JPH10199021A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize recording/reproducing of plural kinds of optical information recording media at a low cost without complication them and moreover, to obtain enough quantity of converging light at the time of recording individual optical information recording medium. SOLUTION: A converging means 60 for approximately equalizing divergence degree of beams of outgoing light from a synthesizing means 20 in the case of the light emitted from a 1st light source 11 and in the case of the light emitted from a 2nd light source 12 respectively is provided between the synthesizing means 20 and the 1st light source 11 and/or the synthesizing means 20 and the 2nd light source 12. When the imaging magnification by an optical element installed between the 1st light source 11 and the optical information recording medium 10 is denoted as m1, while the imaging magnification by the optical element installed between the 2nd light source 12 and the optical information recording medium 10 as m2, the converging means 60 is provided to satisfy 1.3<=m2/m1.

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 on and / or reproducing information from optical information recording media having different thicknesses of transparent substrates.

[0002]

2. Description of the Related Art In recent years, with the practical use of a short-wavelength red semiconductor laser, a high-capacity optical disk having a size similar to that of a CD (compact disk), which is a conventional optical information recording medium (hereinafter, also referred to as an optical disk), has been increased. DV is a high density optical information recording medium
The development of D (digital video disc) is progressing. In this DVD, the numerical aperture NA of the objective lens on the optical disk side is set to 0.6 when a short wavelength semiconductor laser of 635 nm or 650 nm is used. Note that DV
D represents a track pitch of 0.74 μm and a minimum pit length of 0.
4 μm, and the density is reduced to half or less of the CD track pitch of 1.6 μm and the shortest pit length of 0.83 μm.

In an optical pickup device for recording / reproducing a DVD which is a new optical information recording medium, the thickness of the transparent substrate is different from 0.6 mm of DVD to 1.2 mm.
Compatibility with D is required, and various studies have been made. As one of them, there has been proposed an optical pickup device for reproducing DVDs and CDs with one short-wavelength red semiconductor laser (light source) and one condensing optical system as described in JP-A-7-57271. .

However, in an optical pickup device using one short-wavelength red semiconductor laser as a light source as described in the above-mentioned publication, a CD-R (write-once compact disc) as a writable optical information recording medium is used. Recording and / or playback. This is because the reflectance of the CD-R decreases on the short wavelength side, and a required signal (reproduction signal or focus error signal) cannot be obtained.

Therefore, as described in JP-A-8-55363, an optical pickup in which one optical system is provided, and a light source and a detection optical system are provided for each corresponding disk (for DVD and CD-R). A device has been proposed.

[0006]

Generally, when information is recorded on an optical information recording medium, the amount of condensed light several times as large as during reproduction is required. When recording is performed on an optical information recording medium with the optical pickup device described in Japanese Patent Application Laid-Open No. 8-55363, there is a problem that the amount of condensed light is insufficient.

Therefore, the present invention realizes reproduction of a plurality of types of optical information recording media at low cost and without complication, and furthermore obtains a sufficient amount of condensed light when recording on an optical information recording medium. That is the task.

[0008]

The above object can be attained by the following constitution.

(1) A first light source for emitting light of a predetermined wavelength, a second light source for emitting light of a wavelength different from the wavelength of the first light source, and an optical axis of light emitted from the first light source Combining means for substantially matching the optical axis of the light emitted from the second light source with the light source, light collecting means for focusing the light emitted from the combining means on the optical information recording medium, and light reflected from the optical information recording medium. A light receiving device for receiving light, wherein the divergence of light emitted from the synthesizing unit in the case of light emitted from the first light source and the case of light emitted from the second light source. An optical pickup device, wherein conversion means for making the same are substantially the same is provided between the combining means and the first light source or / and between the combining means and the second light source.

(2) The imaging magnification of the optical element between the first light source and the optical information recording medium is m1, and the imaging magnification of the optical element between the second light source and the optical information recording medium is m1. The optical pickup device according to (1), wherein when m2, 1.3 ≦ m2 / m1.

(3) A first light source for emitting light of a predetermined wavelength, a second light source for emitting light of a wavelength different from the wavelength of the first light source, and an optical axis of light emitted from the first light source Combining means for matching the optical axis of light emitted from the second light source with the light source, light collecting means for focusing light emitted from the combining means on an optical information recording medium, and light reflected from the optical information recording medium. And a light receiving means for receiving light from the optical information recording medium, wherein an imaging magnification by an optical element between the first light source and the optical information recording medium is m1, and a magnification between the second light source and the optical information recording medium is Assuming that the imaging magnification by a certain optical element is m2, between the synthesizing unit and the first light source or / and between the synthesizing unit and the second light source such that 1.3 ≦ m2 / m1. An optical pickup device characterized by comprising a conversion means.

(4) The light emitted from the second light source is used for recording optical information on an optical information recording medium and reproducing the optical information recorded on the optical information recording medium (2). Or the optical pickup device according to (3).

