G. Parry

Use of a three‐layer quantum‐well structure to achieve an absorption edge blueshift

Theoretical calculations are used to propose a novel structure for a quantum‐well electro‐optic device which gives a large blueshift of the absorption edge on application of an electric field. The structure provides spatial separation of the electron‐hole pair in the ground state at zero applied field. This is achieved by use of two materials within the well which have a type II band line‐up relative to each other but are type I relative to the barrier material. The combination of InAs0.4P0.6/In0.53Ga0.47As wells with InP barriers is expected to fulfill these requirements and also to operate in the 1.5 μm region.

High tolerances for a low-voltage, high-contrast, low-insertion-loss asymmetric Fabry-Perot modulator

The authors report on the reduction of the operating voltage of a GaAs/AlGaAs multiple-quantum-well asymmetric Fabry-Perot modulator to approximately 4.2 V for a high-contrast ( approximately 15 dB), low-insertion-loss ( approximately 3 dB) device. This improvement on modulator performance makes the device suitable for a practical system and has been accomplished by an increase of the front reflectivity to approximately 43%. The authors discuss general design issues and show that the higher finesse cavity does not have to lead to low fabrication and environmental tolerances. On the contrary, this devices tolerance to fabrication and environmental factors is expected to have been improved.<<ETX>>

Effects of well width on the characteristics of GaAs/AlGaAs multiple quantum well electroabsorption modulators

We compare the characteristics of three electroabsorption modulators fabricated using GaAs/AlGaAs multiple quantum well structures with well widths 47, 87, and 145 A. We find that the narrow well structure provides the largest change in transmission. The 87 A well structure provides the largest contrast ratio, while the wide well sample offers the lowest operating voltage.

Post-growth tailoring of the optical properties of GaAs/AlGaAs quantum well structures

In this paper we describe a method for performing post-growth bandgap engineering in the GaAs/AlGaAs quantum well system. The method used is impurity-free vacancy diffusion. Using both single and multiple quantum well data we show that this allows blue shifts in the optical properties, while retaining both their distinctive excitonic and electrical characteristics. The electrical response is modelled and no comparative degradation of the quantum confined Stark effect is predicted, and this is confirmed experimentally. Possible applications of this technique are mentioned.

Multiple-quantum-well asymmetric Fabry-Perot modulators for microwave photonic applications

We describe the development of InGaAsP multiquantum-well asymmetric Fabry-Perot modulators (AFPM) for RF-over-fiber applications. Advantages of the AFPM include low drive voltage and loss, high linearity and simple fiber alignment. Experimental results of initial devices, exhibiting 5.5-dB modulation depth and >3-GHz operation, are described. The effect of the optical power on the device performance was assessed, and the modulation bandwidth was found to be unaffected by incident optical powers up to 0 dBm. The linearity of the modulation characteristic was measured by carrying out two-tone intermodulation distortion tests, and a third-order intercept point of 30 dBm was observed.

GaAs multiple quantum well microresonator modulators grown on silicon substrates

We report new results on the modulation characteristics of GaAs/AlGaAs asymmetric Fabry-Perot modulators grown on silicon substrates. We discuss factors affecting device performance and evaluate these by growing p-i-n quantum well diodes, and multilayer reflector stacks on silicon. Using data from these test structures we have designed an asymmetric microresonator modulator and achieve, experimentally, a 40% reflection change with only 5 V and a contrast ratio of 7.4 dB, also with 5 V.

An optical study of encapsulant thickness-controlled interdiffusion of asymmetric GaAs quantum well material

The study uses photocurrent spectroscopy and luminescence techniques to investigate the effect of interdiffusion on a GaAs/AlGaAs system with four quantum wells. The wells are non-identical in that the two central wells have equal (symmetric) Al barriers, while the outer two have unequal (asymmetric) ones. This results in the magnitude of the spectral blue-shift induced by the interdiffusion being different for the two well configurations. Investigations are carried out into the response of the two well types to differing levels of interdiffusion. The interdiffusion is brought about by capping with SiO2 followed by annealing, and we show that the extent of the interdiffusion can be controlled by the thickness of the encapsulant, and that the effect saturates for thicker caps.

Effect of device length and background doping on the relative magnitudes of phase and amplitude modulation in GaAs/AIGaAs PIN multiple quantum well waveguide optical modulators: erratum

This erratum Letter points out an error in the caption of Fig. 4 of this paper.

Ultrafast recovery time in a strained InGaAs-AlAs p-i-n modulator

We have performed sub-picosecond resolution measurements of the optical recovery of InGaAs-AlAs multiple quantum well p-i-n structures that exhibit strong excitonic features, a clear quantum confined Stark effect and low photocurrent. The recovery times, measured as a function of applied electrical bias and optical excitation density, are much shorter than that predicted by carrier thermionic emission rates from the quantum wells. An observed ultrafast recovery time of 28 ps makes this material system promising as a fast modulator with low thermal dissipation or as a saturable absorber for semiconductor and fiber laser mode locking.<<ETX>>

Symmetric self-electro-optic effect device using symmetric-cavity quantum well electroabsorption modulators

We report results obtained from a symmetric-cavity Fabry-Perot quantum well modulator in GaAs/AlGaAs. A reflection-change of /spl ap/46% with an insertion loss of 1.3 dB are obtained in the normally-off mode under a reverse bias voltage of 7.5 V. Bistable operation is demonstrated, for the first time using such devices, by connecting two modulators in the symmetric self-electro-optic effect device configuration.<<ETX>>