1. Department of Optics and Optoelectronics, School of Engineering Physics, Ha Noi University of Science and Technology, 1 Dai Co Viet Road, Ha Noi, Viet Nam
2. School of Electrical Engineering, Ha Noi University of Science and Technology, Ha Noi, 1 Dai Co Viet Road, Ha Noi, Viet Nam
3. Department of Physics, Incheon National University, Incheon 406-772, Republic of Korea
4. Department of General Physics, School of Engineering Physics, Ha Noi University of Science and Technology, 1 Dai Co Viet Road, Ha Noi, Viet Nam