Ultrafast All-Optical Switch with an Operational Speed Unlimited by the Slow Relaxation of a High Efficiency Nonlinear Refractive Index Change.

Abstract

We experimentally demonstrate that the switching speed of a novel symmetric Mach-Zehnder (SMZ) all-optical switch, proposed by the present authors, is unrestricted by normally slow relaxation times of highly efficient, incoherent nonlinear refractions. A cross-correlation trace with a full-width at half-maximum of 2 ps was achieved, which is corresponding to nearly full-switching at 1.5 ps. To our best knowledge, this is the fastest switching experiment with incoherent and thus realistic nonlinearities. We also demonstrate that a repetition rate much faster than that implied by the relaxation time of the utilized optical nonlinearity is also possible with the SMZ all-optical switch. We will explain an experimental result under excitation by packets of four control pulses with a pulse interval of 100ps. We point out that the well-known figure of merit for optical nonlinear materials is no longer applicable to the present device and discuss how it is modified to take full advantage of the present device. We also note that a square-like, contrary to the exponential-like, switching characteristic is quite important in practice and show that such square-like modulation is possible with the SMZ all-optical switch.