JP4126799B2 - Optical disk device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disk device, can be applied to, for example, an optical disc apparatus for reproducing a DVD (Digital Video Disk) and a compact disc. The present invention corrects the aberrations of a plurality of laser beams by one astigmatism correction means, and improves optical characteristics with a simple configuration when accessing an optical disc selectively using a plurality of light sources. To be able to.
[0002]
[Prior art]
Conventionally, in a compact disc player which is an optical disc device, various data recorded on the compact disc are processed by irradiating the information recording surface of the compact disc with an optical pickup and processing the result of receiving the return light. It is made to play.
[0003]
In such an optical pickup, a type in which a light emitting element and a light receiving element are individually arranged and a type using an optical integrated element in which the light emitting element and the light receiving element are integrated are proposed. Thus, the overall shape can be reduced in size as compared with the former, and the reliability can be improved.
[0004]
In such an optical pickup, the plane of polarization of the laser beam is arranged a laser diode so as to form an angle of approximately 45 degrees with respect to the scanning direction of the laser beam, thereby no correct astigmatism of the laser beam Even without this, an increase in jitter due to deterioration of optical characteristics can be prevented.
[0005]
[Problems to be solved by the invention]
By the way, in the case of using an optical integrated device, it is convenient if an optical pickup can be configured using an optical integrated device even in an optical disc apparatus for reproducing a DVD because the overall shape can be reduced in size and simplified. it is conceivable that. Furthermore, even in such an optical disc apparatus for DVD, it is considered convenient if a compact disc can be reproduced.
[0006]
In this case, it is considered that an optical disc apparatus capable of reproducing a compact disc and a DVD can be constructed by integrating a light emitting device and a light receiving device for DVD and a light emitting device and a light receiving device for compact disc to constitute an optical integrated device. It is done.
[0007]
However, in the compact disc, the pit depth is λ / 8 wavelength, whereas in the DVD, the pit depth is λ / 4 wavelength. However, it is difficult to detect a tracking error signal by a method similar to that of a compact disk. For example, it is necessary to generate a tracking error signal by a so-called DPD (differential phase detection) method. In the this DPD method, it is necessary to arrange the laser diode so that the plane of polarization of the laser beam with respect to the scanning direction of the laser beam is parallel or perpendicular.
[0008]
Also in order to effectively utilize the inner space of the optical integrated device, the plane of polarization of the laser beam with respect to the scanning direction of the laser beam is desired to place the laser diode to be parallel or perpendicular.
[0009]
However, in this case, the optical disk device has a problem that optical characteristics deteriorate.
[0010]
The present invention has been made in view of the above, proposals when accessing the optical disc by using a plurality of light sources selectively, the optical disc apparatus that can be improved optical characteristics with a simple structure It is something to try.
[0011]
[Means for Solving the Problems]
In the present invention according to claim order to solve such problems, and applied to an optical disk apparatus, the first and second light sources, as the deformation direction of the beam cross-sectional shape of the laser beam by the astigmatism coincides substantially The optical system is an optical system common to the laser beams emitted from the first and second light sources, and astigmatism common to the laser beams emitted from the first and second light sources. It has correction means. In addition, the first and second light sources are spaced apart from each other in the radial direction of the optical disk, and the objective lens is displaced in the radial direction of the optical disk in response to the selective output of the laser beam from the first and second light sources. Let
[0012]
With the configuration according to claim 1 or 5, the first and second light sources are arranged so that the deformation directions of the beam cross-sectional shape of the laser beam due to astigmatism substantially coincide, and the optical system includes the first and second light sources. An optical system that is common to the laser beams emitted from the second light source and that has astigmatism correction means common to the laser beams emitted from the first and second light sources makes simple astigmatism. Astigmatism of laser beams emitted from a plurality of light sources can be corrected together by the aberration correction means, and the optical characteristics can be improved with a simple configuration.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.
[0014]
(1) Configuration of Embodiment FIG. 1 is a cross-sectional view showing an optical system of an optical disc apparatus according to an embodiment of the present invention. The optical disk device 1 reproduces data recorded on an optical disk 2A, which is a DVD, and data recorded on a compact disk 2B.
