JPH10112056A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the optical pickup in which a CD and a DVD(digital video disk) are reproduced using a common optical system and a single light receiving element and a CD-R is reproduced without damaging its reflection film. SOLUTION: The pickup is provided with a first semiconductor laser 1, a second semiconductor laser 2 which has a longer wavelength than the laser 1, a prism 3 which leads the laser beams from the lasers 1 and 2 into a same direction, a collimating lens 4 which makes the laser beams, that passed the prism 3, into parallel beams, an objective lens 6 which converges the paralleled beams onto a recording medium 10 and a light receiving element 7 which receives the reflected light beams from the medium 10. The prism 3 has a first inclined plane 31 which partially reflects the laser beams from the laser 1 and a second inclined plane 32 which partially reflects the laser beams from the laser 2. The lasers 1 and 2 emit respective laser beams in opposite directions and in parallel. Note that the lasers 1 and 2 are arranged at their respective conjugate positions against the single light receiving element 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used for an optical disk device, and more particularly, to an optical pickup that can be commonly used for recording media having different protective layer thicknesses.

[0002]

2. Description of the Related Art Conventionally, compact disks (hereinafter referred to as "CDs") have been widely used as optical disks on which information signals are optically recorded. Nowadays, the technology for increasing the density of optical discs has advanced, and digital video discs (hereinafter referred to as "DVDs") capable of recording and reproducing moving images for several hours on an optical disc having the same diameter as a CD have been put to practical use. ing. Various optical pickups capable of reproducing both CDs and DVDs have been proposed. The basic principle is the same for both CDs and DVDs, but the thickness of the CD is 1.2 mm, whereas the thickness of the DVD is 0.6 mm, which is half the thickness. In order to realize a possible optical pickup, it is necessary to devise to cancel the spherical aberration caused by the difference in the thickness of the disk.

Examples of an optical pickup capable of reproducing both CDs and DVDs include an objective lens switching method and a correction element method. All of these use a common light source. In the objective lens switching method, two objective lenses facing the optical disk are prepared for CD and DVD, and the objective lenses are used for CD playback and DVD playback. The switching element and the correction element method cancel the spherical aberration caused by the difference in the thickness of the disk by using the correction element.

The basic principle of both CDs and DVDs is the same, but the optical pickup for CDs uses a semiconductor laser with a wavelength of 780 nm as the light source, whereas the optical pickup for DVDs realizes high-density recording. For this purpose, a semiconductor laser having a short wavelength of 650 to 630 nm is used as a light source. Therefore, in order to be able to reproduce a CD and a DVD using a common light source as described above, it is necessary to use a short-wavelength semiconductor laser having a wavelength of 650 to 630 nm as a light source. Further, even if a CD is reproduced using such a short-wavelength laser, there is no adverse effect such as breaking a reflective film of the CD. As described above, if a short-wavelength semiconductor laser having a wavelength of 650 to 630 nm is used as a light source, the semiconductor laser can be commonly used for both CDs and DVDs by switching an objective lens or using a correction element.

[0005]

By the way, the CD has various developments. For example, there is a recordable or writable CD-R. The reflection film of the CD-R is designed so that the maximum performance can be obtained by a laser having a wavelength of 780 nm for a CD, and has a high wavelength dependency. Therefore, as described above, when a short-wavelength semiconductor laser having a wavelength of 650 to 630 nm is used so that it can be commonly used for both CDs and DVDs, the reflection film of the CD-R uses such a short-wavelength laser beam. It cannot reflect and cannot read the information signal recorded on the CD-R. Also, CD-
When the short-wavelength laser light as described above is irradiated to the R reflection film, the reflection film absorbs the short-wavelength laser light and generates heat, and the reflection film may be broken.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and can reproduce a CD and a DVD while using a common optical system and one light receiving element. It is another object of the present invention to provide an optical pickup capable of reading a signal from a CD-R without breaking a reflection film.

[0007]

According to the first aspect of the present invention,
A first semiconductor laser, a second semiconductor laser that emits laser light having a longer wavelength than the first semiconductor laser,
A prism that guides laser light from the semiconductor laser and the second semiconductor laser in the same direction, a collimator lens that converts the laser light transmitted through the prism into parallel light,
An optical pickup comprising: an objective lens for condensing the parallel light on a recording medium; and a light receiving element for receiving light reflected by the recording medium, wherein the prism comprises a laser light from a first semiconductor laser. And a second slope that partially reflects the laser light from the second semiconductor laser, and the first semiconductor laser and the second
The semiconductor lasers are characterized in that they emit laser beams in parallel directions facing each other, and are arranged at conjugate positions with respect to a single light receiving element.

