1. Beihang University, School of Instrumentation Science and Opto-Electronics Engineering, Laboratory of Precision Opto-Mechatronics Technology, No. 37 Xueyuan Road, Haidian District, Beijing 100191, China
2. University of Connecticut, Department of Electrical and Computer Engineering, 371 Fairfield Way, U-2157, Storrs, Connecticut 06269, United States