JPH08255372A - Optical pickup - Google Patents

Abstract

PURPOSE: To provide an optical pickup capable of reproducing information from two kinds of optical disks with different thickness of a prescribed part with simple constitution. CONSTITUTION: A cube 104 is turnable around a center O coinciding with an optical axis, and further, a raising mirror having reflection surfaces 104a, 104b on a surface and a back surface is provided in the oblique direction of 45 deg.. Further, the surface opposite to the disks D1, D2 between the reflection surface 104a side of the cube 104 is formed to a recessed surface shape (a concave lens 104c), and another surface is formed by a plane. The focusing position of an objective lens 106 focuses on a recording layer D2b of a t=0.6mm thickness disk D2 by approaching to the objective lens 106 side when the concave lens 104c is not arranged on an optical path, and on the other hand, the focusing position focuses on the recording layer D1b of a t=1.2mm thickness disk D1 by parting from the objective lens 106 when the concave lens 104c is arranged on the optical path.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup, and in particular, information can be read from two types of optical discs in which pits are formed from an incident end face of an optical disc on which a light beam is incident and a thickness t reaching a recording layer surface is different. The present invention relates to a so-called bifocal optical pickup, for example, an optical pickup having compatibility with a low-density optical disk having a thickness t = 1.2 mm and a high-density optical disk having a thickness t = 0.6 mm.

[0002]

2. Description of the Related Art Conventionally, a thickness t from an incident end surface of an optical disk on which a light beam is incident to a pit is formed and reaches a recording layer surface
For example, a hologram system has been proposed as a bifocal optical pickup that is compatible with a = 1.2 mm thick disc and a t = 0.6 mm thick disc. This technique is (1) "DUAL FOCUS OPTICAL HEAD FOR 0.6mm AND 1.2mm
DISK "OPTICAL REVIEW VOL.1 No. 1 (1994) 27-29 (2)" DUAL FOCUS OPTICAL HEAD FOR 0.6mm AND 1.2mm
DISK "Optical Data Storage Topical Meeting 1994 MA
Y 16-18 (3) "2-focal optical head" It is disclosed in the 2nd 1994 optical disk conference '95 .6.7. In this hologram method, one light source (= one wavelength) is used, 0th-order and 1st-order diffracted light is generated by a hologram element, spots at different positions on the optical axis are applied, and the hologram is changed according to the thickness t. The spot is focused on the disc and the reflected light is detected by a single photodetector.

As another conventional example, Japanese Patent Laid-Open No. 6-3
A method using two light sources (= 2 wavelengths) is proposed in FIG. 1 of Japanese Patent No. 25405, and one light source (one wavelength) is used in FIG. On the other hand, a method that can be inserted and removed has been proposed.

FIG. 5 shows a conventional example of this one-wavelength optical lens insertion / removal method. For example, as a correction element 45, a convex lens is moved in the direction orthogonal to the optical path so that it can be inserted into and removed from the optical path. It is possible. In FIG. 5, the disc D1
In the case of a low-density optical disk of t = 1.2 mm, the correction element 45 does not exist on the optical path, and the light beam from the light source 2 causes the collimator lens 12, the beam shaping prism 13, the beam splitter 5, and the quarter wavelength plate. 7. After passing the mirror 42,
The objective lens 8 forms a minute spot light on the recording layer D1b through the substrate D1a of the disc D1.

The light beam reflected by the recording layer D1b of the disc D1 is converted into the objective lens 8, the mirrors 42, 1
It passes through the / 4 wavelength plate 7, is reflected by the beam splitter 5, and enters the photodetector 11 through the condenser lens 26, the concave lens 27, and the cylindrical lens 28. On the other hand, when the disc D1 is a high-density optical disc with t = 0.6 mm, a convex lens is arranged in the optical path as the correction element 45. Therefore, the focus position of the objective lens 8 approaches the objective lens 8, and thus the disc D1 Even if the thickness t of the substrate D1a is small, a minute spot light is formed on the recording layer D1b.

