JP2006313243A - Liquid crystal lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress shift in optical properties such as focal length or focal position due to polarization direction in a liquid crystal lens using two liquid crystal layers. <P>SOLUTION: A first transparent electrode 11a, a first alignment film 12a, a first liquid crystal layer 13, a second alignment film 12b, a second transparent substrate 14, and a second electrode 11b having a hole 111 are formed on one surface of a first transparent substrate 1 in order from the first transparent substrate 1. A third transparent electrode 21a, a third alignment film 22a, a second liquid crystal layer 23, a fourth alignment film 22b, a third transparent substrate 24, and a fourth electrode 21b having a hole 211 are formed on the other surface of the first transparent substrate 1, in order from the first transparent substrate 1. The alignment direction of the first alignment film 12a is the same as the alignment direction of the second alignment film 12b. The alignment direction of the third alignment film 22a is the same as the alignment direction of the fourth alignment film 22b. The alignment direction of the alignment films 22a, 22b is perpendicular to the alignment direction of the alignment films 12a, 12b. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal lens, and more particularly to a liquid crystal lens having two or more liquid crystal layers.

  In recent years, a liquid crystal lens using a liquid crystal material as an optical material has attracted attention in the field of optical communication and the like because it can change the optical characteristics of the lens without requiring mechanical driving. The mechanism of the liquid crystal lens will be outlined with reference to FIG. 9. First, in the liquid crystal lens of this figure, the first transparent substrate 14a and the second transparent substrate 14b are arranged to be spaced apart from each other, and the first transparent electrode 11a is formed on the surface of the first transparent substrate 14a. However, the second electrode 11b having the circular hole 111 is formed on the surface of the second transparent substrate 14b. The liquid crystal layer 13 is sealed between the first alignment film 12a formed on the first transparent electrode 11a and the second alignment film 12b formed on the lower surface of the second transparent substrate 14b.

  In the liquid crystal lens having such a structure, when no voltage is applied between the first transparent electrode 11a and the second electrode 11b, the refractive index of the liquid crystal layer 13 is uniform ((a) in the figure). On the other hand, when a voltage is applied between both electrodes (FIG. 5B), an axisymmetric non-uniform electric field centered on the central axis of the hole 111 is generated at a position facing the circular hole 111, The liquid crystal molecules are reoriented. As a result, the refractive index of the liquid crystal layer 13 is not uniform in the hole 111, and a refractive index distribution close to a square distribution is generated, resulting in a lens action. That is, the angle (inclination) of the liquid crystal molecules is different between the vicinity of the center of the hole 111 and the vicinity of the outer periphery, and this causes a difference in refractive index, so that the refractive index is distributed toward the center of the hole 111. Acts as a lens. By controlling the voltage applied between both electrodes, the refractive index distribution in the hole can be controlled, and the focal length can be moved in the optical axis direction. The lens action is obtained with respect to incident light polarized in the alignment direction of the liquid crystal molecules.

  Patent Document 1 proposes a structure in which two liquid crystal lenses of FIG. 9 are stacked symmetrically with the second electrode 11 ′ in common as shown in FIG. 10. In the liquid crystal lens L ′, the alignment directions of the two pairs of alignment films 12 a and 12 b and alignment films 22 a and 22 b are orthogonal to each other. According to the liquid crystal lens L ′ having such a configuration, a lens effect can be obtained not only for polarized light in a specific direction but also for natural light without using a polarizing plate. Moreover, since a polarizing plate is not used, high light transmittance is obtained.

FIG. 11 shows a schematic diagram when the liquid crystal lens L ′ of FIG. 10 is used in a camera. When the liquid crystal lens L ′ is disposed in front of the camera unit U and the focal point of the optical system of the camera unit U is set at infinity, the desired subject is focused by adjusting the voltage applied to the liquid crystal lens L ′. It is possible to change the focal length of the liquid crystal lens L ′ so that the desired subject can be clearly photographed.
JP 2004-4616 A (claims, (0056) to (0060) stages, FIG. 6)

  However, in the liquid crystal lens L ′ of FIG. 10, the two liquid crystal layers 13 and 23 are largely separated by the two transparent substrates 14 a and 24 a, so that the light flux at the screen periphery of the camera unit U is close to the camera unit U. The liquid crystal layer 13 on the side passes through a region close to the optical axis, but the liquid crystal layer 23 that is separated from the front end of the camera unit by a distance S ′ passes through a portion that is separated from the optical axis by a distance D ′. Since the refractive index is different between a region close to the optical axis of the liquid crystal layer and a region far from the optical axis, the two images depending on the polarization direction may be shifted in the liquid crystal lens L ′ to form a double image. Such a shift in optical characteristics such as a focal length and a focus position due to the polarization direction becomes a serious problem as an optical device. Further, in order to ensure the angle of view of the camera through the light flux in the peripheral portion, if the distance from the camera to the liquid crystal layer is large, the hole diameter required for the liquid crystal lens becomes very large.

