The History & Production of Fiber Optics
Cable Designs for Fiber Optics Networks
Today in North America, there are two basic cable designs that are used for designing fiber optic networks. These are loose-tube, which are used in many outside plants, duct, direct-buried applications, and tight-buffered, which are primarily used inside buildings. Before selecting a cable design, there are still many more decisions to make after determining whether the cables will be used inside or outside.
Resistance to chemicals, moisture, and any other types of in-ground or atmospheric conditions are some environmental concerns. Some mechanical properties that are very important are flexing, tensile strength, bending, and impact resistance.
Loose Tube Fiber Optic Cable Assembly
Loose tube cables are made up of numerous fibers inside a small plastic tube that are coiled around a central strength member and jacketed, providing a small, high fiber count cable. These cables are excellent for outside plant applications since they can be made with the loose tubes filled with water-absorbent powder or gel that withstands high moisture conditions. They also give a more stable transmission under continuous mechanical stress.
Loose tube cables can be strung overhead, buried directly into the ground, and also used in conduits, since they are designed to endure harsh outdoor temperatures, have high tensile strength, and have a large bend radius and diameter. The fibers must be handled carefully and protected to prevent damage since they have only a thin buffer coating.
Without interfering with other protected buffer tubes that are being routed to different locations, the buffer-tube design of the loose tube cable allows easy drop-off of groups of fibers at intermediate points. The loose tube cable design is also helpful in the administration and identification of fibers in the system.
Loose-buffered cables are available in all-dielectric construction, armored construction, and riser-rated constructions.
Tight-Buffered Fiber Optic Cable Assembly
Even though some tight-buffered cable designs are for outdoors, most of them are for indoor applications. These individual fibers are coated with a buffer coating and are protected during routing, handling, and connectorization by the rugged cable structure, which comes from their tight-buffered design. The tensile load is also kept away from the fiber by the yarn strength members.
The tight-buffered design is very flexible. It has low crush and impact resistance along with a low attenuation change at lower temperatures. The tight-buffered design is well-suited for "jumper cables" that connect outside plant cables to terminal equipment, and also for linking various devices in a premises network
The breakout design and distribution design are the two typical constructions of the tight-buffered cables. The breakout design has an individual jacket for each tight-buffered fiber, and the distribution design has a single jacket protecting all of the tight-buffered fibers.
Single-fiber cables have a single fiber strand surrounded by a tight buffer. To terminate loose-tube cables directly into receivers and other active and passive components, single-fiber tight-buffered cables are used as pigtails, patch cords, and jumpers.
Multi-fiber cables have two or more tight-buffer cables that are contained in a common outer jacket. General building, risers, and plenum applications often use multi-fiber, tight-buffered cables. These cables are also used for handling ease and flexibility within buildings and alternative handling and routing.
With these innovative network designs, fiber optics have paved the way for easier, more efficient custom cable assembly. Whether for an administrative, medical, or industrial network, fiber optics networking is quickly becoming the number one choice.
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