Placing Fiber Optic Cable in Underground Plant

Placing Fiber Optic Cable in Underground Plant

1. Overview

This document covers cable placing in conduit, innerduct, handholes, and manhole structures. The innerduct may be direct buried or placed in larger diameter conduits. In some applications, the innerduct may be lashed to an aerial strand.

This document covers conventional cable placing techniques that are used to pull or blow (cable jetting) the cable into the conduit or innerduct.

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2. General Rules

2.1 Route Survey and Inspection

It is recommended that an outside plant engineer conduct a route survey and inspection prior to cable installation. Manholes and ducts should be inspected to determine the optimum splice locations and duct assignments. A detailed installation plan, including cable pulling or blowing locations, intermediate assist points, and cable feed locations should be developed based on the route survey.

2.2 Maximum Rated Cable Load

The maximum rated cable load (MRCL) for most OFS outside plant fiber optic cables is 600 lb; however, the cable documentation should always be checked because lower values of MRCL may apply for some cables. When using pulling equipment to install cable, measures should be taken to ensure that the MRCL is not exceeded. This includes the use of breakaway swivels, hydraulic pressure relief valves, and electronic tension control systems.

2.3 Minimum Bend Diameter

Fiber Optic Diameter Bending During Installation

The minimum bend diameters for OFS cables are defined for both dynamic and static conditions. The dynamic condition applies during installation when a cable may be exposed to the MRCL, e.g., while pulling the cable around a sheave or capstan.

2.4 Temperature Limits

Storage and installation of OFS fiber optic cable is limited to the temperature ranges. Be aware that solar heating due to sunlight exposure can increase the cable temperature well above the ambient temperature.

3. Underground Optical Cable Precautions

Before starting any underground cable placing operations, all personnel must be thoroughly familiar with local company safety practices. Practices covering the following procedures should be given special emphasis:

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4. Innerduct

Fiber optic cable is most often placed in a small-diameter innerduct rather than a large-diameter conduit. For existing conduit structures, multiple innerducts can be placed in a single conduit to provide multiple cable paths in the duct. Innerduct is also recommended because it provides a clean continuous path for the installation of the fiber optic cable.

4.1 Diameter Ratio and Area Ratio

Diameter and Innerduct area ratios.

Diameter ratio and/or area ratio are used to determine the optimal cable OD that should be installed in an innerduct. Either ratio can be used, but consistently using one or the other is important to avoid confusion.

4.2 Direct Buried Applications

Studies have shown that vertical undulations in direct buried innerduct can greatly increase the required cable installation forces.

5. Cable Lubricant

Cable lubricant should be used when placing fiber optic cables. Recommended cable lubricants include Polywater4, Hydralube5, and similar cable lubricants that are compatible with polyethylene cable jackets. Both the winch line (or pulling rope) and the cable should be lubricated.

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6. Cable Placing Methods

6.1 Backfeed Technique

The backfeed technique is a common installation method that is used to divide the cable installation into two separate pulls. The backfeed technique may also be used near equipment offices when one end of the cable must be pulled by hand into the building, or at manhole locations where the cable route changes direction.

6.2 Forward-Feed Technique

In the forward-feed technique, the leading end of the cable and excess cable length are pulled out of the innerduct at an intermediate manhole and stored on the ground in a figure-eight. This technique can be used multiple times during a cable installation to greatly increase the distance between cable splices.

6.3 Figure-Eight Installation Techniques

If figure-eight techniques are used during cable installation, the cable should be handled manually and stored on the ground. Place the cable on tarps to prevent damage from gravel, rocks, or other abrasive surfaces.

Fiber Optic Cable Underground Installation

When figure-eighting heavy cables (264 fibers or more), the cable stack should be offset to prevent sheath dents and cable damage. Although sheath dents do not typically damage fibers, this type of cosmetic damage is undesirable. When utilizing the offset method, each crossover point of the cable stack should be offset about 2 inches instead of being stacked directly on top of each other.

Standard vs Offset Figure Eight

6.4 Handholes

Handholes are frequently used to provide access to cable splices and slack storage coils. On long cable pulls, handholes may be used to facilitate intermediate-assist placing operations. The intermediate-assist handholes are typically installed near obstacles or at a predetermined spacing that coincides with the maximum expected cable installation length.

