JPH10247338A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to record and reproduce, with a common optical pickup, an optical disk having different positions of information recording surfaces in the direction of depth, by providing one or more reflecting optical elements, which reflect or transmit a luminous flux from a light emitting element on the same light path where the luminous flux passes, and transmit or reflect the returning light reflected by the information recording surface to a light receiving element. SOLUTION: When a high density optical disk is recorded/reproduced, a laser diode 3 is made to emit light, which is made into a parallel luminous flux 13 through a collimator lens 5, passing through a circular opening part 9b of an optical filter 9 and simultaneously passing through a polarizing plate part 9a, and being made incident to an objective lens 8. This luminous flux 13 is converted so that an information recording surface 1' of the high density optical disk 1 is irradiated with a reading spot through an objective lens 8, and its reflected light is reflected to a light receiving element 12 by a beam splitter 7, and is further focused on the light receiving element 12 through a detecting lens 11, and is converted into electric signal for thereby recording/ reproducing the high density optical disk 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for recording or reproducing information on a plurality of types of optical disks in which the position of an information recording surface of an information recording medium differs in the thickness direction.

[0002]

2. Description of the Related Art A conventional optical pickup device used for an optical disk device uses a single laser diode, and an optical system is designed for a specific optical disk. The available optical disks are limited to those whose information recording surface is at a substantially constant distance from the light incident surface.

At present, several systems have been proposed as high-density optical disks in which the signal recording density is higher than that of a conventional compact disk (hereinafter referred to as a CD). As an example,
Digital versatile disc or digital
Video discs (hereinafter referred to as DVDs) and the like have been raised, and the distance from the light incident surface to the information recording surface has been reduced to approximately half of that of conventional optical discs (CDs, CD-Rs, etc.). For this reason, when trying to record or reproduce data with a conventional optical disc device, the light spot converging on the information recording surface of a DVD optical disc has many aberrations mainly due to the difference in the distance from the light incident surface to the information recording surface. Included, the light spot size and quality required to reproduce the signal were not obtained.

Conventionally, in order to solve the above-mentioned problem, a laser diode having a wavelength of about 650 nm is mounted on an optical pickup device, and an optical pickup device (Nikkei Mechanical) for switching by moving respective objective lenses corresponding to CD and DVD. 1995.8.7 no.460). However, it is necessary to add a mechanism to switch the lens to the actuator part that moves the objective lens up, down, left and right to focus or to follow the information spot on the information recording track, which is an obstacle to downsizing the optical pickup device. I was Also CD
In the case of -R, the reflectance was extremely low when the wavelength of the laser diode was other than around 780 nm, and there was a disadvantage that recording and reproduction could not be performed with a single laser diode having a wavelength of around 650 nm.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an optical disc in which the position of an information recording surface differs from one another in a thickness direction and a wavelength-dependent optical disc. It is possible to record or reproduce multiple types of optical disks such as an optical disk with the same optical pickup,
An object of the present invention is to provide an optical pickup device whose structure can be simplified and the manufacturing cost of the optical pickup device can be reduced.

[0006]

According to the present invention, there is provided an optical pickup device for recording or reproducing a plurality of types of optical discs having different information recording surface positions in a thickness direction, comprising two or more light emitting elements; A collimator lens that converts the light beam emitted from the light emitting element into a substantially parallel light beam; an objective lens that converges the substantially parallel light beam on an information recording surface; and a difference in polarization direction of the light beam incident on the objective lens. A polarization direction selecting means for regulating a light beam diameter, a light receiving element for converting a return light from the information recording surface of the optical disc to a convergent light beam emitted from the objective lens, and a light receiving element on an optical path through which the light beam passes The light beam emitted from the light emitting element is reflected or transmitted on the same optical path, and the return light reflected on the information recording surface is transmitted or reflected toward the light receiving element. And Kutomo one or more reflective optical elements, those having a.

In the above optical pickup device,
In the polarization direction selecting means, a surface layer of the objective lens other than a circular portion centered on the optical axis of the objective lens is formed of a material having a function as a polarizer.

