JP2009104742A - Optical pickup and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup capable of suppressing influence of manufacturing variation of a light source part with a reduced workload without increasing the number of components. <P>SOLUTION: The optical pickup 1 is provided with a light source part 11 emitting a light beam, a light condensing means 17 condensing the light beam emitted from the light source part 11 on a recording surface 2a of an optical recording medium 2 and an optical member 15 which is disposed between the light source part 11 and the light condensing means 17 and in which a correction film having transmittance distribution in a prescribed direction to correct the influence of manufacturing variation of the light source part 11 is formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup that enables reading of information recorded on an optical recording medium and writing of information to the optical recording medium by irradiating the optical recording medium with a light beam, and a method of manufacturing the same. The present invention relates to a technique for suppressing the influence of manufacturing variations of a light source unit included in a pickup.

  Optical recording media such as compact discs (CD) and digital versatile discs (DVD) are in widespread use. Furthermore, in recent years, the recording density has been further increased, and an optical recording medium capable of high-density recording such as a Blu-ray disc (BD) has been put into practical use. Reading of information recorded on such an optical recording medium and writing of information to the optical recording medium are performed using an optical pickup (see, for example, Patent Documents 1 and 2).

  The optical pickup receives a light source that emits a light beam, an objective lens that focuses the light beam emitted from the light source on the recording surface of the optical recording medium, and a light beam reflected by the recording surface of the optical recording medium. And a light detection unit that performs photoelectric conversion. As a result, the optical pickup irradiates the optical recording medium with a light beam to enable reading of information recorded on the optical recording medium and writing of information to the optical recording medium.

  By the way, when an optical pickup is manufactured, the optical system is usually configured so that the light intensity of the light beam incident on the objective lens is maximized at the center of the objective lens. That is, the light intensity distribution of the light beam incident on the objective lens is set to a light intensity distribution as shown by the dotted line in FIG. FIG. 5 is an explanatory diagram for explaining the light intensity distribution of the light beam incident on the objective lens.

  However, conventionally, it is known that the laser diode (LD) used in the light source unit has manufacturing variations in the emission direction of the light beam emitted from the light emitting point. Due to this manufacturing variation, the emission direction of the light beam emitted from the light source unit is shifted by, for example, 2 to 2.5 ° if it is larger than the originally intended (ideal) emission direction. It is said that there is.

  When a deviation occurs in the emission direction of the light beam emitted from the light source unit, the position of the light beam incident on the objective lens deviates from the originally aimed position. For this reason, for example, as shown in FIG. 5, the light intensity distribution (solid line) of the light beam incident on the objective lens is shifted from the target light intensity distribution (dotted line). When such a deviation in the light intensity distribution occurs, there arises a problem that the quality of information reading and writing by the optical pickup deteriorates.

For this reason, conventionally, in consideration of the manufacturing variation of the LD, when mounting the LD on the optical pickup, the adjustment of the mounting angle of the LD so that the emission direction of the light beam becomes a constant direction (below, This adjustment is sometimes referred to as tilt adjustment).
JP-A-9-134541 JP-A-10-112055

  However, in order to perform the above-described tilt adjustment, it is necessary to prepare an adjustment mechanism dedicated to tilt adjustment. For this reason, extra costs are required. Further, the tilt adjustment has a problem that the work load is large because the operator needs to make fine preparation while actually checking with eyes.

  In view of the above problems, an object of the present invention is to provide an optical pickup capable of suppressing the influence of manufacturing variations of a light source unit with a small work load and without increasing the number of parts. Another object of the present invention is to provide a method of manufacturing an optical pickup capable of suppressing the influence of manufacturing variations of the light source unit with a small work load and without increasing the number of parts.

  In order to achieve the above object, the present invention is an optical pickup used for reading information recorded on an optical recording medium and writing information on the optical recording medium, and a light source unit for emitting a light beam And a condensing unit that condenses the light beam emitted from the light source unit on the recording surface of the optical recording medium, and is disposed between the light source unit and the condensing unit, and has a transmittance distribution in a predetermined direction. And an optical member on which a correction film for correcting the influence of manufacturing variations of the light source unit is formed.

