What type of fiber cable consists of a single fiber strand used for long-distance transmission?

The correct choice is singlemode fiber, which is designed specifically for long-distance communication. Singlemode fiber features a core diameter that is significantly smaller than that of multimode fiber, typically around 8 to 10 microns. This small core allows only a single mode of light to propagate down the fiber, which minimizes signal loss and allows for higher bandwidth over longer distances.

This type of fiber is ideal for applications that require high-speed data transmission across large distances, such as in telecommunications and data backbone installations. The advantages of using singlemode fiber include a longer reach and the ability to support high data rates, making it the preferred choice for long-haul networks.

Other types of fiber, like multimode fiber, are designed for shorter distances and can transmit multiple modes of light, but they encounter modal dispersion that limits their effectiveness over longer distances. Loose tube and breakout fibers refer to specific cable designs or constructions rather than the type of fiber strand utilized for transmission; they can be made of either singlemode or multimode fibers but do not inherently define the distance capabilities of the fiber itself. Therefore, the choice of singlemode fiber is best suited for long-distance transmission applications.