JP2000048388A - Lens for optical pickup, its production, optical pickup and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized thin lens for an optical pickup having necessary optical characteristics and giving a high production yield by specifying a range of the central thickness of the optical face of a lens and the thickness of the shingle part of the lens. SOLUTION: When the central thickness of the optical face of a lens and the thickness of the shingle part of the lens are represented by T1 and T2, respectively, 0<T1<=1.5 and 0<T2<=0.4×T1 are satisfied. An upper die is moved upward to open a cavity and a glass material having a prescribed area is put in the cavity. An inert gas is substd. for the atmosphere around the cavity, the glass material is heated to a prescribed temp. and this prescribed temp. is maintained. The upper die is moved downward to press the glass material while maintaining the prescribed temp. and the glass material is formed in the shape of an objective lens by maintaining a prescribed pressure. Slow cooling is started while maintaining the prescribed pressure and then the pressure is reduced. After rapid cooling, the upper die is moved upward to open the cavity and the resultant objective lens 26 in which the central thickness T1 of the optical face 26b is larger than the thickness T2 of the shingle part 26a is taken out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for an optical pickup for recording and reproducing signals from a mini disk (MD), a magneto-optical disk (MO), a compact disk (CD) and the like (hereinafter referred to as "optical disk"). The present invention relates to a lens, a method of manufacturing the same, an optical pickup including the lens, and an optical disk device including the optical pickup.

[0002]

2. Description of the Related Art FIGS. 12A and 12B are a side view and a plan view showing an example of an optical system of a conventional optical pickup for an optical disk. The optical system of the optical pickup 1 includes an astigmatism correction plate 3a, a grating 3b, a beam splitter 4, a collimator lens 5, which are sequentially disposed in the optical path of the light beam emitted from the semiconductor laser device 2.
Prism mirror 6 and objective lens 7, and Wollaston prism 4 sequentially arranged in the separation optical path of the return light beam from optical disk D reflected by beam splitter 4.
a, a multi-lens 4b and a photodetector 8.

In the optical system of the optical pickup 1 having such a configuration, the light beam emitted from the semiconductor laser element 2 by the operation of the oscillation circuit (module circuit) is converted into an astigmatism correction plate 3a, a grating 3b, a beam splitter 4
Are sequentially transmitted and converted into a parallel light beam by the collimator lens 5. Then, the optical path of the parallel light beam is bent by the prism mirror 6 in the direction of the optical disk D, and is irradiated on the signal recording surface of the optical disk D by the objective lens 7. Then, the return light beam reflected by the signal recording surface is received by the light receiving surface of the photodetector 8, and
A recording signal is detected.

The objective lens 7 is moved to a predetermined servo position so that the light beam from the semiconductor laser element 2 forms a spot at a correct position on the signal recording surface of the optical disc D to enable accurate reproduction of the recorded signal. Fine movement is performed based on the signal. The servo of the objective lens 7 includes a tracking servo for finely moving the objective lens 7 along a radial direction with respect to a recording track of the optical disc D;
Focusing servo is performed to finely move the objective lens 7 in a direction to approach and separate from the signal recording surface of the optical disc D along the optical axis.

The objective lens 7 of the optical pickup 1 described above is generally manufactured by injection molding a plastic material such as an acrylic resin (PMMA) from the viewpoint of cost. That is, as shown in FIG. 13, the objective lens 7 is formed by melting a plastic material, filling the cavity C of the mold P from the runner R via the gate G, and cooling and solidifying it.

[0006]

However, in recent years, with the miniaturization of the optical pickup 1, the objective lens 7 has also become smaller and smaller.
Although the thickness has been reduced, when the lens thickness is small, the gate G portion becomes small, and it becomes difficult to form the lens edge portion with high accuracy. Therefore, the transmitted wavefront aberration required for the objective lens 7 of the optical pickup 1 is required. There is a problem that cannot be obtained. When the gate G portion becomes extremely small, the injection speed and the injection pressure are increased in order to avoid the phenomenon that the plastic material does not fill the cavity C from the gate G, but the jetting phenomenon occurs. There is a problem that the molding yield is easily deteriorated.

SUMMARY OF THE INVENTION In view of the above, the present invention provides a small and thin optical pickup lens having necessary optical performance and a high production yield, a method of manufacturing the same, an optical pickup equipped with the lens, and the optical pickup. It is an object of the present invention to provide an optical disk device provided with the above.

