JPH0973657A - Optical recording medium reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording information reproducing device capable of easily reading an optical disk recording with high density with simple constitution. SOLUTION: The light from a light source is made incident on the translucent substrate 3a of the optical disk at a prescribed angle θ0 for a disk surface normal 13 through a lighting lens 2. Since the substrate 3a has prescribed thickness and refractive index, a pit on an information recording surface 3 is irradiated with the light incident on the substrate 3a after refracted. The reflected light modulated by the pit is made incident on an objective lens 4 through the substrate 3a, and a light receiving surface of a photodetector 7 is irradiated by the reflected light on the optical axis θ0 of the objective lens 4 after through a parallel plane 5 consisting of transparent glass and a cylindrical lens 6. Since the reflected light from the scanned pit on the optical disk rotated by an optical disk reproducing device is the light through the substrate 3a sloped by θ0 to the normal 13, is made incident on the objective lens 4 in the state having the aberration due to the substrate 3a. In such a manner, the pit of the optical disk is irradiated by the light from the light source 1, and the reflected light modulated by the pit is made incident on the photodetector 7, and the pit of the optical disk is image formed on the photodetector 7 without the aberration.

Description

Detailed Description of the Invention

[0001]

[0001]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording information reproducing apparatus for reproducing an optical recording medium such as an optical disk on which information such as images and music is recorded, and particularly, an incoherent light source such as a light emitting diode is used. The present invention relates to an optical pickup device which reads out information by forming an image of a recording medium on a photodetector.

[0003]

[0002]

[0004]

2. Description of the Related Art Conventionally, there is a compact disc (hereinafter referred to as a CD) as an optical disc, and a CD player is known as a reproducing device thereof.

In a CD, pits carrying information bits are arranged on one side of the disc in a spiral form from the inner circumference to the outer circumference of the disc to form a plurality of tracks. Further, in a CD player, a constant linear velocity (CL) is applied to the optical disc so that a light beam of a pickup for reading the pit scans the pit at a relatively constant velocity in the rotation direction of the disc.
Rotate to V) and irradiate the pit with a beam to optically read information.

[0006]

FIG. 5 is a schematic sectional view showing an example of the structure of a conventional CD player pickup. In the figure, 101 is a light source, for example, a red semiconductor laser having a predetermined single wavelength. About half of the laser light emitted from the light source 101 is guided to the objective lens 103 by the half mirror 102a included in the beam splitter 102, and after entering the transparent substrate 104 of the CD and passing therethrough, the pit 105 of the CD.
Form a light spot on top. In addition, the transparent substrate 104 is
When the objective lens 103 is formed of polycarbonate or the like having a predetermined thickness and the thickness of the transparent substrate 104 is taken into consideration in advance, and the transparent substrate 104 is arranged perpendicular to the optical axis of the objective lens 103, It is set so that the smallest spot is formed on the pit 105. Further, the objective lens 103 always irradiates a spot of a predetermined size by following the pit to be scanned even if the disc surface is displaced in the optical axis direction by the warp of the disc or the like while the CD is rotating by the focus control means (not shown). Controlled as.

[0007]

The light reflected by the spot irradiated on the pit 105 is collected again by the objective lens 103,
After the amount of light is halved by the half mirror 102a of the beam splitter 102, the RF signal is detected by the photodetector 106. The photodetector 106 is the objective lens 103.
Is arranged at a position slightly deviated from the position where the pit is imaged, for example, at a position where the reflected light forms a circle of least confusion, and focus control is performed by the astigmatism method.

[0008]

Since the laser light emitted from the light source 101 passes through the half mirror 102a twice and the light amount is halved each time, it is necessary to secure a sufficient light amount for the photodetector 106 to receive the light. Laser light is used at high output.

The conventional pickup device of the CD player is constructed as described above and obtains the RF signal for reading the pits of the CD and reproducing the information.

[0010]

In recent years, with the diversification of information and the increase in density, there has been a demand for optical disks recorded at high density. Since the pits of this high-density optical disc are smaller than those of the conventional one and are arranged at a high density, it is necessary to reduce the beam spot of the laser light when reading each pit. Therefore, a laser light source having a shorter wavelength than that used in the conventional CD player is required.

[0011]

However, when a short wavelength blue semiconductor laser is used for the above-mentioned conventional pickup, there arise problems that the operating life is extremely short, or the device cannot operate at high temperature.

Further, when an SHG type blue laser that halves the wavelength by using optical nonlinearity is used, there is a problem that the structure of the light source is complicated and it is difficult to miniaturize it as compared with a semiconductor laser, and a high density disc is easily read. I couldn't.

[0013]

[0008]

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an optical recording information reproducing apparatus capable of easily reading an optical disk recorded at high density with a simple structure. To do.

