JP2011113577A - Optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the displacement of 3-beam caused by the wavelength change in the temperature change, which generates tracking errors. <P>SOLUTION: An optical pickup includes: a semiconductor laser which is a light source; an objective lens which collects light to a recording medium; a rising mirror which vertically changes the direction of the optical axis; a folding mirror which is arranged between the semiconductor laser and the rising mirror; a fixing member which fixes the folding mirror; and an adhesive for the folding mirror which fixes the folding mirror to the fixing member and which horizontally changes the thickness. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical pickup used in an optical disc recording / reproducing apparatus that records and reproduces a signal surface of an information recording medium by irradiating the information recording medium with a light beam such as a laser beam.

  An optical disc (hereinafter referred to as BD) that is recorded and / or reproduced (hereinafter referred to as recording / playback) with a short-wavelength light beam called a blue laser, and an optical disc (hereinafter referred to as DVD) that is bonded to a substrate of approximately 0.6 mm. ), And optical discs called compact discs (hereinafter referred to as “CDs”), such as optical discs with different thicknesses, can be used for audio / video equipment, personal computer storage media, navigation and music playback, etc. Applications are expanding. For this reason, the usage environment required by the market becomes severe year by year, and the problem of performance deterioration with respect to temperature changes often occurs due to the variety of usage environments.

  Various components used in optical pickups that record and replay such optical disks are subject to changes in the wavelength of the semiconductor laser, expansion / contraction of the adhesive, distortion of the optical components fixed by the adhesive, etc. Since deviation occurs, there is a need for a design that suppresses changes in the optical axis and aberrations within the operating temperature range, and manufacturing that accurately adjusts the optical axes and aberrations at room temperature in consideration of temperature changes.

  One means for correcting the optical axis with high accuracy is proposed in Patent Document 1. That is, in Patent Document 1, a folding mirror is provided between the rising mirror and the semiconductor laser, and a holder for holding the folding mirror can be rotationally adjusted with respect to the mounting plate. By performing the tilt adjustment of the optical axis using the deflection deformation of the mounting plate, the light incident on the objective lens can be adjusted with high accuracy so as to be perpendicular to the signal surface of the optical disk.

JP 2005-004814 A

  Since the optical pickup described in Patent Document 1 has a mechanism for adjusting the optical axis, it can be bonded and fixed after adjusting the optical axis with high accuracy. Is not listed. For example, a CD semiconductor laser with a long wavelength changes in wavelength by about 3 nm with respect to a temperature change of 10 ° C., and the pitch of the sub beam diffracted by the diffraction grating changes to change the sub beam position on the signal surface of the recording medium. However, since a mechanism for correcting this is not provided, the tracking error generated by the sub-beam during CD reproduction is reduced by a temperature change.

  In order to solve the above problems, an object of the present invention is to provide an optical pickup capable of reducing signal deterioration even when there is a wide range of temperature changes in a use environment.

  An optical pickup according to the present invention is disposed between a semiconductor laser as a light source, an objective lens for focusing on a recording medium, a rising mirror for converting the direction of an optical axis to a vertical direction, and the semiconductor laser and the rising mirror. A bending mirror, a fixing member for fixing the bending mirror, and a bending mirror adhesive for fixing the bending mirror to the fixing portion, wherein the bending mirror adhesive is a light reflection direction of the bending mirror. The thickness is different.

  In the optical pickup, it is preferable that the bending mirror has a horizontal end abutted on the fixing member and is fixed to the other end with an adhesive having a thickness.

  In the optical pickup, it is preferable that the bending mirror has a horizontal end abutted on the fixing member and is fixed to the other end with an adhesive having a thickness.

  The optical pickup includes a diffraction grating that generates a sub beam having a distance B from the main beam on the recording medium, which is disposed between the semiconductor laser and the bending mirror with an angle θ with respect to a tangential direction of the recording medium. A configuration in which the moving direction of the sub-beam in the radial direction of the recording medium due to the wavelength change at the time of temperature change and the direction in which the optical axis changes due to the change in the bending mirror adhesive is the same is preferable.

