Research On Fringe-Distortion-Correction Algorithm And Fast Demodulation System Of Low-Coherence Interferometry For Fibre-Optic Fabry-PéRot Sensing

Low coherence interference(LCI)technology is an efficient method for measuring absolute displacement and is widely applied into three-dimensional profiling,optical coherence tomography and optical fiber sensing.As an important LCI system with high precision,resolution,stability and speed,the polarized low-coherence interferometry(PLCI)system has gradually become an important research direction.Distortion-free interference fringe signal with high signal noise ratio(SNR)is expected for high-precision measurement.However,the combined effect of the spectrum emitted by white light LED and the birefringence dispersion in the PLCI system will lead to severe fringe distortion and result in inevitable errors in the demodulation.We have studied the influence of dispersion and proposed a fringe distortion correction algorithm based on spatial frequency domain nonlinear effects,which can effectively eliminate the fringe distortion.And we extend this algorithm to the application of white LED light source where the spectrum contains multiple Gaussian-like peaks.Finally,we have further optimized the performance of the demodulation system,designed and built a fast demodulation system and carried out experimental verification.The specific research contents of this paper include:1)Based on the dispersion formula in the visible range,a mathematical model of the low coherence interference fringe signal with the birefringence dispersion is established,and the influence of the dispersion on interference fringe is analyzed.On this basis,a fringe distortion correction algorithm based on spatial frequency domain nonlinear effect is proposed,which can greatly reduce the distortion of the interference fringe.Then this algorithm is extended to the application of white LED light source with multiple Gaussian-like spectral peaks and realized the fringe distortion correction of the complex spectral light source.2)The proposed algorithm is verified by the simulation and the actual pressure experiment.The experimental result shows that this algorithm can effectively eliminate the distortion of interference fringe in the pressure range of 3～230k Pa,so that the envelope peak and the zero-order peak coincide.The demodulation accuracy is improved with the error less than 0.06 k Pa.3)We perform a performance optimization on the PLCI system.Based on the large core fiber and fast CCD camera,a fast demodulation system is built and the corresponding demodulation software is designed.Finally,the experimental verification of the fast demodulation system are carried out.The experimental results show that the demodulation and sampling speed can achieve 429.18 Hz,which has a leap in the demodulation and sampling speed.