JPH10214435A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable both the reproducing of a high-density disk and the reproducing of a standard density disk. SOLUTION: A polarizing hologram 4 is provided in this device and a central part diffraction area where is formed in the size of area where the influence of spherical abberation in a reflected light from an information recording medium in which the optical characteristic of an objective lens 6 is not properly designed is small and where diffracts an incident reflected light and a peripheral part diffraction area where is formed at the peripheral part of the central part diffraction area and where diffracts the reflected light in a direction different from the diffraction direction by the incident reflected light on the central part diffraction area are formed on the hologram 4. Here, the polarizing hologram 4 and the objective lens 6 are integrally formed so that the center of the objective lens 6 and the center of the central part diffraction area formed on the hologram 4 are not position-shifted when the position of the lens 6 is varied by a tracking or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical pickup device.

[0002]

2. Description of the Related Art Conventionally, a laser beam is condensed to form a laser spot, and the laser spot is applied to a recording member of an information recording medium (hereinafter, referred to as a disk) to form a mark (pit) to form information. 2. Description of the Related Art There is known an optical pickup device that performs recording on a recording member and receives reflected light from the recording member to reproduce information recorded on the recording member. In the following description, an area where a mark exists is called a mark area, and an area between the mark areas is called a space area.

Such a disk has a configuration in which a recording member is sandwiched between transparent members such as plastics. In response to a demand for high-density information in recent years, a high recording density disk called a DVD has been developed. ing.

[0004] The thickness of the transparent member to be irradiated with the laser beam (this transparent member is particularly referred to as a transparent substrate) is 1.2 mm for a disk having a conventional recording density and 0.6 mm for a DVD. It has become.

In this specification, a disk having a conventional recording density is called a standard density disk, and a disk having a higher recording density than the standard density disk is called a high density disk. When you don't need to do that, you simply call it a disk. Therefore, the high density disk is D
Although not limited to VD, this will be described as an example in the following description.

With the development of such high recording density disks,
From the viewpoint of increasing the added value of the optical pickup device, it is desired that information can be recorded or reproduced on a disk having a transparent substrate having a different thickness.

However, since the transparent substrate has a predetermined refractive index as a matter of course, the light condensing characteristics of the laser beam are determined by the optical characteristics of the objective lens and the transparent substrate.

That is, in order to properly reproduce information recorded on a recording member, a laser beam must be focused to about 1.5 μm on a standard density disc and about 1 μm on a high density disc. When laser beams of the same wavelength are focused on disks of different thicknesses by the same objective lens, the focusing characteristics are determined by the objective lens and the transparent substrate, so that spherical aberration increases and an appropriate laser spot can be stored. In some cases, it cannot be formed in a planar shape. For this reason, it has been pointed out that the compatibility between the standard density disk and the high density disk cannot be maintained.

[0009] Such spherical aberration is mainly caused by a change in thickness of the transparent substrate. The spot on the disk surface becomes a blurred spot at the peripheral portion, and the peripheral portion of the reflected light from the disk becomes noise.

Therefore, the objective lens is optimally designed so that the spherical aberration is reduced with respect to a high-density disk having a thin transparent substrate, and the laser beam incident on the objective lens is adjusted with respect to a standard-density disk having a thick transparent substrate. There has been proposed an optical pickup device in which the peripheral portion is shielded from light using an aperture or the like, thereby suppressing the occurrence of spherical aberration.

The above problem will be described in detail with reference to the drawings. 8A and 8B are diagrams showing a focusing state when a laser beam is focused by using an objective lens optimally designed for a high-density disc. FIG. 8A shows a high-density disc HD, and FIG. )
Indicates the case of the standard density disk LD.

As can be seen from FIG. 8A, when the objective lens is optimally designed for the high-density disk HD, all the laser beams L can be focused on the surface of the recording member M. However, such an objective lens can be replaced with a standard density disc L.
When used for D, as shown in FIG. 8B, the focusing property of the peripheral portion of the laser beam L is degraded, and only the substantially central portion of the laser beam L is focused on the recording member M surface. .

