JP2000235716A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate difficulty in manufacture by enabling the focus error detection by, for example, a spot size method without using a hologram element. SOLUTION: This optical device has a diffraction grating element 8 having a first diffraction grating part 9 which emits first and second diffracted light 21a and 21b of ±1st order by diffracting reflected light 20 and a second diffraction grating part 9b which emits third and fourth diffracted light 22a and 22b of ±1st order by diffracting the reflected light 20 at a diffraction angle different from the diffraction angle of the first diffraction grating part described above, and a photodetector substrate 2 having a first photodetecting region to fourth photodetecting regions 10 to 13 for receiving the fourth diffracted light 21a, 21b, 22a and 22b from the first diffracted light on the photodetecting surface 2a of the same plane. The first and second diffracted light 21a and 21b are so set as to focus backward of the photodetecting surface 2a and the third and fourth diffracted light 22a and 22b focus before arrival at the photodetecting surface 2a. A focus error signal is obtained by combining the photoelectric conversion outputs of the first to fourth photodetecting regions 10 to 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical device used for an apparatus for reproducing a recording medium such as an optical disk, and more particularly, to a DVD (Digital Versatile D).
isc) systems and other technologies that are compatible with multiple systems.

[0002]

2. Description of the Related Art In recent years, in contrast to CDs, which are already widely used consumer optical disc systems, recently, higher density DVs have been used.
The D system has been proposed, commercialized, and spread.
Furthermore, there are recordable standards such as DVD-R and DVD-R / W, and various standards such as CD-R, MD and MDdataII, and a technology for reproducing a disc of such various standards exists. It has been developed, and simplification and cost reduction of the configuration for realizing it have been issues.

On the other hand, in accordance with demands for cost reduction and miniaturization, attempts have been made to integrate an optical system of an optical pickup, and a semiconductor laser, a photodetector, a holographic element (Holographic Optical El.)
devices have been developed.
In this device, the semiconductor laser and the photodetector can be arranged close to each other, and the light receiving portion of the hologram element for diffracted light and the emission point of the semiconductor laser can be easily arranged at a substantially conjugate position. Therefore, it is possible to realize focus error detection by a complementary (complementary) spot size method using both ± 1st-order diffracted lights by the hologram element. Note that this method does not require strict position adjustment of the hologram element, does not need to discard one of the ± 1st-order diffracted lights, and has high efficiency, as compared with the knife-edge method that has been put to practical use. Has advantages.

In order to ensure compatibility with a plurality of systems, it is necessary to achieve both focus error detection by a spot size method suitable for device integration and tracking error detection by any method. The phase difference method is almost essential as a tracking error detection method.

In consideration of the above points, the present applicant has previously made it possible to achieve both focus error detection by the spot size method and tracking error detection by the phase method, and to integrate the optical pickup optical system. An optical pickup was proposed (see Japanese Patent Application No. 10-96365).

FIG. 8 is a schematic perspective view of the optical pickup.
FIG. 9 is a plan view of a hologram element, FIG. 10 is a plan view of a light receiving element substrate, FIG. 11 is a view showing a divided area of spot light, and FIG. 12 is a view showing an irradiation state of each light receiving area. 8 to 12, a laser beam from a laser light source (not shown) is converged on an information recording layer (not shown) of the optical disk 50 and is reflected there. A hologram element 51 and a light receiving element substrate 52 are arranged on the optical path of the reflected light.

The hologram element 51 has a substantially optical axis C of the reflected light.
And hologram areas 51a and 51b divided into two areas by using a line passing through the optical disc 50 in a direction perpendicular to the radial direction R (tangential direction T) as a boundary line. These two hologram areas 51a and 51b are:
Each is composed of the same curve group that generates diffracted light of the same continuous wavefront, and diffracts with the same diffraction angle of the reflected light, but diffracts the reflected light in different directions, and It is configured to add a lens effect of converging to one of the diffracted lights and diverging to the other.

The light receiving element substrate 52 has four first to fourth light receiving areas 53 arranged on the same plane light receiving surface 52a.
And the center of each of the four light receiving areas 53 to 56 and the convergence point O of the reflected light from the optical disk 50 are arranged at positions that are all optically equidistant from the center of the hologram element 51. I have.

The four light receiving regions 53 to 56 are irradiated with diffracted light from the hologram regions 51a and 51b, respectively, and the converged diffracted light is applied to the light receiving surface 52a.
And the diffracted light subjected to the divergent action forms a focal point or a focal line behind the light receiving surface 52a. The ± 1st-order diffracted lights have defocuses in directions opposite to each other, and have a predetermined (substantially the same) spot size.
3 to 56, and the size of the optical disk 50 also changes in the opposite direction in accordance with the positional shift of the optical disk 50 in the focus direction.

Further, as shown in detail in FIG.
The first light receiving area 53 and the second light receiving area 54, and the third light receiving area 55 and the fourth light receiving area 56, which are opposed to each other, are divided into four with the direction connecting their centers as the boundary directions + Rα, -Rα. ing. That is, the light receiving areas 53 to 56
Are divided by a central boundary line 57, which is a non-light receiving region, and two outer boundary lines 58, 59, respectively, to form two central divided regions Ea, Eb and two outer end divided regions Ec, Ec. And Ed.

