title: Achieving centimetre-scale supercollimation in a large-area two-dimensional photonic crystal.
abstract: Diffraction, a fundamental process in wave physics, leads to spreading of the optical beams as they propagate. However, new photonic crystal (PhC) meta-materials can be nano-engineered to generate extreme anisotropy, resulting in apparent propagation of light without diffraction. This surprising phenomenon, called supercollimation, effectively freezes the spatial width of a light beam inside a PhC, observed over a few isotropic diffraction-lengths. However, using such experiments to predict the behaviour for longer propagation lengths is difficult, as a tiny error in a measured width can extrapolate to order unity uncertainty in the width at distances over hundreds of diffraction-lengths. Here, supercollimation is demonstrated in a macroscopic PhC system over centimetre-scale distances, retaining spatial width confinement without the need for waveguides or nonlinearities. Through quantitative studies of the beam evolution in a two-dimensional PhC, we find that supercollimation possesses unexpected but inherent robustness with respect to short-scale disorder such as fabrication roughness, enabling supercollimation over 600 isotropic diffraction-lengths. The effects of disorder are identified through experiments and understood through rigorous simulations. In addition, a supercollimation steering capability is proposed.
authors.affiliation: rakich@mit.edu
authors.forename: Peter T
authors.initials: PT
authors.lastname: Rakich
authors.forename: Marcus S
authors.initials: MS
authors.lastname: Dahlem
authors.forename: Sheila
authors.initials: S
authors.lastname: Tandon
authors.forename: Mihai
authors.initials: M
authors.lastname: Ibanescu
authors.forename: Marin
authors.initials: M
authors.lastname: Soljacić
authors.forename: Gale S
authors.initials: GS
authors.lastname: Petrich
authors.forename: John D
authors.initials: JD
authors.lastname: Joannopoulos
authors.forename: Leslie A
authors.initials: LA
authors.lastname: Kolodziejski
authors.forename: Erich P
authors.initials: EP
authors.lastname: Ippen