All-optical control of the time delay in a one-dimensional photonic bandgap formed by double-quantum-wells

In this work, we show the feasibility of all-optical control of time delay in a Bragg grating with an active defect that consists in an asymmetric double quantum-well GaAs/Al_xGa_1−xAs. The double quantum-well is modeled as a Λ-V-type four level system. The refractive index of the defect can be modified by a control field due to the tunneling-induced quantum interference. It is shown that index changes as large as 0.4 can be obtained via cross-phase modulation. This allows for the development of a propagating mode at the selected wavelength. The existence of the mode permits the slow-down of light pulses, thus the system may act as a delay line with a group index as high as 100 operating at bandwidths of tens of GHz. We demonstrate that this defective photonic bandgap structure could enable ultrafast and ultrasensitive nonlinear all-optical switching at moderate powers of the control field.