That is, the portion near the optical axis of the laser beam L can be favorably focused on the surface of the recording member M, but the peripheral portion of the laser beam L is affected by the spherical aberration.
Light cannot be collected on the surface. Therefore, the peripheral portion is in a blurred state.

FIGS. 9A and 9B are schematic diagrams showing the light intensity distribution of the reflected light when the laser light is satisfactorily focused on the surface of the recording member. Is shown. FIG. 9A shows the light intensity distribution of the reflected light when the laser light L is applied to the space area, and FIG.
The light intensity distribution of the reflected light when the mark area is irradiated with the laser light L is shown.

As can be seen from FIG. 1, a portion Ia having a high light intensity exists in an "island-like" manner in the periphery of the reflected light from the space area. On the other hand, there is no such a portion with high light intensity around the reflected light from the mark area.

The light intensity distribution of the reflected light from the space area and the mark area can be divided by a predetermined circle Ib.
It is possible to identify a region where an island region exists by b, and a region with high light intensity by the circle Ib in the reflected light from the mark region.

When a laser spot scans a track in such a situation, the intensity of the received light signal of the reflected light becomes as shown in FIG.
It becomes like the curve Ic in (c). For comparison, the curve Id shows the signal intensity when the peripheral portion of the reflected light is shielded by an aperture described later.

The signal intensity shows a change showing a minimum value at the center of the mark. Therefore, for example, if a threshold value is set as appropriate, it is possible to identify the mark area and the space area based on whether the signal intensity exceeds the threshold value. Therefore, in order to accurately distinguish between the mark area and the space area,
The condition is that the variation D of the signal strength is large.

However, when the spherical aberration at the peripheral portion of the laser spot becomes large and an unfocused portion occurs on the surface of the recording member M and the laser spot diameter becomes large, for example, the central portion of the laser spot becomes the central portion of the mark area. Irradiates the space area at the periphery of the laser spot. Such a situation becomes more remarkable in the high-density disk HD in which the mark length is shortened.

Therefore, even when a laser spot is applied to the center of the mark area, an island-like area having high light intensity appears at the periphery of the reflected light, and the amount of change in signal intensity is small. turn into. That is, the island region Ia appears in the light intensity distribution in FIG. 9B, and the mark region and the space region cannot be accurately distinguished.

In order to solve such a problem, a method has been proposed in which the peripheral portion of the laser beam incident on the objective lens is shielded by the aperture so that the laser beam L in the peripheral portion is not irradiated on the recording member M. (For example, Japan Society of Applied Physics Fall 1995, 29a-ZA-6 "2
Considerations for Compatibility of Disc Types).

That is, since the peripheral portion of the laser beam incident on the objective lens is shielded by the aperture, the laser beam L applied to the recording member M becomes only the laser beam which can be focused on the recording member M. However, even if spherical aberration occurs in the peripheral portion, all the laser beams applied to the disk are in a focused state. This makes it possible to prevent the variation D of the received light signal intensity from decreasing as shown by the curve Id in FIG. 9C.

[0023]

However, this aperture is unnecessary when reproducing a high-density disc HD.

Therefore, it is conceivable to provide a mechanism for moving the aperture in and out of the optical path, to retract the aperture from the optical path when reproducing the high-density disc HD, and to insert and operate the aperture in the optical path when reproducing the standard-density disc LD. .

However, when the aperture is moved in and out of the optical path, high precision is required for the insertion position of the aperture, and high precision is also required for parts and assembly of the aperture insertion / removal mechanism. There was an unfavorable problem in terms of production and cost.

When the position of the objective lens is shifted due to tracking or the like, the optical axis of the objective lens may deviate from the optical axis of the incident laser light. Therefore, there is a problem that even if the area is limited by the aperture, the area where the area is limited does not enter the area of the objective lens with less spherical aberration.

