Graded-index type

Fig. 3. Types of optical fiber (a) multimode stepped index, (b) multimode graded index, and (c) single-mode stepped index.

There are two major types of planar waveguides - those with a graded index and those that are step-indexed, as shown in Fig. 4. Waveguides can be composed of any optically transparent material such as glassy materials and polymers, depending on their structure. 

Figure 7.9 Refractive index profiles of three common types of optical glass fiber multimode step index, multimode graded index, and single mode.

Figure 14.32 Types of optical fibre (a) stepped index fibre, (b) graded index fibre and (c) monomode fibre...

Since all commercially available POF have been of the step-index (SI) type, the modal dispersion limits the possible bit rate of POF links to less than 100 megabit per second (Mb/s). Because of this, it has been thought that POF cannot be utilized for high speed transmission medium. Recently, however, we proposed a large core, low loss, and high bandwidth graded-index polymer optical fiber (GI POF) (7,2) for the first time and we confirmed that 2.5 Gb/s signal transmission for 100 m distance was possible in the GI POF (2,5). 

Figure A.1 Ray trajectories through basic types of optical fibers, (a) Single-mode fiber, (b) Step-index multimode fiber, (c) Graded-index multimode fiber.

The information presented in this publication is intended to give the reader an over view of the processing and properties of the materials listed in the index of this book. More detailed information, on specific grades or applications, should be obtained from the manufacturers of the material or, from the suppliers. We therefore suggest that, the user of such materials, seek and adhere to, the manufacturers or suppliers current instructions for the handling of each grade or type of material they use. Any determination of the suitability of the material for any use contemplated by the user, and the manner of processing and use, is the sole responsibility of the user who must satisfy himself/her-self that the material as processed meets the needs of a particular product or use. 

Much effort has been made by catalyst manufacturers to improve catalyst atttition resistance and thus reduce the formation of fines (see Catalysts, supported). In the 10-year petiod from 1980 to 1990, most catalyst manufacturers improved the atttition resistance of their catalyst by a factor of at least 3—4. This improvement was achieved even though the catalyst zeoHte content duting this petiod was continually increasing, a factor that makes achieving catalyst hardness more difficult. As an example of the type of atttition improvement that has been achieved, the catalyst atttition index, which is directiy related to catalyst loss rate in a laboratory attrition test, decreased from 1.0 to 0.35 for one constant catalyst grade during 1989—1990 (37). 

Such a value for relative temperature index will be specific to a particular grade of a polymer, sometimes even to a specific colour. The difference between grades of a particular species of polymer can be substantial, depending both on the variation in the inherent stability of a material between differing manufacturing methods and also on the type and amount of additives used. It is possible to obtain from the Laboratories a Generic Temperature Index to cover a species of material but this will usually be considerably lower than for many of the individual grades within that species. 

The MWD is the ratio of Mw Mn and is called the polydispersity index. This largely varies from one grade of polymer to the other, depending on the polymerization conditions and the type of catalyst used. Figure 14 shows different types of MWD for the polymers. 

Polyethylenes are whitish and translucent to opaque according to the density and grade. The refractive index varies with the density and type of polyethylene, for example ... 

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