A fiber-optic is made of glass or plastic and transmits signals in the form of light. Optical fibers use reflection to propagate the light through a channel. A high dense glass or plastic core is surrounded by a less dense glass or plastic cladding respectively. The difference in density of the two materials must be enough to reflect the beam of moving light back into the core, instead of being refracted into cladding.

This phenomena is called total internal reflection. Optical fiber can be used as a medium for communication. It is particularly beneficial for long-distance communications, since the light propagates inside the fiber with very little attenuation as related to copper cables. The benefits of optical fiber with deference to copper systems are: Wider bandwidth, a single optical fiber can support many voice calls or TV channels as compared to copper wire. Electrical insulator, optical fibers are non-conductive, so optical fibers can be looped on electric poles alongside high voltage power cables.

Resistance to electromagnetic interference, light transmitted through the optical fiber is not affected by nearby electromagnetic radiation, therefore the information transmitted through the optical fiber is protected from electromagnetic interference. Low attenuation loss over long distances, power loss can be as low as 0.2 dB per km in optical fiber, which allows transmission for greater distances without the need for frequent repeaters. Based on light propagation method, optical fibers can be classified into two main types that are multimode and single mode.  Multimode can be implemented in two forms: step-index and graded-index. Multimode is so named because multiple beams from a light source move through the core in different paths. How these beams move within the cable, depends on the structure of the core. The word index here refers to the index of refraction. In multimode step-index fiber, the density of the core remains same from the center to the edges.

The term step index refers to the suddenness of this change, which contributes to the distortion of the signal as it passes through the fiber. Another type of multimode fiber, called multimode graded-index fiber. As discussed above, the index of refraction is related to density. A graded-index fiber is one with changing densities. Density is much higher at the center of the core and decreases slowly to its lowest at the edge. Single-Mode uses step-index fiber and an extremely focused source of light that bound the beams to a small range of angles. The single mode fiber is manufactured with a far smaller diameter than that of multimode fiber, and with significantly lower density. Multimode fibers are identified by the OM (optical mode) label. Before we discuss the difference between OM3 and OM4 fiber types, these are few thing to know which are common in both types. The connectors used for both types are same, the transceivers used in both fibers are the same, since both operate on 850nm VCSELS (Vertical-Cavity Surface-Emitting Lasers), and the fiber size is same 50/125. Also be noted that OM3 is fully compatible with OM4. 

Nowadays OM3 and OM4 have been everywhere for years, even if OM4 cable has been in production for about 10 years. However, it was standardized in 2009 and is called OM4 cable since then. Previously it was identified by several names such as OM3+ or Enhanced OM3. There is just construction difference between both fiber cables. The difference in internal construction of OM4 cable within 50/125 size allows the OM4 cable to operate on higher bandwidth. When measured at 850nm, OM3 operates at a bandwidth of 2500 megahertz, while OM4 has a bandwidth of 4700 megahertz. An OM3 can support 10 gigabit at 300 meters, whereas an OM4 can support 10 gigabit for a distance of 550 meters. As far as 40 gigabit and 100 gigabit are concerned, OM3 will achieve 100 meters, on the other hand OM4 is capable to reach up to 150 meters.   

As stated earlier, the only variance among an OM3 and an OM4 is the actual fiber cable. The cost for OM4 is higher due to the manufacturing. The wider bandwidth available in OM4 cabling allows longer link lengths for 10 gigabit, 40 gigabit and 100 gigabit systems. Costs vary depending on the construction type of the cable. However, OM4 cable is much expensive as of OM3 cable. There are several factors at here which are used to figure out whether OM3 or OM4 is needed. But the origin is the cost versus what distances needed. In the perfect example, if someone had abundant resources, they would just use single mode fiber. Since single mode has all the bandwidth one need, so one can go quite of distance but it is very expensive. As most of all data centers have their premises under 100 meters so it really just comes down to a costing issue right there.

Author: Fiber-MART.COM

eShop of Fiber Optic Network, Fiber Cables & Tools

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