Distributed fiber-optic acoustic sensing (DAS) is an effective technique for measuring dynamic strain along the optical fiber, using Rayleigh backscattering (RBS) as the sensing mechanism. DAS offers high spatial resolution, excellent sensitivity, and strong immunity to electromagnetic interference, making it suitable for applications such as traffic monitoring, seismic detection, and pipeline surveillance. However, its performance is significantly affected by the phase noise of the light source and the quantization noise introduced by the data acquisition system. In this paper, we propose a novel phase noise compensation method tailored for coherent detection and matched filtering-based φ-OTDR systems. We also investigate the influence of quantization noise on strain resolution, aiming to enhance performance while reducing hardware cost.

In this paper, we introduce a phase noise compensation method into a conventional φ-OTDR system based on coherent detection and matched filtering to enhance its performance. An auxiliary interferometer is employed to reconstruct the real-time phase of the light source. This reconstructed phase is then applied to compensate for phase noise in both the received signal and the matched filter kernel, thus improving the accuracy of pulse compression and the system’s strain measurement capabilities. A communication-grade semiconductor laser with a 100 kHz linewidth is used in the experimental setup. The strain and spatial resolutions are evaluated over an 84 km single-mode optical fiber, both with and without phase noise compensation. To assess the influence of quantization noise, the analog-to-digital (ADC) bit depth of the data acquisition system is varied from 16 bit down to 2 bit.

With phase noise compensation, the system achieves a strain resolution of 51 pε/Hz and a spatial resolution of 6.5 m at the end of an 84 km single-mode fiber using a 100 kHz linewidth laser. These results confirm the effectiveness of the compensation method in significantly enhancing long-distance strain sensing performance. Even when the ADC resolution is reduced to 8 bit, the system maintains a strain resolution of 103 pε/Hz [Fig. 5(a)], demonstrating that high sensing performance can be preserved despite lower quantization resolution. When further reduced to 2 bit, the system still delivers valid strain measurements, indicating strong robustness against quantization noise [Fig. 5(c)]. These findings suggest that the proposed method remains effective under less-than-ideal hardware conditions. Moreover, reducing the ADC resolution to 8 bit significantly lowers hardware costs without compromising sensing quality, offering a practical balance between performance and affordability.

In this paper, we investigate the influence of light source phase noise and ADC quantization noise on distributed fiber-optic acoustic sensing systems. We propose a phase noise compensation approach based on an auxiliary interferometer, and further analyze and test the relationship between the number of quantization bits in the acquisition system and the resulting strain resolution. Experimental results show that, after phase noise compensation, the system achieves a strain resolution of 51 pε/Hz and a spatial resolution of 6.5 m at the end of 84 km of single-mode fiber using a 100 kHz linewidth laser. In addition, by varying the ADC bit depth, the system maintains robust performance, achieving a strain resolution of 103 pε/Hz even with an 8-bit ADC. When the bit depth is reduced to 2 bit, although quantization noise increases, the system still provides valid strain measurements, demonstrating the robustness of the method under low-bit-depth conditions. Furthermore, it is evident that reducing the ADC bit depth to 8 bit significantly lowers hardware cost while maintaining high measurement quality. The phase noise compensation approach offers a more streamlined design compared to traditional methods that rely on narrow-linewidth lasers or complex post-processing algorithms. The results further highlight that even with reduced bit depths, the system can maintain high strain resolution (103 pε/Hz) and spatial resolution (6.5 m), validating its effectiveness in practical applications such as distributed fiber-optic sensing and environmental monitoring.