Optical disk memory for recording reproducible information

An optical disk comprising first and second track groups which form a hill and valley structure, wherein light modulating regions are formed on one of said track groups, and a width of one of said light modulating region is greater than a width of said track, wherein a light beam is focused on said light modulating regions by a lens, and said optical disk satisfied the following expressions:

• H=(2n-1).times..lambda./4,
• and
• r<0.61.lambda./NA;
• where,
• H is the step height between a top surface of one of said land tracks and a bottom surface of said groove track,
• n is a natural number,
• .lambda. is the wavelength of the light beam,
• r is the interval between said neighboring land tracks, and
• NA is the numerical aperture of the lens.

A method for reproducing an information from an optical disk having land tracks and a groove track separating said land tracks, said method comprising:

• irradiating a light beam onto an light modulating region extending from said land track to said groove track, wherein the light beam is reflected by the light modulating region and the intensity of the light beam is changed by the reflection;
• and
• detecting the reflected light beam with a photodetector,
• wherein the light beam is focused on said light modulating regions by a lens, and said optical disk satisfies the following expressions:
• H=(2n-1).times..lambda./4,
• and
• r<0.61.lambda./NA;
• where,
• H is the step height between a top surface of one of said land tracks and a bottom surface of said groove track,
• n is a natural number,
• .lambda. is the wavelength of the light beam,
• r is the interval between said neighboring land tracks, and
• NA is the numerical aperture of the lens.