Theoretical Analysis on the Refractive-Index Distribution and Bandwidth of GradientIndex Polymer Optical Fibers from a Centrifugal Field

Theoretical analysis was applied to analyze the refractive-index distribution (RID) and bandwidth (BW) of gradientindex polymer optical fibers (GI POFs) prepared by a centrifugal field process. The RID of the prepared GI POF could be represented by the equation of n (r ) = n1[1 - 2 (delta)(r/a )g1]/2 . The studied material systems were poly(hexafluoroisopropyl 2-fluoroacrylate) (PHFIP 2-FA) /dibutyl phthalate (DBP) and poly(methyl methacrylate) (PMMA) /benzyl benzoate (BEN). The RID and the BW were significantly affected by an essential parameter k , which was related to the material properties (density difference and molecular weight) and processing properties (rotating speed, temperature, and radius). As k increased, the characteristic constant of RID, g , decreased to a minimum and then increased sharply, owing to the separation of the polymer and the dopant. On the other hand, the relative refractive-index difference of RID, k, increased to a steady value after k increased to a certain value. The variation of RID with k resulted in a local minimum of intermodal dispersion, and thus a maximum bandwidth was obtained. The maximum BW of the PHFIP 2-FA /DBP and PMMA /BEN systems at 1550 nm (100-m fiber length and 2-nm spectral width) for the case of k (not equal to) 0 were 6.7 and 3.2 Gb /s, respectively. The wavelength of light source affects the BW significantly only at k around zero because of the importance of the intramodal dispersion in this case.