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An ultra-long-distance Fiber Bragg Grating (FBG) sensor system using a high-speed swept-wavelength light source (HSLS) is proposed and demonstrated. The light output of the HSLS is amplified and turned on and off, and its timing is synchronized to the sweep signal of the HSLS to reduce optical noise caused by Rayleigh scattering from the transmission fiber. This system can detect changes in FBG reflection wavelengths even when the FBGs are located at a distance of 230 km.

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We present coherent OTDR employing frequency division multiplexing and frequency demultiplexing by software processing. We improved a 5-dB dynamic range against conventional coherent OTDR, and achieved a 100-dB dynamic range with 2 18 measurements at a 1-km spatial resolution.

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