Ultra-High Resolution ϕ-OFDR Strain Sensor Based on BEOF and PMC-OPC Scheme

Distributed optical fiber sensor based on optical frequency domain reflectometer (OFDR) preserves its dominant position in strain measurement fields with high sensitivity, spatial resolution. However, the cross-correlation based frequency-OFDR will degrade the spatial resolution due to the calculation of adding window. The advent of phase-OFDR has significantly alleviated this issue, but it is more susceptible to phase noise. In this paper, the position mismatch compensation-outlier phase correction (PMC-OPC) scheme combined with the backscattering enhanced optical fiber (BEOF) is proposed to address the phase noise problem. The BEOF with high intensity and phase signal-to-noise ratios (SNRs) facilitates the expansion of the strain detection range and the suppression of the phase fading noise. Additionally, it is utilized to identify positional offset on the basis of its distinctive periodicity characteristics. The PMC-OPC approach is employed to address the position mismatch, phase hopping, and random nonlinear phase noise. In the experiments, the high-resolution distributed strain measurement is simultaneously achieved with the theoretical spatial and strain resolutions of 40 μm and 21.05 nϵ under the conditions of 20 nm sweeping range, 25 dB BEOF intensity enhancement, and the strain measurement range of 3600 μϵ. Furthermore, the actual sensing spatial and strain resolutions are measured to be 23.2 mm and 4 μϵ, respectively. The proposed approach not only enables the positioning resolution to reach the theoretical limit of the OFDR system within the given sweep range, but also mitigates the inherent trade-off between the spatial resolution and strain resolution.