Optical fibres

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Optical fibres:

Optical fibres Submitted by K.Vishnu prasanna


introduction An optical fiber or optical fibre is a flexible, transparent fiber made by  drawing  glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fiber is a type of cabling technology that uses light to carry voice and data communications (telecommunications) over distances both great and small.  This presentation will provide a definition of optical fiber, explore the different types and explain how the different types are used.

Optical fiber:

Optical fiber core inner part where wave propagates cladding outer part used to keep wave in core buffer  protective coating  jacket outer protective shield

Types of optical fibers:

Types of optical fibers Single mode  only one signal can be transmitted only one signal can be transmitted use of single frequency use of single frequency Multi mode Multi mode Several signals can be transmitted Several frequencies used to modulate the signal


Construction A hair-thin Fiber consist of two concentric layers of high-purity silica glass the core and the cladding, which are enclosed by a protective sheath as shown in Fig. 2. Core and cladding have different refractive indices, with the core having a refractive index, n1, which is slightly higher than that of the cladding, n2. It is this difference in refractive indices that enables the Fiber to guide the light. Because of this guiding property, the Fiber is also referred to as an “optical waveguide.” Principle of operation

Principle of operation:

Principle of operation The optical Fiber has two concentric layers called the core and the cladding. The inner core is the light carrying part. The surrounding cladding provides the difference refractive index that allows total internal reflection of light through the core. The index of the cladding is less than 1%, lower than that of the core. Light injected into the Fiber and striking core to cladding interface at greater than the critical angle, reflects back into core, since the angle of incidence and reflection are equal, the reflected light will again be reflected. The light will continue zigzagging down the length of the Fiber. Light striking the interface at less than the critical angle passes into the cladding, where it is lost over distance.

Uses of optical fiber:

Uses of optical fiber Communication Optical fiber can be used as a medium for telecommunication and computer networking because it is flexible and can be bundled as cables. 1.Broad bandwidth A single optical fiber can carry over 3,000,000 full-duplex voice calls or 90,000 TV channels. 2.Electrical insulator Optical fibers do not conduct electricity, preventing problems with ground loops and conduction of lightning.

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Sensor s Fibers have many uses in remote sensing. In some applications, the sensor is itself an optical fiber. Depending on the application, fiber may be used because of its small size, or the fact that no electrical power is needed at the remote location, or because many sensors can be multiplexed along the length of a fiber by using different wavelengths of light for each sensor, or by sensing the time delay as light passes along the fiber through each sensor.

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Power transmission Optical fiber can be used to transmit power using a photovoltaic cell to convert the light into electricity. While this method of power transmission is not as efficient as conventional ones, it is especially useful in situations where it is desirable not to have a metallic conductor as in the case of use near MRI machines, which produce strong magnetic fields. Other uses Medical sciences, imaging optics,microscopes etc..,

Advantages of optical Fibres:

Advantages of optical Fibres Can carry much more information Much higher data rates Much higher data rates Much longer distances than co-axial Much longer distances than co-axial cables cables Immune to electromagnetic noise Immune to electromagnetic noise Light in weight Light in weight Unaffected by atmospheric agents Unaffected by atmospheric agents

Disadvantages of optical fiber:

Disadvantages of optical fiber High investment cost Need for more expensive optical transmitters and receivers More difficult and expensive to splice than wires Price Fragility Affected by chemicals Opaqueness  Requires special skills

Characteristics :

Characteristics 1)Wider bandwidth : The optical carrier frequency is in the range 10^ 13 Hz to 10^ 15Hz. 2)Low transmission loss: The fibers having a transmission loss of 0.002dB/km. 3)Dielectric waveguide: Optical fibers are made from silica which is an electrical insulator. Therefore they do not pickup any electromagnetic wave or any high current lightning. 4)Signal security: The transmitted signal through the fibers does not radiate. Further the signal cannot be tapped from a Fiber in an easy manner. 5)Small size and weight: Fiber optic cables are developed with small radii, and they are flexible, compact and lightweight. The fiber cables can be bent or twisted without damage.

Conclusions :

Conclusions We are currently in the middle of a rapid increase in the demand for data bandwidth across the Earth. For most applications optical fibers are the primary solution to this problem. They have potentially a very high bandwidth, with many of the bandwidth limitations now being at the transceivers rather than being an intrinsic property of the fiber allowing easy upgrading of systems without relaying cable.  

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