Integrated, asymmetric twin-waveguide ultrafast all-optical switch

We demonstrate the monolithic integration of a terahertz optical asymmetric demultiplexer (TOAD) in an asymmetric twin-waveguide structure operating at λ=1.55 μm wavelength. The device utilizes a Mach-Zehnder interferometer geometry with counter-propagating signal and control pulses. The device consists of etched waveguides and 3-dB multimode-interference couplers, with a semiconductor optical amplifier (SOA) integrated into each arm of the interferometer and coupled to the passive waveguides by low-loss tapered mode transformers. Signal switching is accomplished via nonlinear gain compression and phase shifts in the SOAs induced by a control pulse propagating in the direction opposite that of the signal. A single control pulse is split in the two arms to provide both ON and OFF operations of the switch, with the switching window of 10-15 ps determined by the relative displacement of the two SOAs. The device is fabricated in an InGaAsP-InP asymmetric twin-waveguide structure grown by gas-source molecular beam epitaxy