JP2006023378A - Projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projector capable of displaying a fine image by reducing the occurrence of moire. <P>SOLUTION: The projector has a spatial optical modulator 17R equipped with aperture parts 61 being a plurality of pixel parts arrayed in a matrix state and modulating incident light in accordance with an image signal, a screen 30 equipped with a lenticular lens 33 being a structural body arranged in a prescribed cycle and transmitting light from the spatial optical modulator 17R, and a prism group 25 being a low-pass filter provided in an optical path between the spatial optical modulator 17R and the screen 30. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a projector, and more particularly, to a technology of a rear projector that displays an image by transmitting light modulated in accordance with an image signal through a screen.

  Conventionally, a so-called rear projector has been proposed that displays an image by transmitting light modulated in accordance with an image signal to a screen. Since rear projectors are relatively easy to increase in screen size, in recent years, expectations for the spread of rear projectors are increasing. The screen of the rear projector is provided with optical elements such as a lenticular lens and a microlens for obtaining a wide viewing angle, for example. When the optical elements arranged in an array are provided on the screen, moire may occur due to the overlap of the periodic structure of the screen and the pixel structure of the spatial light modulator provided by the optical elements. In addition to the occurrence of moiré due to the periodic structures in the components in the rear projector, the moiré may also occur due to the overlapping of the periodic structure in the rear projector and the image pattern. Moire causes degradation of image quality by causing colors and patterns that are not originally included in the image signal to appear. Conventionally, as a technique for reducing moire, for example, there are techniques proposed in Patent Documents 1 and 2.

JP-A-8-289234 JP 2002-139799 A

  The techniques proposed in Patent Documents 1 and 2 both prevent light interference by the configuration of the screen. According to the techniques proposed in Patent Documents 1 and 2, the screen must be constrained to prevent light interference due to its structure. Such a restriction may be an obstacle to realizing a configuration for displaying a fine image by the rear projector or a configuration capable of reducing the cost. Further, as a screen for a rear projector, a technique has been proposed in which light-shielding portions and openings are alternately provided on the light exit surface. The light shielding unit is configured to reduce a decrease in contrast by preventing reflection of external light. The screen of the rear projector further increases the frequency of moiré due to the periodic structure of the light shielding portion and the opening. Thus, the conventional rear projector has a problem that it is difficult to obtain a fine image by reducing the occurrence of moire. The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a projector that can display a fine image by reducing the occurrence of moire.

  In order to solve the above-described problems and achieve the object, according to the present invention, a spatial light modulation device that includes a plurality of pixel units arranged in a matrix and modulates incident light according to an image signal, and a predetermined And a screen that transmits light from the spatial light modulation device, and a low-pass filter that is provided in an optical path between the spatial light modulation device and the screen. A projector can be provided.

  The low-pass filter includes a prism element having a refractive surface, a diffraction grating, an optical element such as a quartz plate. When the light from the spatial light modulator passes through the low-pass filter, the image of the pixel portion is divided into a plurality of images and projected onto the screen. By dividing the image of the pixel portion into a plurality, the periodicity due to the arrangement of the pixel portions in a matrix and the periodicity such as a regular pattern are weakened. In addition, on the screen, for example, optical elements such as a lenticular lens and structures such as a light shielding portion are arranged at a predetermined period. By weakening the periodicity of the projected light and entering the screen, the light interference effect is reduced even when a screen having a periodic structure is used. In this way, it is possible to reduce moire by providing a low-pass filter. According to the present invention, since the low-pass filter is provided in the optical path between the spatial light modulation device and the screen, the screen does not need a restriction on the light interference effect structurally. The screen can be configured to display a fine image or to reduce costs. As a result, it is possible to obtain a projector that can reduce the occurrence of moire and display a fine image.

  According to a preferred aspect of the present invention, the low-pass filter has a prism group including prism elements each having at least a refracting surface, and the prism elements are 3 in a unit area defined by the illumination optical system or the projection optical system. It is desirable that the refractive surface be provided with a period equal to or greater than the period and refract the light from one pixel portion in a predetermined direction. Light from one pixel portion enters the prism group. The light incident on the prism group is refracted by the refracting surface of the prism element, and the optical path is bent in a predetermined direction. By bending light from one pixel portion in a predetermined direction, an image of the pixel portion is divided and projected onto a screen. The image of the pixel portion can be divided into a plurality according to the number of refractive surfaces provided in the prism element. Thereby, the image of a pixel part can be divided | segmented into plurality.

  A substantially uniform image can be obtained by providing three or more prism elements or three or more periods in the unit area. The unit area can be defined by an F number defined by illumination light incident on the spatial light modulator or a projection optical system that projects light onto a screen. Here, the period of the prism elements can be defined by the number of boundary lines forming the boundary between the prism elements when the prism elements are provided in a matrix.

  Preferably, the prism elements of the prism group are provided in a unit area with 5 or more, or 5 cycles or more. Thereby, a substantially uniform projected image can be obtained even at the edge of the image. As described above, a substantially uniform image can be obtained by arranging an appropriate number of prism elements in a unit area. Further, if diffracted light is generated by periodically providing prism elements, it may cause a decrease in image contrast. By providing 15 or less prism elements in a unit area, or less than 15 periods, the occurrence of diffraction phenomenon can be reduced and a good image can be obtained. Furthermore, it is desirable that the prism elements are provided with a period of 12 or less or 12 periods or less within the unit area. As a result, the occurrence of the diffraction phenomenon is further reduced, and an image with good contrast can be obtained.

  Accordingly, it is desirable that the prism group is provided with a prism element in a unit area of 3 to 15 or less, or 3 to 15 cycles. Furthermore, it is desirable that the prism group is provided with prism elements at a cycle of 5 to 12 or 5 cycles to 12 cycles within a unit area. Thereby, light with substantially uniform intensity can be projected onto the screen, and a better image can be obtained by reducing moire and reducing contrast.

According to a preferred aspect of the present invention, the prism element has a flat portion that transmits light from the pixel portion, and is substantially aligned with the optical axis at a position farthest from the flat portion at the intersection of the refractive surface and the optical axis. When the surface formed in the vertical direction is used as a reference surface, when the distance from the reference surface to the flat portion is d, the wavelength of incident light is λ, and the refractive index of the prism element is n, the following conditional expression ( It is desirable to satisfy 1) or (2).
d <0.95 × λ / {2 × (n−1)} (1)
d> 1.05 × λ / {2 × (n−1)} (2)

The prism group generates diffracted light due to the refracted light from the refractive surface and the depth of each prism element constituting the prism group. The distance d from the reference surface to the flat portion is the conditional expression (A)
d = λ / {2 × (n−1)} (A)
When the above condition is satisfied, the prism group improves the diffraction effect. Diffracted light may cause moiré due to light interference on a screen having a periodic structure. In the present invention, it is desirable that diffracted light that causes moiré is not generated, or that the observer does not recognize moiré even when diffracted light is generated. In the present invention, when the conditional expression (1) or (2) is satisfied, the depth d can be set to a numerical value different from the numerical value defined by the conditional expression (A). By satisfying the above conditional expression (1) or (2), generation of diffracted light in the prism group can be reduced. Thereby, generation | occurrence | production of a moire can be reduced.

It is preferable that the following conditional expression (3) or (4) is satisfied.
d <0.9 × λ / {2 × (n−1)} (3)
d> 1.1 × λ / {2 × (n−1)} (4)
More preferably, it is desirable to satisfy the following conditional expression (5) or (6).
d <0.7 × λ / {2 × (n−1)} (5)
d> 1.3 × λ / {2 × (n−1)} (6)
By satisfying any one of the conditional expressions (3) to (6), the intensity of the diffracted light from the prism element can be further reduced. Thereby, generation | occurrence | production of a moire can be reduced further.

  In a preferred aspect of the present invention, the prism element has a flat portion that transmits light from the pixel portion, is substantially perpendicular to the optical axis, and is based on one surface of the substrate on which the prism group is formed. In the case of a surface, it is desirable that the distance from the reference surface to the flat portion and the distance from the reference surface to a predetermined position on the refracting surface are aperiodic.

  One of the structures in which diffracted light is generated by the prism group is a periodic structure of prism elements. The prism group is formed such that the distance from the reference surface to the flat portion and the distance from the reference surface to a predetermined position on the refractive surface are aperiodic. By forming the prism group to be aperiodic, generation of diffracted light due to the periodic structure of the prism element can be reduced. Thereby, generation | occurrence | production of a moire can be reduced.

  As a preferred aspect of the present invention, it is desirable that the prism elements are provided with a period of 15 periods or less within the unit area. One of the structures in which diffracted light is generated by the prism group is a periodic structure of an array of prism elements. The prism group is configured to provide prism elements with a period of 15 periods or less per unit area. The period of the prism elements can be defined by the number of boundary lines forming the boundary between the prism elements when the prism elements are provided in a matrix. By setting the period of the prism elements to 15 periods or less, generation of diffracted light due to the periodic structure of the arrangement of the prism elements can be reduced. Thereby, generation | occurrence | production of a moire can be reduced. Moreover, it is preferable that the prism elements are provided in 10 to 12 cycles per unit area. More preferably, it is desirable that the prism elements are provided in a period of 7 to 9 per unit area. Thereby, generation | occurrence | production of a moire can be reduced further.

  As a preferred aspect of the present invention, the low-pass filter has a phase diffraction grating element that makes the first-order diffracted light incident on a position shifted in a predetermined direction out of the light from the one pixel unit, In addition, it is desirable to provide at a period of 5 cycles or more in the unit area. Light from one pixel portion enters the phase diffraction grating element. The phase diffraction grating element advances diffracted light in a predetermined direction. For example, a phase diffraction grating element divides incident light into a plurality of parts by separating incident light into zero-order light and first-order light. Thereby, the image of a pixel part can be divided | segmented into plurality. In addition, the phase diffraction grating element can provide diffracted light with substantially uniform intensity by providing it with a period of 5 cycles or more in the unit area.

  As a preferred aspect of the present invention, it is desirable that the low-pass filter is a birefringent portion that refracts and separates a part of light from one pixel portion in a predetermined direction. Light from one pixel part enters the birefringent part. The birefringent portion separates incident light into two linearly polarized light, for example, corresponding to the crystal orientation of the birefringent portion. By using a plurality of birefringent portions, light from one pixel portion can be divided into a plurality of portions. Thereby, the image of a pixel part can be divided | segmented into plurality.

