Rayleigh Fading Suppression in One-Dimensional Optical Scatters

A highly coherent wave is favorable for applications in which phase retrieval is necessary, yet a high-coherence wave is prone to encounter Rayleigh fading phenomenon as it passes through a medium of random scatters. As an exemplary case, a phase-sensitive optical time-domain reflectometry (Phi-OTDR) utilizes the coherent interference of backscattering light along a fiber to achieve ultra-sensitive acoustic sensing, but sensing locations with fading will not be functional. Apart from the sensing domain, fading is also ubiquitous in optical imaging and wireless telecommunication, and therefore, it is of great interest. In this paper, we theoretically describe and experimentally verify how the fading phenomenon in one-dimensional (1-D) optical scatters will be suppressed with an arbitrary number of independent probing channels. We initially theoretically explained why fading would cause severe noise in the demodulated phase of Phi-OTDR; then, M-degree summation of incoherent scattered light-waves is studied for the purpose of eliminating fading. Finally, the enhancement and the fluctuation of retrieved phase signal-to-noise-ratio were analytically derived and experimentally verified. This paper provides a guideline for the fading elimination in 1-D optical scatters, and it also provides insight for optical imaging and wireless telecommunication.