| 摘要 |
1513873 Optically-readable records THOMSON - BRANDT 14 May 1975 [15 May 1974] 20456/75 Heading G5R A recording medium optically readable by transmission comprises a transparent sheet 2 carrying at a face 3 thereof a relief impression made up of a succession of peaks and troughs along a track and representing recorded data, and a transparent protective layer on said face 3 having an inner face contacting and following the relief impression and an outer face 9 which is substantially smooth, the sheet 2 and protective layer forming a dioptic element which diffracts the read beam. The protective layer has a different refractive index to that of sheet 2 and to optimise the diffractive action the trough depth e 1 must be made greater than that required in the absence of a protective layer. The sheet 2 may be of polyvinylchloride and the protective layer may be of cellulose nitrate polyvinyl carbazole, polymethyl methacrylate, paylene, or a low refractive index silicone class compound. The sheet 2 may be covered by applying, e.g. by dipping, rolling or spraying, a solution of the protective layer in a solvent which subsequently evaporates. The protective layer may alternatively be applied by deposition from the gas phase. A further protective layer (12), of the same material as sheet 2, may be applied to the outer face of the first protective layer, Fig. 3 (not shown), and a sheet 2 having recordings on each side may have such dual layers covering both sides, Fig. 4 (not shown). The record medium may be a flexible or rigid disc carrying a spool-track recording of a carrier signal angle-modulated by a data signal. |
