JP2002056562A - Optical pickup and optical information recording/ reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup and optical information recording/ reproducing device in which minute mark recording is possible by a super resolution spot and in which no signal deterioration is caused due to increase in a side lobe at the time of reproduction. SOLUTION: A super resolution spot is formed on the recording layer of an optical disk 5, by using a variable phase filter 3 that has three areas 3a-3c capable of producing phase difference in level in the radial direction, and by imparting π phase difference in level between the center area 3b and the areas 3a, 3c on both sides at the time of recording. In the case of reproduction, the phase difference in level is made zero in the areas 3a-3c of the variable phase filter 3, thereby forming an optical spot of a normal diffraction limit causing less side lobe. The variable phase filter 3 can be composed of a homogeneous orientation liquid crystal element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information processing apparatus and an optical information recording / reproducing apparatus to which a coherent light source is applied, and more particularly to a crosstalk removing function for removing a crosstalk component from an adjacent track and a size smaller than a diffraction limit. And a high-density optical disk recording / reproducing apparatus for obtaining a super-resolution light-converged spot.

[0002]

2. Description of the Related Art In recent years, the practical use of digital versatile discs (hereinafter abbreviated as DVD) has greatly expanded the storage capacity of optical discs, and has made it possible to record high-quality, long-time moving picture information. There are also signs of commercialization of high-definition video broadcasting, and research and development of large-capacity storage devices are being actively pursued. Optical discs such as compact discs (hereinafter abbreviated as CDs) and DVDs are widely used as external storage devices for computers. However, since the performance of computers has rapidly increased, the fields of information processing and information communication have been increasing. Also, there is a strong demand for higher density optical disks. In particular, digital video cameras and digital still cameras have begun to spread along with the advancement of computers, and the opportunities to handle large-capacity audiovisual data have increased. It has taken on an important position.

In order to increase the capacity of an optical disk, a small mark is recorded on the optical disk or information is reproduced from smaller pits. The mark size or pit size depends on the light source wavelength of the optical pickup for reading information. It is limited by the light spot size determined by the numerical aperture of the optical lens. When the pit size in the linear direction on the spirally arranged track is reduced below the limit, a sufficient signal amplitude cannot be obtained, and when the interval between the tracks is reduced below the limit, adjacent tracks are recorded. Problems such as adjacent erasure for erasing a mark on a track and crosstalk in which signals from adjacent tracks interfere with each other during reproduction occur, thereby hindering accurate signal recording and reproduction.

A super-resolution technique has been proposed as a technique for achieving high density beyond the limit of the light spot size. For example, in the conventional optical pickup shown in FIG. 13A, an annular phase filter 3 ′ (FIG. 13C)
Light spot 3 having a size equal to or smaller than the diffraction limit.
Get 0 '.

[0005]

However, in this light spot 30 ', the spot width of the main lobe is smaller than that of a normal light spot. However, as shown in FIG. Becomes larger. Therefore, when a conventional optical pickup as shown in FIG. 13A is used for reproduction, pits before and after a pit illuminated by the main lobe and tracks adjacent to the track illuminated by the main lobe are illuminated by the side lobe. The reflected light mixes with the reflected light of the main lobe and is detected by the photodetector 7 '. For this reason, there has been a problem that the noise signal is increased and the signal quality is reduced.

The optical pickup according to the present invention solves the signal degradation due to the side lobe, which has been a problem in the above-described super-resolution optical pickup.

[0007]

In order to solve the above-mentioned problems, an optical pickup according to the present invention comprises: a coherent light source;
A condensing optical system for condensing light from the coherent light source on the information carrier, and a light spot size on the information carrier at the time of recording, a light spot size at the time of reproduction, mainly in a direction perpendicular to the information track. And a spot size adjusting means for reducing the size.

Thus, at the time of recording, while a minute mark is recorded by a super-resolution spot, at the time of reproduction, a normal spot having few side lobes can be used.
It is possible to provide an optical pickup that does not cause reproduction signal degradation due to side lobes.

A first configuration of the optical pickup is characterized in that it has a variable phase filter provided between the coherent light source and the condensing optical system and having a variable phase shift amount. The variable phase filter is preferably divided into at least three regions where a phase step can occur in a direction perpendicular to the information tracks of the information carrier.

[0010] A second configuration of the optical pickup is provided between the coherent light source and the condensing optical system,
A variable wavelength plate having a variable amount of birefringence, and an analyzer provided between the variable wavelength plate and the condensing optical system are provided. The tunable wave plate has at least three phases which can cause a phase step in a direction perpendicular to the information tracks of the information carrier.
Preferably, it is divided into two regions.

