JP2000076693A - Optical disk drive - Google Patents

Abstract

(57) Abstract: In an optical disk apparatus for reproducing optical disk data recorded on an optical disk (D), a light source and a numerical aperture of 0.45 for condensing a light beam supplied from the light source are provided.
Moving the beam spot of the light beam condensed by the objective lens in the radial direction of the optical disc and in the direction perpendicular to the surface of the optical disc to a predetermined position on the optical disc. Control means for reaching the beam spot, and control of the control means detects reflected light from the optical disc obtained when the beam spot reaches a predetermined position on the optical disc, and reproduces optical disc data reflected on the reflected light. And a reproducing means for performing the operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for reproducing optical disk data recorded on a fluorescent optical disk as an information recording medium. In particular, it relates to an improvement of an optical head that supplies a light beam for reproducing data from an optical disk.

[0002]

2. Description of the Related Art Optical discs as information recording media include:
Typical ones are CD (Compact Disk) and CD-ROM
and so on. Such optical disks and optical disk devices have been widely used for more than 10 years. In addition, several years ago, various technologies were developed with the aim of further increasing the density of optical discs. As a result, DVDs (Digital
Deo Disk) has been put into practical use.

[0003]

However, at present, it has not yet been able to cope with the demand for higher density such as high definition and long time recording.

An object of the present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical disk device which can contribute to higher density recording.

[0005]

In order to solve the above problems and achieve the object, an optical disk apparatus according to the present invention provides a light source and a light beam supplied from the light source while suppressing the occurrence of spherical aberration. An optical head for condensing the beam at a predetermined position on the optical disk and a reproducing unit for detecting reflected light from the optical disk and reproducing the optical disk data recorded on the optical disk are provided.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 1 to 4 of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of an optical disk device common to the first to fourth embodiments of the present invention.

As shown in FIG. 1, the optical disk device 1 includes a control unit 4, a motor 6, an optical head 8, and a signal processing unit 10.

First, a recording process for recording data generated by an external device 11 (such as a personal computer) on the optical disk D by the optical disk device 1 will be described. The motor 6 drives the optical disc D to rotate at a predetermined speed under the control of the control unit 4. External device 11
Is transmitted to the signal processing unit 10.
The signal processing unit 10 modulates data transmitted from the external device 11 to generate data for recording. The optical head 8 is provided with a semiconductor laser, and emits a recording light beam reflecting the recording data from the semiconductor laser. The optical head 8 is subjected to tracking control and focus control by the control unit 4. That is,
The beam spot of the recording light beam emitted from the semiconductor laser is moved in the radial direction of the optical disk and in the direction perpendicular to the surface of the optical disk. Thereby, the recording light beam emitted from the semiconductor laser is focused on a predetermined position of the optical disc D. As a result, the optical disc D
Is recorded at a predetermined position.

Next, a reproduction process for reproducing data recorded on the optical disk D by the optical disk device 1 and outputting the data to the external device 11 will be described. The motor 6 drives the optical disc D to rotate at a predetermined speed under the control of the control unit 4. A light beam for reproduction is emitted from a semiconductor laser provided in the optical head 8. Also, this optical head 8
The control unit 4 receives tracking control and focus control. That is, the beam spot of the reproducing light beam emitted from the semiconductor laser is moved in the radial direction of the optical disk and in the direction perpendicular to the surface of the optical disk.
Thus, the reproduction light beam emitted from the semiconductor laser is focused on a predetermined position on the optical disc D. The reflected light of the reproduction light beam focused on this optical disc includes:
The data recorded on the optical disk is reflected. This reflected light is detected by a photodetector (not shown) provided on the optical head 8. The detection result of the reflected light detected by the photodetector is provided to the signal processing unit 10 as a reflected light detection signal. Signal processing unit 10
Generates the data recorded on the optical disc D based on the reflected light detection signal. Further, the signal processing unit 10
Demodulates the generated data to generate playback data,
Output to the external device 11.

Next, a first embodiment will be described with reference to FIGS.

FIG. 2 is a schematic diagram showing a schematic configuration of the optical head 8 of the optical disk device 1 shown in FIG. FIG. 3 shows FIG.
FIG. 3 is a cross-sectional view illustrating a schematic configuration of an optical unit 22 shown in FIG.

As shown in FIG. 2, the optical head 8 is provided with a base 20 on which the optical unit 2 is mounted.
2 and an actuator 24 are provided. The optical head 8 is movable in the radial direction of the optical disk D by a linear motor (not shown).

As shown in FIG. 3, a semiconductor laser 31, a collimator lens 32, a beam splitter 33, a quarter-wave plate 34, a converging lens 35, a concave lens 36, a cylindrical lens 37, a beam splitter 3
8, a photodetector 39, a photodetector 40, and a rising prism 41 are provided.

As shown in FIG. 2, the actuator 24 is provided with an objective lens 43 and a coil 46, and the actuator 24 is driven by a known shaft sliding method.

Next, the flow of a light beam in the optical head 8 will be described. The laser beam R emitted from the semiconductor laser 31 is converted into a parallel light beam by the collimator lens 32, and the beam splitter 33 has a polarization property.
Through. Further, by passing through the quarter-wave plate 34, the polarization state of the parallel light beam is converted from linearly polarized light to circularly polarized light, and the light path is changed by 90 ° by the rising mirror 41 to be incident on the objective lens 43. After being guided by the objective lens 43 and converged, the laser beam R is applied to the optical disc D as a spot. Reflected light R 'on optical disc D
Travels backward in the above optical path, the polarization state is again converted into linearly polarized light by the 波長 wavelength plate 34, and reaches the beam splitter 33. Since the polarization direction of the reflected light R ′ is exactly 90 ° different from the polarization direction of the original laser beam R emitted from the semiconductor laser 31, the reflected light R ′ is reflected by the beam splitter 33. Further, the reflected light R ′ is converged by the converging lens 36 and passes through the concave lens 36. Further, the reflected light R ′ is reflected by the cylindrical lens 3.
7, the beam splitter 3
8, the light reaches a photodetector 39 having four light-sensitive portions in the shape of a “field”. The rest of the reflected light R 'is reflected by the beam splitter 38 and reaches a photodetector 40 having a two-part light sensing unit. The light incident on the predetermined light receiving portion of the photodetector 39 is photoelectrically converted to obtain an information signal, and a focus error signal is obtained by, for example, a known astigmatism method. In addition, while photoelectrically converting light incident on a predetermined light receiving portion of the photodetector 40 to obtain an information signal,
For example, a tracking error signal is obtained by a known push-pull method. Based on the tracking error signal, control is performed to eliminate a radial displacement between the light spot converged by the objective lens 43 and a predetermined track center of the optical disc D. Further, based on the focus error signal, control is performed to eliminate a shift in the optical axis direction between the focus of the light spot converged by the objective lens 43 and the recording surface of the optical disc D.

Next, the fluorescent optical disk (optical disk D) will be described.

Various proposals have been made toward the realization of high-density optical discs, and some are promising. One of these is a fluorescent optical disk utilizing the stimulated emission effect, and its principle configuration is described in detail, for example, in the journal "Optics", Vol. 26, No. 7, p. 348-353. According to the present invention, it is possible to provide a solution to a problem that may cause a problem in putting a fluorescent disk into practical use.

Hereinafter, the configuration and the principle of reproduction of the fluorescent optical disk will be briefly described.

As described in the above-mentioned academic journal, a certain phosphor compound is excited by ultraviolet rays or the like to emit afterglow,
Irradiation with infrared rays having a longer wavelength has been confirmed to increase the afterglow, which is called a photostimulated luminescence effect. As a phosphor that emits stimulating light,
Ia-VIIb group compounds, IIa-VIb group compounds and the like are known. When a crystal of a material that is the base material of a compound is irradiated with an electromagnetic wave such as ultraviolet light having energy higher than the band gap energy of the crystal, a part of the irradiated energy is absorbed by the base element ions, and the crystal enters the crystal. A pair of conduction band electrons and inner shell holes is generated. Hereinafter, this irradiation light is referred to as temporary excitation light. Next, Auger transition of the inner shell hole occurs, and relaxes to conduction band electrons and valence band holes. In this way, electron-hole pairs are generated, and the electrons and holes form excitons. In the case of photostimulated luminescence,
The compound configuration is such that the electrons and holes are separately captured and recombined. In other words, in order to store energy, that is, information, electrons and holes are captured in different places and do not recombine as they are. More specifically, it is trapped by intentionally doped impurities or lattice defects. Hereinafter, this trapped portion will be referred to as an electron capture center. In order to read out the information stored in this way, a stimulus by light is given to excite electrons, and recombine with holes to cause stimulated emission. Hereinafter, the irradiation light at this time will be referred to as secondary excitation light. The light thus emitted is taken into the objective lens in the same manner as in the conventional example, guided to a photodetector via an optical path on the way, and subjected to photoelectric conversion, thereby reproducing information on the optical disk.

