JPS61156221A - Optical element - Google Patents

Abstract

PURPOSE:To dissolve deviation of image forming points relying on the polarizing direction, by variably controlling the length of an optical path by combining two optical elements whose molecule oriented directions become opposite to each other on a plane vertical to the optical axis and changing an applied voltage. CONSTITUTION:Liquid crystal lenses 12a and 12b are formed by enclosing liquid crystal 16 in the hollow cells between one surfaces of adjacent transparent plates 13 and a concave lens 15 and an AC voltage is applied across a pair of transparent electrodes 17 and 18. When the orienting directions of liquid crystal molecules 21a and 21b are made opposite the each other about a plane intersecting the optical axis at right angles and the sizes of the orienting directions are made equal to each other by applying the same voltage across the liquid crystal lenses 12. The molecules 21a and 21b are oriented in a rightward-descending and rightward-descending conditions, respectively. There fore, deviation of image forming positions can be dissolved and, at the same time, the focal distance can be changed by changing the applied voltage, since the advancing course of the abnormal light Le of rays made incident along the optical axis is deviated upwar and then returned to the original condition.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical element that can improve the shift of an image point depending on the polarization direction of incident light.

[Technical background of the invention and its problems]

Liquid crystals can control the orientation of the liquid crystal molecules by controlling the voltage applied to them, and therefore require mechanical lens movement by utilizing changes in the refractive index that accompany changes in the orientation. It is possible to realize a variable focal length lens without any need.

For example, FIG. 6 shows a conventional example. In the figure, a liquid crystal lens 5 is formed by sealing a liquid crystal 4 in a cell formed by interposing a spacer 3 between plano-concave lenses 2a and 2b formed on the inside where transparent electrodes ia and lb face each other. There is.

Both electrodes 1a sandwiching the liquid crystal 4 in this liquid crystal lens 5,
An AC voltage from an AC power source 6 can be applied to 1b, and by changing the applied AC voltage, the orientation of the molecules of the liquid crystal 4 is controlled to realize a variable focal length lens.

However, since the refractive index of the liquid crystal 4 differs depending on the orientation direction of its molecules, when natural light is incident, there is a polarized light wave within the plane of the paper at the latitudinal point and latitude, as shown by the thin line. When the polarized waves are perpendicular to the plane of the paper, the dotted line and thin line become extraordinary light and ordinary light, respectively, and the optical path differs depending on the polarization direction of the incident light as shown in the figure.・In other words, birefringence occurs, and the imaging effect as a lens depends on the polarization direction.
The imaging point on the screen 7 etc. will shift. For this reason,
This has been a major obstacle when applied to optical instruments that require high resolution.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide an optical element that eliminates or reduces the shift of the imaging point depending on the polarization direction.

[Summary of the invention]

The present invention provides for an optical element exhibiting birefringence to be corrected,
The influence of deviation of the imaging point due to birefringence is eliminated or reduced by combining the orientation directions of molecules or dipoles so that they are opposite to each other with respect to a plane perpendicular to the optical axis.

[Embodiments of the invention]

Hereinafter, the uninvented portion will be specifically explained with reference to the drawings.

1 and 2 relate to a first embodiment of the present invention; FIG. 1 shows the first embodiment, and FIG. 2 shows a partially enlarged state of molecular orientation.

The liquid crystal optical lens 11 of the first embodiment has a structure in which liquid crystal lenses 17a and 12b having the same characteristics are stacked.

That is, spacers 14a and 14b are interposed on each of the other surfaces of both transparent plates 13a and 13b, one side of which is adjacent to the other, and formed between each transparent plate 13a and 13b and concave lenses 15a and 15b facing each other. Liquid crystal lenses 16a and 16b are respectively sealed in hollow cells to form a liquid crystal lens 1.
2a.

12b. However, the transparent plates 13a, 13
b and the liquid crystal 16a in the concave lenses 15a and 15b.
, 16b are respectively enclosed on the opposite inner surfaces, transparent electrodes 17a, 17b and 18a,
18b is formed. These pair of transparent electrodes 17
a, 18a; 17b.

The alternating current voltage of an alternating current power source 20 can be applied in a variable manner through a variable resistor 19 between 18b and 18b.

