Spatial Resolution Enhancement of OFDR Sensing System Using Phase-Domain-Interpolation Resampling Method

The expected spatial resolution of the optical frequency domain reflectometry (OFDR) system is hugely degraded by nonlinearity in the lightwave-frequency sweep of the tunable laser source (TLS). We proposed a phase-domain-interpolation-based resampling (PDIR) method to solve this problem, which significantly enhances the spatial resolution. Due to the corresponding relationship between the phase of the beat signal generated from the auxiliary interferometer and sweeping time, the Hilbert transformation was used to obtain the instantaneous phase of the beat signal for coordinate transformation. Theoretical analysis shows that the tuning frequency rate of the TLS is approximately proportional to its phase variation. So the PDIR method can implement even-phase interpolation directly on the beat signal waveform in the new coordinate system. The relationship between the spatial resolution and the interpolation interval was investigated, which guides the choice of the optimum interpolation interval. To verify the feasibility and accuracy of the PDIR approach, we carried out experiments on an OFDR system. A spatial resolution of around 0.15 mm over a 302 m single-mode fiber was achieved with our proposed method. Compared with conventional compensation methods, PDIR possesses a better nonlinearity compensation adequate. Besides, the proposed method is also convenient to operate by interpolating in the phase domain directly.