FIG. 4 is a sectional view showing a schematic configuration of a fluorescent optical disk. Fluorescent optical disk, ie, optical disk D
Is composed of three substrates 205, 206 and 207. Further, each substrate is composed of three transparent substrates 203a, 203b, and 203c that function as substantially transparent bodies for primary excitation light and secondary excitation light, and a phosphor layer described later. The thickness of the transparent substrate 203a is about 0.9
8 [mm], and the thickness of the transparent substrates 203b and 203c is 0.16 [mm]. The substrate 205 and the substrate 206 and the substrate 206 and the substrate 207 are joined by, for example, adhesion by spin coating of an ultraviolet curable resin. After being cured, the ultraviolet-curable resin has bonding layers 202a and 202, which substantially act as transparent bodies for primary excitation light and secondary excitation light.
02b is formed. The transmittance of the bonding layers 202a and 202b is, for example, 95% or more, and the thickness is 0.040 [mm]. One surface of the substrate 205, that is, the surface opposite to the optical disk surface on which the light beam is incident, is coated with the phosphor 201a to form a first recording layer. Substrate 206
The phosphors 201b and 201c are applied to both sides of the recording layer to form a second recording layer and a third recording layer, respectively. Further, a phosphor 201d is applied to one surface of the substrate 207, that is, the surface on which the light beam is incident, to form a fourth recording layer. Further, reference numeral 204 in FIG. 4 indicates electron capture centers formed in each recording layer after the primary excitation light is irradiated. Actually, as in the case of a CD, predetermined information is recorded in a manufacturing process of an optical disk.
Recorded ones are sold as products on the market. Specific examples of the phosphor include RbBr: Tl. This uses ultraviolet light as primary excitation light, and the wavelength of secondary excitation light used for information reproduction is 650 [nm]. At this time, light emission with a wavelength of 360 [nm] is observed.

On the other hand, with respect to the high density, in addition to the multilayer structure, there is a method of reproducing the finer pits with high precision by increasing the numerical aperture of the objective lens and reducing the size of the focused spot. well known. At present, about 0.60 of the highest numerical aperture among the objective lenses for optical disks which are mass-produced in a stable manner. It is of course effective to increase the density of the above fluorescent optical disk by using an objective lens having a high numerical aperture. However, in the case of the above-described fluorescent optical disk having a multilayer structure, the thickness of the transparent substrate through which the light beam converged by the objective lens passes varies depending on the recording layer to be reproduced, and this causes so-called spherical aberration. The amount of occurrence of spherical aberration at this time is proportional to the amount of deviation from the substrate thickness that the objective lens has as its design value, and is proportional to the fourth power of the numerical aperture. Therefore, multilayering and high numerical aperture for high density are in conflict with securing the quality of the focused spot. That is, it is practically impossible to accurately reproduce information on all recording layers with an objective lens having a high numerical aperture of 0.60. For example, when the objective lens is designed so as to be suitable for reproducing the information of the first recording layer, when reproducing the information of the third recording layer and the fourth recording layer, the effective substrate thickness is different from the case of the first recording layer. Is greatly different, a large aberration occurs in the condensed spot, and the reproduction accuracy is reduced. More specifically, since the spherical aberration lowers the central peak intensity of the condensed spot, if the output of the light source remains constant when the spherical aberration occurs, the intensity of the reflected light decreases, and information reading error or the like occurs.

As a means for solving this problem, in the first embodiment, the numerical aperture of the objective lens is set to a certain value or more and a certain value or less, and the amount of spherical aberration is kept low while the focused spot is kept small to some extent.

The first embodiment will be described in detail with reference to FIGS.

First, the wavelength dependence of the beam splitter 33 will be described. As described above, the wavelength of the secondary excitation light is 6
50 [nm], which is equal to the wavelength of the semiconductor laser 31 as the light source. Since the laser light R emitted from the semiconductor laser 31 must be transmitted through the beam splitter 33 after being converted into parallel light by the collimator lens 32, the 45 ° plane of the beam splitter 33 has a center wavelength of 650 [nm] on the transmission side. ] Has high transmittance (for example, 90 [%] or more) with respect to the light. On the other hand, with respect to the reflected light of the optical disk, it is necessary to guide the light to the photodetector side, so that the film characteristic is such that almost all the light having a wavelength of 360 [nm] is reflected. Such a film characteristic can be realized by a dielectric multilayer film, and has been practically used as a so-called dichroic filter.

Next, the effect of limiting the numerical aperture of the objective lens 43 will be described. Until now, in the world of optical disks, it has been practiced to increase the numerical aperture of an objective lens as much as possible to reduce the diameter of a condensing spot in order to increase the density. In the case of a so-called read-only optical disk that has been recorded, a finer pit is recorded in advance, and a finer condensed spot is irradiated on this pit to increase the resolution of a reproduced signal. And so on. More specifically, with the advance of aspherical lens technology, an objective lens having a numerical aperture of 0.60 is now easily realized by crow molding or plastic injection molding. Research and development of fluorescent optical disks have been proceeded based on the same concept. However, the document "Optical disk technology" (Onoe et al.,
As in 1989 (Radio Engineering Co., Ltd.), the amount of spherical aberration caused by an error in the substrate thickness increases in proportion to the fourth power of the numerical aperture of the objective lens.

Now, the objective lens 43 has a substrate thickness of 1.
It is assumed that it is optimally designed as 0 [mm]. As described above, the substrate thicknesses up to the first recording layer and the second recording layer in this embodiment are 0.98 [mm] and 1.02 [mm], respectively.
[Mm]. The calculation results of the cross-sectional intensity distribution of the light beam condensed through a transparent substrate (refractive index 1.574) having a thickness error of 0.02 [mm] are expressed by a numerical aperture of 0.60 and a numerical aperture of 0.60, respectively.
The cases of 0.55, 0.50, 0.45, and 0.40 are shown in FIGS. 5, 10, 15, 20, and 25. From these figures, it can be seen that the thickness error of the substrate is ± 0.02 [m
m], it can be seen that even if the numerical aperture is 0.60, a noticeable decrease in spot quality, for example, an increase in spot diameter, a decrease in center peak intensity, or an increase in side lobe intensity does not occur. That is, it can be expected that a good reproduction signal is ensured for reproduction of the first recording layer and the second recording layer even when the numerical aperture is kept high.

On the other hand, 1.18 [mm] and 1.22 [m] corresponding to the substrate thickness up to the third recording layer and the fourth recording layer.
m], the calculated results of the cross-sectional intensity distribution of the condensed spot obtained as a result of passing through the substrate of
6, 8, 11, 13, 13, 16, 18, and 2 for the cases of 5, 0.50, 0.45, and 0.40
1, FIG. 23, FIG. 26, and FIG. 0.18, 0.22 when compared with the original optimal substrate thickness of the objective lens
There is a substrate thickness error of [mm]. From these figures, it can be seen that when the substrate thickness error increases to about 0.2 [mm], the side lobe intensity increases and the center intensity decreases. Further, it can be seen that the degree is more intense as the numerical aperture is larger. A decrease in the center intensity leads to, for example, a decrease in the degree of modulation or resolution, and as a result, a decrease in the reproduction accuracy, which is a problem.However, if there is enough light source output, the light source output is increased as necessary, and Light power can be kept constant. In consideration of this, in the case of the substrate thickness errors of 0.18 and 0.22 [mm], FIG. 7 shows that the center intensity was rewritten so as to be the original value, that is, 1.0 in FIG. 9, 12, and 1
4, FIG. 17, FIG. 19, FIG. 22, FIG. 24, FIG. 27, and FIG. FIG. 30 summarizes the side lobe intensities that can be read from these figures for the numerical aperture. When spherical aberration occurs due to a large substrate thickness error, it can be clearly seen that the side lobe intensity increases as the numerical aperture increases. The side lobes cause so-called intersymbol interference, and also reduce the reproduction accuracy. Now, suppose that the fluorescent optical disk of this embodiment is
Assuming that light is emitted to a portion irradiated with light having an intensity of 10% or more of the center peak intensity, it is understood that the side lobe intensity exceeds 10% and contributes to light emission at a numerical aperture of 0.60. From the above considerations, in order to prevent intersymbol interference from occurring, the numerical aperture must be at least 0.60 or less, and in view of various margins, more practically, 0.55 or less. It is appropriate to do.

Next, the focused spot diameter will be considered. As described above, if the diameter corresponding to 10% of the center peak intensity is defined as the spot diameter, the spot diameter for each numerical aperture (however, the substrate thickness error is 0.22 [mm], and the center peak intensity is all 1) ) Is as shown in FIG. As a matter of course, the spot diameter increases as the numerical aperture decreases. Increasing the spot diameter particularly causes a decrease in resolution, and lowers the signal reproduction accuracy. Conversely,
In order to ensure a certain reproduction accuracy, the recording density must be reduced. In the case of an optical disk, since one recording layer is a so-called two-dimensional recording, the recording density is very roughly proportional to the square of the spot diameter. In other words, the recording density decreases in inverse proportion to the square of the increase rate of the spot diameter. In order to make this relationship more apparent, the relative value of the spot diameter at each numerical aperture and the relative value of the square of the spot diameter are shown assuming that the spot diameter at a numerical aperture of 0.60 is 1, respectively. 32 and 3
3. The relative value of the square of the spot diameter when the numerical aperture is 0.40 greatly exceeds 2. That is, unless the recording density is reduced to half or less, the reproduction accuracy cannot be ensured. This means that, in addition to the first and second recording layers, a third recording layer and a fourth recording layer were newly provided, and the number of layers was apparently doubled to double the recording capacity. It has to be said that the effect of increasing the recording capacity becomes poor as a whole. On the other hand, if the numerical aperture is 0.45, the relative value of the square of the spot diameter is slightly lower than 2, and
Even if the recording density per layer is reduced in order to ensure reproduction accuracy, the effect of increasing the total recording capacity by doubling the number of layers can be expected. From the above, it is possible to find substantial significance in increasing the density by multi-layering,
The numerical aperture is 0.45 or more.

Therefore, as a whole, the numerical aperture is 0.4
When the value is 5 or more and 0.55 or less, the improvement of the recording capacity is realized by multi-layering while ensuring the accuracy of the reproduction signal.

As described above, the transmittance of the bonding layers 202a and 202b is, for example, 95% or more, and the electron capture center is irradiated with light of a predetermined wavelength having high energy such as near the focal point of the converging spot. Unless the light emission is performed, no stimulated emission occurs, so that signal leakage from recording layers other than the recording layer being reproduced, that is, so-called crosstalk does not occur.