A third configuration of the optical pickup comprises a variable wavelength plate provided between the coherent light source and the condensing optical system and having a variable phase shift amount, and a first polarization component of light from the coherent light source. A variable polarization phase filter that gives an arbitrary amount of phase shift to only the first polarization component and another second polarization component that separates the reflected light from the information carrier; It has a first photodetector for detecting a first polarization component of the reflected light, and a second photodetector for detecting a second polarization component of the reflected light from the information carrier. Preferably, the tunable polarizing phase filter is divided into at least four regions that can produce a phase step in a direction perpendicular to the information tracks on the information carrier.

In order to solve the above-mentioned problems, a first optical information recording / reproducing apparatus according to the present invention has an optical pickup according to the first configuration, and records information on the information carrier. In the method, a phase step is generated between the regions of the variable phase filter, and when information is reproduced from the information carrier, a phase step is not generated between the regions of the variable phase filter.

Also, a second optical information recording / reproducing apparatus according to the present invention has the optical pickup according to the second configuration, and when recording information on the information carrier, the optical pickup of the variable wavelength plate has When a phase difference is generated between the regions and information is reproduced from the information carrier, no phase difference is generated between the regions of the variable wavelength plate.

Further, a third optical information recording / reproducing apparatus according to the present invention is an optical information recording / reproducing apparatus having the optical pickup according to the third configuration, wherein the variable polarization phase filter is provided in four regions. Divided into four areas,
First in the direction perpendicular to the information tracks of the information carrier,
If information is recorded on the information carrier, the first and fourth areas of the tunable polarizing phase filter, and the second and third areas are assumed to be second, third and fourth areas. In the case of reproducing information from the information carrier without giving a phase shift different from each other, and without giving a phase shift to the variable wavelength plate, the first and second regions of the variable polarization phase filter , And the third and fourth regions are provided with phase shift amounts different from each other by π, and the variable wavelength plate is provided with a phase shift amount to form a half-wave plate.

[0015]

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. Figure 1
FIG. 1A is an explanatory diagram illustrating a schematic configuration of an optical pickup included in an optical information recording / reproducing apparatus according to the present embodiment. FIG. 1B is a graph showing a light intensity distribution of a light spot formed on an optical disk by this optical pickup at the time of recording and at the time of reproduction, respectively. The light intensity distribution is a distribution in a direction perpendicular to the information tracks on the optical disc.

As described above, the super-resolution optical pickup is
There is a problem that signal degradation is caused by side lobes appearing in the focused spot. However, when recording information on an optical disk, heating is involved, so the influence of side lobes is small, and it is useful for high-density optical recording that records smaller marks It is. Taking advantage of this advantage, this optical pickup performs micro mark recording with a super-resolution spot during recording,
At the time of reproduction, a normal spot with few side lobes is used. In super-resolution recording, even if the spot size is reduced in the front-rear direction, the effect of the minute spot is lost due to the generation of side lobes in the front-rear direction. Therefore, the optical pickup of the present embodiment has a configuration in which the spot size is reduced only in the direction perpendicular to the information track.

Hereinafter, the configuration of the optical pickup of this embodiment will be described with reference to FIG. This optical pickup includes a semiconductor laser 1 as a light source, a collimating lens 2, a variable phase filter 3, an objective lens 4, a polarizing beam splitter 6, and a photodetector 7.

The semiconductor laser 1 emits polarized light in a direction parallel to the plane of FIG. The emitted light passes through the variable phase filter 3 after passing through the collimating lens 2. The variable phase filter 3 is divided into three regions 3a, 3b, 3c as shown in FIG. 1C, and the longitudinal direction of these regions is parallel to the scanning direction of the light beam on the optical disk 5. As described above, it is disposed between the collimating lens 2 and the polarizing beam splitter 6.

When information is recorded on the optical disk 5, the variable phase filter 3 gives a phase difference of π between the light passing through the central region 3b and the light passing through the regions 3a and 3c on both sides. The light beam having the phase difference has a light intensity distribution as shown in the graph on the left side of FIG. 1B, and on the optical disk 5 in a direction perpendicular to the information tracks as shown in FIG. A super-resolution spot 10a having a reduced spot width is formed. The central region 3b of the variable phase filter 3 at this time
FIG. 3 shows the relationship between the width of the optical disk 5 and each of the spot width, side lobe height, and main lobe peak height formed on the information recording layer of the optical disc 5.

As can be seen from FIG. 3, as the width of the central region 3b is increased, the super-resolution effect increases and the spot width decreases, while the side lobe height increases and the main lobe peak height increases. Decrease. When the side lobe height is 20% or more of the main lobe height, the mark is erased by the side lobe, and when the main lobe peak height decreases, the light emission power of the light source needs to be relatively increased. The optimum width of the central region 3b is about 10 to 20% of the light beam width.

