Fiber Optics

Fiber OpticsAs per Jntuh : 

11/20/2011 https://sites.google.com/site/ganeshbilla/ 1 Fiber OpticsAs per Jntuh

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Evolution of Fiber : 

11/20/2011 https://sites.google.com/site/ganeshbilla/ 3 Evolution of Fiber 1870 – Tyndall demonstrated that light could be guided a water-jet based on the phenomenon of total internal reflection. 1930 – Patents on tubing 1954 – Patent for two-layer glass wave-guide (The development of cladded dielectric wave guides) 1960 – Laser first used as light source 1965 – High loss of light discovered 1970s – Refining of manufacturing process 1980s – OF technology becomes backbone of long distance telephone networks in NA.

Definition : 

11/20/2011 https://sites.google.com/site/ganeshbilla/ 4 Definition Optical fiber is a very thin and flexible medium having a cylindrical shape consisting of three sections: The core, The cladding and The outer jacket

Fiber Composition : 

11/20/2011 5 Fiber Composition An optical fiber consists of 3 distinct parts: 1) the core 2) the cladding 3) the sheath (jacket or coating). The core and cladding act as an optical wave-guide. Core - it is a transmission area of fiber. - typical core diameters range from 50 to 500 m Cladding - it surrounds the core and has a different index of refraction than the core. - it defines the optical boundary of the core and makes sure that total internal reflection occurs at the core outer skin.

Principle of Optical fiber : 

11/20/2011 https://sites.google.com/site/ganeshbilla/ 6 Principle of Optical fiber The light launched inside the core through its one end propagates to the other end due to total internal reflection at the core and cladding interface. This is the principle of optical fiber.

Total Internal Reflection : 

11/20/2011 7 Total Internal Reflection Fiber for light beam propagation

Refraction of Light : 

11/20/2011 8 Refraction of Light Light travels at approximately 3x108 m/s in free space and slower in a material denser than free space. This reduction in speed as it passes from free space into a denser material results in refraction of the light. Fig. 2 shows the light is bent at the interface. The degree to which the ray is bent depends on the index of refraction n of the denser material. n is defined as the ratio between speed of light in free space and speed of light in given material.

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11/20/2011 10 Index of refraction how a light ray passing from material 1 to material 2 is refracted in material 2 when A1 is less than the critical angle.(<c) the condition that exists when A1 is at the critical angle and angle A2 is at 90. The light is directed along the boundary between the 2 materials. (=c) that any light ray incident at an angle greater than A1 of will be reflected back into material 1 with A2 equal to A1.

Total Internal Reflection of Light : 

11/20/2011 11 Total Internal Reflection of Light Total internal reflection forms the basis for light propagation in optical fibers.

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11/20/2011 13 The cone thus form is called acceptance cone

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Numerical Aperture : 

11/20/2011 15 Numerical Aperture Telecommunications optical fiber n1~n2, The acceptance angle for a fiber defines its numerical aperture (NA) The NA is related to the critical angle of the waveguide and is defined as:

Types of Optical Fibers : 

11/20/2011 16 Types of Optical Fibers Optical fibers can be classified based on either the modes they support or the refractive index profile of the fiber. Mode of Propagation Mode simply means path from which light is propagated. If there is only one path for light to take down the cable, it is called single mode. If there is more than one path, it is called multi-mode.

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11/20/2011 https://sites.google.com/site/ganeshbilla/ 17 Index Profile It is a graphical representation of the value of the refractive index across the fiber. The refractive index is plotted on the horizontal axis and the radial distance from the core axis is plotted on the vertical axis. There are 2 basic types of index profiles: step and graded

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11/20/2011 18 A step-index fiber has a central core with a uniform refractive index. The core is surrounded by an outside cladding with a uniform refractive index less than that of the central core. In a graded-index fiber there is no cladding and the refractive index of the core is non-uniform; it is highest at the center and decreases gradually with distance toward the outer edge.

Single-Mode Step-Index Fiber : 

11/20/2011 19 Single-Mode Step-Index Fiber It has a central core that is sufficiently small so that there is essentially only one path that light may take as it propagates down the cable. The refractive index of the cladding is slightly less than that of the central core and is uniform throughout the cladding. Consequently, all light rays follow approximately the same path down the cable and take approximately the same amount of time to travel the length of the cable.

Multi-mode Step-Index Fiber : 

11/20/2011 20 Multi-mode Step-Index Fiber The light rays that strike the core/cladding interface at an angle greater than the critical angle are propagated down the core in a zigzag fashion, continuously reflecting off the interface boundary. There are many paths that a light ray may follow as it propagates down the fiber. As a result, all light rays do not follow the same path and hence do not take the same amount of time to travel the length of the fiber.

Multimode Graded-Index Fiber : 

11/20/2011 21 Multimode Graded-Index Fiber The index of refraction gradually changes across the core Modes that travel further also move faster This reduces modal dispersion so the bandwidth is greatly increased

Step-index and Graded-index : 

11/20/2011 22 Step-index and Graded-index Step index multimode was developed first, but rare today because it has a low bandwidth (50 MHz-km) It has been replaced by graded-index multimode with a bandwidth up to 2 GHz-km

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Attenuation : 

11/20/2011 24 Attenuation

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Advantages of Optical Fibre : 

11/20/2011 26 Enormous bandwidth Electrical isolation Immunity to interference and cross talk Signal security Small size and weight Low transmission loss Ruggedness and flexbility Low cost Advantages of Optical Fibre https://sites.google.com/site/ganeshbilla/

Application of Optical Fibers : 

11/20/2011 27 Application of Optical Fibers Telecommunications Local Area Networks Cable TV CCTV Optical Fiber Sensors Medicine ( Medical Endoscopy)

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11/20/2011 28 Thanking You………. Ref: Jntuh Syllabus 2010-2011 for B.Tech I year Author: Ganesh Billa Asst Prof. of Physics College: Vivekananda Groups of Institutions, Batasingaram, Hayathnagar, RR district. 9491318652 https://sites.google.com/site/ganeshbilla/