JP2009032698A - Illumination optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an illumination optical system capable of extracting necessary reflected light from an object to be illuminated in a range small in distance from the object, and suitable for illumination of an image display device using a reflection type LCD or DMD as a spatial modulator. <P>SOLUTION: This illumination optical system is configured by including: a plate-like transparent base material having a diffraction grating on a surface thereof; and a diffraction grating element formed on the diffraction grating of the transparent base material, and having a separation coating for reflecting or transmitting incident light according to a characteristic of the incident light. In the illumination optical system, the object to be illuminated is illuminated by guiding light to the object by the diffraction grating element, and light reflected by the object is made to permeate the diffraction grating element, and guided to the outside. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an illumination optical system including a diffraction grating element.

  In an image display device in which illumination light is modulated by a spatial modulation element and an image is represented by the modulated light, various optical elements are used to guide the illumination light to the spatial modulation element. When a liquid crystal display (LCD) is used as the spatial modulation element, it is necessary to give the LCD a linearly polarized light with a fixed polarization plane. For this reason, when a light source that emits non-polarized light is used, linearly polarized light suitable for the LCD is extracted using a polarization separation (PBS) prism or a polarizing plate.

  The configuration of the PBS prism is shown in FIG. The PBS prism has a configuration in which a PBS film 51c is sandwiched between two prism pieces 51a and 51b having a right-angled isosceles triangle. The PBS film 51c separates both the P-polarized light and the S-polarized light by selectively transmitting and selectively reflecting the other, but generally, the selectivity of transmission and reflection is not required unless the incident angle is about 45 ° or more. Decreases and separation cannot be performed satisfactorily. For this reason, it is in the form of a square prism PBS prism sandwiched between two prism pieces 51a and 51b.

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

  In the case of a reflective LCD, since the optical path of the illumination light that illuminates the LCD matches the optical path of the reflected light from the LCD, it is necessary to separate the optical path of the illumination light and the reflected light that represents the image somewhere on the optical path. . For this purpose, an optical element that reflects one of illumination light and reflected light and transmits the other is used.

  The above-described PBS prism is also used for this purpose. When a reflective LCD is set so that light whose polarization plane is rotated by 90 ° represents an image, when the light transmitted through the PBS prism is used as illumination light, the light representing the image is reflected by the PBS prism. In addition, when the light reflected by the PBS prism is used as illumination light, the light representing the image is transmitted through the PBS prism, and in either case, the reflected light representing the image is used as the light source. It is possible to guide in a direction different from the direction toward.

  Another optical element for separating the illumination light and the reflected light is shown in FIG. This optical element is formed by forming a large number of grooves 52d having a V-shaped cross section on the upper surface 52a of a transparent flat plate 52, and the lower surface 52b is arranged facing the reflective LCD 53. Light from the light source is guided into the flat plate 52 from the end surface 52c of the flat plate 52, and travels through the flat plate 52 while being totally reflected by the upper surface 52a and the lower surface 52b. Meanwhile, the light hits the surface of the groove 52d and is reflected, and passes through the lower surface 52b to illuminate the LCD 53. 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 to the outside.

  Between the flat plate 52 and the LCD 53, a polarizing plate 54 for making the illumination light linearly polarized light is disposed. The LCD 53 is controlled so that the linearly polarized light whose plane of polarization does not rotate after modulation is not linearly polarized light whose plane of polarization is rotated by 90 °, but becomes light representing an image.

  One method for displaying a color image is to provide each pixel of the LCD with a color filter that selectively transmits red (R) light, green (G) light, or blue (B) light. It has been broken. 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. Therefore, in recent years, illumination light is separated into R light, G light, and B light whose traveling directions are slightly different from each other, and the LCD is provided with a microlens array so that the R light, G light, and B light are separated into separate pixels. Incidence has been made.

  An optical system used for color separation in this method is shown in FIG. This optical system includes three dichroic mirrors 55R, 55G, and 55B. The dichroic mirrors 55R, 55G, and 55B selectively reflect R light, G light, and B light, respectively, and transmit other color light. The mirrors 55R, 55G, and 55B are arranged at an angle to each other and reflect incident light in different directions. In the optical path of the reflected R light, G light, and B light, an angle difference that is twice the angle between the mirrors 55R, 55G, and 55B is generated.

  As shown in FIG. 24, the microlens array 56 provided in the LCD 53 is set so that each microlens 56a faces the adjacent three pixels 53R, 53G, and 53B. R light, G light, and B light enter each micro lens 56a from different directions, and each micro lens converges R light, G light, and B light on different pixels 53R, 53G, and 53B, respectively. Let Thus, all the light from the light source is guided to the pixels of the LCD 53, and a bright image can be provided.

