Long-range, phase-and-polarization diversity coherent reflectometer

A coherent, short-length reference arm reflectometer, which utilizes a 76-MHz repetition rate mode-locked fiber laser, was investigated experimentally for long fiber links (> 10 km). The reflectometer combines the advantages of optical time-domain and frequency-domain reflectometry without the need for high-speed photodetectors and electronics to achieve high spatial resolution of 2.5 mm at 10 km. To our knowledge, this is the highest resolution reported for fiber reflectometry at this distance for reflective type event using non-photon-counting detection. Phase and polarization diversity detection, combined with spectral compression using frequency-chirp, are proposed to improve sensitivity and discrimination against the fiber Rayleigh backscattering background.