JP2000357341A - Diffraction element and optical pickup device equipped with the same - Google Patents

Abstract

(57) [Summary] A CD / DV using a normal DVD-only lens
When a D-compatible optical pickup is configured, it is necessary to make the CD reproduction light incident on the objective lens in a divergent light state, so that it has been difficult to make the detection system common to the DVD system and the CD system. In order to solve the above-mentioned problems, in the present invention, a diffraction element having a lens function is arranged in an optical path of an optical pickup device. The + 1st-order diffracted light of the CD reproduction light diffracted and separated by the diffractive element was made to enter a common photodetector. In this way, the detection system can be shared by selectively guiding the ± 1st-order diffracted light or the 0th-order light of the DVD reproduction light and CD reproduction light diffracted and separated by the diffraction element to a common photodetector.

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 used for reproducing a data signal recorded on an optical information recording medium (hereinafter, referred to as an optical disk). The present invention relates to simplification and cost reduction of a compatible optical pickup device that enables reproduction.

[0002]

2. Description of the Related Art Recently, DVDs have been used as high-density optical disks.
Disks are attracting attention and are spreading rapidly. On the other hand, read-only disks such as CDs and CD-ROMs have already become widespread in the market. Therefore, as an optical pickup device for reproducing information signals from an optical disk, it is desirable that the same device can reproduce all types of optical disks having different disk substrate thicknesses and signal recording densities, such as CD and DVD. Conventionally, a semiconductor laser light source, an objective lens, and a light detection system, each of which is provided independently of one another, satisfying such demands in a single apparatus, have two objective lenses and two objective lenses. Generally, an optical pickup device composed of two detection systems is used. However, such an optical pickup device of two light sources + two objective lenses + two detection systems actually requires components for almost two optical pickups, and the number of components is greatly increased as compared with an ordinary dedicated optical pickup device. The accompanying increase in cost is unavoidable. For such a problem,
Recently, several techniques have been developed and are attracting attention that enable both DVD and CD disks to be reproduced with the same objective lens. When such a technique is used, the objective lens can be integrated into one, which is very effective in reducing the size and cost of an optical pickup device having a DVD / CD compatible function.

[0003] By the way, this one objective lens DVD
At present, two types of / CD compatible technologies have been developed. One method is to use a DVD-only objective lens, limit the effective aperture diameter during CD playback and suppress the spherical aberration that occurs during CD playback by limiting the effective aperture to a predetermined divergent light as shown in FIG. The other one is a method of making it possible to reproduce both the DVD disk and the CD disk as shown in FIG. 3 by making the shape of the objective lens itself a special shape (note that FIG.
Known examples of the former include, for example, JP-A-8-553.
No. 63 and the like. Also, as a known example of the latter, there is, for example, JP-A-10-255305.

[0004] In particular, the latter method using an objective lens having a special shape is capable of irradiating a reproduction light spot onto a disc by irradiating a parallel light to the objective lens with respect to both DVD and CD discs. There is an advantage that the optical pickup device can be greatly simplified by using a common light source or a light detection system with respect to a common lens.

[0005]

On the other hand, the former technique of changing the effective aperture diameter of the DVD-only objective lens and the convergence and divergence of the light beam incident on the objective lens so as to be compatible with DVD / CD is a specially shaped objective lens. Compared to the case where a lens is used, there is an advantage that both DVD and CD can irradiate a better condensed spot on the disc and obtain a good reproduction signal. However, on the other hand, the convergence and divergence of the light beam incident on the objective lens are different between DVD playback and CD playback. Therefore, unlike the case of using a specially shaped objective lens, the light source or the light detection system is common in the conventional configuration. Therefore, it is very difficult to simplify the optical pickup device.

An object of the present invention is to provide a DVD
It is an object of the present invention to provide an optical pickup device having a DVD / CD compatible one objective lens optical pickup device using a dedicated objective lens, in which the detection system is shared between the DVD system and the CD system, thereby greatly simplifying the configuration.