Next, the error detecting means will be described.
As shown in FIG. 11, when the spot light 60 irradiated on the optical disk 50 is divided into four regions, the light in each of the I to IV regions is positioned with respect to each of the light receiving regions 53 to 56 by the position indicated by the Roman numeral in FIG. Will be irradiated. And FIG.
As shown in the figure, the photoelectric conversion signals R from the center divided area Ea and the end divided area Ec on the inner side of the first light receiving area 53 are provided.
The output I signal is obtained by adding i1 and the photoelectric conversion signal Ri2 from the inner-side central divided area Ea and the end-part divided area Ec of the second light receiving area 54 to obtain an output I signal. Eb and the photoelectric conversion signal Ro1 from the end divided region Ed, and the photoelectric conversion signal Ro2 from the center division region Eb and the end division region Ed on the outer side of the second light receiving region 54 are added to output an output IV signal, respectively. obtain.

Also, the photoelectric conversion signal Li1 from the inner side center divided region Ea and the end portion divided region Ec of the third light receiving region 55 and the inner side center divided region Ea and the end portion divided region of the fourth light receiving region 56. Photoelectric conversion signal Li2 from Ec
The output III signal is added to the photoelectric conversion signal Lo1 from the outer-side central divided region Eb and the end divided region Ed of the third light receiving region 55, and the outer-side central divided region Eb of the fourth light receiving region 56. And the photoelectric conversion signal Lo2 from the end divided region Ed to obtain an output II signal.
Then, a tracking error signal is generated by the phase difference method based on the output I-IV signals.

As shown in FIG. 14, the photoelectric conversion signal R1 from the pair of central divided areas Ea and Eb of the first light receiving area 53 and the pair of central divided areas Ea and Ea of the second light receiving area 54 are provided.
The output Ra signal obtained by adding the photoelectric conversion signal R2 from Eb to the pair of end divided regions Ec and Ed of the first light receiving region 53 is output.
And the photoelectric conversion signal R4 from the pair of end divided regions Ec and Ed of the second light receiving region 54 are added to obtain an output Rb signal. Also, the third light receiving area 5
5 and a pair of central divided areas Ec and E of the fourth light receiving area 56.
and the output La signal obtained by adding the photoelectric conversion signal L2 from the pair d to the pair of end divided regions Ec and Ed of the third light receiving region 55.
And the photoelectric conversion signal L4 from the pair of end divided regions Ea and Eb of the fourth light receiving region 56 are added to obtain an output Rb signal. Then, based on the difference level between the output Ra signal and the output Rb signal and the difference level between the output La signal and the output Lb signal, a focus error signal based on a two-system complementary (complementary) spot size method is created. Is configured.

[0014]

However, although the hologram element 51 is used in the above-mentioned prior art optical pickup, complicated design, calculation of the shape formula of a curve group, and enormous coordinates are required in manufacturing the hologram element 51. There is a problem in that work such as calculation of the position is required, and a long process is required until manufacturing.

As described above, in order to ensure compatibility with a plurality of systems, it is essential to achieve both focus error detection and tracking error detection.
In a recording / reproducing system such as D, CD-R, DVD-R, etc., 3
Tracking error detection by the beam method has become mainstream, and the configuration of the optical pickup cannot be compatible with the three-beam method. In other words, the optical pickup irradiates the diffracted light from the hologram element 51 in two different regions onto a circumference centered on the optical axis and at a position substantially adjacent to the tangential direction T. This is because, since the light receiving areas are arranged, if the tracking error detection of the three beam method is applied, the light receiving areas interfere with the light receiving areas of both side beams of the three beams.

Accordingly, the present invention has been made to solve the above-described problems, and enables focus error detection by, for example, a spot size method without using a hologram element. It is an object of the present invention to provide an optical device that solves the above problem. Another object of the present invention is to provide an optical device that can achieve both focus error detection by the spot size method and tracking error detection by the three-beam method.

[0017]

According to a first aspect of the present invention, there is provided an optical device for irradiating an information recording medium with light and reading information using reflected light from the information recording medium. A first diffraction grating portion arranged to diffract the reflected light at substantially the same angle symmetric with respect to the optical axis of the reflected light to emit ± 1st-order first and second diffracted lights; , And diffracts the reflected light at substantially the same angle symmetrical with respect to the optical axis of the reflected light and at an angle different from the first and second diffracted lights. A diffraction grating element having a second diffraction grating portion for emitting the fourth diffracted light; and receiving light from the first light receiving region receiving the fourth diffracted light from the first diffracted light to the fourth light receiving region on the same plane. A light-receiving element substrate provided on a surface thereof, wherein the first diffracted light from the first diffraction grating portion is provided. And the second diffracted light both focuses or focuses behind the light receiving surface, and
The third diffracted light and the fourth diffracted light from the diffraction grating unit form a focal point or a focal line before both reach the light receiving surface, and a point where the optical axis of the reflected light intersects with the light receiving surface is defined as an intersection. The distance from the intersection to the first light receiving area and the second light receiving area where the first and second diffracted lights are irradiated, and the third diffracted light and the fourth light from the intersection.
Each distance to the third light receiving area and the fourth light receiving area irradiated with the diffracted light is set to be different, and the photoelectric conversion output of the first light receiving area or the second light receiving area and the third light receiving area or the third light receiving area A focus error signal is obtained by combining the photoelectric conversion outputs of the four light receiving regions.

