CA1135851A - Optical system for reproducing information - Google Patents
Optical system for reproducing informationInfo
- Publication number
- CA1135851A CA1135851A CA000354379A CA354379A CA1135851A CA 1135851 A CA1135851 A CA 1135851A CA 000354379 A CA000354379 A CA 000354379A CA 354379 A CA354379 A CA 354379A CA 1135851 A CA1135851 A CA 1135851A
- Authority
- CA
- Canada
- Prior art keywords
- lens
- disk
- optical system
- prism
- light source
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1356—Double or multiple prisms, i.e. having two or more prisms in cooperation
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1372—Lenses
- G11B7/1378—Separate aberration correction lenses; Cylindrical lenses to generate astigmatism; Beam expanders
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1372—Lenses
- G11B2007/13727—Compound lenses, i.e. two or more lenses co-operating to perform a function, e.g. compound objective lens including a solid immersion lens, positive and negative lenses either bonded together or with adjustable spacing
Landscapes
- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Head (AREA)
Abstract
OPTICAL SYSTEM FOR REPRODUCING INFORMATION
Abstract of the Disclosure An optical system for storing and reproducing information employs a plano-convex lens for transmitting a light beam from a semiconductor laser onto a disk. A
prism for deriving reflected light from the disk is uni-tarily formed with the lens.
Abstract of the Disclosure An optical system for storing and reproducing information employs a plano-convex lens for transmitting a light beam from a semiconductor laser onto a disk. A
prism for deriving reflected light from the disk is uni-tarily formed with the lens.
Description
5~
This invention relates to optical systems and more particularly to a system for optically :reproducing information stored in a recording medium. ~ ~
Known apparatus for this purpose includes the ~ ~ ;
so-called optical disk wherein a semiconductor laser, for example, is employed as a light source. A light beam !
emergent from the laser is projected onto an information medium (disk) by an optical system, whereby information is recorded on the disk or is reproduced therefrom.
To enable the prior art to be described with the aid of diagrams, the accompanying drawings will first 1 ;
be listed.
Figure 1 is a diagram showing schematically the construction of a prior-art optical disk apparatus, Figure 2 is a diagram showing the construction of an embodiment of this invention, ~ ;
Figures 3(a) and 3(b) are diagxams for explaining ;, the operation of the embodiment shown in Figure 2, Figure 4 is a diagram showing the construction ~0 of another embodiment of this invention, and Figures 5(a) and 5(b) are diagrams each showing portions of other embodiments o~ this invention.
Figure 1 is a diagram showing schematicalIy the optical system of a prior-art optical disk apparatus.
A light beam emitted from a semiconductor laser 1 is fed to a first lens 5 through a prism 20. The prlsm 20 is composed of three prisms 2, 3 and 4, which are assembled into a unitary optical component so that the light beam that enters the prism assembly from the laser 1 passes through ~`
the prisms 2 and 3 to the lens 5, while a light beam that 35~8~
enters the prism assembly from the lens 5 is reflected at the joint plane A between the prisms 2 and 3 and proceeds towards the prism 4. The light beam projected to the lens 5 is substantially collimated by this lens, and is then projected as a minute light qpot onto a disk 8 by a second lens 6 supported on a voice coil 7.
This beam is reflected by the disk 8, and the reflected beam is received by a photodetector 9 after having passed through the lenses 6 and the prisms 3 and 4.
When information is recorded on the disk 8 (by way of example, by cavities formed in the disk surface), the reflected beam has its intensity modulated according to such information which is then reproduced in the form of output signals at the photodetector 9. The voice coil 7 serves to move the secona lens 6 small distances at high speed, and is composed ; for this purpose of a light spot control, i.e. an auto-focusing control or tracking control. -In such apparatus, the beam emitted by the laser has a divergence, or exhibits a ratio of eccentricity about 3 to 1, having an anisotropic (elliptic) far-field pattern. Accordingly, when this beam is focused on the disk, the spot does not show an isotropic (circular) distribution pattern on the disk, and the frequency charac-teristics of the optical recording and reading of the disk are imperfect.
In the prior art apparatus, therefore, in order to bring such a beam spot from a semiconductor laser into a circular distribution pattern7 the size of the aperture of a lens has been appropriately set when the beam is trans--mitted through such lens. That i5, by utilizing the numerical aperture (the so-called NA) of the lens, the elliptic ~ ;
This invention relates to optical systems and more particularly to a system for optically :reproducing information stored in a recording medium. ~ ~
Known apparatus for this purpose includes the ~ ~ ;
so-called optical disk wherein a semiconductor laser, for example, is employed as a light source. A light beam !
emergent from the laser is projected onto an information medium (disk) by an optical system, whereby information is recorded on the disk or is reproduced therefrom.
