[1] Royal Inst Technol, Dept Appl Phys, Roslagstullsbacken 21, SE-10691 Stockholm, Sweden
[2] Electrum 236, SE-16440 Stockholm, Sweden
[3] Acreo Swedish ICT AB, Dept Fiber Opt, Electrum 236, SE-16440 Stockholm, Sweden
[4] KTH Royal Inst Technol, SciLifeLab, Div Prote & Nanobiotechnol, SE-17121 Solna, Sweden