JP2003215318A - Optical element for illumination, its manufacturing method, and video display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve characteristics of a transparent plate-like optical element for illumination which is arranged with one of two surfaces facing each other turned to an illumination object as an exit surface and diffracts light made incident from the end by a diffraction grating disposed along the exit surface to emit the light from the exit surface. <P>SOLUTION: The period of the diffraction grating and differences in height between protrusions and recesses are made equal to or shorter than the center wavelength in the wavelength range of the light made incident from the end part, and wall surface being surfaces between the protrusions and recesses of the diffraction grating are made approximately parallel with adjacent those and are tilted to the surface of the entire diffraction grating. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plate-shaped illumination optical element and an image display device using the same as an illumination optical system.

[0002]

2. Description of the Related Art In a portable information terminal device such as a mobile phone, a notebook personal computer, a PDA electronic notebook, etc., in order to provide an image with low power consumption, a reflective display device that reflects and modulates illumination light, 2. Description of the Related Art An image display device is used that includes a light source that supplies illumination light and a plate-shaped optical element that is arranged in front of a display and guides the illumination light from the light source to the display. By using the ambient light as the illumination light when the environment is bright and supplying the illumination light from the light source when the environment is dark, it is possible to suppress the power consumption for providing the image.

The illumination optical element of such an image display device has a surface on the side far from the display as a satin-finished surface or a prism array, and transmits ambient light to guide it to the display, while it is incident from the end. The illumination light from the light source is reflected by the matte surface or the prism array and guided to the display. Also,
The light reflected and modulated by the display is transmitted and guided to the observer's eye.

However, if the surface of the optical element is a satin-finished surface, the light from the display is scattered when passing through the optical element, so that the image provided to the observer has blurring, a decrease in contrast, and uneven brightness. Occurs.

When the surface of the optical element is a prism array, light is not scattered, but the prism pattern is visually recognized, or moire fringes are generated in the image provided due to the relationship between the prism pattern and the image on the display. . In addition, part of the light that is reflected by the prism array and goes to the display,
The light is reflected by the surface of the display side and reaches the eyes of the observer, causing flare and lowering the contrast. In order to avoid this, it is necessary to perform antireflection treatment on the surface on the display side. Moreover, since the prism array is exposed to the outside (observer side), it is necessary to provide a protective plate or the like to prevent scratches and dirt.

[0006] Japanese Patent Application No. 2000-376169 proposes a plate-shaped illumination optical element having a blazed diffraction grating having a period of light wavelength (650 nm) or less on its surface. With this optical element, the problems of blurring and moire fringes are almost eliminated. It is also possible to dispose the surface on which the diffraction grating is provided on the side of the display, and a member for protecting the diffraction grating is not always necessary and is suitable for thinning.

Each of the above-mentioned illumination optical elements can also be used to guide a backlight, which is illumination light, to a transmissive display that modulates while transmitting illumination light. In recent years, there has been proposed an image display device in which transmissive display devices are arranged on both sides of a plate-shaped illumination optical element so that images can be observed from both front and back sides. An illumination optical element having a diffraction grating is expected to be suitable for a display device using such a transmissive display.

[0008]

However, the diffraction grating generally has a very fine structure, and in particular, Japanese Patent Application No. 2000-3
The shape of the diffraction grating of the optical element proposed in 76169 has a right-angled triangular cross section and is complicated, so that it is difficult to form it precisely. If the shape cannot be precisely formed, the diffraction conditions such as the diffraction efficiency and the diffraction angle will not be as designed, and the brightness will be reduced or the brightness will be uneven. Further, when it is used as an illumination optical system of a reflection type display, the light from the light source that is diffracted by the diffraction grating and travels in the same direction as the light from the image display increases, and the contrast of the image provided decreases.

The present invention has been made in view of the above problems, and is a plate-like optical element for illumination having a diffraction grating, and it is easy to manufacture the grating shape as designed and the optical characteristics. The purpose is to provide excellent products.
Another object of the present invention is to realize an image display device capable of providing a high quality image by including such an optical element.

[0010]

In order to achieve the above object, according to the present invention, one of two facing surfaces is arranged as a light emitting surface and is directed toward an object to be illuminated. Which has a diffraction grating along the exit surface, allows light to enter from the end, diffracts it by the diffraction grating while the light travels inside, and emits it from the exit surface. The period of the grating and the height difference between the convex portion and the concave portion is equal to or less than the central wavelength of the wavelength range of the light incident from the end portion, and the wall surface that is the surface between the convex portion and the concave portion of the diffraction grating,
Adjacent ones are substantially parallel to each other and are inclined with respect to the surface of the entire diffraction grating.

This optical element can use not only the light incident from the end portion for illumination but also the light incident from the surface facing the emission surface. Further, the light reflected by the illumination target can be emitted from the surface facing the emission surface. Since the period and height difference of the diffraction grating are close to those on the short wavelength side of the light to be diffracted, it is possible to set the desired diffraction conditions for the entire light to be diffracted, and also the adjacent wall surfaces. Are substantially parallel to each other, the precision of the shape can be easily ensured, and the designed diffraction condition can be well expressed. Therefore, the optical element has excellent characteristics and is easy to manufacture.

Further, since the wall surface is inclined with respect to the surface of the entire diffraction grating, the amount of light reflected by the diffraction grating or transmitted through the diffraction grating and traveling in the same direction as the light from the illumination target is It is possible to suppress it very slightly. As a result, the reduction in contrast when observing the illumination target from the surface side facing the emission surface is greatly reduced.

The diffraction grating can be provided on the surface of the optical element. When a diffraction grating is provided on the emission surface, transmitted light is emitted, and when a diffraction grating is provided on the surface facing the emission surface, reflected light is emitted from the emission surface.

It is also possible to join two members having different refractive indexes to form an optical element and to provide a diffraction grating at the interface between the two members. In this case, if the member having the larger refractive index is used as the path of the light from the end, the diffraction condition can be set easily. In this configuration, since the diffraction grating is in a protected state, a member for protection is unnecessary.

The inclination angle of the wall surface of the diffraction grating with respect to the surface of the diffraction grating as a whole is preferably 5 ° or more. Here, the tilt angle means the angle formed by the normal line of the surface of the entire diffraction grating and the wall surface. By doing so, it becomes easy to suppress the amount of light traveling in the same direction as the light from the illumination target to a very small amount.

In the structure in which the diffraction grating is located on the exit surface side with respect to the path of the light, the wall surface of the diffraction grating is inclined in the direction away from the end portion through which the light is incident, the farther from the surface facing the exit surface. Good to set. Further, in the configuration in which the diffraction grating is located on the surface side facing the emission surface with respect to the path of the light, the wall surface of the diffraction grating is inclined so that the portion farther from the emission surface is closer to the end portion through which light is incident. It is good to In this way, the amount of light traveling in the same direction as the light from the illumination target can be reliably suppressed to a very small amount.

