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Samples of a 140/100-micron single-fiber optical cable* were tested in a flame environment to determine 1) the effectiveness of Nextel 312** ceramic-fiber sleeving for providing thermal protection to the cable and 2) the effects upon light-signal transmission. The optical cables were tested with and without the protective sleeve (or jacket) in a standard 6-inch diameter propane burner i'2 at flame temperatures ranging from approximately 450° to 860°C (842° to 1580°F). The flame tests were conducted with and without external vibration being applied. During a 30-minute test run of a jacketed cable at a nominal flame temperature of 500°C (932°F) without external vibration applied, the optical intensity (-15 dbm) of the signal passing through the fiber was essentially unchanged, and the signal was uninterrupted. In addition, the shape of the 1-megahertz square-wave output signal was unchanged, as observed on an oscillope. The same test specimen was re-tested for another 30-minute period without vibration at a higher nominal temperature of 735°C (1355°F). During this second run, the output signal was again received continuously without decrease in optical intensity or distortion of the square-wave shape. However, the signal was finally lost due to mechanical failure of the single optical fiber when the specimen holder was removed from the burner after the second run. When the ceramic sleeving was cut open along its length, inspection showed that all of the plastic materials used in the cable construction had completely burned and decomposed. Except for a small amount of white ash, only broken pieces of the glass fiber were found inside the ceramic sleeve. It became evident that the glass fiber alone had survived throughout two 30-minute flame-test runs and was able to pass the signal without interruption or loss of intensity. The results of other test runs are discussed, in which optical cable samples were tested with and without protective sleeving, and with external vibration applied.
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