[1] Australian Natl Univ, Ctr Opt Sci, Australian Photon Cooperat Res Ctr, Canberra, ACT 0200, Australia
[2] CSIC, Inst Opt, E-28006 Madrid, Spain
[3] AT&T Bell Labs, Lucent Technol, Holmdel, NJ 07733 USA
[4] Princeton Univ, Dept Elect Engn, Princeton, NJ 08544 USA