A wavelength-division multiplexing (WDM) optical assembly with increased lane density is disclosed herein. The WDM optical assembly includes a WDM optical core subassembly including an optical signal router for routing an optical signal between a first side and a second side of a substrate. The WDM optical core subassembly further includes a first WDM filter having a first passband and a second WDM filter having a second passband. The WDM optical core subassembly forms a first optical path between a first common port, the first WDM filter, and a first channel port, and to form a second optical path between the second WDM filter, a second common port, and a second channel port. The WDM optical core subassembly 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.