Source: https://patents.google.com/patent/EP0452953A2/en
Timestamp: 2018-06-24 11:54:16
Document Index: 152079221

Matched Legal Cases: ['art 7', 'art 6', 'art 7', 'art 7', 'art 7', 'art 7']

EP0452953A2 - Optical head - Google Patents
EP0452953A2
EP0452953A2 EP19910106332 EP91106332A EP0452953A2 EP 0452953 A2 EP0452953 A2 EP 0452953A2 EP 19910106332 EP19910106332 EP 19910106332 EP 91106332 A EP91106332 A EP 91106332A EP 0452953 A2 EP0452953 A2 EP 0452953A2
EP19910106332
EP0452953A3 (en )
In an optical disc recording-reproducing apparatus using a standard optical disc enclosed in a cartridge (1), an optical plate (19) for correcting various aberrations generated by a focusing lens (18) is comprised therein in order to allow use of a double recording optical disc enclosed in a standard cartridge of the same size; the optical plate (19) is placed in front of the focusing lens (18) when the double recording optical disc is used, and is removed from the front of the focusing lens (18) when the standard optical disc is used.
FIG.1 is a side view of an optical disc recording-reproducing apparatus of an embodiment in accordance with the present invention;
FIG.2(a) is a cross-section of an optical disc according to the draft proposal DP10090 of ISO standard;
FIG.2(b) is a cross-section of an optical disc having recording areas on both sides of the optical disc;
FIG.3 is a graph of a relation between a numerical aperture and a peak intensity ratio of a laser beam.
FIG.1 is a side view of an optical head of an embodiment in accordance with the present invention. Referring to FIG.1, an optical disc 2 is enclosed in a cartridge 1 having an aperture 101 covered by a transparent member 102 on the lower face thereof to allow passing of laser light. The cartridge 1 is set to a driving apparatus comprising a driving motor 4, and the optical disc 2 is rotated by a shaft 5 of the driving motor 4. The cartridge 1 has identification pits (or holes) 23 on the circumferential part thereof. The identification pits 23 are sensed by a detector 3 comprising a light source and a light sensing device, and a kind of cartridge is identified by the position of the identification pits 23. The detected output of the detector 3 is output on a terminal 24.
A moving optical part 7 is movably held by a guide rail 22 secured to the stationary optical part 6, and is moved along the guide rail 22 by a linear driving motor 21 mounted on the moving optical part 7 in a direction shown by arrow A. The moving optical part 7 comprises a reflection mirror 17 for directing the laser beam 16 upward in FIG.1, a focusing lens 18 for focusing the laser beam 16A reflected by the reflection mirror 17 on a recording area 8 of the optical disc on which information is recorded and an optical plate 19 for correcting aberration of the laser beam 16B focused by the focusing lens 18.
Referring to FIG.2(a), a spiral track 28 or a plurality of tracks 28 of concentric circles are formed on a surface of a substrate 27 made of transparent material such as polycarbonate plastics or glass. According to the Draft Proposed DP10090 of ISO Standard, the substrate 27 is 1.2 mm thick (t1) and the entire thickness (t) is 1.4 mm. A recording layer 34 is plated on the face having the tracks 28, and further the recording layer 34 is covered with a protection layer 29 for protecting the recording layer 34 and tracks 28. Recording-reproducing operation of the optical disc 25 is performed by applying a laser beam 16B from the moving optical part 7 to the surface of the substrate 27.
Referring to FIG.2(b), tracks 35 are formed on a surface of a first substrate 30 in a similar manner of the standard optical disc 25. On the other hand, tracks 36 are formed on a surface of a second substrate 31 in a similar manner of the first substrate 30. Then, a recording layer 33 for recording information by variation of status of crystallization is plated on both the tracks 35 and 36. Subsequently, the first substrate 30 is adhered with the second substrate 31 by suitable adhesive substance 37 in a manner that the surface having the tracks 35 of the substrate 30 faces to the surface having the tracks 36 of the second substrate 31. Both the substrates 30 and 31 are 0.6 mm thick (t2) and the adhesive substance 37 is made to 0.2 mm thick, and consequently, the entire thickness is 1.4 mm.
