SubscribeIntroduction: Blown Optical fiber (BOF) is an innovative alternative to the standard installation of a fiber optic cable plant.
This paper will discuss the development and history of this technology along with its advantages and applications. BOF is used in both military and commercial environments. These different environments present vastly different problems; a description of these problems and their associated solutions will be studied.
Problem Statement
In many instances, BOF technology is a superior alternative to conventional fiber optic cabling methods and installation practices. Both BOF and conventional fiber links have at least one common element. You have to install them. According to Bill Schweber of Sumitomo Electric Lightware Corporation, "The stress on the fiber optic cable, caused by the installation crew pulling it through the ducts and around curves, means that the cable may develop tiny cracks, so you have to carefully test the link. Even worse, the cracks may continue to grow after installation, eventually resulting in marginal link performance or even complete failure at a random time after the system is checked out and running properly." (EDN; Boston, May 25, 2000, v45 is11 p40, Bill Schweber)
BOF does not produce the tensile stresses on the fiber as stated above because instead of applying all the stress and pressure at the end of the cable, the fiber floats through pre-installed Micro-ducts under no tension. By installing fiber in this manner you eliminate the potential of creating micro-bends and cracks that could lead to increased attenuation. Other benefits of BOF are added flexibility in installation options, capacity for future growth, lower cable attenuation and the reduction in costly splices.
The History and Development of Blown Optical Fiber (BOF)
British Telecom in London developed BOF in the early 1980's. It was used first commercially in Europe and then Japan. British Telecom holds the master license and has leased this out to two companies: Sumitomo Electric Corporation of Triangle Park, N.C and General Cable.
Under the trademark name of BLOLITE™ General Cable has licensed the BOF technology to shipyards such as Northrop-Grumman Newport News and Norfolk Naval Shipyard. BLOLITE™ has been adopted by the Navy as one of the cabling methods for all new LAN backbones for both large and small platforms and there are over 100 additional Blown Optical Fiber installations in the United States.
The concept of blowing fiber cables has been around for quite some time. Air assisted fiber installations initially incorporated attaching a parachute onto the end of a fiber cable with low-pressure air pushing the parachute and fiber through a conduit. The idea of blowing individual fibers and/or bundles came about quite by accident. While performing an air assisted install the parachute came off the end of the cable and blew out the end of the conduit. This had happened many times but this time instead of shutting down the compressor the technicians left it running while the discussed how they could better secure the parachute to the cable. To their amazement a few minutes later out came the fiber. The technicians went to the engineers for an explanation of how this could happen.
Experimentation discovered that the principle of fluid mechanics, which basically states "molecules travel faster through the center of a tube faster than the outside walls-“ applied to this application. This is due to the friction that molecules exert on each other closer to the center. The molecules traveling fastest along the walls create a high-pressure area forcing the coated fiber to the center of the tube. The fiber can ride this blanket of air through up to three hundred 90-degree turns without touching the sides of the tube as long as the minimum bend diameter is maintained.
The micro-ducts in the BOF cabling are made of a sheath material that can be polyethylene for external use or low-smoke zero halogen for inter or intra-building and military installations. Tests on the tubes include temperature, humidity and water immersion. The fibers are broken out from the tube at interconnection boxes and a furcation or breakout unit maybe used to build up the fiber providing additional protection and strength so a connector can be attached for routing or connection to the end device. (Lightwave; Aug 2000, v17 i9 p202, PennWell Publishing Co.)
Tube cables act as the highway for the fiber and are key elements of the fiber link. Cables are available in various sizes between 1 and 19 individual tubes that provide the routes that the fiber is blown using low-pressure compressed air or nitrogen (Sumitomo’s method). The ability to provide a splice free point-to-point path is one of the BOF advantages. Once the tubes are installed fiber bundles or individual fiber strands containing either single mode, 50 micron or 62.5 micron multimode fibers are blown in.
These fibers can be blown in at rates of up to 150 feet per minute. Currently, the maximum distance a group of 8 fibers can be blown is up to 3280 feet horizontally and 1000 feet vertically, more than enough to meet the needs of most Local Area Network (LAN) applications. Modifications to the bowing unit can add 4 additional fibers for a total of 12 that can be blown simultaneously. This will decrease the horizontal distance to 1640 feet.
General Cable BOF technology is based upon simultaneously blowing individual optical fibers. To facilitate the blowing process, an additional, textured-acryl ate coating is extruded onto standard optical fibers. This additional coating provides color and a dimpled surface somewhat like a golf ball. These dimples create a viscous drag that literally picks up the fiber by friction. This allows the fibers to float in a stress free manner through the center of the tubes during the installation process.
