1. Fujian Provincial Key Laboratory of Optoelectronic Technology and DevicesSchool of Opto‐electronic and Communication EngineeringXiamen University of TechnologyXiamen361024People's Republic of China
2. Department of Electrical and Computer EngineeringUniversity of Wisconsin‐MadisonMadisonWI53706USA
3. Graduate School of Science and EngineeringSaitama UniversitySaitama338‐8570Japan
4. Department of Electronic ScienceXiamen UniversityXiamen361005People's Republic of China