[0007]

In order to achieve the above object, according to the present invention, first and second at least two laser light sources and light emitted from each of the first and second semiconductor laser light sources are provided. An objective lens for condensing the light beam and irradiating a separate light spot to a predetermined position on the optical disc,
A photodetector for receiving each light beam reflected from the optical disc; and a focus of a light spot irradiated on the optical information recording medium by performing predetermined arithmetic processing on a photoelectric conversion signal obtained from the photodetector. In an optical pickup device including at least a predetermined signal processing circuit for generating a shift signal and a tracking error signal and reproducing a data signal recorded on the optical information recording medium, the objective lens, the photodetector, In the optical path between the first
And a diffractive element having a function of diffracting or transmitting each of the first and second light beams emitted from the second laser light source and reflecting off the optical disk, and condensing them together on a predetermined detection surface of the photodetector. Was provided.

The diffractive element emits the first laser light source, reflects the optical disk, and transmits a part or all of the first light beam incident on the diffraction grating.
The first light beam transmitted through the diffraction grating is arranged so as to be condensed on a predetermined detection surface of the detector, and the second laser light source is emitted to reflect the optical disk. A part or all of the second light beam incident on the grating is diffracted, and any one of a + 1st-order diffracted light beam and a -1st-order diffracted light beam of the second light beam diffracted by the diffraction grating Is focused on a predetermined detection surface of the detector.

Alternatively, the diffractive element emits the first laser light source and reflects the optical disk, and then diffracts a part or all of the first light beam incident on the diffraction grating. A function of condensing any one of the + 1st-order diffracted light beam and the -1st-order diffracted light beam of the diffracted first light beam on a predetermined detection surface of the detector; After emitting a laser light source and reflecting off the optical disk, a part or all of the second light beam incident on the diffraction grating is transmitted, and the second light beam transmitted through the diffraction grating is supplied to a predetermined position of the detector. It is arranged to converge on the detection surface.

Alternatively, the diffractive element emits the first laser light source and reflects the optical disk, and then diffracts a part or all of the first light beam incident on the diffraction grating. A function of condensing any one of the + 1st-order diffracted light beam and the -1st-order diffracted light beam of the diffracted first light beam on a predetermined detection surface of the detector; After emitting a laser light source and reflecting the optical disc, a part or all of the second light beam incident on the diffraction grating is diffracted, and the second light beam diffracted by the diffraction grating is reflected by-
It has a function of converging any one of the first-order diffracted light beam and the + 1st-order diffracted light beam on a predetermined detection surface of the detector.

The diffractive element has a concentric grating groove pattern, and has a lens function of diffracting a predetermined divergent light or a convergent light with respect to the light beam incident on the diffractive element.

Alternatively, the diffraction element has a trapezoidal or sawtooth-shaped cross section of a grating groove, and the diffraction element is formed by diffracting one of +1 order light and −1 order light diffracted by the diffraction element. An element having a function of increasing the light intensity more than the light intensity of the other diffracted light.

Alternatively, the diffractive element does not diffract the first linearly polarized light beam having a predetermined polarization direction and has a second polarization direction orthogonal to the polarization direction of the first linearly polarized light beam. A linearly polarized light beam having a function of diffracting light with a predetermined diffraction efficiency, and a polarization anisotropic diffraction element having a function of diffusing the light beam having the second linear polarization with respect to the wavefront of the light beam having the first linear polarization. This is an element composed of a wave plate having a function of relatively shifting the phase of the wavefront by a predetermined amount.

The wave plate has a wavefront of a light beam having the same wavelength λ and composed of the second linearly polarized light with respect to a wavefront of the light beam having the predetermined wavelength λ and composed of the first linearly polarized light. Is shifted by three-half of the wavelength λ.

Alternatively, the wave plate has a predetermined wavelength λ.
And the phase of the wavefront of the light beam having the same wavelength λ and consisting of the second linearly polarized light is shifted by 5/4 of the wavelength λ with respect to the wavefront of the light beam composed of the first linearly polarized light. Has functions.

In the optical pickup device, the first light beam emitted from the first laser light source has a wavelength of 6 nm.
A second light beam having a wavelength of 780 nm to 7 nm having a wavelength of 30 nm to 660 nm and emitting the second laser light source.
Has 90 nm.

Alternatively, in the optical pickup device, a first light beam emitted from the first laser light source is incident on the objective lens in a substantially parallel light state, and
The second light beam emitted from the laser light source is incident on the objective lens in a divergent light state.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a front view schematically showing the arrangement of optical components in the optical pickup device of the present invention.