A tractor feed is used to feed the fibers into the tubes until the friction is sufficient enough to pick up the fiber and move it through the tubes. In the Sumitomo blowing process where fibers are blown in as a bundle, a tip is placed on the end of the fiber bundle keeping it from getting caught on the joints of the push-fit connectors where the tube cables connect together.
The fibers are manufactured so they will feed through the blow head without jamming it and slide along the inner tubes. Here the two companies take different approaches to reducing friction between the tube and the fiber. Sumitomo places a low friction surface material on the fiber bundles themselves where as NEXTGEN puts it on the walls of the tubes.
Advantages and Disadvantages of Blown Optical Fiber
Like the AAMCO add that said "You can pay me now or pay me later." With fiber you want to pay later. Defer the costs, with the concept of "pay as you go." With BOF you do not have to install a large amount of dark fiber for future growth. You can delay this added expense until you actually need it.
Mike Kerwin of CCR/Cablenet states, "From the perspective of the system designer, the technology offers a new way of thinking about optical fiber installation. It's not all or nothing anymore; it can be viewed as an as-needed utility. You can for example, put in the tube cable and then wait for the cost of the opto-electonics to decrease before installing the fiber. You purchase only the capability you need."
Other advantages are that fewer installation technicians may be required. With a conventional system it would typically take a minimum of a four-person team three days to complete a 3,000-foot installation. With BOF a two-man team can perform the installation in less than one day after the micro-ducts are installed.
From a design perspective BOF creates continuous cable runs so there is no need for costly splicing. Any path can be created once the tube plant is in place. As the network changes fiber and drops can be added or systems can be reconfigured. The need to plan a network in advance or guess at the future requirements five years down the road is not necessary.
When a casualty occurs due to a break in a cable a BOF install is easier to repair than conventional fiber. For example, let's say that a "fiber seeking backhoe" cuts a BOF cable causing a major service interruption. A conventional cable would have to have each individual fiber spliced and the damaged section would have to be sealed and protected or you would have to replace the damaged section with two enclosures. These measures are costly and time consuming. When each hour of downtime can result in thousands of dollars in lost revenue, not including the cost of repair, a better alternative is needed.
That alternative is BOF. If that cable run were 800 meters from the source you would cut out the broken section of cable tube and insert a new section coupled at each end with standard push-fit connectors. Once that has been accomplished all that is required is to blow out the broken fiber and blow in the new. This can be done in a relative short period of time. With BOF you are looking at hours verses days using conventional fiber cables.
Can the blown out fiber be reused later at another location? The answer is yes but it’s not recommended according to Hans Berg of KITCO Fiber Optics, “It’s not cost effective and it only works on bundled fibers not individual fibers. Manually winding removed fiber on a spool is problematic and it creates a warehousing nightmare. In addition, the optical parameters of the fiber must be re-tested before re-use to ensure that no fiber damage has occurred. Why reuse and store fiber when the cost of purchasing fiber is fairly cheap these days.” Another viewpoint is by Kurt Templeton of Sumitomo who states, "After a significant amount of testing, we've found that as long as all the installation procedures are followed, there is no problem with reusing the fiber. It does not deteriorate over time. In laboratory tests, fiber bundles have been blown in and out more than 50 times without damage. This is an extreme case for a real world application."
Installation costs for BOF may be slightly higher at first because you have to install the infrastructure and the cost for material is more expensive due to the manufacturing process. The offset is that labor costs are cheaper and in most instances there is no need to install protective inner duct. What this amounts to is that the initial installation costs of both conventional fiber cable and BOF are relatively the same. If the requirement is for long cable runs or where there are only a few fibers and no growth is anticipated then traditional cabling method may be preferred. If the future holds additional growth, unknowns and configuration changes then BOF is the preferred installation.
Applications of Blown Optical Fiber
One of the most interesting applications of BOF is on board US Naval Ships. On 5 November 1997, the first fibers were blown into the USS Truman (CVN-75) fiber optic cable plant. Four 600-foot strands of fiber were blown in just under five minutes. BOF was installed as the backbone of the ships communication, navigation, monitoring, and LAN fiber plant. According to Program Executive Officer, Carrier, Littoral Warfare and Auxiliary Ships (PMS312) it was cost effective to migrate from legacy FDDI (Fiber Distributed Data Interface) Ring/Ethernet local area networks to the IT-21 ATM (Asynchronous Transfer Mode) mesh networks without adverse impact to ship production schedules.
One of the Navy's prime concerns is the ability to repair the network in rapid response to external forces or threats. BOF provides this ability through redundancy and dual routes to the end device or user. Termination of the BOF fibers via furcation units can also be accomplished at a shipboard level reducing down time and costs.
