Development and investigation of the suppressing additive noises methods in fiber-optic interferometric sensors

The results of the investigation and develop of the suppressing additive noise methods in fiber-optic interferometric sensors, in which optical scheme is based on a two-beam Michelson interferometer, are presented. The proposed solutions are designed to reduce the level of additive noise and to increase the signal-to-noise ratio in the fiber-optic interferometric sensor phase signal. The first proposed method assumes the insertion of an additional photodetector into the optical scheme of the sensor, which allows simultaneous registration of the same interference signal twice. In the optical scheme of the second proposed method, an additional fiber delay line is included, which allows to interrogate the same sensor twice. Mathematical analysis based on the coherent averaging of signals is applied for the suppressing of the additive noises. Coherent averaging of signals allows, without changing the useful component of the phase signal, to reduce the additive noise level by the value which is proportional to the square root of the averaged signals number. The experimental study of the proposed suppressing additive noise methods presented a decrease of the noise level by factor of 1.4 and an increase of the signal-to-noise ratio on an average by 2.87 dB in the frequency range from 250 to 2250 Hz in the phase signal of the fiber-optic interferometric sensor. The proposed methods of the suppressing additive noise can be used to increase the signal-to-noise ratio in fiber-optic measuring systems based on the interferometric sensors arrays, such as fiber-optic towed and bottom seismic streamers, perimeter security systems, fiber-optic navigation systems and complexes.