In this case, the same AC voltage (value) is applied to both liquid crystal lenses 12a and 12b, and
The orientation directions of the liquid crystal molecules 12a and 12b are such that they are opposite to each other with respect to a plane orthogonal to the optical axis and have the same size. For example, electrodes 17a, 18b and 1
7b and 18a are electrically connected so that the same alternating current voltage is applied to them.

Therefore, each liquid crystal lens 12a, 12b has liquid crystal molecules 21a in FIG. 2 when AC voltage is applied.
is oriented upward to the right in the plane of the paper, the liquid crystal molecules 21b
is set to be oriented downward to the right. In this way, the deviation of the optical path for the extraordinary light is compensated for.

That is, when no AC voltage is applied, the transparent plate 13a
, 13b (or the transparent electrodes 178, 17b) (or the transparent electrodes 178, 17b) (for example, oriented in the vertical direction in FIG.
As a result, liquid crystal molecules 218 and 21b are aligned in a tilted alignment state as shown in FIG. 2. The tilt angles in this case are made equal by using equivalent liquid crystals.

Therefore, in FIG. 2, for a ray of light incident parallel to the optical axis, for example along the optical axis, a ray of light polarized in a direction perpendicular to the plane of the paper, that is, the ordinary light L0, will take the path shown by the thin line. Even if the path of the light beam polarized in the vertical direction of the paper, that is, the extraordinary light Le, deviates upward when passing through the liquid crystal 16a, as shown by the broken line, it will return in the opposite direction when passing through the next liquid crystal 16b, so that it is a single path. It is possible to eliminate or reduce the deviation of the imaging position when only the liquid crystal lens 12a or 12b is used.

The first embodiment, in which the lenses are combined so as to compensate each other for optical anisotropy, can eliminate the above-mentioned deviation of the imaging point and can realize a lens whose focal length can be varied by the applied voltage (value).

FIG. 3 shows a second embodiment of the invention.

In this second embodiment, four liquid crystal lenses 12a are used to prevent differences in focal length depending on the polarization direction.
, 12b, 22a, and 22b.

That is, the liquid crystal lenses 12a and 12b of the first embodiment described above
In addition, a pair of liquid crystal lenses 22a and 22b are provided.

These liquid crystal lenses 22a and 22b are obtained by rotating the liquid crystal lenses 12a and 12b by 90 degrees around the optical axis. Also, the same AC voltage is applied to the pair of liquid crystal lenses 12a, 12b and the pair of liquid crystal lenses 22a, 22b by AC power supplies 30, 30', respectively.

Corresponding to the alignment direction of the liquid crystal molecules 218, 21b in the liquid crystal isa, 16b being upwardly rightward and downwardly rightward as shown in FIG. 3 by the AC power supply 30,
Liquid crystal molecules 31a, 31 in liquid crystals 26a, 26b
The orientation direction of b also has a similar correspondence.

In other words, the liquid crystal molecules 21a and 21b are tilted in the plane of the paper, while the liquid crystal molecules 31a and 31b are tilted at the same angle of inclination in the direction perpendicular to the plane of the paper. In FIG. 3, when the liquid crystal molecules 31a are oriented such that the transparent electrode 27a side protrudes upward perpendicular to the paper surface, the liquid crystal molecules 31b
The transparent electrode 28b side facing the transparent electrode 27b is tilted downward perpendicular to the paper surface.

According to this second embodiment, it is possible to eliminate or reduce the deviation of the imaging position even for light having an arbitrary polarization direction.

In other words, the relationship between ordinary light and extraordinary light when passing through the pair of liquid crystal lenses 12a and 12b is reversed compared to when passing through the pair of liquid crystal lenses 22a and 22b, so one pair of liquid crystal lenses 12a and 12b (or 22a,
22b) and the other pair of liquid crystal lenses '12a,
22b (or 12a.

12b) and compensate each other, making it possible to compensate for birefringence.

In the second embodiment, the liquid crystal cell is formed into a lens shape, but as shown in a modification of the second embodiment shown in FIG. can also be formed.

The above modification example is, for example, the concave lens 15a in FIG.
, 15b, 25a, 25b as transparent plate 15a',
15b', 25a', 25b'. Note that reference numerals 12a', 12b', 22a', and 22b' indicate liquid crystal optical elements whose optical path lengths can be varied. The rest of the structure is similar to that of the second embodiment, and the same elements are given the same reference numerals.

