Design of circular photonic crystal fiber for OAM extraction SDM applications

Optical fibers are widely used for long links (intercontinental, terrestrial optical backbone) and short scopes (data center, access network). Certain fibers, called optical fibers specialty, also play an essential role in other fields such as medicine (e.g., endoscopy), sensors, laser applications, etc. The constant proliferation of Internet services, combined with the growth in users, makes it necessary to increase the current capacity of networks to optical fiber. Today, the fibers installed and used for transmission at very high-speed use only the fundamental mode (denoted LP) to transmit information: we speak of fiber's single-mode optics. As they now reach the nonlinear limit of Shannon, one of the ideas for increasing the capacity of optical networks is to implement spatial multiplexing (SDM: Space Divison Multiplexing) and to simultaneously use different modes in a so-called slightly multimode fiber (generally supporting a few dozen modes) or different cores in a multicore fiber. Since 2010, several studies have been developed in this direction, mainly on the fibers supporting the LP (Linearly Polarized) modes and, more recently, the OAM (Orbital Angular Momentum) modes, that is, circularly polarized and helical phase modes. In the latter case, the phase and polarization properties limit the coupling between the modes. The design of a suggested circular photonic crystal fibre with support for 18 OAM modes is discussed in this research. The numerical analysis demonstrates that the proposed fibre has very good values for the fibre parameters, including a low containment loss of less than 810–4 dB/m at a wavelength of 1.9 m, a dispersion flat chromatic with a dispersion dissimilarity for the OAM modes that ranges from 75 to 77 ps/nm.km for a wavelength of 1.3 to 1.9 m, and a noteworthy effectual index partition.