[1] Nanyang Technol Univ, Ctr Disrupt Photon Technol, SPMS, TPI, Singapore 637371, Singapore
[2] Nanyang Technol Univ, Div Phys & Appl Phys, Singapore 637371, Singapore
[3] Univ Southampton, Optoelect Res Ctr, Southampton SO17 1BJ, Hants, England
[4] Univ Southampton, Ctr Photon Metamat, Southampton SO17 1BJ, Hants, England
[5] Nanjing Tech Univ Nanjing Tech, 30 South Puzhu Rd, Nanjing 211816, Peoples R China