JPH11202112A - Diffractive optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffractive optical element having a scattering function with high diffraction efficiency by using a diffraction grating aggregate having a simple pattern. SOLUTION: The element element 2 is divided into a mosaic element element 2, each element element 2 is composed of a lattice unit 2 'arranged in a mosaic form, and a linear diffraction grating 6 is formed in each lattice unit 2'. The grating interval and the grating direction of the linear diffraction grating 6 differ depending on the arrangement position of the grating unit 2 ′ on the element element 2, and the illumination light 3 having a specific wavelength is incident on the element element 2 from a predetermined direction. In such a case, linear diffraction is performed so that the diffracted light 4 from the lattice unit 2 ′ enters different regions on the predetermined observation surface 5 corresponding to the arrangement position of the lattice unit 2 ′ in the element element 2. The grid spacing and grid direction of the grid 6 are set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffractive optical element, and more particularly to a diffractive optical element having a scattering function which can be used as a diffuse reflector of a reflection type liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, in a reflection type liquid crystal display device, as shown in FIG. 9, a reflection / diffusion plate 31 made of a metal plate made of matte aluminum or the like is arranged on a side opposite to an observation side of a liquid crystal display element 40. The illumination light 32 incident from the display side of the liquid crystal display element 40 is diffused and reflected forward by the reflection diffusion plate 31 disposed on the back surface thereof, without using a self-luminous backlight in a light place. It can be displayed.
Here, the liquid crystal display element 40 is composed of, for example, a liquid crystal layer 45 such as twisted nematic sandwiched between two glass substrates 41 and 42, and a uniform transparent counter electrode is formed on the inner surface of one of the glass substrates 42. A transparent display electrode 43 and a black matrix (not shown) are provided independently for each pixel on the inner surface of the other glass substrate 41. In addition,
In the case of a color display device, a transparent display electrode 43, a color filter, and a black matrix are independently provided on the inner surface of the other glass substrate 41 for each of the liquid crystal cells R, G, and B. An alignment layer (not shown) is also provided on the liquid crystal layer 45 side of the electrodes 43 and 44. Further, a polarizing plate 46 is provided on the outer surface of the observation side glass substrate 41, and a glass substrate 42 on the opposite side to the observation side. Polarizing plates 47 are attached to the outer surface, for example, and their transmission axes are arranged to be orthogonal to each other. By controlling the voltage applied between the transparent display electrode and the transparent counter electrode of such a liquid crystal display element 40 to change its transmission state, it is possible to selectively display numbers, characters, symbols, pictures, etc. It is.

[0003] Such a reflection type liquid crystal display device has an advantage that power consumption can be small because it does not require a backlight, but it is difficult to see the display because it is displayed by external light. In addition, even under illumination light, in the specular direction where the reflection intensity is the strongest, there is a problem that the contrast is significantly reduced due to surface reflection on the liquid crystal display device.

In order to solve such a problem, conventionally,
There has been a proposal to use a hologram element created by interference exposure as a diffuse reflection plate. Also, a cell type computer generated hologram has been known to obtain a predetermined diffraction characteristic.

[0005]

However, from the viewpoint of providing the optical element with a scattering function, the hologram element formed by interference exposure can realize the scattering function, but has an infinite number of interference fringes on the photosensitive material. Multiple recording is performed, and the diffraction efficiency is reduced in the current photosensitive material. Further, there is a problem that the diffraction efficiency is also reduced due to the recording of noise due to the interference between scattering object beams.

In addition, in the case of a cell type computer generated hologram, it takes a long time to calculate the hologram, so that it is generally impossible to obtain an ideal interference fringe, a lot of noise and a low diffraction efficiency. Further, there is a method for calculating an in-line hologram, but there is a problem that an offline calculation method has not been established.

The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a diffractive optical element having a high diffraction efficiency and a scattering function by using a diffraction grating assembly having a simple pattern. To provide.

