1. Key Laboratory of Opto‐Electronics Information Technology (Tianjin University) Ministry of Education School of Precision Instruments and Opto‐Electronics Engineering Tianjin University No. 92 WeiJin Road Tianjin 300072 P. R. China
2. Key Laboratory of Opto‐Electronics Information Technology (Tianjin University) Ministry of Education School of Precision Instruments and Opto‐Electronics Engineering Tianjin University Tianjin 300072 P. R. China
3. Advantest (China) Co. Ltd. Shanghai 201203 P. R. China
4. School of Physics and Microelectronics Zhengzhou University Zhengzhou Henan 450001 P. R. China