JP2001307367A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve general degrading problem of an optical pickup device, in which the position of a light emitting point is set, for each laser element in a two-wavelength laser unit, relative to the optical axis of an objective lens without taking into consideration the thickness of the base board to the signal recording face of a recording medium. SOLUTION: In the laser elements 2, 3 corresponding to each of the two kinds of recording mediums having a different base board thickness, the one 2 corresponding to the recording medium having a base board thicker to the signal recording face is arranged in a manner that the light emitting point of the laser element 2 is made to coincide with the optical axis of the objective lens 7. As a result, the light emitting point of the laser element 3 corresponding to the recording medium having a thinner base board with less occurrence of coma-aberration is taken off from the optical axis of the objective lens, thereby suppressing as little as possible the occurrence of coma-aberration at the time of reproduction of the recording medium having a thicker base board.

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 capable of reading signals from two types of recording media having different recording densities while having different thicknesses of a substrate up to a signal recording surface.

[0002]

2. Description of the Related Art As an optical pickup device, a CD (Co)
laser diode and DVD (Digital Ver.) that emit a laser beam with a wavelength suitable for the recording density of mpact Discs.
By preparing two types of laser light sources with different wavelengths of a laser diode that emits a laser beam with a wavelength suitable for the recording density of (satileDisc), and switching the light source to be used according to the recording density of the disc from which the signal is read C with different recording density due to single optical pickup
D and DVD are available.

Incidentally, the thickness of the transparent substrate up to the signal recording surface differs greatly between CD and DVD, which is approximately 1: 2. Therefore, an optical pickup device compatible with CD and DVD requires an objective lens having a different numerical aperture (NA) so as to have optical characteristics adapted to each disk.

In order to use an objective lens having a NA corresponding to each of CD reproduction and DVD reproduction, when a single objective lens is used, a laser beam incident on the objective lens according to the laser wavelength of the laser light source used. This is achieved by switching the diameter of the aperture stop that restricts the aperture stop, by using a wavelength selection filter to switch the diameter of this aperture stop, by mechanically switching the aperture stop with a different aperture diameter, or by switching with a liquid crystal shutter. Achieved.

Further, as a method of using a single objective lens to substantially use an objective lens of NA corresponding to CD reproduction and DVD reproduction, an objective lens having two focal points is used. It is also realized by things.

[0006]

As described above, in an optical pickup device using two types of laser light sources having different laser wavelengths, two types of laser elements serving as laser light sources are housed in the same package and the wavelengths of the laser light sources are different. There is a case where a two-wavelength laser unit capable of generating laser beams having two different wavelengths is used.

In an optical pickup device using such a two-wavelength laser unit, the laser beam is emitted from each laser element, so that the light emitting points of each laser element are separated. Therefore, it is impossible to make both light emitting points of each laser element coincide with the optical axis of the objective lens at the same time.

[0008] The deviation between the light emitting point of the laser element and the optical axis of the objective lens causes deterioration of the quality of the laser beam applied to the disk, and the degree of the deterioration is determined by the difference between the light emitting point of the laser element and the optical axis. Corresponds to the off-distance.

Therefore, generally, the optical axis of the objective lens is set at the center of the light emitting point of each laser element, the distance between the light emitting point of each laser element and the optical axis is suppressed, and the laser beam applied to the disc is controlled. A design has been made in which quality deterioration is moderately suppressed for both laser beams emitted from each laser element.

[0010] Alternatively, a high density and important DV
The emission point of the laser element used for D reproduction is made coincident with the optical axis of the objective lens, and the emission point of the laser element used for CD reproduction is deviated from the optical axis to sacrifice the quality of the laser beam used for CD reproduction. It is also conceivable to ensure the quality of the laser beam used for DVD reproduction.

However, the off-axis characteristics relating to the distance of the emission point of each laser element from the optical axis of the objective lens differ greatly due to the occurrence of coma due to the difference in the thickness of the substrate up to the signal recording surface of DVD and CD. Therefore, setting the position of the light emitting point of each laser element with respect to the optical axis of the objective lens without considering the thicknesses of the DVD and CD substrates has caused overall deterioration in the quality of the optical pickup device. Was.

That is, if the light emitting point of the laser element deviates from the optical axis of the objective lens, the laser beam will be inclined at an angle of incidence with respect to the optical axis of the objective lens. Coma is generated in the beam spot. When coma aberration occurs in the beam spot, the jitter characteristic of a reproduced signal obtained from a predetermined light receiving output of the photodetector is deteriorated, and the jitter characteristic is the most important item of the quality of the optical pickup device. Since the degree of occurrence of coma in the beam spot increases as the thickness of the disk substrate increases, the emission point of the laser element corresponding to a CD whose substrate thickness is about twice as large as that of a DVD is determined by the optical axis of the objective lens. If it is deviated from the above, coma aberration is generated at the time of reproducing a CD, so that the overall quality of the optical pickup device is reduced.

[0013]

SUMMARY OF THE INVENTION According to the present invention, there is provided a laser device which corresponds to two types of recording media having different thicknesses of a substrate up to a signal recording surface. The laser element corresponding to the medium is arranged such that the emission point of the laser element coincides with the optical axis of the objective lens. This reduces the occurrence of coma in the beam spot due to the small thickness of the substrate. The light emitting point of the laser element corresponding to the recording medium with the thinner substrate is shifted from the optical axis of the objective lens, and the thicker substrate is used. Minimizes the coma of the beam spot when reproducing the recording medium of
The overall quality of the optical pickup device has been improved.

[0014]

FIG. 1 is an optical layout diagram of an optical pickup device showing one embodiment of the present invention.

