Tài liệu Challenges of Cold Temperatures on OSP Cable Assemblies for FTTP ppt

Challenges of Cold Temperatures on OSP Cable Assemblies for FTTP WHITE PAPER Introduction Fiber-to-the-premise (FTTP) architectures are presenting both new challenges and new opportunities regarding the use of connectors in the outside plant (OSP). At no other time have connectors been as necessary in OSP architectures – and they are destined to become even more prevalent in the days ahead as the FTTP networking market continues to gain momentum. Service providers competing for the FTTP market require the same flexibility in test access and the ability to provision that they have typically enjoyed in the central office. They need to scale service in a cost-effective manner. Splicing is expensive and, since it is basically hard-wiring, is not very flexible. Therefore, to achieve the flexibility required for FTTP networks, it simply makes sense to use connectors at several key points of the network architecture. So for the first time, network architects will be using more connectors – and cable assemblies with connectors attached – to gain the best flexibility for the OSP portions of their FTTP networks. This creates some significant challenges for connectors, particularly their effectiveness in harsher outside environments. Challenges of Cold Temperatures on OSP Cable Assemblies for FTTP Challenges of cold temperatures on OSP cable assemblies for FTTP Page 3 Connectors in the OSP Meeting the unique challenges of FTTP requires the production of components that are cost effective, yet still perform to OSP standards under austere temperature conditions. In this paper, ADC will address one important performance measurement issue for outside plant (OSP) cable assemblies – how well they can adapt to cold temperatures. Insertion loss (IL) failures, for instance, are a direct result of cable and cable assembly component shrinkage due to low temperatures. If this shrinkage isn’t somehow addressed in the manufacturing process, the optical fibers can eventually break. ADC assemblies are designed to overcome the challenges of low temperature effects and the associated problems. Through proven manufacturing techniques, these assemblies prevent shrinkage and the problems – including fiber breakage – that can otherwise result. The environmental operating requirements for cable assemblies in the North American market are defined by industry standards. Telcordia GR-326, Issue 3, requires cable assemblies to be subjected to two one-week thermal cycle tests from -40 degrees C to +75 degrees C 21 times. Each temperature extreme is held for a minimum one-hour period, at which time the insertion loss and return loss are measured. To meet the GR-326 requirement, insertion loss cannot change more than 0.3dB at any time during the test. Telcordia GR-20 defines similar requirements for non- terminated OSP cable. The minimum operating environment in this standard is also -40 degrees C. Cold Temperature Challenges Exposing cable and cable assemblies to low temperatures is typically the most common cause of insertion loss failures in OSP architectures. Figure 1 shows a typical ribbon OSP cable assembly at normal temperatures. But as temperatures approach -40 degrees, the thermoplastic components in the cable breakout, jacketing, and fiber fanout sections will tend to shrink more than the optical fiber. These are the potential problem areas that are addressed in this paper. As temperatures decrease to -40 degrees, the effect on the cable assembly becomes significant as it begins to shrink. The optical fiber in the cable, however, remains at its original length. This can cause the optical fiber to bunch up inside the temporarily shortened assembly, causing microbends and high insertion loss at 1550 nm. The bends generally recover once the cable assembly is brought back to room temperature. This failure mode normally occurs in two places – the cable breakout (the point at which the ribbons break out of the OSP cable), and the fiber fanout (the point where the ribbons break out into individual fibers). Fiber fanout splits the ribbons into individual fibers and up- jackets them to .900mm for termination to the fiber with a connector. Because it is made of plastic, the .900mm up- jacket tube shrinks more than the optical fiber at -40 degrees. Since the optical fiber itself does not bend inside this tube, it will “piston” back into the fiber fanout housing because the .900mm up-jacket tube is smaller. A typical fiber fanout failure caused by cold temperatures is shown in Figure 3. Figure 3 shows the housing with the cover removed. However, with the cover in place, severe bending will occur as the fibers are pushed back into the open space of the fiber fanout. In this particular non-ADC example, all 12 fibers broke at -40 degrees. OSP Cable Cable Breakout Ribbons Ribbon up Jacketing Fiber Fanout OSP Cable Cable Breakout Ribbons Ribbon up Jacketing Fiber Fanout OSP Cable Cable Breakout Up-jacketed Ribbons .900mm Up-jacketed Fibers Fiber Fanout Figure 2: The OSP cable assembly is shown at room temperature (above) and cold temperature (below). Since the cable assembly tends to shrink while the optical fiber remains at its original length, microbends and high insertion loss result. Figure 3: A typical fiber fanout failure shown with the housing cover removed. In this non-ADC example, every individual fiber broke under the stress caused by the shrinking jacket tube. A similar problem occurs at the cable breakout point where the ribbons are split out of the cable. At -40 degrees, the entire OSP cable will shrink up to 5% as allowed by GR-20. Again, since the ribbons do not shrink relative to the plastic cable components, they will bend within the cable breakout, causing microbends and insertion loss problems as they approach -40 degrees. A failure similar to that depicted in Figure 2 can occur. ADC’s Cold Temperature Solution ADC’s ribbon OSP cable assemblies are designed with special features that enable them to endure temperature changes without failure and meet all GR-326 requirements at -40 degrees C. This is accomplished by selecting low- shrink plastic components and filling the fiber fanout and cable breakout sections with a silicone adhesive. This process prevents the fibers from being pushed into an open space where bending can occur. Since the .900mm up-jacketing has a small inside diameter, bending will not occur. The fiber is effectively under a small amount of compression because the .900mm tubes will shrink about 1% at -40 degrees. However, since there are no open spaces for the fiber to bend – in neither the .900mm tube or the fiber fanout – insertion loss remains low. Fiber bend is similarly prevented at the cable breakout point. The ribbons are prevented from bending in the cable breakout housing because it is also filled with silicone adhesive. This procedure forces any excess ribbon length caused by low temperatures to be taken up within the OSP cable. Inside the OSP cable, there is adequate room for the ribbons to adjust at -40 degrees. Summary To summarize, ADC OSP cable assemblies meet the insertion and return loss requirements of GR-326 at low temperatures for the following three reasons: • ADC only uses optical cable that is GR-20 compliant; • ADC’s optical connectors meet the requirements of GR- 326, Issue 3; and • ADC deals with the issues surrounding cable assembly components at -40 degrees C. Components used to construct OSP cable assemblies are typically made of plastic and, therefore, tend to shrink at cold temperatures. ADC’s cable assemblies are factory designed to compensate for cold temperature shrinkage – preventing microbends, high insertion loss, and fiber breakage at -40 degrees C. Challenges of cold temperatures on OSP cable assemblies for FTTP Page 4 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 1314221 05/05 Revision © 2004, 2005 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. WHITE PAPER . environments. Challenges of Cold Temperatures on OSP Cable Assemblies for FTTP Challenges of cold temperatures on OSP cable assemblies for FTTP Page 3 Connectors. Challenges of Cold Temperatures on OSP Cable Assemblies for FTTP WHITE PAPER Introduction Fiber-to-the-premise (FTTP) architectures