JP2002014213A - Blaze grating device, diffraction grating device and illumination optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical device which can well separate light rays different in characteristics although it is thin in thickness and light in weight. SOLUTION: A blaze grating is formed on the surface of a planar transparent substrate and separation coatings to reflect or transmit the incident light according to the characteristics of the incident light are applied on the blaze grating to obtain an optical device having both functions to separate the light into reflected light and transmitted light and to diffract or refract the separated light. Polarization separation films, dichroic films, angle separation films or chiral nematic liquid crystal layers are used as for the separation coatings so as to separate linearly polarized light rays different in polarization plane, light rays different in wavelength, light rays different in incident angle or circularly polarized light rays different in rotation direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blazed grating element and a diffraction grating element, and an illumination optical system including the same.

[0002]

2. Description of the Related Art Illumination light is modulated by a spatial modulation element,
In an image display device in which an image is represented by modulated light,
Various optical elements are used to guide illumination light to the spatial modulation element. Liquid crystal display (LC) as spatial modulation element
When D) is used, the LCD needs to provide a linearly polarized light having a constant polarization plane. For this reason, when using a light source that emits non-polarized light, a polarized light separating (PBS) prism or a polarizing plate is used to extract linearly polarized light suitable for an LCD.

FIG. 21 shows the structure of a PBS prism. P
The BS prism has a configuration in which a PBS film 51c is sandwiched between two prism pieces 51a and 51b whose cross sections are right isosceles triangles. The PBS film 51c selectively separates one of the P-polarized light and the S-polarized light by selectively transmitting the other and selectively reflecting the other. However, in general, unless the incident angle is about 45 ° or more, the selectivity of transmission and reflection is reduced. And separation cannot be performed satisfactorily. For this reason, the two prism pieces 51a, 51
It is in the form of a square prism PBS prism sandwiched by b.

A polarizing plate also transmits linearly polarized light having a constant polarization plane, but absorbs other polarized light components rather than reflecting them.
In PBS prism, both transmitted light and reflected light are LCD
Can be used for the illumination, but only the transmitted light is available in the polarizing plate.

In the case of a reflection type LCD, since the optical path of the illumination light for illuminating the LCD and the optical path of the reflected light from the LCD coincide, the optical path of the illumination light and the reflected light representing an image are separated somewhere on the optical path. There is a need. For this purpose, an optical element that reflects one of the illumination light and the reflected light and transmits the other is used.

The above PBS prism is also used for this purpose. When a reflection type LCD is set so that light modulated and rotated by 90 ° represents an image, when light transmitted through the PBS prism is used as illumination light, light representing the image is reflected by the PBS prism. And also
When the light reflected by the PBS prism is used as the illumination light, the light representing the image passes through the PBS prism, and in any case, the reflected light representing the image is directed in a direction different from the direction toward the light source. I can guide you.

FIG. 22 shows another optical element for separating illumination light and reflected light. This optical element is formed by forming a large number of V-shaped grooves 52d in cross section on the upper surface 52a of a transparent flat plate 52, and is arranged with the lower surface 52b facing the reflective LCD 53. Light from the light source is applied to the flat plate 5 from the end face 52c of the flat plate 52.
2 and travels in the flat plate 52 while undergoing total internal reflection on the upper surface 52a and the lower surface 52b. In the meantime, the light
d, and is reflected by the surface of
Illuminate CD53. The light reflected by the LCD 53 enters the flat plate 52 from the lower surface 52b, passes through the upper surface 52a, and exits outside.

A polarizing plate 54 for converting illumination light into linearly polarized light is disposed between the flat plate 52 and the LCD 53. LCD
Numeral 53 is controlled so that the linearly polarized light whose polarization plane has not been rotated even after the modulation is the linearly polarized light whose polarization plane has not been rotated by 90 ° becomes light representing an image.

As one method of displaying color images, an LCD
Each of the pixels has a color filter that selectively transmits red (R) light, green (G) light, or blue (B) light. However, in this configuration, 2/3 of the white light from the light source is lost by the color filter, and it cannot be said that the light use efficiency is excellent. Thus, in recent years, the illumination light is separated into R light, G light, and B light whose traveling directions are slightly different from each other.
G light and B light have been incident on separate pixels.

FIG. 23 shows an optical system used for color separation in this method. This optical system includes three dichroic mirrors 55R, 55G, and 55B. Dichroic mirrors 55R, 55G, and 55B are R light, G light, respectively.
Light and B light are selectively reflected and light of other colors is transmitted. The mirrors 55R, 55G, and 55B are arranged at an angle to each other, and reflect incident light in different directions. Mirrors 55R, 55R are provided on the optical paths of the reflected R light, G light, and B light.
An angle difference of twice the angle between G and 55B occurs.

As shown in FIG. 24, a micro lens array 56 provided on the LCD 53
a is set so as to face the adjacent three pixels 53R, 53G, and 53B. The R light, the G light, and the B light enter the microlenses 56a from different directions, and the microlenses converge the R light, the G light, and the B light onto different pixels 53R, 53G, and 53B, respectively. Let it. Thus, all the light from the light source is guided to the pixels of the LCD 53, and it is possible to provide a bright image.

A digital micromirror device (DMD) in which a large number of minute mirror elements whose angles are variable are arranged two-dimensionally.
Is also used as a spatial modulation element. Each mirror element of the DMD selectively reflects incident light in one of two predetermined directions depending on its angle. DM
Of the light reflected in two directions by D, one is extracted as light representing an image, and the other is discarded as unnecessary light.

FIG. 25 shows a general optical system for illuminating a DMD. This optical system includes two prisms 57a,
57b are arranged slightly apart from each other. Light from the light source is guided into the prism 57a from the side. The surface 57c facing the prism 57b is set so that the incident angle of the introduced light exceeds the critical angle, the light is totally reflected by the surface 57c, passes through the surface 57d, and passes through the DMD 58.
To illuminate. The light reflected by the DMD 58 is separated into light representing an image and unnecessary light while being separated from the surface 57d by a prism 57a.
to go into. The light entering the prism 57a reaches the surface 57c,
Since the incident angle is smaller than the critical angle, it is transmitted therethrough, and is also transmitted through the prism 57b. Thus, the optical system that illuminates the DMD utilizes the total reflection and transmission of light by the prism surface.

