Characteristics of a DVD double-layer disk in an optical disk drive

In an optical disk drive, when the laser scanning spot is in focus, both the optical readout high-frequency signal (HF) and radial-error (RE) signal are optimized and thus their amplitudes are maximized to achieve best system performance and have jitter at its minimum. However, while reading on a DVD double-layer disk, the maximum RE signal does not align with the system jitter minimum but is displaced by a focus offset. Simulation results demonstrate that the thickness variation of a DVD disk substrate plays an important role to contribute to the focus offset disalignment of RE maximum and jitter minimum. Further, the intervention of interlayer crosstalk degrades both HF and RE signals, which also contributes to the offset behavior while reading a DVD double-layer disk. It is essential that the drive designer be aware of this offset behavior in order to design the optical drive for reliable interchangeability. To appropriately compensate for the focus offset behavior while reading and recording on a DVD double-layer disk, a self-calibration algorithm is proposed to accomplish optimal jitter performance during reading and recording on a DVD double-layer disk.