JP2005092009A - Method and device for driving liquid crystal element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a method and a device for driving a liquid crystal element by which a response time can be shortened even when the diameter of a lens is large. <P>SOLUTION: In the liquid crystal element which uses molecule orientation effect by an irregular electric field distribution, at least one electrode (1st electrode 12) is given a potential gradient for a certain time when a voltage is applied between a 1st electrode 12 and a 2nd electrode 17 which face each other or varied. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for driving a liquid crystal element as, for example, a liquid crystal lens, and in particular to a technique capable of improving problems inherent to liquid crystal appearing in optical characteristics during driving, and consequently increasing response speed. It is related.

  Liquid crystal display elements utilizing the characteristics of liquid crystals continue to be remarkably developed as thin and light flat display elements. The alignment state of the liquid crystal molecules can be easily controlled by treatment of the surface of the glass substrate provided with the two transparent conductive films constituting the liquid crystal display element or by an externally applied voltage.

In a nematic liquid crystal cell, a liquid crystal lens having a spatial refractive index distribution characteristic can be obtained by utilizing the property that liquid crystal molecules are aligned in the direction of an electric field due to the effect of alignment of liquid crystal molecules by an axisymmetric non-uniform electric field. . For example, Japanese Patent Application Laid-Open No. 11-109304 discloses a liquid crystal microlens, which discloses a technique that allows the focal position to be controlled in either the optical axis direction or the direction perpendicular to the optical axis.
JP-A-11-109304

  By the way, although the above-mentioned document discloses a liquid crystal microlens, there is a field where a liquid crystal lens having a lens diameter of 1 mm or more is desired as a field of use of the liquid crystal lens. For example, an imaging lens, a microscope, glasses, an optical fiber switch element, and the like. Therefore, when trying to realize a liquid crystal lens having a lens diameter of about 1 mm, the thickness of the liquid crystal layer becomes 500 μm or more. However, this causes a phenomenon that the alignment of liquid crystal molecules becomes insufficient and the liquid crystal becomes cloudy.

  Another problem is the response characteristics. As for the response characteristic, the response time becomes longer as the liquid crystal layer becomes thicker. For this reason, it is insufficient depending on the product and the place where the liquid crystal lens is used. Therefore, it is conceivable to apply a high voltage in order to increase the response time. However, a further problem here is a phenomenon in which a defect region called a disclination line in which the alignment of liquid crystal molecules is discontinuous occurs. This phenomenon is such that the direction in which the liquid crystal molecules rise from the substrate surface is, for example, the left-right reverse direction near the center of the cell, and a discontinuous line is generated here.

  Regardless of the occurrence of the above-described cloudiness or disclination line, the optical function as a liquid crystal lens cannot be achieved.

  Accordingly, an object of the present invention is to easily realize a liquid crystal lens having a large diameter with a simple configuration, and in addition, even such a liquid crystal lens can increase the response speed. The object is to provide a lens driving method and apparatus.

  In order to achieve the above object, according to the present invention, in a liquid crystal device using a molecular alignment effect due to non-uniform electric field distribution, at least one electrode is applied when a voltage is applied between the opposing electrodes or the voltage is varied. A potential gradient was applied to the fixed time.

  In the present invention, when a potential gradient is applied to the one electrode for a certain period of time, a voltage higher than a predetermined voltage is applied between the counter electrodes, and then the predetermined voltage is applied to increase the response speed.

  The present invention also provides a transparent first substrate, a transparent first electrode on the first substrate, and a transparent second substrate disposed on the first electrode with a liquid crystal layer interposed therebetween. , An apparatus for driving a liquid crystal lens comprising a second electrode provided on the second substrate and having a hole, and when applying a voltage between the first and second electrodes, the first electrode Means are provided for applying a potential gradient to the electrode for a certain period of time.

  When a voltage is applied between the counter electrodes (first and second electrodes) by the above means, a potential gradient is applied to one electrode (first electrode) for a certain period of time. The direction rising from the substrate surface is aligned in one direction. For this reason, when a voltage is applied between the counter electrodes, the occurrence of a disclination line that deteriorates the characteristics of the liquid crystal lens is suppressed. As a result, the voltage applied between the counter electrodes can be increased, and the response characteristics and further the recovery characteristics can be improved. Of course, the optical characteristics are also improved.

