JPH08212578A - Optical pickup device - Google Patents

Abstract

PURPOSE: To reproduce optical recording media with different information pits without causing a distortion in regenerative signal. CONSTITUTION: A light source 2 emits read-out light, and an objective lens 9 converges the read-out light on the recording medium DK, and a control means 13 inserts/draws out a light quantity distribution correction means 6 into/from an optical path between the light source 2 and the objective lens 9 based on an optical recording medium discrimination signal SD from the outside. Thus, since the light quantity distribution correction means 6 inserted into the optical path corrects a light quantity distribution in the normal direction of a recording track, and it makes the numerical aperture NA of the objective lens 9 equal to one revising corresponding to the size of the information pit substantially, optimum reproducing operation for the loaded optical recording medium DK is performed easily.

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, and more particularly to an optical pickup device for reproducing recorded information from any of a plurality of optical recording media having different information pit sizes on a recording track. .

[0002]

2. Description of the Related Art Conventionally, as a reproducing apparatus for reproducing an optical recording medium, a CD (Compact Disk), an LD (Laser vision D)
Disc players capable of reproducing isk) are known.

In such a disc player, the spot diameter of the reading light beam is set to an optimum value according to the size of the information pit of the optical recording medium to be reproduced. The spot diameter R of the reading light beam is the numerical aperture NA of the objective lens.
And is proportional to the ratio of the wavelength λ of the read light beam. That is, R∝λ / NA.

Therefore, when reproducing an optical recording medium having small information pits, it is necessary to reduce the spot diameter R of the read light beam. Therefore, if the wavelength λ of the read light beam is constant, the numerical aperture NA is increased. There is a need to.

In other words, if the wavelength λ of the read light beam is constant, a small information pit can be reproduced if the numerical aperture NA is large (see FIG. 8A), and a large numerical aperture NA is large. This means that the information pit can be reproduced (see FIG. 8 (b)).

[0006]

By the way, the numerical aperture NA of the objective lens is a value peculiar to each objective lens, which means that in a pickup device optimally adjusted with respect to the size of a certain information pit. Has a problem in that it is not suitable for information pits having a size other than the size of the information pit to be adjusted, and the reproduced signal is distorted.

More specifically, as shown in FIG. 7, a reproduction signal obtained by reproducing a larger information pit P (see FIG. 7A) with a pickup device optimally adjusted to a smaller information pit is originally shown in FIG. Where there should be a waveform as shown in FIG. 7C, however, the waveform is distorted in the middle portion of the pit as shown in FIG. 7B.

Therefore, there is a problem that an optical recording medium having different information pit sizes cannot be reproduced by one pickup device, and even if reproduced, accurate information reproduction cannot be performed.

Therefore, an object of the present invention is to provide a pickup device capable of reproducing optical recording media having different information pit sizes without causing distortion in a reproduced signal.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 reproduces recorded information from any of a plurality of optical recording media in which the size of information pits on a recording track is different from each other. In the optical pickup device for reading, a light source for emitting the reading light, an objective lens for condensing the reading light on the recording medium, and an amount of light in the tangential direction of the recording track corresponding to the size of the information pit. And a control means for inserting and removing the light quantity distribution correction means in an optical path between the light source and the objective lens based on an optical recording medium discrimination signal from the outside. To do.

[0011]

According to the first aspect of the invention, the light source emits the reading light and the objective lens focuses the reading light on the recording medium.

At this time, the control means inserts / removes the light quantity distribution correction means in the optical path between the light source and the objective lens based on the optical recording medium discrimination signal from the outside. As a result, the light quantity distribution correcting means inserted in the optical path corrects the light quantity distribution in the tangential direction of the recording track, so that the numerical aperture NA of the objective lens is substantially changed in accordance with the size of the information pit. Is equivalent.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described with reference to the drawings. First Embodiment FIG. 1 shows a schematic configuration diagram of a pickup device of the first embodiment.

The pickup device 1 reflects a laser diode 2 that emits read light, a grating 3 for separating the read light into three beams, and the read light from the laser diode 2 and guides the read light to an objective lens side described later. With
Half mirror 4 that transmits the read light from the objective lens side
, A collimator lens 5 for making the reading light, which is diffused light, parallel light, a slit plate 6 as a light quantity distribution correction means provided with a slit for correcting the light quantity distribution in the tangential direction of the recording track, and a control signal S. _A drive control signal is output based on _C to drive the correction element drive mechanism 7 to drive the slit plate 6
Drive circuit 8 that inserts or removes into the optical path,
The objective lens 9 for condensing the read light on the optical disc DK, the concave lens 10 for beam-shaping the read light from the objective lens 9 that has passed through the half mirror 4, and the read light shaped by the concave lens 10 are received. And a light receiving element 11 for converting the signal into an electric signal and outputting the electric signal, and a disc discriminating sensor 12 for discriminating the disc type based on the thickness of the protective layer (substrate) of the optical disc DK and outputting a disc discriminating signal S _D.
And a control circuit 13 for outputting a control signal S _C for controlling the insertion / removal of the slit plate 6 based on the disc discrimination signal S _D ,
It is configured with.