The number of layers is not limited to four, and the recording capacity can be further increased by utilizing the principle of the above embodiment.

Here, the effects of the first embodiment will be summarized. As described above, the optical disc device according to the first embodiment of the present invention includes the objective lens having a numerical aperture of 0.45 or more and 0.55 or less. Thereby, the numerical aperture is 0.45 or more for a multi-layer fluorescent optical disk which provides a photostimulated emission effect by supplying a light beam of a predetermined wavelength.
A focused spot focused by an objective lens of 0.55 or less is supplied. Therefore, stable information reproduction of multilayer recording can be performed with a single optical head, and high-density recording can be realized.

Next, a second embodiment will be described with reference to FIGS.

The optical head 8 described with reference to FIG.
And the fluorescent optical disk described with reference to FIG. 4 are common to the first and second embodiments. However, in the second embodiment, the point is that the optical unit 222 shown in FIGS. 34, 35, 39, and 40 is employed instead of the optical unit 22 shown in FIGS. Also,
In the second embodiment, the objective lens 43 of the optical head 8 is not limited to the numerical aperture described in the first embodiment. Of course, by limiting to the numerical aperture described in the first embodiment, a further synergistic effect can be obtained together with the invention of the second embodiment.

Here, the fluorescent optical disk described with reference to FIG. 4 will be further described. In order to make use of the characteristics of the stimulated emission system of the fluorescent optical disk and to realize substantial densification, it is necessary to form a multilayer structure in which the number of stacked phosphor substrates is increased.

However, if there is only one objective lens for supplying a light spot converged to the diffraction limit corresponding to such an optical disk having a multilayer structure, the following serious inconveniences occur. Occurs. In general, in the design of an objective lens, a method is used in which the thickness of a transparent substrate through which convergent light is transmitted during actual use is designed to be fixed to a certain value, or is fixed to a value within a certain limited range. Is taken. Therefore, if a condensed spot is formed through a transparent substrate having a thickness exceeding this range during actual use, large aberrations, particularly spherical aberrations, occur.

Meanwhile, in the case of a phosphor optical disk aiming at further higher density, the number of layers is considered to be substantially four or more, and the thickness of each substrate is set to be less than 0.1 due to demand for mass production at low cost and technical restrictions. It is difficult to reduce the thickness to about 1 [mm] or less. Also, considering the current objective lens design and manufacturing capabilities, and aiming for higher density by reducing the diameter of the focused spot,
It is desired that the numerical aperture of the objective lens be 0.45 or more. However, under the above-described conditions, a single objective lens as in the related art is expected to generate large aberrations, particularly spherical aberrations, and it is very difficult to accurately reproduce information on all recording layers. In other words, no matter how the objective lens is designed, it is not possible to provide a good condensing spot with little aberration for all recording layers. For example, when the objective lens is designed so as to be suitable for reproducing the information of the first recording layer, when reproducing the information of the third recording layer and the fourth recording layer, the effective substrate thickness is the same as that of the first recording layer. Is significantly different, a large aberration occurs in the condensed spot, and the reproduction accuracy is reduced. More specifically, since the spherical aberration lowers the central peak intensity of the condensed spot, if the output of the light source remains constant when the spherical aberration occurs, the intensity of the reflected light decreases, and information reading error or the like occurs.

On the other hand, in the second embodiment, the divergence or convergence, which will be described later, is given to the parallel light beam supplied to the objective lens according to the recording layer to be reproduced. , The occurrence of spherical aberration due to the difference is suppressed low, and a high-quality reproduced signal can always be obtained.

The second embodiment will be described in detail with reference to FIGS. 34 to 75 in consideration of the above principle configuration.

FIGS. 34 and 35 are sectional views showing a schematic configuration of the optical section 222. FIG. In the second embodiment, an optical unit 222 shown in FIGS. 34 and 35 is employed instead of the optical unit 22 shown in FIG.

As shown in FIGS. 34 and 35, the optical unit 2
22, a semiconductor laser 231 and a collimator lens 23
2, beam splitter 233, quarter wave plate 234, converging lens 235, concave lens 236, cylindrical lens 237, beam splitter 238, photodetector 239,
A photodetector 240 and a rising prism 241 are provided. Further, the optical section 222 is provided with a convergence imparting means 270. The convergence imparting means 270 is provided with a convex lens holder 264 on which the convex lens 263 is mounted, and a switching means 260 for driving the convex lens holder 264. The switching means 260 includes a housing 261 and a shaft 262.

The feature of the second embodiment is that the collimator lens 2
The point is that a means for imparting divergence or convergence to the light beam collimated at 32 as necessary and a mechanism for moving this means are added. Furthermore, a feature of the second embodiment is that the beam splitter 233 has wavelength dependency. In the second embodiment,
The light beam collimated by the collimator lens 232 is
A case where convergence is given as needed will be described. The means for imparting the convergence is the convergence imparting means 270.

First, the wavelength dependence of the beam splitter 233 will be described. As described above, the wavelength of the secondary excitation light is 650 [nm], which is equal to the wavelength of the semiconductor laser 231 which is the light source. Semiconductor laser 231
The emitted laser light R is converted into parallel light by a collimator lens 232 and then converted into a beam splitter 233.
Must be transmitted through the beam splitter 23
The 45 ° plane of No. 3 has a film characteristic of having a high transmittance (for example, 90% or more) with respect to light having a center wavelength of 650 [nm] on the transmission side. On the other hand, with respect to the reflected light from the optical disk, it is necessary to guide the reflected light to the photodetector side.
[Nm] has such film characteristics that almost all light is reflected. Such a film characteristic can be realized by a dielectric multilayer film, and has been practically used as a so-called dichroic filter.

Next, the convergence imparting means 270 and the mechanism for driving it will be described. In the second embodiment, when reproducing information recorded on the third recording layer or the fourth recording layer, a convex lens 263 described later is not inserted into the optical path. The objective lens 43 has an average value of 1.20 [mm] of the depth from the optical disk surface to the third recording layer and the depth of 1.22 [mm] from the optical disk surface to the fourth recording layer. [Mm] is designed as an appropriate transparent substrate thickness.

On the other hand, when reproducing information recorded on the first recording layer or the second recording layer, the convex lens 263 is inserted into the optical path. First, the convergence imparting means 270 will be described. As shown in FIGS. 36 and 37, the convergence imparting means 270 includes a convex lens 263, a convex lens holder 264 mounted with the convex lens 263, and a switching means 260 for driving these. Further, the switching means 260 includes a housing 261 and a shaft 262. The housing 261 is fixed to the base of the optical unit 22, and one end of the shaft 262 is joined to the convex lens holder 264 by a method such as adhesion. . This switching means 270
As shown in FIG. 34, FIG. 35, FIG. 39, and FIG. 40, the state where the convex lens 263 is inserted in the middle of the optical path of the parallel light beam that goes out of the beam splitter 233 toward the objective lens 43, or is inserted. Achieving any state of no state.

The convex lens 263 has a radius of 200 [m]
m], radius of output surface −200 [mm], thickness 1.504
[Mm], made of glass material BK7. The convex lens holder 264 is a cylinder made of aluminum, and the surface thereof is subjected to a treatment for preventing reflection. Convex lens 2
63 and the convex lens holder 264 are joined by an adhesive, for example, an ultraviolet curing adhesive L1-298 (manufactured by Loctite).

The shaft 2 inside the casing 261
A solenoid coil 265 is wound around 62 at a predetermined position. The housing part 261 has a magnet 266 so as to surround the solenoid coil 265 inside. Further, as shown in FIG. 38, the solenoid coil 265 is connected to the control unit 4 that controls the flow rate of the current by the control signal from the signal processing unit 10. As such a switching means 260, for example, an electromagnetic solenoid such as a self-holding solenoid (model number SH2LC0730) manufactured by Shindengensha may be used.

The switching means 260 performs a switching operation of the position of the shaft 262 and thus of the convex lens 263 as follows. First, when the signal processing unit 10 determines the necessity of the switching of the switching unit 270, the signal is transmitted to the control unit 4 so that the control unit 4 sends a control signal having a predetermined polarity and a current to the solenoid coil 265. The control unit 4 receiving such a control signal from the signal processing unit 10
Supplies a current having a predetermined polarity and magnitude to the solenoid coil 265. Then, due to the interaction between the current flowing through the solenoid coil 265 and the magnetic field generated by the magnet 266, an electromagnetic driving force is generated on the shaft 262 around which the solenoid coil 265 is wound, and the shaft 262 moves in the longitudinal direction. 34, 35, and 3
As shown in FIG. 9 and FIG. 40, when the shaft 262 is located inside the housing 261, the shaft 262 can be made to protrude from the housing 261 by a current having a predetermined polarity and magnitude, thereby making the optical path A convex lens 263 can be inserted inward. Conversely, when the shaft 262 is at a position protruding from the housing 261, the shaft 262 can be pushed into the housing 261 by a current having a predetermined polarity and magnitude, thereby removing the convex lens 263 from the optical path. it can. When the convex lens 263 is inserted into the optical path, the distance between the exit surface of the convex lens 263 and the entrance surface of the objective lens 43 is 30 [mm].

Next, the effect of the second embodiment, particularly its optical effect, will be described based on the results of an optical simulation. First, the characteristics of the spherical aberration will be described based on the aberration diagrams.

FIGS. 41, 46, 51, 56 and 6
1 and FIG. 66 all show coordinates (FX, FY) set at the aperture of the objective lens 43 with respect to each point on the FX axis and a ray bundle incident on each point on the FY axis on the image plane. The shift amount (DX, DY), that is, the lateral aberration is shown. FIG. 41 shows that the optimum thickness of the transparent substrate is 1.20 [mm].
9 shows the spherical aberration characteristics of the condensed spot by the objective lens 43 designed in FIG. In this case, the objective lens 4
FIG. 45 shows the convergence state of the light beam obtained by No. 3. Further, the radius of curvature, the surface interval, and the refractive index of the glass material of each surface constituting the objective lens 43 are as follows.

