1. Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska−Lincoln, Lincoln, Nebraska 68588-0299, United States
2. College of Mechanical & Electrical Engineering, Wenzhou University, Wenzhou 325035, China
3. Department of Electrical and Computer Engineering, University of Nebraska--Lincoln, Lincoln, Nebraska 68588-0511, United States
4. Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China
5. Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
6. School of Optoelectronic Engineering and Instrumentation Science, Dalian University of Technology, Dalian, Liaoning 116023, China
7. Laser Micro/Nano-Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China