The semiconductor laser light source 1a has a wavelength of 650, for example.
It is an element that emits laser light of nm. DVD-ROM
DVD such as disk or DVD-RAM disk
When reproducing a system disk, this semiconductor laser light source 1
a is turned on. The laser beam emitted from the semiconductor laser light source 1a is reflected by the half mirror 11 via the diffraction grating 2a,
The diffraction element 14 is reached. The light beam transmitted through the diffraction element 14 as it is is converted into a wavelength-selective beam splitter 13.
, Is converted into a parallel light beam by the collimating lens 4, passes through a rising mirror 5, a wavelength-selective limiting aperture filter 15, and a DVD objective lens 6, and is applied to a recording surface of an optical disk 7. It is collected.
Further, the optical disk 7 is reflected and follows the same optical path as the outward light, and the objective lens 6, the wavelength selective limiting aperture filter 15, the rising mirror 5, the collimating lens 4,
After passing through the wavelength-selective beam splitter 13, the diffraction element 1
The light beam which enters the diffraction element 4 and passes through the diffraction element 14 as it is passes through the half mirror 11 and is condensed on a predetermined light receiving surface of the photodetector 9 via the detection lens 12.

On the other hand, this optical pickup device has a wavelength of 7
An 80 nm semiconductor laser light source 1b is also mounted.
When reproducing a CD disk such as a D-ROM, the semiconductor laser light source 1b is turned on. Semiconductor laser light source 1
The laser beam having emitted b enters the wavelength-selective beam splitter 13 via the diffraction grating 2b. It reaches the wavelength-selective beam splitter 13. The wavelength-selective beam splitter 13 has a function of transmitting almost 100% of a light beam having a wavelength of 650 nm, while separating a light beam having a wavelength of 780 nm into reflected light and transmitted light at a predetermined reflectance and transmittance. The light beam reflected by the wavelength-selective beam splitter 13 follows the same optical path as the laser light beam emitted from the semiconductor laser light source 1a, enters the objective lens 6, and is focused on the recording surface of the optical disk 7. At this time, since the semiconductor laser 1b is disposed at a position closer to the lens side by a predetermined distance from the focal position of the collimator lens 4, the objective lens 6 has the configuration shown in FIG.
As shown in (b), the light enters a predetermined divergent light state. The wavelength selectivity limiting aperture filter 15 shields the outer peripheral portion of the 780 nm laser beam emitted from the semiconductor laser light source 1b and limits the effective Na of the objective lens to about 0.45. With the above operation, the semiconductor laser 1b
Can form a good converged spot on a CD-based disc. Then, the light is reflected from the optical disk 7 and follows the same optical path as the outward light to reach the objective lens 6, the wavelength-selective limiting aperture filter 15, the rising mirror 5, the collimating lens 4, and the wavelength-selective beam splitter 13, and this wavelength-selective beam The light beam transmitted through the splitter enters the diffraction element 14. Then, as will be described later, the + 1st-order diffracted light or -1 diffracted by the diffraction element 14
The next-order diffracted light passes through the cylindrical lens 12 and is focused on a predetermined light receiving surface of the photodetector 9. The focus servo signal and the tracking servo signal obtained from the photodetector 9 are fed back to the two-dimensional actuator 10, whereby the position of the objective lens 6 and the wavelength-selective limiting aperture filter 15 are controlled.

The above is the schematic configuration of the optical pickup device according to the first embodiment of the present invention.
The specific functions of a and 2b and the specific configuration of the photodetector will be described later.

By the way, in the optical pickup device as shown in FIG. 1, as described above, the DVD reproduction light is incident on the objective lens in a parallel light state, and the CD reproduction light is incident on the divergent light state. The light beams that have passed through the objective lens again are condensed at positions that are far apart from each other. Specifically, a CD emitting the semiconductor laser light source 1b
The reproduction light is focused on a position closer to the objective lens than the DVD reproduction light emitted from the semiconductor laser light source 1a. Therefore, in the configuration of the conventional optical pickup device, it is difficult to detect the servo signal and the information signal by receiving both of these light beams with a single photodetector. In order to solve this problem, in the present invention, the diffraction element 14 is provided in the optical pickup device.

