Coupling analyses of LP0m modes with optical fiber gratings in multimode fiber and their application in mode-division multiplexing transmission

Coupling characteristics of core higher-order modes LP0m with optical fiber gratings written in step-index multimode fiber (MMF) and their application in mode-division multiplexing (MDM) transmission are presented and analyzed in this article. Several long-period fiber gratings (LPFGs) cascaded in one MMF can realize conversion between any two core modes, HE1m(m=1,2,3,...,6) in other words and scalar mode LP0m, in mode order from low to high. These eigenmodes supported in fiber as independent data channels are theoretically proposed to be multiplexed in one MMF by the combination of LPFGs and fiber Bragg gratings (FBGs) united with optical circulators as both multiplexers and de-multiplexers. This method of flexible mode conversion using optical gratings can be practically significant on fiber communication as a mode-selective converter.