  An element called a digital micromirror device (DMD) in which a large number of minute angle variable mirror elements are two-dimensionally arranged 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. Of the light reflected in two directions by the DMD, one is extracted as light representing an image, and the other is discarded as unnecessary light.

  A general optical system for illuminating the DMD is shown in FIG. In this optical system, two prisms 57a and 57b are arranged slightly apart from each other. Light from the light source is guided to 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, and the light is totally reflected by the surface 57c and passes through the surface 57d to illuminate the DMD 58. The light reflected by the DMD 58 enters the prism 57a from the surface 57d while being separated into light representing an image and unnecessary light. The light that has entered the prism 57a reaches the surface 57c. Since the incident angle is smaller than the critical angle, the light is transmitted therethrough and is also transmitted through the prism 57b. As described above, the optical system that illuminates the DMD uses total reflection and transmission of light by the prism surface.

  The polarizing plate has a simple configuration and is flat, and is very easy to use. However, the transmittance of linearly polarized light that passes 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 is transmitted, so that the temperature becomes high and adversely affects other elements such as an LCD disposed in the vicinity. When the intensity of light is increased in order to display a bright image, the polarizing plate becomes particularly hot.

  Since the PBS prism does not absorb light, there is no inconvenience of high temperature, and both transmitted light and reflected light can be used. Further, it is easy to make the transmittance and the reflectance approximately 100%, which is excellent in terms of light utilization 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 a projection-type device that projects light on the screen and forms an image on the screen, the lens back of the projection optical system becomes long, and a large projection optical system is required to display a bright image. Become. The problem of increasing the size and weight of the apparatus also applies to the optical system of FIG. 25 that also uses a prism.

  The optical element shown in FIG. 22 has a simple configuration in which a groove is provided on a flat plate and is easy to use. However, a part of the reflected light from the LCD entering the flat plate is reflected on the surface of the groove, and the flat plate is formed. Cannot penetrate. For this reason, striped dark portions appear in the displayed video. Although it is possible to reduce the conspicuous dark area by reducing the width of the groove, it is not an essential solution.

  In addition, the optical system comprising the three dichroic mirrors shown in FIG. 23 is excellent in terms of light utilization efficiency, but each dichroic mirror is a separate element, so that the mutual angle can be accurately set. difficult. For this reason, it takes time to assemble the optical system, and the manufacturing efficiency is lowered.

  By the way, diffractive optical elements that have a lattice plane in which minute concavo-convex structures are periodically arranged and change the path of light by diffraction are used in various fields of optics. The diffractive optical element includes a bi-level element in which the concave portion and the convex portion of the grating surface are both flat and the level (height) of the flat portion is two, and a multi-layer having one or more levels between the concave portion and the convex portion. There is a level element and a blaze type element having an inclined surface and a sawtooth cross section. Any of the diffractive optical elements can be a transmission type that causes diffraction in transmitted light, or can be a reflection type in which a reflection film is coated on a grating surface to cause diffraction in reflected light. In the case of the transmissive type, an antireflection film is coated on the lattice surface in order to increase the transmittance.

  Although it is not a diffractive optical element, the Fresnel lens also has many small inclined surfaces and is a blazed element having a sawtooth cross section. Diffractive optical elements have an uneven height difference of about the wavelength of light, which causes diffraction, whereas Fresnel lenses have a large uneven height difference of several times the wavelength. To change.

  A diffractive optical element and a Fresnel lens have a great feature that they are thin optical elements. However, it is an illumination optical system using such an optical element, and takes out necessary reflected light from the illumination object within a short distance from the illumination object (for example, a reflective LCD or DMD). An illumination optical system that makes this possible has not been proposed yet.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to extract necessary reflected light from the illumination object within a short distance from the illumination object. Another object of the present invention is to provide an illumination optical system suitable for illumination of an image display device using a reflective LCD or DMD as a spatial modulation element.

  In order to achieve the above object, in the present invention, a plate-shaped transparent substrate having a diffraction grating on its surface, and provided on the diffraction grating of the transparent substrate, reflects incident light according to the characteristics of incident light or A diffraction grating element having a separating coating to be transmitted is included in the illumination optical system, and the light is guided to the illumination object by the diffraction grating element to illuminate the illumination object, and the light reflected by the illumination object is reflected by the diffraction grating element Shall be guided to the outside.

  The diffraction grating element may be provided with a plate-like transparent material that is in close contact with the diffraction grating of the transparent substrate with the separation coating interposed therebetween.

