“…However, if the imaginary part of the positive wavenumber of the core k 1 nearly vanishes, only the LCP mode suffers the material absorption. As shown in [16,17], F 1 and F −1 are separately associated with k 1 and k −1 and represent the RCP field and LCP field, respectively, if β ≈ k 1 . Although, for any mode in the fibers discussed here, both F and F − contribute the modal field, the RCP mode and LCP mode should be mainly determined by F 1 and F −1 , respectively.…”