The present optical pickup is used for an optical disk 5
When the signal is reproduced from, the phase difference between the regions 3a, 3b, 3c of the variable phase filter 3 is set to zero. As a result, at the time of reproduction, the light intensity distribution of the light beam applied to the optical disk 5 becomes as shown in the graph on the right side of FIG.
As shown in FIG. 2B, a normal diffraction-limited light spot 10 with few side lobes is formed on the optical disk 5.

The variable phase filter 3 used in the present optical pickup can be easily manufactured using, for example, a liquid crystal element. FIGS. 4A to 4C show an example of the configuration and operation of the variable phase filter 3 using a liquid crystal element.

The liquid crystal element used as the variable phase filter 3 has a configuration in which nematic liquid crystal is sealed between two opposing glass substrates 60 and 61. FIG.
FIG. 4C schematically shows the liquid crystal molecules 66 for explaining the operation of the liquid crystal element, and the major axis direction of the ellipse is the optical axis direction of the liquid crystal molecules 66. Glass substrates 60, 61
The transparent control electrodes 62, 63, 64 and the counter electrode 6
5 are provided, and an arbitrary electric field can be applied to the liquid crystal molecules 66 by a voltage applied to these control electrodes. The region where the control electrode 62 is formed corresponds to the central region 3b of the variable phase filter 3, and the control electrode 6
The regions where 3, 64 are formed correspond to the regions 3a, 3c. By performing an alignment process on the alignment films (not shown) formed on the control electrodes 62, 63, 64 and the counter electrode 65 in parallel with each other, the liquid crystal element has a configuration called a so-called homogeneous alignment. I have. Note that this orientation processing is performed in a direction perpendicular to the longitudinal direction of the regions 3a, 3b, and 3c, as indicated by the dashed arrows in FIG.

FIG. 4A shows the configuration of the counter electrode 65 and the control electrode 6.
2 shows a state when no voltage is applied between the second, third, and second 64. At this time, the liquid crystal molecules 66 are aligned in a direction in which their optical axes coincide with the alignment direction. When the liquid crystal molecules 66 are aligned in this manner, the nematic liquid crystal has optical anisotropy.

For this reason, both the light incident on the central portion of the liquid crystal element, ie, the central region 3b of the variable phase filter 3, and the light incident on both ends, ie, the regions 3a, 3c, are polarized components parallel to the plane of FIG. Propagates through the liquid crystal element as extraordinary light, and the polarization component perpendicular to the paper surface propagates through the liquid crystal element as ordinary light. For this reason, light incident on each area of the variable phase filter 3 propagates without any phase difference between both polarized waves.

On the other hand, FIG. 4B shows a state of the liquid crystal element when a voltage is applied only to the control electrode 62 at the center of the liquid crystal element. At this time, an electric field is formed between the control electrode 62 and the counter electrode 65 in the thickness direction of the liquid crystal element, and the liquid crystal molecules 66 are aligned along the direction of the electric field. At this time, the polarized light component parallel to the paper surface propagates as ordinary light in the central portion of the liquid crystal element, that is, the central region 3b of the variable phase filter 3, and propagates as extraordinary light in both end portions, that is, the regions 3a and 3c. For this reason, the refractive index felt by light is different in each region, and a phase difference is given between the center and both ends.

The phase difference φ is expressed as φ = d (ne−no) using the thickness d of the liquid crystal layer, the refractive index no of the liquid crystal for ordinary light, and the refractive index ne of extraordinary light.

As described above, in the variable phase filter 3 used in the optical pickup of FIG. 1A, polarized light parallel to the alignment direction of the liquid crystal molecules is incident, and the incident light is
A phase distribution according to the electrode division pattern is provided. In addition, since the polarization component perpendicular to the paper surface propagates as ordinary light in the entire region, there is no phase difference, so that the polarization component propagates as a plane wave without any phase shift regardless of the magnitude of the applied voltage.

The above description is for the case where a sufficiently large voltage is applied between the electrodes. FIG. 4C shows the state of the liquid crystal element when the applied voltage is relatively small. . In this case, in the portion where the control electrode 62 is formed, that is, in the central region 3b of the variable phase filter 3, the liquid crystal molecules 66 in the vicinity of the electrode are more strongly affected by the alignment process than the applied electric field, and the angle close to the electrode surface becomes parallel. Eggplant On the other hand,
The liquid crystal molecules in the middle part of the liquid crystal layer are more strongly affected by the applied electric field than in the alignment treatment and tend to align in the direction of the electric field. As a result, as shown in FIG.
It will form an oblique angle to the electrode surface.