[0015]

[0009]

[0016]

According to the first aspect of the present invention,
An optical recording medium reproducing device for optically reading and reproducing information recorded on a medium, comprising a light source for irradiating the medium with illumination light, and an imaging lens for forming an image on the medium by reflected light from the medium. Arranged on a plane including the condensing means, the focus position control means for controlling the focus position of the image forming lens to control the image forming position of the medium, and the image forming position of the medium formed by the image forming lens. And a detection means for detecting the light condensed by the condensing means, the illumination light enters the medium without passing through the imaging lens, and the optical axis of the illumination light from the light source to the medium surface, The optical recording medium reproducing apparatus is characterized in that the angle formed by the medium surface normal is equal to or larger than the angle formed by the optical axis of the imaging lens and the medium surface normal.

[0017]

According to a second aspect of the invention, in the optical recording medium reproducing apparatus according to the first aspect, the condensing means has an aberration correcting means, and condenses the reflected light accompanied by the aberration caused by the medium. In this case, the optical recording medium reproducing apparatus is characterized in that the aberration is corrected by the aberration correcting means and the medium is imaged.

[0018]

According to a third aspect of the present invention, in the optical recording medium reproducing apparatus according to the first or second aspect, the detecting means includes a first photodetector arranged at an image forming position of the medium, and a first photodetector.
Of the second photodetector, which is arranged on the same plane as the light receiving surface including the light receiving surface of the first photodetector, and which comprises a pair or a plurality of pairs of light receiving surfaces spaced from the light receiving surface of the first photodetector by a predetermined distance. The optical recording medium is characterized in that the focus position control means controls the imaging position of the medium to be located on the light receiving surface of the first photodetector by the light reception output of the second photodetector. It consists of a playback device.

[0019]

[0012]

[0020]

The present invention is constructed as described above.
According to the invention described above, the illumination light of the light source for irradiating the optical disc enters the optical disc without passing through the imaging lens, and the reflected light from the optical disc is condensed using the imaging lens. When optically reading the pits of the optical disk, it is not necessary to provide a beam splitter in the optical path, and the light source can be effectively used without being affected by the decrease in the light amount of the light source. Therefore, a good signal can be demodulated without increasing the light intensity of the light source, so that the high-density optical recording medium can be easily read and the life of the light source can be extended, so that long-time recording can be performed. Withstand regeneration.

[0021]

According to the second aspect of the invention, when the pits of the optical disk having the transparent substrate of a predetermined thickness provided on the pits are optically read through the transparent substrate, The aberration generated by the translucent substrate is corrected by the aberration correcting means so that the pits are imaged, so that an accurate pit image can be obtained and a good signal can be demodulated. The recording medium can be easily read.

[0022]

According to the third aspect of the present invention, each light receiving surface of the photodetector can simultaneously read the information of the adjacent tracks, and by comparing the outputs of the respective light receiving surfaces,
The position of the imaging lens can be controlled so that the photodetector is arranged on the surface including the imaging position of the medium on which the imaging lens forms an image, and the RF signal is separated from the output of each light receiving surface. it can.

[0023]

[0015]

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows an example of the configuration of a pickup of an optical disk reproducing apparatus according to an embodiment of the present invention. In the figure, reference numeral 1 denotes an illumination light source, which is an incoherent light source having a predetermined light emitting area, and is, for example, a light emitting diode which emits blue light. Reference numeral 2 is an illumination lens.

Reference numeral 3 is an information recording surface of an optical disk having pits carried thereon at a high density, and reference numeral 3a is a translucent substrate provided on the upper surface of the information recording surface 3 and having a predetermined thickness. Further, 4 is an objective lens, and 5 is a parallel plate which is arranged at a predetermined angle with respect to the optical axis of the objective lens 4. Reference numeral 6 is a cylindrical lens provided coaxially with the objective lens 4. Reference numeral 7 is a photodetector, the light receiving surface of which is arranged perpendicular to the optical axis of the objective lens 4. Further, 8 and 9 are detectors that output the size of the signal component envelope of the optical disc as a DC value, and 10 is a difference calculation circuit. Reference numeral 11 denotes a focus coil wound around a holder 12 that integrally holds the objective lens 4, the parallel plate 5, and the cylindrical lens 6.

[0026]

Next, the manner in which the light emitted from the light source is applied to the pits of the optical disk and the reflected light modulated by the pits is received by the photodetector will be described.

First, the light emitted from the light source 1 passes through the illumination lens 2 and enters the transparent substrate 3a of the optical disc at a predetermined angle θ ₀ with respect to the disc surface normal 13. Here, since the transparent substrate 3a has a predetermined thickness and a predetermined refractive index, the light incident on the transparent substrate 3a is refracted, and then the pits on the information recording surface 3 are irradiated. At this time, the position of the illumination lens 2 is adjusted in advance so that the light irradiation area is an area for irradiating a plurality of (three or more) tracks on the information recording surface.

[0028]

The reflected light modulated by the pits passes through the transparent substrate 3a again and then enters the objective lens 4. Here, the light incident on the objective lens 4 passes through a parallel plate 5 made of transparent glass or the like and a cylindrical lens 6, and then is irradiated on the light receiving surface of the photodetector 7. Here, the optical axis of the objective lens 4 is with respect to the disk surface normal 13 with respect to the illumination lens 2
Is on the side opposite to the optical axis of and is set to an angle substantially equal to θ ₀ .

[0029]

The photodetector 7 has a first light-receiving surface 7a provided on the light-receiving surface including the optical axis and a track formed on both sides of the first light-receiving surface in which pits of the optical disk are arranged. A pair of second light-receiving surfaces 7 lined in a direction that crosses the track substantially vertically at intervals substantially equal to the pitch of
b, 7c, and when the objective lens 4 is in the in-focus position, the non-diffracted light, so-called zero-order light, of the reflected light from the disk is the first light receiving surface 7a and the second light receiving surface of the photodetector.
The light receiving surfaces 7b and 7c are set to enter.

Although the second light receiving surface is provided as a pair in FIG. 1, it may be provided as a plurality of pairs arranged at equal intervals.

[0031]

Here, when the optical disk reproducing apparatus reads the reflected light from the scanning pit of the rotating optical disk,
When the objective lens 4 is in focus, the position of the objective lens 4 moved in the optical axis direction by the focus coil 11 is at a position where an image is correctly formed on the light receiving surface of the photodetector 7, that is, an image forming position. In this case, the reflected light from the pits passes through the transparent substrate 3a that is inclined by θ _{0 with} respect to the disk surface normal 13, so that it enters the objective lens 4 with the aberration caused by the transparent substrate 3a. . Considering up to the third order, these aberrations are astigmatism and coma. For this reason, a predetermined amount of coma is generated by the parallel plate 5 provided after the pupil plane of the objective lens 4, and the translucent substrate 3a is inclined.
The coma aberration due to is canceled out. Further, a cylindrical lens 6 provided on the optical axis of the objective lens 4 is continued.
The astigmatism due to the inclined translucent substrate 3a,
The astigmatism due to the parallel plate 5 is also canceled.

[0032]

As described above, the light emitted from the light source irradiates the pits of the optical disc, the reflected light modulated by the pits enters the photodetector, and the pits of the optical disc are imaged on the photodetector without aberration. . In this embodiment, the parallel plate is arranged after the objective lens, but the coma aberration can be canceled by disposing the wedge plate instead of the parallel plate. Also, instead of a parallel plate and a cylindrical lens, use a cylindrical lens tilted at a predetermined angle, use a wedge that considers all aberration corrections in the design, or use a holographic optical element to correct aberrations. May be. A similar aberration correction function may be arranged on the side of the illumination lens to correct the aberration.

[0033]

Next, how the focus position of the imaging lens is controlled by using the output of the photodetector 7 will be described. FIG. 2 shows how the light emitted from the light source in FIG. 1 illuminates the pits of the optical disc, and the photodetector 7 receives the reflected light modulated by the pits. In the figure, T represents the center line of the focus control target track in which pits for reading information are arranged, and the first light receiving surface 7a is arranged on the center line by a track direction control mechanism (not shown).

[0034]

Further, the second light receiving surfaces 7b and 7c are on the same plane as the first light receiving surface 7a, and on the line including the first light receiving surface 7a and orthogonal to T, and from the control target track having T. They are arranged up to the center of the second track, that is, on both sides of the first light receiving surface 7a and at positions spaced by the pitch P.

Therefore, on the second light receiving surfaces 7b and 7c,
An image in which the focus is shifted to the front and the rear as compared with the light receiving surface 7a is observed. Further, since the second light receiving surfaces 7b and 7c are separated from each other by the same distance P from the first light receiving surface 7a, their defocus amounts are substantially the same, and the modulation degree of each signal is in a good state. On the other hand, it is about the same.

[0036]

Therefore, when the first light receiving surface 7a is located on the focal point of the objective lens 4, the reflected light from the pits on the first light receiving surface 7a has the maximum modulation degree as shown in FIG. 2 (b).

In FIG. 2, the pits forming the track having the maximum modulation degree are represented by black portions. At this time, since the detectors 8 and 9 for detecting the second light receiving surfaces 7b and 7c respectively output the same level, the difference calculator 10 is set to 0.
Is output.