First surface: radius = 8.14 [mm], surface interval = 1.49 [mm],
Refractive index = 1.8689 Second surface; radius = 163.0 [mm], spacing = 0.8 [mm] Third surface; radius = -4.242 [mm], spacing = 1.51 [m]
m], refractive index = 1.78569 fourth surface; radius = −4.83 [mm], surface interval = 0.3 [mm] fifth surface; radius = 3.83 [mm], surface interval = 1. 51 [mm] Refractive index = 1.8689 Sixth surface; Radius = 8.92 [mm], Surface spacing = 1.9861 [m]
m] Considering that the focused spot diameter is about 1 [μm] or less, the objective lens 43 in the second embodiment has very little residual spherical aberration and has good characteristics. You can see that it is doing. Next, using the objective lens 43 having such characteristics, the substrate thickness is 1.22 [mm].
FIG. 46 shows the spherical aberration of the converged spot when converged on the recording surface of the 1.18 [mm] optical disc.
And FIG. 51. The optimum values of the thickness of the substrate for transmitting the convergent light beam are -0.02 [mm] and +
Since it is shifted by 0.02 [mm], a slight state of spherical aberration is recognized as compared with the result of FIG.
It can be seen that a sufficiently usable condensing spot can be obtained if the substrate thickness error is at a low level and this level of error.
That is, the information recorded on the third recording layer or the fourth recording layer can be reproduced with a single objective lens. The convergence of light rays by the objective lens at this time is shown in FIG.
0 and FIG.

On the other hand, without taking any measures by the above-mentioned objective lens 43, the condensed light spot when condensed on the recording surface of an optical disk having a substrate thickness of 1.02 [mm] and 0.98 [mm]. 56 and 61 are shown in FIGS. 56 and 61, respectively. From these figures, it can be clearly seen that large spherical aberration occurs in the above situation, and it is not possible to reproduce information recorded on the first recording layer and the second recording layer with a single objective lens. Can not. The convergence state of the light beam by the objective lens at this time is shown in FIGS. 60 and 65, respectively. From these figures, no significant deterioration of the convergence state is recognized, but this is due to the fact that although large spherical aberration occurs, it is sufficiently small compared to the size of the objective lens.

Now, with respect to the above characteristics, the characteristics when the convex lens 263 of the second embodiment is inserted into the optical path will be described. FIGS. 66 and 71 show the spherical aberration characteristics of the condensed spot condensed by the convex lens 263 and the objective lens 43, respectively. In both cases, a significant reduction in spherical aberration can be seen as compared with FIGS. 56 and 61, respectively. Although the spherical aberration is slightly larger than the characteristics shown in FIGS. 46 and 51, the spherical aberration is within a sufficiently usable range, and the effect of reducing the spherical aberration by inserting the convex lens 263 is recognized. FIGS. 70 and 75 show the convergence of light rays by the objective lens at this time.

As described above, by appropriately inserting the convex lens 263 into the optical path, the influence of spherical aberration due to the difference in substrate thickness can be greatly reduced, and the possibility of higher density by further multilayering is improved. Can greatly contribute to stabilization of the reproduction characteristics of a fluorescent optical disk.

Further, FIG. 42, FIG. 47, FIG. 52, FIG.
7, FIG. 62, FIG. 67, and FIG. 72 show the spherical aberration in the form of longitudinal aberration in each case described above. The horizontal axis indicates the deviation between the convergence point of each ray and the focal point on the optical axis, and the vertical axis indicates the amount of deviation from the center of the aperture.

FIG. 42 shows the spherical aberration characteristics of the condensed spot by only the objective lens when the substrate thickness is 1.20 [mm]. FIGS. 47 and 52 show the substrate thickness of 1.22 [mm] and It shows the amount of spherical aberration of a condensed spot when condensed on the recording surface of a 1.18 [mm] optical disc. Although a slight increase in spherical aberration is recognized as compared with the result of FIG. 42, it can be also seen that a sufficiently usable condensed spot can be obtained at a still lower level and this level of substrate thickness error. That is, it can be understood that the information recorded on the third recording layer or the fourth recording layer can be reproduced by a single objective lens by expressing spherical aberration in the form of longitudinal aberration.

On the other hand, the light spot on the recording surface of an optical disk having a substrate thickness of 1.02 [mm] and 0.98 [mm] without taking any measures by the objective lens described above. 57 and 62 show the amount of spherical aberration in the form of longitudinal aberration. From these figures, it can be clearly seen that a large spherical aberration occurs in the above situation.

Now, a description will be given of the characteristics when the convex lens 263 according to the present embodiment is inserted into the optical path, with respect to the above characteristics. 67 and 72 show the convex lens 2 respectively.
The figure shows the characteristics when the spherical aberration of the light spot focused by the objective lens 63 and the objective lens 43 is represented by the longitudinal aberration. In both cases, a significant reduction in spherical aberration can be seen as compared with FIGS. 57 and 72, respectively. 47 and 52, the spherical aberration is slightly larger, but within a sufficiently usable range, and the effect of reducing the spherical aberration by inserting the convex lens 263 is recognized.

As described above, by appropriately inserting the convex lens 263 into the optical path, the influence of the spherical aberration due to the difference in the substrate thickness can be greatly reduced, and the possibility of increasing the density by further multi-layering is possible. Can greatly contribute to stabilization of the reproduction characteristics of a fluorescent optical disk.

43, FIG. 48, FIG. 53, FIG.
63, 68, and 73 show distortion characteristics in each of the above cases. The horizontal axis represents the amount of distortion on the image plane in [mm] units, and the vertical axis represents the image height. It can be seen that distortion is at an extremely low level in all cases and does not need to be considered in practice.

Further, FIGS. 44, 49, 54, 5
9, FIG. 64, FIG. 69, and FIG. 74 are cross-sectional views of the point image intensity distribution in each of the above cases. That is, FIG. 44 is a cross-sectional view of a point image intensity distribution of a condensed spot by only the objective lens when the substrate thickness is 1.20 [mm], and FIGS.
FIG. 7 is a cross-sectional view of a point image intensity distribution of a condensed spot formed only by an objective lens when light is condensed on recording surfaces of optical disks of 22 [mm] and 1.18 [mm]. Further, with the objective lens described above, a substrate thickness of 1.0
FIGS. 59 and 64 are cross-sectional views of the point image intensity distribution when light is condensed on the recording surface of the optical disks of 2 [mm] and 0.98 [mm], respectively. On the other hand, FIGS. 69 and 74 show the state of the point image intensity distribution when the convex lens 263 according to the present embodiment is inserted into the optical path. In all the figures, the horizontal axis indicates the amount of deviation from the center of the converging spot, and the unit is [mm]. The vertical axis represents the relative intensity when the central intensity when there is no aberration is set to 1, that is, the so-called Strehl intensity. From these point spreads, a further geometrical optical spot size can be derived as a measure of the characteristic evaluation. Table 1 summarizes the relative center intensity and the geometric optical spot size under the above conditions.

[0063]

[Table 1]

First, the streak strength will be considered.
In general, a so-called Strehl definition is well known in image evaluation, in which a Strehl intensity of 0.8 or more has a minimum basic characteristic as a condensed spot. From this viewpoint, it can be seen from the calculation results that a sufficiently high Strehl strength is obtained when the light is condensed through a substrate having a thickness of 1.20, 1.22, and 1.18 [mm] using only the objective lens. However, the substrate thickness was 1. without taking any measures by the objective lens.
When condensed on optical disks of 02 [mm] and 0.98 [mm], the Strehl strength is 0.154, respectively.
And 0.105, which makes it unusable for use. On the other hand, the convex lens 2 of the second embodiment
When 63 is inserted into the optical path, the Strehl strength becomes 0.885 and 0.978, respectively, and a significant improvement is expected, and the device becomes ready for practical use.

As described above, by appropriately inserting the convex lens 263 into the optical path, it is possible to greatly reduce the decrease in the Strehl strength due to the difference in the substrate thickness, and it is possible to increase the density by further increasing the number of layers. Can greatly contribute to stabilization of the reproduction characteristics of a fluorescent optical disk.

Next, the spot size will be considered.
The numerical aperture of the objective lens 43 whose sectional shape is shown in FIG. 45 is about 0.50, and the wavelength used for the calculation is 650 [nm].
Therefore, the spot size (however, a diameter in a range where the intensity is 13.5% or more of the maximum intensity) is approximately 0.9 to 1.0 [μm] in actual measurement. However, the optical simulation that describes the result in the second embodiment is a so-called ray tracing simulation, which is handled in geometrical optics, and is necessary when the focused light spot is narrowed to near the diffraction limit as in the second embodiment. No consideration is given to wave optics. For this reason,
When the substrate thickness is 1.20 [mm], which is the optimum condition, 0.
At 14 [μm], a value significantly smaller than the actual value is obtained. Therefore, evaluation in absolute value is not performed here,
Evaluation is attempted as a relative value to the spot size of 0.14 [μm].

When light is condensed through a substrate having a thickness of 1.22 and 1.18 [mm] using only the objective lens,
Although the spot size is increased only about two to three times as compared with the case where the substrate thickness is 1.20 [mm], the substrate thickness is not increased by the objective lens 43 and no measures are taken.
When the light is focused on the optical disks of 02 [mm] and 0.98 [mm], respectively, 3.1 and 2.9 [μm]
, Which is 20 times that in the case of the optimum substrate thickness of 1.20 [mm], and it is expected that the condensing spot is too large. In contrast, the convex lens 2 according to the present embodiment
When 63 is inserted into the optical path, the spot size becomes 0.74 and 0.40 [μm], respectively, and significant improvement is expected.