In the case where a diffraction grating is provided at the interface between two members having different refractive indices, in the structure in which the one of the two members farther from the emission surface has a larger refractive index than the one closer to the emission surface,
It is advisable to set the wall surface of the diffraction grating to be inclined in a direction away from the end portion through which light is incident, as it approaches the exit surface.
Further, in the configuration in which one of the two members closer to the emission surface has a larger refractive index than that farther from the emission surface, the wall surface of the diffraction grating is inclined in a direction closer to the end portion through which light is incident, as far as it is from the emission surface. It is good to set it. By doing so, when the member having the larger refractive index is used as the path of light, the amount of light traveling in the same direction as the light from the illumination target can be surely suppressed to a very small amount.

In manufacturing the above-mentioned optical element, a lattice shape having a plane as a whole and a wall surface substantially perpendicular to the plane is produced, and a convex force is applied to the lattice shape by applying a force in the direction along the entire plane. The shape of the diffraction grating may be formed by deforming the portion. Since it is easy to manufacture a lattice shape in which the wall surface is perpendicular to the plane as a whole, and it is easy to deform the convex portion by applying a force, the manufacturing method is extremely simple. Here, the shape of the diffraction grating can be formed on the material itself to be the optical element, or can be formed on another material that can be easily processed and then transferred to the material to be the optical element.

The shape of the diffraction grating may be directly formed by etching or by two-beam interference method. In this case, the etching process is performed from a direction oblique to the plane of the entire diffraction grating, or the bisector of the angle formed by the two beams is inclined with respect to the plane of the entire diffraction grating. Will be processed. Also here, the material itself to be the optical element can be processed, or the shape formed by processing other material can be transferred to the material to be the optical element.

The diffraction grating may be manufactured by molding using a mold having a shape complementary to the diffraction grating. In this way, it is possible to suppress variations in the characteristics of the optical element and facilitate mass production. When separating the diffraction grating and the mold, by moving the mold in a direction parallel to the wall surface of the diffraction grating, it is possible to avoid damage to the convex portion. In the production of the mold, either of directly processing the material or transferring the shape formed on another material can be adopted.

In order to achieve the above object, the present invention also provides an image display device that modulates illumination light into light that represents an image, a light source that emits the illumination light, and the illumination light that the light source emits. In an image display device including an illumination optical system that guides to, the illumination optical system includes any one of the above optical elements. Since the diffraction grating of the optical element can almost express the set diffraction condition, it is possible to provide a high quality image. Moreover, by providing the diffraction grating of the optical element on the emission surface and disposing the emission surface close to the image display device, a member for protecting the diffraction grating is unnecessary, and a thin image display device can be obtained. . Even when an optical element provided with a diffraction grating at the interface between two members is provided, a member for protecting the diffraction grating is not necessary, and similarly, a thin image display device can be obtained.

Here, the image display device may be of a reflection type in which the illumination light is reflected and modulated to be light representing an image. In addition to the general feature that the diffraction grating of the optical element is a fine structure, the amount of light reflected by the diffraction grating or transmitted through the diffraction grating and traveling in the same direction as the light from the image display is very small. Since it is possible to suppress the occurrence of blurring and moire fringes in the image to be provided, it is possible to suppress the deterioration of contrast satisfactorily.

The image display device may be of a transmissive type, which modulates the illumination light while transmitting it to obtain light representing an image. In this case, when the surface of the optical element facing the emission surface is exposed to the outside, light from the outside can be used as illumination light.

According to the present invention, there is also provided a transparent plate-shaped optical element for illumination, which is arranged toward two illumination objects with both of the two surfaces facing each other as an emission surface, and a diffraction grating along the emission surface. In the case where the light is incident from the end, is diffracted by the diffraction grating while the light travels inside, and is emitted from the emission surface, the period of the diffraction grating and the height difference between the convex portion and the concave portion are The wall surface that is equal to or less than the central wavelength of the wavelength range of the light incident from the end and is a surface between the convex portion and the concave portion of the diffraction grating is configured so that adjacent ones are substantially parallel to each other.

The diffraction grating of this optical element produces two reflected lights and one transmitted light, one of the reflected light and the transmitted light is emitted from the two emission surfaces, and the other of the reflected light is inside the optical element. To make progress. Since the period and height difference of the diffraction grating are close to those on the short wavelength side of the light to be diffracted, it is possible to set the desired diffraction conditions for the entire light to be diffracted, and also the adjacent wall surfaces. Are almost parallel,
The precision of the shape can be easily ensured, and the set diffraction condition can be well expressed. Therefore, the optical element has excellent characteristics and is easy to manufacture. The diffraction grating can be provided on the surface of the optical element.

It is also possible to join two members having different refractive indexes to form an optical element and to provide a diffraction grating at the interface between the two members. In this case, if the member having the larger refractive index is used as the path of the light from the end, the diffraction condition can be set easily. In this configuration, since the diffraction grating is in a protected state, a member for protection is unnecessary.

Further, according to the present invention, two transmissive image display devices that transmit illumination light and modulate it into light for displaying an image, a light source that emits the illumination light, and two images of the illumination light emitted by the light source. In an image display device including an illumination optical system that leads to a display, any one of the above optical elements is provided as the illumination optical system. Since the diffraction grating of the optical element can almost express the set diffraction condition, it is possible to provide a high quality image. Moreover, even when the diffraction grating is provided on the surface of the optical element, that is, the emission surface, by disposing the emission surface close to the image display, a member for protecting the diffraction grating is not required, and a thin image display device is provided. Can be Even when an optical element provided with a diffraction grating at the interface between two members is provided, a member for protecting the diffraction grating is not necessary, and similarly, a thin image display device can be obtained.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an optical element for illumination and an image display device of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows the optical configuration of the image display device 1 of the first embodiment. The image display device 1 includes a reflection-type image display device 10 that reflects and modulates illumination light that is applied to light that represents an image, a light source unit 20 that supplies illumination light to the image display device 10, and an image display. The transparent plate-shaped optical element 30 for illumination that guides the illumination light from the light source unit 20 to the image display device 10 is disposed so as to face the device 10.

When the image display device 1 is used in a bright environment, the light L0 from the outside becomes an illumination light which passes through the optical element 30 and illuminates the image display 10. Therefore, when the environment is bright, it is not necessary to supply the illumination light from the light source unit 20.

The image display device 10 is a reflection type liquid crystal display device and has a polarizing plate, a liquid crystal layer, a reflection plate and the like, but it is shown here in a simplified manner. The light source unit 20 includes a light emitting element 21 and a reflector 22, and the light emitted from the light emitting element 21 is reflected by the reflector 22 to be substantially parallel light.

The optical element 30 is arranged parallel to the image display 10. The surface 31 of the optical element 30 close to the image display 10 and the surface 32 far from the image display 10 are parallel to each other except at the ends. End face 3 of optical element 30
3 is inclined with respect to the surfaces 31 and 32, and the light source unit 2
0 is arranged toward this end face 33.

The optical element 30 is formed by joining two transparent and plate-like members 30a and 30b made of different materials. The first member 30a and the second member 30b have different refractive indices, and the first member 30a farther from the image display 10 has a higher refractive index. First member 30a and second member 30b
A diffraction grating 35 is provided on the interface 34.

