Low dispersion and confinement loss photonic crystal fiber for orbital angular momentum mode transmission

In this paper, we design a novel type of photonic crystal fiber (PCF) with a kind of typical micro-structure in its innermost cladding area, which can totally transmit 26 orbital angular momentum modes (OAMs). Over a bandwidth of 300 nm from 1.5 to 1.8 μm, this new type PCF shows a great improvement in dispersion property when it is compared with the total internal reflection PCF for reference. Moreover, other mode properties are also calculated and listed in curves, including effective indices, confinement loss and nonlinear coefficient. And basing on the test results, we further ameliorate the micro-structure and cladding of previous PCF structure and propose two effective ways to reduce the dispersion and confinement loss respectively. One is to insert typical type of micro-structure; the other is to change the arrangement and size of air holes in the cladding area. We finally propose an optimized structure which can support 30 OAM modes with the application of the two ways. Results show the optimized structure performs very well and achieves great progress in terms of dispersion and confinement loss.