According to a second aspect of the present invention, in the optical device according to the first aspect, the first diffraction grating section and the second
The diffraction grating section is characterized by being constituted by a group of straight lines or a diffraction grating having a uniform period.

According to a third aspect of the present invention, in the optical device according to the first or second aspect, the first to fourth light receiving regions are divided at least into three by a dividing line substantially parallel to a diffraction direction. It is characterized in that each is configured.

According to a fourth aspect of the present invention, in the optical device according to the first to third aspects, the light incident on the information recording medium is
A three-beam diffraction grating that divides the light into three light beams and emits the light beams in a direction substantially perpendicular to the diffraction direction of the diffraction grating element and slightly inclined with respect to the track; The reflected light from the light source is incident on the diffraction grating element, and the four diffracted lights divided for each incident light are arranged substantially in a straight line on the light receiving element substrate. I do.

[0021] The invention other than the above-mentioned invention is described in claim 1.
5. The optical device according to claim 4, further comprising a three-beam diffraction grating that divides the light incident on the information recording medium into three light beams that are shifted from each other in a direction orthogonal to the tracking direction and emits the three light beams. Each reflected light from the information recording medium is incident on the diffraction grating element, and the four diffracted lights obtained by dividing each incident light are arranged substantially in a straight line on the light receiving element substrate. An optical device wherein a beam diffraction grating is fixed together in the same housing of the diffraction grating element and the light receiving element substrate.

According to the present invention, since a tracking error signal can be obtained by the three-beam method, it is possible to achieve both focus error detection by the spot size method and tracking error detection by the three-beam method.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic perspective view of an optical pickup 16 according to a first embodiment of the present invention, and FIG. 2 is a view showing a diffraction state of a diffraction grating element and an irradiation state of each diffracted light on a light receiving element substrate. FIG. 3 is a diagram showing a configuration of a diffraction component of the diffraction grating element, and FIGS. 4A to 4C are plan views of main parts showing four light receiving regions and spot lights SP1 to SP4 irradiated to the light receiving regions, respectively. is there. 1 to 4, a light receiving element substrate 2 is fixed on a wiring board 1, and the configuration of the light receiving element substrate 2 will be described later. A laser light source 3 and a micro mirror 4 are fixed on the light receiving element substrate 2 in a straight line. The laser light source 3 is composed of, for example, a semiconductor laser, and is fixed via a submount member 5 fixed on the light receiving element substrate 2. The micromirror 4 has a surface facing the laser light source 3 as a mirror surface (particularly, without a reference numeral),
This mirror surface is configured as a surface inclined at 45 degrees with respect to the horizontal plane.

That is, the emitted light from the laser light source 3 is reflected by the micromirror 4 to be converted into light having a vertical optical axis C, and passes through the vertical optical axis C to be recorded on the information recording medium. It is configured such that light emitted to a certain optical disk 6 and reflected from the optical disk 6 returns through the same optical axis C.

On the optical axis C in the vertical direction, an objective lens 7 and a diffraction grating element 8 are arranged in this order from the optical disk 6 side. The objective lens 7 converges light guided from the laser light source 3 via the diffraction grating element 8 to an information recording layer (not shown) of the optical disc 6.

The diffraction grating element 8 has a partial square shape, and has a circular diffraction component 8a on its lower surface. The diffractive component 8a passes through the optical axis C of the reflected light 20 and has a substantially tangential direction T (the same direction as the track direction) T of the optical disc 6 as a boundary line. It is divided into a lattice part 9b. The first diffraction grating portion 9a and the second diffraction grating portion 9b differ from each other only in the grating interval dimension, but are each formed at equal intervals and by linear gratings that are linear gratings. That is, the first diffraction grating portion 9a and the second diffraction grating portion 9b diffract at substantially the same angle symmetric with respect to the optical axis C of the reflected light 20, respectively. Further, the first diffraction grating portion 9a and the second diffraction grating portion 9b
Are the same in the diffraction direction of the diffracted light (both in the radial direction of the optical disc 6), but are different in the diffraction angle of the diffracted light. And both have only a diffraction effect, but do not have a lens effect.

The light receiving element substrate 2 has four light receiving regions 10 to 13 on a light receiving surface 2a on the same plane.
The four diffracted light beams 21a, 21
1b, 22a, and 22b are respectively irradiated. Specifically, the first to fourth light receiving areas 10 to 1
3 has the same diffraction direction of each diffracted light of the first diffraction grating portion 9a and the second diffraction grating portion 9b and different diffraction angles, and therefore, is arranged on a straight line and has a small diffraction angle. The first light receiving area 10 and the second light receiving area 11 to which the ± 1st-order diffracted light from the diffraction grating section 9a is irradiated are located at a position close to the intersection O1 between the light receiving surface 2a and the optical axis C, the second diffraction area having a large diffraction angle. Third where the ± 1st-order diffracted light from the grating portion 9b is irradiated
The light receiving region 12 and the fourth light receiving region 13 are respectively set at positions far from the intersection O1 between the light receiving surface 2a and the optical axis C.