When the applied voltage is large, the liquid crystal molecules 66 are inclined at an angle closer to perpendicular to the electrode surface, and when the applied voltage is small, the liquid crystal molecules 66 take an angle near parallel to the electrode surface.
At this time, the polarized light component incident on the central portion (central region 3b) of the liquid crystal element, which has a refractive index of an intermediate value between ne and no, senses the refractive index between the central region 3b and the left and right regions 3a, 3b. The phase step amount φ is as follows: φ = α × d (ne−no). Here, α is 0 or more and 1 which is determined by the applied voltage.
It is the following constant. That is, by adjusting the magnitude of the applied voltage, it is possible to set the phase difference amount φ to a desired value.

The above-mentioned liquid crystal device was manufactured as a prototype, and the relationship between the applied voltage and the phase difference was measured. When a red laser beam having a wavelength of 650 nm is incident on an element having a liquid crystal layer thickness d of 10 μm, the phase difference φ continuously and monotonically increases with respect to the voltage applied to the central control electrode 62, and becomes 2π at an applied voltage of 6.2 V. (1 wavelength) phase difference could be given. As described above, it was demonstrated that an arbitrary phase difference can be given only to a specific polarization component by controlling the applied voltage using the liquid crystal element having the configuration shown in FIGS. 4A to 4C.

The voltage O applied to the central control electrode 62
N / OFF is controlled according to whether the operation of the optical information recording / reproducing apparatus is recording / reproducing. During recording and reproduction, the output power of the semiconductor laser 1 is larger during recording than during reproduction. Therefore, the ON / OFF control of the voltage applied to the central control electrode 62 is linked with the output power control of the semiconductor laser 1, and the voltage is applied to the central control electrode 62 when the output power of the semiconductor laser 1 is a predetermined value or more. The apparatus can be configured so that no voltage is applied when the voltage is equal to or less than a predetermined value.

Embodiment 2 Another embodiment of the present invention will be described below with reference to the drawings. The components having the same functions as those described in the first embodiment will be denoted by the same reference numerals, and description thereof will be omitted. FIG. 5A is an explanatory diagram illustrating a schematic configuration of an optical pickup included in the optical information recording / reproducing device of the present embodiment. FIG.
(B) is a graph showing the light intensity distribution of the light spot formed on the optical disk by the optical pickup at the time of recording and at the time of reproduction, respectively. The light intensity distribution is a distribution in a direction perpendicular to the information tracks on the optical disc.

The optical pickup according to the present embodiment has the structure shown in FIG.
As shown in FIG. 1A, the configuration differs from the optical pickup of the first embodiment in that a combination of a variable wavelength plate 15 and an analyzer 16 is used instead of the variable phase filter 3. The same effects as those of the optical pickup of (1) can be obtained.

The variable wavelength plate 15, like the variable phase filter 3 of the first embodiment, is divided into three regions 15a, 15b, and 15c as shown in FIG. The tunable wavelength plate 15 can be formed of a homogeneously aligned liquid crystal element having control electrodes corresponding to the respective divided regions, similarly to the tunable phase filter 3.
As shown in the above, the liquid crystal is different from the variable phase filter 3 in that the orientation direction of the liquid crystal is at 45 degrees to the polarization direction of the incident light beam.

As described above, the homogeneous alignment liquid crystal element has an effect of changing the phase shift of the polarization component parallel to the alignment direction and not giving the phase shift to the polarization component perpendicular to the alignment direction. Function as a variable wavelength plate.

The semiconductor laser 1 emits polarized light in a direction parallel to the plane of the drawing. At the time of signal reproduction, the voltage applied to the central control electrode of the liquid crystal element as the variable wavelength plate 15 is adjusted so that the phase shift in the variable wavelength plate 15 becomes zero. In addition, the analyzer 16 has the same configuration as the emitted light of the semiconductor laser 1,
The optical axis is set so as to transmit polarized light of a component parallel to the paper surface. Thereby, at the time of signal reproduction, the light from the semiconductor laser 1 passes as a plane wave without being modulated by the variable wavelength plate 15 and the analyzer 16, and is shown on the optical disk 5 in the graph on the right side of FIG. A normal light spot having such a light intensity distribution is obtained. As a result, a perfect circular light spot 10 is formed on the optical disc 5 as shown in FIG.