The light from the light source section 20 enters the first member 30a from the end face 33 and travels in the first member 30a while repeating reflection at the interface 34 and total reflection at the surface 32. The diffraction grating 35 produces transmitted light and reflected light by diffraction. The diffraction grating 35 is set so that the reflection angle of the reflected light becomes equal to the incident angle, and the surface 31
The incident angle of the transmitted light with respect to is set to be small. The transmitted light of the diffraction grating 35 is the surface 3 that becomes the emission surface.
1, the image display 10 is illuminated, and the reflected light further travels in the first member 30a. By repeating this, the entire image display 10 is illuminated.

The illumination light that has entered the image display 10 is reflected to form image light that represents an image, and then enters the optical element 30 from the surface 31, and the second member 30b and the first member 30a.
Through the surface 32 and reaches the eye E of the observer. This provides the viewer with an image. The incident angle of the illumination light on the image display 10 is not 0 °, and the image light passes through an optical path different from that of the illumination light. Therefore, the diffraction grating 35
There is a difference between the angle of the illumination light that has passed through and the diffraction grating 35 and the angle of the image light with respect to the diffraction grating 35, and the image light passes through the diffraction grating 35 without being diffracted. The diffraction grating 35 will be described in detail later.

FIG. 2 schematically shows the optical configuration of the image display device 2 of the second embodiment. The image display device 2 is different from the image display device 1 in that the illumination optical element 30 is composed of a single member 30a, and the diffraction grating 35 is provided on the emission surface 31. The other configurations and the principle of providing an image are the same as those of the image display apparatus 1, and the duplicate description will be omitted. A member for protecting the diffraction grating 35 is not required by disposing the emitting surface 31 in contact with the image display device 10 or by disposing the separation distance between them small.

The structure of the diffraction grating 35 of the image display devices 1 and 2 is enlarged and schematically shown in FIG. In the diffraction grating 35, the period Λ and the height difference h between the convex portion and the concave portion are set to be equal to or less than the central wavelength λ of the wavelength range of the light L1 from the light source unit 20.
In addition, the wall surfaces 35a, which are the surfaces between the convex portions and the concave portions (main surfaces that bring about height differences) are all parallel, and the diffraction grating 3
5 is set to be inclined with respect to the plane as a whole (to form an angle α other than 0 ° with respect to the normal line). By setting the period and height difference to be equal to or less than the central wavelength of the light to be diffracted, the desired diffraction condition can be set not only for the light with a long wavelength but also for the light with a short wavelength. Is possible. Further, by making all the wall surfaces 35a parallel to each other, it becomes easy to secure the precision of the shape (realization of the shape as designed).

In general, when illuminating a reflection type image display device by using diffraction, there is a problem that the contrast of the image is lowered due to unnecessary diffracted light. This principle will be described with reference to FIG. When the light L1 having the wavelength λ is incident on the diffraction grating having the period Λ, the relationship of the expression (1) is established between the incident angle θ1 (the counterclockwise direction is positive) and the diffraction angle θ2 of the transmitted light L2.
Here, n1 is the refractive index of the medium on the incident side, n2 is the refractive index of the medium on the outgoing side (transmission destination), and m is the diffraction order. n2 · sin θ2 = n1 · sin θ1 + m · λ / Λ Equation (1)

When the medium on the incident side has a larger refractive index than the medium on the emission side (transmission destination) like the image display devices 1 and 2, and the optical element 30 is arranged in parallel to the image display device 10, The transmitted light L2 having the diffraction order m of -1 is used for illumination. Therefore, when the emission angle of the image light L3 toward the observer is represented by θ3, the relationship of the expression (2) is established. sin θ3 = λ / Λ−n1 · sin θ1 Equation (2)

On the other hand, due to the diffraction on the incident side, the member 30
Unwanted reflected light L5 is generated together with the reflected light L4 traveling in a, and the relationship of the expression (3) is established when the diffraction angle of this unnecessary reflected light L5 is represented by θ5. sin θ5 = λ / Λ−n1 · sin θ1 (3) That is, the unnecessary reflected light L5 travels in the same direction as the image light L3, which causes a reduction in contrast in the observed image.

The contrast of the image on the image display 10 is C, the reflectance of the image display 10 is R, the diffraction efficiency of the transmitted light L2 (the intensity ratio of the light L2 to the light L1) is ηt, and the unnecessary reflected light L5 is Diffraction efficiency (intensity ratio of light L5 to light L1)
Is represented by ηr, the contrast Cobs of the observed image is represented by Expression (4). Cobs = (R.eta.t + .eta.r) / (R / C.eta.t + .eta.r) = (R + .eta.r / .eta.t) / (R / C + .eta.r / .eta.t) Equation (4)

The contrast C of the image on the image display 10
5 is 30 and the reflectance R of the image display 10 is 0.3, the relationship between the diffraction efficiency ratio ηr / ηt and the observed image contrast Cobs is shown in FIG. Generally, since the contrast suitable for observation is 10 or more, the diffraction efficiency ratio ηr
/ Ηt needs to be 0.02 or less.

Table 1 shows the calculation results of the diffraction efficiency in the diffraction grating 35 in which the wall surfaces 35a are all parallel and inclined. Codes Λ, λ, h, n1, n2, α, θ in Table 1
1, ηr and ηt are as described above, a is the width of the convex portion of the incident side member 30a, and ηr0 is the diffraction efficiency of the diffracted light that is specularly reflected (reflected light L4 in FIG. 4). The "tilt A" in the column of the shape of the diffraction grating refers to the shape shown in FIG. 3, that is, the structure in which the upper surface of the convex portion and the lower surface of the concave portion are parallel to the plane of the entire diffraction grating, and the "tilt B" is shown in FIG. Shape shown in
That is, the lower surface of the concave portion is parallel to the plane of the entire diffraction grating, and the upper surface of the convex portion is perpendicular to the wall surface 35a. In this case, the medium on the emission side (transmission destination) is air (n2 = 1), and this corresponds to the diffraction grating 35 of the image display device 2 in which the diffraction grating 35 is provided on the emission surface 31.

[0043] <Table 1> Shape Λ / λ h / Λ a / Λ n1 n2 α θ1 ηr ηt ηr0 ηr / ηt Tilt A 0.66 1 0.5 1.5 1 45 # 60 # 0.0028 0.4980 0.4993 0.0055 Inclination A 0.7475 1 0.5 1.5 1 27 # 50 # 0.0024 0.9869 0.0107 0.0025 Inclination B 0.76 1.25 0.5 1.5 1 11 # 50 # 0.0043 0.5282 0.4673 0.0081 Brace   0.71 1-1.5 1-55 # 0.0006 0.3667 0.6328 0.0016 Rectangle 0.7475 1 0.5 1.5 1 0 # 50 # 0.1665 0.2164 0.6170 0.7695

Table 1 also shows the calculation results of other shapes for comparison. The "blaze" is the shape shown in FIG. 7, that is, the cross section is a right triangle (one of the adjacent wall surfaces corresponds to the entire diffraction grating). Blanze type structure that is inclined with respect to the plane and the other is vertical, and the “rectangle” is the shape shown in FIG.
A structure in which the walls are parallel and perpendicular to the plane of the entire diffraction grating.

