We have developed a cost-effective 2.5 Gb s −1 wavelength-division multiplexing (WDM) bidirectional module using two integrated optical subassemblies, which are composed of a planar lightwave circuit (PLC) platform for upstream operation and a silicon optical bench (SiOB) platform for downstream operation. The module is constructed by employing a flip-chip bonding method with passive alignment using a distributed feedback laser diode (DFB-LD) with a monitoring waveguide photodiode (PD) on a PLC platform and a receiver with a PIN-PD on an SiOB platform. We investigated the optical performance of the transmitter based on the PLC platform and the receiver subassembly module based on the SiOB platform, respectively.