JP2004348816A - Optical pickup and optical recording medium processing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup which does not need to use a converging filter having a waveform selection property, and provide an optical recording medium processing device. <P>SOLUTION: A grating member having a first region for diffracting and passing each of luminous fluxes of first wavelength and a second wavelength, and a second region which surrounds the first region and in which diffraction strength of the luminous flux of the first wavelength is smaller than that in the first region is arranged between a light source and a condenser lens. The grating member performs convergence for the luminous flux of the second wavelength. Therefore, even when the depth of a recording layer of the optical recording medium using the luminous flux of the second wavelength is different from the recording medium making the luminous flux of the first wavelength a reproduction light, the problem of insufficient condensing caused by spherical aberration of the condenser lens can be reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical pickup and an optical recording medium processing apparatus that perform at least one of recording and reproducing information on and from different optical recording media using a plurality of light beams having different wavelengths.
[0002]
[Prior art]
An optical recording medium (for example, an optical disk) for recording and reproducing information by using light is used. Optical recording media include a plurality of standards such as a CD (Compact Disc) and a DVD (Digital Versatile Disc). If the standards differ, the wavelength of light used for recording and reproduction, the recording density, the thickness of the substrate (base material) (Depth from the surface to the recording layer).
[0003]
An optical pickup capable of recording and reproducing information from a plurality of optical recording media having different wavelengths of recording light and different recording layer depths, and an optical recording medium processing device (eg, optical disk device) using the same are proposed. Have been.
[0004]
Here, if the same objective lens is used for reproducing optical recording media (for example, CD, DVD) having different recording layer depths, spherical aberration of the objective lens becomes a problem. For example, when reproducing a CD using an objective lens designed for DVD, the recording surface of the CD deviates from the design focal length of the objective lens. For this reason, the convergence position of the laser beam passing through the central portion and the peripheral portion of the lens shifts (spherical aberration occurs), so that the laser beam cannot be sufficiently focused on the recording surface, and it is difficult to reproduce the CD properly. Become.
[0005]
As a method of improving spherical aberration in such a case, for example, it is known to narrow an aperture of an objective lens during reproduction of a CD. That is, the laser beam passing through the peripheral portion of the objective lens is shielded, and only the laser beam passing through the central portion of the objective lens is focused on the recording surface, whereby the spherical aberration is improved and the reproduction of the CD is facilitated.
[0006]
To narrow the aperture of the objective lens only when playing back a CD, a wavelength-selective aperture filter that changes the spot diameter of the luminous flux on the optical recording medium according to the wavelength of the light is placed in front of the condenser lens. (See, for example, Patent Document 1).
[0007]
[Patent Document 1]
JP-A-2002-279885.
[0008]
[Problems to be solved by the invention]
However, if an aperture is arranged in front of the condenser lens, the actuator unit of the optical pickup becomes large, which may be disadvantageous in terms of reduction in size and weight and cost.
[0009]
In view of the above, an object of the present invention is to provide an optical pickup and an optical recording medium processing apparatus that do not require the use of a wavelength-selective aperture filter.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, an optical pickup according to a main aspect of the present invention includes a first light source that emits a first light beam of a first wavelength, a first light source that is close to the first light source, and A second light source that emits a second light beam having a second wavelength different from the first light source, and collects the first and second light beams emitted from the first and second light sources on an optical recording medium. A first area between the first and second light sources and the first and second light sources, and a first area for diffracting and passing each of the first and second light fluxes; And a grating member having a second region where the diffraction intensity of the first light beam is smaller than the first region.
[0011]
An optical recording medium processing apparatus according to another aspect of the present invention includes: (a) a stage on which an optical recording medium is placed; (b) a first light source that emits a first light beam of a first wavelength; A second light source that is close to the first light source and emits a second light flux having a second wavelength different from the first wavelength; and a first light source that is emitted from the first and second light sources. And a condenser lens for condensing each of the second light fluxes on the optical recording medium, and between the first and second light sources and the condenser lens to diffract each of the first and second light fluxes. An optical pickup comprising: a first region through which the first light beam passes and a second region surrounding the first region and having a diffraction intensity of the first light beam smaller than the first region. It is characterized by having.
[0012]
A first region for diffracting and transmitting each of the first and second wavelength light beams, and a second region surrounding the first region and having a diffraction intensity of the first wavelength light beam smaller than the first region. Is disposed between the light source and the condenser lens. For this reason, the grating member plays the role of a stop for the light beam of the second wavelength. Therefore, even if the depth of the recording layer of the optical recording medium that uses the light beam of the second wavelength is different from that of the optical recording medium that uses the light beam of the first wavelength as the reproduction light, poor focusing due to spherical aberration of the focusing lens. Problem can be reduced.
