JP3853117B2 - Driving method of liquid crystal microlens - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a driving method for improving the recovery characteristics of a liquid crystal microlens used in an optical coupler or the like capable of variably controlling light collecting characteristics and divergence characteristics by voltage.
[0002]
[Prior art]
Various microlenses such as a distributed refractive index type flat microlens and a diffractive microFresnel lens have been developed so far. Since these microlenses are manufactured using a solid material such as glass, the characteristics as lenses are fixed and cannot be varied.
[0003]
A liquid crystal microlens using a nematic liquid crystal as an optical material is known as a microlens capable of changing the characteristics as a lens. In this liquid crystal microlens, a nematic liquid crystal layer is sandwiched between two glass substrates in which a holed pattern electrode having a hole-shaped opening is formed in a region to be a lens portion, and each glass substrate is a hole portion of each electrode. Are arranged so as to face each other. In this liquid crystal microlens, liquid crystal molecules are aligned along a non-uniform electric field that is substantially symmetric with respect to an axis passing through the center of the hole, that is, an optical axis, generated in a hole in the liquid crystal cell. Due to the alignment effect of the liquid crystal molecules in the hole, a refractive index distribution approximated by a parabola is generated, and a lens effect is obtained. Since the refractive index distribution in the hole can be controlled by changing the voltage applied to the liquid crystal cell, a variable focus characteristic in which the focal point moves in the optical axis direction can be obtained.
[0004]
In such a liquid crystal microlens using nematic liquid crystal, it is known that the lens characteristics greatly depend on the structural dimensions such as the diameter of the hole and the thickness of the liquid crystal layer, and the refractive index distribution state is an ideal square. In order to obtain a liquid crystal microlens having good optical characteristics as a distribution, each electrode is a pattern electrode provided with a circular or elliptical hole-shaped region, and the diameter of the hole or the length of the elliptical long axis Japanese Patent Application Laid-Open No. 11-109303 discloses that the thickness of the liquid crystal layer is not more than 1 mm and the thickness of the liquid crystal layer is ¼ to 1 times the diameter of the hole or the major axis of the ellipse. Yes.
[0005]
Further, in a liquid crystal microlens having a hole pattern electrode, a slit is provided continuously with a hole to divide the electrode into a plurality of portions, and a voltage is applied to each of them to perform a three-dimensional focal movement. A liquid crystal microlens that can be used is disclosed in JP-A-11-109304.
[0006]
Furthermore, in a liquid crystal microlens having a hole-patterned electrode, the liquid crystal layer is composed of a composite material of a nematic liquid crystal material and a polymerization-curable monomer, so that desired lens characteristics can be maintained even in the absence of voltage application, Japanese Patent Laid-Open No. 10-239676 discloses a liquid crystal microlens that can change the maintained lens characteristics by controlling the voltage applied to the liquid crystal cell.
[0007]
[Problems to be solved by the invention]
However, a desired refractive index distribution can be obtained for each of the liquid crystal microlenses described above by applying a voltage for driving the liquid crystal cell to reorient the liquid crystal molecules in the holes of the liquid crystal cell by a non-uniform electric field. The time required for the response time, the response time, and the time until the lens effect disappears after the voltage is removed and the liquid crystal molecules in the liquid crystal cell return to the state before applying the electric field, that is, the recovery time is several seconds to several tens of seconds. This is a problem when using a liquid crystal microlens.
[0008]
As a method for improving the response recovery characteristic in the liquid crystal microlens, a method of applying a bias voltage to the liquid crystal cell in advance is known. However, there is a problem that the improvement effect is small in the recovery characteristic.
[0009]
In addition, the response recovery characteristics can be greatly improved by using a composite material in which a liquid crystal monomer capable of being polymerized and cured is used in a nematic liquid crystal material by a method similar to the method disclosed in Japanese Patent Laid-Open No. 10-239676. Although described in “Materials Science Forum” (Vols. 308-311, pages 591-596), the focus variable range of the liquid crystal microlens becomes extremely narrow, and the hole that becomes the liquid crystal microlens becomes clouded to cause incident light. There are problems such as scattering and deterioration of the light collecting characteristics.
[0010]
An object of the present invention is to solve the above-mentioned problems and to provide a driving method of a liquid crystal microlens having excellent recovery characteristics without impairing the characteristics of the lens.
