JP3469720B2 - Optical pickup device - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an audio CD.
The present invention relates to an optical pickup device which is used for a CD-ROM drive device and a DVD device for a device and a computer, and particularly to reduce a wavefront aberration of an optical element by inclining an air layer of a hologram optical element using a diffraction grating.

[0002]

2. Description of the Related Art The structure of a conventional optical pickup device is shown in FIG.
Shown in. This optical pickup device includes an LD (laser diode) 601 with a PD (photodetector), a hologram optical element 602 provided with a diffraction grating, a collimator lens 603, and an objective lens 604 attached to an actuator. . Reference numeral 605 is an optical disk.

The hologram optical element 602 includes a quarter-wave plate 606 and two prisms 607 to 608.
And a parallel plate 609 having diffraction gratings on both sides.

As the diffraction grating, for example, a diffraction grating having an equal pitch is provided on the LD side, and a plurality of grating areas having different grating pitches and grating directions are present on the optical disk 605 side.

Next, the operation of the optical pickup device configured as described above will be described. The light emitted from the LD 601 is incident on the hologram optical element 602, and is incident on the diffraction grating by a parallel plate 609 having diffraction gratings formed on both sides, which is one of the constituent elements of the hologram optical element 602. If this diffraction grating is a polarization-dependent diffraction grating,
The light utilization efficiency is increased. Incident light is a quarter-wave plate 60
Circularly polarized light by 6 and collimator lens 603
Then, it becomes parallel light and is condensed on the optical disk 605 by the objective lens 604.

The reflected light from the optical disk 605 returns via the objective lens 604 and the collimator lens 603, and is 90 ° with respect to the polarization direction of the original LD light by the quarter-wave plate 606.
The polarization direction is rotated, that is, the polarization direction is orthogonal to the original polarization direction. Further, this reflected light is diffracted by the diffraction grating, and each diffracted light enters each PD.

Further, as shown in FIG. 7, the diffraction grating on the side of the optical disk 605 has about half of the LD light in the diffraction grating (region 1) having a grating direction perpendicular to the polarization direction after the LD emission.
One quarter of the light goes to the diffraction grating (region 2) which has a grating direction slightly tilted from the direction perpendicular to the polarization direction, and the remaining one quarter to the diffraction grating (region 3) which has a grating direction tilted to the opposite side. Incident.

On the other hand, the diffraction grating on the LD side is parallel to the grating direction of the area 1 on the disk side, and is applied to a partial area of the parallel plate. This diffraction grating has a function of suppressing the position fluctuation of the returning optical path due to the wavelength fluctuation by diffracting the returning light for the second time.

The PD is divided into four as shown in FIG. Diffracted light from area 1 is divided into two PDs in the center.
It is incident near the center division of (2). By looking at the difference signal of the two-divided PD, the focus signal for the optical disc can be obtained. This focusing utilizes a method called knife edge method.

On the other hand, the diffracted light from the regions 2 and 3 of the diffraction grating is incident on PDs (1) and (3), and a tracking signal by the push-pull method can be obtained.

[0011]

In the conventional optical pickup device as described above, the hologram optical element has two elements.
Since the parallel plate is sandwiched by two prisms, the wavefront aberration (especially astigmatism) of the element is reduced. However, as shown in FIG. 7, since the hologram optical element is arranged in the divergent optical path, there is a problem that astigmatism occurs only with the obliquely arranged flat plate.

Further, the diffraction grating portion is located at a recessed portion so as not to directly touch the inclined surface of the prism. This is because the difference in refractive index between air and the diffraction grating portion is used. That is, this air layer is essential for the function of the hologram optical element. However, when the hologram optical element is manufactured, the air layer becomes thicker, or the air layer (especially from the state in which the plane of the prism and the plane of the parallel plate facing the plane of the prism are parallel to each other is shown in FIG. There is a problem that the wavefront aberration becomes large when it is tilted toward θ (+) to the arrow side.

The present invention has been made in view of the above, and a first object thereof is to reduce the wavefront aberration of an optical element including an optical pickup device using a diffraction grating.

A second object of the present invention is to reduce the wavefront aberration of the optical element including the diffraction grating in the optical pickup device using the diffraction grating and to make the diffraction grating easily by the two-beam interference method. .

A third object is to reduce the wavefront aberration of the optical element including the diffraction grating in the optical pickup device using the diffraction grating without taking a special method when exposing the master.

