JP2003099978A - Optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dynamically detect the thickness of an optical disk in an optical disk device and correct a spherical aberration with a simple constitution dynamically and accurately. SOLUTION: The device is an optical disk device where the optical disk is irradiated with a laser beam to record information to a data-recording surface provided on the inner side of the optical disk and the recorded information is read out by detecting the reflected light from the data-bearing surface, and it is provided with an objective lens for converging the laser beam emitted from a light source on the date-bearing surface of the optical disk, a beam splitter that splits a reflected light on the surface of the optical disk which has the same optical axis that a reflecting light for reading and writing the information to be recorded to the optical disk has and a detecting means which detects the thickness of the optical disk based on the reflecting light on the surface of the optical disk. The detecting means detects the thickness of the optical disk by differentially detecting the reflected light from the surface of the optical disk using a multidivision photoreceptor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc device using an optical pickup that optically records and reproduces information on an optical disc.

[0002]

2. Description of the Related Art Optical disc technology as a high-density and large-capacity recording medium has been put into practical use while expanding its applications such as compact discs and digital video discs. As described above, the optical disc device for highly reliable recording / reproducing of information via light is required to have high performance in optical system technology.

An optical pickup, which is a component of an optical disk device, is required to have a small spot size on the optical disk in order to improve the recording / reproducing performance of the optical disk. The beam spot ω is represented by ω = k · (λ / NA) and is determined by the wavelength (λ) of the semiconductor laser and the numerical aperture NA (Numerical Aperture) of the objective lens.

However, if the wavelength is shortened and the aperture ratio of the objective lens is increased, the tolerance for optical disc thickness error is reduced. Here, the deviation between the thickness of each optical disc (the distance between the surface of the optical disc and the signal surface) and the standard value of the thickness of the optical disc is referred to as an optical disc thickness error. When the thickness of the optical disc changes, spherical aberration occurs on the pits of the optical disc, and the beam spot cannot be sufficiently narrowed, which affects the recording / reproducing performance of the optical disc device.

It is known that the allowable value for the optical disc thickness error is proportional to λ / (NA) ** 4 (where (NA) ** 4 represents the fourth power of NA), and the wavelength ( As λ) decreases and the numerical aperture (NA) of the objective lens increases, the tolerance for optical disc thickness error decreases.

In the optical disk devices shipped in the past, the optical disk thickness error is within the allowable range of the optical disk thickness error because the wavelength of the semiconductor laser is long and the aperture ratio of the objective lens is small. Therefore, spherical aberration that greatly affects the recording / reproducing performance does not occur, and no particular problem has occurred.

A conventional optical pickup optical system will be described below with reference to the drawings.

FIG. 7 is a schematic diagram of a conventional optical pickup.

In the figure, reference numeral 1 is a semiconductor laser, 2 is an objective lens, 3 is a surface of an optical disk, 4 is a signal surface of the optical disk, 5 is a beam splitter, and 6 is a light receiving element.

In the conventional optical pickup shown in FIG. 7, the light emitted from the semiconductor laser 1 passes through the objective lens 2, the surface 3 of the optical disc, and is converged on the signal surface 4 of the optical disc.

The reflected light modulated by the pits on the signal surface 4 of the optical disk passes through the objective lens 2, is reflected by the beam splitter 5, and converges on the light receiving element 6. The light receiving element 6 is multi-divided and outputs a signal according to the amount of received light. From this output signal, focus error signal,
A tracking error signal is generated, and the error signal is used to control an objective lens to constantly generate a laser spot on an optical disc, and recording / reproducing is performed by an optical disc drive device.

[0012]

However, since the next-generation optical disc apparatus realizes higher recording density and larger capacity, the track density of the optical disc can be increased and the shortest pit length can be shortened. It is necessary to make the spot size of the optical pickup smaller than that of the current optical disk device. Therefore, in the next-generation optical disk device, it is necessary to shorten the wavelength of the semiconductor laser and increase the aperture ratio of the objective lens.

