JP2009116991A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device including a front monitor having an optical system simply configured and stably accurately controlling the light amount of luminous flux emitted from a light source. <P>SOLUTION: The front monitor 19 in the optical pickup device 1 is provided along a path of luminous flux emitted from a laser diode 11 to an objective lens 16 so that a light receiving surface of a light receiving unit of the front monitor 19 is substantially perpendicular to an optical axis ax of the luminous flux emitted from the laser diode 11 to the objective lens 16. The front monitor 19 is arranged at a position so that the light receiving unit may receive a portion of the luminous flux emitted from the laser diode 11 without causing vignetting in luminous flux entering an effective region (a region within an effective diameter D) of the objective lens 16. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup apparatus that enables reading of information recorded on an optical recording medium and writing of information on the optical recording medium by irradiating a light beam onto the optical recording medium, and in particular, emitted from a light source. The present invention relates to the arrangement of a front monitor provided for detecting the amount of light flux.

  In recent years, optical recording media such as compact discs (hereinafter referred to as CDs) and digital versatile discs (hereinafter referred to as DVDs) have become widespread. Furthermore, recently, optical recording media such as HD-DVD and Blu-ray disc (hereinafter referred to as BD) have been put into practical use as optical recording media capable of recording information of a larger capacity than DVD.

  Reading information recorded on such an optical recording medium and writing information on the optical recording medium are performed using an optical pickup device. FIG. 5 is a schematic diagram showing a configuration of an optical system of a conventional optical pickup device 100. As shown in FIG. 5, a conventional optical pickup device 100 includes a laser diode 101, a polarizing beam splitter 102, a collimator lens 103, a quarter wavelength plate 104, a rising mirror 105, an objective lens 106, A photodetector 107 and a front monitor 108 are provided.

  In the conventional optical pickup device 100, the light beam emitted from the laser diode 101 is partially reflected by the polarization beam splitter 102, converted into parallel light by the collimator lens 103, and converted into circularly polarized light by the quarter wavelength plate 104, The light is reflected by the rising mirror 105 and condensed on the recording surface of the optical recording medium (not shown) by the objective lens 106.

  On the other hand, the light beam reflected by the optical recording medium is transmitted through the objective lens 106, reflected by the rising mirror 105, converted into linearly polarized light by the quarter wavelength plate 104, and collimated lens 103, polarizing beam splitter. The light passes through 102 and is condensed on the photodetector 107. The photodetector 107 photoelectrically converts the received optical signal and outputs it as an electrical signal.

  Further, the optical pickup device 100 is configured such that a part of the light beam emitted from the laser diode 101 passes through the polarization beam splitter 102 and is guided to the front monitor 108. The front monitor 108 is provided with a light receiving unit that receives light, and the amount of light flux received by the front monitor 108 can be detected.

  When reading and writing information in the optical pickup device 100, in order to stably read and write information, the light amount of the light beam emitted from the laser diode 101 and applied to the optical recording medium is accurately controlled. There is a need. Therefore, in the optical pickup device 100, the front monitor 108 is provided to detect the light amount of the light beam emitted from the laser diode 101, and by feeding back the detected light amount, the light beam irradiated to the optical recording medium is detected. The amount of light is accurately controlled.

  By the way, in the conventional optical pickup device 100, the light beam emitted from the laser diode 101 is separated using the polarization beam splitter 102 so that a part of the light beam emitted from the laser diode 101 enters the front monitor 108. It is configured. However, the film characteristics of the film (for example, a dielectric multilayer film) provided for the polarization beam splitter 102 to separate the light beam may fluctuate due to, for example, an environmental change. For this reason, when a configuration is adopted in which a light beam traveling in a direction different from the direction toward the objective lens 106 is received by the front monitor 108 using the polarization beam splitter 102 as in the conventional optical pickup device 100. In some cases, the amount of the light beam applied to the optical recording medium cannot be accurately controlled due to the change in the film characteristics of the polarization beam splitter 102.

