1. Institute of Modern Optics; Nankai University; Tianjin 300071 China
2. Department of Applied Physics; The Hong Kong Polytechnic University; Kowloon Hong Kong P. R. China
3. College of Chemistry and Materials Science; Sichuan Normal University; Chengdu 610068 China
4. The Hong Kong Polytechnic University Shenzhen Research Institute; Shenzhen 518057 China