[0014]

Since the polarizing plate has a simple structure and is flat, it is very easy to use. However, the transmittance of linearly polarized light passing through the polarizing plate is only about 80%, and a loss occurs in the amount of light. In addition, the polarizing plate absorbs all the polarized light components other than the linearly polarized light that passes through it, so that the temperature of the polarizing plate becomes high, which adversely affects other elements such as an LCD disposed in the vicinity. When the light intensity is increased to display a bright image, the temperature of the polarizing plate becomes particularly high.

Since the PBS prism does not absorb light, there is no disadvantage that the temperature becomes high, and both the transmitted light and the reflected light can be used. Further, it is easy to make the transmittance and the reflectance approximately 100%, which is excellent in light use efficiency. However, since the PBS prism has a thickness equal to the width of the incident surface, the display device is increased in size and weight. When using a projection-type device that projects light representing an image on a screen and forms an image on the screen, the lens back of the projection optical system becomes longer, and a large projection optical system is required to display bright images. Become.
The problem of increasing the size and weight of the device also applies to the optical system of FIG. 25 that uses a prism.

The optical element shown in FIG. 22 has a simple structure in which a groove is provided in a flat plate and is easy to use. However, a part of the reflected light from the LCD entering the flat plate is reflected by the surface of the groove. ,
It cannot pass through a flat plate. Therefore, a striped dark portion occurs in the displayed image. Reducing the width of the groove can reduce the visibility of dark areas to some extent, but is not an essential solution.

The optical system composed of three dichroic mirrors shown in FIG. 23 is excellent in terms of light use efficiency, but since each dichroic mirror is a separate element, the mutual angles are accurately set. Difficult to do. Therefore, it takes time to assemble the optical system, and the manufacturing efficiency is reduced.

Incidentally, diffractive optical elements having a lattice surface in which minute concave-convex structures are periodically arranged and changing the course of light by diffraction are used in various fields of optics. The diffractive optical element includes a bi-level element in which both a concave portion and a convex portion of the grating surface are flat and the level (height) of the flat portion is two.
There are a multi-level element having one or more levels between a concave part and a convex part, and a blazed element having a slope and a saw-tooth cross section. Any diffractive optical element can be of a transmission type that causes diffraction of transmitted light, or a reflection type of coating a grating surface with a reflective film to cause diffraction of reflected light. In the case of a transmission type, an antireflection film is coated on a grating surface to increase the transmittance.

Although not a diffractive optical element, the Fresnel lens also has a large number of small inclined surfaces, and is a blazed element having a sawtooth cross section. Diffractive optical elements have a difference in elevation of about the same as the wavelength of light, which causes diffraction. Fresnel lenses have a difference in elevation of several irregularities that is several times or more the wavelength. To change.

The diffractive optical element and the Fresnel lens have a great feature that they are thin optical elements. However, these grating surfaces are merely coated with a reflection film or an antireflection film, and there is no example in which a functional coating that acts according to the characteristics of light is applied.

The present invention has been made in view of the above-mentioned problems and the current situation of optical elements having a lattice plane, and is an optical element capable of separating light having different characteristics satisfactorily while being thin and lightweight. The purpose is to provide.

[0022]

In order to achieve the above object, according to the present invention, there is provided a plate-shaped transparent base material having a blazed grating on the surface, and a transparent base material provided on the blazed grating, the characteristics of incident light. And a separation coating that reflects or transmits incident light according to the above.

Although this element is a single thin optical element, it has two functions. That is, the incident light can be separated into reflected light and transmitted light by the separation coating according to its characteristics, and the blazed grating can act on the separated transmitted light or reflected light or both. The blaze grating functions as a diffraction grating when the height difference between the irregularities is about the wavelength of the incident light, and acts as a Fresnel lens or mirror when the height difference is about several times the wavelength of the incident light or more.

It is preferable to provide a plate-shaped transparent material in close contact with the blaze grid of the transparent substrate with the separation coating interposed therebetween. The grid surface can be protected. Further, by making the transparent base material and the transparent material from the same material, unnecessary modulation of transmitted light can be avoided. In this case, the blazed grating acts only on the reflected light.

The transparent material has a blazed grating on the surface opposite to the transparent substrate, and is provided on the blazed grating of the transparent material, and reflects the incident light according to the characteristics of the incident light. Alternatively, a configuration may be provided that includes a separation coating to be transmitted and a plate-shaped transparent material that is in close contact with the transparent material blaze grating with the separation coating interposed therebetween. This way,
The transmitted light separated by one separation coating can be further separated into reflected light and transmitted light by the other separation coating. In addition, by inverting the inclination directions of the blaze surfaces of the two blaze gratings, it is possible to avoid incomplete separation due to the incident angle.

The separation coating can reflect or transmit the incident light depending on the polarization characteristics of the incident light. Since the separation coating is provided on the inclined blaze surface, even if it is arranged so that the incident angle to the element is less than 45 °, the incident angle of light to the separation coating can be 45 ° or more. is there. Therefore,
PB with good polarization separation characteristics despite being flat
An S element is obtained.

The separating coating may reflect or transmit the incident light according to the wavelength of the incident light, or reflect or transmit the incident light according to the incident angle of the incident light. Can also. In any case, it is possible not only to separate the light in accordance with the wavelength or the incident angle, but also to exert the function of the blazed grating on the separated light.

In order to achieve the above object, the present invention also provides a plate-shaped transparent substrate having a diffraction grating on the surface and a transparent substrate provided on the diffraction grating, and the incident light is provided in accordance with the polarization characteristics of the incident light. A separation coating that reflects or transmits light;
A plate-like transparent material closely adhered to the diffraction grating of the transparent substrate with the separation coating interposed therebetween constitutes a diffraction grating element.

Although this element is a single thin optical element, it has both the function of polarization separation and the function of diffraction. That is, the incident light can be separated into reflected light and transmitted light by the separation coating according to the polarization characteristics, and the reflected light can be diffracted to change the reflection angle.

Here, it is preferable that the light reflected by the transparent substrate on the separation coating is totally internally reflected and guided to the end face. When only the transmitted light after separation is required, unnecessary reflected light can be discarded from the end face of the element, and the processing of the reflected light becomes easy. In addition, the element does not become hot due to light absorption.