In the optical pickup apparatus, the polarization direction selecting means is a coating having a polarization characteristic applied to the objective lens other than a circular portion centered on the optical axis of the objective lens.

In the optical pickup apparatus, the polarization direction selecting means is disposed on a supporting means for supporting the objective lens, and an opening which does not function as a circular polarizer centered on the optical axis of the objective lens is provided. Having a polarizing plate.

In the above-mentioned optical pickup device, the aperture is provided so that the numerical aperture of the objective lens is 0.3 or more.

Further, the polarizing plate is configured to have an inclined angle with respect to the optical axis of the objective lens.

In each of the optical pickup devices, a laser diode is used as the light emitting element, and the polarization direction of a light beam emitted from at least one laser diode and incident on an objective lens or a polarizing plate is at least different from that of the other. The laser diodes are arranged so as to make an angle of about 90 ° with the polarization direction of the light beam when emitted from one laser diode and incident on the objective lens or the polarizing plate.

In each of the above-described optical pickup devices, a laser diode is used as the light emitting element, and the polarization direction of a light beam emitted from at least one laser diode and incident on an objective lens or a polarizing plate has at least another direction. At least one such that the light beam emitted from one of the laser diodes enters the objective lens or the polarizing plate at an angle of approximately 90 ° with the polarization direction of the light beam.
A wave plate for changing a polarization direction is arranged in an optical path between a laser diode and the reflection optical element.

In each of the optical pickup devices, at least one of the light emitting elements is integrated with the light receiving element to form an integrated module.

In each of the optical pickup devices, at least one of the reflection optical elements is constituted by a half mirror.

In each of the above-described optical pickup devices, at least one of the reflection optical elements is constituted by a prism.

In each of the optical pickup devices,
At least one of the reflection optical elements is constituted by a beam splitter which reflects or transmits light beams depending on the polarization direction of the light beam.

Further, in each of the optical pickup devices, at least one of the reflection optical elements is constituted by a beam splitter that reflects or transmits light depending on a difference in wavelength of a light beam.

[0019]

Embodiments of the present invention will be described with reference to the drawings. 1 and 2 are optical path diagrams showing an optical pickup device according to a first embodiment of the present invention. FIG. 1 shows a state when recording / reproducing a high-density optical disk 1 (for example, DVD), and FIG. Optical disk 2 (for example, CD, CD
-R) when recording / reproducing.

In FIGS. 1 and 2, reference numerals 3 and 4 denote laser diodes for emitting a laser beam. The laser diodes are arranged such that the directions of polarization of the emitted light beams are different from each other by approximately 90 °. 5 and 5
′ Is a collimator lens that converts the laser beam emitted from the laser diodes 3 and 4 into a substantially parallel beam. Reference numeral 6 denotes a beam splitter for reflecting the laser beam transmitted through the collimator lens 5 ′ and transmitting the laser beam transmitted through the collimator lens 5.

Reference numeral 9 denotes an optical filter in which the aperture diameter that determines the diameter of the transmitted light beam varies depending on the polarization direction.
Reference numeral 8 denotes an objective lens having a focal length f, which focuses a laser beam and collects information on the information recording surface 1 'of each of the optical disks 1 and 2.
And 2 ′, and the light beams reflected by the information recording surfaces 1 ′ and 2 ′ of the optical disks 1 and 2 are converted into substantially parallel light beams.

7 is an information recording surface 1 of the optical disks 1 and 2
The beam splitter reflects the light beam reflected by 'and 2' and transmitted through the objective lens 8 and the optical filter 9, and transmits the light beam transmitted through the beam splitter 6. Reference numeral 10 denotes a lens holder for fixing the objective lens 8 and the optical filter 9 so as to be integrated. Reference numeral 11 denotes a detection lens that condenses the light beam reflected by the beam splitter 7 on the light receiving element 12. Reference numeral 12 denotes a light receiving element that detects a light beam condensed by the detection lens 11 as an electric signal.

