Optimization of deep-etched, single-mode GaAs/AlGaAs optical waveguides using controlled leakage into the substrate

This paper presents a detailed experimental and theoretical study of the properties of deep-etched GaAs/AlGaAs optical waveguides designed using a version of the spectral index method which predicts mode losses due to leakage through the lower cladding into the high index GaAs substrate. By predicting and measuring the mode losses due to this mechanism as a function of guide width, we show that waveguides formed by reactive ion etching through the core to the lower cladding layer can be both low-loss (0.2 dB/cm) and single-mode even with core thicknesses and guide widths as large as 4.8 and 5.6 mu m, respectively. We demonstrate the advantages of this type of guide for making compact integrated optic devices.