1. Department of Electrical and Computer Engineering University of Nebraska‐Lincoln Lincoln NE 68588‐0511 USA
2. Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology 1037 Luoyu Road Wuhan 430074 China
3. School of Mechanical Engineering Beijing Institute of Technology Beijing 100081 China
4. Institut de Chimie de la Matière Condensée de Bordeaux Avenue du Docteur Albert Schweitzer F‐33608 Pessac Cedex France