Locating method in fusion splicing process for photonic crystal fiber using nonlinear data fitting and cross-reference

Locating problem is very important in fusion splicing process for the center axes of the core of photonic crystal fibers(PCFs) due to structural characteristic of its cross-section. The aim of this study is to investigate precise locating problem in PCFs fusion splicing process, so a new method for precisely aligning the center axes and cladding air-holes between two photonic crystal fibers is presented using Hough transform location with nonlinear data fitting and cross-reference. The initial shape parameters were obtained first by using all edge pixels of cross-section of photonic crystal fibers, then discarding non-edge data iteratively according to the error of each subsequent fitting. New data were refined repeatedly until the average fitting error is under the defined threshold. Finally, the center and radius of the core and cladding air-hole of photonic crystal fibers are decided accurately in a small scope by using standard Hough transform. The experiment results with this method show that lesser error and preferable precision can be obtained. In addition, with the locating method using nonlinear data fitting and cross-reference applied to three-dimensional alignment system in fusion splicing process for PCFs, the resolution in the directions of X, Y, Z can reach up to 0.05 um per micro-step.