The focusing lens 18 is adequately designed in a manner that various aberrations are minimized with respect to the standard optical disc 25 having the substrate of 1.2 thick. Therefore, in the double recording optical disc 26 shown in FIG.2(b), since the thickness t2 of the first substrate 30 is 0.6 mm, which is thinner than that of the substrate 27 of the standard optical disc 25, the various aberrations increases. In order to correct the various aberrations in the double recording optical disc 26, an optical plate 19 made of a flat-plate optical member is inserted between the focusing lens 18 and the double recording optical disc 26. The laser beam 16B focused by the focusing lens 18 is applied to the double recording optical disc 26 through the optical plate 19. Consequently, the double recording optical disc 26 and the standard optical disc 25 are compatibly usable in the same optical disc recording-reproducing apparatus by insertion or removing of the optical plate 19. In the double recording optical disc 26, the distance between the focusing lens 18 and the recording area 35 must be kept on the same value as that in the standard optical disc 25 to focus the laser light 16B on the recording area 34 which is nearer than the recording area 35 of the standard optical disc 25 to the focusing lens 18. The shift of the focusing lens 18 is performed by the focusing lens drive means 18A (shown in FIG.1).
t3 = (n1 · t1 - n2 · t2)/n3   (1),
refractive index of substrate 27,
refractive index of substrate 30,
refractive index of optical plate 19,
thickness of substrate 27,
thickness of substrate 30.
Recording operation of the standard optical disc 25 is elucidated hereafter for a magneto-optical disc. The direction of magnetization of the recording layer 34 is oriented into a predetermined direction by erasing operation in advance. Subsequently, a laser beam of which the diameter of the cross-section is 1 µm or smaller is applied to a predetermined position of the recording layer 34. The intensity of the laser beam 16B is selected to heat the recording layer 34 to the Curie temperature or higher. Then biasing magnetic field is applied to the recording layer 34 by a magnetic field generating means (not shown) in concurrence with temperature rise of the recording layer 34, and thereby the direction of magnetization of the recording layer 34 is turned over. Namely, the recording of the information is performed by change of the direction of magnetization.
In reproducing operation of the double recording optical disc 26 shown in FIG.2(b), a side of the optical disc which is used presently for in recording-reproducing operation is faced to the moving optical part 7 and is set to the shaft 5 of the driving motor 4. The recording-reproducing operation is similar to that of the standard optical disc 25 shown in FIG.2(a).
D = (NA/λ)²   (2),
wavelength of the laser light.
In order to maintain the reduction of the intensity of the laser beam within several per cent in 0.2 degree of the tilt angle of the optical disc, the numerical aperture NA must be selected to 0.5 -- 0.55.
FIG.3 is a graph of relation between a numerical aperture NA and a "peak intensity" of the laser beam. The peak intensity represents an intensity of the laser light at a part having a maximum intensity in the cross-section of the laser beam focused on the recording layer 34. In the graph, abscissa is graduated by the numerical aperture NA, and ordinate is graduated by the peak intensity. The tilt angle of the optical disc is 0.2 degree, the refractive index of the substrate is 1.5, and the thickness t1 of the substrate of the optical disc is 1.2 mm, 0.6 mm or 0.3 mm. The graph is obtained by the calculation of "diffraction integration" according to "Kilchhoff's diffraction theory", and detailed description of the calculation is omitted.
