1. State Key Laboratory of Integrated OptoelectronicsCollege of Electronic Science and EngineeringJilin University 2699 Qianjin Street Changchun 130012 China
2. Department of Electrical and Computer EngineeringNational University of Singapore Kent Ridge Singapore 117583 Republic of Singapore
3. State Key Laboratory of Precision Measurement Technology and InstrumentsDepartment of Precision InstrumentTsinghua University Haidian district Beijing 100084 China