Optical-pulse-coding phase-sensitive OTDR with mismatched filtering

Optical-pulse-coding (OPC) phase-sensitive optical time-domain reflectometry (Φ-OTDR) sends a train of pulses into a fiber, and has high spatial resolution decided by the duration of a subpulse while achieving signal-to-noise ratio (SNR) enhancement. OPC Φ-OTDR with a shorter measurement time is favorable. However, the scan rate, which is the reciprocal of the measurement time, is not easy to optimize. In this paper, mismatched filtering is introduced into OPC Φ-OTDR for the first time, which can reach the theoretical limit of scan rate determined by the fiber length. Also, the initial phase of each subpulse can be set arbitrarily, showing the capacity for controlling the location of interference fading. Although the design of the mismatched filter is based on the least-squares criterion, satisfactory decoding results are obtained, indicating that more advanced mismatched filter designs are worthy of further investigation to achieve higher performance.