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Types Of Optical Fiber-Single Mode, Multi-Mode, and Multi-Mode Graded Index Fiber

August 3, 2022
written by Adeel Abbas

There are many types of optical fiber. Due to its small size, fiber optics has an extremely wide bandwidth. They are much thinner and light cables. An optical fiber with its protective cases may be typically a 6.0mm in diameter bundle of copper wires now used to carry the same amount of signals.

Optical fiber is used to signal transmission and conversion to sound. There is also power loss in optical fiber. In optical fiber communication signals are transmitted in form of light. Total internal reflection is the basic fiber optics principle for communication.

Types of Optical Fiber

There are three types of optical Fiber which are grouped by the way they propagate light.

  • Single Mode or Mono Mode Step Index Fiber
  • Multi-mode step index Fiber
  • Multi-mode graded index fiber

Mode: The method by which light is propagated within the fiber is called mode.

Single Mode or Mono Mode Step Index Fiber:

Single mode or mono mode step index fiber has a very thin core of about 5 µm diameter and has a relatively larger cladding (of glass or plastic).

image showing the Single Mode or Mono Mode Step Index Fiber:

Source of transmission:

Since it has a very thin core, a strong monochromatic light source such as a laser source has to be used to send light signals through it.

Uses of Single Mode or Mono Mode Step Index Fiber:

 It can carry more than 14 TV channels or 14000 phone calls.

Multi-mode step-index fiber:

This type of fiber has a core of relatively large diameter such as 50 µm.

image showing the Multi-mode step-index fiber

 Source of transmission:

It is used for carrying white light but due to dispersion effects, it is not mostly used.

Example of Multimode step index fiber:   

The core has a constant refractive index n1such as 1.52. The refractive index then changes to a lower value n2 such as 1.48, which remains constant throughout the cladding.

This is called a step-index multimode fiber because the refractive index steps down from 1.52 to 1.48 at the boundary with the cladding.

Uses of Multi-mode step-index fiber:

Multi-mode step-index fiber is useful for a short distance only.

Multi-Mode Graded Index Fiber:

Multi-mode graded-index fiber has a core that ranges in diameter from 50 to 1000 µm. It has a core of relatively high refractive index and the refractive index decreases gradually from the middle to the outer surface of the fiber.

image showing the Multi-Mode Graded Index Fiber

There is no noticeable boundary between core and cladding. This type of fiber is called a multi-mode graded-index fiber.

Source of transmission:

In this type of fiber white light is used.

Uses of multi-mode index fiber:

 It is useful for long-distance applications. The mode of transmission of light through this type of fiber is also the same, i.e continuous refraction from the surfaces of smoothly decreasing refractive index and the total internal reflection from the boundary of the outer surface.