  Furthermore, as a preferred embodiment of the present invention, it is desirable to further have a phase plate on the incident side of the birefringent portion. For example, when a transmissive liquid crystal display device is used as the spatial light modulator, the light modulated according to the image signal is linearly polarized light having a specific vibration direction. Linearly polarized light is converted into circularly polarized light by passing through, for example, a λ / 4 phase plate. The birefringence unit can refract and separate a part of the modulated light in a predetermined direction by converting the modulated light into circularly polarized light. Thereby, a part of the modulated light can be refracted and separated in a predetermined direction.

  Moreover, as a preferable aspect of the present invention, it is desirable that the low-pass filter guides the projected image of the pixel portion to a position at a distance of approximately one half or less of the pitch of the plurality of pixel portions on the screen. The pitch of a plurality of pixel portions refers to the distance between the center positions of the pixel portions between adjacent pixel portions. For each pixel, the periodicity of light incident on the screen can be effectively reduced by guiding the projected image of the pixel portion to a position at a distance of approximately one half or less of the pixel pitch. Thereby, generation | occurrence | production of a moire can be reduced effectively and a high definition image | video can be obtained.

  As a preferred embodiment of the present invention, the screen desirably has a periodic structure. The periodic structure is preferably a light shielding portion and an opening. Moire may occur when the periodic structure of the screen and the pixel structure of the spatial light modulator overlap. In addition, moire may occur when the periodic structure of the components in the rear projector and the image pattern overlap. The projector of the present invention can reduce the generation of moire and obtain a high-quality image even when a screen having a periodic structure is used.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

  FIG. 1 shows a schematic configuration of a projector 10 according to Embodiment 1 of the present invention. The projector 10 according to the present invention is a so-called rear projector that displays an image on the screen 30 by transmitting light modulated in accordance with an image signal to the screen 30. The ultra-high pressure mercury lamp 11 that is a light source unit includes red light (hereinafter referred to as “R light”) that is first color light, green light (hereinafter referred to as “G light”) that is second color light, and third light. Light including blue light (hereinafter referred to as “B light”) that is colored light is supplied.

  The integrator 12 makes the illuminance distribution of the light from the extra-high pressure mercury lamp 11 substantially uniform. The light having a uniform illuminance distribution is converted by the polarization conversion element 13 into polarized light having a specific vibration direction, for example, s-polarized light. The light converted into the s-polarized light is incident on the R light transmitting dichroic mirror 14R constituting the color separation optical system. The R light transmitting dichroic mirror 14R transmits R light and reflects G light and B light. The R light transmitted through the R light transmitting dichroic mirror 14 </ b> R enters the reflection mirror 15. The reflection mirror 15 bends the optical path of the R light by 90 degrees. The R light whose optical path is bent is incident on a spatial light modulator 17R that modulates the R light according to an image signal. The spatial light modulator 17R is a transmissive liquid crystal display device that modulates R light according to an image signal. Note that even if the light passes through the dichroic mirror, the polarization direction of the light does not change. Therefore, the R light incident on the spatial light modulation device 17R remains as s-polarized light.

  The s-polarized light incident on the spatial light modulator 17R is converted into p-polarized light and then incident on a liquid crystal panel (not shown). In the liquid crystal panel, a liquid crystal layer for image display is sealed between two transparent substrates. The p-polarized light incident on the liquid crystal panel is converted into s-polarized light by modulation according to the image signal. The spatial light modulator 17R emits R light converted into s-polarized light by modulation. In this way, the R light modulated by the spatial light modulator 17R is incident on the cross dichroic prism 18 which is a color synthesis optical system.

  The G light and B light reflected by the R light transmitting dichroic mirror 14R have their optical paths bent 90 degrees. The G light and B light whose optical paths are bent enter the B light transmitting dichroic mirror 14G. The B light transmitting dichroic mirror 14G reflects the G light and transmits the B light. The G light reflected by the B light transmitting dichroic mirror 14G is incident on a spatial light modulation device 17G that modulates the G light according to an image signal. The spatial light modulator 17G is a transmissive liquid crystal display device that modulates G light according to an image signal.

  The G light incident on the spatial light modulator 17G is converted into s-polarized light. The s-polarized light incident on the spatial light modulator 17G is incident on the liquid crystal panel as it is. The s-polarized light incident on the liquid crystal panel is converted into p-polarized light by modulation according to the image signal. The spatial light modulator 17G emits G light converted into p-polarized light by modulation. Thus, the G light modulated by the spatial light modulation device 17G enters the cross dichroic prism 18.

The B light transmitted through the B light transmitting dichroic mirror 14G enters the spatial light modulation device 17B that modulates the B light according to the image signal via the two relay lenses 16 and the two reflection mirrors 15. To do. The spatial light modulator 17B is a transmissive liquid crystal display device that modulates B light according to an image signal. The reason why the B light passes through the relay lens 16 is that the optical path length of the B light is longer than the optical path lengths of the R light and the G light. By using the relay lens 16, the B light transmitted through the B light transmitting dichroic mirror 14G is directly used as the spatial light modulation device 1.
7B.

  The B light incident on the spatial light modulator 17B is converted into s-polarized light. The s-polarized light incident on the spatial light modulator 17B is converted into p-polarized light and then incident on the liquid crystal panel. The p-polarized light incident on the liquid crystal panel is converted into s-polarized light by modulation according to the image signal. The spatial light modulator 17B emits B light converted into s-polarized light by modulation. In this way, the B light modulated by the spatial light modulator 17B enters the cross dichroic prism 18 which is a color synthesis optical system. The R light transmitting dichroic mirror 14R and the B light transmitting dichroic mirror 14G constituting the color separation optical system separate light supplied from the ultrahigh pressure mercury lamp 11 into R light, G light, and B light.

  The cross dichroic prism 18 which is a color synthesizing optical system is configured by arranging two dichroic films 18a and 18b perpendicularly to an X shape. The dichroic film 18a reflects B light and transmits R light and G light. The dichroic film 18b reflects R light and transmits B light and G light. Thus, the cross dichroic prism 18 combines the R light, G light, and B light modulated by the spatial light modulators 17R, 17G, and 17B, respectively.

  As described above, the light incident on the cross dichroic prism 18 from the spatial light modulator 17R and the spatial light modulator 17B is set to be s-polarized light. The light incident on the cross dichroic prism 18 from the spatial light modulator 17G is set to be p-polarized light. Thus, by making the polarization direction of the light incident on the cross dichroic prism 18 different, the light emitted from the spatial light modulators for each color light in the cross dichroic prism 18 can be effectively combined. The dichroic films 18a and 18b are generally excellent in the reflection characteristics of s-polarized light. For this reason, R light and B light reflected by the dichroic films 18a and 18b are s-polarized light, and G light transmitted through the dichroic films 18a and 18b is p-polarized light.

  The projection lens 20 projects the light combined by the cross dichroic prism 18 toward the reflection mirror 21. As shown in FIG. 2, the projection lens 20 includes a plurality of concave lenses and convex lenses arranged in parallel on the optical axis. In the projection lens 20, a prism group 25, which is a low-pass filter, is disposed at the pupil position, which is the conjugate position of the stop. The prism group 25 is provided in the optical path between the spatial light modulators 17R, 17G, and 17B and the screen 30. Details of the configuration of the prism group 25 will be described later.

  Returning to FIG. 1, the reflection mirror 21 reflects the projection light from the projection lens 20 toward the screen 30. The screen 30 includes a Fresnel lens 30a, a viewing angle adjustment unit 30b, and a front plate (not shown). The light reflected from the reflection mirror 21 in the direction of the viewing angle adjustment unit 30b passes through the Fresnel lens 30a and then enters the screen 30. The Fresnel lens 30a converts incident light into substantially parallel light and emits it. The light converted into parallel light by the Fresnel lens 30a is incident on the viewing angle adjustment unit 30b. The screen 30 is a transmissive screen that displays a projection image on the surface on the side of the observer OBS by transmitting the projection light. The Fresnel lens 30a has a concentric periodic structure.

  FIG. 3 shows a perspective configuration of a main part of the screen 30. The screen 30 has a lenticular lens sheet 32 that is a viewing angle adjustment unit 30b on the surface on which the projection light from the projection lens 20 is incident. The lenticular lens 33 has a shape having a convex surface on the incident side of the projection light. The lenticular lens 33 has a curved surface such as a part of a cylindrical shape having a longitudinal direction in the Y direction that is the vertical direction when viewed from the observer and a curvature in the X direction substantially perpendicular to the Y direction. The lenticular lens sheet 32 includes a plurality of lenticular lenses 33 arranged in the X direction. The lenticular lens sheet 32 may be configured by arranging lenticular lenses 33 having a longitudinal direction in the X direction in the Y direction.

  FIG. 4 shows a cross-sectional configuration of the main part of the screen 30. A plurality of light shielding portions 34 and a plurality of openings 41 are provided on the light exit surface of the screen 30. As shown in FIG. 5, the light shielding part 34 and the opening part 41 are structures that are arranged at a predetermined period so as to form a stripe having a predetermined width. A lenticular lens sheet 32 made up of a plurality of lenticular lenses 33 is provided on the light incident surface of the screen 30. The lenticular lens 33 is provided at a position corresponding to the opening 41. The lenticular lens 33 is also a structure that is arranged at a predetermined cycle, like the light shielding portion 34 and the opening portion 41. As described above, the screen 30 has a periodic structure with a regular pattern on the incident side and the emission side of the projection light. In addition, the predetermined period which provides the lenticular lens 33 can be determined corresponding to the width of the pixel portion images of the spatial light modulators 17R, 17G, and 17B, for example. In addition, the predetermined period in which the opening 41 and the light shielding part 34 are arranged can be determined corresponding to the arrangement of the lenticular lens 33.

  The lenticular lens 33 condenses incident light in the corresponding opening 41. By providing the lenticular lens 33, it is possible to avoid the projection light from being blocked by the light shielding portion 34, and to reduce the loss of the projection light. The light shielding part 34 is provided between the openings 41. The light shielding unit 34 absorbs external light traveling from the observer side toward the screen 30, for example, illumination light from a lighting fixture or sunlight from outside the room. The screen 30 can reduce reflection of external light and improve the contrast of the image by providing the light shielding portion 34.

