JPS63206721A - Liquid crystal lens - Google Patents

Abstract

PURPOSE:To permit formation of an extremely thin liquid crystal layer by providing a transparent insulating layer on at least one of transparent conductive layers to constitute a titled lens in such a manner that the transparent conductive layers are not shorted from each other and disposing no spacer materials between the two transparent conductive layers. CONSTITUTION:The lens 1A is formed by providing the transparent conductive layers 5, 6 respectively on the opposed surface of flat plate glass 3 consisting of a transparent substrate and a Fresnel lens 2a having grooves for Fresnel provided with peaks flush with each other, superposing the flat plate glass 3 and the Fresnel lens 2a in such a manner that the two conductive layers 5, 6 face each other, coating adhesive agents 12 on the peripheral faces of both the glass and the lens to integrate the glass and the lens and sealing a liquid crystal 7 into the space formed between the two conductive layers 5 and 6. The space for sealing of the liquid crystal is assured even if the liquid crystal lens is formed by sticking the transparent substrates having a lens shape to each other. The lens having the optical characteristics substantially equal to the optical characteristics of the liquid crystal lens formed by using the spacer are obtd. An electrical insulation is provided to the lens by providing the transparent insulating layer 10 on at least one of the conductive layers 6.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a variable focal length liquid crystal lens using liquid crystal;
Jγ specifically relates to short-circuit prevention between two transparent electrodes sandwiching the liquid crystal layer of a liquid crystal lens, responsiveness and recovery time of focal length #Mra, and specifically relates to a liquid crystal lens with modified light transmittance.

[Prior Art] The idea of making a lens with a variable focal length by utilizing the birefringence phenomenon of liquid crystals has already been proposed, for example, in JP-A-52-32348, JP-A-54-99654, and JP-B-Sho.
This can be seen in Publication No. 50339, etc.

An example of such a conventional lens using liquid crystal (hereinafter referred to as liquid crystal lens) will be explained with reference to FIGS. 5(A) and 5(B). Flat glass 33 made of a transparent substrate
are arranged to face each other, transparent conductive layers 35 and 36 are respectively provided on the opposing surfaces, and a liquid crystal 37 is sealed in the space formed when these are bonded together with a bonding agent 38 via a spacer 34. There is.

In the case of a liquid crystal lens, the spacer 34 is provided only around the lens in order to prevent deterioration of the light-condensing property and light scattering in the effective part of the lens, unlike a liquid crystal display in which a spacer is also provided in the effective part of the display. will be placed in An alternating current voltage from an alternating current power source 8 is applied between the transparent conductive layers 35 and 36 so as to be adjustable by a variable resistor 9.

Also, even when this AC voltage is not applied,
The sides of both transparent conductive layers in contact with the liquid crystal are subjected to alignment treatment so that the liquid crystal molecules are aligned in a specific direction, and in the drawing, the liquid crystal molecules are homogeneously aligned.

When a voltage is applied to this liquid crystal lens 31, the liquid crystal lens 3
The molecules of the liquid crystal 37 in 1 rotate so that their long axes are aligned with the direction of the electric field (dielectric of liquid crystal).

(for liquid crystals with positive anisotropy). Here, a polarizing plate PL is combined as shown in FIG. 6 with a liquid crystal lens 31 having a director of liquid crystal molecules indicated by an arrow n in FIG. When the liquid crystal molecules in the liquid crystal lens 31 are rotated by changing the applied voltage, the refractive index of the liquid crystal 37 changes between the refractive index n for extraordinary rays and the refractive index n for ordinary rays. It's changing. Therefore, if the focal length is f, the refractive index is n, and the curvature 1'-diameter of both surfaces of the lens is l, r2, then the focal length of the lens can be expressed as This means that the focal length can be changed.

Furthermore, in Japanese Unexamined Patent Publication No. 60-50510, a liquid crystal lens using a Fresnel lens instead of the spherical lens indicated by reference numeral 32 in FIG. When a liquid crystal lens having a refractive power equal to 2 is used, it can be made thinner and lighter than the liquid crystal lens 31 shown in FIG. 5, and the response and recovery time can be improved.

Furthermore, in the liquid crystal lens proposed by the present applicant in Japanese Patent Application No. 61-47510, when a Fresnel lens is used, the response and recovery time can be further improved by using a Fresnel lens whose Fresnel grooves are aligned. It has been found that improvements can be made.

That is, in a liquid crystal lens using this Fresnel lens, as shown in FIG.
It is composed of a Fresnel lens 42a with a flat plate glass 43 and a Fresnel lens 42a with a flat plate glass 43 formed by Fresnel lens surface force formation in ao. It forms cells.

