Light Confinement in Coreless Twisted Photonic Crystal Fibers

Recent work have shown light confinement can occur during propagation through a twisted coreless photonic crystal fiber (a chiral fiber). In the absence of a twist, the modal profile is assumed known from Bloch theory and assumed not to be confined. By use of asymptotic techniques applied to the field propagation equation, we provide a theoretical framework in support of observed confinement. While we do this for a particular periodic index profile, recent experiments suggest this to be a robust effect. In this work, we also explore the problem both in the linear and the nonlinear regime. We show that an increase in twist rate will result in more confined modes and indications that nonlinearity plays a secondary role on confinement.