  A direct-detection Brillouin optical time-domain reflectometry (BOTDR) is
proposed and demonstrated by using an up-conversion single-photon detector and
a fiber Fabry-Perot scanning interferometer (FFP-SI). Taking advantage of high
signal-to-noise ratio of the detector and high spectrum resolution of the
FFP-SI, the Brillouin spectrum along a polarization maintaining fiber (PMF) is
recorded on a multiscaler with a small data size directly. In contrast with
conventional BOTDR adopting coherent detection, photon-counting BOTDR is
simpler in structure and easier in data processing. In the demonstration
experiment, characteristic parameters of the Brillouin spectrum including its
power, spectral width and frequency center are analyzed simultaneously along a
10 km PMF at different temperature and stain conditions.
