1. Department of Electronics, Chosun College of Science and Technology, Gwangju 61453, Korea
2. Korea Photonics Technology Institute (KOPTI), Gwangju 61007, Korea
3. Center for Nano-Photonics Convergence Technology, Korea Institute of Industrial Technology, Gwangju 61012, Korea
4. School of Information and Communication Engineering, Sungkyunkwan University, Suwon 16419, Korea