(1) Here, the light condensing position on the optical recording medium condensed by the condensing lens may be different in the optical axis direction between the first and second light fluxes.
[0013]
This can be realized, for example, by designing the grating member such that the spread of the light beam passing through the grating member differs at the first and second wavelengths. By doing so, it is possible to reduce the necessity of moving the condenser lens in the optical axis direction according to the depth of the recording layer of the optical recording medium.
(2) In the lattice member, for example, the first and second regions are substantially concentric, and the size of the first region is 0.37 or more and 0.55 or less in numerical aperture of the condensing lens. can do. For example, the luminous flux can be narrowed by the lattice member so as to have a numerical aperture suitable for reproducing a CD.
(3) A concentric step diffraction grating is formed in the first and second regions, and at least one of the number of steps of the concentric step diffraction grating or the depth from the top to the bottom of the steps. May be different in the first and second regions.
[0014]
By making the number of steps of the diffraction grating or the depth from the uppermost step to the lowermost step of the steps different between the first and second regions, the diffraction intensity in the first and second regions can be changed to the first and second regions. It can be different depending on the wavelength.
(4) The diffraction intensity of the light beam passing through the first region may decrease as going from the center of the substantially concentric circle toward the radial direction.
[0015]
By causing the grating member to function as a so-called apodization filter, it is possible to reduce signal degradation that occurs when the condenser lens moves in the tracking direction.
(5) The optical pickup may further include a collimator lens disposed between the condenser lens and the first and second light sources and configured to convert the first and second light beams into substantially parallel light. .
[0016]
Here, by integrally forming the lattice member and the collimator lens, it is not necessary to arrange a plurality of members. For example, by forming a diffraction grating on the surface of the collimator lens, the grating member and the collimator lens can be integrated.
(6) The grating member may convert any of the first and second light beams into substantially parallel light.
[0017]
The lattice member can also function as a collimator lens.
(7) The optical pickup may further include a light receiving element that receives the first and second light beams reflected from the optical recording medium.
[0018]
Information can be reproduced from the optical recording medium by using the light receiving element.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(1st Embodiment)
FIG. 1 is a schematic diagram illustrating an optical pickup 10 according to the first embodiment of the present invention. The optical pickup 10 reads information from optical recording media 20a and 20b such as CDs and DVDs, and includes a light emitting element 11, an optical path changing element 12, a collimator lens 13, a grating member 14, a condenser lens 15, a light receiving element, and the like. An element 16 is provided.
[0020]
Among them, the light emitting element 11, the optical path changing element 12, the collimator lens 13, the lattice member 14, and the light receiving element 16 are installed in the casing 17.
[0021]
The light-emitting element 11 supports a light-emitting element 11a that emits a light flux L1 of a wavelength λ1 (for example, 635 nm) and a light-emitting element 11b that emits a light flux L2 of a wavelength λ2 (for example, 780 nm) in the same housing. It is a two-wavelength light source. The light beam L1 having the wavelength λ1 can record and reproduce an optical recording medium 20a (for example, DVD) having a relatively thin substrate and a relatively high recording density. The light beam L2 having the wavelength λ2 can record and reproduce data on and from the optical recording medium 20b (for example, CD) having a relatively thick recording medium and a relatively low recording density. The light emitting element 11a and the light emitting element 11b are arranged close to each other at a distance L. Specifically, for example, a laser chip for the light emitting element 11a (a chip on which a laser diode is formed) and a laser chip for the light emitting element 11b are formed as the same chip on the same substrate, and are arranged in a package. Thus, the light emitting element 11 can be configured.
[0022]
The optical path conversion element 12 is an optical element such as a beam splitter that converts the optical path of the light beams L1 and L2 emitted from the light emitting element 11.
[0023]
The collimator lens 13 is a lens that converts the light fluxes L1 and L2 whose optical paths have been converted by the optical path conversion element 12 into parallel light.
[0024]
The grating member 14 is an optical member on which a concentric stepped diffraction grating is formed, and an optical aperture and a degree of spread of a passing light beam change according to the wavelengths λ1 and λ2. The details will be described later.
[0025]
The condenser lens 15 is a lens that condenses the light beams L1 and L2 emitted from the grating member 14 on the optical recording media 20a and 20b.