[0008]

The diffractive optical element according to the present invention for achieving the above object is divided into mosaic element elements, and each element element comprises a lattice unit arranged in a mosaic pattern. A linear diffraction grating is formed in the unit, and the grating interval and the grating direction of the linear diffraction grating are different depending on the arrangement position of the grating unit on the element element. The element element has a specific wavelength from a predetermined direction. When the illumination light is incident on the linear diffraction grating, the diffracted light from the lattice unit is incident on different regions on a predetermined observation surface corresponding to the arrangement position of the lattice unit in the element element. And the grid direction is set.

Another diffractive optical element of the present invention is divided into mosaic element elements, and each element element is formed with a curved diffraction grating, and the curved diffraction grating is formed according to the position on the element element. When the grating interval and the grating direction of the diffraction grating are different, and when illuminating light of a specific wavelength is incident on the element element from a predetermined direction, from the curved diffraction grating corresponding to the position of the curved diffraction grating in the element element. The grating interval and the grating direction of the curved diffraction grating are set so that the diffracted light beams enter different regions on a predetermined observation surface.

In still another diffractive optical element according to the present invention, a curved diffraction grating having a wavy curved line having different grating intervals and grating directions according to positions on the surface of the diffractive optical element is formed. When illuminating light of a specific wavelength is incident from a predetermined direction, the curve is set so that diffracted light from the curved diffraction grating is incident on different regions on a predetermined observation surface corresponding to the position of the curved diffraction grating. It is characterized in that a grating interval and a grating direction of the diffraction grating are set.

In the first and second diffractive optical elements, each element may have the same diffraction characteristic.
Further, each element element has a diffraction direction modulated in accordance with the arrangement position on the diffractive optical element surface, and may have a diffraction characteristic of directing diffracted light within the same range at a certain distance from the diffractive optical element surface. .

[0012] In the third diffractive optical element, the curved diffraction grating may be composed of a repeating pattern.
The curved diffraction grating may have a diffraction direction modulated in accordance with the arrangement position on the surface of the diffractive optical element, and may have a diffraction characteristic of directing diffracted light within the same range at a certain distance from the surface of the diffractive optical element.

In the present invention, since the diffraction grating is microscopically simple, the optical element has a high diffraction efficiency and a macroscopically bright scattering function. Further, off-line diffraction in which scattering diffraction is performed in the front direction with obliquely incident illumination light can be realized. Further, noise due to multiplex recording of interference fringes such as a hologram does not occur. Further, in a device using a continuous curved diffraction grating, diffraction noise generated by discontinuous edges does not occur.

[0014]

Embodiments of the diffractive optical element according to the present invention will be described below. FIG. 1 is a diagram for explaining the configuration and operation of the diffractive optical element according to the first embodiment of the present invention. As shown in FIG. 1A, the diffractive optical element 1 of this embodiment
Is composed of element elements 2 having the same characteristics and arranged two-dimensionally in a regular or irregular mosaic. In the case of the figure,
The element elements 2 are arranged in a grid pattern. As shown in FIG. 1B, each element element 2 is composed of lattice units 2 ′ arranged two-dimensionally in a regular or irregular mosaic. In the case of the figure, the lattice units 2 ′ are arranged in a grid pattern in the element element 2. Now, the lattice units 2 'are denoted by the symbols a, b, c, d,...

Now, each element element 2 of the diffractive optical element 1
As shown in FIG. 1A, when the illumination light 3 having a specific wavelength λ that is incident from a predetermined direction is irradiated, if the diffractive optical element 1 is of a reflective type, it is in a reflective direction, and if it is of a transmissive type, it is in a transmissive direction ( In the case of the drawing, it is a reflection type.) The element element 2 is configured so that the diffracted light 4 is diffracted, and the diffracted light 4 is incident on the observation surface 5. Looking at this in detail, the light diffracted by the lattice unit 2 ′ (a) of each element element 2 is reflected in the region a of the observation surface 5.
The light diffracted by the lattice unit 2 ′ (b) is placed in the region b of the observation surface 5 while the light diffracted by the lattice unit 2 ′ (c) is
In the region c, the diffracted light 4 corresponding to the arrangement position of the grating unit 2 ′ is incident on different regions on the observation surface 5. In the case of FIG. 1, the lattice units a, b, c, d,.
.. relative positions and areas a, b, c, d,.
Are similar to each other, but this condition is not always necessary.

