JP2004303332A - Optical pickup apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup apparatus capable of making satisfactory optical characteristics by matching laser beams from a laser emitting point deviating from a lens optical axis with the optical-axis center of an objective lens. <P>SOLUTION: Height of respective laser emitting points 2, 3 differ in a direction orthogonally crossing the optical axis. A short diameter direction of the far-field pattern of each laser beam from the respective laser light emitting points 2, 3 on the objective lens 7 differs from a direction in which each laser beam is arranged. When the direction in which each laser beam is arranged coincides with the tracking control direction of the objective lens, the short diameter direction of the far-field pattern inclines to the direction in which each laser beam is arranged. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention includes a laser unit having at least two laser emission points, and selectively uses laser light emitted from each of the two laser emission points on a single objective lens that can be driven in a tracking control direction. And an optical pickup device for reproducing and / or recording on a recording medium.
[0002]
[Prior art]
As an optical pickup device, a laser emission point emitting a laser beam having a wavelength suitable for the recording density of a CD (Compact Disc) and a laser emission point emitting a laser beam having a wavelength suitable for the recording density of a DVD (Digital Versatile Disc). There is a laser unit having a laser unit having two types of laser emission points, and switching a laser beam to be used in accordance with the recording density of the disc, and using a single optical pickup device to correspond to discs having different recording densities (for example, Patent Document 1).
[0003]
As described above, as a laser unit having two types of laser emission points, a monolithic type in which two laser emission points are formed on a single laser chip, and two separately formed laser chips are provided on a semiconductor base or a stem. There is an installed hybrid type.
[0004]
By the way, since the thickness of the transparent substrate up to the signal recording surface differs greatly between CD and DVD, which is about 1: 2, an optical pickup device compatible with CD and DVD is adapted to each disk by laser light of the wavelength used. It is necessary to vary the NA (numerical aperture) of the objective lens so as to obtain the desired optical characteristics. The wavelength of the laser beam condensed by the objective lens is limited by using a wavelength selection filter or a diffraction grating to reduce the diameter of the aperture stop. By making them different, they are used as objective lenses of NA corresponding to CD and DVD, respectively.
[0005]
Further, as the laser unit, it is conceivable to provide two laser emission points having different laser emission outputs because the laser output differs greatly between recording and reproduction.
[0006]
Further, a laser unit having three or more laser emission points for recording, reproducing, and supporting different types of recording media, or for supporting a recording medium having a higher density than DVD (for example, Blu-Ray disc). Can also be produced.
[0007]
By the way, the laser emission point is formed on the active layer (junction surface) of the laser chip of the laser diode, and the far field pattern of the laser light emitted from the laser emission point has an ellipse whose major axis extends in a direction perpendicular to the active layer due to its structure. It takes shape.
[0008]
Therefore, the light spot formed on the recording surface of the disk has an elliptical shape, and the orientation of the ellipse with respect to the signal track affects the reading accuracy of the pits recorded on the disk.
[0009]
That is, if the minor axis direction of the elliptical spot is made to coincide with the direction of the signal track, the resolution in the signal track direction is improved. The effect of the talk can be reduced.
[0010]
Therefore, in order to achieve both the resolution in the signal track direction and the crosstalk performance between the signal tracks, the major axis direction of the elliptical spot is set at an angle that is set to π / 4 (rad) with respect to the signal track direction. (For example, see Patent Document 2).
[0011]
[Patent Document 1]
JP-A-7-285899 [Patent Document 2]
JP-A-8-63777
[Problems to be solved by the invention]
By the way, in a laser unit having at least two laser emission points, not only a monolithic type in which each laser emission point is formed on an active layer of a single laser chip, but also a hybrid type having individual laser chips, The height of the light emitting point is the same.
[0013]
In the case of a laser unit having two laser emission points, if the height of each laser emission point in the direction orthogonal to the optical axis is the same, the major axis direction of the elliptical spot is inclined with respect to the direction of the signal track. As shown in FIG. 2, the arrangement of the far-field patterns A and B on the objective lens at each laser emission point does not become a direction that can be driven in the tracking control direction of the actuator that drives the objective lens.
[0014]
If the arrangement of the far field patterns at each laser emission point is a direction that can be driven in the tracking control direction of the actuator, light is emitted from the far field pattern on the outer peripheral side of the objective lens, that is, the laser emission point that is off the lens optical axis. When a laser beam is used, it is possible to drive the actuator in the tracking control direction and apply a bias to shift the far field pattern on the outer peripheral side to the optical axis center of the objective lens, thereby performing tracking control.
