What is an optical network?

An optical network is a collection of interconnected terminals who share data in the form of light. The data travels through special kind of cables called optical fibers. Today’s internet, television and telephones are highly dependent on optical networks. Although we don’t see optical fiber cables connecting to our Wi-Fi routers or computers directly but the global optical network is the backbone of the world.


But light travels in a straight line. Does that mean optical fibers have to be laid straight to transmit data?

Although, light travels in a straight line, optical fibers use a very important property of light called refraction. When light travels from one medium to another it tends to bend towards or away from the normal (line perpendicular to the cross section of the mediums). When light travels from an optically denser medium to a rarer medium it tends to deviate away from the normal. At a certain incidence angle (>critical angle) light starts to get reflected from the boundary region. This is called Total Internal Reflection.

This property of light is used by optical fibers to make light through them along its path without ensuring that the fiber is straight.

Optical fiber cables are made of silica and the ones used in the communication industry are generally thinner than human hair. The glass body called the core, is covered with a cladding which generally has a lower refractive index to allow Total Internal Reflection. There are two types of optical fiber cables used in the communication industry. Single Mode Fibers(SMF), which allow only one propagation path and Multi-Mode Fibers(MMF), that allow multiple propagation paths. Normally, SMFs have a smaller core diameter and are used where long-distance data transmission is involved. MMFs on the other hand have a thicker core and are used at places where high power data is transmitted over a short distance.

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Fundamentals of Optical Networks

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