Patent ID: 7135133

Claim:
A method of manufacturing a plastic optical transmission medium with a radially varying refractive index, comprising: preparing a polymeric tube having at least two concentric cylinders of polymeric material, wherein at least one of said at least two concentric cylinders of polymeric material comprises a diffusible additive which modifies the refractive index of said at least one of said at least two concentric cylinders of polymeric material; surrounding said polymeric tube with an outer tubing, wherein said outer tubing has a higher glass transition temperature than any of said at least two concentric cylinders of polymeric material; heating said polymeric tube surrounded by the outer tubing to a temperature which is below the glass transition temperature of the outer tubing and above all of the glass transition temperatures of said at least two concentric cylinders of polymer material, wherein such heating causes diffusion of the diffusible additive in said at least one of said at least two concentric cylinders of polymeric material, wherein such diffusion of the diffusible additive modifies the radial refractive index of said polymeric tube, wherein the method is continuous, wherein heating said polymeric tube surrounded by the outer tubing comprises continuously passing said polymeric tube surrounded by the outer tubing through a heated enclosure, wherein continuously passing said polymeric tube surrounded by the outer tubing through a heated enclosure comprises: continuously admitting said polymeric tube surrounded by the outer tubing into the heated enclosure; continuously winding said polymeric tube surrounded by the outer tubing onto a drum, wherein the drum is located within the heated enclosure; retaining said polymeric tube surrounded by the outer tubing in the heated enclosure for a duration of time adequate to achieve a desired radial refractive index profile of said polymeric tube as said polymeric tube surrounded by the outer tubing is being wound on the drum; and continuously unwinding the polymeric tube surrounded by the outer tubing from the drum.