[1] Dalian Polytech Univ, Res Inst Photon, Dalian 116034, Peoples R China
[2] City Univ Hong Kong, Dept Elect Engn, Kowloon, Tat Chee Ave, Hong Kong, Peoples R China
[3] City Univ Hong Kong, State Key Lab Terahertz & Millimeter Waves, Kowloon, Tat Chee Ave, Hong Kong, Peoples R China