JP3529990B2 - Optical pickup - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical pickup.

[0002]

2. Description of the Related Art As an application of a liquid crystal element such as a liquid crystal panel, reading / writing of recorded information from an optical disk such as a DVD or a CD is performed by using a laser beam. Attempts have been made to contribute to so-called optical pickup performance improvement and function expansion. For example, using a liquid crystal panel, a technique for correcting wavefront aberration caused by tilt of an optical disc body that is a substrate for DVD, CD, or the like,
There is a liquid crystal compatible optical head technology that can reproduce both DVD and CD by one objective lens by substantially switching the NA of the objective lens using a liquid crystal panel.

In all of these liquid crystal panels, electrodes are divided into patterns suitable for the purpose, and a phase difference or a polarization state suitable for the purpose is provided for each light beam transmitted through each electrode region. It is formed so that a voltage that can be obtained is applied.

FIG. 8 shows a main example of a division pattern of electrodes of a liquid crystal panel used for the above applications. In FIG. 8, (a) is a so-called tilt correction pattern for correcting the wavefront aberration caused by the displacement with respect to the displacement of the angle formed by the optical disc and the optical axis of the laser beam. It is a pattern based on the wavefront aberration when the wavefront aberration is viewed on the pupil plane of the objective lens. Also (b)
Is a pattern for an optical pickup capable of reproducing two kinds of recording media having different substrate thicknesses such as DVD and CD, and liquid crystal is independently provided to electrodes of two regions divided by concentric division lines. An applied voltage is applied, and the NA of the objective lens can be changed by controlling the applied voltage to both electrodes.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
As shown in (b), in order to divide the electrode for applying voltage to the liquid crystal layer 404 into a plurality of regions, an electrode separation line in which no electrode is formed at the dividing position (divided parting line). It is necessary to have a part of the so-called pattern gap. It is considered that the size of the pattern gap can be close to 0 because it is sufficient that adjacent pattern regions are not in contact with each other.

However, since no electrode is formed in the pattern gap portion as described above,
The liquid crystal molecules existing in this portion are always in a state where no voltage is applied. Moreover, it is conceivable that such a pattern gap portion can be formed as one line, but in reality, the pattern gap requires a line width of about 20 μm to 150 μm.
That is, a conductive film such as ITO forming an electrode generally has a film thickness of about several hundreds to several thousands angstroms, and a photofabrication process or the like is used when patterning this. At this time, in order to pattern the conductive film such as ITO having the above-mentioned film thickness by etching, the pattern gap is about 200 times the film thickness because of the conditions such as the etching factor.
About 0 times the size is required. Therefore, under these conditions, the actual pattern gap is 20 μm to 15 μm.
A dimension of about 0 μm is required.

As described above, since the voltage is not always applied in the pattern gap, the liquid crystal molecules in this portion do not move in the alignment state when the liquid crystal panel is manufactured, and moreover, such a pattern gap is not formed. Since the width has a dimension of at least 20 μm to 150 μm,
Since the liquid crystal molecules in this portion do not move, the laser light that is not controlled by the liquid crystal panel is wasted in at least this portion, resulting in a loss of the amount of light used as a light bed.

Furthermore, the loss of the amount of light that can be effectively used as the light bed is not limited to the light of the area of the pattern gap, and the loss of the light reaches a larger area. In other words, in other words, although the polarization angle or the amount of phase difference exactly corresponding to the voltage applied to each of the regions divided by the pattern gap should be obtained, it is particularly remarkable in the peripheral portion of the pattern gap. The inventors of the present invention have confirmed that the polarization angle or the amount of phase difference deviates greatly from a desired accurate value.

That is, as shown in FIG. 9, an electrode 602a is formed on an upper (in the figure) substrate 601a, and the electrode 602a is etched away in the right half of the figure to form a pattern gap 603. ing. A common electrode 604 is formed on the lower substrate 601b in the figure so as to cover almost the entire surface thereof. In addition, the electrode 602
A protective film 609 is formed so as to cover a and the common electrode 604. The liquid crystal layer 605 was a P type and was of a homogeneous alignment type. As shown in FIG. 10, the liquid crystal molecules 606 are actually provided with a pretilt angle of several degrees in order to prevent disclination or the like, as in a so-called general liquid crystal display panel.

