Optical fibre forms the backbone of data networks, transporting vast amounts of data between nodes. The maximum bit rate in backbone networks today is 100 Gbit/s per channel. When using all of the channels of an optical fibre, the new process permits a throughput of up to 24.6 Tbit/s (24,600,000,000,000 bit/s) to be attained on the maximum of 48 available channels (comparable to 48 lanes) of the data highways. A collection of 3,696 CDs could thus be transferred over a single optical fibre – a strand thinner than a human hair – at the same time. With the new method, existing networks can double their current transmission capacity by merely replacing the technology in the terminal stations.
“Together with our technology partner Alcatel-Lucent and the experts at Telekom Network Production, we have attained this tremendous transmission performance over the Internet under real-world conditions,” said T-Labs Manager Heinrich Arnold. “With them, we have successfully developed an innovative method by which the transmission capacity of optical fibre can be increased significantly in network operation.”
The Telekom OSIRIS (Optically Supported IP Router Interfaces) research project realszed transmission at a speed of 512 Gbit/s (400 Gbit/s usable bit rate) on a 100 GHz wavelength channel over a distance of 734 km, thus demonstrating a spectral sensitivity of 5 bits/s/Hz in the Deutsche Telekom network.
This impressive transmission performance was reached using innovative transmission technology with two carrier frequencies, two polarization planes, 16-QAM quadrature amplitude modulation and digital offline signal processing for the equalization of fiber influences with soft-FEC forward error correction decoding in the receiver.
The WDM transmission link consisted of a total of 14 standard single-mode fiber sections with dispersion compensation as required for the neighbouring conventional 10 Gbit/s channels.
The high optical input powers of the conventional 10 Gbit/s channels and the dispersion compensation in the fibre sections interfere with the innovative transmission technology due to nonlinearities, including self-phase modulation by the higher input power and cross-phase modulation by the adjacent channels. Despite these worst-case conditions, it was possible to demonstrate the transfer of the innovative high-speed signal simultaneously with conventional 10 Gbit/s signals in adjacent channels in an existing system. This points toward a migration path which would allow the multiplication of transmission capacities to handle the rapid increase of data traffic over networks without having to lay new cables.