Optical time-domain reflectometer

The optical time domain reflectometry, also known by the English name - Optical Time-Domain Reflectometry - OTDR is a method for the identification and analysis of run lengths and reflection characteristics of electromagnetic waves and signals in the wavelength range of the light.

In practice, the field of optical time domain reflectometry, especially in the networking and telecommunications plays an increasingly important role. The OTDR is a direct development of time domain reflectometry, which has its roots in the beginning of radar technology in the 1930s.

The procedure

In the optical time domain reflectometry, a laser pulse duration of 3 microseconds to 20 nanoseconds is coupled into an optical fiber and the backscattered light is measured over time.

From the logarithmically plotted backscatter intensity then the losses of splices on the track and reflections from connectors as well as the attenuation of the fiber (in dB / km) can be determined. The measured signal has a time dependence that can be converted on the group velocity vg in a spatial dependence. Thus, a spatially resolved attenuation measurement can be realized. In varying fishing factors S and changing scattering coefficient α can cause a misinterpretation of the measured signal. This can be compensated by a second measurement at the other end of the fiber and the average of the measured results.

A detailed description of the ( electrical ) process can be found under Time Domain Reflectometry.

• Optical Metrology
• Dimensional Metrology
• Optical Communications