Cross-sectional Structure Reconstruction And Dispersion Study Of Photonic Crystal Fiber Based On Image Processing

With the development and research of photonic crystal fiber(PCF),photonic crystal fiber with special structure and flexibility is more and more widely used.It becomes a highlight of the modem science research that evaluating real optical properties for practical PCFs.According to the disadvantage of photonic crystal fiber that imposed by the irregularity of the fiber cross section,the reconstruction of optical fiber cross-section structure is mainly carried out.Based on image processing,this thesis handles the scanning electron microscopy(SEM)image of the PCF cross-section.And the geometry of fiber is extracted as model of measuring its property.Then,the dispersion properties of photonic crystal fibers is simulated by finite element method on COMSOL multiphysics.It improves the accuracy of the photonic crystal optical properties evaluation.This thesis mainly reconstructs the structure of photonic crystal fiber by image processing algorithm.And the key to accurate modeling is the recognition and accurate extraction of the fiber cross-section image.Firstly,it handles the SEM image of a real photonic crystal fiber by median filter and threshold segmentation algorithm to eliminate the false information.Then the classical Canny operator is used to detect the edge,the improved sub-pixel algorithm is applied to filter the accurate edge information and locate the edge of the PCF cross-section image precisely.Secondly,the improved least squares method based on Random sampling consensus(RANSAC)algorithm is used to fit the feature points of the image.Namely,the RANSAC algorithm screens the extracted image feature points,eliminating feature points with larger error in geometric structure model and handling by improved least-square fitting operations.Then it can obtain the elliptic accurately.Finally,a concentric circle ellipse detection algorithm based on the Hough transform is introduced.The cross-section structure can be well identified and extracted using this algorithm.Then the optimal fiber model is established.It is the dispersion properties of photonic crystal fibers(PCF)simulation that using the obtained reconstruction model of the PCF cross-section by the finite element method combined with the image processing on COMSOL multiphysics.The error of the calculation results is analyzed at the same time.By this means,the structure of an actual photonic crystal fiber product SEM image is reconstructed and its dispersion property is analyzed.And the data calculation results accord with the product parameters.