In FIG. 1C, the diffracted light 4 from each element element 2 is arranged in the lattice unit 2 'of each element element 2 so that the diffracted light 4 is incident on the observation surface 5 as shown in FIG. The shape of the diffraction grating is schematically shown. A linear diffraction grating is engraved on each grating unit 2 ′, and the grating interval and the grating direction of the linear diffraction grating are different depending on the arrangement position of the grating unit 2 ′ on the element element 2. Like the lattice unit 2 '
The light diffracted in (a) is the light diffracted in the region a of the observation surface 5 and the light diffracted in the lattice unit 2 ′ (b) is the light diffracted in the region b of the observation surface 5 with the lattice unit 2 ′ (c). Is such that the diffracted light 4 therefrom is incident on different regions on the observation surface 5 corresponding to the arrangement position of the lattice unit 2 ′, such as region c of the observation surface 5.

Since the element elements 2 arranged two-dimensionally regularly or irregularly on the diffractive optical element 1 all have the same characteristics, the diffracted light 4 from each element element 2 on the observation surface 5
Are shifted from each other by the vertical and horizontal dimensions of the element element 2.
Is larger than the size of the diffractive optical element 1 when the size of the observation surface 5 surrounded by the broken-line frame shown in FIG. Since the diffracted light 4 is incident from all the regions, the diffractive optical element 1 can be used as a reflection type or transmission type diffusion plate having a scattering function with high diffraction efficiency.

The linear diffraction grating engraved on the grating unit 2 'of each element element 2 may be any of an amplitude type, a phase type, a relief type, and a volume type, but it is practical to constitute a relief type. . As the drawing method, there is a method of drawing using an electron beam or a laser beam, a method of exposing by interfering two parallel light beams, and the like, and a method of drawing with a beam is practical.

Here, a method of determining the lattice spacing and the lattice direction of the linear diffraction grating engraved on each lattice unit 2 'of the element element 2 of the diffractive optical element 1 will be described. First, a coordinate system of the diffractive optical element surface and the observation surface as shown in FIG. 7 is set. Point on the diffractive optical element surface (X, Y) in the direction cosine (l _c, m _c,
illumination light 3 of wavelength lambda _c that is incident from the direction of the n _c) is obtained in the form of diffraction grating as it is diffracted as diffracted light 4 to a point on the viewing surface (x, y).

[0020] Generally, the illumination light, respectively direction cosine of the diffracted light _{(l c, m c, n} c), (l l, m l, n l), the wavelength lambda _c, X direction of the diffraction grating, Y-direction When the local spatial frequency F _x, and F _y, the following relationship.

L _l = l _c ± λ _c F _{x ml} = m _c ± λ _c F _{y In} the arrangement of FIG. 7, l _l = (x−X) / √ ｛(x−X) ² + (y− Y) ² +
z ² _ｍml = (y−Y) / √ ｛(x−X) ² + (y−Y) ² +
_{^{z 2} ∴ F x = F}} x (x, y, X, Y, λ c) = (l l -l c) / λ c F y = F y (x, y, X, Y, λ c) = (M ₁ −m _c ) / λ _c Therefore, F _x = [(x−X) / {(x−X) ² + (y−Y) ² + z ² } −l _c ] / λ _c F _y = [(Y−Y) / {(x−X) ² + (y−Y) ² + z ² } −m _c ] / λ _c (1) Here, as shown in FIG. The pitch of 6 is D,
Assuming that the inclination with respect to the X axis is θ, from FIG. 8, θ = tan ⁻¹ (F _x / F _y ) D = 1 / √ (F _x ² + F _y ² ) (2) Each lattice unit 2 ′ of one element element 2
The lattice spacing and the lattice direction of the linear diffraction grating 6 engraved in are determined.

