Passive mode-locking using phase-sensitive amplification

A method is proposed and considered theoretically for using phase-sensitive amplification as the intensity-discrimination (saturable absorption) element in a laser cavity to generate stable and robust mode-locking. The phase-sensitive amplifier acts as a phase filter for selecting the specific intensity-dependent phase rotation of the mode-locked pulse that locks the phase to the amplifier pump phase. The nonlinear phase rotation is analogous to the nonlinear polarization rotation which is used with passive polarizers for mode-locking. It is demonstrated that the phase-sensitive amplification mechanism can indeed result in stable mode-locking. An average cavity model explicitly calculates the stability of the mode-locked pulses.