The present invention concerns an arrangement for reading an optically readable carrier having a substrate with diffractive tracks with respective longitudinal axes and formed of a succession of irregularities with respect to a smooth reference surface. The irregularities have a width of at most two...http://www.google.com.au/patents/US5373500?utm_source=gb-gplus-sharePatent US5373500 - Optical readable carrier with diffractive tracks containing information bearing irregularity
