Optical type information recording medium having specified pit and guide groove shapes

Claim 1

An optical type information recording medium comprising: guide grooves for tracking formed in a concentric or spiral shape at a predetermined pitch; and a pre-format pit formed approximately midway between the guide grooves for recording at least address information; said optical type information recording medium being constructed such that said predetermined pitch is from 1.4 μm to 2.0 μm, said pre-format pit has a depth from 0.46λ/n to 0.58λ/n, where n is the refractive index of a substrate of the medium and λ is the wavelength of a light source for reading the information recorded in the medium, said pre-format pit having a cross-sectional shape defined by a first inequality, F.sub.1 (x)≦y≦F.sub.2 (x) where x and y in said first inequality are coordinates having an origin located at approximately the mid-point between adjacent guide grooves on a substrate face of the medium, F 1 (x) is a function representing the cross-sectional shape of the pre-format pit at a maximum depth in a y-direction and F 2 (x) is a function representing the cross-sectional shape of the pre-format pit at a minimum depth in the y-direction; and when y=f 1 (x)=(1.5/780)(λ/n)((3×10 -3 )x 2 -400), then F 1 (x)=0 when f 1 (x)≧0, F 1 (x)=f 1 (x) when 0≧f 1 (x)≧-0.58λ/n, and F 1 (x)=-0.58λ/n when -0.58λ/n≧f 1 (x); when y=f 2 (x)=(1.5/780)(λ/n)((20×10 -3 )x 2 -350), then F 2 (x)=0 when f 2 (x)≧0, F 2 (x)=f 2 (x) when 0≧f 2 (x)≧-0.46λ/n, and F 2 (x)=-0.46λ/n when -0.46λ/n≧f 2 (x); the cross-sectional shape of said guide grooves is defined by a second inequality, G.sub.1 (x)≦y≦G.sub.2 (x) where x and y in said second inequality are coordinates the origin of which is at a center of a guide groove on the substrate face of the medium, G 1 (x) is a function representing the cross-sectional shape of the guide grooves at a maximum depth in a y-direction, and G 2 (x) a function representing the cross-sectional shape of the guide grooves at a minimum depth in the y-direction, and when y=g 1 (x)=(1.5/780)(λ/n)((1.5×10 -3 )x 2 -150), then G 1 (x)=0 when g 1 (x)≧0, and G 1 (x)=g 1 (x) when g 1 (x)≦0; and when y=g 2 (x)=(1.5/780)(λ/n)((2.5×10 -3 )x 2 -60), then G 2 (x)=0 when g 2 (x)≧0 and G 2 (x)=g 2 (x) when g 2 (x)≦0.