Wayne M. Kachmar 2017-11-07 11:58:26
Wayne M. Kachmar Technical Horsepower Consulting LLC www.technicalhorsepowerconsulting.com The fiber optic communication industry faces an ongoing challenge: the stratification of standards at the connectivity level. In particular, there has been a growing disparity between available cable specifications and connectivity specifications. Fiber optic cable and connectivity specifications have evolved separately over time as cables were installed in new applications such as aircraft, traffic control and stadiums. Clearly, another layer of standards is not the answer. Instead, the paper upon which this article is based attempts to provide a workable solution by adding procedural compatibility tests (“red flag” tests) as a subset of existing cable and connectivity specifications. These relatively simple tests would allow fiber optic cable assembly production facilities and installers to determine whether a particular GR-qualified cable and GR-qualified connector (or splice system) will work together to produce a GR-qualified assembly. The ultimate question is: Where should the optical communication industry add cable/connectivity compatibility tests within existing specifications? The existing standards in the telecommunications industry have been foundational in rapidly allowing development of interconnectable components by many manufacturers. As with any successful technology, the number of uses and users has caused an even larger population of specifications. The primary goal of component specifications is to allow interoperability between devices that make up a whole device and allow for multiple sources of supply for each component. Thus, good standards provide a benchmark that allows different technologies to be developed that will complement each other and clearly identify viable new concepts that can rapidly be incorporated into devices or systems to reduce costs or to improve the devices or system. One concern in the optical communication industry has been the stratification of standards at the connectivity level. In particular, there is a growing disparity between available cable specifications and connectivity specifications. As the optical fiber industry has started to mature, it has spawned many variants in designs and uses as well as many different environments. This led to even more types of specifications and many variations of the technology. While this also may be applied to the optical fibers themselves, this article will be confined to the protective portion of optical transport, the cables and how they attach to connectivity. The term connectivity includes connectors, mechanical splices, fusion splices and how securely the waveguide is attached to its connectivity. This article reviews the gaps between the common optical cable and optical connectivity specifications, noting where each requires differing requirements from the other. A popular example of this issue is the environmental testing requirements in Telcordia GR-409 and Telcordia GR-326. An additional variant of this confusion is the use of breakout devices to mimic simplex cable at the end of large fiber count cables. These furcation tubes also affect the connectivity performance of a cable assembly. Once these differences are defined and the gaps identified, the question arises, Do we need yet another layer of standards to choke development further? This article attempts to provide a workable solution of a possible addition of testing criteria based upon connectivity type (i.e., connector, fusion splice, furcation tube) to bridge this gap. Much like additional safety testing, it can be added to existing specifications, but there is still the question to be answered as to what connector type will be considered. Any specification like this will need to be flexible to accommodate the rapid development of new connectivity concepts to encourage and not restrain development. Historically, Why Two Separate Ecosystems of Standards Developed for Cables & Connectivity In discussing the issues with fiber optic cable and connectivity standards, one must look at the optical communication industry’s history to see how the specifications evolved separately. Initially, standards were created on the then-new optical fiber technology to provide cable makers and connectivity manufacturers with some common sizes and dimensions. At its core, the reason standards exist is to ensure components fit together. Basic examples are the wall plug, phono jack, USB and AWG (American Wire Gauge) for copper wire. Decades ago, when fiber optic communication specifications initially came out, they were purely mechanical standards that addressed dimensions and geometries. Later, the optical communication industry had to agree on how the electro-optic conversion would be accomplished. In other words, what size core would work with what size emitter and how much power would go through? And for example, would this occur via a nonreturn-to-zero or a return-to-zero methodology? For anyone who worked in the industry in the 1970s and 1980s, the real question was this: What size core of fiber, emitter and detector would be optimized to work together? As Fiber Optic Systems Became Mainstream, Industry Needed to Demystify Their Use & Installation Over time, as fiber optic communication has become mainstream, much of the industry’s work has been to shatter the “delicate glass” myth, while making the use and installation of fiber optic cable no more challenging than the installation of copper or coaxial cable. During this time, a set of issues came to the forefront—issues that were different than working with copper or coax. While copper, for example, is malleable and stable, early fiber optic cables had different failure modes that tended to fail over time whereas copper failures were usually evident immediately. Many of the issues were predicated on the fact that fiber is a hair-thin strand of glass. The natural reaction was: “It’s glass. It’s delicate.” In reality, fiber is quite strong. However, optical fiber is an engineered structure. Today’s fiber optic cable can withstand a great deal of tension. It can operate over a wide temperature range. In the past, you