There is disclosed a method of manufacturing of optical devices, for example, semiconductor optoelectronic devices such as laser diodes, optical modulators, optical amplifiers, optical switches, and the like. There is further disclosed Optoelectronic Integrated Circuits (OEICs) and Photonic Integrated Circuits (PICs) including such devices. According to the present invention there is provided a method of manufacturing an optical device (40), a device body portion (15) from which the device (40) is to be made including a Quantum Well Intermixing (QWI) structure (30), the method including the step of plasma etching at least part of a surface of the device body portion (5) prior to depositing a dielectric layer (51) thereon so as to introduce structural defects at least into a portion (53) of the device body portion (5) adjacent the dielectric layer (51). The structural defects substanially comprise “point” defects.