  The separation coating may reflect or transmit incident light according to the incident angle of incident light.

  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.

  Includes a diffraction grating element provided with a separation coating that reflects or transmits incident light on the diffraction grating on the surface of the plate-like transparent substrate, and guides the light to the object to be illuminated by the diffraction grating element According to the illumination optical system of the present invention that illuminates the illumination object and transmits the light reflected by the illumination object through the diffraction grating element to the outside, the distance from the illumination object is short. The necessary reflected light from the illumination object can be extracted. Therefore, it is suitable for illumination of a video display device using a reflective 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. In the present invention, the optical paths of the illumination light and the reflected light from the illumination object overlap, but it is easy to extract only the reflected light from the illumination object by combining the function of the diffraction grating and the function of the separation coating.

  If the diffraction grating element is provided with a plate-like transparent material that is in close contact with the diffraction grating of the transparent substrate with the separation coating interposed therebetween, the diffraction grating and the separation coating can be protected, and the illumination object that passes through the element It is possible to avoid unnecessary modulation of the reflected light from the light.

  If the separation coating reflects or transmits the incident light according to the incident angle of the incident light, it is very easy to place the light source outside the optical path of the light from the illumination object after passing through the diffraction grating element. Thus, for example, the light from the light source can be introduced into the diffraction grating element from the end face of the diffraction grating element.

  Further, 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.

  A basic configuration of a blazed grating element and a diffraction grating element applicable to the illumination optical system of the present invention is schematically shown in FIGS. FIG. 1 shows a blazed grating element 1 having the simplest structure 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 of the unevenness of the blazed grating 12 is about the wavelength of light, the blazed grating 12 becomes a diffraction grating and the blazed grating element 1 becomes a diffraction grating element. Further, if the height difference of the unevenness of the blazed grating 12 is set to be several times the wavelength of light, 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 transparent material 14 that is in close contact with the blazed grating 12 is added to the blazed grating element 1 of FIG. The transparent material 14 can also be made of resin or glass. The materials of the transparent base material 11 and the transparent material 14 may be the same or different. In the blazed grating element 2, the blazed grating 12 and the separation coating 13 are protected.

  The separation coating 13 reflects or transmits the incident light depending on the characteristics of the incident light. Examples of the characteristics of the incident light include a wavelength, a direction of a polarization plane of linearly polarized light, a rotation direction of circularly polarized light, and an incident angle with respect to the separation coating 13.

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

  In the blazed grating element 2, if the refractive indexes of the transparent base material 11 and the transparent material 14 are different from each other, the blazed grating 12 is similar to the blazed grating element 1 with respect to both light transmitted through the separation coating 13 and reflected light. Act. On the other hand, if the refractive indexes of the transparent base material 11 and the transparent material 14 are equal, the blazed grating 12 acts only on the reflected light, and the blazed grating element 2 becomes a mere transparent parallel plate for the transmitted light.

  Hereinafter, some embodiments in which the blazed grating element 2 is a diffractive optical element will be described. The configuration of the optical element 21 of the first embodiment and the action on light are schematically shown in FIG. The optical element 21 includes a PBS film 13 a as the separation coating 13. The PBS film 13a is set to transmit P-polarized light and reflect S-polarized light. The refractive indexes of the transparent base material 11 and the transparent material 14 are 1.62, and the blaze angle of the blazed grating 12 (angle formed by the individual blazed surfaces 12a with respect to the plane of the entire blazed grating) is 30 °.

  The optical element 21 is used in an arrangement in which the incident angle of light on the transparent substrate 11 is 25 °. The light incident on the transparent substrate 11 at an incident angle of 25 ° is refracted and the incident angle with respect to the blazed surface 12a becomes 45 °. Of the light incident on the blazed surface 12 a, the polarization component that becomes P-polarized light with respect to the PBS film 13 a passes through the PBS film 13 a and also passes through the transparent material 14 and goes out of the element 21. This light travels along an optical path that is parallel to and slightly shifted from the light before entering the element 21.

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

  In this optical element 21, the polarization component that becomes P-polarized light can be taken out from the PBS film 13a with almost no change in the path, and the polarization component that becomes S-polarized light can be directed to the PBS film 13a in a completely different direction. Can be thrown away. Moreover, since the element 21 does not absorb light, it does not reach a high temperature.

  The film configuration of the PBS film 13a is shown in Table 1, and the relationship between the transmittance and wavelength for P-polarized light and S-polarized light with an incident angle of 45 ° is shown in FIG. In Table 1, the layer number 0 is the transparent substrate 11 and the layer number 18 is the transparent material 14. The optical film thickness is expressed using 745 nm as a reference wavelength.