It is an object of the present invention to provide an optical pickup device in which the peripheral portion of the reflected light can be separated from the central portion without using an aperture and is free from the influence of spherical aberration.

[0028]

According to the first aspect of the present invention, there is provided a laser generating means for emitting a laser beam to an information recording medium having a transparent substrate having a different substrate thickness, and an optical characteristic for at least one of the information recording mediums. In an optical pickup device which is optimally designed and has an objective lens for condensing incident laser light, and a light receiving means for receiving reflected light from an information recording medium and outputting a reproduction signal and a servo signal, an optical system of the objective lens is provided. A central diffraction region, which is formed in the size of a region where the influence of spherical aberration on reflected light from an information recording medium whose characteristics are not optimally designed is small and diffracts incident reflected light, and a periphery of the central diffraction region And a peripheral diffraction region that diffracts the reflected light in a direction different from the diffraction direction of the reflected light incident on the central diffraction region, and
A polarization hologram provided integrally with the objective lens so that the center of the central diffraction region always coincides with the optical axis of the objective lens, and at least the optical characteristics of the objective lens are not optimally designed. When detecting a reproduction signal from the information recording medium, the polarization hologram separates a peripheral portion and a central portion of the reflected light from the information recording medium, and detects the reproduction signal from the reflected light at the central portion. Features.

That is, when a reproduction signal is detected from an information recording medium in which the optical characteristics of the objective lens are not optimally designed,
The optical characteristics of the objective lens are optimally designed so as to detect the reproduction signal and prevent the signal quality from deteriorating without using the peripheral reflected light having a large influence of spherical aberration in the reflected light from the information recording medium. A central diffraction region for diffracting incident reflected light, and a central diffraction region formed around the central diffraction region. A polarization hologram is formed in which a peripheral diffraction region for diffracting reflected light in a direction different from the direction of diffraction by reflected light incident on the central diffraction region is provided. At this time, when the position of the objective lens fluctuates due to tracking or the like, the polarization hologram is formed integrally with the objective lens so that the center of the objective lens does not deviate from the center of the central diffraction region formed on the polarization hologram. It is characterized by the following.

According to a second aspect of the present invention, the light receiving element comprises a light receiving portion for outputting a photoelectric conversion signal as a servo signal and a light receiving portion for outputting the photoelectric conversion signal as a reproduction signal, and is -1 diffracted by the polarization hologram. It is characterized in that one of the light receiving portions receives the diffracted light of the next light and the other light receiving portion receives the +1 order light.

That is, when diffracting the reflected light by the polarization hologram, the reflected light is emitted as diffracted light of ± n order light (n is an integer), and the diffraction direction is different between the + order and the − order. Since the light amount decreases as the size increases,
Utilizing this, the light receiving element is composed of a light receiving part for receiving the +1 order light and a light receiving part for receiving the −1 order light, and one of the light receiving parts is dedicated to the reproduction signal and the other light receiving part is dedicated to the servo signal. It is characterized in that the number of light receiving sections used for a reproduction signal requiring an operation is reduced.

The invention according to claim 3 is characterized in that each light receiving portion in the light receiving element is divided by a dividing line extending in the diffraction direction of the reflected light in the central diffraction region and the peripheral diffraction region.

That is, when the wavelength of the laser beam fluctuates due to environmental temperature fluctuation or the like, a signal generated from the photoelectric conversion signal of each light receiving unit is incident so as not to be affected, and the light receiving element is mounted. In order to reduce the accuracy, each light receiving portion of the light receiving element is divided by a dividing line extending in the diffraction direction of the reflected light in the central diffraction region and the peripheral diffraction region.

According to a fourth aspect of the present invention, the central diffraction region and the peripheral diffraction region are divided into a plurality of diffraction regions to form a plurality of diffraction regions, and the incident reflected light is diffracted in different directions. Are divided into a plurality of parts so as to individually receive diffracted lights from a plurality of diffraction regions.

