A 3R regeneration scheme for highly spectral efficient signal waveforms

We propose a new regeneration scheme for highly spectral efficient formats and through numerical simulations we prove its necessity against traditional 2R solutions for future high capacity systems All-optical regeneration is seen as a promising approach to improve the capacity and reach of long haul transmission systems. In the past, a full 3R functionality (i.e. Re-amplification, Re-shaping, Re-timing) was essential for the regenerative subsystems which had to deal with the prevailing return to zero (RZ) modulated signals. With the recent introduction of highly spectral efficient signals, characterized by non-return to zero (NRZ) modulation of complex constellations (i.e. m-QAM), the re-timing functionality was overlooked and the efforts were focused on advancing only the 2R performance, through schemes that could remove the noise from the multiple amplitude and phase levels of the signal waveform [1-3]. However, in future transmission systems the channels will be densely packed and tight filtering will be required for any in-line channel selection, e.g. to perform all-optical add-drop multiplexing or signal regeneration. Unavoidably, this will give rise to timing jitter effects that will accumulate along the 2R line and drastically limit the system cascadability. Our proposed 3R scheme, see Fig. 1, combines an advanced non-linear element, which enabled suppression of noise on both signal quadratures, with an optical gate and a pulse reformatting filter, for facilitating sampling at the minimum distortion point and the recovery of the NRZ signal at the output of the subsystem, respectively.