<Table 1> Structure 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 0.25
8 1.385 0.25 7 2.05 0.25
6 1.385 0.25 5 2.05 0.25
4 1.385 0.25 3 2.05 0.25
2 1.385 0.125 1 1.62 0.125
0 1.62

  FIG. 5 shows a form in which the optical element 21 is used as an illumination optical system for a reflective LCD. The optical element 21 is disposed with an inclination of 25 ° with respect to the LCD 31, and a linear light source 41 is disposed in the vicinity of the end face of the element 21. The light source 41 emits non-polarized light. The light emitted from the light source 41 enters the element 21 from the end face and travels through the element 21 while undergoing total reflection. Of the light that travels inside the element 21, the polarization component that is S-polarized with respect to the PBS film 13 a is reflected by the PBS film 13 a, whereby the incident angle with respect to the surface 11 a of the transparent substrate 11 changes. The light passes through the surface 11a when the incident angle becomes less than the critical angle. The light transmitted through the surface 11a becomes illumination light incident on the LCD 31 at an angle of approximately 90 °.

  The operation of the LCD 31 is controlled so 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 element 21. Of the light that has entered the element 21, the polarization component representing the image becomes P-polarized light with respect to the PBS film 13 a, passes through the PBS film 13 a, and exits the element 21 from the transparent material 14. On the other hand, the other polarization component is reflected as S-polarized light with respect to the PBS film 13a, and is directed toward the end face of the element 21 and is emitted toward the light source 41 while being totally reflected as described above.

  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 light flux of the reflected light from the LCD 31 and is less than half that of the conventional PBS prism. Therefore, when a projection-type image display device that projects light representing an image onto a screen is used, the lens back of the projection optical system is significantly shortened, and the projection optical system can be made compact.

  The configuration of the optical element 22 of the second embodiment and the action on light are schematically shown in FIG. The optical element 22 includes a PBS film 13 b as the separation coating 13. The PBS film 13b is set to reflect P-polarized light and transmit S-polarized light, contrary to the first embodiment. The refractive index of the transparent base material 11 and the transparent material 14 is 1.87, and the blaze angle of the blazed grating 12 is 60 °.

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

  The polarization component that is P-polarized with respect to the PBS film 13 b is reflected by the PBS film 13 b and diffracted by the blazed grating 12. The diffracted reflected light is incident on the surface 14a of the transparent material 14 at an incident angle exceeding the critical angle and is totally reflected, reaches the end face of the element 22 and exits from the end face to the outside in the same manner as in the first embodiment.

  The film configuration of the PBS film 13b is shown in Table 2, and the relationship between the transmittance and wavelength for P-polarized light and S-polarized light at an incident angle of 60 ° is shown in FIG. In Table 2, the layer number 0 is the transparent substrate 11 and the layer number 26 is the transparent material 14. The optical film thickness is expressed using 280 nm as a reference wavelength.

<Table 2> Structure of PBS film 13b Layer Refractive index Optical film thickness Layer Refractive index Optical film thickness 26 1.87 25 1.385 0.125
24 2.3 0.25 23 1.385 0.25
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 0.25 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

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

  FIG. 8 shows a form in which the optical element 22 is used as an illumination optical system for a transmissive LCD and an optical system for selectively extracting light representing an image. Two optical elements 22 are arranged before and after the LCD 32, and light from the light source is incident on the one element 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 is incident on the LCD 32 at an angle of approximately 90 °. On the other hand, the polarization component that becomes P-polarized light is reflected by the PBS film 13b and reaches the end face while undergoing total reflection in the element 22. A 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 so that linearly polarized light whose polarization plane does not rotate 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 passes through the element 22 with respect to the PBS film 13 b. The polarization component whose polarization plane is rotated by 90 ° by the modulation and becomes P-polarized with respect to the PBS film 13 b is reflected, reaches the end face while being totally reflected in the element 22, and is absorbed by the absorbing member 15.

  Conventionally, a polarizing plate is used for illumination of a transmissive LCD and extraction of light representing an image. However, by using the optical element 22 instead of the polarizing plate, the transmittance is increased and a bright image can be provided. it can. Further, the element 22 does not reach a high temperature unlike a polarizing plate, and does not adversely affect the LCD.