In order to achieve the above object, the present invention further provides a plate-shaped transparent substrate having a diffraction grating on the surface, and a transparent substrate provided on the diffraction grating. The illumination optical system includes a diffraction grating element including a separation coating that reflects or transmits light, and guides light to the illumination target object by the diffraction grating element to illuminate the illumination target object, and reflects the light reflected by the illumination target object. Is transmitted through the diffraction grating element and guided to the outside.

This illumination optical system is, for example, a reflection type LC.
It can be used for D and DMD illumination. Although the optical paths of the illumination light and the reflected light from the illumination target overlap, the combination of the function of the diffraction grating and the function of the separation coating makes it easy to extract only the reflected light from the illumination target.

The diffraction grating element may be provided with a plate-shaped transparent material in close contact with the diffraction grating of the transparent substrate with the separation coating interposed therebetween. In addition to protecting the diffraction grating and the separation coating, unnecessary modulation of reflected light from the illumination target that passes through the element can be avoided.

The separation coating may reflect or transmit the incident light according to the incident angle of the incident light.
It becomes very easy to arrange the light source outside the optical path of the light from the illumination object after passing through the diffraction grating element. For example, it is possible to adopt a configuration in which light from a light source is guided into the diffraction grating element from the end face of the diffraction grating element.

The separation coating may be a chiral nematic liquid crystal layer that reflects one of two circularly polarized lights having different rotation directions and transmits the other. Illumination light and reflected light from the illumination target can be reliably separated.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic structures of a blazed grating element and a diffraction grating element according to the present invention are schematically shown in FIGS. FIG. 1 shows a blazed grating element 1 having the simplest configuration in which a blazed grating 12 is formed on the surface of a flat transparent substrate 11 and a separation coating 13 is provided on the blazed grating 12. The transparent substrate 11 can be made of, for example, resin or glass.

If the height difference between the irregularities of the blazed grating 12 is set to about the wavelength of light, the blazed grating 12 becomes a diffraction grating.
The blaze grating element 1 becomes a diffraction grating element. If the height difference between the irregularities of the blazed grating 12 is made several times the wavelength of light or more, the blazed grating 12 becomes a Fresnel lens surface, and the blazed grating element 1 becomes a Fresnel lens or a thin mirror having power.

FIG. 2 shows a blazed grating element 2 in which a flat plate-shaped transparent material 14 which is in close contact with the blazed grating 12 with a separation coating 13 interposed therebetween is added to the blazed grating element 1 of FIG. The transparent member 14 can also be made of resin or glass. The materials of the transparent substrate 11 and the transparent material 14 may be the same or different. In the blaze grating element 2, the blaze grating 12 and the separation coating 1
3 is in a protected form.

The separation coating 13 reflects or transmits the incident light according to the characteristics of the incident light. As the characteristics of the incident light, for example, the wavelength, the direction of the plane of polarization of linearly polarized light,
There are a rotation direction of the circularly polarized light, an incident angle with respect to the separation coating 13, and the like.

In the blazed grating element 1, the blazed grating 1
2 acts on both light transmitted through the separation coating 13 and light reflected by the separation coating 13. That is, the blaze grating 12 causes diffraction or refraction of transmitted light, and causes diffraction or reflection of reflected light at a reflection angle different from the incident angle.

In the blazed grating element 2, if the transparent substrate 11 and the transparent material 14 have different refractive indexes, the blazed grating 12
Like the blazed grating element 1, it acts on both the light transmitted through the separation coating 13 and the reflected light. On the other hand, if the transparent substrate 11 and the transparent material 14 have the same refractive index,
The blazed grating 12 acts only on the reflected light, and the blazed grating element 2 becomes a simple transparent parallel plate for the transmitted light.

Hereinafter, several embodiments in which the blaze grating element 2 is a diffractive optical element will be described. FIG. 3 schematically shows the configuration of the optical element 21 of the first embodiment and the effect on light. The optical element 21 includes a PBS film 13a as the separation coating 13. PBS membrane 13
a is set so as to transmit P-polarized light and reflect S-polarized light. The refractive indices of the transparent base material 11 and the transparent material 14 are 1.62, and the blaze angle of the blaze grating 12 (the individual blaze surface 1 with respect to the plane of the entire blaze grating).
2a) is 30 °.

The optical element 21 is used in such an arrangement that the incident angle of light on the transparent substrate 11 is 25 °. Light incident on the transparent substrate 11 at an incident angle of 25 ° is refracted to have an incident angle of 45 ° on the blaze surface 12a. Blaze surface 1
Of the light incident on 2a, a polarized light component that becomes P-polarized light with respect to the PBS film 13a passes through the PBS film 13a, passes through the transparent material 14, and exits the element 21. This light travels along an optical path that is parallel to and slightly displaced from the light before entering the element 21.

The polarization component that becomes S-polarized light with respect to the PBS film 13a is reflected by the PBS film 13a and
Is diffracted by The diffracted reflected light is the transparent substrate 11
At an incident angle exceeding the critical angle and is totally reflected. Most of the light totally reflected on the surface 11a is reflected on the blazed surface 12a, and the remaining portion transmitted between the two blazed surfaces 12a is also totally reflected on the surface 14a of the transparent material 14. These lights are repeatedly reflected on the surface 11 a of the transparent substrate 11, the blazed surface 12 a, and the surface 14 a of the transparent material 14, reach the end face of the element 21, and exit from the end face.

In this optical element 21, a polarized light component that becomes P-polarized light with respect to the PBS film 13a can be extracted with almost no change in the course, and a polarized light component that becomes S-polarized light with respect to the PBS film 13a is completely separated. Can be thrown away. Moreover, since the element 21 does not absorb light, it does not become hot.

Table 1 shows the film configuration of the PBS film 13a, and FIG. 4 shows the relationship between the transmittance and the wavelength for P-polarized light and S-polarized light at an incident angle of 45 °. In Table 1, the layer number 0 is the transparent substrate 1
1 and the layer number 18 is the transparent material 14. The optical film thickness is represented by using 745 nm as a reference wavelength.

