Abstract: Disclosed is apparatus for effecting optical coupling between at least one photo-emissive device and at least one photo-sensitive device while maintaining electrical isolation between the devices. The light-emitting chip and the photo-sensitive chip are mounted on an electrically insulating substrateor substrates with their major faces in substantially the same plane and facing the same direction. The insulating substrate is mounted on a conventional header and leads attached to each of the active regions by conventional methods. The light emitter and sensor are then encapsulated in a single hemispherical dome of electrically insulating material which is substantially transparent to the operative wavelengths of the electro-optical devices. Optical coupling is accomplished by direct coupling between the edges of the chips and by internal reflection from the surface of the dome.