JP2003173562A - Optical pickup device and information recording/ reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably control recording and reproduction using an electro-optical element to eliminate adverse effect of noise for a light source in reproduction, to process receiving signals without deterioration in response speed, and to correct deterioration due to wave aberration, and to stably perform processing of information recording/reproduction to/from an information recording medium. <P>SOLUTION: Transmissivity of an optical beam is set low by the first region of a first electro-optic element 3, thereby enabling semiconductor laser 1 output to be set high in reproduction, reducing effect of return light, and stabilizing light emission of the semiconductor laser 1 to reduce noise. In addition, by the third region of a second electro-optic element 9, light quantity from an information recording medium 8 is unchanged in reproduction; the transmissivity of the optical beam is set low in recording, enabling the light quantity to be controlled to a light receiving element 11, attaining common gain, and performing aberration compensation by the second and fourth regions of the first and second electro-optic elements 3, 9. Thus, the processing of information recording/reproduction can be stably carried out for the information recording medium. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device and an information recording / reproducing device for recording / reproducing information on / from an information recording medium.

[0002]

2. Description of the Related Art An optical pickup device is known as a device for recording information on an information recording medium and reproducing information recorded on the information recording medium. The intensity ratio of the irradiation beam to the information recording medium between the recording light beam and the reproducing light beam is about 1: 5 to 1:15, and the emission power of the light source during recording and reproducing is approximately according to the ratio. It is common to switch. However, in some semiconductor lasers, the lower the output, the worse the noise characteristics.

That is, part of the light beam emitted from the semiconductor laser returns to the semiconductor laser as return light. A resonator different from the semiconductor laser is generated between the return light and the information recording medium. As a result,
The oscillation state of the semiconductor laser becomes unstable and noise occurs in its output. Further, noise is generated in the output of the semiconductor laser even when the temperature changes due to operation or the environment, and particularly when the emission power of the semiconductor laser far exceeds the threshold current value and reaches several tens of mW, disturbance of the disturbance occurs. Stable light emission can be obtained with almost no influence, but when the light emission power is in the vicinity of the threshold current value, the light emission power fluctuates under the influence of disturbance due to the return light described above.

Therefore, information is recorded on the information recording medium.
When writing (erasing) or erasing, the output of the semiconductor laser is set to high power and the light is emitted far beyond the threshold, so it is hardly affected by disturbance, but information is reproduced from the information recording medium. At the time of reading (reading), the semiconductor laser is set to low power and light is emitted at a few mW slightly exceeding the threshold current value, for example, about 5 mW in many cases. It is easily affected by light, and the light emission becomes unstable, and the signal deteriorates due to noise.

In order to solve this problem, Japanese Patent Laid-Open No. 9-27
No. 141, an electro-optical element capable of controlling the light transmittance is arranged in the optical path from the light source to the recording medium, and the light transmittance from the light source is controlled to be low when reproducing information. In addition, there is an optical pickup device in which the transmittance of light from a light source is controlled to a high transmittance when recording information.

Further, the optical pickup device causes the light emitted from the semiconductor laser to be condensed and irradiated on the surface of the information recording medium through the irradiation optical system, and the reflected light from the information recording medium is detected through the detection optical system. And is guided to a light receiving element to receive light. The detection signal (current signal) of the light receiving element in the optical pickup is generally output to the signal processing circuit in the form of being converted into a voltage signal via a current-voltage conversion amplifier incorporated in the optical pickup device.

If the amplitude level of the signal output through the current-voltage conversion amplifier is too low, reproduction of information is hindered. Therefore, the output amplitude level of the gain of the current-voltage conversion amplifier is within a proper range. A configuration is adopted that can be switched so that However, in recent years, it has become necessary to consider a plurality of conditions in order to cope with the type of information recording medium and the conditions such as recording / reproducing. For example, the optical information recording / reproducing apparatus disclosed in Japanese Patent Laid-Open No. 10-255301. Used CD-RW, C, as described in
In order to perform recording, reproduction, and erasing compatible with a plurality of optical discs such as D-DA, CD-ROM, and CD-R, FIG.
It is necessary to make the gain switching circuit shown in FIG. 3 more adaptable to a plurality of combination patterns. As a result, there are problems such as an increase in the number of mounting resistors used in this circuit and a slow signal response speed.

