Nonreciprocal Goos-Hänchen shift by topological edge states of a magnetic photonic crystal

Light transport through a magneto-optical medium: simple theory revealing fruitful phenomena

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.

Enhancing the nonreciprocal Goos-Hänchen shift by the Fano resonance of coupled gyromagnetic chains at normal incidence

We report a resonance-enhanced nonreciprocal Goos-Hänchen (GH) shift for the wave reflected from the coupled gyromagnetic chains. We demonstrate that the Fano resonance enhances the GH shift with high reflectivity at normal incidence, and the resonance results from the interference between the leaky guided modes of the coupled chains. Furthermore, we show that the GH shift can be controlled by the number of stacked chains. The Fano resonance-enhanced GH shift offers a new efficiently way to enhance and control the GH shift for reflected wave beam. Such coupled gyromagnetic chains provide an extremely compact way for the devices such as unidirectional couplers and other integration photonic components, paving the way for the applications of nonreciprocal GH shift.

Adjustable enhanced Goos-Hänchen shift in a magneto-optic photonic crystal waveguide

We have presented adjustable enhanced Goos-Hänchen (GH) shift in a magneto-optical photonic crystal (MOPC) waveguide. The waveguide consists of a top layer of ferrite rods and a lower MOPC with opposite biased dc external magnetic fields (EMFs), and it supports both odd-like and even-like modes simultaneously. The simulation results show the odd-like mode can cause an enhanced negative GH shift, while the even-like mode can result in an enhanced positive GH shift. The physical reason for such negative and positive GH shifts is attributed to the efficient mode coupling and propagation behaviors of the electromagnetic (EM) wave in the waveguide. Furthermore, we have realized the switchable negative/positive GH shift by altering the direction combination of the EMFs. In addition, the magnitudes of both GH shifts can be adjusted by changing the strength of EMF or the width of the waveguide. These results provide new ways to control the transmission behaviors of EM wave and hold promise in applications such as detections, optical switches, and sensors.

Non-Hermitian Physics without Gain or Loss: The Skin Effect of Reflected Waves

Physically, one tends to think of non-Hermitian systems in terms of gain and loss: the decay or amplification of a mode is given by the imaginary part of its energy. Here, we introduce an alternative avenue to the realm of non-Hermitian physics, which involves neither gain nor loss. Instead, complex eigenvalues emerge from the amplitudes and phase differences of waves backscattered from the boundary of insulators. We show that for any strong topological insulator in a Wigner-Dyson class, the reflected waves are characterized by a reflection matrix exhibiting the non-Hermitian skin effect. This leads to an unconventional Goos-Hänchen effect: due to non-Hermitian topology, waves undergo a lateral shift upon reflection, even at normal incidence. Going beyond systems with gain and loss vastly expands the set of experimental platforms that can access non-Hermitian physics and show signatures associated with non-Hermitian topology.