OPTICAL FIBRE CABLE :-
A thin flexible and transparent wire prepared for light propagation is called optical fibre.
The optical fibre has been constructed for the following reasons:
- The light wave cannot traverse long distance in air without any losses.
- To make loss less light wave communication, the optical waves can be guided through optical fibre.
-The optical fibre can be used for the many of industrial application and medical
applications as well.
-The optical fibre consists of two media kept one inside the other.
- The centre transparent medium of optical fibre is called “core” and the outer is cladding.
Classification :-
In the optical fibres the materials used, refractive index and mode of propagation of light are used for classification as follows:
Material Based optical fibres-
The material based classification results to the following types:
1. Plastic made fibres.
2. Glass made fibres.
The plastic made fibres are obtained from polymers of transparent to light, flexibility and
interaction less to light etc,.
For example poly methyl metha acrylate (PMMA), polyethylene (PE), polystyrene (PS) are used as core materials.
Glass made fibre is also fabricated from flexible glass as core with suitable drawing
technique in presence of impurities. Therefore, the above types of optical fibres are limited to some application.
Classification of optical fibres based on refractive index
The types of optical fibre can be classified based on the refractive index are
1. Step index fibres.
2. Graded index fibres.
Step index
If the refractive index of core remains the same from the centre of the core to the core-cladding interface; those optical fibres are known as step index fibres .
The distance room centre of core to interface of fibre vs. refractive index is shown
Graded Index:-
*Modes of propagation based optical fibre:-
Based on modes of propagation of light through core, the following are the types of optical
fibre identified.
- Single mode fibres
- Multimode fibres
* Single mode fibres
Considering the light as electromagnetic radiation, the possible modes of propagation are
transverse electric (TE) modes and transverse magnetic (TM) modes.
If the core size is adjusted to allow only one mode of light wave
propagation is single mode fibre, whose profile is shown below:
*Multi mode optical fibre
If the core size has been adjusted to allow more than one mode of propagation of light
wave is multimode fibre. The profile of multimode fibres is as shown below:
Application :-
- as fibres are very flexible ,they are used in flexible digital cameras.
- fibres are used in mechanical imaging i.e. for inspection of mechanical welds in pipes and engines of rockets,space shuttle,airp airps.
- it is used in medical imaging such as endoscopes and laparoscopes.
- it is used under sea communication
- used in military appreciation such as aircraft,shi sh, thank etc
- nuclear testing application use optical fibre phase sensor and transducer.
-it is used in LAN system of office, industrial plants and Collegs etc.
https://youtu.be/aqazAcE19vw
* Why is cladding necessary in an optical fibre cable?
Since for a low loss transmission, we need to guide ligh by total reflection not by reflection from a mirror surface. Indeed although we can guide light using a mirror for the outer layer of the core, but it has a huge loss (even with perfect mirrors used in professional telescopes).
A thin flexible and transparent wire prepared for light propagation is called optical fibre.
The optical fibre has been constructed for the following reasons:
- The light wave cannot traverse long distance in air without any losses.
- To make loss less light wave communication, the optical waves can be guided through optical fibre.
-The optical fibre can be used for the many of industrial application and medical
applications as well.
-The optical fibre consists of two media kept one inside the other.
- The centre transparent medium of optical fibre is called “core” and the outer is cladding.
Classification :-
In the optical fibres the materials used, refractive index and mode of propagation of light are used for classification as follows:
Material Based optical fibres-
The material based classification results to the following types:
1. Plastic made fibres.
2. Glass made fibres.
The plastic made fibres are obtained from polymers of transparent to light, flexibility and
interaction less to light etc,.
For example poly methyl metha acrylate (PMMA), polyethylene (PE), polystyrene (PS) are used as core materials.
Glass made fibre is also fabricated from flexible glass as core with suitable drawing
technique in presence of impurities. Therefore, the above types of optical fibres are limited to some application.
Classification of optical fibres based on refractive index
The types of optical fibre can be classified based on the refractive index are
1. Step index fibres.
2. Graded index fibres.
Step index
If the refractive index of core remains the same from the centre of the core to the core-cladding interface; those optical fibres are known as step index fibres .
The distance room centre of core to interface of fibre vs. refractive index is shown
Graded Index:-
These types are made of varying refractiveindex of core material. Therefore,the refractive index
changes with distance form the centre of fibre to core-cladding interface. The profile of above is as shown in fig.
Based on modes of propagation of light through core, the following are the types of optical
fibre identified.
- Single mode fibres
- Multimode fibres
* Single mode fibres
Considering the light as electromagnetic radiation, the possible modes of propagation are
transverse electric (TE) modes and transverse magnetic (TM) modes.
If the core size is adjusted to allow only one mode of light wave
propagation is single mode fibre, whose profile is shown below:
*Multi mode optical fibre
If the core size has been adjusted to allow more than one mode of propagation of light
wave is multimode fibre. The profile of multimode fibres is as shown below:
Combination of optical fibres
The refractive index of core and mode of propagation of light in optical fibre usedto
form combination types of optical fibre.
-Step index-single mode fibres
-Step index-multi mode fibres
-Graded index-Single mode fibres
-Graded index-Multi mode fibres
- as fibres are very flexible ,they are used in flexible digital cameras.
- fibres are used in mechanical imaging i.e. for inspection of mechanical welds in pipes and engines of rockets,space shuttle,airp airps.
- it is used in medical imaging such as endoscopes and laparoscopes.
- it is used under sea communication
- used in military appreciation such as aircraft,shi sh, thank etc
- nuclear testing application use optical fibre phase sensor and transducer.
-it is used in LAN system of office, industrial plants and Collegs etc.
https://youtu.be/aqazAcE19vw
* Why is cladding necessary in an optical fibre cable?
Since for a low loss transmission, we need to guide ligh by total reflection not by reflection from a mirror surface. Indeed although we can guide light using a mirror for the outer layer of the core, but it has a huge loss (even with perfect mirrors used in professional telescopes).
On the other hand, light can be reflected by the total reflection property of transparent media without any loss. SO till now we are convinced that we must guide light through total intenal reflection of light. But how can it be done? For total intenal reflection we need two transparent media with different refraction indices. So despite the core which is used for the transmitting the light, we need another transparent medium which has a lower index than the core (to have total internal reflection) and it is the reason of existance of cladding in the fiber.
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