Furthermore, in recent years, it has been proposed to increase the numerical aperture (NA) of an objective lens for converging a light beam on an information recording medium to achieve high density. This is because the spot diameter can be reduced by using an objective lens having a large numerical aperture (NA). However, high NA
As a result, the ratio of aberration deterioration increases. That is, the spherical aberration, which is the main cause of deterioration of the substrate thickness of the information recording medium, is proportional to the fourth power of NA, and the coma aberration, which is the main factor of deterioration due to the inclination of the information recording medium from the optical axis, is the third power of NA. Increases in proportion to.

As a publicly known technique for solving these individual problems, JP-A-10-20263 and JP-A-9-128785 for correcting and detecting wavefront aberration (spherical aberration, coma aberration, astigmatism) are disclosed. , JP-A-11-25
9892 and Japanese Patent Laid-Open No. 2000-15597 are known.

[0010]

However, in the optical pickup device having such a structure, cost reduction due to common parts and simplification of assembly procedure are required.

The present invention is directed to solving such a conventional problem, and an electro-optical element that divides a region of a transmitted light beam stabilizes the light source without being affected by noise during reproduction. Control is possible, the received light signal can be processed without deterioration of response speed, and deterioration can be corrected and controlled by wavefront aberration, so that common parts are used, the number of parts is reduced, and assembly adjustment is simplified. It is an object of the present invention to provide an optical pickup device and an information recording / reproducing device for achieving the above.

[0012]

To achieve this object, an optical pickup device according to the present invention and an optical pickup device relating to an information recording / reproducing apparatus including the same make a light beam from a light source incident on an information recording medium. In an optical pickup device for recording or reproducing information, an electro-optical element for switching the transmittance of a predetermined area through which a light beam is transmitted according to recording or reproducing of information, the electro-optical element being a light source and an information recording medium. Being arranged in the optical path of the and the light source after the light source, the predetermined first area of the electro-optical element is controlled to a low transmittance when reproducing the information from the information recording medium, and is controlled to a high transmittance when recording the information. Further, by the configuration having a second region outside the first region of the electro-optical element for selectively changing the phase difference of the transmitted light flux, the light source is reproduced at the time of reproducing information. From the first area, stable control can be performed without being affected by noise in the light flux, and the light flux incident on the information recording medium by selectively changing the phase difference of the light flux transmitted by the second area. It is possible to suppress the deterioration of the wave front and secure the spot performance of the beam condensed by the objective lens.

Furthermore, in the second region, the phase difference of the light beams that are transmitted concentrically is selectively changed, and the phase difference of the light beams that are transmitted in the radial direction or the tangential direction is changed stepwise. In addition, the wavefront aberration (spherical aberration, coma aberration, astigmatism) can be suppressed by the configuration in which the phase difference of the light fluxes transmitted in the radial direction and the tangential direction is simultaneously and asymmetrically changed.

Further, the electro-optical element is arranged before the detection element in the optical path between the information recording medium and the detection element which receives the light beam reflected from the recording medium, and a predetermined third region of the electro-optical element is provided. With the configuration in which high transmittance is controlled when reproducing information from the information recording medium and low transmittance is controlled when recording information, processing can be performed without deterioration in response speed to reflected light flux, and signal quality of the detection element Can be secured.

Further, a fourth region for controlling the transmittance of the light flux passing therethrough is provided outside the third region of the electro-optical element, and the light-collecting position of each of the third region and the fourth region in the detection element is set. Of the light flux incident on the information recording medium by detecting the difference between the first and second areas and the third and fourth areas having concentric circular shapes and the fourth area having a strip shape in the radial direction or the tangential direction. By detecting the deterioration of the wavefront and performing feedback control, the spot performance of the beam condensed by the objective lens can be secured, and spherical aberration and coma can be detected.

An information recording / reproducing apparatus of the present invention is provided with the optical pickup device according to any one of claims 1 to 10 and has a structure for recording or reproducing information on an information recording medium. -Regeneration can be performed stably.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of an optical system of an optical pickup device according to an embodiment of the present invention. Figure 1
In the optical pickup device of the present embodiment, the semiconductor laser 1 which is the light source, the collimator lens 2, the first electro-optical element 3 having the transmittance changing region and the aberration correcting region.
, The polarization beam splitter 4, the deflection mirror 5, and 1 /
A four-wave plate 6, an objective lens 7, a second electro-optical element 9 having a transmittance changing area and an aberration detection signal generating area, a detecting lens 10, and a light receiving element 11 which is a light beam detecting element.
And a control circuit 12 for controlling the first and second electro-optical elements 3 and 9.

