All-optical phase-modulated data signal regenerator apparatus (10) comprising an optical input (12), an optical signal converter (16), an optical carrier signal source (18), optical signal forming apparatus (20) and an optical output (14). The input (12) is arranged to receive a phase-modulated optical data signal. The signal converter (16) is arranged to receive the data signal and to convert phase modulation of the data signal into a corresponding intensity modulation of an intermediate optical signal. The carrier signal source (18) provides an optical carrier signal. The signal forming apparatus (20) is arranged to receive the carrier signal and the intermediate optical signal, and comprises a first element arranged to receive the intermediate optical signal and to apply a transfer function for effecting reshaping and resizing, and a second element for effecting transfer of an intensity modulation of the intermediate optical signal into a phase modulation on the optical carrier signal to form a regenerated phase-modulated optical data signal. The output (14) is arranged to output the regenerated optical data signal.