A FOX-C approach to flexible optical switching

Flexible switching of high-capacity traffic carried over ’super-channel' dense-wavelength division multiplexing wavelengths is the goal of the European Commission Seventh Framework Programme (FP7) research project.

The €3.6M FOX-C (Flexible optical cross-connect nodes) will develop a flexible spectrum reconfigurable optical add/drop multiplexer (ROADM) for 400Gbps and one Terabit optical transmission. The ROADM will be designed not only to switch super-channels but also the carrier constituent components.

Companies involved in the project include operator France Telecom and optical component player Finisar. However, no major European system vendor is taking part in the FOX-C project although W-Onesys, a small system vendor from Spain, is participating.

“We want to transfer to the optical layer the switching capability”

Erwan Pincemin, FT-Orange

“It is becoming more difficult to increase the spectral efficiency of such networks,” says Erwan Pincemin, senior expert in fibre optic transmission at France Telecom-Orange. “We want to increase the advantages of the network by adding flexibility in the management of the wavelengths in order to adapt the network as services evolve.”

FOX-C will increase the data rate carried by each wavelength to achieve a moderate increase in spectral efficiency. Pincemin says such modulation schemes as orthogonal frequency division multiplexing (OFDM) and Nyquist WDM will be explored. But the main goal is to develop flexible switching based on an energy efficient and cost effective ROADM design.

The ROADM’s filtering will be able to add and drop 10 and 100 Gigabit sub-channels or 400 Gigabit and 1 Terabit super-channels. By using the developed filter to switch optically at speeds as low as 10 Gigabit, the aim is to avoid having to do the switching electrically with its associated cost and power consumption overhead. “We want to transfer to the optical layer the switching capability,” says Pincemin. 

While the ROADM design is part of the project’s goals, what is already envisaged is a two-stage pass-through-and-select architecture. The first stage, for coarse switching, will process the super-channels and will be followed by finer filtering to extract (drop) and insert (add) individual lower-rate tributaries.

The project started in Oct 2012 and will span three years. The resulting system testing will take place at France-Telecom Orange's Lab in Lannion, France.

Project players

The project’s technical leader is the Athens Institute of Technology (AIT), headed by Prof. Ioannis Tomkos, while the administrator leader is the Greek company Optronics Technologies.

Finisar will provide the two-stage optical switch while France Telecom-Orange will test the resulting ROADM and will build the multi-band OFDM transmitter and receiver to evaluate the design.

Athens Institute of Technology will work with Finisar on the technical aspects and in particular a flexible networking architecture study. The Hebrew University is working with Finisar on the design and the building of the ultra-selective adaptive optical filter, and has expertise is free-space optical systems. The Spanish firm, W-Onesys, is a system integration specialist and will also work with Finisar to integrate its wavelength-selective switch for the ROADM. Other project players include Aston University, Tyndall National Institute and the Karlsruhe Institute of Technology.

No major European system vendor is taking part in the FOX-C project.  According to Pincemin this is regrettable although he points out that the equipment players are involved in other EC FP7 projects addressing flexible networking.

He believes that their priorities are elsewhere and that the FOX-C project may be deemed as too forward looking and risky. “They want to have a clear return on investment on their research,” says Pincemin.