Further, without taking a special method when exposing the master, the wavefront aberration of the optical element including the diffraction grating is reduced by the optical pickup device using the diffraction grating, and the diffraction is facilitated by the two-beam interference method. A fourth objective is to be able to fabricate a grating.

[0017]

In order to achieve the above object, an optical pickup device according to a first aspect of the present invention includes a first prism through which emitted light emitted from a laser diode passes, and the first prism. A second prism through which the outgoing light that has passed through is transmitted, and a surface having the diffraction grating in the optical path of the outgoing light that passes through between the slopes of the first prism and the second prism. Are disposed so as to face the inclined surface with a predetermined inclination angle, and a predetermined pair of wedges are provided between the inclined surfaces of the first prism and the second prism and the surface having the diffraction grating. A parallel flat plate forming an air layer.

That is, in the optical path of the light emitted from the laser diode that passes through the first and second prisms, a parallel plate having a diffraction grating is used as the first surface with the diffraction grating.
Since the air layer of the hologram optical element is inclined in a predetermined direction by arranging the inclined surfaces of the second prism with a predetermined inclination angle so as to face each other in a non-parallel manner, a pair of wedge-shaped air layers are used. The wavefront aberration of the hologram optical element is reduced.

An optical pickup device according to a second aspect of the present invention is the optical pickup device according to the first aspect, wherein the diffraction grating has a stamper formed from a master having a predetermined convex portion shape other than the area of the diffraction grating. It is characterized by being manufactured and duplicated from the stamper to the parallel plate.

That is, when the master is exposed to light, the diffraction grating shape portion is formed to have a predetermined convex portion shape other than the area of the diffraction grating so that the air layer of the hologram optical element has a predetermined shape. Since it tilts in the direction, the wavefront aberration of the hologram optical element is reduced by the pair of wedge-shaped air layers.

An optical pickup device according to a third aspect is the optical pickup device according to the first aspect,
The diffraction grating is formed in a protrusion shape on the resist surface by forming the diffraction grating on a substrate coated with a resist by a two-beam interference method and uniformly exposing the resist diffraction grating and a predetermined area using a mask. It is characterized in that the parallel plate is duplicated by a stamper obtained by peeling the resist substrate by performing a sputtering process and an electroforming process on the resist substrate using a resist substrate having a remaining portion.

That is, when the master is exposed, the diffraction grating shape portion is produced by the two-beam interference method, and then the mask is exposed uniformly, leaving the diffraction grating portion, and the air layer of the hologram optical element is inclined in a predetermined direction. Therefore, the wavefront aberration of the hologram optical element is reduced by the pair of wedge-shaped air layers.

An optical pickup device according to a fourth aspect is the optical pickup device according to the first aspect, wherein the diffraction grating is a stamper provided with a groove-shaped region at a predetermined position other than the region of the diffraction grating. It is characterized by being replicated on a parallel plate.

That is, by forming a stamper at a predetermined position in the vicinity of the diffraction grating after the stamper is manufactured, a convex shape is present in the copy from this stamper, so that the air layer of the hologram optical element has a predetermined shape. Since it tilts in the direction, the wavefront aberration of the hologram optical element is reduced by the pair of wedge-shaped air layers.

An optical pickup device according to a fifth aspect is the optical pickup device according to the first aspect, wherein the diffraction grating is produced by a two-beam interference method on a resist-coated glass master. After the sputter process and the electroforming process, the glass master is peeled off, and is duplicated with a stamper that is processed into a groove shape at a predetermined position near the diffraction grating.

That is, by forming a groove at a predetermined position of the stamper, the air layer of the hologram optical element is tilted in a predetermined direction, the wavefront aberration of the hologram optical element is reduced, and the diffraction grating uses the two-beam interference method. Since it is manufactured by, it can be easily manufactured.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION An optical pickup device of the present invention will be described below with reference to the accompanying drawings, referring to [First Embodiment], [Second Embodiment], [Third Embodiment], and [Fourth Embodiment]. It will be described in detail in order.

[Embodiment 1] FIG. 1 is an explanatory diagram showing a configuration of a hologram optical element of an optical pickup device. Reference numerals 101 and 102 are prisms, and 103 is a parallel plate provided with a diffraction grating.

When a diffraction grating is provided near the center of the parallel plate 103, the air layer is inclined, so that a convex portion is formed at the obtuse angle side of the prisms 101 to 102, for example. This convex shape can be formed in the exposure process of the master.

