Flexgrid ROADM update

I’ve blogged in the past about the expected demand for Flexgrid-based transmission systems to accommodate future high-bandwidth signals and, at OFC earlier this month this was again a very hot topic, with numerous workshops and technical sessions covering both component and systems aspects of Flexgrid networks. I was a speaker at a workshop on “Spectrally Flexible Optical Networks” organised by BT and ALU and a straw poll at the end of the workshop indicated that of the approximately 100+ attendees at this particular workshop, well over 95% thought that Flexgrid networks were the way of the future. (A personal plea to future OFC Workshop Organisers: 8am is a ridiculously early start time for a Monday workshop, particularly when you’ve just flown in from Asia/Australia as two of the panel had – it was the equivalent of 3am for us!)

One area of discussion was the need to trade off network OSS complexity against providing full (to the GHz level) flexibility in Flexgrid channel bandwidth and centre frequency allocation. It was clear, as discussed previously, that providing control to the GHz level would be unusable but there was a strong preference from at least two of the major carriers for the minimum bandwidth ‘slice’ to be 12.5GHz to support the existing ITU grid down to 25GHz channel spacing. How this works can be seen in the diagram below which shows how 12.5GHz slices can be used to build up both standard ITU-GRID channels as well as arbitrary Flexgrid channels.

From a Finisar perspective we announced at OFC that we’re now shipping fully Flexgrid-enabled WSS with 12.5GHz channel spacing to allow alignment with ITU G.694.1 channel allocation right down to the 25 GHz channel spacing. This is allowing our customers to demonstrate Flexgrid networking and develop the associated network hardware and control software needed to support Flexgrid implementation.

Whilst Flexgrid WSS are the critical component for future Flexgrid networks, a full Flexgrid component ecosystem is required to support the WSS and it was pleasing to see the first Flexgrid-compatible Optical Channel Monitors (OCMs) being talked about by a couple of vendors at the OFC trade show. The issue of the overall Flexgrid ecosystem is an important one which I’ll return to in a future post.