  The configuration of the optical element 23 of the third embodiment and the effect on light are schematically shown in FIG. In this optical element 23, a blaze grating 12 is also formed on the surface of the transparent material 14 of the optical element 22 of the second embodiment, and a PBS film 13b is provided thereon as a separation coating 13, and the PBS film 13b is sandwiched therebetween. In this embodiment, another transparent material 14 that is in close contact with the transparent material 14 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 blazed surfaces 12a of the two blazed gratings 12 are opposite.

  In this configuration, even when there is light directly transmitted between the two blazed surfaces 12 a of one blazed grating 12, the light can be separated by the PBS film 13 b provided on the other blazed grating 12. Therefore, the separation efficiency is not lowered due to the incident angle, and the degree of freedom of the arrangement angle with respect to the light to be separated is increased.

  The configuration of the optical element 24 of the fourth embodiment and the action on light are schematically shown in FIG. Similar to the optical element 23 of the third embodiment, the optical element 24 includes two sets of the blazed grating 12 and the separation coating 13. The inclination directions of the blaze surfaces of the two blaze gratings 12 are opposite, and each blaze angle is about several degrees. A dichroic film 13B that selectively reflects B light is selected as the separation coating 13 on the blazed grating 12 of the transparent substrate 11, and G light is selected as the separation coating 13 on the blazed grating 12 of the transparent material 14. A dichroic film 13G that reflects light is provided. Further, a dichroic film 11 </ b> R that selectively reflects R light is provided on the surface 11 a of the transparent substrate 11.

  The optical element 24 separates white light into R light, G light, and B light, and causes an angle difference in the optical path of each separated light. Of the white light incident on the element 24, the R light is reflected at a reflection angle equal to the incident angle by the dichroic film 11R. The B light and G light that have passed through the dichroic film 11R enter the element 24, reach the dichroic film 13B, and are separated into G light that passes through the dichroic film 13B and reflected B light.

  The B light reflected by the dichroic film 13B is diffracted by the blazed grating 12, and is output to the outside of the element 24 as light having an angle difference from the R light. The G light that has passed through the dichroic film 13B reaches the dichroic film 13G, is reflected, is diffracted by the blazed grating 12, and is output outside the element 24 as light having an angle difference from the R light and B light.

  The film configurations of the dichroic films 11R, 13B, and 13G are shown in Table 3, Table 4, and Table 5, 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 substrate 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 base material 11 side, and the layer number 22 is the transparent material 14 on the front surface side. The optical film thickness is expressed by using 765 nm for the dichroic film 11R, 451 nm for the dichroic film 13B, and 540 nm for the dichroic film 13G.

<Table 3> Configuration of Dichroic Film 11R Layer Refractive Index Optical Film Thickness Layer Refractive Index Optical Film Thickness 22 1 21 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
0 1.52

<Table 4> Configuration of Dichroic Film 13B Layer Refractive Index Optical Film Thickness Layer Refractive Index Optical Film 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 2.3 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 Film Thickness Layer Refractive Index Optical Film 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 2.3 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 wavelength of the dichroic films 11R, 13B, and 13G with respect to P-polarized light and S-polarized light with an incident angle of 45 ° is shown in FIGS. 11, 12, and 13, respectively. Since refraction occurs when entering the transparent substrate 11, even if the incident angle to the dichroic film 11R is 45 °, the actual incident angle of light with respect to the dichroic films 13B and 13G changes from 45 °. If the blaze angle of the blazed grating 12 is about 5 °, the incident angle to the dichroic film 13B is about 32 ° and the incident angle to the dichroic film 13G is about 22 °.

  The optical element 24 can be used as an illumination optical system of the LCD 53 shown in FIG. 24 having a microlens array. At this time, since the element 24 is a single member, there is no need to adjust the relative angle between the elements as in the optical system shown in FIG. 23, and assembly can be performed quickly and accurately. In order to change 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 may be used.

  The configuration of the optical element 25 of the fifth embodiment and the action on light are schematically shown in FIG. The optical element 25 includes an angle separation film 13 c that reflects or transmits light according to an incident angle as the separation coating 13. Of the light incident on the element 25 from different directions, one is transmitted through the angle separation film 13c, the other is reflected by the angle separation film 13c, is diffracted by the blazed grating 12, and reaches the end face while receiving total reflection. Go outside.

  Table 6 shows the film configuration of the angle separation film 13c, and FIG. 15 shows the relationship between the transmittance and the incident angle with respect to light having a wavelength of 550 nm. In Table 6, the layer number 0 is the transparent substrate 11 and the layer number 22 is the transparent material 14. The optical film thickness is represented with 700 nm as a reference wavelength.