As shown in FIG. 4, the diffractive element 14 has concentric and unequally spaced grating groove patterns 20. From the light beam incident on the diffractive element 4, a more divergent light beam and a more convergent light beam are obtained. It has the function of diffracting and separating the light beam in the state. FIG. 5 is a diagram specifically showing this state. When the light beam 25 condensed on the point P0 on the optical axis enters the diffraction element 14, the light beam passes through the diffraction element 14 as it is and is condensed on the point P0. + 1st-order diffracted light 31 condensed on a point P + 1 located at a position distant by a distance
a and a point P− at a position closer to the point P0 by a predetermined distance.
The light is separated into -1st-order diffracted light 31b condensed into 1 and three light beams. Therefore, the diffraction element 14 is provided in the optical pickup device.
Are arranged so that the 0th-order light of the DVD reproduction light and the + 1st-order light of the CD reproduction light passing through the diffraction element 14 are condensed at almost the same position, and these light fluxes are detected by the same photodetector. Light can be received and a servo signal and an information signal can be independently detected.

FIGS. 6 and 9 are front views showing an embodiment of the optical pickup device for explaining the specific function of the above-described diffraction element 14. FIG. First, Fig. 6 shows DVD-ROM and D
It shows a state where the semiconductor laser light source 1a is turned on to reproduce a DVD-based disc such as a VD-RAM. The laser beam having a wavelength of 650 nm emitted from the semiconductor laser light source 1a is first diffracted and separated by the diffraction grating 2a into three beams (for the sake of simplicity, in FIG. 6, the central one of the three beams is separated). Only the book is shown). After these three light beams are reflected by the half mirror 11,
The light enters the diffraction element 14. The light beam incident on the diffractive element 14 is diffracted and separated into the zero-order light transmitted as it is and the ± 1st-order diffracted light converted to a more divergent and converged state with respect to the incident light beam as described above. Only the wavelength-selective beam splitter 13, the collimating lens 4, the rising mirror 5, the wavelength-selective limiting aperture filter 1
5. The light is condensed on the recording surface of the optical disk 7 via the DVD objective lens 6. At this time, 3
For example, when the disc is a DVD-RAM disc, the interval of the light spots in the disc radial direction substantially matches Tp1 / 2 with respect to the pitch Tp1 of the disc groove portion 300 and the inter-groove portion 301 as shown in FIG. When the central light spot 100a is irradiated to the inter-groove portion as shown in FIG.
a, 102a are arranged so as to irradiate the groove (or vice versa).

Next, each light flux reflected from the optical disk 7 follows the same optical path as the outward path in reverse, and again enters the diffraction element 14. Then, it is diffracted and separated again into the 0th-order light and ± 1st-order diffracted light. Of the 0th-order light, only the 0th-order light that has passed through the diffraction element 14 as it is passes through the half mirror 11 and the detection lens 12 and is on the predetermined light receiving surface of the photodetector 9. Is collected.

The photodetector 9 is divided into, for example, twelve light receiving surfaces as shown in FIG. 8, and four of them are arranged side by side and arranged in parallel. And the optical disk 7
Three light spots 1100a, 101 converged on
The reflected lights a and 102a are applied to the centers of the light receiving surfaces arranged in a cross shape, respectively, to form detection light spots 110 and 111 and 112. By subjecting each output signal obtained from each light receiving surface to a predetermined arithmetic processing, a focus servo signal by the astigmatism method and a DPD (Diff
erential Phase Detection) or DPP (Differ
Detecting a tracking servo signal by the directional push-pull method and reproducing a recorded information signal. The signal detecting means shown in FIG. 8 has no direct relation to the content of the present invention.
In addition, since it is described in Japanese Patent Application No. 10-188509, detailed description is omitted.

On the other hand, CDs such as CD-ROM and CD-R
When reproducing a system optical disc, as shown in FIG.
The semiconductor laser light source 1b having a wavelength of 80 nm is turned on.
The laser beam emitted from the semiconductor laser light source 1b is
After being diffracted and separated into three light beams by b, the light beam is reflected by the wavelength-selective beam splitter 13 and follows an optical path substantially similar to that of DVD reproduction light, the collimator lens 4, the rising mirror 5, and the wavelength-selective limiting aperture filter 15 Through the DVD objective lens 6 and condensed on the recording surface of the optical disk 7 (for simplicity, in FIG. 9, only the central one of the three separated light beams is used as in FIG. 6). it's shown).
At this time, as described above, the position of the semiconductor laser light source 1b is disposed closer to the collimator lens by a predetermined amount with respect to the focal position of the collimator lens 4, so that the laser beam enters the objective lens 6 in a predetermined divergent light state. are doing. Further, the aperture is limited by the wavelength selectivity limiting aperture filter 15 so that the effective NA on the disk side becomes about 0.45 to 0.5.

