We present a design strategy of a dual step-index ring core antiresonant fiber (DSI-RC-ARF) to significantly enhance the number of orbital angular momentum (OAM) modes while preserving their high purity and transmission quality over the O-E-S-C-L-U bands. The proposed fiber features a central ring of high refractive index, surrounded by outer and inner rings of refractive indices that gradually decrease from the central ring in both directions. The proposed fiber consists of a unique core arrangement having a central ring with a higher refractive index that can support up to 206 OAM modes across the 1.28 μm to 1.70 μm wavelength range without any higher-order radial modes or phase distortion. Additionally, the core is surrounded by inner and outer rings with gradually varying refractive indices, which helps to maintain the mode quality above 97% and mode purity mostly above 98%. The fiber also renders a uniform dispersion variation with wavelength, large effective mode area, nonlinear coefficients below 1.62 /W/km throughout the entire bandwidth, very low confinement loss ranging from 10−11 to 10−9 dB/m, and longer 2π and 10 ps walk-off length for higher-order OAM modes with ellipticity and bending. This innovative fiber design enhances the capabilities of antiresonant fibers in modern communication systems, making it ideal for efficient broadband transmission of high-capacity OAM modes.
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