[0011]
[Means for Solving the Problems]
In the present invention , a circular or elliptical hole is provided on one substrate in contact with the liquid crystal layer, and a holed pattern electrode divided into two by slits provided continuously with the hole is formed. In a liquid crystal microlens in which an electrode having the same shape is formed on the side of the substrate facing the liquid crystal layer facing the electrode and the liquid crystal layer is sealed , the lens effect is exhibited by applying a voltage between the opposed electrodes When the lens effect is not exhibited, the polarity of the voltage applied between the other opposing electrodes is reversed while the voltage is applied between the one opposing electrodes divided by the slit. And
[001 2 ]
According to such a method, the recovery time of the liquid crystal microlens can be shortened without impairing the optical characteristics of the liquid crystal microlens.
[001 3 ]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. First, a driving method as an example other than the examples in the present invention will be described in detail, and then described in the order of the embodiments of the present invention.
[0014]
1A and 1B show a method for driving a liquid crystal microlens according to the present invention. FIG. 1A shows an example of a driving method for improving a recovery characteristic by applying a voltage between two electrodes divided by a slit as a driving method of a liquid crystal microlens. In the liquid crystal microlens 1, perforated pattern dividing electrodes 2 and 3 formed on a pair of substrates such as glass (not shown) are arranged to face each other with a predetermined interval through a spacer (not shown). An alignment film such as polyvinyl alcohol or polyimide (not shown) is formed on each of the (hole-punched pattern dividing electrodes 2 and 3). The alignment film is rubbed as an alignment treatment. In this structure, a liquid crystal layer 4 is provided between both alignment film electrodes. The liquid crystal layer 4 is a liquid crystal material such as nematic liquid crystal (in this embodiment, K15 manufactured by Merck) is sealed between both alignment films and sealed by a sealing means (not shown).
[0015]
As shown in FIG. 1A, the hole pattern dividing electrodes 2 and 3 are formed by patterning on a substrate, and the pattern shape is provided with a circular hole portion 5. A slit 6 is provided continuously. The hole pattern dividing electrode 2 is divided into a first part 2a and a second part 2b by the hole part 5 and the slit 6, and the hole pattern electrode 3 is divided into a first part 3a and a second part 3b. It is divided. Both electrodes 2 and 3 are provided with holes 5 and slits 6 having the same shape and the same size, and both the substrates 2 and 3 so that the holes 5 and slits 6 of the electrodes 2 and 3 face each other. Is arranged.
[0016]
In the liquid crystal microlens 1 having the above-described structure, when no voltage is applied, all the liquid crystal molecules remain arranged in parallel with the substrate in the liquid crystal layer 4 and are circular positions opposite to the holes 5. Since the refractive index is uniform within the region and the refractive index distribution does not occur, there is no condensing action and no lens effect can be obtained.
[0017]
On the other hand, when the voltage V1 is applied between the punched pattern electrodes 2 and 3 provided on both substrates, the liquid crystal molecules in the portion sandwiched between the electrodes 2 and 3 rise in a direction perpendicular to the substrates. At the same time, liquid crystal molecules near the electrodes 2 and 3 in the circular region, that is, near the outer periphery of the circular region also rise, but the electric field is weak near the center of the circular region, so that the liquid crystal molecules hardly rise while remaining parallel to the substrate. Here, the electric field continuously weakens from the outer peripheral part of the circular region toward the central part (the electric field is nonuniform), and the rising angle of the liquid crystal molecules continuously decreases. A state in which the refractive index continuously changes in the circular region in accordance with the rising angle is realized, and a lens effect showing a condensing effect is obtained.
[0018]
The present applicant observed the state of interference fringes in a circular region when a voltage having a frequency of 1 kHz was applied using the liquid crystal microlens 1 having the above configuration. As an example, FIG. 2 shows interference fringes when the voltage V1 is 2.5V. FIG. 3 shows the result of obtaining the optical phase difference (optical path difference) from the interference fringe distribution and showing the distance in the diameter direction of the microlens. It has a substantially square distribution characteristic (parabolic shape), and it can be seen that it has a characteristic of a convex lens. When the voltage applied to the liquid crystal microlens 1 is varied, the refractive index distribution changes as a result of the change in the tilt characteristics of the liquid crystal molecules with respect to the substrate, so that the number of interference fringes changes. As a result, it has an equivalent meaning to the change in the shape (curvature) of the convex surface in a normal convex lens, and the focal length can be changed. FIG. 4 shows the condensing spot at the focal position, and FIG. 5 shows the condensing characteristics in the rubbing direction and the direction perpendicular to the rubbing.