FIG. 5 shows a modification of the first embodiment. In this modification, the convex lens-shaped cell in the first embodiment is replaced with a parallel plate-shaped cell, and a liquid crystal is sealed in this cell. In other words, the concave lenses 15a and 15b in Fig. 1 of the whistle are replaced by the transparent plate 1.
Transparent plates 13 facing each other with 5a' and 15b'
Liquid crystals 16a and 16b are sealed between the electrodes a and 13b, respectively. The rest is the same as the first embodiment.

This modification allows the optical path length to be varied, and in particular forms a phase variable element. In other words, depending on the alignment direction of the liquid crystal molecules 21a and 21b, for incident light polarized vertically parallel to the page (corresponding to extraordinary light) and incident light polarized perpendicular to the page (corresponding to ordinary light). The difference in refractive index is different. In other words, the difference in refractive index can be variably controlled by the applied voltage, so that a quarter-wave plate, a half-wave plate, etc., which are widely used in optical equipment, can be easily realized by changing the value of the applied voltage.

Incidentally, the first embodiment can also be said to be an optical lens having both the functions of a phase variable element and a variable focal length lens.

Note that the present invention is not limited to the above-described embodiments, and the cell in which the liquid crystal is sealed may have a different shape.

For example, one surface or the other surface of the cell may be a Fresnel lens surface, or may have sawtooth irregularities to improve responsiveness.

In short, for an optical element such as a lens that has birefringence on one side, optical elements that exhibit similar characteristics are combined to form one or more pairs, and when combined, the orientation direction of molecules or dipoles is They are set in opposite directions with respect to a plane perpendicular to the optical axis and in a relationship in which the magnitudes of their components are equal or in a relationship close to this, or the crystal axes are set in opposite directions.

(If the pairs are made of different birefringent materials, this relationship is not necessarily limited to this.) In addition, in the case of two or more pairs, one pair rotated 90 degrees around the optical axis will have the same relationship as the rest. It is sufficient to set the same relationship as the other pair. Note that one of the pairs may be formed of two or more.

Further, although each of the above-mentioned embodiments uses liquid crystal, the present invention is not limited thereto, and can be similarly applied to materials exhibiting birefringence, such as ceramics.

Note that when the birefringence of a liquid crystal or other birefringent substance can be changed, it is not limited to control by voltage, and may be controlled by the frequency of an applied voltage or by a magnetic field.

Further, the present invention is not limited to those whose birefringence can be variably controlled by applied voltage, etc., but even if the optical element to be corrected cannot be varied and is corrected by an optical element for correction such as a liquid crystal optical element. good. An example of this is a combination of an optical element exhibiting normal birefringence and an optical element formed of liquid crystal. .

〔Effect of the invention〕

As described above, according to the present invention, since the optical elements exhibiting birefringence are combined in such a way that the orientation direction of the molecules or dipoles is so as to eliminate the optical anisotropy with respect to extraordinary light, the imaging point This can eliminate or reduce misalignment.

[Brief Description of the Drawings] Figures 1 and 2 relate to the first embodiment of the present invention, Figure 1 is a configuration diagram showing the first embodiment, and Figure 2 is an enlarged view of the liquid crystal lens in Figure 1. 3 is a block diagram showing the second embodiment of the present invention, FIG. 4 is a block diagram showing a modification of the second embodiment of the present invention, and FIG. 5 is a block diagram showing the first embodiment of the present invention. FIG. 6 is a block diagram showing a modification of the embodiment, and FIG. 6 is a block diagram showing a conventional example. 11...Liquid crystal lens element, 12a, 12b...
・Liquid crystal lens, 13a, 13b ---Transparent plate, 1
5a, 15h...concave lens, 16a, 16b ---
・Liquid crystal, 178.17b -・Transparent electrode, 20・
...AC power supply, 21 a, 21 b...
Liquid crystal molecules, 15a', 15b'--Transparent plate, 3
1a, 31b...liquid crystal molecules. Agent Patent Attorney Susumu Ito 1') 3rd
Figure 12a 12b 22a 22br-1~-mr
-Me1117b /7″・〃 210 31b21b
31a8b 6a, //ZZZ26b 16b 15t) 25b2
50 ~ Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] In an optical element using ceramic or liquid crystal exhibiting birefringence, two or more optical elements in which the orientation directions of molecules or dipoles are opposite to each other with respect to a plane perpendicular to the optical axis are combined, and the value of the applied voltage or An optical element characterized in that an optical path length or focal length is variably controlled by changing the frequency of an applied voltage.