JPH08203115A - Optical system - Google Patents

Abstract

PURPOSE: To make it possible to judge the thickness of a protective layer of disk and to enable reproduction by matching a reproduction mode with the disk of this thickness by forming two aspherical faces corresponding to the respective focuses of an objective lens on one lens face so as to have the two focuses and forming the respective aspherical faces of plural disconnected faces. CONSTITUTION: This optical system consists of the conventional disk 9 having a large thickness, the disk 23 having half the thickness, the two-aspherical face lens 24 having the two aspherical faces, the first luminous flux 27 past the first aspherical face 25 and the second luminous flux 28 passed the second aspherical face 26. The luminous flux transmitted through the two-aspherical face lens 24 on which the same laser beam as heretofore is made incident and which has the two aspherical faces in place of the conventional objective lens separates into the first luminous flux 27 and the second luminous flux 28 and focuses at the respective signal faces of the conventional disk 9 and the disk 23 of half the thickness. Only the one focus of two sheets of the disk acts at this time and the other focus does not act. The distance to the signal surfaces of the disks is judged from the two focus error signals generated when the objective lens is moved in the focus direction and the magnitude of the focus offset voltage of this time and the reproduction is executed by matching the reproduction mode with the disk of this thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system mounted on an optical disk device for optically recording information on a disc-shaped information recording medium (hereinafter referred to as a disk) or reproducing information recorded on the disk. It is a thing.

[0002]

2. Description of the Related Art In recent years, there has been a remarkable improvement in disk reproduction technology. Especially, the optical system for playing discs is improved every day, with higher performance,
Cheaper ones continue to be investigated.

An example of a conventional optical system will be described below with reference to the drawings. FIG. 6 shows a configuration of an optical system of a conventional optical system. In FIG.
A semiconductor laser 1 serves as a light source of an optical system. Reference numeral 2 is a diffraction grating, which passes a laser beam 3
Is separated by a slight angle and divided into three beams, one of which is used for reproducing an information signal and two of which are used for tracking. A half mirror 4 transmits a part of the laser beam 3 and reflects the rest. Reference numeral 5 is a laser mirror, and the direction of the laser beam 3 is converted by the beam direction conversion unit 6. 7
Is a collimator lens and has a function of making the laser beam a parallel beam. Reference numeral 8 denotes an objective lens, which focuses the laser beam 3 on the signal surface 9b of the disk 9 into a spot of about 1 μm.

A photodiode 10 receives a laser beam 3 containing an information signal, detects the signal, and converts the signal into an electric signal. Reference numeral 11 denotes a concave lens, which has a function of correctly focusing the laser beam 3 on the photodiode 10 by moving and adjusting the lens parallel to the optical axis.

The operation of the optical system of the optical system configured as described above will be described below. In FIG. 6, a laser beam 3 is separated from a semiconductor laser 1 by a diffraction grating 2 into three beams, and a half mirror is used. It is incident on 4. A part of the laser beam 3 incident on the half mirror 4 is transmitted and the rest is reflected, but the reflected laser beam is further incident on the laser mirror 5, and most of it is reflected this time, and the direction is changed. Then, the light enters the collimator lens 7. By passing through the collimator lens 7, the laser beam 3 becomes parallel light and is incident on the objective lens 8, and the objective lens 8 causes the laser beam 3 to travel.
Are converged into signal pits on the signal surface 9b of the disk 9.

The laser beam 3 reflected from the disk 9 contains an information signal, but is collected again by the focus lens 8, returns in the reverse optical path, passes through the collimating lens 7, and enters the laser mirror 5. The laser beam 3 that has been redirected by the laser mirror 5 and redirected
When the light enters the half mirror 4, a part of the light that has passed through this time passes through the concave lens 11 and enters the photodiode 10, and the optical signal is detected as an electric signal.

Next, the perspective view shown in FIG. 7 is an example of an actuator for focusing and tracking of the objective lens 8. The actuator will be described below with reference to the drawings.

In FIG. 7, reference numeral 12 denotes a suspension holder which holds one end of the suspension indicated by 13. Reference numeral 13 is a suspension as described above, but a material and a structure are determined because appropriate stiffness and braking performance are required.

Reference numeral 14 is a coil bobbin, to which a coil and an objective lens for driving in the focus direction and the tracking direction are attached. Reference numeral 15 is a tracking coil for driving the objective lens in the radial direction,
Similarly, 16 is a focus coil for driving the objective lens in the focus direction, and 17 and 18 are a tracking coil and a magnet and a yoke for driving the focus coil.

