| Popis: |
The mechanical reliability of fused silica glass fibers is significantly influenced by the properties of their polymer coatings. The primary coating, which is in contact with the fiber surface, is expected to control the chemi stry there, but the secondary coating does have a considerable effect on the strength and aging behavior of the fiber. This observation is confirmed by data obtained for ten fused silica fibers, having the same primary coatings but ten different secondary coatings. These fibers were aged at 85 o C in both de-ionized water and 85% relative humidity for up to 6 weeks and the residual strength as a function of aging time was measured. Dynamic fatigue measurements were carried out on as - received and aged fibers using two-point bending. The results show that the secondary coating has a notable effect on the aging behavior and the coating strip force, but does not greatly influence the dynamic fatigue parameter. Low loss fused silica optical fibers are an excellent medium for the transmission of data. These fibers are made from silica and hence are susceptible to surface flaws which can lead to catastrophic failure. 1 Coatings are used to protect the fiber from abrasion and other flaw inducing mechanisms. These coatings may be polymers, carbon or metals. But for most applications, dual layers of polymer are used. The primary or inner coating has a low modu lus to reduce microbending optical losses, while the secondary or outer coating has a higher modulus. The coating acts as a barrier and impedes the transport of the outside environment to the silica surface and reaction products away. 2 Polymer coatings are readily permeable to environmental agents such as water. Hermetic coatings, such as metals have been effective in preventing water from getting in, but can induce microbending losses. 3 Many researchers have investigated the properties of polymer coating s and their effect on the mechanical reliability of the fiber. Properties like adhesion of the primary to the surface, 4 water permeability, water vapor transport, 5 coating thickness, wetting angles, coating composition, 6,7 ink materials on polymer coatings etc, 8 all affect the strength and fatigue of the fiber. In most of the prior work, both the primary and secondary polymer coatings have been looked at as a complete entity. The primary coating is in contact with the surface of the fiber. Hence, it is normally assumed that it controls the chemical environment at the fiber surface, and consequently controls th e fatigue and strength characteristics, which are sensitive to the adhesion properties of the primary. 9 The primary coating though, is not solely responsible for controlling these phenomena. To investigate whether the secondary coating also has any significant effect on t he properties of the fiber, fibers having the same primary coating but various secondary coatings were used in this study. From our results, it clear that the secondary coating also plays an important part in mechanical reliability. In this study, the thickness of the secondary was kept constant, and only the nature of the coating was changed to see the impact of this change on the strength and fatigue of the fiber. |
