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The magneto-optical (MO) materials are essential for designing nonreciprocal devices, like isolators and circulators. Even though the study of MO effect has a long history, the recent works of fabricating nonreciprocal nanostructures, novel MO metamaterials, and topological photonics have garnered significant attention in both theoretical and experimental research of MO materials. In this work, we consider the planar MO waveguide mode. By setting the general form of the fields and utilizing the boundary conditions, the analytical solution of MO modes is obtained. We have shown the potential of such effective solution in analyzing the dispersions and transport behaviors of MO modes in the waveguide. Crossings and avoided crossings of modes will happen, which may due to the strong coupling of TE and TM modes in the waveguide. Faraday rotation can be observed during the propagation of MO modes and the energy flow will precess in the waveguide. These results can be applied in predicting the evolution of the modes in MO waveguides, which has potential in designing MO nonreciprocal devices.

Electromagnetic wave transmission in a magneto-optical (MO) medium is a basic and old topic but has raised new interest in recent years, because MO medium plays a vital role in optical isolator, topological optics, electromagnetic field regulation, microwave engineering, and many other technological applications. Here, we describe several fascinating physical images and classical physical variables in MO medium by using a simple and rigorous electromagnetic field solution approach. We can easily obtain explicit formulations for all relevant physical quantities, such as the electromagnetic field distribution, energy flux, reflection/transmission phase, reflection/transmission coefficients, and Goos-Hänchen (GH) shift in MO medium. This theory can help to deepen and broaden our physical understanding of basic electromagnetics, optics, and electrodynamics in application to gyromagnetic and MO homogeneous medium and microstructures, and might help to disclose and develop new ways and routes to high technologies in optics and microwave.

Being invisible at will has fascinated humanity for centuries and it has become more tangible with the development of metasurfaces, which have demonstrated the extraordinary ability of wavefront manipulation. However, state-of-the-art invisibility cloaks typically work in a deterministic system with a limited bandwidth and small incident angle ranges. Here, by integrating the phase-change material of Ge 2 Sb 2 Te 5 and the wavefront tailoring functionality of a reflective metasurface, we have achieved a unique carpet cloak that is endowed with broadband invisibility from 6920 to 8220 nm, fully concealing objects over a wide angular span of ±25° and a prominent radar cross-section reduction. Furthermore, the central cloaking wavelength can be continuously tuned with Ge 2 Sb 2 Te 5 film under different intermediate phases by precisely controlling external stimuli, which will provide a flexible and encouraging way to achieve active features once fabricated. Simulation results also show that the cloaking bandwidth can be significantly extended by triggering Ge 2 Sb 2 Te 5 from the amorphous to crystalline states. Importantly, the hybrid metasurface can realize switching of "ON" and "OFF" states in terms of cloaking features by converting Ge 2 Sb 2 Te 5 from the amorphous to the crystalline state. To the best of our knowledge, this is the first metasurface carpet cloak that utilizes the phase-change material of Ge 2 Sb 2 Te 5 to achieve ultra-broadband, wide-angle, continuously tunable and switchable cloaking with low profiles, light weights, and easy access. This design of a reconfigurable cloak is expected to find potential applications in various areas such as vehicle cloaking, illusions and so on.

We demonstrate design, fabrication, and ray trace observation of negative refraction of near-infrared light in a two-dimensional square lattice of air holes etched into an air-bridged silicon slab. Special surface morphologies are designed to reduce the impedance mismatch when light refracts from a homogeneous silicon slab into the photonic crystal slab. We clearly observed negative refraction of infrared light for TE-like modes in a broad wavelength range by using scanning near-field optical microscopy technology. The experimental results are in good agreement with finite-difference time-domain simulations. The results indicate the designed photonic crystal structure can serve as polarization beam splitter.

We propose a line defect waveguide structure along the Gamma-Mu direction in two-dimensional triangular lattice silicon photonic crystal slabs. The modal dispersion relation and the transmission spectra of this waveguide are studied. The results show that by perturbing the width of the line defect and the diameter of the air holes adjacent to the waveguide core, one can control the width of the single mode transmission window and make it far broader than the original one. The proposed Gamma-Mu waveguide will help to build a more flexible network of interconnection channel of light in two-dimensional photonic crystal slabs.