In this paper, Two Dimensional Photonic Crystals based Add Drop filter (ADF) is designed for DWDM applications. The existing work concentrates in Coarse Wavelength Division Multiplexing and few filters reported for DWDM with non-uniform channel spacing, and low quality factor. The proposed ADF enhances the quality factor using Rounded Square Ring Resonator (RSRR) for ensuring efficient bandwidth in supporting WDM systems. The design consists of bus waveguide, drop waveguide and RSRR with inner quasi-square ring in the square lattice. The dielectric constant of the Si rod is 11.68 which are hosted in the air. The line defect is created by removing 4 rods (Quasi ring) in the center of the inner square ring. The line defect in the ring resonator is used to reduce the radiation field components surrounded by the resonator. The performance parameters of ADF are investigated using 2D Finite Difference Time Domain algorithm. The proposed ADF drops a channel at 1636.2 nm, with the bandwidth of 0.7 nm, high quality factor of 2337, and the dropping efficiency of about 100%. The size of the device is 412.76 µm2. It is highly sufficient to support WDM systems for future Photonic Integrated Circuits (PIC). Further, the impact of functional parameters such as transmission efficiency, quality factor, bandwidth are investigated by varying the structural parameters, namely, adjacent rod radius, scatterer rod radius, coupling rod radius, lattice constant, inner rod radius and rod radius. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.