Submarine Cable Systems

Shallow-water systems are similar to their armored loose-buffered terrestrial counterparts, whereas deep-water submarine cables use a special hermetically sealed copper tube to protect the fiber from the effects of deep-water environments. Deep-water and submarine cables also have dual armor and an asphalt compound that is used to fill interstitial spaces and add negative buoyancy. In addition to the significant external physical forces that might be encountered in a submarine environment, the other major concern is the effect of hydrogen on the performance of the optical fiber in cables used in such applications.

The effect of hydrogen on fiber performance depends on specific system characteristics. System attributes include fiber type, system operating wavelength, and cable design and installation method. Hydrogen can chemically react with dopants, such as phosphorus, to produce irreversible absorption peaks, resulting in a significant increase in the attenuation coefficient across various wavelength ranges. This phenomenon, also known as the Type 1 hydrogen effect, occurred primarily in early optical-fiber designs that used a phosphorus dopant. Unlike early phosphorus fibers, current fibers using germania dopants are not susceptible to Type 1 hydrogen effects.

The second hydrogen effect arises from the propensity for molecular hydrogen to diffuse readily through most other materials. When diffused into glass optical fiber, hydrogen creates distinct absorption peaks at certain wavelengths. The most predominant of these occurs at 1240 nm and 1380 nm. The tails of these peaks can extend out, depending on the hydrogen concentration, affecting the optical performance at 1310 nm and 1550 nm. Unlike the Type 1 effect, the effect created by molecular hydrogen is reversible and is known as the Type 2 hydrogen effect. The major sources are typically understood to be the corrosion of the metal armoring and the presence of bacteria. Proper span design must take into consideration hydrogen safety margins for submarine applications. The attenuation coefficient is proportional to the water depth role because as depth increases, the partial pressure of hydrogen increases, resulting in an increase in the amount of interstitial hydrogen that can be present in the fiber.

August 29, 2011

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