Optimization of photonic crystal fibers for transmission of orbital angular momentum modes

Photonic crystal fibers (PCFs) which can transmit orbital angular momentum (OAM) modes are attractive to optical communication due to the large capacity and flexible structure. Herein, a method is proposed to optimize a simple fiber structure by changing the thickness of the annular area. The changes in the effective index, effective index difference, dispersion, effective mode area, nonlinear coefficient, numerical aperture, mode purity, and walk-off length in the thickness range of 2.0 μm to 2.5 μm are determined, compared, and analyzed systematically. The distance between the square air holes and central air hole is the better parameter to optimize the dispersion, effective mode area, and nonlinear coefficient, whereas the radius of the central air hole is more suitable for optimizing the NA, OAM purity and walk-off length. The optimization method and results have great value pertaining to the design and improvement of PCFs for transmission of OAM modes.