JP3031220B2 - Optical recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus for optically writing or reading information on or from a plurality of types of disc-shaped recording media.

[0002]

2. Description of the Related Art An optical recording / reproducing apparatus includes an objective lens for correcting a focus shift due to a vertical movement of a warp of an optical disk such as a CD (compact disk) or a magneto-optical disk and a tracking shift due to eccentricity. It is driven in two axes, a focus direction perpendicular to the surface and a tracking direction parallel to the recording medium surface in the radial direction, to optically record or reproduce.

In recent years, optical disks have been increasing in capacity and density as in DVDs (digital video disks) and the like. There are several means for achieving high density of the disk, but a typical one is to increase the NA of the objective lens (NA: numerical aperture, numerical aperture). As a result, the diameter of the light spot condensed by the objective lens can be reduced, and high density can be achieved. However, when the NA of the objective lens is increased, it becomes more susceptible to aberrations due to the tilt of the disk. In order to reduce this effect, it is necessary to make the disk thinner. Actually, the disk thickness of a CD is about 1.2 mm, while the disk thickness of a DVD is about 0.6 mm in a single layer. Therefore, it is difficult to reproduce a CD with a DVD objective lens. CD and DV
In D, since it is necessary to change the NA of the objective lens, for example, in order to reproduce a CD and a DVD with the same device, use an objective lens corresponding to each of the reproduction of the CD and the reproduction of the DVD. Perform playback.

An example of the above-mentioned conventional optical recording / reproducing apparatus will be described below with reference to the drawings.

FIG. 7 is a plan view of a conventional optical recording / reproducing apparatus, and FIG. 8 is a front view showing an optical configuration of the conventional optical recording / reproducing apparatus.

[0006] Reference numerals 12 and 13 denote disks, for example, 13 is C
In D and 12, discs of two kinds of thickness are selectively arranged like DVD. Reference numerals 1a and 1b denote first and second objective lenses that respectively focus on disks 12 and 13 having two different thicknesses. Usually, the NA of the objective lens 1b is about 0.45, and the NA of the objective lens 1a is about 0.6.
Reference numeral 2 denotes a lens holder for holding the objective lenses 1a and 1b. Reference numerals 5a and 5b denote focusing coils for driving the lens holder 2 in the focusing direction F.
It is fixed to. Reference numerals 6a and 6b denote tracking coils for driving the lens holder 2 in the tracking direction T, which are fixed to the lens holder 2. A fixing member 4 supports the lens holder 2 via metal wires 3a to 3d (3c is disposed below 3a). Wire 3
a to 3d, one end is attached to the lens holder 2 and the other end is attached to the fixing member 4.
The lens holder 2 is arranged so as to be substantially parallel to each other, and translates the lens holder 2 in two axes of a focus direction F and a tracking direction T. 21 is a semiconductor laser that emits a light beam, 28 is a grating lens that splits the light beam emitted from the semiconductor laser into a main beam and two auxiliary beams, and 22 is a collimator that converts the light beam emitted from the grating lens 28 into parallel light. The lens 23 is formed by joining two prisms having substantially triangular and substantially parallelogram cross-sections so that the cross-section becomes substantially trapezoidal. A part of the light beam that has entered the lens 1b and reflected from the disk 13 is reflected, and a part of the light beam that has exited the collimating lens 22 on the surface facing the bonding surface 31 and the bonding surface 31 of the parallelogram prism. Reflected objective lens 1a
A prism with a beam splitter that allows a part of the light beam reflected from the disk 12 to be transmitted through the joint surface 31;
Reference numeral 24 denotes a convex lens for condensing the light beam reflected by the disks 12 and 13 and coming out of the prism 23 with a beam splitter. 25 denotes a part of the light beam condensed by the convex lens 24 and reflects a part thereof. A beam splitter 26, an information detection detector for detecting information with a part of the light beam split by the beam splitter 25, and 27 a focus with a part of the light beam split by the second beam splitter 25 Focus and tracking error detection detector for servo detection for tracking and tracking, 2
Reference numeral 0 denotes an optical table for mounting and fixing various optical elements (21 to 28). Reference numeral 10 denotes the center of the disks 12 and 13, and reference numeral 11 denotes a part of the information track on the center of the light beam incident on the disks 12 and 13 from the semiconductor laser 21.