7. Pulling Fiber Optic Cable

The following instructions assume general familiarity with outside plant cable placing procedures. They also assume that the innerduct is in place and a lubricated pulling tape or rope has been installed in the innerduct.

7.1 Feed Manhole

Breakaway Swivel Connector

Mount the cable reel on the reel carrier so that the cable feeds off the top of the reel. Position the cable reel adjacent to the manhole and in-line with the innerduct. The cable reel should be positioned close enough to the manhole so that excessive cable length is not dragging on the ground, but far enough away to maintain slack cable in the event of a sudden start or stop during the pulling operation. A distance of 10 – 15 feet is generally sufficient. Attach the pull line to the fiber optic cable using a cable grip and swivel connector. Caution: A breakaway swivel connector is required if a tension limited winch is not used to pull the cable.

7.2 Intermediate Manholes

The innerduct in intermediate manholes may be continuous through the manhole or it may be interrupted. In either case, the innerduct should be positioned in a straight path from entry duct to exit duct. If the innerduct is continuous and has been racked, remove the innerduct ties and straighten the innerduct through the manhole. If necessary, slack innerduct can be cut out using an innerduct cutter. Secure the innerduct in the manhole to prevent it from creeping into the main duct during cable placing operations.

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7.3 Pull Manhole

OFS recommends the use of tension-limited winches for pulling fiber optic cable. The tension control may be accomplished by electrical, mechanical, or hydraulic methods. In any case, the tension-limiting device must be routinely calibrated as recommended by the equipment manufacturer. Cable winches that display cable tension but do not have automatic cutoff are not sufficient to protect the cable. If a tension-limited winch is not used, a breakaway swivel must be used to connect the fiber optic cable to the pulling line.

7.4 Capstan Winches

7.4.1 General

Breakaway swivels do not protect the fiber-optic cable after the cable pulling-eye passes the intermediate capstan winch; therefore, intermediate-assist capstan winches must be tension-limited. The capstan must also meet the minimum cable bend-diameters.

7.4.2 Set-up

The capstan winches should be positioned along the cable route where the expected pulling tension will be 600 pounds or less. Proper positioning of the capstans prior to the start of the pull will eliminate construction delays caused when an unplanned intermediate capstan assist must be added to the placing operation.

7.4.3 Slack Cable Loop

During the pulling operation, a slack loop of cable must be maintained on the pull-off side of the capstan as shown in Figure.

Intermediate Manhole Set-up

7.4.4 Adding Intermediate Capstans

 If an intermediate capstan is added during the cable pull and the cable pulling eye has already passed through the manhole, a loop of slack cable must be pulled to the intermediate manhole before cable is wrapped on the capstan.

Adding an Intermediate Assist Capsta

7.4.5 Removing Cable from Intermediate Capstan Assist Winch

At the conclusion of the pull, the cable on the capstan is twist free. However, one twist per wrap will be generated in the cable if it is removed from the capstan and straightened.

8. Blown Optical Cable Installation

Cable blowing systems use high-pressure, high-velocity airflow combined with a pushing force to install the cable. A hydraulic or pneumatic powered drive wheel or drive belt is used to push the cable into the innerduct at the feed manhole. Controls and gauges on the cable blowing system allow the operator to monitor and adjust the air flow and push force that is exerted on the cable. Some cable jetting systems use a plug at the cable end to capture the compressed air and generate a small pulling force on the end of the cable.

9. Optical Cable Coiling

9.1 Coils Stored at Intermediate Holes

Many end users require that coils of slack cable be stored in intermediate manholes along the cable route. These slack storage coils are used for future branch splices or route rearrangements. It is important that the coiling method accommodates the proper coil diameter and does not introduce kinking or excessive twist into the cable.

9.2 Fold-Over Method

The Fold-Over Method is recommended for storing moderate lengths of slack cable. Form a cable bight and then twist the bight to form the first cable coil. Fold the coil over to form the second cable coil.

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9.3 Teardrop Method

The teardrop coiling method is recommended for storing longer lengths of cable since it is easier to roll the cable than perform repetitive folding operations. The cable is stored twist free by rolling the cable bight in a manner similar to that used on the cable end.