The laser beam condensed on the optical disk 7 forms three light spots, which have a spot interval in the disk radial direction of about 1/4 of the track pitch Tp1 of the disk as shown in FIG. It is arranged so that it becomes. Each light beam reflected from the optical disk 7 follows the same optical path as the outward path in reverse, and reaches the wavelength-selective beam splitter 13 again, and a part of the light beam passes through this beam splitter and enters the diffraction element 14. Then, as described above, the light is diffracted and separated into the 0th-order light and ± 1st-order diffracted light. Among them, the light flux incident on the diffraction element 14 becomes more divergent (a state where the convergence point of the convergent light is further away from the diffraction element). Only the + 1st-order diffracted light emitted through the half mirror 11 and the detection lens 12 is condensed on a predetermined light receiving surface of the same photodetector 9 as the DVD reproduction light, and as shown in FIG. , 121, 122 are formed. By subjecting the output signal obtained from each light receiving surface to a predetermined arithmetic processing, a focus servo signal by the astigmatism method and
A tracking servo signal by the spot method is detected and a recorded information signal is reproduced. The signal detecting means shown in FIG. 11 is not directly related to the contents of the present invention and is described in Japanese Patent Application No. 10-188509, as in FIG.

The above is the first embodiment of the present invention. The signal detection system used in the optical pickup device of the present invention is the same as that of the first embodiment of the present invention described with reference to FIGS.
However, the present invention is not limited to this embodiment, and any detecting means may be used. Further, the diffraction element 14 is shown in FIGS.
9 is not limited to the position shown in FIG. 9, and may be arranged anywhere in the optical path from the objective lens 6 to the photodetector 9. Also, the optical component configuration of the optical pickup device is not limited to the embodiment shown in FIGS. 1, 6, and 9. For example, a configuration in which separate collimating lenses are mounted in a DVD playback system and a CD playback system may be used. Of course it doesn't matter. Further, the diffractive element 14 itself is not limited to the above-described configuration. For example, the diffractive element
The luminous flux incident on No. 4 is emitted in a more convergent state (a state where the convergent point of the convergent light is closer to the diffraction element) -1
The next-order diffracted light is correctly focused on a predetermined light receiving surface of the photodetector 9,
Also, of the CD reproduction light diffracted and separated by the diffraction element 14, the zero-order light transmitted through the diffraction element 14 as it is is the same photodetector 9.
May be combined to converge light correctly on the predetermined light receiving surface. For example, of DVD reproduction light diffracted and separated by the diffraction element 14, a light beam incident on the diffraction element 14 is more converged (the converging point of the converged light is more (A state approaching the diffraction element)
The -1st-order diffracted light that exits as described above is correctly condensed on a predetermined light receiving surface of the photodetector 9, and the CD reproduction light diffracted and separated by the diffractive element 14 with respect to the light flux incident on the diffractive element 14. A combination in which + 1st-order diffracted light emitted in a diverging state (a state in which the converging light converges further away from the diffraction element) is correctly collected on a predetermined light receiving surface of the same photodetector 9 may be used.

In the first embodiment, among the light beams diffracted and separated by the diffraction element 14, the light beam actually used for signal reproduction is only the 0th-order light or the + 1st-order diffracted light.
The first-order diffracted light becomes unnecessary stray light. Therefore, the diffraction efficiency of unnecessary -1st-order diffracted light is reduced as much as possible, and conversely, the 0th-order light and +
If the diffraction efficiency of the first-order diffracted light can be improved, the light use efficiency of the optical pickup device of the present invention can be improved.
As a means for improving the diffraction efficiency of one of the ± 1st-order diffracted lights generated by the diffraction element and decreasing the other, there is a technique of blazing (sawtoothing) the grating grooves. This has a triangular or trapezoidal cross-sectional shape having a slope inclined toward the center of the grating groove of the diffractive element 14 as in the second embodiment of the diffractive element of the present invention shown in FIG. 12, for example. When it is formed as 0, it passes through the diffraction element 14 as it is.
+1 to the next light 30 and this 0th light to be more divergent
The intensity of the first-order diffracted light 31a can be increased, and conversely, the intensity of the -1st-order diffracted light can be significantly reduced. Thus, unnecessary stray light components can be reduced, and the light use efficiency can be improved.

