Abstract
In this paper, the results of simulation and experimental investigation of interferometric optical fiber acoustic sensing are primarily presented, and the main area of interest is studying the different algorithms for enhancement of sensor sensitivity. In fact, when light propagates through optical fiber, in a Michelson interferometer, the phase of light changes due to effect of external perturbation as acoustic wave on optical path length and this phase change is detected by demodulation algorithm. It is strived to present the Phase Generated Carrier (PGC) demodulation algorithm based on Differential-Cross-Multiplying (DCM), Arctangentfunction (ATAN) and ATAN based on Coordinate Rotation Digital Computer CORDIC algorithm. Simulation results reveal that PGC demodulation method based on ATAN CORDIC algorithm has better result (signal to noise ratio) than DCM and ATAN without using CORDIC algorithm. On this account, PGC demodulation algorithm based on ATAN method with CORDIC algorithm is applied in the experimental investigation due to simulation results and simpler digital implementation on Field Programmable Gate Array (FPGA). Moreover, acoustic frequency is detected as sidebands of harmonics of phase modulator frequencies. The sensitivity of digital circuit is 5μradHz-0.5 and the minimum detectable phase is 50μrad Acoustic frequency is detected as sidebands of harmonics of phase modulator frequencies, and consequently, the system allows detecting the sinusoidal acoustic wave with different frequencies. It is also detected acoustic frequency by measurement of the reflected optical power. Moreover, in this part, it is packaged sensing arm of interferometer with polymer material (polyurethane) for investigation the effect of polymer on sensitivity enhancement of sensor. It is observed with applying of acoustic wave, the reflected optical power decreases and this reduction is more, when sensing arm is packaged with polymer.
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