9.4 Garden Hose Method

The garden hose method is recommended for large diameter cables because only one turn of cable is handled at a time. The storage coil can be formed directly on the manhole racking as each additional loop is added. Each loop can be taped in place as it is added to the storage coil. This method can be used to store any length of slack cable.

9.5 Coils Stored at Splice Locations

Slack cable must be stored at splice locations to allow for splicing. Typically, a cable length of 50 to 100 feet is required for splicing purposes; however, the actual cable length may vary depending on the accessibility of the manhole.

10. Racking Fiber Optic Cable and Innerduct

Cable racking normally begins in intermediate manholes and proceeds manhole by manhole toward each end of the cable. Slack for racking the fiber optic cable may come from either the feed or the pull manhole depending on which end is closer and the amount of excess cable that is available. The preferred method of obtaining racking slack is pulling by hand. If the cable cannot be moved by hand, a split cable grip can be attached to the cable and the cable can be pulled using a cable winch or a chain hoist. Do not exceed the maximum tension rating or violate the minimum bending diameter of the cable while pulling the slack.

Cable coils should be racked in a location where they will not be damaged, preferably on the manhole wall behind in-place cables. Do not decrease the diameter of the cable coils. If slack cable must be removed from the coil for racking purposes, remove one or more loops from the coil and then enlarge the coil to absorb excess slack. Tie the coil securely in place with plastic ties.

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Fiber Optic Dispersion and other Non-Linear Effects

This article focuses on the parameters that affect available bandwidth in optical fibers, and the dispersion mechanisms of various fiber types and non-linear effects.  Dispersion describes the process of how an input signal broadens out as it travels down the fiber. There are several types of dispersions that we will cover. We’ll also take a cursory look at other important nonlinear effects that can reduce the amount of bandwidth that is ultimately available over an optical fiber.

Dispersion

Fiber Optic Dispersion Bandwidth Illustration

Most of the traffic traveling through fiber networks takes the form of a laser pulse, where the laser is pulsed on and off, effectively forming a digital square wave comprised of “1”s and “0”s. Dispersion causes a pulse to spread out over time, effectively rounding the edges, and making it harder for the detector to determine whether a “1” or a “0” is being transmitted. When this happens, the effective bandwidth of the link is reduced. The three main types of dispersion mechanisms are modal dispersion, chromatic dispersion, and polarization mode dispersion. Because these mechanisms affect fiber networks in different ways, we’ll discuss each in some depth. Please download the full article for more information.

Modal Dispersion

In general, our article on Single-Mode Optical Fiber Selection focuses on single-mode fibers since they comprise the vast majority of fiber kilometers deployed around the world. In contrast to multimode fibers, single-mode fibers are used for all high-capacity, long-distance networks due to their low attenuation and high bandwidth. A main limiting factor of multimode fibers is modal dispersion.

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Illustration of Modal dispersion in a multimode and single optical fibers

Multimode fibers carry multiple modes of light at the same time.  While a mode of light can be thought of as a ray of light, a typical multimode fiber can have up to 17 modes of light traveling along it at once. These modes all traverse slightly different paths through the fiber, with some path lengths longer than others. Modes that take a straighter path will arrive sooner, and modes that bounce along the outer edges of the core of the fiber take a longer path and arrive later. The effect on the end pulse is called modal dispersion, since it is due to the different modes in the fiber. Multimode fibers are designed to reduce the amount of modal dispersion with precise control of the index of refraction profile, through the quantity of dopants used in the core. However, it isn’t possible to completely eliminate modal dispersion in multimode fibers.

Chromatic Dispersion

Chromatic dispersion describes a combination of two separate types of dispersion, namely material dispersion and waveguide dispersion. Light travels at different speeds at different wavelengths, and all laser pulses are transmitted over a wavelength range. Light also travels at different speeds through different materials. These varying speeds cause pulses to either spread out or compress as they travel down the fiber. Fiber designers can use these two points to customize the index of refraction profile to produce fibers for different applications. Chromatic dispersion isn’t always a bad thing. In fact, it can be used as a tool to help optimize network performance.

For example, the first lasers used for fiber transmission operated at 1310 nm, and many networks still use that wavelength. Fiber designers therefore developed the first single-mode fibers to have minimum or zero dispersion at this wavelength. In fact, G.652 fibers are still designed this way. In these fibers, dispersion is higher in the 1550 nm window.

