Field evolution along longitudinally nonuniform finite-cladding fibers of circularly symmetric cross section is analyzed in terms of coupled modes. Local modes are used for abruptly tapered fibers, whereas linear-index fiber modes provide the expansion basis for Kerr-type nonlinear-index fibers. Convergence of the results suggests in both cases that only a finite number of bound modes is sufficient to describe the field adequately. A comparison with simulations given by a finite-difference beam-propagation method that was developed for circularly symmetric waveguides confirms the validity of this assumption.
© 1991 Optical Society of America
François Gonthier, Alain Hénault, Suzanne Lacroix, Richard J. Black, and Jacques Bures, "Mode coupling in nonuniform fibers: comparison between coupled-mode theory and finite-difference beam-propagation method simulations," J. Opt. Soc. Am. B 8, 416-421 (1991)