The present invention relates to an replacement process upon a recording failure in an optical disc having a plurality of layers, an optical disc apparatus and an information recording method for recording information onto the optical disc.
For a DVD-RAM, a Blu-ray Disc (hereinafter, referred to as BD) and an HD DVD Disc (hereinafter, referred to as HD) which can perform recording, their specifications describe an replacement process to be performed upon a recording failure in a data region. After information is recorded and the recorded information is reproduced, the reproduction signal is evaluated. If the reproduced signal is defective, the “replacement process” is executed. That is, upon detection of a recording failure, the replacement process records the same information as the recorded information in a predetermined region on the disc. The predetermined region will be referred to as a spare area and the reproduction signal quality evaluation operation will be referred to as verify. The spare area is arranged in the inner circumference and the outer circumference of the DVD-RAM, the BD, and the HD. The replacement process and improvement of its reliability are detailed in JP-A-2006-85797 and JP-A-2006-185509.
On the other hand, recently, in order to increase the recording capacity, various types of recording discs have multiple layers. Currently, two-layer recording media are normalized in the DVD-R/RW, +RW, BD. Unlike the single-layer disc, the multi-layer disc should consider affect to the other layer upon recording. The multi-layer recording technique is detailed in JP-A-2000-311346.
Since recording into the spare area is for protection upon a recording failure in the data region, it is necessary to increase the reliability of the recording operation as compared to recording operation in the normal data region.
On the other hand, when the optical disc has multiple layers, the following occur as affects from other layers.
[1] Leak-in of a stray light signal is generated by irregularities of inter-layer distance in the disc plane.
[2] Leak-in of a stray light signal and an information signal is generated by a pseudo-focal point and focal point-shifted spot in the layer other than the recording or the reproduction layer.
[3] Recording irregularities are generated by a difference in transmittance in other recorded and unrecorded layers.
The leak-in of the stray light by [1] or [2] lowers the signal S/N, which in turn lowers the servo stability and lowers the reliability of the recording and reproduction operation. Furthermore, when the inter-layer thickness is made constant so as to reduce the multi-layered disc manufacturing cost, the leak-in of the pseudo-signal of [2] is generated. This causes fluctuations by leak-in of a servo error signal and lowering of the signal quality by leak-in of a reproduction signal. In such a condition, an error is caused in the reproduction quality evaluation of a recording signal upon verify and it becomes impossible to guarantee a correct verify operation. As for [3], since the recording film state is different in the mark and the space portion of the data recording portion, the transmittance differs and the recording may not be performed uniformly. These affects become greater as the number of layers in the disc increases and the inter-layer gap decreases.
The aforementioned JP-A-2006-85797 and JP-A-2006-185509 disclose a technique of data rearrangement and modification of a recording position so as to improve the reliability of the replacement process but do not consider the aforementioned problems in the multi-layer disc. Moreover, as a method for improving the reliability among the aforementioned objects, JP-A-2000-311346 discloses a correction method for recording power learning in the recorded and unrecorded portions of the multi-layer disc. According to the method, it is possible to improve the reliability of the recording learning, or recording parameter adjusting, in the multi-layer disc. However, no consideration is taken on the improvement of recording reliability for the recording operation, especially in the recording in the spare area.