For example, a diffraction grating is formed on a resist-coated glass substrate (resist master). The diffraction grating may be produced by either electron beam drawing or two-beam interference. Next, a mask that shields the diffraction grating region and a partial region is used to perform uniform exposure, and this partial region remains as a convex shape on the resist surface. Then, a stamper is produced from this resist master.

The stamper has a surface shape obtained by reversing the surface shape of the master. Therefore, the stamper has a concave shape at a predetermined position. When a 2P resin (photopolymer) or the like is duplicated from the stamper to the parallel plate 103, a convex shape is formed on a part of the surface of the 2P resin. When the slopes of the prisms 101 to 102 are pressed against this surface, the region of the diffraction grating and the air layer formed by the prism slopes are inclined at a predetermined angle.

As one specific example, the length of the parallel plate 103 is 5 mm, the diffraction grating is provided at a position 1.5 μm deeper from the surroundings at approximately the center of the parallel plate 103, and the height of the convex portion is 3 μm. Suppose there is. At this time, the thickness of the air layer is about 3 μm, and the inclination is −2 minutes.

FIG. 2 shows the relationship between the air layer and the wavefront aberration. Here, the plus direction of θ represents the counterclockwise direction in FIG. At this time, the wavefront aberration is 0.002 from FIG.
λ, and wavefront aberration when the air layers are parallel 0.0
It becomes smaller than 10λ.

[Embodiment 2] Using a mask for producing a diffraction grating at a predetermined position and a predetermined region, a resist is exposed by a two-beam interference method to produce a diffraction grating. After the exposure of all the diffraction gratings is completed, a mask that shields the diffraction grating area and the area to be left as the convex shape is prepared. By uniformly exposing (uniformly exposing) in this state, a convex shape is formed as a result.

This will be specifically described with reference to FIG.
First, in FIG. 3A, when a diffraction grating is formed on the resist 300, a mask 302 that transmits only a necessary area of the diffraction grating for forming the diffraction grating and shields the other areas is used, and a glass is formed by a two-beam interference method. A diffraction grating is formed at a position within about 4.5 μm from the surface of the resist applied on the substrate 301.

When exposing a plurality of types of diffraction gratings,
The exposure is performed by changing the condition of the two-beam interference and the position of the mask 302. Next, in FIG. 3B, the portion to be left as a convex portion and the diffraction grating portion are replaced with a mask 303 which shields light. It is irradiated with light (only one light beam is required) almost uniformly,
Exposure for digging down to about 3 μm is performed.

When the fabrication of the master is completed, next, as shown in FIG.
In (c), this master is sputtered with Ni. Further, the Ni layer is thickened by electroforming.
Then, for example, apply an adhesive to an aluminum plate and
Glue the faces together. After the adhesive is cured, the stamper 304 is completed by peeling off only the glass substrate 301.

The surface shape of the stamper 304 is the reverse of the shape of the master. 2P resin (photo trimmer) is dropped on the stamper 304, a glass substrate is placed on the stamper 304, and ultraviolet rays are irradiated to peel the glass substrate.

The surface shape of the 2P resin transferred to the glass substrate is the surface shape of the stamper 304 inverted. Therefore, the surface shape of the master is duplicated. That is, the convex portion on the 2P surface is about 3 μm, and the diffraction grating is located about 4.5 μm below the convex portion and about 1.5 μm below the 2P surface other than the convex portion. When the slopes of the prisms 101 to 102 are pressed against the surface having this surface shape, the convex portion of the 2P surface and the other side are in contact with the slope, and a structure having an air layer as shown in FIG. 1 is obtained. .

When the length of the 2P substrate is 5 mm, the thickness of the air layer is about 3 μm, and the inclination is about −2 minutes. The wavefront aberration at this time is 0.002λ from FIG. 2, which is smaller than the wavefront aberration of 0.010λ when the air layers are parallel.

Strictly speaking, the inclination at which the wavefront aberration of the hologram optical element due to the air layer is minimized is also affected by the thickness of the air layer. The slope at which the wavefront aberration becomes the minimum value as the air layer becomes larger shifts to the negative side. When the thickness of the air layer is 3 μm and the inclination is about −2 minutes, the wavefront aberration becomes the minimum, but this is only an example, and the air layer does not necessarily have to be 3 μm.

FIG. 4 is an explanatory diagram showing the structure of an optical pickup device using the hologram optical element manufactured and structured as described above. This optical pickup device
An LD (laser diode) 401 with a PD (photodetector), a hologram optical element 402 provided with a diffraction grating, a collimator lens 403, and an objective lens 40.
4 and. Reference numeral 405 is an optical disk.

