JPH0677335B2 - Optical pickup device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical pickup device that can be used in a recording / reproducing device such as a compact disc player or a video disc player.

[Conventional technology]

As a conventional optical pickup device, the one shown in FIG. 5 is already known. In such a device, the emitted light of the semiconductor laser 11 is diffracted by the first diffraction element 12 and
It is divided into a first-order diffracted light (main beam) and ± first-order diffracted lights (sub-beams) separated in a direction substantially perpendicular to the paper surface. The three divided beams are further diffracted by the second diffractive element 13, and the 0th-order diffracted light of each beam is collimated by the collimator lens 14.
Through the objective lens 15 and focused on the record carrier 16. At this time, the main beam is focused on the pits of the record carrier 16 so as to read the information signal, and the pit signal (information signal) is obtained from the reflection intensity thereof. Also, the two sub-beams are symmetrical with respect to the main beam,
A tracking error signal is obtained from the reflection intensities of the two sub-beams, which are condensed with a large amount in the track direction and a slight deviation in the radial direction.

In order to obtain a pit signal, a tracking error signal, and a focus error signal, the reflected light from the record carrier 16 passes through the objective lens 15 and the collimator lens 14, is diffracted by the diffraction element 13, and the first-order diffracted light thereof is the light receiving element 17 Be led to. When viewed from the side of the record carrier 16, the diffractive element 13 is divided into two light incident areas 13a and 13b as shown in FIG. 6 (a), and has a symmetrical shape that runs diagonally with respect to the dividing line 13c. The grid of is formed. The light receiving element 17 has six light receiving regions 17a, 17b, 17c, 1 as shown in FIG.
It is divided into 7d, 17e and 17f. The dividing line 13c of the diffraction element 13 is set in the same direction as the radial direction (radial direction) of the record carrier 16.

Here, when the light beam emitted from the semiconductor laser 11 is focused on the record carrier 16, the main beam diffracted by the light incident region 13a of the diffraction element 13 is on the split line A ₁ of the light receiving element 17. Is focused on to form spot Q ₁ , which is the light incident area.
The main beam diffracted by 13b is focused on the dividing line B ₁ to form a spot Q ₂ . In addition, the sub beam is the light receiving area
It is focused on 17e and 17f. The light receiving area of the light receiving element 17
Focus error signal by each resulting output signal _{S 1a · S 1b · S 1c} · S 1d · S 1e · S 1f from 17a · 17b · 17c · 17d · 17e · 17f is _{(S 1a + S 1d) -} (S 1b + S _1c ), the tracking error signal is obtained by S _1e + S _1f , and the pit signal (information signal) is obtained by S _1a + S _1b + S _1c + S _1d .

As another conventional example, an optical pickup device shown in FIG. 7 is known. This device is different from the above-described conventional example in the grating shape of the diffraction element 23 which is the second diffraction element and the light receiving area shape of the light receiving element 27. Diffraction element 23
FIG. 8A shows the arrangement of the gratings of the diffraction element 23 when viewed from the side of the record carrier 26, and FIG. 8B shows the relationship of the arrangement of the light receiving regions of the light receiving element 27. The diffractive element 23 is divided into two light incident areas 23a and 23b, and mutually different synchronizing gratings are formed at right angles to the dividing line 23c. The light receiving element 27 has six light receiving areas 27a and 27b.
・ It is divided into 27c ・ 27d ・ 27e ・ 27f. The direction of the dividing line 23c of the diffraction element 23 is the radial direction. In the focused state, the main beam diffracted in the light incident area 23a is condensed on the dividing line A ₂ to form the spot R ₁ , and the light incident area is formed.
The main beam diffracted by 23b is focused on the dividing line B ₂ to form the spot R ₂ , while the sub-beams are focused on the light receiving regions 27e and 27f. And
Output signals S _2a , S _2b , S _2c , S _2d , S _2e , S _2f obtained from the light receiving areas 27a, 27b, 27c, 27d, 27e, 27f of the light receiving element 27, respectively.
Therefore, the focus error signal is (S _2a + S _2d ) − (S _2b + S
In operation _2c), the tracking error signal in the calculation of the S _2e -S _2f, pit signal (information signal) is obtained, respectively by the operation of the _{S 2a + S 2b + S 2c} + S 2d.

