Multiple Quantum Well Devices Research Articles

High-performance Mach-Zehnder modulators in multiple quantum well GaAs/AlGaAs

We demonstrate Mach-Zehnder interferometric waveguide intensity modulators which employ electrorefraction due to the quantum-confined Stark effect in multiple quantum well (MQW) GaAs/AlGaAs. These devices exhibit average half-wave voltage-length products as low as 3.0 V/spl middot/mm and extinction ratios greater than 23.8 dB, which are superior to any MQW devices of this type. An effective index based model is developed to extract linear and quadratic electro-optic coefficients from the modulation data. Also, the power handling limitations of MQW modulators are discussed in terms of device performance and catastrophic electrical failure.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Resonant tunneling in thin-barrier multiple-quantum-well electroabsorption modulators

We report the clear observation and characterization of room-temperature resonant tunneling in thin-barrier (35-A) GaAs/AlGaAs multiple-quantum-well (MQW) structures (containing as many as 100 quantum wells) and discuss the effects on electroabsorption modulators. The characteristics of similar MQW devices with both thick (60-A) and thin (35-A) quantum-well barriers are studied and compared experimentally and found to be similar, except near the thin-barrier resonant-tunneling field. We present data suggesting a novel exploitation of resonant tunneling for high-power modulators by aligning the resonant-tunneling field with the appropriate wavelength for high absorption. Data from an asymmetric Fabry–Perot electroabsorption modulator are also presented. We also discuss the implications of resonant tunneling on optically bistable self-electro-optic effect devices.

Enhanced modulation bandwidth of strained multiple quantum well lasers

We compare the dynamic properties of bulk, lattice-matched, and strained multiple quantum well (MQW) 1.3 μm Fabry–Perot lasers up to high-bias levels. We show for the first time that long wavelength strained MQW lasers can have a higher intrinsic bandwidth than bulk active and lattice-matched MQW lasers, and that a −3 dB bandwidth of over 30 GHz can be expected from devices with a thin separate confinement heterostructure if a low parasitic device structure is used. The K factor used to determine maximum bandwidth in bulk active laser diodes is shown to be unsuitable for strained MQW devices, where a linear relationship of damping/(resonance frequency)2 is not observed at high power levels.

Strained-layer InGaAs-GaAs-AlGaAs lasers grown by molecular beam epitaxy for high-speed modulation

A study of strained InGaAs quantum wells grown on GaAs by molecular beam epitaxy was performed in order to optimize the growth conditions for strained-layer single- and multiple-quantum-well lasers. Photoluminescence of the quantum wells shows a rapid degradation in material quality as the substrate temperature is reduced below 500 degrees C. Single-quantum-well (SQW) laser structures contain a 55 AA 35% InGaAs quantum well, while multiple-quantum-well (MQW) lasers contain four 25% or 35% InAs mole fraction 55 AA quantum wells. The 35% SQW lasers emit at 1.06 mu m, while the 25% InGaAs MQW lasers emit at 1.07 mu m. The SQW lasers have threshold current densities as low as 83 A/cm/sup 2/ for 150*1000 mu m devices. Microwave modulation bandwidths increase with an increasing In mole fraction and number of quantum wells, as predicted by theory. A differential gain of 5.0*10/sup -15/ cm/sup 2/ is calculated from the microwave response measurements for the 35% MQW devices. >

Comparison of bulk buried heterostructure and multiple quantum well laser amplifier switches

Multiple quantum well (MQW) and bulk laser amplifier switches are directly compared by analysis of the switching speed and the wavelength dependence of contrast (extinction ratio) and noise. The MQW device is found to be three times faster, with 20dB less contrast and 12.5dB less loss at optimum wavelength. It is thus shown that MQW devices are more suitable for use as fast switches.

100 ps waveguide multiple quantum well (MQW) optical modulator with 10:1 on/off ratio

By incorporating two quantum wells into a capillary waveguide, we have made the first MQW optical modulator with an on/off ratio of at least 10:1. Furthermore, this device was used to generate an optical pulse less than 100 ps long, the fastest to date with an MQW device.