[0038]

On the other hand, if the focal position is too far,
As shown in FIG. 2A, the second light receiving surface 7b is better than FIG. 2B, and the modulation degree of the second light receiving surface 7c is poor.
Therefore, the difference calculator 10 outputs a positive value according to this defocus amount.

On the contrary, when the focal position is too close,
As shown in (c), the difference calculator 10 outputs a negative value.

Therefore, the focus coil 12 can be driven based on this output to control the focus of the objective lens 4. By using a track-direction control mechanism (not shown here), the first light-receiving surface can stably follow and reproduce the signal of one track.

[0041]

Further, by using this method, the first light receiving surface and the second light receiving surface are
If the distance of the light receiving surface of is set to, for example, the pitch of the adjacent tracks, the information of the adjacent tracks can be read at the same time. Therefore, if the signals of the adjacent tracks included in the read signals are subtracted, For example, the reproduction RF signal can be separated even when the pits are formed on the first light receiving surface in a state where the tracks are narrowed and the pits cannot be completely separated as a single image like a high density optical disc.

[0042]

Further, in the present invention, what is driven by the focus position control mechanism is only required to include the objective lens, and even if the entire pickup is driven, the objective lens, the parallel plate and the cylindrical lens serve as the focus coil. It is possible to drive only the imaging system integrally configured, or to drive the objective lens and the illumination lens.

[0043]

Since the size of the illumination lens and the intensity distribution there can determine the shape of the illumination independently of the image forming system provided with the objective lens, depending on the illumination system used, for example, as shown in FIG. An illumination lens 15 smaller than the imaging objective lens 14 is used to form a partially coherent imaging system, or an illumination lens 17 larger than the imaging objective lens 16 is used by using, for example, a plurality of illumination lenses 18 as shown in FIG. By appropriately forming the spatial frequency transfer characteristic of the optical system by forming and using it, the same effect as the embodiment of the present invention can be obtained.

In the configuration of FIG. 4, the pupil of the illumination system is larger than the pupil of the imaging system, so that the angle θ ₁ formed by the illumination system optical axis 19 with respect to the disk surface normal 13 forms an image. It is arranged so as to be larger than an angle θ ₂ formed with the system optical axis 20.

[0045]

In the embodiment of the present invention, the light source is the light emitting diode which is an incoherent light source. However, if the illumination optical system is provided with a means such as defocusing so as not to form a diffraction limited spot, the conventional light source is used. The same laser light source can be used, and the same effect can be obtained.

[0046]

Further, in the present embodiment, the second light receiving surface is composed of a pair of light receiving elements, but this is so constructed that the pits are surely placed on any one of the pair of elements by further expanding the elements. It is also possible to configure so as to improve the accuracy of focus position control. Further, the elements may have various shapes as long as the degree of signal modulation can be detected.

[0047]

[0030]

[0048]

Since the present invention is configured as described above, the illumination light of the light source for irradiating the optical disk enters the optical disk without passing through the imaging lens, and the reflected light from the optical disk is used by the imaging lens. Since the light is condensed, it is not necessary to provide a beam splitter in the optical path when optically reading the pits of the optical disk, and the light source can be effectively used without being affected by the decrease in the light amount of the light source. Therefore, a good signal can be demodulated without increasing the light intensity of the light source, so that the high-density optical recording medium can be easily read and the life of the light source can be extended, so that long-time recording can be performed. Withstand regeneration.

[0049]

Further, when the pits of an optical disc having a transparent substrate having a predetermined thickness provided on the pits are optically read through the transparent substrate, the aberration generated by the transparent substrate is corrected. Since the pits are imaged after being corrected by the aberration correction means, an accurate pit image can be obtained and a good signal can be demodulated, and therefore, the high density optical recording medium can be easily read. .

[0050]

Further, each light receiving surface of the photodetector can simultaneously read the information of the adjacent tracks, and by comparing the outputs of the respective light receiving surfaces, the photodetector forms a medium on which the imaging lens forms an image. It is possible to control the position of the imaging lens so that the imaging lens is arranged on the surface including the imaging position, and it is possible to separate the RF signal from the output of each light receiving surface.

[Brief description of drawings]

FIG. 1 shows a configuration example of a pickup of an optical disc reproducing apparatus according to an embodiment of the present invention.

2 shows how the photodetector 7 of FIG. 1 according to the present invention receives reflected light modulated by pits.

FIG. 3 shows a configuration example of a pickup of an optical disc reproducing apparatus in another embodiment of the present invention.

FIG. 4 shows an example of the configuration of a pickup of an optical disc reproducing apparatus according to another embodiment of the present invention.

FIG. 5 is a schematic sectional view showing an example of a configuration of a conventional CD player pickup.

