Although contact metallization causes stress in the underlying material, the magnitude of the resulting change in refractive index is often not appreciated. We investigate here the distribution of the change in refractive index due to stress caused by Ti/Pt/Au contact layers in weakly guiding InGaAsP waveguides operating near 1.3 mu m. Polarization-resolved photoluminescence and beam propagation calculations, combined with a simple stress model, are applicable to general processing-induced stress in InP-based waveguides and to waveguide design.