As shown in FIG. 1, the light beam emitted from the semiconductor laser 1 is converted into a substantially parallel light by the collimator lens 2 and is arranged at the subsequent stage of the semiconductor laser 1 on the optical path between the semiconductor laser 1 and the information recording medium 8. It is incident on the first electro-optical element 3 thus formed. As will be described later, the first electro-optical element 3 has a transmittance changing area of a first area for changing the transmittance between the time of recording information on the information recording medium 8 and the time of reproducing information, and the wavefront aberration of the transmitted light beam. It is formed in the aberration correction area of the second area in which the aberration is corrected by giving the opposite phase. The light beam that has passed through the first electro-optical element 3 is transmitted through the subsequent polarization beam splitter 4, the optical path is bent by 90 degrees by the deflection mirror 5, and the light beam is condensed by the objective lens 7. A quarter-wave plate 6 is arranged between the deflecting mirror 5 and the objective lens 7 to convert linearly polarized light into circularly polarized light and focus it on the information recording medium 8.

Further, the reflected light beam from the information recording medium 8 reverses the optical path at the time of irradiation, and again the objective lens 7, 1/4
It reaches the polarization beam splitter 4 through the wave plate 6 and the deflection mirror 5. The polarization component incident on the quarter-wave plate 6 from the information recording medium 8 is circularly polarized light in the opposite direction to the forward path, and is also 1/4.
The polarized light that has passed through the wave plate is linearly polarized light that is orthogonal to the forward path, and the polarized beam splitter 4 that has passed through the forward path has passed.
Is reflected on the return trip. The reflected light beam reflected by the polarization beam splitter 4 is reflected by the information recording medium 8 and the light receiving element 11.
The light is incident on the second electro-optical element 9 arranged in front of the light receiving element 11. As will be described later, the second electro-optical element 9 changes the transmittance of the information recording medium 8 when recording and reproducing information, or according to the type of the information recording medium 8, the transmittance changing area of the third area. And the aberration detection signal generation region of the fourth region that turns ON / OFF the transmittance of the light beam that is transmitted to generate the aberration signal.

The light beam that has passed through the second electro-optical element 9 passes through the detection lens 10 and reaches the light receiving element 11. The light receiving element 11 is appropriately divided according to the method of generating the servo signal. The reflected light from the information recording medium 8 detected by the light receiving element 11 is output to another control circuit (not shown) as a tracking signal, a focus signal and a reproduction signal.

In the conventional optical pickup device, the output of the semiconductor laser 1 is set to a high power during recording (writing) on the information recording medium 8, so that it is hardly affected by the returning light. On the other hand, when reproducing (reading) information from the information recording medium 8,
Since the output of the semiconductor laser 1 was set to low power, it was easily affected by the returning light.

With the structure of the present embodiment, the amount of light reaching the information recording medium 8 at the time of reproduction (at the time of reading) is the same as that of the conventional one, and the semiconductor laser 1 is several times larger than the light emission power at the threshold current. The output of the semiconductor laser 1 can be increased as compared with the conventional one so as to emit a large amount of mW.
By performing such control, the output from the semiconductor laser 1 can be set higher than before even during reproduction, and the semiconductor laser 1 is less likely to be affected by the returned light.
By setting the transmittance of the first electro-optical element 3 to be low, the rate of light returning to the semiconductor laser 1 is also reduced, the emission of the semiconductor laser 1 is stabilized, and noise can be reduced.

FIG. 2 is a sectional view showing an example of the first electro-optical element 3. Transparent electrodes 16a and 16b made of ITO are formed on the pair of glass substrates 15a and 15b, respectively, and alignment films 17a and 1 made of polyimide are further formed.
7b is formed, and each of the alignment films 17a and 17b has
Alignment treatment by rubbing is performed.

Also, a pair of glass substrates 15a and 15b
Are arranged so as to face each other with a gap therebetween (not shown) with a predetermined gap therebetween.
The space between b is sealed by a sealing material (not shown), and a predetermined liquid crystal is sealed in this space to form a liquid crystal layer 18.

