Image generation unit and projection-type image display device

Abstract

This image generation unit comprises: three light modulation elements, a first light modulation element, a second light modulation element, and a third light modulation element, each of which modulates light on the basis of an image signal to generate image light; and a color separation / synthesis prism including a first prism, a second prism, and a third prism arranged in this order along an optical axis and guiding respective light to three light modulation elements. The third prism has a bottom surface facing the third light modulation element and perpendicular to the optical axis, and a first side surface adjacent to the bottom surface, and a portion of image light from the first light modulation element passes as unnecessary light through the first dichroic surface between the first prism and the second prism, passes through the second prism, and falls on the third prism. The first side surface of the third prism is configured to reflect unnecessary light incident on the third prism toward the bottom surface, and the bottom surface of the third prism is configured to completely reflect the unnecessary light reflected by the first side surface.

Description

[Technical Field]

[0001] The present disclosure relates to an image generating unit and a projection-type image display device including the image generating unit. [Background technology]

[0002] In recent years, projection-type image display devices (projectors) using digital micromirror devices (DMDs) have been developed and are beginning to become widespread. In addition to ON light, which is optically modulated based on a video signal to produce image light, this digital micromirror device also produces OFF light, which does not appear in the video signal and is not used as image light. For this reason, it is necessary to direct the OFF light in a direction different from the image light. For example, a technique has been disclosed that prevents the OFF light from the DMD from entering a color separation / combining prism (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-81931 Summary of the Invention

[0004] Furthermore, the image light modulated by each image display element is guided to the projection unit from each prism. For example, as shown in Fig. 7, image light 2 from first light modulation element 51B is reflected by first dichroic surface 139 between the first prism and second prism and proceeds along optical axis 8 to the projection unit.

[0005] However, a portion of the image light 2 passes through first dichroic surface 139 as unwanted light 16, passes through second prism 136, and enters third prism 137. This unwanted light 16 may be reflected by the first side surface of third prism 137, pass through the bottom surface of third prism 137, and hit third light modulation element 51G, where it is absorbed and generates heat. Such a case where a portion of the image light passes through prisms 134, 136, and 137 as unwanted light has not previously been anticipated.

[0006] Therefore, an object of the present disclosure is to provide an image generating unit that can suppress heat generation due to unnecessary light even when part of the image light becomes unnecessary light and passes through the prism.

[0007] The image generating unit according to the present disclosure includes three light modulation elements, each including a first light modulation element, a second light modulation element, and a third light modulation element, which modulate light based on a video signal to generate image light, and a color separation / combining prism including a first prism, a second prism, and a third prism arranged in that order along an optical axis to guide light to the three light modulation elements. The third prism faces the third light modulation element and has a bottom surface perpendicular to the optical axis and a first side surface adjacent to the bottom surface. A portion of the image light from the first light modulation element passes through a first dichroic surface between the first prism and the second prism as unwanted light, passes through the second prism, and enters the third prism. The first side surface of the third prism is configured to reflect the unwanted light that enters the third prism toward the bottom surface, and the bottom surface of the third prism is configured to totally reflect the unwanted light reflected by the first side surface.

[0008] The projection-type image display device according to the present disclosure includes a light source unit that generates light, the image generation unit, a light-guiding optical system that guides the light from the light source unit to the image generation unit, and a projection optical system that projects the image light generated by the image generation unit.

[0009] According to the image generation unit and the projection-type image display device using the image generation unit of the present disclosure, even if part of the image light becomes unwanted light and passes through the prism, the unwanted light is not allowed to reach the third light modulation element, and heat generation due to the unwanted light can be suppressed. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram showing a configuration of a projection-type video display device including a video generation unit according to a first embodiment. [Figure 2] 2 is a schematic diagram showing an optical system of a projection-type image display device including the image generation unit of FIG. 1. [Figure 3]2 is a schematic perspective view showing a TIR prism and a color separation / combining prism in the projection-type image display device according to the first embodiment. FIG. [Figure 4] 4 is a schematic diagram of the TIR prism and color separation / combining prism of FIG. 3 as viewed from the -Y direction. [Figure 5] 5 is a schematic diagram showing the optical path of unwanted light in a third prism in FIG. 4. [Figure 6] 10 is a schematic diagram of a TIR prism and a color separation / combining prism in a projection-type image display device according to a reference example, viewed from the +Z direction. FIG. [Figure 7] 7 is a schematic diagram of the TIR prism and color separation / combining prism of FIG. 6 as viewed from the -Y direction. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Background to this disclosure> Fig. 6 is a schematic diagram of the TIR prisms 128, 129 and color separation / combining prism 61 (134, 136, 137) in a projection-type image display device according to a reference example, viewed from the +Z direction. Fig. 7 is a schematic diagram of the TIR prisms 128, 129 and color separation / combining prism 61 (134, 136, 137) in Fig. 6, viewed from the -Y direction.

