  The response of a passive mode-locking mechanism, where gain and spectral
filtering are saturated with the energy and loss saturated with the power, is
examined under the presence of higher order effects. These include third order
dispersion, self-steepening and Raman gain. The locking mechanism is maintained
even with these terms; mode-locking occurs for both the anomalous and normal
regimes. In the anomalous regime, these perturbations are found to affect the
speed but not the structure of the (locked) pulses. In fact, these pulses
behave like solitons of a classical nonlinear Schrodinger equation and as such
a soliton perturbation theory is used to verify the numerical observations. In
the normal regime, the effect of the perturbations is small, in line with
recent experimental observations. The results in the normal regime are verified
mathematically using a WKB type asymptotic theory. Finally, bi-solitons are
found to behave as dark solitons on top of a stable background and are
significantly affected by these perturbations.
