Fundamentals of Plastic Optical Fibers

5Fabrication Techniques

Fabrication processes of POFs (plastic optical fibers), regardless of their step-index (SI) or graded-index (GI) profiles, are divided into two main categories: a preform-drawing process and an extrusion process. The extrusion process is further classified into batch extrusion and continuous extrusion. Currently, most SI POF suppliers employ the continuous extrusion process. Section 5.1 summarizes how POFs can be prepared by each process. In contrast to SI POFs, which have been prepared by employing extruders during the early stages of their development, studies of GI POFs started by exploring how to form a desired graded refractive index profile in a cylindrical polymer rod. Section 5.2 discusses several representative techniques for fabricating GI preforms. The preform-drawing method enables a precise control of the fabrication process of rather complicated refractive index profiles. However, these techniques have not been widely accepted in industry because of their batch nature. More recently, GI POFs have also become producible by an extrusion method. In particular, a dopant diffusion method, which can be adopted for a variety of base polymer materials, is employed by a couple of POF companies in Japan and the United States. Finally, Section 5.3 describes the mechanism and a recently developed approach to simulate the refractive index profile obtained by the dopant-diffusion extrusion process.

5.1 Production Processes of POFs

5.1.1 Preform Drawing ...