1. Key Laboratory for Physical Electronics and Devices of the Ministry of Education & Shaanxi Key Lab of Information Photonic Technique; School of Electronic and Information Engineering; Xi'an Jiaotong University; Xi'an 710049 China
2. Department of Physics; University of Arkansas; Fayetteville AR 72701 USA
3. College of Automation; Harbin Engineering University; Heilongjiang 150001 China
4. State Key Laboratory of Precision Spectroscopy; East China Normal University; Shanghai 200062 China
5. National Laboratory of Solid State Microstructures; School of Physics; Nanjing University; Nanjing 210093 China