JPH10186224A - Lens device with constant magnification and variable focal length, and optical pickup device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lens device which forms a single focus and its image- forming position is variable. SOLUTION: This lens device can slides along an optical axis, and has a first lens 26 which converges incident light, a second lens 27 which is fixed in the optical axis and focuses the light converged by the first lens 26 for forming a focus, and an actuator 28 which drives the first lens 26. An optical pick-up device is equipped with the first lens 26 and the second lens 27 as an objective. Therefor, this device and the optical pick-up device have a high SN ratio and a constant recording/reproducing characteristic to disks of different thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens device having a variable focal point having the same magnification and an optical pickup device for recording / reproducing using the same, and in particular, moving the focal point to an image plane at another position having the same magnification. The present invention relates to a lens device having a variable focal point having the same magnification and an optical pickup device capable of recording and reproducing information on and from disks having different thicknesses at the same magnification.

[0002]

2. Description of the Related Art At present, a compact disk known as an optical recording medium has a thickness of 1.2 mm. Recently, a disc having a thickness of 0.6 mm has also emerged as a high-density storage medium. In order to read information stored at a high density, the size of the light spot must be reduced, which requires a short wavelength light source and a numerical aperture (NA).
It is essential to use an objective lens having a large value. However, a lens having a large NA is very unstable with respect to the aberration of the disk substrate when the disk is tilted, so that strict regulation on the disk tilt is required during reproduction. The aberration of the disk substrate is increased in proportion to the thickness of the substrate and the degree of inclination. Therefore, a practical high-density reproduction can be realized by reducing the thickness of the substrate as much as possible and increasing the tolerance for the disk tilt.

With the emergence of disks having different thicknesses, users have come to demand an optical pickup device which can share disks having different thicknesses. On the other hand, 0.6 mm as shown in FIG.
A dual focus optical pickup device for a disc and a 1.2 mm disc has been proposed. Of course, in the optical pickup device proposed in the document, the aberration due to the difference in the thickness of the disk is corrected.

In FIG. 7, reference numeral 1 denotes a 0.6 mm disk, and 2 denotes a 1.2 mm disk indicated by a virtual line. Essentially, one of the disks 1 and 2 is loaded into a disk driver (not shown). The conventional double focus optical pickup device includes a laser diode 3 for generating laser light, a half mirror 4 for reflecting a part of the light and transmitting a part of the light, and a light reflected from the half mirror 4 toward the disk. A collimator lens 5 for traveling in parallel, and a hologram lens 6 for diffracting parallel light by the collimator lens 5
An objective lens 9 for focusing the 0th-order light 7 and the 1st-order diffracted light 8 transmitted by the hologram lens 6 on the disks 1 and 2, respectively, and an arrangement for detecting signals from the reflected lights of the disks 1 and 2 And a photodetector 11.

Here, the 0.6 mm disc 1 is read by the 0-order light 7 transmitted through the hologram lens 6 as shown in FIG. 8, and the 1.2 mm disc 2 is read as shown in FIG. Is read by the first-order diffracted light 8 of the hologram lens 6. Further, the hologram lens 6 is blazed so as to diffract one of the + 1st-order diffracted light and the -1st-order diffracted light in order to prevent a decrease in light efficiency.

However, in a dual focus optical pickup device having a hologram lens as described above, the hologram lens separates the incident light into zero-order light and first-order diffraction light, one of which reads a signal from a loaded disk. Sometimes used. Therefore, the light efficiency becomes very low and the signal-to-noise ratio of the reproduced signal by the photodetector is reduced. Further, since one loaded disc is simultaneously focused on the other disc, the optical interference of the other focus makes it impossible to perform substantial recording.

Further, since two reflected lights from the loaded disk are simultaneously received by the photodetector, it is difficult to detect a high-precision reproduction signal and an accurate focus position signal due to the same light interference. And, when using both the objective lens of the refraction type lens and the hologram lens, the objective lens usually has to have a higher order aspherical coefficient,
Its production is not easy. In particular, when a short wavelength light source is used, there is a disadvantage that the wavefront aberration increases in inverse proportion to the wavelength of light. On the other hand, in order to have constant recording and reproducing characteristics for disks having different thicknesses, not only correction of aberration due to the difference in thickness but also formation of focuses of the same size and intensity on disks having different thicknesses There is a need to.

[0008]

SUMMARY OF THE INVENTION The present invention has been devised in order to solve the above-mentioned conventional problems, and has a lens capable of forming a single focal point and changing the imaging position of the focal point. Providing the device has its purpose. Another object of the present invention is to provide an optical pickup device that can be used for recording and reproduction on disks having different thicknesses by using the lens device. Still another object of the present invention is to provide a lens device capable of changing the imaging position of a single focus at the same magnification and an optical pickup device using the same.

