The optimum refractive–index distribution of the high–bandwidth graded–index polymer optical fiber (POF) was clarified for the first time by consideration of both modal and material dispersions. The ultimate bandwidth achieved by the POF is investigated by a quantitative estimation of the material dispersion as well as the modal dispersion. The results indicate that even if the refractive–index distribution is tightly controlled, the bandwidth of the graded–index POF is dominated by the material dispersion when the required bit rate becomes larger than a few gigabits per second. It is also confirmed that the material dispersion strongly depends on the matrix polymer and that the use of a fluorinated polymer whose material dispersion [(0.078 ns/1nm km)] is lower than that of poly(methyl methacrylate) [(320.305 ns/1nm km)] allows for a 10–Gb/s signal transmission.
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