Optical fibers - Principle and advantages

Optical fiber is a very thin strand of glass or plastic capable of transmitting light from one point to another. Optical fiber can also be called an optical waveguide, since it is a device that guides light. Optical fibers consist of a light-carrying core and a cladding surrounding the core. There are generally three types of construction: glass core/cladding, glass core with plastic cladding, or all-plastic fiber.

Voice, video, and data signals can be encoded into light pulses and sent across an optical fiber. Each time someone makes a phone call, a stream of pulses passes through an optical fiber, carrying the information to the person on the other end of the phone line.

A fiber optic communication system generally consists of five elements: the encoder or modulator, the transmitter, the fiber, the detector, and the demodulator. Electrical input is first coded into a signal by the modulator, using signal processing techniques. The transmitter converts this electrical signal to an optical signal and launches it into the fiber. The signal experiences attenuation as it travels through the fiber, but it is amplified periodically by repeaters. At the destination, the detector receives the signal, converting it back to an electrical signal. It is sent to the demodulator, which decodes it to obtain the original signal. Finally, the output is sent to the computer or to the handset of your telephone, where electrical signals cause the speaker to vibrate and sending audio waves to your ear.

The Principles behind Fiber Optics

Fiber optics work on the principle of total internal reflection. Light reaching the boundary between two materials is reflected such that it never leaves the first material. In the case of fiber optics, light is reflected from the optical fiber core-cladding interface in such a way that it propagates down the core of the fiber. This can be explained by a brief discussion of Snell's law of refraction and law of reflection, and a physical quantity known as index of bottom material. According to Snell's law, the light will be bent from its original path to a larger angle in the second material. As the incoming, or incident angle increases, so does the refracted angle. For the properly chosen materials, the incident angle can be increased to the point that the ray is refracted at 90 degrees and never escapes the first medium. The equation can be solved to give the incoming, or incident, angle which will result in a refracted angle of 90 degrees.This is known as the critical angle.

Advantages

Communication via optical fiber has a number of advantages over copper wire. Wires carrying electrical current are prone to crosstalk, or signal mixing between adjacent wires. In addition, copper wiring can generate sparks, or can overload and grow hot, causing a fire hazard. Because of the electromagnetic properties of current carrying wires, signals being carried by the wire can be decoded undetectably, compromising communications security. Optical fiber carries light, no electricity, and so is not subject to any of these problems.

The biggest single advantage that optical fiber offers over copper wire is that of capacity, or bandwidth. With the rising popularity of the Internet, the demand for bandwidth has grown exponentially. Using a technique called wavelength division multiplexing (WDM), optical networks can carry thousands of times as much data as copper-based networks.
Hence,compared to conventional metal wire (copper wire), optical fibers provide following advantages:

Digital signals: Optical fibers are ideally suited for carrying digital information, which is especially useful in computer networks.

Higher carrying capacity: Because optical fibers are thinner than copper wires, more fibers can be bundled into a given-diameter cable than copper wires. This allows more phone lines to go over the same cable or more channels to come through the cable into your business or home.

Less signal degradation: The loss of signal in optical fiber is less than in copper wire.

Less expensive: Several miles of optical cable can be made cheaper than equivalent lengths of copper wire. This saves your provider and you money. Thinner: Optical fibers can be drawn to smaller diameters than copper wire. Light signals: Unlike electrical signals in copper wires, light signals from one fiber do not interfere with those of other fibers in the same cable. This means clearer phone conversations or TV reception.

Low power: Because signals in optical fibers degrade less, lower-power transmitters can be used instead of the high-voltage electrical transmitters needed for copper wires. Again, this saves your provider and you money.

Non-flammable: Because no electricity is passed through optical fibers, there is no fire hazard.

Lightweight: An optical cable weighs less than a comparable copper wire cable. Fiber-optic cables take up less space in the ground.

Flexible: Because fiber optics are so flexible and can transmit and receive light, they are used in many flexible digital cameras for medical imaging in bronchoscopes, endoscopes, laparoscopes; for mechanical imaging used in inspecting mechanical welds in pipes and engines (in airplanes, rockets, space shuttles, cars); and in Plumbing, to inspect sewer lines.

 

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