[1] Royal Inst Technol, Joint Res Ctr Photon, Hangzhou 310058, Peoples R China
[2] Zhejiang Univ, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Peoples R China
[3] Royal Inst Technol, Dept Microelect & Informat Technol, S-16440 Kista, Sweden
[4] UCL, Dept Elect & Elect Engn, London WC1E 7JE, England
[5] Univ Sheffield, EPSRC, Natl Ctr Technol 3 5, Dept Elect & Elect Engn, Sheffield S1 3JD, S Yorkshire, England