Characterization of Red/Green/Blue Orbital Angular Momentum Modes in Conventional G.652 Fiber

The space domain of lightwaves has attracted increasing interest in optical communications. Lightwaves having helical phase front and carrying orbital angular momentum (OAM) have seen potential applications both in free-space and fiber-based optical communications. The widely deployed conventional ITU-T G.652 fiber is single mode fiber at 1550 nm, which, however, might support high-order modes as well as OAM modes at short wavelength. In this paper, we present detailed theoretical analyses on the mode properties of circularly polarized OAM modes in conventional G.652 fiber at three RGB wavelengths (red at 632.8 nm, green at 532 nm, and blue at 476.5 nm). The G.652 fiber has a 4.6-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> core radius, a 62.5-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> cladding radius, and 0.277% refractive index difference between the core and the cladding. We first study all the cylindrical vector modes (fiber eigenmodes) and synthesize the circular OAM modes by proper linear combination of degenerate fiber eigenmodes supported in the G.652 fiber at three RGB wavelengths. We then calculate the effective mode area and nonlinearity and discuss the tolerance to fiber ellipticity and bending (<inline-formula> <tex-math notation="LaTeX">$\text{n}_{{\text {eff}}}$ </tex-math></inline-formula> differences, <inline-formula> <tex-math notation="LaTeX">$2\pi $ </tex-math></inline-formula> walk-off length, 10-ps walk-off length, loss, and OAM crosstalks) for red, green, and blue OAM modes. Additionally, we investigate the OAM modes properties at another three wavelengths of conventional semiconductor lasers, i.e., 780, 650, and 405 nm. Moreover, we also estimate the fiber attenuation, propagation loss, and communication bandwidth/capacity. The obtained results may stimulate wide interesting OAM related applications using conventional G.652 fiber, especially for hundreds of meters or km-scale short reach/distance applications.