[1] Beijing Univ Posts & Telecommun, Sch Sci, Lab Optoelect Mat & Devices, Beijing 100876, Peoples R China
[2] Beijing Univ Posts & Telecommun, State Key Lab Informat Photon & Opt Commun, Beijing 100876, Peoples R China
[3] Zhejiang Sci Tech Univ, Dept Phys, Ctr Optoelect Mat & Devices, Hangzhou 310018, Zhejiang, Peoples R China
[4] SUNY Coll Potsdam, Dept Phys, Potsdam, NY 13676 USA