The structure of the disc discriminating sensor 12 will now be described. The disc discrimination sensor 12 extracts a low-pass component of the current flowing through the focus coil that drives the objective lens 9 in the focus direction and outputs a low-pass component (not shown) as a direct-current component signal, and a predetermined low-pass component signal voltage. The reference voltage (corresponding to the reference protective layer thickness) is output from the disc discriminating signal S _D , and the disc discriminating sensor 12 includes, for example, a protective layer (substrate). Thickness 0.
DVD (Digital with two 6mm disks stuck together
Video Disk) and a CD (Compac
When setting the reference voltage V _REF for determining t Disk), the protective layer thickness is 0.9 mm (= (0.6 + 1.2)
The voltage of the low frequency component signal corresponding to / 2) is set as the reference voltage.

As a result, in a DVD in which two discs each having a protective layer thickness of 0.6 mm are bonded together, the lens driving distance and the protective layer thickness of 1.2 mm when the focus servo is closed to bring the focus into focus. In the CD, the lens driving distance when the focus servo is closed to bring it into the in-focus state is doubled (= 1.2 when the focus position when the focus servo is not performed is the protective layer surface). /0.6 times) will be different.

Therefore, when the focus servo is not performed, the focus position is adjusted to be on the surface of the protective layer, and when the voltage of the low frequency component signal exceeds the reference voltage, the optical disk is a CD. The discriminating signal is output, and when the voltage V _MDC obtained as the voltage V _DC of the DC component signal does not exceed the reference voltage V _REF , the disc discriminating signal indicating that the optical disc is a DVD is output. ing.

Prior to information reproduction, the pickup device 1
In order to focus on the information recording surface of the optical disc DK, the focus servo is closed to bring it into a focused state. As a result, the low-pass filter of the disc discrimination sensor 12 extracts only the low frequency component of the voltage signal corresponding to the current flowing through the focus coil that drives the objective lens 9 in the focus direction and outputs it as the low frequency component signal to the comparator. .

As a result, the comparator outputs the disc discrimination signal corresponding to the type of the loaded optical disc to the control circuit 13 by comparing the voltage of the low frequency component signal with the reference voltage.

More specifically, when the voltage of the low frequency component signal exceeds the reference voltage, a disk discriminating signal indicating that the optical disk is a CD is output to the control circuit 13, and the voltage of the low frequency component signal is the reference voltage. When the voltage is not exceeded, the control circuit 13 sends a disc identification signal indicating that the optical disc is a DVD.
Output to.

In this case, the DVD has a smaller recording track pitch and a smaller information pit size than the CD from the viewpoint of improving the recording density, and the numerical aperture NA of the objective lens 9 is optimal for reproducing the DVD. Is set to.

As a result, the control circuit 13 outputs a control signal for controlling the insertion / removal of the slit plate 6 to the drive circuit 8 based on the disc discrimination signal. As a result, the drive circuit 8
The drive control signal is corrected based on the control signal.
The slit plate 6 is inserted into or removed from the optical path according to the disc discrimination signal.

Specifically, as shown in FIG. 2, when the loaded optical disc is a CD according to the disc discrimination signal and the slit plate 6 is not inserted in the optical path, the optical path is determined. When the slit plate 6 is inserted in the optical path and the slit plate 6 is inserted in the optical path, the slit plate 6 is left as it is (see FIG. 3B).

As a result, as shown in FIG. 3A, the pupil diameter of the read light beam applied to the optical disk is blocked at both ends in the tangential direction of the recording track, and the tangential direction of the recording track during CD reproduction. 4B and the obtained reproduction signal is as shown in FIG. 7C, and accurate reproduction can be performed.

In the case where the loaded optical disk is a DVD and the slit plate 6 is not inserted in the optical path according to the disk identification signal, the slit plate 6 is left as it is and the slit plate 6 is inserted in the optical path. If
The slit plate 6 is taken out from the optical path.

As described above, according to the first embodiment, the optimum light quantity distribution is corrected according to the size of the information pit of the mounted optical disk, that is, the numerical aperture NA of the objective lens is substantially corrected. Therefore, the optimum reproducing operation for the loaded optical disk can be easily performed.