[0008]

According to the present invention, there is provided a lens for use in an optical pickup,
This is achieved when the center thickness T1 of the optical surface and the thickness T2 of the lens edge satisfy the following expression (1). 0 <T1 ≦ 1.5 and 0 <T2 ≦ 0.4 × T1 (1) Further, according to the present invention, there is provided a lens used for an optical pickup, wherein a molding pressure and a molding temperature are used. This is achieved by using a glass material formed by a reheat press that synchronizes and controls the above. Further, according to the present invention, there is provided a method for producing a lens used for an optical pickup for molding a glass material by reheat press, wherein a molding pressure and a molding temperature in the reheat press are controlled in synchronization. Is achieved by

[0009] According to the above configuration, when the glass material is reheat-pressed, the molding pressure and the molding temperature are controlled in synchronization with each other, so that the occurrence of cracks and the like can be prevented. The restriction on the gate size that has occurred in the injection molding of the material is eliminated, and a small, thin lens with high precision can be obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The embodiments described below are preferred specific examples of the present invention,
Although various technically preferred limitations are given, the scope of the present invention is not limited to these forms unless otherwise specified in the following description.

FIG. 1 and FIG. 2 are a plan view and a plan view showing the embodiment of the optical pickup of the present invention, as viewed from the back. The optical pickup 20 includes an astigmatism correction plate 22a as an astigmatism correction unit and a grating 22b as a light splitting unit which are sequentially arranged in the optical path of a light beam emitted from a semiconductor laser element 21 as a light source. A beam splitter 23 as a light separating unit, a collimator lens 24 as a parallel light converting unit, a prism mirror 25 as an optical path bending unit, an objective lens 26 as a light focusing unit, and a beam from the optical disc 11 reflected by the beam splitter 23. Wollaston prism 2 as light splitting means sequentially arranged in the splitting optical path of the return light beam
7. an optical system having a multi-lens 28 as a light focusing means and a photodetector 29 as a light detecting means, and 2 for holding and moving the objective lens 26 in two axial directions.
A shaft actuator 30 and a module substrate unit 40a in which a module substrate 40 having a module circuit configured to oscillate the semiconductor laser element 21 and emit a light beam are built along a guide 20a provided on the optical pickup 20. The optical disk 11 is fixedly held in an optical base 20b movably supported in the radial direction of the optical disk 11.

FIGS. 3A and 3B are a side view and a plan view showing an example of the optical system. The semiconductor laser element 21
It is a light emitting element using recombination light emission of a semiconductor, and emits a predetermined laser beam. The astigmatism correction plate 22a is a parallel flat plate disposed at a predetermined angle with respect to the optical axis,
The astigmatism of the light beam emitted from the semiconductor laser device 21 is corrected. The grating 22b is a diffraction grating for diffracting incident light, and converts a light beam incident from the semiconductor laser element 21 via the astigmatism correction plate 22a into a main beam composed of 0th-order diffracted light and a side beam composed of ± 1st-order diffracted light. The beam is split into at least three light beams. Therefore, another division element such as a hologram element may be used as long as at least three light beams can be divided and generated.

The beam splitter 23 is a polarization beam splitter provided with its polarization separating film 23a inclined at 45 degrees with respect to the optical axis. The beam splitter 23 receives the light beam from the grating 22b and the signal beam from the signal recording surface of the optical disk 11. The return light beam is polarized and separated. That is, the semiconductor laser element 21
Is transmitted through the polarization splitting film 23a of the beam splitter 23, and a part of the return light beam is reflected by the polarization splitting film 23a of the beam splitter 23.

The collimator lens 24 is a cemented lens combining a convex lens and a concave lens, and converts the light beam from the beam splitter 23 into parallel light. The prism mirror 25 is a mirror having a triangular prism shape, and reflects the parallel light beam from the collimator lens 24 by 90 degrees in the vertical direction and reflects the return light beam from the optical disk 11 by 90 degrees in the horizontal direction. The objective lens 26 is a one-sided convex lens made of a glass material, and the collimator lens 25
Disk 11 that rotates a parallel light beam from the optical disk 11
On a desired track on the signal recording surface of the optical disc. Here, the objective lens 26 is movably supported in a biaxial direction, that is, in a focusing direction and a tracking direction, by a biaxial actuator 30 of a shaft sliding rotation type.