<Table 1> Composition of PBS film 13a Layer Refractive index Optical film thickness Layer Refractive index Optical film thickness 18 1.62 17 1.62 0.125 16 1.385 0.125 15 2.05 0.25 14 1.385 0.25 13 2.05 0.25 12 1.385 0.25 11 2.05 0.25 10 1.385 0.25 9 2.05 0.28 1.385 0.257 72 .05 0.26 6 1.385 0.25 5 2.05 0.25 4 1.385 0.25 3 2.55 0.25 2 1.385 0.125 1 1.62 0.125 0 1. 62

FIG. 5 shows an embodiment in which the optical element 21 is used as an illumination optical system of a reflection type LCD. Optical element 21 is LC
The light source 41 is disposed at an angle of 25 ° with respect to D31, and a linear light source 41 is disposed near the end face of the element 21. The light source 41 emits unpolarized light. The light emitted from the light source 41 is transmitted from the end face to the element 21.
And travels through the element 21 while undergoing total reflection. Of the light traveling inside the element 21, the polarized light component that becomes S-polarized light with respect to the PBS film 13 a is reflected by the PBS film 13 a, so that the incident angle with respect to the surface 11 a of the transparent substrate 11 changes, When the incident angle becomes smaller than the critical angle, the light passes through the surface 11a. The light transmitted through the surface 11a is LC
The illumination light is incident on D31 at an angle of about 90 °.

The operation of the LCD 31 is controlled such that linearly polarized light whose polarization plane is rotated by 90 ° by modulation becomes light representing an image. The light modulated and reflected by the LCD 31 enters the transparent substrate 11 at an incident angle of about 25 ° and enters the inside of the element 21. Of the light that has entered the element 21, the polarization component representing an image becomes P-polarized light with respect to the PBS film 13a,
The light passes through 3a and exits the element 21 from the transparent material 14.
On the other hand, other polarization components are reflected as S-polarized light with respect to the PBS film 13a, and are totally reflected as described above.
1 and exits toward the light source 41.

The distance of the space occupied by the optical element 21 in the direction perpendicular to the LCD 31 is 0.47 (tan 25 °) times the width of the luminous flux of the reflected light from the LCD 31.
It is less than half of the conventional PBS prism. Therefore,
When a projection-type image display device that projects light representing an image on a screen is used, the lens back of the projection optical system is significantly shortened, and the projection optical system can be downsized.

FIG. 6 schematically shows the structure of the optical element 22 of the second embodiment and the effect on light. Optical element 22
Is provided with a PBS film 13b as the separation coating 13. The PBS film 13b is opposite to the first embodiment,
It is set to reflect P-polarized light and transmit S-polarized light. The refractive indexes of the transparent base material 11 and the transparent material 14 are 1.87.
And the blaze angle of the blaze grating 12 is 60 °.

The optical element 22 can be used in such an arrangement that the incident angle of light on the transparent substrate 11 is 0 °. Light entering the transparent substrate 11 travels straight and enters the blazed surface 12a at an incident angle of 60 °. Of the light incident on the blazed surface 12a, a polarized light component that becomes S-polarized light with respect to the PBS film 13b passes through the PBS film 13b, also passes through the transparent material 14, and exits the element 22. This light travels on the extension of the optical path of the light before entering the element 22.

The polarization component that becomes P-polarized light with respect to the PBS film 13b is reflected by the PBS film 13b and
Is diffracted by The diffracted reflected light enters the surface 14a of the transparent member 14 at an incident angle exceeding the critical angle, is totally reflected, reaches the end face of the element 22, and exits from the end face in the same manner as in the first embodiment.

Table 2 shows the film configuration of the PBS film 13b, and FIG. 7 shows the relationship between the transmittance and the wavelength for P-polarized light and S-polarized light at an incident angle of 60 °. In Table 2, the layer number 0 is the transparent substrate 1
1 and the layer number 26 is the transparent material 14. The optical film thickness represents 280 nm as a reference wavelength.

<Table 2> Configuration of PBS film 13b Layer Refractive index Optical thickness Layer Refractive index Optical thickness 26 1.87 25 1.385 0.125 24 2.3 0.25 23 1.385 0.225 22 2.3 0.25 21 1.385 0.25 20 2.3 0.25 19 1.385 0.25 18 2.3 0.25 17 1.385 0.25 16 2.3 0.25 15 1 .385 0.25 14 2.3 0.25 13 1.385 0.25 12 2.3 0.25 11 1.385 0.25 10 2.3 0.225 9 1.385 0.25 8 2. 3 0.25 7 1.385 0.25 6 2.3 0.25 5 1.385 0.25 4 2.3 0.25 3 1.385 0.25 2 2.3 0.25 1 1.385 0.125 0 1.87

The optical element 22 can be used as an illumination optical system of a reflection type LCD, like the optical element 21 of the first embodiment. In this case, since the element 22 can be arranged parallel to the LCD, the distance in the direction perpendicular to the LCD required for the arrangement is extremely short.

FIG. 8 shows a mode in which the optical element 22 is used as an illumination optical system of a transmission type LCD and an optical system for selectively extracting light representing an image. LCD with two optical elements 22
32, and the light from the light source is incident on one of the elements 22 substantially perpendicularly. Of the light that has entered the element 22, the polarization component that becomes S-polarized light with respect to the PBS film 13 b passes through the element 22 and becomes illumination light that enters the LCD 32 at an angle of approximately 90 °. On the other hand, the polarized light component that becomes the P-polarized light with respect to the PBS film 13b is reflected, and reaches the end face while undergoing total reflection in the element 22. The light absorbing member 15 is attached to the end face of the element 22, and the light reaching the end face is absorbed by the absorbing member 15.

The operation of the LCD 32 is controlled such that linearly polarized light whose polarization plane does not rotate even after modulation becomes light representing an image. The light transmitted through the LCD 32 enters the other element 22, and a polarization component representing an image that becomes S-polarized light with respect to the PBS film 13 b passes through the element 22. The polarization plane is 90 due to modulation.
(4) The polarized light component that has been rotated and turned into P-polarized light with respect to the PBS film 13b is reflected, reaches the end face while undergoing total reflection in the element 22, and is absorbed by the absorbing member 15.