In addition, a transparent conductive layer 45 is provided on the inner surface of each of the Fresnel lens 42a and the flat glass 43 constituting the liquid crystal cell.
．． 46 is formed. A nematic type liquid crystal 47 is sealed in this cell to constitute a liquid crystal lens 41A, and from one end of the transparent conductive layer 45, 46, the AC voltage from the AC power source 8 is variable as shown in Fig. 5 above. Resistor 9
It is designed to be applied via the The liquid crystal molecules within the cell are aligned in a specific direction, resulting in homogeneous alignment.

The response time T res of the liquid crystal in a plane-parallel liquid crystal cell configured in this way is determined by the applied voltage being V, the elastic constant and viscosity constant of the liquid crystal being γ1°4, the permittivity in the longitudinal direction of the liquid crystal, and the dielectric constant in the vertical direction. The difference in permittivity of Δε(Δε−ε9
− and ), the permittivity of vacuum is ε. , and the thickness of the liquid crystal layer is expressed as follows.

Here, if everything other than the thickness d of the liquid crystal layer is constant, the response time T res of the liquid crystal is T ras cx= d --・= (3), which is proportional to the square of the thickness of the liquid crystal layer. become.

Therefore, the liquid crystal layer thickness dM of the liquid crystal Fresnel lens 41A using the aligned Fresnel lens 42a shown in FIG.
Valley-aligned Fresnel groove 42bo in the lens component hole shown in the figure.
The Fresnel lens 42b is aligned with the valley formed by the Fresnel lens.
It is much thinner than the liquid crystal layer thickness dv of the liquid crystal Fresnel lens 41B using the above-mentioned liquid crystal Fresnel lens 41B, so that the desired focal length can be quickly adjusted.

These responses and fiil 78 hours in the liquid crystal lens 19 The response time (Trcs) and recovery time (Tree) of the liquid crystal lens depend on the liquid crystal layer thickness (d) and Tresoc.
d・・・・・・・・・・・・(4)Trcc
ocd This is based on the relationship shown in (5).

[Problems to be Solved by the Invention] As described above, by reducing the thickness of the liquid crystal layer in the liquid crystal lens, response/recovery time can be shortened. In order to use liquid crystal lenses in , it is required to further shorten the response and recovery time.

Accordingly, one object of the present invention is to provide a liquid crystal lens that can obtain a response and recovery time that is even shorter than that of current liquid crystal lenses.

[Means and effects for solving the problem] In the present invention, in order to shorten the response/recovery time of the liquid crystal lens, two transparent substrates facing each other, and a A liquid crystal lens comprising a transparent conductive layer provided and a liquid crystal sealed in a lens-shaped space sandwiched between the transparent conductive layers, and whose refractive power is made variable by applying a voltage to the transparent conductive layer. , without disposing a spacer material between the two opposing transparent conductive layers so that the two transparent conductive layers do not short-circuit with each other.

[Example〕 The present invention will be explained below with reference to illustrated embodiments.

1 to 3 show an embodiment of the present invention,
In this embodiment, transparent substrates 2a, 2b, 2c of lens constituent members are used.
This is a case where the present invention is applied to liquid crystal lenses IA, IB, and IC in which transparent conductive layers 5 and 6 are provided over the entire opposing surface of a transparent substrate 3.

The present invention can be understood very clearly by comparing the structure of the liquid crystal lens embodiment shown in FIGS. 1 to 3 with the structure of the conventional liquid crystal lens shown in FIGS. 5 and 7.8. It should be done. That is, the spacers indicated by numerals 34 and 44 in FIG. 5 and FIG. 7.8 are removed in the present embodiment shown in FIGS.
, ds becomes extremely thin. It is easily understood from the above equations (4) and (5) that this shortens the response and recovery time of the liquid crystal lens.

The liquid crystal lens IA of the embodiment shown in FIG. The flat glass 3 and Fresnel lens 2a are polymerized with both conductive layers 5.6 facing each other, and the adhesive 12 is applied to the circumferential surfaces of both to integrate them. The liquid crystal 7 is placed in the space formed by
It is composed of enclosed. Then, the transparent conductive layer 5
and 6, an alternating current voltage is applied from an alternating current power source 8 in a manner that can be adjusted freely by a variable resistor 9.

Further, the liquid crystal lens IB of the embodiment shown in FIG. 2 is exactly the same as the liquid crystal lens IA of the embodiment shown in FIG. It is composed of Further, the liquid crystal lens Ic of the embodiment shown in FIG.
The lens formed by the plate 2C is a spherical concave lens, and the other configurations are the same as those of the embodiment shown in FIGS. 1 and 2 above.

