JPH09204678A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical pickup utilizing a plastic lens having high NA as an objective lens in which the temperature characteristic is sustained suitably. SOLUTION: The optical pickup comprises a finite convergence optical system 100 where a converging light enters into an objective lens 70 from a coupling lens 40. The coupling lens 40 is mounted fixedly on a lens holder while being integrated with the objective lens 70. Since converging light enters into an objective lens 70, temperature characteristics can be sustained suitably even if a plastic lens having high NA is employed as an objective lens. Furthermore, since the coupling lens 40 is integrated with the objective lens 70 and the distance thereof is fixed, optical relationships are not shifted due to adjustment of focusing, tracking, etc., and deterioration of the focusing performance can be avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device used for recording and / or reproducing information on an optical recording medium such as a CD and a DVD.

[0002]

2. Description of the Related Art As an optical pickup device, for example, a device for recording / reproducing information on / from a DVD capable of high density recording, an optical system having a structure shown in FIG. 6 is used. As shown in this figure, a light beam emitted from a semiconductor laser 1 as a light source is incident on a polarization beam splitter 3 via a diffraction grating 2. The incident light beam is reflected at a right angle by the polarization separation film 3a of the polarization beam splitter 3, enters the collimator lens 4, and is emitted as a parallel light beam via the collimator lens 4. The emitted parallel light beam is reflected at a right angle by the total reflection mirror 5, passes through the λ / 4 wavelength plate 6, is converted into circularly polarized light, and then enters the objective lens 7. The incident parallel light flux is converged by the objective lens 7 as a minute light spot on the recording surface 8a of the DVD 8 which is an optical recording medium.

On the other hand, the reflected light from the recording surface 8a of the DVD 8 returns to parallel light through the objective lens 7. Then λ /
By passing through the four-wave plate 6 again, circularly polarized light is converted into linearly polarized light, but the polarization direction of the incident light beam is changed by 90 degrees.

As a result, the light reflected by the total reflection mirror 5 and returned to the polarization beam splitter 3 through the collimator lens 4 passes through the polarization separation film 3a as it is and advances, and the photodetector through the sensor lens 9. Reach 10. A recording signal, a focusing error signal, and the like are detected by the photodetector 10.

As described above, the optical system of the commonly used optical pickup device is an infinite optical system in which the collimator lens collimates the light flux from the light source and makes it enter the objective lens. .

In the optical system of this construction, a glass mold lens or a plastic mold lens is used as the collimator lens and the objective lens which are the constituent elements. Plastic lenses have been widely used in recent years because they are superior to glass lenses in terms of manufacturing cost and manufacturing efficiency. However, the plastic lens has a disadvantage that the temperature characteristics such as the refractive index of the material are worse than the glass lens. Especially, the influence is great in a plastic lens having a high NA.

Here, in the optical pickup device used for recording / reproducing of DVD capable of high density recording as compared with CD, it is necessary to form a minute light spot.
An objective lens having a high NA is required for the optical system. For this reason, in the optical system of the optical pickup device for DVD, the temperature characteristic is a problem particularly because a plastic lens having a high NA is used.

[0008]

In order to solve the problem of temperature characteristics when a plastic lens having a high NA is used as an objective lens, instead of injecting parallel light into the objective lens through a collimator lens, a cup is used. It has been proposed to use a convergent finite optical system that is set so that the convergent light enters the objective lens via the ring lens. Thus, if the incident light of the objective lens is convergent light,
In other words, if the optical system is set so that the imaging magnification of the objective lens is positive, the temperature characteristics when a high NA plastic lens is used as the objective lens can be significantly improved.

However, when the optical system is a finite convergence system, there are the following problems to be solved. First, the objective lens is supported by the lens holder so that it can be moved in the tracking direction and the focusing direction so that the light spot can be accurately formed on the recording track formed on the recording surface of the optical recording medium. There is. When convergent light enters the objective lens from the side of the coupling lens, if the objective lens moves in the tracking direction and the focusing direction in this way, fluctuations in the distance between the objective lens and the coupling lens and effects of misalignment may occur. The optical system may be greatly affected, and the imaging performance may be significantly deteriorated.

Next, when a parallel light flux is incident on the objective lens, the length of the distance between the objective lens and the collimator lens does not matter, but when the convergent light flux is incident on the objective lens, this distance is set. If the length is increased, a large diameter coupling lens is required. Further, when the optical system is a convergent finite system, the optical characteristics of the coupling lens and the objective lens are limited, so that restrictions on the arrangement relationship and the like become severe. Therefore, it is necessary to set the characteristics of these optical elements individually, and there arises a problem that standardization becomes difficult.

An object of the present invention is mainly to propose an optical pickup device suitable for using a high NA plastic lens as an objective lens for recording / reproducing a high density recording medium.