Conventionally, a polarizing plate has been used to illuminate a transmissive LCD or to extract light representing an image. However, by using the optical element 22 instead of the polarizing plate, the transmittance is increased and a bright image is provided. can do. Further, the element 22 does not reach a high temperature unlike a polarizing plate, and does not adversely affect the LCD.

FIG. 9 schematically shows the structure of the optical element 23 of the third embodiment and the effect on light. This optical element 23 has a blazed grating 12 also formed on the surface of a transparent material 14 of the optical element 22 of the second embodiment, and a PBS film 13b provided thereon as a separation coating 13 thereon.
Another transparent material 1 adhered to the transparent material 14 with the S film 13b interposed therebetween
4 is provided. That is, the optical element 23 has a configuration in which the optical elements 22 are overlapped. However, the inclination directions of the blaze surfaces 12a of the two blaze gratings 12 are opposite.

In this configuration, even if there is light directly transmitting between the two blazed surfaces 12 a of one blazed grating 12, the light is transmitted to the P
It can be separated by the BS film 13b. Therefore, the separation efficiency does not decrease due to the incident angle, and the degree of freedom of the arrangement angle with respect to the light to be separated increases.

FIG. 10 schematically shows the structure of the optical element 24 according to the fourth embodiment and its effect on light. This optical element 24 includes two sets of the blazed grating 12 and the separation coating 13 as in the optical element 23 of the third embodiment. The inclination directions of the blaze surfaces of the two blaze gratings 12 are opposite, and the blaze angle of each is about several degrees. As the separation coating 13 on the blaze grating 12 of the transparent substrate 11, a dichroic film 13 that selectively reflects B light
B is provided as a dichroic film 13G for selectively reflecting G light as the separation coating 13 on the blaze grating 12 of the transparent material 14. Further, the transparent substrate 1
A dichroic film 11R for selectively reflecting the R light is provided on the front surface 11a.

This optical element 24 converts white light into R light, G light,
The light is separated into B light, and an angle difference is caused in the optical path of each separated light. Of the white light incident on the element 24, the R light is reflected by the dichroic film 11R at a reflection angle equal to the incident angle. B light and G transmitted through the dichroic film 11R
The light enters the element 24, reaches the dichroic film 13B, and is separated into G light transmitted therethrough and B light reflected.

The B light reflected by the dichroic film 13B is diffracted by the blaze grating 12 and becomes light having an angular difference from the R light, and exits the element 24. The G light transmitted through the dichroic film 13B reaches the dichroic film 13G, is reflected, is diffracted by the blaze grating 12, and
The light and the B light are emitted to the outside of the element 24 as light having an angle difference.

Dichroic films 11R, 13B, 13G
Tables 3, 4, and 5 show the film configurations of Table 3 respectively. In Table 3, the layer number 0 is the transparent substrate 11, and the layer number 22 is air. In Table 4, the layer number 0 is the transparent base material 11, and the layer number 22 is the transparent material 14. In Table 5, the layer number 0 is the transparent material 14 on the transparent substrate 11 side, and the layer number 22 is the transparent material 14 on the front surface side. The optical film thickness is 765 nm for the dichroic film 11R, 451 nm for the dichroic film 13B, and 540 nm for the dichroic film 13G as reference wavelengths.

<Table 3> Constituent layers of dichroic film 11R Refractive index Optical thickness Layer Refractive index Optical thickness 22 1 121 1.385 0.14 20 2.3 0.28 19 1.47 0.28 18 2. 3 0.26 17 1.47 0.25 16 2.3 0.25 15 1.47 0.25 14 2.3 0.25 13 1.47 0.25 12 2.3 0.25 11 1.47 0.25 10 2.3 0.25 9 1.47 0.25 8 2.3 0.25 7 1.47 0.25 6 2.3 0.25 5 1.47 0.25 4 2.3 0 .26 3 1.47 0.28 2 2.3 0.28 1 1.67 0.14 1.52

<Table 4> Configuration of Dichroic Film 13B Layer Refractive Index Optical Thickness Layer Refractive Index Optical Thickness 22 1.52 21 2.3 0.09 20 1.385 0.3 19 2.3 0.15 18 1.47 0.3 17 2.3 0.225 16 1.47 0.25 15 2.3 0.25 14 1.47 0.25 13 2.3 0.25 12 1.47 0.25 11 2 .0.3 0.25 10 1.47 0.25 9 2.3 0.25 8 1.47 0.25 7 2.3 0.25 6 1.47 0.25 5 2.3 0.225 4 1. 47 0.3 3 2.3 0.15 2 1.385 0.3 1 2.3 0.1 0 1.52

<Table 5> Configuration of Dichroic Film 13G Layer Refractive Index Optical Thickness Layer Refractive Index Optical Thickness 22 1.52 21 2.3 0.09 20 1.385 0.3 19 2.3 0.15 18 1.47 0.3 17 2.3 0.225 16 1.47 0.25 15 2.3 0.25 14 1.47 0.25 13 2.3 0.25 12 1.47 0.25 11 2 .0.3 0.25 10 1.47 0.25 9 2.3 0.25 8 1.47 0.25 7 2.3 0.25 6 1.47 0.25 5 2.3 0.225 4 1. 47 0.3 3 2.3 0.15 2 1.385 0.3 1 2.3 0.1 0 1.52

The relationship between the transmittance and the wavelength of the dichroic films 11R, 13B, 13G for the P-polarized light and the S-polarized light at an incident angle of 45 ° is shown in FIGS. In addition, since refraction occurs when the light enters the transparent base material 11, even if the incident angle to the dichroic film 11R is 45 °, the actual incident angle of light to the dichroic films 13B and 13G changes from 45 °. When the blaze angle of the blaze grating 12 is about 5 °, the incident angle on the dichroic film 13B is about 32 °, and the incident angle on the dichroic film 13G is about 22 °.

The optical element 24 can be used as an illumination optical system for the LCD 53 shown in FIG. 24 having a microlens array. At this time, since the element 24 is a single member, it is not necessary to adjust the relative angle between the elements as in the optical system shown in FIG. 23, and the assembly can be performed quickly and accurately. In order to convert the light guided to the LCD 53 into linearly polarized light or to extract light representing an image from the modulated light, a polarizing plate or the above-described optical element 22 must be used.
May be used.