  According to this configuration, by providing a correction film having a transmittance distribution in a predetermined direction on an optical member that is originally required for the optical pickup, the light intensity distribution of the light beam incident on the light collecting means is corrected, It becomes possible to correct the influence of manufacturing variations of the light source unit. For this reason, the influence of the manufacturing variation of the light source unit can be suppressed with a small work load and without increasing the number of parts.

  Further, the present invention provides the optical pickup having the above-described configuration, wherein the light source unit is a laser diode, and the predetermined direction is a direction parallel to a direction parallel to an active layer of the laser diode and a direction perpendicular thereto. The direction in which the light intensity distribution with the smaller radiation angle of the laser light emitted from the laser diode can be corrected is preferable.

  According to this, in an optical pickup having a laser diode whose cross-sectional shape of the emitted light beam is elliptical, the light beam incident on the objective lens is targeted for the direction that is greatly affected by the manufacturing variation of the laser diode. The intensity distribution is corrected. For this reason, it is possible to effectively suppress the influence of manufacturing variations of laser diodes with a simple configuration.

  The optical pickup according to the present invention may further include a parallel light converting unit that is disposed between the light source unit and the light collecting unit and converts a light beam emitted from the light source unit into parallel light. The optical member is preferably disposed between the condensing means and the parallel light converting means.

  According to this configuration, since the light beam incident on the film formed on the optical member (the film for correcting the influence of manufacturing variations of the light source unit) becomes parallel light, the configuration of the film formed on the optical member is more than necessary. There is no need for complication, and film formation can be facilitated.

  In the optical pickup having the above-described configuration, the optical member may be a quarter-wave plate.

  In order to achieve the above object, the present invention provides a light source unit that emits a light beam, and a light collecting unit that condenses the light beam emitted from the light source unit on a recording surface of an optical recording medium. A method for manufacturing a pickup, in which a predetermined optical member disposed between the light source unit and the light collecting unit is not formed with a correction film for correcting the influence of manufacturing variations of the light source unit. One type, a second type having a predetermined transmittance distribution in a predetermined direction and having a correction film for correcting the influence of manufacturing variations of the light source unit, and the predetermined transmittance of the second type Preparing at least three types of a third type having a transmittance distribution symmetrical to the distribution and forming a correction film for correcting the influence of manufacturing variation of the light source unit; and the light source Depending on the manufacturing state A step of selecting one of the predetermined optical members from a plurality of types prepared, and a step of incorporating the selected predetermined optical member into the optical system of the optical pickup. .

  According to this configuration, in order to be able to correct the influence of manufacturing variations of the light source unit, a plurality of types are prepared for the predetermined optical member arranged in the optical pickup, and appropriate depending on the state of the light source unit. The type is selected. For this reason, the influence of the manufacturing variation of the light source part can be suppressed without preparing an adjustment mechanism for tilt adjustment as an optical member that originally arranges the predetermined optical member in the optical pickup. That is, according to the manufacturing method of the present invention, it is possible to suppress the influence of manufacturing variations of the light source unit with a small work load and without increasing the number of parts.

  ADVANTAGE OF THE INVENTION According to this invention, the optical pick-up which can suppress the influence of the manufacture dispersion | variation in a light source part with little work burden and without increasing a number of parts can be provided, and its manufacturing method.

  Embodiments of an optical pickup and a manufacturing method thereof according to the present invention will be described below, and the contents thereof will be described in detail with reference to the drawings.

  An optical pickup is a device that enables reading of information recorded on an optical recording medium and writing of information on the optical recording medium by irradiating the optical recording medium with laser light. First, the configuration of the optical pickup of this embodiment will be described. FIG. 1 is a schematic diagram showing the configuration of the optical system of the optical pickup of the present embodiment.

  As shown in FIG. 1, the optical pickup 1 of this embodiment includes a laser diode 11, a diffraction element 12, a polarization beam splitter 13, a collimator lens 14, a quarter-wave plate 15, and a rising mirror 16. , An objective lens 17, a cylindrical lens 18, and a photodetector 19.

  Note that the configuration of the optical system of the optical pickup 1 shown here is merely an example, and various changes can naturally be made without departing from the object of the present invention.

  The laser diode 11 is a light source that emits a laser beam having a specific wavelength. Here, the specific wavelength is a wavelength determined by an object on which the optical pickup 1 reads and writes information. For example, if the optical pickup 1 has a configuration corresponding to BD, a laser beam having a wavelength of 405 nm, if the configuration corresponds to DVD, a laser beam having a wavelength of 650 nm, and if the configuration corresponds to CD, the wavelength is 780 nm. The laser diode 11 emits the laser beam.

  FIG. 2 is an explanatory diagram for explaining a laser beam emitted from the laser diode 11. The laser diode 11 has a structure in which an active layer 112 is sandwiched between two clad layers 111a and 111b. The active layer 112 traps carriers and light to cause laser oscillation.

  As shown in FIG. 2, the emitted light from the laser diode 11 has a radiation angle in the x-axis direction (direction parallel to the active layer 111) and the y-axis direction (direction perpendicular to the active layer 111). Because of the difference, the cross-sectional shape is elliptical. Note that the radiation angle (θy) in the y-axis direction is larger than the radiation angle (θx) in the x-axis direction.

  The diffraction element 12 includes a diffraction grating having a predetermined diffraction pattern, and has a function of dividing the laser beam emitted from the laser diode 11 into a main beam and two sub beams. The laser beam emitted from the diffraction element 12 is sent to the polarization beam splitter 13.

  The polarization beam splitter 13 reflects 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 transmitted. Note that the return light incident on the polarization beam splitter 13 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 15. The forward laser beam reflected by the polarization beam splitter 13 is sent to the collimating lens 14.

  The collimating lens 14 has a function of converting incident diverging light into parallel light (that is, functions as parallel light converting means). Therefore, the collimating lens 14 converts the laser beam sent from the polarization beam splitter 13 into substantially parallel light. The forward laser beam emitted from the collimating lens 14 is sent to the quarter-wave plate 15.

  The quarter-wave plate 15 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. In addition, a correction film (for example, a dielectric multilayer film) having a transmittance distribution in a predetermined direction is formed (evaporated) on the incident surface 15a on which the outgoing laser beam of the quarter wavelength plate 15 is incident. There is.

  The reason why the above-described correction film is formed on the quarter-wave plate 15 is that the emission direction of the laser beam emitted from the laser diode 11 may deviate from the target emission direction due to manufacturing variations of the laser diode 11. This is to correct the deviation. Therefore, in the case of using a laser diode that is determined that the emission direction of the emitted laser beam is not deviated from the target emission direction with respect to the laser diode 11 disposed in the optical pickup 1, The wave plate 15 does not have the above-described correction film.

  Whether the quarter-wave plate 15 is a type provided with a correction film, and what type of the quarter-wave plate 15 has a correction film when the correction film is provided. Is determined at the time of manufacture according to the state of the laser diode 11 mounted on the optical pickup 1. Details of this point will be described in the manufacturing method of the optical pickup 1 described later. The forward laser beam emitted from the quarter-wave plate 15 is sent to the rising mirror 16.

  The rising mirror 16 reflects the laser beam transmitted from the quarter wavelength plate 15 so that the optical axis thereof is perpendicular to the recording surface 2 a of the optical recording medium 2. The forward laser beam reflected by the rising mirror 16 is sent to the objective lens 17.

  The objective lens 17 focuses the laser beam sent from the raising mirror 16 on the recording surface 2 a of the optical recording medium 2. The objective lens 17 is mounted on an actuator (not shown) and has a focus direction that is a direction in contact with and away from the optical recording medium 2 and a tracking direction that is parallel to the radial direction of the optical recording medium 2 formed in a disk shape. It is possible to move to. Thereby, focusing control for controlling the focal position of the objective lens 17 to always coincide with the recording surface 2a of the optical recording medium 2 becomes possible. Also, tracking control can be performed in which the beam spot formed by being condensed by the objective lens 17 always follows the track formed on the optical recording medium 2.

  The cylindrical lens 18 is reflected by the optical recording medium 2, and returns to the return laser beam that passes through the objective lens 17, the rising mirror 16, the quarter wavelength plate 15, the collimator lens 14, and the polarization beam splitter 13 in this order. Gives astigmatism.

  The photodetector 19 receives the laser beam reflected by the optical recording medium 2 in a light receiving area (not shown) and converts the optical signal into an electric signal. The electric signal output from the photodetector 19 is processed to become a reproduction signal, a focus error signal, a tracking error signal, or the like.

  Next, a method for manufacturing the optical pickup 1 of this embodiment will be described. In manufacturing the optical pickup 1, the above-described laser diode 11, various optical members 12 to 18, and a photodetector 19 are prepared and placed at predetermined positions on a substrate (optical pickup base, not shown) constituting the optical pickup. It is attached.

  At this time, it is known that the laser diode 11 attached to the optical pickup base has a variation in emission direction due to a variation in manufacturing. For this reason, at the time of manufacturing the optical pickup 1, for the laser diode 11 attached to the optical pickup 1, the laser beam emission direction may be described as the originally intended direction (simply the aimed direction). ) To see how far off.

  Here, as shown in FIG. 2, the laser beam emitted from the laser diode 11 has an elliptical cross-sectional shape, and the radiation angle is different between the x direction and the y direction. For this reason, in the x direction in which the radiation angle is smaller than that in the y direction, the laser beam emitted from the laser diode 11 is affected more greatly when it is deviated from the target direction (incident on the objective lens 17). This means that the influence of the light intensity distribution shift caused by the laser beam position shift is large). For this reason, in this embodiment, only the magnitude of the deviation in the x direction, which is greatly affected by the deviation of the light intensity distribution, is examined, and the influence of the deviation is corrected (details will be described later).

  Note that the degree to which the laser beam emission direction is deviated from the target direction is usually investigated at the manufacturing stage of the laser diode. Therefore, normally, since the magnitude of the deviation is known for each laser diode, the known value may be checked. If such characteristics are not known, it is necessary to examine how much the laser beam emission direction is deviated from the target direction for each laser diode. This investigation method may be based on a known method used at the time of manufacturing the laser diode.

  As described above, when the magnitude of the deviation of the laser diode 11 in the x direction is examined, the type of the laser diode 11 that can suppress the influence of manufacturing variations among the three types of quarter wavelength plates 15 prepared in advance. Select one. This will be described in detail below.

  First, what kind of three types of quarter-wave plate 15 prepared in advance will be described. FIG. 3 is a diagram for explaining the configuration of three types of quarter-wave plate 15 prepared in advance. FIGS. 3 (a), 3 (b), and 3 (c) show 1 of each type. A quarter wave plate 15 is shown.

  The type shown in FIG. 3A (hereinafter referred to as the first type) is a simple quarter-wave plate, and no correction film for generating a transmittance distribution is formed.

  In the type shown in FIG. 3B (hereinafter referred to as the second type), a correction film 20 having a predetermined transmittance distribution in a predetermined direction is formed on the right half of the incident surface 15a on which the outgoing laser beam is incident. ing. Here, the predetermined direction is a direction in which the light intensity distribution in the x direction (see FIG. 2) of the laser beam emitted from the laser diode 11 can be corrected (the vertical direction in FIG. 1 and the horizontal direction in FIG. 3 correspond). . In the present embodiment, the forward laser beam incident on the quarter-wave plate 15 is reflected by the polarization beam splitter 13, and the predetermined direction here and the x direction coincide with each other. Not.

  The correction film 20 having the transmittance distribution in the right half is configured so that the deviation in the emission direction of the laser diode 11 in the x direction is a deviation in the minus direction (see FIG. 2). This is so that the correction can be made. Further, regarding the predetermined transmittance distribution formed on the quarter-wave plate 15, the light intensity distribution of the laser beam that is emitted from the quarter-wave plate 15 and enters the objective lens 17 is at the center of the objective lens 17. On the other hand, the distribution can be corrected so as to be as symmetric as possible.