Today’s networks often operate with multiple wavelengths running over them. In these networks, nonlinear effects that result from the multiple wavelengths can affect network operation. We’ll give a brief overview of some of these non-linear effects in this article. Chromatic dispersion is often used as a tool to help optimize these types of networks.

Polarization Mode Dispersion (PMD)

Light is an electromagnetic wave and is comprised of two polarizations that travel down the fiber at the same time. In a perfectly round fiber deployed with perfectly balanced external stresses, these polarizations would reach the end of the fiber at the same time. Of course, our world isn’t perfect. Even small amounts of glass ovality/non-concentricity or non-concentric stresses in the cable can cause one of the polarizations to travel faster than the other, spreading out in time as they travel along the fiber. This phenomenon is called polarization mode dispersion (PMD).

Polarization mode dispersion illustration- delay in two polarizations traveling down an optical fiber.

Cabling and installation affect PMD, and even things like vibration from trains moving down tracks or wind-induced aerial cable vibrations can affect PMD. However, the impacts of these interactions are typically smaller than the inherent PMD caused by the glass manufacturing process.

Manufacturing Caused of Polarization Mode Dispersion (PMD)

There are ways to mitigate PMD. One very effective method is to make the glass fiber as geometrically round and consistent as possible. OFS uses a special technique to accomplish this. Using a patented process called fiber “spinning”; half-twists are translated through the fiber during the draw process, reducing the non-concentricities and ovalities in the glass that are the major contributors to increased PMD.

PMD Chart

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Non-Linear Effects

There are a host of other factors that network, equipment, and fiber designers have needed to consider as network capabilities have grown over the years. These factors often result as we collectively add more and more wavelengths of traffic at greater speeds and higher power levels.

It is not the intent of this article to review each of these in depth, but instead to touch on them so the reader can have a passing familiarity. The highest profile of these factors is four-wave mixing, which led to the development of non-zero dispersion-shifted fibers (NZDF). However, other non-linear effects include self-phase modulation, cross-phase modulation, Raman and Brillouin scattering, and others. As mentioned earlier, chromatic dispersion can be used to offset the effects of four-wave mixing. For those non-linear effects related to higher power levels, increasing the effective area where the light travels down the fiber can help to reduce the impact of these other non-linear effects.

Dispersions and non-linear effects are the least understood issues in the general fiber user population, mainly because the guidelines used to match up today’s fibers and electronics typically work so that the end user doesn’t need to have a detailed background to bring up a system.

OFS has multiple decades of experience with fiber optic networks. Please contact your local OFS representative if you would like additional information regarding any of the items in this article.

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OFS is a market leader in the design and manufacture of standard and custom Dispersion Slope Compensating Modules (DSCMs) also known as Dispersion Compensating Modules (DCMs). Our fixed broadband, reconfigurable, and tunable colorless modules round out a product line that is well-suited for the major transmission fiber types.

Optical Fiber Building Solutions

FTTX Building Optimized Fiber Infrastructure

Optical fiber-to-the-business deployment is accelerating globally to support increasing internet speeds of up to 1 Gigabit per second, and 10 Gigabit speeds that are already available in some regions. Service providers are responding by installing optical fiber both to and deep inside buildings to the living unit.

The Solutions in this 64-page guide can help reduce both first and life cycle costs of optical fiber deployments to residential and business customers.

Solutions for both Greenfield installation during building construction and Brownfield installation in existing buildings are included. Scalable and optimized to fit a broad range of building structures, these solutions offer faster, reliable installation through innovative labor saving technologies, using less space than conventional approaches.

Solutions for both indoor and outdoor deployment offer flexibility to use the best available pathways for each building. The solution building blocks include a wide range of terminals, splitters, point-of-entry modules, riser cables, attic and wall fish fiber, hallway fiber and complete indoor living unit fiber kits. This portfolio allows service providers to select the best solution for each building, and OFS can help design building specific solutions and bills of material as a value added service.

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FIBER TO THE BUILDING BENEFITS 

OFS fiber-to-the-subscriber (FTTx) solutions help to revolutionize the speed of installing fibers; enhance the customer experience; minimize disruption; reduce labor costs; increase subscriber take rates; enable faster time to revenue for service providers; and get Gigabit and higher speeds faster to subscribers.

