1. Korea University of Science and Technology, Department of HCI and Robotics, Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of KoreabKorea Institute of Science and Technology, Center of Opto-Electronic Materials and Devices, Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea