JP2008293599A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device configured to generate a focus error signal by using an astigmatism method, in which a degradation in performance of reading information recorded in an optical recording medium or a degradation in performance of writing information to the optical recording medium can be suppressed. <P>SOLUTION: A photodetector 9 included in the optical pickup device is equipped with: a light receiving part 9a for receiving a reflected light from the optical recording medium; an IC board 9b having a circuit for converting an optical signal received by the light receiving part 9a into an electric signal; and a cover glass 9c disposed so as to cover the light receiving part 9a and secured to the IC board 9b. The cover glass 9c has semi-circular shape having a center CB and a peripheral part SB lower than the center CB, and configured to generate astigmatism for generating an FE signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup device that enables reading and writing of information by irradiating an optical recording medium with a light beam, and in particular, an optical pickup formed so that a focus error signal can be generated using an astigmatism method. It relates to the configuration of the apparatus.

  Optical recording media such as compact discs (hereinafter referred to as CDs) and digital versatile discs (hereinafter referred to as DVDs) are widely used. Recently, in order to further increase the amount of information in the optical recording medium, research on increasing the density of the optical recording medium has been advanced, and for example, a higher-density optical recording medium such as a Blu-ray disc (hereinafter referred to as BD). Has also been put to practical use.

  Incidentally, an optical pickup device is used when reading information recorded on an optical recording medium or writing information on an optical recording medium. FIG. 3 is a schematic diagram showing the configuration of the optical system of the conventional optical pickup device 100. The optical pickup device 100 includes a light source 101, a polarizing beam splitter 102, a collimating lens 103, a rising mirror 104, a quarter wavelength plate 105, an objective lens 106, a cylindrical lens 107, and a photodetector 108. .

  Laser light (linearly polarized light) emitted from the light source 101 is transmitted through the polarization beam splitter 102, converted into parallel light by the collimating lens 103, and reflected by the rising mirror 104 in a direction orthogonal to the recording surface 110 a of the optical recording medium 110. Then, it is made circularly polarized light by the quarter wavelength plate 105 and condensed on the recording surface 110 a of the optical recording medium 110 by the objective lens 106.

  The reflected light reflected by the recording surface 110 a of the optical recording medium 110 has a polarization direction with respect to the laser light (linearly polarized light) emitted from the light source 101 by the quarter wavelength plate 105 after passing through the objective lens 106. The linearly polarized light is rotated by 90 °. Thereafter, it is reflected by the rising mirror 104, passes through the collimating lens 103, is reflected by the polarization beam splitter 102, is given astigmatism by the cylindrical lens 107, and forms a beam spot on the photodetector 108.

  The photodetector 108 has a light receiving element such as a photodiode chip, and a cover glass made of transparent glass is disposed on the light receiving element, and the light receiving element is the cover glass. (See, for example, Patent Document 1).

  When information is read from the optical recording medium 110 by the optical pickup device 100 or when information is recorded on the optical recording medium 110, the focus of the objective lens 106 must always match the recording surface 110 a of the optical recording medium 110. is there. For this reason, the objective lens 106 can be moved in a focus direction parallel to the optical axis direction by an actuator (not shown), and focusing is performed based on a focus error signal generated by an electrical signal from the photodetector 108. Control is performed.

  Several methods, such as an astigmatism method and a spot size method, have been proposed as a method for generating a focus error signal necessary for performing this focusing control, but the optical pickup device 100 uses the astigmatism method. It is a configuration to use. For this purpose, a cylindrical lens 107 that functions as an astigmatism generating element is disposed in the optical system of the optical pickup device 100.

  As shown in FIG. 4, the cylindrical lens 107 provided in the optical pickup device 100 has a beam spot formed on the photodetector 108 when the focal point of the objective lens 106 coincides with the recording surface 110 a of the optical recording medium 110. When the shape is circular and the focus of the objective lens 106 is deviated from the recording surface 110a of the optical recording medium 110, it is adjusted to be an ellipse.

  FIG. 4 is an explanatory diagram for explaining how the shape of the beam spot formed on the photodetector 108 changes depending on the position of the objective lens. FIG. 4A shows the focus of the objective lens 106 recorded. FIG. 4B is a beam spot shape when the focal point of the objective lens 106 is coincident with the recording surface 110a, and FIG. 4C is a focal point of the objective lens 106 when the focal point of the objective lens 106 is the recording surface. This is a beam spot shape in a case where the position is beyond 110a (the upper side of the recording surface 110a in FIG. 3).

