WAVELENGTH OPTIMIZATION OF QUANTUM-WELL MODULATORS IN SMART PIXELS

We extend our recent general discussion of electroabsorption and refra ction in multiple-quantum-well modulators to determine the optimum mod ulator design for smart-pixel applications. In addition to the optimum operating wavelength shift, from that of the zero-voltage exciton, we determine the optimum number of quantum wells, and we calculate the r eflectivity change and the contrast ratio obtainable. This analysis is undertaken for both simple detectors and modulators, meaning that the y are antireflection coated, as well as for devices that include Fabry -Perot resonators. The optimization is performed on a figure of merit that is inversely proportional to the incident optical read energy req uired on a device to switch another, downstream device. We maximize th e figure of merit to minimize the optical read energy. An interesting result is that there should be no significant improvement in our smart -pixel circuit figure of merit with the use of Fabry-Perot resonant mo dulators and detectors. Our results are, of course, material-system sp ecific, but for the 850-nm AlGalAs/GaAs quantum-well system the optimu m wavelength shift from the exciton location is approximately 6 nm. Th e general trends and approach are applicable to other material systems .