  In the above optical pickup, the distance between the other end of the bending mirror and the other end of the adhesive application portion is L, the adhesive thickness t of the other end, the thermal expansion coefficient α of the adhesive, the room temperature of the semiconductor laser Is the wavelength change Δλ with respect to the temperature change ΔT, the angle change Δλ / λ × θ with respect to the tangential direction of the three beams with respect to the temperature change ΔT, and the optical axis change 2 × α × t × due to the adhesive change for the bending mirror. A configuration in which ΔT / L is substantially the same is preferable.

  An optical pickup according to the present invention includes a semiconductor laser that irradiates light, a diffraction grating that divides the light from the semiconductor laser into a main beam and a sub beam, and an objective that condenses the main beam and the sub beam via the diffraction grating onto an optical disc. A lens, an optical member provided in an optical path of light guided from the semiconductor laser to the objective lens, a fixing member to which the optical member is fixed, and an adhesive that bonds and fixes the optical member to the fixing member The thickness of the adhesive provided between the optical member and the fixing member is different.

  That is, according to the present invention, since the thicknesses of the adhesives of the optical member and the fixing member can be made different, signal deterioration can be reduced even when there is a wide range of temperature changes in the usage environment.

  For example, since the bonding thickness of the bending mirror in the horizontal direction is changed, the tilt of the bending mirror can be changed by the expansion and contraction of the adhesive when the temperature changes, and the position change of the sub beam caused by the wavelength change of the semiconductor laser It is possible to correct a phase shift from the disk recording surface due to. In addition, if the amount of phase shift due to sub-beam misalignment due to wavelength change and the amount of sub-beam phase shift due to bending mirror angle change are set to be substantially the same, phase shift due to wavelength change can be corrected almost completely. By providing such a correction mechanism, it is possible to supply a high-quality optical pickup with high reliability, which suppresses changes in sub-beams over a wide temperature range and has extremely small signal changes.

Optical configuration diagram of optical pickup in this embodiment Explanatory diagram of the main beam and sub beam positional relationship on the recording medium surface in the same embodiment Configuration diagram for correcting the spot position at the time of temperature change in the same embodiment

  Hereinafter, the optical pickup of the present embodiment will be described with reference to FIGS.

  FIG. 1 shows an optical configuration diagram of the optical pickup according to the embodiment. In FIG. 1, 1 is a semiconductor laser having a light source of, for example, 780 nm for CD, 2 is a diffraction grating for generating a sub beam for tracking error from light emitted from the semiconductor laser 1, and 3 is light incident at an angle. Is fixed to the fixing member 4 with an adhesive 5. The light reflected by the bending mirror 3 rises in the vertical direction by the rising mirror 6, enters perpendicularly to the objective lens 7, and is condensed on the recording medium (CD disk in the present embodiment).

  The main beam 11 and two sub beams (the preceding sub beam 12a and the following sub beam 12b) are imaged on the signal surface of the recording medium 8. The objective lens 11 of the optical pickup is configured to be movable in two axial directions so as to be able to follow the displacement in the perpendicular direction and the radial direction with respect to the recording medium surface. Of these, tracking for detecting the disc displacement in the radial direction. The error signal is calculated from a difference between signals generated from the two sub beams. The positional relationship between the main beam 11 and the sub beam 12 on the recording medium will be described with reference to FIG.

  FIG. 2 is an explanatory diagram showing the positional relationship between the main beam and the sub beam on the recording medium surface in the embodiment. Reference numerals 13a and 13b denote pit rows on the recording medium at intervals of the pitch P, and pits and spaces including information on the recording medium are alternately arranged on this line. Of the pit trains, 13a is a pit train being read by the optical pickup, and 13b is an adjacent pit train. The pit rows 13a and 13b have a spiral shape that is continuous along the circumference. The tangential direction of the recording medium is TAN, and the radial direction is RAD.

