In recent years, fiber-optics has been utilized more and more to replace copper wire as an appropriate means of communication and data signal transmission. A fiber-optic system can generally be seen as a system with three main components; a transmitter, a transmission medium and a receiver. As a model it is similar to the copper wire system that fiber-optics is replacing. The difference is that fiber-optics use light pulses to transmit information down fiber lines instead of using electronic pulses to transmit information down copper lines.
Unlike copper wire, fiber-optics has some advantages that make it preferable for data transmission. First, data signals travel further through fiber-optics than through copper. Copper transmission is limited to 100 meters (330 feet), whereas fiber cable has limits from 914.4 meters (3000 feet with multimode) to 100 kilometers (62.14 miles with single-mode). Second, fiber-optics is impervious to EMI (electromagnetic interference). Because fiber-optics transmit light pulses, data transmission is unaffected by high-voltage sources or fluorescent light fixtures. Therefore, fiber optics is preferable when data runs extend through electrically “noisy” areas.
There are generally five elements that make up the construction of a fiber-optic strand or cable; the core, cladding, a buffer material, a strength material and the outer jacket. Light pulses entering the fiber core reflect off the core/cladding and thus remain within the core as they move down the line. Surrounding the cladding is a buffer material used to help shield the core and cladding from damage. A strength material surrounds the buffer, preventing stretch problems when the fiber cable is being pulled. The outer jacket is added to protect against environmental damage.
There are two basic types of fiber optic cable that are utilized in computer networking; single-mode and multimode. These provide different performance with respect to both attenuation and time dispersion. The single-mode fiber-optic cable provides the better performance at, of course, a higher cost. Below is a diagram of the typical core and cladding diameters.
Core diameters and fiber modes are expressed in this way, 62.5/125. The “62.5” indicates the core diameter in microns while the “125” indicates the outside diameter (cladding) also in microns. Multimode cable can be 50/125, 62.5/125, while single-mode is 9/125.
Simplex and zip cord: Simplex cables are one fiber, tight-buffered (coated with a 900 micron buffer over the primary buffer coating) with Kevlar (aramid fiber) strength members and jacketed for indoor use. The jacket is usually 3mm (1/8 in.) diameter. Zipcord is simply two of these joined with a thin web. It's used mostly for patch cord and backplane applications, but zipcord can also be used for desktop connections.
Distribution cables: They contain several tight-buffered fibers bundled under the same jacket with Kevlar strength members and sometimes fiberglass rod reinforcement to stiffen the cable and prevent kinking. These cables are small in size, and used for short, dry conduit runs, riser and plenum applications. The fibers are double buffered and can be directly terminated, but because their fibers are not individually reinforced, these cables need to be broken out with a "breakout box" or terminated inside a patch panel or junction box.
Loose tube cables: These cables are composed of several fibers together inside a small plastic tube, which are in turn wound around a central strength member and jacketed, providing a small, high fiber count cable. This type of cable is ideal for outside plant trunking applications, as it can be made with the loose tubes filled with gel or water absorbent powder to prevent harm to the fibers from water. It can be used in conduits, strung overhead or buried directly into the ground. Since the fibers have only a thin buffer coating, they must be carefully handled and protected to prevent damage.
Breakout cables: They are made of several simplex cables bundled together. This is a strong, rugged design, but is larger and more expensive than the distribution cables. It is suitable for conduit runs, riser and plenum applications. Because each fiber is individually reinforced, this design allows for quick termination to connectors and does not require patch panels or boxes. Breakout cable can be more economic where fiber count isn't too large and distances too long, because is requires so much less labor to terminate.
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