(5) The optical pickup device according to (4), wherein light emitted from the first light source reproduces optical information recorded on an optical information recording medium.

(6) The light condensing means condenses light emitted from the first light source on a first optical information recording medium having a transparent substrate having a thickness of t1, and emitted from the second light source. Light is focused on a second optical information recording medium having a thickness t2 (where t2 ≠ t1) of a transparent substrate (1) to (1).
The optical pickup device according to any one of (5).

(7) The light condensing means transmits the light having the wavelength λ1 emitted from the synthesizing means to the first optical information recording medium through the transparent substrate having the thickness t1 on the information recording surface. As a beam spot, light having a wavelength of λ2 emitted from the synthesizing means passes through a transparent substrate having a thickness t2 (≠ t1) of the second optical information recording medium and has a size different from that of the first beam spot on the information recording surface. The optical pickup device according to any one of (1) to (6), wherein the light is focused as a second beam spot.

(8) The wavelength of light emitted from the first light source is λ1, and the wavelength of light emitted from the second light source is λ1.
Assuming that 2, 610 nm ≦ λ1 ≦ 670 nm, 760 n
m ≦ λ2 ≦ 830 nm, and the first optical information recording medium is D
The VD optical disk and the second optical information recording medium are CD-R
The optical pickup device according to (7), which is an optical disk of a system.

(9) At least one optical surface of the optical element constituting the light condensing means has a ring-shaped discontinuous surface centered on an optical axis within an effective diameter (1). The optical pickup device according to any one of (8) to (8).

(10) The optical pickup device according to any one of (1) to (9), wherein the light condensing means is constituted by a coupling lens and an objective lens.

(11) A separating means for guiding the light reflected from the optical information recording medium to the light receiving means is provided between the synthesizing means and the light collecting means.
0) The optical pickup device according to any one of the above.

(12) The converting means and the synthesizing means are integrally formed (1) to (1).
The optical pickup device according to any one of 1).

[0021]

Embodiments of the present invention will be described below with reference to the drawings. When the same function / component is used, the same figure number is assigned. In the following description of the embodiments, the first optical information recording medium (first optical disc) is a read-only optical disc, more specifically, a DVD-type optical disc having a transparent substrate with a thickness t1 = 0.6 mm. The second optical information recording medium (second optical disk) will be described as an optical disk capable of reproducing and recording, more specifically, a CD-R optical disk having a transparent substrate thickness t1 = 1.2 mm.

(First Embodiment) A first embodiment will be described with reference to FIG. 1 which is a schematic configuration diagram of an optical pickup device. First, a case where a DVD-type optical disk (first optical disk) is reproduced will be described.

The first semiconductor laser 11, which is the first light source,
A light source that emits light for reproducing information recorded on the read-only first optical disk 10. In this embodiment, since the first optical disk is a DVD system, a short wavelength semiconductor having a wavelength λ1 of 610 to 670 nm is used. Laser. First
Light emitted from the semiconductor laser 11 enters the dichroic prism 20. This dichroic prism 2
Numeral 0 denotes a synthesizing unit that makes the optical axis of the light emitted from the first semiconductor laser 11 substantially coincide with the optical axis of the light emitted from the second semiconductor laser 12, which will be described later. The light of the wavelength emitted from the semiconductor laser 11 is reflected, and the light of the wavelength emitted from the first semiconductor laser 11 is transmitted and matched. Light emitted from the first semiconductor laser 11, whose optical axis is bent, and emitted from the dichroic prism 20 are transmitted through a polarization beam splitter 40, which will be described later, and enter the condensing unit 30.

The light condensing means 30 is means for condensing the light emitted from the dichroic prism 20 on the optical disk 10 (specifically, on the information recording surface via the transparent substrate of the optical disk 10). The condensing means 30 has a coupling lens 31 and an objective lens 32. In the present embodiment, the coupling lens 31 converts light emitted from the dichroic prism 20 and the polarization beam splitter 40 into parallel light. Objective lens 3 using a collimator lens
As 2, an infinite system objective lens for condensing parallel light on the optical disk 10 is used.

In the focusing means 30, a quarter-wave plate 35 and a stop 36 are provided. 1/4 wavelength plate 35
Changes the light transmitted through the coupling lens 31 from linearly polarized light to circularly polarized light, and the aperture 36 restricts the parallel light flux to a numerical aperture on the optical disk 10 side of the objective lens 32 necessary for reproducing a DVD.

The light beam reflected from the optical disk 10 (more specifically, modulated by the information pits on the information recording surface) passes through the objective lens 32, the quarter-wave plate 35, and the coupling lens 31 again to be polarized. Beam splitter 40
Incident on. The polarizing beam splitter 40 is a separating unit that separates a light beam to guide the light reflected from the optical disk 10 to a light receiving unit 50 described below.
0 and the dichroic prism 20. In the present embodiment, the configuration is such that the light reflected from the optical disk 10 is reflected and bent by the polarization beam splitter 40.