The above-mentioned optical filter 9 is shown in FIGS.
The opening shown in FIG. That is, the diameter is 2 × f × NA ′
Circular opening 9b that does not function as a polarizer
And a polarizing plate portion 9a having a function as a polarizer therearound.
Is provided. Therefore, the optical filter 9 transmits a light beam having a specific polarization direction at the polarizing plate portion 9a,
A light beam having a polarization direction different from that by about 90 ° has a characteristic of not transmitting, and the circular opening 9b acts so as to transmit regardless of the polarization direction.

A laser diode generally emits a linearly polarized light beam. The polarization direction of the light beam 14 emitted from the laser diode 4 is such that it cannot pass through the polarizing plate 9a, and the polarization direction of the light beam 13 emitted from the laser diode 3 is It is in a direction that allows transmission.

As shown in FIG. 2, the NA ′ is a circular aperture 9b of the light beam 14 emitted from the laser diode 4 and converted into a substantially parallel light beam by the collimator lens 5 ′.
Is the numerical aperture of the light beam 14 'passing through only the light beam 14'. As shown in FIG. 1, when the numerical aperture of the laser beam bundle 13 emitted from the laser diode 3 and converted into a substantially parallel light beam by the collimator lens 5 and transmitted through the polarizing plate 9a is NA, NA
> NA '. That is, the polarizing plate portion 9a has the function of restricting the laser beam so that the numerical aperture of the beam that does not pass through it becomes NA ′. In this embodiment, NA
Is set to 0.3 or more, and is determined such that a sufficient resolution convergent light for recording / reproducing on the conventional optical disc 2 is obtained.

The information recording surface 1 'of the high-density optical disk 1 is located substantially at the center in the thickness direction of the substrate of the optical disk, and is different from the information recording surface of the conventional optical disk 2. When recording / reproducing the high-density optical disk 1, the laser diode 3 emits light as shown in FIG. At this time, the light beam 13 emitted from the laser diode 3 and converted into a substantially parallel light beam by the collimator lens 5 is applied to the optical filter 9.
At the same time as the light passes through the circular aperture 9b and the polarizing plate 9a to enter the objective lens 8.

The light beam 13 is condensed by the objective lens 8 so as to irradiate a reading spot on the information recording surface 1 ′ of the high-density optical disk 1, and the reflected light is reflected by the beam splitter 7 toward the light receiving element 12. Then, the light is condensed on the light receiving element 12 by the detection lens 11 and converted into an electric signal, whereby the high-density optical disk 1 can be recorded and reproduced.

When recording or reproducing data on or from the conventional optical disk 2, the laser diode 4 emits light as shown in FIG. At this time, the light beam 14 emitted from the laser diode 4 and converted into a substantially parallel light beam by the collimator lens 5 ′ is cut at the outer periphery of the light beam 14 by the polarizing plate 9 a, and the diameter of the light beam is reduced to the diameter of the circular opening 9 b. Is incident on the objective lens 8 as a light beam 14 'limited to the information recording surface 2'.
Is collected.

In FIG. 2, when it is assumed that the optical filter 9 is not provided, the aberration caused in the light spot formed by focusing on the information recording surface 2 'of the conventional optical disk 2 is caused by the outer light beam among the light beam. But big. Therefore, by arranging the optical filter 9, the light beam of the outer peripheral portion is shaded by the polarizing plate 9 a, so that an appropriate reading spot diameter with less aberration can be obtained.

The light reflected on the information recording surface 2 'is reflected by the beam splitter 7 toward the light receiving element 12, and is condensed on the light receiving element 12 by the detection lens 11, so that the conventional optical disk 2 can be recorded or reproduced. . In the case of an optical disk having wavelength dependency among conventional optical disks, for example, in the case of a CD-R, if a light beam emitted from the laser diode 4 has a wavelength of, for example, 780 nm, recording / reproducing is performed at a sufficient signal level. It is possible.

