1. Nanophotonics Center, NTT Corp., 3-1, Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan
2. NTT Basic Research Laboratories, NTT Corp., 3-1, Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan
3. Université Côte d’Azur, CNRS, CRHEA, Rue B. Grégory, Valbonne 06560, France
4. NTT Device Technology Laboratories, NTT Corp., 3-1, Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan
5. Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan