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 SOAs and SOA based interferometers. Aspects like jitter accumulation, regeneration and conversion to the same wavelength is discussed. It is predicted that jitter accumulation can be minimised by using a 9-10 dB ratio between the signal and CW power also assuring a high extinction ratio.

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, where the noise redistribution and improvement of the signal-to-noise ratio clearly is demonstrated by controlling the input power to an EDFA.

In a similar experiment at 2.5 Gbit/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.