Abstract: An on-line Sagnac interferometric distributed fiber-optic leakage detection device comprising a light generator, an optical fiber coupler, a hollow pipeline, a Faraday rotator mirror, a sensing optical fiber, a delaying optical fiber, a photo detection device and a spectrum analyzer. Signals resulting from a leaky pipeline are obtained by the linear leakage detection system. The signals are analyzed by the spectrum analyzer to discover any null frequency shift so that exact location of the leakage point along the hollow pipeline can be computed.

Abstract: A polarization-insensitive fiber-optic interferometric sensor system has an erbium-doped fiber amplifier (EDFA) at a location between a light source and a sensing array to serve as a post amplifier. An output end of the sensing array is coupled to another EDFA, and further coupled to a receiver, in which this another EDFA is used as an in-line amplifier. As the sensor system is applied for a light source with multiple wavelengths, a dense wavelength division multiplexers (DWDMs) is used to combine the multiple wavelengths into one for amplification, and another DWDM is used to decouple the multiple wavelengths.

Abstract: An on-line Sagnac interferometric distributed fiber-optic leakage detection device comprising a light generator, an optical fiber coupler, a hollow pipeline, a Faraday rotator mirror, a sensing optical fiber, a delaying optical fiber, a photo detection device and a spectrum analyzer. Signals resulting from a leaky pipeline are obtained by the linear leakage detection system. The signals are analyzed by the spectrum analyzer to discover any null frequency shift so that exact location of the leakage point along the hollow pipeline can be computed.

Abstract: This invention concerns with a time-division multiplexing system of polarization-insensitive Michelson interferometric fiber optic sensors, where the compensating interferometer is equipped with a 3.times.3 coupler. It uses the two reflections from the Faraday rotator mirrors of sensor interferometer and compensating interferometer, respectively, in a totally passive manner, to overcome the polarization-induced signal fading in the multiplexing sensor system. The compensating interferometer with matching optical paths is used to reduce the phase-induced intensity noise, at the same time it allows the use of laser source with proper coherence length to reduce the crosstalk between sensors and the crosstalk caused by Rayleigh scattering. This system allows the use of low-loss conventional single-mode optic fiber as lead fiber, and offers advantages in building the fiber optic sensor array system with long-distance lead fiber.