The four optocouplers are called the: Photo-transistor, Photo-darlington, Photo-SCR and Photo-triac as shown below. Optocouplers, also known as opto-isolators or photocouplers, are electronic components that transfer signals between two isolated circuits using light. When the LED. From relay sockets to pluggable relay and optocoupler modules – WAGO delivers versatile, high-performance solutions for every application. They're perfectly suited for industrial automation, process and power engineering, rail systems, shipbuilding, and control cabinet manufacturing. In this guide, you'll learn how they work and how you can use one in your own projects.