enhance the nonlinear response with strong coupling between the localized surface plasmon resonance (LSPR) of gold nanoantenna and the epsilon-near-zero (ENZ) mode of the ITO film. This metasurface exhibits a broadband spectrum (∼730 nm) and a large nonlinear index coefficient n2 of 1.41 cm2/GW, which is approximately 520 times greater than that of a single-layer ITO film. Additionally, we have engineered a perfect absorber using an ITO nonlinear metasurface, with a 38 nm absorption bandwidth ranging from 1085 nm to 1123 nm, achieving near-perfect absorption, with a maximum absorption rate of up to 94% in the short-wave infrared band. These findings offer a promising foundation for the development of ultra-compact and large nonlinear optical devices.

Topological effects manifest in a variety of lattice geometries. While square lattices, due to their simplicity, have been used for models supporting nontrivial topology, several exotic topological phenomena such as Dirac points, Weyl points, and Haldane phases are most commonly supported by non-square lattices. Examples of prototypical non-square lattices include the honeycomb lattice of graphene and 2D materials, and the Kagome lattice, both of which break fundamental symmetries and can exhibit quantized transport, especially when long-range hoppings and gauge fields are incorporated. The challenge of controllably realizing such long-range hoppings and gauge fields has motivated a large body of research focused on harnessing lattices encoded in "synthetic" dimensions. Photons in particular have many internal degrees of freedom and hence show promise for implementing these synthetic dimensions; however, most photonic synthetic dimensions have hitherto created 1D or 2D square lattices. Here we show that non-square lattice Hamiltonians such as the Haldane model and its variations can be implemented using Floquet synthetic dimensions. Our construction uses dynamically modulated ring resonators and provides the capacity for direct k -space engineering of lattice Hamiltonians. This k -space construction lifts constraints on the orthogonality of lattice vectors that make square geometries simpler to implement in lattice-space constructions and instead transfers the complexity to the engineering of tailored, complex Floquet drive signals. We simulate topological signatures of the Haldane and the brick-wall Haldane model and observe them to be robust in the presence of external optical drive and photon loss, and discuss unique characteristics of their topological transport when implemented on these Floquet lattices. Our proposal demonstrates the potential of driven-dissipative Floquet synthetic dimensions as a new architecture for k -space Hamiltonian simulation of high-dimensional lattice geometries, supported by scalable photonic integration, that lifts the constraints of several existing platforms for topological photonics and synthetic dimensions.

Based on our previous research on the phase transition property of non-metallic vanadium oxide for low-temperature catalytic growth of graphene, we further propose that V thin films can be deposited by sputtering and then V2O5 thin films can be prepared by oxidizing the V thin films at 400 °C in a rapid annealing furnace with oxygen, which has a better crystalline structure and surface than the V2O5 thin films directly deposited by sputtering. The V2O5 prepared by oxidation was used to catalyze the growth of graphene at 300 °C in a PECVD furnace. During the growth process, a 10-fold increase in the H2 flow rate (200 sccm) was used to repair and eliminate the suspension bonds and defects of graphene, and the quality of graphene films was improved. Due to the high resistivity of V2O5 at room temperature, V2O5 can be directly used as the interlayer of the device, and the graphene-V2O5-Si (GVS) structure photodetector is proposed, which avoids the damage and impact of the transfer process and catalytic layer removal process in the conventional graphene device process. Additionally, because of the negative temperature coefficient of resistance (TCR) of vanadium oxide materials, the optical response of the GVS device is further extended to 1550 nm.

In recent years, bound states in the continuum (BICs) in the all-dielectric metasurfaces have attracted considerable attention due to the low radiation loss and large quality factor (Q-factor). In this study, we design a highly sensitive refractive index sensor working in multi-scenario based on merging quasi-BIC in the silicon nitride metasurface. By adjusting the thickness of the metasurface and keeping the structural symmetry, nine BICs distributed in momentum space form the merging BIC at the Γ point with significantly enhanced Q-factor. The transmission spectra of the metasurface sensor disperse with the refractive index in multi-scenario. The modulation depth of the Fano resonance spectrum can exceed 99.9%. The sensitivity and figure of merit of the refractive index sensor based on the merging quasi-BIC can reach 41.35 nm/RIU and 13,389.1 RIU-1 for gas, 59.05 nm/RIU and 8,415.9 RIU-1 for blood, and 66.08 nm/RIU and 8,845.8 RIU-1 for cerebrospinal fluid, respectively. Furthermore, we investigate the influence of the structural deviations on the Q-factor, which of the merging quasi-BIC maintains higher than that of the isolated quasi-BIC. Our work offers a method for designing high-sensitivity sensors working in multi-scenarios, which may hold significant potential for enhancing device performance in gas and biological detection.

Control over the magnetic domain structure of garnet films is an important task that is attractive for a wide range of applications. One of the possible approaches here is based on the introduction of additional structured magnetic coverages interacting with the garnet layer. In this study, we demonstrate that arrays of asymmetric ferromagnetic cobalt particles regularly arranged on the surface of Lu,Bi-substituted iron garnet film influence the orientation and width of the stripe domains, as stems from the optical microscopy, magneto-optical and diffraction studies. We also show that triangular-shaped Co particles induce the asymmetry of the magnetic field dependence on the magneto-optical Kerr effect of the composite structure. We assert that the key effect here is the interaction of the residual magnetic moments of Co particles with the surface closure domains.

With the advancement of nano-photonics, near-field optical microscopy technology has gradually attracted widespread attention from researchers in different fields in recent years. In order to address the practicality and integration issues of near-field optical microscopy technology, this paper studies the basic principle and construction scheme of a scattering-type scanning near-field optical microscope (s-SNOM). We designed and built an s-SNOM system that realizes the measurement of impurity particles with a diameter of about 100 nm. The practicality of the system has been experimentally verified. Furthermore, a large ring width amplitude-type Fresnel zone plate (FZP) with a processing error of 100 nm is prepared using UV lithography. Finally, by replacing the focusing lens in the s-SNOM system with the prepared FZP, the recognition of impurity particles with a diameter of about 100 nm can also be achieved. The experimental results indicate that it is possible to achieve the integration of the s-SNOM system without reducing resolution. This study provides a preliminary exploration for the practicality and integration of the SNOM systems.

To unlock the full potential of laser-cooled silica optical fibers, a better understanding of the internal mechanisms of heat generation is required. This work explores ytterbium-doped aluminosilicate fibers produced via industry-standard modified chemical vapor deposition (MCVD) techniques with varied levels of divalent ytterbium to determine their effect on anti-Stokes fluorescence thermal performance. The inclusion of Yb2+ is shown to have a significant negative impact on cooling potential. Yb2+ ions are shown to correlate with heat generation by two distinct mechanisms, absorption and quenching of active Yb3+ ions. This excess heating represents a reduction in quantum efficiency that is detrimental to Yb-doped fiber lasers and amplifiers beyond the laser-cooling application.

Topological photonics allows for the deterministic creation of electromagnetic modes of any dimensionality lesser than that of the system. In the context of two-dimensional systems such as metasurfaces, topological photonics enables trapping of light in 0D cavities defined by boundaries of higher-order topological insulators and topological defects, as well as guiding of optical fields along 1D boundaries between topologically distinct domains. More importantly, it allows engineering interactions of topological modes with radiative continuum, which opens new opportunities to control light-matter interactions, scattering, generation, and emission of light. This review article aims at highlighting recent work in the field focusing on the control of radiation and generation of light in topological metasurfaces.