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Polymer Science and Engineering: The Shifting Research Frontiers
Material and process parameters have been refined to control birefringence and maintain replication integrity. New long flow grades of the materials have been developed specifically for the CD market.
Polymeric Materials for Photonics
Photonics is a technology analogous to electronics in which the photon replaces the electron as the working particle. Many of the applications now accomplished electronically, including transmission, switching, amplification, and modulation, can also be realized using photonics, and there are advantages to be gained by converting to a photon-based technology in some areas. Transmission of light in fiber-optic systems is the direct analogy of electrical transmission in coaxial cable systems.
Fiber-optic systems are now in place all over the world, and they handle much of the world's long-distance telephone traffic. The transmission medium of the fibers employed is based on inorganic glasses, but polymers are used for protective coatings and in cabling structures. Polymers can also be made into optical fibers, but the loss is considerably larger than with the inorganic fibers and only short-distance applications are realistic. The main advantage of polymer fibers is their flexibility when made in larger diameters, which are easier to splice. Today, fiber-optic cables are generally terminated at the area substation level, where the optical signal is converted back to an electrical signal for transmission to the customer. This conversion process is necessary because the optical components needed to reach the individual telephone or terminal are not available at sufficiently low cost at this time. What is required to allow fiber to be connected to the home are inexpensive optical switches and amplifiers, which will enable the advantages of broad-band communications to be brought to every subscriber. Polymeric organic materials will play a major role in the realization of optical technology as fiber to the home becomes a reality.
Two kinds of optical technology need to be developed and commercialized before the photonics revolution can be fully realized. The first is linear optical technology, which includes not only the long-distance fibers mentioned above, but also shorter fibers and the optical equivalent of printed wiring boards of the electrical domain. These optical circuits can be created today by means of a photolithographic procedure in which lines of high refractive index are formed in thin polymer films by photochemical techniques. The circuit pattern is defined by irradiating a photoresist through a mask. The substrate film bared by development of the resist is then exposed to light, which causes the chemistry, for example, the polymerization of monomers, that gives rise to the increase in refractive index needed to form an optical guide.
Nonlinear optical materials will also be required for the manufacture of switches, modulators, and amplifiers, and this technology has not progressed as far as the linear domain. Demonstration-of-principle devices have been fabricated