FIG. 14 schematically shows the structure of the optical element 25 of the fifth embodiment and its effect on light. The optical element 25 includes an angle separating film 13c that reflects or transmits light according to an incident angle as the separating coating 13. One of the lights incident on the element 25 from different directions is transmitted through the angle separating film 13c, and the other is transmitted through the angle separating film 13c.
The light is reflected by c and diffracted by the blazed grating 12, reaches the end face while undergoing total internal reflection, and exits the element 25.

Table 6 shows the film configuration of the angle separating film 13c.
FIG. 15 shows the relationship between the transmittance and the incident angle for light having a wavelength of 550 nm. In Table 6, the layer number 0 is the transparent base material 11, and the layer number 22 is the transparent material 14. Optical film thickness is 70
0 nm is represented as a reference wavelength.

<Table 6> Configuration of Angle Separating Film 13c Layer Refractive Index Optical Thickness Layer Refractive Index Optical Thickness 22 1.62 21 1.62 0.125 20 1.385 0.3525 19 2.2 0.3125 18 1.385 0.3525 17 2.2 0.1175 16 1.385 0.4075 15 2.2 0.125 14 1.385 0.4 13 2.2 0.105 12 1.385 0.395 11 2.2 0.135 10 1.385 0.338 9 2.2 0.275 8 1.385 0.3875 7 2.2 0.4475 6 1.385 0.3525 5 2.2 0.2975 4 1 .385 0.295 3 2.2 0.3225 2 1.385 0.3475 1 1.62 0.125 0 1.62

FIG. 16 shows a mode in which the optical element 25 is used as an illumination optical system of a reflection type LCD. Optical element 25 is L
The linear light source 41 is arranged in parallel with the CD 31 and near the end face of the element 25. Further, a polarizing plate 43 is arranged between the element 25 and the LCD 31. The light source 41 emits unpolarized light. Light emitted from the light source 41 enters the element 25 from the end face, and travels inside the element 25 while being totally reflected. Element 2
The light traveling inside 5 is reflected by the angle separating film 13c, so that the incident angle with respect to the surface 11a of the transparent substrate 11 changes, and passes through the surface 11a when the incident angle becomes smaller than the critical angle. I do. The light transmitted through the surface 11a is LC
This is illumination light that is incident on D31 at a slight angle. This illumination light is linearly polarized by the polarizing plate 43 before entering the LCD 31.

The operation of the LCD 31 is controlled so that the linearly polarized light whose polarization plane has not rotated even after the modulation becomes light representing an image. The light that has been modulated and reflected by the LCD 31 is only light that represents an image by the polarizing plate 43, and the light from the transparent base 11 at a different angle from that when the light exits the transparent base 11.
Enter 5. This light has a small incident angle with respect to the angle separating film 13c, passes through the angle separating film 13c, and exits from the transparent material 14 to the outside of the element 25. Light emitted outside the element 25 may be directly observed, or may be projected on a screen by a projection optical system. Note that the above-described optical element 22 may be provided instead of the polarizing plate 43.

FIG. 17 shows a mode in which the optical element 25 is used as an illumination optical system of a DMD, and light modulated by the DMD is projected by a projection optical system. The DMD 33 is arranged perpendicular to the optical axis of the projection optical system 34, and the element 25 is arranged between the DMD 33 and the projection optical system 34 in parallel with the DMD 33. Also,
A linear light source 41 is arranged near the end face of the element 25. The light emitted from the light source 41 becomes illumination light that enters the DMD 33 slightly obliquely, as in the case of the illumination of the LCD 31 described above.

The operation of the DMD 33 is controlled so that light representing an image is reflected in the vertical direction and other light is reflected in a direction different from the vertical direction. These lights reflected in two directions by the DMD 33 are transmitted from the surface 11a of the transparent substrate 11 to the element 2
Enter 5. These lights have a small incident angle with respect to the angle separating film 13c, and all of them pass through the angle separating film 13c and exit the element 25. Only light representing an image out of the light emitted outside the element 25 enters the projection optical system 34 and is projected on a screen (not shown). In this setting, the projection optical system 34 is compared with the optical system using the prism shown in FIG.
Lens back can be greatly shortened.

As shown in FIG. 18, two optical elements 25 with different settings of the angle separating film 13c are provided, and among the reflected light from the DMD 33 transmitted through the illumination optical element 25, light other than light representing an image. To the angle separation film 1 of the other optical element 25
The light may be reflected at 3c, totally reflected within the element 25, and output from the end face to the outside. In this way, unnecessary light traveling toward the vicinity of the projection optical system 34 can be eliminated,
It is possible to further shorten the lens back of the projection optical system 34. As shown in FIG. 15, the angle separation film 13c
Can be set so as to reliably separate incident light having an incident angle difference of about 10 °. Therefore, it is sufficient for the DMD 33 to be set so that each mirror element faces two directions having an angle difference of about 5 °. Yes, the DMD 33 can be easily manufactured.

The arrangement of the two optical elements 25 can be reversed. Further, instead of using two optical elements 25, as shown in the fourth embodiment, a single optical element including two sets of the blazed grating 12 and the angle separation film 13c is used, and this is used for illumination of the DMD 33. And for separation of the reflected light from the DMD 33.

FIG. 19 schematically shows the structure of the optical element 26 according to the sixth embodiment and its effect on light. The optical element 26 includes a chiral nematic liquid crystal layer 13 d that reflects one of two circularly polarized lights having opposite rotation directions and transmits the other as the separation coating 13, and is attached to the surface 11 a of the transparent substrate 11. A quarter-phase plate 44 is provided. Here, an example is given in which the chiral nematic liquid crystal layer 13d reflects clockwise circularly polarized light and transmits counterclockwise circularly polarized light.

The optical element 26 is capable of separating two linearly polarized lights which are transmitted through the quarter-phase plate 44 and whose polarization planes are orthogonal to each other. By passing through the 1/4 phase plate 44, one of the linearly polarized lights becomes the left-handed circularly polarized light, and the other linearly polarized light becomes the right-handed circularly polarized light. The counterclockwise circularly polarized light passes through the chiral nematic liquid crystal layer 13d and exits the element 26 from the surface 14a of the transparent member 14.

