Using pit-depth modulation to increase capacity and data transfer rate in optical discs

The technique of pit-depth modulation is applied to optical data storage. Pits of M possible depths are written end-to-end to form a groove encoding log,(M) bits in each mark. Data was encoded onto discs with CD, dimensions using standard photoresist-mastering and replication methods. Methods for removing inter-symbol interference are demonstrated on pits as short as 0.6 mu m. A 6-level pattern of 0.6 mu m pits was read by an optical head from a 6x CD-ROM drive and the original levels were recovered with a standard deviation of similar to 6% of the dynamic range. A system prototype read data encoded as 4-level 0.8 mu m pits with a raw bit error rate of 3x10(4).