We present experimental observations of nonlinear propagation effects in an integrated AlGaAs waveguide filter. We demonstrate pulse shaping, pulse compression, and the production of gap solitons within the stop band of the grating for switching powers of ?130 W. This nonlinear behavior is associated with the counterbalancing effects of self-phase modulation and the large dispersion effects introduced by the grating itself.

Nonlinear propagation effects in an AlGaAs Bragg grating filter

We report what is to our knowledge the first demonstration of all-optical time-division demultiplexing and spatial pulse routing in a compact nonlinear GaAs/AlGaAs microring resonator operating at 1.55 µm. Switching is through the refractive-index change induced by two-photon absorption. The switching time of the device, limited by the ring-charging time and the recombination time of the induced carriers, is measured to be 30 ps. The switching on–off contrast, limited by the slight mismatch between the input and output coupling coefficients, exceeds 8 dB. The device can be used for time-division multiplexing as well.

All-optical time-division demultiplexing and spatial pulse routing with a GaAs/AlGaAs microring resonator.

Using a conventional microwave photonic technique, we demonstrate lightwave switching in laterally coupled GaAs-AlGaAs microring resonators by free carrier injection. The ring waveguide is optically pumped just above its bandgap energy, which results in a temporal tuning of the microring resonant wavelengths by the refractive index change due to the induced free carriers. Both the transmission and the phase function of the resonators are investigated and used to demonstrate all-optical switching. The switching time, limited by surface recombination of carriers, is 20 ps. A switching energy of a few picojoules shifts the microring resonance by 1.2 nm.

Lightwave switching in semiconductor microring devices by free carrier injection

Results of all-optical switching and pulse-routing experiments with a distributed-feedback multiple-quantum-well (MQW) nonlinear waveguide, operating at 1.55 µm, are reported. The MQW material has been engineered, through the controlled introduction of defects, to lower the carrier lifetime from 2.5??ns to 280??ps. The energy required for switching is of the order of 1??pJ or less, the switching time is ?600 ps, and the on–off contrast exceeds 17??dB.

All-optical switching and pulse routing in a distributed-feedback waveguide device

An original approach for the control of exciton–exciton Coulomb coupling in semiconductor macroatoms/molecules is proposed. We show that by applying properly tailored external fields, we can induce—or significantly reinforce—excitonic dipoles, which in turn allows one to control and magnify intra- as well as interdot few-exciton effects. Such a dipole–dipole interaction mechanism will be accounted for within a simple analytical model, which is found to be in good agreement with fully three-dimensional calculations. The proposed approach may play an important role for the design and realization of fully optical quantum gates as well as ultrafast optical switches.

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Field-induced Coulomb coupling in semiconductor macroatoms: Application to single-electron quantum devices

We report the experimental observation of butterfly bistability in an InGaAs/InP multiple‐quantum well waveguide with a distributed feedback grating, under cw operation and at sub‐milliwatt input power. Plasma effects on the excitonic optical properties in multiple‐quantum well structures are the basis of the observed bistability. Insight provided by a simple coupled‐mode description of the device and by many‐body theory of the field‐matter interaction is used both for device design and for interpretation of the results. In particular, the unconventional shape of the hysteresis is due to increased optical absorption at high injected optical power.

Butterfly bistability in an InGaAs/InP multiple-quantum well waveguide with distributed feedback

Results of room-temperature experiments with a multiple-quantum-well, nonlinear, contradirectional coupler are reported. A power-dependent, contradirectional coupling condition is demonstrated, inducing an optically controlled switching of optical signals, with a switching energy of 1 pJ.

Nonlinear contradirectional coupler

We report the dynamics of the optical nonlinearity, measured by a weak probe propagating in single-mode ${\mathrm{In}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As/InP quantum-well waveguides, at wavelengths corresponding to the heavy-hole exciton resonance or longer. The experiments are conducted at moderate pump energies (ranging from 0.1 to a few pJ/pulse). We discovered a contribution from the weak longitudinal component of the waveguided TM mode to the dynamical behavior, and show that this dominates the absorption of TM-polarized light and the relevant optical nonlinearities at wavelengths close to the heavy-hole exciton resonance. Moreover, while at the heavy-hole exciton resonance we observe induced transmission, in the transparent region, we observe an induced-absorption behavior. We evaluate the strong impact on the optical response of waveguides of this behavior, whose origin is purely excitonic, as we show in the framework of a simple model. We further show that the diffusion of carriers out of the waveguiding region is negligible with respect to carrier recombination processes.

L. Faustini

Papers

All-optical switching and pulse routing in a distributed-feedback waveguide device

Butterfly bistability in an InGaAs/InP multiple-quantum well waveguide with distributed feedback

Nonlinear contradirectional coupler

Dynamics of nonlinear optical properties in In x Ga 1-x As/InP quantum-well waveguides

Multiple quantum well compressive strained heterostructures for low driving power all-optical waveguide switches