Next, the operation of the conventional optical recording / reproducing apparatus configured as described above will be described. When a thick disk 13 such as a CD or an LD (laser disk) is selectively disposed, a focus in a magnetic circuit (not shown) fixed to the optical bench 20 using the objective lens 1b corresponding to the disk 13 is used. The lens holder 2 is translated in the focus direction F and the tracking direction T with respect to the fixed member 4 fixed to the optical bench 20 via the wires 3a to 3d by the use coils 5a and 5b and the tracking coils 6a and 6b. Servo and information detection in the focus direction F and the tracking direction T are performed. Here, since the optical axis of the objective lens 1b is arranged in the tracking direction T passing through the center of the disk 13, the grating lens 2 is used for servo detection in the tracking direction T when the objective lens 1b is used.
A so-called three-beam tracking method for detecting a difference in the amount of reflected light of the auxiliary beam diffracted by 8 can be used.

When a thin disk 12 such as a DVD is selectively disposed, an objective lens 1a is used corresponding to the disk 12, and focusing coils 5a, 5a in a magnetic circuit (not shown) fixed to an optical table 20 are used. 5b and the tracking coils 6a and 6b, the lens holder 2 is connected to the wires 3a to 3d.
, A translational movement is performed in the focus direction F and the tracking direction T with respect to the fixed member 4 fixed to the optical bench 20 to perform servo and information detection in the focus direction F and the tracking direction T. Here, since the optical axis of the objective lens 1a is not arranged in the tracking direction T passing through the center of the disk 12, the relative angular displacement of the information track 11 with respect to the objective lens 1a at the inner circumference and the outer circumference of the disk 12 is large. Tracking error detection with the auxiliary beam becomes difficult. Therefore, for example, in the servo detection in the tracking direction T when the objective lens 1a is used, the tracking error detection detector 27 is provided by using a dividing line substantially matching the tangential mapping of the information track 11 on the optical axis of the objective lens 1a. And a so-called push-pull method for detecting the difference in the amount of reflected light of the main beam diffracted by the grating lens 28, or a so-called phase difference method for detecting the phase difference of the change in the amount of light of the main beam. At this time, if the effective luminous flux diameters of the objective lens 1a and the objective lens 1b are made substantially the same, the diameters of the light spots incident on the focus and tracking error detecting detector 27 can be made substantially the same. Can be detected.

[0009]

In the optical recording / reproducing apparatus having the above-mentioned structure, there is no need to dynamically switch the objective lenses 1a and 1b depending on the disc to be arranged. Since they are arranged in a direction substantially perpendicular to the focus direction F and the tracking direction T, it is possible to prevent the entire apparatus from being enlarged. However, if the reflectance of the joint surface 31 is α and the transmittance is (1−α), for example, the prism 23 with the beam splitter determines the amount of light beam incident on the convex lens 24 as the amount of light beam emitted from the collimator lens 22. 2α (1-α)
Double. Here, since the reflectance α is 0 or more and 1 or less, the maximum value of 2α (1−α) is 0.5, and there is a problem that the signal light amount of the light beam for information detection is reduced.

An object of the present invention is to solve the above-mentioned conventional problems, and to improve the signal quality by increasing the signal light amount of a light beam for information detection emitted from a prism with a beam splitter. The purpose is to provide.