FIGS. 3 and 4 show an optical pickup device according to a second embodiment of the present invention. This embodiment is different from the first embodiment shown in FIGS. 1 and 2 in that the laser diode 4, the collimator lens 5 ', the detection lens 11, and the light receiving element 12 are used.
The optical system corresponding to the conventional optical disk 2 configured as described above is replaced with a laser diode module 15 in which a laser diode, a light receiving element and a hologram element are integrated, and a collimator lens 16. The hologram element of the laser diode module 15 transmits the light beam from the laser diode toward the optical disk, and diffracts the reflected light from the information recording surface of the optical disk toward the light receiving element. Ray bundle 19 emitted from laser diode module 15
Are arranged so as to differ from each other by 90 ° with respect to the polarization direction of the light beam 13 emitted from the laser diode 3.

A beam splitter 18 for reflecting a light beam 19 emitted from the laser diode module 15 toward the optical disk and reflecting a light beam 20 reflected from the information recording surface toward the laser diode module 15; Ray bundle 1 emitted from diode 3
3 is transmitted, and a beam splitter 17 is provided for reflecting a light beam reflected from the information recording surface toward the light receiving element 12. Between the beam splitter 17 and the light receiving element 12, there is a detection lens 11 for condensing a light beam reflected from the optical disk. The details of the laser diode module are disclosed in JP-A-8-1111039.

In the second embodiment, as shown in FIG. 3, at the time of recording / reproducing on the high-density optical disc 1, the reflected light beam from the information recording surface 1 'of the high-density optical disc 1 is used similarly to the first embodiment. The light is condensed by the detection lens 11 and converted into an electric signal by the light receiving element 12. At the time of recording / reproducing of the conventional optical disk 2, as shown in FIG.
The light beam 19 emitted from the optical disk 5 is reflected by the beam splitter 18 and is condensed by the objective lens 8 on the information recording surface 2 ′ of the conventional optical disk 2.

The light beam reflected from the information recording surface 2 ′ passes through the objective lens 8, is reflected by the beam splitter 18, is collected on a light receiving element (not shown) in the laser diode module 15, and is converted into an electric signal. Is done. With this configuration, the positions of the laser diode 3 and the laser diode module 15 can be adjusted independently at the time of assembly, which simplifies assembly and reduces and adjusts the number of parts. The time can be reduced, and the cost of the optical pickup device can be reduced accordingly.

When a polarizing beam splitter that transmits or reflects light depending on the polarization direction is used as the beam splitter 18, the laser diode module 15
When the light beam emitted from the optical disk is reflected toward the optical disk, and when the light beam reflected from the optical disk is reflected toward the laser diode module 15, the light beam is almost totally reflected, so that the light beam utilization efficiency is improved. Can be obtained. Alternatively, a laser beam having a wavelength of 635 nm is used for the laser diode 3 and a laser beam having a wavelength of 7
80 nm, the reflection of the beam splitter 18
Similarly, when the dichroic coating having the characteristics shown in FIG. 13 is applied to the transmitting surface 18a, the light beam emitted from the laser diode module 15 is reflected toward the optical disk, and the light beam reflected from the optical disk is In the case where the light beam is reflected toward the module 15, the light beam is substantially totally reflected, so that the effect of improving the use efficiency of the light beam can be obtained.

Further, in this embodiment, the wavelength of the light beam emitted from the laser diode module 15 is 780 nm.
However, the wavelength is not limited to 635 nm, and the wavelength of the light beam emitted from the laser diode 3 may be replaced with 780 nm. In this case, the surface 1 of the beam splitter 18
Fig. 13 shows the characteristics of the dichroic coating applied to 8a.
The characteristic shown in FIG.
It is necessary to use a characteristic that transmits light in the vicinity of 80 nm. This configuration is similar to the third embodiment of FIGS. 5 and 6 described below,
It is also applicable to the fourth embodiment of FIGS. 7 and 8 and the fifth embodiment of FIGS. 9 and 10.

In the above description, the surface 18 of the beam splitter 18
Although the coating applied to a is a dichroic coating, the coating is not limited to this, and any coating having the same characteristics may be used.