The first electro-optical element 3 is configured as a liquid crystal cell, and in this liquid crystal cell, the alignment direction of the major axis of the liquid crystal molecule, that is, the rubbing direction is 90 ° in the lower alignment film 17a and the upper alignment 17b. When the alignment treatment is performed differently, the liquid crystal layer is continuously twisted by 90 ° and aligned. Further, as shown in FIG. 2, for example, a polarizing film 19 is vapor-deposited on the side opposite to the semiconductor laser 1 facing the liquid crystal cell in the same area as the transmittance changing area. , And the alignment axis of the liquid crystal molecules on the glass substrate surface adjacent to the polarization axis is aligned.

Under this arrangement, the relationship between the voltage V applied to the liquid crystal cell and the transmittance T is as shown in FIG. That is, when a low voltage is applied to this liquid crystal cell, the plane of polarization of the light from the semiconductor laser 1 incident on this liquid crystal cell is rotated by 90 ° in accordance with the twist of the liquid crystal molecules, and then is absorbed by the polarizing film 19. It

That is, when the voltage applied to the liquid crystal cell is low, the light beam from the semiconductor laser 1 is controlled to have a low transmittance. On the other hand, when a high voltage is applied to this liquid crystal cell, the twisted alignment of the liquid crystal molecules is canceled, and as a result,
The light beam from the semiconductor laser 1 incident on the liquid crystal cell goes straight through the polarizing film 19 without changing its polarization plane. That is, when the voltage applied to this liquid crystal cell is high, the light from the semiconductor laser 1 is controlled to have a high transmittance.

In this liquid crystal cell, since such transmittance control is possible, this liquid crystal cell is used as the first electro-optical element 3.
When used in an optical pickup device as, for example, at the time of recording, the light emission efficiency of the semiconductor laser 1 is set to 35 mW, the transmittance of the first electro-optical element 3 is set to 85%, and the light utilization efficiency up to the information recording medium 8 is 40%. The optical power can be set to about 12 mW and the recording power on the information recording medium 8 can be set to about 12 mW.

On the other hand, during reproduction, the emission power of the semiconductor laser 1 is 8 mW and the transmittance of the first electro-optical element 3 is 30.
%, And in this case, the reproduction power on the information recording medium 8 that has passed through the same optical system as during recording is about 1
It can be set to mW.

As described above, the semiconductor laser 1 has a large influence of noise due to the returning light until the emission power of the semiconductor laser 1 is about 5 mW. However, according to the present embodiment, a sufficient emission power, for example, 8 mW is obtained even during reproduction. Therefore, the influence of noise can be prevented without using a high frequency superposition circuit or the like.

Further, as shown in FIG. 4, an aberration correction area (second area) of wavefront aberration is added to the outside of the transmittance changing area (first area) of the first electro-optical element 3. At least one transparent electrode of the first electro-optical element 3 is divided into a predetermined shape, the applied voltage of each divided portion is variably controlled based on an aberration signal described later, the refractive index of each divided portion is changed, and a passing light beam is passed. By providing a phase difference to, the wavefront aberration such as coma aberration and spherical aberration of the objective lens can be corrected. That is, the refractive index n of the liquid crystal in the second region can be freely changed from n1 to n2 by controlling the voltage applied to the plurality of divided second regions.

The fact that the refractive index n can be changed means that
The optical path difference Δn · d (Δn is the change in the refractive index, d is the cell thickness of the liquid crystal) of the light beam passing through the second region, that is, the phase difference Δn
It means that d (2π / λ) (λ is the wavelength of the light beam) can be given. Therefore, if the applied voltage is controlled according to the wavefront aberration generated in the objective lens 7 (see FIG. 1) and the refractive index n is changed, the wavefront aberration generated by the objective lens 7 can be corrected. .

Typical wavefront aberrations are shown in FIGS. 5 (a) to 5 (c). FIG. 5A is a diagram showing a spherical aberration, FIG. 5B is a coma aberration, and FIG. 5C is a diagram showing an astigmatism. As is clear from FIGS. 5A, 5B, and 5C, the wavefront aberration has a large influence in the peripheral portion of the transmitted light beam. On the other hand, the region affected by the returning light is the central region where the power is high. Therefore, by dividing the region, it is possible to realize both stable semiconductor laser control during reproduction and correction of the wavefront aberration of the transmitted light beam incident on the objective lens with one electro-optical element.