The light reflected by the polarizing beam splitter 40 is received by the light receiving means 50. The light receiving means 50 detects a change in the light amount distribution of the light reflected from the optical disk 10 by the photodetector 51, and focus detection, track detection, and information reading are performed by an arithmetic processing circuit (not shown). In the present embodiment, the focus detection is performed by the astigmatism method. Therefore, the light receiving unit 50 has a cylindrical lens 52 that generates astigmatism. Note that the focus detection and the track detection can be performed by various known methods such as a knife edge method, an SSD method, a push bull method, and a three-beam method.

Based on the focus detection obtained by the arithmetic processing circuit, an objective lens 32 such that a two-dimensional actuator (for focus control), not shown, forms an image of the light from the first semiconductor laser 11 on the first optical disk 10. To move. At this time, the first optical disk (DVD (t1 = 0.6
mm)) The objective lens 32 is set at 2 so that the beam spot on the 10 information recording surface is minimized (best focus).
It is driven by a two-dimensional actuator. Further, based on the track detection, a two-dimensional actuator (for tracking control), not shown, moves the objective lens 32 so that the light from the first semiconductor laser 11 forms an image on a predetermined track.

By the way, the optical pickup device of the present embodiment uses the second optical disc for reproducing or recording the second optical disc.
A semiconductor laser 12 is provided. The second semiconductor laser 12, which is a second light source, is a light source for reproducing information recorded on the second optical disk 10 that can be reproduced and recorded, and recording information on the second optical disk 10. In the present embodiment,
Since the second optical disc is of the CD-R type, the wavelength λ2 (>
λ1) is a semiconductor laser having a wavelength of 760 to 830 nm.

The optical pickup device according to the present embodiment uses light emitted from the first semiconductor laser 11 and light emitted from the second semiconductor laser 12 in order to further increase the amount of condensed light when recording information on an optical disk. A lens 60 having a positive refractive index, which is conversion means for making the divergence of light exiting from the dichroic prism 20 substantially the same as that of the light emitted from the dichroic prism 20, is disposed between the dichroic prism 20 and the second semiconductor laser 12. Is provided. Thus, in the present embodiment, the reproduction of the DVD and the CD-R
Can be recorded and reproduced.

That is, when recording on the second optical disk,
Since it is necessary to guide the emitted light from the second semiconductor laser onto the second optical disc with higher efficiency, the second semiconductor laser 1
2, a coupling numerical aperture NAa (= sin), which is the numerical aperture of the divergence angle of the light beam guided to the second optical disc among the light beams emitted from
(A)) is increased. On the other hand, when reproducing the first optical disk, the intensity of the light beam incident on the objective lens around the lens is desirably about 50% in order to reduce the size of the focused spot.
Numerical aperture NAb (= sin), which is the numerical aperture of the divergence angle of the light beam guided to the first optical disc among the light beams emitted from the optical disk.
(B)) is different from the coupling numerical aperture NAa. That is,
Coupling numerical aperture NAb of the first semiconductor laser 11 for reproduction only
Is different from the value of the coupling numerical aperture NAa on the side of the second semiconductor laser 12 on which recording is performed. In order to achieve this with the common condensing means 30, at least one of the semiconductor laser and the synthesizing means is used. 20 and the divergence angle of the laser
There is provided a conversion means 60 for performing conversion when viewed from the 0 side.

Here, an optical disk of the CD-R system (second
A case where information recorded on an optical disc is reproduced or information is recorded will be described.

The divergence of the light beam emitted from the second semiconductor laser 12 is converted by a lens 60 as a conversion means (the light beam emitted from the first semiconductor laser 11 and the second light beam are converted).
The light emitted from the semiconductor laser 12 and the light emitted from the dichroic prism 20 are made to have substantially the same divergence, and transmitted through the dichroic prism 20 and the polarizing beam splitter 40 to the focusing means 30. The incident light is transmitted through the coupling lens 31 and the quarter-wave plate 35 to become a circularly polarized parallel light beam. This light beam is stopped down by the stop 36, and the second optical disc 1 is
The light is focused on 0 (in the case of recording, information is recorded on the second optical disk here). Then, the second optical disc 1
The light beam reflected from 0 passes through the objective lens 32, the quarter-wave plate 35, and the coupling lens 31 again, enters the polarization beam splitter 40, is reflected there, and is given astigmatism by the cylindrical lens 52. Photodetector 51
A signal for reading information recorded on the optical disc 20 is obtained by using a signal that is incident upward and output from the photodetector 51. Further, a change in light amount distribution due to a change in the shape of a spot on the photodetector 30 is detected, and focus detection and track detection are performed. When reproducing / recording a CD-R (second optical disk 10), the thickness of the transparent substrate is different from that of a DVD (first optical disk). When the thickness of the transparent substrate is increased, spherical aberration occurs, and at a position where the beam spot behind the paraxial focal point has a minimum circle of confusion, the spot size is large and the pits (information) on the second optical disc must be read. Can not.
However, at a position on the front side closer to the objective lens 32 than the position where the minimum circle of confusion occurs, the size of the entire spot is larger than the minimum circle of confusion, but there is a nucleus where the amount of light is concentrated at the center and unnecessary light around the nucleus. A certain flare is formed. The nucleus reproduces (reads) the pits (information) of the second optical disc.
During the reproduction of the second optical disc, the two-dimensional actuator is driven so that the objective lens 32 is in a defocused (front focus) state.

