Study On The Technique Of Synchronously Suppressing Polarization-induced-fading And Crosstalk In Fiber Bragg Grating Time Division Multiplexing Sensing System

As fiber Bragg grating?FBG?hydrophone array based on matched interference has the advantages of high sensitivity,simple structure,small volume,light weight and so on,It has become the most potential new generation underwater acoustic detection system.Both polarization-induced-fading and crosstalk are the key technical problems that constraint the time-division multiplexing?TDM?number and system detection performance.In domestic research,the low level of the crosstalk and polarization independence were realized by the FBG sensor system with 8-TDM which used the ultra-weak?<1%?FBGs and polarization switching method.But low light power make the scheme difficult to apply to long-distance and large-scale FBG sensor system.The thesis has mainly studied the technical proposal that synchronously eliminates the polarization-induced-fading and crosstalk in high-reflectivity FBG arrays.A novel scheme combining the orthogonal polarization switching method and the interference synthesis method is proposed to synchronously suppress the polarization-induced fading and crosstalk in FBG arrays with 2-TDM channels.The main results and innovation points are as follows:1.The crosstalk interference in single-mode FBG arrays with 2-TDM channels is analyzed.The analytical results show that the influence of the polarization perturbation of has exactly the same effect on the crosstalk interference in channel 2 and the main interference in channel 1,which provides the theories foundation for applying the crosstalk synthesis to suppress the crosstalk.2.The crosstalk suppression effect with arbitrary polarization state in the high-reflectivity FBG sensor system by using crosstalk synthesis method is verified through experiment.The crosstalk in channel 2 can reach-40 dB in the 2-TDM system with the FBG reflectivity of 5%.3.The scheme of combining the orthogonal polarization switching method and crosstalk reconstruction method is creatively proposed to synchronously suppress the polarization-induced-fading and the crosstalk.The crosstalk level of lower than-50 dB was achieved for the 2-TDM sensor array with the FBG reflectivity of 5%.The background noise of channel 1 and channel 2 could reach-97.58dB/ Hz^1/2 @1kHz and-101.82dB/ Hz^1/2 respectively and maintain at the lowest level of the 4 polarization channels.