Ultrafast all-optical switch using LT-GaAs based on DFB

Abstract

Simulation of the pump-probe transmission changes of an ultrafast all-optical switch using corrugated index profile, based on optically induced non-linear changes in the band tail region of low temperature grown GaAs (LT- GaAs) is reported in this paper. The device has corrugated surface over the substrate layer, over which is the layer of LT- GaAs forming a smooth interface with GaAs above. Next is a layer of reflection coating. The pump is supplied to the LT-GaAs layer through the mirror and the GaAs layers. The probe comes laterally to the GaAs layer. In the absence of the pump pulse, the non-existence of a strong reflection by the LT-GaAs layer, because of the subtle difference in the refractive index between GaAs and LT-GaAs layers, gets the probe pulse to be acted on by the corrugations (Distributed Feedback principle (DFB)), thus giving a weak output on the other side. In the presence of a strong pump-pulse, the LT- GaAs layer undergoes optically induced non-linear absorption changes and a marked change in the refractive index of the LT-GaAs layer reflects the probe to give a strong output pulse. The simulation is demonstrated around a wavelength of 1.5 m. The reduction in the switching time is as high as 50%. Unprecedented contrast ratio of ~30dB is theoretically visualized during simulation and is attributed to the compounded action of DFB principle in the LT-GaAs layer and wave-guide effect in the GaAs layer. The improvement in the design has an advantage, which aids in the efficient coupling of the probe with any other integrated device and in making use of the non-linear absorption changes effectively. Keywords : Pump, probe , Corrugations, distributed feedback, simulation, LT-GaAs, non-linear, contrast ratio, switch.