Suppression of double Rayleigh scattering-induced excess noise in remotely interrogated fiber-optic interferometric sensors

This letter describes experimental observations of excess noise due to coherent double Rayleigh scattering in the input fiber of a remotely interrogated fiber-optic interferometric sensor. This noise source is generally only observable when a high coherence length laser is used to interrogate the sensor and the fiber length connecting the sensor is in excess of /spl sim/10 km. We present a simplified model to explain how this noise source affects the sensor resolution and demonstrate a method based on laser source modulation to reduce this noise by /spl sim/20 dB in a fiber-optic Michelson interferometric sensor with a 25-km input fiber, at frequencies less than 10 kHz.