[0011]

In order to solve the above-mentioned problems, an optical recording / reproducing apparatus according to the present invention provides a light beam reflected or transmitted by a polarizing beam splitter and an optical path changing device and incident on an objective lens. 4 to convert to polarized light
The polarizing beam splitter has a reflectance or transmittance of a light beam reflected or transmitted by the polarizing beam splitter and incident on the quarter wave plate is greater than 50%. Further, it is formed of a polarizing film having a polarizing property such that the transmittance or the reflectance at the time of transmission or reflection by the polarizing beam splitter after being reflected by the disc-shaped recording media having different thicknesses is greater than 50%. Configuration.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a first method for optically writing or reading information on first and second disc-shaped recording media having different thicknesses selectively disposed at substantially coaxial positions. And a first disc corresponding to the second disc-shaped recording medium, respectively.
And a lens holder for simultaneously holding the second objective lens in a radial direction parallel to the recording medium surface of the first and second disc-shaped recording media and in an optical axis direction perpendicular to the recording medium surface. A light source having linearly polarized light, a polarizing beam splitter having a polarization characteristic for separating a light beam of a light beam from the light source, and a polarizing beam splitter having a driving mechanism; An optical path changing element for causing the split light beam to enter the first and second objective lenses, and a light path changing element for converting the light beam coming out of the polarizing beam splitter and entering the first objective lens into substantially circularly polarized light. A quarter-wave plate, means for detecting a focus error signal on the first and second disc-shaped recording media, means for detecting a tracking error signal on the first and second disc-shaped recording media, First And means for detecting an information signal on the second disk-shaped recording medium. The reflectance or transmittance of the light beam reflected or transmitted by the polarizing beam splitter and incident on the quarter-wave plate is determined by The transmittance or the reflectance when the light beam larger than 50% and reflected or transmitted by the polarizing beam splitter and reflected by the first disc-shaped recording medium is transmitted or reflected by the polarizing beam splitter, respectively, is 50. %, So that there is no need to dynamically switch the objective lens with disk-shaped recording media having different thicknesses, so that there is no need for switching means, and that the first and second disks are not used. It is an object of the present invention to provide an optical recording / reproducing apparatus having a large signal light amount of a light beam for information detection obtained by reflected light from a recording medium and having high signal quality.

Hereinafter, an optical recording / reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a plan view of an optical recording and reproducing apparatus according to Embodiment 1 of the present invention, and FIG. 2 shows an optical configuration of the optical recording and reproducing apparatus according to Embodiment 1 of the present invention. It is a front view.

Numerals 12 and 13 are disks as disc-shaped recording media. For example, 13 is a CD, and 12 is a DVD. 1a, 1b
Are first and second objective lenses that respectively focus on disks 12 and 13 of two different thicknesses. Normal objective lens 1
b is about 0.45, and the NA of the objective lens 1a is about 0.45.
It is about 6. Reference numeral 2 denotes a lens holder for holding the objective lenses 1a and 1b. 5a and 5b are lens holders 2
Is a focusing coil for driving in the focusing direction F, and is fixed to the lens holder 2. Reference numerals 6a and 6b denote tracking coils for driving the lens holder 2 in the tracking direction T, which are fixed to the lens holder 2. A fixing member 4 supports the lens holder 2 via metal wires 3a to 3d (3c is disposed below 3a). The wires 3a to 3d have one end attached to the lens holder 2 and the other end attached to the fixing member 4, and are disposed so as to be substantially parallel to each other. The wires 3a to 3d translate the lens holder 2 in two axes of the focus direction F and the tracking direction T. Let it. Reference numeral 21 denotes a semiconductor laser as a light source for emitting a light beam having linearly polarized light; 28, a grating lens as a diffraction element for splitting the light beam emitted from the semiconductor laser into a main beam and two auxiliary beams; This is a collimating lens that converts the emitted light beam into parallel light. Reference numeral 23 denotes a prism with a beam splitter as a polarizing beam splitter and an optical path changing element. Two prisms having substantially triangular and substantially parallelogram cross sections are joined so that the cross sections become substantially trapezoidal, and have a polarization property. A part of the light beam that has exited the collimating lens 22 at the joint surface 30 is transmitted and incident on the objective lens 1b to reflect a part of the light beam reflected from the disk 13 and the joint surface 3
A part of the light beam that has exited the collimating lens 22 is reflected on the surface opposite to the bonding surface 30 of the 0 and parallelogram prisms, is incident on the objective lens 1a, and a part of the light beam reflected from the disk 12 is reflected on the bonding surface 30. Through. 29 is a quarter-wave plate for converting the light beam emitted from the prism 23 with the beam splitter into circularly polarized light, and 24 is the disk 12, 1
A convex lens 25 for condensing the light beam emitted from the prism 23 with the beam splitter after being reflected by 3; a beam splitter 25 for transmitting a part of the light beam condensed by the convex lens 24 and reflecting a part; Is an information detection detector for detecting information with a part of the light beam split by the beam splitter 25, and 27 is a second beam splitter 2
A focus and tracking error detection detector that performs focus and tracking servo detection with a part of the light beam separated in 5, and 20 is an optical element (21)
To 29). Also, 1
Reference numeral 0 denotes the center of the disks 12 and 13, and reference numeral 11 denotes a part of the information track on the center of the light beam incident on the disks 12 and 13 from the semiconductor laser 21.

