The optical module offers an effective high-speed solution for a growing telecom market. Data rates range from 155 Mbps to 6 Gbps and even up to 10 Gbps. Transmitter optical sub-assemblies (TOSAs) and laser drivers may have different resistances in a given application, so the reflection could be worse if an impedance transfer circuit is not used to absorb it. This report discusses how to use the impedance transfer circuit when we connect a mismatched trace and non-terminated TOSA, as well as what we should take into consideration when we lay out the PCB for optical design.