[0012] As described above, the case where part of the image light passes through the prisms 134, 136, and 137 as unwanted light has not been considered until now.

[0013] After extensive research, the inventors discovered that by configuring the third prism 137 so that the unwanted light 16 reflected by the first side surface 24 is totally reflected by the bottom surface 22, as shown in Figure 4, it is possible to prevent the unwanted light from hitting the third light modulation element, being absorbed, and generating heat, and this led to the present disclosure.

[0014] The image generating unit according to the first aspect includes three light modulation elements, namely, a first light modulation element, a second light modulation element, and a third light modulation element, which modulate light based on a video signal to generate image light, and a color separation / combination prism consisting of a first prism, a second prism, and a third prism arranged in order from the light incident surface along the optical axis from the front to the rear, which guides light to each of the three light modulation elements. The third prism faces the third light modulation element and has a bottom surface perpendicular to the optical axis and a side surface adjacent to the bottom surface. A portion of the image light from the first light modulation element passes through a first dichroic surface between the first prism and the second prism as unwanted light, passes through the second prism, and enters the third prism. The first side surface of the third prism onto which the unwanted light enters is configured to reflect the unwanted light about the bottom surface, and the bottom surface of the third prism is configured to totally reflect the unwanted light reflected from the first side surface of the third prism.

[0015] In the image generating section according to a second aspect, in the above-mentioned first aspect, the first side surface of the third prism may be disposed at an angle other than 90 degrees with respect to the bottom surface.

[0016] The image generating section according to a third aspect may be configured in the above-mentioned second aspect such that the first side surface is disposed to form an obtuse angle with the bottom surface.

[0017] The image generating section according to a fourth aspect is the image generating section according to any one of the first to third aspects, wherein the first side surface may be mirror-finished.

[0018] The image generating unit according to the fifth aspect may be any of the first to fourth aspects, in which the angle 2α between the unwanted light and the optical axis, the angle of incidence θ1 of the unwanted light on the first side surface, the angle of incidence θ2 of the unwanted light on the bottom surface, the angle φ1 between the first side surface and the normal to the bottom surface, and the critical angle θc of the sodium d-line within the third prism satisfy the following equations 1 to 3:

[0019] φ1>0 (Formula 1) θ1=90°-2α-φ1>θc (Equation 2) θ2=2α+2φ1>θc (Equation 3) The image generating unit according to the sixth aspect is any one of the first to fifth aspects, wherein the second side surface of the third prism, which faces the first side surface and the bottom surface, may be provided with an absorption plate that absorbs unnecessary light that is totally reflected at the bottom surface.

[0020] A projection-type image display device according to a seventh aspect includes a light source unit that generates light, a light-guiding optical system that guides the light from the light source unit, an image generation unit according to any one of the first to sixth aspects that modulates the light guided from the light-guiding optical system based on an image signal to generate image light, and a projection optical system that projects the image light.

[0021] Hereinafter, an image generating unit and a projection-type image display device according to an embodiment will be described with reference to the accompanying drawings, in which substantially identical components are designated by the same reference numerals.

[0022] (Embodiment 1) <Projector> Fig. 1 is a block diagram showing the configuration of a projection-type image display device (projector) 100 including an image generation unit according to embodiment 1. Fig. 2 is a schematic diagram showing an optical system of the projection-type image display device including the image generation unit of Fig. 1.

[0023] The projection-type image display device according to the first embodiment includes a light source unit 20, a light-guiding optical system 50, an image generating unit 60, a projection optical system 70, and a control unit 80. The light-guiding optical system 50 is an optical system that guides light from the light source unit 20 to the image generating unit 60. The image generating unit 60 separates the light into the three primary colors of RGB using a color separating / combining prism 61, and modulates each of the RGB lights with an image signal using a digital micromirror device (DMD) to generate image light. The projection optical system 70 projects the generated image light onto a screen or the like to form an image. The control unit 80 controls the light source unit 20, the light-guiding optical system 50, the image generating unit 60, and the projection optical system 70.

