Modeling the Optical Properties of Low-Cost Colloidal Quantum Dot Functionalized Strip SOI Waveguides

We studied the optical absorption of silicon-on-insulator strip waveguides functionalized by a monolayer of colloidal PbS/CdS core/shell quantum dots. The integration is done by Langmuir-Blodgett deposition, which results in a monolayer of quantum dots (QDs) on the waveguides. Experimental absorption coefficients of QD functionalized strip waveguides range from 10-30 cm^-1. These values are about five times larger than the absorption coefficient of QD functionalized planarized waveguides. Using a refractive index as determined from effective medium theory including dipolar coupling between the QDs, we obtain simulated values for the absorption coefficient that are in quantitative agreement with the experimental values and we find that difference with planarized waveguides results from an increased overlap between the QD layer and the guided optical mode in the case of strip waveguides. The modeling of the absorption coefficients of more complex strip waveguides functionalized by colloidal QDs as demonstrated in this study will enable the development and simulation of QD-based photonic devices integrated in silicon.