High-Order Mode Characteristics of a 7-Cell Hollow-Core Photonic Bandgap Fiber

Abstract

For many years, the number and losses of modes have restricted the large-scale application of hollow core photonic bandgap fibers (HC-PBFs) in data transmission. Researchers have successfully reduced fiber loss to an extremely low level; however, little attention has been given to the specific characteristics of the higher-order modes (HOMs) in HC-PBF. In this paper, the high-order mode characteristics of a 7-cell HC-PBF are investigated in detail, and the non-degenerate phenomenon of HE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> is observed. Through an in-depth theoretical analysis by discussing the influence of the structural deformation of the fiber near the core on the high-order mode characteristics, the cause of the phenomenon is described. Thus, an optimized 7-cell HC-PBF for supporting 6 modes is developed. Additionally, the bending losses of all the HOMs in the fiber are measured. Marked bending loss is not observed even when the bending radius is as small as 0.5 cm, which is different from a solid core four-mode fiber. These findings will provide a reference for HC-PBF as a new type of few-mode fiber for the mode division multiplexing field.