d) (6 marks) (i) Explain the following in connection with optical fibre cable: a) Snells Law b) Critical angle Explain what chromatic dispersion is in an optical fibre cable. Explain how the amount of chromatic dispersion affects the choice of light sources and the distance over which the fibre can be used to transmit information. Explain one method of modulation in an optical network. Explain why lasers are used in long distance fibre communications.