Table 1 shows that the diffraction grating uses transmitted light for illumination, has a wall surface inclined with respect to the plane of the entire diffraction grating, and a portion far from the light path is closer to a portion closer to the light path. The shape in which the wall surface is inclined in the direction away from the end surface 33 on which light is incident has a high diffraction efficiency ηt of the transmitted light L2 and is suitable for illumination, and a low diffraction efficiency ratio ηr / ηt, and a high-contrast image. It turns out that it is suitable to provide. However, with the blazed shape shown in FIG. 7, it is difficult to ensure accuracy in the actual formation,
It is difficult to achieve the calculated diffraction efficiency ratio ηr / ηt. On the other hand, the shapes of FIGS. 3 and 6 in which the adjacent wall surfaces are parallel are
It can be formed with high accuracy, and a diffraction efficiency ratio ηr / ηt close to the calculation result can be realized. First, second
The image display devices 1 and 2 of the embodiment have the “inclined A” shape shown in FIG. 3, but may have the “inclined B” shape shown in FIG. 6.

FIG. 9 schematically shows the optical configuration of the image display device 3 of the third embodiment. This video display device 3
The illumination optical element 30 is composed of a single member 30a, the diffraction grating 35 is provided on the surface 32 farther from the image display 10, and light is incident on the wall surface of the diffraction grating 35 farther from the emission surface 31. The end surface 33 is inclined in a direction toward the end surface 33. In the image display device 3, the diffraction grating 3
Two reflected lights having different diffraction angles are generated by 5, and one of them is emitted from the emission surface 31 and the other is a light that travels in the optical element 30.

Table 2 shows the calculation result of the diffraction efficiency in this configuration. The shape of the diffraction grating is “tilt A” shown in FIG. 3, but the light is from the direction opposite to that of FIG. 3 (from the right side of FIG. 3),
It is incident on the diffraction grating 35. In this case, the diffraction efficiency ηr of the reflected light is high, it is appropriate to use this for illumination, and the diffraction efficiency ratio ηt / ηr (the reciprocal of ηr / ηt) is small, so that an image with high contrast can be provided. It turns out that it is suitable for.

[0048] <Table 2> Shape Λ / λ h / Λ a / Λ n1 n2 α θ1 ηr ηt ηr0 ηt / ηr Tilt A 0.7475 0.5 0.5 1.5 1 45 # -50 # 0.4913 0.0048 0.5039 0.0097

FIG. 10 schematically shows the optical configuration of the image display device 4 of the fourth embodiment. The image display device 4 is
Like the image display device 1 of the first embodiment, the optical element 3
0 is composed of two members 30a and 30b, and its interface 34
In addition to providing the diffraction grating 35, the reflected light of the diffraction grating 35 is emitted from the emission surface 31 as in the image display device 3 of the third embodiment. The first member 30a having the larger refractive index is arranged on the image display 10 side, and the light incident from the end face 33 receives the first member 30a.
Try to proceed inside. The direction of inclination of the wall surface of the diffraction grating 35 is the same as that of the image display device 3.

The image to be provided is required to have not only high contrast but also uniform brightness over the whole, and in the case of providing a color image, it is also required to have uniform color tone. An optical element 30 that allows light to enter from the end face 33 and gradually emits light while traveling inside.
Then, since the amount of light traveling inside gradually decreases, in order to uniformly illuminate the entire image display device 10,
It is necessary to change the diffraction efficiency according to the distance from the end face 33. This point will be described with reference to FIG.

In FIG. 11, Ik is given to the diffraction grating 35 by k.
It represents the amount of light immediately before entering the second time, and Tk is the diffraction grating 3
5 represents the amount of light emitted from the optical element 30 upon the k-th incident on 5. Here, the relationship of Expression (5) is established. Ik-1 = Ik + Tk-1 (5)

The amount of light (I1) incident from the end face 33 is 1
Then, even after the nth incidence on the diffraction grating 35, the optical element 30
The amount In of the light traveling inside is obtained by the total sum from k = 1 to k = n−1, and the formula (6) is obtained. In = 1- (n-1) T1 Equation (6)

To keep the amount of emitted light constant, T1 =
Tk (k = 1 ... n) must be established, and the illumination ratio Tn
/ In becomes equation (7). Tn / In = T1 / {1- (n-1) T1} Equation (7)

Since the illumination ratio is the product of the diffraction efficiency η and the area ratio S of the diffraction grating, as shown in equation (8), the diffraction efficiency η or the area ratio S depends on the position on the diffraction grating. By adjusting, the whole image display 10 can be illuminated uniformly. Tn / In = η · S (8) In the optical element 30 of the image display devices 1 to 4, the diffraction grating 35 is used.
Since the wall surfaces 35a of the above are parallel, it is easy to set and realize the diffraction efficiency η and the area ratio S according to the position on the diffraction grating 35.

When the thickness of the member 30a, which is the path of the light, is t, the relationship of the equation (9) is established between the position x of the light incident on the diffraction grating 35 for the nth time and the number n of times of incidence. Where θ
1 is the incident angle as described above. n = 1 + x / (2 · t · tan θ1) Equation (9)

Therefore, the equation (7) becomes the equation (10). Tn / In = T1 / {1-x · T1 / (2 · t · tan θ1)} Equation (10)

Equation (10) means that the illumination ratio for performing uniform illumination is inversely proportional to the distance from the end face 33 side on which light is incident, and the degree of change is uniquely determined by the incident angle θ1. To do. From this, the predetermined incident angle θ1
It is understood that, when the illumination ratio is set so that uniform illumination can be performed in, the light that is incident on the diffraction grating at an incident angle other than the incident angle θ1 cannot be uniformly illuminated.
When the incident angle is smaller than θ1, the brightness becomes closer to the end face 33, and conversely, when the incident angle is larger than θ1, the brightness becomes brighter as the distance from the end face 33 increases.

When the distribution of the illumination ratio of the diffraction grating 35 and the variation of the incident angle of light with respect to the diffraction grating 35 are balanced, both the brightness and the hue are uniform. However, when the incident angle is biased according to the wavelength of light, even if the light of a certain wavelength can be uniformly illuminated, the light of another wavelength cannot be uniformly illuminated. For example, when the incident angle of blue light is smaller than the incident angle of red light, the side closer to the end face 33 is colored in cyan because there is less red light, and the side far from the end face 33 is colored in yellow because there is less blue light. , Not a uniform shade. Therefore, in order to make both brightness and hue uniform, it is necessary to make the incident angle to the diffraction grating 35 the same over the entire wavelength range of the light used for illumination.

Table 3 shows an example of setting of the diffraction grating 35 of the image display device 1 of the first embodiment which is provided at the interface 34 between the two members 30a and 30b and emits the transmitted light. And the diffraction efficiency ηt of transmitted light,
The relationship between the wavelength wl and the diffraction efficiency ratio ηr / ηt is shown in FIGS. 12 and 13, respectively. 12 and 13
In the above, the center wavelength λ of the light having the wavelength wl incident from the end face 33 is set to 1 and expressed as a relative value. From Figure 12,
It can be seen that the diffraction efficiency is high over a wide wavelength range (wl / λ = 0.775 to 1.18) and illumination in a wide wavelength range is possible, and from FIG. 13, the diffraction efficiency ratio ηr / It can be seen that ηt is small and good contrast is obtained over the entire wavelength range.

