WHITE PAPER Extreme-Environment Performance Considerations for FTTX Splitter Modules Considerations for FTTX Splitter Modules Extreme-Environment Performance Optical splitter modules used in FTTX networks contain the splitters that make passive optical networks possible. The module physically protects the splitter and provides a means to connectorize the splitter inputs and outputs. A housing, constructed of plastic or metal, holds the splitter and provides a means to up-jacket the splitter fibers with 2mm furcation tube for connectorization. A certain number of outputs are connectorized. The input fiber may be connectorized, can be a pigtail, or can be attached to the module by means of a backplane. Figure 1: Typical FTTX Splitter Module Module housing (1xN splitter inside) Bending Strain Relief Input Connectors 2 mm Furcation tube Page 3 Industry Standards Telcordia GR-1209 and GR-1221 standards define the operating requirements for splitter modules in North America. GR-1209 defines basic optical performance requirements such as insertion and return loss, polarization-dependent loss (PDL), and uniformity. GR-1209 also defines short-term environmental and mechanical requirements such as input and output proof strength and side loading, and a temperature and humidity profile. GR-1221 defines the splitter modules’ long-term reliability requirements. GR-1221 requires splitters to go through 2,000 hours of high temperature aging, low-temperature aging, thermal cycling, and humidity aging. GR-1221 also subjects samples to impact and vibration testing. The operating extremes defined in GR-1209 and GR-1221 are –40°C to +85°C and up to 95% relative humidity. GR-1209 and GR-1221 will typically be called out by North American service providers deploying passive optical networks. Some service providers may require their network to function at lower temperatures. In these cases, military specifications (MIL SPECs) requiring –55°C minimum operating temperatures may be called out. These operating extremes present challenges when designing splitter modules. Before large-scale North American deployment of FTTx in 2004, most modules containing splitters and connectors were used in central offices. Splitter modules saw stable environments and were therefore not extensively tested. Testing to extreme conditions and deployment in outside plant environments forced service providers and equipment manufacturers to re-evaluate the requirements of splitter modules. GR-1209 and GR-1221 do not consider many characteristics that are important for devices deployed in the OSP. For example, GR-1209 and GR-1221 do not define material properties such as chemical resistance or installation considerations such as the handling of furcation tubes at extreme temperatures. Furcation Tubing Furcation tubing is the material slipped over the splitter inputs and outputs. The furcation tube protects the fiber from physical damage and makes connectorization possible. The furcation tube is usually identical in construction to a 2mm simplex jumper, but the .900mm tight buffered fiber is replaced by a hollow tube. The hollow tube has a .900mm outside diameter and the inside diameter is larger so that a fiber can be inserted. Once the fiber is inserted into the inner tube, a connector can be terminated to the ends. 2mm simplex jumpers are typically used in controlled environments. They are not required to meet the more stringent requirements for outside deployment. It would be risky to choose a furcation tube made out of materials used for controlled environment jumpers that are only rated to -20°C. Some specific requirements of furcation tubing that aren’t explicitly called out in GR-1209 or GR-1221 include cold-temperature handling and cable routing, and thermal expansion and contraction. Extreme-Environment Performance Considerations of FTTX Splitter Modules 2 mm Outer Jacket Inner .900 mm Tube Aramid Strength Members Splitter Input and Output Fibers Inserted Into This Space Figure 2: Furcation Tube Construction Extreme-Environment Performance Considerations of FTTX Splitter Modules Page 4 Cold-temperature handling and cable routing: The outer 2mm jacketing of furcation tube is made of thermoplastic materials. The tubing can become very stiff at cold temperatures. This is no issue in a static situation. However, if new service is turned on at cold temperatures, a technician will have to re-route the up-jacketed splitter outputs in the fiber distribution hub (FDH). If the furcation tube is too stiff because of the cold temperature, routing