LP modes and ideal modes on optical fibers

The transformation from coupled-mode equations for LP modes to those for ideal modes and the expressions of one set of modes in terms of linear combinations of the other set of modes are studied, using the coupled-mode theory. The expressions (including higher-order corrections) of modal fields and propagation constants for ideal modes are given in terms of those for LP modes in three different cases. Thus, cases where a LP mode can or cannot directly replace a corresponding ideal mode are made clear.