By the way, in order to configure the diffractive optical element 1 having the configuration and characteristics as shown in FIG. 1A as a reflection type relief type diffusion plate 10 (FIG. 2), FIG. A concave / convex relief pattern composed of a group of linear diffraction gratings 6 as shown is embossed on, for example, the surface of a transparent resin 11 and a reflective film 12 or a reflective multilayer thin film 1 made of a reflective metal such as aluminum is formed on the embossed concave / convex relief pattern.
2 is formed.

By disposing the reflection type relief type diffusion plate 10 having such characteristics on the side opposite to the observation side of the liquid crystal display element 40 as shown in a cross section in FIG. 2, for example, bright display is possible. A reflective liquid crystal display device can be realized. Here, the liquid crystal display element 40 has, for example, a configuration as described with reference to FIG. By combining the reflection type diffusion plate 10 according to the present invention with the liquid crystal display element 40 in this manner, the illumination light 32 incident from the display side of the liquid crystal display element 40 is adjusted to an angle range θ that matches the observation area of the liquid crystal display device. The diffused light 33 is diffusely reflected, and a bright display can be performed in a bright place without using a self-luminous backlight. Incidentally, the reflection type diffusion plate 10 according to the present invention may be arranged as a reflection plate between the liquid crystal layer and the rear substrate of the reflection type liquid crystal display device. In this case, the reflection layer 12 of the diffractive optical element 1
Will also serve as the light reflective electrode.

Incidentally, the diffractive optical element 1 and the relief type diffusion plate 10 as described above appear colored depending on the observation position or the observation direction, as is apparent from the description of FIG. In order to prevent such coloring, if the diffractive optical element 1 or the diffusing plate 10 itself has a scattering property such as ground glass in addition to the scattering property due to diffraction, it becomes white. To do so, for example,
In the case of the reflection type relief type diffusion plate 10, the front surface side of the transparent resin 11 having a concave-convex relief pattern on the back surface may be formed as a slick surface 18 composed of fine irregularities (FIG. 3A), or Fine powder 19 having a different refractive index may be dispersed (FIG. 3B) to scatter the diffracted light.

Next, FIG. 4 shows a modification of the embodiment of FIG. As apparent from FIGS. 1B and 1C,
When the diffraction grating 6 of the grating unit 2 'of each element element 2 is smoothly connected from a to e on the upper side of the figure, FIG.
A to b to c, the diffraction grating 6 ′ has a continuous curve. Similarly, if the lower sides of FIGS. 1B and 1C are connected smoothly, d to e to f in FIG.
As shown in FIG. 4, the diffraction grating 6 ″ has a continuous curve. However, the grating intervals of the diffraction gratings 6 ′ of a to b to c on the upper side of FIG. F becomes smaller than the grating interval of the diffraction grating 6 ″.

As in this embodiment, the diffractive optical element 1
The element elements 2 having the same characteristic, which are divided and arranged two-dimensionally or irregularly, are not constituted by two-dimensionally or irregularly arranged lattice units 2 ′.
As shown in FIG. 4B, even if the diffraction gratings 6 ′... 6 ″ are formed of continuous curves and the grating intervals are different depending on the position, as shown in FIG. The light diffracted at the position a is in the region a of the observation surface 5, the light diffracted at the position b is in the region b of the observation surface 5, the light diffracted at the position c is the region c of the observation surface 5, and so on. According to the position of the element element 2, the diffracted light 4 therefrom can be made to enter a separate area on the observation surface 5, and as in the embodiment of FIG.
The diffracted light 4 is incident on the observer's eye located substantially at the center of the observation surface 5 from almost all regions of the diffractive optical element 1, and the diffractive optical element 1 has a reflection function having a high diffraction efficiency and a scattering function. It can be used as a diffusion plate of a type or a transmission type.

