1. Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, United Kingdom
2. Wuhan National Laboratory for Optoelectronics and School of Optical and Electrical Information, Huazhong University of Science and Technology, Wuhan 430074, China
3. Center for Optical Materials Science and Engineering Technologies and Department of Materials Science and Engineering, Clemson University, Clemson, South Carolina 29634, USA
4. Department of Physics and Porelabs, Norwegian University of Science and Technology, N-7491 Trondheim, Norway