  In addition, the photodetector 108 includes a light receiving element in which a light receiving unit as shown in FIG. 4 is divided into four regions (A to D) so that a focus error signal can be obtained by the astigmatism method. In this case, the focus error signal (FE signal) is generated as FE signal = (A + C) − (B + D).

  In the above description, the configuration in which the cylindrical lens 107 is disposed in the optical system in order to generate astigmatism has been described. However, an optical pickup apparatus having a configuration in which astigmatism is generated by a half mirror instead of the cylindrical lens 107 is also conventionally seen. It is done. This will also be explained.

FIG. 5 is a schematic diagram showing a configuration of an optical pickup device 200 formed so as to generate astigmatism using a half mirror. In addition, the same code | symbol is attached | subjected about the optical component which overlaps with the optical pick-up apparatus 100 shown in FIG. The optical pickup device 200 is the same as the optical pickup device 100 except that the polarization beam splitter 102 is a half mirror 201 and the cylindrical lens 107 is not disposed. In the optical pickup device 200, the astigmatism generated in the laser light passing through the half mirror 201 is adjusted by the thickness of the half mirror 201 and the refractive index of the material constituting the half mirror 201.
Japanese Patent Laid-Open No. 5-145163

  However, the conventional optical pickup devices 100 and 200 described above have the following problems. In the case of the optical pickup device 100 configured to be able to generate a focus error signal using the cylindrical lens 107, the cylindrical lens 107 (or other astigmatism generating element) is indispensable. As a result, there is a problem that it is difficult to reduce the size of the optical pickup device, the cost is increased, and the work during assembly is increased.

  In this regard, in the configuration in which astigmatism is generated by the half mirror 201, an optical component having a function of separating light is also configured to have a function of generating astigmatism, so that a cylindrical lens is separately disposed. The problem that the number of parts increases as in the case of can be solved.

  However, in either case of the optical pickup devices 100 and 200, there may be a case where a positional deviation occurs during the adjustment of the mounting of the optical component. Further, it is understood that when an environmental test (high temperature, high humidity, low temperature, impact, vibration, etc.) is performed, the optical components arranged in the optical system of the optical pickup devices 100 and 200 may be displaced. ing.

  FIG. 6 is a diagram for explaining how the direction of astigmatism with respect to the light receiving surface of the photodetector 108 is shifted due to the positional deviation of the photodetector 108. As shown in FIG. 6A, for example, when the photodetector 108 rotates around the optical axis and is displaced, the direction of astigmatism generated by the cylindrical lens 107 as shown in FIG. 6B. Deviates from the planned direction (the direction indicated by the solid oval). In this case, for example, there may be a case where the focus pull-in cannot be performed properly, and the reading performance of information recorded on the optical recording medium and the writing performance of information on the optical recording medium are deteriorated. Such a phenomenon also occurs when astigmatism is generated by a half mirror.

  Further, in FIG. 6, the manner in which the photodetector 108 rotates around the optical axis has been described, but a positional shift different from such a positional shift (the optical axis direction in FIG. Even when the relative positional relationship between the photodetector and the astigmatism generating element (cylindrical lens or half mirror) is shifted due to a shift in a plane orthogonal to the axis, the focal position of the objective lens 106 is changed to the optical recording medium 110. This causes a problem that the recording surface 110a cannot be matched. In this case, there arises a problem that information reading performance or the like in the optical pickup device is lowered.

  That is, in the conventional optical pickup devices 100 and 200, the relative relationship between an element (cylindrical lens or half mirror) that generates astigmatism and the photodetector due to the influence of adjustment variations during assembly of the optical pickup device and the influence of environmental conditions. Thus, there is a problem in that the information reading performance and the like in the optical pickup device are deteriorated due to a shift in the positional relationship.

  In view of the above problems, the object of the present invention is to read information recorded on an optical recording medium in an optical pickup device formed so as to generate a focus error signal using an astigmatism method, An object of the present invention is to provide an optical pickup device capable of suppressing a decrease in information writing performance on an optical recording medium.

  In order to achieve the above object, the present invention receives a light source, an objective lens for condensing a light beam emitted from the light source on a recording surface of the optical recording medium, and reflected light reflected by the optical recording medium. And an optical pickup device formed so as to be able to generate a focus error signal using an astigmatism method, the photodetector includes a substrate having a light receiving unit that receives the reflected light, and A cover transparent member arranged to cover the light receiving portion and fixed to the substrate, the cover transparent member generating astigmatism that enables generation of the focus error signal. It is characterized by being formed.

  According to this configuration, since the desired transparent astigmatism is generated using the cover transparent member included in the photodetector, the photodetector and the element that generates astigmatism are integrated. . For this reason, the relative positional relationship between the photodetector and the astigmatism generating element can be made constant regardless of variations during assembly adjustment and environmental conditions. Further, in this case, even when the photodetector is displaced, the astigmatism generation direction with respect to the light receiving surface of the photodetector is not shifted, and astigmatism with respect to the light receiving surface of the photodetector is not caused. The generation direction can always be constant. Therefore, according to this configuration, in the optical pickup device formed so as to be able to generate a focus error signal using the astigmatism method, the reading performance of information recorded on the optical recording medium and the information on the optical recording medium An optical pickup device that can suppress a decrease in writing performance can be provided.

  Further, according to this configuration, since the photodetector and the astigmatism generation element are integrated, as compared with the case where the astigmatism generation element such as a cylindrical lens is arranged in the optical system of the optical pickup device. Thus, the number of parts can be reduced. For this reason, it is possible to reduce the size and cost of the optical pickup device.

  In the optical pickup device having the above configuration according to the present invention, it is preferable that the transparent member for cover has a kamaboko shape having a central portion and a peripheral portion lower than the central portion. According to this, it is easy to realize a configuration for generating astigmatism in the transparent member for the cover of the photodetector easily and at low cost.

  In the optical pickup device having the above configuration according to the present invention, it is preferable that the transparent member for cover and the substrate are welded. It is also possible to fix the cover transparent member and the substrate with an adhesive, but in this case, for example, the relative positional relationship between the cover transparent member and the substrate under environmental conditions such as high temperature and high humidity. May shift. However, when the cover transparent member and the substrate are welded, the relative positional relationship between the cover transparent member and the substrate is very low even under environmental conditions such as high temperature and high humidity. That is, it is possible to suppress a decrease in reading performance of information recorded on the optical recording medium and writing performance of information on the optical recording medium with higher probability.

  In the optical pickup device having the above-described configuration, the transparent member for cover may be made of glass. By forming the cover transparent member with glass, it is easy to obtain a desired lens effect, and it is easy to generate astigmatism appropriate for the cover transparent member.

  According to the present invention, in an optical pickup device formed so as to be able to generate a focus error signal using an astigmatism method, the reading performance of information recorded on an optical recording medium and the writing of information to the optical recording medium It becomes possible to provide an optical pickup device capable of suppressing a decrease in performance. Further, according to the present invention, the number of parts of the optical pickup device formed so that the focus error signal can be generated using the astigmatism method can be reduced, and the optical pickup device can be downsized and the manufacturing cost can be reduced.

  Hereinafter, the content of the present invention will be described in detail with reference to the drawings. However, the embodiment shown here is an example, and the present invention is not limited to the embodiment shown here.

  FIG. 1 is a schematic diagram showing the configuration of the optical pickup device of the present embodiment. As shown in FIG. 1, the optical system of the optical pickup device 1 includes a light source 2, a polarizing beam splitter 3, a collimating lens 4, a rising mirror 5, a quarter wavelength plate 6, and an objective lens 7. And a photodetector 9.

  The light source 2 is composed of a semiconductor laser, and the wavelength of the laser light emitted from the semiconductor laser is appropriately selected depending on the type of the optical recording medium 20 to which the optical pickup device 1 corresponds. For example, when the optical pickup device 1 is compatible with BD, laser light of 405 nm band is emitted from the light source 2, when the optical pickup device 1 is compatible with DVD, 650 nm laser light is emitted from the light source 2. The type of the light source 2 (semiconductor laser) is selected so as to be emitted.

  In the present embodiment, the optical pickup device 1 has one light source 2 in order to support one type of optical recording medium 20. However, the present invention is not limited to this, and a plurality of types of optical recording media 20 are used. When the compatible optical pickup device is used, the number of the light sources 2 may be plural.