In the first embodiment described above, the case where two types of optical disks (CD and DVD) having different protective layer thicknesses are reproduced has been described. However, by setting a plurality of reference voltages in the comparator of the disk discriminating device 12, It is also possible to discriminate three or more types of optical discs and switch the slit plate so as to perform optimum reproduction for each of the three or more types of optical discs. Second Embodiment In the first embodiment, as the light quantity distribution correction means,
Although the slit plate was used, instead of the slit plate, as shown in FIG.
A glass filter 2 coated as shown in FIG. 1 to reduce the light transmittance in the tangential direction of the recording track.
It is also possible to use 0.

As a result, as in the case of the first embodiment, the numerical aperture NA of the objective lens is substantially corrected, and the optimum reproducing operation for the mounted optical disk can be easily performed. Third Embodiment In the second embodiment described above, the glass filter 20 coated instead of the slit plate was used, but instead of the glass filter 20, the glass filter 20 shown in FIG. 6 (a) or FIG. 6 (b) is used. A light quantity distribution correction element 2 having diffraction gratings formed at both ends corresponding to the tangential direction of the recording track as shown.
It is also possible to use 1a and 21b. The difference between the light amount distribution correction element 21a and the light amount distribution correction element 21b is only that the grating direction of the diffraction grating is different, but the grating direction can be set arbitrarily.

According to the light quantity distribution correction element having the diffraction grating, the intensity of the 0th-order light transmitted through the diffraction grating is lower than that of the incident light, that is, the light transmitted through the central portion where the diffraction grating is not provided. By utilizing this, it is possible to easily perform the optimum reproducing operation for the optical disk mounted, which is substantially equivalent to the correction of the numerical aperture NA of the objective lens as in the above embodiments. Fourth Embodiment In each of the above-described embodiments, the light quantity distribution correction element formed with a slit plate, a glass filter, and a diffraction grating is mechanically inserted in the optical path to correct the light quantity distribution in the tangential direction of the recording track. However, it is also possible to dispose an element such as a liquid crystal shutter capable of electrically controlling the transmitted light amount in advance in the optical path and electrically function as a light amount distribution correction element. Fifth Embodiment In each of the above-described embodiments, the light amount distribution correcting element is provided in addition to the original optical system. However, the optical element (eg, grating,
A similar effect can be obtained by providing a coating, a diffraction grating, or the like on a half mirror, a reflection mirror, a collimator lens, an objective lens, and switching and using this optical element.

[0030]

According to the invention of claim 1, the light source is
The reading light is emitted, the objective lens condenses the reading light on the recording medium, and the control means inserts the light quantity distribution correction means in the optical path between the light source and the objective lens based on the optical recording medium discrimination signal from the outside. escape.

As a result, the light quantity distribution correcting means inserted in the optical path corrects the light quantity distribution in the tangential direction of the recording track, so that the numerical aperture NA of the objective lens is substantially changed in accordance with the size of the information pit. Since it is equivalent to what you did,
This makes it possible to easily perform the optimum reproducing operation for the loaded optical disk.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a pickup device according to a first embodiment.

FIG. 2 is an operation explanatory diagram of the first embodiment.

FIG. 3 is an explanatory diagram of an inserted state of a slit plate.

FIG. 4 is a diagram illustrating a light amount distribution state in a tangential direction of a recording track.

FIG. 5 is an explanatory diagram of a glass filter according to a second embodiment.

FIG. 6 is an explanatory diagram of a light amount distribution correction element according to a third embodiment.

FIG. 7 is a diagram illustrating a conventional problem and an effect of the first embodiment.

FIG. 8 is a diagram illustrating a conventional problem.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pickup device 2 ... Laser diode 3 ... Grating 3A ... 1st grating 3B ... 2nd grating 4 ... Half mirror 5 ... Collimator lens 6 ... Slit plate 7 ... Correction element drive mechanism 8 ... Drive circuit 9 ... Objective lens 10 ... Concave lens 11 ... Light receiving element 12 ... Disc discrimination sensor 13 ... Control circuit 20 ... Glass filter 21a, 21b ... Light amount distribution correction element S _C ... Control signal S _D ... Disc discrimination signal DK ... Optical disc

Claims (1)

[Claims] 1. An optical pickup device for reproducing recorded information from any one of a plurality of optical recording media in which the size of information pits on a recording track are different from each other, and a light source for emitting read light and the read light. An objective lens for condensing on the recording medium, a light amount distribution correction unit for correcting the light amount distribution in the tangential direction of the recording track corresponding to the size of the information pit, and an optical recording medium discrimination signal from the outside. An optical pickup device, comprising: a control unit that inserts and removes the light amount distribution correction unit in an optical path between the light source and the objective lens based on the control unit.