[0026]
The light receiving element 16 is a light receiving element that receives the light beams L1 and L2 reflected by the optical recording media 20a and 20b.
[0027]
Next, details of the lattice member 14 will be described.
[0028]
FIG. 2 is a front view illustrating a state where the lattice member 14 is viewed from the front. FIG. 3 is a cross-sectional view illustrating a part of the cross section of the lattice member 14.
[0029]
As can be seen from FIGS. 2 and 3, the grating member 14 is divided into regions A and B, and a concentric step-like (step-like) diffraction grating (concentric holographic diffraction grating) is formed in these regions A and B. FIG. 3 illustrates a concentric step-shaped diffraction grating having the number N of steps, the depth ST of each step (step), and the width W of each step, but the number N of steps and each step (step) are shown. ) Differs between the regions A and B in at least one of the depth ST and the depth from the uppermost stage to the lowermost stage (the product of the depth ST of each stage and the number N of stages).
[0030]
The radius ra of the area A is set so that the numerical aperture of the condensing lens 15 is 0.37 or more and 0.55 or less, and the radius rb of the area B is about 1.93 mm or more. That is, the sizes of the areas A and B are set so as to be the apertures suitable for the axial areas of the CD and DVD and the moving of the condenser lens 15 in the tracking direction, respectively.
[0031]
The step depth ST and the number N of steps of this stepped diffraction grating are set so as to guide the light beams L1 and L2 of the wavelengths λ1 and λ2 to different paths. Specifically, the respective step depths STa and STb and the numbers of stages Na and Nb are set such that the diffraction efficiencies of the light beams L1 and L2 and the spread of the diffracted light in the regions A and B are as follows.
(1) Diffraction efficiency η
The light flux L1 of the wavelength λ1 has the step depths STa, STb and STb of the regions A and B so that the diffraction efficiency η1 does not extremely decrease at the radius ra as shown in FIG. Set the number of stages Na and Nb.
[0032]
The light beam L2 of the wavelength λ2: the step depths STa and STb and the number of steps Na and Nb of the regions A and B are set such that the diffraction efficiency η2 in the region B is smaller than the diffraction efficiency η1 in the region A.
[0033]
This is because, in the region A, the step depth STa and the number of stages Na are set so that the diffraction efficiency η is substantially continuous at both the wavelengths λ1 and λ2, and in the region B, the diffraction efficiency η at the wavelength λ1 is equal to the wavelength λ2. Can be realized by setting the step depth STb and the number of steps Nb so as to be greater than the diffraction efficiency of
[0034]
Specifically, as shown below, the product of the step depths STa and STb and the numbers of stages Na and Nb in the regions A and B is set so that the phase difference with respect to the wavelength λ1 is an integral multiple of the wavelength. . Also, for the wavelength λ2, the number of stages Na and Nb are selected such that the efficiency of the region B is smaller than that of the region A.
[0035]
(N-1) · STa · Na = λ1 · m1 (≠ λ2 · m2)
(N-1) · STb · Nb = λ1 · m3 (≠ λ2 · m4)
Here, n is the refractive index of the grating member 14, and m1 to m4 are natural numbers.
[0036]
For example, the order of the diffracted light in the regions A and B is set to be 0th order for the wavelength λ1 and 1st order for the wavelength λ2.
[0037]
FIG. 4 is a graph showing the diffraction efficiency η of the diffracted light by the grating member 14 corresponding to the center distance r. As shown in FIG. 4, the diffraction efficiency η1 of the wavelength λ1 gradually changes with respect to the center distance r, and the diffraction efficiency η of the light beam L2 of the wavelength λ2 becomes η2 at the radius ra of the boundary between the regions A and B, and greatly changes. It turns out that it is.
[0038]
That is, a so-called apodization filter function is provided for the wavelength λ1. By adjusting the diffracted light intensity distribution in the radial direction, it is possible to play the role of an aperture stop and the role of reducing the amount of signal degradation due to the movement of the condenser lens 15 in the viewing direction. If there is no apodization function, the signal deterioration due to the tilt of the optical recording medium 20b becomes remarkable, and the signal reading ability at the wavelength λ1 decreases.
[0039]
By doing so, the wavelength λ1 is given a numerical aperture NA larger than the wavelength λ2, and the grating member 14 functions as an aperture stop whose numerical aperture NA changes depending on the wavelength. Of the optical recording medium 20b due to the movement of the optical recording medium 20b.
