Bend Optimized Fibers are Best Chosen by Application John George, Andrew Oliviero, Pete Weimann, OFS

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2 Conclusion Despite the fact that we are still in the early stages of FTTP and PON networks, there has been a significant evolution in technologies and deployment strategies. This evolution will continue to improve carriers network performance and return on investment. As demonstrated in this paper, GPON and the 1x64 splitter create a very real and immediate opportunity for FTTP operators to distance themselves even further from the competition and to reap more benefits from their passive optical network. Bend Optimized Fibers are Best Chosen by Application John George, Andrew Oliviero, Pete Weimann, OFS As optical fiber has been pushed to the residence for the past several years, Bend Optimized fibers have enabled installations not possible with conventional single-mode fibers (CSMFs). By dramatically reducing the optical signal loss when fibers are bent either accidentally, or intentionally, Bend Optimized fibers can help decrease space requirements and improve network reliability in Central Offices, CATV Head Ends, Data Centers, and Cabinets. More recently, service providers have desired fiber cable solutions than can be routed inconspicuously in residential environments, for example down hallways in multiple dwelling units (MDUs), or within residences as in home wiring (IHW). Installation of MDU drop cables or fiber IHW should ideally be similar to installation practices used for copper cabling, including use of staples and routing around tight corners. Such installation will intentionally bend fibers tighter than ever, but should also significantly speed up deployments and lower installation costs. Several categories of bend capable optical fibers have been developed over the past two decades and recently new types have been introduced. Given the varying requirements for bending loss, reliability, and backward compatibility for each of the key applications, a simple question arises: Which bend capable optical fiber fits best with each application? Answering this question requires an understanding of applications, which can drive the definition of the bend capable fiber type optimized for each application. Central Offices, Head Ends, Data Centers, and Cabinets These are the mission critical nerve centers of service provider networks. Central Offices, Head Ends, and Data Centers each contain hundreds--and more commonly-- thousands of optical fiber cables, and each fiber may support hundreds or thousands of businesses and residences. A single, spontaneous fiber break could bring down service to thousands of customers. These might include health care institutions, financial institutions, government entities, schools, or businesses. Thus high reliability in the Central Office, Head End, Data Center, or cabinets is paramount. Optical fiber reliability can be viewed in terms of optical loss reliability, and mechanical reliability. A view of mechanical reliability is shown in figure 1 below, and is based on classical modeling equations used by the International Telecommunications Union (ITU) recommendations for optical fiber systems. With traditional rules for fiber management at large bend radii, fiber breakage has not been an issue. As fiber bend radii are dropping, based on improved low bending loss fiber designs, fiber reliability becomes an important consideration for all applications.

3 Fiber Lifetime, years Figure 1 Predicted Optical Fiber Reliability 1ppm failure Probability for Bent Fiber Bend Optimized for MDU/IHW Chance of fiber break Bend Optimized for CO/HE/DC/ Cabinets Bend Radius (mm) Reliable system 0.1m 1m Traditional Installations 0.2m All of the applications discussed above share the same need for low-fiber bending loss, regardless of the minimum acceptable bending radius. Additional loss beyond a few tenths of one decibel (db) for most applications might impair or shut down video and other mission-critical services. In general, one should expect the maximum macro-bending loss of a bend-optimized cable assembly to be less than 0.2 db for a single turn at 1550 nm at 10 mm radius, for the CO/HE/DC/Cabinet applications. Below a 10 mm radius there is risk of random fiber breaks for a length of 20 cm (about 3 turns at 10 mm radius). Another challenge in COs and Head Ends is high optical power transmitted over fiber to support video or DWDM systems. Optical cable assemblies used in these applications should be able to support these high powers under bending conditions without degrading, burning, or excessive signal loss, while maintaining mechanical reliability. Again, for high power applications the 10 mm minimum radius is recommended to balance these needs. MDU and In-Home Wiring Service providers have recently requested fiber drop cables that can be routed down hallways and inside a residence while conforming to corners and being stapled in place. This type of installation promises to be less conspicuous to the customer, and lower the cost of deployment for the service provider. The material cost savings per unit passed, for example, could be $5-$10 per unit in addition to significant labor savings of $10-$20 per unit. The ultra-low-bending loss of these cables, at 0.1 db maximum for one 5 mm radius turn at 1550 nm, enables the stapling and routing around corners with minimal signal loss. An example of such an ultra bend and staple capable MDU/IHW drop cable is shown below in Figure 2.

