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Optical fibers are wave guides that can transmit the light signals from one end to another end.

~ The propagation of light in an optical fibre from one into another is based on the principle of total internal reflection (TIR).

• When a light enters one end of the optical fibre it undergoes total internal reflection from side walls and travel down of the fibre along zigzag path.

Construction of optical fiber :

• Optical Fibre is cylindrical in shape and has two parts of cylindrical material.

• The innermost cylindrical part is lights guiding part and is made up of glass or plastic and is called as 'CORE'.

• The outermost part which is a concentric cylinder surrounding the core, is called as 'CLADDING'.
  It is also made up of similar material of glass and plastic but have lesser refractive index.

• The cladding is enclosed in a polyurethane jacket, which safeguard the fiber against chemical reactions with the surroundings.
  It is called as 'Sheath' or 'Protective Buffer Coating'.