Error mechanisms in a four-level pulse width modulated optical fibre system

The error mechanisms in a four-level PWM optical fibre communication system are investigated. The error mechanisms are related to the noise variance and amplitude of the received signal at the sampling instants. This theory, referred to as the `amplitude theory´, is shown to be more generally applicable than an earlier theory, referred to as the `slope theory´. The slope theory is an extension of the noise analysis for an analog PWM system. Theoretical and experimental results show that the slope theory generally underestimates the BER and that the amplitude theory gives a more accurate evaluation.