(2) The step depths STa and STb and the number of steps Na and Nb are set so that the diffracted light does not have a spread and the incident light beam passes as it is at the spread wavelength λ1. At the wavelength λ2, the width (pitch) W of the stairs is gradually reduced or the number of steps Na or the number of steps is gradually increased from the center to the outside so that the diffracted light has a spread and the incident light beam spreads and passes. By changing the depth STa and the like, the step depth STb and the number of steps Nb are set.
[0040]
FIG. 1 shows the difference in the spread of the diffracted light with respect to the wavelengths λ1 and λ2. The luminous flux L1 having the wavelength λ1 converted into the parallel light by the collimator lens 13 passes through the grating member 14, and the state of the parallel light is maintained as it is. On the other hand, the light beam L2 of the wavelength λ2, which has become parallel light by the collimator lens 13, passes through the grating member 14 and is converted from the parallel light into a divergent light beam having a spread.
[0041]
By doing so, the spread of light can be adjusted according to the difference in the thickness of the base material of the optical recording media 20a, 20b, and the difference in spherical aberration generated in the optical recording media 20a, 20b can be absorbed.
[0042]
The above (1) and (2) can be achieved simultaneously with the same lattice member 14. That is, the light fluxes L1 and L2 of the wavelengths λ1 and λ2 follow different paths, thereby absorbing the difference between the substrate thickness and the numerical aperture of the optical recording media 20a and 20b, and condensing the light flux on each recording layer.
[0043]
Hereinafter, the operation of the optical pickup 10 will be described. In the following description, the light beams L1 and L2 are described in parallel for easy understanding. However, in actuality, depending on the installed optical recording media 20a and 20b, either the light beam 1 or the light beam 2 is emitted from the light emitting element 11. Either one may be emitted.
(1) The first and second light beams emitted from the light emitting element 11 have their optical paths converted by 90 ° by the optical path conversion element 12, become parallel light by the collimator lens 13, and enter the grating member 14.
(2) Since the grating members 14 have different wavelengths λ1 and λ2 of the light beams L1 and L2, they have different effects on the light beams L1 and L2. The light beam L <b> 1 is emitted from the grating member 14 as parallel light emitted from the collimator lens 13. In the light beam L2, the parallel light emitted from the collimator lens 13 becomes divergent light having a spread in the optical axis direction, and the intensity of light passing through the region B becomes weaker than the intensity of light passing through the region A. That is, the second light beam is divergent light, and the diameter of the light beam is reduced.
(3) The light beams L1 and L2 that have passed through the grating member 14 are focused on the recording layers of the optical recording media 20a and 20b. At this time, the light beam L2 is narrowed down from the light beam L1, and is condensed with a small numerical aperture NA. Further, when the light beam L1 is parallel light when passing through the grating member 14, the light beam L2 is divergent light, so that the light beam L2 converges at a position farther from the condenser lens 15 than the light beam L1. In this way, the state of the light beams L1 and L2 emitted from the grating member 14 is adjusted to correspond to the difference in the thickness of the base material of the optical recording media 20a and 20b (the position of the recording layer in the optical axis direction). . As a result, it becomes possible to read the optical recording media 20a and 20b having different thicknesses.
(4) The light beams L1 and L2 reflected by the recording layers of the optical recording media 20a and 20b pass through the condenser lens 15, the grating member 14, the collimator lens 13, and the optical path changing element 12, and enter the light receiving element 16, Information on the optical recording media 20a and 20b is read.
[0044]
In the present embodiment, as shown in FIG. 1, the lattice member 14 is introduced into the optical path on the fixed portion side to absorb the difference between the substrate thickness of the optical recording media 20a and 20b and the numerical aperture NA.
[0045]
Introducing the grating member 14 into the fixed part side optical path has the following advantages.
(1) Since it is not necessary to form a lattice on a surface having a small curvature (for example, a curved surface of a lens), it is easy to manufacture a mold and cost can be reduced.
(2) Since there is no need to attach a special optical element to the biaxial actuator of the movable unit 18, the size and weight of the biaxial actuator can be reduced, and the cost can be reduced.
(3) An optical pickup for recording and reproducing information using a plurality of wavelengths λ1 and λ2 can be realized at low cost.
[0046]
The installation of the apodization filter may be realized by introducing an optical film equivalent to the apodization filter separately from the grating member 14 instead of providing the grating member 14 itself with the apodization filter function as described above.
[0047]
In any case, by installing the apodization filter in the reciprocating optical path on the fixed part side, it is possible to reduce the noise in the signal when the condenser lens 15 is moved in the tracking direction.