The liquid crystal lens IA of each example configured in this manner
~ When comparing ICs with the same lens aperture, the liquid crystal lens IB of the embodiment shown in FIG. 2 has a greater effect when the spacer material is removed than the liquid crystal lens IC of the embodiment shown in FIG. Furthermore, the liquid crystal lens IA having the configuration using the mountain-aligned Fresnel lens 2a shown in FIG. 1 has an even greater effect t! I will be beaten.

The structure in which the spacer material is removed as in the present invention is a structure that has not been seen in conventional liquid crystal lenses or liquid crystal displays. Because liquid crystal displays are made up of transparent flat plates glued together, it is necessary to place a spacer material somewhere in between to create a space to seal in the liquid crystal.
This is because the configuration as in the present invention could not be achieved. Furthermore, when looking at liquid crystal lenses, their configuration has conventionally been based on that of a liquid crystal display, so the idea of completely removing the spacer material has been overlooked and never existed before. In other words, since a liquid crystal lens includes a transparent substrate that takes the shape of a lens, for example, even if the convex Fresnel lens shown in Fig. 1 is used and the transparent substrates are bonded together without using a spacer material, there is still a space in which the liquid crystal can be sealed. It is possible to obtain a liquid crystal lens with almost the same optical characteristics as a liquid crystal lens using a spacer material. The configuration of the present invention that utilizes the unique shape of a liquid crystal lens in this way is a novel configuration that has not been seen before.

In the liquid crystal lenses IA to IC configured by removing the spacer material as described above, the transparent conductive layers 5 and 6 on both transparent substrates will be short-circuited if left as is, so the embodiments shown in FIGS. A transparent insulating layer 10 is provided on at least one transparent conductive layer 6 to provide electrical insulation. The materials forming this insulating layer 10 are SiO2, Ta205. A
A metal oxide film such as l2O3 may be used, or a so-called organic insulating material may be used.

Furthermore, although omitted in this embodiment, when producing a liquid crystal element, an alignment treatment is always performed on the surface in contact with the liquid crystal. Sin, polyimide, etc. can also be used as the material for this alignment layer, and since these materials have high resistance etc.
It is also possible to serve as the insulating layer 10 together with the alignment layer. However, in order to stably secure generally high insulation properties, it is necessary to increase the film thickness (
Slightly thicker (2000A~
8000A). However, when the film thickness is increased in this way, in the case of polyimide, the color of polyimide becomes noticeable, which is not preferable in terms of spectral transmittance as a liquid crystal lens, which is an optical element. In this way, it is possible to have the alignment layer and the insulating layer both function, but the range of material selection is narrowed, so from the perspective of the characteristics of the liquid crystal lens, it is possible to make the alignment layer and the insulating layer use different materials, so to speak. A separate configuration is preferable.

Further, polyvinyl alcohol, which has been conventionally used as a material for the alignment layer, has a rather low resistivity, so in this case as well, a functionally separated structure in which an insulating layer is separately provided is desirable.

In addition, for example, in the case where the effective portion of the lens does not have contact between the two transparent conductive layers, as shown in FIGS. 2 and 3, the transparent insulating layer may be provided only in the peripheral portion where the contact occurs. can improve lens properties such as light transmittance.

Next, FIGS. 4(A), 4(B), and 4(C) are configuration diagrams of a liquid crystal lens 21 showing another embodiment of the present invention. As in the embodiment shown in FIG. 1 above, both transparent conductive layers 5,
If there is no possibility of contact between the two transparent conductive layers 5 and 6 in the effective portion of the lens except for the case where there is contact between the two transparent conductive layers 5 and 6, it is possible to adopt a configuration in which no transparent conductive layer is used as shown in FIG.

That is, the transparent conductive layers 25 and 26 provided on the opposing inner surfaces of the transparent substrate on which the spherical concave lens 22 is formed and the transparent substrate made of the flat glass 23 on the other side are as shown in FIG.
B) shows the planar shape of the transparent conductive EI 25 of the spherical concave lens 22, and FIG. 4(C) shows the transparent conductive layer 2 of the flat glass 23.
6, the voltage applying electrodes 25a, 2 are formed so that they do not come into contact with each other when they are polymerized.
Only 6a is formed so as to be drawn out.