[Problems to be Solved by the Invention]

However, in the optical pickup device having such a configuration, the reflected light spots Q ₁ and Q from the record carrier 16 (26) are generated.
₂ (R ₁ · R ₂ ) must be connected to the dividing line of the light receiving element 17 (27) with extremely high accuracy, which is why the diffraction element 13
(23) and the light receiving element 17 (27) were finely adjusted for installation. However, the diffractive element 13 (23) and the light receiving element 17
If it is attempted to configure (27) so that it can be moved independently, a support mechanism for moving the light receiving element 17 (27) in particular is required, which complicates the structure of the device and hinders downsizing and weight reduction. Will be a factor. In addition, the large number of parts for positioning leads to a complicated manufacturing procedure, resulting in a high manufacturing cost.

Therefore, the semiconductor laser 11 (21) and the light receiving element 17 (27) are housed in the same package, and the reflected light spot Q ₁ · Q
It is conceivable that the light receiving element 17 (27) at ₂ (R ₁ · R ₂ ) is aligned with the dividing line only by the diffraction element 17 (27). However, in the pickup device having such a structure, when the positions of the semiconductor laser 11 (21) and the light receiving element 17 (27) are slightly deviated from the designed values, the beam spot is located at the correct position on the light receiving element 17 (27). Focus is offset because the light is not focused on the surface. In order to remove this focus offset, the diffractive element 13 in the examples shown in FIGS. 5 and 6 and the diffractive element 23 in the examples shown in FIGS. 7 and 8 are translated.
It is necessary to rotate and move the beam spot on the light receiving element 17 (27) to adjust the focus error signal to "0" in the focused state. However, at this time, the light receiving element 17
(27) Since the two main beam spots above move at the same time, each spot cannot be moved and adjusted individually, which makes adjustment very difficult. In addition, the movements of the two spots may cancel each other out on the focus error signal, and in that case, the diffraction element 13 (23) is set to a large Y value.
Need to move in the direction. In this case, in particular, in the example shown in FIGS. 7 and 8, the length of the divided portion of the light receiving element 27 in the Y direction is short. Big Y
When moved in the Y direction, the beam spots R ₁ and R ₂ on the light receiving element 27 move greatly in the Y direction, and there is a danger that the beam spots R ₁ and R ₂ may deviate from the light receiving portion that should originally be focused.

Further, as a common problem of the above two examples, since it is necessary to translate the diffraction element 13 (23) when adjusting the focus / offset, a size having a sufficient margin in advance as compared with the size of the incident beam spot. The diffractive element 13 (23) is required, and the manufacturing cost increases due to the increase in size.

[Means for Solving the Problems]

In order to solve the above problems, an optical pickup device according to the present invention includes a lens system that focuses a light beam from a light source on a record carrier, a light receiving element that detects reflected light from the record carrier, and Provided in the optical path between the light source and the record carrier, and emits a light beam from the light source to detect the pit signal.
An optical pickup provided with a first diffractive element that divides the second-order diffracted light into a pair of first-order diffracted light for tracking error detection, and a second diffractive element that guides the light reflected by the record carrier to the light-receiving element. In the device, the light receiving element is divided into four first to fourth light receiving areas, while the second diffractive element is divided into three first to third light incident areas, and The 0th-order diffracted light that is reflected by the first light incident area is divided into a first light receiving area and a second light receiving area that are divided by a dividing line that runs in the same direction as the diffraction direction. The 0th-order diffracted light which is focused on the dividing line between the areas and is reflected by the record carrier and diffracted by the second light incident area is collected on the first light receiving area. The 0th-order diffracted light which is reflected by the record carrier and is Light diffracted in the third light incident area having the same amount of incident light as that of the second light incident area is set so as to be condensed on the second light receiving area, and is reflected by the record carrier. The pair of first-order diffracted lights that are diffracted by the second diffractive element are combined with the third light receiving region and the fourth light.
The light receiving area and the light receiving area are set so as to be condensed respectively.

