1. Wuhan National Laboratory for Optoelectronics (WNLO) and School of Optical and Electronic InformationHuazhong University of Science and Technology (HUST) 1037 Luoyu Road Wuhan 430074 Hubei P. R. China
2. Department of ElectricalElectronic and Computer EngineeringThe University of Western Australia 35 Stirling Highway Crawley 6009 Australia