Spectral analysis of a sampling optical time-domain reflectometer

A spectral analysis is presented for the backscatter signal of optical time-domain reflectometers (OTDR). Periodic spatial fluctuations in the fiber attenuation produce modulation sidebands in the frequency spectrum of the backscatter signal. Applying the sampling technique to OTDR leads to a considerable improvement of the signal-to-noise ratio (S/N) due to spectrum compression, as a tradeoff with the measurement time. It gives a performance equivalent to digital averaging. Design examples are given at wavelengths of 0.85, 1.3, and 1.55 μm. A practical setup of a sampling OTDR is described