1. Department of Physics and Materials Science; City University of Hong Kong; 83 Tat Chee Avenue Hong Kong SAR China
2. College of Materials Science and Engineering; Shenzhen University; Shenzhen 518060 China
3. Department of Applied Physics; The Hong Kong Polytechnic University; Hong Hum Hong Kong SAR China
4. State Key Laboratory of Tunable Laser Technology, Ministry of Industry and Information Technology Key Lab of Micro-Nano Optoelectronic Information System; HIT Shenzhen; Shenzhen 518055 China
5. City University of Hong Kong Shenzhen Research Institute; Shenzhen 518057 China