  The present invention has been made in view of such a conventional problem. The object of the present invention is to shorten the distance between the liquid crystal layers in a liquid crystal lens using two liquid crystal layers, and to adjust the focal length and the focus depending on the polarization direction. The purpose is to prevent deviations in optical characteristics such as position.

  In order to achieve the above object, in the liquid crystal lens according to the first aspect of the present invention, the first transparent electrode, the first alignment film, the first liquid crystal layer, and the second transparent electrode are sequentially formed on one surface of the first transparent substrate from the first transparent substrate side. An alignment film, a second transparent substrate, and a second electrode having holes are formed, and a third transparent electrode, a third alignment film, and a second liquid crystal are sequentially formed on the other surface of the first transparent substrate from the first transparent substrate side. Forming a layer, a fourth alignment film, a third transparent substrate, and a fourth electrode having a hole; the alignment directions of the first alignment film and the second alignment film are the same direction; the alignment of the third alignment film and the fourth alignment film; The directions are also the same, and the alignment directions of the third alignment film and the fourth alignment film are perpendicular to the alignment directions of the first alignment film and the second alignment film.

  In the liquid crystal lens according to the second aspect of the present invention, a pair of opposing alignments are provided between the fourth transparent substrate on which the fifth transparent electrode is formed and the fifth transparent substrate on which the sixth electrode having holes is formed. An even number of liquid crystal layers sandwiched between films are stacked via a transparent substrate, and the alignment directions of a pair of alignment films are the same direction, and the alignment direction of half the pair of alignment films and the remaining half are It is characterized by being orthogonal.

  Here, the fifth transparent electrode, the even number of liquid crystal layers, the transparent substrate, and the fifth transparent substrate formed on one surface of the fourth transparent substrate are symmetrically centered on the fourth transparent substrate. You may form in the other side of.

  Further, from the viewpoint of further improving the optical characteristics of the lens, it is preferable that the distance between the two electrodes for applying an electric field to the liquid crystal layer is 10 times or more the layer thickness of the liquid crystal layer.

  In addition, from the viewpoint of obtaining an excellent lens effect, it is preferable that the alignment direction of each alignment film is axisymmetric about the optical axis.

  In the liquid crystal lens according to the first invention, since the first transparent substrate is shared and two liquid crystal lenses are laminated on both sides thereof, the number of transparent substrates can be reduced by one as compared with the conventional one. As a result, the distance between the two liquid crystal layers can be shortened, and deviations in optical characteristics such as the focal length and the focus position due to the polarization direction can be suppressed. Further, it can be made thinner than a conventional liquid crystal lens.

  In the liquid crystal lens according to the second invention, since an even number of liquid crystal layers are laminated between the fourth transparent substrate and the fifth transparent substrate, the transparent substrate is compared with the conventional one as in the first invention. The number of sheets can be reduced, whereby the distance between the two liquid crystal layers can be shortened, and deviations in optical characteristics such as the focal length and the focus position due to the polarization direction can be suppressed.

  Here, the fifth transparent electrode, the even number of liquid crystal layers, the transparent substrate, and the fifth transparent substrate formed on one surface of the fourth transparent substrate are symmetrically centered on the fourth transparent substrate. If it is formed on the other surface, the variable focal range can be widened or the optical characteristics can be improved.

  Further, when the distance between the two electrodes for applying an electric field to the liquid crystal layer is 10 times or more the thickness of the liquid crystal layer, the optical characteristics as a lens are improved.

  Further, when the alignment direction of each alignment film is axisymmetric about the optical axis, the alignment of the liquid crystal is symmetric with respect to the optical axis including the pretilt angle. As a result, if the incident angle with respect to the liquid crystal lens is the same, the inclination of the liquid crystal molecules with respect to the incident light will be the same. Is prevented.

  Hereinafter, the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.

