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Fiber Optics and Types

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An Optical Fiber is a cylindrical fiber of glass which is hair thin size or any transparent dielectric medium. The fiber which is used for optical communication is waveguides made of transparent dielectrics.

Main element of Fiber Optics

  • Core: It is the central tube of very thin size made of optically transparent dielectric medium and carries the light transmitter to receiver and the core diameter may vary from about 5um to 100 um.
  • Cladding: It is outer optical material surrounding the core having reflecting index lower than core and cladding helps to keep the light within the core throughout the phenomena of total internal reflection.
  • Buffer Coating: It is a plastic coating that protects the fiber made of silicon rubber. The typical diameter of the fiber after the coating is 250-300 um.

Types of Fiber optics

On the basis of the Number of Modes:

  • Single-mode fiber: In single-mode fiber, only one type of ray of light can propagate through the fiber. This type of fiber has a small core diameter (5um) and high cladding diameter (70um) and the difference between the refractive index of core and cladding is very small. There is no dispersion i.e. no degradation of the signal during traveling through the fiber. The light is passed through it through a laser diode.


  • Multi-mode fiber: Multimode fiber allows a large number of modes for the light ray traveling through it. The core diameter is generally (40um) and that of cladding is (70um). The relative refractive index difference is also greater than single mode fiber. There is signal degradation due to multimode dispersion. It is not suitable for long-distance communication due to large dispersion and attenuation of the signal. There are two categories on the basis of Multi-mode fiber i.e. Step Index Fiber and Graded Index Fiber. Basically these are categories under the types of optical fiber on the basis of Refractive Index

On the basis of Refractive Index:

  • Step-index optical fiber: The refractive index of core is constant. The refractive index of the cladding is also constant. The rays of light propagate through it in the form of meridional rays which cross the fiber axis during every reflection at the core-cladding boundary.


  • Graded index optical fiber: In this type of fiber, the core has a non-uniform refractive index that gradually decreases from the centre towards the core-cladding interface. The cladding has a uniform refractive index. The light rays propagate through it in the form of skew rays or helical rays. it is not cross the fiber axis at any time.


On the basis of Material Used:

  • Plastic Optical Fibres: For transmission of light, polymethylmethacrylate is used as core material
  • Glass Fibres: It is an extremely fine glass fibres, core and cladding of the optical fibre is made of plastic.

Previously Asked Questions

Q1: Consider the following statements: [UGC NET Paper 2 CS 2019]

(a) Fiber optic cable is much lighter than copper cable
(b) Fiber optic cable is not affected by power surges or electromagnetic interference
(c) Optical transmission is inherently bidirectional.

Which of the statements is (are) correct?

1) Only a and b
2) Only a and c
3) Only b and c
4) a, b and c

Ans: Option1 (Only a and b)

Q2: The critical angle θc in an optical fiber is given by ________ Where n1 is refractive index of medium 1 and n2 is the refractive index of medium 2. [ISRO Scientist EC 2011 Paper]
a) sin-1 (n2/n1)
b) sin-1 (n1/n2)
c) sin-1 (n1*n2)
d) sin-1 n2

Ans: Option1 (sin-1 (n2/n1))

Frequently Asked Questions

Q1: What are the 4 common fiber optic connectors?

ST, SC, FC, MT-RJ, & LC connectors are 4 common fiber optic connectors

Q2: What signal is used by fiber optics?

Signals are encoded as pulses of light or laser 

Q3: What are the threats to fiber optics?

Tapping, bending and splicing attacks are threats to fiber optics



Last Updated : 04 Sep, 2023
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