[Action]

According to the above configuration, the focus error signal can be obtained by the difference between the output obtained from the first light receiving area and the output obtained from the second light receiving area, and the output obtained from the third light receiving area can be obtained. , The tracking error signal can be obtained by the difference from the output obtained from the fourth light receiving region,
An information signal can be obtained by the sum of the output obtained from the first light receiving area and the output obtained from the second light receiving area.

Then, in the focus / offset adjustment, the light intensity of the spot formed on the first light receiving area and the light intensity of the spot formed on the second light receiving area are equal to each other and cancel out on the focus error signal. It is sufficient to move and adjust only the spots formed on the dividing line. Therefore, the focus / offset adjustment can be performed only by rotating the second diffraction element to move the spot formed on the light receiving element in a fixed direction.
Further, since it is not necessary to translate the second diffractive element in this way to perform offset adjustment, it is sufficient that the diffractive element has the same size as the incident beam, and the manufacturing cost is reduced by reducing the area. You can also plan.

[Embodiment 1] The following will describe one embodiment of the present invention with reference to FIG. 1 and FIG.

In the optical pickup device according to the present invention, as shown in FIG. 1, the emitted light of the semiconductor laser 1 as the light source is the first
Is diffracted by the diffractive element 2 and is divided into the 0th-order diffracted light (main beam) and the ± 1st-order diffracted light (sub-beams) which are separated from each other in the direction substantially perpendicular to the paper surface. The divided three beams are further diffracted by the second diffractive element 3, and the 0th-order diffracted light of each beam forms a collimating lens 4 which constitutes a lens system 10.
And is focused on the record carrier 6 by the objective lens 5. At this time, the main beam is focused on the pits of the record carrier 6 so as to read the information signal, and the pit signal (information signal) is obtained from the reflection intensity thereof. Also, the two sub-beams are symmetrical with respect to the main beam,
A tracking error signal is obtained from the reflection intensities of the two sub-beams, which are condensed with a large amount in the track direction and a slight deviation in the radial direction. In order to obtain a pit signal, a tracking error signal, and a focus error signal, the reflected light from the record carrier 6 passes through the objective lens 5 and the collimator lens 4, is diffracted by the diffraction element 3, and the first-order diffracted light thereof is the light receiving element 7. Be led to. Here, the semiconductor laser 1 and the light receiving element 7 are housed in the same package and are fixed to each other. Therefore, the adjustment is performed only by the diffraction element 3.

When viewed from the side of the record carrier 6, the diffractive element 3 is divided into the first to third parts by the dividing line 3d running in the radial direction and the dividing line 3e running in the direction orthogonal thereto as shown in FIG. 2 (a). It is divided into third light incident areas 3a, 3b, 3c. The first light incident area 3a is formed in a semicircular shape, while the second and third light incident areas 3b and 3c are set so that the semicircle is equally divided into two and the amounts of incident light are equal to each other. Has been done. Further, the lattice lines of the light incident region 3b and the light incident region 3c run obliquely with respect to the lattice line of the light incident region 3a and are inclined in opposite directions. Also, the grating period of the light incident area 3b is
3a, while the grating period of the light incident region 3c is shorter than that of the light incident region 3a. This is to correct the aberration, but the order of length and length is not limited to that described above.
That is, since it is determined by the relative position of the diffraction element 3, the light source 1, and the condensing point P on the light receiving element 7, the grating interval of the diffraction element 3 gradually changes accordingly. Similarly, each lattice line draws a gentle curve to correct aberration. The light receiving element 7 is divided into first to fourth light receiving regions 7a, 7b, 7e, 7f as shown in FIG.
The dividing line A ₀ that divides the light receiving regions 7a and 7b is provided in the same direction as the diffraction direction with a slight inclination in order to prevent the occurrence of focus offset due to wavelength change.

