JP4008944B2 - Liquid crystal aberration correction element - Google Patents

Description

【Technical field】
[0001]
The present invention belongs to the technical field of a liquid crystal aberration correction element used to correct aberrations occurring during recording / reproduction with an optical pickup in an optical disc apparatus.
[Background]
[0002]
Conventionally, various optical discs such as CD and DVD are known as information recording media. Since these optical discs generate aberrations (distortion of the condensing spot) due to thickness deviation or warping caused by rotation, it is required to correct the aberrations and improve recording / reproducing accuracy.
Particularly recently, BD (Blu-ray Disc) has attracted attention as a next-generation optical disc. In this standard, the light source wavelength is increased from 650 nm to 405 nm, the numerical aperture (NA) of the objective lens is increased from 0.6 to 0.85, and the surface recording density is improved to about 5 times that of the conventional DVD. Here, since the spherical aberration caused by the thickness deviation is inversely proportional to the wavelength of the light source and proportional to the fourth power of NA, the aberration tends to increase rapidly in BD. Therefore, development of a technique for correcting aberrations with higher accuracy has been desired.
[0003]
As a technique for correcting the aberration, a method of driving a collimator lens with an actuator and a method of using a liquid crystal aberration correction element are known.
In the former method, an actuator is required, so that the optical pickup becomes complicated, and there is a problem that it cannot cope with high-precision correction.
On the other hand, the liquid crystal aberration correction element generally divides the electrodes of the liquid crystal panel into concentric circles, thereby performing different phase control between the central portion and the outer edge portion of the light beam.
[0004]
For example, (Patent Document 1) discloses a first electrode layer having a plurality of concentric electrode portions associated with a distribution of spherical aberration generated in an optical disc, and a second electrode layer facing the first electrode layer. A liquid crystal that is sandwiched between the first and second electrode layers and causes a light beam that passes through a phase change in accordance with a voltage applied to the first and second electrode layers. ing.
[0005]
Further, in Patent Document 2, in an optical pickup used in a multi-layer disc reproducing apparatus for reproducing a multi-layer disc having a plurality of recording layers, the recording is arranged and selected in an optical path between a light source and an objective lens. According to the layer, there is described an optical pickup provided with wavefront aberration correction means for correcting wavefront aberration of light emitted from the light source, and the wavefront aberration correction means is configured by a liquid crystal element. It is described that a concentrically divided electrode for applying a voltage is provided.
[0006]
In order to perform good correction, it is ideal to add an opposite phase wave to the generated aberration. Therefore, in the case of the above conventional liquid crystal aberration correcting element, it is desirable to form as many concentric divided electrode regions as possible, but the element is generally of a very small size (about 3 to 4 mm in diameter). It is extremely difficult to increase the area (about 10 tones is the limit).
Therefore, it has been desired to develop a liquid crystal aberration correction element capable of linearly correcting the generated aberration.
[0007]
As another problem, when an opposite phase wave is applied using the liquid crystal aberration correction element as described above, if the generated aberration is large, it is difficult to obtain a phase difference corresponding to the aberration. There was a case. As a result, there is a problem that the aberration cannot be completely corrected.
Therefore, it has been desired to develop a liquid crystal aberration correction element that can sufficiently obtain an absolute amount (phase difference) of the correction while performing linear correction on the generated aberration.
[0008]
[Patent Document 1]
JP 2002-237077 A (Claim 1, paragraph 0014)
[Patent Document 2]
Japanese Patent Laid-Open No. 10-269611 (Claims 1 to 4)
DISCLOSURE OF THE INVENTION
[Problems to be solved by the invention]
[0009]
Accordingly, in view of the above-described conventional situation, the present invention provides a novel liquid crystal aberration correction element that linearly corrects an aberration caused by a thickness deviation of an optical disk and the like, thereby improving recording / reproducing accuracy. With the goal.
