For years, fiber optics has been merely a system for piping light around corners and into the inaccessible places to allow the hidden to be lighted. But now, fiber optics has evolved into a system of significantly greater importance and use. Throughout the world, it is now being used to transmit voice, television and data signals as light waves over flexible hair-thin threads of glass or plastic. Its advantages as compared with conventional coaxial cable or twisted wire pairs are manifold. As a result, millions of dollars are being spent to put these light wave communication systems into operation.
Interest in fiber as a medium began in 1966 when C. Kao and G.A. Hockham at Standard Telecommunications Laboratory predicated that by removing the impurities in the glass, 20 dB/km attenuations would be achievable. At this level, fiber became a practical communication medium. Most of the optical fibers, in use today, are made of either silica glass (SiO2) or plastic. The change in refractive index, between the core and cladding is achieved by the addition of certain dopants to the glass; all-plastic fibers use different plastics for the core and cladding. In order to increase the reflective index, oxides of germanium (GeO2) or phosphorus, (P2¬O¬5) are commonly used. A decrease results from doping with Boron Oxide, (B2O3) or fluorine, (F).
[...] positive terminal of B2 to type collector. When the base emitter bias is about + 0.6 electrons (the majority carriers in the heavily doped n type emitter) cross the junction (as they would in any junction diode) into the base. Their loss is made good by electrons entering the emitter from the external circuit to form the emitter current. At the same time holes from the base to the emitter but, since the type base is lightly doped, this is small compared with the electron flow in the opposite direction, i.e. [...]
[...] The LEDs are made in the form of flat tiny P-N junction enclosed in a semi-spherical dome made up of clear coloured epoxy resin. The dome of a LED acts as a lens and diffuser of light. The diameter of the base is less than a quarter of an inch. The actual diameter varies somewhat with different makes. The common circuit symbols for the LED are shown in fig It is similar to the conventional rectifier diode symbol with two arrows pointing out. [...]
[...] These losses (or attenuations) are measured in decibels per kilometer Advantages of optical fiber The major advantages of optical fiber over other terrestrial communication mediums are: Extremely wide bandwidth. Small-diameter, lighter-weight cables. Lack of cross talk between parallel fibers. Immunity to inductive interference. High-quality transmission. Low installation and operating costs Greater security and safety. Longer life span and environmental stability Electromagnetic pulse (EMP) immunity. Greater reliability and ease of maintenance. No extremely radiated signals. Ease of expansion of system capability. [...]
[...] The working voltage. This is the largest voltage (D.C. or pead a.c.) which can be applied across the capacitor and is often marked on it, e.g. 30V wkg. It is exceeded, the dielectric breaks down and permanent damage may result. The leakage current. No dielectric is a perfect insulator but the loss of charge through it as leakage current' should be small. FIXED CAPACITORS Fixed capacitors can be classified according to the dielectric used; their properties depend on this. The types described below in and (iii) are non-polarized, those in are polarized. [...]
[...] Afterwards, these signals are transferred using an optical fiber at the other end. These signals are converted into electrical signals using a phototransistor. Now these electrical signals are converted into sound signals using a speaker. So the sound signals at the mike are regenerated at the receiver end in the speaker. In the above system, mike, L.E.D., photo-transistor and speaker are all transducers. Optical Fiber works on the principle of total internal reflection of light BLOCK DIAGRAM MIKE: Sound signals made at the mike. [...]
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