  FIG. 6 illustrates a periodic structure in the spatial light modulation device 17R. In the liquid crystal panel of the spatial light modulator 17R, a liquid crystal layer for image display is sealed between two transparent substrates. On the light incident side of the liquid crystal layer, a black matrix portion 62 for light shielding is provided. The black matrix portion 62 blocks the R light incident from the ultra high pressure mercury lamp 11 so as not to be emitted to the screen 30 side. The rectangular area surrounded by the black matrix portion 62 forms an opening 61.

  The opening 61 allows the R light from the extra-high pressure mercury lamp 11 to pass through. The R light that passes through the opening 61 passes through the substrate and the liquid crystal layer. The polarization component of the R light incident on the spatial light modulator 17R is modulated in the liquid crystal layer. Thus, the pixels in the projected image are formed by the light modulated by the liquid crystal layer and transmitted through the opening 61. The opening 61 is a pixel portion that transmits light that forms the pixel. The spatial light modulation device 17R includes a plurality of openings 61, which are pixel portions, and is arranged in a matrix.

  The spatial light modulation device 17R can be regarded as a rectangular periodic region composed of the opening 61 and the black matrix portion 62 around the opening 61 is arranged. Adjacent periodic regions are periodically and repeatedly arranged without gaps. As described above, the spatial light modulator 17R has a periodic structure of a regular pattern on the emission side of the modulated light. Note that the configurations of the spatial light modulators 17G and 17B are the same as those of the spatial light modulator 17R.

  Since the spatial light modulators 17R, 17G, and 17B all have the same configuration, the light from the openings 61 of the spatial light modulators 17R, 17G, and 17B is projected so as to overlap each other. Therefore, when the prism group 25 is not provided, an image of a pattern in which periodic regions are repeatedly arranged is formed on the screen 30 as it is by the light from each of the spatial light modulators 17R, 17G, and 17B. Hereinafter, the configuration of the present invention will be described using a projection image appropriately projected on the screen 30.

  FIG. 7 shows a perspective configuration of the prism group 25. The prism group 25 including a plurality of prism elements 71 is formed on the exit side surface of the transparent plate 70 made of glass or transparent resin. The spatial light modulation device 17R and the prism group 25 in the projection lens 20 are arranged in the relationship shown in FIG. For easy understanding, illustration of other components such as the reflection mirror 21 excluding the spatial light modulator 17R and the prism group 25 is omitted in FIG.

  The R light transmitted through the opening 61 which is one pixel portion proceeds as a conical divergent light. The R light is incident on at least some of the prism groups 25 in the prism group 25. The prism group 25 includes a prism element 71 having at least a refracting surface 72 and a flat portion 73. The flat part 73 is a surface substantially parallel to the surface 80a on which the opening 61 is formed. In each of the prism elements 71, the width PT and the depth H from the ridge line between the refracting surfaces 72 to the flat surface 73 are substantially the same. Accordingly, the prism group 25 is configured by regularly arranging a plurality of prism elements 71 at a constant period.

  The flat part 73 transmits the R light from the opening 61 as it is. The refracting surface 72 refracts and transmits the R light from the opening 61. The refracting surface 72 has an orientation and an inclination angle of the refracting surface 72 that guides the opening 61 image onto the black matrix 62 image on the screen 30. The refracting surface 72 is refracted in a predetermined direction that guides light from one opening 61 onto the black matrix 62 image. As a result, on the screen 30, the opening 61 image is formed so as to overlap with the region of the black matrix 62 image.

  9A, 9B, and 9C are plan views showing the positional relationship between the opening 61 and the prism group 25. FIG. Each prism element 71 has a substantially square shape as shown in FIG. Then, with respect to the direction of the center line CL of the belt-shaped black matrix portion 62 shown in FIG. 9A, the direction along the side portion 71a of each prism element 71 is about 45 ° as shown in FIG. It is configured to make. As described above, the light transmitted through one opening 61 is incident on a part of the prism group 25 including the plurality of prism elements 71.

  FIG. 10 shows the prism group 25 in an enlarged manner. Consider a case where a medium (for example, air) between the prism group 25 and the screen 30 has a refractive index n1, and members constituting the prism group 25 have a refractive index n2. The refracting surface 72 is formed to have an angle θ with respect to a reference surface 73 a obtained by extending the flat portion 73. Hereinafter, the angle θ is referred to as an inclination angle. Of the light transmitted through the projection lens 20, the light in the optical axis direction enters the flat portion 73 substantially perpendicularly. The light perpendicularly incident on the flat portion 73 goes straight without being refracted by the flat portion 73 and forms a projected image on the screen 30.

In contrast, the light incident on the refracting surface 72 is refracted so as to satisfy the following conditional expression.
n1 · sinβ = n2 · sinα
Here, the angle α is an incident angle with respect to the normal line N of the refracting surface 72, and the angle β is an exit angle. In addition, the distance S between the position of the light that travels straight and the position of the refracted light on the screen 30 that is separated from the prism group 25 by the distance L is expressed by the following equation.

S = L × Δβ
Δβ = β-α
Thus, by controlling the prism inclination angle θ of the refracting surface 72, the distance S that is the amount of movement of the opening portion image 61P on the screen 30 can be arbitrarily set. As is clear from FIG. 10, the direction in which the light beam LL2 is refracted depends on the direction of the refracting surface 72. In other words, by controlling the direction of the refracting surface 72 with respect to the opening 61, the direction in which the opening image 61P is formed on the screen 30 can be arbitrarily set.

  When the spatial light modulation device 17R having the above-described configuration is used, a projected image by the R light projected on the screen 30 will be described with reference to FIGS. 11-1 to 11-4. FIG. 11A shows one periodic region image 63 </ b> P on the screen 30. The light incident on the flat portion 73 of the prism element 71 substantially perpendicularly travels straight without being refracted by the flat portion 73. The straightly traveling light forms an opening image (direct transmission image) 61P at the center of the periodic region image 63P on the screen 30.

  Next, consider the light incident on the refractive surface 72 a of the prism element 71. The light incident on the refracting surface 72a is refracted by the direction of refraction, the inclination angle θ, and the refraction direction, the amount of refraction, and the amount of light refracted corresponding to the area P1. As described above, the prism element 71 is configured such that the side portion 71 a forms approximately 45 ° with respect to the center line CL of the black matrix portion 62. Therefore, for example, the light refracted by the refracting surface 72a is, as shown in FIG. 11A, the opening portion image 61Pa at a position away from the opening portion image (direct transmission image) 61P by the distance S described above in the arrow direction. Form. In all of the following description, it is assumed that there is no upside-down and left-right inversion of the image due to the imaging action of the projection lens 20.

  Similarly, the light refracted by the refractive surface 72b forms an opening image 61Pb at the position shown in FIG. The light refracted by the refracting surface 72c forms an opening image 61Pc at the position shown in FIG. The light refracted by the refracting surface 72d forms an opening image 61Pd at the position shown in FIG. 11-4. FIGS. 11A to 11D illustrate the opening region images 61Pa, 61Pb, 61Pc, and 61Pd separately for the same periodic region image 63P.

  Actually, these four opening images 61Pa, 61Pb, 61Pc, and 61Pd are superimposed and projected as shown in FIG. As described above, the prism element 71 includes the four refracting surfaces 72, thereby dividing the opening image 61P of the opening 61 into the four opening images 61Pa, 61Pb, 61Pc, and 61Pd and projecting them onto the screen 30. By dividing the opening portion image 61P into a plurality of portions, the periodicity of the projection light by arranging the opening portions 61 in a matrix is weakened. Further, the periodicity such as a regular pattern in the image can be weakened by dividing the opening portion image 61P into a plurality of portions. By weakening the periodicity of the projection light incident on the screen 30, the light interference effect is reduced even when the screen 30 having a periodic structure is used. Further, even when an image finer (higher resolution) than the display resolution is displayed by the projector 10, light interference caused by the periodic structure in the projector 10 and the periodicity of the image can be reduced.

  Thus, by providing the prism group 25 that is a low-pass filter, it is possible to reduce the occurrence of moire. Since the prism group 25 is provided in the optical path between the spatial light modulators 17R, 17G, and 17B and the screen 30, interference of light can be reduced regardless of the configuration of the screen 30. Eliminates the need for a configuration for reducing light interference. The screen 30 can be configured to display a fine image and to reduce costs without being restricted in structure for preventing light interference. Thereby, there is an effect that the generation of moire can be reduced and a fine image can be displayed.

  In particular, in the present embodiment, the periodic region image 63P is filled with the opening images 61Pa, 61Pb, 61Pc, and 61Pd without a gap. Thus, in the prism element 71, the intersection points CPa, CPb, CPc, CPd of the center line image CLP of the black matrix portion image 62P substantially coincide with one corner portion of the opening portion image (direct transmission image) 61P. Then, the direction of the refracting surface 72 and the inclination angle θ are set. For this reason, the nonuniformity of the projection light to the screen 30 can be reduced, and the periodicity of the projection light can be reduced.

  9-3, it is assumed that one side of the square prism element 71 has a length La and one side of the flat portion 73 has a length Lb. An area La × La occupied by one prism element 71 in the prism group 25 is defined as a unit area. The flat part 73 has an area FS = Lb × Lb. The four refracting surfaces 72a, 72b, 72c and 72d have areas P1, P2, P3 and P4, respectively. Here, the amount of light that has traveled straight through the flat portion 73 corresponds to the area FS of the flat portion 73 occupying the unit area. Similarly, the total amount of light refracted by the four refractive surfaces 72a, 72b, 72c, 72d corresponds to the total area P1 + P2 + P3 + P4 of the refractive surfaces 72a, 72b, 72c, 72d occupying the unit area. Here, if the areas P1, P2, P3, and P4 of the four refracting surfaces 72a, 72b, 72c, and 72d are approximately the same size, the total area is P1 + P2 + P3 + P4 = 4 × P1. In other words, by controlling the area of the flat portion 73 or the refracting surface 72, the amount of light to be straightly moved and the amount of light to be refracted can be arbitrarily set.

  In order to effectively reduce moiré, it is desirable that the amount of light of the projected image (directly transmitted image) transmitted straight through the flat portion 73 is equal to the amount of light of the projected image refracted by the refracting surface 72. . For example, if the length La = 1.0 and the length Lb = 0.707, the unit area of the prism element 71 is 1.0 (= 1.0 × 1.0), and the area FS of the flat portion 73 is 0.00. 5 (= 0.707 × 0.707). The total area (4 × P1) of the four refracting surfaces 72a, 72b, 72c and 72d having the same area is 0.5 (= 1.0−0.5). When the prism element 71 is designed in this way, the amount of light that passes straight through the flat portion 73 and the total amount of light refracted by the four refractive surfaces 72a, 72b, 72c, and 72d can be made equal. Thus, the light intensity ratio can be freely designed by designing the prism surface area ratio to a desired ratio.

