Optical fibre is a guiding medium or material which guides the information carrying light waves. To guide the light waves, optical fibre should be transparent. To minimize the transmission losses through the optical fibre, it is made thin.
Thus, Optical fibre is a thin transparent guiding medium or material which guides the information carrying light waves.

                            Total Internal Reflection

The transmission of light in an optical fibre is based on the phenomenon of total internal reflection. Optical fibre consists of inner most layer known as core, a denser medium and next layer is known as cladding a rarer medium.
The optical fibre mainly consists the following six parts as shown in figure

                                           FIGURE: OPTICAL CABLE
  1. Core
  2. Cladding
  3. Silicon coating
  4. Buffer jacket
  5. Strength member
  6. Outer jacket
  7. Core: A typical glass fibre consists of a central core material. Generally, core diameter is ranges from 5 to 600μm. The core is surrounded by cladding. The core medium refractive is always greater than the cladding refractive index.
  8. Cladding: Cladding refractive index is lesser than the cores refractive index. The overall diameter of cladding is 125μm to 750μm.
  9. Silicon Coating: Silicon Coating is provided between buffer jacket and cladding. It improves the quality of transmission of light.
  10. Buffer Jacket: Silicon coating is surrounded by buffer jacket. Buffer jacket is made of plastic and protects the fibre cable from moisture.
  11. Strength Member: Silicon coating is surrounded by strength member. It provides strength to the fibre cable.
  12. Outer Jacket: Finally, the fibre cable is covered by polyurethane outer jacket. Because of this arrangement fibre cable will not be damaged during pulling, bending, stretching and rolling through the fibre cable is made up of glasses.

• Based on the refractive index of core medium, optical fibres are classified into two categories.
i. Step index fibre
ii. Graded index fibre

• Based on the number of modes of transmission, optical fibres are classified into two categories;
i. Single mode fibre
ii. Multi-mode fibre

• Based on the material used, optical fibres are broadly classified into four categories;
i. All glass fibre
ii. All plastic fibre
iii. Glass core with plastic cladding fibre
iv. Polymer clad silica fibre

  1. It has enormous bandwidth
  2. It has low transmission loss
  3. It has electric isolation
  4. It has signal security
  5. It has small size and less weight
  6. It has low cost
  7. It has immunity cross talk


  1. They are used extensively in communication system.
  2. They are used for exchange of information in cable televisions, space vehicles, submarines, etc.
  3. They are used in industry in security alarm systems, process control and industrial auto machine
  4. They are used in pressure sensors in biomedical and engine control.
  5. They are used in medicine, in the fabrication in endoscopy for the visualization of internal parts of the human body.
  6. They are used in displacement sensor, fluid level detector, liquid level sensor, temperature and pressure sensor.
  7. They are also used in gastroscopy, orthoscopy, couldoscopy, peritonescopy, fiberscopy.