As described above, by appropriately inserting the convex lens 263 into the optical path, the increase in spot size due to the difference in substrate thickness can be greatly improved, and the possibility of higher density by further multilayering is improved. Can greatly contribute to stabilization of the reproduction characteristics of a fluorescent optical disk.

Next, the wavefront aberration will be considered. The evaluation results so far have taken the position of viewing light as a ray,
Although it was so-called geometric optics, evaluation of optical characteristics also requires so-called wave optics, which refers to light from the viewpoint of waves. RMS value evaluation of wavefront aberration is a typical example of this. In the case of the Martial criterion, the evaluation criterion is that if the residual wavefront aberration of the point image of the optical system, that is, the converging spot, is λ / 14 (λ is the wavelength) or less, it can be used as a virtually ideal image. Have given. Table 2 shows the calculation results of the wavefront aberration (RMS value) for each of the above conditions.

[0070]

[Table 2]

In the case where light is condensed through a substrate having a thickness of 1.22 and 1.18 [mm] using only the objective lens,
About 0.02 compared to 1.20 [mm]
Although the wavefront aberration only increased to about 0.03λ, which was well below the criterion of Martial, the substrate thickness was 1.02 without any countermeasure with this objective lens.
When light is condensed on optical disks of [mm] and 0.98 [mm], a large wavefront aberration exceeding 0.3λ remains, and it cannot be used as a condensed spot. On the other hand, when the convex lens 263 according to the present embodiment is inserted into the optical path, the wavefront aberration is 0.056λ.
And 0.024λ, which is greatly improved to a usable level.

As described above, by appropriately inserting the convex lens 263 into the optical path, the increase in wavefront aberration due to the difference in substrate thickness can be greatly improved, and the possibility of higher density by further multilayering is improved. Can greatly contribute to stabilization of the reproduction characteristics of a fluorescent optical disk.

As described above, the transmittance of the bonding layers 202a and 202b is, for example, 95% or more, and the electron capture center is irradiated with light of a predetermined wavelength having high energy such as near the focal point of the converging spot. Unless done,
Since no stimulated emission occurs, signal leakage from recording layers other than the recording layer being reproduced, so-called crosstalk, does not occur.

In the second embodiment, the single convex lens 26
3 describes an optical head having two operation modes of inserting or not inserting it into the optical path. However, the present invention is not limited to this. Can also be set. For example,
By using a concave lens or the like, divergence can be imparted to the light beam supplied to the objective lens, and similar characteristics can be improved.
Also, the number of layers is not limited to four,
It is also possible to increase the recording capacity by further increasing.

Here, the effects of the second embodiment will be summarized. As described above, the optical disc device according to the second embodiment of the present invention provides a multilayer fluorescent optical disc that provides a photostimulated emission effect by supplying a light beam of a predetermined wavelength, according to a recording layer to be reproduced. By means of imparting divergence or convergence, aberration correction can be performed by imparting divergence or convergence to the light beam supplied to the objective lens. Thus, stable information reproduction of multilayer recording can be performed with a single optical head, and high-density recording can be realized.

Next, a third embodiment will be described with reference to FIGS.

The optical head 8 described with reference to FIG.
Is common to the first and third embodiments. However, in the third embodiment, FIG. 34, FIG. 35, FIG.
The point is that the optical unit 322 shown in FIGS. 77, 78, 79, and 80 is used instead of the optical unit 222 shown in FIG. 40. In the third embodiment, the objective lens 43 of the optical head 8 is not limited to the numerical aperture described in the first embodiment. Of course, by limiting to the numerical aperture described in the first embodiment, a further synergistic effect can be obtained together with the invention of the third embodiment.
Furthermore, in the third embodiment, it is assumed that the fluorescent disk described with reference to FIG. 76 is employed instead of the fluorescent optical disk described with reference to FIG.

Here, with reference to FIG. 76, a description will be given of a fluorescent disk which is an object of the third embodiment.

FIG. 76 is a sectional view showing a schematic structure of a fluorescent optical disk. The fluorescent optical disk, that is, the optical disk D, includes three substrates 305, 306, and 307. Further, each substrate is composed of three transparent substrates 303a, 303b, and 303c that function as substantially transparent bodies for primary excitation light and secondary excitation light, and a phosphor layer described later. The thickness of each substrate is 0.2 [mm], and the substrates are bonded to each other by, for example, spin coating of an ultraviolet curable resin. After being cured, the ultraviolet curable resin forms bonding layers 302a and 302b which substantially act as transparent bodies for primary excitation light and secondary excitation light. The transmittance of the bonding layers 302a and 302b is, for example, 95% or more, and the thickness is 0.050 [mm]. Substrate 3
The phosphor 301a is applied to one surface of the optical disk 05, that is, the surface opposite to the optical disk surface on which the light beam is incident, to form a first recording layer. Phosphors 301b and 301c are applied to both surfaces of the substrate 306 to form a second recording layer and a third recording layer, respectively. further,
One surface of the substrate 307, that is, the surface on the side where the light beam is incident, is coated with the phosphor 301d to form a fourth recording layer. Reference numeral 304 in FIG. 76 denotes an electron capture center formed in each recording layer after the primary excitation light is irradiated. Actually, like the CD, predetermined information is recorded in the manufacturing process of the optical disk, and the recorded information is marketed as a product. Specific examples of the phosphor include RbBr: Tl. This uses ultraviolet light as primary excitation light, and the wavelength of secondary excitation light used for information reproduction is 650 [n].
m], and at this time, light emission with a wavelength of 360 [nm] is observed. In order to make use of the characteristics of the stimulated emission system of the fluorescent optical disk and to realize substantial densification, it is necessary to form a multilayer structure in which the number of stacked phosphor substrates is increased.

However, if there is only one objective lens for supplying a light spot converged to the diffraction limit corresponding to such an optical disk having a multilayer structure, serious inconveniences as described below will occur. Occurs. In general, in the design of an objective lens, a method is used in which the thickness of a transparent substrate through which convergent light is transmitted during actual use is designed to be fixed to a certain value, or is fixed to a value within a certain limited range. Is taken. Therefore, if a condensed spot is formed through a transparent substrate having a thickness exceeding this range during actual use, large aberrations, particularly spherical aberrations, occur.

Meanwhile, in the case of a phosphor optical disk aiming at further higher density, the number of layers is considered to be substantially four or more, and the thickness of each substrate is set to 0. 0 due to demands for mass production at low cost and technical restrictions. It is difficult to reduce the thickness to about 1 [mm] or less. Also, considering the current objective lens design and manufacturing capabilities, and aiming for higher density by reducing the diameter of the focused spot,
It is desired that the numerical aperture of the objective lens be 0.55 or more. However, under the above-described conditions, a single objective lens as in the related art is expected to generate large aberrations, particularly spherical aberrations, and it is very difficult to accurately reproduce information on all recording layers. In other words, no matter how the objective lens is designed, it is not possible to provide a good condensing spot with little aberration for all recording layers. For example, when the objective lens is designed so as to be suitable for reproducing the information of the first recording layer, when reproducing the information of the third recording layer and the fourth recording layer, the effective substrate thickness is the same as that of the first recording layer. Is significantly different, a large aberration occurs in the condensed spot, and the reproduction accuracy is reduced. More specifically, since the spherical aberration lowers the central peak intensity of the condensed spot, if the output of the light source remains constant when the spherical aberration occurs, the intensity of the reflected light decreases, and information reading error or the like occurs.

On the other hand, in the third embodiment, according to the recording layer to be reproduced, the collimated light beam supplied to the objective lens is subjected to the aperture restriction described later to lower the substantial numerical aperture of the objective lens. Since the measures are taken, the occurrence of spherical aberration due to the difference in the thickness of the transparent substrate is suppressed to a low level, and a high-quality reproduced signal can always be obtained.

The third embodiment will be described in detail with reference to FIGS. 77 to 83 with the above-described principle configuration in mind.

FIGS. 77 and 78 are cross-sectional views showing a schematic configuration of the optical section 322. In the third embodiment, instead of the optical unit 22 shown in FIG. 2 and the optical unit 222 shown in FIGS. 34 and 35, an optical unit 222 shown in FIGS. 77 and 78 is employed.

As shown in FIGS. 77 and 78, the optical unit 3
22, a semiconductor laser 331, a collimator lens 33
2, beam splitter 333, quarter-wave plate 334, converging lens 335, concave lens 336, cylindrical lens 337, beam splitter 338, photodetector 339,
And a photodetector 340. Further, the optical unit 322 is provided with an aperture limiting unit 370. The aperture limiting means 370 is provided with an aperture plate 364 and a switching means 360. Switching means 360
Is constituted by a housing 361 and a shaft 362.

The feature of the third embodiment is that the collimator lens 3
The point is that an aperture limiting element for limiting the aperture of the light beam collimated in 32 as necessary and a mechanism for moving the aperture limiting element are added. Furthermore, the feature of the third embodiment is that the beam splitter 3
33 has a wavelength dependency.

First, the wavelength dependence of the beam splitter 333 will be described. As described above, the wavelength of the secondary excitation light is 650 [nm], which is equal to the wavelength of the semiconductor laser 331 as the light source. Semiconductor laser 331
The emitted laser light R is converted into parallel light by a collimator lens 332, and then is converted into a beam splitter 333.
Must be transmitted through the beam splitter 33
The 45 ° plane of No. 3 has a film characteristic of having a high transmittance (for example, 90% or more) with respect to light having a center wavelength of 650 [nm] on the transmission side. On the other hand, with respect to the reflected light from the optical disk, it is necessary to guide the reflected light to the photodetector side.
[Nm] has such film characteristics that almost all light is reflected. Such a film characteristic can be realized by a dielectric multilayer film, and has been practically used as a so-called dichroic filter.

