Aspects of the present disclosure provide a method for fabricating a grating coupler. For example, the method can include providing a substrate, forming a plurality of grating elements and a photosensitive material above the substrate, and projecting actinic radiation of varied intensities to expose different regions of the photosensitive material, causing the photosensitive material to generate a solubility-changing agent. The method can also include removing the solubility-changing agent. The actinic radiation of varied intensities can correspond to depths of grooves between the grating elements.