In the liquid crystal panel 600 having such a structure,
When a voltage is applied between the electrode 602a and the common electrode 604, the liquid crystal molecules 606a sandwiched at the position where the electrode 602a and the common electrode 604 face each other are moved so as to rise by the electric field between the electrodes. .
On the other hand, the liquid crystal molecules 6 at the position of the pattern gap 603
Since the electric field does not act on 06b, the liquid crystal molecules 606b in this region remain in the horizontal alignment. As described above, the liquid crystal molecules 606b at the position of the pattern gap 603 remain in the horizontal posture, and the liquid crystal molecules 606a in the region to which the voltage is applied are moved to the posture (tilt angle) completely corresponding to the applied voltage. Was considered to be.

However, since the liquid crystal molecule 606a moved so as to rise is sufficiently separated from the pattern gap 603 in the horizontal distance, it is theoretically moved up to the tilt angle corresponding to the applied voltage. The liquid crystal molecules 606c located closer to the pattern gap 603 than this are in a state where they cannot fully rise, and a predetermined phase difference should be given to the laser light passing through the liquid crystal layer 605 in this region. I can't. This is because the liquid crystal molecules 6 in the vicinity of the pattern gap 603 due to the intermolecular force caused by the polar moment of the liquid crystal molecules 606b in the horizontally aligned state.
It is considered that the movement of 06c is hindered, but in any case, not only the portion of the pattern gap 603 but also the liquid crystal molecule 606 which is in a state where it cannot rise completely.
The problem is that the desired tilt angle change of the liquid crystal molecules cannot be obtained over the wide region 607 where c exists, and as a result, the light in the wide region 607 cannot be effectively used. There is.

As described above, in the conventional technique, the liquid crystal panel 4 used for controlling the optical characteristics of the laser light in the optical pickup as described above should normally move like 606a when a voltage is applied. Liquid crystal molecule 606c
However, since the tilt angle change was slowed by the influence of the liquid crystal molecules 606b in the pattern gap region, there was a problem that the function could not be sufficiently fulfilled.

The present invention has been made to solve such a problem. The present invention reduces the effect that the change in the tilt angle of the liquid crystal molecules 606c that should be moved by applying a voltage becomes dull, and effectively uses the loss of the laser light or the error of the polarization angle or the phase difference amount given to the laser light. It is an object of the present invention to realize an optical pickup capable of effectively utilizing laser light by preventing the above.

[0014]

First, an optical pickup according to the present invention is provided with at least a laser light source, an objective lens, and an optical axis of a laser beam, and a plurality of applied voltages are controlled independently of each other. An optical pickup having a liquid crystal panel in which a transparent electrode divided into regions is formed, wherein the liquid crystal molecules of the liquid crystal panel have a homogeneous alignment, and the pretilt angle of the liquid crystal molecules is 10 to 30 degrees.
For the alignment film of the liquid crystal panel, the alignment film material is applied to the main surface of the substrate.
It is characterized in that it is formed by an oblique vapor deposition method in which vapor deposition is performed obliquely .

In the optical pickup according to the technique of the present invention, the liquid crystal layer of the liquid crystal panel used in the conventional optical pickup is a liquid crystal in a region where the tilt angle is blunted at least under the influence of the voltage-unapplied liquid crystal molecules. By forming a molecule, that is, a region or a liquid crystal molecule including the region further in the entire surface of the liquid crystal layer and having a homogeneous alignment with a pretilt angle of 10 to 30 degrees, the pattern gap as described above is obtained. The liquid crystal molecule 606c at a position closer to the pattern gap 603 caused by the liquid crystal molecule 606b or the like at the position 603.
It is possible to reduce the influence of the tilt angle blunting.

Secondly, the optical pickup of the present invention is divided into at least a laser light source, an objective lens, and a plurality of regions which are provided on the optical axis of the laser beam and whose applied voltage is controlled independently of each other. an optical pickup having a liquid crystal panel that is a transparent electrode is formed, the liquid crystal molecules of the liquid crystal panel is homeotropic alignment, the pretilt angle of the liquid crystal molecules 60 to 80 degrees, the liquid
The alignment film of the crystal panel is made by aligning the alignment film material with respect to the main surface of the substrate.
It is characterized in that it is formed by an oblique vapor deposition method of vapor deposition from one side .

That is, the optical pickup described in the above-mentioned first is one in which the technique of the present invention is applied to an optical pickup using a liquid crystal panel of a homogeneous alignment system. Also, it can be applied to an optical pickup using a homeotropic alignment type liquid crystal panel, and in that case, similarly to the above,
Set the pretilt angle of liquid crystal molecules to 60-80 degrees,
By making the liquid crystal molecules easy to move in advance, it is possible to obtain the same effect as in the first aspect.