  In the present embodiment, if the deviation in the emission direction of the laser diode 11 in the x direction is negative, the second type quarter-wave plate 15 is selected regardless of the magnitude of the deviation. . For this reason, the transmittance distribution of the correction film formed on the quarter-wave plate 15 is in any negative shift amount (the range of manufacturing variation is limited, so the limited range However, the light distribution intensity of the laser beam incident on the objective lens 17 is determined to be as symmetric as possible with respect to the center of the objective lens 17.

  In the type shown in FIG. 3C (hereinafter referred to as the third type), a correction film 20 having a predetermined transmittance distribution in a predetermined direction is formed on the left half of the incident surface 15a on which the outgoing laser beam is incident. ing. Since the predetermined direction is the same as that of the second type quarter-wave plate 15, the description thereof is omitted.

  The configuration in which the correction film 20 having the transmittance distribution is formed on the left half is that the deviation in the emission direction of the laser diode 11 in the x direction is a deviation in the plus direction (see FIG. 2). This is to make it possible. Further, the predetermined transmittance distribution formed on the quarter-wave plate 15 has a symmetric transmittance distribution in comparison with the correction film 20 formed on the second-type quarter-wave plate 15. It is comprised so that it may have.

  Next, the operation when one of the three types of quarter-wave plate 15 is selected according to the state of the laser diode 11 will be described with reference to FIG.

  FIG. 4A is a diagram for explaining a case where there is no deviation in the emission direction of the laser diode 11 in the x direction (the deviation is not necessarily zero and includes a range in which the influence of the deviation can be ignored). When there is no deviation in the emission direction of the laser diode 11 in the x direction, it is not necessary to correct the deviation in the laser diode 11. For this purpose, the first type quarter-wave plate 15 having no function of correcting the light intensity distribution of the laser beam incident on the objective lens 17 is selected. Even if such a selection is made, the light intensity distribution of the laser beam incident on the objective lens 17 becomes substantially symmetrical with respect to the center of the objective lens 17 as shown in FIG.

  FIG. 4B is a diagram for explaining a case where the emission direction deviation of the laser diode in the x direction is deviated in the minus direction (see FIG. 2). If the deviation of the emission direction of the laser diode in the x direction is shifted in the minus direction, and if this deviation is not corrected, the light of the laser beam incident on the objective lens 17 as indicated by the broken line in FIG. The intensity distribution causes a deviation. For this purpose, a second type quarter-wave plate 15 that corrects this deviation is selected.

  Then, by selecting the second type quarter wavelength plate 15, the light intensity of the laser beam passing through the correction film 20 formed on the right half can be reduced to a desired level. Thereby, as shown by the solid line in FIG. 4B, the light intensity distribution of the laser beam incident on the objective lens 17 can be made substantially symmetric (approached) with the center of the objective lens 17 as a reference.

  FIG. 4C is a diagram for explaining a case where the emission direction shift in the x direction of the laser diode is shifted in the plus direction (see FIG. 2). If the deviation of the emission direction of the laser diode in the x direction is shifted in the plus direction, and if this deviation is not corrected, the light of the laser beam incident on the objective lens 17 as indicated by the broken line in FIG. Intensity distribution is shifted. For this reason, a third type quarter-wave plate 15 that corrects this deviation is selected.

  Then, by selecting the third type quarter-wave plate 15, the light intensity of the laser beam passing through the correction film 20 formed on the left half can be reduced to a desired level. Thereby, as shown by the solid line in FIG. 4C, the light intensity distribution of the laser beam incident on the objective lens 17 can be made substantially symmetric (approached) with the center of the objective lens 17 as a reference.

  As described above, in the method of manufacturing the optical pickup 1 of the present embodiment, an appropriate one is selected from the three types of quarter-wave plates 15 prepared according to the state of the laser diode 11, and the laser diode 11 and the optical members 12 to 18 are selected. The photodetector 19 is attached. In this case, it is not necessary to adjust the tilt of the laser diode. For this reason, the work burden at the time of manufacturing the optical pickup 1 can be reduced. Further, there is an advantage that it is not necessary to newly increase the number of parts in order to eliminate the tilt adjustment.