The Wollaston prism 27 is a quadrangular prism, and emits a plurality of light beams by performing polarization separation based on a return light beam from the optical disk 11. The multi-lens 28 is a cylindrical lens and a concave lens, and adjusts an optical path length by giving astigmatism to a return light beam for detecting a focus error signal. The photodetector 29 is a photodetector and receives the return light beam transmitted through the beam splitter 23.

FIG. 4 is a plan view showing an example of a biaxial actuator. The two-axis actuator 30 is attached to the optical base 20 b of the optical pickup 20 so as to be movable in the XY directions and is movable in the optical axis direction with respect to the XY base 31 by the movable portion holder 32. A lens holder 33 supported so as to be swingable about a swing axis, an objective lens 26 whose optical axis is held parallel to the swing axis with respect to the lens holder 33, and a driving unit for the objective lens 26, which will be described later. And

The movable portion holder 32 is entirely made of, for example, a resin such as rubber-like polyester elastomer. The movable portion side 32a is attached to the lens holder 33, and the fixed portion side 32b is attached to the XY base 31. Fixed against. Further, the movable portion holder 32 has a link having a substantially parallelogram vertical cross section so that the movable portion side 32a can move in the vertical direction (focusing direction) indicated by the arrow Fcs in the drawing. Arrow Tr
A pair of vertically extending hinges 32c and 32d are provided so as to be movable in the horizontal direction (tracking direction) indicated by k.

The driving means of the objective lens 26 includes a focusing coil 34 and a tracking coil 35 provided on a lens holder 33, a yoke 36 fixedly disposed on the XY base 31, and a magnet 37 attached thereto.
It is composed of By energizing the focusing coil 34 and the tracking coil 35, the magnetic flux generated in each of the coils 34 and 35 interacts with the magnetic flux generated by the yoke 36 and the magnet 37, so that the lens holder 33 and the objective lens 26 is driven and controlled in the focus direction and the tracking direction.

FIG. 5 is a view showing an apparatus for realizing an embodiment of a method for manufacturing a lens for an optical pickup according to the present invention. This apparatus is a reheat press molding machine 50, and includes an upper die 50A and a lower die 50B having the same configuration and facing each other. The upper mold 50A (lower mold 50B) is used for the objective lens 2
Upper die 52 having a built-in upper punch 51 (lower punch 56) in which a cavity 50a for forming the mold 6 is formed.
(Lower die 57) is fixed to upper die plate 53 (lower die plate 58), and is further connected to upper heat insulating joint 54 (lower heat insulating joint 59).

In such a configuration, the objective lens 26
The molding process will be described. Here, the temperature and pressure in the molding process are changed, for example, by a pattern as shown in FIG. First, as shown in FIG. 5A and FIG.
a is opened, and the glass material 60 measured to a predetermined volume is put into the cavity 50a. And the cavity 50
After the atmosphere around a is replaced with an inert gas, heating is performed, and the temperature is raised until the glass material 60 has a predetermined viscosity and maintained at a predetermined temperature.

Next, as shown in FIGS. 5B and 6,
While maintaining the predetermined temperature, the upper mold 50A is lowered to pressurize the glass material 60, and the objective lens 2 is maintained while maintaining the predetermined pressure.
6 is formed. Then, slow cooling is started during the maintenance of the predetermined pressure, and decompression is started during the slow cooling. The slow cooling and the pressure reduction are synchronized (synchronized) until the temperature of the glass material 60 reaches the glass transition point. The reason why the slow cooling and the reduced pressure are synchronized (synchronized) is that if the slow cooling and the reduced pressure are not synchronized (synchronized), as shown in FIG. Is thin, cracks may be formed in the connection portion, and this is to prevent the occurrence of cracks.

Thereafter, as shown in FIGS. 5 (c) and 6, the upper mold 50A is rapidly cooled to raise the cavity 50A.
a is opened and the completed objective lens 26 is taken out. As shown in FIG. 8, the objective lens 26 is formed such that the center thickness T1 of the optical surface 26b is larger than the thickness T2 of the lens edge portion 26a, that is, the following formula (1) is satisfied. 0 <T1 ≦ 1.5 and 0 <T2 ≦ 0.4 × T1 (1) Although the objective lens 26 is shown as a biconvex lens, a positive mechanics lens (one side convex, one side) A lens which is concave and whose center thickness of the optical surface is larger than the thickness of the lens edge portion) may be used.