In the first embodiment, with respect to DVD reproducing light having a wavelength of 650 nm emitted from the semiconductor laser light source 1a, only the 0th-order light transmitted through the diffractive element 14 as it is on both the forward path and the return path is effective for signal reproduction. And all the diffracted light becomes unnecessary stray light. Therefore, in the diffractive element 14, it is more advantageous to reduce the diffraction efficiency of ± 1st-order diffracted light of the DVD reproduction light having a wavelength of 650 nm as much as possible and to increase the efficiency of the 0th-order light. In such a case, for example, by setting the groove depth of the grating groove to an integral multiple of the wavelength of 650 nm, the diffraction efficiency of the light beam of this wavelength can be made almost zero.

FIG. 13 is a schematic front view of an optical pickup device showing a second embodiment of the present invention. The same components as those in the embodiment shown in FIGS. 1, 6, and 9 are denoted by the same reference numerals. In the present embodiment, the diffraction element 14 is a polarization anisotropic diffraction element formed of a material having polarization anisotropy, and a predetermined wavelength plate 16 is attached to the diffraction element 14 to achieve a configuration of the present invention. The light utilization of the optical pickup device is improved.

That is, for example, as in the third embodiment of the diffraction element of the present invention shown in FIG.
For a light beam incident on this diffraction element in a so-called P-polarized state, ± 1st-order diffracted light hardly diffracts and separates, and for a light beam having S-polarized light, which is a polarization component perpendicular to P-polarized light, A polarization anisotropic diffraction element that diffracts and separates ± 1st-order diffracted light with a predetermined diffraction efficiency, and further attaches a wavelength plate 16 that functions as a 3 / 2λ1 plate to DVD reproduction light having a wavelength λ1 = 650 nm is used as a light. It is arranged in the optical path of the pickup device. And DVD of wavelength λ1 = 650 nm
Reproduction light and CD reproduction light having a wavelength of λ2 = 780 nm are incident on the diffraction element in a P-polarized state on the outward path. Then D
As for the VD reproduction light, unnecessary ± 1st-order diffracted light is not diffracted and separated on the outward path, and the return light reflected from the optical disk passes through the wave plate 16 twice, becomes P-polarized again, and becomes polarized anisotropic. Since the light enters the diffraction element 14, unnecessary ± 1st-order diffracted light is not diffracted and separated even on the return path. On the other hand, for CD reproduction light having a wavelength λ2 = 780 nm,
The λ1 plate 16 functions as a ／ λ2 plate, that is, a λλ2 plate. Therefore, the forward light incident on the polarization anisotropic diffraction element 14 in the P-polarized state does not diffract and separate unnecessary ± 1st-order diffracted light, but the return light reflected from the optical disk passes through the wave plate 16 twice, so that The light is incident on the polarization anisotropic diffraction element 14 in a polarized state. As a result, the ± 1st-order diffracted light can be diffracted and separated at a predetermined diffraction efficiency and guided to the photodetector.

The embodiment of the diffractive element described above detects the backward diffracted light of the CD reproduction light having a wavelength of 780 nm as in the embodiment of the optical pickup device shown in FIGS. 1, 6, and 9. This is an example applied when guiding to a vessel,
Conversely, the backward diffracted light of the DVD reproduction light having a wavelength of 650 nm is guided to the photodetector, and the CD reproduction light of the wavelength 780 nm is guided to the photodetector as the detection light by the luminous flux transmitted through the diffractive element 14 as it is in both the forward path and the return path. In the optical pickup device, the following diffraction element may be used.

That is, for example, as in the fourth embodiment of the diffraction element of the present invention shown in FIG.
For a light beam incident on this diffraction element in a so-called P-polarized state, ± 1st-order diffracted light hardly diffracts and separates, and for a light beam having S-polarized light, which is a polarization component perpendicular to P-polarized light, A polarization anisotropic diffraction element that diffracts and separates ± 1st-order diffracted light with a predetermined diffraction efficiency, and further attaches a wavelength plate 16 that functions as a ５λ1 plate to DVD reproduction light with a wavelength λ1 = 650 nm, It is arranged in the optical path of the pickup device. Then, the wavelength plate 16 has a wavelength λ1 = 65.
Although it functions as a ／ λ1 plate, that is, a １λ1 plate for a DVD reproduction light of 0 nm, the wavelength λ2 = 780 nm
Functions as about 1λ2 for the CD reproduction light. Therefore, according to the same principle as described above, the wavelength λ1 = 650 nm
Of the DVD reproduction light, the ± 1st-order diffracted light is diffracted and separated only on the return path. However, the DVD reproduction light having the wavelength λ2 = 780 nm is not diffracted and separated on the forward and return paths.