In the optical pickup device shown in FIG. 1, when recording (writing) on the information recording medium 8, the output of the semiconductor laser 1 is set to a high power, so that the light beam incident on the light receiving element 11 ( The intensity of the signal light) becomes very high. On the other hand, when reproducing (reading) information from the information recording medium 8,
Since the output of the semiconductor laser 1 is set to low power, the light beam also becomes weak. Furthermore, in recent years, R has been used as the information recording medium 8.
There are multiple types such as OM media, write-once media, and phase change media, and the reflectances of these media are different. In this way, the optimum signal level is recorded /
It depends on the playback or depending on the type of media.

If the amplitude level of the signal is too low, the reproduction of information will be hindered. Therefore, the output amplitude level of the gain of the current-voltage conversion amplifier arranged in the subsequent stage of the light receiving element 11 is in the proper range. The configuration that can be switched is adopted. However, the corresponding information recording medium 8
It has become necessary to consider a plurality of conditions such as the type of recording, or recording / reproduction. For example, when the conventional gain switching circuit as shown in FIG. 13 is configured to be adaptable to a plurality of patterns, the number of mounting resistors increases, resulting in a slow signal response speed.

Therefore, by the second electro-optical element 9, the amount of light from the information recording medium 8 at the time of reproduction is the same as that in the conventional case, and the transmittance from the information recording medium 8 is set to be low at the time of recording, whereby the current-voltage conversion amplifier is set. It is possible to achieve common gain. Further, the light receiving element 11 has a limitation in its dynamic range and is saturated if it is too high. However, since the light amount to the light receiving element 11 itself can be controlled by the second electro-optical element 9, this limitation of the dynamic range is relaxed. can do.

The structure of the second electro-optical element 9 is the same as that of the first electro-optical element 3 shown in FIG. Further, outside the transmittance changing region (third region) of the second electro-optical element 9, there is an aberration detection signal generation region (fourth region) to which a shutter function for generating an aberration detection signal is added. The fourth region is a transmittance changing unit having the same configuration as the third region, and the shape of the transparent electrode is divided according to the generated aberration detection signal.

Here, as shown in FIG. 6 showing a state in which spherical aberration occurs, spherical aberration is a phenomenon in which the focal position is different between the light beam near the axis of the light spot and the light beam in the peripheral portion. If the two light beams are separated and the focus error is detected individually, the spherical aberration amount can be obtained from the difference. On the other hand, the region where the control of the amount of light to the light receiving element 11 shown in FIG. 1 is required is the central region where the power is high. Therefore, by dividing the area, stable signal detection and generation of an aberration detection signal for aberration correction can be realized together as one element regardless of the type of information reproduction / recording and information recording medium. .

Specific examples of aberration correction / detection of the electro-optical elements used as the first electro-optical element and the second electro-optical element will be described below. Needless to say, the transmittance of the light beam from the light source is changed in the illumination light path, and the light amount to the light receiving element is controlled in the detection light path.

If the thickness of the information recording medium is different, spherical aberration occurs when the light beam passes through the substrate of the information recording medium. Example 1 shows the configuration of the electro-optical element in the case of correcting this spherical aberration.

The spherical aberration can be detected by the light receiving element, and the electro-optical element can be driven so as to cancel the spherical aberration to correct the aberration. FIG. 7A shows the wavefront aberration when spherical aberration occurs. With respect to the reference wavefront 22 of the light beam, the wavefront delay 23 is symmetrical to the optical axis 21.
There are a and 23b. When the light is focused on the reference wavefront, the position where the delayed wavefront is focused on the focusing point is defocused.

Therefore, the occurrence of spherical aberration can be known by extracting the difference between the delayed wavefront and the reference wavefront to detect the focus state. For example, in the pattern as shown in FIG. 7B of the electro-optical element, the aberration detection signal of the spherical aberration can be generated based on the signal of the light receiving element when the A region 24 and the B region 25 are selectively transmitted. .

Next, a configuration for correcting the spherical aberration by the electro-optical element based on the aberration detection signal of the spherical aberration will be described. FIG. 8A is a view showing a cross section of the spherical aberration of FIG. As shown in FIG. 8A, the spherical aberration that occurs increases with distance from the optical axis. Therefore, as shown by the broken line in FIG. 8A, if a phase difference opposite to the solid line is given by the electro-optical element (liquid crystal cell), the generated spherical aberration can be canceled. FIG. 8B shows the sum of the solid line and the broken line in FIG. 8A, that is, the spherical aberration after correction. It can be seen that it is much smaller than the original spherical aberration. As a pattern for correcting spherical aberration in the electro-optical element, for example, a pattern as shown in FIG.

