College of Precision Instrument &;
Opto-electronics Engineering;
Tianjin University;
Tianjin 300072;
P. R. China Key Laboratory of Opto-electronics Information and Technical Science (Tianjin University);
Ministry of Education;
Tianjin 300072;
China Laboratory of Optical Fiber Communication C Tianjin University);
Tianjin 300072;
China;