Years of research have reduced plastic loss considerably, but it still remains far higher than that of glass. The best laboratory plastic fibers have minimum loss around 50 dB/km.
At the 650-nm wavelength preferred for communications using red LEDs, commercial plastic fibers have minimum attenuation as low as 150 dB/km. Unlike glass fibers, the loss of plastic fibers is somewhat lower at shorter wavelengths and much higher in the infrared, as shown in Figure 6.8.
For this reason, plastic optical fibers have found only limited applications. One is in flexible bundles for image transmission and illumination, where the light doesn’t have to travel far and the flexibility and lower cost of plastic are important. Another application is in short data links, particularly within automobiles, where the ease of handling plastics is a major advantage and the required distances and data rates are small.

For this reason, plastic optical fibers have found only limited applications. One is in flexible bundles for image transmission and illumination, where the light doesn’t have to travel far and the flexibility and lower cost of plastic are important. Another application is in short data links, particularly within automobiles, where the ease of handling plastics is a major advantage and the required distances and data rates are small.

Another important concern with plastic optical fibers is long-term degradation at high operating temperature. Typically plastic fibers cannot be used above 85°C (185°F). This may sound safely above normal room temperature, but it leaves little margin in many environments. The engine compartments of cars, for example, can get considerably hotter.
Newer plastics can withstand temperatures to 125°C (257°F), but their optical properties are not as good.
Plastic fibers are made using the same principles as glass fibers. A low-index core surrounds a higher index cladding. The refractive-index difference can be large, so many plastic fibers have large numerical apertures. Commercial plastic fibers are multimode types with large cores. Most are step-index but a few are graded-index. There is little interest in single-mode plastic fibers because the material’s high loss makes long-distance transmission impossible.