Characteristics of all-optical ultra-fast 3R regenerators using cascaded second-order nonlinear effect in quasi-phase matched lithium niobate devices

We numerically show that quasi-phase matched lithium niobate devices employing the cascade of second harmonic generation and difference frequency mixing have decision gate characteristics. The decision gate function is realized by a parabolic transmittance for a low-power input and a limiter characteristic for a high-power input. The limiter characteristic is attributed to the large group-velocity mismatch between the fundamental and second harmonic pulses. The operation principle differs from those of other all-optical 2R or 3R regenerators that have been proposed so far. By using such devices, all-optical ultra-fast 3R operation far beyond 200 Gbps can be expected.