[0015]
In the optical pickup device, when the laser light emitting point is deviated from the designed lens optical axis, optical aberration occurs and optical characteristics deteriorate. In an optical pickup device using a laser unit having two laser emission points, it is impossible to align both laser emission points with the lens optical axis, so at least one of the laser emission points is off the lens optical axis. Will be.
[0016]
In the objective lens and other lenses, when the optical axis is shifted, the optical aberration characteristic, that is, the off-axis aberration characteristic is deteriorated. However, as described above, the laser light emitted from the laser emission point that is off the lens optical axis is used as the objective lens. If the laser beam can be shifted to the center of the optical axis, deterioration of optical characteristics can be suppressed even when the laser beam is used.
[0017]
However, when using a laser unit having two laser emission points where the height of each normal laser emission point is the same, as described above, the arrangement of the far field pattern at each laser emission point is not in the tracking control direction. Therefore, even if the objective lens is shifted in the tracking control direction, the laser light passing through the outer peripheral side of the objective lens cannot be aligned with the optical axis center of the objective lens, and the optical characteristics of the laser light cannot be improved.
[0018]
[Means for Solving the Problems]
According to the present invention, the heights of the two laser emission points in the direction orthogonal to the optical axis are different from each other, and the short-axis direction of the far field pattern on the objective lens of each laser light emitted from each laser emission point and the objective When the arrangement direction of each laser beam on the lens is made different from each other, and the arrangement direction of each laser beam is made coincident with the tracking control direction of the objective lens, each of the laser beams on the objective lens is aligned with respect to the arrangement direction of each laser beam. The direction of the short diameter direction of the far field pattern in the laser beam is inclined. Thus, by shifting the objective lens in the tracking control direction, it is possible to align the laser light from the laser emission point that is off the optical axis of the lens with the optical axis center of the objective lens.
[0019]
【Example】
FIG. 1 is an optical layout diagram of an optical pickup device showing one embodiment of the present invention.
[0020]
The optical pickup device of FIG. 1 shows a basic optical configuration including a two-wavelength laser unit for reading a signal from a CD and a DVD.
[0021]
Reference numeral 1 denotes a two-wavelength correspondence having a first laser emission point 2 emitting a laser beam having a wavelength suitable for CD, for example, 780 nm, and a second laser emission point 3 emitting a laser beam having a wavelength suitable for DVD, for example, 650 nm. Laser unit.
[0022]
The laser beams emitted from the first laser emission point 2 and the second laser emission point 3 of the laser unit 1 form ± 1 order light beams used for tracking control via the diffraction grating 4 to form three beams. After being formed, the optical axis is bent by the surface of the parallel plate type half mirror 5 which is obliquely arranged, and is formed into parallel light by the collimator lens 6. And irradiates the signal recording surface of the disk D.
[0023]
The objective lens 7 is configured such that the diameter of an aperture stop that restricts a laser beam incident on the basis of a laser wavelength can be switched, or a bifocal lens can be used to provide NAs corresponding to CD reproduction and DVD reproduction, respectively. It is designed to act as a lens.
[0024]
The laser light modulated and reflected by the signal recording surface of the disk D returns to the objective lens 7, returns to the half mirror 5 via the collimator lens 6, passes through the half mirror 5, and reaches the photodetector 8, The light is received by the photodetector 8.
[0025]
The photodetector 8 has a CD light receiving section (not shown) used for CD reproduction and a DVD light receiving section (not shown) used for DVD reproduction, and emits light by the first laser element 2. The laser light is received by each light receiving area of the CD light receiving unit, and a recording signal of the CD is obtained, and each control signal used for focusing control and tracking control corresponding to the CD is obtained.
[0026]
On the other hand, the laser light emitted by the second laser element 3 is received by each light receiving area of the DVD light receiving section of the photodetector 8, so that a DVD recording signal is obtained and used for focusing control and tracking control corresponding to the DVD. The obtained control signals are obtained.
[0027]
By the way, the laser unit 1 has the first laser emission point 2 and the second laser emission point 3 having different heights in the direction orthogonal to the optical axis, and each of the laser emission points 2 and 3 emits light. The far-field patterns a and b of the laser light on the objective lens 7 are as shown in FIG. 3, and the short-axis directions of the far-field patterns a and b are 0 and π with respect to the arrangement direction of each laser light on the objective lens 7. / 2 (rad).