Thirdly, the optical pickup according to the present invention is characterized in that, in the optical pickup described in the first aspect, the liquid crystal panel is arranged so as to be inclined by the pretilt angle with respect to the optical axis. It is an optical pickup.
Fourthly, the optical pickup according to the present invention is the same as the optical pickup according to the second aspect, except that the liquid crystal panel is
The optical pickup is arranged so as to be inclined with respect to the optical axis by an angle obtained by subtracting the pretilt angle from the degree.

Fifthly, in the optical pickup described in the first aspect, the director of the liquid crystal molecules aligned at the pretilt angle of the liquid crystal layer when the voltage is not applied is directed to the straight direction of the light. The optical pickup is characterized in that the main surface of the liquid crystal panel is disposed so as to be inclined with respect to the straight traveling direction of the light so that the liquid crystal panel is oriented in an orthogonal direction.

Alternatively, in the sixth aspect, in the optical pickup described in the second aspect, the director of the liquid crystal molecules aligned at the pretilt angle of the liquid crystal layer when the voltage is not applied is directed toward the straight direction of the light. In the optical pickup, the main surface of the liquid crystal panel is arranged so as to be inclined in a direction parallel to the direction of the straight line of the light.

That is, in the above-mentioned first or second technique, the pretilt angle of the liquid crystal molecules is set to a relatively large angle, so that in some cases, the liquid crystal panel may strictly be exactly the desired polarization angle or position. It may be considered that the liquid crystal panel that realizes the amount of phase difference does not function.

Therefore, according to the third or fifth technique, even if the liquid crystal molecules are given a relatively large pretilt angle as described above, the liquid crystal molecules are tilted by the pretilt angle of the liquid crystal molecules with respect to the optical axis. Arrange the liquid crystal panel. Alternatively, the director of the liquid crystal molecules is orthogonal to the straight direction of the light (and the opposite direction of 180 degrees, that is, the recording surface of the information recording medium-the objective lens-the beam splitter-the optical axis of the optical system connecting the laser light sources). Thus, the main surface of the liquid crystal panel is adjusted and arranged so as to be oblique to the direction in which the light travels straight. As a result, the maximum amount of retardation that can be provided by the liquid crystal can be made the same as when no pretilt angle is provided.

Similarly, with respect to the function of the liquid crystal panel for an optical pickup that corrects the error of the polarization angle and the amount of phase difference due to the tilt angle of the optical disc, similarly, a large pretilt angle is applied to the liquid crystal molecules in the state where no voltage is applied. Even if it is added, since the director of the liquid crystal molecule is orthogonal to the optical axis, it is possible to prevent the deviation of the optical characteristics of the liquid crystal panel in that state (so-called initial condition). Therefore, the function of correcting the error of the polarization angle or the amount of phase difference can be effectively achieved.

Further, since the main surface of the liquid crystal panel is arranged so as to be inclined with respect to the optical axis, even if the laser light is reflected by the surface of the glass substrate or the transparent electrode of the liquid crystal panel, the reflected light is reflected by the optical axis. Since it is reflected in the direction away from, it will not be a stray light and enter the light receiver.

In the case of the fourth or sixth technique,
The technique used for the liquid crystal panel of the homogeneous alignment system described in the third or fifth is applied to the liquid crystal panel of the homeotropic alignment system, and the operation-effect is basically the same as that of the third or fifth structure. It goes without saying that it is similar to technology.

Seventhly, in the optical pickup according to any one of the first to sixth aspects, the optical pickup is an optical pickup for reading information on an optical disc, and the liquid crystal panel includes the optical disc and the laser. The liquid crystal panel is characterized in that it is controlled so as to correct the wavefront aberration caused by the displacement with respect to the displacement of the angle formed by the optical axis of the beam. That is, the technique of the present invention is particularly suitable for such an optical pickup.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an optical pickup according to the present invention will be described below in detail with reference to the drawings. (Embodiment 1) As shown in FIG. 1, the optical pickup of the present embodiment transmits a laser light source 1 and a light P emitted from the laser light source 1 and transmits reflected light from an optical disc P '.
A beam splitter 2 that reflects the light P, an objective lens 5 that guides the light P transmitted through the beam splitter 2 so as to focus on the recording surface of the information recording medium 6, and a collimator that makes the light P from the laser light source 1 parallel light. It has a lens 3 and a condenser lens 7 that converges the light P ′ reflected by the beam splitter 2 onto a light receiving element 8. As will be described later, FIG. 1A shows a case where the main surface of the liquid crystal panel 4 is arranged at an angle θ with respect to the optical axis, and FIG. The figure shows the case where they are arranged so as to be orthogonal to the axis.