  The polarization beam splitter 3 has a function of transmitting one of two linearly polarized light whose polarization directions are orthogonal to each other and reflecting the other. The optical pickup device 1 of the present embodiment is configured such that laser light is transmitted in the forward path and laser light is reflected in the return path.

  The collimating lens 4 has a function of converting laser light emitted from the light source 2 and transmitted through the polarization beam splitter 3 into parallel light. Further, the rising mirror 5 has a function of reflecting the laser beam emitted from the light source 2 and changing the optical axis direction to a direction orthogonal to the recording surface 20 a of the optical recording medium 20.

  The quarter wavelength plate 6 is arranged so as to be circularly polarized when linearly polarized light is incident. Further, the circularly polarized light incident on the quarter wavelength plate 6 is converted into linearly polarized light. The objective lens 7 focuses the incident laser light on the recording surface 20 a of the optical recording medium 20. The objective lens 7 can be moved by an actuator 8 in a focus direction parallel to the optical axis direction and a direction parallel to the radial direction of the optical recording medium 20 (the paper surface direction in FIG. 1).

  In such an optical system, the laser light emitted from the light source 2 is transmitted through the polarization beam splitter 3, converted into parallel light by the collimator lens 4, reflected by the rising mirror 5, and circular by the quarter wavelength plate 6. The light is polarized and condensed on the recording surface 20 a of the optical recording medium 20 by the objective lens 7. The laser beam condensed on the recording surface 20a of the optical recording medium 20 is reflected, passes through the objective lens 7, and is emitted from the light source 2 by the quarter wavelength plate 6 (linearly polarized light) and the polarization direction. Is reflected by the rising mirror 5, passes through the collimating lens 4, is reflected by the polarization beam splitter 3, and is condensed on the photodetector 9.

  The laser beam condensed on the photodetector 9 is converted into an electric signal and sent to the signal processing unit 10. In the signal processing unit 10, an RF signal, a focus error signal (FE signal), a tracking error signal (TE signal), and the like are generated. The actuator control unit 11 performs focusing control and tracking control based on the FE signal and the TE signal obtained by the signal processing unit 10.

  The focusing control is control performed so that the focal position of the objective lens 7 always matches the recording surface 20a of the optical recording medium 20. The tracking control is control performed so that the beam spot formed by converging the laser light emitted from the light source 2 by the objective lens 7 always follows the track formed on the optical recording medium 20. It is.

  The optical pickup device 1 of the present embodiment is configured to obtain an FE signal by a so-called astigmatism method. When an FE signal is obtained by the astigmatism method, it is necessary to generate desired astigmatism, but the optical pickup device 1 of the present embodiment is devised for a configuration that generates this astigmatism. Hereinafter, this point will be described.

  FIG. 2 is a schematic perspective view showing the configuration of the photodetector 9 provided in the optical pickup device 1 of the present embodiment. The photodetector 9 covers the light receiving unit 9a that receives the reflected light from the optical recording medium 20, an IC substrate 9b that has a circuit that converts the optical signal received by the light receiving unit 9a into an electrical signal, and the light receiving unit 9a. And a cover glass 9c fixed to the IC substrate 9b. The light receiving unit 9b is divided into four light receiving regions (A to D) so that an FE signal can be obtained by the astigmatism method.

  As shown in FIG. 2, the cover glass 9 c provided in the photodetector 9 has a kamaboko shape having a central part CB and a peripheral part SB lower than the central part CB. Thus, the reason why the cover glass 9c is formed in a semi-cylindrical shape is to generate a desired astigmatism in the laser light passing through the cover glass 9c so that an FE signal can be generated by the astigmatism method. .

  That is, when the shape of the beam spot of the laser light passing through the cover glass 9c (formed on the light receiving portion 9a of the light detector 9) is the focal point of the objective lens 7 in front of the recording surface 20a, FIG. When the object lens 7 has an ellipse as shown in a) and the focus of the objective lens 7 coincides with the recording surface 20a, it becomes a circle as shown in FIG. 4B, and the focus of the objective lens 7 exceeds the recording surface 20a. 4C, the cover glass 9c is formed so as to have an ellipse as shown in FIG. 4C (an ellipse in the direction opposite to that when the focal point of the objective lens 7 is in front of the recording surface 20a). . Since astigmatism is generated by the cover glass 9c, the FE signal is generated as FE signal = (A + C) − (B + D) by the astigmatism method.