becomes difficult and bending can occur, causing high insertion loss. Standard jumper jacketing materials such as PVC become very stiff at temperatures lower than –20°C. Proper design requires that furcation tubes be made of different materials. Polyurethane is one possible choice for the outer jacket. This material remains relatively flexible to temperatures as low as –60°C and is resistant to fungus and chemicals commonly used in telecommunications. Some types of PVC outer jacketing can also become permanently stiff if exposed to high temperatures for extended periods of time. As the PVC ages, plasticizers in the cable degrade causing the jacket to stiffen. Polyurethane is also resistant to this phenomenon, making it suitable for both very hot and extremely cold environments. Cold-temperature handling of furcation tube can be evaluated several ways. First, the furcation tube should be tested to FOTP-104 (Fiber Optical Cable Cyclic Flexing Test), but performed at -40°C. It could also be tested to FOTP-37 (Low or High Temperature Bend Test for Fiber Optic Cable). There should be no evidence of cracking of the outer jacket after the tests are completed. Second, the ability to re-route furcation tube within a cable management system must be evaluated. There are no existing industry standards to evaluate this property. However, this property can still be subjectively tested by simulating cable routing at cold temperatures. A test was performed where furcation tube made of PVC and polyurethane were wrapped around a small mandrel and aged at -40°C for 2 hours (see Figure 3). The mandrel was removed and the cables were allowed to uncoil themselves using only the weight of the connector (see Figure 4). The polyurethane furcation tube was much more flexible at -40°C than PVC. This property makes polyurethane an ideal choice for furcation tube jacketing because bending losses are less likely to occur when an installation take place at cold temperatures. Figure 3: Test sample on Mandrel at -40°C Figure 4: PVC and Polyurethane Tubes at -40°C PVC Polyurethane Extreme-Environment Performance Considerations of FTTX Splitter Modules Page 5 Thermal expansion and contraction All furcation tubes are made of thermoplastics. Plastics tend to expand at high temperatures and contract at low temperatures. However, the optical fiber will remain the same length over these temperature extremes. If the expansion and contraction of the plastic materials over the fiber are not accounted for, fiber bending and high insertion loss could occur. Thermal affects usually cause insertion losses problems at cold temperatures. Plastics contract while fibers remain the same length at low temperatures. If the fiber within the .900mm inner tube of the furcation tube is bound within, bending will occur because the fiber will buckle within the inner diameter (ID) of the tube (shown in figure 5), causing high insertion losses (1550 nm and 1625nm). There are several methods to deal with this issue. The first is to use plastics that do not contract at –40°C. Such materials include polytetrafluoroethylene (PTFE). Unfortunately, PTFE is very expensive and doesn’t bond well to the epoxy in a connector, and is therefore not the best choice. Other less expensive materials more suitable for connectorization, such as polyvinylidene difluoride (PVDF) or Hytrel ®1 , contract only 0.5% to 0.9% at –40°C. Figure 6 shows expansion and contraction data for various tube materials. Even this small amount of change in the tubing can cause the fiber to bend. One can compensate for this slight contraction by freeing one end of the fiber from the tube and providing a space for the fiber to expand into as the .900mm inner tube contracts. An example of such a design is shown in figure 7. Bending at cold temperatures can be avoided by letting the far end of the fiber float freely with respect to the tube. As the tube contracts, the fiber will push into the “expansion chamber” where it has sufficient room to move and not violate bend radii. Such a design prevents bending losses in environments as cold as –60°C and allows for a variety of plastic materials to be used for the .900mm inner tube. .900 mm tube .900 mm tube Input or output fiber at room temperature Connector Connector Input or output fiber at -40°C Figure 5: Tube Contraction Illustration Figure 7: Expansion Chamber Concept 84 15 36 38 38 32 26 80 82 26 34 14 38 1.00% 0.90% 0.80% 0.70% 0.60% 0.50% 0.40% 0.30% 0.20% 0.10% 0.00% -0.10% -0.20% -0.30% -0.40% -0.50% -0.60% -0.70% -0.80% -0.90% -1.00% Temperature