Fiber Optic Cable (FOC): Fiber Optic Cables (FOC) are constructed with a number of loose tubes stranded in layers under a common sheath. Every loose tube has usually a bundle of 12 fiber strands inside. Both loose tubes and fiber-strands have a unique color-coded ID. Depending on the FOC Fiber-Count, the number of loose tubes varies.

The sheath, the armor and some filling compounds inside the FOC core protect the fibers from mechanical stresses during installation and from external damaging agents such as humidity, UV radiation,also resistance of acids,alkalies,water,nuclear radiations etc.
Technical vision on Fiber Optic Cable

Fiber Optic Cable Sections ( FOCS)


A single piece of Fiber Optic Cable (FOC) rarely fits the intended length to install end-to-end. In most situations, and especially in Long-Distance Networks, several pieces of FOC are required. A number of those pieces are then concatenated and joined in order to build the entire link. Those individual cable pieces are called Fiber Optic Cable Sections (FOCS). A Fiber Optic Splice Closure (FOSC) is then installed to splice the fiber-strands between consecutive FOCS creating a Cable Transition Point (CTP).

Several reasons may determine the need to split a FOC into a number of FOCSs, including but not limited to:

To fit with the FOC reel capacity. Delivered FOC lengths by the supplier impose and upper limit on the maximum FOCS length.

To ease logistics and installation. The size of the FOC reels increases with the length delivered. Large reels are difficult to move and the efficiency and cost to install may be also impaired.
To construct Cable Branching Points (CBP) and Cable Transition Points (CTP).
To create specific maintenance sections. Usually the procedure to repair a FOC breakage is to install another FOCS between two points located further in both directions from the breakage point. Whether breakage risky spots along the route are identified, a recommended action is to design FOCS in a way that fit over those risky areas.


Both ends of each FOCS must be terminated in a Physical Path Enclosure (PPE) such as Manhole (MH)/HH or vault. FOCS can also terminate in a Site Entrance Facility (SEF). Each FOCS is then defined by its start/end points, which, in turn, according to the route followed by the civil infrastructure, determines its length.


Fiber Optic Cable (FOC) Delivery Lengths


Fiber Optic Cables (FOCs) are delivered from factory at standard lengths that don’t match accurately with length requirements in the field. Although some manufacturers have the ability to deliver FOCs in customized lengths, they are usually delivered in standard and predetermined lengths.Generally FOC manufacturer provide the length of FOC reels of 2 KM,6 KM and 8 KM. Mostly 2 KM,4 KM FOC reels used in the FOC installation. 6 KM and 8 KM FOC reels used in the Long Distance network & Junction network also.

Sub-ducting: Single Fiber Optic Cable Per Conduit


Considering their small cross section, multiple Fiber Optic Cables (FOC) can be placed into a single conduit to maximize its usage. Furthermore, FOCs can be installed into conduits filled with other existing cables. However this method is not recommended because there is high potential to damage the existing cable during the installation.

The suggested practice when multiple Fiber Optic cable FOCs are installed in a single conduit is to pull them together at the same time. However this method has also some drawbacks, such as the increased difficulty to remove a single cable from a bundle of cables that was installed together as the cables tend to twist around each other inside the conduit.

To accomplish that, empty large-size ducts should be filled with sub-ducts or micro ducts bundles before Fiber Optic cable (FOC) installation. This technique is called Sub-ducting. All the sub-ducts or micro ducts bundles are installed simultaneously.

Sub-ducts and micro ducts bundles are smaller diameter conduits, intended for placement into large-size conduits. Their purpose is to subdivide the larger conduit space into discrete continuous pathways, in order to optimize the capacity of the available underground space while leaving the duct arranged to host the future Fiber Optic cable FOCs. Only a single Fiber Optic cable (FOC) must be installed in a sub-duct or micro duct.

Method Of FOC Placement : Pulling and Blowing


Fiber Optic Cables (FOC) can be install by the using the two basic methods of installation: Pulling and Blowing. The cable installation method is selected based on site conditions,site lengths and availability of machinery & resources. Sub-ducts and Micro ducts bundles used for Sub-ducting can also be installed using both methods.


Pulling Method 
A system to place Fiber Optic cable FOCs for shorter length runs of underground plant and in previously installed underground, buried, and aerial ducts. The Fiber Optic cable (FOC) is pulled through an existing conduit with the help of a pre-installed rope, manually or using a winch. Empty conduit or duct would require a pull rope to be installed first. Blowing can follow a pull line directly or blowing a lightweight line through the conduit using compressed air accomplishes this.

