This paper demonstrates an approach for fabricating large-scale photonic crystal (PhC)-based devices using a combination of optical and focused ion beam (FIB) lithography techniques. Optical lithography along with reactive ion etching parameters is optimized to realize the layout of device structure and thereafter FIB milling is optimized to realize the designed PhC structure at those identified locations. At first, with the help of a specially designed mask and using optical lithography along with reactive ion etching, a number of rectangular areas of dimension of along with input and output waveguides of width and thickness of have been fabricated. Subsequently, use of FIB milling, a periodic PhC structure of lattice constant of 600 nm, having a hole diameter of along with a defect hole diameter of have been realized successfully on the selected areas. This method shows a promising application in fabricating PhC structure with device size at large scale, eliminating the problems of standard nanolithography techniques.