JP2862903B2 - Variable power mirror lens - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable-refractive-power mirror lens that utilizes the fact that an optical material exhibiting birefringence changes its refractive power by applying a voltage or the like.

[Conventional technology]

A typical example of a lens that can change the refractive power of a single lens by adjusting the voltage applied from the outside is a so-called liquid crystal lens using a liquid crystal material. It has already been proposed in JP-A-52-32348, JP-A-54-99654, and JP-A-59-224820.

For example, a variable refractive index liquid crystal lens described in Japanese Patent Application Laid-Open No. 59-224820 uses a polarizing plate whose transmission axis is aligned with the direction of the liquid crystal director when the liquid crystal is initially aligned. As a result, when no voltage is applied, the liquid crystal lens exhibits refracting power to extraordinary light, and when sufficient voltage is applied, the liquid crystal molecules sealed between the electrodes rotate so as to be parallel to the lines of electric force. However, the refracting power changes without changing the lens shape, and indicates the refracting power for ordinary light. At an intermediate applied voltage, the refractive power can be changed continuously according to the value of the applied voltage.

Further, Japanese Patent Application Laid-Open No. Sho 62-170933 proposes a variable refractive power mirror lens using the above variable refractive power lens in a reflection type instead of a transmission type. The variable-power mirror lens shown in FIG. 4 is roughly divided into a polarizing plate 2 for converting incident light into linearly-polarized light having a specific polarization direction, and a polarizing plate for refracting the polarized light by a desired refractive power. It comprises a lens unit 1 of each side having a refractive power provided behind the polarizing plate, and a reflecting mirror 3 provided behind this lens unit 1 in a direction for reflecting the transmitted light of the lens again into the lens.
More specifically, the lens portion 1 is formed by bonding a transparent substrate 4 having a concave portion and a flat transparent substrate 5 via a spacer 6 and enclosing a liquid crystal 7 in a lens-shaped space formed by this. . Further, the transparent substrates 4 and 5
The transparent conductive layers 8 and 9 and the alignment layers 10 and 11 are formed on the surfaces facing each other. The transparent conductive layers 8 and 9 have a voltage adjusting circuit 12 for applying a voltage between the conductive layers and an alternating voltage source 13.
And the switch 14 are connected in series.

The light incident on the variable power mirror lens having such a configuration is given a predetermined refractive power by the variable power mirror lens and is refracted. When the voltage applied between the transparent conductive layers 8 and 9 is changed by the voltage adjusting circuit 12, the liquid crystal molecules of the liquid crystal 7 sealed in the lens portion rotate according to the voltage change, and the director of the liquid crystal molecules changes. As a result, the refractive power of the liquid crystal lens changes and the viewing angle can be changed.

[Problems to be solved by the invention]

Such a refractive power variable mirror lens is not limited to a liquid crystal lens, and generally uses a combination of polarizing plates to utilize the birefringence, and converts incident light into light linearly polarized in a specific direction.
A variable refractive power effect is produced for the polarized light.

If a polarizing plate is not used, for example, in the case of a convex lens, light that has received refracting power as ordinary light and light that has received refracting power as extraordinary light will form two focal points, and a double image will be generated. Therefore, it is indispensable to use polarized light for many of such variable power lenses.

However, since such a conventional lens uses light polarized to either ordinary light or extraordinary light by a polarizing plate, the transmittance of the light through the polarizing plate is at most 50%, and the available light amount Has the disadvantage of being less than half.

In addition, when such a variable power mirror lens is used in combination with another optical component such as a polarizing beam splitter instead of a single unit, the other optical component and the polarizing plate of the variable power mirror lens are just in crossed Nicols. There is also a common drawback with optical systems that handle polarized light that the relationship between the polarizer and the analyzer may be formed, and the distortion of the lens of the optical system may appear colored.

In view of the above, the present invention has been made in view of the above-mentioned problems, and it is possible to increase the available light quantity to improve the light reflectance, and to achieve double light even when non-polarized light is incident. It is an object of the present invention to provide a variable refractive power mirror lens that does not generate an image.

[Means for solving the problem]

In order to solve the above-mentioned problems and achieve the object, the present invention is made of a lens made of an optical material exhibiting birefringence and having a refractive power that changes according to an external signal, and a lens transmitted through the lens again. A variable-refractive-power mirror lens having a mirror for guiding the light into the inside, wherein both ordinary light and extraordinary light are guided into the optical material exhibiting the birefringence of the lens, and a quarter wavelength is provided between the lens and the mirror By arranging the plates, a variable-refractive-power mirror lens having the same refractive power for light beams having orthogonal polarization directions is configured.

