JPS62129816A - Liquid crystal lens with focal length - Google Patents

Abstract

PURPOSE:To adjust focal length sufficiently by varying the refractive index of liquid crystal to 1.5-1.9 so that the quantity of variation in refractive index is >=0.1 and also varying the refractive index of substrates which constitute a liquid crystal cell to 1.55-1.85. CONSTITUTION:The liquid crystal cell 1 which is formed in the shape of a lens while having liquid crystal molecules oriented in a proper direction is applied with an electric field or magnetic field from an externally applying means 5 to control the orientation state of liquid crystal molecules of the liquid crystal 2, thereby varying the refractive index of the liquid crystal 2 stepwise or continuously. The focal length of this liquid crystal lens is adjusted sufficiently in practical use on condition that variation in the refractive index of the liquid crystal 2 is 1.5-1.9 and the quantity of the variation is >=0.1. Then when the refractive index of the substrates 3 constituting the liquid crystal cell is larger than that to ordinary light and smaller than that to extraordinary light, i.e. 1.55-1.85, the liquid crystal lens 1 is applied to a spectacle lens to realize short-distance and long-distance spectacle.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a variable focal length liquid crystal lens, and in particular, the focal length can be changed to become either a concave lens or a convex lens by changing the applied voltage, etc. This invention relates to a variable focal length liquid crystal lens.

[Conventional technology]

When the crystalline lens of the eyeball has been removed due to an eye disease such as cataract, conventional lenses with a fixed focal length are used. It is necessary to use them properly according to each situation, which causes great inconvenience in real life. Therefore, there has been a desire for a spectacle lens whose focal length can be freely changed. Further, the focal length of a variable focus lens called a zoom lens used in an optical lens is controlled by changing the distance between lens groups each composed of a plurality of single lenses. Therefore, a lens movable mechanism is essential to move the lens group, and the demands for miniaturization and low cost cannot be fully satisfied, and the focus 1 [! There has been a desire for a variable focal length lens whose distance can be freely changed.

Liquid crystals generally have an elongated rod-like molecular structure with a length of several tens of amps and a width of about several amps, and also have dielectric anisotropy, with the dielectric constant parallel to the axial direction of the liquid crystal molecules and the dielectric constant in the direction perpendicular to the axial direction of the liquid crystal molecules generally being It does not match. A liquid crystal in which the former is larger than the latter is called a positive liquid crystal, and the opposite is called a negative liquid crystal.

A field-effect liquid crystal with positive dielectric anisotropy is placed between two transparent electrode substrates, the liquid crystal molecules are oriented parallel to the substrates, and an alternating voltage above a threshold is applied to the liquid crystal cell. The force acting on the dipole moment of the liquid crystal molecules causes the liquid crystal molecules to change the direction of the liquid crystal molecular axis in the direction of voltage application. Therefore, depending on the magnitude of the applied voltage, the orientation of the liquid crystal molecules, which were oriented parallel to the substrate, can be continuously changed in a direction perpendicular to the substrate. Therefore, the apparent refractive index of the liquid crystal cell for incident light polarized in the orientation direction of the liquid crystal molecules changes continuously from the value for extraordinary light to the value for ordinary light.

This so-called electric field-controlled birefringence effect is determined by the relative relationship between electrical energy and elastic energy, so
It is known that it does not depend on the thickness of the liquid crystal cell and changes depending on the applied voltage rather than the applied electric field. In other words,
The liquid crystal cell is shaped like a lens, and even if the thickness of the liquid crystal cell differs from place to place, optically uniform changes in refractive index can be obtained. In other words, a liquid crystal with positive dielectric anisotropy is sealed between lens-shaped substrates with liquid crystal molecules aligned in an appropriate direction, and the alignment direction of the liquid crystal molecules is controlled by applied voltage to change the apparent appearance of the liquid crystal cell. By changing the refractive index, the focal length of the liquid crystal lens can be continuously changed from the value Fe for extraordinary light to the value Fo for ordinary light. When a vertically aligned liquid crystal with negative dielectric anisotropy is used, the change in focal length with respect to the applied voltage is reversed. Since the alignment state of liquid crystal molecules can be changed by applying a magnetic field instead of applying a voltage, it is also possible to create a variable focal length lens using a magnetic field.

[The problem that the invention seeks to solve, −χ] However,
Conventional liquid crystal lenses use CLUB (cyanopentyl biphenyl), for example, as the liquid crystal to be sealed.
, n, = 1,719), for example, if PMMA (polymethyl methacrylate) is used as the substrate constituting the liquid crystal cell (n = 1,49), the focal length can be changed, but only by changing the applied voltage. It was not possible to switch between a concave lens and a convex lens, or to continuously switch between a concave lens and a convex lens while changing the focal point ff1ll.

Moreover, MBBA (para-methoxybenzylidene-para-butylaniline) was used for the liquid crystal (no=1,545).

