A hollow-core circular photonic crystal fiber mode selective coupler for generating orbital angular momentum modes

We propose orbital angular momentum (OAM) mode generation using an all-fiber coupler based on hollow-core circular photonic crystal fibers (PCF). Using the mode-matching method, we calculated the coupling efficiency of high-order vector modes excited by the OAM coupler. The coupler's structure with optimal parameters was designed to achieve high mode purity and good coupling efficiency for broadband operation. By selecting the proper center-to-center distance and coupling length, the designed mode selective coupler (MSC) generated no more than third-order OAM mode coupling. The MSC's maximum coupling efficiency was more than 51% and its mode purity was in excess of 52% across the entire C + L band. The OAM MSC's design provides a key basis for constructing an all-fiber mode division multiplexing (MDM) communication system.

Automated summary

The study presents a method for generating orbital angular momentum modes using an all-fiber coupler, achieving high coupling efficiency and mode purity for broadband operation through optimized parameters. By adjusting the center-to-center distance and coupling length, efficient coupling of OAM modes can be achieved in the C+L band.