An optocoupler including: a substrate comprising a photodetector; a transparent electrically-insulating layer disposed over the photodetector; and an organic electroluminescent device having an organic electroluminescent layer disposed between a first and a second electrode disposed over the transparent electrically-insulating layer; the photodetector arranged to detect light emitted from the organic electroluminescent device; wherein the optocoupler comprises a second current path between the first and second electrodes in addition to a first current path between the first and second electrode which in operation causes the organic electroluminescent layer to emit light.