1. School of Instrument Science and Opto‐electronics EngineeringHefei University of Technology Hefei Anhui 230009 P. R. China
2. Department of Electrical EngineeringHong Kong Polytechnic University Kowloon 99077 Hong Kong P. R. China
3. Aston Institute of Photonic TechnologiesAston University Birmingham B4 7ET United Kingdom
4. State Key Laboratory of Environmental Friendly Energy MaterialsSouthwest University of Science and Technology Mianyang Sichuan 621000 P. R. China
5. Key Laboratory of Specialty Fiber Optics and Optical Access NetworksShanghai University Shanghai 200072 P. R. China
6. Institute of Automation and Electrometry SB RAS Novosibirsk 630055 Russia