Optocoupler is made of semiconductor material. The LED is used as a light source while the phototransistor is used as a light sensor. Commercially. An Optocoupler or an Opto-isolator (also known as photocoupler and optical isolator) is an electronic component that transfers signals using optical path between two electrically isolated circuits through light. The main purpose of an optocoupler is to prevent high voltages or voltage spikes on one side of the barrier from. All optocouplers consist of two elements: a light source — almost always a light-emitting diode (LED) — and a photosensor — typically a photoresistor, photodiode, phototransistor, silicon-controlled rectifier (SCR), or triac.