JPS62238520A - Optical modulator - Google Patents

Abstract

PURPOSE:To execute good optical modulation even with incident light having an optional polarizing component and to prevent an increase of a cell gap by constituting a diffraction grating of an optical member having rugged shapes of a checkered pattern in the plane. CONSTITUTION:This optical modulator is provided with two sheets of substrates 7, 7, the diffraction grating 2 disposed to one of the substrate 7 surfaces, which face each other, between the substrates 7, a refractive index variable material 1 packed between the diffraction grating 2 and the substrates 7, and means for controlling the refractive index variable material 1. The diffraction grating 2 is constituted of the optical member formed with the plural rugged shapes having the checkered pattern in the plane, by which diffraction is generated regardless of the polarizing direction of the incident light. The good optical modulation is thereby executed even with the incident light having an optional polarizing component at the time of making the optical modulation such as passage and shielding of light by utilizing the refractive index variable material such as liquid crystal 1 and the diffraction grating 2. In addition, an electric field can be efficiently impressed to the liquid crystal 1 without expanding the cell gap and the simple optical modulator which does not decrease the effective height of the diffraction grating 2 is obtd.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a light modulation device, and in particular to a light modulation device that modulates light such as passing light or blocking light by using a diffraction grating and a variable refractive index material such as a liquid crystal. The present invention relates to a light modulation device suitable for display, optical recording, optical coupling, optical communication, optical calculation, and other devices.

(Conventional technique j4r) A conventionally well-known light modulation element consists of a pair of polarizing plates arranged so that the polarization directions are perpendicular to each other, and a pair of transparent substrates arranged between the pair of polarizing plates. The device consists of a device in which a liquid crystal is sealed with the substrate surfaces perpendicular to each other subjected to alignment treatment, and the alignment state of this liquid crystal is switched between a twisted state and a state perpendicular to the substrate surface, thereby modulating the incident light. There is a so-called TN (twisted nematic) type liquid crystal display element that does this. This type of display element has a simple structure and is easy to drive, so it is used in a wide variety of applications.It also uses two polarizing plates to transmit and block the light beam, so it can be used at the time of extinction, that is, when the speed of light is passing. The transmittance was poor, and it could not be said to be a desirable light modulation element from the viewpoint of luminous flux utilization efficiency.

In addition, as a similar type of display element using liquid crystal, there is a so-called guest-host mode liquid crystal display element that uses a dye mixed into liquid crystal molecules, but since the dye is present in this display element, the The transmittance was about 75% at best.

On the other hand, Japanese Patent Publication No. 53-1928 and USP 4,25
1.1:17, etc., a display element and a variable subtractive color filter element are disclosed in which a reflection type or transmission type phase diffraction path r and a liquid crystal are combined. Although the elements disclosed in these documents are certainly boasting luminous flux utilization efficiency,
The device disclosed in the publication merely exhibits a decorative effect, and is not satisfactory as a display device for displaying characters or images or a light modulation device for transmitting or blocking light beams. Further, the variable subtractive color filter element disclosed in IJSP4, 251, 137 fills a refractive index variable material, such as liquid crystal, between at least one of the substrates having an optically isotropic diffraction grating structure, and applies an electric field to the liquid crystal. A first device that modulates light by changing the refractive index of the liquid crystal by applying an applied voltage and utilizing the diffraction effect of a diffraction grating, and a pair of opposing devices for modulating incident light having an arbitrary polarization component. A diffraction grating is formed on the substrate surface so that the alignment directions are perpendicular to each other, and liquid crystal is filled between the substrates to change the refractive index by controlling the alignment state of the liquid crystal molecules. This is a second device that makes spectral transmittance characteristics variable by changing the refractive index difference. However, although the first device has high light utilization efficiency and high performance as a variable color reducing filter, it cannot cope with the modulation of incident light having polarization components of any one color, and a second device has been disclosed. .

On the other hand, in the second device, since the diffraction gratings are formed on the surfaces of a pair of opposing substrates so that their arrangement directions are perpendicular to each other, the distance is at least twice that of the diffraction grating of the first variable subtractive filter, i.e. There is a cell gap, which has the disadvantage that the refractive index of the refractive index variable material is lowered below the intensity of the electric field, which is a means of controlling the refractive index. Also, two diffraction gratings
Since the layers are superimposed, the alignment direction of the liquid crystal in the boundary region is disturbed, resulting in a decrease in the effective height of the diffraction grating. Again 1
Since two layers of diffraction gratings are superimposed, this device requires more than twice as many manufacturing steps as the first device, resulting in high costs.