could easily crush it, but not so today. Fiber optic cable can withstand impact and torque (twist). Over the decades, the optical communication industry moved from developing a highly specialized, high-tech laboratory product to a mainstream, real-world product that reliably transmits data in many challenging environments. As Technology Matured, Cable & Connector Manufacturers Created Different Specifications Within the optical communication industry, manufacturers of cables and manufacturers of connectors perceived their critical areas differently. This stems from the fact that the business models to manufacture cable and connectors are very different. Cable making is a process industry, and the process must run continuously, much like an oil refinery processing crude oil into gasoline, kerosene and diesel. On the other hand, connectivity is typically an assembly process. Parts are machined and assembled in a specific way to perform a specific function, much like an automobile assembly line. When comparing an oil refinery to an auto assembly line, clearly the two operations are quite different. And their perspectives are quite different. Naturally, it makes sense that the cable manufacturers and the companies developing connectors and connector assemblies used different methods to create their specifications. This has resulted in a variety of disconnects (no pun intended). This situation is not unique to the optical communication industry. Over the years, similar issues have shown up in a variety of areas in the copper world. For instance, the so-called zip cords—two-wire extension cords—had an insulation displacement connector that was very low-tech and cheap (it could be purchased in a five-and-dime store). The plug and socket snapped over the zip cord. But if the zip cord was not exactly the right size, this caused significant failures. When a load was added such as an iron or a toaster, it would immediately pop and fail. Similar systems in the fiber world were running into these same types of mechanical issues (see Figure 1 and Figure 2). Again, cable manufacturers and connector manufacturers used different approaches and methods to create their specifications. The cable makers’ basic concern was: Can we get signal (optical light) from Point A to Point B? Will the cable withstand the abuse of being installed? And will it continue to work over time? Their primary focus was cable as a transport mechanism. What happened on the ends—connectorization—was not as important to them. On the other hand, connector manufacturers focused on interface standards, which meant the tip of the connector received extreme dimensional clarity and control. This was to assure that connectors from different manufacturers using a standard interface sleeve would always align and transmit optical energy with acceptable losses. Also, almost every component in a connector was solid. It could be clearly defined by a mechanical drawing with tolerances and dimensioning. By comparison, everything in a cable, other than the actual glass fiber and central strength member made of steel or glass-reinforced plastic rod, is relatively soft and pliable. Essentially, the optical communication industry has approached specification writing from two very different perspectives. This has resulted in the creation of significantly different specifications. Here is one example. There were generic material specifications for cables that required jackets to be a certain size with a certain amount of tensile strength and flexibility. On the other hand, the connector manufacturers developed extremely rigid component tolerances that measured, among other things, concentricity in microns. New Applications Further Complicated Industry Standards In the past few decades, end users began installing fiber optic cable in a wide variety of unique applications beyond telecommunications. Just a few examples include the following: • Traffic control to run city streetlights. • Aircraft, with the Boeing 777 being the first “fly by light” airplane. • Subway tunnels/stations for security monitoring. • Hotels and stadiums to provide wireless backhaul capability and video links. The many different applications required the optical communication industry to think differently about the cable, the connector and the assembly. Not surprisingly, end users perceived this as a working system, much the way you would buy electrical parts today and expect them to fit together. For many years, the fiber optic components did work together within a generic statement of agreement. However, at the time cable specifications were nominal measurements of geometry and performance specifications whereas connector specifications were geometric critical dimension products. This is a clear difference in the way specifications were created and used. At this point in the industry’s history, we began to run into a natural stratification of the specification systems. As a general rule, the cablers assumed the end effects of the cable were unimportant, as long as the bulk of the signal was passed over the long haul. Most did not give attention to fibers extruding out the end of the cable or whether the end of the cable would have end effects from being pulled into place. Most cable manufacturers did not give serious attention to connectorization in the specifications. Some manufacturers, to their credit, did develop systems to ensure their cable would work with the majority of connectors. Meanwhile, some connectivity manufacturers did design connectors to work with a variety of cables. However, one perception is that the connectivity professionals assumed cables were designed of solid, stable materials—just like their connectors. They expected that temperature and physical forces from installation would not change any portion of the cable. Soon these parochial views clashed with reality. Many early cable terminations required highly skilled technicians and engineers working in sterile conditions. In those days, connectors were much more complex devices. Plus, end effects were compensated for in a number of ways. In many cases, the fusion splices or the connectors were housed in splice trays where the technician or engineer