[0009]

According to the present invention, there is provided a lens apparatus for forming a variable focal point having the same magnification, wherein the lens apparatus is movable in an optical axis direction. A first lens that converges, a second lens that is spatially fixed and converges light converged by the first lens to form a focal point, and a second lens that changes a focal position of the second lens. Lens driving means for moving the first lens.
An optical pickup device of the present invention that achieves the above object is an optical pickup device for forming focal points of the same magnification on disks having different thicknesses, wherein the optical pickup device can move in the optical axis direction with a light source that generates light. A first lens that focuses light generated from the light source, a second lens that is spatially fixed, and focuses light focused by the first lens to form a focal point on a disc; A lens driving means for moving the first lens so that the focal points of the two lenses are formed on disks having different thicknesses, and means for detecting a signal from light reflected from the disk. .

[0010]

Embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. FIG. 1 shows the configuration of an optical pickup device having a lens device for forming a variable focus according to the present invention. Reference numerals 21 and 22 are disks having different thicknesses, for example, a 0.6 mm disk and a 1.2 mm disk, respectively. Of course, one of the disks 21 and 22 is loaded into a driver (not shown).

An optical pickup device for forming a variable focus according to the present invention comprises a laser diode 23 for generating a laser beam as a light source, a half mirror 24 for partially reflecting light and partially transmitting light, and a half mirror 24. A collimator lens 25 for traveling the light reflected toward the disks 21 and 22 in parallel, a first lens 26 provided to be movable along the optical axis and converging the parallel light by the collimator lens 25, and an optical axis A second lens 27 for refocusing the light focused by the first lens 26 to form a focal point on the loaded disk while keeping the light focused on the disk, and moving the focal point of the second lens 27 from the position of the loaded disk to another. First lens 2 provided for moving to the position of
6 comprises an actuator 28 for driving the optical disk 6, a sensor lens 29 arranged to detect a signal from light reflected from the loaded disk, and a photodetector 30.

Referring to FIG. 2, the first lens 26 and the second
As the distance (D) from the lens 27 changes, the position of the focal point formed by the second lens 27 also changes. Therefore, by appropriately moving the first lens 26, the 0.6 mm disk 21 is read at the focal point of the second lens 27 accompanying the first lens 26 as shown in FIG.
The mm disk 22 can be read. In addition, the present invention provides the distance (D1, D1) between the first lens 26 and the second lens 27.
2), and from the exit surface of the second lens 27,
By optimizing the working distance (W1, W2) to each first surface of the optical disc 22, a focal point having the same magnification is formed on both disks 21, 22. The following is an example of the present invention, and is lens data for optimal design through simulation verification for 0.6 mm disc and 1.2 mm disc.

First lens (aspherical lens) Thickness: 1.13 mm Refractive index: 1.515 First surface curvature: 4.05 mm Conical constant: 0.20 Aspherical coefficient: 0.72e ^-3 , -0.03 12e ^-4 , -0.
89e ^-5 , 0.92e ^-6 Second surface curvature: 4.72 mm Conical constant: -0.17 Aspheric coefficient: -0.14e ^-2 , 0.10e ^-3 , 0.2
7e ^-4 , -0.33e ^-6

Second lens (aspherical lens) Thickness: 3.48 mm Refractive index: 1.515 First surface curvature: 3.04 mm Conical constant: 0.07 Aspherical coefficient: -0.79e ^-2 , -0 .63e ^-3 , 0.2
7e ^-3 , -0.21e ^-4 Second surface curvature: -8.44 mm Conical constant: 8.80 Aspheric coefficient: -0.79 e ^-2 , 0.14 e ^-1 , -0.
14e ^-2 , 0.55e ^-3

0.6 mm disk (substrate refractive index: 1.5
1) At the time of use The distance (D1) between the first lens and the second lens: 0.26 mm Working distance (W1): 1.91 mm At the time of use of a 1.2 mm disk (substrate refractive index: 1.51) First lens and second Lens spacing (D2): 1.57 mm Working distance (W2): 1.5 mm

As described above, the present invention uses an aspherical lens to correct aberration caused by a difference in thickness of a disk. The first lens according to the embodiment has almost no optical magnification. Accordingly, the second lens forms a focal point at a constant magnification regardless of the position where the first lens is moved. On the other hand, the moving distance of the first lens is within 0.3 mm, but such a distance can be easily driven by the above-described actuator, for example, the piezoelectric element. Next, as a result of the above embodiment, 0.6 mm
The light intensity distributions of the focal points formed on the disc and the 1.2 mm disc respectively are attached to FIGS. In the drawing, the horizontal axis indicates the size of the light spot. According to these results, it can be seen that the change rate of the size of the spot formed between the 0.6 mm disk and the 1.2 mm disk according to the present invention is within 5%, and hardly changes, that is, the spot is formed at the same magnification.

[0017]

According to the present invention, a variable focal point having the same magnification is formed by two lenses and formed at the same magnification on disks having different thicknesses. Since light is not split, a high light efficiency is obtained. And the signal-to-noise ratio is improved during recording and reproduction. In addition, since focal points having the same magnification are formed on disks having different thicknesses, an optical pickup device whose characteristics do not change according to the thickness of the disk can be provided. It is obvious that the present invention is not limited to the above embodiments, and that many modifications can be made by those having ordinary skill in the art without departing from the technical concept of the present invention.