As described above, it is possible to selectively diffract the necessary ± 1st-order diffracted light selectively depending on the wavelength and whether the light is the forward path light or the backward path, or not to diffract and separate the unnecessary ± 1st-order diffracted light simply by transmitting the light. Therefore, the light use efficiency of the optical pickup device can be greatly improved.

[0038]

As described above, according to the present invention,
In a compatible optical pickup device capable of reproducing a plurality of types of optical discs different from each other, an optical pickup device of one objective lens + I detection system can be easily configured without specially setting an objective lens. This is extremely effective in simplifying the pickup device and reducing the price.

[Brief description of the drawings]

FIG. 1 is a schematic front view showing a first embodiment of an optical pickup device of the present invention.

FIG. 2 is a schematic front view showing an example of an objective lens used in a compatible optical pickup device.

FIG. 3 is a schematic front view showing another example of the objective lens used in the compatible optical pickup device.

FIG. 4 is a schematic front view showing a first embodiment of the diffraction element of the present invention.

FIG. 5 is an enlarged view and a ray diagram of the diffraction element for explaining the principle of the first embodiment of the diffraction element of the present invention.

FIG. 6 is a schematic front view of an optical pickup device for explaining a DVD reproduction principle in the first embodiment.

FIG. 7 is a partially enlarged view of the disk showing the arrangement of the optical spots for DVD reproduction on the disk in the first embodiment.

FIG. 8 is a partially enlarged view and a block diagram of the detector for explaining the positional relationship between the light receiving surface of the photodetector and the detection light spot and the principle of signal detection during DVD reproduction in the first embodiment.

FIG. 9 is a schematic front view of an optical pickup device for explaining the principle of CD reproduction in the first embodiment.

FIG. 10 is a partially enlarged view of the disk showing an arrangement of the light spot for CD reproduction on the disk in the first embodiment.

FIG. 11 is a partial enlarged view and a block diagram of the detector for explaining the positional relationship between the light receiving surface of the photodetector and the detection light spot and the principle of signal detection during CD reproduction in the first embodiment.

FIG. 12 is an enlarged view and a ray diagram of a diffraction element for explaining the principle of a second embodiment of the diffraction element of the present invention.

FIG. 13 is a schematic front view showing a second embodiment of the optical pickup device of the present invention.

FIG. 14 is an enlarged view and a schematic view of a diffraction element for describing the principle of a third embodiment of the diffraction element according to the present invention.

FIG. 15 is an enlarged view and a schematic view of a diffraction element for describing the principle of a fourth embodiment of the diffraction element according to the present invention.

[Explanation of symbols]

1a ... Semiconductor laser light source for DVD reproduction, 1b ... Semiconductor laser light source for CD reproduction, 2a, 2b ... Diffraction grating, 4 ...
Collimating lens, 6 Objective lens, 7 Optical disk, 9 Photodetector, 11 Half mirror, 13 Wavelength selective beam splitter, 14 Diffraction element, 15
Wavelength selectivity limiting aperture, 16 ... Wave plate.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Takeshi Nakao 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture F-term (reference) 5D119 AA05 AA40 AA41 FA05 FA08 JA24 JA28 JA31 JA46 LB04

Claims (11)

