This disclosure is concerned with transceiver modules. In one example, a transceiver module includes a receiver optical subassembly, as well as a transmitter optical subassembly having a header assembly and an externally modulated laser (EML). The header assembly includes a base with first and second sides, as well as a platform attached to the base and having an inside portion near the first side of the base and an outside portion near the second side of the base. The platform of the header assembly further includes a conductive pathway extending through part of the platform. The EML is supported by the platform and electrically communicates with the conductive pathway of the platform. The EML can be passively or actively cooled.