[Brief description of the drawings]

FIG. 1 is a layout diagram showing an optical configuration of an optical pickup device including a lens device having the same magnification variable focus according to the present invention.

FIG. 2 is an arrangement diagram illustrating an optical path of a lens device having the same variable magnification focal point according to the present invention.

FIG. 3 is a lens profile showing an optical path for a 0.6 mm disk by a lens device having the same magnification variable focus according to the present invention.

FIG. 4 is a lens profile showing an optical path for a 1.2 mm disk by the lens apparatus having the same magnification variable focus according to the present invention.

FIG. 5 is an optical profile showing an intensity distribution of a focus formed on a 0.6 mm disk by a lens device having the same magnification variable focus according to the present invention.

FIG. 6 is an optical profile showing an intensity distribution of a focus formed on a 1.2 mm disk by a lens apparatus having the same variable magnification focus according to the present invention.

FIG. 7 is a layout diagram showing an optical configuration of a conventional dual focus optical pickup device.

FIG. 8 is a partial layout diagram showing an optical path for a 0.6 mm disk by a conventional dual focus optical pickup device.

FIG. 9 is a partial layout diagram showing an optical path for a 1.2 mm disk by a conventional dual focus optical pickup device.

[Explanation of symbols]

 21, 22 disk 23 laser diode (light source) 26 first lens 27 second lens 28 actuator (lens driving means) 30 photodetector (signal detecting means)

Claims (8)

[Claims] 1. A lens device for forming a variable focal point, comprising: a first lens movable in an optical axis direction for converging incident light; and a spatially fixed first lens converged by said first lens. A second lens for converging light to form a focal point, and lens driving means for moving the first lens so as to change the position of the focal point of the second lens. A lens device having a focal point. 2. The lens apparatus according to claim 1, wherein the first lens has no optical magnification. 3. The lens apparatus having the same magnification variable focus according to claim 1, wherein the first lens and the second lens satisfy the following condition. First lens (aspherical lens) Thickness: 1.13 mm Refractive index: 1.515 First surface curvature: 4.05 mm Conical constant: 0.20 Aspherical coefficients: 0.72e ^-3 , -0.12e ^-4 , -0.
89e ^-5 , 0.92e ^-6 Second surface curvature: 4.72 mm Conical constant: -0.17 Aspheric coefficient: -0.14e ^-2 , 0.10e ^-3 , 0.2
7e ^-4 , -0.33e ^-6 Second lens (aspheric lens) Thickness: 3.48 mm Refractive index: 1.515 First surface curvature: 3.04 mm Conical constant: 0.07 Aspheric coefficient: -0 .79e ^-2 , -0.63e ^-3 , 0.2
7e ^-3 , -0.21e ^-4 Second surface curvature: -8.44 mm Conical constant: 8.80 Aspheric coefficient: -0.79 e ^-2 , 0.14 e ^-1 , -0.
14e ^-2 , 0.55e ^-3 4. An optical pickup device for forming a focal point of the same magnification on disks having different thicknesses, comprising: a light source for generating light; and a light source movable in an optical axis direction, for converging light generated from the light source. A first lens that is spatially fixed, a second lens that focuses light focused by the first lens to form a focal point on the disc, and a disc that has a different focal point by the second lens. An optical pickup device comprising: lens driving means for moving a first lens so as to be formed as described above; and means for detecting a signal from light reflected from the disk. 5. The optical pickup device according to claim 4, wherein the first lens has no optical magnification. 6. The optical pickup device according to claim 4, wherein the first lens is moved within a range of 0.3 mm or less. 7. The optical pickup device according to claim 4, wherein the working distance from the second lens to the disk is set differently according to the thickness of the disk. 8. The first lens and the second lens have a length of 0.6 m.
5. The optical pickup device according to claim 4, wherein the following conditions are satisfied for the m disk and the 1.2 mm disk. First lens (aspherical lens) Thickness: 1.13 mm Refractive index: 1.515 First surface curvature: 4.05 mm Conical constant: 0.20 Aspherical coefficients: 0.72e ^-3 , -0.12e ^-4 , -0.
89e ^-5 , 0.92e ^-6 Second surface curvature: 4.72 mm Conical constant: -0.17 Aspheric coefficient: -0.14e ^-2 , 0.10e ^-3 , 0.2
7e ^-4 , -0.33e ^-6 Second lens (aspheric lens) Thickness: 3.48 mm Refractive index: 1.515 First surface curvature: 3.04 mm Conical constant: 0.07 Aspheric coefficient: -0 .79e ^-2 , -0.63e ^-3 , 0.2
7e ^-3 , -0.21e ^-4 Second surface curvature: -8.44 mm Conical constant: 8.80 Aspheric coefficient: -0.79 e ^-2 , 0.14 e ^-1 , -0.
When using a 14e- ² , 0.55e- ³ 0.6mm disc (substrate refractive index: 1.51) Distance between the first lens and the second lens: 0.26mm Working distance: 1.91mm 1.2mm disc (substrate refraction) Rate: 1.51) In use, the distance between the first lens and the second lens: 1.57 mm Working distance: 1.5 mm