Which situation does not impact optical fiber cables causing degradation in performance?

The situation where the unwanted coupling of a signal's electromagnetic energy with that of another does not typically impact the performance of optical fiber cables. In optical communications, the signals are transmitted as light through the fiber, and the main concerns for degradation often revolve around physical and environmental factors that directly affect the fiber itself.

Excessive bending can cause attenuation or loss of light as it reflects or refracts improperly within the fiber. Environmental temperature changes can alter the optical properties of the fiber and its materials, potentially impacting signal quality. Moisture exposure can lead to physical damage or degradation of the fiber's protective coatings, resulting in increased loss or performance issues.

In contrast, electromagnetic interference primarily affects electrical signals in copper cables rather than the light signals in optical fibers. Since light in optical fibers is transmitted using total internal reflection, the interaction with electromagnetic fields does not cause the same degradation experienced in copper systems. Therefore, the effects described in the other scenarios are significantly linked to the physical integrity and environmental conditions affecting optical fiber cables, while electromagnetic coupling does not play a determining role in their performance degradation.