Implementation methods of repetitive sampling on an OTDR for alignment of ghost reflection in short-period measurement with a short-length fiber

This paper discusses implementations of a repetitive sampling measurement for OTDR considering ghost effect for short period measurement with a short-length fiber. Repetitive sampling is done to acquire higher equivalent sampling rate with a low sampling clock in the data acquisition. However, the repetitive sampling can cause misalignment of ghost reflection which produces a distortion. This study analyzes the effect of ghost on the repetitive sampling measurement result. The implementations which can be categorized based on the delay object, delaying sequence, and delay looping steps are analyzed for the distortion possibility and proposed to avoid a mis-aligned ghost reflection measurement. The experiment with an OTDR that has an equivalent sampling rate of 10 GHz obtained using a 10 MHz sampling clock and 100 ps delay is shown to validate the method.