When the information recording medium is tilted and tilted, coma aberration occurs when the light beam passes through the substrate of the information recording medium. Example 2 shows a configuration of an electro-optical element in the case of correcting this coma aberration.

The coma aberration is detected by the light receiving element 11,
The aberration can be corrected by driving the electro-optical element so as to cancel this coma aberration. FIG. 10A shows the wavefront aberration when the coma aberration is generated. With respect to the reference wavefront 22 of the light beam, there is a wavefront advance 26a and a wavefront 26b with the optical axis 21 as a boundary. When the light is focused on the reference wavefront, the positions where the advanced wavefront and the delayed wavefront are focused on the focus point are defocused.

Therefore, the state of coma aberration can be known by extracting the difference between the advanced wavefront and the delayed wavefront to detect the focus state. For example, in the pattern as shown in FIG. 10B of the electro-optical element,
An aberration detection signal of coma can be generated based on the signal of the light receiving element when the A ₁ area 27 and B ₁ area 29 and the A ₂ area 28 and B ₂ area 30 are selectively transmitted.

Similarly, FIG. 11A is a diagram showing a cross section of a state in which coma aberration occurs due to tilting. In this case also, by using the electro-optical element (liquid crystal cell), as shown in FIG.
By giving a phase difference as shown by the broken line in (a), coma aberration due to tilt can be canceled (FIG. 11).
(See (b)). As a pattern for correcting coma aberration in the electro-optical element, for example, a pattern as shown in FIG. 9B can be cited.

Further, astigmatism occurs when the light beam passes through the substrate of the information recording medium due to birefringence of the information recording medium. Example 3 shows a configuration of an electro-optical element in the case of correcting this astigmatism.

Astigmatism can be detected by the light-receiving element, and the electro-optical element can be driven so as to cancel this astigmatism to correct the aberration. The astigmatism detection method can be performed based on the same idea as the above-described coma aberration and spherical aberration detection methods. As a pattern for correcting astigmatism in the electro-optical element, for example, a pattern as shown in FIG.

Further, it is possible to eliminate a plurality of aberrations at the same time by combining the patterns shown in FIGS. 9A to 9C, and further, the electro-optical element described above can be used in combination with the first and the first shown in FIG. The second area and the fourth area of the second electro-optical element may be combined and applied.

FIG. 12 is a perspective view of an information recording / reproducing apparatus using the above-mentioned optical pickup device. In FIG. 12, 31 is a cartridge, 32 is an optical disk, 33 is a shutter, 34 is a case, 35 is an opening, 36 is a spindle motor, 37 is a carriage moving mechanism, and 38 is a carriage. In the information recording / reproducing apparatus shown in FIG. 12, various signal processing circuits, various input / output terminals and the like are omitted, but it goes without saying that they are necessary components in an actual apparatus.

[0053]

As described above, according to the present invention,
By using the electro-optical element arranged in the latter stage of the light source in the optical path between the light source and the information recording medium, part of the light beam is transmitted with low efficiency when reproducing information, and is controlled by switching to high efficiency transmission when recording, It is possible to realize stable control in which the light source is not affected by noise even at the time of reproduction, and the phase difference of the transmitted light beam is selectively changed by the second area outside the transmittance changing area and incident on the information recording medium. The wavefront deterioration of the light beam (spherical aberration, coma aberration, astigmatism) can be suppressed, and the spot performance of the light beam focused by the objective lens can be secured.

Further, by using the electro-optical element arranged in front of the light receiving element for detecting the reflected light beam from the information recording medium, a part of the light beam is transmitted with high efficiency at the time of reproducing information.
At the time of recording, control is performed by switching to low-efficiency transmission, and it is possible to secure the signal quality by processing the received light signal without degrading the response speed, and selectively transmit the reflected light beam from the information recording medium and transmit it. The spot of the beam focused by the objective lens is detected by detecting the difference in the focusing position of the area, detecting the deterioration due to the wavefront aberration (spherical aberration, coma aberration) of the light beam incident on the information recording medium, and performing feedback control. Performance can be secured.

Further, the information recording / reproducing apparatus equipped with the optical pickup device can provide an information recording / reproducing apparatus capable of stably recording / reproducing information on / from the information recording medium.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an optical system of an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a sectional view showing an example of a first electro-optical element (liquid crystal cell).

