| 摘要 |
PURPOSE:To track two spots by making the interval between centers of two laser spots in the radial direction of a disc slightly shorter or longer than a half of the interval between mountains of V grooves. CONSTITUTION:The interval between centers of two laser spots in the radial direction of the disc is made shorter than a half of the interval between mountains of V groooves by 2delta. When the interval between mountains of V grooves is denoted as P, a 2sin(2pidelta/P)-fold signal of a tracking signal due to one laser spot is obtained. In this case, a recording part (recording bits) 22 is obtained on a recording material thin film 21. The upper limit of the length delta is deltamax=(P/2- nu)/2 where nu is the width of recording bits 22 for the purpose of preventing overlap of recording bits 22-1 and 22-2. For example, if the track pitch P is 1.6mum and the recording bit width nu is 0.6mum, the upper limit deltamax is 0.1mum, and the tracking signal from two spots is >=77% of that due to only one spot and is enough. |
