In a previous study, 10-Gbps bidirectional optical subassembly (BOSA) techniques for optical network units were constructed by combining a TO-can-packaged transmitter optical subassembly (TOSA) and receiver optical subassembly (ROSA) to a metal housing via a laser welding technique.1 In general, the metal housing containing a lens, filter, and fiber is firmly mounted on a transceiver package and supports the BOSA structure, which is widely used to take an uncooled laser, such as a distributed feedback laser in a TOSA. However, we need to consider the laser cooling issue of an electroabsorptive modulated laser (EML) BOSA for 10-Gbps optical line terminal (OLT) applications. An EML typically needs a thermoelectric cooler (TEC) to stabilize the wavelength and optical output power. Thus, dissipation of the TEC joule heat is the most important consideration in designing an EML BOSA structure. To efficiently dissipate the TEC joule heat, the base plate of the EML BOSA package is generally fabricated using copper tungsten (CuW), and should be tightly mounted on a transceiver package. Thus, most components not contained in the EML TOSA package such as metal housings, filters, and lenses are jointed at the window of the EML TOSA package using a laser welding technique. As such, in terms of mechanical reliability, the weight on the welding joint should be minimized in order to reduce mechanical stress incurred by external mechanical shock and vibration.