Further, the liquid crystal panel 4 gives a phase difference of a total of 1/4 wavelength or a phase difference of an odd multiple of 1/4 wavelength before or after the incident laser beam is transmitted, or the laser beam is transmitted. At this time, a plurality of applied voltages are controlled independently of each other in order to control the optical characteristics of the transmitted light, such as giving a phase difference amount according to the angle formed by the information recording medium 6 and the optical axis of the laser light. An electrode divided into regions is formed. In addition, almost all liquid crystal layers of the liquid crystal panel 4 are homogeneously aligned with pretilt angles of liquid crystal molecules of 10 to 30 degrees. Although the liquid crystal panel 4 is arranged between the objective lens 5 and the beam splitter 2 in FIG. 1, it may be arranged anywhere on the optical axis between the laser light source 1 and the objective lens 5.

The laser light source 1, the beam splitter 2, the collimator lens 3, the objective lens 5, the information recording medium 6, the condenser lens 7 and the light receiving element 8 are the same as those used in the conventional general optical pickup. The specifications are used. The laser light source 1 is 680 nm to 780 n
A laser beam having a wavelength of about m is generated and emitted. Further, as the beam splitter 2, for example, a prism beam splitter using a prism, a polarizing beam splitter also having a polarization characteristic, or a light transmitting / reflecting plate such as a half mirror can be used.

The information recording medium 6 is a CD or D
A liquid crystal panel control circuit 9 controls a voltage applied to an electrode having a plurality of divided areas of the liquid crystal panel 4 on an optical disk such as a VD. When the liquid crystal panel 4 of FIG. 1 has an electrode pattern as shown in FIG. 8B having a function of substantially changing the NA of the objective lens 5, no voltage is applied to the liquid crystal when reproducing a DVD. Like the transparent glass, the liquid crystal panel does not exert any optical action on the transmitted light. Then, when playing back a CD, for example, FIG.
A predetermined voltage is applied to the electrodes in the outer region so that the outer region of the regions (electrodes) divided into the pattern as shown in (b) acts as a quarter-wave plate.

When the liquid crystal panel 4 of FIG. 1 has a function of correcting the wavefront aberration caused by the displacement of the angle formed by the optical disk and the optical axis of the laser beam, for example, as shown in FIG. The control circuit for controlling the panel 4 corrects the wavefront aberration caused by the tilt angle of the optical disc based on a signal from a tilt sensor (that is, a sensor for detecting the tilt angle of the optical disc) not shown. , Outputs the voltage to be applied to each divided region.

Regarding the operation of the liquid crystal panel 4 and the structure of the liquid crystal panel control circuit 9 for applying a voltage to the liquid crystal panel 4 as described above, for example, Japanese Patent Application No.
-199500, Japanese Patent Application No. 9-56318, and the like. Hereinafter, the liquid crystal layer inside the liquid crystal panel 4 will be described in detail. As shown in FIG. 2, the liquid crystal panel 4 used in the optical pickup according to the present invention is arranged between the liquid crystal molecules 606b to which no voltage is applied, which are substantially present in the pattern gap 603 of the electrode 602a. Even if the liquid crystal molecule 606c is dragged due to the intermolecular force, the liquid crystal molecule 606c is influenced by the liquid crystal molecule 606b so that a sufficient tilt angle can be obtained without slowing the movement of the tilt angle. The pretilt angle θ of the liquid crystal layer 605 on almost the entire surface of the liquid crystal panel including the area
It is controlled by the alignment films 608a and 608 so that the angle is in the range of 0 to 30 degrees (360 degrees notation). That is, as compared with FIG. 9, the region in which the liquid crystal molecules can move sufficiently to give a predetermined phase difference is dramatically improved, and the adverse effect at the pattern gap 603 is significantly reduced. Of.

Next, the effect of controlling the pretilt angle θ of the liquid crystal molecules to 10 to 30 degrees as described above was confirmed by experiments. This will be described below. When the pretilt angle θ of the liquid crystal molecule as shown in FIG. 9A is set to 0 degrees or several degrees (up to about 5 degrees at most) as in the related art and the problem to be solved, It was found that the amount of retardation given to the transmitted light of the liquid crystal panel becomes much lower than the theoretical value (ideal value) from the pattern gap 603 to a considerable extent.

