Telecommunication applications are widespread, ranging from global networks to local telephone exchanges to subscribers homes to desktop computers. These involve the transmission of voice, data, or video over distances of less than a meter to hundreds of kilometers. Fiber optics is employed for this purpose. Benefits of Fiber Optics :
Fiber optics has several advantages over traditional metal communications lines:
- Fiber optic cables are much thinner and lighter than metal wires.
- Fiber optic cables have a much greater bandwidth than metal cables. This means that they can carry more data.
- The low attenuation and superior signal integrity found in optical systems allow much longer intervals of signal transmission than metallic-based systems.
- Fiber optic cables are less susceptible than metal cables to interference.
- The voice-grade copper systems longer than a couple of kilometers (1.2 miles) require in-line signal repeaters for satisfactory performance, but optical systems go over 100 kilometers (km), or about 62 miles, with no active or passive processing.
- Data can be transmitted digitally (the natural form for computer data) rather than analogically.
- Unlike metallic-based systems, the dielectric nature of optical fiber makes it impossible to remotely detect the signal being transmitted within the cable. The only way to do so is by actually accessing the optical fiber itself.
The main disadvantage of fiber optics considered was that the cables are expensive to install but as electronics prices fall,Fiber optics is affordable today, and optical cable pricing remains low. As bandwidth demands increase rapidly with technological advances, fiber will continue to play a vital role in the long-term success of telecommunications.
Operational Principle of Fiber optics:Total Internal Reflection:
When a light ray traveling in one material hits a different material and reflects back into the original material without any loss of light, total internal reflection occurs.
Since the core and cladding are constructed from different compositions of glass, theoretically, light entering the core is confined to the boundaries of the core because it reflects back whenever it hits the cladding. For total internal reflection to occur, the index of refraction of the core must be higher than that of the cladding. The index of refraction (IOR) is a way of measuring the speed of light in a material. Light travels fastest in a vacuum, such as outer space. The actual speed of light in a vacuum is 300,000 kilometers per second, or 186,000 miles per second. Index of Refraction is calculated by dividing the speed of light in a vacuum by the speed of light in some other medium.The Index of Refraction of a vacuum by definition has a value of 1.
The Information Transmission Sequence :
As depicted above, information (voice, data, or video) is encoded into electrical signals. At the light source, these electrical signals are converted into light signals.
It is important to note that fiber has the capability to carry either analog or digital signals. Many people believe that fiber can transmit only digital signals due to the on/off binary characteristic of the light source. The intensity of the light and the frequency at which the intensity changes can be used for AM and FM analog transmission.
Once the signals are converted to light, they travel down the fiber until they reach a detector, which changes the light signals back into electrical signals. This area from light source to detector constitutes the passive transmission subsystem; i.e. that part of the system manufactured and sold by Corning Cable Systems.
Finally, the electrical signals are decoded into information in the form of voice, data, or video.
Transmission Modes:
Once light enters an optical fiber, it travels in a stable state called a mode. There can be from one to hundreds of modes depending on the type of fiber. Each mode carries a portion of the light from the input signal.
Every telecommunications fiber falls into one of two categories: single-mode or multimode.
It is impossible to distinguish between single-mode and multimode fiber with the naked eye. There is no difference in outward appearance, only in core size. Both fiber types act as a transmission medium for light, but they operate in different ways, have different characteristics, and serve different applications.
Fiber optic Applications :
Optical fiber is used extensively for transmission of data signals. Private networks are owned by firms such as IBM, Rockwell, Honeywell, banks, universities, Wall Street firms, and more. These firms have a need for secure, reliable systems to transfer computer and monetary information between buildings to the desktop terminal or computer, and around the world. The security inherent in optical fiber systems is a major benefit.
Cable television or community antenna television (CATV) companies also find fiber useful for video services. The high information-carrying capacity, or bandwidth, of fiber makes it the perfect choice for transmitting signals to subscribers.
Finally, one of the fastest growing markets for fiber optics is intelligent transportation systems, smart highways with intelligent traffic lights, automated toll booths, and changeable message signs to give motorists information about delays and emergencies.
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[Diagrams courtesy: Corning Cable Systems]
1 comment:
Great blog. Keep up the good work. Cheers:-)
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