As today s evolving data centers

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1 IT CORNER Next Generation Optical Fiber Connectivity Solutions for the Mission Critical Data Center BY BILL CHARUK As today s evolving data centers confront bandwidth capacity challenges, the migration from 10 gigabits per second (Gb/s)to 40 and 100 Gb/s, and higher density and cloud computing requirements, choosing the correct connectivity method has never been more important to meet the demands for optimum reliability, performance, scalability, cost effectiveness, and time to restoration. Various research studies assert that the physical layer accounts for nearly 60 to 80% of network downtime, elevating connectivity from an important focus to a mission critical and crucial decision. As the data center evolves with growing challenges, so must the connectivity solutions evolve simultaneously and harmoniously to resolve those challenges. Therefore, optical fiber and connectivity manufacturers have innovated the next generation connectivity solution the field installable splice-on connector or SOC. The splice-on connector (MPO, SC, LC, FC, ST) has now been added to the mix of familiar legacy field installable connectivity methods still widely used: Field installable (puck and polish) connectors, Pre-polished/Mechanical connectors Factory Pre-terminated cable assemblies To make an educated connectivity decision, it is important to become familiar with the splice-on connector and to evaluate the advantages and disadvantages of each popular connectivity method deployed today as they pertain to the high density data center environment and according to the following major criteria: Performance and reliability for multimode and single-mode fiber types Flexibility, speed, and ease of use for fiber installations and cable builds, MACs, and restoration Scalability and future proofing Within the examination of the connector methods, references to cost effectiveness are also made, providing the essential information with which to determine the correct connectivity decision to meet the needs of the data center today and tomorrow. PERFORMANCE AND RELIABILITY To determine any methodology s appropriateness for a network, industry standards and specifications must be considered. Table 1 shows the current allowable connection and channel insertion loss for next generation systems operating at 40 or 100 Gigabits per second. Notice the low loss requirements for the connections in the optical pathway. The last highlighted column lists the allowable connection loss budget that comprises a cumulative loss based upon fiber, lengths, channel insertion and other specific characteristics and, not connector loss (i.e. the total loss of a mated pair of connectors). All connector methods used in data centers need to meet these specifications to allow for seamless system upgrades to the next generation speeds and to ensure that the network will work reliably over the installed fiber optic link. The field installable puck and polish method s advantages can be rapid deployment in the field and low cost. Its success, however, depends on the experience of the Table 1: Channel Insertion Loss and Connection Loss Budgets for 40G and 100G Systems Data Rate Designation Mb/s Fiber Type Number of Fibers Max Link Length (Meters) Max Channel Insertion Loss (db) Allowable Connection Loss Budget (db) 40-Gbe 40GBase-SR4 40,000 OM Gbe 40GBase-SR4 40,000 OM Gbe 100GBase-SR10 100,000 OM Gbe 100GBase-SR10 100,000 OM THE DATA CENTER JOURNAL 23

2 installer and requires a fairly high skill set to achieve required insertion and return loss performance by hand polishing the end face of the ferrule to precisely the correct angle. Limitations include use of epoxies, an average 10% failure rate in large projects due to human error and fatigue, limited viability in single-mode systems, and often unacceptable return loss for APC (angled polish connectors). Another disadvantage is that puck and polish connectors are blind terminations, for which no actual or estimated loss associated with the connector is available until the full link is completed and personnel are in place at both ends of the link to complete power through testing. The mechanical connector method aligns a cleaved fiber with a pre-polished stub and utilizes a cam or crimp mechanism to mechanically splice the fibers. The advantages of this termination method include installation speed, low skill set, and the factory polished and inspected end face. Unlike the puck and polish method, these relatively expensive connectors offer various end face polishes from the factory, which are tested prior to use. The major disadvantage to this method is the reflectance and attenuation associated with the mechanical splice. To combat this, index matching gel is used to ensure reflections do not occur. However, this also presents a risk to the data center systems. The refractive index of index matching gel is temperature dependent. Figure 2 shows the relationship between temperature and the return loss as a function of the refractive index of the gel. Obviously, when the data center systems are operating normally, the performance of index matching gel is a low risk. If the data center should experience a temperature excursion, the gel may not be able to maintain system optical integrity or could even begin to flow out of the connector. While a data center may never see these temperatures, it is prudent to design the optical network in such a manner where this will not be a possible outcome of a temperature excursion due to loss of cooling capability, even for brief periods. Another consideration is that this method is also a blind termination process, requiring additional test equipment and time to test. Pre-terminated cable assemblies offer strong advantages, primarily the installed Figure 2: Return Loss and Refractive Index as a Function of Temperature Image 1: LC, SOC Components connectors that have been tested to meet attenuation performance standards. They also do not require any skill, other than connector cleaning, for use. Unfortunately, this solution has nontechnical drawbacks that make them an expensive and inconvenient solution for the data center. The pre-terminated cable method is costly when ordered from the factory. With space at a premium, storage of cable slack can be problematic. Even when the lengths are engineered, the addition of a small amount of cable length can lead to storage issues over time. The next generation solution, the splice-on connector (MPO, SC, LC, ST), is a hybrid technology consisting of a prepolished connector (APC, UPC, PC) and fiber stub that can be fusion spliced directly on the end of an optical fiber. Essentially, the SOC provides the advantages of a pigtail without the negative inventory or storage issues for a splice tray or cable slack. The SOC also takes advantage of a factory polished end face that has been tested for attenuation and inspected for other defects. The use of fusion splicing is an advantage in and of itself in that there is no serious question in the industry of the fusion splice s quality for reduced attenuation and the elimination of reflectance. When the fusion splice is hermitically sealed within the heat shrink or protective sleeve, an ultra reliable optical fiber termination is achieved that is more robust and optically superior to the mechanical splice. The SOC, in effect, is a connector/ pigtail that generates a factory-quality connection in a field installable method. The connector can be attached directly to a 250 micron or 900 micron buffered fiber, affording the flexibility for customized on-site cable builds at exact lengths, while eliminating the limitations of factory preterminated cables. To install this connector, today s easy to use, low skill fusion splicer with the appropriate fiber/connector holders is 24 THE DATA CENTER JOURNAL