  The prism group 25 that is a low-pass filter may be arranged in the optical path between the spatial light modulators 17R, 17G, and 17B and the screen 30. For example, a prism group 135 may be provided on the exit surface of the cross dichroic prism 18 as in the projector 130 shown in FIG. By adopting a configuration in which each color light synthesized by the cross dichroic prism 18 is incident on the prism group 135, the prism group 135 can be made one, and the projector 130 can be simplified. Note that a prism group 25 may be provided between each of the spatial light modulators 17R, 17G, and 17B and the cross dichroic prism 18. When the prism group 25 is provided for each color light, the refraction angle can be set corresponding to each wavelength. As a more preferable embodiment, as shown in FIG. 2, the low-pass filter can be reduced in size and light intensity by inserting the low-pass filter at a position where the projection light is condensed at a high density by inserting it at the pupil position of the optical path. It is possible to achieve both uniformity.

  The configuration of the screen 30 is not limited to the above, and any configuration having a periodic structure with a regular pattern may be used. For example, the screen 30 may have a configuration in which the light shielding portion 34 is not provided. The projector 10 can obtain an effect of reducing the occurrence of moire due to the regular arrangement of the lenticular lenses 33 even when the light shielding portion 34 is not provided on the screen 30. In addition, as long as the light shielding portion 34 is not provided, the lenticular lens sheet 32 may be provided on the viewer side of the screen 30. The lenticular lens sheet 32 serves to widen the viewing angle of the screen 30 by being provided on the viewer side of the screen 30. Also in this case, generation of moire can be reduced by using the prism group 25.

  Further, the screen 30 may be configured to include a microlens array instead of the lenticular lens sheet 32. As the microlens array, for example, an array in which circular microlens elements are arranged in a matrix can be used. Further, for example, when a plurality of rod integrators that make light substantially uniform are regularly arranged, or when a structure that scatters light is regularly arranged, the use of the prism group 25 reduces the occurrence of moire. can do.

  The screen 30 of this embodiment includes both a Fresnel lens 30a and a lenticular lens sheet 32. An object of the present invention is to reduce moire caused by a spatial light modulator having a periodic structure and a screen structure having periodicity. Therefore, the present invention is effective not only for the projector 100 having both the Fresnel lens 30a and the lenticular lens sheet 32 in the screen 30, but also for the projector having at least one periodic structure in the screen.

  Further, the spatial light modulator is not limited to the case where a transmissive liquid crystal display device is used. As the liquid crystal display device, a reflective liquid crystal display device may be used. For example, a DMD that is a tilt mirror device has a structure in which micromirrors are arranged in a matrix. For this reason, even when DMD is used as the spatial light modulator, moire can be reduced as in the case of using a liquid crystal display device. In addition, when using a self-luminous element such as an organic EL element, it is possible to reduce the occurrence of moire due to the periodic structure of the pixel.

  FIG. 14 illustrates changes in the intensity distribution of the projection light caused by providing the prism group 25. In each graph shown in FIG. 14, the vertical axis represents the intensity I of the projection light, and the horizontal axis represents the distance x in the X direction (I and x are arbitrary units). The distance S (see FIG. 10), which is the amount of movement of the opening portion image 61P, is a distance that is approximately half or less of the pitch of the plurality of opening portions 61 due to the inclination angle θ of the refractive surface 72 of the prism group 25. Here, the pitch of the plurality of openings 61 refers to the distance between the center positions of the adjacent openings 61.

  It is assumed that three images of the opening 61 that is a pixel portion are arranged around the respective positions of x = 0, 20, and 40 on the screen 30. When the prism group 25 is not provided, the projection light A1 exhibits an intensity distribution having a peak at the center of the aperture 61 image. Further, since the image of the opening 61 is projected as it is onto the screen 30, the intensity I of the projection light becomes substantially zero at the position of x = 10, 30 where the image of the black matrix portion 62 is formed. The greater the difference ΔI between the maximum and minimum values of the intensity I of the projection light, the stronger the periodicity of the projection light, and the more likely moire occurs.

  When the prism group 25 that forms the image of the opening 61 is provided at a position that is approximately a half of the pitch of the opening 61, the light from the opening 61 is separated into light that is refracted and light that travels straight. . The intensity of the light B2 that travels straight from the opening 61 is weakened as much as part of the light is separated compared to the light A1. The light refracted by the prism group 25 becomes light C2 having a peak at the positions of x = 10 and 30, which are positions shifted by a half pitch. The intensity difference ΔI of the light A2 that is a combination of the light B2 that travels straight through the prism group 25 and the light C2 that is refracted can be reduced compared to the light A1.

  When the prism group 25 that forms an aperture image is provided at a position that is approximately a quarter of the pitch of the aperture 61, the light from the aperture 61 is shifted by a quarter pitch from the light B3 that travels straight. It is separated into light C3 and D3 having a peak at the position. The light A3 obtained by combining the lights B3, C3, and D3 can reduce the intensity difference ΔI compared to the light A1. When the intensity difference ΔI is reduced, the regularity of the projection light due to the pixel structure is weakened, and the light interference in the periodic structure of the screen 30 can be reduced. Further, light interference due to the overlap between the periodic structure in the projector 10 and the pattern of the image can be reduced. In this way, the generation of moire can be reduced by providing the prism group 25 that guides the projected image of the opening 61 to a position at a distance of approximately one half or less of the pitch of the opening 61 that is the pixel portion. Can do.

  Here, the example in which the projected image of the opening 61 is shifted in the X direction has been described. However, the position is not limited to the X direction and is about a half or less of the pitch of the opening 61 in the Y direction. It is also possible to guide the projection image of the opening 61. Further, when the projection image of the opening 61 is shifted to a position in the oblique direction, the projection image may be guided to a position having a distance of approximately one half or less of the pitch in the oblique direction of the plurality of openings 61.

  In the prism group 25, the position of the opening 61 image can be set as appropriate in accordance with the direction and inclination angle of the refracting surface 72. For example, as shown in FIG. 15A, the opening portion image 151P is separated into a position separated by a distance S in an oblique 45 ° direction indicated by an arrow. Then, a new opening image 150P may be formed by the four opening images 151Pa, 151Pb, 151Pc, and 151Pd. Further, as shown in FIG. 15B, the new aperture image 153P is formed by separating the aperture image 152P at a position separated by the distance S and superimposing the two aperture images 152Pa and 152Pb. good.

  FIGS. 16-1 to 16-4 show examples of various variations of the shape of the prism elements. For example, FIG. 16A shows a prism group 161 in which trapezoidal prism elements each having a refractive surface 161a and a flat portion 161b are provided at a predetermined interval. FIG. 16-2 shows a prism group 162 having a refracting surface 162a and a flat portion 162b, in which trapezoidal prism elements are provided without gaps. FIG. 16C shows a prism group 163 having a refracting surface 163a and a flat portion 163b, and triangular prism elements provided at predetermined intervals. FIG. 16-4 shows a blazed prism group 164 composed only of the refractive surface 164a. As described above, various variations can be made using the direction of the refracting surface, the inclination angle, and the area as parameters.

  FIG. 17 shows a schematic configuration in which a part of another form of the prism group is enlarged. The prism group 210 includes a first prism element 211 having a quadrangular pyramid shape and a second prism element 212 having a quadrangular pyramid shape. The first prism element 211 is formed so that one side thereof forms approximately 45 ° with respect to the center line CL. The second prism element 212 is formed so that one side thereof is substantially parallel to the center line CL. Further, a flat portion 215 is provided around the first prism element 211 and the second prism element 212.

  As shown in FIG. 18, an aperture image (direct transmission image) 220P is formed by the light transmitted through the flat portion 215. Then, an opening portion image 213P is formed in the 45 ° direction with respect to the center line image CLP by the refractive surface 213 of the first prism element 211. The refraction surface 214 of the second prism element 212 forms an opening image 214P in a direction parallel to the center line image CLP. Then, the direction of the refracting surface and the inclination angle are set so that these projected images fill the black matrix portion 62 image without any gap. Thereby, unevenness in intensity of the projected image can be reduced. Further, the shape of the prism group that causes the same refraction action as that of the prism group 210 can be variously modified. For example, a prism group 230 having a refracting surface 231 and a flat portion 232 as shown in FIG. 19 can be used. In this way, it is possible to form the prism refracting surface and the flat surface in an arbitrary shape with a desired area ratio.

  FIG. 20 illustrates a perspective configuration of a main part of a prism group 240 that is a low-pass filter according to the second embodiment. The prism group 240 of this embodiment can be applied to the projector 10 of the first embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted. The prism group 240 includes two sets of prism elements 241a and 241b. The prism element 241a has a substantially trapezoidal cross-sectional shape in the y-axis direction that is the first direction. The prism element 241a has a longitudinal direction in the x-axis direction, which is a second direction substantially orthogonal to the y-axis direction, which is the first direction. Of the trapezoidal shape having a cross-sectional shape in the y-axis direction of the prism element 241a, the two inclined surfaces Y1 and Y2 function as refractive surfaces. Of the cross-sectional shape of the prism element 241a in the y-axis direction, the upper surface Y0 functions as a flat portion. For this reason, the light incident on the slope Y1 or the slope Y2 is refracted in a direction corresponding to the angle of the slope. A refracted transmission image is formed by the refracted light. Further, the light incident on the upper surface Y0 is transmitted as it is. A direct transmission image is formed by the light transmitted as it is.

  The prism element 241b has the same configuration as the prism element 241a. Of the cross-sectional shape of the prism element 241b in the x-axis direction, the two inclined surfaces X1 and X2 function as refractive surfaces. Of the cross-sectional shape of the prism element 241b in the x-axis direction, the upper surface X0 functions as a flat portion. The two sets of prism elements 241a and 241b are provided so that their longitudinal directions are substantially orthogonal to each other.

