Optical Frequency-Domain Reflectometry for Distributed Sensing Using Laser Current Modulation With Optical Saturation and Phase Cross-Correlation

Abstract

We propose and experimentally demonstrate an optical frequency-domain reflectometry (OFDR) scheme for distributed sensing that combines direct current modulation of a telecom-grade distributed feedback laser with optical power equalization via saturable optical amplifier dynamics and phase-correlation processing. The approach enables wideband frequency sweeps of 210 GHz within millisecond time scales, achieving sub-millimeter OFDR spatial resolution in a compact and cost-effective architecture. Such high-resolution operation requires large current excursions, which induce significant optical power variations throughout the sweep. To mitigate this effect, a semiconductor optical amplifier operated in a controlled saturation regime is used to flatten the optical power profile during the sweep, thereby improving the signal uniformity without altering the laser frequency evolution. In addition, a phase-correlation algorithm is introduced to remove amplitude-induced bias in the cross-correlation used for sensing, improving the reliability of frequency-shift estimations for temperature and strain measurements. Experimental results, supported by a statistical analysis of outliers (defined as deviations over ±1.5 °C from a reference), show that the combined use of optical power equalization and phase correlation significantly enhances robustness and reduces large estimation errors. These results provide a practical pathway toward high-resolution, low-cost distributed OFDR sensing and are applicable to a broad class of swept-source and frequency-agile reflectometry systems.