[1] Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA
[2] Purdue Univ, Sch Elect & Comp Engn, W Lafayette, IN 47907 USA
[3] Bell Labs, Lucent Technol, Murray Hill, NJ 07974 USA
[4] Univ Calif Santa Barbara, Dept Elect & Comp Engn, Santa Barbara, CA 93106 USA
[5] Agere Syst, Berkeley Hts, NJ 07922 USA