[1] Univ Toronto, Dept Elect & Comp Engn, 10 Kings Coll Rd, Toronto, ON M5S 3G4, Canada
[2] Univ Toronto, Dept Phys, Toronto, ON M5S 1A7, Canada
[3] Univ Southampton, Optoelect Res Ctr, Southampton SO17 1BJ, Hants, England
[4] Univ New S Wales, Opt Commun Grp, Sydney, NSW 2053, Australia