As the wavelength of the semiconductor laser becomes shorter and the numerical aperture of the objective lens becomes larger, spherical aberration occurs on the pits of the optical disc due to the influence of the optical disc thickness error, which has not been a problem in the past. Due to this spherical aberration, the beam spot cannot be sufficiently narrowed down, so that the desired power cannot be obtained during recording on the optical disc, sufficient chemical change of the material is not completed and the writing characteristics deteriorate, and the resolution of the optical disc device signal deteriorates during reproduction. Then, there arises a problem that the reproduction performance is deteriorated.

Further, even in an optical disc having a plurality of recording layers, the thickness of the layer through which light is transmitted is different from that of a specific recording layer in another recording layer, so that spherical aberration occurs in the pits and a beam is generated. The spot cannot be sufficiently narrowed down, which causes a problem that the recording / reproducing performance of the optical disk device deteriorates.

In order to correct spherical aberration, Japanese Patent Laid-Open No. 11-1
Japanese Patent No. 95229 discloses that a light source for detecting the thickness of an optical disc is provided separately from a recording / reproducing light source, and a distance between a surface and a recording layer is indirectly obtained from a focus error signal.
That is, it discloses a technique of providing an actuator that moves the collimator lens in order to detect the thickness of the optical disc and reduce the spherical aberration.

However, since a new light source or actuator is separately provided, the number of parts is increased, and a space for placing the light source is required, resulting in a problem that the size of the device becomes large. In addition, if the optical disc thickness is detected via the focus error signal, there is also a problem that the moving distance fluctuates due to variations in the moving speed of the actuator, and errors easily occur.

An object of the present invention is to solve these problems, to provide an optical disk device having a mechanism for detecting the optical disk thickness, and further to have a function of correcting spherical aberration of a laser spot formed on a pit of an optical disk. It is to provide an optical disk device having the same.

[0018]

The optical disk device of the present invention is recorded by irradiating the optical disk with a laser beam to record information on a recording surface inside the optical disk and detecting reflected light from the recording surface. In an optical disc device for reading information, an objective lens for converging a laser beam emitted from a light source onto a recording surface of the optical disc, and a reflected light for reading and writing information to be recorded on the optical disc, which is reflected light from the optical disc surface. It is characterized in that it is provided with a beam splitter for separating those having the same optical axis, and a detection means for detecting the optical disc thickness based on the reflected light from the optical disc surface.

In the optical disk device of the present invention, the detecting means has a multi-divided light receiving element for receiving the reflected light, and the multi-divided light receiving element differentially detects the reflected light from the surface of the optical disk. It is characterized by detecting the thickness.

In the optical disk device of the present invention, the detecting means includes a multi-divided light receiving element that receives the reflected light, and a light-shielding means that blocks a part of the reflected light from the disk surface in front of the multi-divided light receiving element. The light shielding means is placed at a position where the reflected light converges when the thickness of the optical disc is standard, and the convergence position of the reflected light moves to the front and rear of the light shielding means due to the variation of the optical disc thickness. The thickness of the optical disk is detected by performing differential detection by the multi-divided light receiving element by utilizing the change in the position and amount of light received by the divided light receiving element.

In the optical disk device of the present invention, the detecting means includes a multi-divided light receiving element for receiving the reflected light, and a light-shielding means for blocking a part of the reflected light from the disk surface in front of the multi-divided light receiving element. The multi-segment light receiving element is arranged at a position that coincides with the converging position of the reflected light when the optical disc thickness is a standard value, and the converging position of the reflected light is multi-segment light receiving due to variation of the optical disc thickness. The thickness of the optical disc is detected by performing differential detection by the multi-divided light receiving element by utilizing the fact that the position and amount of light received by the multi-divided light receiving element changes as the element moves back and forth. .

In the optical disk device of the present invention, the light shielding means is a plate-like member which faces the reflected light and intercepts half of the light when the convergent position of the reflected light is at a position before and after the light shielding means. Characterize.