A winch mechanism is usually used to pull the rope with the Fiber Optic cable (FOC) attached. The winch should have a tension meter to monitor the amount of tension being placed on the Fiber Optic cable (FOC) during the pull. This monitor will reduce the risk of damaging the Fiber Optic cable (FOC).

Lubricants should be used to reduce friction during the pulling and therefore allow longer cable pulls.When the cable is attached to the pull rope, it is recommended that a swivel be used between the two. This swivel will allow the FOC and the pull rope to move independently in the conduit during the pull and prevent unnecessary twisting of the FOC.


Pulling method tends to be more popular for standard FOCs and in large-size ducts and sub-ducts. It is possible to place FOCs using this approach in PPS lengths up to 500 meter, depending upon the geometry of the conduit plant encountered. But longer pulls achievement can be possible if mid-assist points are available during the pulling method.

On very long pulling work the use of mid-assists is very common. Mid-assist equipment can be as very simple as a technician pulling on the cable midway or it can be a capstan type device that provides a controlled amount of pulling tension to the FOC to reduce the tension and increase the possible length of the pull.

Jetting or Blowing Method
Few years ago the practice of pulling cable has frequently been replaced with a newer method that uses compressed air to blow the Fiber Optic cable (FOC) into the conduit. The conduit or duct pipe should also be capable of withstanding the pressure of the air being introduced.


Cable blowing requires specialized equipment in simple word we can say blower that utilizes high volume air compressors. There are two categories of air-assisted Fiber Optic Cable  placement: Low Volume/High Pressure, and High Volume/Low Pressure. In the first case (Jetting) a dart seal is attached to the end of the Fiber Optic Cable (FOC) and compressed air is introduced into the duct built the pressure behind the seal, thus air forcing the dart forward and creating a tensile pull on the end of the Fiber Optic Cable (FOC). At the same time, the Fiber Optic Cable (FOC) is inserted into the conduit through a manifold seal using a tractor pusher. The Fiber Optic Cable (FOC) then experiences simultaneous push and pull forces applied during the process. In the second case of Blowing, the Fiber Optic Cable (FOC) is tractor fed into the conduit, again through a manifold seal, but this time has no dart seal. Instead, Fiber Optic cable progress is based on the viscous drag of high volume air alone.


Jetting/Blowing process facilitates much longer lengths of  Fiber Optic Cable (FOC) than traditional cable pulling methods, and the tension forces applied to the  Fiber Optic Cable (FOC) is significantly reduced. They are most effective in smaller conduits/ducts, up to 40 mm diameter. Using blowing techniques it is possible to place  Fiber Optic Cable (FOC) in micro ducts in PPS lengths up to 2,000 m, depending upon the geometry of the path.

Fiber Optic Cable Placement: Mechanical and Thermal Consideration



Fiber optic cable (FOC) installation in underground conduit routes needs some special considerations. Failing to follow such a procedure can result in fiber/FOC damages or high optical power losses after installation. We have to know that all Fiber optic cable (FOC) are very sensitive to damage during shipping, handling, and installation.

Some of the important parameters that need special attention during Fiber optic cable (FOC) installation are:

➤Fiber optic cable (FOC) bending radius:  Fiber optic cable (FOC) are designed with a minimum bending radius details provided by the manufacturers. The 
Fiber optic cable (FOC) should never be try to bent below its minimum bending radius. Against the instruction can result in bending losses and/or fiber breaks in the Fiber optic cable (FOC). Generally the minimum bending radius under the load during Fiber optic cable (FOC) installation is 20×D, where D is the outer diameter of the Fiber optic cable (FOC). Permanent bending radius may be lower, generally 10xD.

Fiber Optic Cable pulling tension: Fiber optic cable (FOC) are designed with a maximum tensile strength and the Fiber optic cable (FOC) should never be pulled beyond its value. Exceeding the fiber optic cable’s pulling tension can shorten its in-service lifetime or occur partial cut. The effects contribute to the pulling force build-up in theFiber optic cable (FOC) are-

Fiber optic cable (FOC) weight,Coefficient of friction,Cable compressive force,Cable Twist and environmental temperature.

Fiber Optic Cable Slack Loop


A Cable Slack Loop is a coil of Fiber Optic Cable (FOC) correctly stored in some selected
Physical Path Enclosures (PPE) for maintenance purposes, to facilitate splicing conveniently or for future network expansion. The usual length of fiber optic cable loop is between 10m to 20m, it also depend upon the telecom operator instruction guide line.Cable loops add an extra length ofFiber optic cable (FOC) when compared to the length measure at ground level.

