JP2001084609A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize complementary focus error detection by making nearly coincident two positions wherein the ±1st order diffracted light beams by a first diffraction area of light having a first wavelength make incident on a light receiving element substrate, with two positions wherein the ±1st order diffracted light beams by a second diffraction area of the light having a second wavelength make incident on the light receiving element substrate. SOLUTION: A first position P1 and a second position P1' wherein the ±1st order diffracted light beams b1, b1' of light having a first wavelength λ1 by a first diffraction area 11 make incident on a light receiving element substrate 15 respectively nearly mutually coincide with the first position P1 and the second position P1' wherein the ±1st order diffracted light beams b4, b4' of the light having a second wavelength λ2 by a second diffraction area 13 make incident on the light receiving element substrate 15. Therefore, with respect to two wavelengths λ1, λ2, a focus error signal by a complementary spot size method is calculated based on an output from a pair of optical detecting diodes in the positions P1, P1' proximate to a conjugate point C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used for a reading device for an optical information recording medium such as an optical disk, and more particularly to a DVD (Digital Versat).
The present invention relates to an optical device suitable for a compatible playback system of an ile disc) and a CD-R (Compact Disc-write once) and capable of being miniaturized, and an optical pickup using the same.

[0002]

2. Description of the Related Art In recent years, a CD, which is a consumer optical disk system that has been widely used, has recently been replaced with a higher density DV.
The D system has been proposed and commercialized, and its spread has begun.
In a DVD player which is this reproducing apparatus, in order to avoid duplication of the apparatus and complexity of use, compatible reproduction of a CD is indispensable. Similarly, a CD-R (Compact Disc-write once) that can be reproduced by a CD player is also required to have a compatible reproduction function. Therefore,
Techniques for reproducing discs of such various standards have been developed, and further, simplification of the configuration for realizing the disc and cost reduction have been issues.

[0003] In particular, in the above-described CD-R, since the reflectance of the recording medium has a large wavelength dependence, the DV-D
A laser light source in the 780 nm band different from the 650 nm band for D is indispensable, and a pickup optical system incorporating the two wavelength light sources is required.

For this reason, conventionally, two independent pickups are mechanically coupled, or a light receiving and emitting integrated element is independently attached to each wavelength, and synthesized on the same optical axis by a dichroic prism, and a part of an objective lens or the like is used. Those that share an optical system have been developed. Further, there has been proposed a semiconductor laser chip in which two semiconductor laser chips having different wavelengths are mounted on the same package, and other components are independent but the optical axis is shared.

On the other hand, in accordance with demands for cost reduction and miniaturization, attempts are being made to integrate optical pickup optical systems. For example, a semiconductor laser (LD), a photodetector (PD), and a hologram element (HOE: Holo)
A device that integrates graphic optical elements has been developed and is being applied to DVDs as well as CDs. In addition, the academic society has proposed a device further integrated at two wavelengths (for example, ISOM'98 Technical Digest p.
p22-, Tu-D-01).

As described in the above document, in an integrated device in which a semiconductor laser or a photodetector can be arranged in the immediate vicinity, it is easy to arrange a light receiving portion of the diffracted light by the hologram element and a light emitting point of the semiconductor laser at a substantially conjugate position. It is possible. Therefore, a complementary (complementary) spot size method (“SSD method”: Spot Size Detection) utilizing both ± 1st-order diffracted light from the hologram element
Focus error detection can be realized. This method is
Compared to other practical knife edge methods,
There are advantages that strict position adjustment of the hologram element is not always necessary, and that it is not necessary to discard one of the ± 1st-order diffracted lights and the efficiency is high.

FIG. 7 shows the spot size method (“SSD”).
FIG. 10 is an explanatory diagram for explaining focus error detection by “Method: Spot Size Detection” (Japanese Patent Laid-Open No. 5-1141).
7). More specifically, FIG. 7A is a schematic side view of a device that performs the focus error detection, and FIG. 7B is a schematic plan view of a photodiode or the like that detects diffracted light in the device.

As shown in FIG. 7A, in this focus error detecting device, the reflected light reflected by the optical disk 357 is separated into a pair of conjugate lights b1 and b1 'by the hologram element 355 through the objective lens 356. Is done. Here, the hologram element 355 is configured such that the conjugate light b1 is focused above the light receiving element substrate 350, and the conjugate light b1 'is focused below the substrate 350.