[0006]

[Problems to be Solved by the Invention]

(1) However, in the hologram system, one light source (= 1 wavelength) is used, and different spots are focused on the disk according to the thickness t. There is a point.

The light utilization efficiency cannot be increased. The first-order emission diffraction efficiency is 29% at the time of emission and 30% at the time of incidence,
Since the total efficiency is 8.7% in a round trip, only about 1/10% of the reflected light intensity can be obtained for normal reading. Therefore, in order to set the optical power on the optical sensor to about 10 μW, it is necessary to increase the utilization efficiency of the emitted light of the laser diode (LD), which requires a beam shaping prism and the horizontal direction of the LD. The ratio of vertical divergence angle (aspect ratio) must be close to "1". However, the achievable values are about 8 ° and 32 ° due to the structure of the LD and the self-excited oscillation structure, and in order to make the astigmatism of the LD negligible, a low NA (numerical aperture) is required. Since the collimator lens is required, the problem of the light efficiency of the hologram element system is important.

The parts are complicated and the development cost is high. In order to create a hologram element, it is necessary to form the mask by electronic drawing, and it is necessary to take measures against wavelength dependence.

A pseudo signal countermeasure section for the servo detection signal is required, and the circuit becomes complicated. In servo detection signal, t =
If a focus search operation is performed when reproducing a 0.6 mm thick disc, t = 1.2 at the preceding position on the optical axis.
Since the reading spot of the mm-thick disc is focused ahead of time on the signal surface of the t = 0.6 mm-thick disc, an S curve having a low level is formed in advance in the astigmatism error detection system. Since this position is not the normal focus position, the usual servo control circuit needs to be further devised such as control for continuing the operation of bringing the objective lens closer to the disk. Otherwise, the focus servo may be pulled into the wrong position.

The tolerance of mounting dimensions is narrowed. It is expected that the hologram element and the objective lens will be integrally processed in the future, but until then, the hologram element and the objective lens are separate elements, and therefore high assembly precision is required. -Wavelength fluctuation Since the wavelength is designed to be a specific wavelength, characteristics such as diffraction efficiency change when the wavelength changes, and chromatic aberration correction is required because compensation must be performed in consideration of the change, which complicates.

(2) In the two-light source system disclosed in Japanese Patent Laid-Open No. 6-325405, an optical element for each light source is separately required, which increases the size and weight. (3) Although the problems of (1) and (2) above can be solved by the one-wavelength / optical lens insertion / removal method shown in FIG. 5, there are the following problems. Since the correction element 45 is moved in the direction orthogonal to the optical path, that is, in the linear direction, accuracy within the movable distance range is important, and the number of adjustment steps is increased. In addition, the center of the lens must be perfectly aligned with the optical axis and the lens should not be tilted with respect to the optical axis. Furthermore, since the driving force in linear motion is proportional to the position of the movable part, a large driving force is required.

In view of the above-mentioned conventional problems, it is an object of the present invention to provide an optical pickup capable of reproducing information from two types of optical disks having different thicknesses with a simple structure.

[0013]

In order to achieve the above object, the present invention is rotatably arranged between a first angle and a second angle, and when the first angle is set, a light source and an objective lens are used. The lens unit is arranged in the optical path of the optical system to be formed, and the rotating lens unit is arranged so that the lens unit is arranged outside the optical path at the second angle. I am trying to rotate between the angles. Further, the light beam is formed by a rising mirror that is formed in a cube shape and is rotatable in an angle range of at least 180 ° about the optical axis of the light beam as a rotation axis, and a reflecting surface is formed on each of the front surface and the back surface. And a cube-shaped optical system for refracting the light beam reflected by the reflecting surface with different refracting power by two lens systems formed in each of the reflecting directions of the reflecting surface. According to the present invention, it is preferable that the focusing position of the objective lens is moved by rotating the cube-shaped optical system so that one of the two lens systems is arranged in the optical path according to the thickness t. It is a mode.