It is another object of the present invention to provide a novel liquid crystal aberration correction element that not only corrects aberrations linearly but also has a large correction amount.
[Means for Solving the Problems]
[0010]
In order to solve the above-described problem, a liquid crystal aberration correcting element of the present invention includes a liquid crystal and a plurality of electrodes facing each other with the liquid crystal interposed therebetween, and a plurality of non-electrodes in which no electrode material is present in at least one of the electrodes A portion is formed, and inside the non-electrode portion, the liquid crystal is configured to be non-uniformly aligned when a voltage is applied.
【The invention's effect】
[0011]
The liquid crystal aberration correction element of the present invention produces a lens effect by forming a plurality of non-electrode portions on an electrode and orienting liquid crystal molecules along a non-uniform electric field distribution formed at the positions of the non-electrode portions. Let As a result, it is possible to linearly correct the aberration caused by the thickness deviation of the optical disk. The alignment state of the liquid crystal can be controlled by the applied voltage, and the correction amount can be arbitrarily changed accordingly.
According to the present invention, the distortion of the focused spot is corrected, and the recording / reproducing accuracy can be improved. Therefore, it is suitable as a correction element for the next generation high density optical disc.
[0012]
In addition, the liquid crystal aberration correcting element of the present invention changes the size and arrangement interval of the plurality of non-electrode portions depending on the positions on the electrodes, and the plurality of linear electrodes are arranged along the arrangement pattern of the non-electrode portions. It is characterized by being arranged at intervals. Thereby, the phase difference obtained by the non-electrode part is forcibly increased at a plurality of places where the linear electrodes are arranged, and the phase difference curve resulting from the non-electrode part as a whole is emphasized. A big state can be obtained.
[Brief description of the drawings]
[0013]
FIG. 1 is a plan view of a liquid crystal aberration correction element according to an embodiment (1).
FIG. 2 is an enlarged view of a portion A in FIG.
FIG. 3 is a cross-sectional view of the liquid crystal aberration correcting element according to Embodiment (1).
FIG. 4 is a diagram for explaining a state when a voltage is applied to the liquid crystal aberration correcting element according to the embodiment (1).
FIG. 5 is a plan view of a liquid crystal aberration correcting element according to Embodiment (2).
FIG. 6 is a plan view of a liquid crystal aberration correcting element according to Embodiment (3).
FIG. 7 is a diagram schematically showing the amount of phase change obtained by the liquid crystal aberration correcting element according to Embodiment (3).
FIG. 8 is a diagram for explaining a manufacturing process of the liquid crystal aberration correcting element according to the embodiment (3).
[Explanation of symbols]
[0014]
1 liquid crystal aberration correcting element 10 liquid crystal 20 electrode 21 electrode 201 non-electrode portion 30 substrate 31 substrate 40a~40d linear electrodes 400 electrodes 50 SiO ₂ film E field S1, S2 terminal R1~R3 resistance P, Q phase difference curve INVENTION BEST MODE FOR IMPLEMENTING
[0015]
The present invention includes a liquid crystal and a plurality of electrodes facing each other with the liquid crystal interposed therebetween, and at least one of the electrodes is formed with a plurality of non-electrode portions where no electrode material is present. Corrects liquid crystal aberrations by aligning the liquid crystal in a non-uniform manner when applying voltage, and changing the size and spacing of multiple non-electrode parts along the radial direction when the electrodes are divided concentrically. An element is provided (first invention).
[0016]
According to this configuration, a weak electric field is formed in the vertical direction with respect to the electrode at the center of the formed non-electrode part, and an electric field is inclined at the end of the non-electrode part. By aligning liquid crystal molecules non-uniformly along the electric field distribution, a lens effect is obtained in which the refractive index continuously changes from the center to the periphery of the non-electrode part. Therefore, by allowing the light beam to pass through the lens portion, a predetermined phase difference is given and the aberration is corrected. Further, by changing the size or arrangement interval of the non-electrode portions, the phase difference obtained in each region is set, and the entire element is optimally corrected according to the aberration. Furthermore, according to this configuration, the spherical aberration is favorably corrected by changing the obtained phase difference concentrically.