Incidentally, since the lens 60 as the above-mentioned conversion means has a conjugate relationship between the first and second light sources and the optical disk, the image forming magnification by the optical element between the first semiconductor laser 11 and the optical disk. Is m1, and when the imaging magnification by the optical element between the second semiconductor laser 12 and the optical disk is m2, 1.3 ≦ m2 / m1. If the lower limit of the condition of the image forming magnification ratio (m2 / m1) is exceeded, the diameter of the condensed spot on the first optical disc by the first semiconductor laser is set to an appropriate size.
If the light quantity of the condensed spot on the second optical disc by the semiconductor laser is reduced and reproduction / recording becomes difficult, or if the light quantity of the condensed spot on the second optical disc by the second semiconductor laser is made appropriate, the first semiconductor laser will The diameter of the condensed spot on the first optical disk becomes large, and reproduction becomes difficult. More preferably, the lower limit of the imaging magnification ratio is 1.5 ≦ m2 / m1.

The condition of the imaging magnification ratio m2 / m1 is preferably 3.3 or less (m2 / m1 ≦ 3.3). If the upper limit is exceeded, if the light quantity of the condensed spot on the first optical disc by the first semiconductor laser is made appropriate, the diameter of the condensed spot on the second optical disc by the second semiconductor laser becomes large, making reproduction / recording difficult. Or
When the diameter of the condensed spot on the second optical disc by the second semiconductor laser is set to an appropriate size, the light quantity of the condensed spot on the first optical disc by the first semiconductor laser is reduced, so that reproduction becomes difficult. Becomes complicated (for example, a complicated optical surface is indispensable), and production becomes difficult.

Further, the above-mentioned imaging magnification m1 is 1/6 ≦ |
It is preferable to satisfy the condition of m1 | ≦ 1/9. Exceeding the upper limit lowers the amount of condensed light, while exceeding the lower limit increases the spot diameter, making reproduction difficult. It is preferable that the imaging magnification m2 satisfies the condition of 1/3 ≦ | m2 | ≦ 1/5. Exceeding this upper limit reduces the amount of condensed light, while exceeding the lower limit increases the spot diameter,
Reproduction becomes difficult.

(Second Embodiment) Next, a second embodiment will be described with reference to FIG. 2, which is a schematic configuration diagram of an optical pickup device. In the second embodiment, the first light source 11 and the second light source 1 in the first embodiment described above are used.
2. The arrangement of the synthesizing unit 20, the separating unit 40, and the light receiving unit 50 is changed, and the same figures and numbers are given to the same functions and components as those in the first embodiment. Omitted.

In the present embodiment, the dichroic polarizing prism 21 as the synthesizing means emits the light emitted from the second semiconductor laser 12 (however, the lens 6 as the converting means).
By reflecting the s-polarized light component of the light whose divergence is converted by 0) and transmitting the light emitted from the first semiconductor laser 11, the optical axis of the light emitted from the first semiconductor laser 11 and the second The optical axis of the light emitted from the semiconductor laser 12 is substantially matched.

In the present embodiment, the dichroic polarization beam splitter 41 serving as the separating means reflects the s-polarized light component of the light emitted from the first semiconductor laser 11 and the p-polarized light of the light reflected from the optical disk 10.
By transmitting the polarized light component, the light beam is separated to guide the light reflected from the optical disk 10 to the light receiving unit 50.

When reproducing information recorded on a DVD optical disk (first optical disk) in the present embodiment, the light beam emitted from the first semiconductor laser 11 is converted by the polarizing prism 41 into an s-polarized light component. The light is made incident, reflected by the light, transmitted through the dichroic polarizing prism 21, and made incident on the light collecting means 30. This light passes through the coupling lens 31 and the quarter-wave plate 35 to become a circularly polarized parallel light beam. Then, this light beam is stopped down by the stop 36 and is condensed on the first optical disk 10 by the objective lens 32. The luminous flux reflected from the first optical disk 10 is again transmitted to the objective lens 32, the quarter-wave plate 35, the coupling lens 31, the dichroic polarizing prism 21,
A signal for reading information recorded on the optical disk 20 using a signal output from the photodetector 51 after passing through the dichroic polarization beam splitter 41, given astigmatism by the cylindrical lens 52, and incident on the photodetector 51. Is obtained. Further, a change in light amount distribution due to a change in the shape of a spot on the photodetector 30 is detected, and focus detection and track detection are performed.