As shown in FIG. 2, when the conjugate point of the light emitting point of the laser light source 3 is Q, the optical distance from the center P of the diffraction component 8a to the conjugate point Q is L, and the optical distance of the diffraction component 8a is L. Light receiving surface 2 of first and second diffracted lights 21a and 21b from center P
The optical distance to the intersection Q1 with a is L1, and the diffraction component 8
Assuming that the optical distance from the center P of a to the intersection Q2 of the third and fourth diffracted lights 22a and 22b with the light receiving surface 2a is L2, the light receiving element substrate is set such that the relationship of L = (L1 + L2) / 2 is established. 2 are arranged. In FIG. 2, curved surfaces whose optical distances are L, L1, and L2 are shown as S, S1, and S2.

That is, the first to fourth diffracted light beams 21a, 21a
Since b, 22a, and 22b have no added lens power, they converge at the position of the curved surface S equidistant from the optical distance L, so that the first and second optical distances L1 <L are satisfied. The first and second diffracted light beams 21a and 21b that irradiate the second light receiving regions 10 and 11 focus or focus behind the light receiving surface 2a and have an optical distance L2> L. The third and fourth diffracted lights 22a and 22b that irradiate the fourth and fourth light receiving regions 12 and 13 are configured to form a focal point or a focal line before reaching the light receiving surface 2a.

Each of the four light receiving regions 10 to 13 has a central region Ea and outer regions Eb, Eb, which are arranged in a direction R (radial direction) orthogonal to the tangential direction T, that is, the diffraction direction as a boundary direction. Ec is divided into three parts, and the division ratio is set such that the spot light amount in the central area part Ea and the two outer area parts Eb and Ec are the same in the just focus state.

The focus error is detected in the first light receiving area 1
The photoelectric conversion signals of the central region Ea of 0 and the two outer regions Eb and Ec of the third light receiving region 12 are added to output F.
The p1 signal is transmitted to the two outer region portions E of the first light receiving region 10.
The output Fm1 signal is obtained by adding each of the photoelectric conversion signals of b, Ec and the central area Ea of the third light receiving area 12.
Then, a difference level between the output Fp1 signal and the output Fm1 signal is detected to obtain a focus error signal. Further, the respective photoelectric conversion signals of the central region Ea of the second light receiving region 11 and the two outer region portions Eb and Ec of the fourth light receiving region 13 are added, and an output Fp2 signal is obtained. Each of the photoelectric conversion signals of the outer region portions Eb and Ec and the central region portion Ea of the fourth light receiving region 13 are added to obtain an output Fm2 signal. Then, a difference level between the output Fp2 signal and the output Fm2 signal is detected to obtain a focus error signal. That is,
It is configured to obtain two focus error signals.

On the other hand, the objective lens 7, the diffraction grating element 8, the micromirror 4, the laser light source 3, the light receiving element substrate 2 and the wiring substrate 1 are in the same casing 15
It is fixed integrally inside. Note that the diffraction grating element 8, the micro mirror 4, the laser light source 3, the light receiving element substrate 2, and the wiring substrate 1 constitute an optical device 15. FIG.
Although the wiring board 1 and the diffraction grating element 8 are illustrated as being separated for convenience of explanation, in practice, the diffraction grating element 8 is mounted on the wiring board 1 and the light receiving element substrate 2 and the laser The light source 3 is sealed.

Next, the operation of the above configuration will be described. When laser light is emitted from the laser light source 3, the emitted light is reflected by the micromirror 4 and changed to light having an optical axis C in the vertical direction. After passing through the diffraction grating element 8, the light having the optical axis C is usually collimated by a collimator lens (not shown), and focused on an information recording layer (not shown) of the optical disk 6 by an objective lens 7. tie. The reflected light from the optical disk 6 enters the diffraction grating element 8 while converging again on the reverse path.

Here, the light that has passed through the diffraction grating element 8 as the 0th-order diffracted light converges on the conjugate point Q, and the first and second light receiving regions 10 and 11 correspond to the optical distance L to the conjugate point Q.
The optical distance L1 to the third and fourth light receiving regions 12 and 13 is shorter by a certain dimension.
Are set longer by a certain dimension, the ± 1st-order diffracted lights 21a and 21b from the first diffraction grating portion 9a are not reflected on the light receiving surface 2a.
Focus or focal line behind the second diffraction grating portion 9b
Are focused or focused before reaching the light receiving surface 2a. And ± 1st-order diffracted light 2
± 1a, 21b semicircular spot light SP1, SP2
Semicircular spot light SP of first-order diffracted lights 22a and 22b
3 and SP4 have defocuses in directions opposite to each other in accordance with the positional deviation in the focus direction.

More specifically, in the "disc focusing" state shown in FIG. 4B, the spot lights SP1 and SP2 of the ± 1st-order diffracted lights 21a and 21b and the spot lights SP3 and SP4 of the ± 1st-order diffracted lights 22a and 22b. Have substantially the same size.
4A, the spot lights SP1 and SP2 of the ± 1st-order diffracted lights 21a and 21b are large, and the spot lights SP3 and SP3 of the ± 1st-order diffracted lights 22a and 22b.
SP4 becomes smaller. "Disc far" shown in FIG. 4 (c)
In the state (1), the spot lights SP1 and SP2 of the ± 1st-order diffracted lights 21a and 21b are small, and the ± 1st-order diffracted lights 22a and 22b
Spot light SP3, SP4 becomes larger.