[0017]
[0018]
[0019]
Further, the present invention includes a liquid crystal and a plurality of electrodes facing each other with the liquid crystal interposed therebetween, and a plurality of non-electrode portions where no electrode material is present in at least one of the electrodes is sized according to positions on the electrodes. Alternatively, it is formed in an arrangement pattern in which the arrangement interval or both are changed, and a plurality of linear shapes are applied inside the non-electrode portion so that liquid crystals are non-uniformly oriented when a voltage is applied, and different voltages are applied. The present invention provides a liquid crystal aberration correcting element in which electrodes are arranged at predetermined intervals along the arrangement pattern (second invention).
[0020]
According to this configuration, the phase difference curve corresponding to the generated aberration can be obtained by changing the size of the non-electrode portion or the arrangement interval with the lens effect as described above, and a plurality of linear electrodes can be obtained. By disposing and applying a voltage to a predetermined part, the above-mentioned phase difference curve is emphasized and an optimum correction amount is obtained.
[0021]
[0022]
[0023]
Further, according to the present invention, in the liquid crystal aberration correcting element according to the second invention, the sizes and arrangement intervals of the plurality of non-electrode portions change along the radial direction when the electrodes are divided concentrically. The linear electrodes of the book are arranged in an annular shape along the arrangement pattern changing concentrically (third invention).
[0024]
According to this configuration, the phase difference at a plurality of locations along the radial direction of the electrode is forcibly raised by the linear electrodes arranged in an annular shape, and the spherical aberration is well corrected in combination with the action of the non-electrode portion. Is done.
[0025]
Further, according to the present invention, in the liquid crystal aberration correcting element according to the first or third invention, the arrangement interval of the plurality of non-electrode portions is irregular in each of the concentrically divided regions on the electrode. Features (fourth invention).
[0026]
According to this configuration, the wavefront disturbance due to the light interference effect is prevented by making the interval between adjacent non-electrode parts irregular (random).
[0027]
Furthermore, the invention is characterized in that in the liquid crystal aberration correcting element according to the first to fourth inventions, the shape of the non-electrode part is circular (fifth invention).
[0028]
According to this configuration, the shape of the non-electrode portion is optimized with respect to the generated aberration.
[0029]
Hereinafter, the present invention will be described in detail.
First, an embodiment (1) of the present invention is shown in FIGS. 1 is a plan view of the liquid crystal aberration correction element 1, FIG. 2 is an enlarged view of a portion A in FIG. 1, and FIG. 3 is an enlarged view of a cross section of the liquid crystal aberration correction element 1. As shown in FIG. 3, the liquid crystal aberration correction element 1 includes a liquid crystal 10, two electrodes 20 and 21 and substrates 30 and 31 that are opposed to each other with the liquid crystal 10 interposed therebetween, and the electrode 20 includes an electrode material. A plurality of non-electrode portions 201 that are not formed are formed in a hole shape. In FIG. 3, an antireflection film (AR film) provided on the substrates 30 and 31, a liquid crystal alignment film generally provided between the electrodes 20 and 21 and the liquid crystal 10, a transparent insulating layer, and the like are illustrated. Omitted. Further, a lead wire or the like is connected to the electrode 20 and the electrode 21 in order to apply a voltage.
[0030]
As shown in FIG. 1, the size and arrangement interval of the plurality of non-electrode portions 201 are continuously changed depending on the position on the electrode 20. Although the number of the non-electrode portions 201 is illustrated as small in FIG. 1 for the sake of convenience, in practice, a large number of non-electrode portions 201 are finely formed as shown in FIG. In this embodiment (1), along the radial direction R when the electrode 20 is divided into concentric circles, the size d1 of the non-electrode portion 201 is once changed from a large diameter to a small diameter and then becomes a large diameter again. In addition, a continuous pattern is formed so that the arrangement interval d2 is once changed from a wide interval to a narrow interval and then becomes a wide interval again.