According to a second aspect of the present invention, the first slope and the second slope of the prism are formed orthogonal to each other, and the first slope partially reflects the laser light from the first semiconductor laser. The laser beam is reflected and transmits the laser light from the second semiconductor laser, and the second inclined surface partially reflects the laser light from the second semiconductor laser and transmits the laser light from the first semiconductor laser. Preferably, it is formed.

It is more preferable that a hologram element for correcting aberration is provided between one of the first semiconductor laser and the second semiconductor laser and the prism. It is more preferable that a hologram element for aberration correction, which is driven integrally with the objective lens, is interposed between the objective lens and the collimator lens.

The first semiconductor laser and the second semiconductor laser are preferably arranged at positions conjugate to each other with respect to the collimating lens. A quarter-wave plate acting only on laser light emitted from one of the first semiconductor laser and the second semiconductor laser is provided between the prism and the objective lens. It may be arranged between them.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an optical pickup according to the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 1 denotes a first semiconductor laser as a light source, and reference numeral 2 denotes a second semiconductor laser as a light source. The first semiconductor laser 1 is for recording / reproducing a DVD which is a high-density optical disc, and has a wavelength of 650 to 63.
A laser beam having a short wavelength of 0 nm is emitted. The second semiconductor laser 2 is for CD reproduction, and emits laser light having a wavelength of 780 nm, which is longer than that of the first semiconductor laser 1.
The first semiconductor laser 1 and the second semiconductor laser 2 emit laser light in a direction in which the optical axes are parallel to each other with the prism 3 interposed therebetween.

Although the first semiconductor laser 1 and the second semiconductor laser 2 face each other as described above, they are out of alignment with each other, and the laser light from the first semiconductor laser 1 is , And the laser light from the second semiconductor laser 2 is incident on the second slope 32 of the prism 3. The first slope 31 and the second slope 3
2 are formed at right angles to each other, and a multilayer film is formed on each of the slopes 31 and 32, and reflects the laser beams from the first semiconductor laser 1 and the second semiconductor laser 2 in the same direction ( (Left in FIG. 1). The multilayer film formed on the first slope 31 acts as a half mirror for partially reflecting the laser light having a wavelength of 650 to 630 nm from the first semiconductor laser 1, and the second semiconductor laser 2 780 nm from the laser beam. The multilayer film formed on the second slope 32 partially reflects the laser light from the second semiconductor laser 2 and transmits the laser light from the first semiconductor laser 1.

Although it is theoretically possible to configure the first slope 31 and the second slope 32 of the prism 3 as a half mirror, if the first and second slopes 31 and 32 are configured by half mirrors, By the time the laser light emitted from the semiconductor lasers 1 and 2 reaches the light receiving element 7, the light amount is about 1 /
However, there is a practical problem. In this regard, since the first slope 31 and the second slope 32 of the prism 3 are formed with a multilayer film having the above-described characteristics, the laser light emitted from the semiconductor lasers 1 and 2 is applied to the light receiving element 7. Thus, the amount of light decay is small, and reading errors of signals recorded on the disk 10 can be reduced.

The prism 3 is composed of one right-angle prism and two right-angle prisms whose size is half that of the right-angle prism.
The bottom surfaces of the right-angle prisms are bonded to each other, and the bonding surfaces are the first slope 31 and the second
Of the slope 32, these slopes 31, 32,
A multilayer film having the above characteristics is formed. Accordingly, since the first slope 31 and the second slope 32 of the prism 3 are formed at right angles to each other to form an orthogonal coordinate system, there is an advantage that the prism 3 can be easily processed.
There is also an advantage that machining and assembling are facilitated also on the mount side for holding the lens.

The first light partially reflected by the first slope 31
Laser light from the semiconductor laser 1 or the second slope 3
The laser light from the second semiconductor laser 2 that is partially reflected by the laser beam 2 is emitted from the left end face of the prism 3 in FIG. 1 and passes through the collimator lens 4 arranged opposite to the left end face to become parallel. Light flux. A mirror 5 is provided obliquely at an angle of 45 ° with respect to the optical axis in front of the collimator lens 4. An objective lens 6 is arranged on the optical axis reflected by the mirror 5, and a parallel laser beam passes through the objective lens 6, so that a disk 10 as a recording medium is
Are converged on the recording track of the recording medium. First
The semiconductor laser 1 and the second semiconductor laser 2 are arranged at positions optically conjugate to each other with respect to the collimator lens 4.

