An optical sensor having at least one optical transmitting unit for production of a transmitted light beam, a photosensitive flat detector with semitransparent characteristics, through which the transmitted light beam passes, and which re-receives reflection light beams, i.e., from an object, and an evaluation unit for the photoelectric current of the photosensitive flat detector, at least for detection of an object. The photosensitive flat detector advantageously includes an organic polymer layer comprising a photosensitive substrate. An “Organic Photosensitive Diode” (OPD) is particularly advantageously used as the photosensitive flat detector with semitransparent characteristics.