An opto-coupler, also known as an opto-isolator, is an electronic component that transfers electrical signals between two isolated circuits using light. It typically consists of a light-emitting diode (LED) and a photosensor (such as a phototransistor or photodiode) enclosed in a single package. When an electrical signal is applied to the LED, it emits light, which is detected by the photosensor to generate a corresponding signal in the output circuit. This design provides electrical isolation between input and output, preventing noise, voltage spikes, or high voltages from propagating between circuits, thus enhancing system safety and stability. Opto-couplers are widely used in power supplies, industrial controls, medical equipment, and communication systems.