Theoretical Analysis of a 750-nm Bandwidth Hollow-Core Ring Photonic Crystal Fiber With a Graded Structure for Transporting 38 Orbital Angular Momentum Modes. - Chunhua Jia; Hongzhi Jia; Ning Wang 028; Junyu Chai; Xun Xu; Yu Lei; Gang Liu; Yanting Peng; Jilong Xie (IEEE Access, 2018)