Distributed Vibration Sensing Using a 3 MHz linewidth DFB laser over 55.9 km of Weakly-Coupled Multicore Fiber Enabled by Balanced Delay Line Laser Interferometry

We propose balanced delay line laser interferometry to effectively mitigate the signal-to-noise ratio (SNR) degradation caused by laser phase noise. For the first time, we demonstrate forward-transmission-based distributed vibration sensing using phase detection with a cost-effective 3 MHz linewidth distributed feedback (DFB) laser over 55.9 km of weakly-coupled 7-core fiber. Additionally, we show that our interferometry-based scheme can measure low-frequency vibration signals down to 149 Hz using a 3 MHz linewidth DFB laser.