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Submarine Makers Test Their Own Optical Fiber

Photonics Spectra
Jul 1998
Aaron J. Hand

As part of a modernization of its Trident II submarine, General Dynamics Defense Systems is installing a faster network, phasing out its Ethernet system in favor of a fiber distributed data interface system. While optical fiber will speed up the network, problems with flexibility and durability could prove difficult in a submarine environment.


Fiber optic cables crossing a submarine door's hinges allow the door to be opened at least 10,000 times without damage to the fiber. Courtesy of General Dynamics.

In its submarines, General Dynamics puts the electronics on doors so the sailors can get to both sides of any system. Over the submarine's 20-year life expectancy, as those doors open and close, the cable crossing the hinges is expected to have to flex up to 10,000 times. But when the engineers consulted the government's qualified parts list, they found that no fiber optic cable supplier had tested its products to anything close to 10,000 flexes, since military specifications require only 500-flex capabilities.

Simpler is better

In traditional bending situations, engineers switch the glass fiber to copper to cross the hinge, requiring electro-optical translators to make the switch. If General Dynamics' engineers could develop a system using only the fiber optic cable, they could reduce the necessary hardware, saving on cost and complexity by translating at the board level. If the cable lasted for only 500 flexes, however, it would have to be replaced every year. That, along with the need for a counter to indicate when the cable needed to be changed, also would increase cost and complexity.

The ideal solution would be to use fiber optic cable that would last the necessary 10,000 flexes and would be durable enough to be bundled with other, more rigid cable types. So the engineers at General Dynamics set out to test existing fiber optic cable, hoping to prove extended capabilities, according to Bert Pritchard, lead engineer on the project.

The tests so far have done just that. General Dynamics has tested cable from BICC Brand-Rex Co., which passed with flying colors, and has begun testing samples from Chromatic Technologies Inc. of Franklin, Mass.

Not only did Brand-Rex's fiber optic cable survive 10,000 flexes, but the engineers machine-flexed the cable more than 52,000 times without observing any power loss or damage to the fiber or cladding. They would have considered even a 0.1-dB loss a failure, but that failure never came. The cable also held up well to rough handling tests and to flexing tests while bundled with Ethernet and power cables.

To get the fiber optic cable it needs, General Dynamics is doing the testing for the cable makers. The suppliers could use this information in their marketing. In fact, General Dynamics hopes they do, Pritchard said, because that would ensure that they would not make any changes that would jeopardize the high reliability of the cable.

Accent on ApplicationsApplicationsdefensefiber optics

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