[1] Univ Twente, MESA Inst Nanotechnol, Opt Sci Grp, POB 217, NL-7500 AE Enschede, Netherlands
[2] Univ Twente, MESA Inst Nanotechnol, Integrated Opt Microsyst Grp, POB 217, NL-7500 AE Enschede, Netherlands
[3] KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, Electrum 229,Isafjordsgatan 22 24, S-16440 Kista, Sweden