Optical recording medium, manufacturing method for optical recording medium, information recording/reproducing method and information recording/reproducing device

Abstract

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.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to an optical recording medium irradiated with light to record or reproduce information. Particularly, it relates to a layer-interval structure of an optical recording medium having three or more information recording surfaces, and a method or a device for reproducing information on the multilayer optical recording medium or recording information therein.[0003]2. Description of the Background Art[0004]A high-density and large-capacity optical information recording medium is on the market—typically, an optical disk such as a DVD or a BD. The optical disk has recently become increasingly popular as a recording medium for recording an image, music or computer data. In order to increase the recording capacity, an optical recording medium having a plurality of recording layers has been offered, as described in Japanese Patent Laid-Open Publication No. 2001-155380 or Japanese Patent Laid-Open Pub...

AI Technical Summary

Benefits of technology

[0015]It is an object of the present invention to provide an optical disk (optical recording medium) capable of preventing a back focus at the face thereof and reducing the interference between beams reflected by each recording surface in consideration of a refractive index, and having a multilayer disk structure of three, four or more recording layers capable of widening the distance between the face and the recording layer closest to the face to the maximum.

Problems solved by technology

This causes the problem of super imposing multiple reflected beams from images formed on the back sides of other layers on the reflected beam from the fourth recording surface 401d which should be naturally read to thereby hinder the recording / reproduction.

The mixed beams tend to interfere and form a brightness distribution through interference on a light-receiving element, and the brightness distribution varies according to the change in the phase difference between the reflected beam from the fourth recording surface 401d and a reflected beam from another layer which is caused by a slight dispersion of intermediate-layer thicknesses inside of the face of an optical disk, thereby significantly deteriorating the quality of a servo signal and a reproductive signal.

However, if there are a large number of recording layers, the quantity of light returning from the recording layers decreases to thereby heighten the reflectance of the face relatively.

Accordingly, interference with a luminous flux on a reproduction layer occurs likewise, thereby significantly deteriorating the quality of a servo signal and a reproductive signal.

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