Therefore, by detecting the difference level between the output Fp1 signal and the output Fm1 signal and the difference level between the output Fp2 signal and the output Fm2 signal, two focus error signals can be obtained by the complementary spot size method. it can. It should be noted that the configuration may be such that only one of the difference levels is detected, and a focus error signal is obtained by a single-system complementary spot size method.

That is, when applying the spot size method, two pairs of ± 1st-order diffracted lights are formed without focusing on a pair of ± 1st-order diffracted lights, and one pair of the ± 1st-order diffracted lights is focused on the front and the other. This is realized by using a pair of ± 1st-order diffracted lights as rear pins and using one light flux of each of the front and rear pins. With such a configuration, a hologram element having a lens power is not required, and the hologram element can be realized by the diffraction grating element 8 which is easy to manufacture. Become.

Further, as shown by a broken line U in FIG. 4B, if each of the light receiving regions 10 to 13 is further divided at the center,
As in the prior art, the tracking error signal can be detected by the phase difference method.

Further, similarly to the prior art, the optical axis C from the laser light source 3 to the optical disk 6 and the optical axis C from the optical disk 6 to the light receiving element substrate 2 are shared, and the four diffraction grating elements 8 ± 1st order diffracted light 21a, 21b, 22
a and 22b can be received by a single light receiving element substrate 2,
Used for optical system integration. Therefore, the optical device 15 in which the optical system of the optical pickup 16 is integrated can be configured to be compact.

Further, in the above prior art, since the dividing direction + Rα, -Rα of each light receiving area does not completely coincide with the radial direction, crosstalk components of other areas are mixed. Division direction of areas 10 to 13+
Rα, -Rα coincide with the radial direction, and the spot light S
Since the division can be made at the center of P1 to SP4, a crosstalk component in another area is not mixed, and a tracking error signal free from errors due to the crosstalk component can be created.

Next, a second embodiment of the present invention will be described.
The second embodiment differs from the first embodiment only in the configuration of the diffraction grating element 8, and the other configurations are the same. Therefore, the description of the same portions will be omitted, and only different components will be described. FIG. 5 is a plan view of the diffraction component 8a of the diffraction grating element 8 according to the second embodiment, and FIGS.
Light receiving areas and spot lights SP1 to SP illuminated on the light receiving areas
It is a principal part top view which shows P4.

5 and 6, the diffraction component 8a of the diffraction grating element 8 has a circular shape, passes through the optical axis C, and is aligned with a line in the tangential direction T (track direction) and the radial direction R. Are divided into four regions by two straight lines perpendicular to the line, and the regions arranged diagonally of the four regions are defined as a first diffraction grating portion 9a and a second diffraction grating portion 9b having the same diffraction grating configuration. It is configured. First diffraction grating section 9
The configurations of a and the second diffraction grating section 9b are the same as those of the first embodiment.

The ± first-order diffracted light 2 from the first diffraction grating portion 9a
1a and 21b are a first light receiving area 10 and a second light receiving area 11
, And each spot light SP1, SP2 is 1
/ 4 circle has a shape arranged at diagonal positions. The ± 1st-order diffracted lights 22a and 22b from the second diffraction grating section 9b irradiate the third light receiving area 12 and the fourth light receiving area 13, respectively, and the spot lights SP3 and SP4 are arranged at 1/4 circles at diagonal positions. Shape. Then, each of the spot lights SP1 to SP1
The size of SP4 changes as shown in FIGS. 6A to 6C depending on the state of defocus on the optical disk.

In the second embodiment, the same effects as in the first embodiment can be obtained. Then, similarly to the first embodiment, two systems of focus error signals by the complementary spot size method can be obtained. Here, when there is a radial deviation in the light intensity in the light beam, one system side of the focus error signal calculation becomes strong and an offset occurs in the signal. However, in the second embodiment, the diagonal component of the light beam is Since they are separated as a set, the above-described offset does not occur.

Further, since the diagonal components of the light beam are separated as a set, the output obtained by adding the photoelectric conversion output of the first light receiving area 10 and the photoelectric conversion output of the second light receiving area 11 and the third light receiving A so-called two-element DPD tracking error signal can be easily obtained from outputs of two systems, that is, an output obtained by adding the photoelectric conversion output of the area 12 and the photoelectric conversion output of the fourth light receiving area 13.

Further, since each of the light receiving regions 10 to 13 is divided into three, the photoelectric conversion output of each of these outer regions Eb and Ec is used, or as shown by a broken line U in FIG. By further dividing each of the light receiving regions 10 to 13 at the center, a tracking error signal can be detected by a so-called four-element phase difference method.

FIG. 7 is a schematic perspective view of an optical pickup according to a third embodiment of the present invention. In FIG. 7, the main beams from the first diffraction grating portion 9a and the second diffraction grating portion 9b are omitted, and only two side beams are shown. In FIG. 7, in the third embodiment, the first
The same components as those in the embodiment are denoted by the same reference numerals in the drawings, and description thereof will be omitted. Only different components will be described.

