1. a Department of Physics and Electronics , Osaka Prefecture University , 1-1 Gakuen-cho, Sakai , Osaka , 593 , Japan
2. b Department of Information Systems Engineering , Osaka Sangyo University , -1-1 Nakagaito, Daito , Osaka , 574 , Japan
3. c Department of Physical Electronics , Tokyo Institute of Technology , 2-12-1, O-okayama, Meguro , Tokyo , 152 , Japan