As uses for optical fiber have become more varied, manufacturers have begun producing, cables to meet specific needs. Cable configurations vary based on the type of use, the location, and future expansion needs, and it is likely that more will be created as future applications emerge.
Bear in mind that different cable arrangements are variations on a theme. Different combinations of buffer type, strength members, and jackets can be used to create cables to meet the needs of a wide variety of industries and users.
Let’s look at some of the commonly available optical fiber cables.
Breakout cables are used to carry optical fibers that will have direct termination to the equipment, rather than being connected to a patch panel. Breakout fiber cable consist of two or more simplex cables bundled with a strength member and central member covered with an outer jacket. These cables are ideal for routing in exposed trays or any application requiring an extra rugged cable that can be directly connected to the equipment.
When it is necessary to run a large number of optical fibers through a building, distribution cable is often used. Distribution cable consists of multiple tight-buffered fibers bundled in a jacket with a strength member. These cables may also feature a dielectric central member to increase tensile strength, resist bending, and prevent the cable from being kinked during installation.
Distribution cables are ideal for inter-building routing. Depending on the jacket type they may be routed through plenum areas or riser shafts to telecommunications rooms, wiring closets, and workstations. The tight-buffered optical fibers are not meant to be handled muchbeyond the initial installation, because they do not have a strength member and jacket. Distribution cables may carry up to 144 individual tight-buffered optical fibers, many of which may not be used immediately but allow for future expansion.
Ribbon cable is a convenient solution for space and weight problems. The cable contains fiber ribbons, which are actually coated optical fibers placed side by side, encapsulated in Mylar tape similar to a miniature version of wire ribbons used in computer wiring. A single ribbon may contain 4, 8, or 12 optical fibers. These ribbons can be stacked up to 22 high.
Because the ribbon contains only coated optical fibers, this type of cable takes up much less space than individually buffered optical fibers. As a result, ribbon cables are denser than anyother cable design. They are ideal for applications where limited space is available, such as in an existing conduit that has very little room left for an additional cable.
Ribbon cables come in two basic arrangements. In the loose tube ribbon cable, fiber ribbons are stacked on top of one another inside a loose-buffered tube. This type of arrangement can hold several hundred fibers in close quarters. The buffer, strength members,and cable jacket carry any strain while the fiber ribbons move freely inside the buffer tube.
The jacketed ribbon cable looks like a regular tight-buffered cable, but it is elongated to contain a fiber ribbon. This type of cable typically features a small amount of strength member and aripcord to tear through the jacket.
While ribbon fiber provides definite size and weight savings, it does require special equipment and training to take advantage of those benefits. Connectors, strippers, cleavers, and fusion splicers must all be tailored to the ribbon fiber. For these reasons, ribbon fiber may not be the best solution in all situations.
Armored cable can be used for indoor applications and outdoor applications. An armored cable typically has two jackets. The inner jacket is surrounded by the armor and the outer jacket or sheath surrounds the armor.
An armored cable used for outdoor applications is typically a loose tube fiber construction designed for direct burial applications. The armor is typically a corrugated steel tape surrounded by an outer polyethylene jacket. This combination of outer jacket and armor protects the optical fibers from gnawing animals and the damage that can occur during direct burial installations.
Armored cable used for indoor applications may feature tight-buffered or loose-buffered optical fibers, strength members, and an inner jacket. The inner jacket is typically surrounded by a spirally wrapped interlocking metal tape armor. This type of armor is rugged and provides crush resistance. These cables are used in heavy traffic areas and installations that require extra protection, including protection from rodents.
Hybrid cable, as applied to fiber optics, combines multimode and single-mode optical fibers in one cable. Hybrid cable should not be confused with composite cable, although the terms have been used interchangeably in the past.
Composite Cable, as defined by the National Electrical Code (NEC), is designed to carry both optical fiber and current carrying electrical conductors in the same run. This composite cable consists of optical fibers along with twisted-pair wiring typical of telephone wiring. This arrangement is convenient for networks that carry fiber optic data and conventional telephone wiring to the same user. Composite cable also provides installers with a way to communicate during fiber installation and provides electrical power to remote equipment, such as repeaters, along the fiber’s route.
Simplex cordage, consists of a single optical fiber with a tight buffer, an aramid yarn strength member, and a jacket. Simplex cordage gets its name from the fact that, because it is a single fiber, it is typicalyy used for one-way, or simplex, transmission, although bidirectional communications are possible using a single fiber.
Duplex cordage, also known as zipcord, is similar in appearance to household electrical cords. Duplex cordage is a convenient way to combine two simplex cords to achieve duplex, or two-way, transmissions without individual cords getting tangled or switched around accidentally.