[0015]
Here, the compact disc 2B can reproduce the recorded data by processing the return light obtained by irradiating the information recording surface with a laser beam through a transparent substrate having a thickness of 1.2 mm. It is an optical disk. On the other hand, the DVD 2A can reproduce the recorded data by processing the return light obtained by irradiating the information recording surface with a laser beam through a transparent substrate having a thickness of 0.6 [mm]. It is an optical disk.
[0016]
In this optical disc apparatus 1, the optical pickup 3 is arranged so as to be movable in the radial direction of the optical disc by a predetermined thread mechanism. The optical pickup 3 irradiates the optical disk 2A or 2B with the laser beam emitted from the optical integrated element 4 via the astigmatism correction plate 5, the collimator lens 6, the aperture 7, and the objective lens 8, and from the optical disk 2A or 2B. The obtained return light is incident on the integrated optical element 4 through the objective lens 8, the aperture 7, the collimator lens 6, and the astigmatism correction plate 5.
[0017]
The optical disc apparatus 1 processes the light reception result of the return light in the optical integrated element 4 to generate a tracking error signal, a focus error signal, and a reproduction signal. The optical disk apparatus 1 moves the objective lens 8 based on these tracking error signal and focus error signal to perform tracking control and focus control, and processes the reproduction signal to reproduce the data recorded on the optical disks 2A and 2B.
[0018]
Here, the optical integrated element 4 is configured by condensing a light emitting element and a light receiving element for a compact disc, and a light emitting element and a light receiving element for a DVD integrally in a package. In the optical integrated element 4, the semiconductor laser diode chips constituting each of these light emitting elements are arranged with a spacing of about 100 [μm] in the radial direction of the optical disks 2A and 2B, and controlled by a system controller (not shown). By selectively driving these two semiconductor laser diode chips according to 2B, laser beams having wavelengths corresponding to the respective optical discs 2A and 2B are selectively emitted toward the optical discs 2A and 2B. Return light is received by the light receiving element.
[0019]
The astigmatism correction plate 5 is a parallel plate-like transparent plate member, and is inclined in the optical path of the laser beam while being inclined with respect to the optical axis of the laser beam. The astigmatism correction plate 5 has an astigmatism amount equal to the astigmatism of the laser beam, and its inclination, plate thickness, etc. are given so as to give astigmatism in the direction to cancel the astigmatism of this laser beam. It is made to be selected. As a result, the astigmatism correction plate 5 corrects astigmatism of laser beams having different wavelengths.
[0020]
The collimator lens 6 converts the laser beam transmitted through the astigmatism correction plate 5 into a substantially parallel light beam and emits it.
[0021]
The aperture 7 is formed by depositing a dielectric film on a transparent plate member to form a circular opening at the center. In the aperture 7, a dielectric film is formed around the opening. The dielectric film selectively blocks light having a wavelength of 780 [nm], which is the wavelength of a laser beam for a compact disc, and also a laser for DVD. A filter that transmits light having a wavelength of 650 [nm], which is the wavelength of the beam, is configured. As a result, the aperture 7 transmits the compact disc laser beam by shaping the beam shape with the beam diameter determined by the opening, while transmitting the DVD laser beam without changing the beam shape. It is made like that.
[0022]
The objective lens 8 is an aspheric plastic lens made by injection molding of a transparent resin, and a DVD laser beam that is incident with substantially parallel rays by selecting the refractive index of the transparent resin and the shape of each lens surface. The laser beams corresponding to the information recording surfaces of the corresponding optical disks 2A and 2B can be condensed with respect to the laser beam for the compact disk. As a result, the objective lens 8 constitutes a so-called bifocal lens corresponding to a DVD laser beam and a compact disc laser beam.
[0023]
Further, the objective lens 8 is configured to be movable in the radial direction of the optical discs 2A and 2B and the direction along the optical axis by an actuator having a voice coil motor configuration, so that the actuator can be moved according to the tracking error signal and the focus error signal. It can be driven to perform tracking control and focus control.