  FIG. 1 is a schematic view showing an example of a liquid crystal lens L according to the first invention. In the liquid crystal lens of FIG. 1, a first transparent electrode 11a made of an ITO film (indium tin oxide) or the like is formed on one side (right side in the figure) of the first transparent substrate 1, and the surface thereof is made of polyimide or the like. A first alignment film 12a is formed. A second alignment film 12b is formed on the surface of the second transparent substrate 14 on the first transparent substrate side, and a second electrode 11b made of aluminum or the like is formed on the opposite side surface. A circular hole 111 (see FIG. 2) is formed at the center of the second electrode 11b. The first transparent substrate 1 and the second transparent substrate 14 are arranged in parallel and spaced apart from each other, the periphery between the substrates is sealed by a sealing member (not shown), and a liquid crystal agent is sealed in the space formed between the substrates. Thus, the liquid crystal layer 13 is configured. The alignment directions of the first alignment film 12a and the second alignment film 12b are the same.

  On the other hand, on the other side (left side in the figure) of the first transparent substrate 1, the same laminated structure as that on the right side is formed symmetrically with the first transparent substrate 1 as the center. That is, the third transparent electrode 21a, the third alignment film 22a, the second liquid crystal layer 23, the fourth alignment film 22b, the third transparent substrate 24, and the fourth electrode 21b are formed in order from the first transparent substrate 1. And the circular hole 211 (refer FIG. 2) is formed in the center part of the 4th electrode 21b. In addition, the alignment directions of the third alignment film 22a and the second alignment film 22b are the same, and are orthogonal to the alignment directions of the first alignment film 12a and the second alignment film 12b.

  FIG. 2 shows a side view of the liquid crystal lens of FIG. 1A is a left side view of the liquid crystal lens of FIG. 1, in which a circular hole 211 is formed in the center of the fourth electrode 21b, and a groove formed in the fourth alignment film 22b by rubbing treatment is shown in FIG. It can be seen from the hole 211. The direction of the groove is the orientation direction. FIG. 4B is a right side view of the liquid crystal lens of FIG. 1, and similarly to the above, a circular hole 111 is formed in the center of the second electrode 11b and is formed in the second alignment film 12b by rubbing treatment. The groove is visible from this hole 111. As can be understood from these drawings, the alignment directions of the second alignment film 12b (the same for the first alignment film 12a) and the fourth alignment film 22b (the same for the third alignment film 22a) are orthogonal to each other.

  Here, FIG. 3 and FIG. 4 show another embodiment of the alignment film. The alignment films forming a pair shown in FIGS. 3 and 4 have the alignment directions that are axially symmetric about the optical axis. In the alignment film of FIG. 3A, the alignment direction is a radial direction centered on the optical axis, and in the alignment film of FIG. 3B, the alignment direction is a concentric circle centering on the optical axis. In the alignment films shown in FIGS. 4A and 4B, the inclination of the alignment direction from the radial direction is + 45 ° and −45 °. When the orientation direction is asymmetric with respect to the optical axis, the light incident obliquely to the liquid crystal lens differs in the tilt of the liquid crystal molecules relative to the light depending on the direction. The focus position may vary depending on the position of the part (so-called single blur). However, as described above, when the alignment direction of the alignment film is symmetric with respect to the optical axis, the incident angle to the liquid crystal lens is the same. If so, the inclination of the liquid crystal molecules with respect to light is the same regardless of the direction, and so-called one-sided blur does not occur even when the liquid crystal lens of the present invention is used in an imaging system.

  In the liquid crystal lens having such a configuration, a predetermined AC voltage is applied between the first transparent electrode 11a and the second electrode 11b and between the third transparent electrode 21a and the fourth electrode 21b shown in FIG. As described above, a non-uniform electric field is generated in the liquid crystal layers 13 and 23. As a result, a refractive index distribution is generated in the liquid crystal layers 13 and 23, and a lens action is exhibited in the liquid crystal layers 13 and 23.

  The liquid crystal molecules of the liquid crystal layer 13 and the liquid crystal layer 23 are aligned so as to be orthogonal by the alignment film. If the P-polarized light is condensed by the liquid crystal layer 13 and the S-polarized light is transmitted, the P-polarized light is transmitted and the S-polarized light is condensed by the liquid crystal layer 23. In the opposite case, condensing and transmission of P-polarized light and S-polarized light are reversed. Therefore, all the light that has passed through the liquid crystal layer 13 and the liquid crystal layer 23 is collected, and this liquid crystal lens can obtain a lens action against natural light without using a polarizing plate. In addition, since a polarizing plate is not used, a higher light transmittance can be obtained than in the prior art.

