High Performance Quantum Well Asymmetric Fabry-Perot Reflection Modulators: Effect of Layer Thickness Variations

Abstract

ABSTRACTWe present a study of the effects of the active cavity layer thickness variation on the operating characteristics of normally-on low-voltage high performance asymmetric Fabry-Perot modulators. For a modulator consisting of 25.5 periods of a multiple-quantum-well active region (100Å GaAs / 45Å (GaAs/AlAs) short period superlattices) with 5 pairs and 20.5 pairs of top and bottom quarter-wave stacks respectively, assuming only layer thickness variation in the active cavity caused by Ga flux nonuniformity, the shift of the Fabry-Perot mode wavelength is ∼5.8 times that of the QW heavy-hole exciton. This affects the relative distance between the wavelengths of the quantum well exciton and the Fabry-Perot resonance, and hence the performance of the modulators. Also, the tolerable percentage change of the Fabry-perot mode wavelength should be less than 0.13% in order that such modulator arrays have at least 10:1 contrast ratios at a fixed optimum operating wavelength. This defines the epitaxial growth tolerance for obtaining the uniformity of the operating wavelength of an array and the precision with which we can obtain a desired wavelength, its reproducibility, and its uniformity across a wafer.