A New Approach to Speed Fiber to the MDU. By John George, Director, FTTx Solutions, OFS and David Mazzarese, PhD, Systems Engineering Manager

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2 A New Approach to Speed to the MDU By John George, Director, FTTx Solutions, OFS and David Mazzarese, PhD, Systems Engineering Manager The business case for to the Home (FTTH) is being supported through mass deployment and success of both large and smaller service providers globally. However, a barrier for bringing fiber to customers in nearly 700 million apartments and condominiums (Multiple Dwelling Units or MDUs) across the globe remains unconquered - until now. In the past few years nearly all fiber to the MDU deployments have been in fact fiber to the building (FTTB). Video-driven bandwidth demands, and the higher value of fiber connected homes, have contributed to intense interest in running fiber to each MDU unit (FTT-MDU). With cost improvement trends driving the cost of optical networking units (ONUs) which are required for each subscriber from $800 in 2002 to below $300 in large volumes today, the business case for FTTH-MDU has never been better. Now further reductions in ONUs are possible with new indoor units which do not require expensive outdoor-rated connectors and hardening to survive harsh environments. With the ONU cost-barrier broken, what is the next challenge to running fiber to and into individual MDU residences?

3 Traditional fiber architectures within MDUs have followed a paradigm traditionally used in enterprise applications. Unfortunately, this approach has been problematic and expensive for most MDU deployments due to insufficient pathways and spaces available for routing conventional optical fiber cabling systems, and the slow speed and high cost of indoor fusion splicing. Complicating matters is the difficulty service providers may encounter in getting access to the building from skeptical owners, who may not be amenable to disruptive and lengthy installations. The result is high labor and material costs stemming from highly customized installations that can vary greatly by building, particularly within existing older buildings. To help improve the FTT-MDU business case, a new Spooled Distribution System (SDS) has been developed to break the MDU deployment barrier by helping reduce the labor required for installation of a MDU fiber backbone by up to 50 percent, while minimizing inventory and simplifying installation procedures. Traditional MDU FTTH Installations The conventional approach to FTT-MDU has been to run individual fiber cables from a single point in the basement to each floor of a building, because of the need to centralize splitters or electronics. Although the approach depicted in Figure 1 may be typical, some problems are obvious. A large amount of cable termination and handling is required at each cable end. Even with dedicated riser cables pre-terminated on one end, significant fiber management and splicing is still required. Additionally, the volume of riser space needed to support these single-floor cables is substantial, even with the size advantages provided by fiber. Most older buildings have insufficient riser space to support this traditional approach, and even in new buildings many developers will be unwilling to provide sufficient riser and fiber management spaces. Figure 1: Traditional architecture for FTT-MDU deployment Traditional FTT-MDU Terminals & Drops Ceiling Living Floor Many cables and floors passed OSP Closure Splitter/Splice Enclosure

4 What alternatives exist to the traditional approach? A completely pre-engineered and preterminated riser cable using a single high-fiber-count trunk cable with factory installed access points could be installed in the MDU riser shaft. Such Terminal Distribution Systems have been used with mixed results for single-family residential FTTH applications. This approach can require very accurate and extensive up-front engineering surveys of each building; and delay deployments if a custom or standardized distribution cable assembly does not properly fit the building. Spooled Distribution System for FTT-MDU A more practical distribution system for FTT-MDU would adapt to the realities of typical riser pathways and spaces. It would also minimize the fiber management footprint, and enable quick and easy cable slack storage. The result dramatically reduces installation time and expense by up to 50 percent, and accomplishes these objectives with a minimal amount of piece-parts and an intuitive design philosophy. This balance is achievable using intuitively field-adaptable elements in something deployed in an aggregation architecture. The Spooled Distribution System using the aggregation architecture, as shown in Figure 2, is an example of an aggregation architecture implementation for MDUs. The SDS leverages bend-optimized ZWP single-mode optical fiber, compact multi-fiber connector technology, and creatively spooled fiber management to enable speedy FTT-MDU deployment within a small footprint. Figure 2: Spooled Distribution System for FTT-MDU V-Linx MDUSpooled Di ib i S Ceiling Drop Assembly Floor Terminals Combiner Entry FDH OSP Closure

5 The Spooled Distribution System utilizes four flexible elements: an entry fiber distribution hub (FDH) housing compact PLC splitters; a combiner assembly, consisting of a spooled riser cable preterminated in a small aggregation terminal; drop terminal assemblies with spooled and pre-terminated feeder tethers; and robust drop-cable assemblies. The spooling aspect of the SDS is a key to its advantages, enabling it to be insensitive to the number of floors in a building, the distance between floors, and the locations of terminals on each floor. By spooling the combiner and tether cables on a hub concentric with the terminals, these elements can easily be adapted to the most buildings. The fully-factory-terminated SDS can be deployed without the need for field splicing in the building, or with only a single fusion splice at one end of the drop cable, depending on the carrier s preference. The SDS may be repeated for each set of five floors, with a combiner and five individual terminals, as shown in Figure 2. For the lower floors or in a low riser building, the fiber drop terminal tether can be pulled to connect (or splice) directly into the entry FDH. In an eight-story building, one combiner/riser assembly would be deployed serving the top five floors with a drop terminal on each floor, while the bottom three floors could be served by fiber drop terminal tethers pulled to connect directly into the entry FDH. For high rise buildings, this five-floor-per-combiner architecture would simply be repeated. Spooled Distribution System Elements Entry FDH The Entry FDH (Figure 3) accommodates up to four compact 1x32 splitter modules to serve up to 144 living units. Typically, this FDH would be placed in the basement of the MDU, and would be connected to the OSP network through a fusion-spliced, 4-fiber feeder cable. Riser terminations can be either spliced, or plugged in with multi-fiber connectors to feed the riser backbone. Figure 3: Entry Distribution Hub

