40 Gbit=s Transmission and Cascaded All-optical Wavelength Conversion over 1 000 000 Km

Introduction: All-optical wavelength converters (AOWC) are envisioned to be part of future high-speed networks. In particular, they might replace optical-to-electrical-to-optical (OEO) wavelength translator units in optical crossconnects [1]. However, to be practical, AOWCs must be able to convert signals that have been degraded during transmission over reasonable distances. Tolerance to timing jitter, noise accumulation and pulse degradation of the incoming signal are therefore required. Moreover, the converted signal has to have a signal quality that allows for subsequent fibre transmission. 3R regenerative (re-amplification, re-shaping and re-timing) capabilities are therefore required of an AOWC. Various 3R regenerative AOWCs for 40 Gbit =s and higher have been demonstrated [2–5]. However, while fibre transmission based on all-fibre regenerators over 1 million km has been demonstrated [6], there exist only few experiments that show operation of all-optical wavelength converters in a cascade and with wavelength conversion ranges of e.g. the whole C-band such as needed in a network with all-optical crossconnects. So far, loop experiments comprising AOWCs have demonstrated transmission distances of 2000 [7] and 4000 km [8] with loop lengths of 100 and 40 km, respectively. In this Letter we report the first 400 km recirculating loop experiment with an all-optical wavelength converter. We cascade 2500 devices, with a total of 1 000 000 km of fibre transmission. The result has been achieved with a 3R regenerative wavelength converter comprising a semiconductor optical amplifier (SOA) based AOWC for performing both wavelength conversion and retiming and a fibre based regenerator for signal reshaping.