What do zig-zag lines at the end of the graph indicate?

The zig-zag lines at the end of a graph typically represent the end of the fiber. When analyzing fiber optic measurements using a time-domain reflectometer (TDR) or optical time-domain reflectometer (OTDR), the graph displays the backscattered light as it travels through the fiber. As the light reaches the end of the fiber, the return signal can bounce erratically and create a zig-zag pattern due to how the fibers reflect light, especially if the termination is not perfect or is subject to certain physical characteristics. This visual indication is vital for technicians to identify where the actual end of the fiber is located in relation to the measured data, allowing for accurate troubleshooting and system integrity assessments.

The other choices do not correctly interpret the zig-zag pattern. A potential fault typically shows a more consistent reflection change rather than an erratic pattern, high back reflection is characterized by a sharp peak rather than a zig-zag, and measurement noise usually manifests as random variations throughout the graph, not specifically as a zig-zag at the end.