[0012]

According to the present invention, light emitted from a light source is taken out through a coupling lens, guided to an objective lens, and formed by the objective lens as a light spot on a recording surface of an optical recording medium. In the pickup device, the coupling lens and the objective lens are integrated so as to move integrally in the focusing direction and the tracking direction.

Further, a configuration is adopted in which the light flux guided from the coupling lens to the objective lens is convergent light. In other words, the optical system is configured so that the imaging performance of the objective lens is positive.

In the optical pickup device of the present invention thus constructed, the coupling lens and the objective lens move integrally. Therefore, during focusing and tracking adjustment, fluctuations in the distance between these lenses and misalignment do not occur.

Therefore, it is possible to prevent the imaging efficiency from being lowered during focusing and tracking adjustment.

Further, since the optical system is set so that the incident light from the coupling lens to the objective lens is a convergent light flux, even when the objective lens or the objective lens and the coupling lens are plastic molded products. The temperature characteristics thereof can be maintained in a suitable state. In particular, it is extremely effective to apply the present invention to an optical pickup device that records / reproduces on / from a high-density optical recording medium such as a DVD, which requires an objective lens with a high NA.

Here, in order to integrate the coupling lens and the objective lens, each lens has a lens body portion and an annular collar portion formed on the outer periphery of the lens body portion. A configuration may be adopted in which a reference surface for fitting and fixing both lenses is formed in the collar portion.

In general, the coupling lens and the objective lens are supported by a lens holder that supports the objective lens so as to be movable in the focusing direction and the tracking direction. In this case, a reference surface for mounting and fixing on the lens holder may be formed on at least one of the coupling lens and the objective lens.

Alternatively, both the coupling lens and the objective lens are formed with reference surfaces for mounting and fixing on the lens holder, and the lens holder can mount and fix the objective lens from the optical recording medium side. The mounting surface and the lens mounting surface on which the coupling lens can be mounted and fixed are formed from the side opposite to the optical recording medium, and the objective lens and the coupling lens may be mounted and fixed on these lens mounting surfaces.

The structure of the present invention can also be applied to an optical pickup device of a conventional type in which a parallel light flux is incident on the objective lens from the coupling lens.

In this case, a collimator lens is used as the coupling lens, but the optical system can be made compact by integrating these lenses.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

1A and 1B are schematic configuration diagrams of an optical system of a DVD optical pickup device to which the present invention is applied. Since the basic configuration is the same as that of the conventional optical system shown in FIG. 6, the corresponding parts will be denoted by the same reference numerals.

The optical system of the optical pickup device 100 shown in the figure includes a semiconductor laser 1 as a light source, and a linearly polarized light beam emitted from the semiconductor laser 1 is incident on a polarization beam splitter 3 via a diffraction grating 2. The incident light flux is
The light is reflected at a right angle by the polarization separation film 3a of the polarization beam splitter 3 toward the total reflection mirror 5, is reflected at a right angle by the total reflection mirror 5, and is converted into circularly polarized light through the λ / 4 wavelength plate 6. After that, the light enters the coupling lens 40, becomes a light beam within a predetermined solid angle, that is, a convergent light beam, and enters the objective lens 70. The convergent light flux incident on the objective lens 70 is converted into a minute light spot by the objective lens 70, and the optical recording medium (DVD) 8
The light is focused on the recording surface 8a.

The reflected light from the recording surface 8a of the optical recording medium 8 is again the objective lens 70 and the coupling lens 40.
And reaches the λ / 4 wave plate 6. By passing through the λ / 4 wavelength plate 6, the light is returned from circularly polarized light to linearly polarized light.
However, the polarization direction of the incident light beam is shifted by 90 degrees. As a result, the light reflected by the total reflection mirror 5 and returned to the polarization beam splitter 3 passes through the polarization separation film 3 a as it is and advances, and reaches the photodetector 10 via the sensor lens 9. A recording signal, a focusing error signal, and the like are detected by the photodetector 10.

Thus, the optical pickup device 1 of this example
The optical system includes a coupling lens 40 to an objective lens 7
It is a convergent finite system set so that the light flux incident on 0 becomes a convergent light flux. In addition, the coupling lens 40
The objective lens 70 is a plastic molded product, and both are integrated as described later. The magnification of these integrated lenses is, for example, +5 to +15.
It functions as a finite lens within a certain range. further,
The objective lens 70 is a high NA plastic lens,
For example, NA is set to 0.65.

Next, the integrated coupling lens 40
The objective lens 70 is generally held by a lens holder. For example, it is attached and fixed to a shaft slide type lens holder.