That is, the diffraction grating element 8 has a diffraction component 8a on its upper surface and a three-beam diffraction grating 17 on its lower surface.
Having. Since the configuration of the diffraction configuration unit 8a is the same as that of the first embodiment, the same reference numerals are given to the drawings and the description is omitted.

The three-beam diffraction grating 17 is
The light incident on the beam is split into three light beams 30 to 32 in a direction substantially perpendicular to the diffraction direction of the diffraction grating element 8 and slightly inclined with respect to the track, and emitted. .

The light receiving surface 2a of the light receiving element substrate 2 is provided with two pairs of side light receiving regions 33a, 33b, 34a and 34b in addition to the first to fourth light receiving regions 10 to 13. One pair of side light receiving regions 33a, 33b is arranged in parallel on both outer sides of the first light receiving region 10 and the third light receiving region 12, and the other pair of side light receiving regions 34a, 33b.
Reference numeral 34b is arranged in parallel on both outer sides of the second light receiving area 11 and the fourth light receiving area 13. Then, the tracking error detection can be obtained by calculating the difference level between the photoelectric conversion signals of the one side light receiving regions 33a and 33b and the difference level between the photoelectric conversion signals of the other side light receiving regions 34a and 34b. Is configured.

As in the first embodiment, the objective lens 7, the diffraction grating element 8 having the three-beam diffraction grating 17, the micro mirror 4, the laser light source 3, and the light receiving element substrate 2
The wiring board 1 is integrally fixed in the same housing 14. Incidentally, the diffraction grating element 8 having the three-beam diffraction grating 17, the micromirror 4, the laser light source 3, the light receiving element substrate 2, and the wiring substrate 1 constitute an optical device 15. In FIG. 7, the wiring substrate 1 and the diffraction grating element 8 are
Although shown as separated for convenience of explanation,
Actually, the diffraction grating element 8 is mounted on the wiring substrate 1, and the light receiving element substrate 2 and the laser light source 3 are sealed.

In the above configuration, when laser light is emitted from the laser light source 3, the emitted light is reflected by the micromirror 4 and is changed to light having a vertical optical axis C.
The light having the optical axis C is diffracted / branched by the three-beam diffraction grating 17 of the diffraction grating element 8, and is split into three beams of a main beam and side beams on both sides. The three light beams are focused on an information recording layer (not shown) of the optical disk 6 by the objective lens 7. The three reflected lights from the optical disk 6 are incident on the diffraction grating element 8 again while converging along the reverse path.

Three reflected lights incident on the diffraction grating element 8,
That is, the main beam and the side beams on both sides are diffracted by the first diffraction grating portion 9a and the second diffraction grating portion 9b in the same manner as in the first embodiment, and are diffracted and branched into four diffracted lights, respectively. Is done. The main beam is applied to the first to fourth light receiving areas 10 to 13, and one side beam is applied to the side light receiving areas 33 a and 34 a,
The other side beam is applied to the side light receiving regions 33b and 34b.

The spot light of the main beam is used for focus error detection by, for example, the spot size method as in the first embodiment, and the spot light of the two side beams is used for focus error detection by the three beam method. Used for detection.

That is, according to the third embodiment, the tracking error signal of the three-beam method is obtained from the difference level between the photoelectric conversion signals of the pair of side light receiving regions 33a and 33b or the pair of side light receiving regions 34a and 34b. Therefore, for example, it is possible to achieve both the focus error detection by the spot size method and the tracking error detection by the three-beam method.

As described above, according to the first and second embodiments, since the respective light receiving areas 10 to 13 of the light receiving element substrate 2 are arranged in a straight line, a space can be secured in a direction perpendicular to the light receiving areas 10 to 13. The degree of freedom in arranging components on the substrate 2 is increased. For example, as in the first and second embodiments, the laser light source 3
And a micro mirror 4 can be arranged. Further, as in the third embodiment, for example, the side light receiving regions 33a, 33
Since b, 34a and 34b can be arranged, an area for tracking error detection by the three-beam method can be secured.

According to the first and second embodiments, the light receiving areas 10 to 13 of the light receiving element substrate 2 are arranged in a straight line, but the first and second diffraction grating portions 9a and 9b are inclined. And each light receiving area 10-1 on the light receiving element substrate 2
3 may be arranged in a zigzag manner, and coexistence with other functions and components is also possible.

According to the first to third embodiments, the first diffraction grating portion 9a and the second diffraction grating portion 9b are formed on the same surface, but may be formed on different surfaces. However, the configuration on the same surface is more compact.

According to the first to third embodiments, the first diffraction grating portion 9a and the second diffraction grating portion 9b are formed on the same surface, and these respective diffracted lights 21a, 21b, 22a, 22b.
To the different light receiving positions, the first diffraction grating portion 9a
Although it was necessary to configure the diffraction angles of the first and second diffraction grating portions 9b and 9b to be different from each other, if the first and second diffraction grating portions 9a and 9b were formed on different surfaces, both diffraction angles would be reduced. Even if they are the same, the respective diffracted lights 21a, 21b, 22a, and 22b can be applied to different light receiving positions. With this configuration, there is an advantage that diffraction gratings having the same configuration can be used. Of course, the first diffraction grating portion 9a and the second diffraction grating portion 9
Even when b is formed on a different plane, both diffraction angles may be different.

