Patent ID: 7529169

Claim:
An optical disc device for recording and reproducing information by forming marks and lands in a rewritable DVD disc, comprising: recording means for recording information using a reference write strategy and an alternative write strategy in which pulse widths of 3T, 4T and 5-14T marks are individually varied by a set amount with respect to the reference write strategy, when the information is recorded using a 1T strategy; reproducing means for reproducing the recorded information using each of the reference write strategy and the alternative write strategy; mark length measuring means for measuring a length of each of the marks from the reproduced information; memory for storing the measured length of each of the marks, and also storing a theoretical length of each of the marks; contractile rate computing means for computing inherent contractile rates of the marks from the measured lengths and the theoretical lengths of the marks stored in the memory; variance computing means for computing a variation rate of the inherent contractile rate of each of the marks from the computed inherent contractile rate when pulse widths of 3T, 4T and 5-14T marks are individually varied by a set amount with respect to the reference write strategy, and obtaining a variance of each of the marks based on equation 1 : K = ∑ i = 3 14 ⁢ ⁢ ( dev ⁢ ⁢ ( iT ) - Avg ) 2 * R ⁢ ⁢ ( iT ) , ( 1 ) where dev(iT) is a deviation of the iT mark; “Avg” is a mean value of the deviations of all the marks; and where R(iT) is a probability of occurrence of mark (iT) and is a known value; and write strategy setting means for setting the write strategy such that the variance when the pulse widths of the 3T, 4T and 5-14T marks are individually varied is minimized.