The E/O, O/E, and O/O measurement utilities have been discussed in this chapter. This utility is essentially an advanced de-embedding tool allowing one to remove the effects of one optical conversion device to learn the properties of the other. There are a large number of configuration choices, particularly in the 4-port cases, but the measurement principle is the same: use a good VNA calibration to characterize the converting pair and then de-embed the effects of a calibrated/characterized device to analyze the DUT. Signal-to-noise ratio is often a limiting uncertainty factor so it is important to carefully choose drive levels (as high as possible without being nonlinear), IF bandwidth, and averaging in order to optimize the measurements. The analysis of this chapter pertains mainly to the use of the MN4765X OE calibration module with the MS464XX VNA and, optionally, with the MN4775X E/O converter (which together all form a ME7848A optoelectronic measurement system).