The optical disk device of the present invention is characterized by further comprising spherical aberration correcting means for correcting spherical aberration on the recording surface of the optical disk.

The spherical aberration correcting means of the optical disk device of the present invention is located between the objective lens and the beam splitter.

[0025]

DETAILED DESCRIPTION OF THE INVENTION A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a first embodiment of a disc thickness detecting mechanism of the present invention, and FIG. 2 is a schematic diagram showing reflected light and a beam spot shape at a light receiving element when the optical disc thickness is a standard thickness, FIG. 3 is a schematic diagram showing the reflected light when the optical disc thickness is thicker than the standard thickness and the beam spot shape at the light receiving element, and FIG. 4 shows the reflected light when the optical disc thickness is thinner than the standard thickness. FIG. 3 is a schematic diagram showing a beam spot shape on a light receiving element.

In the figure, reference numeral 1 is a semiconductor laser, 2 is an objective lens, 3 is a surface of an optical disk, 4 is a signal surface of the optical disk, 5 is a beam splitter for main signal, 6 is a light receiving element for main signal, and 7 is An optical disc thickness detecting beam splitter, 8 is a light shielding plate, and an optical disc thickness detecting light receiving element 9.

The optical pickup of the present invention shown in FIG. 1 is constructed by adding an optical disc thickness detecting section 11 to the present general optical pickup device.

The optical disc thickness detecting mechanism of the second embodiment of the present invention shown in FIG. 5 includes a general optical pickup optical system,
And an optical disc thickness detecting section 11 for detecting the optical disc thickness. A general optical pickup optical system includes a semiconductor laser 1 that emits a laser beam, an objective lens 2 that focuses light on a signal surface 4 of an optical disk, a surface 3 of an optical disk, a signal surface 4 of an optical disk that records a signal, and a main signal. A main signal beam splitter 5 that separates and reflects the light and guides it to the light receiving element 6, and a main signal light receiving element 6 that receives the main signal and generates a read signal, a focus error signal, and a tracking error signal.

In the optical disk device of the present invention, the light emitted from the semiconductor laser 1 passes through the objective lens 2,
The light is surrounded by c1 and c2, passes through the surface 3 of the optical disc, and is converged on the signal surface 4 of the optical disc. The converged light is modulated and reflected by the pits on the signal surface 4 of the optical disc. After that, the light returns through the same path as before the reflection, passes through the objective lens 2, is reflected by the beam splitter 5, and converges on the light receiving element 6. The light receiving element is multi-divided and outputs a signal according to the amount of received light. A focus error signal and a tracking error signal are generated from this output signal, the error signal is used to control the objective lens to constantly generate a laser spot on the optical disc signal surface 4, and recording / reproducing of the optical disc drive device is performed. ing.

The optical disc thickness detecting section 11 according to the present invention is
It includes a shielding plate 8 for blocking light, two optical disc thickness detecting light receiving elements 9, and a differential amplifier (not shown) that outputs a proportional value to the difference between the outputs of the optical disc thickness detecting light receiving elements 9. The light emitted from the semiconductor laser 1 passes through the objective lens 2 and converges on the optical disc signal surface 4, and the light from the objective lens 2 (the light surrounded by c1 and c2).
However, the reflected light when entering the optical disk surface 3 is used.

The reflected light from the optical disk surface 3 shown in FIG. 1 becomes light surrounded by c3 and c4, passes through the objective lens 2, is separated by the beam splitter 7, passes through the light shielding plate 8, and is on the light receiving element 9. Is irradiated. The light shielding plate 8 is a flat plate that blocks light and is arranged perpendicular to the optical axis 8a.

FIG. 2 shows that the thickness of the optical disk 31 is 3 mm.
It is a figure which shows the state of light in case 2 is a standard. FIG. 2A is an enlarged / detailed view of the portion a in FIG. 1, and FIG. 2B is an enlarged / detailed view of b in FIG. The reflected light from the optical disk surface 3 enters the objective lens 2, is reflected by the beam splitter 7, converges at the position of d, becomes divergent light, and is then irradiated to the light receiving element 9.

