An optocoupler takes an electrical signal, turns it into light, then flips it back into electricity on the other side. They use light to pass signals between circuits. Unlike transformers or capacitors, which can only transfer AC signals across the isolation barrier, optocouplers can. An optocoupler (or opto-isolator) is a component that transfer signals between circuits using light. In this guide, you'll learn how they work and how you can use one in your own projects. A Light Emitting Diode inside the chip shines on a photo-diode, photo-transistor or other photo device.