Abstract :
The author looks at what can be done about the limit to how much data optical fibres can carry. Digging ditches to bury more optical fibre is expensive, so operators are looking at ways to squeeze extra capacity from the fibres they already have in the ground by borrowing from the modulation schemes used in wireless. These schemes can encode relatively high numbers of bits per second per Hz of available spectrum, using phase states or phase states combined with polarisation states to carry the information.
