JP2001076376A - Light pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of troubles (an aberration caused by an oblique incidence of light on an objective lens) owing to the angle difference of the optical axis between luminous fluxes from respective lasers. SOLUTION: Laser beams having different wavelengths from plural adjacent light emitting points are formed into nearly parallel light by a collimator lens 4, and a micro spot is formed on an optical information recording medium by the nearly parallel light via an objective lens 6. In such a case, the grating or hologram 7, which nearly vertically makes incident laser beams having different wavelengths from plural light emitting points on the objective lens 6, is prepared.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical pickup device used for an optical disk device, an optical card device, an optical tape device and the like.

[0002]

2. Description of the Related Art As an optical pickup device mounted on an optical disk device to enable reproduction of information on both a DVD (digital video disk) and a CD (compact disk), a short-wavelength laser for DVD (having a wavelength of approximately 650 nm laser) and CD laser (wavelength about 780)
There is known a two-wavelength-compatible optical pickup device that reproduces information from DVDs and CDs as optical disks by using lasers of two types of wavelengths differently from each other.

In this two-wavelength compatible optical pickup device, two lasers and holograms having different wavelengths among components for reproducing information from each of a DVD and a CD are provided.
An example in which a light receiving element is integrated is disclosed in JP-A-11-149.
652. FIG.
An example of an optical pickup device using a two-wavelength compatible integrated unit as described in Japanese Patent No. 49652 is shown.

In FIG. 2, an integrated unit 1 for two wavelengths
Comprises a laser 2 for CD, a short wavelength laser 3 for DVD, a hologram (not shown), a light receiving element, and the like. The light beam from the laser 2 for the CD is converted into substantially parallel light by the collimating lens 4, reflected by the mirror 5, and emitted to the CD (not shown) by the objective lens 6. On the other hand, DV
The light beam from the short-wavelength laser 3 for D becomes substantially parallel light by the collimating lens 4, is reflected by the mirror 5, and is irradiated on the DVD (not shown) by the objective lens 6.

[0005]

In the optical pickup device as shown in FIG. 2, since the light emitting points of the laser 2 for CD and the short-wavelength laser 3 for DVD are physically separated, C
The optical axes of the light beams from the laser 2 for D and the short-wavelength laser 3 for DVD have a certain angle. For example, the distance between the light emitting points of the laser 2 for CD and the short wavelength laser 3 for DVD is 0.5 mm, and the focal length of the collimating lens 4 is 15 m.
m, the angle between the optical axes of the light beams from the laser 2 for CD and the short-wavelength laser 3 for DVD is defined as θ.
From SIN θ = 0.5 / 15, θ = 1.9 °.

That is, when the light beam from the laser 2 for CD enters the collimator lens 4 and the objective lens 6 at 0 °, the light beam from the short-wavelength laser 3 for DVD enters the collimator lens 4 and the objective lens 6 at 1.degree. Incident at 9 °,
In particular, a problem occurs in that a large aberration occurs in the objective lens 6. Further, the light beam from the short-wavelength laser 3 for DVD may be largely displaced from the center of the objective lens 6, and the light may not enter the entire objective lens 6. In addition, the mirror 5 and the objective lens 6 are displaced upward by, for example, d with respect to the two-wavelength compatible integrated unit 1, which hinders the thinning of the optical pickup device.

[0007] It is an object of the present invention to provide an optical pickup device capable of improving a problem caused by an optical axis angle difference between light beams from respective lasers. A second object of the present invention is to provide an optical pickup device capable of using an inexpensive grating.

Another object of the present invention is to provide an optical pickup device capable of improving light use efficiency. An object of the invention according to claim 4 is to provide an optical pickup device that can be made thin.

[0009]

In order to achieve the above object, according to the first aspect of the present invention, laser beams having different wavelengths from a plurality of adjacent light-emitting points are converted into substantially parallel light by a collimating lens. An optical pickup device for forming a minute spot on an optical information recording medium via an objective lens by using a grating or a hologram for causing laser beams having different wavelengths from the plurality of light emitting points to be incident on the objective lens substantially perpendicularly. It is a thing.

