A bi-directional optical module with an improved optical crosstalk between the transmitter unit and the receiver unit is disclosed. The optical module provides the LD, the PD, the WDM filter secured with the block, and the package with the co-axial shape. The block provides a slant surface, where the WDM filter is secured thereon, the bottom surface facing the PD mounted on the package, and an aperture connecting the slant surface and the bottom surface. The PD is enclosed within a space formed by the bottom surface and the primary surface, which electrically and optically isolates the PD from the LD.