[0028]
The arrangement direction of each laser beam is set perpendicular (π / 2 (rad)) to the direction of the signal track. That is, the direction of the elliptical spot formed on the recording surface of the disk is set at an angle of π / 2 (rad) -θ with respect to the signal tracks, and both the resolution in the signal track direction and the crosstalk performance between the signal tracks are compatible. It is planned. In this case, in order to achieve both the resolution in the signal track direction and the crosstalk performance between the signal tracks, a certain angle range is set around θ = π / 4 (rad), and θ = π / 6 to π / 3 (rad) is set.
[0029]
The objective lens 7 can be driven in a tracking direction perpendicular to the signal track direction by an actuator (not shown). Therefore, a bias is applied to the tracking control signal for driving the actuator in the tracking control direction. By applying the laser beam, the laser beam on the outer peripheral side emitted from the laser emission point deviated from the optical axis of the lens can be shifted to the center of the optical axis of the objective lens 7, whereby the laser beam on the outer peripheral side is used. Even in this case, it is possible to suppress deterioration of optical characteristics such as RF signal quality and jitter performance, which are read signals from the disk.
[0030]
FIG. 4 conceptually shows optical characteristics of the objective lens 7 with respect to a shift in the tracking control direction. When the far-field pattern a or A shown in FIG. 3 or FIG. When the far field pattern b shown in FIG. 3 is shifted from the center of the optical axis of the objective lens 7 in the tracking control direction, the curve becomes a curve connecting the 示 す points, On the other hand, when the far field pattern B shown in FIG. 2 is shifted not only in the tracking control direction but also in the direction orthogonal to the tracking control direction from the optical axis center of the objective lens 7, as shown by the curve connecting the X points Become.
[0031]
That is, when the far field pattern b on the objective lens 7 is shifted from the center of the optical axis of the objective lens 7 in the tracking control direction, the objective lens 7 is shifted in the tracking control direction so that the position of the broken line is centered on the optical axis. Displacement improves the optical characteristics.
[0032]
As described above, the first laser emission point 2 and the second laser emission point 3 of the laser unit 1 are set so that the minor axis direction of the far field pattern with respect to the arrangement direction of each laser light on the objective lens 7 is set to the angle of θ. Are made different in the direction orthogonal to the optical axis. One way to make the heights of these light-emitting points different is to install them directly on the stem 14 as shown in FIG. In this case, as shown in FIG. 5B, when the silicon substrate 15 is formed on the stem 14, the substrate 14 has the first laser chip 12 and the first laser chip 12 each having the first laser emission point 2. When the first laser chip 12 and the second laser chip 13 are installed, the first laser chip 12 The active layer 12a on which the first laser emission point 2 is formed is arranged close to the stem 14 or the substrate 15 side as the installation surface, and the second laser chip 13 is placed on the active layer on which the second laser emission point 3 is formed. 13a is arranged close to the upper side where the electrode 13b is formed. Note that an electrode 12b is also formed above the first laser chip 12.
[0033]
In the first laser chip 12 and the second laser chip 13, the positions of the active layer 12a and the active layer 13a are deviated from the center of the thickness, respectively, and the first laser chip 12 and the second laser chip 13 are mounted on a plane on the stem 14 opposite to each other. The minor-axis direction of the far-field pattern with respect to the arrangement direction of the laser beams on the objective lens 7 is set to the angle θ by the difference in height and the interval between the light emitting point 2 and the second laser light emitting point 3.
[0034]
As another method, when the first laser chip 12 and the second laser chip 13 are directly mounted on the stem, a step is formed on the stem 14 as shown in FIG. 6A, and a silicon substrate 15 is formed on the stem. In this case, steps are provided in the substrate 15 and / or the stem 14 as shown in FIGS. 6B and 6C, and the first laser chip 12 and the second By making the height of the installation surface of the laser chip 13 different, the heights of the first laser emission point 2 and the second laser emission point 3 can be made different.
[0035]
Therefore, the minor-axis direction of the far-field pattern with respect to the arrangement direction of each laser beam on the objective lens 7 is set to the angle θ by the height difference and the interval between the first laser emission point 2 and the second laser emission point 3. .
