[1] Univ Cambridge, Cambridge CB2 1TN, England
[2] Univ Cambridge, Ctr Photon Syst, Dept Engn, Cambridge CB2 1TN, England
[3] Univ Cambridge, Photon, Cambridge CB2 1TN, England
[4] Univ Cambridge Sidney Sussex Coll, Cambridge CB2 3HU, England
[5] Univ Cambridge Jesus Coll, Cambridge CB5 8BL, England
[6] Univ Cambridge, Dept Engn, Photon Res, Cambridge CB2 1TN, England
[7] Avago Technol, R&D, Singapore, Singapore