[0024] Each of the components that make up this projection-type image display device 100 will be described below.

[0025] <Light source part> Light source section 20 is mainly composed of first light source unit 101a, second light source unit 101b, splitting / combining mirror 102, and phosphor wheel 118. In addition to these, light source section 20 also includes lens groups 103, 106, 113, 116, and 117 and mirror groups 104 and 114.

[0026] The first light source unit 101a and the second light source unit 101b may be configured with a plurality of solid-state light sources such as laser diodes (LDs) or light-emitting diodes (LEDs). In the first embodiment, among laser diodes, a laser diode that emits blue light is used as the solid-state light source. Here, the laser diode is a type of laser light source.

[0027] The light emitted from first light source unit 101a and second light source unit 101b is, for example, blue light having a wavelength of 440 nm or more and 470 nm or less, and is also used as excitation light for exciting phosphor 119 contained in phosphor wheel 118.

[0028] <Phosphor wheel> Phosphor wheel 118 rotates around rotation axis 122 extending along the optical axis of the excitation light. This phosphor wheel 118 is a reflective phosphor wheel that emits fluorescence in the opposite direction to the incident direction of the excitation light. That is, phosphor wheel 118 includes substrate 121, phosphor 119 that is coated on substrate 121 in an annular shape along the rotation direction of substrate 121, and a motor (not shown) for rotating substrate 121 on which phosphor 119 is formed. A reflective film for reflecting the fluorescent light emitted by phosphor 119 is formed on the surface of substrate 121. Phosphor 119 emits fluorescence containing yellow light in response to the excitation light emitted from first light source unit 101a and second light source unit 101b.

[0029] The excitation light is diffused by the top hat diffusion element 115 and focused by the lenses 116 and 117 onto the phosphor 119, which then emits fluorescence.

[0030] The phosphor is an example of a light-emitting material, and is a phosphor that emits fluorescence in a wavelength range from green to yellow. The phosphor 119 is preferably a phosphor that efficiently absorbs blue excitation light, efficiently emits fluorescence, and has high resistance to thermal quenching. The phosphor 119 is, for example, Y3A 119, a phosphor having a garnet structure activated by cerium. l5 O 12 :Ce 3+ is.

[0031] The light source unit 20 guides the light 1 containing blue excitation light and yellow fluorescence to the light guide optical system 50 .

[0032] <Light guiding optical system> The light-guiding optical system 50 is an optical system that guides the light 1 from the light source unit 20 to the image generation unit 60. The light-guiding optical system 50 mainly includes a rod integrator 111, lens groups 108, 110, 123, and 124, and mirror groups 109 and 125.

[0033] Rod integrator 111 is a solid rod made of a transparent material such as glass. Rod integrator 111 can homogenize the spatial intensity distribution of the excitation light emitted from first light source unit 101a and second light source unit 101b and the fluorescence from phosphor wheel 118. Rod integrator 111 may be a hollow rod whose inner wall is made of a mirror surface. Rod integrator 111 is a type of light homogenizing element.

[0034] <Video Generation Unit> Fig. 3 is a schematic perspective view showing TIR prisms 128 and 129 and color separation / combining prism 61 (134, 136, 137) in the projection display device according to embodiment 1. Fig. 4 is a schematic view of TIR prisms 128 and 129 and color separation / combining prism 61 (134, 136, 137) in Fig. 3 as viewed from the -Y direction.

[0035] For convenience, in Figure 3, the direction of optical axis 8 of the image light generated by each light modulation element (DMD) is shown as the +X direction. Also, in each figure, the height direction of each triangular prism (134, 136, 137) of color separation / combining prism 61 is shown as the -Y direction. Furthermore, the Z direction, which is perpendicular to the X and Y directions, is also shown.

[0036] The image generating unit 60 includes TIR prisms 128 and 129 that guide the illumination light 1 from the light-guiding optical system 50 to the color separation / synthesis prism 61, the color separation / synthesis prism 61 consisting of three prisms, a first prism 134, a second prism 136, and a third prism 137, that separate the illumination light 1 into the three primary colors of RGB and combine them, and three digital micromirror devices (DMDs), a first DMD (51B), a second DMD (51R), and a third DMD (51G), that generate image light by modulating the separated image signals for each of the three primary colors of RGB.

