Verification of Optical Fiber and Cable Reliability

As environments are becoming increasingly harsh, the ability of optical fiber cable to withstand such environments is of the utmost importance to outside plant users. Laboratory accelerated aging environments have long been used as a measure to predict field performance of optical fiber and cables' ability to withstand harsh environments. However, there has been an issue in linking the laboratory environments with actual field exposure. To this end, actual field data from such a cable should provide real evidence of an optical fiber cable's ability to withstand these environments, thus providing the link between actual long-term reliability and laboratory tests. In the present study, a 10 year-old field-aged cable was extracted from its deployed environment and tested to determine its resilience in withstanding mechanical and environmental conditions. In order to assess its resilience, a wide range of tests was performed on the aged cable and its components. The results of these tests were compared to test results obtained from unaged samples of the same era as well current data on the same design. Surface roughness of the fiber was determined using an Atomic Force Microscope (AFM). Strength testing was conducted to verify failure probability. In addition, fiber strip force testing and Fourier Transform InfraRed (FTIR) analysis were conducted to determine the effect of aging on the coating materials. Optical and material performances of the cable under mechanical stress were compared to historical test data on the single-armored, sixposition, loose-tube cable design. These tests were performed in accordance to industry standard requirements. Testing results showed that there exists no significant degradation in the optical fiber cable's performance, which verifies laboratory testing and speaks to the true reliability of optical fiber cable. Cable Design and History The design is a single-armored, six-position cable (see Figure 1) which contains two live gel-filled 2.5/1.5 mm tubes with six fibers each, three soft fillers and one hard filler. The cable was manufactured in 1987 in compliance with Bellcore Specifications TR-TSY-000020, Issue 3 requirements. The fiber is Corning SMF-28 CPC3 standard single-mode optical fiber. In 1987, the cable was installed in Oregon, at the base of the Cascade Mountain foothills, between the town of Medford and the Rogue River. The geography of the installation site indicates that it is a river valley surrounded by four mountain ranges. East of Medford are the Cascade Mountains with an elevation of 4,000(1219.5m) to 9,500 feet(2896m) and west of Medford are the Coast Range Mountains with an elevation of 3,500(921.1m) to 5,500 feet(1676.8m). North of Medford is the Umpqua Divide with elevations from 3,500(921.1m) to 5,500 feet(1676.8m) and south of Medford are the Siskiyous Mountains with elevations from 3,000(914.6m) to 7,600 feet(2317m). The approximate mean annual temperature for Medford is 53°F(11.7°C) with recorded low temperatures of 0°F(-17°C) and high temperatures of 100°F(37°C). The mean annual precipitation averages 20.6-in(52.4 cm.) and average annual snowfall is 8.1 in (20.6cm). Because of it’s geographical location, Medford is subjected to annual flooding and mudslides. A mudslide in 1997 was responsible for 200 feet (61m) of this cable surfacing in a washout. The customer decided to reroute and replace the cable since the vicinity of a mudslide remains unstable for long periods. After rerouting the new cable, 86 feet of the 1987 cable was removed from a manhole and sent back to Pirelli Cable and Systems North America research facility for evaluation. The 10-year-old field aged cable was an opportunity to benchmark and compare some of the mechanical, material and optical performances of a field-aged cable with original test results recorded on this 1987 cable design. Figure 1. Loose-Tube Cable Structure