[1] Beijing Univ Posts & Telecommun, State Key Lab Informat Photonicsx & Opt Commun, Beijing 100876, Peoples R China
[2] Beijing Univ Posts & Telecommun, Sch Sci, Beijing 100876, Peoples R China
[3] Renmin Univ China, Dept Phys, Beijing 100872, Peoples R China
[4] Renmin Univ China, Beijing Key Lab Optoelect Funct Mat & Micronano D, Beijing 100872, Peoples R China