[0009] As shown in FIG. 7 (b), each of the conjugate light beams b 1, b 1 ′ is received by light detection diodes 352 and 353 provided on a light receiving element substrate 350. The photodetector diodes 352 and 353 are located in the regions 352a, 352b, 352c and 35, respectively, in the X direction orthogonal to the Y direction in which the conjugate lights b1 and b1 'are split.
3a, 353b, and 353c.

With such a configuration, the focus error signal FE of the laser beam for the optical disc 357 is formed.
Sets the outputs of the light receiving areas 352a, 352b, and 352c to w1, w2, and w3, respectively.
Outputs of 353b and 353c are w4, w5 and w6, respectively.
FE = (w1 + w3 + w5) − (w2 + w4 + w6) (1)

That is, when the laser light emitted from the laser light source 351 and raised by the raising mirror 354 is incident on the optical disk 357 via the objective lens 356, the laser light is focused on the disk 357. If it is, the size of the spot S1 on the photodetector diode 352 and the size of the spot S2 on the photodetector diode 353 are the same, and the focus error signal F of the equation (1) is obtained.
E becomes zero. On the other hand, when the laser light is out of focus with respect to the optical disk 357, the spot S1 on the detection diode 352 and the detection diode 35
3, the focus error signal FE in the equation (1) has a positive or negative value different from zero. Therefore, the polarity of the focus error signal FE before and after the focal point is inverted. Therefore, the laser beam can be focused on the optical disk 357 by detecting the focus error signal FE.

[0012]

However, if it is attempted to achieve both the focus error detection by the spot size method and the two-wavelength optical system, the wavelength dependence of the diffraction angle by the hologram element becomes a problem.

That is, in the diffraction grating, the characteristics such as the diffraction angle are determined by the mathematical relationship between the periodic structure and the wavelength of light, and therefore, the diffraction angle greatly changes for different wavelengths. More specifically, in the “spot size method”, which is a focus error detection method suitable for an integrated device using the hologram element, a photodetector that detects a hologram element diffracted light very near a conjugate point of a semiconductor laser emission point It is essential to arrange a light receiving surface. However, when light of different wavelengths is made incident on the same hologram element, the optimum photodetector light-receiving surface position is greatly different due to the above-mentioned characteristic change. Therefore, it has been difficult to integrate the semiconductor laser and the photodetector on the same photodetector substrate. Further, it has been difficult to derive compatible solutions for aberration correction and the like for optimizing the lens function of the hologram element.

For example, the aforementioned two-wavelength integrated device (IS
OM'98 Technical Digest pp22 ~, Tu-D-01)
In this case, only one of the ± 1st-order diffracted lights is used for each wavelength, and the above-described complementary configuration is not realized.

Accordingly, an object of the present invention is to provide an optical device which realizes a complementary focus error detection utilizing both ± 1st-order diffracted lights in an optical system using two wavelengths of light as described above.

[0016]

An optical device according to the present invention for achieving the above object is an optical device for reading information from an information recording medium by using light of first and second different wavelengths. A hologram element divided into regions in a plane and including at least a first diffraction region and a second diffraction region; a light receiving element substrate provided below the hologram element and including a plurality of light receiving regions in the same plane; Two positions where ± 1st-order diffracted light of the first diffraction region of the light having the first wavelength is incident on the light receiving element substrate, and the second position of the light having the second wavelength. The two positions at which the ± 1st-order diffracted light from the diffraction region is incident on the light receiving element substrate are made to substantially coincide with each other, and the focus error is determined based on the outputs from the plurality of light receiving regions arranged at the two positions. signal Is detected.

Further, another optical device of the present invention has at least a first laser light source that outputs a laser light of a first wavelength and a second laser light source that outputs a laser light of a second wavelength. A hologram element divided into regions in a plane and including at least a first diffraction region and a second diffraction region; a light receiving element substrate provided below the hologram element and including a plurality of light receiving regions in the same plane; The first and second laser light sources are arranged close to each other at about 100 μm, so that they can be regarded as approximately the same light emitting point and share substantially the same optical axis, and the first ± 1 due to the first diffraction region of incident light having a wavelength
Two positions where the next-order diffracted light enters the light receiving element substrate;
The incident light having the second wavelength, the two positions where the ± 1st-order diffracted light by the second diffraction region is incident on the light receiving element substrate are made to substantially coincide with each other, The light emitting point of the light source or a conjugate point thereof is set to be substantially equidistant from the center of the hologram element, and detects a focus error signal based on outputs from the plurality of light receiving regions arranged at the two positions. It is characterized by doing so.

