An Optical Time Domain Reflectometer (OTDR) injects optical pulses into fiber optic cables and measures the light that is scattered or reflected back to characterize the cable. It can measure the distance, loss, and other properties of fusion splices, connectors, bends, and other components in the cable. An OTDR is used to test the integrity of fiber optic cables and diagnose problems.

1. The Optical Time Domain Reflectometer (OTDR) is useful for testing the integrity of fiber optic
cables.An optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to
characterize an optical fiber. An OTDR is the optical equivalent of an electronic time domain
reflectometer. It injects a series of optical pulses into the fiber under test. It also extracts, from the same
end of the fiber, light that is scattered (Rayleigh backscatter) or reflected back from points along the
fiber. The strength of the return pulses is measured and integrated as a function of time, and plotted as a
function of fiber length.
Using an OTDR, we can:
1. Measure the distance to a fusion splice, mechanical splice, connector, or significant bend in the
fiber.
2. Measure the loss across a fusion splice, mechanical splice, connector, or significant bend in the
fiber.
3. Measure the intrinsic loss due to mode-field diameter variations between two pieces of single-mode
optical fiber connected by a splice or connector.
4. Determine the relative amount of offset and bending loss at a splice or connector joining two
single-mode fibers.
5. Determine the physical offset at a splice or connector joining two pieces of single-mode fiber, when
bending loss is insignificant.
6. Measure the optical return loss of discrete components, such as mechanical splices and connectors.
7. Measure the integrated return loss of a complete fiber-optic system.
8. Measure a fiber’s linearity, monitoring for such things as local mode-field pinch-off.
9. Measure the fiber slope, or fiber attenuation (typically expressed in dB/km).
10. Measure the link loss, or end-to-end loss of the fiber network.
11. Measure the relative numerical apertures of two fibers.
12. Make rudimentary measurements of a fiber’s chromatic dispersion.
13. Measure polarization mode dispersion.
14. Estimate the impact of reflections on transmitters and receivers in a fiber-optic system.
15. Provide active monitoring on live fiber-optic systems.
16. Compare previously installed waveforms to current traces.