That is, according to the present invention, a light source for emitting a light beam, an objective lens for condensing the light beam, and a rotatable arrangement between a first angle and a second angle are provided. When the angle is 1, the lens unit is arranged in the optical path of the optical system formed by the light source and the objective lens,
Light having a rotating lens means configured to dispose the lens portion outside the optical path at an angle of, and a means for rotating the lens means between the first angle and the second angle. Pick-up provided.

That is, according to the present invention, a light source for emitting a light beam and a cube-shaped light source are rotatable in an angular range of at least 180 ° about an axis intersecting the optical axis of the light beam. The light beam is reflected by a rising mirror having reflecting surfaces formed on the front surface and the back surface, and is reflected by the reflecting surface by two lens systems formed in each of the reflecting directions of the reflecting surface. A cube-shaped optical system that refracts a beam with different refracting powers, an objective lens that condenses a light beam refracted by one of the two lens systems of the cube-shaped optical system onto an optical disc, and a thickness of a predetermined portion of the optical disc. 2 according to
An optical pickup having a cube drive mechanism that moves the focus position of the objective lens by rotating the cube-shaped optical system so that one of the two lens systems is arranged in the optical path is provided.

[0016]

According to the present invention, the lens portion is arranged in the optical path of the optical system formed by the light source and the objective lens at the first angle according to the thickness t of the predetermined portion of the optical disk, and at the second angle. Since the lens portion is arranged outside the optical path, or the focus position of the objective lens is moved by rotating the cube-shaped optical system so that one of the two lens systems is arranged in the optical path, It is possible to perform reproduction from two types of optical disks having different thicknesses t of a predetermined portion with a simpler configuration than the conventional hologram element, two light source system, one light source / optical lens linear direction insertion / removal system.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a schematic view showing an embodiment of an optical pickup according to the present invention, FIG. 2 is an explanatory view showing a rotating mechanism of the cube of FIG. 1, and FIG. 3 is an explanatory view showing a stopper of the cube of FIG. 4A and 4B are explanatory views comparing the optical systems of FIGS. 1A and 1B.

FIG. 1A shows a case of reproducing from a low-density optical disc D1 of t = 1.2 mm, and FIG. 1B shows t =.
The case of reproducing from a 0.6 mm high-density optical disc D2 is shown. Here, the distance between the substrate D1a of the disc D1 and the substrate D2a of the disc D2 with respect to the objective lens 106.
That of the recording layer D1 of the disc D1
b and that of the recording layer D2b of the disc D2 are the thickness t
Depends on. In FIG. 1, a beam splitter 102, a collimator 103, and a cube 104 are arranged in the optical path of the light beam emitted from the LD 101.

The cube 104 is rotatable about a center O coinciding with the optical axis, and a raising mirror having reflecting surfaces 104a and 104b on its front and rear surfaces is provided in a 45 ° oblique direction thereof. . Further, of the side of the reflecting surface 104a of the cube 104, the surface facing the disks D1 and D2 is formed into a concave shape (concave lens 104c), and the other surface is formed into a flat surface. Here, the concave lens 104c
Has a negative refractive power corresponding to the thickness t of the disc D1,
Also, the other surface of the cube 104 has no refractive power. The cube 104 can be rotated around the center O by a motor 110 as shown in FIG. 2, and when it is rotated by 180 ° as shown in FIG. It is configured to be positioned.

Returning to FIG. 1, the λ / 4 plate 105 and the objective lens 1 are provided in the optical path reflected by the reflecting surfaces 104a and 104b.
06 and disks D1 and D2 are arranged, and a cylindrical 107 and an optical sensor 108 are arranged in the optical path reflected by the beam splitter 102.