Referring to FIG.3, when the thickness t1 is 1.2 mm and the numerical aperture NA is 0.5, the peak intensity is reduced to 99 %. On the other hand, when the numerical aperture NA is 0.65, the thickness t1 must be 0.6 mm and below in order to maintain 99 % of peak intensity. Furthermore, when the numerical aperture NA is 0.75, the thickness t1 must be 0.3 mm and below in order to maintain 99 % of peak intensity. In other words, an optical system having a large numerical aperture NA can be employed by reduction of the thickness of the substrate.
Influence of dust in recording-reproducing operation of an optical disc increases in proportion to the reduction of the thickness of the substrate of the optical disc, because the cross-section area of a laser beam on the surface of the substrate decreases in proportion to the reduction of the thickness of the substrate. The dust problem in the optical disc recording-reproducing operation is described in "System coding parameters, mechanics and electro-mechanics of the reflective video disc player", (IEEE Trans. on Consumer Electronics, page 309 -- 317, and FIG.19, Nov. 1976). According to this paper, when the thickness t1 is 0.6 mm or more, influence of dust can be ignored with respect to dust having a diameter of 75 µm and below. Moreover, when the thickness t1 is 0.3 mm, the influence of dust can be ignored with respect to dust having a diameter of 20 µm and below. Since the optical disc is enclosed in the cartridge 1, dust having 20 µm of diameter can not be entered into the cartridge 1. Therefore, the substrate of 0.3 mm thick is usable in the recording-reproducing apparatus.
Furthermore, in the optical disc having a thin substrate such as 0.3 or o.6 mm thick, the optical recording-reproducing operation is preferable to the magneto-optical recording-reproducing operation, because rotation of mere 0.2 degree of the plane of polarization must be detected in the magneto-optical recording-reproducing operation. On the contrary, in the optical recording-reproducing operation, the reproducing operation can be performed by detecting variation of reflection index by 20 -- 30 %.
R = (NA2/NA1)²   (3),
first numerical aperture,
second numerical aperture.
For example, the first numerical aperture NA1 is 0.53, and when the value 0.53 of the first numerical aperture NA1 is increased to a value 0.65 of the second numerical aperture NA2, the increase ratio R is about 1.5 ((0.65/0.53)²). Consequently, the recording capacity of the double recording optical disc 26 becomes three times (1.5 x 2 = 3) of that of the standard optical disc (384 MB, for example).
laser light emitting means (9) for emitting laser light,
collimating means (10,15) for collimating said laser light emitted by said laser light emitting means (9),
focusing means (18) for focusing said laser light collimated by said collimating means (10) on a recording area of an optical disc (2),
a beam splitter (11) for separating laser light reflected from said recording area (8) of said optical disc (2),
laser light sensing mean (14) for detecting laser light separated by said beam splitter (11),
at least one optical plate (19) for correcting aberration of said focusing means (18), and
actuator means (20) for positioning said optical plate (19) between said optical disc (2) and said focusing means (18) or for removing said optical plate (19) therefrom.
An optical disc recording-reproducing apparatus comprising:
collimating means (10) for collimating said laser light emitted from said laser light emitting means (9),
focusing means (18) for focusing said laser light collimated by said collimating means (10) on a recording area (8) of an optical disc (2) for recording information by means of said optical head.
a beam splitter (11) for separating laser light reflected from said recording area of said optical disc (2),
laser light sensing means (14) for detecting laser light separated by said beam splitter,
actuator means (20) for positioning said optical plate (19) perpendicular to the optical axes of said focusing means (18) or for removing said optical plate (19) therefrom.
An optical disc recording-reproducing apparatus in accordance with claim 2, wherein
said optical disc (2) is enclosed in a cartridge (1) having at least one identification pit (23) for identifying said optical disc (2) enclosed in said cartridge (1), and said identifying pit (23) is detected by a sensing means (3), hence said actuator means (20) is controlled by the output of said sensing means (3).
a first substrate (30) of at least 0.6 mm thick having a recording layer (33) on one side thereof,
a second substrate (31) of at least 0.6 mm thick having a recording layer (33) on one side thereof, and adhered to said first substrate (30) with adhesive substance (37) of at most 0.2 mm thick in a manner that the recording layer (33) of said second substrate (31) is faced to the recording layer (33) of said first substrate (30).
