JP2001160234A - Optical pickup system - Google Patents

Abstract

[PROBLEMS] For example, in a system having a recording / reproducing optical system for DVD and CD, the light use efficiency on the CD side is improved to increase the recording speed, and the NA on the CD side is increased to record. It improves the characteristics, simplifies the overall optical layout and allows for a smaller device. When performing recording and reproduction of a CD, a divergent light beam from a second hologram unit 29 on which a semiconductor laser chip is mounted is coupled by a finite anamorphic lens 3 ', and the intensity distribution is changed from an elliptical shape. It is shaped into a circular shape. Here, the light beam transmitted through the anamorphic lens 3 'becomes divergent light. According to the above configuration, the beam shape of the semiconductor laser can be shaped from an ellipse to a circle in the diverging light path, so that the light use efficiency is improved and the objective lens 27 is improved.
Even when recording / reproducing an optical disk having a substrate thickness different from the designed value of the above, since the spherical aberration is corrected by using the luminous flux incident on the objective lens 27 as divergent light, a large numerical aperture (NA) is possible, and diffraction is possible. A critical board spot can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup, and more particularly, to an optical pickup applicable to a laser printer optical system, such as a CD, a DVD, and an S-DVD.
The present invention relates to an optical pickup in an optical disk drive for recording and reproducing optical disks of a plurality of standards having different substrate thicknesses.

[0002]

2. Description of the Related Art FIG. 10 is a schematic configuration diagram showing an optical system layout of a recent CD / DVD dual-purpose optical pickup. In FIG. 10, reference numeral 21 denotes a first hologram unit, 22 denotes a first collimating lens, and 23 denotes a beam. Shaping prism, 24 is a mirror, 25 is a dichroic prism, 26 is a wavelength-selective aperture, 27 is an objective lens, 28 is a DVD or CD disk, 29 is a second hologram unit, 30
Is a second collimating lens.

[0003] (When performing DVD recording and reproduction) wavelength 650
The divergent light beam emitted from the first hologram unit 21 on which the semiconductor laser chip of nm is mounted is converted by the first collimator lens 22 into a parallel light beam. Since the converted light flux has an elliptical intensity distribution, it is shaped into a circular beam by a pair of beam shaping prisms 23. The shaped light beam is reflected by a mirror 24, further reflected by a dichroic prism 25, narrowed by a wavelength-selective aperture 26 to a beam diameter corresponding to NA 0.6, and then formed by an objective lens 27 with a substrate thickness of 0.6 mm. A spot is formed on the DVD disk 28.

The wavelength-selective aperture 26 and the objective lens 2
7 are integrally driven by an actuator (not shown) in the track direction and the focus direction. Since the objective lens 27 is designed in accordance with the thickness, wavelength, and NA of the DVD substrate, the spot becomes almost as small as the diffraction limit. The reflected light from the DVD disk 28 travels backward in the first optical path, is diffracted by the hologram of the first hologram unit 21, enters the light receiving element near the semiconductor laser chip, and generates various signals.

(When reproducing a CD) Wavelength 780n
The divergent light beam emitted from the second hologram unit 29 on which the m semiconductor laser chips are mounted is slightly condensed by the second collimating lens 30, but still passes through the dichroic prism 25 as divergent light. The intensity distribution of the transmitted light beam remains elliptical without being shaped into a circle. The divergent light is selectively transmitted through only a part of the center by the wavelength selective aperture 26.

The objective lens 27 is for an infinite system DVD (parallel light incidence, substrate thickness 0.6 mm, wavelength 650 nm).
As is well known (for example, Japanese Patent Laid-Open No. 10-2553)
No. 06), and under the condition of the CD system (substrate thickness 1.2 mm, wavelength 780 nm), when used as a finite system (incident divergent light) with a certain magnification, a condensed spot about the diffraction limit can be obtained. The reflected light from the CD disk 28 travels backward in the first optical path, is diffracted by the hologram of the second hologram unit 29, and is incident on a light receiving element near the semiconductor laser chip to generate various signals.

The problem here is that since the light beam on the CD side is always divergent light, beam shaping using a prism like the DVD side cannot be performed. If the divergent light is beam-shaped by a prism, astigmatism will occur, and the disk surface spot will not be restricted to the diffraction limit. Since beam shaping cannot be performed, the light beam from the semiconductor laser enters the objective lens 27 in an elliptical shape. In order to increase the RIM (luminous flux intensity at the lens entrance pupil end) in order to narrow the spot on the disk surface, only the center of the ellipse must be used. Therefore, the light amount loss increases, and the light use efficiency deteriorates.