The optical device may further comprise an optical distance L1 from a center of the hologram to a center of a first light receiving area which is a light receiving area of the + 1st order diffracted light, and an optical distance of the -1st order diffracted light from the center of the hologram. L2 is the optical distance from the center of the second light receiving area, which is the light receiving area, L0 is the optical distance from the center of the hologram to the light emitting point, Lp is the optical distance from the center of the hologram to the light receiving plane of the light receiving element substrate, The basic pitch of the first diffraction region is Λ1, the basic pitch of the second diffraction region is Λ2, and the first wavelength is λ.
1. When the second wavelength is λ2, L0 = L1 = L2 Lp = L0cos {arcsin (λ1 / Λ1)} = L0cos {arcsi
n (λ2 / Λ2)} such that L1, L2, {1, and {2} are substantially satisfied.
It is desirable to determine

Further, the optical device further includes the first device.
A hologram element having a diffraction area and a second diffraction area is formed on one surface of a plate-shaped light transmission medium such as a glass plate, and is formed on another surface of the plate-shaped light transmission medium in a direction orthogonal to the lattice direction of the hologram element. It is preferable to form another hologram element having a lattice direction.

Further, the hologram element of the optical device is arranged at a pair of the first diffraction regions arranged at diagonal positions sandwiching the center of the hologram element and at another diagonal position sandwiching the center. And a pair of the second diffraction regions.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the figures, identical or similar elements are indicated by identical or similar numbers.

A first embodiment of the present invention is an optical device for reading information from an information recording medium such as an optical disk by using light having a first wavelength and light having a second wavelength. In this optical device, the hologram element that generates a pair of conjugate lights by receiving the reflected light from the optical disk includes a first diffraction area and a second diffraction area.
The first diffraction region and the second diffraction region have a grating pitch at a first position where ± 1st-order diffraction light of the light having the first wavelength by the first diffraction region is incident on a light receiving element substrate. And the second position and the first position and the second position where the ± 1st-order diffracted light of the light having the second wavelength by the second diffraction region is incident on the light receiving element substrate are substantially coincident with each other. Has been determined.

More specifically, as shown in FIG. 1, the hologram element 10 includes a pair of first diffraction areas 11 arranged at diagonal positions sandwiching the center O of the hologram element 10.
And a pair of second diffraction regions 13 arranged at other diagonal positions sandwiching the center O. Note that the center O of the hologram element is determined as the intersection of the hologram element and a straight line that passes through the conjugate point of the light emission points of the light having the first and second wavelengths and is parallel to the optical axis of the objective lens.

Also, the first wavelength is λ1, the second wavelength is λ2, the basic pitch of the first diffraction region is Λ1,
When the basic pitch of the second diffraction region is Λ2,
The basic pitches Λ1 and Λ2 are selected so as to satisfy λ1 / Λ1 = λ2 / Λ2 (2).

Further, in this embodiment, the distance from the center of the hologram element to the center of the light receiving area at the first position and the second position is equal to the light emitting point of the light having the first and second wavelengths or a conjugate point thereof. The distance is set to be substantially equal to the distance from a point to the center of the hologram element. Here, the center of the light receiving region means the center of the light receiving region in a direction (X-axis direction in FIG. 1) orthogonal to the grating axis direction of the first and second diffraction regions.

FIG. 2 shows the operation of the first embodiment.

More specifically, FIG. 2A shows ± first-order diffracted lights b1 and b1 ′ when light having a first wavelength λ1 is incident on the first diffraction area 11 of the hologram element 10. . FIG. 2B shows ± 1st-order diffracted light b when light having a second wavelength λ2 is incident on the first diffraction region 11.
2 and b2 '. FIG. 2C shows that the first wavelength λ1 is applied to the second diffraction area 13 of the hologram element 10.
± 1st order diffracted light b3, b3 ′ when light having
Is shown. FIG. 2D shows ± first-order diffracted lights b4 and b4 ′ when light having a second wavelength λ2 is incident on the second diffraction area 13.

As described above, in this embodiment, the first wavelength is λ1, the second wavelength is λ2, the basic pitch of the first diffraction region is Λ1, and the basic pitch of the second diffraction region is Λ1. Λ2, the basic pitches Λ1, Λ
2 is determined so as to satisfy λ1 / Λ1 = λ2 / 2 (2).

