The Early History of the Optocoupler

The optocoupler is still today a key element for safe interfacing control electronics to high power electrical circuits, but with an interesting origin, more related to the initials of the early use of semiconductors in counting devices and on the other side to early analog electronic music circuits. Its development started in the late fifties of the last century at the Bell Labs and HP research laboratories, and already in the early sixties IBM obtained the patent of the most popular configuration with an III-V semiconductor based LED emitter and a Silicon phototransistor as receiver. The first industrial application, however, is related to the development of early digital counter displays, enabling the interfacing of transistor based electronics with high voltage requiring Nixie display tubes. Since the seventies of the last century space applications of this device became important and the future of this electronic component in this field will strongly depends on the possibility to obtain higher reliability also under extreme conditions.