Next, the aperture limiting element and the mechanism for driving the aperture limiting element will be described. In the third embodiment, when reproducing information recorded on the first recording layer or the second recording layer, the aperture plate 364 is not inserted into the optical path. Objective lens 4
3 is a depth of 0.2 from the optical disk surface to the first recording layer.
0.225 [mm] which is an average value of [mm] and a depth of 0.25 [mm] from the optical disk surface to the second recording layer.
Is designed as an appropriate transparent substrate thickness.

On the other hand, when reproducing information recorded on the third recording layer or the fourth recording layer, the aperture plate 364 is inserted into the optical path. First, the opening limiting means 370 will be described. As shown in FIGS. 81 and 82, the opening limiting means 370 includes an opening plate 364 having a circular opening 363,
It comprises switching means 360 for driving this. Further, the switching means 360 includes a housing 361 and a shaft 362, the housing 361 is fixed to the base of the optical unit 22, and one end of the shaft 362 is connected to the opening plate 36.
4 is bonded by a method such as adhesion. As shown in FIGS. 77 to 80, this switching means 370 can be either in a state where the aperture plate 364 is inserted in the optical path of the parallel light beam going out of the beam splitter and going to the objective lens, or in a state where it is not inserted. That state is realized.

The aperture plate 364 is made of, for example, a molded product of ABS resin, and its surface is subjected to a process for preventing reflection. The opening diameter is about 2.47 mm, and the opening plate 364 is provided.
Since the light beam diameter before reaching is approximately 4.0 mm,
The beam diameter is converted to about 62%. When the light beam thus reduced in diameter reaches the objective lens 43, the numerical aperture of 0.60 when the aperture is not limited is increased.
The numerical aperture after limiting the aperture is effectively 0.37.

The switching means 360 performs the switching operation of the position of the shaft 362, and eventually the opening plate 364, as follows. First, when the signal processing unit 10 determines the necessity of switching by the switching unit 370, the signal is transmitted to the control unit 4 so that the control unit 4 sends a control signal having a predetermined polarity and a current to the solenoid coil 365. The control unit 4 receiving such a control signal from the signal processing unit 10
Supplies a current having a predetermined polarity and magnitude to the solenoid coil 365. Then, an interaction between the current flowing through the solenoid coil 365 and the magnetic field generated by the magnet 366 generates an electromagnetic driving force on the shaft 362 around which the solenoid coil 365 is wound, and the shaft 362 moves in the longitudinal direction. That is, as shown in FIGS. 77 to 80, when the shaft 362 is located inside the housing portion 361, the shaft 362 can be made to protrude from the housing portion 361 by a current having a predetermined polarity and magnitude. Thus, the aperture plate 364 can be inserted into the optical path. Conversely, when the shaft 362 is at a position protruding from the housing portion 361, the shaft 362 can be pushed into the housing portion 361 by a current having a predetermined polarity and magnitude.
4 can be eliminated.

Next, the relationship between the numerical aperture and the optical characteristics of the optical head in the optical disk device will be described. Until now CD
The thickness of the substrate of an optical disk widely used for (compact disk) and the like is 1.2 mm, and a general thickness tolerance at this time is about 0.05 mm. The thickness error of the substrate causes so-called spherical aberration in the condensed spot, and the amount of the generation is described in, for example, p62 of the document "Optical Disk Technology" (Onoe et al., Radio Technology Company, 1989). {(n ² -1) / (8n ³ )} × (NA) ⁴ × △ d (1) where n: refractive index of the substrate NA; numerical aperture of the objective lens Δd; thickness error of the substrate it can. As can be seen from the above equation, the spherical aberration increases in proportion to the thickness error of the substrate. In other words, if the objective lens is used in a state where it deviates greatly from the thickness of the substrate that is appropriate for the objective lens, a large spherical aberration will occur in the condensed spot, and the optical quality of the spot will be significantly reduced. Become.

By the way, in an optical disk system which has been used in many products so far, the NA is about 0.55 or less, and the refractive index n is a polycarbonate resin substrate which has been used and is widely used. 1.5740. Therefore, even when high-density support is achieved, no special measures need to be taken unnecessarily on the device side.
Consider the relationship between the thickness error Δd of the disk substrate and the numerical aperture NA of the objective lens in order to secure performance equal to or higher than the conventional one. This becomes extremely important from the viewpoint of not increasing the manufacturing cost, the manufacturing difficulty, and reducing the reliability.

The depth from the optical disk surface to the third recording layer is 0.45 [mm], and the depth from the optical disk surface to the fourth recording layer is 0.5 [mm]. 475 [mm]. That is, the value is 0.25 [mm] far from the substrate thickness as a design value of the objective lens. By the way, as can be seen from the equation (1), the spherical aberration depends on the numerical aperture NA, and specifically, increases in proportion to the fourth power of NA. In other words, N
By reducing the value of A, spherical aberration can be reduced. This embodiment focuses on this. As the material of the substrate, the same material as that used in the related art is used. Therefore, if the refractive index is the same, the spherical aberration does not increase.
The condition of A is expressed as (NA) ⁴ × 0.25 ≦ (0.55) ⁴ × 0.05 (2) using the equation (1). Thus, the following relationship is obtained: NA ≦ 0.37 (3) The basis for setting the numerical aperture after conversion by the aperture limiting means to 0.37 in the third embodiment is as described above.

By the way, from the viewpoint of simply reducing the spherical aberration by reducing the numerical aperture, if the numerical aperture is set to 0.37, all the components from the first recording layer to the second recording layer can be used without using the aperture limiting means. It can be reproduced without any problem.
However, in this case, there is a disadvantage that the recording capacity as a whole does not increase so much. This will be described below. In general, when the recording capacity of an optical disc is roughly estimated, it is proportional to the square of the numerical aperture. The ratio of the two numerical apertures is 0.60 / 0.37 = 1.62, and the square is 2.6. Now, if the recording capacity per layer is estimated to be 1 based on 0.37, which is the numerical aperture during reproduction of the third recording layer and the fourth recording layer, the difference in numerical aperture during reproduction is The capacity of both the first recording layer and the second recording layer is estimated to be 2.6. Therefore, the recording capacity of the entire four layers according to the third embodiment is 7.2, while the total capacity when all are reproduced by an objective lens having a numerical aperture of 0.37 is 4. That is, by adopting the method of the third embodiment,
The recording capacity increases by about 80%.

As described above, the transmittance of the bonding layers 302a and 302b is, for example, 95% or more, and the center of the electron capture is irradiated with light of a predetermined wavelength having high energy such as near the focal point of the converging spot. Unless the light emission is performed, no stimulated emission occurs, so that signal leakage from recording layers other than the recording layer being reproduced, that is, so-called crosstalk does not occur.

The third embodiment is directed to an optical head having two operation modes for determining whether or not an aperture limiting means having a single numerical aperture is inserted into an optical path. However, the present invention is not limited to this. Instead, it is possible to set several types of apertures in the aperture limiting means without changing the principle configuration. Further, the number of layers is not limited to four, and the recording capacity can be increased by further increasing the number.

Here, the effects of the third embodiment will be summarized. As described above, the optical disc device according to Embodiment 3 of the present invention provides a multi-layer fluorescent optical disc that provides a photostimulated emission effect by supplying a light beam of a predetermined wavelength, according to the recording layer to be reproduced. The numerical aperture can be selected by changing the effective diameter of the light beam supplied to the objective lens. Thus, stable information reproduction of multilayer recording can be performed with a single optical head, and high-density recording can be realized.

Next, a fourth embodiment will be described with reference to FIGS.

The optical head 8 described with reference to FIG.
Is common to the first and fourth embodiments. However, in the fourth embodiment, the point is that an actuator 140 shown in FIG. 84 is employed instead of the actuator 24 shown in FIG. The optical unit 22 shown in FIG. 3 is common to the first and fourth embodiments. Furthermore, the fluorescent optical disk described with reference to FIG.
The third embodiment and the fourth embodiment are common.

In the fourth embodiment, by selecting an objective lens according to the recording layer to be reproduced, the occurrence of spherical aberration due to the difference in the thickness of the transparent substrate can be suppressed to a low level, and a high-quality reproduction signal can always be obtained. is there.

Embodiment 4 will be described with reference to FIGS. 84 to 86. A feature of the fourth embodiment is that there are a plurality of objective lenses. Furthermore, a feature of the fourth embodiment is that the beam splitter 33 has wavelength dependency. Since the wavelength dependence of the beam splitter 33 has already been described, it is omitted here.

Referring to FIGS. 84 to 86, an actuator 140 employed in place of the actuator 24 shown in FIG. 2 will be described.

A first objective lens 143a and a second objective lens 143b are mounted on the lens holder 149. The lens holder 149 has a rotary bearing 170,
The lens holder 149 is supported so as to be rotatable around the shaft 145 by engaging with the shaft 145 and to be movable in the axial direction of the shaft 145. The shaft 145 protrudes from the actuator base 146. The actuator base 146 has a yoke 14
7 is formed, and the yoke 147 has a magnet 148.
a and the magnet 148b are arranged at predetermined positions. Here, the magnet 148a is magnetized so that the N pole and the S pole are magnetized in such a manner that the magnet 148a is divided into two parts by a plane orthogonal to the optical axis of the objective lens. The N and S poles are magnetized in a divided form. When the first objective lens 143a is selected, a driving force for moving the lens holder 149 in the focus direction is generated due to an electromagnetic field interaction between a current flowing through the first coil 144a and a magnetic field generated by the magnet 148a. However, when the second objective lens 143b is selected, the second coil 144b
Of the lens holder 149 in the focusing direction is generated by an electromagnetic field interaction between a current flowing through the lens holder 148 and a magnetic field generated by the magnet 148b. Also, the first objective lens 1
When 43a is selected, the electromagnetic field interaction between the magnetic field generated by the magnet 148b and the current flowing through the second coil 144b generates a rotational force that rotates the lens holder 149 around the axis, and the second rotational force is generated. When the objective lens 143b is selected, an electromagnetic field interaction between a magnetic field generated by the magnet 148a and a current flowing through the first coil 144a generates a rotational force that rotates the lens holder 149 around an axis. Based on this rotational force, tracking control is performed, and the lens holder 149 is rotated to perform a switching operation between the first objective lens 143a and the second objective lens 143b. As can be seen from the above description, when the first objective lens 143a is selected, the first coil 14
4a is connected to a focus control circuit, and when the second objective lens 143b is selected, the first coil 144a
a is connected to the tracking control circuit. Conversely, the second coil 144b is connected to the tracking control circuit when the first objective lens 143a is selected, and is connected to the focus control circuit when the second objective lens 143b is selected. You. The switching element used for switching the connection is arranged at least upstream of the power amplifier to prevent breakage of the circuit during the switching operation.