Accordingly, ± first-order diffracted lights b1, b1 of the light having the first wavelength λ1 by the first diffraction area 11
'Diffraction angle θ1 = arcsin (λ1 / Λ1), and the second wavelength λ2 by the second diffraction region 13
The diffraction angle θ4 = arcsin (λ2 / Λ2) of the ± first-order diffracted lights b4 and b4 ′ of the light having Therefore, FIG. 2A and FIG.
As shown in (d), the first position P1 and the second position P1 where the diffracted light beams b1 and b1 ′ enter the light receiving element substrate 15.
′ And the first position P1 and the second position P1 ′ where the diffracted light beams b4 and b4 ′ are incident on the light receiving element substrate 15 substantially coincide with each other.

As shown in FIG. 1B, the diffracted lights b2 and b2 'of the light having the second wavelength λ2 by the first diffraction region 11 are formed on the light receiving element substrate 15. And a position P separated from the positions P1 and P1 '.
2, P2 '. Further, as shown in FIG. 1C, the first wavelength λ1 by the second diffraction region 13 is used.
The diffracted lights b3 and b3 'having the above-mentioned are incident on the light receiving element substrate 15 at positions P3 and P3' closer to each other than the positions P1 and P1 '.

Further, as described above, in this embodiment, the distance from the center of the hologram element to the center of the light receiving area at the first position and the second position is equal to the first and second positions.
The distance from the light emitting point of the light having the second wavelength or the conjugate point thereof to the center of the hologram element is set to be substantially equal. That is, when the optical distance from the conjugate point C of the light emitting point (not shown) of the semiconductor laser to the hologram center O is L0, from the hologram center O,
The optical distance from the center of the hologram O to the center of the light-receiving area A2 of the -1st-order diffracted light b1 'or b4' is L2, and the optical distance from the center of the hologram O to the center of the light-receiving area A2 of the + 1st-order diffracted light b1 or b4 is L2. When L1 and L2 are L0
Is set to be equal to

This means that the position of the light receiving element substrate 15 for receiving the diffracted lights b1 to b4 'is determined as follows with respect to the diffraction element substrate 17 on which the hologram element is mounted. That is, referring to FIG. 2A, an arc q is drawn with the center O of the hologram element 10 as the center and the radius L0 as the distance from the hologram center O to the conjugate point C. On the other hand, the hologram element 10
L1 and L2 in the direction of the diffraction angle ± θ1 from the center O of
Draw. Then, an intersection between the arc q and the straight lines L1 and L2 is obtained. The position of the light receiving element substrate 15 is determined such that the upper surface of the light receiving element substrate 15 passes through this intersection.

By determining the position of the light receiving element substrate 15 in this manner, the ± 1st-order diffracted lights b1, b1 ', b4, b4 due to the diffraction areas 11, 13 when no lens power is applied to the hologram element 10. 'Focuses on the surface of the light receiving element substrate 15. When lens power is given to the hologram element 10, focusing power is added to one of the ± first-order diffracted lights and diverging power is added to the other of the ± first-order diffracted lights. Shifting upward or downward in the opposite direction provides the prerequisite for performing the complementary spot size method.

As described above, when the position of the light receiving element substrate 15 is set, the optical distance Lp from the center O of the hologram element to the light receiving plane of the light receiving element substrate 15 is Lp = L0 cos {arcsin (λ1 / Λ1) )} = L0 cos {arcsin (λ2 / Λ2)} (3)

The position P1 of the light receiving element substrate 15,
P1 'is a photodetector diode 3 in FIG.
Light detection diodes similar to 52 and 353 (not shown)
Is provided. Therefore, according to this embodiment, for two wavelengths λ1 and λ2, the focus error signal by the complementary spot size method is transferred to the position P close to the conjugate point C.
1, and can be calculated based on the output from the pair of photodetector diodes at P1 '.

Therefore, the optical device of this embodiment has the following advantages.

1) As described above, for a laser beam having two different wavelengths λ1 and λ2, a focus error signal can be obtained by a complementary spot size method (SSD).

2) The first and second diffraction regions 11, 1
3 is formed on one surface of the diffraction element substrate 17,
The work of creating a hologram element is facilitated.

3) As described later, the diffraction element substrate 1
7, it is possible to form a linear grating for three-beam tracking on the other surface. With this, CD
For a disk, tracking error detection by the three-beam tracking method can be performed.

In the above description, the light having the first wavelength λ1 and the light having the second wavelength λ2 are, for example,
DVD laser light having a wavelength of 650 nm;
This is a CD laser beam having a wavelength of 80 nm.

FIGS. 1 and 3 show a second preferred embodiment of the optical device according to the present invention.