That is, the central diffraction region and the peripheral diffraction region are divided into a plurality of portions to form a plurality of diffraction regions, and the reflected lights incident on the plurality of diffraction regions are diffracted in different directions. . The light receiving element is divided into a plurality of parts so as to individually receive the diffracted lights from the plurality of diffraction areas, thereby reducing the influence of a change in the incident position of the diffracted lights.

The invention according to claim 5 is characterized in that the laser generating means and the light receiving means are formed integrally.

That is, the apparatus is characterized in that the laser generating means and the light receiving means are integrally formed to reduce the size of the apparatus.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an optical system in an optical pickup device according to the present invention.

The optical pickup device includes a laser generating means for emitting laser light, a collimator lens for converging the laser light from the laser generating means into substantially parallel light, and passing the laser light from the collimating lens 2. A beam splitter for deflecting the reflected light from the disk, a polarization hologram for diffracting the laser light passing therethrough, a １ ／ λ plate for changing the phase of the laser light by ４λ, a numerical aperture for the high-density disk, The objective lens 6 is designed to optimize the optical characteristics such as spherical aberration and focus the incident laser light.
A detection lens 7 for converging the reflected light, a light receiving element 8 for receiving the reflected light converged by the detection lens 7 and outputting a tracking signal, a focus signal and a reproduction signal, a polarization hologram 4 and a １ ／ λ plate 5 as an objective lens 6 has a holding member 9 and the like.

The polarization hologram 4 is, as shown in FIG.
It consists of a circular central diffraction region 41 and a peripheral diffraction region 42 formed around it. The gratings formed in each are formed in a uniform direction, but have different densities (grating intervals). . Therefore, the diffraction angle of the diffracted light diffracted by the central diffraction region 41 and the diffraction angle of the diffracted light diffracted by the peripheral diffraction region 42 become different.

Incidentally, the size of the peripheral diffraction area 42 is formed in accordance with the size of the peripheral area where the influence of spherical aberration on the reflected light from the disk whose optical characteristics of the objective lens 6 are not optimally designed is remarkable. ing.

The light receiving element 8 has two light receiving sections 80 and 85 as shown in FIG.
4 and the light receiving section 85 is divided into light receiving areas 86 to 89, and the photoelectric conversion signals S81 to S84 and S86 are respectively provided.
To S89.

At this time, the directions of the dividing lines of the regions 81 to 84 and 86 to 89 are set to the diffraction directions of the diffracted light on the polarization hologram 4. Thereby, the mounting accuracy of the light receiving element 8 in the diffraction direction is reduced, and even if the wavelength of the laser beam emitted from the laser generating means 1 is slightly changed due to a change in environmental temperature, the photoelectric conversion signals S81 to S84,
It is possible to prevent the signals generated from S86 to S89 from fluctuating.

The operation will be described based on the above configuration. The laser light emitted from the laser generating means 1 is converged into substantially parallel light by the collimating lens 2, passes through the beam splitter 3, and enters the polarization hologram 4.

The laser light emitted from the laser generating means 1 is linearly polarized, and its polarization direction is set so as not to be diffracted by the polarization hologram 4. A hologram having no polarization may be used instead of the polarization hologram 4, but in that case, a part of the laser beam directed to the disk is diffracted, so that the light utilization rate decreases.

Then, the laser beam emitted from the polarization hologram 4 enters the ４λ plate 5 and becomes circularly polarized, enters the objective lens 6, is condensed by the objective lens 6, and irradiates the disk. .

The laser light reflected by the disk passes through the objective lens and is incident again on the λλ plate 5 to convert circularly polarized light into linearly polarized light. The polarization direction is rotated by 90 degrees in the polarization direction of the laser light (outgoing path) pierced from the laser generation means 1, and is diffracted by the polarization hologram 4.

Incidentally, the objective lens 6 forms a laser spot by condensing the laser beam and irradiates the laser spot on a track formed on the recording member. A deviation may occur from the track. In such a case, the position of the objective lens 6 is adjusted by the tracking signal.

Therefore, the polarization hologram 4 is
And the center position of the objective lens 6 and the center position of the polarization hologram 4 are shifted. Such a situation causes the following disadvantages.

That is, the peripheral diffraction region 42 formed on the polarization hologram 4 is formed corresponding to the size of the peripheral portion where the influence of spherical aberration on the reflected light from the standard density disk is remarkable, and the central diffraction region 42 is formed. 41 and peripheral diffraction area 4
The reflected light that has passed through 2 is diffracted in different directions, thereby separating the peripheral portion and the central portion where the influence of spherical aberration on the reflected light is remarkable.

For this reason, if the center position of the objective lens 6 and the center position of the polarization hologram 4 deviate, it becomes impossible to properly separate the central part and the peripheral part in the reflected light.

Therefore, in the present invention, the polarization hologram 4 and the λλ plate 5 are integrated with the objective lens 6 by the holding member 9 so that the center position of the objective lens 6 and the center position of the polarization hologram 4 do not shift. I have.

Therefore, the reflected light from the disk is always properly separated by the polarization hologram 4 into a central portion and a peripheral portion where the influence of spherical aberration is remarkable.

In this way, the central portion and the peripheral portion of the reflected light from the standard density and high density disks are separated and incident on the beam splitter 3, deflected by the beam splitter, and condensed by the detection lens 7. The light is received by the light receiving element 8. Since the reflected light is diffracted by the polarization hologram 4 in directions different from the central part and the peripheral part, the light receiving element 8
The incident position to the light source differs.

Therefore, as described above, the light receiving sections 80 and 85 in the light receiving element 8 are divided into the light receiving section 85 for receiving the central portion of the reflected light and the light receiving section 80 for receiving the peripheral portion.

When the reproduction signal Rf is obtained from the reflected light from the high-density disk, the respective regions 81 to 84, 86
Rf = S81 + S82 + S83 + S84 + S86 + S8 using all photoelectric conversion signals from
7 + S88 + S89, and when the reproduction signal Rf is obtained from the reflected light from the standard density disc, it can be obtained by using the photoelectric conversion signal of only the central portion of the reflected light as Rf = S86 + S87 + S88 + S89. it can. Therefore, since the peripheral portion where the influence of the spherical aberration is remarkable does not contribute to the reproduction signal, the quality of the reproduction signal does not deteriorate.

The focus signal Fo of the high-density disc and the standard-density disc can be obtained by, for example, the beam size method as follows: Fo = (S86 + S89)-(S87 + S88) This allows focusing on a standard density disc in which only the center of the laser beam is correctly focused.

Fo = (S81 + S84)
+ S86 + S89)-(S82 + S83 + S87 + S8
8).

In the case of a high-density disc, the tracking signal Tr is Tr = (S81 + S82)-(S83 + S84) or (S81 + S82 + S86 + S87)-(S83 + S8).
4 + S88 + S89), and for a standard density disc, Tr = (S86 + S87)-(S88 + S89).

In the above description, it has been described that the diffracted lights from the central diffraction area 41 and the peripheral diffraction area 42 of the polarization hologram 4 are separately received by the light receiving sections 80 and 85. In this case, the diffraction by the polarization hologram 4 generally becomes ± nth order diffracted light, and as the order increases, the diffraction angle increases, but the light intensity decreases.

On the other hand, considering the ease of mounting the light receiving element 8, it is preferable that the light receiving element 8 is large, and the wavelength of the laser light emitted from the laser generating means may fluctuate due to environmental temperature changes. Since the diffraction angle of the diffracted light fluctuates with this, it is preferable that the light receiving units 80 and 85 be large so as to cope with the fluctuation of the diffraction angle.

Therefore, when the light receiving portions 80 and 85 receive the diffracted light from the central diffraction region 41 and the peripheral diffraction region 42, the light from the central diffraction region 41 and the light from the peripheral diffraction region 42 are received. It is important to increase the angle with the diffracted light. For this reason, for example, the light receiving unit 80 receives the −1st order light and the light receiving unit 85 receives the + 1st order light by making use of the characteristics of the polarization hologram 4. It is preferable to receive light.

As described above, in the case where the peripheral portion where the spherical aberration is remarkable in the reflected light of the standard density disk type is not used for the reproduced signal, and the reproduced signal is obtained from the reflected light from the high density disk, Since the reflected light is used in both the peripheral portion and the central portion, the relative signal strength does not deteriorate. Therefore, quality degradation of the reproduction signal can be prevented.

Further, in the above description, the optical path separation of the forward and backward paths of the laser beam is performed by the beam splitter 3, but it is also possible to perform the optical path separation utilizing the diffraction by the polarization hologram 4.

FIG. 6 is a schematic configuration diagram of an optical pickup device showing an example of such a configuration. The basic configuration is substantially the same as that of the optical pickup device shown in FIG. 1, except that the beam splitter 3 is not used.

FIG. 6 shows a case where the laser generating means and the light receiving element are integrated, but the present invention is not limited to this. However, by integrating them, there is an advantage that the size of the device is reduced and the handling is easy.

The optical pickup device shown in FIG. 6 diffracts the reflected light incident through the objective lens 6 by the polarization hologram 4. At this time, a central polarization region and a peripheral polarization region 42 are formed in the polarization hologram 4, and the optical paths of the reflected light diffracted through the respective regions are different.

The reflected light having its optical path separated in this way is condensed by the collimating lens 2 and received by the light receiving element 8.

As a result, the reflected light diffracted by the peripheral diffraction area 41 is received by the light receiving section 80, and is reflected by the central diffraction area 41.
The reflected light diffracted by is received by the light receiving section 85, and the above-described reproduction signal and the like can be obtained.

The present invention is not limited to the above-described light receiving element, but may have a configuration as shown in FIG.

The light receiving element 50 shown in FIG. 7A includes light receiving units 51 and 54 for obtaining a servo signal such as a focus signal and a tracking signal and a light receiving unit 5 for obtaining a reproduction signal.
The light receiving units 54 and 59 are used to receive the central part of the reflected light, and the light receiving units 51 and 60 are used to receive the peripheral part of the reflected light.

The light receiving section 51 is divided in a direction perpendicular to the grating direction formed in the polarization hologram 4 to form light receiving areas 52 and 53, and the light receiving section 54 is divided in a direction perpendicular to the light receiving areas 55 to 58. Has formed. Then, the photoelectric conversion signals S52, S53, S55 to S
58, S59 and S60 are output.

As a result, the reproduced signal Rf can be obtained by Rf = S59 + S60 for a high-density disc, and can be obtained by Rf = S59 for a standard-density disc.

The focus signal Fo can be determined by the beam size method for both the high-density disc and the standard-density disc according to the following equation: Fo = (S55 + S57)-(S56 + S58).

In the case of a high-density disc by the push-pull method, the tracking signal Tr is Tr = S52-S53 or (S52 + S55 + S5
6)-(S53 + S57 + S58), and for a standard density disc, Tr = (S55 + S56)-(S57 + S58).

The tracking signal by the phase method is
As shown in FIG. 7B, the light receiving section 59 corresponding to a high frequency is divided into four to form regions 61, 62, 63, and 64, and the photoelectric conversion signals S61, S62, S63, and S64 at that time are used. It is obtained by comparing the phases of Tr = S61 + S63 and S62 + S64.

Further, the present invention is not limited to the polarization hologram 4 having the above-described configuration, but may have the configuration shown in FIG. In this case, the light receiving element preferably has a configuration shown in FIG.

In the polarization hologram 20 shown in FIG. 4, a region corresponding to the central diffraction region 41 is formed by a semi-circular diffraction region 22.
And diffraction regions 23 and 24 having a quarter circle shape, and regions corresponding to the peripheral diffraction region 42 are diffraction regions 21 and 24.
5 and 26.

FIG. 5 shows a light receiving element 30 configured to correspond to the configuration of the polarization hologram 20.
The light receiving element 30 is formed by three light receiving portions 31, 32, and 35. The light receiving portion 32 is divided into two light receiving regions 33 and 34, and the light receiving portion 35 is divided into four light receiving regions 36 to 39. Thereby, each area 31, 33, 34, 3
6 to 39, the photoelectric conversion signals S31, S33, S34,
S36 to S39 are output.

The diffracted light diffracted by the diffraction area 21 is received by the light receiving section 31, the diffraction area 22 is the light receiving section 32, the diffraction area 23 is the light receiving area 37, 24 is 38, and 25 is 36.
26 is received at 39.

In the case of a high-density disc, the reproduced signal Rf is Rf = S31 + (S33 + S34) + S36 + S37 +
S38 + S39, and in the case of a standard density disc, Rf = (S33 + S34) + S37 + S38, so that the peripheral portion of the reflected light from the standard density disc does not contribute to the reproduction signal.

The reproduction signal Rf may be obtained by the following calculation. That is, for a high-density disc, Rf = S31 + (S33 + S34), and for a standard-density disc, Rf = S33 + S34.

The focus signal Fo is obtained by the knife edge method according to the following equation: Fo = S33-S34

Further, the tracking signal Tr can be obtained by Tr = (S36 + S37)-(S38 + S39) for a high-density disc, and can be obtained by Tr = S37-S38 for a standard-density disc.

As described above, the polarization hologram 20 is divided into a plurality of diffraction regions, and the light receiving element is divided so as to individually receive the diffracted light from each region. Can be suppressed to a small extent even if the value fluctuates.

When the diffracted light from one diffraction area is received over a plurality of light receiving areas, the signals of the plurality of light receiving areas are calculated by the shift of the light receiving element due to the aging or the environmental temperature change and the fluctuation of the diffraction angle. The obtained signal fluctuates. Also, high accuracy is required for the positional relationship of the light receiving elements.

If the diffracted light from one diffraction area is received without straddling a plurality of light receiving areas, even if the light receiving element is displaced or the diffraction angle fluctuates, the light is not received from the light receiving area. Since there is no need to do so, it is less susceptible to aging and environmental temperature fluctuations, and adjustment is easy.

[0088]

According to the first aspect of the present invention, the optical characteristics of the objective lens are formed in the size of the area where the influence of the spherical aberration on the reflected light from the information recording medium for which the optimum design is not optimally made is small, and A central diffraction region for diffracting reflected light, and a peripheral diffraction region formed around the central diffraction region and diffracting the reflected light in a direction different from the direction of diffraction by the reflected light incident on the central diffraction region. When the position of the objective lens fluctuates due to tracking or the like, the center of the objective lens is
Since the polarization hologram is formed integrally with the objective lens so that the center of the central diffraction region formed on the polarization hologram does not deviate from the center, the optical signal of the objective lens is not optimally designed. When detecting the reproduction signal, it is possible to detect the reproduction signal without using the reflected light of the peripheral part where the influence of the spherical aberration in the reflected light from the information recording medium is large, and to prevent the deterioration of the signal quality.

According to the second aspect of the invention, when the reflected light is diffracted by the polarization hologram, the reflected light is ±
The light is emitted as diffracted light of the nth order light (n is an integer), and the diffraction direction is different between the + order and the − order, and the light amount decreases as the order increases.
A high-frequency operation is required because it is composed of a light receiving unit for receiving primary light and a light receiving unit for receiving -1st light, and one light receiving unit is dedicated to reproduction signals and the other light receiving unit is dedicated to servo signals. It is possible to reduce the number of light receiving sections used for the reproduction signal, and to reduce the cost of the device.