  In the liquid crystal lens of FIG. 1, the distance between the liquid crystal layer 13 and the liquid crystal layer 23 is shorter than the conventional one. Thereby, it is possible to suppress the double image formation depending on the polarization direction. As shown in FIG. 5, when the liquid crystal lens L of FIG. 1 is disposed in front of the camera unit U, the camera unit U has a distance corresponding to the distance between the liquid crystal layer 13 and the liquid crystal layer 23. The distance S from the front surface to the liquid crystal layer 23 is shorter than before. As a result, the light flux at the peripheral edge of the screen of the camera unit U passes through the region of the liquid crystal layer 23 at a distance D from the optical axis (the hatched portion in the figure), and the effective diameter of the liquid crystal lens, that is, the fourth electrode 21b and the fourth electrode. The holes 211 and 111 formed in the two electrodes 11b can be made small. It is known that the optimum value of the distance between the electrodes is proportional to the effective diameter. Therefore, if the effective diameter is reduced, the optimum inter-electrode distance can be shortened and the thickness of the liquid crystal lens L can be reduced. If the thickness of the liquid crystal lens L is reduced, the liquid crystal lens L and the camera unit U can be brought closer to each other, thereby further reducing the effective diameter. Thus, by shortening the distance between the liquid crystal layers, the liquid crystal lens L and the apparatus using the same can be miniaturized and the performance can be improved.

  In the liquid crystal lens L of FIG. 1, the first transparent electrode 11a and the third transparent electrode 21a are formed on both surfaces of the first transparent substrate 1, but the first transparent substrate 1 is not so affected as to affect the electric field. When the thickness is reduced, only one of the first transparent electrode 11a and the third transparent electrode 21a may be formed. Further, when using a transparent electrode having rigidity, the first transparent substrate may not be used.

  Next, a liquid crystal lens according to the second invention will be described. A major feature of the liquid crystal lens of the present invention is that an even number of liquid crystal layers are laminated between a pair of electrodes. An example of the liquid crystal lens according to the present invention is shown in FIG. In the liquid crystal lens of FIG. 6, a pair of alignment films 32a is provided between the fourth transparent substrate 4 with the fifth transparent electrode 31a formed on the surface and the fifth transparent substrate 5 with the sixth electrode 31b formed on the surface. , 32b and a liquid crystal layer 33b sandwiched between a pair of alignment films 35a, 35b are stacked with a light-transmitting substrate 34 interposed therebetween. The alignment directions of the paired alignment films are the same, and the alignment directions of the alignment films 32a and 32b and the alignment films 35a and 35b are orthogonal to each other. Note that, by narrowing the distance between the fifth transparent electrode 31a and the sixth electrode 31b, a slight difference in non-uniform electric fields acting on the liquid crystal layer 33a and the liquid crystal layer 33b can be ignored.

  In the liquid crystal lens having such a configuration, one set of electrodes can be further eliminated and the thickness of the liquid crystal lens can be further reduced as compared with the liquid crystal lens of FIG. In addition, wiring is facilitated as much as the number of electrodes is reduced.

  FIG. 7 shows another embodiment of the liquid crystal lens according to the second invention. In the liquid crystal lens of FIG. 7, four liquid crystal layers 33a to 33d are disposed between the fifth transparent electrode 31a and the sixth electrode 31b. In the same manner as described above, the alignment directions of the paired alignment films are the same, and the alignment directions of the alignment film pairs are alternately rotated by 90 °. For ease of explanation, if one of the orthogonal alignment directions is a “vertical direction” and the other is a “horizontal direction”, the alignment directions of the alignment films 32 a and 32 b and the alignment films 36 a and 36 b are the vertical directions. The alignment direction of 35a, 35b and the alignment films 37a, 37b is a horizontal direction. Of course, the alignment direction of the continuous alignment films 32a, 32b, 35a, and 35b may be the vertical direction, and the alignment direction of the continuous alignment films 36a, 36b, 37a, and 37b may be the horizontal direction, but the optical characteristics of the liquid crystal lens are improved. In view of the above, it is desirable that the orientation direction of the alignment film pair is alternated between the vertical direction and the horizontal direction.

  In the liquid crystal lens of FIG. 7, if the thickness of each of the liquid crystal layers 33 a to 33 d is the same as that of each liquid crystal layer of the liquid crystal lens of FIG. 6, the focal length range that can be changed by the applied voltage is widened. On the other hand, if the thickness of the liquid crystal layers 33a to 33d is half of each liquid crystal layer of the liquid crystal lens of FIG. 6 and the total thickness of the entire liquid crystal layer is the same, the variable focal length is the same, but the focal length according to the polarization direction Deviations such as the focus position can be further suppressed. In addition, since the thickness of the liquid crystal layer is reduced, the alignment response of the liquid crystal molecules is accelerated.