As shown in FIG. 1, the hologram element 10 of the second embodiment has a structure similar to that of the first embodiment.
A pair of the first diffraction regions 11 arranged at diagonal positions sandwiching the center O of the hologram element 10 and a pair of the second diffraction regions 13 arranged at other diagonal positions sandwiching the center O
And. More specifically, the first diffraction region 11 and the second diffraction region 13 are located at a pair of diagonal directions when a circular region on the diffraction element substrate is divided by a cross, as shown in the drawing, and the like. Are formed at positions existing in a pair of diagonal directions. Thereby, even if the intensity of the incident light incident on the hologram element 10 is shifted in the vertical and horizontal directions in FIG. 1, the intensity of the diffracted light does not become unbalanced.

In the second embodiment, the basic pitch of the first diffraction area is set to Λ1 and the basic pitch of the second diffraction area is set to Λ2, as in the first embodiment. ing. That is, the hologram element 10
Out of the two wavelengths of light incident on the
When the wavelength of the second light is λ2, the basic pitches Λ1 and Λ2 are selected to satisfy λ1 / 1 = λ2 / Λ2 (2).

Further, in the second embodiment, the position of the light receiving element substrate 15 with respect to the diffraction element substrate 17 is set in the same manner as in the first embodiment. Therefore, distances L1 and L2 from the center of the hologram element to the center of the light receiving area at the first position and the second position are:
The distance L0 from the light emission point of the light having the first and second wavelengths or a conjugate point thereof to the center of the hologram element is substantially equal to the distance L0.

Therefore, when incident light having the first wavelength λ1 and incident light having the second wavelength λ2 enter the hologram element 10, the first and second diffraction regions 1
The ± 1st-order diffracted lights by 1 and 13 enter the light receiving element substrate 15 in the same manner as in the first embodiment.

That is, as shown in FIG. 3A, when the incident light having the first wavelength λ1 is incident on the hologram element 10, the diffracted light (± 1
The next-order diffracted light b1 and b1 ′ enter the positions P1 and P1 ′ on the light receiving element substrate 15. On the other hand, in the above case, the second
± 1st order diffracted light b3, b3 diffracted by the diffraction area 13
′ Are incident on the light receiving element substrate 15 at positions P3 and P3 ′ inside (closer to each other) than the positions P1 and P1 ′.

As shown in FIG. 3B, when the incident light having the second wavelength λ2 is incident on the hologram element 10, the diffracted light b2, b2
Is incident on positions P2 and P2 'on the light receiving element substrate 15 outside the positions P1 and P1'. In the above case, the ± first-order diffracted lights b4 and b4 ′ diffracted by the second diffraction area 13 are incident on the positions P1 and P1 ′ on the light receiving element substrate 13.

As shown in FIG. 3 (c) or (d),
The positions P1, P2, P3 on the light receiving element substrate 15
P1 ', P2', and P3 'have the ± 1st-order diffracted light b1,
Light detection diode 21 as a light receiving element for detecting b1 ', b2, b2', b3, b3 ', b4, b4'
a to 21p are provided.

More specifically, the light receiving element 2 is located at the position P1.
1a, 21b, 21c, and 21d are provided, and the position P1
′ Are provided with light receiving elements 21e, 21f, 21g, 21h, and the light receiving elements 21m, 21m are located at the position P2.
n at the position P2 ′.
o, 21p are provided, and the light receiving element 2 is located at the position P3.
1i and 21j are provided, and light receiving elements 21k and 21l are provided at the position P3 '. In FIG. 3 (c), the thin striped patterns provided on the light receiving elements 21a to 21d and 21e to 21h indicate that the diffracted lights b1 and b1 'by the first diffraction region 11 enter these light receiving elements. And the rough striped pattern given to the light receiving elements 21i to 21l indicates that the diffracted lights b3 and b3 ′ by the second diffraction region enter these light receiving elements. The stripe pattern on the light receiving element in FIG. 3D also indicates the same as above.

The light receiving element 2 provided at the positions P1 and P1 '
1a to 21d and 21e to 21h are used for focus error detection. More specifically, the light receiving element 2
When the outputs from 1a to 21d and 21e to 21h are a to d and e to h, the focus error signal FE is expressed as FE = (a + d + f + g)-(b + c + e + h).

As described above, the hologram element 1
When the incident light having the first wavelength λ1 is incident on 0, the diffracted lights b1 and b1 ′ by the first diffraction region 11 are emitted.
Are input to the light receiving elements 21a to 21d and 21e to 21h. In addition, the hologram element 10
When the incident light having the wavelength λ2 is input, the diffracted lights b4 and b4 ′ by the second diffraction area 13 also
1a to 21d and 21e to 21h. Therefore, according to the above configuration, both the incident light having the first wavelength λ1 and the incident light having the second wavelength λ2
By detecting the focus error signal FE, it is possible to detect a focus error of light incident on the recording disk.