In a further development of the embodiment of FIG. 4, instead of forming the diffractive optical element 1 from a set of element elements 2,
The diffraction grating can be constituted by one diffraction grating which is formed of a curve and has a different grating interval depending on the position. This embodiment is shown in FIG. As shown in a plan view of an arbitrary area 7 of the diffractive optical element 1 in FIG. 5B, the diffractive optical element 1 has a continuous wave-like curve, and the diffraction gratings 16...
6 ′, and in the case of FIG.
The portion has a relatively narrow grating interval, and the diffraction grating 16 'has a relatively wide grating interval. As shown in FIG. 5A, light diffracted in the region a of the diffraction grating 16 is observed. The light diffracted in the region a of the surface 5 is diffracted in the region b of the observation surface 5, the light diffracted in the region c is reflected in the region c of the observation surface 5,
The light diffracted in the area d of the diffraction grating 16 ′ is
The light diffracted in the region e is in the region e on the observation surface 5
The light diffracted in the region f is incident on the observation surface 5 so that the diffracted light 4 corresponding to the position of the diffractive optical element 1 is incident on different regions on the observation surface 5. 1, the diffracted light 4 is incident on the observer's eye located substantially at the center of the observation surface 5 from almost all regions of the diffractive optical element 1, The diffractive optical element 1 can be used as a reflection type or transmission type diffusion plate having a scattering function with high diffraction efficiency.

By the way, in each of the embodiments shown in FIGS. 1, 4 and 5, the element element 2 or the diffraction grating in any area on the surface of the diffractive optical element 1 has the same diffraction characteristic regardless of the position. Was something. That is, as shown in FIG. 6A, different positions (regions) 1 ′ of the diffractive optical element 1,
Observable area 5 'where light diffracted from 1 "can be observed,
5 "are shifted from each other by the position (area) 1 ', 1". In the case of FIG. 6A, the left and right end areas 1', 1 "of the diffractive optical element 1 can be observed. The area is limited to the area hatched, and becomes narrower.

Therefore, in another embodiment, the element element 2 or the diffraction grating on the surface of the diffractive optical element 1 is not made to have the same diffraction characteristic regardless of the position.
In the embodiment, the diffraction grating 6 in the element element 2,
The shapes such as 6 ′ and 6 ″ are deformed according to the position of the element element 2 in the diffractive optical element 1. In the embodiment of FIG. Deformed according to the middle position, and diffracted light 4
At a certain position (a position at a distance L from the diffractive optical element 1). This state is shown in FIG. As shown in FIG. 6B, observable regions 5 ′ and 5 ″ in which light diffracted from different positions (regions) 1 ′ and 1 ″ of the diffractive optical element 1 can be observed are distance L from the diffractive optical element 1. , The matching area 5 '
Since the entire surface of the diffractive optical element 1 is visible in (5 ″), the observable range is wider than in the case of FIG.

Although several embodiments of the diffractive optical element of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications are possible. When the diffractive optical element 1 according to the present invention is configured as a reflection type relief type diffusion plate 10 (FIG. 2), a semi-transmissive reflection film 12 is used and the opposite side of the liquid crystal display element 40 is used. By illuminating the backlight light source in a dark place and turning on the backlight light source in a dark place, a liquid crystal display device capable of bright display and capable of transmissive and reflective display can be obtained. Further, the diffractive optical element of the present invention can be used, for example, as a reflection plate for display, etc., in addition to the reflection diffusion plate for reflection type liquid crystal display devices. Further, the diffractive optical element of the present invention may be configured as a transmissive plate without the reflective layer 12 in addition to the reflective plate.

[0031]

As is clear from the above description, according to the diffractive optical element of the present invention, since it is a microscopically simple diffraction grating, the optical element has a high diffraction efficiency and a macroscopically bright scattering function. Becomes Further, off-line diffraction in which scattering diffraction is performed in the front direction with obliquely incident illumination light can be realized. Further, noise due to multiplex recording of interference fringes such as a hologram does not occur. Further, in a device using a continuous curved diffraction grating, diffraction noise generated by discontinuous edges does not occur. Therefore, it can be used as a diffusion plate for a liquid crystal display device, a reflection plate for display, or the like.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the configuration and operation of a diffractive optical element according to a first embodiment of the present invention.