3 The data center is a unique environment within the enterprise network. The data center is the only network where speed, reliability, security and optical performance must remain uncompromised at all times. This is true during initial installations of optical links, repairs and restorations, moves, and any changes or rerouting that may occur over the life of the data center. required. As backward compatibility with existing fusion splicers allows for more widespread adoption of this technology, connector jigs have been developed to retro-fit on many popular fusion splicers already owned by many installers. In addition to the factory polished end face, there are other major advantages. First, by using a fusion splicer with splice loss estimation capability, the technician can overcome the blind splice and get a reading of the estimated splice loss before actually fusing the fiber onto the pre-cleaved fiber stub of the connector. This step increases both productivity and yield while immediately ensuring acceptable insertion loss within specified tolerances. Figures 3 and 4 show the comparative performance results of the various connector methodologies. Figure 3: Insertion Loss Comparison Figure 4: Return Loss Comparison FLEXIBILITY, SPEED, AND EASE OF USE FOR FIBER INSTALLATIONS AND CABLE BUILDS, MACS, AND RESTORATION The data center is a unique environment within the enterprise network. The data center is the only network where speed, reliability, security and optical performance must remain uncompromised at all times. This is true during initial installations of optical links, repairs and restorations, moves, and any changes or rerouting that may occur over the life of the data center. Next generation technologies have the overall advantage of having solved the limitations of preceding technologies. Likewise, the splice-on connector has essentially eliminated the weaknesses of the connector methods having preceded it. By using the fusion splicer with immediate performance feedback, the SOC solves the blind terminations and blind splices, along with the problematic epoxies, associated with the puck and polish and mechanical connector methods to improve speed, productivity and performance. Also, the SOC comes in all varieties of needed connector types and polishes not all made available by these methods. The SOC also solves the major limitations of pre-terminated cables by eliminating the shorts, excess slack, storage, pulling terminated cables through conduit that can damage the connectors, and logistic delays associated with this method. Pre-terminated cables are often used in emergency repair situations and are ordered for same day or next day delivery. Significant downtime of the optical path is possible when waiting for delivery of the assembly. If inventory is kept on site for these occurrences, having the correct length of jumper will result in high inventory costs. Similarly, the pre-terminated cable method slows down immediate data center moves, adds, and changes (MACs) while continually adding to project costs. With the SOC, exact cable builds can be now be accomplished on-site quickly and easily, as well as repairs, restorations, and any MACs crucial to the data center. If a new optical link needs to be established or an old one repaired, one end of an optical cable can be connectorized. The cable can then be easily routed to the termination point within the data center without having to be concerned about damaging connectors during the installation. The second end can then be terminated at the exact required length so there is no additional slack needed to be stored anywhere along the pathway. THE DATA CENTER JOURNAL 25

