We describe novel optical switching schemes operating at femtosecondtime scales by employing free carrier (FC) excitation. Suchunprecedented switching times are made possible by spatially patterningthe density of the excited FCs. In the first realization, we rely ondiffusion, i.e., on the nonlocality of the FC nonlinear response of thesemiconductor, to erase the initial FC pattern and, thereby, eliminatethe reflectivity of the system. In the second realization, we erase theFC pattern by launching a second pump pulse at a controlled delay. Wediscuss the advantages and limitations of the proposed approaches anddemonstrate their potential applicability for switching ultrashortpulses propagating in silicon waveguides. We show switching efficienciesof up to 50% for 100 fs pump pulses, which is an unusually highlevel of efficiency for such a short interaction time, a result of theuse of the strong FC nonlinearity. Due to limitations of saturation andpattern effects, these schemes can be employed for switchingapplications that require femtosecond features but standard repetitionrates. Such applications include switching of ultrashort pulses,femtosecond spectroscopy (gating), time-reversal of short pulses foraberration compensation, and many more. This approach is also thestarting point for ultrafast amplitude modulations and a new routetoward the spatio-temporal shaping of short optical pulses.

Y. Sivan, G. Ctistis, E. Yüce, A. P. Mosk

2015

06/2015

Opt. Express

23

16416-16428

Dynamic gratings, Modulators, ultrafast optics