In the prism group 240 of this embodiment, the plane side of the prism element 241a and the plane side of the prism element 241b face each other and are fixed. However, the present invention is not limited to this, and any of the following configurations (1) to (3) may be used.
(1) A configuration in which the surface on which the slopes Y1, Y2, etc. of the prism element 241a are formed and the surface on which the slopes X1, X2, etc. of the prism element 241b are formed face each other and are fixed.
(2) A configuration in which the surface on which the slopes Y1, Y2, etc. of the prism element 241a are formed and the plane side of the prism element 241b face each other and are fixed.
(3) A configuration in which the flat surface side of the prism element 241a and the surface on which the inclined surfaces X1, X2, etc. of the prism element 241b are formed face each other and are fixed.
Although FIG. 20 illustrates the configuration in which the prism surfaces are in contact, a configuration in which both surfaces are in contact with air may be employed.

  FIG. 21 shows the splitting of incident light by the prism group 240. In FIG. 21, incident light XY travels from the left side toward the right side. In addition, in a part of FIG. 21, for convenience of explanation, the light beam is specified by using the signs of the slopes Y0, Y1, and Y2. Incident light XY is split into three light beams, a light beam Y1 and Y2 refracted on the slope and a light beam Y0 that is transmitted through the upper surface as it is, by a prism element 241a indicated by a dotted line. The three branched light beams Y0, Y1, and Y2 are further branched into three light beams by the prism element 241b. As a result, the incident light XY is branched into nine light beams Y1X1, Y1X0, Y1X2, Y0X1, Y0X0, Y0X2, Y2X1, Y2X0, and Y2X2.

  Next, the positions of the nine branched light beams on the projection plane will be described with reference to FIG. A region of a direct transmission image by the light ray Y0X0 is shown surrounded by a thick frame. Projected images of the pixel portion by the refracted light can be formed in directions orthogonal to the longitudinal directions of the prism elements 241a and 241b. The prism group 240 is configured such that the longitudinal directions of the two sets of prism elements 241a and 241b are substantially orthogonal to each other. As a result, a region of a refracted transmission image by the eight light beams Y1X1, Y1X0, Y1X2, Y0X1, Y0X2, Y2X1, Y2X0, and Y2X2 is formed around the region of the direct transmission image by the light beam Y0X0. In FIG. 22, each region is shown with a light beam symbol. Further, the direct transmission image by the light beam Y0X0 is formed periodically adjacent to the positions of the plurality of openings 61. The prism group 240 forms a refracted transmission image in a region between the direct transmission images of the light beam Y0X0 by the prism elements 241a and 241b. Thereby, the periodicity of the projection light can be reduced.

The prism group 240 has a total light intensity of PW0 via the upper surface Y0 of the prism element 241a that is a flat surface and the upper surface X0 of the prism element 241b, and light that passes through the inclined surfaces Y1, Y2, X1, and X2 that are refractive surfaces. When the total strength is PW1,
PW0 ≧ PW1
Is satisfied. PW0 and PW1 are the light intensities on the screen 30.

  The sum of the light intensities of the directly transmitted image by the light beam Y0X0 corresponds to the areas of the upper surfaces Y0 and X0 which are flat portions. Further, the sum of the light intensities of the refracted transmission images by the light rays Y1X1, Y1X0, Y1X2, Y0X1, Y0X2, Y2X1, Y2X0, and Y2X2 corresponds to the areas of the inclined surfaces Y1, Y2, X1, and X2 that are refracting surfaces. Here, if the total light intensity PW1 of the refracted transmission image by the light rays Y1X1, Y1X0, Y1X2, Y0X1, Y0X2, Y2X1, Y2X0, Y2X2 becomes larger than the total light intensity PW0 of the direct transmission image, the observer May recognize double images such as ghosts, for example.

  In the present embodiment, PW0 ≧ PW1 is satisfied. For this reason, generation | occurrence | production of a moire can be reduced similarly to the said Example 1. FIG. Moreover, it is preferable that PW0> PW1 is satisfied. More preferably, it is desirable to satisfy PW0> 0.9 × PW1. As a result, the original pixel information can be maintained while uniforming the light intensity distribution by the pixel arrangement, so that moire can be reduced and a higher definition projection image can be obtained.

  FIG. 23A shows the light intensity distribution of the projected image on the screen 30. In FIG. 23-1, the horizontal axis represents position coordinates on the screen 30, and the vertical axis represents arbitrary intensity units. For the sake of simplicity of explanation, the BB cross section passing through the approximate center of the three regions of the direct transmission image region I shown in FIG. 22, the adjacent direct transmission image region K, and the region J between these regions will be described. To do. That is, the part indicated by reference numeral I on the horizontal axis in FIG. 23-1 corresponds to the area I in FIG. 22, the part indicated by reference numeral J corresponds to the area J in FIG. 22, and the part indicated by reference numeral K is the area in FIG. Corresponds to K.

  As shown in FIG. 23A, in the screen 30, the first peak value Pa of the intensity distribution in the region I and the region K of the projected image 61 of the opening 61 formed by light from the upper surfaces Y0 and X0 which are flat portions. Is larger than the second peak value Pb of the intensity distribution of the region J of the projected image of the opening 61 formed by light passing through the inclined surfaces Y1, Y2, X1, and X2 that are refractive surfaces. For example, the second peak value Pb is set to a power distribution that is approximately half of the first peak value Pa. The power distribution of the light intensity can be controlled according to the area ratio between the upper surfaces Y0 and X0 of the prism elements 241a and 241b and the inclined surfaces Y1, Y2, X1 and X2. Further, the region between the first peak value Pa and the second peak value Pb has a light intensity corresponding to a predetermined intensity distribution curve CV. Thereby, the periodicity of the projection light can be reduced, and the occurrence of moire can be reduced.

  Modified examples of the light intensity distribution are shown in FIGS. 23-2, 23-3, and 23-4, respectively. In FIG. 23-2, each of the two first peak values Pc of the light intensity distributions of the region I and the region K is larger than the second peak value Pc of the region J. In FIG. 23C, the first peak value Pe of the light intensity distribution in the region I and the region K is larger than the two second peak values Pf in the region J. In FIG. 23-4, the first peak values Pg of the light intensity distributions in the region I and the region K are substantially the same as the second peak value Pg in the region J. In these power distributions, the periodicity of the projection light can be reduced, and the occurrence of moiré can be reduced.

FIG. 24 illustrates a cross-sectional configuration of a main part of a prism group 280 that is a low-pass filter according to the third embodiment. The prism group 280 of the present embodiment can be applied to the projector 10 of the first embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted. In the prism group 280, two refracting surfaces 280a form periodic V-shaped grooves. The reference surface 281 formed in the direction substantially perpendicular to the optical axis AX at the position farthest from the flat portion 280b at the intersection of the refracting surface 280a and the optical axis AX is separated from the flat portion 280b by a distance d. The distance d corresponds to the depth of the V-shaped groove. Hereinafter, the distance d will be appropriately referred to as the depth d. The distance d satisfies the conditional expression (1) or (2).
d <0.95 × λ / {2 × (n−1)} (1)
d> 1.05 × λ / {2 × (n−1)} (2)

Here, the refractive index of the members constituting the prism group 280 is n, and the wavelength of light incident on the prism group 280 is λ. In this embodiment, the distance d (depth) is 1100 nm. The depth of the V-shaped groove is conditional expression (A),
d = λ / {2 × (n−1)} (A)
If the above condition is satisfied, the diffraction effect by the prism group 280 is improved.

In this embodiment, light in the visible light region is used as the incident light among the light from the ultrahigh pressure mercury lamp 11. For example, when the wavelength λ of incident light is 480 nm and the refractive index n of the prism group 280 is 1.46, from the conditional expression (A),
d = 480 / {2 × (1.46-1)}
= 522nm
It becomes.

Similarly, when the wavelength λ of incident light is 650 nm and the refractive index n of the prism group 280 is 1.46, from the conditional expression (A),
d = 650 / {2 × (1.46-1)}
= 707nm
It becomes.

  Thus, when the wavelength λ of the incident light is 480 nm, diffracted light is effectively generated when the depth d of the V-shaped groove is 522 nm. Further, when the wavelength λ of the incident light is 650 nm, diffracted light is effectively generated when the depth d of the V-shaped groove is 707 nm. The diffracted light may cause moiré when the light interferes with the screen 30 having a periodic structure. In the present embodiment, it is desirable that the depth d of the V-shaped groove does not cause diffracted light or that the observer does not recognize even when diffracted light is generated.

For this reason, in the present embodiment, the distance d (depth) defined by the conditional expression (A) can be made different from satisfying the conditional expression (1) or (2). For example, in this embodiment, when the wavelength λ = 480 nm, from the conditional expression (1),
d <0.95 × λ / {2 × (n−1)}
= 0.95 × 480 / {2 × (1.46-1)}
= 496nm
From conditional expression (2),
d> 1.05 × λ / {2 × (n−1)}
= 1.05 × 480 / {2 × (1.46-1)}
= 548nm
It becomes.

Further, when the same calculation is performed at the wavelength λ = 650 nm, from the conditional expression (1),
d <0.95 × λ / {2 × (n−1)}
= 0.95 × 650 / {2 × (1.46-1)}
= 671nm
From conditional expression (2),
d> 1.05 × λ / {2 × (n−1)}
= 1.05 × 650 / {2 × (1.46-1)}
= 742nm
It becomes. In this embodiment, the depth d is 1100 nm as described above. Thereby, since the conditional expression (2) is satisfied at any wavelength λ, generation of diffracted light in the prism group can be reduced. Thereby, there exists an effect that generation | occurrence | production of a moire can be reduced.

In the present embodiment, it is preferable that the following conditional expression (3) or (4) is satisfied.
d <0.9 × λ / {2 × (n−1)} (3)
d> 1.1 × λ / {2 × (n−1)} (4)
More preferably, it is desirable to satisfy the following conditional expression (5) or (6).
d <0.7 × λ / {2 × (n−1)} (5)
d> 1.3 × λ / {2 × (n−1)} (6)
By satisfying any one of the conditional expressions (3) to (6), the intensity of the diffracted light from the prism group 280 can be further reduced. Thereby, generation | occurrence | production of a moire can be reduced further.

