Multi-layer optical information recording medium

A multi-layer optical information recording medium comprising four or more information recording layers on which signal information is recorded with any one of information pits whose concave-convex surfaces or phases change and recording marks whose reflectances or phases change,

• wherein the information recording layers are denoted by the m-th information recording layers, where m is any integer that is 0 or larger, an information recording layer that is farthest from an objective lens of a reproduction optical pickup being denoted by a 0th information recording layer, spacers being interposed between the information recording layers, the spacers being made of a transparent material and having nearly constant thicknesses,
• wherein when the thickness of the spacer interposed between the m-th information recording layer and an (m+1)th information recording layer is denoted by tm, the thickness of the spacer interposed between the (m+1)-th information recording layer and a (m+2)-th information recording layer is denoted by tm+1, the difference between the thicknesses tm and tm+1 of the spacers is denoted by Δtm, the sum of the thicknesses of the spacers interposed between the m-th information recording layer and a (m+a)-th, where a is any integer that is 2 or larger, information recording layer is denoted by (tm+tm+1+ . . . +tm+a−1), the sum of the thicknesses of the spacers interposed between the (m+a)-th information recording layer and a (m+b)-th, where b is any integer that is 2 or larger, is denoted by (tm+a+tm+a+1+ . . . +tm+b−1), and the difference between the sum (tm+tm+1+ . . . +tm+a−1) and the sum (tm+a+tm+a+1+ . . . +tm+b−1) is denoted by Δtm−sum, then the thicknesses of the spacers are designated so that Δtm and Δtm−sum satisfy formulas (1) and (2):
• Δtm>ACCT×Rm+1×Rm+2×Tm+12×nλ/(2NA2) (1)
• Δtm−sum>ACCT×Rm+a×Rm+b×Tab2×nλ/(2NA2) (2)
• where ACCT represents a crosstalk index, Rm+1, Rm+2, Rm+a, and Rm+b represent an intensity reflectances associated with reflective films formed on the (m+1)-th layer, (m+2)-th layer, (m+a)-th layer, and (m+b)-th layer, respectively, Tm+1 represents an intensity transmissivity of the spacer tm+1, Tab represents an intensity transmissivity from the (m+a)-th information recording layer to the (m+b)-th information recording layer, n represents a refractive index of the spacer material, and NA represents a numerical aperture of the objective lens.