For example, in FIG. 11, if the divergence angles of the light beam from the light source 1 by the semiconductor laser chip on orthogonal planes are 8 ° and 22 °, respectively, and the RIM is 40% or more, the light beam emitted from the light source will Is 27% (shaded area) without shaping and 60% (elliptical area) with shaping.

As described above, the optical path on the CD side without beam shaping has a low light utilization efficiency and cannot increase the board power. If a high-output semiconductor laser chip is forcibly mounted on the hologram unit, thermal effects on the light-receiving element and stray light pose a problem. Therefore, the CD side was only used for reproduction.

However, there is a strong demand for recording discs such as CD-R and CD-RW, and an optical pickup capable of recording both CD / DVD has been desired. In order to perform beam shaping in a finite optical path using a conventional technique, for example, see
The configuration is as shown in FIG. That is, divergent light from a semiconductor laser is converted into parallel light by a collimator lens, shaped by a beam shaping prism, and then diverged by a divergent lens. However, the above configuration is changed to C
When applied to an optical pickup for both D / DVD, the number of components is increased and the optical path is extended, so that there is a problem that the size cannot be reduced, and the adjustment becomes severe and the environment becomes unstable.

On the other hand, in the finite system, when the objective lens moves in the direction perpendicular to the optical axis due to the tracking operation, aberration is more likely to occur than in the infinite system. For this purpose, an objective lens which can be used in an infinite system for both CD / DVD, and peripheral components thereof are being developed. When such a component is used, beam shaping can also be performed on the CD side. For example, JP-A-9
JP-A-54973 discloses a CD / DVD dual-purpose objective lens system that corrects only spherical aberration on the CD side caused by a difference in substrate thickness by using a wavelength-selective HOE. However, in the method using the wavelength-selective hologram disclosed in the above publication, the diffraction efficiency of the hologram is low, and the power of the CD-side disc surface is deteriorated.

Japanese Patent Application Laid-Open No. H10-143905 discloses that a light beam incident on an objective lens is divided into three zones,
Use one or two zones for DVD, and use one or three zones for DVD C
A D / DVD dual-purpose objective lens system is disclosed. However, in the method using the phase adjusting element described in the above publication,
The spot peak intensity on the DVD side decreases due to the influence of the second light flux in the text.

Japanese Patent Application Laid-Open No. Hei 10-334504 discloses a CD / DVD objective lens system in which a wavelength-selective phase plate corrects only spherical aberration on the CD side caused by a difference in substrate thickness. . However, in the system using the wavelength selection phase plate disclosed in the above publication, the NA on the CD side is
When the number is increased, the width of the peripheral orbicular zone film becomes narrow, processing becomes difficult, and the arrangement accuracy becomes severe. In addition, wave front deterioration and light amount reduction occur, for example, such that diffraction flare light is easily generated. As a result, a conventional optical pickup could not realize a desired optical pickup.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and improves the light use efficiency on the CD side to increase the recording speed, and increases the NA on the CD side to improve the recording characteristics. It is an object of the present invention to provide an optical pickup system that can simplify an optical layout and reduce the size of the device.

[0015]

According to the first aspect of the present invention, there is provided an optical pickup system in which a plurality of types of optical disks having different substrate thicknesses can be applied, and recording and reproduction are performed on the optical disks by using a common objective lens. And an anamorphic lens that emits a divergent light beam, and couples a light beam emitted from a semiconductor laser by the anamorphic lens.

According to a second aspect of the present invention, in the first aspect of the present invention, the wavefront shape of the divergent light is a spherical wave.

According to a third aspect of the present invention, in the first aspect of the present invention, the anamorphic lens in which the emitted light beam is divergent light is a first anamorphic lens, and the first anamorphic lens operates. A second anamorphic lens is provided in an optical path different from the optical path so that the emitted light beam becomes parallel light, and the second anamorphic lens couples the light beam emitted from the second semiconductor laser. It is a characteristic.

According to a fourth aspect of the present invention, the first anamorphic lens in the third aspect of the invention is replaced with an optical system having an anamorphic lens and a concave lens having the same shape as the second anamorphic lens. It is characterized by having been constituted by.

