Realization of broadband index-near-zero modes in nonreciprocal magneto-optical heterostructures

TL;DR

This paper demonstrates tunable index-near-zero modes with nonzero group velocities in nonreciprocal magneto-optical systems, enabling applications like perfect optical buffers and advancing research in cloaking and high-resolution imaging.

Contribution

It introduces the realization of tunable INZ modes with zero wavenumber and nonzero group velocity in nonreciprocal magneto-optical heterostructures, supported by theoretical and numerical analysis.

Findings

INZ modes with tunability in nonreciprocal systems

Experimental demonstration at Dirac point frequencies

Potential for perfect optical buffers in microwave and terahertz regimes

Abstract

Epsilon-near-zero (ENZ) metamaterial with the relative permittivity approaching zero has been a hot research subject in the past decades. The wave in the ENZ region has infinite phase velocity ($v=1/\sqrt{\varepsilon\mu}$), whereas it cannot efficiently travel into the other devices or air due to the impedance mismatch or near-zero group velocity. In this paper, we demonstrate that the tunable index-near-zero (INZ) modes with vanishing wavenumbers ($k=0$) and nonzero group velocities ($v_\mathrm{g} \neq 0$) can be achieved in nonreciprocal magneto-optical systems. This kind of INZ modes has been experimentally demonstrated in the photonic crystals at Dirac point frequencies and that impedance-matching effect has been observed as well. Our theoretical analysis reveals that the INZ modes exhibit tunability when changing the parameter of the one-way (nonreciprocal) waveguides. Moreover, owing to the zero-phase-shift characteristic and decreasing $v_\mathrm{g}$ of the INZ modes, several perfect optical buffers (POBs) are proposed in the microwave and terahertz regimes. The theoretical results are further verified by the numerical simulations performed by the finite element method. Our findings may open the new avenues for research in the areas of ultra -strong or -fast nonlinearity, perfect cloaking, high-resolution holographic imaging and wireless communications.