Microstructure ring fiber for supporting higher-order orbital angular momentum modes with flattened dispersion in broad waveband

We design and numerically simulate a microstructure ring fiber, which supports 146 orbital angular momentum (OAM) modes at 1.1 μm and 70 OAM modes at 2.0 μm with flattened dispersion and low nonlinear coefficient. The fiber consists of an air hole at the center and a high refractive index ring between two well-ordered air hole rings in the cladding. It is found that the number of well-separated OAM modes decreases linearly with the increasing wavelength. Moreover, the waveguide dispersions of the modes are flat with wavelengths, which has a minimum variation of 2.92416 ps/nm/km over 900 nm bandwidth from 1.1 to 2.0 μm for HE13,1 mode. In addition, the nonlinear coefficient keeps lower than 1.8/W/km. The designed fiber may pave the way to applications in fiber-based OAM mode-division-multiplexing systems.