Abstract: We present and demonstrate a technique for remote sensing of fiber Bragg gratings (FBGs) beyond 150 km. The system combines Raman, Brillouin, and erbium gain in a linear cavity fiber laser and deploys a novel heterodyne detection technique to avoid the signal-to-noise ratio limitations produced by Rayleigh scattering. Two FBGs located in series were interrogated at 155 km away from the processing unit using 0.6 W of Raman pump and less than 2 mW of Brillouin pump provided by a tunable wavelength-swept laser. Heterodyne detection brings forth a signal-to-noise ratio of approximately 10 dB in our measurements.

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