φ-OTDR Based on Orthogonal Frequency-Division Multiplexing Time Sequence Pulse Modulation

This study introduces an innovative phase-sensitive optical time-domain reflectometer (φ-OTDR) technology based on orthogonal frequency-division multiplexing (OFDM) and nonlinear frequency modulation (NLFM) pulse modulation sequences. The proposed approach addresses the inherent trade-offs among spatial resolution, frequency response range, and sensing distance that conventional φ-OTDR systems encounter. This method optimizes spatial resolution and sensing distance by modulating both the frequency and phase of optical pulses. Moreover, it enhances sidelobe suppression by adjusting the nonlinearity of frequency modulation, reducing interference between adjacent signals, and improving the signal-to-noise ratio (SNR). Additionally, orthogonal frequency-division multiplexing expands the frequency response range. This paper elucidates the fundamental principles and implementation of OFDM-NLFM time-domain pulse modulation techniques and designs, experimentally validates a φ-OTDR system based on this method, and conducts comprehensive testing and analysis of the system’s performance. The experimental results demonstrate that the proposed φ-OTDR system achieves an 11 m spatial resolution and a frequency response range of 1–10 kHz over a 16.3 km optical fiber, utilizing a 65 MHz frequency bandwidth with multiplexed signals across four frequencies. This innovative approach reduces hardware resource consumption, opening up promising prospects for various practical engineering applications in optical fiber sensing technology.