A photonic quasi-crystal fibre supporting stable transmission of 150 OAM modes with high mode quality and flat dispersion

A photonic quasi-crystal fibre (PQF) with a high refractive index ring is designed and analysed numerically by the finite element method. In the wavelength range between 1.4 and 1.7 µm, the PQF supports transmission of 150 orbital angular momentum (OAM) modes. The effective refractive index differences between the eigenmodes of the PQF are greater than 10⁻⁴, so that the OAM modes can be separated effectively while the single-mode state is maintained in the radial direction. The PQF also exhibits high mode quality and low confinement loss. At 1.4–1.7 μm, the mode qualities of all eigenmodes are higher than 97.6%, the confinement losses are in the range of 10⁻⁹ dB/m–10⁻¹² dB/m. Meanwhile the minimum dispersion change is 23.9 ps/(km·nm) and the maximum effective mode area can reach 313 µm². The PQF has excellent properties and prospects in large-capacity OAM mode division multiplexing communications.