Telecommunications Systems Essay Research Paper Everything You — страница 2

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and the substrate is minimized, producing good thermal stability during temperature cycling. The enclosure and booting material further aids the resistance to hot, humid environments. This resistance has been demonstrated over several thousand hours at accelerated conditions (e.g., 85oC/85%RH). This bond is much stronger than epoxy and is not susceptible to degradation from humidity. While the damp heat test results have been relatively good, this is also the test where component reliability is affected. With long-term exposure to humidity, epoxies tend to soften and swell and the bond between fibers and substrate is weakened. This rarely leads to catastrophic failure, but the resulting variations in insertion loss may exceed the performance specification of the splitter. To

improve the long-term reliability of our components, Gould has developed the GlasSolderTM package which augments the epoxy with a glass solder material forming a true chemical bond with both the optical fiber and the substrate. See figure 1. Not only does this method provide a bond which is stronger than an epoxy bond and impervious to moisture, but it is also fast and inexpensive for use in a practical, fused coupler manufacturing process. Process Description Glass solders are inorganic compositions that are often used for making strong, insulating and sometimes hermetic joints or seals between different materials such as glass, ceramics and metals. Usually mixtures of silica and other metal oxides, glass solders form strong ionic bonds which are particularly impervious to

moisture. To be used in coupler packaging, glass solders must be chemically and physically compatible with silica fibers and substrates. This means the glass solder must have a surface energy less than that of silica, so that upon the application of heat it softens and sufficiently wets the surfaces. This is essential for obtaining adhesion and bond strength. Additionally, the glass solder should exhibit a thermal coefficient which is similar to silica in order to prevent the formation of cracks. The glass solder is applied in a slurry form. The slurry is comprised of the glass powder, a binder and a carrier or vehicle. The binder, which is eventually burned away when the slurry is heated, provides dimensional stability to the powder after the vehicle has evaporated. The heat

required to soften and fuse the glass solder is applied only where the glass solder has been deposited. This is accomplished by using a C02 laser operating at a wavelength of 10.6mm. Evaluation Tests Specific mechanical tests, including vibration, impact, and fiber retention, were performed to evaluate the strength of the bonds between the glass solder and the optical fibers and the substrate. For* the fiber retention tests, standard singlemode fibers were secured to silica substrates with a small (-2 mm diameter) bead of glass solder using the process described above. Tensile forces were then applied to the fiber leads by attaching weights of known mass. All five samples in this study were able to support tensile loads in excess of 5kgf (49N) without failure of the glass solder

bonds. By comparison, similar samples prepared using epoxies typically failed at substantially lower pull-out forces.Couplers packaged using the GlasSolderTM technique proved to be quite robust when tested for both vibration and impact. The vibration tests were conducted over the frequency range of 10Hz to 55Hz, in accordance with the test conditions specified in Bellcore TR-NWT-001209. The samples were subjected to simple harmonic motion amplitude of 1.52 mm (0.060″) for a period of two hours of three mutually perpendicular axes. The average change in insertion loss following the vibration test was only -0. 1 dB. During the impact tests, conducted from a height of 1.8 meters, each coupler was dropped eight times along each of three mutually perpendicular axes. The components

were packed in a container with sand in order to fully transmit the shock of the impact throughout the coupler package. The average change in insertion loss following the impact tests was only -0.1dB. Figure 2. Long term damp heat test (85C/85%RH) for couplers with epoxy alone and with the addition of the glass solder. Note that, to further accelerate the effects of the hot, humid environment, the test was conducted with an open substrate, ie., without the tube and boots shown in figure 1. In order to test the thermal compatibility of the glass solder with silica fibers and substrates, seventeen fully packaged couplers were subjected to temperature cycle tests between -40oC and 125oC. Each coupler was tested for five temperature cycles and actively monitored throughout the test.