4 Whether the case is installing new equipment requiring new type of connectors or addressing any MACs, the fusion splice-on connector allows for real-time scalability and upgrades. The technician can exchange connector types and build customized cable assemblies on-site in minutes, thereby eliminating dependency on the factory and its related logistical delays and costs. The same applies for quick restorations. Since the fusion splicer completes the connection operation, all the technician needs to do is move the SOC from the splice area, move the heat shrink protection sleeve over the splice and place it in the curing oven on the splicer. Assembly of the final connector is simple; slide the connector housing over the ferrule assembly and capture the strength yarns on the backside of the connector; the total process of a single fiber termination takes less than three minutes to complete. SCALABILITY AND FUTURE PROOFING TO MEET THE NEEDS OF THE DATA CENTER TODAY AND TOMORROW To ensure the high-density and 40 and 100 Gigabit speed migration of the data center, which requires at least six to 12 times more fiber, the nextgeneration MPO SOC connector has been developed. Until recently, the MPO has typically been installed in a factory and shipped to the field, since no puck and polish versions exist. With the escalated use of high precision mass fusion splicers, MPO SOCs are able to be field installed with very high quality and reliability. The immediate on-site scalability of the SOC to customize the optical fiber Image 2: MPO SOC Components infrastructure of the data center ensures an already future-proofed data center network. The MPO version enjoys the same advantages of the single fiber connector. Depending on the type of cable to be terminated, productivity and speed for fiber installations, MACs, and restoration are greatly improved. For example, terminating 12 fibers simultaneously on a ribbon cable versus twelve individual LC connectors on 3mm single fiber cable can save approximately 86% on installation time. Chart 1 below shows a comparison of installation times using an MPO SOC connector versus single fiber connections on 3mm cable and 900 micron fiber. Chart 1 shows that as the fiber counts increase, the time savings increase dramatically when using the MPO SOC. Of course, to be a viable solution, the methodology must meet industry standards for optical pathways. In Table 2, the initial Table 1outlining network standards is revisited and now includes the maxi- Chart 1: Termination Time Study MPO Versus Single Fiber Solutions for Various Fiber Counts 26 THE DATA CENTER JOURNAL

5 Table 2: Network Specifications as They Relate to Limiting Case MPO SOC Connector. Data Rate Designation Mb/s Fiber Type Number of Fibers Max Link Length (Meters) Max Channel Insertion Loss (db) Allowable Connection Loss Budget (db) LYNX2 MPO SOC Maximum Loss (db) 40-Gbit Ethernet 40GBase-SR4 40,000 OM Gbit Ethernet 40GBase-SR4 40,000 OM Gbit Ethernet 100GBase-SR10 100,000 OM Gbit Ethernet 100GBase-SR10 100,000 OM mum expected connector loss for the MPO SOC. It is clear from the data presented that there exists ample headroom for additional splices in the system and still be able to meet the end to end loss budgets required for 40G/100G transmission. The MPO SOC complies to US: EIA/TIA-604-5, FOCIS 5 and International: IECX standards. CONCLUSION Next generation data centers require next generation connectivity solutions. By combining the advantages of legacy connection technologies into one which uses the latest advancements in fusion splicer technology, the splice-on connector enables rapid, high quality connectivity with the speed, performance, and immediate scalability required by today s evolving data center. As fiber counts continue to increase with the advent of 40G and 100G transmission schemes, installation of single and MPO connectors in the field, resulting in excellent optical integrity, will be a requirement for optimum customer service and reduced operating costs, while lowering risks associated with legacy methodology and connector design. Finally, the MPO 4thLevelAd_DataCenterJournal(SeptFacilitiesInsertion).pdf 1 8/19/12 11:08 AM SOC is ready to support the coming higher speed networks, which will one day become ubiquitous in the data center and allow for graceful growth when further advancements in network transmissions continue to emerge. About the Author: With over 20 years of experience in the communications and information industry, Bill Charuk serves as senior technical manager for Sumitomo Electric Lightwave ( com), overseeing its Data Center Solutions division. Bill can be reached at bcharuk@ sumitomoelectric.com Sumitomo Electric Lightwave. All rights reserved. TM th Take Your Network To The Highest Level TakeÊYourÊNetwork ToÊTheÊHighestÊLevel 100GÊNEXTÊGEN 40GÊTOMORROW Lynx2ÊCustomFit Splice-OnÊConnectors 10GÊTODAY 1GÊLEGACY Lynx2-MPO Hardware OpticalÊFiberÊCable, FusionÊSplicersÊ&ÊTools IntroducingÊtheÊRevolutionaryÊ4 th ÊLevelÊDataÊCenterÊSolutionÉ EnablingÊFlexibleÉÊReal-TimeÉÊOn-SiteÉOpticalÊFiberÊInfrastructureÊDesign Optimum Performance Immediate Scalability Faster Moves, Adds & Changes Real-Time Cable Builds Faster Restorations Less Downtime and more Contact Customer Service Today at THE DATA CENTER JOURNAL 27 info@sumitomoelectric.com