On the other hand, at the time of information recording, the voltage applied to the central control electrode of the liquid crystal element as the variable wavelength plate 15 is adjusted so as to give a phase shift of π only to the central region 15b of the variable wavelength plate 15. At this time, since the central region 15b of the variable wavelength plate 15 functions as a half-wave plate, the light passing through the central region 15b rotates the polarization direction by 90 degrees and cannot pass through the analyzer 16. As a result, the light beam that has passed through the analyzer 16 has an intensity distribution as if the central portion was shielded, and a super-resolution effect can be obtained as in the first embodiment. As a result, the light beam applied to the optical disk 5 has a light intensity distribution as shown in the graph on the left side of FIG. 5B, and the optical disk 5 has a light intensity distribution as shown in FIG. The light spot 10 whose size in the direction perpendicular to the information track is reduced as compared with the light spot 10
a is formed.

Embodiment 3 Still another embodiment of the present invention will be described below with reference to the drawings. In addition,
Also in the present embodiment, the same reference numerals are given to configurations having the same functions as the configurations described in the above-described embodiments, and description thereof will be omitted.

In the first and second embodiments, the optical pickup for reducing the mark width at the time of recording has been described. However, when the track density is improved beyond a certain level, the recording information of the adjacent track is erased at the time of recording. In addition to the problem of crosstalk, crosstalk during playback also becomes a problem.

For example, in a read-only digital versatile disk (DVD-ROM), laser light having a wavelength of 650 nm is focused by an objective lens having a numerical aperture of 0.6, and the focused spot diameter on the disk is 0 at full width at half maximum. .6 μm. Further, the track interval is set to 0.74 μm.

Here, by increasing the pit size and track interval formed on the disc by 1.3 times in the radial direction, the optical disc having the track interval narrowed to 0.57 μm can be used to collect light under the above conditions. If a signal is reproduced using a system, signal degradation occurs before normal signal reproduction cannot be performed due to a crosstalk component in the reproduced signal.

In addition to the above-mentioned digital versatile disk, generally, when recording information on an optical disk is read out by a condensed spot, if the track spacing is increased to the same level as the condensed spot diameter, crosstalk may be reduced. The effect is noticeable.

The optical disk system (optical information recording / reproducing apparatus) according to the present embodiment uses a super-resolution spot at the time of recording and operates a crosstalk canceller at the time of reproduction in order to solve the above-mentioned problem of crosstalk. This configuration is compatible with high-density optical disks. The crosstalk canceller is included in the signal by detecting the signal of the adjacent track using a separate light spot in addition to the light spot tracing on the track to be reproduced and performing an electrical differential operation. This is a technique for removing a crosstalk component from an adjacent track.

Examples of the crosstalk canceller are described in detail in, for example, JP-A-7-320295. This means that two light intensity peaks (sub-spots) are generated on the left and right of the main spot, and the position of each sub-spot is made to coincide with the adjacent tracks on both sides of the reproduction target track scanned by the main spot. , A crosstalk component from an adjacent track is also detected. FIG. 6A shows a configuration of an optical disk system according to the present embodiment, which combines a crosstalk canceller disclosed in Japanese Patent Application Laid-Open No. 7-320295 and a super-resolution technique.

As shown in FIG. 6A, this optical disc system comprises a semiconductor laser 1, a collimating lens 2, a variable wavelength plate 25, a variable polarizing phase filter 17, a polarizing beam splitter 6a, a half mirror 6b, and an objective lens 4. , Condensing lenses 8 a and 8 b, photodetectors 7 and 9, and an optical pickup having a differential calculator 23.

The variable polarization phase filter 17 is shown in FIG.
As shown in (b), four regions 17a, 17b, 17
c and 17d, and are arranged between the variable wavelength plate 25 and the collimating lens 2 such that the longitudinal direction of these regions is parallel to the scanning direction of the light beam on the optical disk 5.

The variable polarization phase filter 17 can be easily formed using a liquid crystal element, similarly to the variable phase filter 3 of the first embodiment. That is, the first embodiment
4A to 4C, a homogeneously aligned liquid crystal element in which a nematic liquid crystal is sealed between glass substrates, and has four regions 17a, 17b, 17
The configuration may be such that control electrodes are provided corresponding to c and 17d, respectively. The orientation direction of the liquid crystal is parallel to the polarization direction of the incident light beam, as shown by the dashed arrow in FIG.

Similarly, the variable wavelength plate 25 can be easily formed using a liquid crystal element. That is, FIG.
As in the case of the variable phase filter 3 shown in FIGS. 4A to 4C, a nematic liquid crystal is sealed between glass substrates to obtain a homogeneous alignment configuration. However, as shown in FIG. 9, a uniform control electrode is formed on the entire surface of the device, and the alignment direction of the liquid crystal is
The direction is 45 degrees with respect to the polarization direction of the incident light beam.

