New ways of tackling bandwidth limitations to meet the demands of ‘anytime, anywhere’ data consumption

It is important that developments in transmission technology keep pace with the demand for ‘anywhere, anytime’ access to data. The viability of using new photonics technology and a focus on performance improvement (increased capacity, reduced latency) of data-centre interconnects must be explored.

ADDAPT, an EU-funded project, is doing just that. The project recently announced in a paper it published on the website of the International Society for Optics and Phonics, that is has managed to successfully transmit an effective bitrate of over 100Gb/s through 100m of multimode fiber. By exploiting the versatility of a multiband approach (i.e., carrierless amplitude phase modulation, CAP), the team explains they generated a multiband CAP signal consisting of 10 bands – each with a rate of 2.5Gbaud – to modulate the 850nm single-mode VCSEL.

The project employed bit- and power-loading techniques, and assigned modulation schemes to the bands ranging from a 64-symbol constellation (64-CAP) to a 4-symbol constellation (4-CAP). A researcher explains, ‘We carried this assignment out according to the signal-to-noise ratio of each frequency band to ensure a BER below the 7 % overhead FEC threshold (i.e., 3.8×10−3) for all bands.’

Multiband CAP modulation provides the same advantages as discrete multitone (DMT) modulation, when it comes to bit and power loading, but with a lower peak-to-average power ratio. This permits the non-flat frequency response of the transmission channel to be mitigated and the maximisation of spectral efficiency. Recent advances mean that single-mode-operation VCSELs are now available and these laser sources reduce transmission impairments that can arise from intermodal dispersion. As a result, explains the project, the bit-error rate (BER) performance is below forward error corrections (FEC) thresholds and, researchers add, longer links are possible. By reducing the modulation order of the bands, thereby decreasing the total bitrate, ADDAPT was able to increase the resilience of the transmission.

To sum up in the project’s own words, ‘We have experimentally validated the feasibility of achieving 100Gb/s short-range links with cost-effective MMF and 850nm VCSELs (…) In our future work, we will focus on assessing and implementing the necessary analog and digital technologies to enable these high-speed optical links in real time.’

ADDAPT (Adaptive Data and Power Aware Transceivers for Optical Communications) is focused on marketable solutions that meet the existing standards. It combines the complementary skills and know-how of 3 large companies, 3 SMEs and 2 universities. Project members and partners include device manufacturers, suppliers of communication equipment and network operators from 7 EU and associated countries.

For more information, please see:
project website