  In the liquid crystal lens of FIG. 7, four liquid crystal layers 33a to 33d are stacked. However, the number of liquid crystal layers is not limited as long as it is an even number. The number and thickness of the liquid crystal layers may be determined as appropriate from the required variable focal length, optical characteristics, and the like.

  The liquid crystal lens of FIG. 8 is formed on the other surface of the fourth transparent substrate 4 with the structure formed on one surface of the fourth transparent substrate 4 in the liquid crystal lens of FIG. It is a thing. Also in this liquid crystal lens, if the thickness of each liquid crystal layer 33a, 33a ', 33b, 33b' is the same as that of each liquid crystal layer of FIG. 6, the focal length range that can be changed by the applied voltage is widened. On the other hand, if the thickness of the liquid crystal layers 33a, 33a ′, 33b, and 33b ′ is half of each liquid crystal layer of the liquid crystal lens of FIG. 6 and the total thickness of the entire liquid crystal layer is the same, the variable focal length is the same. Deviations such as the focal length and focus position due to the polarization direction can be further suppressed, and the alignment responsiveness of the liquid crystal molecules can be increased by reducing the thickness of the liquid crystal layer.

It is a schematic diagram which shows an example of the liquid crystal lens which concerns on 1st invention. FIG. 2 is a left / right side view of the liquid crystal lens of FIG. 1. It is a figure which shows other embodiment of alignment film. It is a figure which shows other embodiment of alignment film. It is a schematic diagram at the time of using the liquid-crystal lens of FIG. 1 for the optical system of a camera. It is a schematic diagram which shows an example of the liquid crystal lens which concerns on 2nd invention. It is a schematic diagram which shows the other example of the liquid crystal lens which concerns on 2nd invention. It is a schematic diagram which shows the other example of the liquid crystal lens which concerns on 2nd invention. It is a figure for demonstrating the mechanism of a liquid crystal lens. It is a schematic diagram which shows the conventional liquid crystal lens. It is a schematic diagram at the time of using the liquid-crystal lens of FIG. 10 for the optical system of a camera.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st transparent substrate 4 4th transparent substrate 5 5th transparent substrate 11a 1st transparent electrode 11b 2nd electrode 12a 1st alignment film 12b 2nd alignment film 13 1st liquid crystal layer 14 2nd transparent substrate 21a 3rd transparent electrode 21b Fourth electrode 22a Third alignment film 22b Fourth alignment film 23 Second liquid crystal layer 24 Third transparent substrate 31a Fifth transparent electrode 31b Sixth electrode 32a, 32b, 35a, 35b, 36a, 36b Alignment films 33a, 33b, 33c , 33d Liquid crystal layer 111, 211 hole

Claims (5)

A first transparent electrode, a first alignment film, a first liquid crystal layer, a second alignment film, a second transparent substrate, and a second electrode having holes are formed on one surface of the first transparent substrate in order from the first transparent substrate side. In addition, a third transparent electrode, a third alignment film, a second liquid crystal layer, a fourth alignment film, a third transparent substrate, and a hole are formed on the other surface of the first transparent substrate in order from the first transparent substrate side. A fourth electrode is formed;
The alignment directions of the first alignment film and the second alignment film are the same direction, the alignment directions of the third alignment film and the fourth alignment film are also the same direction, and with respect to the alignment directions of the first alignment film and the second alignment film. A liquid crystal lens, wherein the alignment directions of the third alignment film and the fourth alignment film are orthogonal to each other.   A liquid crystal layer sandwiched between a pair of opposing alignment films is interposed between the fourth transparent substrate on which the fifth transparent electrode is formed and the fifth transparent substrate on which the sixth electrode having a hole is formed via the transparent substrate. An even number of layers are stacked, the alignment directions of the pair of alignment films are the same, and the alignment direction of the half of the pair of alignment films and the remaining half are orthogonal to each other.   The fifth transparent electrode, the even number of liquid crystal layers, the transparent substrate, and the fifth transparent substrate formed on one surface of the fourth transparent substrate are symmetrically formed around the fourth transparent substrate. The liquid crystal lens according to claim 2, wherein the liquid crystal lens is formed on the other surface.   The liquid crystal lens according to any one of claims 1 to 3, wherein a distance between two electrodes for applying an electric field to the liquid crystal layer is 10 times or more a thickness of the liquid crystal layer.   The liquid crystal lens according to claim 1, wherein the alignment direction of each alignment film is axisymmetric about the optical axis.

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