The time-domain ABCD matrix formalism is based on the propagation of a Gaus
sian pulse which is characterized by the pulsewidth and chirp. In this pape
r, the time-domain ABCD matrix of th SPM (self phase modulation) is perfect
ed so as to acquire more information. With the time-domain ABCD matrices of
amplitude modulation, filtration from the optical bandpass, group velocity
dispersion and SPM, the detailed characteristics of actively mode-locked f
iber laser are described and the steady-state solutions are derived for two
simple cases. The application of the formalism is also helpful to understa
nd the mechanism of mode-locking in an actively mode-locked fiber laser.