The light shielding plate 8 of the optical disc thickness detecting section 11 is installed at the focal point position d of the reflected light so as not to affect the reflected light when the thickness of the optical disc is standard. Therefore, the light receiving elements 901 and 902 divided into two are uniformly irradiated with light, and the light receiving elements 901 and 902 detect the respective outputs. From the output of the light receiving element 901 to the light receiving element 90
When the calculation (differential calculation) for obtaining the difference when the output of 2 is subtracted, the difference becomes 0.

FIG. 9 shows the structure of the light receiving element 9 of FIG. 1 and the relationship between the light receiving element 9 and the driver 12 of FIG. 5 in more detail. The output of the light receiving element 901 and the output of 902 are connected to the positive input and the negative input of the differential amplifier 13, respectively, and the output of the differential amplifier 13 is connected to the driver 12 for driving the spherical aberration correction element 10.

In the diagram shown in FIG. 3, the optical disk 31 has a thickness of 3
2 shows the state of the light (laser beam) when it is thicker than the standard, FIG. 3 (a) is an enlarged view of FIG. 1a, and FIG. 3 (b) is an enlarged view of b of FIG. Is. The focal point of the reflected light is moved to the side of the light receiving element by an amount thicker than the standard thickness. Therefore, the light blocking plate 8 blocks the light coming from the right half, and the light is emitted only to the 902 side as shown in FIG. 3b. As a result, from the output of the light receiving element 901 to the light receiving element 902
When the calculation (differential calculation) for obtaining the difference when the output of 1 is subtracted, the output of the differential amplifier 13 becomes negative.

FIG. 8 shows a view of the light from the beam splitter 7 toward the light receiving element 9 in the case of FIG. According to this, the right half of the light bundle 8b having the optical axis 8a is blocked by the light shielding plate 8. Further, the side passing through the portion of the light shield plate 8 where the light (light flux 8b) strikes is linear.

FIG. 4 shows that the thickness of the optical disk 31 is 3
2 shows the appearance of light when it is thinner than the standard, a in Fig. 1
4A is an enlarged view of FIG. 4B and FIG. 4B is an enlarged view of FIG. 1B. The focus of the reflected light is the optical disc 31.
Is moved by a smaller amount than the standard thickness. Therefore, the optical disc thickness detecting mechanism 8 shields the light and irradiates the light only on the 901 side as shown in the figure. As a result, the light receiving element 9
When the calculation (differential calculation) for obtaining the difference when the output of the light receiving element 902 is subtracted from the output of 01, the output of the differential amplifier 13 becomes positive.

At the stage of designing and manufacturing, several kinds of optical discs having different thicknesses were prepared, and the thicknesses of these optical discs were measured by a separate measuring device to clarify the relation between the differential output from the multi-divided light receiving element and the optical disc thickness in advance. Keep it. When the disk thickness is plotted on the horizontal axis and the differential output is plotted on the vertical axis, a signal as shown in FIG. 6 can be obtained.

Next, recording / reproducing of the optical disk to be measured is performed so that the laser spot is always irradiated on the signal recording surface of the optical disk.

In this state, the value of the differential output from the multi-divided light receiving element 9 for detecting the optical disc thickness is taken out, and the disc thickness is discriminated from the relationship between the disc thickness and the differential output which has been clarified in advance. Specifically, since the deviation of the disc thickness from the standard value (hereinafter sometimes simply referred to as the disc thickness) is substantially proportional to the differential output, the disc thickness can be obtained by applying a proportional constant to the differential output. Therefore, it may be considered that the output of the differential amplifier 13 represents the disc thickness.

By calculating the output from the light receiving element 9 in this manner, the optical disc thickness can be detected.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 is a schematic view of the optical disc thickness detecting mechanism of the second embodiment, and FIG. 6 shows the relationship between the optical disc thickness and the differential output from the multi-divided light receiving element, that is, the output of the differential amplifier 13. It is a figure, and both are in a substantially proportional relationship.