  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, three types of the quarter wavelength plate 15 are prepared, and one of the three types is selected according to the state of the laser diode 11. However, it is not limited to this. In order to more appropriately correct the influence of the deviation in the emission direction of the laser diode 11, the type in which the correction film 20 of the quarter wavelength plate 15 is formed may be further increased.

  In the above embodiment, the quarter wavelength plate 15 is provided with the correction film 20 for correcting the influence of the manufacturing variation of the laser diode 11. However, the correction film for correcting the influence of manufacturing variations of the laser diode 11 may be formed on an optical member other than the quarter wavelength plate. However, the optical member provided with such a correction film is preferably disposed at a position where parallel light is incident so that a correction film having a desired transmittance distribution can be easily formed. Considering this point, in the present embodiment, a correction film for correcting the influence of manufacturing variations of the laser diode 11 is formed on the quarter-wave plate 15 on which the laser beam emitted from the collimator lens 14 is incident. It is configured.

  In addition, the optical pickup of the present embodiment is configured to correspond to one type of optical recording medium, but is not limited thereto. That is, for example, the present invention can also be applied to an optical pickup having a plurality of optical systems according to the type of the corresponding optical recording medium.

  According to the present invention, it is possible to provide an optical pickup that can suppress the influence of manufacturing variations of the light source unit with a small work load and without increasing the number of components, and a method for manufacturing the optical pickup. is there.

These are the schematic which shows the structure of the optical system of the optical pick-up of this embodiment. These are the figures for demonstrating the laser beam radiate | emitted from a laser diode. These are the figures for demonstrating the structure of the three types of 1/4 wavelength plate prepared previously at the time of manufacture of the optical pick-up of this embodiment. Explains the operation when one of the three types of quarter-wave plates prepared in advance is selected in accordance with the state of the laser diode at the time of manufacturing the optical pickup of the present embodiment. FIG. These are the figures for demonstrating the light intensity distribution of the light beam which injects into the objective lens with which an optical pick-up is equipped.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up 2 Optical recording medium 2a Recording surface 11 Laser diode (light source part)
14 Collimating lens (parallel light conversion means)
15 1/4 wavelength plate (optical member)
17 Objective lens (condensing means)
20 Correction film

Claims (5)

An optical pickup used for reading information recorded on an optical recording medium and writing information on the optical recording medium,
A light source that emits a light beam;
Condensing means for condensing the light beam emitted from the light source unit on the recording surface of the optical recording medium;
An optical member disposed between the light source unit and the light condensing unit, having a transmittance distribution in a predetermined direction and having a correction film formed to correct the influence of manufacturing variations of the light source unit;
An optical pickup comprising: The light source unit is a laser diode,
The predetermined direction is a direction capable of correcting the light intensity distribution of the laser beam emitted from the laser diode having a smaller radiation angle out of the direction parallel to the active layer of the laser diode and the direction perpendicular to the active layer. The optical pickup according to claim 1, wherein the optical pickup is provided. A parallel light converting unit disposed between the light source unit and the light collecting unit and converting a light beam emitted from the light source unit into parallel light;
The optical pickup according to claim 1, wherein the optical member is disposed between the light collecting unit and the parallel light converting unit.   The optical pickup according to claim 3, wherein the optical member is a ¼ wavelength plate. A method of manufacturing an optical pickup comprising: a light source that emits a light beam; and a condensing unit that condenses the light beam emitted from the light source on a recording surface of an optical recording medium,
A predetermined optical member disposed between the light source unit and the light condensing unit is a first type in which a correction film for correcting the influence of manufacturing variations of the light source unit is not formed, and predetermined in a predetermined direction. A second type having a transmittance distribution and a correction film for correcting the influence of manufacturing variations of the light source unit is formed, and transmission symmetrical to the predetermined transmittance distribution of the second type Preparing at least three types of a third type having a rate distribution and forming a correction film for correcting the influence of manufacturing variations of the light source unit;
Selecting one of the predetermined optical members from a plurality of types prepared according to the manufacturing state of the light source unit;
Incorporating the selected predetermined optical member into the optical system of the optical pickup;
An optical pickup manufacturing method comprising:

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