FIGS. 5 and 6 show an optical pickup device according to a third embodiment of the present invention. In this embodiment, the optical system including the laser diode 3, the light receiving element 12, the detection lens 11, and the collimator lens 5 of the second embodiment shown in FIGS. 3 and 4 is replaced with a laser diode module 21 and a collimator lens 25. Yes, beam splitter 2
Since only one is required, and there is no need to adjust the position of the light receiving element, there is an advantage that the assembling time can be further reduced.

FIGS. 7 and 8 show an optical pickup device according to a fourth embodiment of the present invention. This embodiment is an example in which a material or a coating 8a having the same action as the optical filter 9 attached integrally with the objective lens 8 in the first embodiment shown in FIGS. 1 and 2 is formed on the surface of the objective lens. It is. In this embodiment, a member for integrally fixing the objective lens and the optical filter is unnecessary, so that the objective lens can be reduced in weight and size, and is an embodiment suitable for miniaturization of the optical pickup.

FIGS. 9 and 10 show an optical pickup device according to a fifth embodiment of the present invention. This embodiment is different from the first embodiment shown in FIGS.
And the beam splitter 6 are each a plate-like member 23,
24 is an example. This embodiment is an embodiment suitable for miniaturization, weight reduction and cost reduction as compared with the first embodiment.

The wavelength of the light beam emitted from the laser diode in the embodiment is 780 nm as the wavelength corresponding to the conventional optical disk 2, but is not limited to this as long as it is within the range defined by the CD standard. Further, although 635 nm is used as the wavelength corresponding to the high-density optical disk 1, the wavelength is not limited to this as long as it is within the range defined by the DVD standard, and may be, for example, 650 nm or 680 nm.

[0042]

The optical pickup device of the present invention can be manufactured with a simple structure, and a conventional optical disk such as a CD and a DVD in which the position of the information recording surface of the information recording medium differs in the thickness direction.
Such a high-density optical disk can be recorded or reproduced by one optical pickup device.

Also, since there are a plurality of laser diodes, an optical disc having a wavelength dependency can be obtained by appropriately selecting the wavelength emitted by at least one laser diode.
For example, recording or reproduction of a CD-R is possible.

Further, even in an optical pickup device having two optical systems, such as a CD system and a DVD system, each optical system can be independently adjusted in an assembling process by using a laser diode module. , The assembling time can be shortened, and the cost can be reduced accordingly.

Further, since the optical pickup device of the present invention can be constituted by inexpensive parts, the manufacturing cost of the optical pickup device can be reduced.

[Brief description of the drawings]

FIG. 1 is an optical path diagram showing an optical pickup device according to a first embodiment of the present invention.

FIG. 2 is an optical path diagram showing an optical pickup device according to a first embodiment of the present invention.

FIG. 3 is an optical path diagram showing an optical pickup device according to a second embodiment of the present invention.

FIG. 4 is an optical path diagram showing an optical pickup device according to a second embodiment of the present invention.

FIG. 5 is an optical path diagram showing an optical pickup device according to a third embodiment of the present invention.

FIG. 6 is an optical path diagram showing an optical pickup device according to a third embodiment of the present invention.

FIG. 7 is an optical path diagram showing an optical pickup device according to a fourth embodiment of the present invention.

FIG. 8 is an optical path diagram showing an optical pickup device according to a fourth embodiment of the present invention.

FIG. 9 is an optical path diagram showing an optical pickup device according to a fifth embodiment of the present invention.

FIG. 10 is an optical path diagram showing an optical pickup device according to a fifth embodiment of the present invention.

FIG. 11 is a plan view showing a circular opening of an optical filter used in each embodiment of the present invention.

FIG. 12 is a diagram illustrating an operation of an optical filter using a polarizing plate used in each embodiment of the present invention.