terminated the cable and coiled up the loose fiber inside the splice tray, so only the fiber itself was meeting the connector. Either there was no strength member in the splice tray or there was a furcation tube fitted over the individual optical fiber. Basically, the loose tube cable needed the furcation tube configuration to attenuate any length differences occurring at the cable ends either from thermal shrinkback or installation end effects. Effectively, there was a gap between the fiber coming out of the loose tube and the furcation tube that acted as a shock absorber. In fact, in many early applications, the loose tube cable was spliced onto a connectorized pigtail to allow an expansion joint in the assembly. Over time, this evolved into indoor cables and loose tube breakout kits that may or may not be buffered (see Figure 3). Ideally, Issues Resulting from Specification Differences Would be Dealt With Any issues that arose due to the differences in specifications, ideally, would be dealt with by one group or the other—cable manufacturers or connectivity manufacturers— taking into account the perspectives of the opposite design methodology. For example, a major manufacturer of cables would develop recommended practices for its cable to work with a number of connectors. Or perhaps connector manufacturers would test a variety of relatively different cables within the field. In reality, the optical communication industry does not have a generic definition regarding which cable will work with which connector to produce a GR-qualified assembly. This is a critical factor. The industry never based a set of standards between the cable specifications and the connectivity specifications to reference one another directly. While existing specifications refer to test methods, they do not clarify whether a particular cable and connector will work together to meet requirements. This was done to allow unfettered development of the back of the connector system. Over time, several manufacturers have experimented with different methods to mechanically secure the cable and connector or the fiber and connector. However, the rapid development of new lower-cost connectors and cables has outpaced these efforts. In addition, new manufacturers are also entering the market and may not always understand these dynamics. Unfortunately, the cable and connector manufacturers that have driven the specification process have focused on what they perceive as their respective area of concern. For example, fiber optic cables are often pulled into ducts, trenched and hung on poles. Therefore, cable manufacturers have focused on ensuring the cable will carry the bulk signal after withstanding abuse from installation, which can include heavy equipment such as backhoes and bulldozers. Plus, they have focused on whether the cable will still transmit light in hot or cold temperatures. By comparison, the connectivity manufacturers have focused on what happens at the end of the cable. Questions they may ask themselves are: Will the fiber be under zero tension at the back of our connector? Will it pull out of its splice when the cable is installed and tensioned? This specification issue came to a head with preconnectorized cables: outdoor cables with breakout kits that were preterminated. Depending on the installation practices for some manufacturers, the cable would pass all its cable specifications, but would actually fail, because the end effects would pull or push the fiber in or out of the termination area. Clearly, the optical communication industry does not need to create new specifications. However, when discussing connectorization, some questions to consider include: • Will the optical fiber push back when the physical contact ferrules engage and move, or will the connector have to absorb that 1 to 2 mm space? Some early connectors had bulk to accommodate such issues (see Figure 4). • How will the strength elements work with a specific connector or splice case? These materials have evolved. The specifications call out a tensile performance characteristic for the cable, but they don’t call out a strength member specification for attaching to the connector. Therefore, it becomes incumbent upon a cable manufacturer to conduct the research (after testing, they can inform buyers whether a cable meets, say, Telcordia GR-409 for indoor cables as well as GR-326 for connector testing for back shell retention). Today, buyers might see that a cable meets, for instance, GR-20 and GR-409 or the fiber meets ITU-T G.652D (or another individual fiber specification). But buyers generally don’t see the following statement: “This fiber cable meets the cable assembly tests of GR-326.” Existing standards such as Telcordia GR-20/GR-409 for cable and GR-326 for connectors and assemblies provide bulk cable test criteria or finished assembly test criteria. These specifications address how the cable performs as a cable, but do not address the end effects. They do not help assembly houses and end users define what will or will not work together. For example, GR-326 addresses terminating a cable onto a connector, but it does not specify how the cable must interact with that connector. It is left to the assembly house to solve this problem. Therefore, cable assembly production facilities must create an engineering study to ensure the cable and connector will be compatible. Presently, they must assemble the fiber optic cable assembly and put it through a battery of tests. Overall, the assembly house or the installer is left on its own accord to determine if a specific GR-qualified cable and GR-qualified connector will work together to produce a working GR-qualified assembly. This is a failing of these standards to provide a solid foundation for assembly houses and installers to select quality cables and connectors, and to know that, if they follow the process, these components will perform as specified. Proposing a Workable Solution: Conduct “Red Flag” Compatibility Tests Over time, a series of relatively simple tests have been identified. These simple tests allow the industry to more clearly define whether a particular GR-qualified cable and a particular GR-qualified connector (or splice system) will work together to produce a GR-qualified assembly. These procedural tests, which the author calls “red flag” tests, were developed to look at compatibility between cables and connectors (reference Table 1). This series of tests allows technicians or engineers to determine whether a cable or furcation system will work with a given connector type—without having to actually assemble the components. Each “red flag” test can be conducted without using expensive or complicated test fixtures and equipment. Each test defines individual properties that are critical to an interface between a cable and a connector. The “red flag” compatibility tests are: 1.Fiber/buffer push-back test. 2.Cable jacket to core bonding. 