The optical pickup device shown in FIG. 1 has a configuration capable of reading a signal from a CD and a DVD.

Reference numeral 1 denotes a first light emitting a laser beam having a wavelength suitable for CD, for example, 780 nm, on the same semiconductor substrate.
A laser element 2 is installed, and a second light emitting a laser beam having a wavelength suitable for DVD, for example, 650 nm.
A two-wavelength laser unit in which a laser element 3 is installed and the first laser element 2 and the second laser element 3 are housed in the same package.

The laser beams emitted from the first laser element 2 and the second laser element 3 of the two-wavelength laser unit 1 form ± 1 order light beams used for tracking control via the diffraction grating 4. After the three beams are formed, the optical axis is bent by the surface of the obliquely arranged parallel plate type half mirror 5, and the collimator lens 6
The light is then incident on the objective lens 7 and converged by the objective lens 7 to irradiate the signal recording surface of the disk D.

The objective lens 7 is designed so that the diameter of an aperture stop for limiting a laser beam incident on the basis of a laser wavelength can be switched, or a bifocal lens can be used for CD reproduction and DVD reproduction, respectively. It is configured to act as a lens with a corresponding NA.

The laser beam 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 passes to the photodetector 8. The light arrives and is received by the photodetector 8.

The photodetector 8 has C used for CD reproduction.
D light receiving unit (not shown) and DVD used for DVD playback
A light receiving section (not shown) is formed, and a laser beam emitted by the first laser element 2 is received by each light receiving area of the CD light receiving section, so that a recording signal of the CD is obtained and the CD corresponding to the CD is obtained. Each control signal used for the focusing control and the tracking control is obtained.

On the other hand, the laser beam emitted by the second laser element 3 is received by each light receiving area of the DVD light receiving section of the photodetector 8, and a DVD recording signal is obtained.
Each control signal used for focusing control and tracking control corresponding to the DVD is obtained.

Incidentally, in the two-wavelength laser unit 1, the first laser element 2 for CD is arranged at the center in the direction orthogonal to the emission direction of the laser beam. Then, the two-wavelength laser unit 1 is attached to an optical housing (not shown) in which each optical element is installed so that the light emitting point of the first laser element 2 coincides with the optical axis of the objective lens 7.

That is, the light emitting point of the first laser element 2 is arranged so as to coincide with the optical axis of the objective lens 7, while the light emitting point of the second laser element 3 is deviated from the optical axis of the objective lens 7.

Here, the first with respect to the optical axis of the objective lens 7
FIG. 2 shows the off-axis characteristics of the coma generated in the DVD and the CD related to the distance at which the light emitting point of each of the second laser elements deviates.

That is, due to the difference in the thickness of the substrate up to the signal recording surface, in DVDs and CDs, frames generated in accordance with the distance that the optical axis of the laser beam incident on the objective lens 7 deviates from the optical axis of the objective lens 7. In the case of a DVD having a thin substrate, the amount of aberration is greatly different, and the off-axis characteristic of coma is much better than that of a CD.

Therefore, with respect to DVD reproduction, coma aberration is sacrificed when the light emitting point of the second laser element 3 deviates from the optical axis of the objective lens 7, but in the case of DVD, the off-axis characteristic of coma aberration is good. Therefore, the amount of increase in coma aberration is kept very small, and the reproduction of a CD having a poor off-axis characteristic of coma aberration can be achieved by adjusting the light emitting point of the first laser element 2 to the optical axis of the objective lens 7 Is suppressed.

[0027]

As described above, the present invention minimizes the amount of increase in coma aberration in consideration of good off-axis characteristics of coma aberration when reproducing a recording medium having a thinner substrate. The coma aberration is suppressed by making the emission point of the laser element corresponding to the recording medium with a poor off-axis characteristic of the coma aberration with the thicker substrate coincide with the optical axis of the objective lens. Provided is an optical pickup device whose quality is improved.

According to the present invention, a laser element corresponding to a recording medium having a thicker substrate is arranged at the center in a direction orthogonal to a laser beam emitting direction.
Since we use a wavelength laser unit,
It is easy to make the light emitting point of the laser element coincide with the optical axis of the objective lens.

[Brief description of the drawings]

FIG. 1 is an optical layout diagram showing an optical system of an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing off-axis characteristics of coma aberration generated in DVDs and CDs with respect to a distance from a light emitting point of each of first and second laser elements with respect to an optical axis of an objective lens.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 2 wavelength laser unit 2 1st laser element 3 2nd laser element 7 Objective lens 8 Photodetector

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Nakamura 2-5-5 Keihanhondori, Moriguchi-shi, Osaka F-term in SANYO Electric Co., Ltd. 5D119 AA41 BA01 BB01 CA13 DA05 EA02 EA03 EC24 EC45 EC47 FA08 FA34 JA43 LB04 5F073 AB27 AB29 BA04 BA05 EA18 FA11 FA23 FA30

Claims (2)

[Claims] 1. A two-wavelength laser unit having two types of laser elements having different laser wavelengths, wherein a laser beam generated from each of the two types of laser elements is selectively incident on a single objective lens and a signal is output. An optical pickup device for reading signals of two types of recording media having different thicknesses of a substrate up to a recording surface, wherein the thickness of the substrate up to the signal recording surface of the laser elements respectively corresponding to the two types of recording media is reduced. An optical pickup device, wherein a light emitting point of a laser element corresponding to a thicker recording medium is aligned with an optical axis of an objective lens. 2. A laser element corresponding to a recording medium having a thicker substrate up to the signal recording surface is disposed at the center of the two-wavelength laser unit in a direction orthogonal to a laser beam emission direction. Claim 1
An optical pickup device as described in the above.