Improving Spatial Resolution of Chaos OTDR Using Significant-Bit Correlation Detection

Chaos optical time-domain reflectometry (chaos OTDR) has an advantage of high spatial resolution without tradeoff of measure distance by utilizing correlation detection based on broadband chaotic laser. However, achieving a high spatial resolution usually requires a wideband photodetector and a high-speed data acquisition card. In this letter, we propose a significant-bit correlation method to improve spatial resolution of the chaos OTDR instead of increasing hardware bandwidth. In this method, the reference and echo chaotic signals are quantized with multi-bit analog-to-digital converter (ADC), and some least significant bits (LSBs) are extracted to construct new time series for calculating cross correlation. Our experimental results demonstrate that the spatial resolution is significantly enhanced as the number of LSBs decreases. Under a detection bandwidth of 200 MHz, the spatial resolution is approximately improved five times from 21 cm to 4 cm with 6-LSBs correlation. The improvement of spatial resolution is attributed to bandwidth enhancement caused by the LSBs' extraction.