Partial response recording in radial direction

Virtually all modulation methods developed for optical disk systems are designed in the same way as communication systems. Namely, the modulated output is always considered as a 1-D signal stream, even though the recorded signals on the disc form 2-D pit-patterns. We propose a novel recording method which utilizes the 2-D nature of optical disks. With this method, which we name RPR (Radial direction Partial Response), we can use narrower track pitch for ROM systems. Using DVD equivalent optical pickup, we demonstrate that low enough error rate can be obtained with 0.45 micron track pitch and a linear recording density of 0.29 microns/bit. By adopting ZCAV (Zone Constant Angular Velocity) format, and by carefully choosing the length of sync area, the proposed method is possible to increase the capacity of conventional optical disc systems. This method read out information recorded in two adjacent tracks at the same time. The crosstalk between two adjacent tracks is removed by pre-coding. We show experimental results when this method, RPR, is applied to the SCIPER multilevel signal recording method.