A regenerator (7.x, 7.1-7.3) for regenerating optical signals on optical transmission links (4), in particular for use in a Dense Wavelength Division Multiplex (DWDM) optical transmission system. The regenerator (7.x, 7.1-7.3) comprises optical amplification means (7.xa, 7.xd) for compensating optical power losses, and a deterministic adaptation unit (7.xb) comprising means being adapted to compensate deterministic transmission impairments of the optical transmission link (4), in particular optical dispersion compensating means being adapted to compensate for chromatic dispersion of said link (4). The proposed regenerator (7.x, 7.1-7.3) further comprises a non-deterministic adaptation unit (7.xc) comprising means for compensating time variant non-deterministic transmission impairments, in particular polarisation mode dispersion. In this way, the proposed regenerator overcomes transmission limitations and improves robustness of long and ultra-long-haul multi-span DWDM transmission systems with respect to deterministic and non-deterministic transmission impairments.