Wavelength Converters ∗

After a short introduction to the different requirements to and techniques for wavelength conversion, focus is on cross-gain and cross-phase modulation in SOA based converters. 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 extinction 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 10Gbit/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 20Gbit/s. By controlling the input power to an EDFA, the noise redistribution and improvement of the signal-to-noise ratio is demonstrated. In a similar experiment at 2.5Gbit/s, the regeneration causes a reduction 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 converters 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 wavelength conversion is assessed at 2.5Gbit/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 20Gbit/s. The insertion penalty for this dual-stage converter is below 2 dB and is mainly caused by extinction ratio degradation from the crossgain converter. Finally, a new device for all-optical wavelength conversion has been proposed and 2.5Gbit/s operation has been simulated with good results. key words: optical frequency conversion, wavelength division