On the other hand, the clockwise circularly polarized light is reflected by the chiral nematic liquid crystal layer 13d, is diffracted by the blaze grating 12, re-enters the １ ／ phase plate 44, and becomes linearly polarized light. This linearly polarized light is totally reflected on the surface of the 位相 phase plate 44, and once again passes through the 位相 phase plate 44 to return to the clockwise circularly polarized light and re-enter the transparent substrate 11. The clockwise circularly polarized light is similarly reflected by the chiral nematic liquid crystal layer 13d and the quarter-phase plate 4
4 reaches the end face of the element 26 while undergoing total internal reflection on the surface of the element 4 and exits from the end face.

FIG. 20 shows an embodiment in which the optical element 26 is used as an illumination optical system of a reflection type LCD. Optical element 26 is L
Arranged in parallel with the CD 31, circularly polarized light clockwise from the end face is guided to the element 26. The circularly polarized light travels through the element 26 while being reflected as described above. In the meantime, the light is reflected by the liquid crystal layer 13 d to change the incident angle with respect to the surface of the １３ phase plate 44, and when the incident angle becomes smaller than the critical angle, the light goes out and the illumination light of the LCD 31 Becomes This illumination light is converted into linearly polarized light by transmitting through the quarter-phase plate 44.

The operation of the LCD 31 is controlled such that linearly polarized light whose polarization plane is rotated by 90 ° by modulation becomes light representing an image. The light modulated and reflected by the LCD 31 enters the element 26 and is converted into circularly polarized light by the 位相 phase plate 44. At this time, the linearly polarized light whose polarization plane has been rotated due to the modulation, that is, light representing an image, is left-handed circularly polarized light, and the linearly polarized light whose polarization plane has not been rotated returns to right-handed circularly polarized light. These two circularly-polarized lights are applied to the chiral nematic liquid crystal layer 13d.
And only the left-handed circularly polarized light representing the image is
, And the clockwise circularly polarized light is reflected by the liquid crystal layer 13 d and exits the element 26 from the end face. Thus, only the light representing the image is extracted.

In each of the above embodiments, the blaze grating 12 is set to cause only diffraction of light.
You may make it give more power. This can be realized by changing the diffraction angle continuously by gradually changing the period and the unit structure for each part, instead of having the blaze grating 12 with a constant periodic structure over the entire structure. . In addition, a bi-level or multi-level diffraction grating is provided in place of the blaze grating 12,
A configuration in which the separation coating 13 is provided thereon may be adopted.

[0086]

The blazed grating element of the present invention in which a separation coating for reflecting or transmitting incident light according to the characteristics of the incident light is provided on the blazed grating on the surface of the plate-shaped transparent substrate is a single thin blazed grating element. Although it is an element, incident light can be separated into reflected light and transmitted light by a separation coating according to its characteristics, and a blazed grating can act on the separated transmitted light or reflected light or both.
The light after separation can be diffracted or refracted depending on the setting of the height difference of the unevenness of the blaze grating.

By providing a plate-shaped transparent material that is in close contact with the blazed grating of the transparent substrate with the separating coating interposed therebetween, the grating surface can be protected and unnecessary modulation of transmitted light is avoided. You can also.

With a configuration having two sets of the blaze grating and the separation coating, the transmitted light separated by one separation coating can be further separated into reflected light and transmitted light by the other separation coating. Is obtained. In addition, by inverting the inclination directions of the blaze surfaces of the two blaze gratings, it is possible to avoid incomplete separation due to the incident angle.

Assuming that the separation coating reflects or transmits incident light according to the polarization characteristics of the incident light, a PBS having a plate-like shape and excellent polarization separation characteristics can be used.
Element.

A separation coating for reflecting or transmitting incident light according to the polarization characteristics of the incident light is provided on the diffraction grating on the surface of the plate-shaped transparent substrate, and the plate is provided on the diffraction grating of the transparent substrate with the separation coating interposed therebetween. The diffraction grating element of the present invention in which a transparent material is adhered to a single thin element, can separate the polarization of light and cause diffraction of the separated reflected light to change the reflection angle.

When the reflected light after separation is totally reflected inside and guided to the end face, unnecessary reflected light can be discarded from the end face of the element, and the processing of the reflected light becomes easy and the light is absorbed. The temperature of the element does not rise.

A diffraction grating element provided with a separation coating for reflecting or transmitting incident light according to the characteristics of the incident light is provided on the diffraction grating on the surface of the plate-shaped transparent substrate, and the light is illuminated by the diffraction grating element. The illumination optical system of the present invention, which guides the object to illuminate the illumination target and transmits the light reflected by the illumination target through the diffraction grating element to the outside, has a short distance from the illumination target. Within the range, required reflected light from the illumination object can be extracted. Therefore, it is suitable for illumination of an image display device using a reflection type LCD or DMD as a spatial modulation element. When a projection-type image display device is used, the lens back of the projection optical system is shortened, and the projection optical system can be downsized.

If the separation coating reflects or transmits the incident light according to the incident angle of the incident light, the light source is disposed outside the optical path of the light from the illumination object after passing through the diffraction grating element. This becomes very easy, and for example, it is possible to adopt a configuration in which light from a light source is guided into the diffraction grating element from an end face of the diffraction grating element.

If the separation coating is a chiral nematic liquid crystal layer that reflects one of two circularly polarized lights having different rotation directions and transmits the other, the illumination light and the reflected light from the illumination object can be reliably separated. it can.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a basic configuration of a blazed grating element and a diffraction grating element of the present invention.

FIG. 2 is a cross-sectional view schematically showing another basic configuration of the blazed grating element and the diffraction grating element of the present invention.

FIG. 3 is a cross-sectional view schematically showing a configuration of the optical element according to the first embodiment and an action on light.

FIG. 4 is a view showing the relationship between the transmittance and the wavelength of P-polarized light and S-polarized light at an incident angle of 45 ° of the PBS film provided in the optical element of the first embodiment.

FIG. 5 is a cross-sectional view showing a mode in which the optical element according to the first embodiment is used as an illumination optical system of a reflective LCD.

FIG. 6 is a cross-sectional view schematically showing the configuration of the optical element according to the second embodiment and the effect on light.

