Optical fiber communication technology uses optical fiber for transmission of communication signals, instead of copper pair or coaxial cables or radio microwave. The optical fiber is made of glass (silica). Why is there a shift from copper to silica? Silica’s low cost notwithstanding, there are a number of advantages offered by this new technology as well. In fact, there is no other technology that can surpass optical fiber in its role in current telecommunication’s massive needs, which include voice telephony, video transmission, data transmission, video conferencing, Internet, etc.
Optical Fiber Cable for communication is made of glass. The fiber is made of a core, a cladding, and a protective jacket. The core and the cladding are both made of silica, but the core is doped with another material, such as germanium, to increasing its “refractive index.”
The principle of propagation of light in this fiber is illustrated. A basic principle that the light follows is that whenever a ray of light enters a medium of higher refractive index, it bends slightly toward the medium of higher refractive index instead of traveling straight as below picture.
The refractive index of the core is increased by doping the silica with another material, such as germanium, whereas the cladding is generally made of pure silica. Thus, the refractive index of core is kept more than that of the cladding. Hence, when the light rays are fed into the core, those rays that are directed toward the cladding bend toward the core while passing through the cladding. Now if the angle of incident light on the core is adjusted so that the rays that tend to enter the cladding are bent to such an angle that they actually fail to enter the cladding and get totally reflected inside the core, no rays will enter the cladding. Any angle less than this angle will produce the same result. This phenomenon is called “total internal reflection” of the light wave and results in the propagation of the whole of the light through the fiber. In the telecommunication applications, this angle is normally in the range of 5.7° to 11.5°.
While we can transmit light through the optical fiber, how does it help the communication of signals such as PDH, SDH, etc. To use this light transmission, we need to convert our electrical signals to the light (optical signal) and send them onto the fiber and at the receiving end convert them back into electrical signals to establish a communication link.
What is Optical Fiber Cable made?
The principle of propagation of light in this fiber is illustrated. A basic principle that the light follows is that whenever a ray of light enters a medium of higher refractive index, it bends slightly toward the medium of higher refractive index instead of traveling straight as below picture.
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| Propagation of light |
The refractive index of the core is increased by doping the silica with another material, such as germanium, whereas the cladding is generally made of pure silica. Thus, the refractive index of core is kept more than that of the cladding. Hence, when the light rays are fed into the core, those rays that are directed toward the cladding bend toward the core while passing through the cladding. Now if the angle of incident light on the core is adjusted so that the rays that tend to enter the cladding are bent to such an angle that they actually fail to enter the cladding and get totally reflected inside the core, no rays will enter the cladding. Any angle less than this angle will produce the same result. This phenomenon is called “total internal reflection” of the light wave and results in the propagation of the whole of the light through the fiber. In the telecommunication applications, this angle is normally in the range of 5.7° to 11.5°.
While we can transmit light through the optical fiber, how does it help the communication of signals such as PDH, SDH, etc. To use this light transmission, we need to convert our electrical signals to the light (optical signal) and send them onto the fiber and at the receiving end convert them back into electrical signals to establish a communication link.
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