1. Department of Physics, Fukuoka University of Education, Munakata, Fukuoka 811-4192, Japan
2. Department of Electronics Engineering and Computer Science, Fukuoka University, Fukuoka 814-0180, Japan
3. Department of Electrical Engineering, Fukuoka University, Fukuoka 814-0180, Japan
4. Faculty of Engineering Sciences, Kyushu University, Fukuoka 816-8580, Japan