Research On Noise Suppression And Error Correction In OCDP

As an effective technique with high accuracy to measure and evaluate the characteristics of polarization in high-birefringence polarization-maintaining fiber and multifunctional integrated optic chip(MFIOC),the Optical Coherence Domain Polarimetry(OCDP)based on white-light interference is a versatile tool which can completely and independently control the quality of the reciprocity of the fiber optic gyros and its components.The OCDP distinguishes and localizes the crosstalk by scanning optical path with a scanning optical delay line.However,the drawback of the mechanical translating stage in the optical delay line leads to a not constant scan speed.The interference signal will keep an unequal interval optical path due to the scan error.In another word,there will be a phase modulation term added to the ideal interference signal,which influences the uniformity of the interference fringes,extends the signal bandwidth and produces some side-band peaks.Consequently,it is difficult to implement signal processing and dispersion compensation algorithm.The sensitivity and accuracy of the OCDP will be affected.Based on previous work about white-light interference measurement of our lab,this dissertation researched on the correction method of the speed variation resulted from the mechanical translating stage.With the photoelectric noise was analyzed and suppressed,we achieved the OCDP system with optical path error correction.After the instrumental performance was tested,we used this OCDP system to measure the MOFIC and the polarization-maintaining fiber rings.The main contents of the dissertation are as follows.Firstly,according to white-light interference theory,this dissertation introduced the measurement principle of the polarization crosstalk using OCDP system,and analyzed the influence of scanning error to interference signal.Secondly,we used Uniform time-sampling Fourier Transform Spectroscopy(UTSFTS)algorithm to resample the simulation signal and the experimental interference signal,which was to verify the effectiveness of resampling.Based on the work that the key problem for the implementation of the resampling correction algorithm was discussed,we finished the system software with resample and demodulation function and acquired perfect signal which is sampled by uniform optical path interval.Thirdly,we built a Mach-Zehnder interferometer using a 3×3 coupler with a 1310 nm high coherence light source and a 1550 nm low coherence light source injected into the interferometer together.Because the laser interference fringes record the speed variation within scan range,the algorithm uses one laser interference signal as the reference signal to resample the interference signal produced by two different lights and implement uniformity correction.At the same time,the system utilizes the corrected laser interference signal to measure the scan distance.Eventually,we analyzed the photoelectric noise of the system and suppressed circuit noise,noise power spectral density of the photoelectric detection circuit is-139.4dB/Hz.According to the requirements of the system,we constructed the OCDP system with optical path error correction including optics,circuit,signal processing and scanning control software.Above all,it is experimentally demonstrated that the OCDP system with optical path error correction obtained the polarization crosstalk sensitivity and dynamic range which are better than-90 dB and 90 dB,respectively,when the scan speed of the optical path is 12mm/s.Furthermore,the optical scanning position accuracy can reach 1?m.By measuring the Y waveguide repeatedly,polarization extinction ratio measurement accuracy is better than 0.5dB.