Tài liệu Dramatic Attenuation in Fiber Access Terminals at Low Temperatures doc

white paper OmniReach ™ FTTP Solutions The Situation It is common in applications where access terminals are used to terminate only a portion of the fibers brought into the enclosure–allowing the remainder of the fibers to pass through. When loose tube cable is used, the sub-units that are not terminated are "expressed" through, and the sub-unit material is not opened at any point. To provide customers with adequate sub-unit length for splicing under all conditions, ADC specifies a mid-span access length of 150" to 170". Testing of the enclosure with expressed sub-units of this length alerted ADC to potential low temperature issues. While there are no written standards governing this application, ADC has concluded that in some - but not all - cases, loose tube OSP cable, dielectric or armored, can experience excessive attenuation loss at low temperatures (0˚C to -40˚C). Subsequent research also reveals that the issue becomes more severe for cables exposed to initially high temperatures (greater than 50˚C) prior to their exposure to low temperatures. Attenuation loss can be as high as 10 to 20 dB in extreme cases. After identifying the problem, ADC proactively began researching the probable cause and discovered information from a 1998 Bellcore white paper that outlined similar problems with certain fibers in varying temperature environments. The paper, entitled "Time- and Temperature- Dependent Material Behavior and Its Impact on Low-Temperature Performance of Fiber Optic Cables," by Osman S. Gebizlioglu, seemed to address the very issue ADC was observing in several of its own case studies. According to the paper, "a series of service-affecting field failures in cold weather (-40 degrees C to 0 degrees C) initially and in more moderate conditions (up to 15 degrees C) recently have raised concerns about the temperature-dependent transmission performance of loose tube fiber optic cables." The effect was transmission loss "resulting from fiber microbending due to random fiber contacts with the buffer tube walls caused by the axial shrinkage of the buffer tubes relative to the cable central member." With Bellcore's previous research confirming ADC's own data, engineers set out to pinpoint and formulate a preventative process for dealing with the issue in the field. Dramatic Attenuation in Fiber Access Terminals at Low Temperatures Problem Solved Believing that the contraction of the sub-unit could be pulling the fiber and causing microbends, ADC set out to test the theory. Choosing a sub-unit that was exhibiting high attenuation loss at low temperature, they stripped the sub-unit material off the entire mid-span access area. The goal was to eliminate the clamps and panels as being part of the problem. After stripping the mid-span section, the attenuation disappeared - thus isolating the problem to the fiber sub-unit alone. Although this, in itself, provided a potential field solution–stripping the entire length of sub-unit material was both labor-intensive and risky to the fiber. As a result, ADC set out to establish a craft- friendly procedure that would simplify the solution to the problem. Using a typical fiber cutting tool to apply "ring cuts" to the buffer tubes that are expressed through the cabinet, the same end result is possible. The ring cut is a radial cut through the sub-unit wall without removing material. For the mid-span length required in the ADC access terminal, three ring cuts are applied - one at the entrance point, one at the exit point, and one in the center of the slack loop in the mid-span access. Each ring cut is then protected by sliding a protective sleeve over the cut - about three inches in length. Finally, a small metal "carrier" provides a method of bundling up to six of the protective tubes together and securing them to the sides of the enclosure panel. This prevents movement during any future maintenance activity. Final Notes Ribbon cable is not susceptible to the same low temperature attenuation issue since the ribbon strands are completely removed from the center tube for accessing individual fibers. Rather, the issue appears to be isolated to specific types of loose tube fibers, depending on each manufacturer's own specifications. The major variables from manufacturer to manufacturer include the sub-unit material, the sub-unit dimensions (specifically the inner and outer diameters), the type of gel used, and the amount of extra fiber within a sub-unit length. Any or all of these variables can present different effects in terms of this attenuation issue. ADC is working to help customers build reliable, high-performance networks with confidence. By proactively addressing and solving potential problems such as these, ADC continues to reaffirm its role as the industry leader in customer satisfaction. References O.S. Gebizlioglu, "Time- and Temperature-Dependent Material Behavior and Its Impact on Low- Temperature Performance of Fiber Optic Cables." (1998) ADC Telecommunications, Inc., P.O. Box 1101, Minneapolis, Minnesota USA 55440-1101 Specifications published here are current as of the date of publication of this document. Because we are continuously improving our products, ADC reserves the right to change specifications without prior notice. At any time, you may verify product specifications by contacting our headquarters office in Minneapolis. ADC Telecommunications, Inc. views its patent portfolio as an important corporate asset and vigorously enforces its patents. Products or features contained herein may be covered by one or more U.S. or foreign patents. An Equal Opportunity Employer 1304851 9/04 Original © 2004 ADC Telecommunications, Inc. All Rights Reserved Web Site: www.adc.com From North America, Call Toll Free: 1-800-366-3891 • Outside of North America: +1-952-938-8080 Fax: +1-952-917-3237 For a listing of ADC’s global sales office locations, please refer to our web site. . confirming ADC's own data, engineers set out to pinpoint and formulate a preventative process for dealing with the issue in the field. Dramatic Attenuation. Attenuation in Fiber Access Terminals at Low Temperatures Problem Solved Believing that the contraction of the sub-unit could be pulling the fiber and causing