Method for compensating the constant component of noise in the reflectogram of a fiber-optic communication line under conditions of insufficient dynamic range of an optical backscatter reflectometer in the time domain

A method for compensating for the constant noise component of reflectograms for a coherent optical backscatter reflectometer in the time domain is proposed. The presented solution ensures correct visualization of reflectograms, improves their readability and allows recording weak reflected signals from a fiber communication line. The experimental testing of the method was carried out on a working sample of a coherent optical reflectometer. To compensate for the constant component of reflectogram noise, it is proposed to record the noise signal from the input path of the reflectometer immediately before sending the optical probing signal to the communication line. The data obtained in this way do not contain a useful signal from the connection line. In this case, the data can be used to determine the constant component of the noise level by calculating its root mean square value. Compensation for the constant noise level is performed by subtracting the constant component of the noise from the data of the entire reflectogram. The described method was tested on a working sample of a coherent optical reflectometer developed at the Light-Guided Photonics Research Center of ITMO University. The technique was tested on two test fiber lines: a 200-km-long optical fiber and a 300-km-long line with three optical amplifiers. It was shown that the application of the technique allows to significantly expand the dynamic range of signals presented on reflectograms by more than 10 dB and to increase the distinguishability of weak signals at the noise level of the device. The practical significance of the work lies in the possibility of compensating for the constant component of noise in the reflectogram of a fiber-optic communication line with optical amplifiers without calibrations and preliminary settings of the coherent optical reflectometer.