Next, the lens holder 1 immediately after the switching operation
49 will be described. Since the lens holder 149 contains a magnetic material, a magnetic attraction force acts between the lens holder 149 and the magnetic field before the switching operation, so that the lens holder 149 is at the neutral position in the focus direction and the neutral position in the tracking direction. When the lenses are switched, the position of the first objective lens 143a coincides with the new neutral position of the second objective lens 143b due to the effect of the magnetic attraction. In this way, even when the two objective lenses are switched, the lens holder 149 is almost stable and finally settles at a predetermined position.

The numerical apertures of the two objective lenses 143a and 143b are both 0.60. Of the two objective lenses, the first objective lens 143a is for reproducing information recorded on the first recording layer and the second recording layer. It is designed as 0.225 [mm] which is an average value of a depth 0.2 [mm] from the surface to the first recording layer and a depth 0.25 [mm] from the optical disk surface to the second recording layer. ing.
On the other hand, the second objective lens 143b is for reproducing information recorded on the third recording layer and the fourth recording layer,
More specifically, the appropriate thickness of the transparent substrate is a depth of 0.45 [mm] from the optical disk surface to the third recording layer and a depth of 0.5 [mm] from the optical disk surface to the fourth recording layer. It is designed as an average value of 0.475 [mm]. When reproducing the information recorded on the first recording layer and the second recording layer, the light beam converged by the first objective lens 143a is shifted from the original proper transparent substrate thickness of the first objective lens 143a by 0%. Although the light is transmitted through a transparent substrate having a thickness shifted by 0.025 [mm], this is a thickness error within a sufficiently allowable range and has substantially no adverse effect. Similarly, when reproducing the information recorded on the third recording layer and the fourth recording layer, the light beam converged by the second objective lens 143b is applied to the proper transparent substrate of the second objective lens 143b. The light passes through the transparent substrate having a thickness shifted from the thickness by 0.025 [mm], but this is a thickness error within a sufficiently allowable range, and has substantially no adverse effect. As described above, since the objective lens is selected according to the recording layer to be reproduced, the occurrence of spherical aberration due to the difference in the thickness of the transparent substrate is suppressed to a low level, and a high-quality reproduced signal can always be obtained.

As described above, the transmittance of the bonding layers 302a and 302b is, for example, 95% or more, and the electron capture center is irradiated with light of a predetermined wavelength having high energy such as near the focal point of the converging spot. Unless the light emission is performed, no stimulated emission occurs, so that signal leakage from recording layers other than the recording layer being reproduced, that is, so-called crosstalk does not occur.

In the above embodiment, the configuration of an optical head having two objective lenses has been described. However, the present invention is not limited to this, and the number of objective lenses can be increased without changing the principle configuration. It can be increased. Similarly, the number of layers can be increased.

Here, the effects of the fourth embodiment will be summarized. As described above, the optical disc device according to the fourth embodiment provides a plurality of multi-layer fluorescent optical discs that provide a photostimulated emission effect by supplying a light beam of a predetermined wavelength and that reproduce information from different recording layers. An objective lens can be appropriately selected and used. This enables stable information reproduction of multilayer recording with a single optical head,
High density recording can be realized.

[0110]

According to the present invention, it is possible to provide an optical disk apparatus that can contribute to higher density recording.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an optical disk device common to Embodiments 1 to 4 of the present invention.

FIG. 2 is a diagram showing a schematic configuration of an optical head of the optical disk device shown in FIG. 1, and a diagram for explaining features of the objective lens according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a schematic configuration of an optical unit according to the first embodiment of the present invention.

4 is a diagram showing a cross section of an optical disk (a fluorescent optical disk to be processed in the first and second embodiments) to be processed by the optical disk apparatus shown in FIG. 1;

FIG. 5 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.60 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.02 [mm].

FIG. 6 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.60 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.18 [mm].

FIG. 7 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.60 and the error in the thickness of the substrate of the fluorescent optical disk is about ± 0.18 [mm];
It is a figure showing signs that it was corrected so that center intensity might be set to 1.0.

FIG. 8 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.60 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.22 [mm].

FIG. 9 is a diagram showing the intensity distribution of the cross section of the converged spot when the numerical aperture of the objective lens is 0.60 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.22 [mm];
It is a figure showing signs that it was corrected so that center intensity might be set to 1.0.

FIG. 10 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.55 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.02 [mm].

FIG. 11 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.55 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.18 [mm].

FIG. 12 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.55 and the error in the thickness of the substrate of the fluorescent optical disk is about ± 0.18 [mm]; It is a figure showing signs that it was corrected so that center intensity might be set to 1.0.

FIG. 13 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.55 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.22 [mm].

FIG. 14 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.55 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.22 [mm]; It is a figure showing signs that it was corrected so that center intensity might be set to 1.0.

FIG. 15 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.50 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.02 [mm].

FIG. 16 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.50 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.18 [mm].

FIG. 17 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.50 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.18 [mm]; It is a figure showing signs that it was corrected so that center intensity might be set to 1.0.

FIG. 18 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.50 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.22 [mm].

FIG. 19 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.50 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.22 [mm]; It is a figure showing signs that it was corrected so that center intensity might be set to 1.0.

FIG. 20 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.45 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.02 [mm].

FIG. 21 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.45 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.18 [mm].

FIG. 22 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.45 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.18 [mm]; It is a figure showing signs that it was corrected so that center intensity might be set to 1.0.

FIG. 23 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.45 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.22 [mm].

FIG. 24 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.45 and the error in the thickness of the substrate of the fluorescent optical disk is about ± 0.22 [mm]; It is a figure showing signs that it was corrected so that center intensity might be set to 1.0.

FIG. 25 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.40 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.02 [mm].

FIG. 26 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.40 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.18 [mm].

FIG. 27 is a diagram showing the intensity distribution of the cross section of the converged spot when the numerical aperture of the objective lens is 0.40 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.18 [mm]; It is a figure showing signs that it was corrected so that center intensity might be set to 1.0.

FIG. 28 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.40 and the thickness error of the substrate of the fluorescent optical disk is about ± 0.22 [mm].

FIG. 29 is a diagram showing the intensity distribution of the cross section of the converging spot when the numerical aperture of the objective lens is 0.40 and the error in the thickness of the substrate of the fluorescent optical disk is about ± 0.22 [mm]; It is a figure showing signs that it was corrected so that center intensity might be set to 1.0.

FIG. 30 is a diagram showing the relationship between the numerical aperture and the side lobe intensity.

FIG. 31 is a diagram showing a relationship between a numerical aperture and a focused spot diameter.

FIG. 32 is a diagram illustrating a relationship between a numerical aperture and a relative value of a focused spot diameter.

FIG. 33 is a diagram showing the relationship between the numerical aperture and the relative value of the square of the focused spot diameter.

FIG. 34 is a cross-sectional view illustrating a schematic configuration of an optical unit according to Embodiment 2 of the present invention.

35 is a cross-sectional view illustrating a schematic configuration of an optical unit according to Embodiment 2 of the present invention, and is a diagram illustrating a state in which a convex lens holder is moved by a switching unit provided in the optical unit, in conjunction with FIG. 34; .

FIG. 36 is a diagram showing a state in which a convex lens is mounted on a convex lens holder provided in an optical unit according to Embodiment 2 of the present invention.

FIG. 37 is a cross-sectional view showing an internal structure of a switching unit provided in the optical unit according to Embodiment 2 of the present invention.

FIG. 38 is a diagram illustrating a signal processing unit according to the second embodiment of the present invention;
FIG. 3 is a block diagram illustrating an electrical connection of a control unit and a switching unit.

FIG. 39 is an enlarged sectional view of a part of an optical unit according to Embodiment 2 of the present invention.

40 is an enlarged cross-sectional view of a part of an optical unit according to Embodiment 2 of the present invention, and is a diagram showing, together with FIG. 39, how a convex lens holder is moved by switching means provided in the optical unit. .

FIG. 41 shows lateral aberrations of spherical aberration of a focused spot when a light beam is focused on a fluorescent optical disk having a substrate thickness of 1.20 [mm] without inserting a convex lens into an optical path. FIG.

FIG. 42 shows the longitudinal aberration of spherical aberration of a focused spot when a light beam is focused on a fluorescent optical disk having a substrate thickness of 1.20 [mm] without inserting a convex lens into the optical path. FIG.

FIG. 43 is a diagram showing distortion of a converging spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 1.20 [mm] without inserting a convex lens into an optical path.

FIG. 44 is a cross-section showing a point image intensity distribution of a condensed spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 1.20 [mm] without inserting a convex lens into the optical path. FIG.

FIG. 45 is a diagram showing an arrangement of an optical system when condensing a light beam on a fluorescent optical disk having a substrate thickness of 1.20 [mm] without inserting a convex lens into an optical path.