[Explanation of symbols]

 1 ... Illumination light source 2 ... Illumination lens 3 ... Information recording surface 3a ... Translucent substrate 4 ... Objective lens 4 5 ... Parallel Flat plate 6 ... Cylindrical lens 7 ... Photodetector 7a ... First light receiving surface 7b ... Second light receiving surface 7c ... Second light receiving surface 8.・ ・ ・ Detector 9 ・ ・ ・ ・ ・ Detector 10 ・ ・ ・ Difference calculation circuit 11 ・ ・ ・ ・ Focus coil 12 ・ ・ ・ ・ Holder 13 ・ ・ ・ ・ ・ ・ Disk surface normal 14 ・ ・ ・Image objective lens 15 ... Illumination lens 16 ... Imaging objective lens 17 ... Illumination lens 18 ... Illumination lens 19 ... Illumination system optical axis 20 ... Imaging system optical axis

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[Procedure amendment]

[Submission date] October 31, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Detailed description of the invention

[Correction method] Change

[Correction contents]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording information reproducing apparatus for reproducing an optical recording medium such as an optical disk on which information such as images and music is recorded, and particularly, an incoherent light source such as a light emitting diode is used. The present invention relates to an optical pickup device which reads out information by forming an image of a recording medium on a photodetector.

[0002]

2. Description of the Related Art Conventionally, there is a compact disc (hereinafter referred to as a CD) as an optical disc, and a CD player is known as a reproducing device thereof. The CD has a plurality of tracks in which pits carrying information bits are spirally arranged on one side of the disc from the inner circumference to the outer circumference of the disc. In a CD player, the optical disc is rotated at a constant linear velocity (CLV) so that the light beam of a pickup for reading the pit scans the pit at a relatively constant velocity in the disc rotation direction, and the beam is irradiated onto the pit. To read the information optically.

FIG. 5 is a schematic sectional view showing an example of the structure of a conventional CD player pickup. In the figure, 101 is a light source, for example, a red semiconductor laser having a predetermined single wavelength. About half of the laser light emitted from the light source 101 is guided to the objective lens 103 by the half mirror 102a included in the beam splitter 102, and after entering the transparent substrate 104 of the CD and passing therethrough, the pit 105 of the CD.
Form a light spot on top. In addition, the transparent substrate 104 is
When the objective lens 103 is formed of polycarbonate or the like having a predetermined thickness and the thickness of the transparent substrate 104 is taken into consideration in advance, and the transparent substrate 104 is arranged perpendicular to the optical axis of the objective lens 103, It is set so that the smallest spot is formed on the pit 105. Further, the objective lens 103 always irradiates a spot of a predetermined size by following the pit to be scanned even if the disc surface is displaced in the optical axis direction by the warp of the disc or the like while the CD is rotating by the focus control means (not shown). Controlled as.

The light reflected by the spot irradiated on the pit 105 is collected again by the objective lens 103,
After the amount of light is halved by the half mirror 102a of the beam splitter 102, the RF signal is detected by the photodetector 106. The photodetector 106 is the objective lens 103.
Is arranged at a position slightly deviated from the position where the pit is imaged, for example, at a position where the reflected light forms a circle of least confusion, and focus control is performed by the astigmatism method.

Since the laser light emitted from the light source 101 passes through the half mirror 102a twice and the light amount is halved each time, it is necessary to secure a sufficient light amount for the photodetector 106 to receive the light. Laser light is used at high output. The conventional pickup device of the CD player is constructed as described above and obtains the RF signal for reading the pits of the CD and reproducing the information.

In recent years, with the diversification of information and the increase in density, there has been a demand for optical disks recorded at high density. Since the pits of this high-density optical disc are smaller than those of the conventional one and are arranged at a high density, it is necessary to reduce the beam spot of the laser light when reading each pit. Therefore, a laser light source having a shorter wavelength than that used in the conventional CD player is required.

However, when a short wavelength blue semiconductor laser is used for the above-mentioned conventional pickup, there arise problems that the operating life is extremely short, or the device cannot operate at high temperature. In addition, S that halves the wavelength using optical nonlinearity
When the HG type blue laser is used, there is a problem that the structure of the light source is complicated and it is difficult to make the size smaller than that of the semiconductor laser, and the high density disc cannot be easily read.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an optical recording information reproducing apparatus capable of easily reading an optical disk recorded at high density with a simple structure. To do.

[0009]

According to the first aspect of the present invention,
An optical recording medium reproducing device for optically reading and reproducing information recorded on a medium, comprising a light source for irradiating the medium with illumination light, and an imaging lens for forming an image on the medium by reflected light from the medium. Arranged on a plane including the condensing means, the focus position control means for controlling the focus position of the image forming lens to control the image forming position of the medium, and the image forming position of the medium formed by the image forming lens. And a detection means for detecting the light condensed by the condensing means, the illumination light enters the medium without passing through the imaging lens, and the optical axis of the illumination light from the light source to the medium surface, The optical recording medium reproducing apparatus is characterized in that the angle formed by the medium surface normal is equal to or larger than the angle formed by the optical axis of the imaging lens and the medium surface normal.

