Advance of Plastic Optical Fibers
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ADVANCE OF PLASTIC OPTICAL FIBERS FUMIO IDE* AND TAKASHI YAMAMOTO** *Mitsubishi Rayon Co.,LTD., Research and Development Department, Tokyo, Japan. **Mitsubishi Rayon Co.,LTD., Central Research Laboratory, Hiroshima, Japan.
ABSTRACT Plastic optical fibers (so called POF) are already in wide use in a large number of fields. This paper gives an overview of the field including the advantages of plastic optical fibers, the various types of fibers and the materials in them. Then, the properties of three types of fibers which have recently been developed, are discussed. The first is fibers with a poly-methyl-methacrylate (PMMA) core, which have a low transmission loss. Another is heat resistant fibers for use in automobiles. And the third is the multi-fiber type for image guides. And finally, the applications of these fibers and their future prospect are discussed.
INTRODUCTION There are many advantages that plastic optical fibers have over those made of silica. First of all, they are more flexible and are more resistant to impact and vibration. They also have a larger numerical aperture. These two factors make them easier to handle and make it easier to connect the ends. And as a result of all of these, the use of plastic fibers brings down the total cost of a system. Due to such advantages, the application fields of POF have been sharply expanded from the initial uses for simple displays and light guides to the uses for optical sensors, data transmission, outdoor signs and so on.
STRUCTURE AND TYPES OF POF Plastic fibers have a plastic core and cladding, and all the commercially available ones are of the multi-mode step-index type. The graded-index type in being studied by Dr. Koike and Dr. Ohtsuka of Keio University in Japan, and it is not on the market yet (1]. The diameter of plastic fibers is roughly 3 to 10 times larger than that of silica ones. But, even though they are larger, they are much more flexible and much tougher, which is one of the advantages of plastic. Also, the cladding layer is far thinner than the core diameter. This is another feature which distinguishes plastic from silica fibers. Plastic fibers are classified into two main categories depending on the core material (table 1). Fibers with a PMMA core are the most readily available in Japan and have about a 90% share of the market for plastic fibers. But recently, other materials have been developed to improve the heat resistance. They include engineering plastics, such as polycarbonate (PC), and the thermosetting polymers, such as polysiloxane, both of which are on the market. MATERIALS FOR POF The core materials for POP are usually amorphous homopolymers, because crystalline polymers, graft copolymers, mixed polymers and random copolymers tend to give the fluctuations in density and refractive index distribution, which cause the transmission loss. At present, there have been used methyl methacrylate polymer (PMMA), polystyrene (PS), polycarbonate (PC) and polysiloxane for the core of the commercially available POF. In addition to these, some m
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