The application of BOF on board U S Naval ships is planned for all future new ship construction with a projected submarine application in the near future. The latest aircraft carrier added to the fleet the USS Reagan has over one million feet of BOF installed with additional BOF planned.
Northrop Grumman/Newport News (NGNN) developed the method of installing fiber optics aboard ships utilizing BOF technology. The process involves installing a tube cabling system throughout the ship connected by tube connection boxes or blow through boxes and transitioning to conventional cable through fiber optic interconnection boxes via a furcation unit. A single cable consists of an outer thermoset jacket surrounding seven smaller tubes or micro-ducts. The micro-ducts can be configured to support any length of fiber run within the plant, bypassing interconnection boxes where necessary, thereby minimizing light loss by providing point-to-point connections.
According PMS312 the Navy lists the advantages as; Ability to control light loss, Reduces the cost of adding fiber based systems, Allows new fiber technology to be easily and cost effectively inserted into the ship (i.e. most systems now run on multi-mode fiber, future systems may require single mode fiber), Allows fiber to be installed as required thereby minimizing up front costs, Distributes the cost of adding fiber across individual systems as they are installed in the ship, Allows for rapid repair of damaged cable/fiber while maintaining the same degree of light loss (i.e. blow out damaged fiber, repair tubing, blow in new fiber).
The BOF system in the CVN 75 replaced a conventional MIL-STD type fiber optic cable plant, which was installed aboard the CVN 74. A cost comparison shows that the conventional install totaled for material and installation $2,520,000 on the CVN 74. The BOF totaled $1,400,000 for CVN 75. BOF has far exceeded PMS312s expectations: increased capability and flexibility at a reduced acquisition and life cycle cost.
There is only one company in the United States authorized by General Cable certified to provide training to installers of BLOLITE™. KITCO Fiber Optics out of Virginia Beach, VA KITCO has been the sole provider of commercial BLOLITE™ training for the last seven years. They also train all Navy fiber optic technicians world wide in the repair of shipboard fiber optics in strict compliance to the Military Standard 2042B. KITCO also is the single provider of fiber optic training to all Naval aviation communities. A new Navy fiber optic maintenance plan calls for sailors to be trained for repair and termination of BOF at the shipboard level (organizational maintenance level). KITCO Fiber Optics’ expertise in the field of BOF and training will ensure that fleet personnel have the ability and knowledge to repair and support their equipment, systems and networks whether in port or at sea.
Summary
The benefits of choosing Blown Optical Fiber (BOF) for a network design can be realized without incurring a casualty repair, system upgrade or reconfiguration. If a standard or conventional cable installation were used these modifications would require extensive disruptions to the work place. System down time is the number one mission-critical component of any repair or modification. When thousands of dollars are tied to each hour of downtime, getting the network up and running in the shortest and most efficient manor is the goal of any user.
BOF has proven its ability to be the best method for reducing downtime and costs associated with fiber optic cable repairs. When addressing expansions, changes and modifications to the on site network. The ease that fiber can be added, rerouted, removed or repaired provides network designers and administrators the best tool for meeting the challenges and costs of planning for future growth.
By using BOF companies can defer initial capitol investment costs when expenses are the highest in the life cycle of the network. Future growth does not have to be purchased until it is actually needed. They do not need to include the costs of running dark fiber for anticipated growth. If more fiber is needed, all that is required is to blow more fiber through existing empty Micro-ducts. The "pay as you go" principle when installing a fiber optic infrastructure makes economic sense and provides a better return on investment.
The advantages far exceed the disadvantages when deciding which method to use. Real-world case studies demonstrate how much faster and less expensive it actually is. Due to its inherent flexibility, BOF is ideally suited to any application. Whether deployed in the aircraft carrier USS Truman CVN 75 or on the University of California, Riverside campus, BOF has proved itself a viable technology.
References
1. Building Magazine; June 2000, issue 20, Jim Allen
2.Cablenet Systems; Newsletter, Air-blown fiber eases installation.
3.Communication News; Nokomis, Oct 1999, v36, is10, p34-36
4.Eddie, Steve; Blown Fiber vs. Conventional Fiber Optic Cabling Disaster Recovery and Cost Analysis,
5.EDN; Boston, May 25, 2000, v45 is11 p40, Bill Schweber
6.Lightwave; Aug 2000, v17 i9 p202, PennWell Publishing Company
7.Polymer Engineering and Science; Dec 15, 1996 v36 n23 p2815
8.Program Executive Officer, Carriers, Littoral Warfare and Auxiliary Ships (PMS312), Subj: AIRCRAFT CARRIER AIR BLOWN FIBER OPTIC CABLE PLANT, 26 March 1998