The light receiving elements 21m, 21n, 21
Outputs from i, 21j, 21k, 211, 21o, and 21p are used to detect a tracking error of light incident on the optical disk 120 (FIG. 4).

More specifically, first, the positions P3, P3
', The light receiving elements 21i, 21j, 21k, 21l
Is used to detect the tracking error for the laser light having the first wavelength λ1. More specifically, the detection of the tracking error is performed by a differential phase detection method (DPD) in this embodiment, and four signals DPD1, DPD2, and DP for performing the detection are used.
D3 and DPD4 are calculated based on outputs of the light receiving elements 21i to 21l and outputs from the light receiving elements 21a to 21h. That is, the light receiving elements 21a to 21h
When the outputs of the signals D are respectively a to h, the signal DPD1
DPD4 is: DPD1 = (j + k), DPD2 = (c + d + e +
f), DPD3 = (i + 1), DPD4 = (a + b + g + h).

Signals DPD1, DPD2, DPD3, and DPD4 representing a tracking error of the laser light having the second wavelength λ2 with respect to the optical disk 120.
Is calculated based on the outputs from the light receiving elements 21a to 21h and 21m to 21p. More specifically, when the outputs from the light receiving elements 21a to 21h and 21m to 21p are a to h and m to p, the signals DPD1 to
DPD4 is represented by the following equation.

DPD1 = (c + d + e + f), DPD2
= (N + p), DPD3 = (a + b + g + h), DPD4 = (m + o) Therefore, the laser light having the first wavelength λ1 and the laser light having the second wavelength λ2 are output from the light receiving elements 21a to 21p. The optical disk 120 of light
Can be detected.

The recording signal RF of the optical disk 120
Is represented by the sum of outputs from the light receiving elements 21a to 21p. That is, RF = (a + b + c +... + O + p).

FIG. 4 shows a specific example in which the second embodiment is mounted on an optical pickup device.

In FIG. 4, reference numeral 101 denotes the optical disc 12
0 denotes an incident optical axis, 102 denotes an incident light beam to the objective lens 119, 111 denotes a focus of the incident light beam 102, 115 denotes a semiconductor laser that outputs a laser beam, and 116 denotes the semiconductor laser. Reference numeral 117 denotes a submount on which the objective lens 119 is mounted.
, 118 denotes a micromirror, 121 denotes a track formed on the optical disk, 122 denotes an optical pickup package, and 123 denotes a housing on which the pickup is mounted. As shown, in this specific example, the axial direction of the grating of the diffraction regions 11 and 13 is the same as that of the track 121.
In the tangential direction (Y-axis direction in the figure).

Accordingly, the laser light emitted from the semiconductor laser 115, raised by the micro mirror 118, and converged on the optical disk 120 by the objective lens 119 is
After being reflected by the optical disk 120, the light is diffracted by the first diffraction area 11 or the second diffraction area 13 via the objective lens 119, and ± first-order diffracted lights b2, b2 ′, b4,.
As b4 ', the light receiving areas 21a to 21h, 21m to 21
incident on p. Here, the case where the second wavelength λ2 is used is shown.

As described above, the light receiving areas 21a to 21a
The focus error of the light beam emitted from the objective lens 119 with respect to the optical disk 120 can be detected from the output from the optical disk 21h. The light receiving areas 21a to 21h and 2
The output from the optical disc 120
The tracking error of the emitted light beam with respect to the track 121 can be detected.

FIGS. 5 and 6 show a third preferred embodiment of the optical device according to the present invention.

In the third embodiment, when a CD disk is used, the tracking error can be detected by a so-called three-beam method. For this reason, as shown in FIG. 5, the third embodiment uses a hologram element 10 having the first diffraction area 11 and the second diffraction area 13 on one surface of the diffraction grating substrate 17 made of a light transmitting medium.
And on the other surface of the diffraction grating substrate 17,
Another hologram element 224 having a lattice axis direction in a direction orthogonal to the lattice axis direction of the hologram element 10 was formed. More specifically, the hologram element 10 having the first diffraction region 11 and the second diffraction region 13 is formed on the upper surface of the diffraction element substrate 17, and the three-beam generation diffraction grating 224 is formed on the lower surface of the diffraction element substrate 17. Formed.