OPTICAL FIBER BUILDING CHALLENGES AND SOLUTIONS 

  • Time to revenue: Fast and easy to install pre-terminated solutions can speed installation and reduce labor costs.
  • No pathways, requiring labor intensive cut and patch: Compact surface mounted fiber solutions.
  • Limited closet space: Smaller enclosures can enable installation of multiple operator connections in a small telecommunications closet.
  • Multiple boxes for splicing and splitter connections: Single box pre-terminated solutions can require less space and enable faster provisioning.
  • No duct space: Compact surface mounted fiber solutions either inside or on the outside of the building do not require duct.
  • Shared infrastructure: Compact cables can support multiple service providers in telecommunication pathways.
  • Fiber bends around many corners: Bend-insensitive fiber specified to support bend radius as low as 2.5 mm.
  • Disruptive/noisy to tenants: Optical solutions that are virtually invisible can be installed quickly and quietly and preserve the building decor.
  • Service disruptions and lost subscribers: Full solution of fiber, cable and connectors from one company, designed to work together. Factory tested to Tier 1 standards.
  • Multiple building types: Solutions to fit each building type.

PRE-TERMINATED vs. FIELD TERMINATED OPTICAL FIBER

Pre-terminated solutions are increasingly used to install fiber in Multiple Dwelling Unit (MDU) buildings to save time and money in higher labor cost regions. Pre-terminated products with built-in slack management are preferred so installers can neatly manage excess slack and use a single component to support multiple deployment lengths. Nevertheless, field terminated solutions can complement pre-terminated parts of the indoor or outdoor network and, for low labor cost markets, field terminated solutions may be preferred. OFS offers both pre-terminated and field terminated solutions to fit the needs of each service provider.

OPTICAL FIBER SPECIFICATIONS OPTIMIZED TO THE APPLICATION

Installing optical fiber in buildings and homes often requires conforming the fiber around sharp corners. EZ- Bend® Single-Mode Fiber offers outstanding bend performance down to a 2.5 mm radius for the most challenging in-residence and MDU applications. Compatible with the installed base of conventional G.652.D single-mode fibers, the fiber meets and exceeds ITU-T G.657.B3 recommendations. EZ-Bend fiber uses patented, groundbreaking EZ-Bend Optical Technology from OFS to provide three times lower loss at tight bends than competing G.657.B3 products.

Centralized, Distributed and Distributed Cascaded Splitting

As FTTx deployment accelerates globally to meet increasing bandwidth needs, service providers must install optical fiber both to and inside the building for business and residential subscribers. Building types include duplexes, garden style, low rise (less than 10 floors), mid rise (10 to 15 floors), high rise (16 to 40 floors) and skyscrapers (40 floors and above). To provide building Gigabit services, providers must place optical cables in building risers and ducts, install optical fiber in hallways, and then take this fiber deep into the units, connecting to an indoor Optical Network Terminal (ONT). How can providers accomplish this in buildings that can vary widely in design, materials and available pathways?

Splitter Architectures

Cascaded SplitterA typical PON network consists of the Optical Line Terminal (OLT) in a central office, head end or cabinet, connected by a feeder cable to optical splitters, and then to distribution cables downstream in the network. Choosing the right architecture depends upon end-user density, projected subscription rates and distance from the OLT. Splitter placement is important in FTTx design as it can significantly affect plant and electronics costs.

Three common types of splitter architectures are used when deploying FTTx:

  • Centralized splitting
  • Distributed splitting
  • Distributed cascaded splitting

To help meet these needs, the OFS portfolio supports all three splitter architectures, and features a broad range of solutions to meet the requirements of virtually any MDU deployment. For flexibility and regional preferences, these offers include a mix of pre-connectorized, in-field fusion splicing and mechanical connector solutions from which OFS can configure customized designs for each type of building.

