A. Rivers

All‐solid‐state subpicosecond passively mode locked erbium‐doped fiber laser

Using a semiconductor saturable absorber, an erbium‐doped fiber laser has been passively mode locked to yield pulses of 840 fs with pulse energies of 0.85 nJ. Stable mode locking at the fundamental roundtrip frequency and also at the second and third harmonic has been achieved.

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.

THE DESIGN AND APPLICATION OF III-V MULTIQUANTUM WELL OPTICAL MODULATORS

The application of an electric field across a quantum well structure induces a shift in the exciton dominated absorption edge. This effect is exploited in a number of optoelectronic devices including electro-absorption modulators, electron-refraction modulators, and optoelectronic logic devices. We will discuss how such modulators may be designed to operate at low voltages, with large changes in transmission or reflection and at high speeds. The choice of well widths, barrier widths, the use of coupled wells, and the enhancement due to Fabry Perot structures will all be considered. Results will be included for GaAs-GaAlAs, GaInAs-InP, and GaAs on silicon structures. Applications of these devices in optical interconnection of electronic circuits, and optoelectronic logic will be reviewed.

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.

Implementation of symmetric Fabry-Perot quantum well electroabsorption modulators in symmetric self-electrooptic effect devices

We report results from a symmetric cavity electroabsorption modulator (SCEM) in GaAs/AlGaAs. A reflection change of ∼ 45% with an insertion loss of 1.3 dB is obtained under 7.5 V in the normally-off mode. We discuss the factors that affect the device performance and compare the attainable performance with that of the normally-off asymmetric Fabry-Perot modulator (AFPM). We also propose a new method for an improvement of the restricted tolerances of SCEMs. Finally, we demonstrate bistable operation using two SCEMs in the symmetric self-electrooptic effect device (S-SEED) configuration, and attempt to evaluate the potential of this type of modulator for SEED applications.