That is, the phase difference amount at a position sufficiently far from the pattern gap 603 is set as a reference value of 1, and the ratio of the phase difference amount measured at each position to this is plotted as a dimensionless amount on the vertical axis, and the horizontal axis. When the respective positions are plotted, the curve becomes such that the phase difference amount becomes dull over a wide region (D) as shown in FIG. 9B.

On the other hand, FIG. 2 to which the technique according to the present invention is applied.
In the case of the liquid crystal panel as shown in (a), a graph plotted in the same manner as the above was drawn, and as a result, a curve as shown in FIG. A region (D) in which the liquid crystal molecule 606b in its original state drags the liquid crystal molecule 606c in its vicinity to rise and blunts its tilt angle (D).
It has been confirmed that the power consumption can be reduced to a fraction of the conventional one. In particular, the amount of retardation slowed (decreased) as shown in FIG.
Is greater than 5%, and the distance D from the end of the pattern gap 603 in a region that adversely affects the usable light amount is measured. As a result, the conventional D = 13 μm at θ = 2 ° With the technique according to the present invention, when θ = 10 degrees as shown in FIG. 2, D = 17 μm and the value is halved.
= 20 degrees, D = 3.8 μm, and θ = 30 degrees, D = 3.
0 μm, and according to the present invention, D is 1
It was confirmed that / 2 to 1/3 or less could be dramatically improved.

The result of confirming the relationship between D and θ by an experiment is shown in FIG. As described above, according to the present invention, it is possible to reduce the blunting of the tilt angle of the liquid crystal molecules due to the pattern gap of the electrodes, and thus, it is possible to sufficiently obtain a desired phase difference for the laser light passing through each divided region. Can be given to.

Further, the liquid crystal layer 6 of the liquid crystal panel 4
There are other effects obtained by setting the pretilt angle θ of 05 to 10 to 30 degrees. That is, FIG. 4 is a diagram showing a graph (A) when the pretilt angle is θ = 2 degrees and a graph (B) when the pretilt angle is θ = 10 degrees, but as shown in FIG. When 1.5 V (volt) is applied to the liquid crystal layer, the phase difference obtained in the case of the liquid crystal layer of θ = 2 degrees is about 0.1 μm. , The obtained phase difference is about 0.25 μm,
It can be seen that the phase difference is dramatically improved by more than twice. That is, by increasing the pretilt angle θ in this way, the rising threshold voltage of the liquid crystal layer can be lowered, and thus the operating voltage level of the liquid crystal panel 4 can be lowered, so that especially the power supply voltage It can be said that the characteristics are suitable for optical pickups used in portable electronic devices and electronic devices mounted on automobiles that are severely limited.

On the other hand, on the other hand, as the pretilt angle θ is increased, the obtained phase difference amount is decreased conversely. That is, the phase difference amount when the pretilt angle θ = 0 degree is set to 1 as a reference value, and the ratio of the phase difference amount for each pretilt angle θ to this is taken as a dimensionless amount on the vertical axis, and the horizontal axis shows the pretilt angle. As a result of plotting the change of θ and plotting the change, the graph as shown in FIG. 5 was obtained. As is clear from the figure, the phase difference amount obtained as the pretilt angle θ is increased is Conversely, as the pretilt angle θ exceeds 30 degrees, the phase difference amount becomes θ = 0.
Compared to the case of, it fell to about 70%, and from this point the function as a substantial quarter wave plate,
In some cases, the function of correcting the tilt angle of the optical disc cannot be fully fulfilled. Further, when the pretilt angle θ exceeds 40 degrees, the amount of phase difference becomes half or less compared with the case of θ = 0, and the obtained phase difference becomes about 1/8 at most or substantially less than that, which is completely practical. It becomes unsuitable.

Therefore, it is considered that the preferable value of the pretilt angle θ in the liquid crystal panel according to the present invention is the above-mentioned 30 degrees as an appropriate upper limit. Although the inside of the liquid crystal panel 4 used in the optical pickup according to the present invention has been described above, the liquid crystal panel 4 further includes, as shown in FIG.
The main surface thereof is not orthogonal to the optical axis of the optical system (that is, the central axis of the path of the laser beam) connecting the recording surface of the information recording medium 6 to the objective lens 5 to the beam splitter 2 to the laser light source 1, and the above-mentioned pretilt They are arranged with an inclination angle of about 90-θ corresponding to the angle θ, whereby the director of liquid crystal molecules in the liquid crystal panel 4 in the absence of voltage application is installed so as to be orthogonal to the optical axis. Has been done. In addition, in FIG. 6 and FIG. 7, similar portions are denoted by the same reference numerals.