Brownfield Outdoor Facade Solution

The Outdoor Facade Solution is used when property owners want to preserve the decor of the building exterior. The compact EZ-Bend Indoor/Outdoor cable is placed vertically on the exterior wall of the residence from an outdoor wall mount box to an indoor SlimBox® unit. The indoor SlimBox can be factory configured with SCA adapters or fanouts for a pre-terminated solution, or for fusion splicing. EZ-Bend jumpers are used for the path to each living unit. Pre-terminated EZ-Bend Jumpers are recommended for faster installation, or a mechanical connector may be used for field termination in the SlimBox Wall Plate. The 80×80 InvisiLight® Module can be used as a “fiber extension” to any location in the living unit. Alternatively, instead of EZ-Bend jumpers, the InvisiLight MDU solution may be placed in the hallway to the living units (not shown).

Brownfield Outdoor Facade Solution

Brownfield Outdoor Facade Solution

Greenfield Pre-Terminated Solution

TELECOMMUNICATION ROOM

  • Compact basement box for a progressive customer activation;
  • The basement box (SlimBox 64F Terminal) allows fusion splices for the outside plant cable;
  • Ideal for buildings with low penetration rates: One splitter can be installed and the management of the customers is done through the SCA ports. A parking area permits easy connection of new customers;
  • Several boxes can be connected for modular expansion. Connections between multiple SlimBoxes are possible through access openings between them.

RISER BACKBONE

  • SCA pre-terminated cables for quick plug and play installation;
  • EZ-Bend patch cords directly from the apartment unit may be used for small buildings.

HORIZONTAL DEPLOYMENT

  • Direct deployment from the telecommunication closet to the apartment unit;
  • Ideal for Greenfield installation;
  • The EZ-Bend jumper is connected to an adapter installed in the SlimBox Wall Plate (inside the living unit).

INSIDE THE LIVING UNIT

  • An SCA mechanical connector can be used to terminate the EZ-Bend Jumper inside the living unit;
  • The InvisiLight ILU Solution is a complementary product used to extend the fiber inside the apartment.

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Greenfield Fusion Spliced or Field Terminated Solution

TELECOMMUNICATION ROOM

  • Compact basement box for a progressive customer activation (parking up to 48 connectors in the SlimBox 64F Terminal);
  • The basement box (SlimBox 64F Terminal) allows fusion splices for the outside plant cable and the internal cables (up to 96 fusion splices – 8 splice trays with 12 splices in each one);
  • Ideal for buildings with low penetration rate: One splitter can be installed with management of the customers done through the SCA ports. A parking area permits easy connection of new customers;
  • Several boxes can be connected for modular expansion. Connections between SlimBoxes are possible through access openings between them.

RISER BACKBONE

  • ACCUMAX® cables may be used for quick and easy installation:
  • SCA pre-terminated pigtails are used for fusion splicing inside the basement and floor boxes.

HORIZONTAL DEPLOYMENT

  • Direct deployment from the telecommunication closet to the apartment unit through EZ-Bend cable (ruggedized 3.0 or 4.8 mm);
  • The horizontal cable is fusion spliced or field terminated with a mechanical connector in the SlimBox 12F Terminal (floor distribution box) and in the SlimBox Wall Plate (inside the living unit).

INSIDE THE LIVING UNIT

  • An SCA mechanical connector can be used to terminate the EZ-Bend Jumper inside the living unit or a pre-terminated pigtail can be used;
  • The InvisiLight ILU Solution is a complementary product used to extend the fiber inside the apartment.

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Brownfield Pre-Terminated Solution

Brownfield Pre-Terminated Solution

Brownfield Pre-Terminated Solution

TELECOMMUNICATION ROOM

  • Compact basement box for progressive customer activation;
  • The basement box (SlimBox™ 64F Terminal) allows fusion splices to the outside plant cable;
  • Ideal for buildings with low penetration rate: One splitter can be installed with management of the customers done through the SCA ports. A parking area permits easy connection of new customers;
  • Boxes can be added for modular expansion. Connections between SlimBox units are easily made using jumpers through multiple ports designed into the box.

RISER BACKBONE

  • SCA pre-terminated cables for quick plug and play installation:
  • It is possible to place InvisiLight 2.0 mm 12-Fiber multifiber cord directly from the basement box and down hallways in small or garden style buildings.

HORIZONTAL DEPLOYMENT

  • The InvisiLight MDU Point of Entry (POE) Module offers a discrete solution using field termination inside the module;
  • Virtually invisible installation using the InvisiLight 12F Pre-terminated 2.0 mm cord.

