Index-matching elastomers for fiber optics

Silicone elastomers have been prepared to match the index of refraction of the core of optical fiber. The system is composed of a vinyl-terminated dimethyldiphenylsiloxane copolymer crosslinked with tri- or tetrafunctional silanes in the presence of a chloroplatinic acid catalyst. The refractive index of the copolymer was determined as a function of diphenyl content and temperature. By measuring the reflected power from the elastomer-encapsulated end of a single-mode optical fiber it was found that a copolymer with 15% diphenyl content crosslinked with 1,3-diphenyl-1,1,3,3-tetrakis(dimethylsiloxy)disiloxane with a hydride/vinyl stoichiometry of unity has a perfect index match at about 30 degrees C. Environmental testing under 85/85 conditions has shown the material to be capable of protecting biased positive-intrinsic-negative (p-i-n) devices for more than 5000 h. Some other advantages of the system are that it is relatively nontoxic, environmentally stable, and can be easily cured at temperatures below 120 degrees C.<
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