Group Velocity Mismatch Effects in Ultrafast Optical Modulators Based on Cascaded Second Order Nonlinearities

Abstract

The intensity dependent phase and amplitude modulation arising from cascaded second order optical nonlinear processes in frequency doubling crystals are getting growing attention1, 2, 3 for all-optical switching devices and to obtain passive mode-locking techniques complementary to the Kerr-lens mode-locking (KLM)4, 5. Up to now these effects have been theoretically and experimentally investigated in stationary conditions, i.e. with interacting pulses fundamental and second harmonic at co and at 2ω respectively, much longer than their propagation delay through the nonlinear crystal length, as determined by their Group Velocity Mismatch (GVM). Due to the high nonlinearity of the available frequency doubling crystals, the obtained phase shift can be much higher that with the usual Kerr materials. Nevertheless, in nonstationary conditions arising when the fundamental pulse duration is equal to or shorter than the propagation delay we have to take into account of the GVM effects.