According to the first to third embodiments, the first diffraction grating portion 9a and the second diffraction grating portion 9b are formed at equal intervals and by linear gratings which are linear gratings. However, it may be constituted by a diffraction grating of a straight line group such as chirped grating or a diffraction grating having a uniform period such as curved grating. All of them have simple designs and are easy to manufacture.

According to the first to third embodiments, the first diffraction grating portion 9a and the second diffraction grating portion 9b are respectively constituted by linear gratings. However, in order to correct some aberrations. A hologram element having a small lens power can also be used.

According to the first to third embodiments, focus error detection is performed by the spot size method by dividing each of the four light receiving areas 10 to 13 into three parts. The focus error can be detected by the knife edge method or the astigmatism method by changing the method.

According to the first to third embodiments, the diffraction grating element 8 is configured to separate the light into four light beams. However, only two of the light beams are used to focus light, for example, by a spot size method. Detection may be performed, and in this case, the setting of the light receiving position has more flexibility. Other light fluxes may be used for other purposes, and when not used, the diffraction grating portions 9a and 9b may be blazed to reduce the intensity of unnecessary light fluxes, so that the efficiency is effectively increased. good.

According to the first to third embodiments, the first diffraction grating portion 9a and the second diffraction grating portion 9b of the diffraction grating element 8 are configured to split the light into four light beams. A grating unit, a fourth diffraction grating unit, or more diffraction grating units may be further provided to separate the light into 6 light beams, 8 light beams, or more light beams.

According to the first to third embodiments, the tracking error detection and the focus error detection are performed. However, the tracking error detection may be performed without using the tracking error detection. good. In this case, 2 to 4 light receiving areas of the light receiving element substrate 2 are sufficient.

According to the first to third embodiments, the objective lens 7, the diffraction grating element 8, the light receiving element substrate 2, the laser light source 3 and the like are integrally fixed to the same housing 14. May be configured separately.

According to the first to third embodiments, the laser light source 3 is fixed to the light receiving element substrate 2 via the sub-mount member 5, but the conjugate of the light emitting point of the laser light source 3 on the optical axis C. Although the point (convergence point) Q is configured to be located, the laser light source 3 may be configured separately from the optical device 15. That is, it may be arranged at a position where the light emitting point of the laser light source C or its conjugate point is not located on the optical axis C. However, when the laser light source 3 is fixed to the light receiving element substrate 2 as in the above embodiments, the optical system is more integrated.

According to the first to third embodiments, the laser light source 3 is connected to the light receiving element substrate 2 via the submount member 5.
Although fixed above, the laser light source 3 may be directly fixed to the light receiving element substrate 2 as long as the conjugate point of the light emitting point of the laser light source 3 can be located near the light receiving surface 2a of the light receiving element substrate 2. With this configuration, the number of components can be further reduced and the thickness can be reduced.

[0070]

As described above, according to the optical device of the first aspect of the present invention, the reflected light is diffracted at substantially the same angle symmetrical with respect to the optical axis of the reflected light to generate the ± 1st order light. A first diffraction grating portion for emitting the first and second diffracted lights; and a first diffraction grating disposed on an optical path of the reflected light, at substantially the same angle symmetric with respect to an optical axis of the reflected light, and at the first and second diffraction angles. A diffraction grating element having a second diffraction grating portion that diffracts the reflected light at an angle different from that of light and emits ± 1st-order third and fourth diffracted lights; and A light-receiving element substrate having first to fourth light-receiving regions on the same plane light-receiving surface for receiving the four diffraction lights, respectively, wherein the first and second diffraction lights from the first diffraction grating portion are provided. Both focus or focus behind the light receiving surface, and the second
The third diffracted light and the fourth diffracted light from the diffraction grating unit form a focal point or a focal line before both reach the light receiving surface, and a point where the optical axis of the reflected light intersects with the light receiving surface is defined as an intersection. The distance from the intersection to the first light receiving area and the second light receiving area where the first and second diffracted lights are irradiated, and the third diffracted light and the fourth light from the intersection.
Each distance to the third light receiving area and the fourth light receiving area irradiated with the diffracted light is set to be different, and the photoelectric conversion output of the first light receiving area or the second light receiving area and the third light receiving area or the third light receiving area Since the focus error signal is obtained by combining the photoelectric conversion outputs of the four light receiving areas, the four diffracted lights from the diffraction grating element are irradiated on the light receiving element substrate, and the first and second light receiving areas are so-called. The rear spot light spot is irradiated on the third and fourth light receiving areas with the so-called front focus light spot, and a focus error signal by the spot size method is obtained by combining these light receiving outputs, which is difficult to manufacture. Focus errors can be detected using, for example, the spot size method, using a diffraction grating that is easy to manufacture, instead of a hologram element that has high performance. It can be.

According to a second aspect of the present invention, in the optical device according to the first aspect, the first diffraction grating portion and the second diffraction grating portion are each formed of a straight line group or a diffraction grating having a uniform period. With the configuration, in addition to the effects of the first aspect, the design is simple and the manufacture is easy.

According to the invention of claim 3, in the optical device according to claim 1 or 2, the first device
To the fourth light receiving region are each divided at least into three by a dividing line substantially parallel to the diffraction direction.
The light receiving output of the center divided portion of the light receiving region or the second light receiving region and the end divided portion of the third light receiving region or the fourth light receiving region, and the end divided portion of the first light receiving region or the second light receiving region and the third light receiving region or The focus error can be detected by the spot size method using the light receiving output from the center division of the fourth light receiving area.

