A method of fabricating an optical device comprises steps of forming a silicon-based optical component in a substrate; depositing an ILD layer on the substrate and the silicon-based optical component; forming a thermal tuning assembly comprising a first metallic material in the ILD layer and above the silicon-based optical component, wherein the thermal tuning assembly comprises a core above the silicon-based optical component, a plurality of grids spaced apart from the core, and a pair of neck portions connecting the grids to the core, wherein a width of a strip in each grid is greater than a width of the core; forming at least one conductive plug comprising the first metallic material penetrating the ILD layer and coupled to the silicon-based optical component; and forming a plurality of conductive lines comprising a second metallic material coupled to the thermal tuning assembly.