  FIG. 25 illustrates a cross-sectional configuration of a main part of a prism group 290 that is a low-pass filter according to the first modification of the present embodiment. About the same part as said prism group 280, the overlapping description is abbreviate | omitted. In this modification, the distances d1, d3, d5 from the reference surface 291 to the flat portion 290b and the distances d2, d4, d6 from the reference surface 291 to a predetermined position on the refractive surface 290a are aperiodic. It is formed as follows. The reference surface 291 is one surface of the substrate that is substantially perpendicular to the optical axis AX and on which the prism group 290 is formed. Here, the predetermined position on the refracting surface 290a means a position closest to the reference surface 291 among the refracting surfaces 290a.

  One of the structures in which diffracted light is generated by the prism group 290 is a periodic structure of prism elements. In the present embodiment, the generation of diffracted light due to the periodic structure of the prism element can be reduced by the above-described aperiodic configuration. By reducing the generation of diffracted light in the prism group, it is possible to reduce the occurrence of moire.

  FIG. 26 illustrates a perspective configuration of a main part of a prism group 300 that is a low-pass filter according to the second modification of the present embodiment. About the same part as said prism group 280, the overlapping description is abbreviate | omitted. In this modification, the prism elements 301 of the prism group 300 are arranged on the transparent plate 302 along the shapes of substantially straight lines La1, La2, La3, La4, and La5. The number of the substantially straight lines La1, La2, La3, La4, La5 is five per unit area aφ. The number of the substantially straight lines La1, La2, La3, La4, and La5 may be 15 or less per unit area. The prism elements 301 are provided with a cycle of 15 cycles or less per unit area. The unit area aφ will be described later.

  FIG. 27 is a front view of the vicinity of the unit area aφ. Six straight lines Lb1, Lb2, Lb3, Lb4, Lb5, and Lb6 are formed substantially orthogonal to the substantially straight lines La1, La2, La3, La4, and La5. The straight lines Lb1, Lb2, Lb3, Lb4, Lb5, and Lb6 may also be 15 or less per unit area. Thus, the prism elements 301 of the prism group 300 are formed in a substantially orthogonal lattice shape.

  FIG. 28 shows an optical path from the ultrahigh pressure mercury lamp 11 to the screen 30 for explaining the unit area aφ. In FIG. 28, for convenience of explanation, only an ultrahigh pressure mercury lamp 11 and an integrator 12 constituting the illumination system ILL and the projection lens 20 constituting the projection system PL are shown as optical systems, and other color separation optical systems are shown. Such illustration is omitted. For convenience, the projection lens 20 is shown as a biconvex single lens. In FIG. 28, the projection lens 20 and the projection system PL coincide. For the sake of convenience, the light transmitted through the spatial light modulation device 17R is shown.

  Illumination light from the ultra-high pressure mercury lamp 11 enters the integrator 12. The integrator 12 illuminates the spatial light modulator 17R by superimposing illumination light from the ultrahigh pressure mercury lamp 11. The illumination light from the integrator 12 enters the spatial light modulator 17R with a predetermined angular distribution. The position OBJ on the spatial light modulator 17R is illuminated in a superimposed manner with light of various incident angles. Then, the light from the position OBJ enters the prism group 300 while spatially spreading at the F number of the illumination system ILL. The light emitted from the spatial light modulator 17R passes through the prism group 300 and enters the projection lens 20.

The modulation surface of the spatial light modulation device 17R and the screen 30 are in a conjugate relationship. For this reason, the position OBJ on the spatial light modulator 17R forms an image at the position IMG on the screen 30. At this time, the light from the position OBJ on the spatial light modulator 17R is projected onto the screen 30 by the projection lens 20 with the F number that is the same as or smaller than the F number of the projection lens 20. The following three relationships (B), (C), and (D) are conceivable between the F number of the illumination system ILL and the F number of the projection system PL.
(B) F number of illumination system ILL> F number of projection system PL (C) F number of illumination system ILL = F number of projection system PL (D) F number of illumination system ILL <F number of projection system PL

In any relationship, only the light in the angular range defined by the smaller F number of the illumination system ILL or the projection system PL is effectively projected on the screen 30 on the spatial light modulator 17R. For example, in the case of the relationship (B) or (C), the following equation is established.
1 / (2FILL) = sin θa
Here, FILL is the F number of the projection system PL, and θa is the angle formed with the optical axis of the light emitted from the position OBJ.

  The light emitted from the spatial light modulator 17R at the spatial spread angle θa irradiates a unit area aφ which is a circular area on the prism group 300. Thus, all the light from the unit area aφ on the prism group 300 is projected onto the screen 30 by the projection lens 20. On the other hand, in the case of the relational expression (D), the unit area aφ on the prism group 300 that is effectively projected onto the screen 30 is defined by the F number of the illumination system ILL.

  Accordingly, in any of the relationships (B), (C), and (D), the light from the unit area aφ on the prism group 300 is effectively projected on the screen 30 by the projection lens 20. As described above, one of the structures in which diffracted light is generated by the prism group 300 is a periodic structure in which prism elements are arranged. In this modification, the prism group 300 is arranged along the shapes of substantially straight lines La1 to La5 and Lb1 to Lb6 per unit area aφ. For this reason, the number of substantially straight lines is 15 or less per unit area aφ. Thereby, generation | occurrence | production of the diffracted light resulting from the periodic structure of the arrangement | sequence of a prism element can be reduced, and generation | occurrence | production of a moire can be reduced. In addition, the prism elements can be provided with a period of three or more in the unit area aφ to obtain a substantially uniform image.

  Further, the total area of the refracting surfaces 72 refracted in a predetermined direction and the total area of the flat portion 73 per unit area aφ may be the same value in any unit area. Thereby, the diffracted light is reduced in the projected image, and the projection image of the opening 61 is formed on the screen 30 that is separated from the prism group 300 by a predetermined distance so as to be superimposed on the region of the projection image of the black matrix portion 62. Is done. Therefore, unevenness of the projection light on the screen 30 can be reduced, and the periodicity of the projection light can be reduced.

  In the present modification, it is preferable that the prism group is provided with prism elements at a period of 3 to 15 per unit area aφ, or 3 to 15 cycles. More preferably, in the prism group, it is desirable to provide the prism elements at a period of 5 or more and 12 or less, or 5 or more and 12 or less per unit area aφ. Accordingly, the generation of diffracted light due to the periodic structure of the arrangement of the prism elements can be surely reduced, moire can be surely reduced, and a uniform image can be obtained.

  FIG. 29A shows a cross-sectional configuration of a main part when the prism group 330 is made of glass. In this case, the depth d1 = about 30 nm and the angle θ1 with respect to the reference plane 331 = about 0.06 °. FIG. 29-2 shows a cross-sectional configuration of a main part when the prism group 330 is made of acrylic or ZEONEX (trade name). An optically transparent resin substrate 332 and glass substrate 333 are formed on the prism group 330. In this case, the depth d2 = about 1 μm and the angle θ2 = about 0.97 °. Thus, since both the depth and the angle are larger than the configuration of FIG. 29-1, the prism group 330 can be easily manufactured.

  FIG. 30 illustrates a cross-sectional configuration of a main part of a prism group 340 that is a low-pass filter according to Modification 3 of the present embodiment. About the same part as said prism group 280, the overlapping description is abbreviate | omitted. The prism group 340 of this modification is configured by alternately arranging three prism elements 341a, 341b, and 341c and fixing them with an optical adhesive. As shown in FIG. 31, the prism elements 341a and 341c are band-shaped prism elements formed so that the directions of inclination of the refracting surfaces 351a and 352c are opposite to each other. The prism element 341b is a parallel plate on which a flat portion 351b is formed. Then, the prism elements 341a, 341b, and 341c are set as one set, and a plurality of sets are arranged to constitute the prism group 340. Further, the prism group 340 is provided so as to overlap in two directions substantially orthogonal to each other. Thereby, it has a function similar to that of the prism group having the flat portion 351b and the refracting surfaces 351a and 351c that are refracted in two substantially orthogonal directions.

  In this modification, substantially flat prism elements 341a, 341b, and 341c may be manufactured. For this reason, the prism group 340 can be manufactured very simply. In addition, diffracted light can be reduced by arranging 15 or less prism elements 341a, 341b, and 341c per unit area aφ.

  FIG. 32 shows a top view of a main part of a prism group 360 that is a low-pass filter according to the fourth modification of the present embodiment. About the same part as said prism group 280, the overlapping description is abbreviate | omitted. In the prism group 360 of this modification, the positions and depths of the prism elements 361a, 361b, and 361c are arranged in the unit area aφ in a non-periodic (random) manner. Thereby, diffracted light can be reduced. Further, the total area of the refracting surfaces 362 refracted in a predetermined direction and the total area of the flat portion 363 per unit area aφ may be the same value in any unit area aφ. Note that the present invention is not limited to each configuration described in this embodiment. The configuration in which the prism group does not generate diffracted light, or the configuration in which the observer does not recognize even when diffracted light is generated may be a configuration in which the configurations of the present embodiment are arbitrarily combined.

  FIG. 33 illustrates a perspective configuration of a main part of a phase diffraction grating element 370 that is a low-pass filter according to the fourth embodiment. The phase diffraction grating element 370 according to the present embodiment can be applied to the projector 10 according to the first embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted. The phase diffraction grating element 370 is configured by arranging substantially square recesses 371 in a checkered pattern on the surface of the transparent plate 372. Similarly to the first embodiment, when the phase diffraction grating element 370 is not provided, an image of a pattern in which periodic regions are repeatedly arranged is projected onto the screen 30 as it is by the light from the spatial light modulators 17R, 17G, and 17B. The phase diffraction grating element 370 causes the first-order diffracted light out of the light from one pixel unit to enter a position shifted in a predetermined direction.

  FIG. 34 shows the relationship among the spatial light modulator 17R, the phase diffraction grating element 370, and the screen 30. In order to facilitate understanding, illustration of other components such as the spatial light modulator 17R, the phase diffraction grating element 370, and the reflection mirror 21 excluding the screen 30 is omitted. The R light transmitted through the opening 61 which is one pixel portion proceeds as a conical divergent light. The R light is incident on a part of the phase diffraction grating element 370.

  The concave portion 371 of the phase diffraction grating element 370 and the convex portion around the concave portion 371 have a surface substantially parallel to the exit surface of the spatial light modulator 17R. The light in the optical axis direction is incident substantially perpendicular to the surface of the phase diffraction grating element 370 that is substantially parallel to the spatial light modulator 17R. The light incident substantially perpendicularly to the phase diffraction grating element 370 does not receive a refraction action at the phase diffraction grating element 370 and goes straight as it is as the 0th order light.

