title: Optical activity in twisted solid-core photonic crystal fibers.
abstract: In this Letter we show that, in spectral regions where there are no orbital cladding resonances to cause transmission loss, the core mode of a continuously twisted photonic crystal fiber (PCF) exhibits optical activity, and that the magnitude of the associated circular birefringence increases linearly with twist rate and is highly reproducible. In contrast to previous work on twist-induced circular birefringence, PCF has zero linear birefringence and an on-axis core, making the appearance of circular birefringence rather unexpected. A theoretical model based on symmetry properties and perturbation theory is developed and used to show that both spin and orbital angular momentum play a role in this effect. It turns out that the degenerate left- and right-circularly polarized modes of the untwisted PCF are not 100% circularly polarized but carry a small amount of orbital angular momentum caused by the interaction between the core mode and the hollow channels.
authors.affiliation: Max Planck Institute for the Science of Light, Guenther-Scharowsky Strasse 1, 91058 Erlangen, Germany.
authors.forename: X M
authors.initials: XM
authors.lastname: Xi
authors.affiliation: Max Planck Institute for the Science of Light, Guenther-Scharowsky Strasse 1, 91058 Erlangen, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Weiss
authors.affiliation: Max Planck Institute for the Science of Light, Guenther-Scharowsky Strasse 1, 91058 Erlangen, Germany.
authors.forename: G K L
authors.initials: GK
authors.lastname: Wong
authors.affiliation: Max Planck Institute for the Science of Light, Guenther-Scharowsky Strasse 1, 91058 Erlangen, Germany and School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom.
authors.forename: F
authors.initials: F
authors.lastname: Biancalana
authors.affiliation: Department of Physics, University of Strathclyde, Glasgow G4 0NG, United Kingdom.
authors.forename: S M
authors.initials: SM
authors.lastname: Barnett
authors.affiliation: Department of Physics, University of Glasgow, Glasgow G12 8QQ, United Kingdom.
authors.forename: M J
authors.initials: MJ
authors.lastname: Padgett
authors.affiliation: Max Planck Institute for the Science of Light, Guenther-Scharowsky Strasse 1, 91058 Erlangen, Germany and Department of Physics, University of Erlangen-Nuremberg, Staudtstrasse 7, 91058 Erlangen, Germany.
authors.forename: P St J
authors.initials: PS
authors.lastname: Russell