Mariana Trench Romance

Phase 3

Technological breakthrough

They overcame one problem after another, came up with a groundbreaking manufacturing method, and developed an Optical Fiber unit with high water pressure resistance. However, a problem arose during the final test. They overcame days of trials and finally completed the project.

This was an extremely challenging development order, but based on the experience gained with the Dolphin-3K, the company achieved a number of breakthroughs. For example, they overcame one problem after another, such as establishing technology to prevent cable twisting and buckling, and introducing manufacturing know-how for cables with a breaking tension of 50 tons. In addition, because the cable was a single piece measuring 12,000m in length, Fujikura handled manufacturing across three factories. They made the most of their experience and know-how to get through the challenge.

In the development of the primary cable, we established an original tensile strength member processing technology. By utilizing the principle of pressurized steam, we devised a groundbreaking manufacturing method that can reduce the size of the rod system while maintaining ultra-strength. Meanwhile, in the development of the secondary cable, we completed a slot-type pressure-Optical Fiber unit filled with soft resin to prevent Optical Fiber from being crushed by water pressure.

1992年3月に無事納入を果たした後、綿密な性能試験を経て、1994年3月1日"かいこう"の最終試験が、報道関係者同乗のもと、マリアナ海溝で行われた。ところが、夕方のニュースでは、ケーブルが原因で大幅延期との報道がなされ、フジクラ社内でも大騒ぎとなる。二次ケーブルの光系ブラックアウトだった。急遽"かいこう"を船上に引き上げ、調査したが、まったく異常はなく、原因を特定できず。二次ケーブルは、大深度の水圧に耐えるような構造としていた。その後の解体調査により、光ファイバが長手方向に圧縮され、局部的に座屈の一種であるマイクロベンディングを発生。光の損失が急増していたのである。原因究明のためには、高水圧実験水槽の中で1,500kgf/㎠という高水圧下条件をつくり、ケーブルサンプルに連続屈曲や捩れ、あるいはその組み合わせ挙動を与え、光ファイバの損失レベルを測定。約3ヶ月不眠不休での調査確認試験を敢行した。

As a countermeasure, a method was introduced in which the tensile body layers were filled with jelly so that the movement of the tensile body would not be restricted even under high water pressure. Retests were conducted with this newly designed cable one year after the problem occurred.