[0031]
When a voltage is applied between the electrodes 20 and 21, the state of the electric field E in the vicinity of the non-electrode portion 201 is as shown in FIG. That is, a strong electric field is formed in the direction a perpendicular to the electrode at the portion a where the electrode 20 and the electrode 21 are opposed to each other, and the portion b which is the central portion of the non-electrode portion 201 is weak in the direction perpendicular to the electrode. An electric field is formed. Then, in the portion c close to the boundary between the non-electrode portion 201 and the electrode 20, the electric field is inclined toward the electrode 20.
[0032]
Then, when the dielectric anisotropy of the liquid crystal 10 is positive, since the liquid crystal molecules are aligned along the electric field E, the liquid crystal molecules are aligned perpendicular to the electrodes in the portion a, and the electric field is weak in the portion b. The state remains parallel to the electrode, and the portion c is oriented obliquely. That is, the liquid crystal is in a non-uniform alignment state inside the non-electrode portion 201. At this time, the refractive index for light passing through the element (abnormal light) forms a distribution that continuously decreases from the center to the periphery of the non-electrode portion 201. Will be shown. Thereby, a phase difference can be given to the passing light.
Therefore, as shown in FIG. 1, when the size and arrangement interval of the non-electrode portion 201 are continuously changed depending on the position on the electrode, the phase difference obtained at each position is different. By appropriately designing the arrangement pattern of the non-electrode portion 201, the aberration can be linearly corrected for the entire element.
[0033]
In addition, when the voltage to apply is changed, the orientation state of a liquid crystal molecule changes according to it. For example, when the voltage is increased, the liquid crystal molecules are vertically aligned even at the center of the non-electrode portion 201, and conversely, a concave lens effect is exhibited in which the refractive index increases from the center to the periphery of the non-electrode portion 201. . In other words, the phase difference curve obtained for the entire device can be changed by the applied voltage. For example, the correction amount is calculated based on the reproduction (RF) waveform, and the voltage is controlled according to the result. It is also possible to correct the aberration to be performed in real time.
[0034]
Further, in the example of FIG. 1, the size and arrangement interval of the non-electrode portions 201 are changed along the radial direction R. In this way, a phase difference curve that changes concentrically in accordance with the arrangement pattern of the non-electrode portions 201 is obtained, so that the spherical aberration caused by the disc thickness deviation can be corrected well. In addition, since the size and the arrangement interval of the non-electrode portion 201 are continuously changed, it is not a stepwise discontinuous correction as in the conventional aberration correction element in which the electrodes are concentrically divided, but more linear. Correction is possible.
[0035]
Furthermore, it is preferable that the arrangement interval of the non-electrode portions 201 be irregular (random arrangement) in each region (for example, the region X and the region Y) divided concentrically on the electrode 20. That is, as shown in FIG. 2, the arrangement intervals h1 and h2 are slightly different. In this way, it is possible to prevent a situation in which light passing through adjacent non-electrode portions interferes with each other and disturbs the wavefront.
If it is expected that there will be almost no interference effect due to the relationship between the wavelength of light and the arrangement interval, h1 and h2 may be arranged regularly.
[0036]
Conventionally known general electrodes can be used as the electrodes 20 and 21. Specifically, an ITO electrode in which an indium-tin oxide film is formed on the transparent substrates 30 and 31 is preferably used. The electrode 20 on the side where the non-electrode portion 201 is formed may be configured by evaporating a metal such as aluminum on the substrate 30.
[0037]
In addition, as a method of forming the non-electrode portion 201, a method in which the electrode 20 is first formed on the entire surface of the substrate 30 and then a plurality of non-electrode portions 201 are formed in a desired arrangement pattern by a photo process is suitably used. . In this way, it is possible to easily create a fine arrangement pattern that changes continuously. Alternatively, a method of performing through a mask when the electrode 20 is vapor-deposited or plated on the substrate 30 may be used.