[Action]

The operation based on such means will be described. As for the way of light incident on an optical system combining a quarter-wave plate and a mirror, first, when linearly polarized light is incident on the quarter-wave plate, the emitted light becomes circularly polarized light, and this circularly polarized light is reflected by the mirror. When you do so, the rotation will be in the opposite direction. When this circularly polarized light is incident again on the previous quarter-wave plate, it returns to linearly polarized light, but the polarization direction is shifted from the first linearly polarized light by 90 °.
This principle is applied to the variable refractive power mirror lens of the present invention.

First, in order to explain that the variable-power mirror lens according to the present invention does not produce a double image even when light which is not linearly polarized by the polarizing plate, that is, non-polarized light is incident, linearly polarized light which is polarized in a certain direction first. However, a description will be given with reference to FIG. In this figure, the refraction that occurs at the Sakai interface between the quarter-wave plate and the birefringent material is omitted for simplicity. Now, in FIG. 3, it is assumed that the optical axis of a lens made of an optical material exhibiting birefringence is in the vertical direction on the paper, and that the polarization direction of the incident light indicated by a broken line is parallel to the paper. Is expressed as A. First, the incident linearly polarized light A has a refractive power De for extraordinary light.
In response, the light path bends. Next, the emitted light enters the quarter-wave plate, is reflected by the mirror, and is again quarter-wave.
When the light returns through the wave plate, the polarization direction is shifted by 90 °, so that it receives the refracting power Do for ordinary light.
When the above is expressed by an equation, assuming that the final refractive power for the incident light A is D _A , when the mirror lens can be regarded as a thin lens, D _A = De + Do (1). In a variable-refractive-power mirror lens made of an optical material having birefringence, liquid crystal molecules rotate according to an external signal (V) such as a voltage, and the refractive power De with respect to extraordinary light changes. That, De is a function and V, since it is De = De (V) (2 ), the final power D _A is expressed as _{D A = De (V) +} Do (3).

On the other hand, it is assumed that the polarization direction of the incident light indicated by the solid line in FIG. 3 is a direction perpendicular to the paper surface, and this is represented by B. After that, it will receive De refractive power. If this is expressed by an equation in the same way as A, the final refractive power D _B is D _B = Do + De (V) (4), and from equations (3) and (4), D _A = D _B (5) It turns out that it becomes. In the above description, the refractive power De for extraordinary light that changes with voltage is the apparent refractive power of the lens viewed from the incident light direction.

The above equation (5) shows that the variable refractive power mirror lens of the present invention acts on light having any two orthogonal polarization directions with the same refractive power, and from this, it can be seen that light having any polarization direction can be obtained. That is, it can be understood that even if non-polarized light enters, it functions as a variable refractive power mirror lens without generating a double image.

〔Example〕

Hereinafter, embodiments of the present invention will be described. FIG. 1 is a sectional view for explaining a first embodiment of a variable power mirror lens according to the present invention. The same members as those of the conventional variable refractive power mirror lens shown in FIG. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The variable power mirror lens of this embodiment shown in FIG. 1 is roughly divided into three parts. The first is a variable-power lens unit 1 that refracts incident light, which is natural light, with a desired refractive power. The second is a quarter-wave plate 15 which is provided behind the variable-power lens unit 1 and which transmits light transmitted from the variable-power lens unit 1 in a direction that vibrates in directions perpendicular to each other. It functions to provide a quarter-wavelength optical path difference. Third is the reflection mirror 3
And is provided behind the quarter-wave plate 15,
It functions to reflect the transmitted light of the quarter-wave plate 15 back into the quarter-wave plate.

Further, the variable-refractive-power lens unit 1 has an optical glass substrate 4 having a concave portion and a flat optical glass substrate 5 bonded together with an insulating spacer 6 therebetween. In this case, a nematic liquid crystal 7 is sealed as an optical material showing the following. Further, transparent conductive layers 8 and 9 made of ITO (Indium Tin Oxide) are formed on the surfaces of the optical glass substrates 4 and 5 facing each other. Further, a liquid crystal alignment layer 1 made of polyvinyl alcohol is provided on the surfaces of the transparent conductive layers 8 and 9.
The liquid crystal 7 is sealed between the alignment layers 10 and 11, respectively. In addition, the above transparent conductive layer
A voltage adjustment circuit 12, an alternating voltage source 13, and a switch 14 are connected in series to 8, 9, respectively.

The manner in which the light incident on this embodiment configured as described above proceeds as described above is omitted here. However, according to the variable refractive power mirror lens shown in this embodiment, not a polarizing plate but a quarter By using a one-wavelength plate, a variable-refractive-power mirror lens having a high reflectance can be obtained. Therefore, it can be combined with a half mirror which has been practically impossible due to a decrease in the amount of light, and the application range of the variable refractive power mirror lens can be expanded.