FIG. 9 is a view showing the shape and dimensions of a specific example of the objective lens 26 manufactured by using the reheat press molding machine 50. FIGS. 10A and 10B show the transmitted wavefront aberration for evaluating the performance. It is a figure which shows a figure, and a figure which shows surface roughness. In addition, the objective lens 26 is a trade name L-BAL35A (OHAR
The glass material 60 of A) is formed so that the numerical aperture NA is 0.45. As is clear from the figure, the center thickness T1 of the optical surface 26b is 0.8 mm, the outer diameter of the optical surface 26b is 2.4 mm, and the thickness T2 of the lens edge portion 26a is 0.3.
Even with a small and thin objective lens 26 having an outer diameter of 3.1 mm and an outer diameter of the lens edge 26a of 3.1 mm, excellent transmitted wavefront aberration and surface roughness can be obtained.

Using a conventional large and heavy objective lens, for example, a CD-R of a laptop computer
If an attempt is made to increase the speed of the OM drive, the size of the two-axis actuator responsible for focusing and tracking becomes large, and it becomes difficult to mount the OM drive on the CD-ROM drive. However, the objective lens 26 is small and thin.
Since it has high performance and high accuracy, it is suitable for the optical pickup lens of the CD-ROM drive.

FIG. 11 is a block diagram showing an embodiment of the optical disk apparatus of the present invention. The optical disk device 10 records a signal by irradiating a light beam onto a signal recording surface of the rotating optical disk 11 and records a signal from the signal recording surface of the rotating optical disk 11. An optical pickup 20 for reproducing a recording signal by a beam and a control unit 13 for controlling them are provided. Here, the control unit 13 includes an optical disk drive controller 14, a signal demodulator 15, an error correction circuit 16, an interface 17, a head access control unit 18, and a servo circuit 19.

The optical disk drive controller 14 includes:
The drive control of the spindle motor 12 is performed at a predetermined rotation speed.
The signal demodulator 15 demodulates the recording signal from the optical pickup 20 and sends the demodulated signal to the error correction circuit 16. The error correction circuit 16 corrects the error of the recording signal from the signal demodulator 15 and sends it to an external computer or the like via the interface 17. Thus, an external computer or the like can receive a signal recorded on the optical disk 11 as a reproduction signal. The head access control unit 18 controls the optical pickup 20 to, for example, the optical disk 11
It is moved to a predetermined upper recording track by a track jump or the like. The servo circuit 19 moves the objective lens held by the biaxial actuator of the optical pickup 20 in the focusing direction and the tracking direction at the moved predetermined position.

The optical pickup 20 according to this embodiment
The optical disk device 10 incorporating the above is configured as described above, and operates as follows. First, the spindle motor 12 rotates, and the optical disk 11 rotates.
Then, the optical pickup 20 moves in the radial direction of the optical disc 11 along the guide 20a, and the objective lens 2
The optical axis of No. 6 is moved to a desired track position on the optical disc 11. In this state, the light beam from the semiconductor laser element 21 is corrected for astigmatism by the astigmatism correction plate 22a, is split into three light beams by the grating 22b, and then passes through the beam splitter 23. And
The light is converted into a parallel light beam by the collimator lens 24. Then, the light is reflected by the prism mirror 25 toward the optical disk 11, and is reflected through the objective lens 26.
Focused on one signal recording surface.

The return light beam from the optical disk 11 again enters the beam splitter 23 via the objective lens 26, the prism mirror 25 and the collimator lens 24.
Then, the light is reflected by the polarization separation film 23 a of the beam splitter 23, and is reflected by the Wollaston prism 27 and the multi-lens 2.
The light is converged on the photodetector 29 through 8. Then, the recording signal of the optical disk 11 is reproduced based on the detection signal of the photodetector 29.

At this time, the signal demodulator 15 detects a tracking error signal based on a detection signal from the photodetector 29 and also detects a focusing error signal using an astigmatism method. Then, the servo circuit 19 servo-controls a drive current to the focusing coil 34 and the tracking coil 35 via the optical disk drive controller 14. That is, the magnetic field generated in the focusing coil 35 acts on the magnetic field generated by the magnet 37 and the coil 36, so that the lens holder 33 is moved and adjusted in the focusing direction, thereby performing focusing. Further, the magnetic field generated in the tracking coil 35 acts on the magnetic field generated by the magnet 37 and the yoke 36, so that the lens holder 33 is moved and adjusted in the tracking direction to perform tracking.

