J.E. Zucker

Optical Stark effect on excitons in GaAs quantum wells

We describe the first reported experimental observation of an extremely fast shift of the n = 1 exciton transition energy in GaAs quantum-well heterostructures. The shift is produced by optical pumping below the band gap and is not associated with a carrier or exciton population. We interpret the shift in terms of an optical Stark effect. We present a model for the Stark effect on the ground-state exciton in quantum wells and find good agreement between the predictions of the model and our experimental results.

Electro‐optic phase modulation in GaAs/AlGaAs quantum well waveguides

We present the first absolute measurements of the electric‐field‐induced refractive index change in GaAs/AlGaAs quantum well waveguides. Phase and intensity modulation are characterized as a function of wavelength both above and below the n=1 exciton resonances.

Strained quantum wells for polarization-independent electrooptic waveguide switches

A polarization-independent quantum well waveguide switch is demonstrated. By altering the composition and hence the degree of built-in strain, the bandgap of In/sub 1-x/Ga/sub x/As/InP quantum wells is engineered to produce equal field-induced refractive-index change in TE and TM polarizations. At the same time, the enhanced electrooptic effects characteristic of unstrained quantum wells are maintained, such that the voltage-length product for switching is only 3 V-mm. >

Miniature Mach-Zehnder InGaAsP quantum well waveguide interferometers for 1.3 mu m

Electrooptic Mach-Zehnder interferometers with active lengths as small as 350 mu m are discussed. These strip-loaded waveguide devices utilize the electrooptic effect in InGaAsP/InP quantum wells to achieve pi phase shift with single arm drive voltages of 12 V and 6 V drive in push-pull operation.<<ETX>>

Compact directional coupler switches using quantum well electrorefraction

We have utilized excitonic electrorefraction in reverse‐biased InGaAsP/InP quantum well heterostructures to produce directional coupler switches with active lengths under 600 μm operating at 1.3 and 1.55 μm wavelengths.

Large refractive index changes in tunable-electron-density InGaAs/InAlAs quantum wells

Measurements of electrorefraction and electroabsorption in a multiple-quantum-well waveguide structure in which each InGaAs quantum well is provided with an individual electron reservoir are presented. External bias transfers electrons into the wells, thus quenching the absorption and producing a refractive index change at wavelengths below the bandedge which is linear in the applied voltage. It is shown that in this type of structure both the change in refractive index per applied field and the ratio of optical phase to intensity modulation can be significantly enhanced over those found in the quantum confined Stark effect.<<ETX>>

Room‐temperature excitonic saturation in CdZnTe/ZnTe quantum wells

We present the first measurements of room‐temperature excitonic absorption saturation in a II‐VI semiconductor quantum well. Strong room‐temperature excitonic absorption in CdZnTe/ZnTe quantum wells is found to saturate at an incident optical intensity that is considerably higher than that for III‐V quantum wells. We show that this phenomenon can be interpreted in terms of the smaller excitonic Bohr radius characteristic of wide‐gap II‐VI compounds.

Polarization-independent strained InGaAs/InGaAlAs quantum-well phase modulators

Polarization-independent phase modulation in In/sub 1-x/Ga/sub x/As/InGaAlAs multiple-quantum-well waveguides is demonstrated for the first time. It is shown that by increasing the Ga fraction and hence the tensile strain in the quantum well the electric-field-induced refractive index change in the TM polarization Delta n/sub TM/ can be made to approach that in the TE polarization Delta n/sub TE/. At 1.523 mu m, the ratio Delta n/sub TM// Delta n/sub TE/=1 for x=0.7 with a phase shift coefficient of 17.4 degrees /V-mm was achieved. Polarization independence was maintained over the entire range of reverse bias voltage.<<ETX>>

Optical waveguide intensity modulators based on a tunable electron density multiple quantum well structure

With a recently developed semiconductor heterostructure it has become possible to tune continuously the electron density in multiple quantum wells. Here we demonstrate the first electro‐optic waveguide intensity modulators based on this concept. We achieve a 22 dB on/off ratio for 9 V applied at 1.54 μm wavelength in a rib waveguide electroabsorption modulator. Electrorefractive devices include a waveguide Mach–Zehnder interferometer with an active length 650 μm operating at 1.58 μm wavelength with 5.4 V half‐wave voltage. We show that the operating voltage can be further reduced by operating the Mach–Zehnder modulators in push‐pull configuration.

Quantum well waveguide intensity modulator at visible wavelengths using CdZnTe/ZnTe quantum wells

We demonstrate the first waveguide intensity modulator for visible wavelengths based on the quantum‐confined Stark effect. The active waveguide core is composed of 58 Cd0.42Zn0.58Te/ZnTe quantum wells surrounded by Cd0.12Zn0.88Te cladding layers. We obtain ≳10 dB modulation depth at 640 nm with 4 V bias in a 500‐μm‐long waveguide.