[0036]
The laser unit 1 described in the above embodiment is a so-called hybrid type in which the first laser chip 12 and the second laser chip 13 are mounted in the same package. The heights of the first laser emission point 2 and the second laser emission point 3 are made different by a monolithic type in which one laser emission point 2 and the second laser emission point 3 are formed on one laser chip. The minor-axis direction of the far-field pattern with respect to the direction in which the laser beams are arranged can be set to the angle θ.
[0037]
In the above embodiment, the optical pickup device corresponding to reproduction of CD and DVD using the laser unit corresponding to two wavelengths is described. A configuration in which two laser emission points having different laser emission outputs from a laser emission point to be provided, or a configuration in which three or more laser emission points are provided in order to correspond to recording, reproduction and recording media of different types. Even if it does, it can be dealt with without departing from the scope of the claims of the present invention.
[0038]
【The invention's effect】
As described above, in the present invention, since the heights of at least two laser emission points of the laser unit are different from each other, when the alignment direction of each laser light is made to coincide with the tracking control direction of the objective lens, The direction of the short diameter direction of the far field pattern in each laser beam on the objective lens can be tilted with respect to the arrangement direction of each laser beam, and the objective lens is shifted from the lens optical axis by shifting in the tracking control direction. The optical characteristics can be improved by adjusting the laser light from the laser emission point to the center of the optical axis of the objective lens.
[0039]
In particular, in order to make the height of each laser emission point different, the active layer of the laser chip forming each laser emission point is arranged with one laser emission point close to the installation surface side, and the other laser emission point is By arranging the laser chip close to the electrode side of the laser chip, the installation surface can be flattened, and the configuration can be made easy.
[Brief description of the drawings]
FIG. 1 is an optical layout diagram showing an example of an optical system of an optical pickup device according to the present invention.
FIG. 2 is a view for explaining the arrangement direction of far field patterns at each laser emission point when the major axis direction of an elliptical spot is inclined with respect to the direction of a signal track when the height of each laser emission point is the same. FIG.
FIG. 3 is a view for explaining the arrangement direction of a far field pattern at each laser emission point when the major axis direction of an elliptical spot is inclined with respect to the direction of a signal track when the height of each laser emission point is different. FIG.
FIG. 4 is a characteristic diagram conceptually showing optical characteristics of the objective lens 7 with respect to a shift in a tracking control direction.
FIG. 5 is a configuration diagram showing an embodiment in which the height of a first laser emission point 2 and a second laser emission point 3 of the laser unit 1 are different.
FIG. 6 is a configuration diagram showing another embodiment in which the height of the first laser emission point 2 and the second laser emission point 3 of the laser unit 1 are different.
[Explanation of symbols]
Reference Signs List 1 laser unit 2 first laser emission point 3 second laser emission point 7 objective lens 8 photodetector 12 first laser chip 12a active layer 13 second laser chip 13a active layer 14 stem 15 substrate

Claims (5)

A laser unit having at least two laser emission points, and selectively using laser light emitted from each of the two laser emission points on a single objective lens that can be driven in a tracking control direction. An optical pickup device for performing reproduction and / or recording, wherein the height of each laser light emitting point in a direction orthogonal to the optical axis is different, and the laser light emitted from each laser light emitting point emits a laser beam on an objective lens. When the minor axis direction of the field pattern and the arrangement direction of each laser beam passing through the objective lens are made different, and when the arrangement direction of each laser beam is made to coincide with the tracking control direction of the objective lens, the arrangement of the laser beams is performed. That the short-axis direction of the far-field pattern of each laser beam on the objective lens The optical pick-up apparatus according to symptoms. The active layer of the laser chip forming each laser emission point of the laser unit is arranged such that one laser emission point is located closer to the installation surface side on which the laser chip is installed, and the other laser emission point is located on the electrode side of the laser chip. 2. The optical pickup device according to claim 1, wherein the heights of the respective laser light emitting points are different from each other so as to be arranged close to each other. The method according to claim 1, wherein the laser emitting points are formed on the same laser chip by differentiating the crystal growth method of the semiconductor material constituting the laser chip, and the heights of the laser emitting points are different. 2. The optical pickup device according to 1. 2. The method according to claim 1, wherein the laser emission points are formed by different laser chips, and the heights of the laser emission points are made different by changing the height of an installation surface on which these laser chips are installed. An optical pickup device as described in the above. 2. The direction of the short diameter direction of the far field pattern in each laser beam on the objective lens with respect to the direction in which the laser beams are arranged, is inclined at π / 6 to π / 3 (rad). 3. Optical pickup device.

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