1. School of Physics & Information Technology Shaanxi Normal University Xi'an 710119 P. R. China
2. School of Electronic Engineering Xi'an University of Posts and Telecommunications Xi'an Shaanxi 710121 P. R. China
3. School of Information Science and Engineering Shandong Provincial Key Laboratory of Laser Technology and Application Shandong University, and Qingdao Shandong 266237 China
4. School of Life Science Shaanxi Normal University Xi'an Shaanxi 710119 China
5. School of Optical and Electronic Information National Engineering Laboratory for Next Generation Internet Access System Huazhong University of Science and Technology Wuhan 430074 China
6. School of Electronic and Information Engineering Qingdao University Qingdao 266071 China
7. School of Mechanical and Material Engineering Xi 'an University Xi 'an 710065 China