Phase.3 Technological Breakthrough
We were able to get stuck in and solve one problem after another. We devised an epoch-making manufacturing method, and developed an optical fiber unit with high water pressure resistance. However, a problem arose during the final test. Nevertheless, we overcame days of trials and at last completed development.
Primary cableAlthough an extremely difficult development order, we achieved a number of breakthroughs based on our experience with "DORFIN 3K". We cleared hurdles again and again, obstacles like that of establishing technology to prevent cable twisting and buckling, and introduction of manufacturing know-how of cables having a breaking strength of 50 tons. Cables were manufactured at three of our plants, since the length of the cable was as long as 12,000 m. We devoted all of our experience and know-how to deal with the many challenges that arose. In the development of the primary cable, a unique tension member processing technology was established. We devised an epoch-making manufacturing method for making the rod system smaller while maintaining ultra-high strength utilizing the principle of pressurized steam. Meanwhile, in the development of the secondary cables, we completed a slot-type pressure-equalizing optical fiber unit filled with soft resin, so that the optical fiber would not be crushed by the water pressure.
Secondary cableAfter completing successful delivery in March 1992, and after a scrupulous performance test, KAIKO's final test was conducted in the Mariana Trench with journalists on board. In the news of that evening, it was reported that the test would be delayed for a substantial period of time. This caused a flurry within Fujikura; an optical system black out had occurred in the secondary cable. "KAIKO" was quickly pulled onto the mother ship and examined, but no abnormality was detected and no cause was identified. The secondary cable was designed with a structure capable of resisting water pressure at great depths. The dismantling investigation conducted afterward revealed that the optical fiber was compressed in a longitudinal direction, locally generating micro bending, a kind of buckling, resulting in a sudden increase of optical losses.To investigate the cause, we created a circumstance under 1,500 kgf/㎠ in a high water pressure experimental tank. We then measured the loss level of the optical fiber by continuously bending and twisting cable samples. We implemented investigation verification testing, gaining little sleep or rest for nearly three months.
We introduced as a countermeasure, a procedure to fill the member layer with a gel substance so that the tension members could still move freely, even in a high-water pressure situation. One year passed from the time the problem was discovered to when we were able to implement re-testing using the newly designed cable.