<Table 3> Shape Λ / λ h / Λ a / Λ n1 n2 α θ1 Inclination A 0.6725 0.5 0.5 1.5 1.3 45 # 65 #

The relationship between the wavelength wl and the diffraction efficiency ηr of the reflected light in the diffraction grating 35 of the image display device 4 of the fourth embodiment which is provided at the interface 34 between the two members 30a and 30b and emits the reflected light, and Wavelength wl and diffraction efficiency ratio ηt / η
Examples of the relationship with r are shown in FIGS. 14 and 15, respectively. Here, the setting of the diffraction grating 35 is as shown in Table 3 except that the traveling direction of light is opposite and the incident angle θ1 is −65 °. Also in this case, it can be seen from FIG. 14 that it is possible to illuminate in a wide wavelength range, and from FIG. 15, it can be seen that good contrast can be obtained over the entire wavelength range.

When light of a wide wavelength range as shown in FIGS. 12 and 13 or FIGS. 14 and 15 is used for illumination,
When the diffraction efficiency ηt of the transmitted light or the diffraction efficiency ηr of the reflected light changes depending on the wavelength, the hue of the provided image also slightly changes. However, by correcting the incident angle θ1 according to the wavelength, it is possible to suppress the variation in hue.

Table 4 shows an example in which the diffraction grating 35 of the image display device 1 is set as shown in Table 3 and the incident angle θ1 is further corrected. This is because the incident angles θ1 of the central wavelength λ and the other two wavelengths are different. By doing so, the variation of the hue is suppressed to about half as compared with the case where the incident angles θ1 are the same, and an image with a substantially uniform hue can be provided.

<Table 4> wl / λ θ1 ηr ηt ηr0 ηr / ηt 0.82 67.5 # 0.0032 0.1333 0.8623 0.0241 1 65 # 0.0004 0.1122 0.8873 0.0037 1.18 62.5 # 0.0007 0.0932 0.9061 0.0071

A structural example of a liquid crystal display used as the video display 10 is schematically shown in FIG. This liquid crystal display includes a polarizing plate 11, a retardation plate 12, a transparent substrate 13, a color filter 14, and a liquid crystal layer 1 in order from the side of the optical element 30 for illumination.
5 and the diffuse reflection electrode 16. By providing the color filter 14 in which the wavelength range of light to be transmitted differs for each minute portion, it is possible to modulate the illumination light in a plurality of wavelength ranges at once and provide a color image.

FIG. 16 also shows the optical element 30 of the image display device 1 of the first embodiment in which the diffraction grating 35 is provided at the interface 34 between the two members 30a and 30b together with the liquid crystal display, and the emission surface 31 is It is in contact with the polarizing plate 11. The image display devices 2 to 4 according to the other embodiments also include the exit surface 31 of the optical element 30.
A thin structure can be obtained by arranging so that it contacts the polarizing plate 11.

The above optical element 30 can also be used as an illumination optical system of a video display device provided with a transmissive video display that modulates the illumination light while modulating it into light for displaying an image. The outline of the optical configuration of the image display devices 5 and 6 of the fifth and sixth embodiments provided with the transmissive image display 10 is schematically shown in FIGS. 17 and 18, respectively. Fifth shown in FIG.
The video display device 5 of the embodiment is a modification of the video display device 1 of the first embodiment, and the video display 10 is changed from a reflective liquid crystal display to a transmissive liquid crystal display 10 ′. is there. A video display device 6 of the sixth embodiment shown in FIG.
In the above, the image display device 2 of the second embodiment is modified in the same manner, and the image display device 10 is changed from a reflective liquid crystal display device to a transmissive liquid crystal display device 10 '.

Since the optical element 30 is thin, the image display devices 5 and 6 having the transmissive image display 10 'can be made thin as a whole. 17 and 18, the optical element 30 and the image display 10 'are shown separated from each other, but it is also possible to arrange them so that they are in contact with each other.

In the conventional plate-shaped optical element for illuminating the transmissive image display, the surface farther from the image display has a matte surface like the conventional optical element for illuminating the reflective image display. Alternatively, a prism array is provided, and a reflecting plate is provided on the surface of the prism array in order to prevent light amount loss due to leakage of light from the surface. However, in the optical element 30 that emits light by diffraction, the image display device 1
It is possible to totally reflect the light on the surface 32 farther from 0 ', and it is not necessary to provide a reflector. Further, by not providing the reflector, it becomes possible to introduce external light from the surface 32 and use it for illuminating the image display 10 ′.
When the environment is bright, it is not necessary to supply the illumination light from the light source unit 20.

The optical elements 30 of the image display devices 3 and 4 of the second and third embodiments that emit reflected light can also be used as an illumination optical system of an image display device having a transmissive image display 10 '. it can. Also in this case, the transmitted light can be suppressed very slightly, and it is not necessary to provide a reflecting plate on the surface 32 far from the image display 10 '.

The optical element 30 shown in each of the above embodiments is itself thin and is not limited to an image display device.
Even if it is used for other optical devices, the feature of being thin can be utilized. For example, it is suitable as an illuminating optical system of an observing apparatus such as a microscope, which has a short optical focal length and has a short distance from an object to be illuminated. Further, in a photographing device such as a scanner, which is composed of a large number of image pickup optical systems corresponding to minutely divided subjects and in which the distance between the subject and the photographing optical system needs to be shortened, the distance between the subject and the photographing optical system is increased. It is useful as an illumination optical system to be arranged.

A method of manufacturing the shape of the diffraction grating 35 in which the wall surfaces 35a are parallel to each other and inclined to the plane as a whole will be described. This lattice shape can be formed on the material itself of the plate-shaped members 30a and 30b that form the optical element 30, or can be formed on another material that can be easily processed and then the material of the members 30a and 30b can be formed. It can also be transferred to the surface.

For example, first, a prototype having the above-mentioned lattice shape is produced, a die having an inverted shape (complementary shape) of the above-mentioned lattice shape is produced from the prototype, and finally, a member is formed from the die. It is possible to transfer the shape to the material of 30a or 30b. By doing so, it is possible to efficiently mass-produce the optical element 30 having the diffraction grating 35 having a uniform grating shape. It should be noted that it is possible to adopt a general method such as electroforming for manufacturing the mold from the prototype, and here,
Only the production of the prototype and the transfer of the shape from the mold to the material of the member 30a or 30b will be described.

In order to manufacture the prototype, a lattice shape in which the wall surfaces are parallel to each other and perpendicular to the plane as a whole is formed on the surface of the material as the prototype, and a force in the direction along the plane as a whole is applied to this. The two-step method in which the convex portion is deformed to incline the wall surface by adding the method and the one-step method in which the lattice shape parallel to each other and inclined with respect to the entire plane is directly formed on the surface of the material to be the prototype There is.

