Abstract. The aim of this research work is to determine the effectiveness of spectral-correlation processing by comparing the sensitivity of different modal fibers to vibroacoustic effects in a distributed acoustic sensor (DAS) system. Single-mode (SMF, ITU-T G.652) and specially doped low-mode (FMF 21/125, 5-LP-modal, GeO₂-based) optical fibers were taken as the object of research. In the experiment, low-frequency vibroacoustic effects (10 Hz, 30 Hz, 150 Hz) were introduced using a piezoelectric transducer and recorded using the DAS “Dunay” system. The same conditions were created for SMF and FMF fibers. At a frequency of 150 Hz, the sensitivity to vibration for FMF was 8.5% higher, and at 30 Hz – 7.9%. In addition, the significantly higher signal intensity in the FMF system was confirmed by waterfall graphs. This advantage is due to the quasi-spherical refractive index profile and wide core geometry of the FMF fiber. In addition, it was shown that the combination of LP01 and LP11a modes, although it causes intermodal interference, can be solved by temporal correction methods. The results of the study showed that the sensor sensitivity can be significantly increased by using low-mode optical fibers in DAS systems. Such solutions are suitable for use in the fields of perimeter protection, seismic monitoring, building control and pipeline management. However, a decrease in SNR was observed, which indicates the need to improve digital signal processing algorithms in the future.

Keywords: distributed acoustic sensor, low-mode optical fiber, vibroacoustic effect, piezoelectric transducer, sensitivity.