To enable the prior art to be described with the aid of diagrams, the accompanying drawings will first 1 ;
be listed.
Figure 1 is a diagram showing schematically the construction of a prior-art optical disk apparatus, Figure 2 is a diagram showing the construction of an embodiment of this invention, ~ ;
Figures 3(a) and 3(b) are diagxams for explaining ;, the operation of the embodiment shown in Figure 2, Figure 4 is a diagram showing the construction ~0 of another embodiment of this invention, and Figures 5(a) and 5(b) are diagrams each showing portions of other embodiments o~ this invention.
Figure 1 is a diagram showing schematicalIy the optical system of a prior-art optical disk apparatus.
A light beam emitted from a semiconductor laser 1 is fed to a first lens 5 through a prism 20. The prlsm 20 is composed of three prisms 2, 3 and 4, which are assembled into a unitary optical component so that the light beam that enters the prism assembly from the laser 1 passes through ~`
the prisms 2 and 3 to the lens 5, while a light beam that 35~8~
enters the prism assembly from the lens 5 is reflected at the joint plane A between the prisms 2 and 3 and proceeds towards the prism 4. The light beam projected to the lens 5 is substantially collimated by this lens, and is then projected as a minute light qpot onto a disk 8 by a second lens 6 supported on a voice coil 7.
This beam is reflected by the disk 8, and the reflected beam is received by a photodetector 9 after having passed through the lenses 6 and the prisms 3 and 4.
When information is recorded on the disk 8 (by way of example, by cavities formed in the disk surface), the reflected beam has its intensity modulated according to such information which is then reproduced in the form of output signals at the photodetector 9. The voice coil 7 serves to move the secona lens 6 small distances at high speed, and is composed ; for this purpose of a light spot control, i.e. an auto-focusing control or tracking control. -In such apparatus, the beam emitted by the laser has a divergence, or exhibits a ratio of eccentricity about 3 to 1, having an anisotropic (elliptic) far-field pattern. Accordingly, when this beam is focused on the disk, the spot does not show an isotropic (circular) distribution pattern on the disk, and the frequency charac-teristics of the optical recording and reading of the disk are imperfect.
In the prior art apparatus, therefore, in order to bring such a beam spot from a semiconductor laser into a circular distribution pattern7 the size of the aperture of a lens has been appropriately set when the beam is trans--mitted through such lens. That i5, by utilizing the numerical aperture (the so-called NA) of the lens, the elliptic ~ ;
- 2 - ~
... . ~ . . .
~L358~1 ~
distribution pattern can be converted into a circular distribution pattern.
With such a prior art arrangement, however, there is the disadvantage that a lens having a predetermined NA
must be used. Further, in the case of a low NA, combined lenses (e.g. 2 or 3 lenses3 must be used, which results in a complicated construction. ;
~ oreover, in apparatus as shown ln Figure lj outputs from the photodetector 9 must be made sufficiently great to permit the information signals to be detected with a good signal-to-noise ratio. To this end, the facets of the prism and the lens, for example, one facet 3a of the . , .
prlsm 3 and one facet 5a of the first lens 5, must be pro-vided with thin films to prevent reflection of the light beams and to lessen to the utmost losses in the prism and -`
the lens. In the apparatus shown in Figure 1, however~
the elements of the system, i.e~, the prism and the lenses, are all separate, SQ that the optical efficiency lS low.
The number of anti-reflection films on the prism, lens etc.
becomes large, resulting in a high c~st. Further disadvan~
tages are that, since the prism and the lenses are separate, adjustment of the opitcal axes of the prism and lenses is difficult~ and that the whole apparatus becomes large on ; account of the large number of components involved.
This invention has for its object -to provide a simple optical system which brings a beam spot to be projected onto a disk surface into a circular distribution pattern and also reduces the influences on the spot of parent abberations ascribable to a lens.
Another object of this invention is to provide an optical system that has a high optical efficiency,
... . ~ . . .
~L358~1 ~
distribution pattern can be converted into a circular distribution pattern.
