JPH08315402A - Optical pickup device - Google Patents

Abstract

PURPOSE: To improve focusing to each of plural kinds of optical disks which are different in thickness by using an objective lens as a multifocal lens. CONSTITUTION: The objective lens is specified as a bifocal lens, which is set to converge long focal light to a CD and also a digital video disk(DVD) having its geometrical thickness of 1.2mm and short focal light to a DVD having its geometrical thickness of 0.6mm on their respective recording surfaces 6A and 6B (a broken line in the figure shows a position of the recording surface of DVD having 0.6mm geometrical thickness).

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 for reproducing a signal recorded on an optical disc,
More specifically, the present invention relates to an optical pickup device capable of signal reproduction for each of a plurality of optical discs having different thicknesses.

[0002]

2. Description of the Related Art Optical discs are used as various recording media because of their large recording density and large capacity and their excellent random access. Therefore, many types of optical discs are known, such as CD (compact disc), DVD (digital video disc), and LD (laser disc), depending on the application or field of use. An optical pickup device that reproduces a signal from such various optical disks has a substantially similar configuration as shown in FIG. 7, regardless of the type of the optical disk.

That is, in general, an optical pickup device focuses a laser beam 102 output from a semiconductor laser 101 on a recording surface 106 A of an optical disk 106 by an objective lens 105 via a half mirror 103 and a collimator lens 104, and records this. The return light from the surface 106 A receives the objective lens 10
5, the data signal and the error signal (focus error signal, tracking error signal) are obtained by being incident on the four-divided photodiode 107 via the collimator lens 104 and the half mirror 103. further,
According to this error signal, the objective lens 105 is moved up and down and left and right to perform focus control and tracking control.

[0004]

As described above, the optical pickup device has substantially the same structure for various optical discs, so that a so-called compatible player capable of reproducing signals from various optical discs using one optical pickup device. If the device is configured, it is not necessary to arrange each player device according to the type of the optical disc, which is convenient.
By the way, the optical disc has a thickness or N depending on its type.
A is often different. In particular, the thickness may vary greatly. For example, the CD and DVD have the same 120 mm diameter, but the CD thickness is 1.2 mm standard.
The thickness is expected to be either 0.6 mm or 1.2 mm, or both.

In addition, the LD has a structure in which two 1.2 mm thick single disk discs are stuck together with the recording surface inside, and the thickness of one side is 1.2 mm, which is the same as the thickness of the CD. In general, the material of the protective plate of DVD is P
In contrast to C (polycarbonate) resin, the material of the protective plate of LD is generally acrylic resin and has different refractive indexes from each other.
Is different from. As described above, when it is attempted to share the optical pickup device with a plurality of optical discs having different geometrical thicknesses or optical thicknesses, focusing may be difficult.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical pickup device capable of favorably focusing on each of a plurality of optical disks having different geometrical thicknesses and optical thicknesses. It is a thing.

[0007]

The optical pickup device of the present invention is an optical pickup device provided with an objective lens for focusing a light beam from a laser light source on an optical disc, wherein the objective lens is a signal reproducing position for the optical disc. When set to, the light beam is focused at two positions, a first position on the recording surface of the optical disc having a large optical thickness and a second position on the recording surface of the optical disc having a small optical thickness. It is characterized in that it is formed so as to obtain.

Further, the objective lens of the optical pickup device is constructed by spatially combining a long focus Fresnel lens and a short focus Fresnel lens, or by spatially combining a long focus diffractive lens and a short focus diffractive lens. It is desirable to do. The above "optical thickness" means
It refers to the product of the geometrical thickness, which is the actual spatial thickness, and the refractive index of the material.

[0009]

According to the above optical pickup device, when the objective lens is composed of a multifocal lens and the signal reproduction of the optical disc having a large optical thickness is performed, the long focal light from the objective lens is emitted from the disc. The light is focused on the recording surface, and when the signal is reproduced from the optical disk having a small optical thickness, the short focus light from the objective lens is focused on the recording surface of the disk.