[0038]
FIG. 5 shows an embodiment (2) of the present invention. The liquid crystal aberration correction element 1 has a plurality of non-electrode portions 201 formed on the electrode 20 as in the above-described embodiment (1), but the non-electrode portions 201 have the same diameter. Then, the arrangement interval of the non-electrode portions 201 is continuously changed from a wide interval to a narrow interval and again to a wide interval from the center of the electrode 20 to the periphery. As described above, when the arrangement of the non-electrode portions 201 is made sparse and dense, the non-electrode portion 201 can be obtained in a region where the density of the non-electrode portions 201 is high and thin due to a lens effect in each non-electrode portion when a voltage is applied. The phase difference is different, and the spherical aberration of the light beam passing through the element as a whole can be linearly corrected.
[0039]
Next, Embodiment (3) of this invention is demonstrated based on FIGS. The liquid crystal aberration correction element 1 of FIG. 6 forms a plurality of non-electrode portions 201 on the electrode 20 that sandwiches the liquid crystal, and the size and arrangement interval of the non-electrode portions 201 are radiused, as in the first embodiment (1). It is continuously changed in the direction R. The embodiment (3) is characterized in that the annular linear electrodes 40a to 40d are arranged along the arrangement pattern of the non-electrode portion 201 (pattern changing concentrically).
[0040]
The linear electrodes 40a to 40d are connected to the terminals S1 and S2, and are configured such that different voltages are applied using the resistors R1 to R3.
A phase difference curve obtained by the liquid crystal aberration correcting element 1 is schematically shown in FIG. As shown in FIG. 7, when the phase difference curve P is obtained by the lens effect of the non-electrode portion 201, the liquid crystal is more aligned in the portions s, t, u, v where the linear electrodes 40a to 40d are disposed, As a result, the phase difference is increased by a predetermined amount, and as a result, a phase difference curve Q having a large correction amount is obtained. Here, the positions where the linear electrodes 40 a to 40 d are disposed and the voltage value applied to each can be determined based on the phase difference curve P caused by the non-electrode portion 201. That is, it is preferable to set a voltage value proportional to the phase change amount of the phase difference curve P. For example, when a voltage of 1 V is applied between the terminals S1 and S2, the linear electrode 40a (corresponding to s in FIG. 7). Applied voltage is 0V, 0.6V for the linear electrode 40b (corresponding to t), 1V for the linear electrode 40c (corresponding to u), and 0.1V for the linear electrode 40d (corresponding to v). The resistors R1 to R3 can be set so that Needless to say, the linear electrodes 40a to 40d are not limited to the circuit configuration of FIG.
[0041]
FIG. 8 shows an example of a manufacturing process of the liquid crystal aberration correcting element 1 according to the embodiment (3). First, as shown in FIG. 8A, an electrode 400 (low resistance film, several to several tens Ω) such as ITO is formed on a glass substrate 30. In this example, the SiO ₂ film 50 is formed between the substrate 30 and the electrode 400. This film is a passivation film that prevents elution of the sodium content from the substrate 30 and can be provided as necessary.
[0042]
Subsequently, as shown in FIGS. 8B and 8C, the electrode 400 is patterned to form the linear electrode 40a, and the electrode 20 (high resistance film, several tens to several hundreds) such as ITO is formed thereon. kΩ). And as shown in FIG.8 (d), the target board | substrate with which the linear electrode 40a (40b-40d) and the electrode 20 were formed is obtained by forming the some non-electrode site | part 201 in a predetermined position. be able to. The linear electrode 40a is extremely thin (several to several tens of μm) compared to the size of the element, and may be made of an opaque metal other than ITO depending on the case.