[Claims] An optical information recording medium comprising: a first and a second at least two laser light sources; and light beams emitted from the first and the second semiconductor laser light sources are condensed to a predetermined position on an optical information recording medium. An objective lens for irradiating each with a separate light spot,
A photodetector for receiving each light beam reflected from the optical information recording medium, and the optical information recording medium was irradiated on the optical information recording medium by performing a predetermined arithmetic processing on a photoelectric conversion signal obtained from the photodetector. In an optical pickup device including at least a predetermined signal processing circuit that generates a defocus signal and a tracking error signal of a light spot and reproduces a data signal recorded on the optical information recording medium, the objective lens and the In the light path between the light detector and
The first and second light beams emitted from the first and second laser light sources and reflected by the optical information recording medium are diffracted or transmitted, respectively, and are condensed together on a predetermined detection surface of the photodetector. A diffractive element characterized by having a diffractive element having a function of causing it to function, and an optical pickup device equipped with the diffractive element. 2. The diffractive element emits the first laser light source and reflects the optical information recording medium, and then transmits a part or all of the first light beam incident on the diffraction grating. After the first light beam transmitted through the diffraction grating is arranged so as to be condensed on a predetermined detection surface of the detector, and after emitting the second laser light source and reflecting the optical information recording medium, Diffracting part or all of the second light beam incident on the diffraction grating, and any one of a + 1st-order diffraction light beam and a -1st-order diffraction light beam of the second light beam diffracted by the diffraction grating. 2. The diffractive element according to claim 1, further comprising a function of converging the diffracted light beam on a predetermined detection surface of the detector, and an optical pickup device equipped with the diffractive element. 3. The diffraction element, after emitting the first laser light source and reflecting the optical information recording medium, diffracts a part or all of the first light beam incident on the diffraction grating, and + Of the first light beam diffracted by the diffraction grating
A function of condensing one of the first-order diffracted light beam and the first-order diffracted light beam on a predetermined detection surface of the detector, and emitting the second laser light source to record the optical information. After reflecting the medium, a part or all of the second light beam incident on the diffraction grating is transmitted, and the second light beam transmitted through the diffraction grating is collected on a predetermined detection surface of the detector. 2. The diffraction element according to claim 1, wherein the diffraction element is arranged so as to emit light, and an optical pickup device equipped with the diffraction element. 4. The diffraction element emits the first laser light source and reflects the optical information recording medium, and then diffracts a part or all of the first light beam incident on the diffraction grating, and + Of the first light beam diffracted by the diffraction grating
A function of condensing one of the first-order diffracted light beam and the first-order diffracted light beam on a predetermined detection surface of the detector, and emitting the second laser light source to record the optical information. After reflecting the medium, a part or all of the second light beam incident on the diffraction grating is diffracted, and the -1st-order or + 1st-order diffraction light beam of the second light beam diffracted by the diffraction grating 2. The diffraction element according to claim 1, further comprising a function of converging any one of the diffracted light beams on a predetermined detection surface of the detector. 5. The diffractive element has a concentric grating groove pattern, and has a lens function of diffracting a predetermined divergent light or a convergent light with respect to a light beam incident on the diffractive element. The diffraction element according to any one of claims 1 to 4, and an optical pickup device equipped with the diffraction element. 6. The diffraction element has a trapezoidal or saw-tooth shape in a cross section of a grating groove, and the diffraction element diffracts one of +1 order light and −1 order light diffracted by the diffraction element. 6. A device according to claim 1, further comprising: a function of increasing the light intensity of the second diffracted light than the light intensity of the other diffracted light.
And the optical pickup device equipped with the same. 7. The diffractive element does not diffract a first linearly polarized light beam having a predetermined polarization direction and has a second polarization direction orthogonal to the polarization direction of the first linearly polarized light beam. A polarization anisotropic diffraction element having a function of diffracting the linearly polarized light beam at a predetermined diffraction efficiency; and a light beam having the second linearly polarized light with respect to the wavefront of the light beam having the first linearly polarized light. 7. The diffraction element according to claim 1, comprising a wave plate having a function of relatively shifting the phase of the wavefront by a predetermined amount. 8. The first wavelength plate having a predetermined wavelength λ.
And a function of shifting the phase of the wavefront of the light beam composed of the second linearly polarized light by 分 の of the wavelength λ with respect to the wavefront of the light beam composed of the linearly polarized light. 8. A diffraction element according to claim 7, and an optical pickup device equipped with the same. 9. The wave plate having a predetermined wavelength λ.
And a function of shifting the phase of the wavefront of the second linearly polarized light beam by 分 の of the wavelength λ with respect to the wavefront of the linearly polarized light beam. 8. A diffraction element according to claim 7, and an optical pickup device equipped with the same. 10. A first light beam emitted from the first laser light source has a wavelength of 630 nm to 660 nm, and a second light beam emitted from the second laser light source has a wavelength of 780 nm to 790 nm. The optical pickup device according to any one of claims 1 to 9, further comprising: 11. A first light beam emitted from the first laser light source is incident on the objective lens in a state of substantially parallel light, and a second light beam emitted from the second laser light source is emitted by the second laser light source. The optical pickup device according to any one of claims 1 to 10, wherein the light is incident on the objective lens in a divergent light state.