Coherent Rayleigh Backscatter Phase Noise in Digitally Enhanced Fiber Interferometers

The coupling of Rayleigh backscatter induced phase noise in bi-directional, inline fiber interferometers compromises detection sensitivity for Fourier frequencies less than 1 Hz. Here we report experimental and theoretical work highlighting the coupling of backscatter phase noise, and its subsequent range-gating and suppression using Digitally Enhanced Homodyne Interferometry. Between two in-line fiber interferometers, each with a differential arm-length of 8 km, we demonstrate a relative stability of $10 Hz\sqrt Hz$ at a Fourier frequency of 100 mHz.