Plastic Fiber Technique Improves Cost

Michael D. Wheeler

A Florida company has developed and patented a method for the continuous production of graded-index plastic optical fiber. James K. Walker, CEO of Nanoptics Inc. in Gainesville, Fla., presented an overview of the method at the Plastic Optical Fiber World '98 Convention.
Graded-index plastic optical fiber soon could be the enabling technology in some digital communications links.
Plastic fiber's light weight and large-diameter core make it flexible and easy to handle. However, manufacturers have failed to embrace it because of its high cost. Manufacturing it by the batch has been cost-prohibitive and produced fiber of varying qualities.
Continuous-production methods usually relied on the use of low molecular weight additives or two monomers. The additives reduced the fiber's thermal stability, which affected the fiber's refractive index. A low refractive index corresponds to a low bandwidth.
The two-monomer method led to phase separation, which inhibited the light from traveling long distances in the fiber.

New approach
Nanoptics began its development effort two years ago. Walker's team investigated two methods to achieve continuous production: an acrylic polymer plus additives, and two acrylic-based copolymers.
The first method suffered from poor thermal stability, but the second worked better. The copolymers mixed well, resulting in long-term temperature stability that meets current specifications, Walker said.
The gradient-index fiber has a bandwidth of more than a gigabit per second over 100 m. The company is improving its attenuation length to 120 dB/km, with large-scale production slated for 1999.