According to a second aspect of the invention, in the optical recording medium reproducing apparatus according to the first aspect, the condensing means has an aberration correcting means, and condenses the reflected light accompanied by the aberration caused by the medium. In this case, the optical recording medium reproducing apparatus is characterized in that the aberration is corrected by the aberration correcting means and the medium is imaged.

According to a third aspect of the present invention, in the optical recording medium reproducing apparatus according to the first or second aspect, the detecting means includes a first photodetector arranged at an image forming position of the medium, and a first photodetector.
Of the second photodetector, which is arranged on the same plane as the light receiving surface including the light receiving surface of the first photodetector, and which comprises a pair or a plurality of pairs of light receiving surfaces spaced from the light receiving surface of the first photodetector by a predetermined distance. The optical recording medium is characterized in that the focus position control means controls the imaging position of the medium to be located on the light receiving surface of the first photodetector by the light reception output of the second photodetector. It consists of a playback device.

[0012]

The present invention is constructed as described above.
According to the invention described above, the illumination light of the light source for irradiating the optical disc enters the optical disc without passing through the imaging lens, and the reflected light from the optical disc is condensed using the imaging lens. When optically reading the pits of the optical disk, it is not necessary to provide a beam splitter in the optical path, and the light source can be effectively used without being affected by the decrease in the light amount of the light source. Therefore, a good signal can be demodulated without increasing the light intensity of the light source, so that the high-density optical recording medium can be easily read and the life of the light source can be extended, so that long-time recording can be performed. Withstand regeneration.

According to the second aspect of the invention, when the pits of the optical disk having the transparent substrate of a predetermined thickness provided on the pits are optically read through the transparent substrate, The aberration generated by the translucent substrate is corrected by the aberration correcting means so that the pits are imaged, so that an accurate pit image can be obtained and a good signal can be demodulated. The recording medium can be easily read.

According to the third aspect of the present invention, each light receiving surface of the photodetector can simultaneously read the information of the adjacent tracks, and by comparing the outputs of the respective light receiving surfaces,
The position of the imaging lens can be controlled so that the photodetector is arranged on the surface including the imaging position of the medium on which the imaging lens forms an image, and the RF signal is separated from the output of each light receiving surface. it can.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows an example of the configuration of a pickup of an optical disk reproducing apparatus according to an embodiment of the present invention. In the figure, reference numeral 1 denotes an illumination light source, which is an incoherent light source having a predetermined light emitting area, and is, for example, a light emitting diode which emits blue light. Reference numeral 2 is an illumination lens. Further, 3 is an information recording surface of an optical disk in which pits are carried at high density, and 3a is a transparent substrate provided on the upper surface of the information recording surface 3 and having a predetermined thickness. Further, 4 is an objective lens, and 5 is a parallel plate which is arranged at a predetermined angle with respect to the optical axis of the objective lens 4. Reference numeral 6 is a cylindrical lens provided coaxially with the objective lens 4. Reference numeral 7 is a photodetector, the light receiving surface of which is arranged perpendicular to the optical axis of the objective lens 4. Further, 8 and 9 are detectors that output the size of the signal component envelope of the optical disc as a DC value, and 10 is a difference calculation circuit. Reference numeral 11 denotes a focus coil wound around a holder 12 that integrally holds the objective lens 4, the parallel plate 5, and the cylindrical lens 6.

Next, the manner in which the light emitted from the light source is applied to the pits of the optical disk and the reflected light modulated by the pits is received by the photodetector will be described. First, the light emitted from the light source 1 passes through the illumination lens 2 and enters the transparent substrate 3a of the optical disc at a predetermined angle θ ₀ with respect to the disc surface normal 13. Here, since the transparent substrate 3a has a predetermined thickness and a predetermined refractive index, the light incident on the transparent substrate 3a is refracted, and then the pits on the information recording surface 3 are irradiated.
At this time, the position of the illumination lens 2 is adjusted in advance so that the light irradiation area is an area for irradiating a plurality of (three or more) tracks on the information recording surface.

The reflected light modulated by the pits passes through the transparent substrate 3a again and then enters the objective lens 4. Here, the light incident on the objective lens 4 passes through a parallel plate 5 made of transparent glass or the like and a cylindrical lens 6, and then is irradiated on the light receiving surface of the photodetector 7. Here, the optical axis of the objective lens 4 is with respect to the disk surface normal 13 with respect to the illumination lens 2
Is on the side opposite to the optical axis of and is set to an angle substantially equal to θ ₀ .