The optical disk device 1 according to the above embodiment
In the optical pickup 20 and the optical pickup 20, the two-axis actuator 30 is shown as having a movable portion holder 32. However, the present invention is not limited to this. It may be.

[0031]

As described above, according to the present invention, it is possible to realize the required optical performance and to realize the miniaturization and thinning. Further, the production yield can be increased.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of an optical pickup of the present invention.

FIG. 2 is a plan view of the optical pickup of FIG. 1 as viewed from the back.

FIG. 3 is a side view and a plan view showing an example of an optical system of the optical pickup of FIG. 1;

FIG. 4 is a plan view showing an example of a two-axis actuator of the optical pickup of FIG. 1;

FIG. 5 is a view showing an apparatus for realizing an embodiment of a method for manufacturing a lens for an optical pickup of the present invention.

FIG. 6 is a view showing temperature and pressure patterns in a molding process by the manufacturing apparatus of FIG. 5;

FIG. 7 is a diagram for explaining a problem when the temperature and pressure patterns of FIG. 6 are not taken;

8 is a side view showing a lens shape obtained by a molding process using the manufacturing apparatus of FIG.

FIG. 9 is a diagram showing the shape and dimensions of a specific example of a lens manufactured using the manufacturing apparatus of FIG. 5;

FIG. 10 is a diagram illustrating transmitted wavefront aberration for evaluating the performance of the lens in FIG. 9 and a diagram illustrating surface roughness.

FIG. 11 is a block diagram showing an embodiment of the optical disk device of the present invention.

FIG. 12 is a side view and a plan view showing an example of an optical system of a conventional optical pickup for an optical disk.

FIG. 13 is an illustration for explaining a method of manufacturing the lens of the optical pickup in FIG. 12;

[Explanation of symbols]

10 optical disk device, 11 optical disk, 1
2 ... Spindle motor, 13 ... Control unit, 14.
..Optical disk drive controller, 15 ... signal demodulator, 16 ... error correction circuit, 17 ... interface, 18 ... head access control unit, 20 ...
· Optical pickup, 20a ··· Guide, 20b ···
-Optical base, 21 ... semiconductor laser element, 22a
..Astigmatism correction plates, 22b ... gratings, 2
Reference numeral 3 denotes a beam splitter, 24 denotes a collimator lens, 25 denotes a prism mirror, 26 denotes an objective lens, 26a denotes a lens edge portion, 26b denotes an optical surface,
27: Wollaston prism, 28: Multi-lens, 29: Photodetector, 30: Biaxial actuator, 31: XY base, 32: Moving part holder, 33: Lens Holder, 34: Focusing coil, 35: Tracking coil, 36
... Yoke, 37 ... Magnet, 40 ... Module board, 41 ... Holder, 41a ... Solder pool, 42 ... Stepped through capacitor, 42a ...
・ Core wire, 42b ・ ・ ・ Element, 43 ・ ・ ・ Flexible wiring board, 50 ・ ・ ・ Reheat press molding machine, 60 ・ ・ ・
Glass material

Claims (5)

[Claims] 1. A lens for use in an optical pickup, wherein a center thickness T1 of an optical surface and a thickness T2 of a lens edge portion satisfy the following expression (1). 0 <T1 ≦ 1.5 and 0 <T2 ≦ 0.4 × T1 (1) 2. A lens for use in an optical pickup, wherein the lens is formed of a glass material formed by a reheat press that controls a molding pressure and a molding temperature in synchronization with each other. 3. A method for manufacturing a lens used for an optical pickup for molding a glass material by reheat press, wherein a molding pressure and a molding temperature in the reheat press are synchronized and controlled. Manufacturing method of lens. 4. A light source for emitting a light beam, an oscillating circuit operating during signal recording and signal reproduction to emit the light beam from the light source, and a signal recording surface of an optical disc for emitting the light beam from the light source. An optical pickup comprising: a lens to be focused on the optical pickup, wherein the lens is made of a glass material formed by a reheat press that controls the molding pressure and the molding temperature in synchronization with each other. . 5. An optical disk apparatus for operating an oscillation circuit during signal recording and signal reproduction to emit a light beam from a light source, focus the light beam on a signal recording surface of the optical disk via a lens, and record and reproduce the signal of the optical disk. An optical disc device, wherein the lens is made of a glass material formed by a reheat press that controls a molding pressure and a molding temperature in synchronization with each other.