Optical Fibre (Types and Application)

Introduction:
Copper wires and co-axial cables carries a electronic information inthe form of radio waves and
microwaves. However information carring capacity in these is limited due to their limited band width and not sufficient as perthe modern communication technique. If we use light waves insted of microwave or radiowave the number of signal can be increased. The light wave transmission is possible in optical fibre.
Optical fibre are made up of plastic conduicts or glass as thin like a human hair.  which is designed to guide wave along the length of the fibre with the help of succesive total internal reflections from side walls of optical fibre. The light moves in zig-zag path. Major fraction comes out from one end of the optical fibre a small fraction of light escape through side walls.

Construction:
Optical Fibre consists at three region.
(i) The innermost region through which light pass called core.
(ii) The core area is surrounded by a central area called cladding.
(iii) Sheath the outermost region. Sheath products the core and cladding from abrasion contamination and give mechanical strength to fibre.

Types of optical fibre:
(i) Single Mode Fibre (SMF)
(ii) Multi Mode Fibre (MMF)
A Single Mode Fibre can support a one mode of propogation and small core region while Multi Mode Fibre has large core and support more than one mode of propogation. Single Mode Fibre and Multi Mode Fibre are furthur classified depending upon Index Profile. Index Profile of a MMF can be either Step Index (SI) or Graded Index (GRIN) type. SMF  is usually Step Index.
(a) Single Mode Step Index Fibre:
It consists of a very thin core of uniform refractive index surrounded by a cladding of refractive index lower than that of core. It is known as Step Index Fibre because refractive index abruptly changes at the core-cladding boundary. The Fibre is surrounded by some opaque protective sheath.
(b) Multi Mode Step Index Fibre:
It is same as Single Mode Step Index Fibre with exception of a large core diameter.
(c) Grain Index Fibre (GRIN) :
GRIN is a Multi Mode Fibre which has got concentric layers of refractive indices. Which means that the refractive index varies with distance from the fibre axis. It has a large core diameter.

Application of Optical Fibre:
(i)  A coherent optical fibre bundle can greatly enhance the size of the image on the TV screen. In case we have to use the conventional method of getting larger images then the projection systems becomes quick bulky and unmanageable.
(ii) Fibre optics are finding large number of application in medical fields. Many parts of the human body which are otherwise inaccesible can be studied by illumination with fibre optics. A bundle of MMF is used to illumination a part of human organ and the other part to collect the reflected light. This fibrescopic technique is employed for endoscopic applications. Fibre optics can be employed to attach a detached retina or rectify other eye defects using lasers.
(iii) In heart problems also lasers angioplasty is replaced the ballon angioplasty and bypass surgery.
(iv) Main application of Optical fibre is in communication. (transmittting light signal through optical fibre)


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