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<sub>g</sub>) 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<sub>g</sub> at the core region was improved to
104 °C while that of conventional GI POF is 86 °C. Stability of attenuation at 85 °C/dry and 75 °C/85 %RH were
clarified to be as high as that of non-doped step index POF.