1. Department of Optical Information and Systems, Graduate School for the Creation of New Photonics Industries, Hamamatsu
431-1202, Japan
2. Network System Research Institute, National Institute of Information and Communications Technology, Koganei 184-8795,
Japan
3. NTT Basic Research Laboratories,
Atsugi 243-0198, Japan
4. Department of Information Physics and Computing, The University of Tokyo, Tokyo 113-8656, Japan
5. Department of Informatics, Kyushu University, Fukuoka 819-0395, Japan
6. Department of Information and Computer Sciences, Saitama University, Saitama 338-8570, Japan