1. Laboratoire
de Photonique et de Nanostructures, CNRS, route de Nozay, 91460 Marcoussis, France
2. LIMMS/CNRS-IIS,
Institute of Industrial Science, University of Tokyo, Komaba 4-6-1
Meguro-ku, Tokyo 153-8505, Japan
3. Department
of Applied Mathematics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands