JPH10208289A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce high and standard density disks. SOLUTION: The peripheral section of the reflected light beams from the information recording medium, to which the optical characteristics of an objective lens are not optimally designed, is greatly affected by the spherical aberration effect. A passing light quantity control means, which has a light quantity control member 114 having an aperture window 113, is provided between a detection lens 10 and a light receiving means 20 so that the peripheral section is not received by the means 20 and the quality of the reproduced signals is improved. When reflected light beams from the medium are made incident on the means 20, the position of the member 114 is controlled by a prescribed position 121 of the lens 10 side, the peripheral section, in which the adverse effect caused by the spherical aberration of the reflected light beams is great, is shielded and the beams only pass through a central section.

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 1.0 μm on a high density disc. When laser beams of the same wavelength are focused on disks having different transparent substrate thicknesses by the same objective lens, an appropriate laser spot cannot be formed on the recording member surface because the focusing characteristics are determined by the objective lens and the transparent substrate. In such a case, spherical aberration increases. For this reason, it has been pointed out that the compatibility between the standard density disk and the high density disk cannot be maintained.

The deterioration of the spherical aberration is mainly caused by a change in the thickness of the transparent substrate, so that the peripheral portion of the laser spot on the disk surface is blurred, and the non-information signal is reflected on the peripheral portion of the reflected light. Light will be present.

Therefore, an objective lens is optimally designed to minimize spherical aberration for a high-density disk having a thin transparent substrate, and a laser beam incident on the objective lens is applied to a standard-density disk having a thick transparent substrate. An optical pickup device has been proposed in which the peripheral portion of the optical pickup 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. 5A and 5B are diagrams showing a focusing state when a laser beam is focused using an objective lens optimally designed for a high-density disc. FIG. 5A shows a high-density disc HD, and FIG. )
Indicates the case of the standard density disk LD.

As can be seen from FIG. 5A, when the objective lens is optimally designed for the high-density disk HD, all the laser beams L can be focused on the recording member M surface. However, such an objective lens can be replaced with a standard density disc L
When used for D, as shown in FIG. 5B, the focusing property of the peripheral portion of the laser beam L is deteriorated, 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. 6A and 6B 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. 6A 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 the laser spot scans the track in such a situation, the intensity of the received light signal of the reflected light is 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. 6B, 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 change amount D of the received light signal intensity from decreasing as shown by the curve Id in FIG.

[0023]

However, this aperture is not required when reproducing a high-density disk DH.

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.

It is therefore 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.

[0027]

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. An objective lens that is optimally designed and condenses the incident laser light, a detection lens that converges the reflected light from the information recording medium, and receives the reflected light converged by the detection lens to generate a reproduction signal and a servo signal. An optical pickup device having a light receiving means for outputting
The position is variably provided between the detection lens and the light receiving means,
In addition, when a reflected light from an information recording medium having an optimally designed optical characteristic of an objective lens is provided, the light receiving member is provided at a predetermined position on the light receiving means side. When the reflected light from the information recording medium whose optical characteristics of the objective lens are not optimally designed is incident, the reflected light is positioned at a predetermined position on the detection lens side. Further, there is provided a passing light amount restricting means for blocking a peripheral portion, which is largely affected by the spherical aberration of the reflected light, with an opening window and passing only the central portion.

That is, since the peripheral portion of the reflected light from the information recording medium in which the optical characteristics of the objective lens are not optimally designed is greatly affected by the spherical aberration, the peripheral portion is not received by the light receiving means so that the reproduction signal or the like is not generated. In order to improve the signal quality of
A light quantity limiting member having a light quantity limiting member having an opening window is provided. When the reflected light from the information recording medium in which the optical characteristic of the objective lens is optimally designed enters, the position of the light amount limiting member is positioned at a predetermined position on the light receiving means side, and the reflected light is blocked by the opening window. Without passing through,
When reflected light from an information recording medium whose optical characteristics of the objective lens are not optimally designed is incident, the position of the light amount limiting member is positioned at a predetermined position on the detection lens side to reduce the spherical aberration of the reflected light. The peripheral portion having a large influence protrudes from the opening window, so that the peripheral portion is shielded from light and only the central portion is passed.

According to a second aspect of the present invention, there is provided a concave lens disposed between the detecting lens and the passing light amount restricting means to increase the focal length of the detecting lens.

That is, a concave lens is provided between the detection lens and the passing light quantity limiting means to increase the movable amount of the light quantity limiting member, thereby reducing the positional accuracy and the like of the light quantity limiting member.

The invention according to claim 3 is characterized in that the opening window of the light quantity limiting member is formed in a tapered shape so that the opening diameter increases from the detection lens side to the light receiving means side.

That is, by forming the aperture window of the light quantity limiting member in a tapered shape so that the aperture diameter increases from the detection lens side to the light receiving means side, the reflected light is prevented from being largely diffracted by the aperture window. It is characterized by having done.

[0033]

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 3 for deflecting the reflected light from the disk, a λλ plate for changing the polarization direction of the laser light by 45 degrees,
Optical characteristics such as numerical aperture and spherical aberration are optimally designed for a high-density disc, an objective lens 5 for condensing incident laser light, a detection lens 10 for converging reflected light, and a reflection light converged by the detection lens. It has a passing light amount limiting means 11 for limiting the light passing amount, a light receiving means 20 for receiving the reflected light and outputting a tracking signal, a focus signal and a reproduction signal.

As shown in FIG. 2, the passing light amount restricting means 11 comprises two opposing electromagnets 111 and 112 and a magnetic material such as iron for limiting the passing light amount of the laser light passing therethrough with the opening window 113 formed. And a cylindrical position regulating member 115 for regulating the distance between the electromagnets 111 and 112 and regulating the position of the light amount regulating member 114 in the direction perpendicular to the optical axis.

It should be noted that the light quantity limiting member 114 is
It is important to be able to smoothly move between the positions 1 and 112 without resistance. In this sense, the position regulating member 115 is preferably a non-magnetic material.

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 １ ／ λ plate 4. By passing through the ４λ plate 4, the laser light is changed from linearly polarized light to circularly polarized light, enters the objective lens 5, is condensed by the objective lens 5, and irradiates the disk.

The laser beam irradiated on the disk in this manner is reflected by the recording member, is condensed by the objective lens 5, and is incident on the ４λ plate. Then, the laser beam is incident on the beam splitter 3. At this time, the laser beam passes through the 1 / 4.lambda.
Since the beam is rotated by 0 degrees, the beam is deflected by the beam splitter 3 and emitted in the direction of the detection lens 10. Thereby, optical path separation is performed. Thereafter, the light is converged by the detection lens 10, passes through the passing light amount limiting unit 11, and is received by the light receiving unit 20.

At this time, when the light receiving means 20 receives the reflected light from the high-density disk, a current is supplied to the electromagnet 112 and no current is supplied to the electromagnet 111.

Thus, the light quantity limiting member 114 is attracted to the electromagnet 112 on the light receiving means 20 side, and the electromagnet 11
2 comes into contact with the light-receiving-unit-side position regulating surface 122 that is the side surface.

The diameter of the reflected light at this position is
Since the size is slightly smaller than the size of the opening window 113 provided in the light receiving portion 14, the reflected light is detected by the light receiving means 20 without limiting the light amount. In FIG. 2, a solid line indicates a region of the reflected light received by the light receiving unit 20.

On the other hand, when the light receiving means receives the reflected light from the standard density disk, no current is supplied to the electromagnet 112 and current is supplied to the electromagnet 111.

Thus, the light quantity limiting member 114 is attracted to the electromagnet 112 on the detection lens 10 side, and the electromagnet 1
11 comes into contact with the detection lens side position regulating surface 121 which is a side surface of the eleventh embodiment.

The diameter of the reflected light at this position is
Since the size of the reflected light is slightly larger than the size of the opening window 113 provided in the
Will be detected. In FIG. 2, a dotted line indicates a region of the reflected light received by the light receiving unit 20.

The light amount of the reflected light is set so as to shield the peripheral portion of the reflected light from the standard density disk which is significantly affected by spherical aberration. Therefore, even when an objective lens whose optical characteristics are optimally designed for a high-density disk is used to focus laser light on a standard-density disk and reproduce information, etc., the influence of spherical aberration is not affected. It is possible to obtain a reproduction signal and a servo signal which are not used.

Incidentally, the above-described peripheral area where the influence of spherical aberration on the reflected light from the standard density disk is remarkable is extremely small. For this reason, the moving amount of the light amount limiting member 114 is small, and high processing accuracy and mounting accuracy are required for the passing light amount limiting means 11, and it is desirable to reduce the processing accuracy and mounting accuracy from the viewpoint of low cost of the apparatus.

FIG. 3 is a diagram showing a partial configuration of a pickup device constructed from such a viewpoint. A concave lens 12 is provided between a detection lens 10 and a passing light amount restricting means 11, and the light is converged by the detection lens 10. The focal length of the reflected light is made longer.

As a result, the degree of convergence of the laser beam passing through the passing light amount restricting means 11 is reduced, so that the position regulating member 115 can be lengthened, and the light amount restricting member 1 can be made longer.
The required accuracy of the fourteen regulation positions is reduced, and the processing accuracy and assembly accuracy of each member can be reduced.

The opening window 113 provided in the above-mentioned light quantity limiting member 114 is perforated perpendicular to the plate surface of the light quantity limiting member 114. In this configuration, the reflected light may be diffracted on the side wall of the opening window 113.

Therefore, as shown in FIG. 4, by forming the side wall of the opening window 113 in a tapered shape, diffraction on the side wall is prevented.

The light amount limiting member 114 shown in FIG. 4 is tapered so that the opening diameter increases from the surface 117 of the detection lens 20 to the surface 118 of the light receiving means 20.

As a result, since the diffraction of the reflected light by the aperture window is reduced, it is possible to obtain a high quality reproduced signal or the like.

In the above description, the light amount limiting member 114 is moved by the electromagnets 111 and 112, but the present invention is not limited to this.

[0054]

According to the first aspect of the present invention, there is provided a passing light amount restricting means having a light amount restricting member having an opening window to reflect light from an information recording medium in which an optical characteristic of an objective lens is optimally designed. When light is incident, the position of the light amount limiting member is positioned at a predetermined position on the light receiving means side to allow the reflected light to pass through without blocking, and to record information on which the optical characteristics of the objective lens are not optimally designed. When the reflected light from the medium enters, the position of the light quantity limiting member is positioned at a predetermined position on the detection lens side, and the peripheral portion where the influence of the spherical aberration of the reflected light is large is shielded and passes only through the central portion. Since the optical characteristics of the objective lens are not optimally designed, the peripheral portion where the influence of the spherical aberration of the reflected light from the information recording medium is large is not received by the light receiving means, and the signal quality of the reproduced signal and the like is improved. Door is possible.

According to the second aspect of the present invention, since the concave lens is provided between the detection lens and the passing light amount limiting means to increase the movable amount of the light amount limiting member, the positional accuracy of the light amount limiting member is reduced. can do.

According to the third aspect of the present invention, since the opening window of the light amount limiting member is formed in a tapered shape so that the opening diameter increases from the detection lens side to the light receiving means side, reflected light is transmitted to the opening window. To prevent large diffraction.

[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 detailed configuration and operation of a passing light amount limiting unit.

FIG. 3 is a diagram illustrating the detailed configuration and operation of the passing light amount limiting unit when a concave lens is provided between the detection lens and the passing light amount limiting unit.

FIG. 4 is a diagram showing another configuration of the light amount limiting member.

FIG. 5 is a diagram illustrating light-collecting characteristics due to differences in transparent substrates.

FIG. 6 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 λλ plate 5 objective lens 10 detection lens 11 passing light quantity limiting means 12 concave lens 20 light receiving means 111, 112 electromagnet 113 opening window 114 light quantity limiting member 115 position regulating member 119 tapered opening window

Claims (3)

[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. An optical pickup device having an objective lens that emits light, a detection lens that converges reflected light from the information recording medium, and a light receiving unit that receives the reflected light converged by the detection lens and outputs a reproduction signal and a servo signal. Wherein said information recording device is provided with a light amount limiting member having a position variably provided between said detection lens and said light receiving means and having an aperture window formed therein, and said optical characteristic of said objective lens is optimally designed. When the reflected light from the medium enters, it is located at a predetermined position on the light receiving means side, passes the reflected light through the opening window without blocking the light, When the reflected light from the information recording medium whose characteristics are not optimally designed is incident, a peripheral portion where the reflected light is greatly affected by spherical aberration is located at a predetermined position on the detection lens side by the opening window. An optical pickup device comprising a passing light amount restricting means for blocking light and passing only through a central portion. 2. The optical pickup device according to claim 1, further comprising a concave lens disposed between said detection lens and said passing light amount restricting means to increase a focal length of said detection lens. 3. An opening window of said light quantity limiting member is formed in a tapered shape so that an opening diameter increases from said detection lens side to said light receiving means side. An optical pickup device as described in the above.