2, 3 and 4 show an example of a shaft sliding type lens holder which can be used in this embodiment. As shown in these figures, the entire optical pickup device 100 in which the lens holder is incorporated is assembled to an assembly portion 110 in the main body of the optical disc device (not shown). In the main body of the optical disc device, a disc mounting portion 120 for inserting the optical recording medium 8 is formed at a position facing the optical pickup device 1. The optical recording medium 8 mounted here is in a case 210, and a case opening 211 for recording / reproducing is formed in the case 210. The opening 211 is closed by a shutter (not shown).

When the optical recording medium 8 stored in the case 210 is inserted into the disc mounting portion 120, the shutter that closes the case opening 211 is opened in association with this inserting operation, and the opening 211 is opened. Through the optical recording medium 8
The recording surface 8a of is exposed. The recording surface 8a exposed through the opening 211 is irradiated with the light beam L from the optical pickup device 1 side, and information is written on the recording surface 8a and information is read from the recording surface 8a. Since the structure of the mounting portion of such an optical disc is known, further description is omitted.

The lens holder 13 of the optical pickup device 100 is supported by a holder shaft 15 which extends vertically from the bottom plate 4a of the device frame 14 at substantially the center thereof.

In detail, the axis 15a of the holder shaft 15
And is supported rotatably around its axis 15a. Holder shaft axis 15a
Are set to be parallel to the optical axis of the objective lens 7.

Further, the lens holder 13 and the device frame 1
4 between the magnetic drive circuits 16 and 17 for focusing.
And a magnetic drive mechanism including the magnetic drive circuits 18 and 19 for tracking. The focusing magnetic drive circuits 16 and 17 move the lens holder 13 up and down along the holder shaft 15 to focus the objective lens 7 attached thereto. Further, the magnetic drive circuits for tracking 18 and 19 cause the lens holder 13 to rotate around the holder shaft 15 and slightly move in the radial direction of the recording surface 8a of the optical recording medium 8 to form tracks. Is aligned with.

The lens holder 13 has a horizontally long octagonal outline shape as a whole. A through hole 131, through which the holder shaft 15 penetrates, is formed in the center thereof in the vertical direction, and a circular lens mounting hole 132 is formed at a position adjacent to the through hole 131. This lens mounting hole 1
On the lower side of 32, a circular through hole 133 that forms an optical path of a light beam in a coaxial state is continuous.

In FIG. 5A, only the lens holder 13 is taken out and shown. An annular step surface 133 for mounting and fixing the coupling lens 40 is formed on the inner peripheral surface of the lens mounting hole 132 of the lens holder 13. The coupling lens 40 includes a lens main body portion 41 and an annular flange portion 42 integrally formed on the outer circumference thereof. The annular end surface 42a of the annular flange portion 42 and the outer peripheral surface 42b continuous with the annular end surface 42a function as a reference surface for mounting and fixing the coupling lens 40 on the annular step surface 133 of the lens holder 13.

An annular inner peripheral surface 42c on the other side of the annular flange portion 42 formed on the coupling lens 40 and an annular end surface 42d continuous with the annular inner peripheral surface 42c function as a reference surface for fitting and fixing the objective lens 70. .

The objective lens 70 also has a lens body portion 71.
And an annular collar portion 72 formed on the outer periphery thereof. The annular end surface 72a on one side of the annular flange portion 72 and the outer peripheral surface 72b continuous with the annular end surface 72a are formed on the coupling lens 40 side.
It functions as a reference surface that can be fitted and fixed to 2d and the annular inner peripheral surface 42c.

Therefore, in this example, FIG.
As shown in FIG.
2, the coupling lens 40 is mounted and fixed, and thereafter, if the objective lens 70 is fitted and fixed from the upper side to the coupling lens 40 side, these lenses can be fixed at preset positions. it can. Of course, the coupling procedure may be such that the coupling lens 40 and the objective lens 70 are integrated in advance, and the integrated compound lens is mounted and fixed in the mounting hole 132 of the lens holder 13.

FIG. 5B shows another example of the mounting and fixing mechanism for the coupling lens 40 and the objective lens 70 with respect to the lens holder 13. In this example, the optical recording medium 8 in the lens mounting hole 132 of the lens holder 13 is
A lens mounting surface 135 for mounting and fixing the objective lens 70 is formed on the side, and a lens mounting surface 136 for mounting and fixing the coupling lens 40 is formed on the opposite side. A reference surface 73 is formed on the objective lens 70 and a reference surface 43 is also formed on the coupling lens 40 so as to match these mounting surfaces 135, 136. With this configuration as well, by mounting and fixing the lenses 70 and 40 on the lens holder 13, their positioning is automatically performed.

Further, in this embodiment, since the objective lens is attached above and below the reference surface of the lens holder, FIG.
As compared with the case where two objective lenses are overlapped as in the embodiment of FIG. 7, the center of gravity viewed from the lateral direction (direction orthogonal to the holder axis) can be brought closer to the center position of the lens holder, and the lens holder can be rotated. The movement of time can be stabilized.