For example, Patent Document 1 shows a configuration in which a light guide member (parabolic mirror, optical fiber, prism) for guiding a part of a laser beam emitted from a light emitting element to a front monitor light receiving element is shown. However, in the case of the configuration disclosed in Patent Document 1, a light guide member is required to guide light to the front monitor light receiving element. For this reason, the number of optical members provided in the optical pickup is increased, and the number of parts increases, resulting in, for example, an increase in cost.
JP 2006-318623 A

  In view of the above points, an object of the present invention is to provide a configuration that can simplify the configuration of an optical system and can stably and accurately control the amount of light emitted from a light source in an optical pickup device including a front monitor. That is.

  In order to achieve the above object, the present invention includes a light source, an objective lens that condenses a light beam emitted from the light source on a recording surface of an optical recording medium, and a light receiving unit that receives light, and is emitted from the light source. And a front monitor that detects the amount of light emitted from the light source. The front monitor has a light receiving surface of the light receiving unit along a path along which the light emitted from the light source reaches the objective lens. It is provided so as to be substantially perpendicular to the optical axis of the light beam emitted from the light source and reaching the objective lens, and from the light source without generating vignetting on the light beam incident on the effective area of the objective lens. It is characterized in that it is arranged at a position where a part of the emitted light beam can be received by the light receiving part.

  According to this, since the front monitor has a configuration in which the light beam emitted from the light source is arranged with the light receiving surface of the light receiving unit directed in a specific direction along the path to the objective lens, the light emitted from the light source is emitted. A part of the luminous flux can be received without using a light guide member such as a mirror. Further, according to the present invention, the front monitor can receive a part of the light beam emitted from the light source and traveling in the direction toward the objective lens. That is, the front monitor is not configured to detect the light amount of the light beam after separating the light beam traveling in a direction different from the direction toward the objective lens using a separation element such as a beam splitter. For this reason, the influence by the fluctuation | variation of the film | membrane characteristic of a separation element can be suppressed. Furthermore, according to the present invention, even if the front monitor is arranged along the path where the light beam emitted from the light source reaches the objective lens, vignetting does not occur in the light beam incident on the effective area of the objective lens. As described above, according to the present invention, the configuration of the optical system can be simplified, and the amount of light emitted from the light source can be stably and accurately controlled.

  According to the present invention, in the optical pickup device configured as described above, the rising mirror that reflects the optical axis of the light beam emitted from the light source so as to be directed in a direction substantially perpendicular to the recording surface of the optical recording medium. The front monitor is disposed between the light source and the rising mirror, and is displaced in a direction substantially perpendicular to the optical axis when viewed in plan from the optical recording medium side. It may be arranged in a state.

  According to this, when the front monitor is mounted on the base member constituting the optical pickup device, it is possible to easily secure a place where the front monitor is arranged, and the manufacture of the optical pickup device is facilitated.

  In the optical pickup device having the above configuration according to the present invention, it is preferable that the front monitor is disposed at a position for receiving a part of divergent light emitted from the light source. According to this, since the light beam incident on the front monitor is divergent light, it is easy to increase the amount of light that can be received by the light receiving unit of the front monitor.

  According to the present invention, in the optical pickup device configured as described above, a collimating lens that converts incident diverging light into parallel light is provided between the light source and the objective lens, and the front monitor includes the collimating lens. It is good also as arrange | positioning near. According to this, the front monitor can receive the light beam at a position where the light beam of the diverging light emitted from the light source is sufficiently expanded, and the vignetting is not generated in the light beam incident on the effective area of the objective lens, and a large amount of light is obtained. Easy to get.

  According to the present invention, in the optical pickup device configured as described above, when viewed along a direction parallel to the optical axis, the front monitor is disposed so that a part thereof overlaps the collimating lens. It is good as well. According to this, since the front monitor is arranged near the light beam emitted from the light source and reaching the objective lens, it is easy to increase the amount of light received by the light receiving unit.

  In the optical pickup device having the above configuration according to the present invention, it is preferable that the light receiving portion of the front monitor is provided at a position close to the optical axis side. According to this, since the light receiving part of the front monitor is arranged near the light beam emitted from the light source and reaching the objective lens, the amount of light received by the light receiving part can be increased.

  According to the present invention, there is provided an optical pickup device including a front monitor, which can simplify the configuration of an optical system and can stably and accurately control the amount of light emitted from a light source. it can.

  Embodiments of the optical pickup device of the present invention will be described below, and the contents thereof will be described in detail with reference to the drawings.

  FIG. 1 is a view for explaining the configuration of the optical pickup device of the present embodiment, and is a view when the optical system is viewed from above. Of course, the laser controller 21 is not an element constituting the optical system. FIG. 2 is a view for explaining the configuration of the optical pickup device of the present embodiment, and is a view when the optical system is viewed from the side. For easy understanding, the optical recording medium 2 is also shown.

  As shown in FIGS. 1 and 2, the optical pickup device 1 of the present embodiment includes a laser diode 11, a polarizing beam splitter 12, a collimating lens 13, a quarter wavelength plate 14, a rising mirror 15, An objective lens 16, a cylindrical lens 17, a light detector 18, and a front monitor 19 are provided.

  The laser diode 11 is a light source that emits a laser beam (light beam) having a specific wavelength. In the optical pickup device 1 of the present embodiment, the wavelength of the laser beam emitted from the laser diode 11 is 405 nm so that information can be read from and written to the BD. The laser beam emitted from the laser diode 11 has an elliptical cross section, but it is parallel to the paper surface in FIG. 1 in the horizontal direction (the direction perpendicular to the paper surface in FIG. 1). (Direction) is a state where the beam is expanded. That is, the radiation angle of the laser beam emitted from the laser diode 11 is larger in the horizontal direction than in the vertical direction.

  The polarization beam splitter 12 transmits linearly polarized light having a predetermined polarization direction emitted from the laser diode 11. On the other hand, the return light (laser beam on the return path) reflected by the optical recording medium 2 is reflected. Note that the return light incident on the polarization beam splitter 12 is 90 ° different in polarization direction from the linearly polarized light emitted from the laser diode 11 due to the action of the quarter-wave plate 14. The forward laser beam transmitted through the polarizing beam splitter 12 is sent to the collimating lens 13.

  The collimating lens 13 has a function of converting incident diverging light into parallel light. For this reason, the laser beam of divergent light transmitted from the polarization beam splitter 13 is converted into parallel light by the collimating lens 13. The forward laser beam emitted from the collimating lens 13 is sent to the quarter-wave plate 14.

  The quarter-wave plate 14 converts the forward laser beam, which is linearly polarized light, into circularly polarized light, and converts the backward laser beam, which is circularly polarized light, into linearly polarized light whose polarization direction is 90 ° different from that of the forward laser beam. It has a function. The forward laser beam emitted from the quarter-wave plate 14 is sent to the rising mirror 15.

  The rising mirror 15 reflects the laser beam transmitted from the quarter wavelength plate 14 so that the optical axis ax is perpendicular to the recording surface 2 a of the optical recording medium 2. The forward laser beam reflected by the rising mirror 15 is sent to the objective lens 16.

  The objective lens 16 focuses the laser beam sent from the rising mirror 15 on the recording surface 2 a of the optical recording medium 2. The objective lens 16 has an effective diameter D as shown in FIGS. 1 and 2, and is incident on the effective diameter D (effective area) to form a beam spot formed on the recording surface 2a of the optical recording medium 2. Contributes to reading and writing information.

  Here, the “effective diameter of the lens” generally refers to an “area where a light beam passes in order to obtain a predetermined optical performance (effective area)”, and is used in this sense also in this specification. Even if the light beam passes through a portion wider than the effective region, the optical performance is not affected. Conversely, if the light beam passes only through a portion narrower than the effective region, the predetermined optical performance cannot be obtained.

