BER Degradation by Signal-Reshaping Processors With Noninstantaneous Response

We show analytically that if the response of a signal-reshaping processor is slower than (or comparable to) the time scale of variations of the temporal profile of the input signal, then such a processor necessarily degrades the signal's bit error rate (BER). Here, the BER comparison is made for the cases where the receiver is placed immediately before and immediately after the processor. As primary examples of such processors, we consider all-optical 2R (reamplification and reshaping) regenerators, but also mention that the aforementioned BER degradation can occur in wavelength converters and electronic components of the receiver.