La fibre optique

[pic 1]Since we have invented internet we are always researching the best way to get a better connection, since some years we invented the optical fiber which is nowadays the best way to get internet. During this expression I'm going to explain what is optical fiber how it works and how we work on it during our practice in optic.[pic 2]

First of all optical fiber is a cylindrical flexible transparent made of  glass or polymer, the fiber is really small for example it's thicker than a human hair, it measures about 9μm (micrometer) . The fiber is protected by several materials, first there is a 900 μm sheath then there is kevlar and finally a bigger sheath.

The optical fiber has we know it nowadays was developed during the 60's when the laser was invented, because that's combination of the laser and optical fiber that permit us to send information. Indeed Charles Kao and Georges Hockman are the first men who were recognized to successful in sending information through optical fiber, unfortunately it wasn't and it's still not unanimous.

How it operates?

When can assimilate optical fiber as a road, on this road the light circulates through the fiber by refraction. Indeed we are exploiting refractive proprieties of the fiber such that guide light so that we have least loss on the signal, in fact the main difficulty is to guide correctly the signal that's why Mr Kao and Hockman weren't recognize unanimously they had so much loss that they loss the signal after it travels some centimetres.

The operating principle is not so difficult to understand, indeed with the laser we send lighting signal so the light is travelling through the optical fiber because  its refractive index is a somewhat higher than the sheath that permit us to contain the light that is totally reflected between the two materials finally this principle is based on total reflection principle.

There are two process based on total reflection principle first there is the step index fiber and the graded-index fiber. In first one we can see that refractive index falls almost instantly from a value in the heart to a lesser value in the sheath, in the second one the refractive index change is more progressive.

Practical Application in class:

During our practical application in optic with Ms Houlbert, we had a manipulation on the optical fiber during this sitting we had to set up connectors on each extremity of the optical fiber.

 We had several tools in order to do it properly:

• Kevlar scissors
• 3mm cable stripping
• Optical fiber stripping
• Connectors glue
• Syringe
• Polymerisation oven
• Optical fiber cleaver
• Polishing hold
• Polishing paper
• Microscope objective
• Alcohol
•  Cleaner paper

Before we started anything we had to check if connectors are clean and that the hole is empty, then check if the optical fiber isn't broken and that the cable is in a good repair.

Next we started the manipulation first we had to prepare the fiber as it was showed on the picture so we began by stripping the bigger sheath about 35mm, then cut the Kevlar on 20mm, cut the 900 μm diameter sheath and finally the optical fiber sheath with the miller wire stripping. Furthermore after stripping the optical fiber sheath we had to clean the fiber with alcohol and check if we didn't broke the fiber at the same time, it's really important to get a clean fiber or it won't go through the connector's ceramic ferule. Then we had to pass the fiber through the connectors, it's a really delicate manipulation because if we break the fiber in the connector's ferule it would clogged the ferule.

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