FIG. 2 is a sectional view of an example of a reflection type liquid crystal display device using a reflection type relief type diffusion plate according to the present invention.

FIG. 3 is a cross-sectional view showing a configuration in which a reflection type relief type diffusion plate according to the present invention has a scattering property like ground glass.

FIG. 4 is a diagram for explaining the configuration and operation of a diffractive optical element according to another embodiment.

FIG. 5 is a diagram for explaining the configuration and operation of a diffractive optical element according to yet another embodiment.

FIG. 6 is a diagram for explaining the configuration and operation of a diffractive optical element according to still another embodiment.

FIG. 7 is a diagram for setting a coordinate system of a diffractive optical element surface and an observation surface.

FIG. 8 is a diagram for defining a pitch and a tilt of a diffraction grating.

FIG. 9 is a cross-sectional view of a liquid crystal display device using a conventional reflection diffusion plate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Diffractive optical element 1 ', 1 "... Different position (area) of diffractive optical element 2 ... Element element 2' ... Grating unit 3 ... Illumination light 4 ... Diffracted light 5 ... Observation surface 5 ', 5" ... Observable area 6, 6 ', 6 ": Diffraction grating 7: Arbitrary region 10: Reflective and relief type diffuser plate 11: Transparent resin 12: Reflective film (reflective multilayer thin film) 16, 16': Diffraction grating 18: Slip surface 19 ... Fine powder 32 ... Illumination light 33 ... Diffusion light 40 ... Liquid crystal display device

Claims (8)

[Claims] 1. A mosaic element element is divided into each element element, each element element is composed of a lattice unit arranged in a mosaic form, and a linear diffraction grating is formed in each lattice unit.
Depending on the arrangement position of the grating unit on the element element, the grating interval and the grating direction of the linear diffraction grating are different, and when illumination light of a specific wavelength is incident on the element element from a predetermined direction, the The grating interval and the grating direction of the linear diffraction grating are set so that the diffracted light from the grating unit is incident on different regions on the predetermined observation surface in accordance with the arrangement position of the grating unit in the above. A diffractive optical element characterized by the above-mentioned. 2. A mosaic element element is divided into a plurality of element elements. Each element element is formed with a curved diffraction grating, and the lattice spacing and the grating direction of the curved diffraction grating are changed according to the position on the element element. When the illumination light of a specific wavelength is incident on the element element from a predetermined direction, the diffracted light from the curved diffraction grating on the predetermined observation surface corresponds to the position of the curved diffraction grating in the element element. Wherein the grating interval and the grating direction of the curved diffraction grating are set so as to be incident on different regions. 3. A curved diffraction grating having a wavy curved line whose grating interval and grating direction are different according to the position on the surface of the diffractive optical element, and illumination light of a specific wavelength is applied to the diffractive optical element from a predetermined direction. In the case of incidence, the grating interval and the grating direction of the curved diffraction grating are set such that the diffracted light from the curved diffraction grating is incident on different regions on a predetermined observation surface corresponding to the position of the curved diffraction grating. A diffractive optical element characterized in that: 4. The diffractive optical element according to claim 1, wherein each element element has the same diffraction characteristic. 5. A diffraction direction of each element element is modulated according to an arrangement position on the surface of the diffractive optical element, and has a diffraction characteristic of directing diffracted light within the same range at a fixed distance from the surface of the diffractive optical element. 3. The diffractive optical element according to claim 1, wherein: 6. The diffractive optical element according to claim 3, wherein said curved diffraction grating has a repeating pattern. 7. A diffraction direction of the curved diffraction grating is modulated in accordance with an arrangement position on the surface of the diffractive optical element, and a diffraction characteristic of directing diffracted light within a same range at a predetermined distance from the surface of the diffractive optical element. 4. The diffractive optical element according to claim 3, comprising: 8. The diffractive optical element according to claim 1, wherein the diffractive optical element is arranged as a reflection plate on a part of the reflection type liquid crystal display device.