Light Emitting Diodes (LEDs), Laser Diodes, and Vertical Cavity Surface Emitting Lasers (VCSELs) are finding their way into more and more applications today. These applications include facial scanners for security, LIDAR for collision avoidance and self-driving cars, as well as optical telecommunications. While the VCSEL is a relatively simple device in terms of its electrical behavior, it also has optical properties and behaviors that must be tested as well. This requires a different approach to testing than with a standard discrete diode. Engineers need to test both the electrical and optical properties of these devices, sometimes at very high frequencies.