  Embodiments of the present invention will be described below with reference to the drawings. First, a configuration of a liquid crystal lens to which the present invention is applied will be described, and a driving method thereof will be described. A liquid crystal lens to which the present invention is applied includes a transparent first substrate 11, a transparent first electrode 12 on the first substrate, and a liquid crystal layer 13 sandwiched on the first electrode 12. The transparent second substrate 14 and the second electrode 17 provided on the second substrate 14 and having the holes 20 are basically configured. Then, a means for applying a potential gradient to the first electrode 12 for a certain period of time before applying a voltage between the first and second electrodes 12 and 14 is provided.

  The transparent first electrode 12 is made of ITO (indium tin oxide). On the other hand, the second electrode 17 is formed of an aluminum thin film. Therefore, this liquid crystal lens can obtain a non-uniform electric field symmetric with respect to the central axis of the hole 20 by applying a voltage between the first electrode 12 and the second electrode 17. Therefore, due to the liquid crystal molecular alignment effect, the liquid crystal layer 13 exhibits spatially different refractive index distribution characteristics and functions as a liquid crystal lens. Further, the surfaces of the first electrode 12 and the second substrate 14 facing the liquid crystal layer 13 are respectively covered with alignment films 15 and 16 such as a polyimide film or a polyvinyl alcohol film. The surfaces of the alignment films 15 and 16 such as a polyimide film or a polyvinyl alcohol film are rubbed in one direction so that liquid crystal molecules are uniformly arranged.

  As described above, in the liquid crystal lens, no electrode is formed on the surface of the second substrate 14 facing the liquid crystal layer 13, and an aluminum thin film is interposed between the second electrode 17 and the liquid crystal layer 13. The glass (insulating layer) which is the second substrate 14 is interposed. Therefore, the thickness of the liquid crystal layer 13 is small, which contributes to obtaining a lens having a large diameter. That is, liquid crystal molecular alignment with a small layer thickness is effective for constructing a large lens. Further, since the liquid crystal molecules can be driven reliably, the problem of cloudiness does not occur. It also contributes to the ease of liquid crystal driving described later.

  In the liquid crystal lens according to the present embodiment, the thickness of the liquid crystal layer 13 is 130 μm, the thicknesses of the substrates 11 and 14 are 1.3 mm, and the diameter of the hole 20 is 7.0 mm. It is possible.

  However, in the liquid crystal lens according to the present embodiment, the thickness of the second substrate 14 is particularly important for defining the distance between the second electrode 17 and the liquid crystal layer 13. The thickness of the substrate 14 is preferably 1 μm to 5 mm, particularly several μm to several mm, for example, 2 μm to 3 mm. That is, the substrate 14 is not limited to a glass substrate, but may be other insulating layers. In this case, a separate substrate may be used to hold the thin insulating layer. As the insulating layer, a silicon oxide film, a silicon nitride film, or the like can be used. The diameter of the hole 20 is preferably about several μm to several tens of mm, but is not particularly limited.

  Around the hole 20, for example, a light blocking member that restricts light passing through the hole 20, a so-called black matrix, is provided between the substrate 14 and the electrode 17 and having an opening smaller in size than the hole 20. Also good. That is, although the characteristics of the peripheral part of the hole 20 are poor, by providing the black matrix, good characteristics can be obtained also in the peripheral part of the hole 20. Carbon or the like can be used as the black matrix.

  In the liquid crystal lens configured as described above, when a voltage is applied between the second electrode 17, which is an aluminum thin film, and the transparent first electrode 12, a non-uniform electric field is generated over the entire wide region of the liquid crystal layer 13. Distributed over. For this reason, molecular alignment regions having different refractive indexes are distributed and formed in the liquid crystal layer 13. In this way, a large size lens is realized.

  Various refractive index distributions vary depending on the applied voltage. Therefore, the focal length of the lens is a function of the external voltage, and the focal length of the lens can be arbitrarily changed by the external voltage.

  In FIG. 2, in order to explain the characteristics of the present invention, a potential gradient that can provide a potential gradient to the first electrode 12, the second electrode 17, the driving means 21, and the first electrode. The setting means 22 is extracted and shown.

  In this invention, the 1st electrode 12 is comprised using the material with comparatively high resistance, For example, what added the indium oxide to the zinc oxide, or tin oxide can be mentioned. The electrical resistance is preferably about 100Ω to 1MΩ. Here, the electrode 12 having a resistance value of about 10 kΩ was used. Terminals 111 and 112 are provided. The direction in which the terminals 111 and 112 are arranged is preferably a direction parallel to the rubbing direction.