[0043]
The arrangement pattern of the plurality of non-electrode portions 201 is not limited to the above embodiments (1) to (3). That is, according to the aberration etc. which generate | occur | produce, the magnitude | size of the non-electrode site | part 201, an arrangement | positioning space | interval, or both can be suitably set with the position on the electrode 20. FIG. Specifically, for example, contrary to FIG. 1, when the size of the non-electrode portion is continuously changed from a small diameter to a large diameter or a small diameter from the center to the periphery of the electrode 20, or FIG. On the contrary, there is a case where the arrangement interval of the non-electrode portions is continuously changed from a narrow interval to a wide interval or a narrow interval from the center of the electrode 20 toward the periphery. 1 and 5 are not limited to the case where the size and the arrangement interval are changed concentrically. For example, when the electrode 20 is divided into left and right areas, different arrangement patterns are formed in the respective areas. You may do it. In this case, coma caused by the warp of the disk can be effectively corrected.
[0044]
In each of the above embodiments, the non-electrode portion 201 is formed only on the electrode 20, but the non-electrode portion may be formed on both the electrode 20 and the electrode 21. In this case, since the liquid crystal molecules are aligned non-uniformly even in the vicinity of the electrode 21, the obtained lens effect becomes stronger and the correction amount can be increased.
Further, the electrode 20 is composed of several divided electrodes, each of which is formed with a plurality of non-electrode portions, and a different voltage is applied to each electrode to give a more complicated phase difference curve as a whole. it can.
[0045]
Further, the opposing electrodes are not limited to a pair as described above, and more electrodes may be stacked with the liquid crystal sandwiched therebetween.
[0046]
In the above-described embodiments (1) to (3), the case where the shape of the plurality of non-electrode portions 201 is circular has been described. However, the present invention is not limited to this. Can be made into another shape. Specific examples include an elliptical shape and a semicircular shape.
[0047]
The liquid crystal aberration correcting element 1 as described above constitutes an optical pickup together with, for example, a laser light source, a polarizer, a half-wave plate, a quarter-wave plate, an objective lens, a light receiving element, etc., and is used by being incorporated in an optical disc apparatus. be able to.
Since the generated aberration can be corrected linearly, it can be suitably used for next-generation BDs and high-density optical disks such as multilayer disks.
[Industrial applicability]
[0048]
The liquid crystal aberration correction element of the present invention is used in an optical disc apparatus to correct aberrations that occur during recording / reproduction with an optical pickup.

Claims (5)

  A liquid crystal and a plurality of electrodes opposed to each other with the liquid crystal interposed therebetween, wherein at least one of the electrodes is formed with a plurality of non-electrode portions where no electrode material is present; A non-uniformly oriented liquid crystal aberration correcting element configured such that the size and arrangement interval of the plurality of non-electrode portions change along the radial direction when the electrodes are divided concentrically. A liquid crystal and a plurality of electrodes opposed to each other with the liquid crystal interposed therebetween, and at least one of the electrodes has a plurality of non-electrode portions where no electrode material is present, the size and / or the arrangement interval depending on the position on the electrodes The liquid crystal is configured to be non-uniformly oriented when a voltage is applied inside the non-electrode portion, and a plurality of linear electrodes that apply different voltages are formed in the arrangement pattern. A liquid crystal aberration correction element arranged at a predetermined interval along the line. The liquid crystal aberration correction element according to claim 2, wherein the size and arrangement interval of the plurality of non-electrode portions change along a radial direction when the electrodes are divided concentrically, and the plurality of linear electrodes are: A liquid crystal aberration correcting element, wherein the liquid crystal aberration correcting element is arranged in an annular shape along the concentrically changing arrangement pattern.   4. The liquid crystal aberration correction element according to claim 1, wherein the intervals between the plurality of non-electrode portions are irregular in each of the concentric areas on the electrode. 5. The liquid crystal aberration correction element according to claim 1, wherein the non-electrode portion has a circular shape.

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