For comparison, a conventional variable refractive power mirror lens shown in FIG. 4 was manufactured, and the amount of reflected light was measured with the variable refractive power mirror lens in this embodiment. In the lens of this embodiment, the reflected light is 80% of the incident light, while only 30% reflects the light.
% Light intensity.

Further, since the polarizing plate is not used, there is no problem peculiar to the polarizing optical system, such as the above-mentioned lens distortion.
Furthermore, the rotation of the oscillating surface of the light by the quarter wave plate,
Normal light and extraordinary light compensate each other. Astigmatism on the optical axis can be removed.

Next, another embodiment of the present invention will be described. FIG. 2 shows a second embodiment of the present invention. This embodiment is different from the above-described embodiment in that the surface of the transparent substrate 4 of the variable-power lens unit 1 facing the transparent substrate 5 has a sawtooth shape as shown in FIG. However, the point is that a Fresnel lens is configured.

The second embodiment also has the same operation and effect as the first embodiment. Further, in this embodiment, since the refractive power variable mirror lens unit 1 itself can be made thinner, the effect that the fluctuation of the principal point position due to the variable refractive power can be made very small can be obtained.

As described above, the refractive power variable mirror lens according to the present invention described in the embodiments can be used as, for example, a fender mirror of an automobile to be a fender mirror that can easily change a field of view from a driver's seat, and reduce a blind spot. can do. Further, if the present invention is applied to a reflecting mirror of an exposure optical system used in a copying machine or the like, it is possible to easily produce an optical system in which the movement of a lens is reduced as compared with the related art when changing the copy magnification. Further, if this mirror lens is used for a viewfinder of a camera, a viewfinder optical system having a variable magnification can be configured.

In the first and second embodiments, a nematic liquid crystal is used as an optical material exhibiting birefringence. However, the present invention is not limited to this. For example, lithium niobate or lithium tantalate may be used. A material whose crystal exhibits an electro-optic effect can also be used as an optical material exhibiting birefringence.

〔The invention's effect〕

As described above, the present invention includes a lens made of an optical material exhibiting birefringence and having a refractive power that changes according to an external signal, and a mirror for guiding light transmitted through the lens back into the lens. In the mirror lens, both ordinary light and extraordinary light are guided into the optical material exhibiting the birefringence of the lens, and a quarter-wave plate is disposed between the lens and the mirror, so that orthogonal polarization directions are provided. By making the refractive power equal to the light having the following, it is possible to provide a variable refractive power mirror lens that has a high light reflectance and does not generate a double image.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of a variable power mirror lens of the present invention, FIG. 2 is a cross-sectional view showing a Fresnel lens type variable power mirror lens according to a second embodiment of the present invention, FIG. 3 is a schematic view showing an optical path when arbitrary linearly polarized light is incident on the variable power mirror lens of the present invention, and FIG. 4 is a sectional view of a conventional variable power mirror lens. DESCRIPTION OF SYMBOLS 1 ... Variable refractive power lens part 2 ... Polarizing plate 3 ... Reflecting mirror 4, 5 ... Transparent substrate 6 ... Spacer 7 ... Birefringent material (liquid crystal) 8, 9 ... Transparent conductive layer 10, 11 ... ... Orientation layer 12 ... Voltage adjustment circuit 13 ... AC voltage source 14 ... Switch 15 ... Quarter wavelength plate

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-170933 (JP, A) JP-A-54-68262 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02F 1/13 G02F 1/01

Claims (5)

(57) [Claims] 1. A variable-refractive-power mirror lens comprising a lens made of an optical material exhibiting birefringence and having a refractive power that changes according to an external signal, and a mirror for guiding light transmitted through the lens back into the lens. Wherein both ordinary light and extraordinary light are guided into the optical material exhibiting the birefringence of the lens, and a quarter-wave plate is disposed between the lens and the mirror, so that the lenses have orthogonal polarization directions. A variable-refractive-power mirror lens having equal refractive power to light. 2. A variable refractive power mirror lens according to claim 1, wherein said lens is a liquid crystal lens. 3. The variable refractive power mirror lens according to claim 1, wherein said lens has a Fresnel shape. 4. The variable refractive power mirror lens according to claim 2, wherein said lens has a structure in which a nematic liquid crystal is sealed between two substrates and a transparent electrode layer is formed on a surface of said substrate. A variable-refractive-power mirror lens comprising a voltage adjusting circuit, an alternating voltage source, and a switch connected in series to an electrode layer. 5. The variable refractive power mirror lens according to claim 4, wherein the space for enclosing the nematic liquid crystal has a plano-convex shape.