13-05-2017, 02:49 PM
Optical fibers can be used to transmit light and, therefore, information over long distances. Fiber-based systems have largely replaced radio transmitter systems for the transmission of long-distance optical data. They are widely used for telephony, but also for Internet traffic, high-speed local area networks (LAN), cable television (CATV), and increasingly for shorter distances within buildings. In most cases, silica fibers are used, except for very short distances, where plastic optical fibers may be advantageous.
Compared to electrical cable-based systems, the focus of fiber-optic communications (light-wave communications) has advantages, the most important of which are:
• The capacity of fibers for data transmission is enormous: a single silica fiber can transport hundreds of thousands of telephone channels, using only a small part of theoretical capacity. Over the past 30 years, progress in fiber link transmission capabilities has been significantly faster than p. Progress in speed or storage capacity of computers.
• Light propagation losses in fibers are surprisingly small: ≈ 0.2 dB / km for modern single-mode silica fibers, so many tens of kilometers can be laid without amplifying the signals.
• A large number of channels can be reamplified into a single fiber amplifier, if necessary for very large transmission distances.
• Due to the high attainable transmission speed, the cost per transported bit can be extremely low.
• In comparison to electrical cables, the fiber optic cables are very light.
• Fiber optic cables are immune to problems with electrical cables, such as ground circuits or electromagnetic interference (EMI). Such issues are important, for example, for data links in industrial settings.
Mainly because of their very high data transmission capacity, fiber optic transmission systems can achieve much lower cost than systems based on copper coaxial cables, if high data rates are needed. For low data transmission speeds, where their total transmission capacity can not be used, fiber optic systems may have a lower economic advantage, or even be more expensive (not due to fibers, but to additional transceivers) . The main reason, however, for the still widespread use of copper cables for the "last mile" (connecting to homes and offices) is simply that copper cables are already established, while new digging operations would be Needed to establish more fiber optic cables.