In FIG. 5, semiconductor lasers 1 and 2 are objective lenses, 3 is the surface of an optical disk, 4 is a signal surface of the optical disk, 5 is a beam splitter for main signal, 6 is a light receiving element for main signal, and 7 is optical disk thickness detection. Beam splitter, 8 a shading plate, 9 a light receiving element for detecting an optical disc thickness, 1
Reference numeral 0 is a spherical aberration correction element.

The optical disc thickness detecting mechanism of the second embodiment of the present invention shown in FIG. 5 is based on a general optical pickup optical system, an optical disc thickness detecting section 11 for detecting the optical disc thickness, and a signal indicating the detected optical disc thickness. Spherical aberration correction element 10
A driver 12 that outputs a signal for driving the optical disc and a spherical aberration correction element 10 that corrects the spherical aberration caused by the deviation of the disc thickness from the standard value are provided. A general optical pickup optical system includes a semiconductor laser 1 that emits a laser beam, an objective lens 2 that focuses light on a signal surface 4 of an optical disk, a surface 3 of an optical disk, a signal surface 4 of an optical disk that records a signal, and a main signal. A main signal beam splitter 5 that separates and reflects the light and guides it to the light receiving element 6, and a main signal light receiving element 6 that receives the main signal and generates a read signal, a focus error signal, and a tracking error signal.

In a general optical pickup optical system, the light emitted from the semiconductor laser 1 passes through the objective lens 2, passes through the surface 3 of the optical disc, and converges on the signal surface 4. The converged light is modulated by the information on the signal surface and reflected. After that, it follows the same path, passes through the objective lens 2, is reflected by the beam splitter 5, and is converged on the light receiving element 6. The light receiving element is multi-divided and outputs a signal according to the amount of received light. A focus error signal and a tracking error signal are generated from this output signal, the objective lens is controlled by using these error signals, and a laser spot is always generated on the optical disc signal surface 4 to perform recording / reproduction of the optical disc drive device. ing.

In the optical disc thickness detecting section 11, the light emitted from the semiconductor laser 1 passes through the objective lens 2 and is converged on the optical disc signal surface 4, and the light from the objective lens 2 is incident on the optical disc surface 3. Utilizing the reflected light when doing,
The optical disc thickness is detected by the differential output of the multi-division light receiving element 9 for detecting the optical disc thickness.

At the stage of designing and manufacturing, several kinds of optical discs having different thicknesses were prepared, and the thicknesses of these optical discs were measured by a separate measuring device to clarify the relationship between the differential output from the multi-divided light receiving element and the optical disc thickness in advance. Keep it. When the disk thickness is plotted on the horizontal axis and the differential output is plotted on the vertical axis, a signal as shown in FIG. 6 can be obtained.

Next, the recording / reproducing of the optical disk to be measured is performed so that the laser spot is always irradiated on the signal recording surface of the optical disk.

In this state, the value of the differential output from the optical disc thickness detecting multi-division light receiving element 9 is taken out, and the disc thickness is discriminated from the relationship between the disc thickness and the differential output which has been clarified in advance. Specifically, since the deviation of the disc thickness from the standard value is approximately proportional to the differential output, the disc thickness can be obtained by applying a proportional constant to the differential output. Therefore, it may be considered that the output of the differential amplifier 13 represents the disc thickness. A value of the actual proportional constant of the differential amplifier 13 is selected so that the correction of the spherical aberration correction element 13 described later is appropriately executed. The configuration and operation up to the detection of the disc thickness are the same as those in the first embodiment, and a part of the description is not repeated.