According to a fifth aspect of the present invention, there is provided an optical pickup system in which a plurality of types of optical disks having different substrate thicknesses can be applied, and the optical disk performs recording and reproduction using a common objective lens. Wherein the anamorphic lens couples a light beam from a semiconductor laser.

According to a sixth aspect of the present invention, in the fifth aspect of the invention, the wavefront shape of the convergent light is a spherical wave.

[0021]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In all the drawings for describing the embodiments, portions having the same functions are denoted by the same reference numerals, and are the same as in the conventional example, and the repeated description thereof will be omitted. [Inventions of Claims 1 and 2] FIGS. 1 and 2 are views for explaining that a finite anamorphic lens can be designed in principle. In each figure, 1 is a light source and 2 is a hologram. Is a cover glass of the hologram unit in which is formed, 3 is an anamorphic lens, 4 is a DVD objective lens, 5 is a disk, and H and H 'are principal points.

FIG. 1 is a diagram showing a configuration and an optical path of a conventional infinite anamorphic lens system. FIG. 1A shows an optical path in the YZ plane, and FIG. 1B shows an XZ plane. .
The divergent light flux from the light source 1 by the semiconductor laser has different divergence angles on the YZ plane and the XZ plane. Since the divergence angle on the YZ plane is small, the position of the principal point H is set at a position relatively far from the light source 1. On the other hand, since the divergence angle on the XZ plane is large, the position of the principal point H ′ is set to a position relatively close to the light source 1. As a result, the exit beam diameter becomes equal on the two surfaces, and the beam shape is shaped from an ellipse to a circle.

In the anamorphic lens, the two principal points H and H 'can be independently moved by changing the surface shape. For example, in the YZ plane of the optical system shown in FIG. 2A, when the radius of curvature of the reference spherical surface of the two planes is changed and H is moved to the left without changing the focal length on the YZ plane, the emitted light is divergent light. Becomes H ′ can be similarly moved on the XZ plane shown in FIG. Where 2
The position of H 'may be set so that astigmatism does not occur on one surface. In such a design, when the infinite system is changed from the infinite system to the finite system, the original shaping magnification slightly changes. However, there is no problem if the infinite system shaping magnification is set in advance in consideration of this.

[Invention of Claim 2] What is important here is that
The purpose is to make the exit wavefront from the anamorphic lens a secondary shape (spherical surface). DVD objective lens is 1.2
Although a fourth order spherical aberration is generated by a CD substrate having a thickness of mm,
When this is directly corrected by the aspherical surface coefficient of the anamorphic lens, a large wavefront aberration occurs if there is a tracking lens shift of the objective lens. According to a trial calculation, when the objective lens is moved by 0.2 mm in the direction orthogonal to the optical axis, the wavefront aberration of the secondary wavefront is 0.023λrm.
In the s and quaternary wavefronts, it increases by 0.216 λrms.
Therefore, the method of correcting only the aberration generated on the CD substrate as described in Japanese Patent Application Laid-Open No. H10-334504 is weak against lens shift, and therefore needs to be driven integrally with the lens. This assembly adjustment accuracy becomes very severe. The finite system is more vulnerable to lens shift than the infinite system. However, when the exit wavefront is formed in a secondary shape (spherical surface), the amount of increase in wavefront aberration can be suppressed to a value that is practically acceptable.

FIG. 3 is a diagram showing the configuration and optical path of the optical system of the finite anamorphic lens 3 'designed as described above. FIG. 3A shows the YZ plane, and FIG.
This is shown in FIG. In FIG. 3, 4 is an infinite objective lens, and 5 is a CD disk having a substrate thickness of 1.2 mm. 4 and 5 show lens data.

FIG. 6 is a diagram showing an embodiment in which a finite anamorphic lens 3 'is arranged instead of the collimator lens 30 on the CD side of the conventional optical pickup shown in FIG. The optical path on the DVD side is the same as the conventional example in FIG. (When performing CD recording / reproduction) The divergent light beam from the second hologram unit 29 on which a semiconductor laser chip having a wavelength of 780 nm is mounted is coupled by the finite anamorphic lens 3 'of the present invention, and has an intensity distribution. Are shaped from elliptical to circular. Here, the light beam transmitted through the anamorphic lens 3 'becomes divergent light. The following is the same as the conventional example.