Next, the operation of the optical recording / reproducing apparatus of the first embodiment configured as described above will be described.

When a thick disk 13 such as a CD or LD (laser disk) is selectively disposed, the disk 13
The focusing coil 5 in a magnetic circuit (not shown) fixed to the optical bench 20 using the objective lens 1b corresponding to
a, 5b and the tracking coils 6a, 6b cause the lens holder 2 to translate in the focusing direction F and the tracking direction T with respect to the fixed member 4 fixed to the optical bench 20 via the wires 3a to 3d. F. Perform servo and information detection in the tracking direction T. Here, since the optical axis of the objective lens 1b is disposed in the tracking direction T passing through the center of the disk 13, the diffraction by the grating lens 28 is performed for the servo detection in the tracking direction T when the objective lens 1b is used. A so-called three-beam tracking method for detecting a difference in the amount of reflected light of the auxiliary beam can be used.

When a thin disk 12 such as a DVD is selectively disposed, a focusing coil 5a, a focusing coil 5a in a magnetic circuit (not shown) fixed to an optical table 20 using an objective lens 1a corresponding to the disk 12 is used. 5b and the tracking coils 6a and 6b, the lens holder 2 is connected to the wires 3a to 3d.
, A translational movement is performed in the focus direction F and the tracking direction T with respect to the fixed member 4 fixed to the optical bench 20 to perform servo and information detection in the focus direction F and the tracking direction T. Here, as shown in the conventional example, when the objective lens 1a is used, the tracking error detection detector 27 is used for servo detection in the tracking direction T.
Is divided into two parts by a dividing line substantially matching the tangential mapping of the information track 11 on the optical axis of the objective lens 1a, and a so-called push-pull method for detecting a difference in reflected light amount of the main beam diffracted by the grating lens 28, or A so-called phase difference method for detecting a phase difference of a change in light amount of the main beam is used. At this time, if the effective luminous flux diameters of the objective lens 1a and the objective lens 1b are made substantially the same, focus,
Since the diameter of the light spot incident on the tracking error detection detector 27 can be made substantially the same, the servo signal can be detected with the same division pattern. Further, since there is no need to dynamically switch the objective lens depending on the disc, there is no need for a switching means, and the objective lens is arranged in a direction substantially perpendicular to the focus direction and the tracking direction, thereby preventing the entire apparatus from being enlarged.

The joining surface 30 of the prism 23 with a beam splitter has polarization characteristics. For example, when the light beam from the semiconductor laser 21 is an S-polarized beam perpendicular to the plane of FIG. The reflectance of S-polarized light is Rs, the transmittance of S-polarized light is (1-Rs), and the transmittance of P-polarized light is Tp, P
Assuming that the reflectance of the polarized light is (1−Tp), the amount of the light beam incident on the convex lens 24 because the light passes through the quarter-wave plate 29 is Rs (1-Tp) of the light beam emitted from the collimating lens 22. Rs + Tp) times. Here, when Rs and Tp are set to be larger than 0.5, Rs (1-R
s + Tp)> 0.5, so that the signal light amount of the light beam for information detection is larger than in the case of using the conventional non-polarized beam splitter represented by 2α (1−α), so that more stable optical performance is obtained. Optical recording / reproducing apparatus having the above.

