Error-free operation of any fiber optic transmission link requires that the individual components of the link meet critical performance parameters. Given that many different vendors contribute various components to the link, it is important that they all interoperate with each other under worst-case conditions. The fibre channel standard has defined specifications and test methods to help insure interoperability of various vendors' components and to provide margin in the link for worst-case conditions. Jitter specifications have been allocated for each component in the link (serdes, transmitter, fiber, receiver, PWB, etc). An important receiver test parameter often overlooked is the stressed-receiver sensitivity. Stressed testing is used to evaluate receiver performance under the estimated worst-case conditions of eye closure (also referred to as intersymbol interference or ISI). This app note will focus on creating a stressed test source using a Maxim MAX3748 evaluation board, bias tee, Bessel Thompson (BT) filter and a 4Gbps 850nm VCSEL.