Abstract
Based on the coupling mode theory and numerical simulation, intramode-group coupling in orbital angular momentum (OAM) fibers with elliptical deformation is analyzed in depth. The elliptical deformation not only introduces a time delay difference between even and odd modes of the same high-order vector mode but also destroys the structure of the high-order vector modes; the structural damage depends on the strength of the elliptical deformation. When the elliptical deformation is relatively small, the structural damage of high-order vector modes can be ignored and coupling can be thought as occurring only between two OAM modes composed of the same high-order vector mode. While the elliptical deformation becomes larger, the structural damage cannot be ignored, coupling appears among four OAM modes in the same OAM mode group, and the coupling between two OAM modes composed of the same high-order vector mode is more serious. The results will pave the way for the establishment of accurate propagation models and the optimization of the OAM fiber design.
Highlights
TO solve the pending capacity crunch of optical fiber communication in the decades, mode division multiplexing (MDM) is considered a promising method to overcome the capacity bottleneck imposed by the nonlinear Shannon limit in the single-mode fiber [1]-[4]
Lixian Wang first proposed the concept of “orbital angular momentum (OAM) polarization mode dispersion (PMD)” and generalized the form describing the PMD in a single mode fiber to rewrite OAM-PMD in OAM fibers [16]. They laid a foundation for the research of OAM mode coupling; the conclusion that perturbations only introduce the effective refractive index difference between even and odd modes is incomplete because they do not consider the structural damage of eigenmodes
The OAM modes in fibers are formed by superposing degenerate even and odd modes of the same high-order vector modes with a phase difference of ±π/2
Summary
TO solve the pending capacity crunch of optical fiber communication in the decades, mode division multiplexing (MDM) is considered a promising method to overcome the capacity bottleneck imposed by the nonlinear Shannon limit in the single-mode fiber [1]-[4]. Lixian Wang first proposed the concept of “OAM polarization mode dispersion (PMD)” and generalized the form describing the PMD in a single mode fiber to rewrite OAM-PMD in OAM fibers [16] They laid a foundation for the research of OAM mode coupling; the conclusion that perturbations only introduce the effective refractive index difference between even and odd modes is incomplete because they do not consider the structural damage of eigenmodes. As a consequence, they can only analyze the coupling between two OAM modes composed of the same high-order vector modes.
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