apparatus and method for 3r regeneration of optical digital signals in which a modulator , preferably an electroabsorption modulator , is driven by an electrical clock synchronised with optical input pulses and is located downstream of a 2r regenerator so as to receive its output . because the pulses are reshaped by the 2r regenerator before they are retimed by the modulator , a smaller proportion of the pulse energy is likely to be lost in retiming , and the effect of “ chirp ” from the 2r regenerator may be diminished because the parts of the pulse most affected by it are removed in retiming .