Hybrid-structured photonic crystal fiber for propagating vortex beams by multiple-core channels

Abstract

.Photonic crystal fibers (PCFs) have been extensively studied to enhance communication capacity and spectral efficiency by supporting orbital angular momentum (OAM) modes. However, the structural fragility resulting from the central air hole in PCFs undermines the fiber’s roundness. We introduce a hybrid PCF that replaces the central air hole with a material with a high refractive index. This innovation not only enhances the fiber’s structural strength but also introduces an additional communication channel. Furthermore, this method increases the amount of OAM modes supported for transmission in the ring. Numerical results demonstrate that significant differences in refractive indices exist between adjacent vector modes, with high mode quality (ranging from 74.6% to 97.6%) and a small effective mode area (ranging from 23.5 to 59.5 μm2). The proposed hybrid PCF can transmit 20 OAM modes in the inner core and 54 OAM modes in the outer ring. The spacing between the two layers of air holes has a minimal impact on the effective mode area and mode quality. However, the effective mode area decreases and the mode quality increases with the enlargement of the diameter of air holes. In addition, a decrease in doping concentration results in lower mode quality and a larger effective mode area. Moreover, the proposed hybrid PCF can be employed in OAM-based mode division multiplexing for high-capacity short-range fiber optic communication.