A wavelength-division multiplexing (WDM) optical assembly (210) with increased lane density is disclosed herein. The WDM optical assembly (210) includes a WDM optical core subassembly (200) including an optical signal router (206) for routing an optical signal between a first side (204A) and a second side (204b) of a substrate (202). The WDM optical core subassembly (200) further includes a first WDM filter (208A) having a first passband and a second WDM filter (208B) having a second passband. The WDM optical core subassembly (200) forms a first optical path between a first common port (216A), the first WDM filter (208A), and a first channel port (218A), and to form a second optical path between the second WDM filter (208B), a second common port (216B), and a second channel port (218B). The WDM optical core subassembly (200) increases lane density while decreasing size and complexity by including a plurality of common ports in optical communication with the same plurality of WDM filters.