title: Twist-induced guidance in coreless photonic crystal fiber: A helical channel for light.
abstract: A century ago, Einstein proposed that gravitational forces were the result of the curvature of space-time and predicted that light rays would deflect when passing a massive celestial object. We report that twisting the periodically structured "space" within a coreless photonic crystal fiber creates a helical channel where guided modes can form despite the absence of any discernible core structure. Using a Hamiltonian optics analysis, we show that the light rays follow closed spiral or oscillatory paths within the helical channel, in close analogy with the geodesics of motion in a two-dimensional gravitational field. The mode diameter shrinks, and its refractive index rises, as the twist rate increases. The birefringence, orbital angular momentum, and dispersion of these unusual modes are explored.
authors.affiliation: Max Planck Institute for the Science of Light, Staudtstrasse 2, 91058 Erlangen, Germany.
authors.forename: Ramin
authors.initials: R
authors.lastname: Beravat
authors.affiliation: Max Planck Institute for the Science of Light, Staudtstrasse 2, 91058 Erlangen, Germany.
authors.forename: Gordon K L
authors.initials: GK
authors.lastname: Wong
authors.affiliation: Max Planck Institute for the Science of Light, Staudtstrasse 2, 91058 Erlangen, Germany.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Frosz
authors.affiliation: Max Planck Institute for the Science of Light, Staudtstrasse 2, 91058 Erlangen, Germany.
authors.forename: Xiao Ming
authors.initials: XM
authors.lastname: Xi
authors.affiliation: Max Planck Institute for the Science of Light, Staudtstrasse 2, 91058 Erlangen, Germany.
authors.forename: Philip St J
authors.initials: PS
authors.lastname: Russell
keywords: Photonic crystal fibers; fiber optics; orbital angular momentum; photonic bandgap materials; photonic crystals