Then, the spherical concave lens 22 and the flat glass 23 on which the conductive layers 25 and 26 are formed are superposed as shown in FIG. 4(A), and the liquid crystal 27 is formed in the space between the conductive layers 25 and 26. The liquid crystal lens 21 is constructed by enclosing the liquid crystal lens 21 and applying an adhesive 24 to the circumferential surfaces of both. Also, this liquid crystal lens 2
1 is a transparent substrate 22 on which transparent conductive layers 25 and 26 are etched in the shapes shown in FIG. 4(B) and FIG. 4(C), respectively.
．． It is constructed by pasting together 23 pieces, and ■
- Since the transparent insulating layer 10 in the embodiments shown in FIGS. 1 to 3 is not formed, it is advantageous in terms of the light transmittance of the lens and the manufacturing cost of the lens.

Of course, this configuration also improves the response and recovery characteristics since there is no spacer material.

In addition, in order to obtain better response and recovery characteristics, the voltage applied Mi25 a is used as the electrode extraction position.

The formation of 26a on the peripheral part of the lens is not limited to the above embodiment, but may be formed up to the innermost part of the lens as long as the two transparent conductive layers 25 and 26 do not come into contact with each other. In order to further reduce alignment unevenness, electrodes may be provided at several symmetrical peripheral positions.

Further, in each of the above embodiments, adhesive 12 is applied to the peripheral surface of the liquid crystal lens.
．． Conventionally, both transparent substrates of a liquid crystal lens were bonded together using an adhesive mixed with a spacer material, but since the present invention does not use a spacer material, the adhesive The area to be coated is the peripheral surface of the liquid crystal lens.

Next, an experimental example of response/recovery characteristics and lens distortion due to weight will be described, comparing a liquid crystal lens manufactured according to the present invention with a conventional liquid crystal lens.

The liquid crystal lens according to the present invention and the conventional liquid crystal lens used in this experiment were manufactured as follows.

That is, the liquid crystal lenses according to the present invention are liquid crystal lenses IA and IB having the respective configurations shown in FIGS. Prepare an acrylic Fresnel lens and a flat glass with an ITO transparent conductive layer.
A 102 transparent insulating layer was deposited, and then an alignment layer was formed using PVA (polyvinyl alcohol) and an alignment treatment was performed, and the Fresnel lens and flat glass were bonded together without using a spacer. The liquid crystal was filled in by dropping the liquid crystal onto the Fresnel lens side before bonding the two together, and then bonding the flat glass over it.

In this example, a transparent insulating layer with a thickness of about 85 OA was used, but in order to obtain a more stable one in terms of manufacturing, a thickness of about 20 OA was used.
It is preferable to set it as 00A-3000A.

Further, liquid crystal lens IB was produced in the same manner as in liquid crystal lens IA, except that instead of using the protrusion-aligned Fresnel lens, a valley-aligned Fresnel lens was used.

On the other hand, the conventional liquid crystal lens has the configuration shown in FIG. 7, and this liquid crystal lens 41A does not provide a transparent insulating layer on the flat glass, but connects the Fresnel lens and the flat glass via a φ20 μm spacer. It was made by pasting them together.

(Experiment on response/recovery time with and without spacer) This experiment used the liquid crystal lens IA according to the present invention described above and the conventional liquid crystal lens 41A described above.The liquid crystal lens used for determining ΔFJ was φ26 mm. The most time-consuming part was measured. The depth of the groove of the Fresnel lens in this part is about 100 μm at the deepest part.

In addition, the thickness of the spacer used in conventional liquid crystal lenses is approximately 2
It is 0 μm.

First, apply an AC voltage of 16v to the liquid crystal lens,
After that, when the power supply circuit system was opened, the focal length of the liquid crystal lens changed from a long focus to a short focus, and this capsulation was observed using a photodiode and an oscilloscope connected to it. When apj was determined as the recovery time, the recovery time of the conventional liquid crystal lens was about 10 seconds, but the recovery time of the liquid crystal lens IA of the present invention was shortened to about 5 seconds.

At the center of the liquid crystal lens, the ratio of the depth of the Fresnel lens groove to the spacer thickness is clearly small (approximately 4 μm in this example), so the degree of improvement in recovery speed is more remarkable than at the periphery.

This confirmed that the present invention in which the spacer material was removed is effective in improving response and recovery characteristics. In addition, in an experiment on the light transmittance of a liquid crystal lens conducted at the same time, it was found that the lens IA according to the present invention was several percent lower than the conventional lens 41A.
An improvement in light transmittance was observed. This is understood to be because the thickness of the liquid crystal layer has become thinner, so that the scattering and absorption of light by the liquid crystal has decreased, and the liquid crystal lens of the present invention in which the spacer material is removed also has an advantage in this respect.

