Performance of circular photonic crystal fiber transmitting orbital angular momentum modes under macro-bending

Circular photonic crystal fibers (C-PCFs) have been proved to be a good candidate for orbital angular momentum (OAM) modes supporting fiber, because they possess many excellent features, such as good quality of OAM modes, large separation of the effective indices, low confinement loss, flat dispersion and a large mode field effective area. This paper gives evidence that the C-PCF also shows good performance in the perspective of bending strength. We establish a model to research the macro-bending characteristics of the C-PCF using conformal transformation. Through the analyses, we find that phases of all OAM modes are not sensitive to bending and higher order OAM modes show better bending resistance. Besides that, the 9 mm radius of curvature can be taken as the bending tolerance of the C-PCF, considering mode field characteristics, loss, intra-mode walk-off and inter-mode crosstalk. Finally, the comparison is presented between the C-PCF and ring-core fiber (RCF) with similar OAM modes, and we can conclude that the C-PCF shows an obviously better performance, immune to bending, than that of the RCF. (paper)