  The objective lens 16 is mounted on the actuator 20 and is a tracking direction (FIG. 2) that is parallel to the focus direction that is in contact with and away from the optical recording medium 2 and the radial direction of the optical recording medium 2 that is formed in a disk shape. In this case, the direction perpendicular to the paper surface is applicable). This is because focusing control for controlling the focal position of the objective lens 16 to always coincide with the recording surface 2a of the optical recording medium 2 and a beam spot formed by being condensed by the objective lens 16 are always performed. This is because it is possible to execute tracking control for controlling the track to follow the tracks formed on the track.

  As shown in FIG. 2, in the optical pickup device 1 of the present embodiment, the diameter of the laser beam incident on the objective lens 16 is larger than the effective diameter D of the objective lens 16 by a predetermined amount. This will be described with reference to FIG. FIG. 3 is a diagram for explaining the reason why the diameter of the laser beam incident on the objective lens 16 is larger than the effective diameter D of the objective lens 16 in the optical pickup device 1 of the present embodiment.

  As described above, the objective lens 16 moves in the tracking direction (which coincides with the horizontal direction) for tracking control. For this reason, as shown in FIG. 3, the effective area of the objective lens 16 naturally moves in the tracking direction. For this reason, assuming that the diameter of the laser beam incident on the objective lens 16 is the same as the effective diameter of the objective lens 16, if the objective lens 16 is moved by tracking control, the laser beam incident on the effective area of the objective lens 16 is vignetted. Will occur.

  For this reason, the diameter (incident diameter) of the laser beam incident on the objective lens 16 needs to be determined in consideration of the maximum moving range of the effective area of the objective lens 16 during tracking control (see FIG. 3). . If the incident diameter is made too large, the optical pickup device will be increased in size, and in this embodiment, it is almost equal to the maximum moving range of the effective area of the objective lens 16.

  In the present embodiment, the laser beam reflected by the rising mirror 15 is directly incident on the objective lens 16, but the present invention is not limited to this configuration. In other words, an aperture may be provided in front of the objective lens 16 so that the diameter of the laser beam incident on the objective lens 16 is reduced to a predetermined size. In this case, the aperture is also mounted on the actuator 20 and moves together with the objective lens 16.

  Returning to FIG. 1, the cylindrical lens 17 is reflected by the optical recording medium 2 and passes through the objective lens 16, the rising mirror 15, the quarter wavelength plate 14, and the collimating lens 13 in this order. Astigmatism is given to the reflected laser beam on the return path. The return laser beam emitted from the cylindrical lens 17 is sent to the photodetector 18.

  The photodetector 18 receives the laser beam transmitted from the cylindrical lens 17 in a light receiving region (not shown) and converts the obtained optical signal into an electrical signal. The electrical signal output from the photodetector 18 is processed into a reproduction signal, a focus error signal, a tracking error signal, and the like.

  The front monitor 19 has a light receiving portion 19a (see FIG. 4) for receiving light (details of the position where the light receiving portion 19a is provided will be described later), and detects the light amount of the laser beam emitted from the laser diode 11. To do. The front monitor 19 is electrically connected to a laser control unit 21 that controls driving of the laser diode 11. Then, the front monitor 19 transmits the light quantity detection result to the laser control unit 21.

  The laser control unit 21 controls driving of the laser diode 11 based on the signal sent from the front monitor 19 so that the laser power emitted from the laser diode 11 becomes a target value. That is, the amount of the laser beam emitted from the laser diode 11 can be controlled by the presence of the front monitor 19.

  The front monitor 19 is disposed along a path along which the laser beam emitted from the laser diode 11 reaches the objective lens 16 so that the light receiving surface of the light receiving portion 19a is substantially perpendicular to the optical axis ax. For this reason, the front monitor 19 receives a part of the light beam emitted from the laser diode 11 and traveling in the direction of the objective lens 16. Therefore, even when the film characteristics of the polarization beam splitter 12 fluctuate, it is possible to accurately control the light amount of the light beam applied to the optical recording medium 2.

  Further, the front monitor 19 is arranged so that vignetting does not occur in the laser beam incident on the effective area of the objective lens 16 by arranging the front monitor 19. As described above, in consideration of the movement of the objective lens 16 during tracking control, a laser beam having a diameter larger than the effective diameter D of the objective lens 16 is incident on the laser beam incident on the objective lens 16. It is composed. That is, the effective diameter of the collimating lens 13 is configured to be a predetermined amount larger than the effective diameter D of the objective lens 16.

  Therefore, if the front monitor 19 is arranged outside the effective diameter of the collimating lens 13, the laser that enters the effective area of the objective lens 16 due to the presence of the front monitor 19 including the case where the objective lens 16 moves in the tracking direction. No vignetting on the beam. From this aim, in the present embodiment, the front monitor 13 is disposed outside the effective diameter of the collimating lens 13.

  Further, the front monitor 19 is disposed close to the collimating lens 13 at a position in front of the collimating lens 13 (on the laser diode 11 side). Accordingly, the front monitor 19 receives the divergent laser beam emitted from the laser diode 11. Since the collimating lens 13 is disposed close to the collimating lens 13, a sufficient amount of light can be obtained while satisfying the condition that the laser beam incident on the effective region of the objective lens 16 does not cause vignetting.

  Further, the front monitor 19 is arranged so that a part thereof overlaps the collimating lens 13 when viewed along a direction parallel to the optical axis ax (that is, when viewed in the left-right direction in FIG. 1). Yes. This is to arrange the front monitor 19 as close to the optical axis ax as possible so that the amount of light received by the light receiving portion 19a of the front monitor 19 can be increased. Of course, as described above, the front monitor 19 is a position where it remains outside the effective diameter of the collimating lens 13.

  Further, the front monitor 19 is arranged in a state shifted in a direction substantially perpendicular to the optical axis ax in the plane of FIG. That is, the front monitor 19 is disposed in a state shifted in the horizontal direction with respect to the optical axis ax. As described above, in the present embodiment, the laser beam emitted from the laser diode 11 has a large emission angle in the horizontal direction. For this reason, the arrangement of the front monitor 19 of the present embodiment is a preferable arrangement in order to obtain a large amount of light without causing vignetting in the laser beam incident on the objective lens 16.

  Further, when the front monitor 19 is arranged so as to be shifted in the horizontal direction with respect to the optical axis ax as described above, other optical members (for example, the beam splitter 12 and the collimating lens 13) provided in the optical pickup device 1 are used. , A quarter-wave plate 14, a rising mirror 15, etc.) and can be easily placed on a base (not shown) constituting the optical pickup device 1. For this reason, the configuration of the optical pickup device 1 can be simplified.

  Next, the position of the light receiving unit 19a included in the front monitor 19 will be described with reference to FIG. FIG. 4 is a diagram for explaining the light receiving portion 19a of the front monitor 19 provided in the optical pickup device 1 of the present embodiment, and is a schematic plan view when the front monitor 19 is viewed along the optical axis ax. . In FIG. 4, the collimating lens 13 is also shown.

  As shown in FIG. 4, the light receiving portion 19a of the front monitor 19 is formed not near the center of the light receiving surface but near the optical axis ax. That is, the distance L between the outer end face of the front monitor 19 and the light receiving portion 19a is configured to be as small as possible. With this configuration, a part of the laser beam emitted from the laser diode 11 can be received efficiently.

  In addition, although the shape of the light-receiving surface of the light-receiving part 19a is substantially circular in this embodiment, it is not limited to this, and the shape of the light-receiving surface can be changed to various shapes.

  Further, the light receiving portion 19a may not be formed close to the optical axis ax as in the present embodiment, but may be arranged in the middle, for example. However, the front monitor 19 usually needs to secure a certain size because it is necessary to secure a joint for soldering or a gain amplifier may be provided inside the front monitor 19. There is. For this reason, it is effective to arrange the light receiving portion 19a closer to the optical axis ax as in the present embodiment.

  When the optical pickup device 1 is configured as described above, even when the film characteristics of the polarization beam splitter 12 fluctuate, the light quantity of the light beam applied to the optical recording medium is stabilized without being affected by the fluctuation. And can be controlled accurately. Further, it is possible to accurately control the light amount of the light beam applied to the optical recording medium without providing an extra optical member.