  Next, the positional relationship of the reproduction beam will be described. When the distance between the main beam 11 and the sub beam 12b is D1, and the angle between the pit row 13a and θ is θ, the distance D2 = D1 × θ between the pit row 13a and the sub beam 12b in the radius RAD direction is 1 / of the pitch P of the pit row. Θ is adjusted to be 4 times. The distance between the two sub-beams in the radial direction is 2 × D2 = ½ × P, and the polarity is reversed, so that the amplitude of the tracking error is maximized.

  Next, the beam change at the time of temperature change is demonstrated. Since the diffraction angle at the diffraction grating 2 is proportional to the wavelength, the wavelength change when the semiconductor laser 1 having the wavelength λ at room temperature T is increased by the temperature ΔT is Δλ, the change in the distance between the main beam 11 and the sub beam 12b is ΔD1, and the pits. Assuming a change ΔD2 in the radial direction between the row 13a and the sub beam 12b, ΔD1 = Δλ / λ × D1, ΔD2 = Δλ / λ × D2, and the temperature change ΔT makes the distance between the two sub beams in the radial direction normal. The deviation from the adjustment position is 1/2 × P by 2 × ΔD2 = 2 × Δλ / λ × D2 = 1/2 × P × Δλ / λ. This is equivalent to the fact that the sub beams 12b and 12c arranged at an angle θ with respect to the tangential direction of the pit row 13a are changed in angle by θ × Δλ / λ.

  Next, means for correcting the sub-beam position shift caused by the wavelength change Δλ caused by the temperature change ΔT will be described with reference to FIG.

  FIG. 3 is a plan view showing a configuration for correcting the spot position at the time of temperature change in the first embodiment, and is an optical configuration diagram of the optical pickup of the first embodiment of the present invention in FIG. The periphery of the bending mirror 3 is shown. In FIG. 3, the end of the bending mirror 3 has a fixing member 4 and a joint portion 9 that are in contact with each other, and the bending mirror 3 has a thickness t at a location away from the joint portion 9 by t at the fixing portion 4. It is fixed by the adhesive 5 having a coefficient of thermal expansion α with the thickness changed.

  With respect to temperature change ΔT (plus change), the thickness t of the adhesive for the bending mirror 3 changes by t × α × ΔT, and the angle of the mirror 3 changes by t × α × ΔT / L. This angle change is β, and the bending mirror after the change by ΔT is 3 ′. When the optical axis incident on the folding mirror 3 of light from the semiconductor laser 1 at room temperature is R1 and the reflected light is R2, the folding mirror 3 is inclined by β with respect to the temperature change ΔT. Therefore, the reflected light from the folding mirror 3 Changes from R2 to R2 ′ changed by 2 × β.

  In FIG. 2, when the optical axis changes by 2 × β with respect to the temperature change ΔT, the angle with the pit row of the recording medium 8 also changes by the same amount, so the 3 beam angle with respect to the pit row 13a also changes by 2 × β. This is an angle change θ × Δλ / λ that is equivalent to a sub-beam distance change caused by a wavelength change Δλ with respect to a temperature change ΔT, and the direction of the change is reversed, and acts in the direction of correcting the three-beam position shift due to the wavelength change. In addition, when the three beam position angle shift due to the wavelength with respect to the temperature change ΔT and the angle change of the three beams due to the expansion of the adhesive are equal, Δλ / λ × θ = 2 × β = 2 × α × t × ΔT / L, The sub-beam angle deviation caused by the wavelength change of the semiconductor laser 1 can be corrected by the adhesive of the bending mirror 3.

  2 and 3, the temperature change ΔT is described as being positive. However, when ΔT is negative, the three-beam position shift due to the wavelength in FIG. 2 and the angle shift due to the adhesive change in FIG. 3 are opposite to those described above. Therefore, even when ΔT is negative, the positional deviation due to the wavelength can be corrected by the change of the optical axis due to the shrinkage of the adhesive for the bending mirror as in the case of positive.