As a result, the light beam can be focused on the recording surface regardless of whether the signal is reproduced from an optical disk having a large optical thickness or the signal is reproduced from an optical disk having a small optical thickness. The compatibility can be improved. Further, if the multifocal objective lens is composed of a Fresnel lens or a diffractive lens (HOE lens), the lens thickness can be made thin, so that the apparatus can be made compact and the aberration can be made small. It is possible.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an optical pickup device according to an embodiment of the present invention. That is, this optical pickup device has a laser beam 2 (for example, a wavelength of 63%) output from the semiconductor laser 1 by the power supply from the LD power source 1A.
(5 nm) is reflected by the half mirror flat plate 3, collimated by a collimator lens 4, and made into a focused light beam at two far and near positions by an objective lens 5 composed of a bifocal Fresnel lens. Is irradiated onto the recording surface 6A. The optical disk 6 is set by a chucking member (not shown) so that the lower surface position is substantially constant.

Pits carrying signal information are arranged in a track shape on the recording surface 6A, and the reflected light of the laser beam 2 from the recording surface 6A carries the signal information and the objective lens 5 and the collimator. The light enters the half mirror plane plate 3 through the lens 4, and the half mirror plane plate 3
And is incident on the four-divided photodiode 7. The photodiode 7 calculates the amount of light received at each of the four divided diode positions to obtain a data signal and focus and tracking error signals.

Since the half mirror flat plate 3 is inserted at an angle of 45 ° with respect to the optical path of the return light from the optical disk 6, it has the same function as a cylindrical lens and transmits through the half mirror flat plate 3. The thus-formed light beam has astigmatism, and the focus error amount is determined according to the shape of the beam spot of the return light on the photodiode 7 divided into four. The collimator lens 104 may be omitted depending on the situation. Further, a grating lens may be inserted between the semiconductor laser 1 and the half mirror plane plate 3 to provide 3
It is also possible to detect tracking errors with the beam.

By the way, in this optical pickup device, C
It is configured so that signal reproduction is possible for both the D and DVD optical discs 6. The CD has a uniform geometrical thickness of 1.2 mm, and the DVD has a geometrical thickness of 0.6 mm and 1.2 mm. Focusing is surely performed on any of these optical discs 6. It is supposed to be done. Note that C
Both D and DVD are PC (polycarbonate; refractive index n _D
= 1.584) and the NA is
The former is about 0.45, the latter is about 0.6 or
It is set to be about 0.55.

It is desirable that the optical thicknesses of the CD and the DVD are substantially equal to each other in order to surely perform the focusing, but if the geometrical thickness of the optical disk 6 itself is different, as a result, the optical thickness is increased. As described above, the objective lens 5 has different thicknesses.
Is a bifocal lens, and the CD and geometrical thickness are 1.2m
Long focal length and geometrical thickness for DVD of m
For a 0.6 mm DVD, short focal light is recorded on each recording surface 6.
A, 6B (Dashed line in Figure 1 shows DV with geometrical thickness of 0.6 mm
It is set to focus on the recording surface position of D).

This bifocal objective lens 5 has a long-focus aspherical lens (large NA) as shown in FIG. 2 (a) and FIG. 2 (b).
It is constructed by spatially combining two Fresnel lenses as shown in FIGS. 2 (c) and 2 (d), each of which is a Fresnelized short-focus aspherical lens (small NA) as shown in FIG.
As a mode for spatially combining, as shown in FIG. 2 (e), one of the two Fresnel lenses forms an odd-numbered portion of the concentric ring zone, and the other forms an even-numbered portion of the concentric ring zone. Alternatively, as shown in FIG. 2F, one of the two Fresnel lenses may form an outer peripheral portion of the lens and the other may form an inner peripheral portion of the lens.

