Unidirectional Wave Propagation in Low-Symmetric Colloidal Photonic-Crystal Heterostructures.

Vassilios Yannopapas

doi:10.3390/nano5010376

Abstract

We show theoretically that photonic crystals consisting of colloidal spheres exhibit unidirectional wave propagation and one-way frequency band gaps without breaking time-reversal symmetry via, e.g., the application of an external magnetic field or the use of nonlinear materials. Namely, photonic crystals with low symmetry such as the monoclinic crystal type considered here as well as with unit cells formed by the heterostructure of different photonic crystals show significant unidirectional electromagnetic response. In particular, we show that the use of scatterers with low refractive-index contrast favors the formation of unidirectional frequency gaps which is the optimal route for achieving unidirectional wave propagation.

Highlights

Photonic computing holds promise for superior processing of information in terms of speed, liability and bandwidth
T + refers to the transmittance of light incident from the left (001) face of the photonic crystals (PCs) slab, i.e., a wave propagating from left to right whereas T − refers to the transmittance of light incident from the right
We have shown numerically that it is possible to obtain unidirectional EM wave propagation with plain, linear, dielectric photonic crystals consisting of colloidal micro- or nanospheres without applying external magnetic fields or using nonlinear materials

Summary

Introduction

Photonic computing holds promise for superior processing of information in terms of speed, liability and bandwidth. Key ingredients in a photonic/optical computer are the waveguiding devices which steer light among different photonic components (diodes, optical transistor, optical buffers, etc.). This is accomplished in the microwave regime via conventional metallic waveguides, in the optical regime it still is a subject of intensive research as commercially available optical fibers cannot efficiently bend light around sharp corners at micrometer or even lower dimensions. Perhaps the most robust method for steering and bending light in the micrometer scale are the so-called photonic-crystal fibers [1]. Device performance in photonic-crystal fibers can be deteriorated by fabrication imperfections which lead to important backscattering of light, especially at sharp edges

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Conclusion