INSIDE THE LIVING UNIT

  • InvisiLight ILU Solution is complementary and connects to the InvisiLight MDU installation;
  • InvisiLight ILU Solution is installed with the same tools and procedures as the InvisiLight MDU Solution

This 64-page guide with illustrations and part specifications will help in  selecting the right fiber optic cables and accessories to reduce both the first and life cycle costs of fiber deployments to business customers inside buildings.

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Choosing Between Single Mode vs Multimode Fibers

Single Mode vs Multimode Fibers

Learn the differences and when to use single mode or multimode fibers.

Cloud computing and web services continue to drive increased bandwidth demand, pushing data communications rates from 1 and 10G to 40 and 100G and beyond in enterprise and data center networks.


These higher speeds might lead system designers to believe that single-mode optical fiber enjoys an increasing advantage over multimode optical fiber in premises applications. However, higher Ethernet speeds do not automatically mean that single-mode optical fiber is the right choice.


Although single-mode optical fiber holds advantages in terms of bandwidth and reach for longer distances, multimode optical fiber easily supports most distances required for enterprise and data center networks, at a cost significantly less than single-mode.


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Total Cost Comparison of Single Mode vs Multimode Fibers

Optical Fiber Networks

Multimode optical fiber continues to be the more cost-effective choice over single-mode optical fiber for shorter-reach applications. While the actual cost of multimode cable is greater than that of single-mode fiber optic cable, it is the optics that dominate the total cost of a network system, dwarfing variation in cable costs.


On average, single-mode transceivers continue to cost from 1.5 to 4 – 5 times more than multimode transceivers, depending on the data rate. As faster optoelectronic technology matures and volumes increase, prices come down for both, and the cost gap between multimode and single-mode decreases. However, single-mode optics have always been more expensive than their equivalent multimode counterparts. This fact is supported by the difference in multimode vs. single-mode 10G optics, a common Ethernet speed used today.


Multimode transceivers also consume less power than single-mode transceivers, an important consideration especially when assessing the cost of powering and cooling a data center. In a large data center with thousands of links, a multimode solution can provide substantial cost savings, from both a transceiver and power/cooling perspective.


Finally, the fact that multimode optical fiber is easier to install and terminate in the field is an important consideration for enterprise environments, with their frequent moves, adds and changes.

The Difference Between Multimode and Single-Mode Fibers

The way in which these two fiber types transmit light eventually led to their separate names. Generally designed for systems of moderate to long distance (e.g., metro, access and long-haul networks), single-mode optical fibers have a small core size (< 10 µm) that permits only one mode or ray of light to be transmitted. This tiny core requires precision alignment to inject light from the transceiver into the core, significantly driving up transceiver costs.

In comparison, multimode optical fibers have larger cores that guide many modes simultaneously. The larger core makes it much easier to capture light from a transceiver, allowing source costs to be controlled. Similarly, multimode connectors cost less than single-mode connectors as a result of the more stringent alignment requirements of single-mode optical fiber. Single-mode connections require greater care and skill to terminate, which is why components are often pre-terminated at the factory. On the other hand, multimode connections can be easily performed in the field, offering installation flexibility, cost savings and peace of mind.


For these reasons, multimode optical fiber systems continue to be the most cost-effective fiber choice for enterprise and data center applications up to the 500 – 600 meter range.


Beyond the reach of multimode optical fibers, it becomes necessary to use single-mode optical fiber. However, when assessing single-mode optical fibers, be sure to consider newer options. A bend-insensitive, full-spectrum single-mode optical fiber provides more transceiver options, greater bandwidth and is less sensitive to handling of the cables and patch cords than is conventional single-mode optical fiber.


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Which Multimode Fiber Type and Why?

At one time, the network designer or end user who specified multimode optical fiber for short reach systems had to choose from two fiber types defined by their core size, namely, 50 micron (µm) or 62.5 µm. Now, that choice is slightly different: choose from OM3, OM4, or the new OM5 grade of 50 µm multimode optical fibers. Today, 62.5 µm OM1 multimode optical fiber is virtually obsolete and is relegated for use with extensions or repairs of legacy, low bandwidth systems. In fact, 62.5 µm OM1 fiber supports only 33 meters at 10G and is not even recognized as an option for faster speeds.


