C. L. Chuang

Picosecond all‐optical switching in single‐mode GaAs/AlGaAs strip‐loaded nonlinear directional couplers

Room‐temperature all‐optical switching has been achieved in single‐mode strip‐loaded nonlinear directional couplers with a GaAs/AlGaAs multiple quantum well guiding layer. For low input intensities nearly complete (1:3–1:5) cross coupling occurs, while at high input intensities switching occurs so that most (>3:1) of the light stays in the input guide. The effects of carrier diffusion are minimized by the use of picosecond pulses. The response time and the recovery time of the nonlinear directional couplers are measured with pump‐probe experiments, and the origin of the nonlinearity is attributed to fast electronic effects.

Ultrafast modulation with subpicosecond recovery time in a GaAs/AlGaAs nonlinear directional coupler

All‐optical modulation is observed at room temperature in a GaAs/AlGaAs multiple quantum well nonlinear directional coupler using femtosecond pulses. The origin of the ultrafast (<500 fs) recovery of the device is attributed to the optical Stark effect.

Fabrication of GaAs nanometer scale structures by dry etching

Nanometer-sized features as small as 400Ahave been fabricated in single-quantum-well GaAs/A1GaAs heterostructures for studies of quantum confinement effects in quantum dots. The features have been fabricated by dry-etching techniques using nanometer-sized etch masks by a novel surface deposition of colloidally-suspended spherical particles. SEM was used to examine the feature size.

Current controlled GaAs/AlGaAs multiple quantum well phase shifter operating at 0.9 μm

An optical phase shifter with current injection has been demonstrated in a GaAs/AlGaAs multiple quantum well (MQW) single mode waveguide. Phase shifts at different wavelengths have been measured and compared with the theory in L. Banyai and S. W. Koch, Z. Physik B 63, 283 (1986). A 3π phase shift has been achieved in a 400‐μm‐long waveguide with almost no material absorption.

Integrated-mirror etalons for 1.3-μm operation grown by molecular-beam epitaxy

The design and growth of a Fabry‐Perot etalon for operation at 1.3 μm is described. The etalon consists of two integrated mirrors, each with 12 pairs of GaAlInAs/AlInAs quarter‐wave layers, and a spacer of GaInAs/AlInAs multiple quantum wells between them. The etalon is grown lattice matched to InP. At 1.35 μm the peak transmission is 50% and the full width/half maximum linewidth is 16 nm.

Subpicosecond All-Optical Modulation Using The Optical Stark Effect In A Nonlinear Directional Coupler

All-optical modulation in a GaAs/AlGaAs multiple quantum well nonlinear directional coupler is observed at room temperature using femtosecond pulses. The ultrafast (< 1 ps) response and recovery of the device is attributed to the optical Stark effect. All-optical switching in various nonlinear optical devices is of interest because of its possible application in high-speed photonic switches. In semiconductor devices, which exploit the relatively large optical nonlinearities near a semiconductor bandedge, the source of the nonlinearity is typically the presence of free carriers photoexcited by a temporally short pump (i.e. control) beam. Previously we have demonstrated all-optical switching both in a GaAs/AlGaAs multiple quantum well (MQW) nonlinear etalon, as well as in a MQW nonlinear directional coupler (NLDC) using real carrier excitations to generate the nonlinearities. In both cases the device has a response which follows the pulse, and a recovery time which was limited to ≈10ns by the recombination and the diffusion of the photo-generated carriers. Recently, the operation of a nonlinear etalon with a subpicosecond recovery time was demonstrated. This was accomplished by using femtosecond pulses tuned in the semiconductors transparency region to generate instantaneous nonlinearities which were present only while the pump travelled through the etalon. In this case the source of the optical nonlinearity was the now well known optical Stark effect. Here we report the first observation of ultrafast switching, including < 1ps recovery time, in a GaAs/AlGaAs NLDC. We believe the optically-induced temporally-short index change responsible for this fast switching is generated by the optical Stark effect.