INVITED PAPER Joint Special Issue on Recent Progress in Optoelectronics and Communications Wavelength Converters

SUMMARY After a short introduction to the different re- quirements to and techniques for wavelength conversion, focus is on cross-gain and cross-phase modulation in SOA based convert- ers.Aspects like jitter accumulation, regeneration and conversion to the same wavelength is discussed.It is predicted that jitter accumulation can be minimised while also assuring a high extinc- tion ratio by using a 9-10 dB ratio between the signal and CW power.Using this guideline simulations show that 20 cross-gain modulation converters can be cascaded at 10 Gbit/s with only ∼20 ps of accumulated jitter and an extinction ratio of ∼10 dB. The regenerative capabilities of the cross-phase converters are described and verified experimentally at 20 Gbit/s.By control- ling the input power to an EDFA, the noise redistribution and improvement of the signal-to-noise ratio is demonstrated.In a similar experiment at 2.5 Gbit/s, the regeneration causes a reduc- tion of the required input power to an in-line EDFA of ∼6 dB for a power penalty of 1 dB at a bit error rate of 10−9.If two convert- ers are concatenated the power requirement is reduced ∼8 dB. Obviously, the power reduction allows for longer spans between in-line EDFAs.A simple scheme for regeneration without wave- length conversion is assessed at 2.5 Gbit/s resulting in ∼4.5 dB lower required EDFA input power.The scheme is characterised by a quasi-digital transfer function that is ideal for regeneration. A combination of cross-gain and cross-phase conversion is used to perform conversion to the same wavelength at 20 Gbit/s.The insertion penalty for this dual-stage converter is below 2 dB and is mainly caused by extinction ratio degradation from the cross- gain converter.Finally, a new device for all-optical wavelength conversion has been proposed and 2.5 Gbit/s operation has been simulated with good results.