[0024]
In this tracking control, when reproducing the compact disk 2B, the objective lens 8 is moved by being offset in the radial direction of the optical disk 2B by the actuator, as much as the light emitting elements are arranged apart from each other in the optical integrated element 4. Thus, deterioration of the characteristics of the optical system when the compact disk 2B is reproduced is prevented.
[0025]
The matrix calculation circuit 9 performs a matrix calculation process on the light reception result output from the optical integrated element 4 to change the signal level according to the tracking error amount, the tracking error signal TE whose signal level changes according to the tracking error amount, and the signal level according to the focus error amount. A reproduction signal RF whose signal level changes according to the focus error signal FE and the pit train is generated. At this time, the matrix calculation circuit 9 generates these tracking error signals for DVD and compact disc, respectively.
[0026]
FIG. 2A is a plan view showing the optical integrated element 4 as viewed from the laser beam emission direction, and FIG. 2B is a cross-sectional view of the optical integrated element 4 in the circumferential tangent direction of the optical discs 2A and 2B. FIG. In the optical integrated device 4, an optical system 16 is formed by arranging a prism 14 and semiconductor laser diode chips 15A and 15B on a semiconductor substrate 17, and the optical system 16 is housed in a package 18 and wired, and then transparently sealed. It is created by sealing with a lid glass 19 as a member.
[0027]
Here, the semiconductor laser diode chips 15A and 15B are spaced apart by a distance of about 100 [μm] in the radial direction of the optical discs 2A and 2B, and each is a laser beam for DVD having a wavelength of 650 [nm] corresponding to the DVD, compact. A compact disc laser beam having a wavelength of 780 [nm] corresponding to the disc is emitted toward the prism 14. The semiconductor laser diode chip 15A and 15B, the optical disc 2A, the light-receiving surface of 2B, the polarization plane is such that a parallel to the scanning direction of the laser beam, or arranged as to be in a direction perpendicular to the scanning direction . Further, the semiconductor laser diode chips 15A and 15B are arranged so that, for example, the astigmatism generation amounts are almost equal by sorting, and are arranged so that the deformation directions of the beam cross-sectional shapes of the laser beams due to astigmatism substantially coincide. Is done. As a result, the optical disc apparatus 1 can correct astigmatism with respect to the laser beams emitted from these two light sources by one astigmatism correction plate 5, and when reproducing a DVD by the DPD method. A tracking error signal can be detected.
[0028]
The prism 14 is an optical element that separates the laser beam and the return light, and is formed in a substantially rectangular shape having a slope on one side surface. The prism 14 reflects the laser beam emitted from the semiconductor laser diode chips 15A and 15B by the inclined surface and emits the laser beam toward the collimator lens 5, and returns the incident return light by tracing the optical path of the laser beam in reverse. Lead inside from the slope.
[0029]
In the prism 14, the return light incident from the inclined surface is incident on the lower surface, where a light amount of about 50% is transmitted, and the remaining light amount of the return light is reflected toward the upper surface. Further, the prism 14 reflects almost 100% of the return light toward the lower surface on the upper surface, and emits the return light reflected on the upper surface from the lower surface.
[0030]
For this reason, the prism 14 has a mirror surface formed on the upper surface by vapor deposition, and the light quantity ratio of the return light emitted from the inclined surface side (hereinafter referred to as the front side) and the side farther from the inclined surface (hereinafter referred to as the rear side). Is approximately 1: 1, a beam splitter surface and an antireflection surface are formed on the lower surface on the front side by the same vapor deposition process.
[0031]
In the semiconductor substrate 17, the light receiving surfaces 25 A and 26 A for DVD and the light receiving surfaces 25 B and 26 B for compact disc are respectively applied to the portions where the return light from the DVD laser beam and the return light from the compact disc laser beam are incident from the prism 14. Is formed.
[0032]
In FIG. 3, the optical integrated element 4 is formed on the semiconductor substrate 17 by the return light transmitted through the prism 14 in this manner in a just-focused state, as shown partially enlarged in the light receiving surface. The semiconductor laser diode chip 15A, so that the beam spot shape is substantially a focal line shape on the rear side, and an elliptical shape having a major axis in a direction orthogonal to the rear focal line extension direction on the front side. The direction of 15B, the size of the prism 14 and the like are selected.
