Analytical expression for the coupling between two optical fiber cores with alpha -power refractive-index distribution

The authors derive closed-form expression for the coupling coefficient and the butt coupling overlap integral for the coupling between two linearly polarized modes of any order, each propagating an alpha -power refractive-index optical fiber with uniform cladding. To show the usefulness of these formulas, they present numerical results for the coupling between two identical single-mode fibers and clearly demonstrate the variations of the coupling properties as the fiber structure changes. These results are useful when performing coupled-mode analysis of couplers formed between two fibers with the assumed index profiles. The authors also apply the obtained general formulas to evaluating the coupling characteristics between two identical single-mode fibers for various core index distributions.<>