[1] Beijing Univ Posts & Telecommun, State Key Lab Informat Photon & Opt Commun, Beijing 100876, Peoples R China
[2] Beijing Univ Posts & Telecommun, Sch Sci, Beijing 100876, Peoples R China
[3] China Univ Geosci, Sch Engn & Technol, Beijing 100083, Peoples R China
[4] Chinese Acad Sci, Inst Semicond, State Key Lab Superlattices & Microstruct, Beijing 100083, Peoples R China