In the present embodiment, when reproducing or recording information recorded on a CD-R type optical disk (second optical disk), a light beam emitted from the second semiconductor laser 12 is converted by a lens 60 as a conversion means. The divergence is converted (the divergence of the light emitted from the dichroic polarizing prism 21 is substantially the same between the case of the light emitted from the first semiconductor laser 11 and the case of the light emitted from the second semiconductor laser 12). Dichroic polarizing prism 2
The light is incident on the light source 1 so as to be an s-polarized light component, is reflected by the light, and is incident on the light collecting means 30. This light is condensed on the second optical disc 10 by the coupling lens 31, the quarter-wave plate 35, and the objective lens 32 (stopped by the stop 36). Is recorded). Then, the light beam reflected from the second optical disk 10 is again transmitted to the objective lens 32 and the 波長 wavelength plate 3.
5. The coupling lens 31, the dichroic polarizing prism 21, and the dichroic polarizing beam splitter 41 transmit the light, enter the photodetector 51, and use the signal output from the photodetector 51 to output information recorded on the optical disc 10. A read signal is obtained. Further, a change in the light amount distribution due to a change in the shape of the spot on the photodetector 51 is detected, and focus detection and track detection are performed.

In this embodiment, similarly to the above-described first embodiment, a lens 60 having a positive refractive index, which is a conversion means, is connected to the dichroic polarizing prism 21 and the second
By providing between the semiconductor laser 12 and the semiconductor laser 12, in the present embodiment, the reproduction of the DVD and the reproduction of the CD-
R can be recorded / reproduced, and at the time of recording a CD-R, the amount of condensed light on the CD-R can be sufficiently increased. Further, the lens 60 as the conversion means is 1.3 from another viewpoint, similarly to the first embodiment described above.
変 換 m2 / m1. Further, the lower limit of the imaging magnification ratio is preferably 1.5 ≦ m2 / m1. The upper limit of the imaging magnification is preferably 3.3 or less. Further, the above-mentioned imaging magnifications m1 and m2 are 1/6 ≦
| M1 | ≦ 1/9 and 1/3 ≦ | m2 | ≦ 1/5 are preferably satisfied.

(Third Embodiment) Next, a third embodiment will be described with reference to FIG. 3, which is a schematic configuration diagram of an optical pickup device. In the third embodiment, the first light source 11 and the second light source 1 in the first embodiment described above are used.
2. The arrangement of the synthesizing unit 20, the separating unit 40, and the light receiving unit 50 is changed, and the same figures and numbers are given to the same functions and components as those in the first embodiment. The description will be omitted, and only different points will be described.

The present embodiment is functionally different from the first embodiment in that the polarizing beam splitter 42 serving as the separating means is configured to use the light emitted from the first semiconductor laser 11 or the second semiconductor laser 12. The light reflected from the optical disk 10 is transmitted to the light receiving unit 50 by reflecting light emitted from the optical disk 10 (light emitted from the dichroic prism 20 as a combining unit) and transmitting light reflected from the optical disk 10. Is separated.

Here, the polarizing beam splitter 42 is a non-polarizing beam splitter having substantially the same reflectance for both p-polarized light and s-polarized light at the wavelength of the first semiconductor laser 11, and s-polarized light for the wavelength of the second semiconductor laser 12. It has almost the characteristics as a polarizing beam splitter that has a large reflectance and a large transmittance of p-polarized light. By using such a beam splitter 42, the amount of light traveling from the second semiconductor laser 11 to the first optical disk is kept high, and the fluctuation of the reproduced signal due to the birefringence of the optical disk substrate during DVD reproduction by the first semiconductor laser 11 is reduced. Can be suppressed.

(Fourth Embodiment) Next, a fourth embodiment will be described with reference to FIG. 4 which is a schematic configuration diagram of an optical pickup device. In the above-described first to third embodiments, one light receiving unit 50 is configured to detect the light reflected from the first optical disk and the light reflected from the second optical disk, but in the fourth embodiment, Two light receiving means (a first light receiving means 53 and a second light receiving means 54) are provided, the first light receiving means 53 receives light reflected from the first optical disk, and the second light receiving means 54 receives light reflected from the second optical disk. It differs greatly in that it is configured to detect.

For this purpose, in the present embodiment, a first polarizing beam splitter 43 for the first light receiving means 53 and a second polarizing beam splitter 44 for the second light receiving means 54 are provided as separating means. I have.