Here, when the light beam emitted from the semiconductor laser 1 is in focus on the record carrier 6, the main beam diffracted in the light incident region 3a of the diffraction element 3 is on the dividing line A ₀ of the light receiving element 7. To form a spot P ₁ on the light incident area 3b.
The main beam diffracted by is focused on the light receiving region 7a to form a spot P ₂ , and the main beam diffracted by the light incident region 3c is focused on the light receiving region 7b to form a spot P ₃ . The sub-beam diffracted by the diffractive element 3 is focused on the light receiving areas 7e and 7f. Then, the light receiving area 7a
・ Output signals S _a・ S _b・ S _e・ S _f obtained from 7b ・ 7e ・ 7f respectively
Therefore, the focus error signal can be obtained by S _a −S _b calculation by the single knife edge method, the tracking error signal can be obtained by S _e −S _f calculation by the 3-beam method, and the pit signal can be obtained by S _a + S _b calculation. become.

According to the above arrangement, since the time of adjustment of the focus offset, the light intensity of the spot P ₂ · P ₃ are equal to one another, are offset in on the focus error signal (S _a -S _b), the spot P ₁
Only move and adjust. Therefore, by rotating the diffraction element 3 and moving the spot P ₁ formed on the light receiving element 7 in the X direction,
Offset adjustment is possible. In addition, since it is not necessary to translate the diffractive element 3 in this way to perform offset adjustment, it is sufficient that the diffractive element 3 has the same size as the incident beam, and thus the manufacturing cost can be reduced. .

[Embodiment 2] Another embodiment of the present invention will be described with reference to FIGS. 3 and 4. The members having the same functions as those in the first embodiment are designated by the same reference numerals and the description thereof is omitted.

As shown in FIG. 3, the optical pickup device according to the present embodiment has the same arrangement relationship of each element within the lens system 10, but differs in the shape of the light incident region of the second diffraction element 8. There is. That is, as shown in FIG. 4A, the diffractive element 8 is parallel to the dividing line 8d running in the radial direction through the center of the diffractive element 8 at a constant interval when viewed from the record carrier 6 side. With the dividing line 8e running in, three light incident areas
It is divided into 8a / 8b / 8c. The light incident area 8a is formed in a semicircular shape, while the light incident areas 8b and 8c are set so that the semicircles are equally divided into two and the amounts of incident light are equal to each other. Further, the lattice lines of the light incident region 8b and the light incident region 8c run obliquely with respect to the lattice line of the light incident region 8a and are inclined in opposite directions. The grating period of the light incident area 8b is longer than that of the light incident area 8a, while
The lattice period of 8c is shorter than that of the light incident region 8a. As with the first embodiment, the order of length and shortness is not limited to that described above. As in the first embodiment, the light receiving element 7 also has four light receiving regions 7a, 7b, 7e, 7f as shown in FIG.
Is divided into

Here, when the light beam emitted from the semiconductor laser 1 is in focus on the record carrier 6, the first beam of the diffraction element 8
The main beam diffracted in the light incident area 8a of the
Is condensed on top dividing line A ₀ to form a spot P _1, the main beam diffracted by the second light incident region 8b is converged to form a spot P ₂ on the first light receiving region 7a , The main beam diffracted by the third light incident region 8c is condensed on the second light receiving region 7b to form a spot P ₃ . The sub-beam diffracted by the second diffractive element 8 is focused on the third and fourth light receiving regions 7e and 7f. Then, the light receiving area 7a
Output signals each obtained from _{7b · 7e · 7f S a ·} S b · S e · S S from the focus error signal knife edge method by _{f a} -
By the calculation of S _b , the tracking error signal is calculated by the 3-beam method.
By the calculation of S _e −S _f , the pit signal is obtained by the calculation of S _a + S _b .

With the above-described structure, as in the first embodiment, the focus / offset can be adjusted by moving only the spot P ₁ .