According to the third aspect of the present invention, each light receiving portion of the light receiving element is divided by the dividing line extending in the diffraction direction of the reflected light in the central diffraction region and the peripheral diffraction region. When the wavelength of the laser beam fluctuates, the reflected light incident on the light receiving unit is prevented from deviating from the light receiving unit, and the mounting accuracy of the light receiving element can be reduced.

According to the fourth aspect of the invention, the central diffraction region and the peripheral diffraction region are divided into a plurality of portions to form a plurality of diffraction regions, and the reflected light incident on the plurality of diffraction regions is Diffraction in different directions. Then, since the light receiving element is divided into a plurality of parts so as to individually receive the diffracted lights from the plurality of diffraction areas, it is possible to reduce the influence when the incident position of the diffracted lights fluctuates.

According to the fifth aspect of the present invention, since the laser generating means and the light receiving means are integrally formed, the size of the apparatus can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical system in an optical pickup device applied to the description of an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a polarization hologram.

FIG. 3 is a diagram showing a configuration of a light receiving element.

FIG. 4 is a diagram showing another configuration of the polarization hologram.

FIG. 5 is a diagram showing another configuration of the light receiving element.

FIG. 6 is a schematic configuration diagram of an optical system in another configuration of the optical pickup device.

FIG. 7 is a diagram showing another configuration of the light receiving element.

FIG. 8 is a diagram illustrating light-collecting characteristics depending on a difference in the thickness of a transparent substrate.

FIG. 9 is a diagram for explaining an effect obtained by shielding a peripheral portion of reflected light.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser generating means 2 collimating lens 3 beam splitter 4, 20 polarization hologram 5 1 / 4λ plate 6 objective lens 7 detection lens 8, 30, 50 light receiving element

Claims (5)

[Claims] 1. A laser generating means for emitting a laser beam to an information recording medium having a transparent substrate with a different substrate thickness, and an optical characteristic which is optimally designed for at least one of the information recording media to collect an incident laser beam. In an optical pickup device having an objective lens that emits light and light receiving means that photoelectrically converts reflected light from the information recording medium and outputs a reproduction signal and a servo signal, the optical characteristics of the objective lens are not optimally designed. A central diffraction region is formed in a size of an area where the influence of spherical aberration on the reflected light from the information recording medium is small, and diffracts the incident reflected light; A peripheral diffraction region that diffracts the reflected light in a direction different from the diffraction direction of the reflected light incident on the partial diffraction region, and is provided integrally with the objective lens. A polarization hologram provided so that the center of the central diffraction region always coincides with the center of the objective lens, and detects a reproduced signal from the information recording medium in which at least the optical characteristics of the objective lens are not optimally designed. At this time, the peripheral part and the central part in the reflected light from the information recording medium are separated by the polarization hologram,
An optical pickup device for detecting a reproduction signal from the reflected light at the central portion. 2. The light-receiving element has a light-receiving unit that outputs a photoelectric conversion signal as a servo signal and a light-receiving unit that outputs a photoelectric conversion signal as a reproduction signal.
2. The optical pickup device according to claim 1, wherein the -1st-order diffracted light of the reflected light diffracted by the polarization hologram is received, and the other light-receiving unit is arranged to receive the + 1st-order light. . 3. Each of the light receiving sections in the light receiving element is:
3. The optical pickup device according to claim 2, wherein the light is divided by a dividing line extending in a diffraction direction of the reflected light in the central diffraction region and the peripheral diffraction region. 4. The central diffraction region and the peripheral diffraction region are divided into a plurality of diffraction regions to form a plurality of diffraction regions, and diffract incident reflected light in different directions, respectively. 2. The device according to claim 1, wherein the light beam is divided into a plurality of light beams so as to individually receive the diffracted light from the diffraction region.
An optical pickup device as described in the above. 5. The apparatus according to claim 1, wherein said laser generating means and said light receiving means are formed integrally.
The optical pickup device according to claim 1.