Broadband super-collimation in a hybrid photonic crystal structure

Rafif E Hamam,Steven G Johnson,Mihai Ibanescu,J D Joannopoulos,Marin Soljacic

doi:10.1364/oe.17.008109

Abstract

We propose a two dimensional (2D) photonic crystal (PhC) structure that supports super-collimation over a large frequency range (over 4 times that of a traditional square lattice of holes). We theoretically and numerically investigate the collimation mechanism in our 2D structure, in comparison to that of two other frequently used related PhC structures. We also point out the potential importance of our proposed structure in the design of super-collimation-based devices for both monochromatic and polychromatic light.

Highlights

The ability of photonic crystals (PhCs) to “mold the flow of light” [1] has resulted in a remarkable variety of fascinating optical phenomena, such as omnidirectional reflection [2, 3, 4], low loss bends [5], high-Q cavities [5], efficient spontaneous emission [6, 7], negative refraction [8, 9], enhancement of nonlinear effects [10], ultrafast all-optical switching [11], and thermal emission design [12]
It was first described by Kosaka et al [13], and subsequently by several other groups [14, 15, 16, 17, 18, 19]. In all these demonstrations of super-collimation, the nondiffractive propagation is achieved by having a flat constant-frequency contour (CFC) in the dispersion relation of the PhC
The band diagram of these PhCs would consist of extended frequency ranges over which the CFCs are

Summary

Introduction

The ability of photonic crystals (PhCs) to “mold the flow of light” [1] has resulted in a remarkable variety of fascinating optical phenomena, such as omnidirectional reflection [2, 3, 4], low loss bends [5], high-Q cavities [5], efficient spontaneous emission [6, 7], negative refraction [8, 9], enhancement of nonlinear effects [10], ultrafast all-optical switching [11], and thermal emission design [12]. The super-collimation property in such a structure manifests itself only in a narrow frequency interval, within which the CFC’s curvature flips sign This is depicted, where we show a typical color contour plot of the first TE (electric field in the plane of periodicity) band for the structure of Fig. 1(a). In this manuscript, we investigate the phenomenon of super-collimation in this 2D hybrid PhC structure [21, 22], and show how it simultaneously inherits useful properties from both of the structures in Fig. 1(a) and Fig. 1(c): the sign flip of the CFCs’ concavity (due to the discrete translational symmetry) from the 2D holes-in-dielectric structure, and the extended frequency range (over 4 times the frequency range of a traditional square lattice of holes) of the flat CFCs (due to the weakly coupled waveguides), from the waveguide array structure. Considerations concerning the coupling of light into and out of our proposed structure are very similar to those in PhC structures previously used for supercollimation, such as the holes-in-dielectric structure studied in [17]

Super-collimation mechanism in our proposed structure

Holes-in-dielectric structure

Waveguide arrays

Conclusion