FIG. 7 shows an embodiment in which the DVD side of the optical pickup shown in FIG. 6 is replaced with an optical system using an infinite anamorphic lens 3. The optical path on the CD side is the same as in the embodiment shown in FIG. (During recording / reproduction of DVD) The divergent light beam from the hologram unit 21 on which a semiconductor laser chip having a wavelength of 650 nm is mounted is known, for example, from Japanese Patent Application Laid-Open No. 6-274931.
The light is converted into a parallel light beam by the infinite system anamorphic lens 3 disclosed in Japanese Patent Application Laid-Open Publication No. HEI 7-284, and the intensity distribution is shaped from elliptical to circular. The following optical paths are the same as in the conventional example.

FIG. 8 shows a concave lens in which the CD side of the optical pickup having the structure shown in FIG. 7 is replaced by an optical system using an infinite anamorphic lens 3 having the same shape as the DVD side. It is a figure which shows the Example of the structure which made the diverging light in 31. The optical path on the DVD side is the same as the embodiment shown in FIG. (When performing CD recording / reproduction) The divergent light beam from the hologram unit 29 on which a semiconductor laser chip having a wavelength of 780 nm is mounted is collimated into parallel light by the infinite anamorphic lens 3 having the same shape as the DVD side. The concave lens 31 converts this parallel light into divergent light. The following optical paths are the same as in the conventional example.

FIG. 9 shows a divergent finite anamorphic lens 3 'on the CD side of the optical pickup shown in FIG. 7 placed on a convergent finite anamorphic lens 3 ". 11 is a diagram showing an embodiment of a changed configuration.
For S-DVDs with higher recording density than VD, NA is DV
D is larger than D, so the substrate thickness is 0.6mm to 0.4.
mm. At this time, in order to use the DVD objective lens, the incident light beam to the S-DVD objective lens may be converted into convergent light. The optical path of the DVD is the same as the embodiment shown in FIG.

(When recording / reproducing S-DVD) The divergent light beam from the hologram unit 29 on which a semiconductor laser chip having a wavelength of 400 nm is mounted is collimated by a finite anamorphic lens 3 'in which the emitted light becomes convergent light. Is done. The following optical paths are the same as in the conventional example.

[Invention of Claim 6] In the case of convergent light, the wavefront shape is made into a spherical wave as in the case of divergent light, thereby suppressing an increase in wavefront aberration with respect to the track lens shift of the objective lens. Can be.

Although the embodiment of the finite anamorphic lens has been described above, the present invention is not limited to the above-described embodiment, and is applicable to a case where the lens is used in an optical pickup having a single optical path, This is also effective when the lens is used in an optical pickup having three or more optical paths.

[0033]

As is apparent from the above description, according to the first aspect of the present invention, in an optical pickup for recording and reproducing a plurality of optical disks having different substrate thicknesses using a common objective lens, the emitted light beam is Since the luminous flux from the semiconductor laser is coupled by an anamorphic lens that becomes divergent light, (1) the beam shape of the semiconductor laser can be shaped from an ellipse to a circle in the divergent light path, The light use efficiency is improved, and (2) even when recording / reproducing an optical disc having a substrate thickness different from the design value of the objective lens, the spherical aberration is corrected by using the luminous flux incident on the objective lens as diverging light, so Numerical aperture (NA) is possible, and it becomes possible to form a diffraction-limited board surface spot, and (3) a finite anamorphic lens
The configuration of the conventional collimating lens + shaping prism + diverging lens is simplified, and the device can be downsized.

According to the second aspect of the present invention, since the wavefront shape of the divergent light emitted from the anamorphic lens is a spherical wave, the wavefront aberration increases even when the optical axis is vertically moved by the tracking operation of the objective lens. Can be suppressed.

According to the third aspect of the present invention, in an optical path different from the anamorphic lens in which the emitted light beam is divergent light,
It has an anamorphic lens in which the emitted light beam becomes parallel light, and the anamorphic lens couples the light beam from the other semiconductor laser. Compared to the layout used, the optical axes of both optical paths can be aligned in parallel, so that the layout can be downsized and the flexible connection can be simplified.

According to the fourth aspect of the present invention, the anamorphic lens that emits a divergent light beam, the lens having the same shape as the anamorphic lens that emits another light beam as a parallel light, and a concave lens are used. By replacing with
By using two identical parts, the cost of parts and housing can be reduced.