The photodetector 7 has a first light-receiving surface 7a provided on the light-receiving surface including the optical axis and a track formed on both sides of the first light-receiving surface in which pits of the optical disk are arranged. A pair of second light-receiving surfaces 7 lined in a direction that crosses the track substantially vertically at intervals substantially equal to the pitch of
b, 7c, and when the objective lens 4 is in the in-focus position, the non-diffracted light, so-called zero-order light, of the reflected light from the disk is the first light receiving surface 7a and the second light receiving surface of the photodetector.
The light receiving surfaces 7b and 7c are set to enter.
Although the second light receiving surface is provided as a pair in FIG. 1, it may be provided as a plurality of pairs arranged at equal intervals.

Here, when the optical disk reproducing apparatus reads the reflected light from the scanning pit of the rotating optical disk,
When the objective lens 4 is in focus, the position of the objective lens 4 moved in the optical axis direction by the focus coil 11 is at a position where an image is correctly formed on the light receiving surface of the photodetector 7, that is, an image forming position. In this case, since the reflected light from the pits passes through the transparent substrate 3a inclined by θ _{0 with} respect to the disk surface normal 13, it is incident on the objective lens 4 in a state of having aberration due to the transparent substrate 3a. . Considering up to the third order, these aberrations are astigmatism and coma. For this reason, a predetermined amount of coma is generated by the parallel plate 5 provided after the pupil plane of the objective lens 4, and the translucent substrate 3a is inclined.
The coma aberration due to is canceled out. Further, a cylindrical lens 6 provided on the optical axis of the objective lens 4 is continued.
The astigmatism due to the inclined translucent substrate 3a,
The astigmatism due to the parallel plate 5 is also canceled.

As described above, the light emitted from the light source irradiates the pits of the optical disc, the reflected light modulated by the pits enters the photodetector, and the pits of the optical disc are imaged on the photodetector without aberration. . In this embodiment, the parallel plate is arranged after the objective lens, but the coma aberration can be canceled by disposing the wedge plate instead of the parallel plate. Also, instead of a parallel plate and a cylindrical lens, use a cylindrical lens tilted at a predetermined angle, use a wedge that considers all aberration corrections in the design, or use a holographic optical element to correct aberrations. May be. A similar aberration correction function may be arranged on the side of the illumination lens to correct the aberration.

Next, how the focus position of the imaging lens is controlled by using the output of the photodetector 7 will be described. FIG. 2 shows how the light emitted from the light source in FIG. 1 illuminates the pits of the optical disc, and the photodetector 7 receives the reflected light modulated by the pits. In the figure, T represents the center line of the focus control target track in which pits for reading information are arranged, and the first light receiving surface 7a is arranged on the center line by a track direction control mechanism (not shown).

Further, the second light receiving surfaces 7b and 7c are on the same plane as the first light receiving surface 7a, and on the line including the first light receiving surface 7a and orthogonal to T, and from the control target track having T. They are arranged up to the center of the second track, that is, on both sides of the first light receiving surface 7a and at positions spaced by the pitch P. Therefore, on the second light receiving surfaces 7b and 7c,
An image in which the focus is shifted to the front and the rear as compared with the light receiving surface 7a is observed. Further, since the second light receiving surfaces 7b and 7c are separated from each other by the same distance P from the first light receiving surface 7a, their defocus amounts are substantially the same, and the modulation degree of each signal is in a good state. On the other hand, it is about the same.

Therefore, when the first light receiving surface 7a is located on the focal point of the objective lens 4, the reflected light from the pits on the first light receiving surface 7a has the maximum modulation degree as shown in FIG. 2 (b).
In FIG. 2, the pits forming the track having the maximum modulation degree are represented by blackened portions. At this time, the detectors 8 and 9 for detecting the second light-receiving surfaces 7b and 7c respectively output the same level, so that the difference calculator 10 outputs 0.

On the other hand, if the focal position is too far,
As shown in FIG. 2A, the second light receiving surface 7b is better than FIG. 2B, and the modulation degree of the second light receiving surface 7c is poor.
Therefore, the difference calculator 10 outputs a positive value according to this defocus amount. On the contrary, when the focal position is too close, the difference calculator 10 outputs a negative value as shown in FIG.
Therefore, the focus coil 12 can be driven based on this output to control the focus of the objective lens 4. By using a track-direction control mechanism (not shown here), the first light-receiving surface can stably follow and reproduce the signal of one track.