, = 1,755). Particularly when liquid crystal lenses are applied to eyeglasses, for example, in presbyopic glasses, it is necessary to correct visual acuity with a concave lens when viewing far objects, and to correct visual acuity with a convex lens when viewing near objects. However, with conventional liquid crystal lenses, it is not possible to use both a concave lens and a convex lens in a single lens, and it is extremely inconvenient to have to carry two glasses, one for distance vision and one for near vision. . Commonly used eyeglass lenses such as glass include bifocal lenses that have refractive indices for distance and near vision, and multifocal lenses whose focal length is continuously changed by polishing the lens surface to an aspherical surface. There is a lens (Omni 7 Ocal Lens). However, bifocal lenses have the problem that the boundary between the distance and near vision areas is noticeable and image jump is unavoidable, and the omni7 ocal lens has the problem of high cost due to the hassle of polishing the aspherical surface. was there.

Means for Solving Problem C] Applying an electric field or magnetic field from the outside to a liquid crystal cell having a lens shape in which liquid crystal molecules are aligned in an appropriate direction to control the alignment state of the liquid crystal molecules, and refraction of the liquid crystal. In a liquid crystal lens whose refractive index is changed stepwise or continuously, the change in the refractive index of the liquid crystal is in the range of 1°5 to 1.9, and the amount of change in the refractive index is at least 0.1. and the refractive index of the substrate constituting the liquid crystal cell is 1.55 to 1.85, and the refractive index of the substrate is larger than the refractive index of the liquid crystal for ordinary rays and lower than the refractive index of the liquid crystal for extraordinary rays. By changing the electric field or magnetic field, the focal length can be changed so that the liquid crystal lens becomes either a concave lens or a convex lens. One of the substrates constituting the liquid crystal cell may have a Fresnel lens structure, and furthermore, TN liquid crystal may be used.

[Effect]

In the present invention, the substrate constituting the liquid crystal cell is made of a material whose refractive index is larger than the refractive index for ordinary rays of the liquid crystal and smaller than the refractive index for extraordinary rays, so that the applied voltage or magnetic field can be changed. By doing so, the focal length is changed so that the liquid crystal lens becomes either a concave lens or a convex lens. In particular, at least one of the substrates constituting the liquid crystal cell may have a Fresnel lens structure, and furthermore, TN liquid crystal may be used. In these cases, the thickness of the liquid crystal layer can be effectively reduced, and a liquid crystal lens with improved characteristics can be provided.

〔Example〕

An embodiment of the present invention will be described based on the drawings. FIG. 1 shows the M! of this embodiment. The liquid crystal cell body 1 consists of a liquid crystal 2, a substrate (hereinafter referred to as a substrate) 3 with transparent electrodes facing each other across the liquid crystal, and the substrates 3, 3.
An insulating spacer 4 is provided between the substrates to electrically insulate the substrates and to prevent the liquid crystal from leaking to the outside. An applying means 5 for applying an electric field to the liquid crystal 2 is connected to the transparent electrode. In this embodiment, one of the substrates 3 forms a concave lens, and the liquid crystal 2 sealed in the liquid crystal cell 1 itself has the shape of a convex lens.

Next, based on FIG. 2, the focal length of the liquid crystal cell 1 will be calculated. Here, the refractive index of the concave lens of the substrate 3 is assumed to be n, and its radius of curvature is assumed to be R1.

Further, the refractive index of the convex lens formed of the liquid crystal 2 is a function of the applied voltage, so it is assumed to be n(v), and its radius of curvature is assumed to be R2.

Incidentally, the focal length of a plano-convex lens or a plano-concave lens is expressed by the following equation using a refractive index and a radius of curvature.

However, it is positive for a convex lens and negative for a concave lens.

Therefore, the combined focal length of the concave lens (focal length f) of the substrate 3 and the convex lens X' (focal length rz) formed by the liquid crystal 2 is calculated as follows.

The composite focal length "is expressed as , and from Figure @2, R = R, = R2. Substrate 3
Although the lens is a concave lens, fl is negative, so (
Substituting equation 1) into equation (2), the α distance f before synthesis becomes, that is, n(v) is the refractive index ■ corresponding to extraordinary rays and the refractive index n corresponding to ordinary rays depending on the applied voltage. (no≦n(v)≦nJ) The relationship between the refractive index of the liquid crystal 2 and the composite focal length is as shown in Figure 3.In other words, the refractive index of the liquid crystal 2 is n. From various voltages, the voltage that becomes equal to n, the refractive index of the group @3 (■ →
), the focal length becomes negative. Further, when the voltage is changed from a voltage that makes the refractive index of the liquid crystal 2 11 to a voltage that makes it +16 (■→■), the focal length becomes positive. Therefore, between the voltage applied to the liquid crystal cell 1 and ■,
This liquid crystal lens becomes a concave lens, and the applied voltage changes from ■ to ■.
Between them, it becomes a convex lens. Therefore, the refractive index n of the substrate 3.

