• A semiconductor device which allows electrical signals to be transferred between circuits, devices, or systems, while maintaining electrical isolation between them. A photocoupler may consist, for instance, of an LED or IRED for signal transmission, and a photodetector, such as a photodiode, for signal reception. The signal transmitter converts the electrical signal into an optical signal, while the receiver restores the original electrical signal. Used, for instance, in communications, and in control systems. Also spelled photo-coupler. Also called photoisolator, optical coupler, optical isolator, optocoupler, optically-coupled isolator, or optoelectronic isolator.