The Research On Blu-Ray Disc Tilt And Tilt Detect Method

In the digital multimedia field, disc capacity is increasing remarkably with the needs of high quality image and longer playing time. Accordingly, the accuracy of servo system must be further improved. Two-dimensional servo system which is commonly used in DVD reading system could not achieve current servo requirement. In the next-generation blue-ray disc system, the influence of disc radial tilt is too significant to ignore, we need to detect and servo it to improve the performance of blue-ray disc system. In this thesis, we made detailed analysis on the effect of radial tilt on disc reading and servo signals.In the frame of scalar diffraction theory, and by using practical model of blue-ray disc, we calculate and analysis the intensity distribution of focusing spot and exit pupil, also including DPP tracking error signal in both ideally and radial tilt occurred situations. Detailed analysis is set forth on the offset of tracking error signal using DPP method. In 50GB blue-ray disk system, a more practical disc model including elliptical pit shape is used to simulation. Compare to the traditional rectangular pit shape model, it significantly improve the accuracy of the result when calculate DPP tracking error signal.Result shows that the intensity distribution of focusing spot and exit pupil is unbalance when radial tilt occurred. In 25GB blue-ray disc system the allowable radial tilt angle should be smaller then 0.39o to make sure that the blue-ray disk is read correctly. So we may consider to add radial tilt servo system when tilt angle larger than 0.39o.In 50GB blue-ray disc system, the sensitive of radial tilt is more remarkable, to make sure the system read correctly the tilt angle should be smaller than 0.15o.As the result, we need to add radial tilt servo system to improve its performance. Compared the calculate result of DPP tracking error signal between elliptical pit shape and traditional rectangular pit shape model, we could draw the conclusion that the elliptical pit shape model can significantly improve the accuracy of calculation.