INFORMASJONSBAERER MED SPIRALFORMET STRUKTUR

摘要

1391541 Record carriers; optical playback apparatus PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 1 March 1972 [4 March 1971] 9487/72 Heading G5R [Also in Divisions G2 and G1] A disc record carrier 1 has spiral or concentric tracks 12, 13 in which audio and/or video information in the form of frequency-modulated or phase-modulated signals is stored as a crenellated structure 3-7 in which the upstanding blocks 3, 5, 7 have different lengths and spacings and have a height comparable to optical wavelengths. The record may be of, e.g. polyvinyl acetate, made lithographically, or by photographic and etching methods. The blocks 3, 5, 7 preferably have a coefficient of reflection or transmission equal to that of the intervening areas 4, 6. The record 1 is played back optically by transmission or reflection as the disc is rotated. As shown, light from a source 20 passes through a polarizer 21, a Wollaston prism 22 and the record 1, and is focused on a detector 23 by a lens 25 via a second Wollaston prism 24 and an analyser 26. The prism 24 splits the beam into two diverging perpendicularly-polarized beams with intensities which may differ due to the varying path length of the light in the record 1. The prisms 22, 24 may be replaced by Savart plates having the same function. In an alternative arrangment, Fig. 3 (not shown) a Michelson interferometer (32) splits the transmitted beam. In a further embodiment, Fig. 4 (not shown) the record is illuminated with a collimated beam to produce diffraction. The + 1st and - 1st order beams are phase-shifted by 90 degrees relative to the zero order beam by a phase plate (68) and are combined by a lens (67). The tracks may alternatively be scanned by a focused point of light, Fig. 6 (not shown). In a reflection arrangement, Fig. 5 (not shown) light scattered by the side faces of the blocks 3, 5, 7 is focused on a detector (73) by an annular lens (75). A suitable light source is a laser, photo-diode or gas discharge tube. A suitable detector is a photomultiplier or solid-state device.