Optoisolator, also known as an optocoupler or photocoupler, is a device used to separate two electrical circuits by using light. It consists of a light-emitting diode (LED) and a light-sensitive semiconductor device, typically a phototransistor or photodiode. The LED emits light that is then detected by the semiconductor device, creating an electrical signal that is isolated from the original circuit. Other synonyms for optoisolator include photoelectric isolator, optoelectronic isolator, light-coupled isolator, and photo-isolator. These devices are commonly used in electrical systems where a high level of electrical isolation is required, such as in power converters, motor drives, and medical equipment.