The first step of the two-step method is schematically shown in FIG. A resist 42 is provided on the upper surface of a substrate 41 serving as a prototype, and the resist 42 is processed by an electron beam drawing machine 43, a stepper 44, or a two-beam interferometer 45 to form a fine line-and-space pattern. The height of the convex portion is adjusted by etching.

In the second step of the two-step method, gravity, centrifugal force, frictional force, etc. are used as the force applied to the substrate 41. When gravity is used, the convex portions are softened by heating or applying chemicals, and the substrate 41 is temporarily held in the vertical direction as shown in FIG. In FIG. 20, the dotted line is the initial shape of the convex portion,
The solid line represents the shape after being deformed by gravity. afterwards,
The convex portion is hardened by cooling or drying the chemical, and the deformed shape is fixed.

When utilizing the centrifugal force, the substrate 41 having the convex portion softened is attached to the disk 46 as shown in FIG.
The disc 46 is rotated. The centrifugal force can be adjusted by the rotation speed, and the inclination angle of the wall surface can be finely controlled. In the case of utilizing the frictional force, as shown in FIG. 22, a nozzle 47 is arranged beside the substrate 41 whose convex portion is softened, and a gas or a liquid is projected from the nozzle 47 in a direction parallel to the substrate 41. Spray on the department. Alternatively, as shown in FIG. 23, the softened convex portion is rubbed with the cloth rod 48 in one direction. In either case, the convex portion inclines toward the downstream side (direction of the arrow) in the direction of the force, and the wall surface inclines with respect to the plane of the entire lattice shape.

The one-step method can be performed by dry etching or two-beam interference method. FIG. 24 schematically shows how the lattice shape is formed by etching. Board 4
A mask 49 having a fine line-and-space pattern is provided on the substrate 1, and etching ions are guided from a direction oblique to the substrate 41 as indicated by an arrow. When adopting the two-beam interference method, as shown in FIG. 25, a resist 42 is provided on the substrate 41, and the two beams are irradiated so that the bisector of the angle formed by the two beams is inclined with respect to the substrate 41. To do. The angle α formed by the bisector of the angle formed by the two light fluxes and the normal line of the substrate 41 is
It becomes the inclination angle of the wall surface. After patterning the resist 42, etching is performed as necessary to adjust the height of the convex portion.

The member 30a is manufactured by using a mold made from a prototype.
Alternatively, FIG. 26 shows how 30b is molded. As the mold, a moving mold 51 manufactured from a prototype and having a desired inverted lattice shape and a flat plate-shaped fixed mold 52 are used. After the molding, when separating the molds 51 and 52 from the member 30a or 30b, in order to avoid the damage of the convex portion of the member 30a or 30b, the mold 51 is parallel to the wall surface 35a.
To move. In order to reliably move the mold 51 in this direction, it is desirable to form a guide surface 51a parallel to the wall surface 35a at the part of the mold 51 that is the edge of the member 30a or 30b.

The diffraction grating 35 has two members 30a and 30b.
When it is provided on the interface 34, one of the members 30a and 30b is formed by molding, and the liquid material to be the other is poured into the lattice shape to form the optical element 30. It does not matter which of the members 30a and 30b is manufactured by molding.

It should be noted that thick photosensitive materials and photosensitive resin materials are
A volume hologram produced by recording interference fringes caused by light flux light can have a change in refractive index due to a layered structure in which the period is equal to or less than the wavelength of light to be diffracted and is parallel to each other.
The present invention can be made to have the desired optical characteristics. However, the range of change in the refractive index in the material is 0.05
Since it is as narrow as or less than that, it is necessary to increase the thickness of the material and it is difficult to manufacture it by molding.

FIG. 27 schematically shows the optical configuration of the image display device 7 of the seventh embodiment. The image display device 7 is
Two transmissive image display devices 10 ′, a light source unit 20 for supplying illumination light to the image display device 10 ′, and two illumination light beams from the light source unit 20 arranged between the two image display devices 10 ′. It is composed of a transparent and plate-like optical element 30 'for illumination which leads to one image display 10'.

The illumination optical element 30 'in the image display device 7 has a diffraction grating 35' whose wall surfaces are substantially parallel to each other and substantially perpendicular to the plane as a whole. This diffraction grating 3
5'has a shape close to that shown in FIG. 8, and this optical element 30 'has a diffraction efficiency of transmitted light in this lattice shape as shown in the "rectangle" column of Table 1 above. η
This is based on the fact that there is no significant difference between the diffraction efficiency ηr of t and the reflected light.

The optical element 30 'comprises three plate-shaped members 30.
a, 30b, 30c are joined together to form a diffraction grating 35 '.
Is the first member 30a and the second member 30 located at the center.
It is provided at the interface 34 with b. Second and third members 3
The refractive indices of 0b and 30c are equal to each other and smaller than the refractive index of the first member 30a. The optical element 30 ′ allows the light from the light source unit 20 to enter the first member 30 a from the end face 33, and
While traveling through the member 30a, the transmitted light emitted from one emission surface 31 and the reflected light emitted from the other emission surface 32 are generated by diffraction in the diffraction grating 35 '.

Even in the conventional optical element for illumination having a satin-finished surface or a prism array, it is possible to illuminate two image displays with the same brightness by using two surfaces as a satin-finished surface or a prism array. Is. However, it is difficult to control the transmissivity of the satin surface or the prism array so that the entire image display can be illuminated with uniform brightness.

On the other hand, in the diffraction grating 35 ', it is easy to control the transmittance for each site by setting the diffraction efficiency ηt, ηr or the area ratio S. Further, the wall surfaces are not strictly perpendicular to the plane of the diffraction grating 35 'as a whole, but are tilted slightly in one direction so that the diffraction efficiencies ηt and ηr of the transmitted light and the reflected light are substantially equal to each other. It is also possible to illuminate the two video displays 10 'with the same brightness. For this purpose, the inclination angle of the wall surface may be 5 ° or less. Furthermore, the first
The diffraction grating 35 ′ may be provided only on the interface between the member 30 a and the second member 30 b, and it is not necessary to provide the diffraction grating even on the interface between the first member 30 a and the third member 30 c. Is also excellent.

A setting example of the diffraction grating 35 'is shown in Table 5, and the relationship between the wavelength wl and the diffraction efficiencies ηt and ηr of transmitted light and reflected light in this setting example is shown in FIG. In addition, here
Since the inclination angle α of the wall surface is 0 °, the diffraction efficiency ηt,
Although there is a slight difference in ηr, the difference between the diffraction efficiencies ηt and ηr can be almost eliminated by slightly inclining the wall surface as described above.

<Table 5> Shape Λ / λ h / Λ a / Λ n1 n2 α θ1 Rectangle 0.6725 0.5 0.5 1.5 1.3 0 # 65 #

If the cross section of the diffraction grating is substantially symmetrical, for example, even if the cross section has a sine wave shape or an isosceles triangular shape, the diffraction efficiency of transmitted light and reflected light is designed in the same manner as the diffraction grating 35 '. It is possible to make them equal. However, it is actually difficult to manufacture a diffraction grating having such a complicated cross-sectional shape as designed. On the other hand, the diffraction grating 35 ′ whose wall surfaces are substantially parallel can be easily manufactured almost as designed, and the set diffraction condition can be well expressed.

