NTT Electrical Communications Laboratories (ECL's) are developing a very large-capacity optical transmission system having information speed on the multigigabit/second order [1]. Equipment design for this system is difficult due to its very large signal bit rate. In the case of terminal equipment, these difficulties are closely related to the line code. This paper discusses a bit insertion code as a high-speed optical line code and its performance. Using this code, a new configuration for the terminal equipment that enables very high-speed signal processing is proposed. This configuration gives the equipment flexibility and numerous advantages in terms of economy.

The structure for introducing fibers into the pressure housing of a submarine optical repeater is studied. As a result of investigations into sealing materials, fiber strength, and optical characteristics, the following structure is adopted. Fibers, whose primary coat is metal instead of silicone, are fixed by epoxy resin to withstand water pressure, and the outside surface of the resin is covered with solder to keep the resin free from water vapor. Experimental results show that this structure meets the requirements.