  The embodiment described above is an example, and the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the object of the present invention.

  In the above embodiment, the front monitor 19 is arranged in a state of being shifted in the horizontal direction (vertical direction in FIG. 1) with respect to the optical axis ax. However, the present invention is not limited to this configuration. That is, for example, the front monitor 19 may be arranged in a state of being shifted in a direction perpendicular to the optical axis ax (a direction perpendicular to the paper surface in FIG. 1). In particular, the laser beam emitted from the laser diode 11 is preferable when the vertical radiation angle is wide.

  Further, in the embodiment described above, the front monitor 19 is arranged close to the collimating lens 13. However, the configuration is not limited to this, and the front monitor 19 may be arranged at a position away from the collimating lens 13. Further, it is not intended to be limited to the front of the collimating lens 13.

  In the embodiment described above, the front monitor 19 is arranged so that a part thereof overlaps the collimator lens 13 when viewed along the optical axis ax direction. Not intended. In other words, the front monitor 19 and the collimating lens 13 may be configured not to overlap when viewed along the optical axis ax direction.

  In addition, in the present embodiment, the optical pickup device 1 is configured to support BD. However, the present invention is not limited to this. In other words, the present invention is naturally applicable to an optical pickup device corresponding to an optical disc other than the BD, and can also be applied to an optical pickup device corresponding to a plurality of types of optical discs.

  According to the optical pickup device of the present invention, a front monitor can be provided with a simple configuration of the optical system, and the light quantity of the light beam emitted from the light source can be stabilized without being affected by environmental changes. Can be controlled accurately. Therefore, the optical pickup device of the present invention is industrially useful.

These are figures for demonstrating the structure of the optical pick-up apparatus of this embodiment, and are the figures at the time of seeing an optical system from the top. These are figures for demonstrating the structure of the optical pick-up apparatus of this embodiment, and are the figures at the time of seeing an optical system from the side. These are the figures for demonstrating the reason for making the diameter of the laser beam which injects into an objective lens larger than the effective diameter of an objective lens in the optical pick-up apparatus of this embodiment. These are figures for demonstrating the light-receiving part of the front monitor with which the optical pick-up apparatus of this embodiment is provided, and is a schematic plan view at the time of seeing a front monitor along an optical axis. These are the schematic diagrams which show the structure of the optical system of the conventional optical pick-up apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up apparatus 2 Optical recording medium 2a Recording surface 13 Collimating lens 15 Raising mirror 16 Objective lens 19 Front monitor 19a Light receiving part ax Optical axis D Effective diameter of objective lens

Claims (6)

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 front monitor that has a light receiving portion that receives light and detects the amount of light emitted from the light source;
In an optical pickup device comprising:
The front monitor is
A light receiving surface of the light receiving unit is substantially perpendicular to an optical axis of a light beam emitted from the light source and reaching the objective lens along a path along which the light beam emitted from the light source reaches the objective lens. Provided,
Further, the optical pickup device is disposed at a position where a part of the light beam emitted from the light source can be received by the light receiving unit without causing vignetting in the light beam incident on the effective area of the objective lens. . A rising mirror that reflects the optical axis of the light beam emitted from the light source so as to be directed in a direction substantially perpendicular to the recording surface of the optical recording medium;
The front monitor is disposed between the light source and the rising mirror, and is displaced in a direction substantially perpendicular to the optical axis when viewed in plan from the optical recording medium side. The optical pickup device according to claim 1.   The optical pickup device according to claim 1, wherein the front monitor is disposed at a position for receiving a part of divergent light emitted from the light source. Between the light source and the objective lens, a collimating lens that converts incident diverging light into parallel light is provided,
The optical pickup device according to claim 3, wherein the front monitor is disposed in proximity to the collimating lens.   5. The optical pickup device according to claim 4, wherein when viewed along a direction parallel to the optical axis, the front monitor is arranged so that a part of the front monitor overlaps the collimating lens. .   6. The optical pickup device according to claim 1, wherein the light receiving portion of the front monitor is provided at a position close to the optical axis side.

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