1. School of Optical-Electrical and Computer Engineering , University of Shanghai for Science and Technology , Shanghai 200093 , China
2. School of Optical and Electronic Information , Huazhong University of Science and Technology , Wuhan , Hubei 430074 , China
3. Department of Physics , University of Dayton , 300 College Park , Dayton , OH 45469 , USA
4. Department of Electro-Optics and Photonics , University of Dayton , 300 College Park , Dayton , OH 45469 , USA