FIG. 3 is an enlarged view of the lens shown in FIG. 2 (f). In this bifocal objective lens 15, the lens outer peripheral portion 15A is composed of a long focus Fresnel lens, and the lens inner peripheral portion 15B is composed of a short focus Fresnel lens. The light beam 2 incident on this objective lens 15 is Long-focus light 2A is generated at the outer peripheral portion 15A and the lens inner peripheral portion
At 15B, the short focus light is 2B. Therefore,
If this optical pickup device is used, as shown in FIG. 4A, for a CD and a DVD 26 having a geometrical thickness of 1.2 mm, the long-focus light 2A is focused on the recording surface 26A. The geometric thickness is 0.6 as shown in 4 (b).
The short focal light 2B is recorded on the recording surface 36 of the DVD 36 mm of 36 mm.
Optical discs of any thickness will be focused on A.
Focusing can be made excellent also in 26 and 36.

The objective lens 5 is not limited to the Fresnel lens, as described above, as long as it can focus the light beam 2 at two predetermined positions, far and near. For example, in FIG.
A long-focus diffractive lens A (HOE lens; large NA) as shown in FIG. 5A and a short-focus diffractive lens B (HOE lens; small NA) as shown in FIG. As shown in (c), one of the two diffractive lenses may form an odd-numbered portion of the concentric ring-shaped zone, and the other may form an even-numbered portion of the concentric ring-shaped zone. As shown in FIG. 5D, one of the two diffractive lenses may form an outer peripheral portion of the lens, and the other may form an inner peripheral portion of the lens.

Further, as shown in FIG. 6, the lens outer peripheral portion
A so-called progressive lens configuration may be used in which 25A is formed by a long-focus lens having a small curvature and the inner peripheral portion 25B is formed by a short-focus lens having a large curvature. The optical pickup device of the present invention is not limited to that of the above embodiment, and various other modifications can be made. For example, in the above embodiment, the laser light is emitted from the lower side of the optical disc, but the entire apparatus of the optical disc and the optical pickup may be arranged upside down and the laser beam may be emitted from the upper side. Is.

The types of optical discs to be used are not limited to CDs and DVDs, but LDs, MDs, etc.
It is of course possible to target other optical discs such as (mini discs), and the objective lens has three or more focal points to enable signal reproduction for three or more optical discs with different optical thicknesses. May be Although the plurality of optical beams are configured to be coaxial with each other in the above embodiment, it is of course possible to configure the optical beams so that they are off-axis from each other.

[Brief description of drawings]

FIG. 1 is a schematic view showing an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a diagram showing in detail the configuration of the objective lens shown in FIG.

FIG. 3 is an enlarged view of the objective lens shown in FIG.

FIG. 4 is a view for explaining the operation of the device shown in FIG.

FIG. 5 is a diagram showing an objective lens having a shape different from that of the objective lens shown in FIG.

6 is a diagram showing an objective lens having a shape different from that of the objective lens shown in FIG.

FIG. 7 is a schematic view showing a conventional optical pickup device.

[Explanation of symbols]

 1,101 Semiconductor laser 2,102 Laser light 2A Long focus light 2B Short focus light 3,103 Half mirror plane plate 4,104 Collimator lens 5,15,25,105 Objective lens 6,106,26,36 Optical disk 6A, 6B , 106A, 26A, 36A Recording surface 7,107 Four-division photodiode 15A, 25A Lens outer peripheral part 15B, 25B Lens inner peripheral part

Claims (3)

[Claims] 1. An optical pickup device comprising an objective lens for focusing a light beam from a laser light source onto an optical disc, wherein the optical beam is optically reflected when the objective lens sets the optical disc at a signal reproducing position. Of the optical disc having a large optical thickness and a second position on the recording surface of the optical disc having a small optical thickness. Optical pickup device. 2. The optical pickup device according to claim 1, wherein the objective lens is formed by spatially combining a long focus Fresnel lens and a short focus Fresnel lens. 3. The optical pickup device according to claim 1, wherein the objective lens is formed by spatially combining a long focus diffractive lens and a short focus diffractive lens.