Two-dimensional run-length-limited code and partial response maximum likelihood system with multi-track recording

In optical disk systems, user data is recorded along a continuous spiral track by using 1D run-length-limited (RLL) codes. Track pitch and bit pitch are strongly related to the wavelength of the laser and the numerical aperture (NA) of the lens. A narrower track pitch or bit pitch increases cross-talk and degrades the signal to noise ratio (S/N). Certain phase-change optical disk formats adopt land and groove recording, because the phase difference of the light reflected from adjacent tracks decreases cross-talk. A cross-talk cancellation scheme using 2D equalization has been studied (Y. Tomita et al, Jpn. J. Appl. Phys., vol. 40, pt. 1, no. 3B, pp. 1716-1722, 2001). Canceling cross-talk is one way to increase recording density. However, if inter-track interference (ITI) remaining in the read-out signal increases, amplification of noise at the filter of the cross-talk canceller increases. Thus, for extremely high-density recording, the read-write and detection method should incorporate a means of dealing with heavy ITI. In this paper, we propose a 2D RLL code and a 2D partial response maximum likelihood (PRML) system that has the potential to increase media capacity of next-generation optical disk systems without significantly changing the laser wavelength or the lens NA.