〔The invention's effect〕

The optical pickup device according to the present invention, as described above, a lens system for condensing the light beam from the light source on the record carrier, a light receiving element for detecting the reflected light from the record carrier,
A first diffractive element that is provided in the optical path between the light source and the record carrier and divides the light beam from the light source into a 0th-order diffracted light for detecting a pit signal and a pair of 1st-order diffracted light for detecting a tracking error. And a second diffractive element for guiding the light reflected by the record carrier to the light receiving element, wherein the light receiving element is a first to a fourth element.
The second diffractive element is divided into the first light receiving region and the first light receiving region.
Through the third light incident area, the 0th-order diffracted light reflected by the record carrier and diffracted by the first light incident area has a direction substantially the same as the diffraction direction. The 0th-order diffracted light which is condensed on the dividing line between the first light receiving region and the second light receiving region divided by the dividing line and is reflected by the record carrier, The light diffracted in the light incident area is converged on the first light receiving area and is the 0th-order diffracted light reflected by the record carrier and has the same incident light quantity as that of the second light incident area. The light diffracted by the third light incident area is set so as to be condensed on the second light receiving area, and is a pair of first-order diffracted light reflected by the record carrier. The light diffracted by the second diffraction element is focused on the third light receiving region and the fourth light receiving region, respectively. It is a configuration that is set to so that.

Thus, in adjusting the focus / offset, only the spot formed on the dividing line may be moved and adjusted. Therefore, the focus / offset adjustment can be performed only by rotating the second diffraction element to move the spot formed on the light receiving element in a fixed direction. In addition, since it is not necessary to translate the second diffractive element in this way to perform offset adjustment, it is sufficient that the diffractive element has the same size as the incident beam, thereby reducing the manufacturing cost. It also plays an effect.

[Brief description of drawings]

FIGS. 1 and 2 show an embodiment of the present invention. FIG. 1 is a schematic basic configuration diagram of an optical pickup device, and FIG. 2 (a) is a light incident on a second diffractive element. FIG. 3 is an explanatory view schematically showing a region, FIG. 3B is an explanatory view schematically showing a light receiving region of a light receiving element, and FIGS. 3 and 4 show other embodiments. Is a schematic basic configuration diagram of the optical pickup device, FIG. 4 (a) is an explanatory view schematically showing a light incident area of the second diffraction element, and FIG. 4 (b) is a schematic illustration of a light receiving area of the light receiving element. FIGS. 5 and 6 show conventional examples, FIG. 5 is a schematic basic configuration diagram of the optical pickup device, and FIG. 6 (a) is light incidence of the second diffractive element. Explanatory diagram schematically showing a region, FIG. 7B is an explanatory diagram schematically showing a light receiving region of a light receiving element, FIG. 7 and FIG.
FIG. 7 shows another conventional example, FIG. 7 is a schematic basic configuration diagram of an optical pickup device, and FIG. 8 (a) is an explanatory diagram schematically showing a light incident region of a second diffraction element. FIG. 2B is an explanatory diagram schematically showing the light receiving area of the light receiving element. 1 is a semiconductor laser (light source), 2 is a first diffraction element, 3 ...
Reference numeral 8 is a second diffraction element, 4 is a collimating lens, 5 is an objective lens, 6 is a record carrier, 7 is a light receiving element, and 10 is a lens system.

Claims (1)

[Claims] 1. A lens system for condensing a light beam from a light source on a record carrier, a light receiving element for detecting reflected light from the record carrier, and an optical path provided between the light source and the record carrier. The light beam from the light source is used for pit signal detection.
An optical pickup provided with a first diffractive element that divides the second-order diffracted light into a pair of first-order diffracted light for tracking error detection, and a second diffractive element that guides the light reflected by the record carrier to the light-receiving element. In the apparatus, the light receiving element is divided into four first to fourth light receiving areas, while the second diffractive element is divided into three first to third light incident areas. The 0th-order diffracted light that is reflected by the first light incident area is divided into a first light receiving area and a second light receiving area that are divided by a dividing line that runs in the same direction as the diffraction direction. The 0th-order diffracted light which is focused on the dividing line between the areas and is reflected by the record carrier and diffracted by the second light incident area is collected on the first light receiving area. The 0th-order diffracted light which is reflected by the record carrier and is The light diffracted in the third light incident area having the same amount of incident light as the second light incident area is set to be focused on the second light receiving area, and the record carrier is set. The pair of reflected first-order diffracted lights, which are diffracted by the second diffractive element, are set so as to be focused on the third light receiving region and the fourth light receiving region, respectively. Optical pickup device.