4 Figure 2 MDU and In-Residence Optical Drop Cable using OFS EZ-Bend Technology (4.7 mm cable shown routed around thirty five 3.2 mm radius corners and stapled twenty five times) Unlike the traditional connectivity applications, the MDU/IHW bend capable drop installation involves intentionally bending the fiber to radii down to somewhere between 5 mm and 7.5 mm, through stapling and routing the cable around corners. All things being equal, mechanical reliability of the glass in MDU/IHW cable will inherently be much lower than that in the CO/HE/DC/Cabinet applications: the stress on the fiber at 5 mm bend radius is four times higher than stress on a fiber at a 10 mm bend radius, and over forty times higher than fiber following the traditional 32 mm bend radius fiber management upon which the historical optical fiber reliability experience is based. This leads to new questions for the industry: Is the reliability risk associated with these intentional sharp bends acceptable in MDU/IHW applications given the first-cost benefits of using bendable cables? One consideration with the MDU or single family residential application is that only one subscriber is supported for each optical drop cable. Is it acceptable in this case to lower the reliability expectation? Is the reliability of nanovoid types of fibers the same or lower than that of solid glass fibers which have decades of field service and are supported by well established reliability models? This is unexplored territory in practice and one that the industry will study in the coming months as the market desire for bendable cables intensifies. Additional Considerations All of the applications discussed above share the same need for low-fiber-bending loss, regardless of the minimum acceptable bending radius. Additional loss beyond a few tenths of one decibel (dbs) for most applications might impair or shut down video and other mission critical services. In general, one should expect the macro-bending loss of a bend-optimized cable assembly to exhibit less than 0.2 db of loss for a single turn at 1550 nm, at the minimum radius appropriate and reliable for that application.

5 Another bend capable cable consideration is splice compatibility. Is the bendable fiber backward compatible to splice with traditional G.652 fibers with low loss of less than 0.1 db per splice? Optical cables are available today that minimize both bending loss and splice loss using traditional splicing machines and programs. Fibers that are standards compliant to ITU-T G.652D, for example, may not necessarily splice seamlessly to other G.652D fibers. A Bend-Capable Solution Matrix The following matrix is a simple guide to determining the optimized fiber for each bend challenged application. Applications Solution Examples ITU-T Bending Loss (one turn), standard connections loss, and design life at min radius. Central Office premise cable, Splitter cabinets, Enterprise, Data Center, MDU riser/backbone. AllWave FLEX cable assemblies, indoor cables G.657A G.652D Compliant 0.2 db 1550 nm 0.5 db 1625 nm (10 mm radius) r10 66% lower loss than G.657A 0.25 db max connection loss 40 year Central office crossconnect, OC-48, OC-192 and OC-768 systems, Blue Tiger Jumpers G.657B G.652D compliant 0.1 db 1550 nm 0.25 db 1625 nm (10 mm radius) r10 DWDM, High Power 0.15 db max connection loss applications. 40 year double strength fiber MDU drop cables and in home FTTH drop cables. MDU/in residence drop cables using Much better than G657B, 0.1 db 1550 nm 0.25 db 1625 nm r5 Super bendable copper cable like installation. EZ-Bend Technology (2008) G652D compatible ( 5 mm radius) 20 year (Ed. Note: These solutions use OFS products. Other products are also available that could be used.) Conclusion Bend-capable fibers provide significant value to many applications. There are three bend capable solutions that each are optimized for key application spaces. By choosing the solution optimized for the application, one can achieve best balance of reliability and optical performance in bending challenged systems.