  Thus, a three-beam position change caused by a change in the wavelength of the semiconductor laser when the temperature changes can be corrected by a change in the thickness of the bending mirror adhesive, and a high-quality optical pickup having a small characteristic change with respect to the temperature change is provided. be able to.

  A semiconductor laser usually has a characteristic that, when the temperature is high, the wavelength of the light to be irradiated becomes long, whereas when the temperature is low, the wavelength of the light to be irradiated is short. In addition, the adhesive usually has a characteristic of expanding when the temperature is high and contracting when the temperature is low. Therefore, by using these characteristics, as described above, the deviation of the sub beam condensed on the optical disk due to the change in wavelength can be canceled by the change in the optical path (semiconductor laser to objective lens) due to the expansion / contraction of the adhesive. I have to.

  The present invention is not limited to the above embodiment, and can be implemented in various forms. An example will be described below.

  In this embodiment, the three-beam method at the time of CD reproduction has been described. However, the present invention can also be applied to other methods using a sub beam for a tracking error signal.

  As described above, the optical pickup according to the present invention is an optical disc recording / reproducing apparatus that records and reproduces an information recording medium by irradiating the information recording medium with a light beam such as a laser beam, or a light used for an optical disc reproducing apparatus. Applicable to pickup.

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Diffraction grating 3 Bending mirror 4 Fixing member 5 Adhesive 6 Standing mirror 7 Objective lens 8 Recording medium 9 Current part (of bending mirror) 11 Main beam 12 Sub beam 13 Pit row

Claims (7)

A semiconductor laser as a light source, an objective lens for focusing on a recording medium, a rising mirror that converts the direction of the optical axis to a vertical direction, a bending mirror disposed between the semiconductor laser and the rising mirror, and the bending mirror An optical pickup comprising: a fixing member that fixes the bending mirror; and a bending mirror adhesive for fixing the bending mirror to the fixing portion, wherein the bending mirror adhesive has different thicknesses in the horizontal direction. 2. The optical pickup according to claim 1, wherein the bending mirror is fixed to the fixing member by an adhesive having a thickness at the other end in contact with the fixing member. A diffraction grating for generating a sub-beam having a distance B from the main beam on the recording medium disposed between the semiconductor laser and the bending mirror and inclined by an angle θ with respect to the tangential direction of the recording medium, 3. The light according to claim 1, wherein a moving direction of the sub beam in the radial direction of the recording medium due to a change in wavelength is the same as a direction in which the optical axis changes due to the change in the adhesive for the bending mirror. pick up. L is the distance between the other end of the bending mirror and the other end of the adhesive application portion, the adhesive thickness t of the other end, the thermal expansion coefficient α of the adhesive, the wavelength λ of the semiconductor laser at room temperature, Assuming that the wavelength change Δλ with respect to the temperature change Δt, the angle change Δλ / λ × θ with respect to the tangential direction of the three beams with respect to the temperature change ΔT and the optical axis change 2 × α × t × ΔT / L due to the adhesive change for the bending mirror are substantially abbreviated. The optical pickup according to claim 3, wherein the optical pickups are the same. A semiconductor laser that emits light;
A diffraction grating for dividing light from the semiconductor laser into a main beam and a sub beam;
An objective lens for condensing the main beam and the sub beam through the diffraction grating onto the optical disc;
An optical member provided in an optical path of light guided from the semiconductor laser to the objective lens;
A fixing member to which the optical member is fixed;
An adhesive that bonds and fixes the optical member to the fixing member;
With
The thickness of the adhesive provided between the optical member and the fixing member is different.
Optical pickup. When the arrangement of the optical member with respect to the fixing member is adjusted, the thickness of the adhesive is different in such a direction that the sub beam condensed on the optical disc rotates about the main beam.
The optical pickup according to claim 5. When the arrangement of the optical member with respect to the fixing member is adjusted, the thickness of the adhesive is adjusted so that the sub beam condensed on the optical disk rotates so as to approach the tangential direction of the objective lens around the main beam. Becomes thicker,
The optical pickup according to claim 5.

Images