Ultra-Long-Distance Interferometric DOFS Over 300 km Without In-Line Repeater

An interferometric distributed optical fiber sensing system with a sensing range over 300 km is proposed. This system employs Raman fiber amplifier with bidirectional pumping in conjunction with a bidirectional EDFA, without the use of in-line relay amplifier. Through an analysis of the interference light transmission within the system, the minimum SNR required to effectively demodulate the phase is determined, and the corresponding sensing fiber loss is experimentally quantified. By utilizing ultra-low-loss G654E single mode fiber, the system can achieve high-performance sensing without signal degradation within the 300 km range, and the positioning error is less than 8 m. To the best of our knowledge, this is currently the longest distributed optical fiber sensing system without in-line repeater. The system offers potential applications in fields such as perimeter security and submarine cable monitoring.