Bit-error-ratio improvement with 2R optical regenerators

We show that an all-optical optical regenerator can improve the bit-error ratio (BER) of a signal passing through it only if the regenerator has different power transfer functions for the logical ones and logical zeros. A regenerator that operates with a single transfer function-which constitute most of optical regenerators reported in the literature-cannot improve the BER, but can only reduce the BER degradation when, for example, placed before optical amplifiers. Of all the optical regenerators reported to date, only the one proposed by Mamyshev, based on filtering a self-phase modulated signal, has different transfer functions for the logical ones and the logical zeros. This makes the Mamyshev scheme a superior candidate for ultrahigh-speed all-optical regeneration.