Orbital-Angular-Momentum Polarization Mode Dispersion in Optical Fibers

The orbital-angular-momentum (OAM) modes in optical fibers have polarization mode dispersion (PMD) properties similar to those of single-mode fibers (SMFs). The +l and -l order OAM modes supported by the same fiber vector modes undergo random cross coupling and exhibit a frequency-dependent time delay. We name this effect “OAM-PMD” and extend the formalism developed for PMD in SMFs to describe OAM-PMD. The characteristics of the modal beat lengths, birefringence correlation lengths, and the mean value of OAM-PMD are investigated. A fixed-analyzer technique is proposed and demonstrated to characterize this phenomenon in OAM fibers. Two different types of OAM fiber are examined. The measured results are compared with the theoretical calculations.