Under the gun, Smith and Boyle went into an office and, in one hour, emerged with the basic plans for the CCD, the sensor still used in digital photography today. A CCD works like this: Light hits a tiny grid of photosensitive silicon cells, each which build a charge proportional to the intensity of the light hitting it. This charge can be measured precisely and we can know exactly how bright that portion should be. Add filters, and color can be discerned too.
The experiment itself, which was carried out at by the firms R&D focused Bell Labs division on the Innovation City campus in Villarceaux (Paris), is understood to have used 155 lasers. Each laser was operating at different frequencies and carrying 200Gbps of data (single-carrier data channels) over a 50GHz frequency grid.
Normally such signals suffer from distortions and noise, which limit performance, but it’s understood that Alcatel-Lucent were able to resolve this by using an enhanced version of Wavelength Division Multiplexing (WDM) that works by splitting light up into different wavelengths so that it can carry more data (a variety of other methods were also used).