[0033]
The light receiving surfaces 25B and 26B on the compact disc side are formed in a substantially rectangular shape side by side in the circumferential tangential direction of the compact disc, and are formed by being divided in the radial direction of the compact disc by a dividing line extending in the circumferential tangential direction. Is done. Thus, the light receiving surfaces 25B and 26B receive the beam spot formed on each light receiving surface by dividing the light spot into four in the radial direction of the compact disc in a state of just tracking, and the light reception result of each divided light receiving surface. Are each output. In the following description, regarding the small light receiving surfaces divided in this way, the outside on the front side is indicated by symbols m and p, and the inside on the front side is indicated by symbols n and o. The rear side outside is indicated by symbols q and t, and the rear side inside is indicated by symbols r and s.
[0034]
On the other hand, the DVD-side light receiving surfaces 25A and 26A are similarly formed in a substantially rectangular shape along the circumferential tangent direction of the optical disc 2A, and the rear-side light receiving surface 26A is a rear-side light receiving surface for a compact disc. It is created in the same way as 26B.
[0035]
On the other hand, in addition to the configuration of the front side light receiving surface 25B for the compact disc, the front side light receiving surface 25A is further divided into two in the circumferential tangential direction of the optical disc. Thereby, in the semiconductor substrate 17, a tracking error signal can be generated by a so-called DPD method. In the following description, the small light-receiving surface on the DVD side divided in this way is indicated by symbols a and d for the front side outside and the slope side, and by symbols b and c for the inside and slope side of the front side. . The outer side of the front side and the side far from the slope are indicated by symbols e and h, and the inner side of the front side and the side far from the slope are indicated by symbols f and g. The rear side outside is indicated by symbols i and l, and the rear side inside is indicated by symbols j and k.
[0036]
The semiconductor substrate 17 performs current-voltage conversion processing on the light reception results of each of the divided light receiving surfaces a to t, and then performs calculation processing and outputs the result. In the matrix calculation circuit 9, the calculation output is further calculated and tracking is performed. An error signal, a focus error signal, and a reproduction signal are generated.
[0037]
That is, for a compact disc, a difference signal is generated between the inner light receiving surface and the outer light receiving surface on the front side and rear side light receiving surfaces 25B and 26B, respectively, and this difference signal is subtracted on the front side and rear side. As a result, a focus error signal represented by (m + p + r + s) − (n + o + q + t) is generated. Further, in the front side and rear side light receiving surfaces 25B and 26B, a difference signal is generated between the inner periphery side light receiving surface and the outer periphery side light receiving surface, respectively, and this difference signal is added on the front side and rear side, thereby (m + n + s + t )-(O + p + q + r) to generate a tracking error signal. In addition, a reproduction signal represented by (m + n + o + p + q + r + s + t) is generated by adding all light reception results on the front side and rear side light receiving surfaces 25B and 26B.
[0038]
On the other hand, on the DVD side, similarly, a focus error signal represented by (a + d + e + h + j + k) − (b + c + f + g + i + l) and a reproduction signal represented by (a + b + c + d + e + f + g + h + i + j + k + l) are generated. On the other hand, as shown in FIG. 4, for the tracking error signal TE for DVD, the inner circumference side and the outer circumference side of the optical disc 2A are respectively provided for each group of the light receiving surfaces divided in the direction in which the light receiving surfaces 25A and 26A are arranged. The addition results 42A to 42D add the light reception results of each of the two light receiving surface portions corresponding to, respectively, and thereby detect the received light amount on the inner peripheral side and the outer peripheral side for these groups. Further, the phase comparison circuits 43A and 43B compare the phase of the light reception results on the inner circumference side and the outer circumference side for each group, and then add them by the addition circuit 44 to generate the tracking error signal TE.