In the case of a P type liquid crystal panel as shown in FIG. 6,
The liquid crystal molecule is a so-called homogeneous alignment type liquid crystal panel in which the liquid crystal molecules are substantially parallel to the glass substrate 401 when no voltage is applied, but the liquid crystal molecules 500 have a predetermined pretilt angle θ (θ = 10 to 30 degrees) due to the alignment film 403. Is given.

Therefore, according to the present invention, as already shown in FIG. 1A, the liquid crystal panel 4 is tilted by θ degrees corresponding to the pretilt angle θ, and the liquid crystal of the liquid crystal layer in the liquid crystal panel 4 is tilted. The molecules are arranged so as to intersect the optical axis of the objective lens 5 at right angles. For example, the pretilt angle or the angle formed by the director of liquid crystal molecules in the pretilt state with respect to the substrate is θ = 2.
In the case of 0 degree, the main surface of the liquid crystal panel 4 may be arranged so as to be inclined so as to intersect the optical axis at an angle of θ = 20 degrees. FIG. 6 also shows a case where the liquid crystal panel 4 is arranged at such an angle θ. In FIG. 6, 401 is a glass substrate, 402a and 402b are transparent electrodes divided into two regions, 404 is a liquid crystal layer, and 405 is a pattern gap. With such an arrangement, even when no voltage is applied to the transparent electrode 402a at the time of DVD reproduction and all the liquid crystal molecules are in a state orthogonal to the optical axis, the entire surface of the liquid crystal panel 4 is complete. It works as a 1/4 wavelength plate. Therefore, the laser light composed of the linearly polarized wave incident on the liquid crystal panel 4 is emitted as a completely circularly polarized wave after passing through the liquid crystal panel 4.

As described above, the liquid crystal panel 4 is tilted by an angle θ corresponding to the pretilt angle θ, and the liquid crystal molecules are arranged so as to intersect at right angles with the optical axis when no voltage is applied. The maximum possible phase difference amount can be made the same as when the pretilt angle is not given. Figure 1
In the case of (b), the maximum amount of phase difference is reduced by the amount corresponding to the pretilt angle of the liquid crystal molecules, but the decrease in phase difference due to the pretilt angle shown in FIG. 5 can be eliminated. Therefore, the utilization efficiency of light in the liquid crystal panel 4 is improved, and unnecessary light does not leak to the light receiving element 8, so that the S / N can be improved.

Further, the glass substrate 40 of the liquid crystal panel 4
1, the transparent electrode 402a and the alignment film 403 also have a pretilt angle θ.
Therefore, even if the laser light is reflected on these surfaces, the reflected light is reflected in the direction of leaving the optical axis, so that it becomes stray light and enters the light receiving element 8. Such things will disappear. This allows the glass substrate 4 of the liquid crystal panel 4 to be used without using an antireflection film or the like.
It is possible to solve the conventional problem that stray light caused by reflected light on the main surface such as 01 enters the optical system and adversely affects its function as an optical pickup.

(Embodiment 2) In the first embodiment, the case where a homogeneous alignment type liquid crystal panel is used as the liquid crystal panel 4 has been described. However, the application of the technique according to the present invention applies to such a type of liquid crystal panel. The present invention is not limited to the panel, but can be applied to an optical pickup using a homeotropic alignment type liquid crystal panel.

Also in this case, similarly to the technique described in detail in the first embodiment, the pretilt angle θ of the liquid crystal molecules is set in advance to an angle that facilitates movement of the liquid crystal molecules. The same effect as the embodiment can be obtained. In the case of such a homeotropic alignment type liquid crystal panel, a preferable pretilt angle θ is 6
It is 0 to 80 degrees.

Furthermore, as in the first embodiment, the liquid crystal panel 4 has an optical system whose main surface connects the recording surface of the information recording medium 6 to the objective lens 5 to the beam splitter 2 to the laser light source 1. The liquid crystal molecules 5 are arranged not at right angles to the optical axis but at an inclination of about the above-described pretilt angle θ, so that the liquid crystal molecules 5 in the liquid crystal panel 4 in the absence of voltage application
00 directors are installed so as to be orthogonal to the optical axis.

