We investigate both theoretically and experimentally how the use of an all-optical decision element (ODE) in front of a conventional receiver improves, in return-to-zero (RZ) systems, the receiver performance when the signal bandwidth exceeds the bandwidth of the available optoelectronic components. A theoretical analysis of the ODE behavior shows the field of applicability of the investigated solution. The experimental evaluation of the performance improvement in an RZ system is realized using an ODE based on two cascaded nonlinear optical loop mirrors. Benefits in terms of bit error rate for different signal bandwidths and for a different received optical signal-to-noise ratio are presented. Substantial agreement of the experimental results with the theoretical analysis is obtained. The impact of the ODE in the presence of relevant thermal noise at the receiver is also considered. The ODE can extend the use of common band-limited receivers to wide-bandwidth signals and can be an alternative solution to the development of wideband receivers.
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