BT Delivers 3Tbps via Existing 359km Commercial Grade Fibre Optic Link - ISPreview UK
BT and Huawei have successfully harnessed a record spectral efficiency of 5.97bit/s/Hz in order to deliver super channel speeds of 3Tbps (Terabits per second) over an existing 359km long fibre optic link using commercial grade hardware and software in a real world environment.

The connection itself, which made use of Huaweis OSN 9800/8800 and iManager U2000 platform, was conducted using a field fibre optic link between the operators Adastral Park R&D HQ in Suffolk and the BT Tower in London. Apparently this approach works by compressing the gaps between transmission channels, usually set at 50GHz, which enabled it to be around 50% more efficient than a typical core network like.

The results also appear to represent an improvement on BTs earlier test with Alcatel-Lucent, which in January 2014 used an almost identical link to deliver data speeds of up to 1.4Tbps (Terabits per second) via a spectral efficiency of 5.7 bits per second per Hertz (here). In both cases the ability to harness existing links and commercial kit is key to the attractiveness.
Neil J. McRae, BTs Chief Network Architect, said:

Flexgrid technology is evolving quickly, and this trial has been invaluable in demonstrating the feasibility of this emerging technology in a real, truly testing environment.

Combined with BTs continuing investment in its network infrastructure, this outstanding breakthrough suggests were well-prepared for a future where new and exciting services are delivered by faster, more data-hungry applications. The trial result also demonstrates how well be able to maximise the efficiency of BTs existing investments, extending the life of our core network infrastructure whilst continuing to meet the needs of a 21st Century digital society
Key Highlights of the Trial:

A real-time 3Tbps super channel, comprising of 15 x 200Gbps (16-QAM) sub channels, bundled together to provide combined capacity.

Sub channels separated by as little as 33.5GHz, resulting in record spectral efficiency of 5.97b/s/Hz an increase of around 50 percent in spectral efficiency compared to conventional 50GHz fixed grid infrastructure.
A 3Tbps super channel, configured and monitored from a live operational environment: BTs Transport Network Operations Centre (TNOC) in Cambridge.
Trials performed using production grade 16-QAM transponders, Flexgrid hardware and management software.
Spectral width configured in slices of 12.5GHz, up to a total spectral slot of 550GHz.
Its important to point out that such developments are currently more focused on helping operators like BT to deliver more capacity to other network operators, such as big broadband ISPs and mobile providers, rather than end-users. So you wont be getting that 3Tbps link to your home for a very long time, although history does tend to show that corporate performance eventually filters down to home users too.

As it stands though BT has yet to launch an official product based on the new approaches theyre testing, although no doubt something will follow in the future.