Highly dispersive coupled ring-core fiber for orbital angular momentum modes

In this work, we propose and design a highly dispersive coupled ring-core fiber (CRF) with two concentric high-index rings using Schott glass for orbital angular momentum (OAM) modes. By properly selecting the fiber geometrical parameters, the OAM130,1 mode supported in the proposed CRF has a large negative chromatic dispersion (CD) of −20 271 ps/(nm km) at 1260.4 nm. We also show that the proposed CRF could be an excellent candidate for various CD-related applications of OAM modes in the optical fiber. The dispersion of the OAM3,1 mode can reach down to −75 273 ps/(nm km) at 1491 nm. Furthermore, the effect of the geometrical parameters on chromatic dispersion for different OAM modes is investigated. Adjusting the parameters of the inner ring or the outer ring could greatly influence the peak value of the dispersion, while moving the two high-index rings at the same time mainly changes the position of the crossing wavelength.