When no electric field is applied to the liquid crystal element serving as the variable wavelength plate 25, the liquid crystal molecules are arranged parallel to the alignment direction, and birefringence occurs in a direction parallel to the optical axis of the liquid crystal molecules, thereby acting as a wavelength plate. When an electric field perpendicular to the substrate surface is applied to the liquid crystal element by applying a voltage to the control electrode, the liquid crystal molecules are aligned parallel to the applied electric field, that is, perpendicular to the substrate surface. In this case, the optical characteristics of the liquid crystal element become isotropic in the plane and lose birefringence.
By properly selecting the thickness of the liquid crystal layer, it functions as a half-wave plate or a quarter-wave plate when no electric field is applied, and the phase shift can be made zero by applying an electric field. The variable wavelength plate 25 can be realized.

Next, the operation of the optical disk system of this embodiment having such a configuration will be described.

First, the operation during signal reproduction will be described. The semiconductor laser 1 emits, for example, linearly polarized light having only a polarized light component parallel to the plane of FIG. The phase shift amount of the variable wavelength plate 25 is adjusted so as to function as a quarter-wave plate at the time of signal reproduction. The emitted light of the semiconductor laser 1 passes through the variable wavelength plate 25, and generates a polarized light component parallel to the polarized light perpendicular to the plane of FIG. 6A. Or later,
A polarization component perpendicular to the paper surface is called a main beam, and a polarization component parallel to the paper surface is called a sub-beam.

The tunable polarizing phase filter 17 has the property of giving a phase shift only to a polarization component parallel to the plane of the paper and not to a phase shift to a polarization component perpendicular to the plane of the paper. Accordingly, the main beam is not given a phase shift by the variable polarization phase filter 17, and the light spot on the optical disk 5 condensed by the objective lens 4 has a normal diffraction limit as shown in FIG. (Main spot 10).

As shown in FIG. 7B, the position of the main spot 10 is controlled on the track 12 to be reproduced, and the reflected light is intensity-modulated according to the pit (not shown) of the track 12 to be reproduced. Is done. At this time, if the optical disk is made high-density by reducing the track interval, as described above, the main spot 10 also irradiates the adjacent tracks 13 and 14, and the crosstalk component is included in the reproduced signal. Mixed.

When the signal is reproduced, the tunable polarizing phase filter 17 is used as shown in FIG.
The phase between c and 17d and the two regions 17a and 17b on the left are π
The sub-beam is given a phase shift that differs only by When the sub-beam is condensed on the optical disk 5 by the objective lens 4, as shown in FIG. 7B, two light intensity peaks (sub-spot 1
1) is formed, and the respective peaks are located on the left and right adjacent tracks 13 and 14. The reflected light of these sub spots is intensity-modulated according to the pits on the adjacent tracks 13 and 14.

The reflected light from the optical disk 5 is split into a main beam and a sub-beam by a polarization beam splitter 6b, detected by photodetectors 7 and 9, respectively, and mainly reflected on a signal on a track 12 to be reproduced. 21 and
A sub signal 22 mainly reflecting the signals on the adjacent tracks 13 and 14 is obtained. By electrically generating a differential signal of both signals at an appropriate ratio by the differential calculator 23, a signal from which a crosstalk component has been removed from the main signal 21 can be obtained.

On the other hand, when recording information on the optical disc 5,
The amount of phase shift is adjusted so that the variable wavelength plate 25 functions as a half-wave plate. At this time, all of the laser light that has passed through the variable wavelength plate 25 becomes a polarization component perpendicular to the plane of FIG. 6A and passes through the variable polarization phase filter 17. When recording information, the variable polarization phase filter 17
As shown in (a), two central regions 17b and 17c,
It is adjusted so as to give a phase shift different by π between the two outer regions 17a and 17d. As a result, similarly to the first embodiment, the laser light focused on the recording layer of the optical disk 5 is, as shown in FIG. 7A, a super-solution having a reduced spot size in the direction perpendicular to the information tracks. An image spot 10a is formed. This enables narrow mark recording.

The variable polarization phase filter 17 is not limited to a configuration example in which each region has a uniform width as shown in FIG. For example, FIGS. 10 (a) to 10 (c)
May be used. According to these division patterns, there is also an effect that the height of a side lobe generated in a direction perpendicular to the information track is reduced.

In the case of the pattern shown in FIG.
The spot size is also reduced in the front-back direction of the information track. In this case, the reduction ratio in the direction perpendicular to the information track is 10% with respect to the spot size during reproduction.
Although it is possible to achieve this, the reduction ratio in the front-rear direction of the information track is preferably 5% or less in order to perform normal recording.

