Experimental investigation of a method based on synchronous frequency hopping of an optical source for fading noise suppression in a coherent optical time-domain reflectometer

Subject of study. This paper presents the results of an experimental study of a method based on synchronous frequency hopping of an optical source for fading noise suppression in a coherent optical time-domain reflectometer. Aim of study. The aim of the study is to reduce the measurement error of a coherent reflectometer using the method of synchronous frequency hopping of the optical source. The optimal frequency-hopping step and period are determined to ensure the maximum suppression of fading noise in reflectograms obtained by optical reflectometry. Method. For the experimental investigation of the proposed method, frequency hopping of the optical source with an adjustable step, synchronized with the repetition rate of the optical pulses launched into the fiber under test, was implemented in a coherent optical time-domain reflectometer. As a criterion for evaluating the efficiency of the method, the standard deviation of reflectograms, relative to the trend of optical losses in the fiber under test, was used in the interferometric measurements. Main results. The experimental results demonstrate that the proposed method based on the synchronous frequency hopping of the optical source reduces the measurement error in the Rayleigh backscattering power by up to 8.8 times for optical pulse durations ranging from 1 µs to 100 µs. In addition, upon increasing the reflectogram acquisition period from 1.5 ms to 1 s, the fading noise level of the coherent reflectometer decreases, and the measurement error in the Rayleigh backscattering power decreases by up to 5.8 times at a pulse duration of 10 µs. Practical significance. The obtained results enable the formulation of requirements for the frequency-hopping step and period of the frequency-hopping cycle of an optical source to ensure minimum fading noise and measurement error in a coherent optical time-domain reflectometer.