Fiber Optics Explained Fiber Cable Types

Fiber Cable Types

Simplex vs. Duplex

    Simplex- A cable in which a single fiber optic strand (core and cladding) exists. These cables are most often utilized where a one-way transmission or receiving line is required to operate, meaning information is running in only one direction for all device use. In exception to this rule, multiplex data signals allow simplex fibers to be used bi-directionally. Simplex fibers are available in multimodesingle-mode, or polarized maintaining forms.

    Duplex- A cable in which two separate fiber optic strands exist. Most duplex fiber cables are formatted in the ‘zipcord’ styling, where each fiber strand has independent coatings that are linked together with a thin layer of coating material. This design can allow for a duplex cable to be pulled apart and used as two simplex cables.  Duplex is most used where separate transmit and receive signals are necessary i.e. one strand transmits in one direction while the other strand transmits in the opposite direction. Duplex cables are sometimes classified into half-duplex and full-duplex categories, however it is important to note that this categorization is based on the transmitter/receiver capabilities in the considered system and not the cable itself. In half-duplex connections information can be transmitted in only one direction at a time. In full-duplex connections information can be run in both directions simultaneously.

    Zipcord- a style of cable construction that joins two cable lines into one with a thin layer of insulation. If desired this connecting layer can easily be pulled apart by hand. Zipcords are useful in avoiding tangled cables and keeping certain cables together if needed. In fiber optics zipcord format is most often seen in duplex fiber optics cables.

    Round- also known as interconnect, is a style of jacketing for cable. Round fiber optic cables house two fiber lines within one exterior cable, so are functionally duplex cables but from the outside look like a single cable.

    Distribution- also known as non-breakout style, a distribution cable bundles several (usually between 4-144, but up to 1008) fiber strands into one reinforced cable. Distribution cables are lined with a protective layer of aramid yarn, wrapping the whole of the fiber lines, though each individual fiber line is not reinforced with this yarn. Distribution cables, then, require breakout boxes or patch panels for safe junction and/or connection of each fiber. Distribution cables are popular indoor use cables in networking scenarios and are available plenum and riser rated (see special ratings below). 

    Breakout- breakout cables house several individual fiber lines, however in the breakout format each individual fiber line is reinforced with aramid yarn within the larger breakout cable. Beyond this, breakouts are known for their rugged and tough design, considerable crush resistance, and tensile strength. Because each fiber line is reinforced, breakouts allow the user to “breakout” any number of desired cables at any point along the run and continue to route the remainder to another point. Fibers that are thus separated from the main distribution cable can then be terminated with connectors without the need for a patch panel or termination box.

    Tight Buffered- Tight Buffered cables feature fiber lines that each have a secondary layer of coating applied directly to their initial 250micron layer; this second layer acts as reinforcement to the individual fiber lines and makes them easier to handle and terminate, but feasible only for indoor, low-hazard areas. Zipcords, distribution, and breakout cables are all examples of Tight Buffered cables. 


Special Purpose Cables

    Loose Tube- Loose Tube cables are constructed with a central strength member and a small protective plastic tube along the wall of the jacket which creates a funnel for several fibers to run. Loose Tubes prevent strain damage on fibers and can be made to provide specific environmental protection. Outdoor cables are loose tube formatted.  

    Interlocking Armor Cable- This cable style features a jacketed aluminum outer structure designed to provide indoor/outdoor protection from severe industrial or weather conditions, increase security, and add flexibility. Distribution or breakout cables can be run through these armors. General ruggedness in a compact package make these cables easy to install and very dependable. Due to their aluminum body, these cables are conductive and must be grounded per NEC requirements. Interlocking Armor Cables are available with plenum, riser, and LSZH ratings (see special ratings below)

    Indoor/Outdoor- the name of these cables does not mislead- indoor/outdoor cables were designed to meet the safety and durability requirements for both indoor and outdoor conditions, making in-building transition points unnecessary. Indoor/outdoor cables are available in a variety of cable types and may house up to 288 fibers.

    Outdoor- Outdoor cables vary among themselves according to the conditions in which they will be installed. Among outdoor cable types there are aerial cables, which are strung (usually) along telephone poles and must be weather and strain resistant, direct burial cables, that are buried directly in trenches and must be extra rugged to resist the pressure of dirt and rocks surrounding them, underground cables, which must have high strain resistance as they are installed by being pulled through underground tubing, and submarine or aquatic cables, that require extra tight sealing to prevent water leakage. Each outdoor cable type is being continually improved upon as designers learn by experience what their cables need to provide in order to protect fiber under any conditions.


Special Ratings

    Plenum- is a fire-safety rating awarded to cables that have undergone rigid tests as outlined by the NFPA (National Fire Protection Association). Plenum rated cables are fire resistant, produce low smoke when burned, and do not have metal conduits. Plenum cables are named after the areas in buildings which they were designed to be routed, the plenum space, which can be defined as air circulation space above dropped ceilings or below raised floors. Before plenum rated cables, in the event of a fire, ordinary cables running through plenum space excited the spread of fire. The plenum cable rating was created to ensure cables routed through plenums do less to spread fire. 

    Riser- is a fire-safety rating designed for cables that are to be run vertically, from floor to floor, in their routing. Riser rating tests are not as stringent as plenum rating tests, but do require riser cables to self-extinguish and prevent flames from travelling upward when aflame.

    LSZH (Low Smoke Zero Halogen)- LSZH is the designation for a certain kind of plastic developed as a safety precaution. In fiber optics LSZH cables are jacketed with this plastic. Because many non-LSZH cable jackets contain various halogens and heavy metals, the smoke they produce upon burning is not only toxic and potentially fatal to humans and animals, but can mix together in high temperatures to create corrosives such as hydrochloric acid. LSZH plastics are dense in metal hydrates, a chemical combination high in water molecules, greatly reducing the amount of smoke they produce when burned and dramatically reducing the toxicity and corrosive reactions resultant of its burning.


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