The sampling point of an Optical Time Domain Reflectometer (OTDR) refers to the discrete points along the length of the fiber at which the OTDR measures the optical characteristics of the fiber.

Fig: The dots in the above graph represent the sampling points

When an OTDR sends a pulse of light into a fiber optic cable, it measures the backscattered light and reflections that occur along the length of the fiber. The OTDR then samples the returning light signal at regular intervals along the fiber's length. These sampling points are used to generate a trace or graph that represents the signal strength or optical characteristics of the fiber over its entire length.

The sampling point spacing, also known as the sampling resolution, determines the level of detail and accuracy of the OTDR measurements. A finer sampling resolution allows for more precise measurements but may require longer measurement times and generate larger amounts of data.

Click here to know more about sampling resolution of an OTDR.