The embodiments described above do not limit the present invention, and various modifications can be made within the scope of the invention. For example, in the above, an optical disc is exemplified as the optical information carrier, but as the optical disc, a phase change optical disc, a magneto-optical disc, a dye-based write-once optical disc,
Various other discs can be used.

In each of the embodiments described above, the configuration is described in which the phase shift amounts applied to the outgoing light at the time of recording and at the time of reproduction are made different from each other by using a liquid crystal element or the like. Embodiments are also contemplated.

For example, as shown in FIG. 11A, an optical pickup having a filter moving mechanism 51 for mechanically inserting / removing the phase filter 43 in the optical path between the collimator lens 2 and the polarization beam splitter 6. Is also an embodiment of the present invention. The phase filter 43 is as shown in FIG.
As shown in the figure, the area is divided into three areas 43a, 43b, and 43c, and a central area 43b and areas 43a, 43
A phase difference of π is provided between the transparent substrate 3c and the transparent substrate 3c. Specifically, it can be manufactured by selective etching removal of a part of the surface of the glass substrate or resin molding. The phase filter 43 is inserted into the optical path between the collimator lens 2 and the polarization beam splitter 6 at the time of recording by the filter moving mechanism 51, and is removed at the time of reproduction, thereby obtaining a signal shown in FIG.
The same effect as that of the optical pickup is obtained.

Alternatively, an optical pickup having a configuration as shown in FIG. 12 is also an embodiment of the present invention. This optical pickup includes two semiconductor lasers 1, and the above-described phase filter 43 is arranged in the optical path of light emitted from one of the semiconductor lasers 1a. The semiconductor laser 1a is used as a light source during recording, and the other is used during reproduction. Since the configuration uses the semiconductor laser 1b, the same effects as above can be obtained.

[0064]

According to the present invention, recording / reproducing of a recording / reproducing-type high-density optical disk having a high track density becomes possible.

[Brief description of the drawings]

FIG. 1A is an explanatory diagram illustrating a schematic configuration of an optical pickup included in an optical information recording / reproducing apparatus according to an embodiment of the present invention, and FIG. 1B is a diagram illustrating light of a light spot formed by the optical pickup. Graph showing intensity distribution, (c)
Is a plan view showing a configuration of a variable phase filter provided in the optical pickup;

FIGS. 2A and 2B are views showing a state of a light spot formed by the optical pickup of FIG. 1A, wherein FIG. 2A is an explanatory diagram at the time of recording and FIG.

FIG. 3 is a graph showing a change in a super-resolution spot shape with respect to a central region width of a variable phase filter.

FIGS. 4A to 4C are explanatory diagrams illustrating a change in a liquid crystal alignment state according to an applied voltage when a variable phase filter is configured by a liquid crystal element.

FIG. 5A is a diagram illustrating a schematic configuration of an optical pickup included in an optical information recording / reproducing apparatus according to another embodiment of the present invention, and FIG. 5B is a diagram illustrating an optical spot formed by the optical pickup; Graph showing light intensity distribution, (c)
Is a plan view showing a configuration of a variable wavelength plate provided in the optical pickup;

FIG. 6A is an explanatory diagram showing a schematic configuration of an optical pickup included in an optical information recording / reproducing apparatus according to still another embodiment of the present invention, and FIG. 6B is a diagram illustrating a variable polarization phase included in the optical pickup. Plan view showing the configuration of the filter

FIGS. 7A and 7B are views showing a state of a light spot formed by the optical pickup of FIG. 6A, wherein FIG. 7A is an explanatory diagram at the time of recording, and FIG.

FIGS. 8A and 8B show phase shifts of the variable polarization phase filter of the optical pickup shown in FIG. 6A, wherein FIG. 8A is an explanatory diagram at the time of recording and FIG.

FIG. 9 is an explanatory diagram showing an orientation direction of a variable wavelength plate.

FIGS. 10A to 10C are plan views showing another configuration example of the variable polarization phase filter of the optical pickup in FIG. 6A;

11A is an explanatory view showing an optical pickup according to still another embodiment of the present invention, and FIG. 11B is a plan view showing a configuration of a phase filter provided in the optical pickup.

FIG. 12 is an explanatory view showing an optical pickup according to still another embodiment of the present invention.