According to a second aspect of the present invention, in the optical pickup device according to the first aspect, the grating or the hologram is disposed between the collimating lens and the objective lens.

According to a third aspect of the present invention, in the optical pickup device according to the second aspect, the distance between the grating or hologram and the collimating lens is substantially equal to the distance between the collimating lens and the plurality of light emitting points. It was done.

According to a fourth aspect of the present invention, in the optical pickup device according to any one of the first to third aspects, the diffraction direction of light by the grating or hologram is:
The direction is away from the objective lens.

[0013]

FIG. 1 shows an embodiment of the present invention.
This embodiment is an embodiment of the invention according to claims 1, 2 and 4. The two-wavelength compatible integrated unit 1 includes a laser 2 for a CD.
And a short wavelength laser 3 for DVD, a hologram (not shown), a light receiving element, and the like. Laser 2 for CD
Is substantially parallel light by the collimating lens 4,
The light is diffracted by the grating (or hologram) 7, reflected by the mirror 5, and irradiated by the objective lens 6 onto a CD as an optical information recording medium (not shown), so that a minute spot is formed on the CD. The reflected light from the CD passes through the objective lens 6, the mirror 5, the grating (or hologram) 7, and the collimator lens 4 again, and the 0-order light,
The light is split into primary light and primary light and is incident on each light receiving portion of the light receiving element, and the signal processing system processes the signal from each light receiving portion to detect a reproduction signal, a tracking error signal, and a focus error signal. . Thus, the CD is the laser 2 for the CD.
The information is recorded by irradiating a light beam modulated with the information from the CPU, and the signal processing system detects the reproduction signal and reproduces the recorded information of the CD.

On the other hand, the light beam from the DVD short-wavelength laser 3 is converted into substantially parallel light by the collimating lens 4 and diffracted by the grating (or hologram) 7.
The light is reflected by the mirror 5 and irradiated on a DVD (not shown) by the objective lens 6. The reflected light from the DVD passes through the objective lens 6, the mirror 5, the grating (or hologram) 7, and the collimator lens 4 again, and the hologram in the two-wavelength integrated unit 1 causes the 0-order light, the + 1st-order light, and the -1st-order light. The signal is input to each light receiving section of the light receiving element, and the signal processing system processes the signal from each light receiving section to detect a reproduction signal, a tracking error signal, and a focus error signal. As described above, information is recorded on the DVD by irradiating a light beam modulated with information from the DVD short-wavelength laser 3, and the signal processing system detects a reproduction signal to reproduce the recorded information of the DVD.

Here, for example, the wavelength of the laser 2 for CD is 780 nm, and the wavelength of the short wavelength laser 3 for DVD is 650 nm.
nm, the distance between the light emitting points of the laser 2 for CD and the short-wavelength laser 3 for DVD is 0.5 mm, the focal length of the collimating lens 4 is 15 mm, and the pitch P of the grating (or hologram) 7 is 5.4 μm. Then, the light beam from the laser 2 for CD enters the collimator lens 4 at 0 ° and enters the grating (or hologram) 7 at 45 °.
Incident.

Assuming that the angle at which the light beam enters the grating (or hologram) 7 is α, the first-order diffraction angle of the grating (or hologram) 7 is β, and the wavelength of the light beam is λ, P (SINα−SINβ) = λ , CD
The light beam from the laser 2 for use has an emission angle (first-order diffraction angle β) of the grating (or hologram) 7 of 34.3 °.

On the other hand, the light beam from the short wavelength laser 3 for DVD enters the collimator lens 4 at 1.9 ° and enters the grating (or hologram) 7 at 43.1 °. The exit angle (primary diffraction angle β) of the grating (or hologram) 7 of the light beam from the short-wavelength laser 3 for DVD is 34.3 ° from P (SINα−SINβ) = λ.
And the light flux from the laser 2 for CD is the same. That is, by appropriately selecting the angle of the mirror 5, the CD
It is possible to make both the light beam from the laser 2 for DVD and the light beam from the short-wavelength laser 3 for DVD perpendicularly enter the objective lens 6.