In the present embodiment, when reproducing information recorded on a DVD optical disk (first optical disk), the light beam emitted from the first semiconductor laser 11 passes through the polarizing prism 43 and becomes a dichroic prism. 20
And is incident on the light collecting means 30. This light is supplied to the first optical disc 10 by the coupling lens 31, the quarter-wave plate 35, and the objective lens 32 (stopped by the stop 36).
Focused on top. Then, the light beam reflected from the first optical disk 10 is again transmitted to the objective lens 32, the quarter-wave plate 35,
The light passes through the coupling lens 31 and is reflected by the dichroic prism 20 and the first polarization beam splitter 43.
Astigmatism is given by the first cylindrical lens 56, the light is incident on the first photodetector 55, and a signal for reading information recorded on the optical disc 10 is obtained using a signal output from the first photodetector 55. . Further, the first photodetector 55
By detecting a change in light amount distribution due to a change in the shape of the spot, focus detection and track detection are performed.

In the present embodiment, when reproducing information recorded on a CD-R type optical disk (second optical disk) or recording information on the second optical disk, the second
The divergence of the light beam emitted from the semiconductor laser 12 is converted by the lens 60 as the conversion means (the first semiconductor laser 1).
In the case of light emitted from the first semiconductor laser 12 and the case of light emitted from the second semiconductor laser 12, the dichroic prism 20
The divergence of the light exiting from the
Polarizing beam splitter 44, dichroic prism 2
The light passes through 0 and enters the light collecting means 30. This light is coupled to a coupling lens 31, a quarter-wave plate 35, and a stop 36
The second optical disc 1 by the objective lens 32
It is focused on zero. Then, the light beam reflected from the second optical disk 10 is again transmitted to the objective lens 32 and the 波長 wavelength plate 3.
5. The light passes through the coupling lens 31 and the dichroic prism 20, is reflected by the second polarization beam splitter 44, enters the second photodetector 58 via the second cylindrical lens 57, and is incident on the second photodetector 58. A signal for reading information recorded on the optical disk 10 is obtained by using the signal output from 58. Further, a change in light amount distribution due to a change in the shape of a spot on the photodetector 30 is detected, and focus detection and track detection are performed.

Since the lens 60 as the conversion means has the same function as that of the above-described first to third embodiments,
Although the description is omitted, also in the present embodiment, one light collecting means 30 is used, and in the present embodiment, reproduction of DVD and CD-
R can be recorded / reproduced, and at the time of recording a CD-R, the amount of condensed light on the CD-R can be sufficiently increased.

Next, the objective lens 32 preferably used in the first to fourth embodiments will be described. The preferred objective lens 32 is a convex single lens having a positive refractive power having a double-sided aspherical shape, and a ring-shaped discontinuous surface centered on the optical axis is provided on at least one refractive surface (optical surface). , Within the effective diameter (diameter narrowed by the aperture 36). More specifically, the objective lens 32 includes a plurality of ring-shaped divided surfaces coaxial with the optical axis on a refracting surface on the light source side, and a step in the optical axis direction is provided at a boundary between the divided surfaces. .

This will be described more specifically with reference to FIG. FIG. 5 is a sectional view (a) and (c) schematically showing the objective lens 32 and a front view (b) viewed from the light source side.
(A) is a schematic diagram when light is condensed on a DVD as the first optical disc 10, and (c) is a second optical disc 10.
FIG. 4 is a schematic diagram when light is focused on a CD-R. The dashed line indicates the optical axis.

The refracting surface S1 on the light source side and the refracting surface S2 on the optical disk 10 are both convex lenses having an aspherical shape and having a positive refractive power. A plurality (3 in this embodiment) concentric with the axis
), The first divided surface Sd1 to the third divided surface Sd3, and the boundary between the divided surfaces Sd1 to Sd3 is provided with a step. The first divided surface Sd1 and the third divided surface Sd3 are formed on the first aspherical surface such that the best wavefront aberration of the light beam emitted from the first semiconductor laser 11 and condensed on the first optical disk is 0.05λrms or less. The second divided surface has a spherical surface smaller than the amount of spherical aberration generated when the light beam of the second semiconductor laser 12 is condensed on the second optical disk via the lens having the first aspheric surface. The second aspherical surface is formed near the required numerical aperture, which is the numerical aperture on the optical disk side of the objective lens 32 required for reproducing the information of the second optical disk on the first aspherical surface. Are combined into an objective lens 32.

In this objective lens 32, a light beam (first light beam) passing through the first division surface Sd1 including the optical axis is used for reproducing information recorded on the first optical disk and recording / recording information recorded on the second optical disk. Used for reproduction, the first division surface Sd
The light beam (second light beam) passing through the second divided surface Sd2 outside the first divided surface Sd2 is mainly used for recording / reproducing information recorded on the second optical disk, and the third divided surface S outside the second divided surface Sd2 is used.
The light beam (third light beam) passing through d3 is mainly used for reproducing information recorded on the first optical disc. This objective lens 3
According to 2, the light from the light source is suppressed while the light quantity loss is suppressed.
Reproduction / recording of two optical disks can be performed by one condensing optical system. Moreover, in this case, most of the third light flux is unnecessary light during reproduction of the second optical disc, but this unnecessary light is
Since the aperture 36 is not used for reproducing the optical disk, the aperture 36 is set to the numerical aperture necessary for reproducing the first optical disk.
The reproduction can be performed without any means for changing the numerical aperture of the diaphragm 36.