[0090]

A transparent, plate-like optical element for illumination which is arranged toward an object to be illuminated with one of two facing surfaces as an emission surface, and which has a diffraction grating along the emission surface. , The light is made incident from the end portion, is diffracted by the diffraction grating while the light is traveling inside, and is emitted from the emission surface. The height difference is equal to or less than the central wavelength of the wavelength range of the light incident from the end, and the wall surface that is the surface between the convex portion and the concave portion of the diffraction grating is substantially parallel to each other and the surface of the diffraction grating as a whole. With the configuration that is inclined with respect to, it is possible to set a desired diffraction condition for the entire wavelength range of the light used for illumination, and furthermore, a diffraction grating that can well express the set diffraction condition. Optical element with excellent characteristics because it has It made. Moreover, it is easy to manufacture.

In particular, since the wall surface of the diffraction grating is inclined with respect to the surface of the entire diffraction grating, the light reflected by the diffraction grating or transmitted through the diffraction grating and traveling in the same direction as the light from the illumination target object. Can be suppressed to a very small amount, and a decrease in contrast when observing the illumination target from the surface side facing the emission surface can be suppressed well.

If two members having different refractive indexes are joined to form an optical element and the diffraction grating is provided at the interface between the two members, the diffraction grating will be in a protected state. It is not necessary to separately provide the member.

When the inclination angle of the wall surface of the diffraction grating with respect to the surface of the entire diffraction grating is 5 ° or more, the amount of light reflected by the diffraction grating or transmitted through the diffraction grating and traveling in the same direction as the light from the illumination target. It becomes easy to suppress the value to a very small degree.

The diffraction grating is located on the emission surface side with respect to the path of light, and the wall surface of the diffraction grating is inclined in a direction away from the end portion through which light is incident on the portion farther from the surface facing the emission surface. In addition, the diffraction grating is located on the surface side facing the exit surface with respect to the path of the light, and the wall surface of the diffraction grating is inclined in a direction closer to the end where light is incident, as far as it is from the exit surface. With such a setting, the amount of light reflected by the diffraction grating or transmitted through the diffraction grating and traveling in the same direction as the light from the illumination target can be reliably suppressed to an extremely small amount.

When a diffraction grating is provided at the interface between two members having different refractive indices, the one of the two members farther from the emission surface has a larger refractive index than the one closer to the emission surface,
The closer the wall surface of the diffraction grating is to the exit surface, the more inclined it is in the direction away from the end where light is incident.
Of the two members, the one closer to the emission surface has a larger refractive index than the one farther from the emission surface, and the wall surface of the diffraction grating is inclined in the direction closer to the end where light is incident, as far away from the emission surface as possible. The same applies to the setting.

A diffraction grating is produced by forming a lattice shape in which the entire surface is a plane surface and the wall surface is substantially perpendicular to the entire plane surface and applying a force in a direction along the entire plane surface to deform the convex portion. The method for producing the optical element described above for forming the shape is extremely simple.

The method of directly forming the shape of the diffraction grating by etching or the two-beam interference method is also simple.

If the diffraction grating is manufactured by molding using a metal mold having a shape complementary to the diffraction grating, variations in the characteristics of the optical element can be suppressed, and mass production is easy.

In an image display device provided with an image display device for modulating illumination light into light representing an image, a light source for emitting the illumination light, and an illumination optical system for guiding the illumination light emitted by the light source to the image display, When the above-mentioned optical element is provided as the illumination optical system, the diffraction grating of the optical element can almost express the diffraction condition as set, so that it is possible to provide a high quality image. Moreover, by providing the diffraction grating of the optical element on the emission surface and disposing the emission surface close to the image display device, a thin image display device can be obtained. When an optical element provided with a diffraction grating is provided at the interface between two members,
It becomes a thin image display device.

In particular, even when the image display is of a reflection type that modulates illumination light and modulates it into light representing an image, it is possible to prevent the occurrence of blurring and moire fringes, and to use the diffraction grating of the optical element. Due to the feature (1), it is possible to suppress the deterioration of the contrast satisfactorily and to provide a high quality image.

A transparent plate-like optical element for illumination which is arranged toward two illumination objects with both of the two facing surfaces as emission surfaces, and which has a diffraction grating along the emission surfaces,
As in the present invention, in which light is incident from an end portion, diffracted by the diffraction grating while the light travels inside, and emitted from the emission surface, the period of the diffraction grating and the height of the convex and concave portions are reduced. If the difference is equal to or less than the central wavelength of the wavelength range of light incident from the end, and the wall surface that is the surface between the convex portion and the concave portion of the diffraction grating is configured to be substantially parallel to each other,
It is possible to set a desired diffraction condition for the entire wavelength range of light used for illumination, and further, since it has a diffraction grating that can well express the set diffraction condition,
It becomes an optical element with excellent characteristics. Moreover, it is easy to manufacture.

When two members having different refractive indexes are joined to form an optical element and the diffraction grating is provided at the interface between the two members, it is not necessary to separately provide a member for protecting the diffraction grating.

Illumination that guides the illumination light emitted from the light source and the light source that emits the illumination light to the two image display devices that transmits the illumination light and modulates the light to represent the image. In the image display device including the optical system, when the above-mentioned optical element is provided as the illumination optical system, the diffraction grating of the optical element can almost express the set diffraction condition, thereby providing a high-quality image. It is possible. Even when the diffraction grating is provided on the surface of the optical element, that is, the exit surface, by disposing the exit surface close to the image display,
A member for protecting the diffraction grating is not needed, and a thin image display device can be obtained. Even when an optical element having a diffraction grating provided at the interface between two members is provided, a thin image display device is obtained.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an optical configuration of a video display device according to a first embodiment.

FIG. 2 is a sectional view schematically showing an optical configuration of an image display device according to a second embodiment.

FIG. 3 is an enlarged cross-sectional view schematically showing the shape of the diffraction grating of the optical element used in the first to sixth embodiments.

FIG. 4 is a diagram showing a principle of reducing the contrast of an image provided by unnecessary diffracted light in an optical element for illumination having a diffraction grating.

FIG. 5 is a diagram showing an example of a relationship between a diffraction efficiency ratio of an optical element and a contrast of an observed image in the image display device of the second embodiment.

FIG. 6 is an enlarged cross-sectional view schematically showing another shape of the diffraction grating of the optical element used in the first to sixth embodiments.

FIG. 7 is an enlarged sectional view schematically showing the shape of a blazed diffraction grating.

FIG. 8 is an enlarged cross-sectional view schematically showing the shape of a diffraction grating whose wall surface is perpendicular to the plane of the entire grating.

FIG. 9 is a sectional view schematically showing an optical configuration of an image display device according to a third embodiment.

FIG. 10 is a cross-sectional view schematically showing an optical configuration of the image display device of the fourth embodiment.

FIG. 11 is a diagram illustrating the amount of light emitted from each part of the illumination optical element.

FIG. 12 is a diagram showing an example of the relationship between the wavelength of light and the diffraction efficiency of transmitted light in the optical element of the image display device of the first embodiment.

