Which of the following is a visual indication of a fault in a fiber optic cable?

A light display on the cable surface using a visual fault locator is a definitive visual indication of a fault in a fiber optic cable. Visual fault locators emit a bright light that can be used to identify breaks, bends, or faults along the length of the fiber. When a fiber optic cable is damaged, the light emitted from the fault locator will not adequately propagate through the damaged section, resulting in a visible break or change in the pattern of the light emission on the cable surface. This method allows technicians to visually pinpoint the location of the fault quickly and effectively, facilitating repair and maintenance efforts.

In contrast, while a sudden drop in network speed may suggest a fault, it is not a direct visual indication and could be caused by other network issues unrelated to the fiber itself. Similarly, noise in the transmitted signal indicates signal degradation but does not provide a visible cue about where the fault may lie in the physical cable. A change in color of the cable may occur due to environmental factors or material degradation, but it does not directly indicate a fault within the fiber structure. This makes the light display from a visual fault locator the most effective and clear visual indication of an issue in a fiber optic cable.