[0019]
In this embodiment, the diameter of the hole is 300 μm, the thickness of the liquid crystal layer 4 is 100 μm, and the width of the slit 6 is 10 μm. 2, 3, 4, and 5, it can be seen that the influence on the lens effect by the slit 6 that divides the punched pattern electrode into two is small.
[0020]
When the voltage applied to the first portions 2a and 3a of the electrodes 2 and 3 is different from the voltage applied to the second portions 2b and 3b, the voltage is lower in the circular region closer to the higher voltage electrode portion. Since the rising angle of the liquid crystal molecules with respect to the substrate is larger than that closer to the electrode portion, the center of the refractive index distribution is shifted from the center of the circular region to a lower voltage. In other words, if this liquid crystal microlens is considered as a normal convex lens, the center of the convex surface is shifted from the center of the circle to the lower voltage side, and the focal point moves in a plane perpendicular to the optical axis direction. The light incident on the circular area is deflected from the optical axis and collected.
[0021]
When the voltage applied to the liquid crystal microlens 1 is removed, the alignment effect due to the electric field on the liquid crystal molecules disappears, so the liquid crystal molecules are aligned parallel to the substrate along the rubbing direction by the alignment effect due to the rubbing applied to the alignment film surface. Return to the original state. The time required at this time is the recovery time. Normally, the recovery time becomes longer with characteristics close to the square of the thickness of the liquid crystal layer 4, so that the liquid crystal panel used in a liquid crystal display or the like has a thick liquid crystal layer while the thickness of the liquid crystal is about several μm. The problem with liquid crystal microlenses is that the recovery time is very slow, from several seconds to several tens of seconds.
[0022]
As a method for forcibly aligning liquid crystal molecules in a direction parallel to the substrate surface, there is a method of applying an electric field in the in-plane direction of the substrate, “Appl. Phys. Lett.” (Vol. 26, page 603), “Liquid crystal and Its application (Industry Books Co., Ltd.) "(page 195). This is because in a liquid crystal cell used in a normal liquid crystal display, a liquid crystal is inserted between two electrode substrates and operated by applying a voltage, but one electrode is divided into a comb-like shape. The control voltage applied between the opposing electrodes and the drive voltage applied between the adjacent comb electrodes are operated independently of each other. In addition, a driving method of a liquid crystal cell called “in-plane switching” in which display is performed by applying a voltage between electrodes provided on the same substrate to reorient liquid crystal molecules is also known.
[0023]
Therefore, in FIG. 1A, after removing the voltage V1 applied between the hole pattern electrodes 2 and 3 of the liquid crystal microlens 1, immediately between the first portion 2a and the second portion 2b of the electrode 2 and the electrode When a voltage V2 is applied between each of the first portion 3a and the second portion 3b through the slit 6, liquid crystal molecules that are aligned by a nonuniform electric field in the circular region are applied to the substrate surface generated by the voltage V2. Due to the alignment effect caused by the electric field in the parallel direction, the alignment state of the liquid crystal molecules quickly becomes the original state parallel to the substrate. Here, the time required for the liquid crystal cell to recover from the “state showing the lens effect” to the original “state showing no lens effect” in which no voltage is applied is the square of the electric field component in the direction parallel to the substrate. It is known to exhibit inversely proportional characteristics. The electric field component parallel to the substrate is not uniform within the circular region, but when the voltage V2 is increased, the electric field component parallel to the substrate also increases, and as a result, the recovery time is greatly shortened. Here, for application and switching of the voltages V1, V2, etc., relays (relays) or analog switches using semiconductor elements can be used. Especially when high speed operation is required, it is desirable to use an analog switch.
[0024]
FIG. 6 shows the temporal change of the light intensity at the focal point, that is, the improved recovery characteristic when the voltage V2 is applied immediately after the voltage V1 applied to the liquid crystal microlens 1 is removed. Here, the voltage of V2 is 3V. From FIG. 6, it can be seen that the recovery time is shortened to about 1 second.
[0025]
When the voltage V1 is applied to the liquid crystal microlens 1 and the voltage V2 is changed from 0 to 80 V, the recovery time is the time when the light intensity at the focal point when the liquid crystal cell exhibits the lens effect is reduced to 10%. The V2 voltage dependency of the recovery time is shown as a black square in FIG. When there is no electric field in the parallel direction on the substrate, that is, when V2 is set to 0 V, the recovery time is about 10 seconds. However, when V2 is increased to 80 V, the recovery time can be improved to about 5.5 milliseconds. did it.
