Embodiments of a scalable optical network unit (ONU) architecture for multi-dwelling units (MDUs) that has a low initial cost (or first port cost) and a low maintenance cost are provided herein. The ONU architecture is scalable in that a growing number of end users can share a single drop fiber that couples the ONU to a passive optical network. The ONU architecture utilizes a multiplexer module to allow the ONU to be daisy chained with one or more additional ONUs.