Nonreciprocal lensing and backscattering suppression via magneto-optical nonlocality

Abstract

We introduce a special kind of nonreciprocal electromagnetic response which gives rise to backscattering suppression in the bulk, a long-sought feature in topological photonics, as well as nonreciprocal lensing - an effect when the same structure focuses light incident from one direction and defocuses light propagating in the opposite way. We predict this response in spin spirals and in specially designed metamaterials, validating the key predictions.

Figures (3)

• Figure 1: (a) Isofrequency contours for the medium with quasi-moving spatial dispersion. Inversion symmetry of the contours is broken. Different colors encode the values of $\chi_\text{qm}$ labeled at the curves, $\lambda$ denotes the wavelength in vacuum. For simplicity, we assume permittivity $\varepsilon=1$. (b) Spiral arrangement of spins in the lattice enabling quasi-moving spatial dispersion. (c) Metamaterial configuration producing enhanced quasi-moving response. Arrows indicate the direction of magnetization of the cylinders.
• Figure 2: (a) Artistic image of a non-reciprocal lens, with light paths traced for left-to-right and right-to-left propagation. (b) Focal distance for the fixed light polarization computed for two opposite propagation directions. Material characteristics $\varepsilon_\perp=2.9$, $\varepsilon_\parallel=1.0$, $N=30$, $g=0.9$, $\beta=0.3 \pi$. The focal distance is multiplied by the combined curvature $\kappa = 1/R_{1} - 1/R_{2}$ of the refractive surfaces.
• Figure 3: Asymmetric scattering in the quasi-moving medium: (a) A schematic image of a random defect excited by an electromagnetic wave and radiating mostly forward. (b) Radiation pattern for the $x$-aligned dipole in quasi-moving medium with $\chi_\text{qm}=-0.2$ shown in $Oxz$ plane. (c) The ratio of power radiated in the forward $+z$ direction to the total radiation power versus the strength of the quasi-moving effect $\chi_\text{qm}$.