[1] Univ Southampton, Dept Phys & Astron, Southampton SO17 1BJ, Hants, England
[2] Swiss Fed Inst Technol, Inst Quantum Elect, ETH Honggerberg, HPT, CH-8093 Zurich, Switzerland
[3] GigaTera Inc, CH-8953 Dietikon, Switzerland
[4] Picarro, Sunnyvale, CA 94086 USA
[5] CNRS, UPR20, Lab Photon & Nanostruct, F-91460 Marcoussis, France
[6] Univ Montpellier 2, F-34095 Montpellier 05, France