FIG. 46 shows the lateral aberration of the spherical aberration of the focused spot when a light beam is focused on a fluorescent optical disk having a substrate thickness of 1.22 [mm] without inserting a convex lens into the optical path. FIG.

FIG. 47 shows the longitudinal aberration of spherical aberration of a converged spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 1.22 [mm] without inserting a convex lens into the optical path. FIG.

FIG. 48 is a diagram showing distortion of a converging spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 1.22 [mm] without inserting a convex lens into an optical path.

FIG. 49 is a cross section showing a point image intensity distribution of a converged spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 1.22 [mm] without inserting a convex lens into the optical path. FIG.

FIG. 50 is a diagram showing an arrangement of an optical system when a light beam is focused on a fluorescent optical disk having a substrate thickness of 1.22 [mm] without inserting a convex lens into an optical path.

FIG. 51 shows lateral aberrations of spherical aberration of a focused spot when a light beam is focused on a fluorescent optical disk having a substrate thickness of 1.18 [mm] without inserting a convex lens into the optical path. FIG.

FIG. 52 shows the longitudinal aberration of the spherical aberration of the focused spot when a light beam is focused on a fluorescent optical disk having a substrate thickness of 1.18 [mm] without inserting a convex lens into the optical path. FIG.

FIG. 53 is a diagram showing distortion of a converging spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 1.18 [mm] without inserting a convex lens into an optical path.

FIG. 54 is a cross-sectional view showing a point image intensity distribution of a converging spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 1.18 [mm] without inserting a convex lens into the optical path. FIG.

FIG. 55 is a diagram showing an arrangement of an optical system when condensing a light beam on a fluorescent optical disk having a substrate thickness of 1.18 [mm] without inserting a convex lens into an optical path.

FIG. 56 shows lateral aberrations of spherical aberration of a converging spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 1.02 [mm] without inserting a convex lens into an optical path. FIG.

FIG. 57 shows longitudinal aberrations of spherical aberration of a focused spot when a light beam is focused on a fluorescent optical disk having a substrate thickness of 1.02 [mm] without inserting a convex lens into the optical path. FIG.

FIG. 58 is a diagram showing distortion of a converging spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 1.02 [mm] without inserting a convex lens into an optical path.

FIG. 59 is a cross-section showing a point image intensity distribution of a condensed spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 1.02 [mm] without inserting a convex lens into an optical path. FIG.

FIG. 60 is a diagram showing an arrangement of an optical system when a light beam is focused on a fluorescent optical disk having a substrate thickness of 1.02 [mm] without inserting a convex lens into an optical path.

FIG. 61 shows lateral aberrations of spherical aberration of a focused spot when a light beam is focused on a fluorescent optical disk having a substrate thickness of 0.98 [mm] without inserting a convex lens into the optical path. FIG.

FIG. 62 shows the longitudinal aberration of spherical aberration of a converged spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 0.98 [mm] without inserting a convex lens into the optical path. FIG.

FIG. 63 is a diagram showing a distortion of a converged spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 0.98 [mm] without inserting a convex lens into an optical path.

FIG. 64 is a cross-sectional view showing a point image intensity distribution of a focused spot when a light beam is focused on a fluorescent optical disk having a substrate thickness of 0.98 [mm] without inserting a convex lens into the optical path. FIG.

FIG. 65 is a diagram showing an arrangement of an optical system when condensing a light beam on a fluorescent optical disk having a substrate thickness of 0.98 [mm] without inserting a convex lens into an optical path.

FIG. 66 shows the lateral aberration of the spherical aberration of the focused spot when the light beam is focused on a fluorescent optical disk having a substrate thickness of 1.02 [mm] with the convex lens inserted in the optical path. FIG.

FIG. 67 shows longitudinal aberration of spherical aberration of a converged spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 1.02 [mm] in a state where a convex lens is inserted in an optical path. FIG.

FIG. 68 is a diagram illustrating a distortion of a converged spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 1.02 [mm] with a convex lens inserted in an optical path.

FIG. 69 is a cross-section showing a point image intensity distribution of a condensed spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 1.02 [mm] in a state where a convex lens is inserted in an optical path. FIG.

FIG. 70 is a diagram showing an arrangement of an optical system when condensing a light beam on a fluorescent optical disk having a substrate thickness of 1.02 [mm] with a convex lens inserted in an optical path.

FIG. 71 shows lateral aberrations of spherical aberration of a converged spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 0.98 [mm] in a state where a convex lens is inserted in an optical path. FIG.

FIG. 72 shows the longitudinal aberration of the spherical aberration of the focused spot when a light beam is focused on a fluorescent optical disk having a substrate thickness of 0.98 [mm] with the convex lens inserted in the optical path. FIG.

FIG. 73 is a diagram showing distortion of a converging spot when a light beam is condensed on a fluorescent optical disk having a substrate thickness of 0.98 [mm] with a convex lens inserted in the optical path.

FIG. 74 is a cross section showing a point image intensity distribution of a focused spot when a light beam is focused on a fluorescent optical disk having a substrate thickness of 0.98 [mm] in a state where a convex lens is inserted in an optical path. FIG.

FIG. 75 is a diagram showing an arrangement of an optical system when condensing a light beam on a fluorescent optical disk having a substrate thickness of 0.98 [mm] with a convex lens inserted in the optical path.

76 is a diagram showing a cross section of an optical disk (a fluorescent optical disk to be processed in the third and fourth embodiments) to be processed by the optical disk device shown in FIG. 1;

FIG. 77 is a cross-sectional view illustrating a schematic configuration of an optical unit according to Embodiment 3 of the present invention.

FIG. 78 is a cross-sectional view showing a schematic configuration of an optical unit according to Embodiment 3 of the present invention, and is a diagram showing a state in which a convex lens holder is moved by switching means provided in the optical unit together with FIG. 77. .

FIG. 79 is an enlarged cross-sectional view of a part of the optical unit according to Embodiment 3 of the present invention.

FIG. 80 is an enlarged cross-sectional view of a part of an optical unit according to Embodiment 3 of the present invention, and is a diagram showing, together with FIG. 79, how a convex lens holder is moved by switching means provided in the optical unit. .

FIG. 81 is a diagram showing a schematic configuration of an aperture plate provided in an optical unit according to Embodiment 3 of the present invention.

FIG. 82 is a cross-sectional view showing an internal structure of a switching unit provided in an optical unit according to Embodiment 3 of the present invention.

FIG. 83 is a signal processing unit according to Embodiment 3 of the present invention;
FIG. 3 is a block diagram illustrating an electrical connection of a control unit and a switching unit.

FIG. 84 is a view showing a schematic configuration of an actuator according to Embodiment 4 of the present invention.

85 is a diagram showing a schematic configuration of an actuator according to Embodiment 4 of the present invention, similarly to FIG. 84.

FIG. 86 is a diagram showing an internal configuration of an actuator according to Embodiment 4 of the present invention.

[Explanation of symbols]

 D: optical disk (fluorescent optical disk) 1: optical disk device 4: control unit 6: motor 8: optical head 10: control unit 11: external device

Claims (4)

[Claims] 1. An optical disc apparatus for reproducing optical disc data recorded on a fluorescent optical disc, comprising: a light source; and an objective lens having a numerical aperture of 0.45 to 0.55 for condensing a light beam supplied from the light source. Control means for moving a beam spot of the light beam condensed by the objective lens in a radial direction of the optical disc and in a direction perpendicular to the surface of the optical disc so that the beam spot reaches a predetermined position on the optical disc; Reproducing means for detecting reflected light from the optical disc obtained when the beam spot reaches a predetermined position on the optical disc under the control of the control means, and reproducing the optical disc data reflected on the reflected light; An optical disc device, comprising: 2. An optical disk device for reproducing optical disk data recorded on a fluorescent optical disk, wherein a light source and a light beam supplied from the light source are subjected to processing for imparting divergence or convergence. Processing means; an objective lens for condensing the light beam processed by the processing means; and a beam spot of the light beam condensed by the objective lens in a radial direction of the optical disc and in a direction perpendicular to the surface of the optical disc. Moving the laser beam so that the beam spot reaches a predetermined position on the optical disc; and controlling the control means to detect reflected light from the optical disc obtained when the beam spot reaches a predetermined position on the optical disc. Reproducing means for reproducing the optical disk data reflected on the reflected light. Disk device. 3. An optical disk device for reproducing optical disk data recorded on a fluorescent optical disk, comprising: a light source; and an aperture for performing aperture restriction processing for restricting aperture of a light beam supplied from the light source. Restriction processing means; an objective lens for condensing the light beam subjected to the aperture restriction processing by the aperture restriction processing means; and an objective lens condensed by the objective lens in a radial direction of the optical disk and in a direction perpendicular to the surface of the optical disk. Control means for moving the beam spot of the light beam to reach the predetermined position on the optical disk; and controlling the control means to control the beam spot from the optical disk obtained when the beam spot reaches the predetermined position on the optical disk. Reproducing means for detecting reflected light of the optical disk and reproducing the optical disk data reflected on the reflected light; Optical disk apparatus characterized by comprising. 4. An optical disc apparatus for reproducing optical disc data recorded on a fluorescent optical disc, comprising: a light source; a plurality of objective lenses for condensing a light beam supplied from the light source; And selecting means for selecting a predetermined objective lens, and moving a beam spot of the light beam condensed by the objective lens selected by the selecting means in a radial direction of the optical disk and in a direction perpendicular to the surface of the optical disk. Control means for causing the beam spot to reach a predetermined position on the optical disc, and control of the control means to detect reflected light from the optical disc obtained when the beam spot reaches a predetermined position on the optical disc, Reproducing means for reproducing the optical disk data reflected on the reflected light. Disk apparatus.