We propose a poly vinylidene fluoride (PVDF)-clad graded index plastic optical fiber (GI POF) which exhibits excellent mechanical strength and low bending loss property. A main concern of PVDF-clad GI POFs is the bandwidth degradation due to its specific waveguide structure compared to the conventional poly-methyl-methacrylate (PMMA)-based GI POF. We design the index profile of PVDF-clad GI POFs to maintain high bandwidth under a restricted mode launch condition. However, when mode coupling exists in PVDF-clad GI POFs, the bandwidth can be degraded. Hence, for high bandwidth performance, we investigate a way to reduce the mode coupling in PVDF-clad GI POFs. We find that the fiber numerical aperture (NA) is a key factor in controlling the mode coupling. By adjusting the NA of the GI core region to be as high as 0.17, bandwidth higher than 2 GHz for 100 m distance is achieved by the PVDF-clad GI POF. In addition, the propagating mode properties of the optimized PVDF-clad GI POF are investigated, particularly when the fiber is statically bent, because such a fiber bending can enhance mode coupling. We find that the high bandwidth performance is maintained in the PVDF-clad GI POF, even under severe bending conditions if the GI core region has an NA of 0.17.
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