FIG. 13 is a diagram showing an example of the relationship between the wavelength of light and the diffraction efficiency ratio in the optical element of the image display device of the first embodiment.

FIG. 14 is a diagram showing an example of the relationship between the wavelength of light and the diffraction efficiency of reflected light in the optical element of the image display device of the fourth embodiment.

FIG. 15 is a diagram showing an example of the relationship between the wavelength of light and the diffraction efficiency ratio in the optical element of the image display device of the fourth embodiment.

FIG. 16 is a sectional view schematically showing a configuration example of a reflective liquid crystal display used as a video display in the video display devices of the first to fourth embodiments.

FIG. 17 is a cross-sectional view schematically showing an optical configuration of the image display device of the fifth embodiment.

FIG. 18 is a sectional view schematically showing the outline of the optical configuration of the image display device of the sixth embodiment.

FIG. 19 is a diagram schematically showing a first step of a method for producing the shape of the diffraction grating of the optical element used in the first to sixth embodiments in two steps.

FIG. 20 is a diagram schematically showing a second step of the method for producing the shape of the diffraction grating of the optical element used in the first to sixth embodiments in two steps.

FIG. 21 is a diagram schematically showing another second step of the method for producing the shape of the diffraction grating of the optical element used in the first to sixth embodiments in two steps.

FIG. 22 is a diagram schematically showing another second step of the method for producing the shape of the diffraction grating of the optical element used in the first to sixth embodiments in two steps.

FIG. 23 is a diagram schematically showing another second step of the method of producing the shape of the diffraction grating of the optical element used in the first to sixth embodiments in two steps.

FIG. 24 is a diagram schematically showing a method of forming the shape of the diffraction grating of the optical element used in the first to sixth embodiments in one step.

FIG. 25 is a diagram schematically showing another method for producing the shape of the diffraction grating of the optical element used in the first to sixth embodiments in one step.

FIG. 26 is a cross-sectional view showing how the diffraction grating of the optical element used in the first to sixth embodiments is produced by molding.

FIG. 27 is a cross-sectional view that schematically shows the outline of the optical configuration of the video display device of the seventh embodiment.

FIG. 28 is a diagram showing an example of the relationship between the wavelength of light and the diffraction efficiency of transmitted light and reflected light in the optical element of the image display device of the seventh embodiment.

[Explanation of symbols]

1, 2, 3, 4, 5, 6, 7 Video display device 10 Reflective image display 10 'transmissive image display 11 Polarizer 12 Phase plate 13 Transparent substrate 14 color filters 15 Liquid crystal layer 16 Diffuse reflection electrode 20 light source 21 Light emitting element 22 reflector 30 Illumination optical element 30 'illuminating optical element 30a First member 3bb Second member 30c Third member 31 surface 32 surface 33 Edge 34 Interface 35 diffraction grating 35 'diffraction grating 35a wall surface 41 prototype substrate 42 resist 43 electron beam drawing machine 44 stepper 45 two-beam interferometer 46 rotating disk 47 nozzles 48 cloth stick 49 mask 51 moving mold 51a guide surface 52 Fixed mold

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Claims (17)

[Claims] 1. A transparent, plate-like optical element for illumination, which is disposed toward an object to be illuminated with one of two facing surfaces as an emission surface and has a diffraction grating along the emission surface. , The light is made incident from the end, diffracted by the diffraction grating while the light travels inside, and is emitted from the emitting surface. The period of the diffraction grating and the height difference between the convex and the concave are different from the end. The wavelength is equal to or less than the central wavelength of the wavelength range of the incident light, and the wall surface that is the surface between the convex portion and the concave portion of the diffraction grating is substantially parallel to each other and is inclined with respect to the surface of the diffraction grating An optical element characterized by being present. 2. The optical element according to claim 1, which is formed by joining two members having different refractive indexes, and a diffraction grating is provided at an interface between the two members. 3. The optical element according to claim 1, wherein the angle of inclination of the wall surface of the diffraction grating with respect to the surface of the diffraction grating as a whole is 5 ° or more. 4. The diffraction grating is positioned on the exit surface side with respect to the path of light, and the wall surface of the diffraction grating is inclined in a direction away from the end portion through which light is incident, as far away from the surface facing the exit surface as possible. The optical element according to any one of claims 1 to 3, wherein: 5. The diffraction grating is located on the surface side opposite to the emission surface with respect to the path of light, and the wall surface of the diffraction grating is inclined in a direction closer to the end portion through which light is incident, the farther from the emission surface. The optical element according to any one of claims 1 to 3, wherein: 6. The direction farther from the exit surface of the two members has a larger refractive index than the one closer to the exit surface, and the closer the wall surface of the diffraction grating is to the exit surface, the more distant from the end where light is incident. The optical element according to claim 2 or claim 3, wherein the optical element is inclined. 7. The direction closer to the emission surface of the two members has a larger refractive index than the one farther from the emission surface, and the wall surface of the diffraction grating is closer to the end portion through which light is incident, as far away from the emission surface as possible. The optical element according to claim 2 or claim 3, wherein the optical element is inclined. 8. A lattice shape having a plane as a whole and a wall surface substantially perpendicular to the plane of the whole is produced, and a force in a direction along the plane of the whole is applied to the lattice shape to deform the convex portion, The method of manufacturing an optical element according to claim 1, wherein a shape of a diffraction grating is formed. 9. The method of manufacturing an optical element according to claim 1, wherein the shape of the diffraction grating is directly formed by etching. 10. The method of manufacturing an optical element according to claim 1, wherein the shape of the diffraction grating is directly formed by a two-beam interference method. 11. The method of manufacturing an optical element according to claim 1, wherein the diffraction grating is manufactured by molding using a mold having a shape complementary to the diffraction grating. 12. An image display device including an image display device that modulates illumination light into light representing an image, a light source that emits the illumination light, and an illumination optical system that guides the illumination light emitted by the light source to the image display device. A video display device comprising the optical element according to any one of claims 1 to 7 as an illumination optical system. 13. The image display device according to claim 12, wherein the image display device is a reflection type device that modulates the illumination light while modulating it to obtain light representing an image. 14. The video display device according to claim 12, wherein the video display is a transmissive type that modulates while illuminating light is transmitted and is modulated into light representing an image. 15. A transparent, plate-like optical element for illumination, which is arranged toward two illumination objects with both of two facing surfaces as emission surfaces, and which has a diffraction grating along the emission surfaces. , The light is made incident from the end, diffracted by the diffraction grating while the light travels inside, and is emitted from the emitting surface. The period of the diffraction grating and the height difference between the convex and the concave are different from the end. An optical element having a wavelength equal to or less than the central wavelength of the wavelength range of incident light and having a wall surface that is a surface between the convex portion and the concave portion of the diffraction grating being substantially parallel to each other. 16. The optical element according to claim 15, which is formed by joining two members having different refractive indexes, and a diffraction grating is provided at an interface between the two members. 17. A transmission-type two image display device that modulates illumination light while transmitting it to generate light representing an image, a light source that emits the illumination light, and the illumination light that the light source emits to two image displays. An image display device provided with an illumination optical system for guiding the image display device, comprising the optical element according to claim 15 or 16 as an illumination optical system.