13A is an explanatory diagram showing a schematic configuration of a conventional super-resolution optical pickup, FIG. 13B is a graph showing a light intensity distribution of a light spot formed by the optical pickup, and FIG. Plan view showing the configuration of a phase filter provided in an optical pickup

[Explanation of symbols]

 1, 1 'Semiconductor laser 2, 2' Quarter-wave plate 3 Variable phase filter 3 'Phase filter 4, 4' Objective lens 5, 5 'Optical disk 6, 6' Polarization beam splitter 7, 7 'Photodetector 8 Photodetector 10 Main spot 11 Sub spot 12 Track to be reproduced 13 and 14 Adjacent track 15 Variable wavelength plate 17 Variable polarization phase filter 21 Main signal 22 Sub signal 23 Differential operation unit 25 Variable wavelength plate 60, 61 Glass substrate 62 Center Control electrode 63 Left control electrode 64 Right control electrode 65 Counter electrode 66 Liquid crystal molecules

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kiminori Mizuuchi 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. F term (reference) 5D119 AA14 AA22 BA01 BB02 BB03 DA01 EB02 EB04 JA06

Claims (12)

[Claims] 1. A coherent light source, a condensing optical system for condensing light from the coherent light source on an information carrier, and a light spot size on the information carrier at the time of recording is smaller than a light spot size at the time of reproduction. An optical pickup comprising: a spot size adjusting means for reducing a size of the light beam mainly in a direction perpendicular to the information track. 2. The information processing apparatus according to claim 1, wherein the spot size adjusting means includes a variable phase filter which is provided between the coherent light source and the light collecting optical system and has a variable phase shift amount. 2. The optical pickup according to claim 1, wherein the optical pickup is divided into at least three regions that can cause a phase difference in a direction perpendicular to the information track. 3. The variable phase filter according to claim 2, wherein the variable phase filter is divided into three regions, and a width of a central region is in a range of 10% to 20% of a width of a light beam passing through the variable phase filter. Optical pickup. 4. The optical pickup according to claim 2, wherein the variable phase filter is configured using a homogeneously aligned liquid crystal element oriented in parallel to a polarization direction of light from the coherent light source. 5. The spot size adjusting means is provided between the coherent light source and the condensing optical system, and comprises: a variable wavelength plate having a variable birefringence; and the variable wavelength plate and the condensing optical system. 2. The light according to claim 1, wherein the variable wavelength plate is divided into at least three regions that can cause a phase step in a direction perpendicular to an information track of the information carrier. pick up. 6. The optical pickup according to claim 5, wherein the variable wavelength plate is configured using a homogeneously aligned liquid crystal element aligned in parallel to a polarization direction of light from the coherent light source. 7. A variable wavelength plate having a variable phase shift amount installed between the coherent light source and the condensing optical system, wherein the spot size adjusting means comprises: a variable wavelength plate and the condensing optical system. And is divided into at least four regions that can cause a phase step in a direction perpendicular to the information track of the information carrier, and an arbitrary amount of phase shift is applied only to a first polarization component of light from the coherent light source. And a variable polarization phase filter for providing, a polarized light separating means for separating the reflected light from the information carrier into the first polarized light component and another second polarized light component; 2. The apparatus according to claim 1, further comprising a first photodetector for detecting one polarization component, and a second photodetector for detecting a second polarization component of the reflected light from the information carrier.
Optical pickup as described. 8. The optical pickup according to claim 7, wherein the variable wavelength plate is configured using a homogeneously aligned liquid crystal element oriented in a direction substantially 45 degrees with respect to a polarization direction of light from the coherent light source. . 9. The optical pickup according to claim 7, wherein the variable polarization phase filter is configured using a homogeneously aligned liquid crystal element oriented in parallel to a polarization direction of light from the coherent light source. 10. An optical pickup according to claim 2, wherein when information is recorded on the information carrier, a phase step is generated between the regions of the variable phase filter, When reproducing information from an information carrier,
An optical information recording / reproducing apparatus, wherein a phase step is not generated between the regions of the variable phase filter. 11. When the optical pickup according to claim 5 or 6 is used to record information on the information carrier, a phase difference is generated between the regions of the variable wavelength plate, and the information carrier transmits the information. Wherein the optical information recording / reproducing apparatus does not generate a phase difference between the regions of the variable wavelength plate when reproducing. 12. An optical information recording / reproducing apparatus having the optical pickup according to claim 7, wherein the variable polarization phase filter is divided into four regions.
When the four regions are first, second, third, and fourth regions in the direction perpendicular to the information track of the information carrier, the variable polarization is used when information is recorded on the information carrier. Providing different phase shift amounts to the first and fourth regions and the second and third regions of the neutral phase filter, and not providing the variable wavelength plate with a phase shift amount; In the case of reproducing, the first and second regions and the third and fourth regions of the variable polarization phase filter are provided with phase shift amounts different from each other by π, and the variable wavelength plate is provided with a phase shift amount. Give a half
An optical information recording / reproducing device, which is a wavelength plate.