Optical Fiber50 µm multimode optical fibers were first deployed in the 1970s for both short and long reach applications. But as data rates increased, 50 µm fiber’s reach became limited with the LED light sources used at the time. To resolve this, 62.5 µm multimode optical fiber was developed and introduced in the 1980s. With its larger core, 62.5 µm optical fiber coupled more signal power than 50 µm optical fiber, allowing for longer reach (2 kms) at 10 Mb/s to support campus applications. That was the only time when 62.5 µm fiber offered an advantage over 50 µm optical fiber.


With the advent of gigabit (1 Gb/s) speeds and the introduction of the 850 nm VCSEL laser light source in the mid-1990s, we saw a shift back to 50 µm optical fiber, with its inherently higher bandwidth. Today, 50 µm laser-optimized multimode (OM3, OM4, and OM5) optical fibers offer significant bandwidth and reach advantages for short reach applications, while preserving the low system cost advantages of multimode optical fiber.

Planning for the Future

Industry standards groups including IEEE (Ethernet), INCITS (Fibre Channel), TIA, ISO/IEC and others continue to include multimode optical fiber as the short reach solution for next generation speeds. This designation reinforces multimode optical fiber’s continued economic advantage for these applications.


IEEE includes multimode optical fiber in its 40G and 100G Ethernet standards as well as its pending 50G, 200G, and 400G standards. In addition, TIA issued a new standard for the next generation of multimode optical fiber called wide band (OM5) multimode optical fiber. This new version of 50 µm optical fiber can transmit multiple wavelengths using Short Wavelength Division Multiplexing (SWDM) technology, while maintaining OM4 backward compatibility. In this way, end users can obtain greater bandwidth and higher speeds from a single fiber by simply adding wavelengths. The OFS version of this fiber is called LaserWave® WideBand Optical Fiber. This new fiber allows for continued economic benefit in deploying short reach optics using multimode optical fiber – as opposed to more expensive single-mode optics.

In Conclusion

In general, multimode optical fiber continues to be the most cost-effective choice for enterprise and data center applications up to the 500 – 600 meter range. Beyond that, single-mode optical fiber is necessary.


>> Download the Full Article to Learn More about the Difference between Multimode or Single-Mode Optical Fibers

Single-Mode Optical Fiber Selection Guide

Single-mode selection guide cover

Download the OFS single-mode optical fiber selection guide for terrestrial applications. Optical fiber applications include transcontinental, regional, metropolitan, home/business access and in-building fiber optic systems. The guide describes several families of OFS optical fibers and provides recommendations for single-mode fibers used in Outside Plant (OSP) as well as Indoor (Premises, Enterprise) applications and their benefits.

 

Selecting the right single-mode fiber for your application can help lower system costs. Characteristics such as lower loss, larger effective area, optimized dispersion and tight bend performance can provide economic benefits compared to using a standard G.652.D single-mode fiber. Please contact OFS for more thorough explanations of the various fiber value propositions to assist with the selection process.

 

OFS families of Single-Mode Optical Fibers include:

• TeraWave® Optical Fibers - ITU-T G.654 long haul fiber with optimized large effective area designed specifically to support coherent systems.
• TrueWave® Optical Fibers – ITU-T G.655 and/or G.656 Non-Zero Dispersion fibers (NZDF) that have reduced chromatic dispersion characteristics to simplify dispersion compensation.
• AllWave® Optical Fibers – ITU-T G.652.D standard single-mode fibers. AllWave Fibers provide seamless splicing and are zero water peak (ZWP) and can be used everywhere from long haul to shorter reach in-building applications. Some of these fibers are also G.657 compliant.
• AllWave® FLEX and EZ-Bend® Optical Fibers are ITU-T G.657 bend insensitive single-mode fibers

 

Loass Chart

Single-Mode Optical Fiber Application Comparison Charts Include:
• Long Haul - >1000 km*
• Regional, Metro, Utility, Wireless Backhaul - 60 to 1000 km
• FTTx: Home, Business, Cell Site - Up to 60 km - All types and data rates of PON and single-mode point-to-point networks.
• High Density Applications

 

 

Premises, Drop, Cabinet and Connectivity Application Selection Charts Include:
• Central Office, Head End, Data Center, Cabinets, Fiber to the Antenna, General In-Building
• Drop and in the Living Unit