# US 5,708,651 A · Optical disk having reduced track pitch and optical disk playback apparatus containing the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,708,651 A - Document ID: US5708651A - Status: Granted - Kind: A - Application number: 08/738,656 - Filed: 1996-10-30 - Granted: 1998-01-13 - Earliest claimed: 1994-01-19 - Assignees: Kabushiki Kaisha Toshiba - Inventors: Toshihiro Sugaya; Yoshinori Honguh - Web page: https://patentgrep.com/patent/US5708651A ## CPC - H04N 9/8042: {involving data reduction} - G11B 7/0051: {involving phase depth effects} - G11B 7/0938: {servo format, e.g. guide tracks, pilot signals} - G11B 7/24038: Multiple laminated recording layers - H04N 5/85: on discs or drums - G11B 7/24079: Width or depth (G11B7/24076 takes precedence) - G11B 7/24085: Pits - H04N 9/87: Regeneration of colour television signals (H04N9/80 takes precedence) - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract An optical disk comprises a substrate, and a recording layer which is formed on the substrate and on which information is recorded at specific pitches in the form of pit trains, wherein the information is reproduced by projecting a light beam via an object lens, and when the wavelength of the light beam is .lambda. .mu.m and the numerical aperture of the object lens is NA, the track pitch is set in the range of (0.72 to 0.8).times..lambda./NA/1.14 .mu.m, and each of the pits has a trapezoid cross section whose upper width is in the range of (0.3 to 0.5).times..lambda./NA/1.14 .mu.m and whose lower width is in the range of (0.2 to 0.32).times..lambda./NA/1.14 .mu.m or whose inner wall has an angle of 30.degree. to 70.degree.. ## Claims ### Claim 1 An optical disk comprising: a circular 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; and a reflecting layer formed on said substrate, said information being reproduced by projecting a light beam via an objective lens, 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. ### Claim 2 (depends on 1) An optical disk according to claim 1, further comprising: a secondary substrate having secondary information recorded thereon at said track pitch, said secondary information being recorded as a second plurality of pit trains, each of said pit trains including a plurality of pits; and a secondary reflecting layer formed on said secondary substrate, said reflecting layer and said secondary reflecting layer being disposed between said substrate and said secondary substrate. ### Claim 3 (depends on 2) An optical disk according to claim 2, further comprising a pair of protective films formed on said reflecting layer and said secondary reflecting layer, respectively, between said reflecting layer and said secondary reflecting layer. ### Claim 4 (depends on 3) An optical disk according to claim 3, further including an adhesion layer formed between said protective films to adhere them to each other. ### Claim 5 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. ### Claim 6 (depends on 5) An optical disk apparatus according to claim 5, wherein said sensing means produces a push-pull signal and a playback signal, said push-pull signal representing a difference between signals sensed in at least two areas along a track of said optical disk, and wherein each of said pits has a depth to enable both said push-pull signal and said playback signal to have large levels. ### Claim 7 (depends on 5) An optical disk apparatus according to claim 5, wherein said sensing means has a function of expanding said information compressed according to MPEG2 and recorded on said optical disk according to MPEG2, to reproduce said information. ### Claim 8 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.