(Problems to be Solved by the Invention) The present invention uses a refractive index variable material such as a liquid crystal and a diffraction grating to perform optical modulation such as passing light or blocking light. To provide a simple light modulation device which can perform good optical modulation even when the cell cap is enlarged, can efficiently apply an electric field to a liquid crystal without enlarging a cell cap, and does not reduce the effective height of a diffraction grating. With the goal.

(Means for Solving the Problems) A diffraction grating arranged on one of the opposing substrate surfaces between two substrates and the nη substrate, a refractive index variable material filling the space between the diffraction grating and the +Wr substrate, and In the light modulation device having a means for controlling a variable refractive index material, the diffraction grating is constituted by a plurality of uneven optical members having a checkered pattern in a plane.

Other features of the invention are described in the Examples.

(Actual Jj'ts Example) FIG. 1 is a perspective view of a diffraction grating that is a part of the optical modulation device according to the present invention. In this embodiment, a plurality of 7-concave and convex optical members are arranged regularly in the X direction and the Y direction on a transparent substrate 41, that is, in a checkered pattern, and are light transmitting. Height 2° ゛゛Figure 2 (A), (B
) is an explanatory diagram of the operating principle of an optical modulation device according to an embodiment of the present invention. The figure (8) shows nematic liquid crystal 1, which will be described later.
(B) shows the case where an electric field is applied.

In the figure, 1 is a nematic liquid crystal with positive dielectric anisotropy, 2 is a diffraction grating, and each of these elements constitutes a grating member. 6 is a transparent electrode, and 7 is a transparent substrate.

3 is incident light, 50. 5.5' is the emitted light.

In this embodiment, when no electric field is applied to the liquid crystal 1 shown in FIG. When the light modulator 8 is oriented in a random direction, the light modulator 8 receives two lights, a light 31 perpendicular to the plane of the paper and a light 32 parallel to the plane of the paper, polarized in a direction orthogonal to the director of the liquid crystal 1. When light with arbitrary polarization component is incident,
The apparent refractive index of the liquid crystal 1 for the light 31, 32 that has passed through the grooves of the diffraction grating 2 is the extraordinary refractive index n. and ordinary refractive index n
The intermediate value between () is (ne + no) / 2. Here, since the refractive index ng of the material of the diffraction grating 2 is configured to be ng = (n6 + no)/2, the light modulation device 8 receives the incident light:
]1.32, it is considered to be approximately isotropic. As a result, the incident lights 31 and 32 are not diffracted and pass through the light modulation device 8 as they are as the output lights 50. That is, when the light modulator 8 does not apply an electric field to the liquid crystal 1, the incident light 31 and 32 do not change at all and are in a non-display state. That is, it is in a normally oven state.

Next, as shown in FIG. 2(B), the liquid crystal 1;1. When an electric field is applied by the transparent voltage Vi6 which is a part of the lJ control means, the liquid crystal l is homeotropically aligned. For this reason, the light modulator 8 receives light having polarization characteristics similar to those described above: ll, 32
When these lights are incident, the refractive index of the liquid crystal 1 with respect to these lights is the ordinary refractive index n. I feel it.

On the other hand, the refractive index for light passing through the convex portion of the diffraction grating 2 is n
g, and n g # n g. Therefore, a phase difference occurs between the light that passed through the convex portion of the diffraction grating 2 and the light that passed through the liquid crystal part, and the incident lights: ]l and 32 are each diffracted. Ru.

At this time, since the diffraction grating of this embodiment is made up of uneven portions in a checkered pattern, a diffraction phenomenon occurs regardless of the polarization direction of the incident light.

In this way, in this embodiment, when an electric field is applied to the liquid crystal 1, the grating member consisting of the liquid crystal 1 and the diffraction grating 2 acts as a diffraction grating, and the incident light 31, 32 is diffracted and output, and the output light 5, 5'. That is, when the light modulator 8 applies an electric field to the liquid crystal 1, the incident light: 11, 32, which goes straight, disappears and can be brought into a light diffraction state.

FIG. 3 is an explanatory diagram of the operating principle of an optical modulation device according to another embodiment of the present invention. In this embodiment, a nematic liquid crystal having a negative dielectric anisotropy is used instead of the nematic liquid crystal having a positive dielectric anisotropy used in FIG. 2.

