Theoretical Analysis of a 750-nm Bandwidth Hollow-Core Ring Photonic Crystal Fiber With a Graded Structure for Transporting 38 Orbital Angular Momentum Modes

Abstract

In this paper, a novel hollow-core ring photonic crystal fiber (HR-PCF) is proposed based on As2S3. It supports the transmission of up to 38 orbital angular momentum (OAM) modes. It is composed of a concentric ring cladding of air holes gradually increasing in diameter. In addition, the center also has a large circular air hole. A numerical simulation is accomplished using the finite-element method. Different geometrical parameters of the proposed HR-PCF include the number of air hole rings in the cladding and the background material. These parameters are varied to determine the optimal structure. The properties of the synthesized OAM vector modes are simulated and analyzed systematically and theoretically. Through the simulation of different parameters, we show that the optical fiber structure based on a three-ring cladding and As2S3 material can support 38 OAM modes. This configuration also has better eigenmode characteristics, such as the effective refractive index difference between vector modes with the same topological charge number. This difference can exceed 10−4, preventing these modes from coupling to linear polarization modes. In addition, the vector mode dispersion curve becomes smoother with increasing wavelength, and the confinement loss remains low, ranging from 10−10–10−9dB/m. Moreover, we also discuss effective mode area and nonlinear coefficients and their applications. We also investigated that various effects on the dispersions by details of the proposed HR-PCF, such as air hole spacing between adjacent rings and the diameter of the center circular air hole. This system offers some promising applications for short-distance, high-volume communications due to the increased number of OAM transfer modes.