Enhancing performance of coherent OTDR systems with polarization diversity complementary codes

Monitoring the optical phase change over a fiber paves the way for a wide range of applications that induce fast strain variations as detection of vibration and acoustic signals. However, the quality of the estimated fiber channel response strongly depends on the method used to optically excite the optical fiber sensor and capture the optical field variations. In this paper, we show that distributed optical fiber sensing systems can advantageously exploit techniques from the telecommunication domain, as those used in coherent optical transmissions, to enhance their performance in detecting mechanical events, while jointly offering a much simpler setup than widespread pulse-cloning or spectral-sweep based schemes with acousto-optic modulators. In this paper, we periodically capture an overall fiber Jones matrix estimate thanks to a novel probing technique using two mutually orthogonal complementary pairs of binary sequences applied simultaneously in phase and quadrature on two orthogonal polarization states. A perfect channel response estimation of the sensor array is achieved, subject to conditions detailed in the paper, thus enhancing the sensitivity and bandwidth of coherent $phi$-OTDR systems.