Erbium Doped Fibre Lasers up t 1618 nm for Optical Communication beyond the L-band

Up to a few months ago it was expected theoretically that erbium doped DFB fibre lasers could not be made to operate at wavelengths above the L-band (1570nm-1610nm). This is due to the combination of very low gain and problems with two-photon absorption in the erbium. In addition semiconductor DFB lasers are difficult to get beyond the L-band. Therefore no transmission systems have ever been made in this wavelength region despite that low loss transmission should still be possible in standard fibres. With the increasing demand for optical bandwidth it will soon be essential to use the entire low loss region for optical fibres. Communication beyond the L-band will therefore probably be necessary within the next 1-3 years.Through careful optimisation of the DFB fibre laser cavity and by using a high gain fibre we have demonstrated stable single-mode lasers up to 1618nm. We have performed 10Gbit/s transmission over 80km with such a DFB fibre laser at 1613nm. Only a minor power penalty was observed compared to standard transmission.We also show that the intrinsic properties of the DFB fibre lasers remain very good at these long wavelengths. We even observe a few dB improvement of the noise-floor suppression. For frequencies above 1MHz the RIN noise drops below the measurement limit for a state-of-the-art HP lightwave analyser.