The operation of the actuator configured as described above will be described. In FIG. 7, a suspension holder 12 fixed to an optical system base (not shown)
The coil bobbin 14 is attached to the free end of the suspension 13 attached to the so that the objective lens 8 attached to the coil bobbin 14 by the tracking coil 15, the focus coil 16, the magnet 17 and the yoke 18 can freely move in the tracking direction and the focus direction. It has become. Then, in the disc reproducing state, the objective lens 8 detects a signal for tracking control and focus control together with the information signal of the disc, and controls the current flowing to the tracking coil 15 and the focus coil 16 based on the signal. Are doing

FIG. 8 is a diagram in which a conventional objective lens tries to perform focus search on a disc. In FIG. 8, 19 is the initial position of the objective lens, 20 is the movement of the objective lens during focus search, 21 is the position where the focus error signal is generated by the astigmatism method, and 22 is the passage of time. The above focus search operation will be described. First, when the disc 9 starts rotating, the objective lens 8 in the initial position of the objective lens approaches the disc 9 to a certain position and moves away from the disc 9 as shown by the movement 20 of the objective lens. At this time, when the lens reaches the position of 21 focus error signal generation, a focus error signal is generated by the astigmatism method. This signal is detected and focus control is activated to cause the objective lens 8 to follow the rotation of the disk 9 for reproduction. To do.

[0012]

However, in the above-mentioned structure, the thickness of the protective layer of the disk shown in 9a of FIG. 6 is limited to one kind, and it is not possible to discriminate a plurality of kinds of disk thicknesses. This is an obstacle to compatibility of multiple formats.

In view of the above problems, the present invention provides an optical system having a configuration effective for discriminating and reproducing a plurality of types of disc thickness.

[0014]

To achieve this object, the optical system of the present invention optically records information on a recording medium composed of a signal recording surface and a protective layer for protecting the signal recording surface, or signals. An optical system for reproducing information recorded on a recording surface, wherein an optical element, an objective lens for converging a light flux of the optical element to a signal recording surface, a holding means for holding the objective lens, and an objective lens are used for signal recording. The objective lens includes at least two aspherical surfaces corresponding to respective focal points formed on one lens surface so that the objective lens has at least two focal points. Is composed of a plurality of surfaces which are intermittent.

[0015]

According to the present invention, according to the above-mentioned structure, at least two aspherical surfaces that connect at least two focal points of the objective lens are intermittently formed by one lens, and when the objective lens is moved in the focus direction. To determine the thickness of the protective layer of the disc by determining at least two focus error signals that occur and the distance from each focus offset voltage when each focus error signal occurs to the signal surface of the disc. Thus, it is possible to discriminate the respective discs having a plurality of types of protective layer thicknesses, match the reproducing conditions of the optical system to the protective layer thicknesses, and reproduce.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical system according to an embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows the relationship between the lens and the disk of the optical system of the present invention, FIG. 2 shows a part of the surface of the lens, and FIG. 3 shows an enlarged sectional view of the surface.

In FIG. 1, 9 is a conventional thick disk, 23 is a half-thick disk, 24 is a lens having two aspherical surfaces, and 27 is a first aspherical surface shown at 25 in FIG. The first luminous flux, 28 is the second luminous flux which has passed through the second aspherical surface shown by 26 in FIG. 2, and 2 shown in FIG.
5 to 28 are similar aspherical surfaces and light fluxes.

FIG. 4 shows a state in which the objective lens is trying to perform focus search on the disk in the optical system of the present invention.

FIG. 4 is the same as that shown in FIG. 8 in the conventional example, in which 23 is a half-thick disk and 24 is a disk.
Is a double aspherical lens having two aspherical surfaces, and 29 is a double focus error signal generated in the optical system of the present invention. FIG. 5 is a diagram for explaining two types of double focus error signals generated when a disc having two types of thickness is applied, where 30 is an offset voltage and 31 is a case where a disc having half the thickness is applied. The double focus error signals A and 32 are generated when the conventional disc is applied, and the double focus error signals B and 33 are generated at the reference offset voltage when no offset is applied, and are based on 0 volt.

The operation of the optical system of the present invention constructed as described above will be described below with reference to FIGS.

First, the laser beam until it enters the objective lens is the same as the conventional one, but as shown in FIG. 1, a two aspherical lens 24 having two aspherical surfaces is used instead of the conventional objective lens. The transmitted light flux is divided into a first light flux 27 and a second light flux 28 and focused on the signal surfaces of the conventional disc 9 and the half-thickness disc 23, respectively. At this time, of course, two discs cannot be applied at the same time, so that only one focus works and the other focus does not work.

