Refraction
Critical angle
TIR
Optical Fibres
Signal degradation
As you increase the angle of incidence, the angle of refraction slowly gets closer to 90*.
You will eventually reach the critical angle. This is where the refracted ray travels right down the boundary between the two mediums.
At the critical angle there is total internal reflection.
The refractive index of medium 1 has to be larger than the refractive index of medium 2.
When the angle of incidence is the same value as the critical angle the refracted light travels down the boundary and there is a bit of reflection.
When the angle of incidence is bigger than the critical angle there is total internal reflection with no refraction whatsoever.
If the angle of incidence has a value less than the critical angle then there will be refraction with a bit of partial reflection.
The fibre is extremely narrow meaning that the light always hits the core-cladding boundary at an angle of incidence which is larger than the critical angle. This means that all of the light is internally reflected until it reaches the end of the fibre, which is where total internal reflection stops happening.
The signal can carry more information because light has a high frequency.
The cladding acts as protection to the core which could possibly allow light to escape.
Light doesn't heat up the fibre so almost no energy is lost as heat.
An optical fibre is a high refractive index core surrounded by a lower refractive index cladding (allowing TIR).
The signal can travel very quickly and with minimal signal loss.
Modal Disperion
Absorption - some of the energy is lost from the material that the fibre is made from. The energy loss results in the amplitude of the signal decreasing.
Material Dispersion
Using a monochromatic light can stop material dispersion.
This is caused by light waves entering the fibre at different angles.
This causes them to take different paths down the fibre. Rays that travel down the middle will reach the end quicker than ones that take longer paths
This can be reduced by using a single mode fibre where light is allowed down only a very narrow path.
As light is made up of different wavelengths, some waves will take longer to get to the end of the fibre than others, causing material dispersion.
Material dispersion is caused by different amount of refraction experienced by different wavelengths.
Optical fibre repeaters can be used to regenerate the signal every so often to signal degradation from both absorption and dispersion.