(Experiment on lens distortion due to weight) Liquid crystal lenses IA and IB of the present invention and conventional liquid crystal lens 4
A load was applied to a region of φ15 m −2 from the Fresnel lens side using 1 A and applying an AC voltage of 12 V. At this time, the current flowing through the power supply circuit system and the voltage drop across a resistor inserted in the circuit were measured with a voltmeter, and the distortion and short circuit caused by the pressurization of the liquid crystal lens were observed.

The liquid crystal lens IB and the conventional liquid crystal lens 41A are as follows:
The current flowing through the system increases with the weight, and the liquid crystal lens I
B was saturated at about 4 kg. Also, with the conventional liquid crystal lens 41A, the weight gradually increased up to about 7kg, but 8k
A short circuit occurred due to the load of g. On the other hand, the liquid crystal lens IA was stable with almost no change in current.

In addition, in order to check the loading history, the above experiment was repeated, and the voltage drop was measured for the liquid crystal lens IA and the conventional liquid crystal lens 41A within 1 minute after the pressurization was stopped. With lens IA, the voltage hardly changed even after repeated experiments, whereas with conventional liquid crystal lens 41A, as the number of pressurizations increased, the value of voltage drop gradually changed due to distortion of the liquid crystal lens5. After two pressurization cycles, the value increased by about 7%.

From this experiment, it was confirmed that the liquid crystal lens having the structure shown in FIG. 1, in which the effective part of the lens has a contact area between the Fresnet lens and the flat glass, has excellent mechanical stability.

This is because conventional liquid crystal lenses are required to have higher optical properties such as light condensing properties than liquid crystal displays, so spacers that act as sources of light scattering cannot be placed in the effective portion of the lens. Therefore, in the effective part of the lens, in addition to the electrical problem of short-circuiting of the transparent electrode, there was a problem that the optical characteristics such as distortion of the lens due to external pressure deviated from the designed value. As a secondary effect, such a problem can be solved by constructing a liquid crystal lens using a lens such as an aligned Fresnel lens, and a liquid crystal lens with high quality and precision can be manufactured.

In addition, although the aligned Fresnel lens used in the above example had all the peaks at the same height, it is also possible to use a Fresnel lens in which there is a peak in contact with the opposing flat glass at every few annular zones of the Fresnel lens. It is clear that a similar effect can be expected in this regard even if a lens is applied.

[Effects of the Invention] As described above, according to the present invention: (1) Since the liquid crystal layer can be made extremely thin, response and recovery time when changing the focal length can be shortened.

(2) Since the liquid crystal layer can be made extremely thin, light scattering, etc. can be suppressed, and light transmittance can be improved.

(3) By providing a transparent insulating layer, it is possible to eliminate short circuits between transparent conductive films in the effective portion of the lens.

(4) By providing a portion where the transparent substrate comes into contact with the transparent insulating layer in the effective portion of the lens, a liquid crystal lens with high quality and precision that is resistant to external pressure etc. can be obtained.

It is possible to provide a liquid crystal lens that exhibits remarkable effects such as:

[Brief explanation of the drawing]

1 to 3 are enlarged sectional views of a liquid crystal lens according to an embodiment of the present invention, in which FIG. 1 shows a liquid crystal lens using a Fresnel lens with peaks aligned, and FIG. 2 shows a liquid crystal lens using a Fresnel lens with valleys aligned. 3 is a cross-sectional view of a liquid crystal lens using a spherical concave lens, and FIGS. 4(A), 4(B), and 4(C) are liquid crystal lenses showing other embodiments of the present invention; ) is an enlarged sectional view, (B) is a plan view of a spherical concave lens, (C) is a plan view of a flat glass, and FIGS. 5(A) and 5(B) show an example of a conventional liquid crystal lens, (A) is an enlarged cross-sectional view, (B) is a cross-sectional view of the main part, Figure 6 is a perspective view of a liquid crystal lens combined with a polarizing plate, and Figure 7 is a conventional lens using an aligned Fresnel lens. Enlarged sectional view of liquid crystal lens FIG. 8 is an enlarged sectional view of a conventional liquid crystal lens using a valley-aligned Fresnel lens.

Claims (1)

[Claims] Two opposing transparent substrates, a transparent conductive layer provided on the opposing sides of the transparent substrates, and a lens-shaped space sandwiched between the transparent conductive layers. In a liquid crystal lens having an encapsulated liquid crystal, the refractive power of which is made variable by applying a voltage to the transparent conductive layer, the liquid crystal lens has an encapsulated liquid crystal, in which the refractive power of the liquid crystal lens can be changed by applying a voltage to the transparent conductive layer, without disposing a spacer material between the two opposing transparent conductive layers. A liquid crystal lens characterized in that its layers are constructed so that they do not short-circuit with each other.