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Higher-speed signal transmission is strongly required on a printed circuit board to handle massive data in electronic systems. So, signal transmission loss of copper wiring on a printed circuit board has been studied. First, total signal loss was divided into dielectric loss and conductor loss quantitatively based on electromagnetic theory. In particular, the scattering loss due to surface roughness of copper foil has been examined in detail. And the usefulness of the copper foil with low surface roughness has been demonstrated.

We are concerned with the realization of high speed secure communication system which is an urgent desire from the data center system. It has been proved that a quantum stream cipher by Yuen 2000 protocol (so called Y-00 or ar\) has remarkable security under quantum individual attack. So it is very attractive in implementing 1 -^ 10 G bit/sec optical data center communication system. This paper introduces a system with some randomizations to reinforcement of the security in future implementation. Furthermore, we report the data transmission of 2.5 Gbit/sec in the real commercial network of 192 Km in Tokyo, and also a demonstration of High Definition Television (HDTV: 1.4 Gbit/sec) transmission of 40 Km by 2.5 Gbit/sec transceiver based on the basic model, which is immediately applicable to medical and broadcasting system.

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