Diffusion-assisted coextrusion process for the fabrication of graded-index plastic optical fibers

The diffusion-assisted coextrusion process is introduced as a method to fabricate graded-index plastic optical fibers (GI-POFs). In this process, two or more polymeric materials containing additives for refractive index modification are fed separately into a coextrusion die where a concentric multilayer structure is formed. Subsequently, the diffusion of additives takes place in a diffusion zone, creating a nonequilibrium concentration profile, and hence the refractive index profile. A theoretical analysis for the prediction of the refractive index profile obtainable by this process indicates that it is difficult to obtain a near-parabolic refractive index profile unless a very large residence time in the diffusion zone is provided. However, significant changes in the refractive index profile can be induced by adopting a multilayer approach. Furthermore, the bandwidth estimated by the ray analysis indicates that a small variation of the refractive index profile created by the additive diffusion can result in a significant increase in the bandwidth, suggesting that the diffusion-assisted coextrusion process is a viable method to fabricate GI-POFs with a bandwidth higher than 400 Mbits/s for 100 m.