It is a challenging issue to develop a graded index polymer optical fiber (GI-POF) with sufficiently high thermal stability to be installed in the in-vehicle networks. Generally, a radial refractive index profile within the GI-POF is formed by adding a dopant to a polymer. This addition of the dopant significantly decreased the Tg of the polymer due to the plasticization. We demonstrated that 9-bromophenanthrene (BPT) had little plasticization on poly methyl methacrylate compared to conventional dopants, and propose the BPT as a potential dopant for the GI-POF.

Radial refractive index profiles within the graded index plastic optical fiber (GI-POF) is formed by adding a dopant to a polymer. This addition of the dopant significantly decreased the T g of the polymer due to the plasticization. This disadvantage made the installation of the GI-POF difficult, especially in vehicle networks in which high thermal stability is required. We have suggested 9-bromophenanthrene (BPT) as a novel dopant induced less plasticization for poly(methyl methacrylate) (PMMA) than the conventional dopants. However, although the fabricated GI-POF using BPT had high enough thermal stability for vehicle networks, the attenuation was 800 dB/km and it could not be used. This high attenuation was caused by contaminant in the fabrication process of fibers. In this study, we succeeded to fabricate a GI-POF with low-attenua-tion and high-thermal stability using highly pure BPT. Its attenuation was improved to 240 dB/km at 650 nm, which was enough transparency for vehicle networks. The T g of the GIPOF was improved to 107 C from 90 C. The thermal stability of the GI-POF below 85 C/dry and 75 C/85%RH was demonstrated to be as high as that of the commercially available step index POF. The bandwidth of the GI-POF could be estimated over 4.0 GHz for the 50-m fiber. These results demonstrated that our GI-POF should qualify to be used in vehicle network.

The graded index polymer optical fiber (GI POF) has been proposed as a media for very short reach network because of its high flexibility, low laying cost and excellent transmission characteristics. However, the plasticization efficiency which causes by the high refractive dopant decreases the glass transition temperature (T g ) in the center of the core and deteriorates thermal stability of fibers. In this paper, thermally stable PMMA based GI POF was successfully fabricated for the first time by designing dopant molecule which has little plasticizer effect. T g at the core region was improved to 104 o C while that of conventional GI POF is 86 o C. Stability of attenuation at 85 o C/dry and 75 o C/85 %RH were clarified to be as high as that of non-doped step index POF.

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