Fujitsu has developed a basic architecture for digital-signal processing in optical transceivers that transmits data at 400 Gbps over a single wavelength. This will help connect multiple data centres scattered within a metropolitan area at low cost.
The typical approach used till now has been to observe the output signal of the transmitter and compensate for signal distortions in order to have the transmitter provide the highest quality signal possible. But when transmitting at 400 Gbps, the desired processing accuracy becomes very high, so it is difficult to compensate at the transmitter’s end without a significant increase in costs for components and circuits. Under the architecture developed by Fujitsu, a specially designed reference signal is transmitted on the transceiver side and this is used at the receiving end to effectively compensate for distortion. The technology accurately compensates for variations in the characteristics of transceiver components and distortions introduced in the transmission path, making it possible to communicate at 400 Gbps per wavelength using inexpensive optical transceiver components. Fujitsu has successfully performed repeater-less transmission tests over a distance of 160 km.
Further, existing receivers need to carry on phase recovery, which is used to detect the signal after compensating for distortion in the transmission path. However, this has been problematic when the effect of the transmitter’s distortion is significant. To resolve this, Fujitsu’s architecture uses the transmitter’s own reference signal, making it possible to perform phase recovery without having to compensate for distortion in the transmission path. Receivers using this technology will first apply phase recovery and transmitter-distortion compensation, and then compensate for distortion in the transmission path, making it possible to recover modulated data even from highly distorted signals.
The technology can be applied to integrated optical transceiver components using silicon photonics, which is expected to reduce costs and contribute to building next-generation distributed computing platforms that will support 5G mobile networking and diverse internet of things (IoT) services.