FIG. 3 is a diagram showing a relationship between a transmittance and an applied voltage in a liquid crystal cell.

FIG. 4 is a diagram showing a transmittance changing region (first region) of the first electro-optical element and an aberration correction region (second region) of wavefront aberration.

5A is a spherical aberration, FIG. 5B is a coma aberration, and FIG.
Is a diagram showing how astigmatism is occurring

FIG. 6 is a diagram showing how spherical aberration occurs.

FIG. 7A is a phase when spherical aberration is generated,
FIG. 3B is a diagram showing a pattern for selectively transmitting an electro-optical element.

8A is a diagram showing a cross section of spherical aberration and a phase difference for correcting it, and FIG. 8B is a diagram showing spherical aberration after correction.

9A is a pattern for correcting spherical aberration in an electro-optical element, FIG. 9B is a pattern for correcting coma aberration, FIG.
FIG. 6C is a diagram showing a pattern for correcting astigmatism.

10A is a diagram showing a phase when coma aberration is generated, and FIG. 10B is a diagram showing a pattern for selectively transmitting an electro-optical element.

11A is a diagram showing a cross section of coma aberration and a phase difference for correcting it, and FIG. 11B is a diagram showing coma aberration after correction.

FIG. 12 is a perspective view of an information recording / reproducing device using an optical pickup device.

FIG. 13 is a diagram showing an example of a conventional gain switching circuit.

[Explanation of symbols]

1 Semiconductor Laser 2 Collimating Lens 3 First Electro-Optical Element 4 Polarizing Beam Splitter 5 Deflection Mirror 6 Quarter Wave Plate 7 Objective Lens 8 Information Recording Medium 9 Second Electro-Optical Element 10 Detection Lens 11 Light-Receiving Element 12 Control Circuits 15a, 15b Glass substrates 16a, 16b Transparent electrodes 17a, 17b Alignment film 18 Liquid crystal layer 19 Polarizing film 21 Optical axis 22 Reference wavefronts 23a, 23b, 26b Wavefront delay 24 A area 25 B area 26a Wavefront advance 27 A ₁ area 28 A ₂ area 29 B ₁ area 30 B ₂ area 31 cartridge 32 optical disk 33 shutter 34 case 35 opening 36 spindle motor 37 carriage moving mechanism 38 carriage

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Claims (11)

[Claims] 1. An optical pickup device for recording or reproducing information by causing a light beam from a light source to enter an information recording medium, wherein the transmittance of a predetermined area through which the light beam is transmitted is changed according to recording or reproducing of the information. An optical pickup device comprising an electro-optical element for switching. 2. The electro-optical element is arranged in the optical path between the light source and the information recording medium after the light source, and a predetermined first region of the electro-optical element is arranged when reproducing information from the information recording medium. 2. The optical pickup device according to claim 1, wherein the optical pickup device is controlled to have a low transmittance and is controlled to have a high transmittance when the information is recorded. 3. Outside the first region of the electro-optical element,
3. The optical pickup device according to claim 2, further comprising a second region that selectively changes the phase difference of the light flux that is transmitted. 4. The optical pickup device according to claim 3, wherein the phase difference of the light beams that are transmitted concentrically in the second region is selectively changed. 5. The optical pickup device according to claim 3, wherein in the second region, the phase difference of the light flux transmitted in the radial direction or the tangential direction is changed stepwise. 6. The optical pickup device according to claim 3, wherein in the second region, the phase difference between the light beams transmitted in the radial direction and the tangential direction is changed simultaneously and asymmetrically. 7. The electro-optical element is arranged in a preceding stage of the detection element in an optical path between an information recording medium and a detection element which receives a light beam reflected from the recording medium, and the electro-optical element is arranged at a predetermined position. 7. The light according to claim 1, wherein the three areas are controlled to have a high transmittance when reproducing information from the information recording medium and have a low transmittance when recording the information. Pickup device. 8. Outside the third region of the electro-optical element,
8. A fourth region for controlling the transmittance of a light flux that passes therethrough, wherein the detection element detects a difference between the third region or the fourth region and a light-condensing position. Optical pickup device. 9. The optical pickup device according to claim 8, wherein the third region and the fourth region are concentric circles. 10. The optical pickup device according to claim 8, wherein the fourth region has a strip shape in the radial direction or the tangential direction. 11. An information recording / reproducing apparatus comprising the optical pickup device according to claim 1 for recording or reproducing information on an information recording medium.