Referring to FIG. 9, the outputs of the light receiving element 901 and the light receiving element 902 in the light receiving element 9 are connected to the positive input and the negative input of the differential amplifier 13, respectively, and the output of the differential amplifier 13 is spherical. It is connected to a driver 12 for driving the aberration correction element 10, and the output of the driver 12 is connected to the spherical aberration correction element 10. The driver 12 is a differential amplifier 13 that indicates the deviation of the disc thickness from the standard value.
Then, an amplitude modulation or pulse width modulation (PWM) signal is generated from the output of the above to drive the spherical aberration correction element 10. In this way, the spherical aberration correction element 10 is controlled to correct the deviation of the detected optical disc thickness from the standard value, and the spherical aberration is corrected.

The spherical aberration correction element 10 is generally known to use a liquid crystal shutter. The spherical aberration correction element 10 gives an appropriate phase difference to the light beam so as to dynamically correct the spherical aberration caused by the deviation of the detected optical disc thickness from the standard value, and suppresses the corrected spherical aberration. In addition, any object that can dynamically correct spherical aberration can be used.

The optical disc thickness detecting section 11 may have a structure as shown in FIG. As shown in FIG. 10A, when the disc thickness is standard (for example, 1.2 mm), the light receiving element 9 is arranged so that the reflected light converges at the position of the optical disc thickness light receiving element 9.
To place. That is, the light receiving element 9 is arranged at the focal point of the reflected light when the disc thickness is standard. In FIG. 10A, the light coming from the right half is blocked by the light blocking plate 8 and does not reach the light receiving element 9, but the light coming from the left half converges at one point at the position of the light receiving element 9. Here, the solid line representing light represents light that actually passes, and the dotted line is the light that has been entered above for convenience of description, and is light that does not actually exist. The alternate long and short dash line represents the optical axis. The same applies hereinafter.

As shown in FIG. 10B, when the disc thickness is thicker than the standard, the light coming from the left half is shielded by the light shielding plate 8.
Since the light advances so as to converge at a position farther from the light receiving element (in reality, the light receiving element 9 does not converge), the light is received in a semicircular shape on the light receiving element 901 side of the light receiving element 9. Light entering from the right half is blocked by the light shield plate 8 and does not reach the light receiving element 9 (light receiving elements 901 and 902).
As shown in FIG. 10C, when the disc thickness is thinner than the standard, the light coming from the left half travels so as to converge at a position closer to the light receiving element as viewed from the light shielding plate 8, so that among the light receiving elements 9 Light is received in a semicircular shape on the side of the light receiving element 902. Light entering from the right half is blocked by the light shield plate 8 and does not reach the light receiving element 9. If the outputs of the light receiving elements 901 and 902 are connected to the differential amplifier 13 as shown in FIG. 9 with such a configuration, the deviation from the standard value of the optical disc thickness is in a relation substantially proportional to the output as shown in FIG.

The optical disk thickness detection method shown in the first and second embodiments of the present invention is an example, and there is another method using astigmatism, but the difference in focal position is used. All detection systems are applicable.

As described above, in the present invention, since the optical disc thickness is detected by the reflected light from the optical disc surface, it is possible to dynamically correct the occurrence of spherical aberration due to the difference in optical disc thickness. Therefore, even when the thickness of the optical disc to be recorded / reproduced during the operation of the optical disc changes, the occurrence of spherical aberration can be appropriately corrected both before and after the change. Therefore, it is possible to improve the recording / reproducing performance of the optical disc device.

[0057]

The first effect of the optical disk device of the present invention is that the optical disk device for detecting the thickness of the optical disk and correcting the spherical aberration can be made compact and thin. The reason is that the optical disc thickness detection unit employs a mechanism for detecting the optical disc thickness by using the light reflected on the surface of the optical disc. This is because only one actuator and one actuator are required, the number of parts is small, and the space in the thickness direction and the front direction of the device can be saved, so that the device can be downsized.

The second effect of the optical disk device of the present invention is
That is, spherical aberration can be dynamically corrected. The reason is that the spherical aberration correcting means can be used because it is possible to calculate how much spherical aberration has occurred by detecting the optical disc thickness. As a result, there is an advantage that the recording / reproducing performance of the optical disk device is improved.

