a continuous extrusion process is provided capable of producing graded index plastic optical fiber at commercially useful speeds , e . g ., at least 1 m / sec for 250 μm outer diameter fiber . moreover , it is possible to predict the refractive index profile of the fiber , prior to actual fabrication , by performing a finite element analysis using various parameters of the extrusion process . such prediction allows one to tune the parameters of the process to obtain a desirable outcome , while avoiding the need for substantial trial and error with the extrusion equipment .