That is, as shown in FIG. 7, in the case of the N-type liquid crystal panel, the liquid crystal molecules when no voltage is applied are made of the glass substrate 4.
The liquid crystal panel is a so-called homeotropic alignment type liquid crystal panel in which the alignment state is nearly perpendicular to 01, but the liquid crystal molecules 500 are given a predetermined pretilt angle θ (θ = 60 to 80 degrees) by the alignment film 403. Has been. Therefore, the liquid crystal panel 4 is set to 90-θ corresponding to this pretilt angle θ.
The liquid crystal molecules 500 are arranged so as to be parallel to the optical axis of the objective lens 5 by arranging the liquid crystal molecules at an angle. For example, when the pretilt angle θ = 70 degrees, that is, when the angle θ = 70 degrees formed by the director of the liquid crystal molecules in the substantially pretilt state is set, the main surface of the liquid crystal panel 4 is set to the optical axis. It is sufficient to incline so that they intersect at an angle of 20 degrees.

As described above, the liquid crystal panel 4 is tilted by an angle corresponding to the pretilt angle θ, and the liquid crystal molecules 500 are arranged parallel to the optical axis when no voltage is applied. Similar to the embodiment, it is possible to eliminate the decrease in the amount of phase difference due to the pretilt angle. Therefore, the utilization efficiency of light in the liquid crystal panel 4 is improved, and unnecessary light is prevented from leaking to the light receiver 8.
The S / N can be improved.

Further, the glass substrate 40 of the liquid crystal panel 4
1, the transparent electrode 402a and the alignment film 403 also have a pretilt angle θ.
Therefore, even if the laser light is reflected on these surfaces, the reflected light is reflected in the direction away from the optical axis, and becomes stray light.
It will not be incident on. This allows the glass substrate 40 of the liquid crystal panel 4 to be used without using an antireflection film or the like.
It is possible to solve the conventional problem that stray light caused by reflected light on the principal surface such as 1 enters the optical system and adversely affects its function as an optical pickup.

In either of the homogeneous alignment method and the homeotropic alignment method, the above 10
As a method for producing an alignment film for achieving a large pretilt angle of -30 degrees or 60-80 degrees, it is possible to use a method such as a rubbing method that is widely used for alignment films of conventional TN liquid crystal panels. Since it cannot be practically used in the case of obtaining a pretilt angle of about 8 degrees, another manufacturing method is required.

For example, a method of forming an alignment film, which is a so-called oblique evaporation method, in which an alignment film material such as an oxide such as silicon dioxide or a metal is obliquely vapor-deposited with respect to the main surface of the substrate, is preferably used. Can be formed. Alternatively, it goes without saying that any manufacturing method can be used as long as it is a manufacturing method of the alignment film capable of obtaining the pretilt angle as described above.

In each of the above embodiments, the pretilt angle of liquid crystal molecules is 10 to 3 over the entire surface of the liquid crystal panel.
Although the case of controlling to 0 degree has been described, in view of the technical effect of the present invention, it is not always necessary to cover the entire surface of the liquid crystal panel, and the intermolecular force of liquid crystal molecules in which a voltage is not always applied in the pattern gap portion Only the liquid crystal molecules in the region where the liquid crystal molecules that are influenced and have the tilt angle dragged, that is, the liquid crystal molecules in the region D described in FIG. 9 are controlled to the pretilt angle of 10 to 30 degrees as described above. However, it goes without saying that it is good.

However, in this case, it is necessary to selectively form the alignment film for controlling the pretilt angle of 10 to 30 degrees as described above only in the region D. In such a case, since the method of forming a uniform oblique vapor deposition film over almost the entire surface of a general liquid crystal panel as described above cannot be used as it is, only the area D is exposed. However, the manufacturing method is such that the substrate is masked with a photoresist or the like so as to cover other portions, and the oblique vapor deposition film is selectively formed only on the portion exposed from the masking (photoresist or the like). It is possible to selectively form an alignment film that achieves a pretilt angle of 10 to 30 degrees only in the above region.

As described above, the present invention is a technique particularly suitable for improving the performance and expanding the functions of the liquid crystal panel used for the optical pickup.

[0055]

As described above in detail, according to the present invention, it is possible to effectively reduce the influence that the change of the tilt angle of the liquid crystal molecules to which the voltage is applied to move is reduced, and it is effective. It is possible to realize an optical pickup that can effectively and accurately use laser light by preventing loss of usable laser light or generation of an error in the amount of phase difference given to the laser light.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a structure of an optical pickup according to a first embodiment.