FIG. 13 is a graph showing wavelength transmission characteristics of a dichroic coating used in each example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 High-density optical disk (DVD etc.) 1 'Information recording surface 2 Conventional optical disk (CD etc.) 2' Information recording surface 3 Laser diode (For high-density optical disk recording / reproduction) 4 Laser diode (For conventional optical disk recording / reproduction) 5, 5 '... collimator lens 6 beam splitter 7 beam splitter 8 objective lens 9 optical filter 10 lens holder 11 detection lens 12 light receiving element 13 light beam 14 light beam 15 laser diode module (conventional optical disk recording / reproducing) 16) Collimator lens (for laser diode module) 17 Beam splitter 18 Beam splitter 19 Ray bundle emitted from laser diode module 20 Ray bundle reflected from optical disk 21 Laser diode module (high density optical disk) Recording-reproducing) 22 beam splitter 23 a plate-like member 24 a plate-like member

Claims (13)

[Claims] 1. An optical pickup device for recording or reproducing a plurality of types of optical discs having different information recording surface positions in a thickness direction, wherein two or more light emitting elements and a light beam emitted from the light emitting elements are substantially parallel. A collimator lens as a light beam, an objective lens that converges the substantially parallel light beam on the information recording surface, and a polarization direction selecting unit that regulates a light beam diameter by a difference in a polarization direction of the light beam incident on the objective lens, A light receiving element for converting a return light from the information recording surface of the optical disk to a convergent light beam emitted from the objective lens, and a light beam emitted from the light emitting element on an optical path through which the light beam passes are the same. At least one reflective optical element for transmitting or reflecting the return light reflected or transmitted on the optical path and reflected on the information recording surface toward the light receiving element. The optical pickup apparatus according to claim. 2. The polarization direction selecting means, wherein a surface layer of the objective lens other than a circular portion centered on an optical axis of the objective lens is formed of a material having a function as a polarizer. 2. The pickup device according to 1. 3. The light according to claim 1, wherein the polarization direction selecting means is a coating having a polarization characteristic applied to the objective lens other than a circular portion centered on the optical axis of the objective lens. Pickup device. 4. The polarizing plate according to claim 1, wherein the polarization direction selecting unit is a polarizing plate that is disposed on a supporting unit that supports the objective lens and has an opening that does not function as a circular polarizer centered on the optical axis of the objective lens. The optical pickup device according to claim 1, wherein: 5. The optical pickup device according to claim 2, wherein the aperture is provided so that the numerical aperture of the objective lens is 0.3 or more. 6. The optical pickup device according to claim 4, wherein the polarizing plate has an inclined angle with respect to an optical axis of the objective lens. 7. A laser diode is used as the light emitting element, and a polarization direction of a light beam emitted from at least one laser diode and incident on an objective lens or a polarizing plate is emitted from at least one other laser diode. 7. The optical pickup device according to claim 1, wherein the laser diode is disposed so as to make an angle of about 90 degrees with the polarization direction of the light beam when entering the objective lens or the polarizing plate. 8. A laser diode is used as the light emitting element, and a polarization direction of a light beam emitted from at least one laser diode and incident on an objective lens or a polarizing plate is emitted from at least one other laser diode. A wavelength plate that changes the polarization direction in the optical path between the at least one laser diode and the reflective optical element so that the polarization direction of the light beam when entering the objective lens or the polarization plate is substantially 90 °. The optical pickup device according to claim 1, wherein the optical pickup device is disposed. 9. The optical pickup device according to claim 1, wherein at least one of the light emitting elements is an integrated module integrated with the light receiving element. 10. At least one of said reflective optical elements
2. The device according to claim 1, wherein the first and second mirrors are constituted by half mirrors.
10. The optical pickup device described in any one of items 1 to 9. 11. At least one of the reflective optical elements
10. The optical pickup device according to claim 1, wherein each of the optical pickup devices comprises a prism. 12. At least one of said reflective optical elements
2. The device according to claim 1, wherein said beam splitter is configured to reflect or transmit light beams depending on a difference in polarization direction.
10. The optical pickup device described in any one of items 1 to 9. 13. At least one of said reflective optical elements
10. The optical pickup device according to claim 1, wherein the optical pickup device comprises a beam splitter that reflects or transmits light beams depending on a difference in wavelength of a light beam.