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OPTICAL FIBER COMMUNICATION. Introduction . A communication system transmits information (voice, picture, data etc) from one place to another. Information is often modulated by carrier waves whose frequency can vary from a few megahertz to several hundred Terahertzes.

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Introduction
Introduction

  • A communication system transmits information (voice, picture, data etc) from one place to another. Information is often modulated by carrier waves whose frequency can vary from a few megahertz to several hundred Terahertzes.

  • Optical communication systems use high carrier frequencies (∼100 THz) in the visible or near-infrared region of the electromagnetic spectrum.

  • Optical signal may propagate from the Fiber optic cable or in free space.


Basic fiber properties
Basic Fiber Properties

  • Cylindrical

  • Waveguide

  • Low loss

  • Usually fused silica

  • Core has higher index than cladding

  • Operates on total internal reflection



Advantages of ofc
Advantages of OFC

  • Small size and weight

  • Greatly increased bandwidth and capacity

  • Environmental Protection

  • Resistant to temperature variations , radiation and corrosion

  • Improved ruggedness and flexibility

  • Low per-channel cost

  • Lower installation cost

  • Overall System Economy

  • Immunity to interference crosstalk

  • Electrically isolation

  • Secure; Cannot be trapped without affecting signal


Refraction and reflection 1
Refraction and reflection [1]

  • The relationship at the interface is known as Snell’s law and is given by



Acceptance Angle

If a ray is not within the acceptance cone defined by 2θ0 ,, it will be lost

Pravin R. Prajapati , AP , EC dept


Optical fiber
Optical fiber

  • An optical fiber is a dielectric waveguide that operates at optical frequencies.

  • According to the type of the material used, optical fibers are classified into plasticor glass fibers.

  • As per the operating classes, they are classified as singlemode and multimode fibers.

  • Depending upon the refractive index variation, they are classified as step-index or graded index fibers.




Optical sources and detectors
Optical sources and Detectors

  • The transmission of data through optical fiber takes place in the form of light.

  • The signal to be transmitted has to be converted in to an optical signal before transmission. Optical sources are used for this purpose.

  • The two most prominently used optical sources include Light Emitting Diodes(LEDs) and Lasers which are available right from visible range from far infrared range.


Optical sources
Optical Sources

  • LEDs

  • LEDs produce nonlinear incoherent light.

  • LEDs can provide light output in the visible spectrum as well as in the 850 nm, 1350 nm and the 1500 nm windows.


Lasers
Lasers

  • The term Laser stands for Light Amplification by Stimulated Emission of Radiation.

  • Here the word Light stands for the Electromagnetic Radiation which covers the range from ultraviolet region to the infrared region.

  • Laser Diode produces linear coherent light. That means all the wavelengths contained in Laser light are in the same phase. This is the main advantage of Laser light over ordinary light sources.

  • The Laser light is monochromatic in nature(one colour).


Optical detector photodetection
Optical Detector(Photodetection)

  • Photo detection is the process where the optical power is converted in the electric signal.

  • It sense the luminance power fall on it and convert the optical power in to varying electric signal.

  • For this purpose detector must have high sensitivity, wide Bandwidth and sharp response.

  • Photo detector design criteria are size, sensitivity, Bandwidth, and temperature variation tolerance.

  • Semiconductor based photo detectors are

    (a) Photo Diode

    (b) PIN Diode

    (c) Avalanche Photo Diode


Requirement of photodetector
Requirement of photodetector

  • It should have

  • high sensitivity,

  • fast response,

  • low noise

  • low cost,

  • high reliability.

  • Its size should be compatible with the fiber-core size


Wavelength division multiplexing
Wavelength Division Multiplexing

  • Multiplexing is a process where multiple combined into one signal over a shared medium.

  • In WDM, Multiple channels of information carried over the same fiber, each using an individual wavelength.

  • Dense WDM is WDM utilizing closely spaced channels


References
References

  • Optical Fiber Communications by Gerd Keiser, 4th Edition (Mc Graw Hill).

  • Optical Fiber Communication by John M. Senior (PHI/Pearson)


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