FIG. 2 is an enlarged schematic diagram showing a pattern gap portion of a liquid crystal panel 4 used in the optical pickup of the first embodiment.

FIG. 3 is a graph showing a result of experimentally confirming a relationship between an affected region D and a pretilt angle θ.

FIG. 4 shows the relationship between the pretilt angle θ and the applied voltage as θ = 2
FIG. 7 is a diagram showing a graph in which experiments were performed for the case of θ and the case of θ = 10 degrees.

FIG. 5 is a graph showing a result obtained by an experiment regarding a relationship between a pretilt angle θ and a phase difference amount.

FIG. 6 is a cross-sectional view showing a state in which the liquid crystal panel 4 used in the optical pickup of the first embodiment is tilted at an inclination angle of about θ corresponding to the pretilt angle θ with respect to the straight traveling path of the laser light. Is.

FIG. 7 shows a state in which the liquid crystal panel 4 used in the optical pickup of the second embodiment is arranged with an inclination angle of about 90-θ corresponding to the pretilt angle θ with respect to the straight traveling path of the laser light. FIG.

FIG. 8 is a diagram exemplifying three types of electrode division patterns of a liquid crystal panel 4 used for an optical pickup.

FIG. 9 is a diagram showing a pattern gap portion in the liquid crystal panel 4 of the optical pickup.

FIG. 10 is a diagram schematically showing a case where a liquid crystal molecule 500 in a liquid crystal panel is provided with a conventional pretilt angle θ of several degrees (about 5 degrees at most).

[Explanation of symbols]

1 ... Laser light source 2 ... Beam splitter 3 ... Collimator lens 4 ………… Liquid crystal panel 5 ... Objective lens 6 ... Information recording medium 7 ... Condensing lens 8 ... Light receiving element

Continuation of the front page (56) References JP-A-9-245370 (JP, A) JP-A-9-128785 (JP, A) JP-A-6-317776 (JP, A) JP-A-5-222411 (JP , A) JP-A-5-313169 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B 7/12 G11B 7/135

Claims (7)

(57) [Claims] 1. A liquid crystal panel having at least a laser light source, an objective lens, and a transparent electrode provided on the optical axis of a laser beam and divided into a plurality of regions whose applied voltages are controlled independently of each other. Wherein the liquid crystal molecules of the liquid crystal panel are in a homogeneous alignment,
A pretilt angle of the liquid crystal molecules in the 10-30 degrees, the orientation film of the liquid crystal panel, pairs of alignment film material on the substrate main surface
The optical pickup is characterized by being formed by an oblique deposition method in which it is obliquely deposited . 2. A liquid crystal panel having at least a laser light source, an objective lens, and a transparent electrode which is provided on the optical axis of a laser beam and is divided into a plurality of regions whose applied voltages are controlled independently of each other. an optical pickup having a liquid crystal molecules of the liquid crystal panel is homeotropic alignment, the pretilt angle of the liquid crystal molecules 60 to 80 degrees, the orientation film of the liquid crystal panel, an alignment film material on the substrate main surface versus
An optical pickup characterized by being formed by an oblique vapor deposition method of obliquely vapor depositing . 3. The optical pickup according to claim 1, wherein the liquid crystal panel is arranged at an angle of the pretilt angle with respect to the optical axis. 4. The optical pickup according to claim 2, wherein the liquid crystal panel is tilted with respect to the optical axis by an angle obtained by subtracting the pretilt angle from 90 degrees. 5. The optical pickup according to claim 1, wherein a director of the liquid crystal molecules aligned at the pretilt angle of the liquid crystal layer when the voltage is not applied is a direction orthogonal to a straight traveling direction of the light. The optical pickup is arranged such that the main surface of the liquid crystal panel is inclined with respect to the straight traveling direction of the light. 6. The optical pickup according to claim 2, wherein a director of liquid crystal molecules aligned at the pretilt angle of the liquid crystal layer when the voltage is not applied is parallel to a straight traveling direction of the light. An optical pickup characterized in that the main surface of the liquid crystal panel is arranged so as to be inclined with respect to the straight traveling direction of the light. 7. The optical pickup according to claim 1, wherein the optical pickup is an optical pickup for reading information on an optical disc, and the liquid crystal panel is an optical axis of the optical disc and the laser beam. An optical pickup which is a liquid crystal panel controlled so as to correct a wavefront aberration caused by the displacement of an angle formed by the displacement.