[0026]
Next, an embodiment of the present invention is shown in FIG. In the present embodiment, in the liquid crystal microlens 1 having a hole pattern electrode divided into two by a slit, the polarity of a voltage applied between one opposing electrodes is reversed. . That is, in FIG. 1B, the polarity of the voltage V′1 applied between the first portion 2a of the hole pattern electrode 2 and the first portion 3a of the hole pattern electrode 3 is reversed. , To shorten the recovery time. Here, the voltage V1 and the voltage V′1 have the same amplitude (same voltage value).
[0027]
The voltage component V1-V′1 that is effectively applied through the slit 6 between the first portion 2a and the second portion 2b of the electrode 2 and between the first portion 3a and the second portion 3b of the electrode 3 is When the polarity of V′1 is the same as the polarity of V1, it is 0, and there is no voltage component parallel to the substrate. When the polarity of V′1 is reversed, the effective value of V1−V′1 is twice the value of V1 (or V′1), so that a voltage twice that of V1 (or V′1) is It is effectively applied in parallel to the substrate through the slit. That is, when an electric field component parallel to the substrate is generated, the liquid crystal molecules are forcibly aligned in a direction parallel to the substrate, and the lens effect disappears rapidly. That is, the recovery time can be shortened. Here, in order to reverse the polarity of V′1, a relay (relay) or a semiconductor analog switch can be used. Especially when high speed operation is required, it is desirable to use an analog switch.
[0028]
The relationship between the recovery time and the voltage in the case of the embodiment according to the present invention is shown as a white square as Method 2 in FIG. Here, in embodiments of the present invention has been 2.5V applying a voltage of V1 and V'1 initially, changing the value of Invert simultaneously V1 and V'1 the polarity of the voltage V'1 Let me measure. In the case of the embodiment of the present invention, the electric field component parallel to the substrate is doubled as compared with the driving method for improving the recovery characteristics by applying a voltage between the electrodes divided into two by the slit. The characteristics will be improved further.
[0029]
In the embodiment of the present invention, the punched pattern electrodes divided by the slits are paired with a voltage, and the liquid crystal molecules are perpendicular to the substrate in the electrode portions other than the circular region. Therefore, when the polarity of the voltage of V′1 is reversed again to show the lens characteristics, the liquid crystal molecules can be easily reoriented in the electric field direction. That is, there is an advantage that the response time can be improved.
[0030]
【The invention's effect】
According to the present invention, by reversing the polarity of the voltage applied Oite to the liquid crystal microlens having a punching pattern electrodes of the same shape which is divided by the slit, at one of the opposing electrodes, the liquid crystal microlens optical The recovery characteristics can be greatly improved without impairing the physical characteristics.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a method for driving a liquid crystal microlens of the present invention.
FIG. 2 is a diagram showing an interference image of a liquid crystal microlens.
FIG. 3 is a diagram showing an optical phase difference distribution of a liquid crystal microlens.
FIG. 4 is a diagram showing a condensing spot at the focal point of a liquid crystal microlens.
FIG. 5 is a diagram showing light collection characteristics in a rubbing direction of the liquid crystal microlens and in a direction perpendicular to the rubbing.
FIG. 6 is a diagram showing temporal change of light intensity at the focal point, that is, improved recovery characteristics.
FIG. 7 is a diagram illustrating a result of improving a recovery time characteristic of a liquid crystal microlens according to an embodiment of the present invention .
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Liquid crystal microlens 2 and 3 Hole pattern division | segmentation electrode 2a, 3a 1st part 2b, 3b 2nd part 4 Liquid crystal layer 5 Hole part 6 Slit

Claims (1)

On one substrate, a circular or elliptical hole is provided on the side in contact with the liquid crystal layer, and a hole pattern electrode divided into two by a slit provided continuously with the hole is formed. In a liquid crystal microlens in which an electrode having the same shape is formed on the surface side of the opposing substrate in contact with the liquid crystal layer and the liquid crystal layer is enclosed , the lens effect is obtained from a state in which the lens effect is exhibited by applying a voltage between the opposing electrodes. A liquid crystal micro that reverses the polarity of the voltage applied between the other opposing electrodes in a state in which a voltage is applied between one opposing electrode divided by the slit when not shown Driving method of the lens.

Images