Optical disk having reduced track pitch and optical disk playback apparatus containing the same

An optical disk apparatus comprising:

• an optical disk including a circular substrate and a reflecting layer formed on said substrate, said substrate having information recorded thereon with a track pitch, said information being recorded as a plurality of pit trains, each of said pit trains including a plurality of pits;
• an objective lens disposed so as to face said optical disk;
• means for projecting a light beam onto said optical disk via said objective lens;
• and
• means for sensing reflected light of said light beam projected on said optical disk by said projecting means to reproduce said information recorded on said optical disk,
• wherein when wavelength of said light beam is .lambda. .mu.m and numerical aperture of said objective lens is NA, said track pitch is in the range of (0.72 to 0.8).times.(.lambda./NA)/1.14 .mu.m, radial tilt is not more than 9.5 mrad, thickness of said substrate is 0.6 mm, and diameter of said circular substrate is 120 mm.

An optical disk comprising:

• a pair of transparent circular substrates with surfaces facing one another, each of said transparent circular substrates having information recorded thereon at a track pitch, said information being defined by a plurality of pit trains, each of said pit trains including a plurality of pits, said information being reproduced by projecting a light beam via an objective lens;
• a pair of reflecting layers coated on said facing surfaces of said pair of circular substrates, respectively;
• a pair of protective layers formed on said pair of reflecting layers, respectively;
• and
• an adhesive layer formed between said protective layers to adhere said pair of protective layers to one another,
• wherein when wavelength of said light beam is .lambda. .mu.m and numerical aperture of said objective lens is NA, said track pitch is between (0.72 to 0.8).times.(.lambda./NA)/1.14 .mu.m, radial tilt is not more than 9.5 mrad, thickness of each of said substrates is 0.6 mm, and diameter of said circular substrates is 120 mm.