Inverse-raised-cosine fibers for next-generation orbital angular momentum systems

After a brief review of basic concepts of orbital angular momentum (OAM) in optical fibers, some general guidelines to design fiber profiles for OAM transmission are drawn. Following these guidelines, a novel few-mode fiber (FMF) for OAM transmission, based on the inverse-raised-cosine (IRC) function, is designed and numerically analyzed in terms of effective index separation among modes, differential group delay, and chromatic dispersion. Results are compared with those of the inverse-parabolic graded-index (IPGI) fiber. The proposed fiber performs comparably to the IPGI except for a wider modal separation that may reduce channel crosstalk.