  In the present invention, this electric resistance is effectively used, and when a voltage is applied between the counter electrodes 12 and 17, a current is passed through the first electrode 12 to give a potential gradient. At this time, between the terminals 111 and 112 of the first electrode 12, for example, as shown in FIG. 3, voltages V1 and V2 are given a given time Δt. After a certain time has elapsed, both terminals 111 and 112 become V0.

  During a certain time Δt, the electric field in the liquid crystal layer is inclined in a certain direction, and the alignment of the liquid crystal molecules is also aligned in the certain direction. As a result, it was confirmed that when driven by the driving means 21, liquid crystal molecular alignment was reliably obtained and no disclination line was generated. That is, in the present invention, the disclination line is improved so as not to easily occur. As a result, a large voltage may be output from the driving means 21 in order to speed up the response.

  That is, when applying the above-described potential gradient for a certain time to one electrode 12, a voltage larger than a predetermined voltage is applied between the counter electrodes 11 and 12, and then the predetermined voltage is applied. Thereby, it is possible to drive with a large voltage without generating a disclination line, and to increase the response speed.

  The experiment was performed with V1 = 210 Vrms, V2 = 270 Vrms, and V0 = 80 rms as voltages for applying a potential gradient. In addition, Δt was variously selected and the change in focus was observed. FIG. 4 shows the observation results. The horizontal axis in FIG. 4 is the focus response time. The vertical axis represents the focus state. From this result, it can be seen that the response time depends on Δt.

  In FIG. 5, the horizontal axis indicates Δt, and the vertical axis indicates the response time (τ). It can be seen that the response time is shortened by applying a potential gradient to the first electrode 12 as shown in FIG.

  The focal length is changed by changing the voltage applied between the transparent first electrode 12 and the aluminum thin film second electrode 17. The focal length of the liquid crystal cell varies depending on the applied voltage. That is, the focusing force for light changes with voltage. The minimum focal length is about 76 cm and is obtained in the vicinity of 35 Vrms. As the voltage continues to increase, the director near the center continues to rotate, while the director near the hole saturates. The refractive index profile is flattened and the focal length is longer. The phase retardation profile can be adjusted by the hole diameter and the substrate thickness. In order to obtain good performance, it is necessary to increase the hole size according to the thickness of the substrate. In such a structure, a liquid crystal lens of almost any size can be realized by using glass substrates or thin films having various thicknesses as the intermediate insulating layer.

  In a liquid crystal lens having a liquid crystal layer, since the liquid crystal layer can be made relatively thin with respect to the diameter of the hole, the operation speed can be made much higher than that of a conventional liquid crystal lens. In the cell structure of the liquid crystal lens of the present invention, due to the fact that the electric field is perpendicular to the surface in the vicinity of a conductor such as metal, the angle between the electric field and the director at an arbitrary position of the liquid crystal lens is almost All directors rotate in the same direction. Therefore, even when a voltage is applied, no disclination line is generated. This indicates that a high voltage can be applied to increase the operation speed. In particular, since the method for applying the potential gradient described in FIG. 3 is used, the occurrence of the disclination line can be reliably suppressed.

  The present invention is not limited to the above embodiment. In the above embodiment, a voltage is applied to the first electrode 12 with a waveform as shown in FIG. However, the present invention is not limited thereto, and a potential gradient may be applied to the first electrode 12 even during driving. In this way, the liquid crystal molecules of the liquid crystal layer 13 are aligned in the direction of the potential gradient. As a result, the refractive index distribution that is axially symmetric when there is no potential gradient in the first electrode 12 becomes an asymmetric distribution in the direction of the potential gradient, and the function of deflecting from the direction in which incident light goes straight is obtained.

  In this case, the direction of deflection of the incident light can be changed by appropriately changing the position where the voltage is applied to the electrode 12, that is, the positions of the terminals provided at both ends of the electrode 12. As a result, by changing the voltage applied between the electrode 12 and the electrode 17 and the voltage applied to both ends of the electrode 12, it is possible to obtain a three-dimensional variable focus characteristic. This liquid crystal lens can be applied to various uses such as an optical switch in free space and a switch between optical fibers.