With the above configuration, as shown in FIG.
Beams (three beams) B for detecting a tracking error with respect to the track 221 of the optical disc 220
1, B2 and B3 are generated.

More specifically, as shown in FIG. 6, laser light (wavelength λ2 = 78) emitted from the semiconductor laser 215 is used.
0 nm) is raised by a mirror 218, and three beams B1, B2, and B3 arranged in the Y-axis direction are generated by the three-beam generation diffraction grating 224. This beam B1,
B2 and B3 are incident on the track 221 side by side in the tangential direction, so that a tracking error of a beam with respect to the track 221 can be detected by a so-called three-beam method.

Referring again to FIG.
In order to detect the three beams B1, B2, and B3 reflected from the light receiving element 20, the light receiving element on the light receiving element substrate 15 is configured as follows. That is, as shown in FIGS. 5C and 5D, in order to detect a tracking error of the CD laser light having the second wavelength λ2, both sides of the light receiving elements 21a to 21n for detecting the focus error and the like. , Light receiving elements 21o and 21p are arranged. More specifically, the light receiving elements 21o and 21p include the light receiving elements 21a to 21n.
Are arranged in a direction orthogonal to the grating axis direction of the three-beam generation diffraction grating 224 (Y-axis direction in FIGS. 5C and 5D).

With the above configuration, the three beams B1 to B3
Is detected by the light receiving element 21o, the light receiving elements 21a to 21h, or the light receiving element 21p. That is,
The track 2 of the laser light for CD having the wavelength λ2
The tracking error with respect to the light receiving element 21
Assuming that outputs from o and 21p are o and p, detection is performed by calculating a tracking error signal TE (3 beams) = op based on these outputs.

The third embodiment is different from the third embodiment in that the three-beam generation diffraction grating 224 is provided and the light receiving element 21 is provided.
The configuration is the same as that of the second embodiment except that the arrangement of m to 21p is changed.

That is, for example, the hologram element 10
Is divided into the first diffraction area 11 and the second diffraction area 13 in the mode shown in FIG. The basic pitch of the first diffraction area 11 and the second diffraction area 13 is set in the same manner as in the first and second embodiments.

The distance between the light receiving element substrate 15 and the diffraction element substrate 17 is set in the same manner as in the first and second embodiments.

The arrangement of the light receiving elements 21a to 21l is the same as the arrangement of the light receiving elements 21a to 21l in the second embodiment (see FIGS. 3C and 3D). However, the light receiving elements 21m and 21n of the third embodiment are arranged so as to occupy the positions of the light receiving elements 21m and 21n of the second embodiment or the positions of the light receiving elements 21o and 21p of the second embodiment, respectively. .

Therefore, also in the third embodiment, the first light-receiving element 21a to 21p based on the signals from the light-receiving elements 21a to 21p.
Laser light having the wavelength λ1 and the second wavelength λ2
With respect to the laser beam having the following, a focus error signal by a complementary (complementary) spot size method can be detected, and a tracking error signal by a differential phase detection method (DPD) can be obtained for a DVD optical disc.

In FIGS. 5C and 5D, the light-receiving element having a fine stripe pattern also receives the diffracted light from the first diffraction area 11 in the light-receiving element. This indicates that diffracted light from the second diffraction region 13 is incident on a light receiving element having a stripe pattern with a wide interval.

In the third embodiment, FIG.
As shown in (c), when the incident light having the first wavelength λ1 is input to the hologram element 10, the diffracted light is not incident on the light receiving elements 21o and 21p (ie, The diffraction fringes of the diffraction grating 224 for generating three beams are designed so that the intensity of the diffracted light in this direction becomes zero.

As described above, according to the third embodiment, the laser beam having the first wavelength λ1 and the second
The focus error signal can be detected by the complementary (complementary) spot size method for the laser beam having the wavelength λ2 of the wavelength λ2, and the tracking error signal of the three-beam method can be obtained for the CD optical disc, and the DVD
A tracking error signal of the differential phase detection method (DPD) can be obtained for the optical disc for use.

The present invention also includes an optical pickup having the optical device of the present invention. This optical pickup includes, for example, a casing 123, an objective lens 119, and an optical device including the hologram element 11 and the light receiving elements 21a to 21p as shown in FIGS.
Is provided.

[0076]

As described above, according to the present invention,
Complementary focus error detection using both ± 1st-order diffracted light can be realized with a two-wavelength optical system.