In the first embodiment of the present invention, Rs and Tp are set to be larger than 0.5 because the light beam reflected by the bonding surface 30 enters the quarter-wave plate 29. The transmitted light beam is a quarter-wave plate 2
In the case of an optical recording / reproducing apparatus having a configuration in which the light is incident on the P.9, the S-polarized light transmittance (1-Rs) and the P-polarized light reflectance (1-T
Needless to say, the same effect can be obtained by setting p) to be larger than 0.5.

(Embodiment 2) Next, an optical recording / reproducing apparatus according to Embodiment 2 of the present invention will be described with reference to the drawings.

FIG. 3 is a front view showing an optical configuration of an optical recording / reproducing apparatus according to Embodiment 2 of the present invention.

The basic configuration and operation are the same as in the first embodiment of the present invention. In the second embodiment of the present invention, the prism 23 with the beam splitter is formed by joining two prisms having substantially the same parallelogram cross-sectional shape so that the cross section is substantially a parallelogram. The bonding surface 30 has a polarizing property, and the surface of each parallelogram prism facing the bonding surface 30 is a reflection surface.

By using the prism with the beam splitter of this shape, the same effect as that of the first embodiment of the present invention can be obtained, and two flat plates (23a, 23a) as shown in FIG.
The desired prism with a beam splitter can be obtained by simply cutting (cut line is shown by a broken line) into a parallelogram shape after laminating b), thereby improving mass productivity.

(Embodiment 3) Next, an optical recording and reproducing apparatus according to Embodiment 3 of the present invention will be described with reference to the drawings.

FIGS. 5 and 6 are plan views showing the positional relationship between the optical recording and reproducing apparatus according to the third embodiment of the present invention and a disk.

The basic configuration and operation are the same as in the first embodiment of the present invention. In the third embodiment of the present invention, the optical bench 20 and the disc center 1 are switched by a switching means (not shown).
0 is relatively shifted in a direction perpendicular to the focus direction F and the tracking direction T so that the objective lens 1
The optical axes a and 1b are made to coincide with each other in the tracking direction T including the disk center 10. In this case, switching means is required as compared with Embodiments 1 and 2 of the present invention. However, in both the case of using the objective lens 1a and the case of using the objective lens 1b, three beams are used for servo detection in the tracking direction T. The tracking method can be used, and there is no need to switch the detection method depending on the disk. It goes without saying that the same effects as those of the first and second embodiments of the present invention can be obtained with respect to prevention of enlargement of devices other than the switching means and stabilization of optical performance.

As the switching means, a chassis (not shown) on which the entire optical recording / reproducing apparatus is mounted may be moved by using a motor, a plunger or the like as a power source, or a spindle motor (shown in FIG. May be moved using another motor or plunger as power.

[0029]

The optical recording / reproducing apparatus according to the present invention is a four-minute optical element for converting a light beam from a light source into a circularly polarized light beam incident on an objective lens via a polarizing beam splitter and an optical path polarizing element. And a disc-shaped light beam having a reflectivity or a transmissivity of more than 50% for a light beam reflected or transmitted by the polarizing beam splitter and incident on the quarter-wave plate, and having a different thickness. After being reflected by the recording medium,
By forming the polarizing beam splitting element to have a polarization characteristic such that the transmittance or reflectance when transmitted or reflected by the polarizing beam splitting element is greater than 50%,
The amount of signal of the light beam for information detection obtained by reflection from the disk-shaped recording medium can be increased, and an optical recording / reproducing apparatus with high signal quality can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view of an optical recording / reproducing apparatus according to a first embodiment of the present invention.