According to the fourth aspect of the present invention, the above-mentioned first to first aspects are provided.
3. The optical device according to 3, wherein the light incident on the information recording medium is divided into three light beams in a direction substantially orthogonal to the diffraction direction of the diffraction grating element and slightly inclined with respect to the track and emitted. A three-beam diffraction grating is provided, each reflected light of the three light beams from the information recording medium is incident on the diffraction grating element, and the four diffracted lights divided for each incident light are respectively transmitted to the light receiving element substrate. Claims 1 to 3 are configured so as to be arranged substantially on a straight line.
In addition to the effects of the invention of (3), since a tracking error signal of the three-beam method can be obtained, it is possible to achieve both a focus error detection by the spot size method and a tracking error detection by the three-beam method.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of an optical pickup according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a diffraction state of the diffraction grating element according to the first embodiment of the present invention, and a state of irradiation of each light beam on a light receiving element substrate.

FIG. 3 is a diagram showing a configuration of a diffraction component of the diffraction grating element according to the first embodiment of the present invention.

FIGS. 4A to 4C are plan views of main parts showing four light receiving regions and spot lights SP1 to SP4 applied to the light receiving regions, respectively, according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating a configuration of a diffraction component of a diffraction grating element according to a second embodiment of the present invention.

FIGS. 6A to 6C are plan views of main parts showing four light receiving areas and spot lights SP1 to SP4 applied to the light receiving areas according to the second embodiment of the present invention.

FIG. 7 is a schematic perspective view of an optical pickup according to a third embodiment of the present invention.

FIG. 8 is a schematic perspective view of an optical pickup according to the prior art.

FIG. 9 is a plan view of a hologram element according to the prior art.

FIG. 10 is a plan view of a light receiving element substrate according to the prior art.

FIG. 11 is a diagram showing a divided area of a spot light according to the prior art.

FIG. 12 is a diagram showing an irradiation state of each light receiving region according to the prior art.

FIG. 13 is a diagram illustrating detection of a tracking error signal according to the prior art.

FIG. 14 is a diagram illustrating detection of a focus error signal according to the prior art.

[Explanation of symbols]

 Reference Signs List 2 light receiving element substrate 2a light receiving surface 6 optical disk (information recording medium) 8 diffraction grating element 9a first diffraction grating section 9b second diffraction grating section 10 first light receiving area 11 second light receiving area 12 third light receiving area 13 fourth light receiving area Reference Signs List 14 housing 15 optical device 17 diffraction grating for three beams 20 reflected light 21a first diffracted light 21b second diffracted light 22a third diffracted light 22b fourth diffracted light C optical axis O1 intersection

Claims (4)

[Claims] 1. An optical device for irradiating an information recording medium with light and reading information using reflected light from the information recording medium, wherein the optical device is disposed on an optical path of the reflected light, and is arranged with respect to an optical axis of the reflected light. A first diffraction grating section that diffracts the reflected light at substantially the same symmetrical angle and emits first and second ± first-order diffracted lights;
It is arranged on the optical path of the reflected light, diffracts the reflected light at substantially the same angle symmetrical with respect to the optical axis of the reflected light, and at an angle different from the first and second diffracted lights, and ± 1st-order A diffraction grating element having a second diffraction grating portion for emitting three-dimensional and fourth diffraction light, and a first light-receiving region to a fourth light-receiving region for receiving the fourth diffraction light from the first diffraction light, respectively. A light receiving element substrate provided on a flat light receiving surface, wherein the first diffracted light from the first diffraction grating portion and the second
Both the diffracted lights form a focal point or a focal line behind the light receiving surface, and the third and fourth diffracted lights from the second diffraction grating portion both focus or focus before reaching the light receiving surface. The first light receiving area and the second light receiving area where the first diffracted light and the second diffracted light are radiated from the intersection at a point where a line intersects and where the optical axis of the reflected light intersects the light receiving surface. Setting each distance to a region to be different from each distance from the intersection to the third light receiving region and the fourth light receiving region irradiated with the third diffracted light and the fourth diffracted light; Photoelectric conversion output of the light receiving area or the second light receiving area;
An optical device wherein a focus error signal is obtained by combining a photoelectric conversion output of a third light receiving area or a fourth light receiving area. 2. The optical device according to claim 1, wherein the first diffraction grating portion and the second diffraction grating portion are each constituted by a group of straight lines or a diffraction grating having a uniform period. Optical device. 3. The optical device according to claim 1, wherein the first to fourth light receiving regions are each configured by dividing at least three by a dividing line substantially parallel to a diffraction direction. Characteristic optical device. 4. The optical device according to claim 1, wherein light incident on the information recording medium is substantially perpendicular to the diffraction direction of the diffraction grating element and slightly tilted with respect to the track. A three-beam diffraction grating that divides the light into three light beams and emits the three light beams is provided. Each reflected light of the three light beams from the information recording medium is incident on the diffraction grating element, and is divided for each incident light. An optical device, wherein the four diffracted lights are arranged on a substantially straight line on the light receiving element substrate.