57-km single-ended spontaneous Brillouin-based distributed fiber temperature sensor using microwave coherent detection.

We present a novel technique for performing single-ended distributed fiber temperature measurements by use of microwave heterodyne detection of spontaneous Brillouin scattering. Brillouin frequency-shift measurements were obtained for a sensing length of 57 km, with a spatial resolution of 20 m. The rms error in frequency measurements at the far end of the sensing fiber was less than 3 MHz, and the overall frequency dependence on temperature was 1.07+/-0.06 MHz/K.