Next, specific numerical examples of the objective lens 32 preferably used in the above-described first to fourth embodiments will be shown. It should be noted that a collimator lens is used as the coupling lens 31, and by optimizing the design of the collimator lens, it is possible to make a substantially illuminated parallel light beam incident on the objective lens. Assuming that a collimator lens capable of emitting a parallel light beam is used, the configuration after the light beam enters the objective lens will be described. In addition, the aperture disposed on the light source side of the objective lens is defined as the first surface, and the radius of curvature of the i-th lens surface is ri in this order.
The distance from the third surface is di (the value is changed to di 'during CD-R reproduction / recording), and the refractive index at the wavelength of the light beam of the semiconductor laser at that interval is represented by ni. .

When an aspherical surface is used for the optical surface, the expression of the aspherical surface is as follows.

[0057]

(Equation 1)

[0058] Here, X is the axis in the optical axis direction, H is the axis perpendicular to the optical axis, and the traveling direction of light is positive, r is the paraxial radius of curvature, K is the conic coefficient, Aj is the aspherical coefficient, and Pj is the aspherical surface. (Where Pj ≧ 3).

This example is an example of the objective lens 32 in which the refraction surface S1 is divided into three as described above, and a step is provided at the boundary between the first division surface Sd1 and the third division surface Sd3.

Tables 1 and 2 show the optical data of the objective lens.

[0061]

[Table 1]

[0062]

[Table 2]

In the objective lens of this embodiment, the position where the first aspherical surface intersects the optical axis and the position where the second aspherical surface intersects the optical axis are the same. Also, ni ′ in Table 1 is the second light source (λ
2 = 780 nm).

FIG. 6 is a graph showing the relative intensity distribution of the condensed spot when the best spot shape is obtained during DVD reproduction. FIG. 7 is a diagram showing the case when the best spot shape is obtained during CD-R reproduction. 3 shows a relative intensity distribution diagram of the focused spot of FIG.

In the above description, when writing information to the second optical disk, the power of the second semiconductor laser 12 is controlled to be several times higher than during reproduction. Also,
Since the light reflected from the second optical disc has a flare, it is preferable to provide a detector so that the flare does not enter the light receiving surface of the detector (or does not adversely affect the light detection). A detector as described in Japanese Patent Application No. 8-247773 is used.

In the above description, the light collecting means 3
Coupling lens (collimator lens) 3 as 0
Although the objective lens 32 and the infinite system objective lens 32 are used, the coupling lens 31 is not used, and the objective lens is configured such that the light emitted from the combining unit 20 is directly incident, or the divergence of the light emitted from the combining unit 20 is reduced. A coupling lens 31 and an objective lens to which the divergent light is incident, or a coupling lens to change the light flux from the light source into convergent light and an objective lens to which the convergent light is incident Is also good.

In the above description, the dichroic prism is used as the synthesizing means. However, the present invention is not limited to this, and an optical element having the same function, for example, a hologram element or a polarizing element can be used.

In the above description, the polarizing beam splitter is used as the separating means. However, the present invention is not limited to this. For example, an optical element having a similar function, such as a parallel plate half mirror or a hologram element, may be used. it can.

In the above description, the lens 60 is provided between the combining means and the second light source as the converting means. However, the present invention is not limited to this, and the converting means having the same function is provided by the combining means and the first light source. And the optical element may be provided both between the combining means and the second light source and between the combining means and the first light source. Further, when the first optical disc is a DVD and the second optical disc is a CD-R, the conversion means having the same function provided between the synthesizing means and the first light source may be a lens having a negative refractive power, Further, in this case, by using a glass lens as the conversion means and a plastic lens as the coupling lens, an optical system excellent in temperature compensation can be obtained.

In the above description, the combining means and the conversion means are constituted by separate optical elements. However, they may be constituted integrally, for example, a hologram having power on the incident surface and / or the dichroic surface. Or a hologram beam splitter in which two light sources are arranged close to each other so that the divergence is converted at the same time as the synthesis.

In the above description, the CD-R
(Recordable medium) and DVD (reproduction-only medium) have been described, but CD (reproduction-only medium and may be read-only for CD-R) and DVD-
R (recordable medium). In this case, DVD-R emits light emitted from the second light source (in this case, the wavelength of the second light source is 610 nm or more and 670 nm or less), and CD is the light emitted from the second light source. 1 light source (in this case, the wavelength of the first light source is 7
(Being 60 nm or more and 830 nm or less) is condensed on the optical information recording medium, and the condition of the imaging magnification ratio at this time is the same as that described above.

[0072]

According to the present invention described above, a plurality of optical information recording media can be realized at low cost and without complicating the recording / reproduction. The amount of condensed light can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical pickup device according to a first embodiment.