6 Combiner Spooled Riser Cable Assembly The next element is a simplified riser assembly, in which a compact bend optimized ZWP ribbon riser cable (<9 mm in diameter) is terminated with multiple 12-fiber MPO connectors in a small interface housing called the Combiner (Figure 4). Typically, a 60-fiber Combiner unit will be installed on the third floor of a MDU, and every fifth floor above that (3, 8, 13, etc). Figure 4: Combiner Assembly and Spool Tool Drop Terminal with Spooled Tether The system utilizes a unique terminal that is similar to the combiner, intended to be installed at each floor or area within the MDU. Five 12-fiber terminals, placed throughout the building, can be fed from a 60-fiber combiner. Typically terminals are installed on each of the two floors above and below the combiner, with one terminal installed on the same floor as the combiner. Figure 5: Spooled Drop Terminal. Robust MDU Drop Assemblies The drop assemblies that connect to each subscriber are the last element of the system. These crush resistant, staple capable drop assemblies include robust crush resistant cordage housing ZWP bend optimized fiber, and high performance factory installed connectors that feed each living unit. The assemblies are capable of navigating MDU pathways to and within units, using easy attachment and routing methods. These drop assemblies are available connectorized on one or both ends, typically with SC-APC connectors.

7 Figure 6: Robust Drop Assembly How Bend Optimized Enables the Spooled Distribution System The Spooled Distribution System uses a bend-optimized, zero-water-peak, single-mode fiber to enable the small enclosures while protecting the optical services against the bends which can occur in the MDU and in home installations. One of the most demanding applications for optical fibers is within MDUs and homes. Cables may be forced into tight spaces and around corners for aesthetic reasons and to reduce the cost of cable bend management elements. Couple the desire to make deployment of optical fibers as easy as copper plus the need for smaller enclosures, and it becomes apparent that the bending loss performance of standard single-mode fiber (SMF) does not meet provider needs. SMF has difficulty transmitting video signals through bends tighter than about 30 mm in diameter. The objective for a bending optimized fiber should be meeting the key requirements for successful FTTH or FTTH-MDU deployment: Compatibility with the existing base of single-mode fiber Easy splicing and connector mounting Full spectrum performance Reliability

8 Bend Capable Options In order to meet the requirements of the new G.657B low bending loss fiber standard, recommended for indoor use, and the G.652 standard single-mode fiber requirements to be embedded base compatible, a modified cladding design is required. The modified cladding designs that will be discussed here all use a fundamental fiber design approach patented by AT&T Bell Labs (now OFS Labs). The patent teaches that if the refractive index of the glass cladding that surrounds the lightcarrying core is reduced to a lower level than the index of the cladding, the light will be better confined in the core during fiber bending. The result has been a fiber design having a ring of low-index cladding around the core. Here are two basic structures that have been employed to reduce the index of the cladding in this circular area. One approach uses fluorine added to the glass cladding during fiber processing, and the other utilizes holes or voids arrayed in a ring shaped structure around the core. Since both fluorine and holes/voids have a lower index of refraction than the cladding, the result with both fiber structures is fundamentally the same a low index ring around the core, which reduces bending loss. There are two structures for the flouring low index approach and two structures for the hole/bubble void approach as shown. Protected Core Trench Assisted Hole Assisted Random Void Core carries the light signal Lower refractive index cladding helps keep light in the core Lower refractive index bubbles or voids in cladding helps keep light in the core Lower refractive index holes cladding helps keep light in the core Cladding low index helps keep light in core

9 The protected core fiber (PCF), using the fluorine ring directly around the core, is the most widely accepted and deployed design. Trench assisted fiber (TAF)uses a deep fluorine outside of the core to create the low index trench. Hole assisted fibers (HAF) use precise longitudinal holes around the core, and have been introduced by Japanese manufacturers. The newly developed random void fiber (RVF) uses an array of voids and bubbles near the core of the fiber to create the low index ring. A comparison of the attributes of these four structures is shown in figure 8 below. Figure 8 Various Bend Capable s Benefit Enabling Feature Protected Core Trench Assisted Hole Assisted Random Void (new) Improved network performance G.657B compliant low macro bending loss for inside wiring and G.652D compliant. No G.652? Easy to clean connector end faces to faciliate low reflection for video support Holes/voids can trap fluids/debris and create film Compact fiber management <15 mm bend radius fiber management Fast and easy installation Backward compatible - Easy splicing and testing with standard SMF parameters to installed base. Requires special splice recipe Holes or voids can complicate and slow splicing Reliability under bending Solid Structure??? current reliability theory and experience is based on solid fiber structure Pure, inclusion free synthetic silica glass??? if natural quartz used Conclusion A new optical aggregation architecture, the Spooled Distribution System, can improve the business case for fiber to each unit within MDUs and homes. This solution can lower installation labor costs by up to 50 percent, reduce inventory requirements, and speed system deployments to help win customers faster. It is enabled by the use of bend optimized fiber which optimally balances the needs for optical system performance, low cost deployment, backward compatibility, and reliability. Together, they can help make successful to the MDU deployments a reality.