A2 Applied Science - Working Waves - Fibre Optics

Fibre Optics 

Simple Fibres

Advantages:

- Simple to make

- Low critical angle so tighter curve possible

Disadvantages:

- Easily scratched leading to light losses.

- Multi-path dispersion leads to sharp pulses becoming rounded and limits maximum rates of pulses.

Step Index Fibres

Cladding = Twenty-five micro meters

Core = Fifty to two-hundred micro meters

Cladding: Low refractive index

Core:High refractive index

Advantages:

- Relatively cheap to make

- Scratch resistant

Disadvantages:

- Multi-path dispersion

- Limits range and bandwidth.

Graded Index Fibres 

Core = Fifty to one hundred micro meters.

Edge = Low refractive index

Centre = High refractive index

Advantages:

- Rays that travels straight through the centre of the fibre goes through more slowly. The rays that travels near the edges travel through more quickly so all the rays take the time the same time to travel regardless of the path they take. Thus preventing dispersion.

- Dispersion is prevented so fibres can be used for longer, higher bandwidth links.

Disadvantages:

- Difficult to make

- Dispersion can only be prevented at one wavelength.

Monomode Fibres

Cladding = Low refractive index.

Core = High refractive index.

Advantages:

- Single path through the fibre so no dispersion.

Disadvantages:

- Expensive to make and needs tiny, more expensive lasers to get into the small core.

- Harder to connect as…