<Table 6> Configuration of Angle Separating Film 13c Layer Refractive Index Optical Film Thickness Layer Refractive Index Optical Film 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 0.38 9 2.2 0.2075
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

  A form in which the optical element 25 is used as an illumination optical system of a reflective LCD is shown in FIG. The optical element 25 is arranged in parallel with the LCD 31, and a linear light source 41 is arranged in the vicinity of the end face of the element 25. A polarizing plate 43 is disposed between the element 25 and the LCD 31. The light source 41 emits non-polarized light. The light emitted from the light source 41 enters the element 25 from the end face and travels through the element 25 while undergoing total reflection. The light traveling inside the element 25 is reflected by the angle separation film 13c, whereby the incident angle with respect to the surface 11a of the transparent substrate 11 changes, and when the incident angle becomes less than the critical angle, the surface 11a is To Penetrate. The light transmitted through the surface 11a becomes illumination light that is incident on the LCD 31 at an angle. This illumination light is converted into linearly polarized light by the polarizing plate 43 before entering the LCD 31.

  The operation of the LCD 31 is controlled so that linearly polarized light whose polarization plane does not rotate after modulation becomes light representing an image. The light modulated and reflected by the LCD 31 is only light that represents an image by the polarizing plate 43, and enters the element 25 from the transparent substrate 11 at an angle different from that when it exits the transparent substrate 11. This light has a small incident angle with respect to the angle separation film 13 c, passes through the angle separation film 13 c, and exits the element 25 from the transparent material 14. The light emitted to the outside of the element 25 may be observed directly, or may be projected onto a screen by a projection optical system. Note that the optical element 22 described above may be disposed in place of the polarizing plate 43.

  FIG. 17 shows a form in which the optical element 25 is used as a DMD illumination optical system and light modulated by the DMD is projected by the projection optical system. The DMD 33 is disposed perpendicular to the optical axis of the projection optical system 34, and the element 25 is disposed between the DMD 33 and the projection optical system 34 in parallel with the DMD 33. Further, a linear light source 41 is disposed near the end face of the element 25. The light emitted from the light source 41 becomes illumination light that enters the DMD 33 at a slight angle, 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 the two directions by the DMD 33 enter the element 25 from the surface 11 a of the transparent substrate 11. These lights have a small incident angle with respect to the angle separation film 13 c, and both pass through the angle separation film 13 c and exit to the outside of the element 25. Of the light emitted outside the element 25, only the light representing the image enters the projection optical system 34 and is projected onto a screen (not shown). In this setting, the lens back of the projection optical system 34 can be significantly shortened compared to the optical system using the prism shown in FIG.

  As shown in FIG. 18, two optical elements 25 having different settings of the angle separation film 13 c are provided, and light other than the light representing the image is reflected on the other side of the reflected light from the DMD 33 transmitted through the illumination optical element 25. The light may be reflected by the angle separation film 13c of the optical element 25 and totally reflected in the element 25 to be emitted 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, and the lens back of the projection optical system 34 can be further shortened. As shown in FIG. 15, the angle separation film 13c can be set to reliably separate incident light having a difference of about 10 ° in the incident angle. Therefore, DMD 33 has an angle difference of about 5 ° for each mirror element. It is sufficient to set the two directions so that 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 as the illumination of the DMD 33. It may be used for the purpose of separating the reflected light from the DMD 33.

  The configuration of the optical element 26 of the sixth embodiment and the action on light are schematically shown in FIG. The optical element 26 includes a chiral nematic liquid crystal layer 13d that reflects one of two circularly polarized light whose rotation directions are opposite to each other and transmits the other as the separation coating 13, and is attached to the surface 11a of the transparent substrate 11. A worn ¼ phase plate 44 is provided. In this example, the chiral nematic liquid crystal layer 13d is set to reflect clockwise circularly polarized light and transmit counterclockwise circularly polarized light.

  The optical element 26 can separate two linearly polarized lights whose polarization planes that are transmitted through the ¼ phase plate 44 and are orthogonal to each other. By passing through the quarter phase plate 44, one linearly polarized light becomes counterclockwise circularly polarized light, and the other linearly polarized light becomes clockwise circularly polarized light. The counterclockwise circularly polarized light passes through the chiral nematic liquid crystal layer 13 d and exits from the surface 26 a of the transparent material 14 to the outside of the element 26.

  On the other hand, the clockwise circularly polarized light is reflected by the chiral nematic liquid crystal layer 13d, diffracted by the blazed grating 12, and reenters the quarter phase plate 44 to become linearly polarized light. The linearly polarized light is totally reflected on the surface of the ¼ phase plate 44, and is transmitted again through the ¼ phase plate 44. This clockwise circularly polarized light reaches the end face of the element 26 while receiving reflection by the chiral nematic liquid crystal layer 13d and total reflection at the surface of the quarter phase plate 44, and goes outside from the end face.