FIG. 7 is a view showing the relationship between the transmittance and the wavelength of P-polarized light and S-polarized light at an incident angle of 60 ° of the PBS film provided in the optical element of the second embodiment.

FIG. 8 is a cross-sectional view showing a mode in which the optical element of the second embodiment is used as an illumination optical system of a transmission type LCD and an optical system for extracting light representing an image.

FIG. 9 is a cross-sectional view schematically illustrating the configuration of the optical element according to the third embodiment and the effect on light.

FIG. 10 is a cross-sectional view schematically showing the configuration of an optical element according to a fourth embodiment and the effect on light.

FIG. 11 is a view showing the relationship between the transmittance and the wavelength of P-polarized light and S-polarized light at an incident angle of 45 ° of an R light reflecting dichroic film provided in the optical element of the fourth embodiment.

FIG. 12 is a diagram showing the relationship between the transmittance and the wavelength of P-polarized light and S-polarized light at an incident angle of 45 ° of a B light reflecting dichroic film provided in the optical element of the fourth embodiment.

FIG. 13 is a view showing the relationship between the transmittance and the wavelength for P-polarized light and S-polarized light at an incident angle of 45 ° of a G light reflecting dichroic film provided in the optical element of the fourth embodiment.

FIG. 14 is a cross-sectional view schematically showing the configuration of the optical element according to the fifth embodiment and the effect on light.

FIG. 15 is a view showing the relationship between the transmittance and the incident angle of light having a wavelength of 550 nm of an angle separation film provided in an optical element according to a fifth embodiment.

FIG. 16 shows an optical element according to a fifth embodiment as a reflection type LCD.
Sectional drawing which shows the form used as an illumination optical system of FIG.

FIG. 17 is a cross-sectional view showing an embodiment in which the optical element according to the fifth embodiment is used as an illumination optical system of a DMD.

FIG. 18 is a cross-sectional view showing a mode in which the optical element according to the fifth embodiment is used as an illumination optical system of a DMD and an optical system for extracting light representing an image.

FIG. 19 is a cross-sectional view schematically showing the configuration of the optical element according to the sixth embodiment and the effect on light.

FIG. 20 shows a reflection type LCD using an optical element according to the sixth embodiment.
Sectional drawing which shows the form used as an illumination optical system of FIG.

FIG. 21 is a diagram showing a configuration of a PBS prism.

FIG. 22 is a view showing a conventional optical element for separating illumination light and reflected light of a reflective LCD.

FIG. 23 shows R light, G light, and white light having an angle difference in an optical path.
FIG. 4 is a diagram showing a conventional optical system for separating into B light.

FIG. 24 is a diagram showing a configuration of an LCD that includes a microlens array and is illuminated with R light, G light, and B light having an optical path with an angle difference.

FIG. 25 is a diagram showing a conventional optical system for illuminating a DMD.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 2 Blaze grating element 11 Transparent base material 11a Transparent base surface 11R Dichroic film 12 Blaze grating 12a Blaze surface 13 Separation coating 13a, 13b Polarization separation film 13B, 13G Dichroic film 14 Transparent material 14a Transparent material surface 15 Light absorbing member 21 , 22, 23, 24, 25, 26 Diffraction grating element 31 Reflective LCD 32 Transmission LCD 33 DMD 34 Projection optical system 41 Light source 43 Polarizer 44 1/4 phase plate

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13 505 G02F 1/13 505 1/1335 1/1335 F-term (Reference) 2H038 AA55 BA06 2H049 AA43 AA45 AA63 AA65 BA05 BA07 BA43 BB62 BB66 BC22 2H088 EA12 GA02 GA17 HA13 HA16 HA20 HA21 HA23 JA04 MA01 2H091 FA07Z FA14Z FA19Z FA41Z 2H099 AA11 BA09 CA17 DA05

Claims (12)

[Claims] 1. A plate-shaped transparent substrate having a blazed grating on a surface thereof, and a separation coating provided on the blazed grating of the transparent substrate and reflecting or transmitting incident light according to characteristics of the incident light. A blazed grating element, comprising: 2. The blazed grating device according to claim 1, further comprising a plate-shaped transparent material that is in close contact with the blazed grating of the transparent substrate with the separation coating interposed therebetween. 3. The transparent material has a blazed grating on a surface opposite to the transparent substrate, and is provided on the blazed grating of the transparent material, and the incident light depends on characteristics of the incident light. 3. The blaze grating element according to claim 2, further comprising: a separation coating that reflects or transmits light; and a plate-shaped transparent material that is in close contact with the transparent material blaze grating with the separation coating interposed therebetween. 4. The blazed grating device according to claim 1, wherein the separation coating reflects or transmits the incident light according to the polarization characteristics of the incident light. 5. The blazed grating device according to claim 1, wherein the separation coating reflects or transmits the incident light according to the wavelength of the incident light. 6. The blazed grating device according to claim 1, wherein the separation coating reflects or transmits incident light according to an incident angle of the incident light. 7. A plate-shaped transparent substrate having a diffraction grating on its surface, and a separation coating provided on the diffraction grating of the transparent substrate and reflecting or transmitting incident light according to the polarization characteristics of the incident light. A diffraction grating element comprising a plate-shaped transparent material that is in close contact with the diffraction grating of the transparent substrate with the separation coating interposed therebetween. 8. The diffraction grating element according to claim 7, wherein the transparent substrate totally reflects the light reflected by the separation coating inside and guides the light to an end face. 9. A transparent substrate in the form of a plate having a diffraction grating on its surface, and a separation coating provided on the diffraction grating of the transparent substrate and reflecting or transmitting incident light according to characteristics of the incident light. A diffraction grating element for guiding light to the illumination target by the diffraction grating element to illuminate the illumination target, and transmitting light reflected by the illumination target to the outside through the diffraction grating element. Illumination optical system. 10. The illumination optical system according to claim 9, wherein the diffraction grating element includes a plate-shaped transparent material that is in close contact with the diffraction grating of the transparent substrate with the separation coating interposed therebetween. 11. The illumination optical system according to claim 9, wherein the separation coating reflects or transmits the incident light according to an incident angle of the incident light. 12. The illumination optical system according to claim 9, wherein the separation coating is a chiral nematic liquid crystal layer that reflects one of two circularly polarized lights having different rotation directions and transmits the other.