EP19910106332 1990-04-20 1991-04-19 Optical head Withdrawn EP0452953A3 (en)
JP106157/90 1990-04-20
JP328715/90 1990-11-27
EP19980104596 EP0862166B1 (en) 1990-04-20 1991-04-19 Method for recording/reproducing information on/from a recording optical disc
EP19980104595 EP0862165B1 (en) 1990-04-20 1991-04-19 System for recording/reproducing information on/from a recording optical disc
EP19980104594 EP0855702B1 (en) 1990-04-20 1991-04-19 Optical disc
EP19980104596 Division EP0862166B1 (en) 1990-04-20 1991-04-19 Method for recording/reproducing information on/from a recording optical disc
EP19980104595 Division EP0862165B1 (en) 1990-04-20 1991-04-19 System for recording/reproducing information on/from a recording optical disc
EP19980104594 Division EP0855702B1 (en) 1990-04-20 1991-04-19 Optical disc
EP0452953A2 true true EP0452953A2 (en) 1991-10-23
EP0452953A3 true EP0452953A3 (en) 1992-11-25
EP19980104594 Expired - Lifetime EP0855702B1 (en) 1990-04-20 1991-04-19 Optical disc
EP19980104596 Expired - Lifetime EP0862166B1 (en) 1990-04-20 1991-04-19 Method for recording/reproducing information on/from a recording optical disc
EP19980104595 Expired - Lifetime EP0862165B1 (en) 1990-04-20 1991-04-19 System for recording/reproducing information on/from a recording optical disc
EP19910106332 Withdrawn EP0452953A3 (en) 1990-04-20 1991-04-19 Optical head
EP (4) EP0855702B1 (en)
DE (6) DE69132579D1 (en)
EP0569597A1 (en) * 1991-11-20 1993-11-18 Sony Corporation Optical disk
EP0831466A2 (en) * 1996-09-24 1998-03-25 Nec Corporation Optical head having multiple light sources having different wavelengths
EP0439100A2 (en) * 1990-01-22 1991-07-31 Sharp Kabushiki Kaisha Optical head device
PATENT ABSTRACTS OF JAPAN, vol. 2, no. 32, 28th February 1978; & JP-A-52 153 705 (MITSUBISHI DENKI K.K.) 21-12-1977 *
EP0569597A4 (en) * 1991-11-20 1993-12-22 Sony Corporation Optical disk
EP1736976A2 (en) 1993-02-01 2006-12-27 Matsushita Electric Industrial Co., Ltd. Compound objective lens having two focal points and apparatus using the lens
EP0836178A1 (en) * 1993-02-01 1998-04-15 Matsushita Electric Industrial Co., Ltd. Optical disk
EP0831466B1 (en) * 1996-09-24 2002-04-10 Nec Corporation Optical head having multiple light sources having different wavelengths
EP0862166A1 (en) 1998-09-02 application
KR970011407B1 (en) 1997-07-10 grant
DE69132426D1 (en) 2000-10-26 grant
EP0862165A1 (en) 1998-09-02 application
DE69132425D1 (en) 2000-10-26 grant
DE69132579T2 (en) 2001-06-28 grant
EP0862166B1 (en) 2000-09-20 grant
EP0855702B1 (en) 2000-09-20 grant
EP0855702A2 (en) 1998-07-29 application
DE69132579D1 (en) 2001-05-10 grant
EP0452953A3 (en) 1992-11-25 application
DE69132425T2 (en) 2001-03-08 grant
US5148421A (en) 1992-09-15 grant
DE69132426T2 (en) 2001-03-08 grant
EP0855702A3 (en) 1998-09-02 application
EP0862165B1 (en) 2000-09-20 grant