Control of surface modes in hollow dual-core photonic crystal fibers

The coupling of the surface modes and the fundamental modes is the root of the disappearance of coupling points between the two cores of the hollow dual-core photonic crystal fibers. In order to study the mechanism of the appearance and control of surface modes, the full vector finite element method and the plane wave expansion method were used to study the effect of the silica ring or the core radius on the surface modes and the change of the uncoupling point. The numerical simulation shows that with the same core radius, the uncoupling point moves to longer wavelength with the increase of the normalized thickness of the silica ring. And the optimal range of core radius that is free of surface modes is from 0.9 to 1.0 when the normalized thickness of the silica ring is set to 1. The results provide theoretical evidence to design the novel hollow dual-core photonic crystal fibers, enriching and consummating the theoretical foundation for the hollow dual-core photonic crystal fibers.