FIG. 2 is a schematic configuration diagram of an optical pickup device according to a second embodiment.

FIG. 3 is a schematic configuration diagram of an optical pickup device according to a third embodiment.

FIG. 4 is a schematic configuration diagram of an optical pickup device according to a fourth embodiment.

5A and 5C are a cross-sectional view schematically showing a preferred objective lens and a front view as viewed from the light source side.

FIG. 6 is a relative intensity distribution diagram of a converged spot when the best spot shape is obtained during DVD reproduction.

FIG. 7 is a relative intensity distribution diagram of a converged spot when the best spot shape is obtained during CD-R reproduction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Optical disk (optical information recording medium) 11 1st semiconductor laser (1st light source) 12 2nd semiconductor laser (2nd light source) 20, 21 Dichroic prism (synthesis means) 30 Condensing means 31 Coupling lens 32 Objective lens 36 Aperture 40-44 Polarizing beam splitter (separating means) 50, 53, 54 Light receiving means 51, 55, 58 Photodetector 60 Lens (converting means)

Claims (12)

[Claims] A first light source that emits light having a predetermined wavelength; a second light source that emits light having a wavelength different from the wavelength of the first light source; and an optical axis of light emitted from the first light source. Synthesizing means for making the optical axis of the light emitted from the second light source substantially coincide with light; condensing means for condensing light emitted from the synthesizing means on an optical information recording medium; and light reflected from the optical information recording medium. And a light receiving unit that receives light from the light source. In the case of light emitted from the first light source and light emitted from the second light source, the degree of divergence of light emitted from the combining unit is determined. An optical pickup device, characterized in that conversion means for making substantially the same are provided between the synthesizing means and the first light source or / and between the synthesizing means and the second light source. 2. The imaging magnification of an optical element between the first light source and the optical information recording medium is m1, and the imaging magnification of an optical element between the second light source and the optical information recording medium is m.
2. The optical pickup device according to claim 1, wherein 1.3 ≦ m2 / m1 when 2. A first light source that emits light having a predetermined wavelength; a second light source that emits light having a wavelength different from the wavelength of the first light source; and an optical axis of light emitted from the first light source. Synthesizing means for matching the optical axis of light emitted from the second light source, condensing means for condensing light emitted from the synthesizing means on an optical information recording medium, and light reflected from the optical information recording medium An optical pickup device having a light receiving unit for receiving light, wherein an imaging magnification by an optical element between the first light source and the optical information recording medium is m1, and an imaging magnification is between the second light source and the optical information recording medium. When the imaging magnification by the optical element is m2,
An optical pickup characterized in that a conversion means is provided between the synthesizing means and the first light source or / and between the synthesizing means and the second light source so that 1.3 ≦ m2 / m1. apparatus. 4. The light emitted from the second light source performs recording of optical information on an optical information recording medium and reproduction of optical information recorded on the optical information recording medium.
Or the optical pickup device according to 3. 5. The optical pickup device according to claim 4, wherein light emitted from the first light source reproduces optical information recorded on an optical information recording medium. 6. The light condensing means condenses light emitted from the first light source on a first optical information recording medium having a transparent substrate having a thickness of t1, and emits light emitted from the second light source. The optical pickup device according to any one of claims 1 to 5, wherein the light is focused on a second optical information recording medium having a thickness t2 (where t2 ≠ t1) of the transparent substrate. 7. The light condensing means transmits the light having a wavelength λ1 emitted from the synthesizing means to a first beam having a predetermined size on an information recording surface via a transparent substrate having a thickness t1 of a first optical information recording medium. As a spot, light having a wavelength of λ2 emitted from the synthesizing means has a size different from that of the first beam spot on the information recording surface via a transparent substrate having a thickness t2 (≠ t1) of the second optical information recording medium. The optical pickup device according to claim 1, wherein the light is focused as a second beam spot. 8. When the wavelength of light emitted from the first light source is λ1 and the wavelength of light emitted from the second light source is λ2, 610 nm ≦ λ1 ≦ 670 nm 760 nm ≦ λ2 ≦ 830 nm, The optical pickup device according to claim 7, wherein the optical information recording medium is a DVD optical disk, and the second optical information recording medium is a CD-R optical disk. 9. The optical device according to claim 1, wherein at least one optical surface of the optical element constituting the light condensing means has a ring-shaped discontinuous surface centered on an optical axis within an effective diameter.
The optical pickup device according to any one of Items 1 to 8, 10. The optical pickup device according to claim 1, wherein the light condensing means includes a coupling lens and an objective lens. 11. The apparatus according to claim 1, wherein a separating means for guiding the light reflected from the optical information recording medium to the light receiving means is provided between the combining means and the light collecting means. An optical pickup device according to any one of the above. 12. The optical pickup device according to claim 1, wherein said converting means and said combining means are integrally formed.