In the optical pickup device shown in FIG. 2, the mirror 5 and the objective lens 6 are shifted upward by, for example, d from the integrated unit 1 for two wavelengths.
However, in the present embodiment, it is possible to shift the light beam downward by the grating (or hologram) 7 (to make the diffraction direction of the light by the grating or hologram 7 away from the objective lens 6). By appropriately setting the distance to the hologram (or hologram) 7, the mirror 5 and the objective lens 6 can be shifted downward by d, thereby achieving a reduction in thickness.

According to this embodiment, laser beams having different wavelengths from a plurality of light emitting points adjacent to each other are converted into substantially parallel light by the collimating lens 4, and the substantially parallel light is used as an optical information recording medium via the objective lens 6. An optical pickup device for forming a minute spot on a CD or DVD is provided with a grating or hologram 7 for causing laser beams having different wavelengths from the plurality of light-emitting points to enter the objective lens 6 substantially perpendicularly. A defect (aberration caused by obliquely entering light into an objective lens) caused by an angle difference of an optical axis between light beams from the lens can be improved.

According to this embodiment, the grating or hologram 7 is mounted on the collimating lens 4.
And the objective lens 6, an inexpensive grating or hologram can be used.

Further, according to this embodiment, the diffraction direction of light by the grating or hologram 7 is
Since the direction is away from the objective lens 6, a thin optical pickup device can be realized.

In this embodiment, the grating (or hologram) 7 is arranged between the collimating lens 4 and the mirror 5, but the grating (or hologram) 7 is connected between the collimating lens 4 and the two-wavelength integrated unit 1. It may be arranged between them.

FIG. 3 shows another embodiment of the present invention. This embodiment is an embodiment of the third aspect of the present invention. In FIG. 3, the center of the intensity of the laser beam is indicated by a broken line. In this embodiment, if the focal length of the collimating lens 4 (the distance between the collimating lens 4 and the light emitting point of the laser 2 for CD and the short wavelength laser 3 for DVD) in the above embodiment is f, the grating (or By setting the distance between the hologram 7 and the collimating lens 4 to be f, the intensity center of the light beam from the laser 2 for CD and the intensity center of the light beam from the short-wavelength laser 3 for DVD are matched. .

According to this embodiment, the distance between the grating or hologram 7 and the collimating lens 4 and the distance between the collimating lens 4 and the light emitting points of the laser 2 for CD and the short-wavelength laser 3 for DVD are substantially the same. As a result, it is possible to improve the light use efficiency.

The present invention is not limited to the above embodiment, but can be applied to an optical pickup device used for an optical disk device, an optical card device, an optical tape device and the like.

[0026]

As described above, according to the first aspect of the invention, it is possible to improve the problem caused by the difference in the optical axis angle between the light beams from the respective lasers. According to the invention of claim 2, it is possible to use an inexpensive grating or hologram. According to the third aspect of the invention, it is possible to improve the light use efficiency. According to the invention of claim 4, a thin optical pickup device can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one embodiment of the present invention.

FIG. 2 is a schematic diagram showing a conventional optical pickup device.

FIG. 3 is a schematic view showing another embodiment of the present invention.

[Explanation of symbols]

 1 Integrated unit for 2 wavelengths 2 Laser for CD 3 Short wavelength laser for DVD 4 Collimating lens 5 Mirror 6 Objective lens 7 Grating (or hologram)

Claims (4)

[Claims] 1. A laser beam having different wavelengths from a plurality of adjacent light-emitting points is converted into substantially parallel light by a collimating lens, and the substantially parallel light forms a minute spot on an optical information recording medium via an objective lens. An optical pickup device, comprising: a grating or a hologram for causing laser beams having different wavelengths from the plurality of light emitting points to be incident on the objective lens substantially perpendicularly. 2. The optical pickup device according to claim 1, wherein said grating or hologram is disposed between said collimating lens and said objective lens. 3. An optical pickup device according to claim 2, wherein a distance between said grating or hologram and said collimating lens is substantially equal to a distance between said collimating lens and said plurality of light emitting points. Optical pickup device. 4. The optical pickup device according to claim 1, wherein a diffraction direction of the light by the grating or the hologram is a direction away from the objective lens.