Therefore, in a DVD or CD-R compatible pickup or reproducing apparatus, downsizing, simplification, low cost, and high efficiency can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing first, second, and third optical devices according to the present invention;
FIG. 13 is a schematic diagram illustrating a hologram element according to a third embodiment.

FIG. 2 is an explanatory diagram showing an operation of the first embodiment.

FIG. 3 is a schematic diagram showing the configuration and operation of an optical device according to a second embodiment of the present invention.

FIG. 4 is a schematic diagram showing a specific example in which the second embodiment of the present invention is applied to an optical pickup.

FIG. 5 is a schematic diagram showing a third preferred embodiment of the optical device of the present invention.

FIG. 6 is a schematic view showing a third embodiment of the optical device of the present invention.

FIG. 7 is an explanatory diagram showing a conventional focus error detection device.

[Explanation of symbols]

 10: hologram element 11: first diffraction area 13: second diffraction area 15: light receiving element substrate 17: diffraction element substrate 21a to 21p: light receiving element 224: diffraction grating for generating three beams

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D118 AA03 AA26 BA01 BB02 BF02 BF03 CC12 CC17 CD02 CD03 CD08 CF03 CF05 CG07 CG26 DA20 5D119 AA04 AA41 AA43 BA01 CA09 DA01 DA05 EA02 EA03 EC45 EC47 FA05 FA08 JA15 KA19

Claims (5)

[Claims] An optical device for reading information from an information recording medium using light of first and second different wavelengths, wherein the optical device is divided into regions on the same plane, and includes at least a first diffraction region and a second diffraction region. A hologram element comprising: a diffraction area; and a light receiving element substrate disposed below the hologram element and having a plurality of light receiving areas in the same plane. The two positions where the ± 1st-order diffracted light by the diffraction region is incident on the light receiving element substrate and the ± 1st-order diffracted light by the second diffraction region of the light having the second wavelength are incident on the light receiving element substrate 2
An optical device wherein the two positions substantially coincide with each other, and a focus error signal is detected based on outputs from the plurality of light receiving regions arranged at the two positions. 2. An optical device for reading information from an information recording medium using light, comprising at least a first laser light source for outputting a laser light of a first wavelength, and a laser of a second wavelength. A second laser light source that outputs light, a hologram element that is divided into regions in the same plane and includes at least a first diffraction area and a second diffraction area, and is disposed below the hologram element and includes a plurality of light-receiving elements. A light-receiving element substrate having an area in the same plane, wherein the first and second laser light sources are arranged close to each other to about 100 μm, so that they can be regarded as substantially the same light-emitting point and at the same time substantially the same light The incident light having the first wavelength has two positions where ± 1st-order diffracted light by the first diffraction region is incident on the light receiving element substrate, and has the second wavelength. Incident light The second
The two positions at which the ± 1st-order diffracted light from the diffraction region is incident on the light-receiving element substrate are made substantially coincident with each other, and the two positions and the light emitting point of the light source or a conjugate point thereof are defined by the hologram. An optical device, wherein the focus error signal is set based on outputs from the plurality of light receiving regions arranged at substantially equal distances from a center of an element and arranged at the two positions. 3. The optical device according to claim 1, wherein an optical distance from a center of the hologram to a center of a first light receiving area, which is a light receiving area of the + 1st-order diffracted light, is L1. L2, the optical distance from the center of the hologram to the center of the second light receiving area, which is the light receiving area of the -1st order diffracted light, L0, the optical distance from the center of the hologram to the light emitting point, and the light receiving element substrate from the center of the hologram. The optical distance to the light receiving plane is Lp, the basic pitch of the first diffraction region is Λ1, the basic pitch of the second diffraction region is Λ2, the first wavelength is λ1, the second wavelength is λ2, L0 = L1 = L2 Lp = L0cos {arcsin (λ1 / Λ1)} = L0cos {arcsi
n (λ2 / Λ2)} such that L1, L2, {1, and {2} are substantially satisfied.
An optical device characterized in that: 4. The optical device according to claim 1, wherein the hologram element having the first diffraction area and the second diffraction area is formed on one surface of a diffraction element substrate made of a light transmitting medium. An optical device, wherein a diffraction grating having a grating axis direction substantially perpendicular to a grating axis direction of the hologram element is formed on another surface of the diffraction element substrate. 5. The optical device according to claim 1, wherein the hologram element includes a pair of the first diffraction regions arranged at diagonal positions sandwiching a center of the hologram element, and the center of the hologram element. And a pair of the second diffraction regions arranged at other diagonal positions sandwiching the second diffraction region.