vs. Length Temperature Percent change in Length LCP-Filled PVDF Hytrel PTFE PVDF Figure 6: Length Data for Various .900mm Tube Materials 1 Hytrel is a registered trademark of E.I. du Pont de Nemours and Company Extreme-Environment Performance Considerations of FTTX Splitter Modules Page 6 Material Selection — Fungus, Salt Spray, Industrial Atmosphere, and Chemical Resistance In addition to temperature and humidity, a splitter module deployed in the outside plant has to be resistant to a variety of environmental stresses. The following are additional criteria that should be applied to splitter modules deployed in extreme environments. All plastic materials in the splitter module should have a zero fungus rating per ASTM G-21. Selecting materials with these ratings will prevent fungus from growing within the splitter that could cause long-term reliability issues. The materials used to make the splitter module should also be resistant to incidental contact with common chemicals used by equipment installers. Such chemicals are defined in Telcordia GR-2898 and GR-487 and include wasp spray, cable blocking gel, WD-40, kerosene, hydrosol, ammonia, isopropyl alcohol, sodium hydroxide, and sulfuric acid. Splitter modules are usually installed in FDH cabinets deployed in a variety of environments. These cabinets may not be completely sealed from the environment. FDH cabinets can be installed near marine locations where salt can corrode metallic components. They could also be installed near industrial sites where sulfuric corrosion is an issue. Materials should be tested for salt spray resistance per ASTM B117 and industrial atmosphere resistance per ASTM B809. Splicing One purpose of the splitter module is to up-jacket the input and output fibers to which connectors can be attached. One method is to slide the fibers into a hollow furcation tube, then directly connectorize the splitter output fiber. Another method is to splice pigtails to the splitter outputs, then house the splices inside the module. Splices have three drawbacks: • Splicesaddlosstothesplitter.Misalignmentsofthe cores in the splice will increase insertion loss of the splitter module. • Aspliceaddsanotherdevicetothesplitter.More devices mean more opportunities for a failure, which decreases the long-term reliability of the splitter module. • A1x32splittermodulewithsplicingwillhavetohouse up to 32 splice protectors. Such storage requirements make the splitter module larger, which increases the size of the FDH cabinet. Splitter modules without splices have lower loss, are more reliable in the long-term, and are generally smaller in size. Input and Output Strain Relief The 2mm furcation tubes exiting the splitter module must be strain-relieved to protect the fragile, expensive planar lightwave circuit (PLC) splitter inside. However the requirements of GR-1209 are insufficient to guarantee the PLC splitter remains undamaged. GR-1209 only requires that the inputs and outputs withstand a 1 kg (2.2 lb) load. This load could easily be applied to the splitter during installation. Instead, the splitter inputs and outputs should withstand at least 6.8 kg (15 lbs) of force. This load is the same pull-force required for fiber optic connectors per GR-326. Because the connectors have to withstand this pull force, the cable attached to the splitter also needs to withstand this force. A splitter purchaser should make sure splitter modules’ inputs and outputs meet GR-326 requirements, not the lesser GR- 1209 requirements. Summary FTTX splitter modules need to withstand extreme operating environments. The requirements of GR-1209 and GR-1221 cover some of these, but are incomplete. In addition to meeting Telcordia requirements, a splitter’s inputs and outputs should remain flexible to at least –40°C and should account for thermal expansion and contraction of the plastics in the tube. In addition, the splitter materials should be fungus and chemical resistant, should withstand loads higher than those specified in GR-1209, and should not contain splices. 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. 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 104898AE 8/07 Revision © 2007 ADC Telecommunications, Inc. All Rights Reserved WHITE PAPERWHITE PAPER . PAPER Extreme-Environment Performance Considerations for FTTX Splitter Modules Considerations for FTTX Splitter Modules Extreme-Environment Performance. contraction. Extreme-Environment Performance Considerations of FTTX Splitter Modules 2 mm Outer Jacket Inner .900 mm Tube Aramid Strength Members Splitter