Low-loss and helical-phase-dependent selective excitation of high-order orbital angular momentum modes in a twisted ring-core fiber

Abstract

We propose a method for the selective generation of high-order orbital angular momentum (OAM) modes by twisting a ring-core fiber (RCF). Theoretically, 22 OAM modes can be generated in the twisted RCF with effective mode separation. We experimentally demonstrate the excitation of OAM modes up to the fourth order. The positive or negative topological charge is determined by the clockwise or counterclockwise twist direction, indicating that the helical phase of the OAM can be controlled by the twist orientation. Compared with other fiber-based methods, the high-order OAM modes generated by our approach have the characteristics of low loss (minimum 0.3 dB), high mode purity (maximum 98%), and simple fabrication. This has potential applications in high-resolution imaging, high-capacity fiber-optics communication, vortex-optics sensing, and other fields.