  A form in which the optical element 26 is used as an illumination optical system of a reflective LCD is shown in FIG. The optical element 26 is arranged in parallel with the LCD 31, and circularly polarized light clockwise from the end face is introduced into the element 26. This circularly polarized light travels in the element 26 while receiving reflection as described above. In the meantime, the incident angle with respect to the surface of the quarter phase plate 44 is changed by being reflected by the liquid crystal layer 13d, and when the incident angle becomes less than the critical angle, the light goes outside and the illumination light of the LCD 31 It becomes. The illumination light is linearly polarized by passing through the ¼ phase plate 44.

  The operation of the LCD 31 is controlled so 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 quarter phase plate 44. At this time, the linearly polarized light whose plane of polarization has been rotated by the modulation, that is, the light representing the image becomes counterclockwise circularly polarized light, and the linearly polarized light whose plane of polarization has not rotated returns to clockwise circularly polarized light. These two circularly polarized lights reach the chiral nematic liquid crystal layer 13d, and only the counterclockwise circularly polarized light representing the image is transmitted through the liquid crystal layer 13d, and the clockwise circularly polarized light is reflected by the liquid crystal layer 13d and is external to the element 26 from the end face. Get out. In this way, only the light representing the image is extracted.

  In each of the above embodiments, the blazed grating 12 is set to cause only diffraction in the light. However, the blazed grating 12 may further have power. This can be realized by changing the diffraction angle continuously by changing the period and the unit structure little by little, instead of making the blazed grating 12 a constant periodic structure throughout. . Further, a bi-level or multi-level diffraction grating may be provided instead of the blaze grating 12, and a separation coating 13 may be provided thereon.

  The blazed grating element is composed of a plate-like transparent substrate having a blazed grating on the surface, and a separation coating that is provided on the blazed grating of the transparent substrate and reflects or transmits the incident light according to the characteristics of the incident light. It may be configured. Although this element is a single thin optical element, it has two functions. That is, incident light can be separated into reflected light and transmitted light according to the characteristics by the separation coating, and a blaze grating can act on the separated transmitted light or reflected light or both. The blazed grating becomes a diffraction grating if the height difference of the unevenness is made about the wavelength of the incident light, and acts as a Fresnel lens or mirror if the height difference is made about several times the wavelength of the incident light.

  You may make it provide the plate-shaped transparent material closely_contact | adhered to the blazed grating | lattice of a transparent base material on both sides of separation coating. The grid surface can be protected. Further, by making the transparent base material and the transparent material from the same material, unnecessary modulation of the transmitted light can be avoided. In this case, the blaze grating acts only on the reflected light.

  The transparent material has a blazed grating on the surface opposite to the transparent substrate, and is further provided on the blazed grating of the transparent material to reflect or transmit the incident light according to the characteristics of the incident light. It is good also as a structure provided with the separation transparent coating and the plate-shaped transparent material closely_contact | adhered to the blazed grating | lattice of the transparent material on both sides of the separation coating. In 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. It is also possible to avoid incomplete separation due to the incident angle by reversing the direction of inclination of the blaze surfaces of the two blaze gratings.

  The separation coating can reflect or transmit incident light depending on the polarization characteristics of the incident light. Since the separation coating is provided on an inclined blazed surface, the incident angle of light on the separation coating can be made to be 45 ° or more even if the incidence angle to the device is less than 45 °. is there. Therefore, it is possible to obtain a PBS element having a good polarization separation characteristic while being flat.

  The separation coating can also reflect or transmit incident light depending on the wavelength of the incident light, or reflect or transmit incident light depending on the incident angle of the incident light. In either case, it is possible not only to separate the light according to the wavelength and the incident angle, but also to act as a blazed grating on the separated light.

  In addition, a plate-like transparent base material having a diffraction grating on the surface, a separation coating that is provided on the diffraction grating of the transparent base material and reflects or transmits incident light according to the polarization characteristics of the incident light, and a separation coating You may comprise a diffraction grating element with the plate-shaped transparent material pinched | interposed and closely_contact | adhered to the diffraction grating of the transparent base material. Although this element is a single thin optical element, it has both a polarization separation function and a diffraction function. That is, incident light can be separated into reflected light and transmitted light in accordance with the polarization characteristics by the separation coating, and the reflection angle can be changed by causing diffraction in the separated reflected light.