2 and 3 are views for supplementary explanation of FIG. 1. FIG. 2 is a top view of the two aspherical lenses 24 having these two aspherical surfaces, and 25 is a view. 1 is a first aspherical surface for generating the first light flux 27, and 26 is a second aspherical surface for generating the second light flux 28. Further, in FIG. 3, reference numerals 25 and 26 denote first and second aspherical surfaces, respectively, and 27 and 28 denote first and second light fluxes generated therefrom.

Next, FIG. 4 shows a lens having two aspherical surfaces in the optical system of the present invention for focus search. The two aspherical lenses 24 at the initial position 19 of the objective lens are the disk 9 or the thickness. Half the disk 23 moves toward and away from the disk 9 or 23 to some extent, as shown by the movement 20 of the objective lens. Focus error signal generation position 2 at this time
Up to 1, the two aspherical lenses 24 move and a focus error signal is generated by the astigmatism method. At this time, the two aspherical lenses 24 have two focal points, and when the focus search is performed, the signal surface of one disc is set to two.
One beam spot will pass, and two focus error signals, that is, a double focus error signal 29 will be successively generated. The position where the double focus error signal is generated varies depending on the thickness of the disc, and the focus offset voltage at that time also varies. That is, in the focus error signal A when the conventional disc 9 is applied, the first focus error signal is generated at the position of the reference offset voltage 33 in the offset voltage 30, but when the half-thickness disc 23 is applied. In the focus error signal B, the first focus error occurs before the position of the reference offset voltage 33, and the second focus error signal comes to the position of the reference offset voltage 33. Therefore, one focus error signal is generated when the reference offset voltage is generated, but the other one focus error signal is detected by detecting whether it occurs at a place where the offset voltage is larger or smaller than that. The disc 9 or the half-thickness disc 23 is discriminated, and the mode of the disc having that thickness is set and reproduced.

[0025]

As described above, according to the present invention, each aspherical surface having at least two focal points is composed of one objective lens, and each aspherical surface having each focal point has a plurality of intermittent surfaces. And at least two focus error signals generated when the objective lens is moved in the focus direction, and the distance from the magnitude of each focus offset voltage when each focus error signal occurs to the signal surface of the disc. The thickness of the protective layer of the disc is determined and the reproduction mode is adapted to the disc of that thickness so that the disc can be reproduced.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a configuration and an operation in an embodiment of the present invention.

FIG. 2 is a diagram for supplementary explanation of FIG.

FIG. 3 is a diagram for supplementary explanation of FIG.

FIG. 4 is a diagram for explaining the operation in the embodiment of the present invention.

FIG. 5 is a diagram for supplementary explanation of FIG.

FIG. 6 is a diagram for explaining the configuration and operation of an optical system of a conventional optical system.

FIG. 7 is a diagram for explaining the configuration and operation of an actuator system of a conventional optical system.

FIG. 8 is a diagram for explaining the operation of an actuator system of a conventional optical system.

[Explanation of symbols]

 24 2 aspherical lens 25 1st aspherical surface 26 2nd aspherical surface 27 1st light flux 28 2nd light flux

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomonada Kamei 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Yutaka Murakami, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. An optical system for optically recording information on a recording medium comprising a signal recording surface and a protective layer for protecting the signal recording surface, or reproducing the information recorded on the signal recording surface. An optical element, an objective lens for converging the light flux of the optical element onto the signal recording surface, a holding means for holding the objective lens, and the holding means for allowing the objective lens to move in the signal recording surface direction. The objective lens has at least two aspherical surfaces corresponding to respective focal points formed on one lens surface so that the objective lens has at least two focal points, and each aspherical surface has a plurality of intermittent aspherical surfaces. The optical system is characterized in that 2. The optical system according to claim 1, wherein at least two aspherical surfaces that are interrupted in a plurality are concentrically subdivided surfaces. 3. A moving means for electromagnetically moving the holding means by applying a voltage, and a detecting means for detecting the light flux of the optical element reflected from the recording surface of the recording medium and converting it into an electric signal. The holding means is moved in the optical axis direction of the objective lens by applying a voltage to the means, and the position of the holding means when the detection means detects that the light beam is focused on the signal recording surface is different, and 2. A discriminating unit for discriminating the distance to the signal recording surface and discriminating the thickness of the protective layer of the recording medium by utilizing different voltages of the moving unit.
Alternatively, the optical system according to claim 2.