I. Bar-Joseph

Quantum‐confined Stark effect in InGaAs/InP quantum wells grown by organometallic vapor phase epitaxy

We report the first observation of the quantum‐confined Stark effect in InGaAs/InP multiple quantum wells grown by organometallic vapor phase epitaxy. The effect is observed both in transmission and photoconductivity measurements. The observed spectral shift agrees with the theory.

Room‐temperature electroabsorption and switching in a GaAs/AlGaAs superlattice

We report room‐temperature observation of Wannier–Stark localization in a GaAs/AlGaAs superlattice. We show that large modulation can be obtained over a wide spectral range and demonstrate the operation of a self‐electro‐optic effect device.

Color center lasers passively mode locked by quantum wells

Using multiple-quantum-well (MQW) saturable absorbers, a NaCl color center was passively mode locked to produce 275-fs transform-limited, pedestal-free pulses with a peak power as high as 3.7 kW. The pulses are tunable from lambda =1.59 to 1.7 mu m by choosing MQWs with different bandgaps. The output pulses from the laser were shortened to 25 fs using the technique of soliton compression in a fiber. The steady-state operation of the laser requires the combination of a fast saturable absorber and gain saturation. >

Broad bandwidths from frequency-shifting solitons in fibers.

By pumping a fiber in the anomalous group-velocity-dispersion regime with a color-center laser we generate pulses with tau greater, similar 100 fsec covering a wide spectral range of 1.55 microm < lambda < 1.85 microm. Cross-correlation measurements show the lack of correlation between different parts of the spectrum. Computer simulations show that modulation instability and the soliton self-frequency-shift effect initiate a multisoliton collision process that results in narrow, high-intensity, fundamental solitons. The observed broad spectra correspond to an ensemble average over these solitons, which start from noise and frequency shift by different amounts.

Modulation of absorption in field-effect quantum well structures

Experimental and theoretical investigations of the absorption in a single-modulation-doped quantum well (QW) used as conducting channel of a field-effect transistor are presented. By applying a voltage to the gate, the electron concentration can be varied between 0 and approximately 10/sup 12/ cm/sup -2/. The continuous transition can be optically followed from an undoped to a highly doped QW. Effects of band filling are observed, along with renormalized effects at the first subband edge and electrostatic effects at the higher ones. It is shown that optical techniques can give in situ information on the electron density and temperature as well as on the electrostatic fields inside field-effect structures. >

Self‐electro‐optic effect device and modulation convertor with InGaAs/InP multiple quantum wells

We report the first observation of the self‐electro‐optic effect in InGaAs/InP multiple quantum wells, grown by organometallic vapor phase epitaxy. Clear bistability and switching are observed over a range of 40 nm around 1.61 μm with 20–30 V bias. We demonstrate the operation of a modulation convertor, which converts a modulation from a carrier at 1.6 μm onto a carrier at 0.85 μm and vice versa.

Optical reading of field-effect transistors by phase-space absorption quenching in a single InGaAs quantum well conducting channel

We present the first observation of absorption quenching by electrical control of the carrier density in a single semiconductor quantum well used as conducting channel in a field‐effect transistor. The effect is large enough to allow direct reading of the transistor logic state.

Electroabsorption and refraction by electron transfer in asymmetric modulation‐doped multiple quantum well structures

We present a novel heterostructure that exhibits large electroabsorption and refraction. The structure is periodic with a stackable building block, thus it allows large contrast and waveguide operation. The mechanism used is the quenching of absorption produced by transfer of electrons from a reservoir into a quantum well. We demonstrate the principle by presenting differential absorption and refraction spectra on a ten‐period device.

Measurement of multigigahertz waveforms and propagation delays in modulation-doped field-effect transistors using phase-space absorption quenching

High‐speed waveforms (up to 20 GHz) in InGaAs/InAlAs modulation‐doped field‐effect transistors (FETs) are measured using 10–20 ps optical probe pulses via the quenching of the absorption in the quantum well gate channel due to Pauli exclusion. The technique is a noncontact probe of the charge density in the gate, and hence, of the logic state of the FET. This charge‐sensitive probing technique is combined with voltage‐sensitive electro‐optic sampling to study internal dynamics of the FET. A gate channel charging time of 11 ps and a gate to drain propagation delay of 15 ps are measured.

Room-temperature operation of a GaAs/AlGaAs superlattice self-electrooptic-effect device

Summary form only given. The authors report the room-temperature operation of a blue-shift SEED (self-electrooptic-effect device) using Wannier-Stark localization in a GaAs/Al/sub 0.3/Ga/sub 0.7/As superlattice. They demonstrate that large modulation can be obtained over a wide spectral range and bias with contrast comparable to MQW (multiple quantum-well) SEEDs. Wannier-Stark localization associated with a blue shift of the superlattice (SL) absorption edge was clearly observed in the photocurrent measurements. Bistability of the SL SEED was obtained over a wide spectral range and was almost constant between 745 and 755 nm. The demonstration of large modulation bandwidth and optical switching behavior of the SL SEED makes this device an excellent candidate for optical signal processing and optical computing. >