With such a prior art arrangement, however, there is the disadvantage that a lens having a predetermined NA
must be used. Further, in the case of a low NA, combined lenses (e.g. 2 or 3 lenses3 must be used, which results in a complicated construction. ;
~ oreover, in apparatus as shown ln Figure lj outputs from the photodetector 9 must be made sufficiently great to permit the information signals to be detected with a good signal-to-noise ratio. To this end, the facets of the prism and the lens, for example, one facet 3a of the . , .
prlsm 3 and one facet 5a of the first lens 5, must be pro-vided with thin films to prevent reflection of the light beams and to lessen to the utmost losses in the prism and -`
the lens. In the apparatus shown in Figure 1, however~
the elements of the system, i.e~, the prism and the lenses, are all separate, SQ that the optical efficiency lS low.
The number of anti-reflection films on the prism, lens etc.
becomes large, resulting in a high c~st. Further disadvan~
tages are that, since the prism and the lenses are separate, adjustment of the opitcal axes of the prism and lenses is difficult~ and that the whole apparatus becomes large on ; account of the large number of components involved.
This invention has for its object -to provide a simple optical system which brings a beam spot to be projected onto a disk surface into a circular distribution pattern and also reduces the influences on the spot of parent abberations ascribable to a lens.
Another object of this invention is to provide an optical system that has a high optical efficiency,
- 3 -~5135~ ::
includes a small number of components and can be simply adjusted.
In order to accomplish such ob]ects, -this invention provides a plano-convex lens as the lens through which the beam from the semiconductor laser is projected.
Description of the Preferred Embodiments Fiyure 2 is a diagram showing the construction ~ ;;
of an embodiment of this invention. A light beam L from ~
~ . . .
a semiconductor laser 21 is emitted towards a polarizing beam splitter 22 and enters a plano-convex lens 23. In a part of a holder 25 which supports the beam splitter 22, a circular opening 24 is provided in the optical path.
The angle of view ~ of the opening 24 towards the laser 21 is set so as to satisfy ~ ere, ~1 and ~"
denote half divergence angles of the beam of the laser in a direction perpendicular to the junction of the laser and in a direction parallel thereto, respectively. This construc~
tion renders the NA of the lens 23, in effect, sin ~ and obviates the need to complicate- the system by employing f~.
20 a lens of a predetermined NA as the lens 23. Use of the ~' single plano-con~ex lens 23 avoids the combined lenses of the prior art and arranging its plane face towards the laser 21 satisfactorily removes aberrations.
Since the semiconductor laser employed as the O
light source has a single wavelength (for example, 8,300 A), a lens for correcting for chromatic aberration is unnecessary.
Secondly, since the NA is small in consideration of the half divergence angle (for example, a~ - 8 ~) of the laser 21 a lens for correcting for an off-axial beam can be 30 dispensed with. Thirdly, the wave front of the beam from the .r ;
semiconductor laser is a fairl~ good spherical wave and need ,~,"
~35i85~L :
not be corrected. In the light of these points, even the single lens used will be satisfactory. When making even a single lens, if it includes a curvature, a jig conforming to that curvature must be prepared. In addition, the step of polishing the plane face is inevitably involved as a prelimi-nary step before precisely forming the curvature. Therefore, as a single lens having the property of convergence, a plano-convex lens i5 advantageous from the standpoint of manufacture.
There will now be explained a method of setting the 10 plano-convex lens in Figure 2. Let's consider cases where the ;;
directions of curvatures are different as shown in Figures !' 3(a~ and 3(b) with respect to the beam from the laser 21.
In the case of Figure 3(a), the lncident beam enters the lens at an angle ~ to the normal to the entrance facet. In the case of Figure 3(b), this angle becomes ~, and the emergent beam emerges at an angle ~ relative to the normal to the exit facet. It is accordingly obvious that ~ > ~, r holds ~ -true.
~ In order to lessen aberrations of the lens, the 20 angle of the incident beam relative to the normal to the r~
entrance facet needs to be made as narrow as possible~ This ~;
is especially significant in relation to spherical aberration.
Accordingly, the setting illustrated in Figure 3(b) is better.
In other words, the plano-convex lens should be arranged with its plane face towards the light source.
Figure 4 is a diagram showing another embodiment of this invention in whiah the optical system is further simplified. A light beam emitted from a semiconductor laser 41 passes through prisms 42 and 43 and a first lens 45 to be substantially collimated, and -the collimated beam is projected as a minute light spot on a disk 8 by a second lens 46 which is supported by a voice coil (not shown~.
A reflected beam from the optical disk 8 passes through the second lens 461 the first lens 45 and the prism 43, is reflec-.
ted by the joint plane A between the prisms 42 and 43, passes through a lens 44 and is received by a photodetector ~ -9. In this embodiment, one facet 5a of the lens 45 is - ;
designed to be planar and is stuck to one facet 3a of the prism 43 so as to assemble this lens and prism into a unitary structure. By sticking the first lens 45 and the prism 43 -together, it becomes unnecessary to evaporate anti-reflection film onto the facet 5a of the lens 45 and the facet 3a of the prism 43, and also the loss of the light `
is reduced. Further, the optical system is more readily adjusted, is less subject to vibration and can be more easily miniaturized.