  In the optical pickup device 1 of the present embodiment, the photodetector 9 and the element that generates astigmatism are integrated. For this reason, if the assembly accuracy of the photodetector 9 is well managed, the relative positional relationship between the photodetector 9 and the element that generates astigmatism does not shift when the optical system is assembled. In addition, even when the photodetector 9 is displaced due to environmental conditions (for example, high temperature and high humidity), the relative positional relationship between the photodetector 9 and the element that generates astigmatism. Is constant, and the astigmatism generation direction with respect to the detection surface of the photodetector 9 is constant. Therefore, in the optical pickup device 1, it is possible to suppress the reading of information from the optical recording medium 20 and the deterioration of the performance of writing information to the optical recording medium 20.

  Further, since the photodetector 9 itself has a function of generating astigmatism, it is not necessary to separately arrange an aberration generating element such as a cylindrical lens in the optical system of the optical pickup device 1. The number of points can be reduced, and the optical pickup device 1 can be downsized and the manufacturing cost can be reduced.

  In addition, although the structure performed using an adhesive agent may be sufficient as the joining method of IC substrate 9b and the cover glass 9c in the photodetector 9, it is preferable to heat and weld. By welding the junction between the IC substrate 9b and the cover glass 9c, the possibility that the cover glass 9c fixed to the IC substrate 9b is displaced due to environmental conditions can be reduced.

  Further, in the present embodiment, the cover glass 9c of the photodetector 9 is formed in a semi-cylindrical shape so as to generate a desired astigmatism. However, the present invention is not limited to this configuration, and the cover glass 9c is not used. Other configurations may be used as long as the point aberration can be generated. That is, for example, the cover glass 9c may be a flat plate shape, and the refractive index of the cover glass 9c may be distributed by adjusting the material for forming the cover glass 9c to generate a desired astigmatism. Absent.

  Further, in the optical pickup device 1 of the present embodiment, the member that covers the light receiving portion 9a of the photodetector 9 is made of glass. However, the present invention is not limited to this, and various modifications can be made without departing from the object of the present invention. Is possible. For example, a cover that covers the light receiving portion 9a may be formed of a light transmissive plastic or the like, and may have a function of generating astigmatism.

  According to the present invention, in an optical pickup device formed so as to be able to generate a focus error signal using an astigmatism method, the reading performance of information recorded on an optical recording medium and the writing of information to the optical recording medium A decrease in performance can be suppressed. Therefore, it can be said that the optical pickup device of the present invention is industrially useful.

These are the schematic diagrams which show the structure of the optical pick-up apparatus of this embodiment. These are the schematic perspective views which show the structure of the photodetector with which the optical pick-up apparatus of this embodiment is provided. These are the schematic diagrams which show the structure of the optical system of the conventional optical pick-up apparatus. These are explanatory drawing for demonstrating a mode that the shape of the beam spot formed on a photodetector changes with the position of an objective lens. FIG. 4 is a schematic view showing a configuration of an optical system of an optical pickup device having an optical system of a type different from that in FIG. 3 for a conventional optical pickup device. These are the figures explaining a mode that the direction of astigmatism with respect to the light-receiving surface of a photodetector shifts | deviates by the position shift of a photodetector in the conventional optical pick-up apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up apparatus 2 Light source 7 Objective lens 9 Photodetector 9a IC board 9b Light-receiving part 9c Cover glass (transparent member for cover)
20 Optical recording medium 20a Recording surface

Claims (4)

A light source;
An objective lens for condensing the light beam emitted from the light source on the recording surface of the optical recording medium;
A photodetector for receiving the reflected light reflected by the optical recording medium;
In an optical pickup device formed so that a focus error signal can be generated using an astigmatism method,
The photodetector includes a substrate having a light receiving portion that receives the reflected light, and a cover transparent member that is disposed so as to cover the light receiving portion and is fixed to the substrate.
The optical pickup apparatus according to claim 1, wherein the cover transparent member is formed so as to generate astigmatism capable of generating the focus error signal.   2. The optical pickup device according to claim 1, wherein the transparent member for cover has a kamaboko shape having a central portion and a peripheral portion lower than the central portion.   The optical pickup device according to claim 1, wherein the transparent member for cover and the substrate are welded.   4. The optical pickup device according to claim 1, wherein the cover transparent member is made of glass.

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