This paper is concerned with an experimental approach to determining the feasibility of an optical PCM system at high bit rates. One necessary development is a high speed modulation technique using a semiconductor injection laser. The other is a high sensitivity receiving technique. First, this paper shows that high speed modulation with less pattern effect and less extinction ratio degradation can be effectively performed by adding the undershoot and overshoot to the driving current pulse in an injection laser. Second, this paper shows that a current feedback amplifier, consisting of an emitter-grounded bipolar transistor, is advantageous in high sensitivity of a high speed optical PCM receiving circuit, and to increase in repeater spacing. Finally, it is shown experimentally that the repeater spacing can be lengthened up to 5 km with a conventional graded index multimode fiber or up to 5.9 km with a single-mode fiber. It is confirmed by experiments that an optical transmission could be applied to a long distance and large capacity transmission system.

In this paper, the electrochemical device is introduced, the behavior of which is suggested by the chronopotentiometry. A sudden increase in resistance of the device occurs after some charge passes through the device. This novel device inexpensively constructs a ULF rectangular waveform generator together with one O. P. amplifier and three resistors only.

A three-terminal optical branch for multimode fiber was fabricated. Two pieces of optical fiber were side ground and glued together with the ground surfaces, the third optical fiber was butt-joined to the coupled fibers. The distribution ratio was 1:0.84 and the insertion loss was 3.2 dB for incoherent LED (8700) as well as for coherent He-Ne laser (6328).