  Phase diffraction grating element 370 generates diffracted light in addition to zero-order light. Of the diffracted light generated by the phase diffraction grating element 370, the first-order diffracted light has the maximum intensity. The phase diffraction grating element 370 of the present embodiment is configured to form the aperture 61 image using first-order diffracted light having high intensity among diffracted light. The relationship between the incident angle α and the diffraction angle β of the light incident on the phase diffraction grating element 370 can be expressed by the following conditional expression depending on the pitch d1 of the phase diffraction grating element 370 and the wavelength λ of the incident light.

mλ = d1 (sin α + sin β)
Here, m is the order of the diffracted light. From using the first-order diffracted light,
λ = ± d1 (sin α + sin β)
It is.

In the diffraction direction, when one of a pair of light beams that differ by a certain angle difference Δθ goes straight, and the other is diffracted and incident at the same position,
d1 = λ / {sin α−sin (α−Δθ)}
It becomes. If the light beam emitted from the spatial light modulator 17R is substantially parallel light, α≈0 °.
d1≈λ / sinθ
It becomes.

The 0th-order light from the phase diffraction grating element 370 travels straight from the phase diffraction grating element 370 to form the opening 61 image. On the screen 30 that is separated from the phase diffraction grating element 370 by a distance L, the distance S between the incident position of the zeroth-order light and the incident position of the first-order diffracted light is expressed by the following equation.
S = L × Δθ
Therefore,
S≈ (λ × L) / d1
It becomes.

  By controlling the pitch d1 of the concave portions 371 of the phase diffraction grating element 370, the distance S that is the amount of movement of the opening portion image 61P on the screen 30 can be arbitrarily set. The pitch d1 of the concave portions 371 of the phase diffraction grating element 370 can be set to 400 to 700 nm, for example. The direction in which the incident position of the first-order diffracted light is shifted can be arbitrarily set by controlling the direction of the phase diffraction grating element 370.

The depth d2 of the concave portion 371 of the phase diffraction grating element 370 is expressed by the following equation when the refractive index of the phase diffraction grating element 370 is n.
d2 = λ / {2 (n−1)}
In this case, about 70% of the first order diffracted light can be extracted theoretically with respect to the specific transmission wavelength λ.

  The 0th-order light generated by the phase diffraction grating element 370 is not refracted by the phase diffraction grating element 370 but goes straight to form an aperture 61 image. Further, the primary light generated by the phase diffraction grating element 370 is incident on a position shifted in a predetermined direction, thereby forming an opening 61 image on the black matrix portion 62 image. In this manner, the phase diffraction grating element 370 divides the image of the opening 61 into a plurality of images and projects the image onto the screen 30 as in the prism group 25 of the first embodiment. Thereby, there is an effect that the generation of moire can be reduced and a fine image can be displayed. At this time, diffracted light having substantially uniform intensity can be obtained by having a pattern of five cycles or more in a unit area.

  The phase diffraction grating element 370 is not limited to a configuration in which a rectangular phase grating pattern is provided, and may be configured to have a phase grating pattern such as a sine wave shape, a blazed shape, a trapezoidal shape, or a triangle. The pattern of the image of the opening 61 projected by the phase diffraction grating element 370 can be appropriately set according to the design of the phase diffraction grating element 370 as in the case of the prism group 25 of the first embodiment. Further, the phase diffraction grating element 370 is not limited to the configuration provided on the pupil of the projection lens 20 as in the prism group 25 of the first embodiment, and may be provided on the exit surface of the cross dichroic prism 18.

  FIG. 35 shows a perspective configuration of a main part of a birefringent portion 390 that is a low-pass filter according to the fifth embodiment. The birefringent portion 390 of the present embodiment can be applied to the projector 10 of the first embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted. The birefringent portion 390 includes crystal plates 392 and 394. Further, λ / 4 phase plates 391 and 393 are provided on the incident side of the quartz plates 392 and 394, respectively. The quartz plates 392 and 394 are so-called anisotropic media that exhibit different refractive indexes depending on the direction of the vibration plane of light. Each quartz plate 392 and 394 separates one incident light into two polarized lights each having a different vibration direction.

  FIG. 36 shows the polarization state of light in the birefringent portion 390. As described in the first embodiment, the modulated light emitted from each of the spatial light modulators 17R, 17G, and 17B is linearly polarized light having a specific vibration direction. The light emitted from the quartz plate 392 is also linearly polarized light having a specific vibration direction. Each crystal plate 392 and 394 cannot separate incident light into two when only linearly polarized light in a single vibration direction is incident as it is.

  A λ / 4 phase plate 391 provided on the incident side of the crystal plate 392 converts linearly polarized light from each of the spatial light modulators 17R, 17G, and 17B into circularly polarized light. By converting the incident light into circularly polarized light, the quartz plate 392 can separate the incident light into two. The quartz plate 392 emits linearly polarized light whose vibration directions are orthogonal to each other. A λ / 4 phase plate 393 provided on the incident side of the crystal plate 394 converts each linearly polarized light from the crystal plate 392 into circularly polarized light. By converting incident light into circularly polarized light, the quartz plate 394 can further separate each incident light into two.

  The birefringence unit 390 is configured in the order of the crystal plate 391, the λ / 4 phase plate 392, the crystal plate 393, and the λ / 4 phase plate 394 from the incident side, thereby separating the modulated light into two in a desired direction. be able to. The birefringent portion 390 is not limited to the case where the quartz plates 392 and 394 and the λ / 4 phase plates 391 and 393 are arranged with a space therebetween, and may be configured to overlap each other.

  For example, when a DMD is used as a spatial light modulator, modulation according to an image signal is performed regardless of the vibration direction of polarized light. In this case, since the modulated light is not only linearly polarized light in a single vibration direction, the modulated light can be directly incident on the birefringent portion 390. Therefore, when a spatial light modulation device that performs modulation regardless of polarization, such as DMD, a λ / 4 phase plate 391 on the incident side of the crystal plate 392 is not required.

  FIG. 37 explains the separation of light by the quartz plates 392 and 394. Here, the illustration of the λ / 4 phase plates 391 and 393 is omitted. It is assumed that the crystal plate 392 is provided so that the rotation angle with respect to the crystal orientation is 0 °. For example, the light beam B, which is linearly polarized light that vibrates in the vertical direction, of the light beam A behaves as if it travels in an isotropic medium on the crystal plate 392. For example, the light beam B travels by being refracted by a predetermined refractive index on the quartz plate 392.

  On the other hand, the crystal plate 392 exhibits a refractive index different from that of the light beam B with respect to the light beam C that vibrates in a direction substantially orthogonal to the vibration direction of the light beam B among the light beams A. For this reason, the light beam C is refracted so as to travel in a different direction from the light beam B on the quartz plate 392. In this way, the quartz plate 392 separates the single light beam A into two light beams B and C, which are two linearly polarized light beams whose vibration directions are substantially orthogonal to each other. In the figure, points B and C indicate the light beam B and the light beam C, respectively, and the double-headed arrows indicate the vibration directions of the respective linearly polarized light.

The distance between the light beam B and the light beam C exiting the crystal plate 392, that is, the light beam separation width p1 is determined by the thickness t1 of the crystal plate 392. The separation width p of the light beam by the quartz plate can be easily determined by the following equation using the thickness t of the quartz plate.
d = 5.9 × 10 ⁻³ × t

  It is assumed that the crystal plate 394 is arranged by being rotated by an angle θ with respect to the crystal orientation. The quartz plate 394 refracts, for example, linearly polarized light that oscillates in the direction of a straight line that forms an angle θ with respect to the horizontal plane among incident light. For example, the light beam E, which is a part of the light beam B, behaves as if it travels in an isotropic medium on the crystal plate 394. The light beam E is linearly polarized light that oscillates in a direction substantially perpendicular to a plane that forms an angle θ with the horizontal plane. For example, the light ray E travels by being refracted by a predetermined refractive index on the quartz plate 394.

  On the other hand, the crystal plate 394 is different from the light E in the light beam F that vibrates in a direction substantially perpendicular to the vibration direction of the light beam E of the light beam B, that is, in a direction that forms an angle θ with respect to the horizontal plane. Indicates the rate. For this reason, the light beam F undergoes a refraction action different from that of the light beam E on the quartz plate 394 and travels in a direction different from that of the light beam E. In this way, the crystal plate 394 separates the single light beam B into two light beams E and F, which are two linearly polarized light beams whose vibration directions are substantially orthogonal to each other. As in the case of the light beam B, the light beam C is separated into the light beam G and the light beam H. The separation width p2 of the light beam by the crystal plate 394 is determined by the thickness t2 of the crystal plate 394.

  In this way, the quartz plates 392 and 394 separate the light beam A into four light beams F, G, E, and H. The rays F, G, E, and H are separated so as to be located at the apex of the parallelogram having an angle θ in a plane perpendicular to the optical axis. The light beam separation pattern by the quartz plates 392 and 394 can be set as appropriate depending on the thicknesses t1 and t2 of the quartz plates 392 and 394 and the angle with respect to the crystal orientation.

  The birefringent portion 390 can project four opening 61 images from one opening 61 image. Part of the light incident on the birefringent portion 390 is refracted in a predetermined direction, thereby forming an aperture 61 image on the black matrix portion 62 image. In this manner, the birefringent portion 390 divides the image of the opening 61 into a plurality of images and projects the same onto the screen 30 as in the prism group 25 of the first embodiment. Thereby, there is an effect that the generation of moire can be reduced and a fine image can be displayed. One light beam can be separated into two light beams by a single quartz plate. For this reason, according to the number of crystal plates provided in the birefringence part 390, it is possible to appropriately set the number of the opening 61 images to be divided and projected from one opening 61 image.

  When the polarization component of incident light is biased, the intensity of the light divided by the birefringence unit 390 may be biased. In this case, for example, by using a depolarizing plate, it is possible to eliminate the bias of the polarization component and reduce the bias of the intensity of the divided light. Thereby, the light intensity of each opening 61 image divided by the light from one opening 61 can be made substantially the same, and the periodicity of the projection light can be effectively reduced.

  FIG. 38 illustrates changes in the intensity distribution of the projected light due to the provision of the birefringent portion 390. In each graph shown in FIG. 38, the vertical axis represents the intensity I of the projection light, and the horizontal axis represents the distance x in the X direction (I and x are both arbitrary units). Similar to the first embodiment, the amount of movement of the image of the opening 61 due to refraction at the birefringent portion 390 is a distance of approximately one half or less of the pitch of the plurality of openings 61.