The disk 10 has a reflective film protected by a transparent protective film having a constant thickness, and the recording tracks are formed on the reflective film. The reflected light of the laser beam by the reflection film of the disk 10 returns to the objective lens 6, the mirror 5, and the collimator lens 4 in this order, and the second slope 32 of the prism 3,
The light passes through the first slope 31 in order, is emitted from the right end face of the prism 3, and is received by the light receiving element 7 arranged opposite to the right end face of the prism 3. Accordingly, the laser beams emitted from the first semiconductor laser 1 and the second semiconductor laser 2 are respectively reflected on recording media having different thicknesses and received by the single light receiving element 7. The first semiconductor laser 1 and the second semiconductor laser 2 are arranged at optically conjugate positions with respect to the single light receiving element 7, respectively. Converge on the light receiving surface of the light receiving element 7 of FIG.

As is well known, the light receiving element 7 is, for example, 4
A tracking error and a focusing error are detected by a laser beam coupled to the splitting element being offset on the splitting element. The objective lens 6 is driven in a tracking direction and a focusing direction according to a tracking error detection signal and a focusing error detection signal, and performs tracking control and focusing control, and also detects a signal recorded on the disk 10. It is well known.

In the optical pickup configured as described above, when recording or reproducing a DVD, laser light is emitted from the first semiconductor laser 1 having a short wavelength. Part of this laser light is reflected at right angles by the first slope 31 of the prism 3,
The light passes through the second slope 32, is converted into a parallel light beam by the collimating lens 4, is reflected at a right angle by the mirror 5, and is converged on the reflecting film of the disk 10 by the objective lens 6. Disc 1
The laser light reflected at 0 is reflected by the objective lens 6, the mirror 5,
Returning to the order of the collimating lens 4, detection, tracking and focusing of a signal transmitted through the second slope 32 and the first slope 31 of the prism 3 and converged on the light receiving surface of the light receiving element 7 and recorded on the disk 10. Is detected.

When reproducing a CD, CD-ROM, or CD-R, a laser beam is emitted from the second semiconductor laser 2 having a long wavelength. A part of this laser light is reflected at a right angle by the second slope 32 of the prism 3,
Are reflected by the mirror 5 at a right angle, and are converged on the reflecting film of the disk 10 by the objective lens 6. The laser beam reflected by the disk 10 returns to the objective lens 6, the mirror 5, and the collimating lens 4 in the same order as in the recording and reproduction of the DVD, and passes through the second slope 32 and the first slope 31 of the prism 3. Then, the detection of the signal converged on the light receiving surface of the light receiving element 7 and recorded on the disk 10 and the detection of tracking and focusing are performed.

As described above, according to the embodiment shown in FIG. 1, the first semiconductor laser 1 and the second semiconductor laser 2 which emits a laser beam having a longer wavelength than the first semiconductor laser 1, A prism 3 for guiding laser beams from the first semiconductor laser 1 and the second semiconductor laser 2 in the same direction, a collimating lens 4 for converting the laser beam transmitted through the prism 3 into parallel light, and recording the parallel light In an optical pickup including an objective lens 6 for condensing light on a disk 10 as a medium and a light receiving element 7 for receiving light reflected by the disk 10, the prism 3 is a laser light from the first semiconductor laser 1. Slope 31 that partially reflects light
And a second inclined surface 32 that partially reflects the laser light from the second semiconductor laser 2. The first semiconductor laser 1 and the second semiconductor laser 2 face each other in a parallel direction. The laser light is emitted to the light receiving element 7 and the light receiving elements 7 are arranged at conjugate positions with respect to the single light receiving element 7, respectively.
DVD playback and CD playback using a common optical system including a collimator lens 4, an objective lens 6, a light receiving element 7, etc.
And the semiconductor lasers 1 and 2 that emit laser light of a wavelength suitable for each reproduction can be used properly. In particular, since a single light receiving element 7 is used, it is not necessary to dispose a plurality of light receiving elements, and the cost of parts and the cost of mounting can be reduced.

Further, compared with a conventional optical system in which two optical systems are integrated and switched according to the type of disk, the number of optical components is reduced to reduce the cost and reduce the size and weight. Since there is no need for a switching mechanism, there is an advantage that the mechanism is simplified, the function is enhanced, and the time required for switching is not required. CD-
When reproducing R, it is sufficient to use the second semiconductor laser 2 which emits a laser beam having a long wavelength suitable for it.
Reproduction can be performed without breaking the reflective film of the CD-R.