Duct Fill Ratio (DFR)


Duct Fill Ratio is the ratio between the cross sectional area occupied by the Fiber Optic Cables (FOC) (or occupied by subducts), based on their outside diameter, and the inner space of the common conduit wherein they are installed.The DFR can be used to determine appropriate conduit size or determine how many FOCs can be placed in an existing conduit. The maximum recommended ratio can be affected by several factors, including application type, path geometry, length, number of FOCs, and the number of conduit bends.

Using traditional pulling techniques, the DFR has an upper limit. In contrast to traditional pulling techniques, excessive conduit clearance adds difficulties to cable blowing installations and a DFR lower limit is dictated as well. Large clearance facilitates the FOC to form a helix, which transfers some of the axial load laterally into the wall causing friction. The air velocity moving over the FOC can also be maximized with a minimum volume of air when the free volume is low. Higher air velocities result in improved drag forces on the FOC.

Fiber Optic Cable Branching Point and Fiber Optic Cable termination Point


Cable Branching Point (CBP) is a term used to describe a location where one or more Optical Circuits (OC) are diverted from the main route. In those locations, a Fiber Optic Splice Closure (FOSC) has to be installed to splice the fiber-strands between the main FOC and the branch FOC.

FOCs allow mid-span branching. In mid-span branching, only the branched fiber-strands are
actually spliced to the diverted FOC/route. The rest of fiber-strands contained in the main FOC bypasses that point without any splice.

Cable Termination Point (CTP) is a term used to describe a location where one or more Optical Circuits (OC) need to be transitioned between two different FOCs. CTPs can be required by a number of reasons, including but not limited to:

➤Changes in FOC Fiber-Count. The CTP is produced to join two FOCs with different Fiber-Count. This is a typical situation where a large Fiber-Count FOC is split into a number of lower Fiber-Count FOCs.

➤Changes in FOC installation environment. The CTP is produced to transition between two FOCs with different construction architectures. This is a typical situation in the locations where underground installation changes into aerial installation (or vice versa). It is also produced at the locations where the FOC installation techniques are different on both sides (traditional pulling vs blowing).

➤Joining Fiber Optical Cable Sections* (FOCS). A single piece of FOC rarely fits the intended length end-to-end. In most situations, and especially in long-distance networks, several concatenated pieces of FOC are required. Those pieces are then joined to build the entire link. Those individual FOC pieces are called FOCSs. A CTP is produced at the locations where two consecutive FOCS are joined.

➤Connecting a new FOC with an existing FOC. The CTP is produced at the location where both cables are joined.

Fiber Optic Cable Splice Closure (FOSC)


A Fiber Optic Splice Closure (FOSC) is a passive housing device in which the fiber -strands of a number of Fiber Optic Cables (FOC) are spliced between them.FOSC are usually weatherproof closures, commonly made of tough plastic that envelops the exposed area between spliced FOCs. FOCs enter into a FOSC through cable entry ports, where the jackets are removed to expose the loose tubes. FOSCs also contain a number of splice trays to facilitate the splicing process and protect the exposed fibers from mechanical damage.


Fiber Jointing Schematics (FJS)


A Fiber Jointing Schematic (FJS) is a document that provides the splice matrix representing how the fiber strands from different FOCs are spliced. That information can be presented in several formats, such as a table or a graphic. Every Fiber Optic Splice Closure* (FOSC) has an associated FJS.

Fiber Junction Schematics for each Fiber Optic Splice Closure (FOSC) is a deliverable component of the F-OSP Design Documentation. The information to be displayed in FJSs are:

➤FOC assignment to FOSC cable entry ports. Each FOC enter into the FOSC through a cable entry port. The entry port must have the right size to fit the FOC diameter while conserving sealing properties.

➤Loose Tube assignments to Splice Trays. FOCs are constructed with a number of loose tubes stranded in layers under a common sheath. Every loose tube contains usually a bundle of 12 fibers. Depending on the FOC Fiber-Count, the number of Loose Tubes varies. Every Loose Tube and every fiber strand has a unique ID defined by its color. The Loose Tubes must be transported inside the FOSC up to a specific Splice Tray and each tray has a unique ID.

➤Splice matrix. The splice matrix defines the arrangement of splices between couples of fibers housed in each tray.