The third effect of the optical disk device of the present invention is
Since the reflected light from the surface of the optical disc is used directly for detection, there is no problem that the moving distance fluctuates due to the variation of the moving speed of the actuator, and an error easily occurs, and the disc thickness can be accurately detected. There is.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a diagram showing reflected light when the optical disc has a standard thickness.

FIG. 3 is a diagram showing reflected light when the optical disc thickness is thicker than the standard thickness.

FIG. 4 is a diagram showing reflected light when the optical disc thickness is thinner than the standard thickness.

FIG. 5 is a diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between an optical disc thickness and an output of a differential amplifier.

FIG. 7 is a diagram showing a configuration of a conventional optical pickup.

FIG. 8 is a diagram of light seen from a beam splitter toward a light receiving element in the case of FIG. 3;

FIG. 9 is a diagram showing a configuration and a connection relationship of a light receiving element for detecting an optical disc thickness.

FIG. 10 is a diagram showing reflected light from another optical disc thickness detection unit.

[Explanation of symbols]

1 Semiconductor laser 2 Objective lens 3 Optical disc surface 4 Optical disc signal surface 7 Beam splitter for optical disc thickness detection 8 light shield 9 Light receiving element 10 Spherical aberration correction element 11 Optical disc thickness detector 12 drivers 13 Differential amplifier

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5D118 AA01 AA13 AA16 BA01 CD02                       DA12                 5D119 AA01 AA11 AA22 AA29 BA01                       EA03 EB02 EC01 JA09                 5D789 AA01 AA11 AA22 AA29 BA01                       EA03 EB02 EC01 JA09

Claims (7)

[Claims] 1. An optical disc apparatus, wherein an optical disc is irradiated with a laser beam to record information on a recording surface inside the optical disc, and the reflected information from the recording surface is detected to read the recorded information. The objective lens for converging the generated laser beam on the recording surface of the optical disc, and the beam for separating the reflected light of the optical disc surface having the same optical axis as the reflected light for reading and writing information to be recorded on the optical disc An optical disk device comprising: a splitter; and a detection means for detecting the optical disk thickness based on the light reflected by the optical disk surface. 2. The detection means has a multi-division light receiving element for receiving the reflected light, and detects the thickness of the optical disc by differentially detecting the reflected light from the surface of the optical disc by the multi-division light receiving element. The optical disk device according to claim 1, wherein: 3. The detecting means includes a multi-segment light receiving element for receiving the reflected light, and a light-shielding means in front of the multi-segment light receiving element for interrupting a part of the reflected light from the disk surface, The light shielding means is placed at a position where the reflected light converges when the thickness of the standard optical disc is changed, and the variation of the optical disc thickness moves the converged position of the reflected light before and after the light shielding means to receive the other divided light receiving element. 3. The optical disc apparatus according to claim 1, wherein the thickness of the optical disc is detected by performing differential detection by the multi-division light receiving element by utilizing the change in the position and amount of light. 4. The detection means includes a multi-division light receiving element for receiving the reflected light, and a light-shielding means in front of the multi-division light receiving element for interrupting a part of the reflection light from the disk surface, The multi-segment light receiving element is placed at a position that coincides with the convergent position of the reflected light when the optical disc thickness is a standard value, and the convergent position of the reflected light moves to the front and back of the multi-segment photo detector due to fluctuations in the optical disc thickness. 3. The thickness of the optical disc is detected by performing differential detection by the multi-division light receiving element by utilizing the fact that the position and amount of light received by the multi-division light receiving element is changed.
The optical disk device described. 5. The light shielding means faces the reflected light,
When the convergent position of the reflected light is at a position before and after the light shielding means, it is a plate-like object that intercepts half of the light. The optical disk device according to claim 3 or 4. 6. The optical disc apparatus according to claim 1, further comprising a spherical aberration correcting unit that corrects spherical aberration on the recording surface of the optical disc. 7. The optical disk device according to claim 6, wherein the spherical aberration correction means is located between the objective lens and the beam splitter.