| 摘要 |
An optical recording medium is capable of preventing a back focus at the face thereof and reducing the interference between beams reflected by each recording surface, thereby improving the quality of a servo signal and a reproductive signal. In a disk having (N-1) layers if N is a natural number (more than three), if a cover-layer thickness and intermediate-layer thicknesses are d1, d2, . . . dN, then a difference of 1 μm or above is set between the sum of di to dj and the sum of dk to dm for arbitrary natural numbers i, j, k, m (i≦̸j≦̸k≦̸m≦̸N). If the refractive indexes are different from a standard value or different for each layer, the thickness of each layer is converted on the basis of the spread width of light according to the thickness.
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