KAWASAKI, JAPAN: Fujitsu, a provider of information and communications technology, announces the development of a basic architecture for digital-signal processing in optical transceivers capable of transmitting data at a rate of 400 gigabits per second over a single wavelength.

The architecture connects multiple datacenters scattered within a metropolitan area/city with high capacity and lower costs. At present achieving 400 Gbps per wavelength has required the use of expensive components that have been optimized and selected for specific purposes. The expectation of decreasing the costs of components for optical transceivers by using cheaper parts or using alternate technologies such as CMOS or silicon photonics, which are also being developed in parallel–  have relatively poor performance. Due to piece-to-piece performance variations of the components, economically transmitting over distances of roughly 100 km, the distance needed for communications between datacenters, has not been possible using current methods.

Fujitsu have developed a new transceiver architecture in which, on the transmitter side, a specially designed referencesignal is transmitted (which remains relatively unaffected by the transmitter's own signal distortions along the transmission path) and is combined with the data signal. This combined signal is then sent, and the receiver can then effectively compensate for the transmitter's signal distortion. The technology features:

New transmission architecture using a novel reference signal

The typical approach used up to now has been to observe the output signal of the transmitter and compensate for signal distortions there 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 on the transmitter's end without significant increase of costs for components and circuits. Fujitsu has developed a new architecture in which, by transmitting a specially designed reference signal, it is possible to compensate for the transmitter's signal distortion on the receiver's end.

New compensation technology in the receiver

Existing receivers need to carry on phase recovery, which is used to detect the signal after compensating for distortion in the transmission path, but this has been problematic when the effect of the transmitter's distortion is significant. Fujitsu developed technology that, by using the transmitter's own reference signal, makes 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.

This technology can be applied to integrated optical transceiver components using silicon photonics, a technology expected to reduce costs and contribute to building next-generation distributed computing platforms that will support 5G mobile networking and diverse IoT services.