Waves

n = c/c(s)

Refractive index of air - 1

n1 sin x1 = n2 sinx2

Cladding - protects the core and prevents information being lost 

Modal dispersion - light enters at different angles so takes different paths down the fibre ruded with a single mode cable wwhich only lets light follow a very narrow path.

Material dispersion - different wavelengths experience different amounts of refraction so take different amounts of time to travel. Prevented using monochromatic light

Pulse broadening is where the recived signal is broader than the initail signal with broden pulses sometimes overalpping resulting in a loss of information

Absorption is where some of the signal's energy is absorbed bt eh material reducing the amplitude of the signal