In such a structure, t = 1.2 mm
When reproducing the low-density optical disc D1 of FIG.
As shown in (a), the cube 104 is rotated and positioned so that the reflecting surface 104a and the concave lens 104c of the cube 104 face the disc D1. In this case, the light beam emitted from the LD 101 passes through the beam splitter 102 and is collimated by the collimator 103,
Then, it is reflected by the reflecting surface 104a of the cube 104 at an angle of 90 °, then diffused by the concave lens 104c according to its negative refracting power, and then passes through the λ / 4 plate 105 and the objective lens 106 causes the substrate D1 of the disc D1.
A minute spot light is formed on the recording layer D1b through a.

Then, the light beam reflected by the recording layer D1b of the disc D1 is condensed by the objective lens objective lens 106, then passes through the λ / 4 plate 105, is collimated by the concave lens 104c, and is reflected on the reflecting surface of the cube 104. The light beam is reflected at an angle of 90 ° by 104a, then collected by the collimator 103, and then by the beam splitter 1.
It is reflected by 02 at an angle of 90 °, and then is imaged on the light receiving surface of the optical sensor 108 by the cylindrical lens 107.

On the other hand, when reproducing from the high density optical disc D2 of t = 0.6 mm, the cube 104 is rotated so that the reflecting surface 104b of the cube 104 faces the disc D1 as shown in FIG. 1 (b). And be positioned. In this case, the light beam emitted from the LD 101 passes through the beam splitter 102, is collimated by the collimator 103, is then reflected by the reflecting surface 104 b of the cube 104 at an angle of 90 °, and is diverged or converged by the cube 104. Without passing through, the light passes through the cube 104, then the λ / 4 plate 105, and the objective lens 106 forms a minute spot light on the recording layer D2b through the substrate D2a of the disc D2.

Then, the light beam reflected by the recording layer D2b of the disc D2 is collimated by the objective lens objective lens 106, then passes through the λ / 4 plate 105, and then is reflected by the reflecting surface 104b of the cube 104 at an angle of 90 °. Is passed through the cube 104 without being diverged or converged by the cube 104, is then focused by the collimator 103, and is then beam splitter 102.
Is reflected at an angle of 90 °, and then is imaged on the light receiving surface of the optical sensor 108 by the cylindrical lens 107.

A specific example of this optical system will be described with reference to FIG. First, when the concave lens 104c is not arranged in the optical path, as shown in FIG.
6, an optical system with f = 2.8 mm and NA = 0.6 is configured. The focus position of the objective lens 106 in this case is t = 0.6 m because the concave lens 104c is closer to the objective lens 106 side than the optical system shown in FIG.
Focus on the recording layer D2b of the m-thick disc D2.

On the other hand, when the concave lens 104c is arranged in the optical path as shown in FIG. 4 (b), the concave lens 1
The focal length f of 04c is 36.9 mm, the concave lens 104c
The distance between the focal point and the objective lens 106 is 48 mm, and an optical system with a relatively low NA is constructed. In this case, the focus position of the objective lens 106 is farther than the objective lens 106, so t = 1.2 mm thickness. Focus on the recording layer D1b of the disc D1.

Therefore, according to the above-described embodiment, the mirror (reflecting surface 104) is set up in the diagonal direction of the cube 104.
a, 104b) and one reflecting surface 104a
Since the concave lens 104c is formed only on the side and the cube 104 is rotated so that the concave lens 104c can be inserted into and removed from the optical path, t = 1.2 mm thick disc D1 and t = 0.6 mm thick disc D2. Compatible with.

In this case, since the cube 104 is rotated, the optical systems for the disks of t = 1.2 mm thickness and t = 0.6 mm completely coexist, and therefore, the optical paths are different from those of the conventional example (FIG. 5). It is possible to reduce the adjustment man-hours as compared with the configuration in which insertion and removal are possible in the orthogonal direction. Further, in this rotation method, after the initial adjustment, the accuracy of the optical axis and the center of the concave lens 104c and the inclination angle are determined by the accuracy of the rotation angle, so that the assembly accuracy can be maintained for a long time. That is, since the reflecting surfaces 104a and 104b of this embodiment always intersect the optical axis, the angle adjustment only needs to be performed on the reflecting surfaces 104a and 104b, and if the center of rotation is adjusted, the angle accuracy is the accuracy of the parts. Can be secured only by. Further, the moment of inertia of the rotating body does not directly correspond to its mass, but becomes an integrated sum of the radius from the center of rotation and the mass at that point, and it can be driven with a smaller driving force than in the conventional linear movement system.