[0039]
(3) Operation of Embodiment In the above-described configuration (FIG. 1), the optical disc apparatus 1 receives the return light by irradiating the optical discs 2A and 2B with a laser beam in the optical pickup 3, and receives a predetermined signal processing circuit. Thus, the information recorded on the optical discs 2A and 2B is reproduced by processing the result of receiving the return light.
[0040]
That is, in the optical disk device 1, the optical pickup 3 emits a laser beam from the optical integrated element 4, and the laser beam is converted into a substantially parallel beam by the collimator lens 6, and then transmitted through the aperture 7 and guided to the objective lens 8. Then, the light is condensed on the information recording surfaces of the optical disks 2A and 2B by the objective lens 8. Further, the return light obtained by the irradiation of the laser beam is received by the objective lens 8 and is incident on the optical integrated element 4, and the result of receiving the return light is obtained by the optical integrated element 4.
[0041]
In the optical disc apparatus 1, a tracking error signal TE is generated from the result of receiving the return light, and the objective lens 7 is moved in the radial direction of the optical discs 2A and 2B by a servo circuit so that the tracking error signal TE has a predetermined signal level. Tracking control. Similarly, a focus error signal is generated, and the objective lens 7 is moved in the vertical direction so that the focus error signal has a predetermined signal level, thereby performing focus control.
[0042]
That is, when the optical disk loaded in the optical disk apparatus 1 is a DVD 2A, in the optical disk apparatus 1, the semiconductor laser diode chips 15A and 15B arranged side by side in the radial direction of the optical disks 2A and 2B in the optical integrated device 4 (FIG. 3). Of these, a laser beam is selectively emitted from the semiconductor laser diode chip 15A for DVD, and this laser beam is irradiated onto the DVD 2A. The return light from the DVD 2A is received by the DVD light receiving surfaces 25A and 26A via the prism 14.
[0043]
On the other hand, when the optical disk loaded in the optical disk apparatus 1 is the compact disk 2B, the optical disk apparatus 1 is more selective than the semiconductor laser diode chip 15B of the compact disk among the semiconductor laser diode chips 15A and 15B (FIG. 3). The laser beam is emitted to the compact disc 2B. The return light from the compact disk 2B is received by the light receiving surfaces 25B and 26B for the compact disk via the prism 14.
[0044]
Further, these light reception results are processed by the matrix calculation circuit 9 to generate a reproduction signal RF, a tracking error signal TE, and a focus error signal FE for a compact disc and a DVD, respectively.
[0045]
In this way, when each laser beam is selectively emitted to access the optical discs 2A and 2B, in the optical disc apparatus 1, the astigmatism correction plate 5 which is a transparent plate member of a parallel plate is in the optical path of the laser beam. The astigmatism is inclined and arranged, and the astigmatism of the laser beam is corrected by the astigmatism correction plate 5.
[0046]
In the correction of astigmatism, the optical disk apparatus 1, as the polarization plane with the disk surface is parallel or perpendicular to the scanning direction of the laser beam, also the deformation direction of the beam cross-sectional shape of the laser beam by the astigmatism is substantially Since the semiconductor laser diode chips 15A and 15B having substantially the same amount of astigmatism are arranged in pairs so as to coincide with each other, two astigmatism correction plates 5 are commonly used and two laser beams are used. Astigmatism can be corrected and the optical characteristics can be improved with a simple configuration.
[0047]
In the optical disc apparatus 1 can be arranged a semiconductor laser diode chip 15A and 15B as the plane of polarization of the laser beam with respect to the scanning direction of the laser beam is parallel or perpendicular, a tracking error signal by the DPD method for DVD Can be generated, and the internal space of the optical integrated device can be effectively used to prevent the optical integrated device 4 from becoming large.
[0048]
(3) Effects of Embodiments According to the configuration described above, a laser beam is selectively emitted from a semiconductor laser diode chip that is a light source that is spaced apart in the radial direction of the optical disc, and the optical disc is applied to the optical disc by a common optical system. By correcting the aberration of these laser beams with a single astigmatism correction means when condensing, the optical characteristics can be improved with a simple configuration.
