MECHANICAL APPROACH TO THE EVALUATION OF THE LOW-TEMPERATURE THRESHOLD OF ADDED TRANSMISSION LOSSES IN SINGLE-COATED OPTICAL FIBERS

An easy-to-use method is developed for the evaluation of thermally induced forces in single-coated optical fibers. Our calculations show that the increase in the lateral pressure at the cladding/ coating interface adequately reflects the experimentally observed increase in the added transmission losses at low temperatures. The measurements were carried out on loose fibers in a test chamber, where mechanical effects other than the thermally induced shrinkage of the coating were thought to be excluded. We suggest, therefore, that the thermally induced lateral pressure be used as a tentative criterion of the low temperature threshold of the expected added optical losses in single-coated fibers. Obviously, the increase in this pressure reflects the increase in the axial thermal loading as well. It is concluded that single-coated optical fibers can be successfully employed in transmission media operated at moderately low temperatures (for instance, in undersea systems), otherwise a dual-coated fiber design should be considered. The final selection of the most feasible coating design must be based, of course, on all the material, optical, chemical, technological, mechanical, environmental, and cost considerations. © 1990 IEEE