3.Sensitivity of the strength elements and connector crimp method to each other. 4.Cable core to jacket strength element shrink-back after installation and thermal testing. 5.Environmental movement of cable parts. Assembly houses could easily set up and conduct these basic tests—or they can ask the cable manufacturers to conduct the tests. The goal is to easily and quickly evaluate cables and connectors, so the industry can get closer to having a uniform offering of “any connector fits any cable, as long as it meets a defined set of basic tests.” In addition, if the optical communication industry wants to displace copper connectivity in the highbandwidth areas, our industry must move to a set of easy, agreeable connectorization test criteria that manufacturers can stand up to. This can give fiber optic cable assembly houses the capability to shop a number of manufacturers for cables and connectors and know that “Cable A” and “Connector J” will be compatible. When this occurs, manufacturers can be more competitive in pricing and end customers can shop best prices. This can allow optical systems to compete on a commodity basis with conventional copper CAT5/ CAT6 systems. As it stands, one must do a tremendous amount of research and engineering experimentation to ensure a given cable is compatible with a given connector. Assembly houses and installers are burdened with the task to determine whether a specific GR-qualified cable (either Telcordia GR-20 or GR-409) and a GR-qualified connector will work together to produce a qualified GR-326 fiber optic cable assembly. This can involve a significant amount of expensive testing. Further complicating matters, many cables and connectors are not currently compatible. As more manufacturers enter the marketplace, it becomes increasingly more difficult to verify that any given cable and connector will function as required when assembled together. Where Should These “Red Flag” Tests Be Added Within Existing Specifications? Creating a new set of specifications is not an option. Ultimately, the optical communication industry needs to define where these compatibility tests should reside. For instance, should Telcordia GR-326 have a cable qualification section? Or should there be a separate section of GR-20/GR-409 that defines performance of these tests for connector use? In other words, should a section of GR-326 be applicable to cables, where these tests are created? Perhaps the specification states: “In order to be a GR-326 assembly, the cable must pass the following tests...” Or perhaps insert test criteria for “red flag” tests in a separate section of the cable specification: GR-20 or GR-409? Alternatively, a GR-20 or GR-326 specification could be referenced. Clearly, many different options may be identified and discussed. Conclusion Eventually, the optical communication industry must define certain “red flag” compatibility tests and make the data available to users and installers. Working together, cable manufacturers and connectivity manufacturers can seek a way to incorporate these compatibility tests into industry specifications, whether this information is immediately integrated into an existing standard, or it is addressed during the next revision process. For further discussion, contact the autor via email at: firstname.lastname@example.org www.technicalhorsepowerconsulting.com Acknowledgements: Special thanks to Fiber Optic Center for providing photographs and for assistance with connector information. References: 1 Telcordia GR-20 Issue 4 Generic Requirements for Optical Fiber and Optical Fiber Cable Jul. 2013. 2 Telcordia GR-326 Issue 4 Generic Requirements for Singlemode Optical Connectors and Jumper Assemblies Feb. 2010. 3 Telcordia GR-409 Issue 2 Generic requirements for Indoor Fiber Optic Cable Nov. 2008. 4 EIA/TIA RS 455A Standard Test Procedure for Fiber Optic Fibers, Cables, Transducers, Sensors, Connecting and Terminating Devices, and Other Fiber Optic Components. 5 ANSI/TIA/EIA 568-B.3 Optical Fiber Cabling components standard April 2000. Author: Wayne M. Kachmar is President of Technical Horsepower Consulting LLC, in North Bennington, VT, USA, which provides technical support related to design and processing optical cable. He is a 38-year veteran of the optical cable industry. During that time he has developed many unique cable designs for many specialized applications including optical sensor cables embedded in the Antarctic ice pack, flight-critical aerospace cables, medical laser transport cables and numerous military applications. During his career he has participated in many standards bodies including EIA, NJATA, NECA and SMPTE to help create cable and connector test methods. In 1988, he founded Northern Lights Cable Inc., which was acquired by progressively larger cable and connectivity companies, most recently, TE Connectivity. Wayne Kachmar retired from TE Connectivity as a Fellow in Electro-optic Engineering (their highest technical role). He is the inventor on more than 50 patents in fiber optic product designs and technologies. He holds an AAS degree in electrical technology from SUNY. The paper from which this article was generated was presented at IWCS 2017TM in Orlando, FL, USA. The “IWCS International Cable & Connectivity Symposium” is produced annually by International Wire & Cable Symposium, Inc. (IWCS, Inc.), and is recognized as the premier technical event in the wire and cable industry. www.iwcs.org
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