Further, by using this method, the first light receiving surface and the second light receiving surface are
If the distance of the light receiving surface of is set to, for example, the pitch of the adjacent tracks, the information of the adjacent tracks can be read at the same time. Therefore, if the signals of the adjacent tracks included in the read signals are subtracted, For example, the reproduction RF signal can be separated even when the pits are formed on the first light receiving surface in a state where the tracks are narrowed and the pits cannot be completely separated as a single image like a high density optical disc.

Further, in the present invention, what is driven by the focus position control mechanism is only required to include the objective lens, and even if the entire pickup is driven, the objective lens, the parallel plate and the cylindrical lens serve as the focus coil. It is possible to drive only the imaging system integrally configured, or to drive the objective lens and the illumination lens.

Since the size of the illumination lens and the intensity distribution there can determine the shape of the illumination independently of the image forming system provided with the objective lens, depending on the illumination system used, for example, as shown in FIG. An illumination lens 15 smaller than the imaging objective lens 14 is used to form a partially coherent imaging system, or an illumination lens 17 larger than the imaging objective lens 16 is used by using, for example, a plurality of illumination lenses 18 as shown in FIG. By appropriately forming the spatial frequency transfer characteristic of the optical system by forming and using it, the same effect as the embodiment of the present invention can be obtained. In the configuration of FIG. 4, since the pupil of the illumination system is larger than the pupil of the imaging system, the angle θ ₁ formed by the illumination system optical axis 19 with respect to the disk surface normal 13 is the imaging system optical axis. It is arranged to be larger than the angle θ ₂ formed by 20.

In the embodiment of the present invention, the light source is the light emitting diode which is an incoherent light source. However, if the illumination optical system is provided with a means such as defocusing so as not to form a diffraction limited spot, the conventional light source is used. The same laser light source can be used, and the same effect can be obtained.

Further, in the present embodiment, the second light receiving surface is composed of a pair of light receiving elements, but this is so constructed that the pits are surely placed on any one of the pair of elements by further expanding the elements. It is also possible to configure so as to improve the accuracy of focus position control. Further, the elements may have various shapes as long as the degree of signal modulation can be detected.

[0030]

Since the present invention is configured as described above, the illumination light of the light source for irradiating the optical disk enters the optical disk without passing through the imaging lens, and the reflected light from the optical disk is used by the imaging lens. Since the light is condensed, it is not necessary to provide a beam splitter in the optical path when optically reading the pits of the optical disk, and the light source can be effectively used without being affected by the decrease in the light amount of the light source. Therefore, a good signal can be demodulated without increasing the light intensity of the light source, so that the high-density optical recording medium can be easily read and the life of the light source can be extended, so that long-time recording can be performed. Withstand regeneration.

Further, when the pits of an optical disc having a transparent substrate having a predetermined thickness provided on the pits are optically read through the transparent substrate, the aberration generated by the transparent substrate is corrected. Since the pits are imaged after being corrected by the aberration correction means, an accurate pit image can be obtained and a good signal can be demodulated, and therefore, the high density optical recording medium can be easily read. .

Further, each light receiving surface of the photodetector can simultaneously read the information of the adjacent tracks, and by comparing the outputs of the respective light receiving surfaces, the photodetector forms a medium on which the imaging lens forms an image. It is possible to control the position of the imaging lens so that the imaging lens is arranged on the surface including the imaging position, and it is possible to separate the RF signal from the output of each light receiving surface.

Claims (3)

[Claims] 1. An optical recording medium reproducing apparatus for optically reading and reproducing information recorded on a medium, the light source irradiating illumination light onto the medium, and the medium by reflected light from the medium. A condensing means having an image forming lens for forming an image; a focus position control means for controlling a focus position of the image forming lens to control an image forming position of the medium; A detection unit that is arranged on a surface including the image formation position of the medium and detects the light condensed by the light condensing unit, and the illumination light is incident on the medium without passing through the image formation lens. The angle formed by the optical axis of the illumination light from the light source to the surface of the medium and the medium surface normal is opposite to the angle formed by the optical axis of the imaging lens and the medium surface normal. Optical recording medium characterized by being equal or larger Body regeneration device. 2. The optical recording medium reproducing apparatus according to claim 1, wherein the condensing unit has an aberration correcting unit, and when condensing the reflected light accompanied by the aberration caused by the medium, An optical recording medium reproducing device, characterized in that the aberration is corrected by an aberration correcting means to form an image on the medium. 3. The optical recording medium reproducing apparatus according to claim 1, wherein the detecting unit includes a first photodetector arranged at an image forming position of the medium, and the first photodetector. Second light receiving surface, which is arranged on the same plane as the light receiving surface including the light receiving surface and is separated from the light receiving surface of the first photodetector by a predetermined distance.
The photodetector, and the focus position control means controls the image formation position of the medium to be located on the light receiving surface of the first photodetector by the light reception output of the second photodetector. An optical recording medium reproducing device characterized by the above.