Figures 5(a) and 5(b) are diagrams showing portions of other~embodiments of this invention. A
component 30 shown in Figure 5(a) is shaped in such a way tha~ the first lens 45, the prism 43 and the lens 44 depicted in Figure 4 are unitarily formed during manufacture, whil~
20 a component 40 shown in Figure 5(b) is shaped in such a ~ `~
way that the first lens 45 and the prism 43 are unitarily formed during manufacture, the lens 44 being subsequently applied. Such unitary formation can be realized with a known technique, for example, by the resin molding of plastics. By unitarily forming at least the first lens 45 and the prism 43 during manufacture, the numbers of components of the optical system can be significantly reduced.
~., ~' ; - 6 -
includes a small number of components and can be simply adjusted.
In order to accomplish such ob]ects, -this invention provides a plano-convex lens as the lens through which the beam from the semiconductor laser is projected.
Description of the Preferred Embodiments Fiyure 2 is a diagram showing the construction ~ ;;
of an embodiment of this invention. A light beam L from ~
~ . . .
a semiconductor laser 21 is emitted towards a polarizing beam splitter 22 and enters a plano-convex lens 23. In a part of a holder 25 which supports the beam splitter 22, a circular opening 24 is provided in the optical path.
The angle of view ~ of the opening 24 towards the laser 21 is set so as to satisfy ~ ere, ~1 and ~"
denote half divergence angles of the beam of the laser in a direction perpendicular to the junction of the laser and in a direction parallel thereto, respectively. This construc~
tion renders the NA of the lens 23, in effect, sin ~ and obviates the need to complicate- the system by employing f~.
20 a lens of a predetermined NA as the lens 23. Use of the ~' single plano-con~ex lens 23 avoids the combined lenses of the prior art and arranging its plane face towards the laser 21 satisfactorily removes aberrations.
Since the semiconductor laser employed as the O
light source has a single wavelength (for example, 8,300 A), a lens for correcting for chromatic aberration is unnecessary.
Secondly, since the NA is small in consideration of the half divergence angle (for example, a~ - 8 ~) of the laser 21 a lens for correcting for an off-axial beam can be 30 dispensed with. Thirdly, the wave front of the beam from the .r ;
semiconductor laser is a fairl~ good spherical wave and need ,~,"
~35i85~L :
not be corrected. In the light of these points, even the single lens used will be satisfactory. When making even a single lens, if it includes a curvature, a jig conforming to that curvature must be prepared. In addition, the step of polishing the plane face is inevitably involved as a prelimi-nary step before precisely forming the curvature. Therefore, as a single lens having the property of convergence, a plano-convex lens i5 advantageous from the standpoint of manufacture.
There will now be explained a method of setting the 10 plano-convex lens in Figure 2. Let's consider cases where the ;;
directions of curvatures are different as shown in Figures !' 3(a~ and 3(b) with respect to the beam from the laser 21.
In the case of Figure 3(a), the lncident beam enters the lens at an angle ~ to the normal to the entrance facet. In the case of Figure 3(b), this angle becomes ~, and the emergent beam emerges at an angle ~ relative to the normal to the exit facet. It is accordingly obvious that ~ > ~, r holds ~ -true.
~ In order to lessen aberrations of the lens, the 20 angle of the incident beam relative to the normal to the r~
entrance facet needs to be made as narrow as possible~ This ~;
is especially significant in relation to spherical aberration.
Accordingly, the setting illustrated in Figure 3(b) is better.
In other words, the plano-convex lens should be arranged with its plane face towards the light source.
Figure 4 is a diagram showing another embodiment of this invention in whiah the optical system is further simplified. A light beam emitted from a semiconductor laser 41 passes through prisms 42 and 43 and a first lens 45 to be substantially collimated, and -the collimated beam is projected as a minute light spot on a disk 8 by a second lens 46 which is supported by a voice coil (not shown~.
