Design and test results of an optical fiber feedthrough for an optical submarine repeater

A new hermetic sealing Structure is described in which optical fibers are metal coated and sealed off. The gap between the fibers and the metal pipe is filled with solder. The sealing structure is used as a feedthrough of a repeater for a long-haul optical fiber submarine cable system. According to theoretical study, airtightness was found reliable for a long period of time by utilizing a self-seal effect operating at the time of pressurizing through the structure where circumferences of fibers are soldered for sealing. Manufacture on trial proved that perfect airtightness was achieved even after a heat cycle test (60°C- - 10°C) and shock test (50 G). The incremental loss due to temperature changes in the range from 60°C to - 10°C was less than 0.015 dB and an incremental loss of 0.06 dB or less was observed when the structure was pressurized by 800 kg/cm², however no residual loss could be found.