Next, another embodiment of the optical pickup according to the present invention will be described. The embodiment shown in FIG. 2 differs from the embodiment shown in FIG. 1 in that a hologram element 17 for correcting aberration is interposed between the second semiconductor laser 2 and the prism 3. Since the first semiconductor laser 1 and the second semiconductor laser 2 having different wavelengths use an optical system in common, if the optical system is designed so that the aberration is reduced by the laser light of one wavelength, The aberration increases with laser light. In addition, it is unavoidable to generate aberrations when one lens converges on a disc (for example, a CD and a DVD) having different thicknesses. Therefore, the hologram element 17 is added so as to correct the aberration so that the difference between the wavelength and the disc thickness is reduced.

Instead of the hologram element 17 in the embodiment shown in FIG. 2, a hologram element 18 for correcting aberration is interposed between the objective lens 6 and the collimator lens 4 as in the embodiment shown in FIG. You may. in this way,
By adding a hologram element 18 for correcting aberration between the objective lens 6 and the collimating lens 4, the first semiconductor laser 1 and the second semiconductor laser 2 having different wavelengths can be obtained.
Are used in common with an optical system, and even if light is condensed on a disc (for example, CD and DVD) having a different thickness with one lens, the aberration is small with respect to the difference between each wavelength and the disc thickness. Can be corrected so that

Instead of hologram element 17 in the embodiment shown in FIG. 2, first semiconductor laser 1 and prism 3
A hologram element for aberration correction may be interposed between the hologram element and the hologram element. Also, as in the embodiment shown in FIG.
When the hologram element 18 is provided between the hologram element 18 and the collimator lens 4, the hologram element 18 may be provided integrally with the objective lens 6, and the hologram element 18 may be driven integrally with the objective lens 6 during tracking and focusing. . In this way, even if the objective lens 6 is driven in the tracking direction or the focusing direction, the objective lens 6 and the hologram element 18 move while maintaining the relative positional relationship. Accordingly, there is an advantage that the aberration correction amount does not change and the aberration correction amount is stabilized.

According to the embodiments shown in FIGS. 2 and 3,
Even if a laser beam of any wavelength is used while using a common optical system, the aberration can be corrected so as to reduce the aberration, so that an optical disc such as a CD or a DVD can be appropriately recorded and reproduced.

Next, the embodiment shown in FIG. 4 will be described. The embodiment shown in FIG. 4 is different from the embodiment shown in FIG. 1 in that the second inclined surface 32 of the prism 3 has a function as a deflecting beam splitter. A quarter-wave plate 12 that is effective for laser light, for example, laser light from the second semiconductor laser 2 is arranged. However, the 波長 wavelength plate 12
May be located anywhere between the prism 3 and the objective lens 6. In the example of FIG. 4, a diffraction grating 11 is arranged between the second semiconductor laser 2 and the prism 3.

As described above, the second slope 3 of the prism 3
2 has a function as a deflecting beam splitter, and by disposing a quarter-wave plate 12 between the prism 3 and the objective lens 6, the coupling efficiency of the optical system can be increased. That is, the linearly polarized laser light emitted from the second semiconductor laser 2 is reflected by the second slope 32 having a function as a beam splitter, converted into circularly polarized light by the quarter wavelength plate 12, and circularly polarized. The laser light reflected back from the disk and returned again passes through the quarter-wave plate 12 to be converted into linearly polarized light in a direction orthogonal to the original linearly polarized light, thereby causing the second inclined surface 32 to pass through. Through the first slope 31 and converge on the light receiving surface of the light receiving element 7;
This is because the laser light emitted from the semiconductor laser 2 is efficiently transmitted to the light receiving element 7.

The function as a polarizing beam splitter may be provided on the first inclined surface 31 of the prism 3 so as to effectively work only on the laser light emitted from the first semiconductor laser 1.

If the diffraction grating 11 is arranged between the second semiconductor laser 2 and the prism 3 as in the embodiment shown in FIG. 4, the laser light from the semiconductor laser 2
As a result, the light is split into three light beams of zero-order light, positive first-order light, and negative first-order light to form three beams. Therefore, tracking control of a well-known three-beam type can be performed. Thus, the second
The diffraction grating 11 may be arranged between the semiconductor laser 2 and the prism 3, or the first semiconductor laser 1 and the prism 3
And a diffraction grating may be arranged between them.

[0030]

According to the first aspect of the present invention, the first semiconductor laser, the second semiconductor laser that emits laser light having a longer wavelength than the first semiconductor laser, the first semiconductor laser, A prism for guiding the laser light from the second semiconductor laser in the same direction, a collimating lens for converting the laser light transmitted through the prism into parallel light, an objective lens for condensing the parallel light on a recording medium, and a recording lens. In an optical pickup including a light receiving element that receives light reflected by a medium, the prism has a first inclined surface that partially reflects laser light from the first semiconductor laser, and a laser light from the second semiconductor laser. And a first semiconductor laser and a second semiconductor laser emit laser light in parallel directions facing each other, and a single light receiving element. Since they are arranged at conjugate positions with respect to each other, while using a common optical system including a prism, a collimating lens, an objective lens, a single light receiving element, etc., it is possible to reproduce the recording media having different thicknesses, Semiconductor lasers that emit laser light of a wavelength suitable for each reproduction can be used properly. When a CD-R as a recording medium is reproduced, a semiconductor laser that emits a laser beam having a long wavelength suitable for the recording medium may be used, so that reproduction can be performed without breaking the reflective film of the CD-R. it can.

