High-thermally stable and high-bandwidth graded index plastic optical fiber for vehicle networks

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-attenuation 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.