Here, in the above embodiment, the rotating cube 1
No. 04 concave lens 104c and no concave lens (no refracting power)
Although the focus position of the objective lens 106 is shifted by the combination of, the combination may be any combination as long as the diffused light flux is incident on the objective lens, for example, no lens +
A combination such as a convex lens, two convex lenses having different refractive powers or a concave lens may be used. Also, when reproducing a low-density optical disk of t = 1.2 mm, a low NA is good in terms of signal characteristics,
A diaphragm for determining A may be provided in the optical path.

Therefore, according to the present invention, in addition to the inventions described in claims 1 and 2, the following optical pickup can be obtained. (1) The optical pickup according to claim 2, wherein one of the two lens systems has a concave lens and the other has no refractive power. (2) The optical pickup according to claim 2, wherein one of the two lens systems has no refractive power and the other is a convex lens. (3) The optical pickup according to claim 2, wherein the two lens systems are convex lenses having different refractive powers. (4) The optical pickup according to claim 2, wherein the two lens systems are concave lenses having different refractive powers.

[0031]

As described above, according to the present invention, the lens portion is arranged in the optical path of the optical system formed by the light source and the objective lens at the first angle according to the thickness of the predetermined portion of the optical disc. Then, the lens portion is arranged outside the optical path at the second angle, or one of the two lens systems is arranged in the optical path according to the thickness of a predetermined portion of the optical disc. Since the focus position of the objective lens is moved by rotating the system, the hologram element, the two light source method, the one light source and the optical lens linear direction insertion / removal method as in the conventional example has a simpler structure and a predetermined portion. Information can be reproduced from two types of optical discs having different thicknesses.

[Brief description of drawings]

FIG. 1 is a configuration diagram schematically showing an embodiment of an optical pickup according to the present invention.

FIG. 2 is an explanatory view showing a rotating mechanism of the cube shown in FIG.

3 is an explanatory view showing a stopper of the cube of FIG. 1. FIG.

FIG. 4 is an explanatory diagram comparing the optical systems of FIGS. 1 (a) and 1 (b).

FIG. 5 is a configuration diagram showing a conventional bifocal optical pickup.

[Explanation of symbols]

 101 Laser diode (light source) 104 Cube (cubic optical system) 104a, 104b Reflecting surface, rising mirror 104c Concave lens 106 Objective lens D1, D2 Optical disk

Claims (2)

[Claims] 1. A light source that emits a light beam, an objective lens that collects the light beam, and a rotatably arranged angle between a first angle and a second angle, and when the angle is the first angle. A rotating lens means configured such that a lens portion is arranged in an optical path of an optical system formed by the light source and the objective lens, and the lens portion is arranged outside the optical path at the second angle; An optical pickup having means for rotating the lens means between the first angle and the second angle. 2. A light source which emits a light beam, which is formed in a cube shape and is rotatable in an angle range of at least 180 ° about an axis intersecting the optical axis of the light beam, and the front surface and the back surface thereof. The light beams are reflected by the rising mirrors each having a reflecting surface, and the light beams reflected by the reflecting surface are differently refracted by the two lens systems formed in the respective reflecting directions of the reflecting surface. A cube-shaped optical system that refracts; an objective lens that focuses a light beam refracted by one of the two lens systems of the cube-shaped optical system onto an optical disc; A cube drive mechanism that moves the focus position of the objective lens by rotating the cube-shaped optical system so that one of the two lens systems is arranged in the optical path. The optical pick-up that.