According to the second aspect of the present invention, since the first slope and the second slope of the prism are formed orthogonal to each other, there is an advantage that the prism can be easily processed, and the mount for holding the prism is provided. The side also has the advantage that processing and assembly are easy. The first slope partially reflects the laser light from the first semiconductor laser and transmits the laser light from the second semiconductor laser, and the second slope is the laser light from the second semiconductor laser. Is partially reflected and the laser light from the first semiconductor laser is transmitted, so that the amount of laser light emitted from the semiconductor laser to the light receiving element is less attenuated, and a reading error of a signal recorded on a recording medium is reduced. Can be reduced.

According to the third aspect of the present invention, since the hologram element for aberration correction is interposed between one of the first semiconductor laser and the second semiconductor laser and the prism, a common optical system is provided. When using laser light of any wavelength, the aberration can be corrected so as to reduce the aberration, and even if the recording medium has a different thickness such as a CD and a DVD, these can be appropriately reproduced. be able to.

According to the fourth aspect of the present invention, since the hologram element for aberration correction, which is driven integrally with the objective lens, is interposed between the objective lens and the collimator lens.
Even if the objective lens is driven in the tracking direction or the focusing direction, the objective lens and the hologram element move while maintaining the relative positional relationship, and the amount of aberration correction varies according to the amount of movement of the objective lens. There is an advantage that the correction amount of the aberration is stabilized without performing.

According to the sixth aspect of the present invention, the quarter-wave plate acting only on the laser light emitted from one of the first semiconductor laser and the second semiconductor laser is provided with the prism and the objective. Since it is arranged between the lens and the lens, the coupling efficiency of the optical system can be increased, and the attenuation of the laser beam can be reduced.

[Brief description of the drawings]

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

FIG. 2 is an optical layout diagram showing another embodiment of the optical pickup according to the present invention.

FIG. 3 is an optical arrangement diagram showing still another embodiment of the optical pickup according to the present invention.

FIG. 4 is an optical arrangement diagram showing still another embodiment of the optical pickup according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first semiconductor laser 2 second semiconductor laser 3 prism 4 collimating lens 6 objective lens 7 light receiving element 12 波長 wavelength plate 17 hologram element 18 hologram element 31 first slope 32 second slope

Claims (6)

[Claims] 1. A first semiconductor laser, a second semiconductor laser that emits laser light having a wavelength longer than that of the first semiconductor laser, and lasers from the first semiconductor laser and the second semiconductor laser. A prism that guides light in the same direction, a collimating lens that converts the laser light transmitted through the prism into parallel light, an objective lens that collects the parallel light on a recording medium, and reflected light that is reflected by the recording medium A light receiving element for receiving the laser light, wherein the prism partially reflects the laser light from the second semiconductor laser and a first inclined surface that partially reflects the laser light from the first semiconductor laser. The first semiconductor laser and the second semiconductor laser emit a laser beam in parallel directions facing each other, and have a single light receiving element. An optical pickup characterized in that disposed in each conjugate position with respect to. 2. A first slope and a second slope of the prism are formed to be orthogonal to each other, and the first slope partially reflects laser light from the first semiconductor laser and forms a second semiconductor laser. The laser beam from the first semiconductor laser is transmitted, and the second inclined surface partially reflects the laser beam from the second semiconductor laser and transmits the laser beam from the first semiconductor laser. Optical pickup. 3. The optical pickup according to claim 1, wherein a hologram element for aberration correction is interposed between one of the first semiconductor laser and the second semiconductor laser and the prism. 4. The optical pickup according to claim 1, wherein a hologram element for aberration correction, which is driven integrally with the objective lens, is interposed between the objective lens and the collimator lens. 5. The optical pickup according to claim 1, wherein the first semiconductor laser and the second semiconductor laser are arranged at positions conjugate to each other with respect to the collimator lens. 6. A quarter-wave plate that acts only on laser light emitted from one of the first semiconductor laser and the second semiconductor laser is disposed between the prism and the objective lens. The optical pickup according to claim 1, 2, 3, 4, or 5.