[0040]

As described above, in the optical pickup device of the present invention, the objective lens and the coupling lens, which are components of the optical system, are integrated. Therefore, there is an advantage that the optical system can be made compact.

Further, the present invention employs a configuration in which the objective lens and the coupling lens are integrated and the incident light from the coupling lens to the objective lens is set to be convergent light. According to this structure, the coupling lens moves together with the objective lens during tracking and focusing adjustment. When the coupling lens is attached to the apparatus frame without being attached to the lens holder, the optical axis of the coupling lens and the optical axis of the objective lens are deviated when the objective lens is slightly moved by tracking adjustment. The deviation causes optical characteristic deterioration. In the present invention, since such a shift of the optical axis does not occur, the optical relationship between them is maintained without shift. Therefore, even if the objective lens uses a convergent finite optical system having a positive imaging magnification, the imaging performance is less likely to deteriorate due to the tracking and focusing adjustments.

Further, even when a plastic molded product is used as the objective lens and the coupling lens, since the optical system is a convergent finite system in which a condensed light beam is made incident on the objective lens, the temperature characteristic is preferably maintained. can do. Therefore, the optical system of the optical pickup device for an optical recording medium such as a DVD for performing high-density recording / reproduction that requires a high NA plastic lens as an objective lens can be made stable with respect to temperature changes. . In other words, it is easy to use a plastic molded lens that is inexpensive to manufacture and has good manufacturing efficiency.

Furthermore, according to the present invention, since one or both of the objective lens and the coupling lens are provided with the reference plane for fitting and fixing, these lenses can be easily integrated. be able to. Similarly, in the present invention, since the mounting surface of these lenses is formed on the lens holder side and the reference surface is formed on the lens side so as to match this, these lenses are The work of mounting and fixing the lens holder can be easily performed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical system of an optical pickup device for a DVD to which the present invention is applied.

FIG. 2 is a schematic configuration diagram showing a mechanical configuration of the optical pickup device of FIG. 1 centering on a lens holder.

3 is a schematic cross-sectional view of a portion cut along line III-III in FIG.

FIG. 4 is a schematic cross-sectional view of a portion cut along line IV-IV in FIG.

5A is a schematic cross-sectional view of the lens holder of FIG. 2, and FIG. 5B is a schematic cross-sectional view showing another example of the mounting structure of the objective lens and the coupling lens with respect to the lens holder.

FIG. 6 is a schematic configuration diagram of an optical system of a general DVD optical pickup device.

[Explanation of symbols]

 100 Optical Pickup Device 1 Semiconductor Laser 2 Diffraction Grating 3 Polarizing Beam Splitter 4 Collimator Lens 40 Coupling Lens 41 Lens Main Body 42 Annular Collar 42a Annular End 42b Outer Surface 42c Annular Inner Surface 42d Annular End 43 Surface 5 Total reflection mirror 6 λ / 4 wavelength plate 7, 70 Objective lens 71 Lens body portion 72 Annular collar portion 72a Annular end surface 72b Outer peripheral surface 73 Reference surface 8 Optical recording medium (DVD) 8a Recording surface 9 Sensor lens 10 Light Detector 13 Lens holder 132 Lens mounting hole 133 Annular step surface 135, 136 Lens mounting surface

Claims (6)

[Claims] 1. An optical pickup device, wherein light emitted from a semiconductor laser is taken out through a coupling lens, guided to an objective lens, and is formed as a light spot on the recording surface of an optical recording medium by the objective lens. The optical pickup device is characterized in that the lens and the objective lens are integrated so as to move integrally in the focusing direction and the tracking direction. 2. The optical pickup device according to claim 1, wherein the light flux guided from the coupling lens to the objective lens is set to be convergent light. 3. The optical pickup device according to claim 2, wherein at least the objective lens of the objective lens and the coupling lens is a plastic molded product. 4. The coupling lens and the objective lens according to claim 1, wherein each of the coupling lens and the objective lens has a lens main body portion and an annular collar portion formed on an outer periphery of the lens main body portion. An optical pickup device, comprising: a reference surface for fitting and fixing both lenses to each other at the collar portion. 5. The coupling lens and the objective lens according to claim 4, wherein the coupling lens and the objective lens are supported by a lens holder that movably supports the objective lens in a focusing direction and a tracking direction. An optical pickup device, wherein at least one of the objective lenses has a reference surface for mounting and fixing the lens holder. 6. The reference surface for mounting and fixing on the lens holder according to claim 5, wherein both the coupling lens and the objective lens are formed, and the lens holder is provided on the optical recording medium. A lens mounting surface on which the objective lens can be mounted and fixed, and a lens mounting surface on which the coupling lens can be mounted and fixed from the side opposite to the optical recording medium. An optical pickup device, wherein a lens and the coupling lens are mounted and fixed.