Manuscript received January 29;
1988;
revised May 5;
1988. This work was supported in part by the Agency of Industrial Science and Technology;
Ministry of International Trade and Industry. The authors are with the Opto-Electronics Research Laboratories;
NEC Corporation;
4-1-1;
Miyazaki;
Miyamae-ku;
Kawasaki;
213;
Japan. IEEE Log Number 8823282;