Efficient numerical method for the analysis of large hollow-core Bragg fibers

Liquid-filled hollow-core Bragg fibers have been used for sensing applications. For ease of filling process, the core size is kept very large (∼1mm diameter). The periodic bilayers, however, remain on the scale of a few microns only. This large difference in scales for the index variation and in the variation of the modal field in these two regions makes it difficult to obtain the propagation characteristics. We have developed a method based on the radial collocation method along with a variable transformation to balance the widely different scales of variation. The method is efficient as it takes advantage of the azimuthal symmetry to reduce a 2D eigenvalue problem to a 1D eigenvalue problem. Further, the balancing of scales through appropriate variable transformation significantly reduces the requirement on the number of collocation points (nodes), making the method very efficient. Using this method, we have obtained the propagation characteristics of a practical large hollow-core Bragg fiber. We have also obtained spectral characteristics by analyzing the field in the bilayers. We have also shown that the computational effort can be reduced with this method for standard solid core Bragg fibers also.