The hologram optical element 402 includes a quarter wavelength plate 406 and two prisms 101 to 102.
And the parallel plate 103 are joined in the state shown in FIG.

Next, the operation of the optical pickup device configured as described above will be described. The light emitted from the LD 401 enters the hologram optical element 402 and enters the parallel plate 103 having diffraction gratings formed on both sides, which is one of the constituent elements of the hologram optical element 402. If this diffraction grating is a polarization-dependent diffraction grating, most of the light directed to the optical disc 405 can be transmitted. The incident light becomes circularly polarized light by the quarter-wave plate 406, and becomes parallel light by the collimator lens 403.
It is focused on the optical disc 405 by the objective lens 404.

The reflected light from the optical disk 405 returns via the objective lens 404 and the collimator lens 403, and is 90 ° from the polarization direction of the original LD light by the quarter-wave plate 406.
The polarization direction is rotated, that is, the polarization direction is orthogonal to the original polarization direction. Further, this reflected light is diffracted by the diffraction grating, and each diffracted light enters each PD. In this embodiment, the knife edge method is used for focusing and the push-pull method is used for tracking. However, other methods may of course be used as long as they do not affect the effects of the present invention.

[Third Embodiment] A stamper is manufactured from a master on which a predetermined diffraction grating is manufactured. The diffraction grating is manufactured by electron beam drawing, two-beam interference, or another method. The stamper has a surface shape that is the reverse of the shape of the master. The stamper is processed into a groove at a predetermined position. This groove processing may be performed by cutting, laser processing or any processing method.

For example, the length of the parallel plate 103 is 5 mm
Then, the diffraction grating is provided at a position 1.5 μm deeper from the surroundings at approximately the center of the parallel plate 103, and the height of the convex shape is 3
μm. At this time, the thickness of the air layer is about 3 μm
Then, the inclination becomes -2 minutes.

Since the relationship between the air layer and the wavefront aberration is as shown in FIG. 2, the wavefront aberration at this time is 0.
002λ, which is smaller than the wavefront aberration of 0.010λ when the air layers are parallel.

[Fourth Embodiment] FIGS. 5A to 5C are explanatory views showing a manufacturing process of a diffraction grating according to a fourth embodiment. In FIG. 5, a resist 502 is applied to a glass substrate 501, a mask 503 for producing a diffraction grating is used, and a diffraction grating is produced only in a predetermined region by a two-beam interference method. The diffraction grating is formed at a depth of about 1.5 μm from the resist surface. After the Ni sputter process and the electroforming process, the Ni surface is adhered to an aluminum plate or the like, the glass substrate 501 is peeled off, and a stamper 504 is made. When the parallel plate 103 used for the hologram optical element has a length of 5 mm, a groove of about 3 μm is cut on the stamper 504 at a portion corresponding to the end of the parallel plate 103.

The stamper 504 is not required to be cut to form a groove having a depth of about 3 μm. For example,
Laser processing such as carbon dioxide laser or excimer laser may be used.

The surface shape including the diffraction grating of 2P resin reproduced by the surface shape of this stamper has a convex shape of 3
The ridge is raised by .mu.m, and the diffraction grating portion is recessed by 1.5 .mu.m. When the inclined surface of the prism is in contact with the surface having this surface shape, the thickness of the air layer near the diffraction grating is about 3 μm, and the inclination thereof is −2 minutes.

Therefore, as shown in the graph of FIG.
The wavefront aberration is 0.002λ, which is smaller than the wavefront aberration of 0.010λ when the air layers are parallel.

Further, strictly speaking, as in the first embodiment,
The inclination that minimizes the wavefront aberration of the hologram optical element due to the air layer is also affected by the thickness of the air layer. The larger the air layer, the more the inclination when the wavefront aberration becomes the minimum value shifts to the negative side. The wavefront aberration is minimized when the thickness of the air layer is 3 μm and the inclination is −2 minutes, but this is only an example, and the air layer does not necessarily have to be 3 μm.

Therefore, also in this embodiment,
It can be used for the hologram optical element 402 of the optical pickup device as described in FIG. As a result, the number of optical components can be reduced and the device can be easily assembled.

[0055]

As described above, according to the optical pickup device (claim 1) of the present invention, the first and second optical pickup devices are provided.
In the optical path of the light emitted from the laser diode which passes through the prism, a parallel plate having a diffraction grating is provided on the inclined surface of the first and second prisms with a predetermined inclination angle. By arranging to face each other non-parallel,
Since the air layer of the hologram optical element tilts in a predetermined direction,
The pair of wedge-shaped air layers reduces the wavefront aberration of the hologram optical element.