If is set between the refractive index f16 corresponding to extraordinary rays and the refractive index corresponding to ordinary rays (that is, the substrate 3 is made of a corresponding material), this liquid crystal lens can be changed into a convex lens or a concave lens. I can do it. Note that if a voltage is applied such that the refractive index of the liquid crystal 2 becomes 01, the focal length of the liquid crystal lens becomes infinite and becomes a non-prescription lens.

Next, FIG. 4 shows the reciprocal of the composite focal length f.

A phenomenon similar to that in Figure 153 is understood.

Therefore, like a conventional liquid crystal lens, the refractive index of the substrate constituting the liquid crystal cell (for example, n-1, 49) is larger than the refractive index of the liquid crystal for ordinary rays (for example, n, = 1.535), and the extraordinary rays (for example, n6 = 1.719), the focal length of this liquid crystal lens cannot be changed so that it becomes either a concave lens or a convex lens; The only thing that can be done is to change the focal length.

The liquid crystal suitable for use in liquid crystal lenses has a change in refractive index within the range of 1.5 to 1.9, and if the change in refractive index is 0.1 or more, the focal length is sufficient for practical use. can be adjusted.

If this example is applied to eyeglass lenses and the condition that the refractive index of the substrate constituting the liquid crystal cell is greater than the refractive index for ordinary rays of the liquid crystal and smaller than that for extraordinary rays is satisfied, bifocal glasses can be realized. can.

Further, in order to determine the focal length of the substrate 3, at least one of the substrates 3 may have a curved inner surface relative to the liquid crystal 2, and may also have a Fresnel lens structure. At least one of the substrates 3 may have a biconvex lens shape or a biconcave lens shape.

Further, if a liquid crystal cell made of TN liquid crystal is used, the alignment of liquid crystal molecules becomes good, so a liquid crystal lens with good characteristics can be provided. The orientation direction of liquid crystal molecules is concentric, radial,
In order to achieve variable focus with a single lens, for example, in the case of concentric alignment, it is necessary to combine it with a polarizing plate having concentric polarization characteristics, and similarly, in the case of radial alignment, it is necessary to combine it with a polarizing plate having concentric polarization characteristics. Therefore, it is necessary to combine it with a polarizing plate that has radial polarization characteristics.

Note that the present invention is not limited to spectacle lenses (it goes without saying that it can also be applied to general optical equipment).

〔effect〕

In the present invention configured as described above, the substrate constituting the liquid crystal cell is formed of a material whose refractive index is larger than the refractive index of the liquid crystal for ordinary rays and smaller than the refractive index of the liquid crystal for extraordinary rays. By changing the applied voltage or magnetic field, the focal length of the liquid crystal lens can be changed so that it becomes either a gate lens or a convex lens. Therefore, the present invention has outstanding effects in that one lens can be used as a gate lens and a convex lens, the focal length can be changed, and the cost is low because polishing and the like are easy.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of this embodiment, and FIG.
4 are diagrams showing the composite focal length of the present liquid crystal lens. 1...Liquid crystal cell body 2...Liquid crystal 3...Substrate 4
...Insulating spacer 5...Applying means patent applicant
JES Co., Ltd. 7. -,. Agent Patent attorney Yu Izumi → ・1 other person 9 , /- Loss 1n Hikigu mo groan) Nee,, Late worker = Knee 18 Trap - Aim 5 J6. f, Suku=Nishijigo〉O Human jaw L+Ba

Claims (5)

[Claims] (1) Applying an external electric or magnetic field to a liquid crystal cell having a lens shape in which liquid crystal molecules are aligned in an appropriate direction to control the alignment state of the liquid crystal molecules, and changing the refractive index of the liquid crystal stepwise or continuously. In a liquid crystal lens that changes to
The change in the refractive index of the liquid crystal is in the range of 1.5 to 1.9, and the amount of change in the refractive index is at least 0.1,
The refractive index of the substrate constituting the liquid crystal cell is 1.55 to 1.55.
85, and the refractive index of the substrate is larger than the refractive index of the liquid crystal for ordinary rays and smaller than the refractive index of the liquid crystal for extraordinary rays, and by changing the electric or magnetic field, . A variable focal length liquid crystal lens, wherein the focal length is changed so that the liquid crystal lens becomes either a concave lens or a convex lens. (2) The variable focal length liquid crystal lens according to claim 1, wherein at least one of the substrates constituting the liquid crystal cell has an inner surface curved relative to the liquid crystal. (3) The variable focal length liquid crystal lens according to claim 1, wherein at least one of the substrates constituting the liquid crystal cell has a Fresnel lens structure. (4) The variable focal length liquid crystal lens according to claim 1, wherein at least one of the substrates constituting the liquid crystal cell has a biconvex lens shape or a biconcave lens shape. (5) Claim 1 in which the liquid crystal cell is made of TN liquid crystal
The variable focal length liquid crystal lens according to any one of items 1 to 4.