A reflected beam from the optical disk 8 passes through the second lens 461 the first lens 45 and the prism 43, is reflec-.
ted by the joint plane A between the prisms 42 and 43, passes through a lens 44 and is received by a photodetector ~ -9. In this embodiment, one facet 5a of the lens 45 is - ;
designed to be planar and is stuck to one facet 3a of the prism 43 so as to assemble this lens and prism into a unitary structure. By sticking the first lens 45 and the prism 43 -together, it becomes unnecessary to evaporate anti-reflection film onto the facet 5a of the lens 45 and the facet 3a of the prism 43, and also the loss of the light `
is reduced. Further, the optical system is more readily adjusted, is less subject to vibration and can be more easily miniaturized.
Figures 5(a) and 5(b) are diagrams showing portions of other~embodiments of this invention. A
component 30 shown in Figure 5(a) is shaped in such a way tha~ the first lens 45, the prism 43 and the lens 44 depicted in Figure 4 are unitarily formed during manufacture, whil~
20 a component 40 shown in Figure 5(b) is shaped in such a ~ `~
way that the first lens 45 and the prism 43 are unitarily formed during manufacture, the lens 44 being subsequently applied. Such unitary formation can be realized with a known technique, for example, by the resin molding of plastics. By unitarily forming at least the first lens 45 and the prism 43 during manufacture, the numbers of components of the optical system can be significantly reduced.
~., ~' ; - 6 -
Claims (3)
1. An optical system for reproducing information having a light source including a semiconductor laser, a lens disposed between the light source and a disk whereby a beam from the laser is projected onto the disk; characterized in that said lens is a plano-convex lens with a plane face disposed towards the light source.
2. An optical system as defined in claim 1, characterized in that an opening smaller than the divergence of the beam from the light source is located between said light source and said lens.
3. An optical system for reproducing information having a light source including a semiconductor laser, a plano-convex lens for transmitting a beam from the light source onto a disk, and a prism for deriving a reflected beam from the disk, wherein said lens and said prism are of unitary construction.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP85976/1979 | 1979-06-25 | ||
| JP1979085976U JPS566038U (en) | 1979-06-25 | 1979-06-25 | |
| JP4559280A JPS56142507A (en) | 1980-04-09 | 1980-04-09 | Optical system |
| JP45592/1980 | 1980-04-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1135851A true CA1135851A (en) | 1982-11-16 |
Family
ID=26385603
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000354379A Expired CA1135851A (en) | 1979-06-25 | 1980-06-19 | Optical system for reproducing information |
Country Status (5)
| Country | Link |
|---|---|
| CA (1) | CA1135851A (en) |
| DE (1) | DE3023617A1 (en) |
| FR (1) | FR2460022B1 (en) |
| GB (1) | GB2052132B (en) |
| NL (1) | NL8003540A (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4406520A (en) * | 1980-08-14 | 1983-09-27 | Universal Pioneer Corporation | Beam splitter optical system of signal pickup device |
| JPS5958637A (en) * | 1982-09-28 | 1984-04-04 | Sony Corp | Optical reproducing device |
| JP2633535B2 (en) * | 1986-09-18 | 1997-07-23 | ソニー株式会社 | Optical pickup device |
| US4890901A (en) * | 1987-12-22 | 1990-01-02 | Hughes Aircraft Company | Color corrector for embedded prisms |
| KR100200873B1 (en) * | 1996-01-11 | 1999-06-15 | 윤종용 | Optical pickup device |
| DE19816040A1 (en) * | 1998-04-09 | 1999-10-14 | Heidelberger Druckmasch Ag | Gradient aperture for exposure devices |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2178245A (en) * | 1936-06-24 | 1939-10-31 | Klangfilm Gmbh | Sound recording apparatus |
| DE2638276C3 (en) * | 1976-08-25 | 1981-03-12 | Remy, Ernst, Dipl.-Phys. Dr., 8000 München | Optical pinhole for laser technology applications |
| NL7703076A (en) * | 1977-03-22 | 1978-09-26 | Philips Nv | DEVICE FOR READING A RADIATION-REFLECTING RECORD CARRIER. |
-
1980
- 1980-06-12 FR FR8013058A patent/FR2460022B1/en not_active Expired
- 1980-06-18 NL NL8003540A patent/NL8003540A/en not_active Application Discontinuation
- 1980-06-19 CA CA000354379A patent/CA1135851A/en not_active Expired
- 1980-06-20 GB GB8020215A patent/GB2052132B/en not_active Expired
- 1980-06-24 DE DE19803023617 patent/DE3023617A1/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| GB2052132A (en) | 1981-01-21 |
| DE3023617A1 (en) | 1981-01-08 |
| NL8003540A (en) | 1980-12-30 |
| GB2052132B (en) | 1983-07-06 |
| FR2460022B1 (en) | 1987-09-11 |
| FR2460022A1 (en) | 1981-01-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |