Anomalous Effects of an InGaAs Cap Layer on Optical Properties of a Quantum-Well Waveguide Structure for Indium Phosphide-Based Electro-Optical Modulators

We report an experimental and theoretical study of the mechanisms of optical losses in a quantum-well waveguide structure for indium phosphide-based electro-optical modulators. It is shown that the presence of an InGaAs cap layer with a high refractive index and high optical loss can lead to anomalously high attenuation of the fundamental TE0 mode. The attenuation is observed near the degeneracy of the dispersion curves of the first two TE polarization modes, which manifests itself at InGaAs cap layer thicknesses of approximately 0.31 μm. The numerical simulation data are in good agreement with the experimentally measured optical losses in such structures.