<p>The opto-coupler includes a transparent substrate (2) which has electrodes on its top and underside. The electrode sets are coupled to a light emitter (22) on one substrate surface and to a light receiver (26) on the other substrate surface. The light receiver is located opposite to the light emitter. The light emitter and receives are covered in plastics (30). Pref. the substrate is so formed as to contain a fastening region, whose one side forms a protrusion, while the other side forming a recess. The light emitter and receiver are coupled to the fastening region in mutual opposition across the substrate.</p>