  It is assumed that three images of the opening 61 that is a pixel portion are arranged around the respective positions of x = 0, 20, and 40 on the screen 30. When the birefringent portion 390 is not provided, the projection light becomes light A1 having an intensity with the peak at the center of each opening 61 image. Further, since the image of the opening 61 is projected as it is onto the screen 30, the intensity I of the projection light is substantially zero at the position of x = 10, 30 where the image of the black matrix 62 is formed. As the difference ΔI between the maximum value and the minimum value of the intensity I of the projection light is larger, the periodicity of the projection light is strengthened and moire tends to occur.

  When the birefringent portion 390 that forms the image of the opening 61 is provided at a position that is approximately a half of the pitch of the opening 61, the light from the opening 61 is separated into light that is refracted and light that goes straight. The The intensity of the light B5 that travels straight from the opening 61 is weakened as much as part of the light is separated compared to the light A1. The light refracted by the birefringent portion 390 becomes light C5 having an intensity having a peak at a position of x = 10, 30 that is a position shifted by a half pitch. The light A5 that is a combination of the light B5 that travels straight through the birefringent portion 390 and the light C5 that is refracted can have a smaller intensity difference ΔI than the light A1.

  When the intensity difference ΔI is reduced, the regularity of the projection light due to the pixel structure is weakened, and the light interference in the periodic structure of the screen 30 can be reduced. Further, light interference due to the overlap between the periodic structure in the projector 10 and the pattern of the image can be reduced. As described above, by providing the birefringent portion 390 that guides the projected image of the opening 61 to a position that is approximately one-half or less of the pitch of the opening 61 that is the pixel portion, the occurrence of moire is reduced. be able to.

  The pattern of the image of the opening 61 projected by the birefringent portion 390 can be appropriately set according to the design of the birefringent portion 390, as in the case of the prism group 25 of the first embodiment. In particular, the birefringent portion 390 can change the number of crystal plates according to the number of divisions of the image of the opening 61. Similar to the prism group 25 of the first embodiment, the birefringence unit 390 is not limited to the configuration provided on the pupil of the projection lens 20 but may be provided on the exit surface of the cross dichroic prism 18. In addition, the birefringent portion 390 is not limited to a configuration using quartz as an anisotropic medium, and other optical crystals such as lithium niobate and calcite can be used.

  In the projector 10 described above, a cooling unit that cools the low-pass filter of each embodiment may be provided. By making the low-pass filter coolable, deterioration of the low-pass filter due to heat can be reduced, and generation of moire can be reliably reduced. The projector 10 uses the ultra-high pressure mercury lamp 11 as the light source unit. However, for example, a laser light source or a solid light emitting element such as a light emitting diode element (LED) may be used.

  As described above, the projector according to the present invention is useful for viewing presentations using high-quality images and viewing high-definition moving images.

1 is a schematic configuration diagram of a projector according to a first embodiment of the invention. Explanatory drawing of the arrangement position of a prism group. The principal part perspective block diagram of a screen. The principal part cross-section block diagram of a screen. The principal part plane block diagram of a screen. Explanatory drawing of the periodic structure in a spatial light modulator. The perspective block diagram of a prism group. Explanatory drawing of the relationship between a spatial light modulator and a prism group. Explanatory drawing of the positional relationship between an opening part and a prism group. Explanatory drawing of the positional relationship between an opening part and a prism group. Explanatory drawing of the positional relationship between an opening part and a prism group. Explanatory drawing of a structure of a prism group. Explanatory drawing of an opening part image. Explanatory drawing of an opening part image. Explanatory drawing of an opening part image. Explanatory drawing of an opening part image. Explanatory drawing of a projection image when an opening part image is superimposed. Explanatory drawing of the arrangement position of a prism group. The figure explaining the change of the intensity distribution of the projection light by a prism group. Explanatory drawing of a projection image when an opening part image is superimposed. Explanatory drawing of a projection image when an opening part image is superimposed. Explanatory drawing of the variation of a prism element. Explanatory drawing of the variation of a prism element. Explanatory drawing of the variation of a prism element. Explanatory drawing of the variation of a prism element. The principal part upper surface block diagram of a prism group. Explanatory drawing of a projection image when an opening part image is superimposed. The principal part upper surface block diagram of a prism group. FIG. 6 is a perspective configuration diagram of a main part of a prism group according to a second embodiment. The figure explaining the branching of the incident light by a prism group. Explanatory drawing of the projection image by the branched light. The figure which shows light intensity distribution of a projection image. The figure which shows light intensity distribution of a projection image. The figure which shows light intensity distribution of a projection image. The figure which shows light intensity distribution of a projection image. FIG. 6 is a cross-sectional configuration diagram of a main part of a prism group according to a third embodiment. FIG. 10 is a cross-sectional configuration diagram of main parts of a prism group according to a first modification of the third embodiment. FIG. 10 is a perspective configuration diagram of a main part of a prism group according to a second modification of the third embodiment. The figure explaining a unit area. The figure explaining a unit area. Explanatory drawing of the variation of a prism group. Explanatory drawing of the variation of a prism group. FIG. 10 is a cross-sectional configuration diagram of main parts of a prism group according to a third modification of the third embodiment. The cross-sectional block diagram of a prism element. FIG. 10 is a top configuration diagram of a main part of a prism group according to a fourth modification of the third embodiment. FIG. 10 is a perspective view of a principal part of a phase diffraction grating element according to a fourth embodiment. Explanatory drawing of the relationship between a spatial light modulator, a phase diffraction grating element, and a screen. FIG. 10 is a perspective view of a main part of a birefringent portion according to a fifth embodiment. The figure which shows the polarization state of the light in a birefringent part. Explanatory drawing of isolation | separation of the light by a quartz plate. The figure explaining the change of the intensity distribution of the projection light by a birefringence part.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Projector, 11 Super high pressure mercury lamp, 12 Integrator, 13 Polarization conversion element, 14R R light transmission dichroic mirror, 14GB light transmission dichroic mirror, 15 Reflection mirror, 16 Relay lens, 17R, 17G, 17B Each spatial light modulation device, 18 cross dichroic prism, 18a, 18b dichroic film, 20 projection lens, 21 reflection mirror, 25 prism group, 30 screen, 30a Fresnel lens, 30b viewing angle adjustment unit, 32 lenticular lens sheet, 33 lenticular lens, 34 light shielding unit, 41 Aperture, 61 Aperture, 61P, 61Pa, 61Pb, 61Pc, 61Pd Aperture image, 62 Black matrix portion, 62P Black matrix portion image, 63P Periodic region image, 70 through Plate, 71 Prism element, 71a Side, 72, 72a, 72b, 72c, 72d Refraction surface, 73 Flat part, 73a Reference surface, 80a surface, CL center line, CLP center line image, 130 projector, 135 prism group, 150P , 151P, 151Pa, 152P, 152Pa, 153P Aperture image, 161, 162, 163, 164 Prism group, 161a, 162a, 163a, 164a Refractive surface, 161b, 162b, 163b Flat part, 210 Prism group, 211, 212 prism Element, 213, 214 refracting surface, 213P, 214P, 220P Aperture image, 215 flat portion, 230 prism group, 231 refracting surface, 232 flat portion, 240 prism group, 241a, 241b prism element, 280 prism group, 280a refracting surface 280b Flat part, 281 Reference plane, AX optical axis, 290 prism group, 290a refracting surface, 290b Flat part, 291 Reference plane, 300 prism group, 301 prism element, 302 Transparent plate, ILL illumination system, PL projection system, 330 prism Group, 331 Reference surface, 332 Resin substrate, 333 Glass substrate, 340 Prism group, 341a, 341b, 341c Prism element, 351a, 351c Refractive surface, 351b Flat part, 360 Prism group, 361a, 361b, 361c Prism element, 362 Refraction Surface, 363 flat portion, 370 phase diffraction grating element, 371 concave portion, 372 transparent plate, 390 birefringence portion, 391, 393 λ / 4 phase plate, 392, 394 quartz plate

Claims (11)

A spatial light modulator that includes a plurality of pixel units arranged in a matrix and modulates incident light according to an image signal;
A screen having a structure disposed at a predetermined cycle, and transmitting light from the spatial light modulator;
A projector comprising: a low-pass filter provided in an optical path between the spatial light modulator and the screen. The low-pass filter has a prism group composed of prism elements having at least a refractive surface,
The prism element is provided with a period of three or more periods within a unit area determined by an illumination optical system or a projection optical system,
The projector according to claim 1, wherein the refracting surface refracts light from the one pixel unit in a predetermined direction. The prism element has a flat portion that transmits light from the pixel portion,
When a surface formed in a direction substantially perpendicular to the optical axis at a position farthest from the flat portion at the intersection of the refracting surface and the optical axis is a reference plane,
The distance from the reference plane to the flat portion is d,
The wavelength of the incident light is λ,
The projector according to claim 2, wherein when the refractive index of the prism element is n, one of the following conditional expressions is satisfied.
d <0.95 × λ / {2 × (n−1)}
d> 1.05 × λ / {2 × (n−1)} The prism element has a flat portion that transmits light from the pixel portion,
When one surface of the substrate that is substantially perpendicular to the optical axis and on which the prism group is formed is a reference surface,
The distance from the reference surface to the flat portion and the distance from the reference surface to a predetermined position on the refractive surface are formed so as to be aperiodic, respectively. The projector described.   The projector according to claim 2, wherein the prism elements are provided with a cycle of 15 cycles or less within the unit area. The low-pass filter has a phase diffraction grating element that makes the first-order diffracted light incident on a position shifted in a predetermined direction out of light from the one pixel unit,
The projector according to claim 1, wherein the phase diffraction grating element is provided with a period of 5 periods or more in the unit area.   The projector according to claim 1, wherein the low-pass filter is a birefringence unit that refracts and separates a part of light from one pixel unit in a predetermined direction.   The projector according to claim 7, further comprising a phase plate on an incident side of the birefringent portion.   The said low-pass filter guides the projection image of the said pixel part to the position of the distance of about 1/2 or less of the pitch of these pixel parts on the said screen. The projector according to item.   The projector according to claim 1, wherein the screen has a periodic structure.   The projector according to claim 10, wherein the periodic structure is a light shielding part and an opening part.

Images