Macro-bending Losses of Circular Photonic Crystal Fiber Supporting 14 OAM Modes

Analysis of Bending-Induced Degradation of Orbital Angular Momentum Modes in Optical Fibers

“…In spite of the fact that the fiber bending is inevitably involved in practical uses of the optical fibers, the effect of the fiber bending on OAM mode propagation has not been studied sufficiently with theoretical and numerical bases. There have only been a few investigations on the additional propagation loss or OAM mode deformation caused by the bending [10][11][12]. More serious impairments on OAM modes due to the fiber bending have not been investigated in depth.…”

“…In this paper, we theoretically investigated the bending-induced impairments on a OAM l = −1 mode in three types of optical fibers: Vortex fiber (VF) [13], ring core fiber (RCF) [11], and photonic crystal fiber (PCF) [10,14]. The bending effects were investigated in terms of the bending loss, topological charge number degradation, and intermodal crosstalk.…”

“…Those three types of fibers (VF, RCF, and PCF) were chosen as the representative types of OAM mode fibers that have been designed or experimentally demonstrated in the recent literature. The specific structures of the chosen fiber types were also adopted from the literature [10,11,13,14]. The PCF structure considered in reference [10], where its bending loss was investigated numerically, was first chosen, and then, the structures of VF and RCF of about the same mode sizes as the PCF were chosen for a fair comparison.…”

“…The specific structures of the chosen fiber types were also adopted from the literature [10,11,13,14]. The PCF structure considered in reference [10], where its bending loss was investigated numerically, was first chosen, and then, the structures of VF and RCF of about the same mode sizes as the PCF were chosen for a fair comparison. In the VF, depicted in Figure 1a,d, there are three different core regions whose radii and refractive indices are r 1 = 4 µm, r 2 = 3 µm, r 3 = 1.5 µm, n 1 = 1.44, n 2 = 1.48, n 3 = 1.433, and n 4 = 1.455, respectively [13].…”

“…In this work, we considered one of the previously demonstrated RCF structures [11], whose structural parameters are r 1 = 6.7 µm, r 2 = 1.9 µm, n 1 = 1.444, and n 2 = 1.473 at 1.55 µm. The PCF, depicted in Figure 1c,f, consists of the central point defect (enlarged air hole) of d 1 = 2.4 µm and the ring-shaped defect (absence of air holes) in the concentrically arranged air holes of d 2 = 1.6 µm embedded in the matrix of n = 1.444 [10,14]. In all the fiber structures, step index profiles were assumed for simplicity.…”