[1] City Univ Hong Kong, Dept Mat Sci & Engn, Kowloon, Hong Kong, Peoples R China
[2] City Univ Hong Kong, State Key Lab Terahertz & Millimeter Waves, Kowloon, Hong Kong, Peoples R China
[3] City Univ Hong Kong, Shenzhen Res Inst, Shenzhen 518057, Peoples R China
[4] Guangxi Normal Univ, Dept Phys, Guilin 541000, Guangxi, Peoples R China
[5] City Univ Hong Kong, Ctr Funct Photon, Kowloon, Hong Kong, Peoples R China