  FIG. 6 further shows another embodiment of the present invention. Of course, the above-described embodiment and this embodiment may be combined, and the present invention may be applied to a case where some embodiments are deleted. In FIG. 6, the second electrode 17 is divided into electrodes 171 and 172. Other components are the same as those shown in FIG. In the embodiment shown in FIG. 6, the recovery time can be shortened. When the voltage applied between the first and second electrodes 12 and 17 is removed, the alignment effect due to the electric field on the liquid crystal molecules disappears. Then, due to the alignment effect by rubbing, the liquid crystal molecules return to the original state aligned parallel to the substrate along the rubbing direction. The time required at this time is the recovery time. The recovery time becomes longer with characteristics close to the square of the thickness of the liquid crystal layer 13.

  Therefore, in this embodiment, the voltages Va and Va applied between the first and second electrodes 12 and 17 are removed, and then the voltage Vb is applied between the electrodes 171 and 172 for a predetermined time. . Then, the electric field is inclined in the lambing direction, and the liquid crystal molecules are arranged along this. That is, the lens state is restored to the non-lens state. By applying the voltage Vb, the recovery time is greatly shortened. Therefore, in combination with the previously improved response time, the recovery time is improved in the present embodiment, and as a result, a large-sized liquid crystal lens capable of high-speed response can be provided. The idea of the present invention can be applied not only to liquid crystal lenses but also to all liquid crystal elements that utilize molecular alignment effects based on non-uniform electric fields.

  In the embodiment shown in FIG. 6, the hole 20 and the slit are formed in the second electrode 17. However, the present invention is not limited to this, and the first electrode 12 may be configured in the same structure as the second electrode 17 as shown in FIG. This is effective when a liquid crystal microlens is configured. In this case, unlike the structure of FIG. 1, it is not necessary to provide an insulating layer between the electrodes, and the first and second electrodes 12 and 17 are provided on the opposing surface of the opposing substrate. A voltage Vb is applied between the divided electrodes of the first and second electrodes 12 and 17. The application timing of the voltage Vb is at the start of driving and at the time of recovery.

Sectional drawing which shows the basic composition of one embodiment of this invention. Explanatory drawing which shows the characteristic part in one embodiment of this invention. The figure which shows the example of the voltage waveform shown in order to demonstrate operation | movement of one embodiment of this invention. The figure which shows the example of the change of the focus position of the liquid crystal lens by this invention. The figure which shows the result of having measured the response speed to the lens characteristic of this invention. Explanatory drawing which shows other embodiment of this invention. Explanatory drawing which shows other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... 1st board | substrate, 12 ... 1st electrode, 13 ... Liquid crystal layer, 14 ... 2nd board | substrate, 17 ... 2nd electrode, 20 ... Hole, 21 ... Drive means, 22 ... Electric gradient setting means, 23 ... control means.

Claims (7)

In the liquid crystal device using molecular alignment effect due to non-uniform electric field distribution,
A method of driving a liquid crystal element, wherein a potential gradient is applied to at least one electrode for a certain period of time when a voltage is applied between the opposing electrodes or when the voltage is varied.   2. The method of driving a liquid crystal element according to claim 1, wherein when a potential gradient is applied to the one electrode for a predetermined time, a voltage larger than a predetermined voltage is applied between the counter electrodes, and then the predetermined voltage is applied. A transparent first substrate, a transparent first electrode on the first substrate, a transparent second substrate disposed on the first electrode with a liquid crystal layer interposed therebetween, and the second substrate An apparatus for driving a liquid crystal lens comprising a second electrode provided on a substrate and having a hole,
A driving device for a liquid crystal element, comprising means for applying a potential gradient to the first electrode for a predetermined time when a voltage is applied between the first and second electrodes.   The liquid crystal element driving device according to claim 3, wherein the first electrode has an electric resistance of 100Ω to 1 MΩ.   5. The liquid crystal element driving device according to claim 4, wherein the second electrode is divided with a slit at the center, and a voltage is also applied between the two divided electrodes. A first electrode having a first hole provided on a transparent first substrate, a second electrode having a second hole provided on a transparent second substrate, and the first and second electrodes A device for driving a liquid crystal lens comprising a liquid crystal layer therebetween,
To apply a potential gradient between two electrodes divided by providing a slit in at least one of the first and second electrodes at a time different from the time for applying a voltage between the first and second electrodes. A device for driving a liquid crystal element comprising the means described above.   7. The liquid crystal element driving device according to claim 6, wherein both of the first and second electrodes are divided with a slit in the center, and a voltage is also applied between the divided electrodes.

Images