FIG. 2 is an exemplary front view showing the optical configuration of the optical recording / reproducing apparatus according to the embodiment;

FIG. 3 is a front view showing an optical configuration of an optical recording / reproducing apparatus according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram showing a method for producing a prism with a beam splitter in the optical recording and reproducing apparatus of the embodiment.

FIG. 5 is a plan view showing a positional relationship between the optical recording and reproducing apparatus and a disk according to a third embodiment of the present invention;

FIG. 6 is a plan view showing the positional relationship between the optical recording and reproducing apparatus of the embodiment and a disk;

FIG. 7 is a plan view of a conventional optical recording / reproducing apparatus.

FIG. 8 is a front view showing an optical configuration of a conventional optical recording / reproducing apparatus.

[Explanation of symbols]

 1a, 1b Objective lens 2 Lens holder 3a to 3d Wire 4 Fixing member 12, 13 Disc 20 Optical table 21 Semiconductor laser 22 Collimating lens 23 Prism with beam splitter 24 Convex lens 25 Beam splitter 26 Detector for information detection 27 Focus and tracking error detection Detector 28 Grating lens 29 Quarter wave plate 30 Joint surface

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-197038 (JP, A) JP-A-4-212731 (JP, A) JP-A-61-175942 (JP, A) JP-A-9-99 155170 (JP, A) JP-A-9-120573 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B ^7/ 09-7/22

Claims (5)

(57) [Claims] 1. The first and second disks for optically writing or reading information on first and second disk-shaped recording media having different thicknesses selectively disposed at substantially coaxial positions. A lens holder for simultaneously holding first and second objective lenses respectively corresponding to the shape recording medium;
And an objective lens driving device having a mechanism for driving in a radial direction parallel to the recording medium surface of the second disk-shaped recording medium and in an optical axis direction perpendicular to the recording medium surface. A light source having: a light beam having a polarization characteristic for separating a light beam of a light beam from the light source; and the first and second light beams separated by the polarizing light beam separation element. An optical path changing element for entering the objective lens; a quarter-wave plate for converting a light beam coming out of the polarizing beam splitter and entering the first objective lens into substantially circularly polarized light; A means for detecting a focus error signal on the first and second disc-shaped recording media; a means for detecting a tracking error signal on the first and second disc-shaped recording media; and the first and second disk Is composed of a means for detecting an information signal on a recording medium, the reflected or transmitted by the above polarizing beam splitter 4
The light beam incident on the half-wave plate has a reflectance or transmittance of more than 50%, and is reflected or transmitted by the polarizing beam splitter and reflected by the first disc-shaped recording medium. An optical recording / reproducing apparatus, wherein the transmittance or the reflectance when each of the light is transmitted or reflected by the polarizing beam splitter is greater than 50%. 2. The method according to claim 1, wherein the first disc-shaped recording medium is thinner than the second disc-shaped recording medium, and the first objective lens has a larger NA than the second objective lens.
An optical recording / reproducing apparatus according to claim 1. 3. A diffraction element having a function of generating a main beam and at least two auxiliary beams in an optical path between the light source and the first and second objective lenses, wherein a tracking error is generated by the two auxiliary beams. The optical recording / reproducing apparatus according to claim 1, wherein a signal is obtained. 4. The optical recording / reproducing apparatus according to claim 1, wherein the polarizing beam splitter and the optical path changing element are constituted by parallelogram prisms having substantially the same cross-sectional shape and having a polarizing film on a joint surface. apparatus. 5. The method according to claim 5, wherein the recording medium passes through the center of the selectively disposed first disc-shaped recording medium or the second disc-shaped recording medium , and
On a straight line in the radial direction parallel to the recording medium surface of the disc-shaped recording medium
4. The optical recording / reproducing apparatus according to claim 1, further comprising means for selectively arranging the optical axis of the first objective lens or the second objective lens.