(2nd Embodiment)
FIG. 5 is a schematic diagram illustrating an optical pickup 10a according to the second embodiment of the present invention. In the present embodiment, a diffraction grating is formed on the lower surface of the collimator lens 15a, and the collimator lens 15a and the grating member 14a are formed integrally. In other respects, the description is omitted because it is not essentially different from the first embodiment.
[0048]
The grating member 14a can absorb the difference between the base material thickness and the numerical aperture NA of the optical recording media 20a and 20b by utilizing the fact that the light fluxes L1 and L2 follow different paths depending on the wavelengths λ1 and λ2.
(Third embodiment)
FIG. 6 is a schematic diagram illustrating an optical pickup 10b according to the third embodiment of the present invention. In the present embodiment, the optical pickup 10b does not have a collimator lens, and instead, the grating member 14b also functions as a collimator lens. In other respects, the description is omitted because it is not essentially different from the first embodiment.
[0049]
The grating member 14b can absorb the difference between the substrate thickness and the numerical aperture NA of the optical recording media 20a and 20b by utilizing different paths according to the wavelengths λ1 and λ2.
[0050]
【The invention's effect】
As described above, it is possible to provide an optical pickup and an optical recording medium processing apparatus that do not require the use of a wavelength-selective aperture filter.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a configuration of an optical pickup according to a first embodiment of the present invention.
FIG. 2 is a front view illustrating a state where the lattice member is viewed from the front.
FIG. 3 is a cross-sectional view illustrating a part of a cross section of the lattice member.
FIG. 4 is a graph showing the diffraction efficiency of diffracted light by a grating member having an apodization filter function, corresponding to the center distance thereof.
FIG. 5 is a schematic diagram illustrating a configuration of an optical pickup according to a second embodiment of the present invention.
FIG. 6 is a schematic diagram illustrating a configuration of an optical pickup according to a third embodiment of the present invention.
[Explanation of symbols]
10, 10a, 10b Optical pickup 11 (11a, 11b) Light emitting element 12 Optical path conversion element 13 Collimator lens 14 Grid member 15 Condensing lens 16 Light receiving element 17 Casing 18 Actuator 20 (20a, 20b) Optical recording medium

Claims (12)

A first light source that emits a first light beam of a first wavelength among light sources of at least two or more wavelengths;
A second light source that is close to the first light source and emits a second light flux having a second wavelength different from the first wavelength;
A condenser lens for condensing each of the first and second light beams emitted from the first and second light sources on an optical recording medium;
A first region between the first and second light sources and the condenser lens for diffracting and passing each of the first and second light beams, and surrounding the first region; A grating member having a second region in which the diffraction intensity of the first light beam is smaller than the first region;
An optical pickup comprising: 2. The optical pickup according to claim 1, wherein light-condensing positions condensed on the optical recording medium by the condensing lens are different in the optical axis direction between the first and second light fluxes. 2. The optical pickup according to claim 1, wherein the first and second regions are substantially concentric. 4. The optical pickup according to claim 3, wherein the size of the first area is 0.37 or more and 0.55 or less in numerical aperture of the condenser lens. 4. The optical pickup according to claim 3, wherein a concentric stepped diffraction grating is formed in the first and second regions. 6. The optical pickup according to claim 5, wherein at least one of the number of steps of the concentric diffraction grating and the depth from the top to the bottom of the steps differs in the first and second regions. . 4. The optical pickup according to claim 3, wherein the diffraction intensity of the light beam passing through the first area decreases from the center of the substantially concentric circle toward the radial direction. 2. The apparatus according to claim 1, further comprising a collimator lens disposed between the condenser lens and the first and second light sources and configured to convert the first and second light beams into substantially parallel light. Optical pickup. The optical pickup according to claim 8, wherein the grating member and the collimator lens are formed integrally. 2. The optical pickup according to claim 1, wherein the grating member converts one of the first and second light beams into substantially parallel light. The optical pickup according to claim 1, further comprising a light receiving element that receives the first and second light beams reflected from the optical recording medium. (A) a stage on which an optical recording medium is placed;
(B) a first light source that emits a first light beam of a first wavelength;
A second light source that is close to the first light source and emits a second light flux having a second wavelength different from the first wavelength;
A condenser lens for condensing each of the first and second light beams emitted from the first and second light sources on the optical recording medium;
A first region between the first and second light sources and the condenser lens for diffracting and passing each of the first and second light beams, and surrounding the first region; An optical recording medium processing apparatus, comprising: an optical pickup having a grating member having a second region in which the diffraction intensity of one light beam is smaller than the first region.

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