Mechanical approach to the evaluation of the low temperature threshold of added transmission losses in single-coated optical fibers

An easy-to-use calculation procedure for the evaluation of thermally induced forces in single-coated optical fibers is discussed. The 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 excluded. It is suggested 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. The increase in this pressure reflects the increase in the axial thermal loading as well. Single-coated optical fibers can be successfully used in transmission media operated at moderately low temperatures (for instance, in undersea systems) which do not cause large thermally induced forces; otherwise, a dual-coated fiber design should be considered. The final selection of the most feasible coating design must be based on all the material, optical, chemical, technological, mechanical, environmental, and cost considerations