What is Sampling Resolution of an Optical Time Domain Reflectometer (OTDR)?

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- GoPhotonics

Jun 3, 2024

The sampling resolution of an OTDR (Optical Time Domain Reflectometer) refers to the spacing between consecutive data points along the length of the fiber being tested. It determines the level of detail and precision with which the OTDR can capture and analyze the optical characteristics of the fiber. The sampling resolution (Δz) is measured in metres (m) and can be expressed by the following equation:


Where c is the speed of light in a vacuum

n is the refractive index of the optical fiber (typically around 1.468 for silica fibers)

and Δf is the bandwidth of the OTDR's detection system

The factor of 2 in the denominator accounts for the fact that the light travels to the sampling point and then back to the OTDR, effectively doubling the distance for the round trip.

When an OTDR sends a pulse of light into a fiber optic cable and measures the backscattered light and reflections, it samples the returning light signal at regular intervals along the fiber's length. The spacing between these sampling points is the sampling resolution.

A finer sampling resolution means that there are more data points measured per unit length of fiber, providing higher detail and precision in the OTDR trace. This allows the OTDR to detect and analyze smaller features such as closely spaced events like splices, connectors, or bends, and accurately measure loss over short distances.

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