Recovery of clock pulses of wavelength division multiplexed optical signals

Method for recovering clock pulses of wavelength division multiplexed optical signals, the method comprising the steps of:

• (i) providing a laser cavity formed between a plurality of reflectors to define a cavity length and comprising a nonlinear medium;
• (ii) optically-pumping said cavity at a wavelength selected to give efficient parametric amplification within said medium;
• (iii) copropagating said optical signals through said nonlinear medium with said pump radiation;
• (iv) recirculating a proportion of the output from said laser cavity back through said laser cavity;
• and
• (v) adjusting said cavity length to correspond to an integer multiple of bit periods of at least one of said multiplexed optical signals;
• whereby the interaction between the pump radiation and at least one of said copropagating multiplexed optical signals within the nonlinear medium generates idler waves symmetrically about said pump wavelength by four wave mixing and said idler waves are recirculated through said cavity to be amplified by parametric amplification in order to recover wavelength division multiplexed clock pulses.