  Here, the transparent base material may be totally reflected inside the light reflected by the separation coating and guided to the end face. When only the transmitted light after separation is necessary, unnecessary reflected light can be discarded from the end face of the element, and the processing of the reflected light becomes easy. Further, the device does not absorb light and the temperature does not rise.

Sectional drawing which shows typically the basic composition of the blaze | braze grating | lattice element and diffraction grating element which can be applied to the illumination optical system of this invention. Sectional drawing which shows typically another basic composition of the blaze | braze grating | lattice element and diffraction grating element which can be applied to the illumination optical system of this invention. Sectional drawing which shows typically the structure with respect to the optical element of 1st Embodiment, and the effect | action with respect to light. The figure which shows the relationship between the transmittance | permeability and wavelength with respect to P polarization | polarized-light and S polarization | polarized-light with an incident angle of 45 degrees of the PBS film with which the optical element of 1st Embodiment was equipped. Sectional drawing which shows the form which uses the optical element of 1st Embodiment as an illumination optical system of reflection type LCD. Sectional drawing which shows typically the structure with respect to the optical element of 2nd Embodiment, and the effect | action with respect to light. The figure which shows the relationship between the transmittance | permeability and wavelength with respect to P polarization | polarized-light and S polarization | polarized-light with an incident angle of 60 degrees of the PBS film | membrane with which the optical element of 2nd Embodiment was equipped. Sectional drawing which shows the form which uses the optical element of 2nd Embodiment as an illumination optical system of transmission type LCD, and an optical system which takes out the light showing an image | video. Sectional drawing which shows typically the structure with respect to the structure of the optical element of 3rd Embodiment, and the effect | action with respect to light. Sectional drawing which shows typically the structure with respect to the structure of the optical element of 4th Embodiment, and the effect | action with respect to light. The figure which shows the relationship between the transmittance | permeability and the wavelength with respect to P polarization | polarized-light and S polarization | polarized-light with an incident angle of 45 degrees of the dichroic film of R light reflection with which the optical element of 4th Embodiment was equipped. The figure which shows the relationship between the transmittance | permeability and wavelength with respect to P polarization | polarized-light and S polarization | polarized-light with an incident angle of 45 degrees of the dichroic film of B light reflection with which the optical element of 4th Embodiment was equipped. The figure which shows the relationship between the transmittance | permeability and wavelength with respect to P polarization | polarized-light and S polarization | polarized-light with an incident angle of 45 degrees of the dichroic film of G light reflection with which the optical element of 4th Embodiment was equipped. Sectional drawing which shows typically the structure with respect to the optical element of 5th Embodiment, and the effect | action with respect to light. The figure which shows the relationship between the transmittance | permeability with respect to the light of wavelength 550nm, and an incident angle of the angle separation film with which the optical element of 5th Embodiment was equipped. Sectional drawing which shows the form which uses the optical element of 5th Embodiment as an illumination optical system of reflection type LCD. Sectional drawing which shows the form which uses the optical element of 5th Embodiment as an illumination optical system of DMD. Sectional drawing which shows the form which uses the optical element of 5th Embodiment as an optical system which takes out the light which represents the illumination optical system of DMD, and an image | video. Sectional drawing which shows typically the structure with respect to the structure of the optical element of 6th Embodiment, and the effect | action with respect to light. Sectional drawing which shows the form which uses the optical element of 6th Embodiment as an illumination optical system of reflection type LCD. The figure which shows the structure of a PBS prism. The figure which shows the conventional optical element for isolate | separating the illumination light and reflected light of reflection type LCD. The figure which shows the conventional optical system for isolate | separating white light into R light, G light, and B light with an angle difference in an optical path. The figure which shows the structure of LCD provided with the micro lens array and illuminated with R light, G light, and B light with an angle difference in an optical path. The figure which shows the conventional optical system which illuminates DMD.

Explanation of symbols

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

Claims (4)

A plate-like transparent base material having a diffraction grating on the surface, and a diffraction grating element provided on the diffraction grating of the transparent base material and provided with a separation coating that reflects or transmits the incident light according to the characteristics of the incident light ,
An illumination optical system characterized in that light is guided to an illumination object by the diffraction grating element to illuminate the illumination object, and light reflected by the illumination object is guided through the diffraction grating element to the outside.   The illumination optical system according to claim 1, wherein the diffraction grating element includes a plate-shaped transparent material that is in close contact with the diffraction grating of the transparent base material with the separation coating interposed therebetween.   The illumination optical system according to claim 1, wherein the separation coating reflects or transmits incident light according to an incident angle of incident light.   The illumination optical system according to claim 1, 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.

Images