Enhancing the Effect of Nonlinear Frequency Sweep Correction in OFDR With Improved Reference Frequency

Abstract

Correcting the nonlinear frequency sweep of the tunable laser source in optical frequency domain reflectometry (OFDR) is critical for accurate measurement. It is common to correct the nonlinear frequency sweep by adding an unbalanced auxiliary interferometer in the OFDR system. However, there is a contradiction between the delay length of the auxiliary interferometer and the correction effect. A short delay length is beneficial for capturing the instantaneous frequency deviation, but it degrades the correction effect due to the low beat frequency. A longer path difference provides more references for the correction, whereas worsens the correction effect due to larger noise. This paper proposes a method introducing an acousto-optic modulator as the frequency shifter in the auxiliary interferometer, which can generate a larger beat frequency with a short delay length. With a matched signal processing method, the contradiction between the delay length and the correction effect is effectively relaxed. This method can be combined with many correction methods to improve their effects further. In experiments, the spatial resolutions and robustness for different correction methods are all improved with the proposed method. It demonstrates a wide-range effect in the promotion of OFDR technique.