Directed diffraction without negative refraction

TL;DR

This paper investigates electromagnetic wave propagation in 2D photonic crystals, revealing wave bending phenomena within partial bandgaps that challenge the need for negative refraction explanations.

Contribution

It demonstrates that wave bending in photonic crystals can occur without invoking negative refraction or superlensing, providing a new perspective on wave behavior in these structures.

Findings

Waves bend away from forbidden directions within partial bandgaps

Negative refraction is not necessary to explain wave bending

Wave propagation analyzed using FDTD and plane-wave expansion methods

Abstract

Using the FDTD method, we investigate the electromagnetic propagation in two-dimensional photonic crystals, formed by parallel air cylinders in a dielectric medium. The corresponding frequency band structure is computed using the standard plane-wave expansion method. It is shown that within partial bandgaps, waves tend to bend away from the forbidden directions. This phenomenon perhaps need not be explained in terms of negative refraction or `superlensing' behavior, contrast to what has been conjectured.