High-Performance Optical Frequency-Domain Reflectometry Based on High-Order Optical Phase-Locking-Assisted Chirp Optimization

We present optical frequency-domain reflectometry with high performance in terms of an ultralong range window, high spatial resolution, and precision enabled by a high-order optical phase-locked loop (OPLL)-assisted commercial fiber laser. Due to elaborate loop designs that allow matching with the nonlinear frequency modulation response of the laser, the potential tuning capability can be fully exploited, leading to efficient optimization of the frequency chirp range and rate in addition to chirp linearization and an enhancement of the dynamic coherence. A nearly Fourier-transform-limited spatial resolution is realized over multiples of the intrinsic coherence length. Practically, a cm-level spatial resolution is demonstrated along the entire fiber link. We achieved a spatial resolution of ~3.2 cm and ~4.3 cm for backscatter no more than 130 km and reflections at 242 km, respectively, corresponding to a high range resolution factor of up to 1.78 × 10
^-7
in the latter case. The precision of the backscatter measurement is verified to be at least 0.5 dB throughout the entire measurement range. Moreover, the limiting factors resulting in a degeneration of the spatial resolution are carefully investigated. The proposed approach can be readily applied to other lasers, offering a powerful tool for a variety of applications.