Further, according to the optical pickup device (Claim 2) of the present invention, when the master is exposed, the diffraction grating shape portion is uniformly exposed with the mask leaving the diffraction grating portion and the convex portion shape. By forming the convex shape, the air layer of the hologram optical element tilts in a predetermined direction, so that the wavefront aberration of the hologram optical element is reduced by the pair of wedge-shaped air layers.

According to the optical pickup device of the present invention (claim 3), when the master is exposed, the diffraction grating shape portion is produced by the two-beam interference method, and then the diffraction grating portion is left with a mask. Likewise, the air layer of the hologram optical element tilts in a predetermined direction, so that the wavefront aberration of the hologram optical element can be reduced by the pair of wedge-shaped air layers, and the diffraction grating can be easily formed by the two-beam interference method. It becomes possible to produce.

According to the optical pickup device of the present invention (claim 4), the stamper is formed and then groove-shaped processing is performed at a predetermined position in the vicinity of the diffraction grating. Since there is a partial shape, the air layer of the holographic optical element tilts in a predetermined direction, and therefore an optical element including a diffraction grating is used in an optical pickup device using the diffraction grating without taking a special method when exposing the master. The wavefront aberration can be reduced.

Further, according to the optical pickup device of the present invention (claim 5), the air layer of the hologram optical element is tilted in a predetermined direction by forming a groove at a predetermined position of the stamper, and the hologram optical element is inclined. Wavefront aberration is reduced and the diffraction grating is made by the two-beam interference method, so there is no need to take a special method when exposing the master,
The optical pickup device using the diffraction grating can reduce the wavefront aberration of the optical element including the diffraction grating, and the diffraction grating can be easily manufactured by the two-beam interference method.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a hologram optical element of an optical pickup device according to an embodiment.

FIG. 2 is a graph showing the relationship between the inclination of the air layer and the wavefront aberration according to the embodiment.

FIG. 3 is an explanatory diagram showing a manufacturing process of the diffraction grating according to the second embodiment.

FIG. 4 is an explanatory diagram showing a configuration of an optical pickup device using the hologram optical element according to the embodiment.

FIG. 5 is an explanatory diagram showing a manufacturing process of the diffraction grating according to the fourth embodiment.

FIG. 6 is an explanatory diagram showing a configuration of an optical pickup device using a conventional hologram optical element.

FIG. 7 is an explanatory diagram showing a state of a diffraction grating on the disc side.

FIG. 8 is an explanatory diagram showing a split state of a PD and incidence of diffracted light.

[Explanation of symbols]

101,102 prism 103 parallel plate 302,303,503 mask 304,504 Stamper 402 Holographic optical element

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Claims (5)

(57) [Claims] 1. A first prism through which emitted light emitted from a laser diode is transmitted, a second prism through which emitted light transmitted through the first prism is transmitted, the first prism and the second prism. In the optical path of the transmitted outgoing light between the inclined surface of the prism and the prism, the surface having the diffraction grating is disposed so as to face the inclined surface with a predetermined inclination angle, and A predetermined distance between the inclined surfaces of the prism and the second prism and the surface having the diffraction grating.
An optical pickup device comprising: a pair of parallel flat plates that form a pair of wedge-shaped air layers. 2. The stamper is manufactured from a master having a predetermined convex shape in a region other than the diffraction grating region,
The optical pickup device according to claim 1, wherein the optical pickup device is duplicated from the stamper to the parallel plate. 3. The diffraction grating is formed by forming the diffraction grating by a two-beam interference method on a substrate coated with a resist and uniformly exposing the resist by using a mask that shields the resist diffraction grating and a predetermined region. Characterized in that it is replicated to the parallel plate by a stamper obtained by using a resist substrate having a protruding portion left on its surface and subjecting the resist substrate to a sputtering process and an electroforming process to peel off the resist substrate. The optical pickup device according to claim 1. 4. The light according to claim 1, wherein the diffraction grating is duplicated into a parallel plate by a stamper having groove-shaped regions at predetermined positions other than the diffraction grating region. Pickup device. 5. The diffraction grating is produced by forming the diffraction grating on a resist-coated glass master by a two-beam interference method, peeling the glass master after sputtering and electroforming.
The optical pickup device according to claim 1, wherein the optical pickup device is duplicated by a stamper that is processed into a groove shape at a predetermined position near the diffraction grating.