FIG. 4A shows the case where no electric field is applied to the liquid crystal 1, and FIG.

In this embodiment, when no electric field is applied to the liquid crystal 1 shown in FIG.
is homeotropically aligned in the concave portion of the diffraction grating 2.

Now the light 31 that strikes the optical modulator 8 with polarization characteristics similar to those described above.
．． 32, that is, light having an arbitrary polarization component is made incident.

Then, out of the incident light 31 and 32, the light that passes through the groove portion of the diffraction grating f2 has the ordinary refractive index n of the liquid crystal l. The light that has passed through the convex portion of the diffraction grating 2 senses the refractive index n8 of the diffraction grating 2.

Here, the liquid crystal l and the diffraction grating 2 are n. = n g7), no phase difference occurs between the light passing through the liquid crystal portion and the light passing through the convex portion of the diffraction grating Y-.

Therefore, the incident light beams ll and 32 are not diffracted and pass through the light modulation device 8 as they are as the output light beam 50. That is, it is in a normally open state.

Next, when an electric field is applied to the liquid crystal l shown in FIG. When the light 31 and 32 having the above-mentioned polarization characteristics are incident on this light modulation device, both of these lights have the extraordinary refractive index n of the liquid crystal 1. and the ordinary refractive index n. Therefore, the apparent refractive index of 7-night crystal 1 is the extraordinary refractive index n
e and the ordinary refractive index n. is the intermediate value (n(,+no)/2).

On the other hand, the light that has passed through the convex portion of the diffraction grating 2 has a refractive index n
g, the structure is configured so that ng≠(n (2+ n □ ) / 21), a phase difference occurs between the light passing through the liquid crystal part, and the incident light 31.32 is diffracted. It passes as emitted light 5.5'.

That is, it can be brought into a light diffraction state.

In each of the above embodiments, the light-transmissive concavo-convex shaped portion for providing a phase difference to the diffraction grating may be a cylindrical shape instead of a square prism shape, or an asymmetric shape such as a polygonal shape, an elliptical shape, a rectangular shape, etc. depending on the purpose. It may be composed of members.

In this embodiment, a transmissive light modulation element is shown, but it is also possible to form a reflective element by, for example, forming a light reflection pattern 1 on one substrate. However, in the case of a reflective type, the behavior of diffracted light within the element becomes complicated, so in consideration of the design and application of actual display elements, it is preferable to use a transmissive type light modulation element in the present invention. desirable. In this case, as a matter of course, the diffraction grating, the refractive index variable material, the substrate, etc. are made of members that are transparent to the wavelength used.

(Effects of the Invention) According to the present invention, when performing light modulation using a liquid crystal and a diffraction grating, by constructing the diffraction grating from an optical member having an uneven shape of a checkered pine forest in a plane, it is possible to obtain a polarized light component of 0 to 0. It is possible to perform good optical modulation even for incident light of 4T, prevent the cell cap from increasing, efficiently apply an electric field to the liquid crystal, and do not reduce the effective height of the diffraction grating. A simple light modulation device can be achieved. Also, normally open is achieved at the same time.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a portion of an optical modulation device according to the present invention, and FIGS. 2 and 3 are explanatory views of the operation of a portion of an embodiment of the present invention. In FIGS. 2 and 3, (A) shows the case where no electric field is applied to the liquid crystal 1, and (B) shows the case where an electric field is applied to the liquid crystal 1. In the figure, 2 is a diffraction grating, 3 is an incident light, 4 is an absolute MIIQ, 5.5', 50 is an output light, 6 is a transparent electrode, 7
8 is a transparent substrate, and 8 is a light modulation device.

Claims (4)

[Claims] (1) A diffraction grating disposed on one of the opposing substrate surfaces between two substrates, a refractive index variable material filling the space between the diffraction grating and the substrate, and means for controlling the refractive index variable material. 1. A light modulation device comprising: the diffraction grating comprising a plurality of concavo-convex optical members having a checkered pattern in the plane. (2) The light modulation device according to claim 1, wherein the substrate, the refractive index variable material, and the diffraction grating member are transparent. (3) The light modulation device according to claim 1, wherein the refractive index variable material is a liquid crystal. (4) The light modulation device according to claim 2, wherein the arrangement of the liquid crystals is random.