Low frequency cutoff effects in fiber optic communication systems

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Virginia Tech


The presence of low frequency cutoffs in the forward path of the information signal leads to inter-symbol interference (ISI) and degradation of the signal to noise ratio at the sampling instant in digital on-off keying (OOK) systems. The low frequency cutoffs occur as a result of the presence of power separation filters in a line wire system and gain instability of APD's to D.C. in fiber optic systems. Also, it is easier to design amplifiers that do not extend to D.C. The ISI which manifests itself in the form of baseline wander can cause appreciable degradation in the signal to noise ratio. This thesis investigates two ways of combating the baseline wander problem. They are quantized feedback and line coding schemes. A detailed performance evaluation of quantized feedback scheme is performed. An overview of line coding schemes is given and some specific codes are evaluated in terms of S/N degradation at the receiver.