1. Department of Advanced Fiber Engineering, Inha University, 253 Young‐hyun‐dong, Nam‐gu, Incheon, 402–751 (Republic of Korea)
2. Department of Information and Communications, Gwangju Institute of Science and Technology, 1 Oryong‐dong, Buk‐gu, Gwangju, 500–712 (Republic of Korea)
3. Department of Physics, Inha University, 253 Young‐hyun‐dong, Nam‐gu, Incheon, 402–751 (Republic of Korea)