Theoretical and experimental estimation of the dynamic range of a coherent optical time-domain reflectometer

Subject of study. This paper introduces an original method for calculating the dynamic range of a coherent optical time-domain reflectometer. Using this method, the upper theoretical limit of the operating range of such a reflectometer can be calculated by considering the influence of the local oscillator (LO) power and the noise level of a selected balanced photodetector. Aim of study. The aim was to determine the dependence of the dynamic range of a coherent reflectometer on the optical power of the LO at a given noise level of the balanced photodetector. In addition, the limitations of this dependence in real circuits were evaluated. Method. The dynamic range was calculated for two cases: (i) for a given optical power of the LO signal and (ii) for the ideal theoretical maximum sensitivity of the balanced photodetector. The calculation results were verified based on an operating prototype of a coherent optical reflectometer; the parameters of the prototype were used in the calculations. Main results. The dependence of the dynamic range of the coherent reflectometer on the LO power was determined. For a pulse duration of 3 µs, an output optical power of 10 dBm, a reflectometer circuit loss of 11.5 dB, and an LO power of 225.9 µW, the maximum dynamic range value was 35.4 dB, which was obtained by averaging over 2 15 reflectograms. Both excess and insufficient LO optical powers reduced the dynamic range of the coherent reflectometer. Practical significance. The proposed calculation method is suitable for designing coherent reflectometers with a specified dynamic range and operating distance and for assessing the potential for further increasing the dynamic range.