[0049]
(4) Other Embodiments In the above-described embodiment, the description has been given of the case where the astigmatism correcting means is configured by arranging the parallel plate-shaped transparent plate members obliquely, but the present invention is not limited to this. Alternatively, astigmatism correction means may be configured by arranging a cylindrical lens, a hologram, a Fresnel lens, or the like. In the case where a coupling lens or the like is used, astigmatism generation means may be configured on the coupling lens or the like.
[0050]
Further, in the above-described embodiment, the case where the objective lens is displaced in conjunction with the switching of the laser beam has been described. However, the present invention is not limited to this, and the entire optical system may be displaced. If sufficient characteristics are obtained, the displacement may be omitted.
[0051]
In the above-described embodiment, the case where the light receiving surface is configured exclusively for DVDs and compact discs has been described. However, the present invention is not limited to this and is widely applied to the case where the light receiving surface is configured in common. be able to.
[0052]
In the above-described embodiment, the case of reproducing a compact disc and a DVD has been described. However, the present invention is not limited to this, and can be widely applied to, for example, accessing a compact disc and a CD-R. .
[0053]
In the above-described embodiment, the case of accessing two types of optical disks has been described. However, the present invention is not limited to this, and can be widely applied to the case of accessing a plurality of types of optical disks.
[0054]
In the above-described embodiment, the case where the optical pickup is configured by the optical integrated element in which the light emitting element and the light receiving element are integrated has been described. However, the present invention is not limited to this, and the light emitting element and the light receiving element are separately provided. The present invention can be widely applied also when it is placed on the body.
[0055]
【The invention's effect】
As described above, according to the present invention, by correcting aberrations of a plurality of laser beams by one astigmatism correction unit, it is easy to access an optical recording medium selectively using a plurality of light sources. The optical characteristics can be improved with a simple configuration.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an optical disc apparatus according to an embodiment of the present invention.
FIGS. 2A and 2B are a plan view and a cross-sectional view showing an optical integrated device applied to the optical disc apparatus of FIG.
3 is a plan view showing a light receiving surface of the optical integrated device in FIG. 2; FIG.
4 is a block diagram for explaining generation of a tracking error signal by the optical integrated device of FIG. 2; FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical disk apparatus, 2A, 2B ... Optical disk, 3 ... Optical pick-up, 4 ...... Optical integrated element, 5 ... Astigmatism correction plate, 5 ... Collimator lens, 6 ... Aperture, 7 ... ... objective lens, 14 ... prism, 15A, 15B ... semiconductor laser diode chip, 25A, 25B, 26A, 26B ... light-receiving surface

Claims (3)

In an optical disc apparatus for reproducing information recorded on the optical disc by irradiating the optical disc with a laser beam and receiving a return light obtained from the optical disc and processing a light reception result,
First and second light sources that emit the laser beam at different wavelengths;
A light receiving element for receiving return light obtained from the optical disc ;
An optical system for condensing the laser beams emitted from the first and second light sources onto the optical disc and guiding return light obtained from the optical disc to the light receiving element;
The first and second light sources and the light receiving element are:
It is housed in one package,
The first and second light sources are:
The amount of astigmatism is almost the same,
Arranged so that the deformation direction of the beam cross-sectional shape of the laser beam due to astigmatism substantially coincides and is spaced apart in the radial direction of the optical disc ,
The optical system is
An optical system having an objective lens common to the laser beams emitted from the first and second light sources;
Is formed by a transparent member of a parallel plate, it has a astigmatism correction element which is common in the first and the laser beam emitted from the second light source,
The optical disc apparatus is
An optical disc apparatus , wherein the objective lens is displaced in a radial direction of the optical disc in response to a selective output of the laser beam from the first and second light sources . The light receiving element is
Dividing the light receiving surface into a first direction corresponding to the scanning direction of the laser beam and a second direction perpendicular to the first direction, and outputting the light reception results of the divided light receiving surfaces, respectively. The optical disc apparatus according to claim 1 . The first and second light sources are:
Wherein in parallel with the scanning direction of the laser beam, or an optical disk apparatus according to claim 1 in which the polarizing plane to be perpendicular to the scanning direction, characterized by comprising a set.

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