Characteristics and reduction of coherent fading noise in Rayleighbackscattering measurement for optical fibers and components

The characteristics of fading noise in Rayleigh backscattering measurements made with coherent lightwaves such as in coherent-OTDR (optical time-domain reflectometry) and coherent-OFDR (optical frequency-domain reflectometry) are studied. The effects of frequency shift averaging on fading noise reduction are clarified theoretically, and the relationships between measurement accuracy and other parameters, such as spatial resolution and frequency variation range are derived. The calculated results of loss measurement accuracy are in good agreement with experimental data. The formula can also be applied to low-coherence interferometric OTDR