According to the fifth aspect of the present invention, in an optical pickup for recording and reproducing a plurality of optical disks having different substrate thicknesses by using a common objective lens, an anamorphic lens in which an emitted light beam becomes convergent light is used. Since the light beam from the semiconductor laser is coupled, (1) the beam shape of the semiconductor laser can be shaped from an ellipse to a circle in the convergent light path, and the light use efficiency is improved,
(2) Even when recording / reproducing an optical disk having a substrate thickness different from the design value of the objective lens, a large numerical aperture (NA) is possible because the spherical aberration is corrected by using the luminous flux incident on the objective lens as convergent light. (3) The structure of the conventional collimating lens + shaping prism + converging lens is simplified by the finite anamorphic lens, and the size of the apparatus is reduced. be able to.

According to the sixth aspect of the present invention, since the wavefront shape of the convergent light is a spherical wave, it is possible to suppress an increase in wavefront aberration even with respect to vertical movement of the optical axis due to the tracking operation of the objective lens. .

[Brief description of the drawings]

FIG. 1 is a view for explaining the design of a finite anamorphic lens applied to the present invention, and is a view showing a conventional infinite anamorphic lens.

FIG. 2 is a diagram illustrating an optical system for explaining the design of a finite anamorphic lens, and is a diagram illustrating the optical system of the obtained finite anamorphic lens.

FIG. 3 is a diagram illustrating an optical path of a finite anamorphic lens for each orthogonal plane.

FIG. 4 is a diagram showing lens data of an anamorphic lens.

FIG. 5 is a diagram showing other lens data of an anamorphic lens.

FIG. 6 is a schematic diagram showing the configuration of an embodiment of the optical pickup of the present invention.

FIG. 7 is a schematic diagram showing the configuration of another embodiment of the optical pickup of the present invention.

FIG. 8 is a schematic diagram showing a configuration of still another embodiment of the optical pickup of the present invention.

FIG. 9 is a schematic diagram showing a configuration of still another embodiment of the optical pickup of the present invention.

FIG. 10 is a schematic configuration diagram illustrating an example of an optical system of a conventional CD / DVD dual-purpose optical pickup.

FIG. 11 is a diagram for explaining light use efficiency of light beams having different divergence angles in a perpendicular plane.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... Hologram unit cover glass, 3
... Infinite anamorphic lens, 3 ', 3 "... Finite anamorphic lens, 4 ... DVD objective lens, 5
... Disc, 21 ... First hologram unit, 22 ...
A first collimating lens, 23 a beam shaping prism,
24 ... Mirror, 25 ... Dichroic prism, 26 ...
Wavelength selective aperture, 27 ... objective lens, 28 ... DV
D or CD disk, 29 ... second hologram unit, 30 ... second collimating lens, 31 ... concave lens,
H, H ': principal point.

Claims (6)

[Claims] 1. An anamorphic optical system in which a plurality of types of optical disks having different substrate thicknesses are applicable, and an optical pickup system that performs recording and reproduction on the optical disk by using a common objective lens has an emitted light beam as divergent light. An optical pickup system comprising a lens, and coupling a light beam emitted from a semiconductor laser by the anamorphic lens. 2. The optical pickup system according to claim 1, wherein a wavefront shape of the divergent light is a spherical wave. 3. The optical pickup system according to claim 1, wherein the anamorphic lens in which the emitted light beam is divergent light is a first anamorphic lens, and an optical path on which the first anamorphic lens operates. A second anamorphic lens in which an emitted light beam becomes parallel light is provided in an optical path different from that of the second anamorphic lens, and a light beam emitted from the second semiconductor laser is coupled by the second anamorphic lens. Optical pickup system. 4. The optical pickup system according to claim 3, wherein the first anamorphic lens is replaced by an optical system having the same shape as the second anamorphic lens and a concave lens. An optical pickup system characterized by comprising. 5. An anamorphic lens in which a plurality of types of optical discs having different substrate thicknesses can be applied and an optical pickup system that performs recording and reproduction on the optical disc by using a common objective lens has an emitted light beam as convergent light. An optical pickup system comprising: a luminous flux from a semiconductor laser coupled by the anamorphic lens. 6. The optical pickup system according to claim 5, wherein the wavefront shape of the convergent light is a spherical wave.