[0037] Furthermore, the image generating unit 60 may be provided with a light shielding plate 14, similar to the reference example shown in Figure 6, which is arranged on the forward side of the optical axis 8 of the first prism 134 and absorbs a portion of the OFF light generated by the third modulation element 51G that is transmitted through the third prism 137, the second prism 136, and the first prism 134.

[0038] <TIRプリズム> TIR prisms 128 and 129 guide illumination light 1 from light-guiding optical system 50 to color separation / combining prism 61. TIR prism 128 is made of a light-transmitting member, and has a surface 130 facing TIR prism 129, and a surface 131 facing a first prism 134 of color separation / combining prism 61. An air gap is provided between TIR prism 128 (FIG. 2: surface 130) and TIR prism 129, and the angle of incidence of light incident on TIR prism 128 onto surface 130 is greater than the critical angle, so the light incident on TIR prism 128 is reflected by surface 130. On the other hand, although an air gap is provided between the TIR prism 128 (FIG. 2: surface 131) and the first prism 134 (FIG. 2: surface 144), the angle at which the light reflected by surface 130 is incident on surface 131 (incident angle) is smaller than the critical angle, so the light reflected by surface 130 is transmitted through surface 131.

[0039] <Light modulation element: Digital micromirror device (DMD)> The light modulation elements 51G, 51R, and 51B are, for example, digital micromirror devices (DMDs). The first DMD (51B), second DMD (51R), and third DMD (51G), which are digital micromirror devices, are composed of a plurality of movable micromirrors, each of which corresponds to one pixel. The first DMD (51B), second DMD (51R), and third DMD (51G) generate image light by changing the angle of each micromirror based on a video signal, thereby switching whether or not to reflect light toward the projection unit 70. The first DMD (51B), second DMD (51R), and third DMD (51G) are a type of light modulation element. Each of the three DMDs is configured to modulate light based on a video signal to generate image light.

[0040] Strictly speaking, the light guided to the first DMD (51B) is the first component light (blue component light) separated from the light 1 guided from the light guide optical system 50, and the light modulated by the first DMD (51B) is the first modulated light 2. Similarly, the light guided to the second DMD (51R) is the second component light (red component light), and the light modulated by the second DMD (51R) is the second modulated light 4. Furthermore, the light guided to the third DMD (51G) is the third component light (green component light), and the light modulated by the third DMD (51G) is the third modulated light 6.

[0041] 4 and 8, the first DMD (51B), second DMD (51R), and third DMD (51G) emit first modulated light 2, second modulated light 4, and third modulated light 6, which are ON light as image light, and also emit OFF light 9a, 9b, and 9c, which do not become image light, away from the optical axis (X direction). Note that the first modulated light 2, second modulated light 4, and third modulated light 6 represent image light emitted along the width of the first DMD (51B), second DMD (51R), and third DMD (51G), respectively. Similarly, the OFF light 9a, 9b, and 9c represent OFF light emitted along the width of the third DMD (51G).

[0042] 7 shows only the OFF light 9a, 9b, and 9c emitted from the third DMD (51G), which is the third modulation element. The OFF light emitted from the other first DMD (51B) and second DMD (51R) is omitted from the drawing.

[0043] 7, the OFF light 9a, 9b, and 9c pass through the third prism 137, the second prism 136, and the first prism 134, and are absorbed by the light blocking plate 14. For example, the OFF light 9a and 9b pass through the third prism 137, the second prism 136, and the first prism 134, and are absorbed by the light blocking plate 14, and the OFF light 9c is absorbed by the light blocking plate 14.

[0044] <Color separation and synthesis prism> The color separation / combining prism 61 is made of a translucent material and includes a first prism 134, a second prism 136, and a third prism 137 arranged in this order along the optical axis 8. The color separation / combining prism 61 may be, for example, a Philips dichroic prism. Surface 133 of the first prism 134 is, for example, a dichroic mirror surface that transmits red and green component light and reflects blue component light. Therefore, of the light 1 reflected by surface 130 of the TIR prism 128, the red and green component light transmit through surface 133, and the blue component light is reflected by surface 133. The blue component light reflected by surface 133 is reflected by surface 144 and directed to the first DMD (51G). Surface 135 of the second prism 136 is a dichroic mirror surface that transmits green component light and reflects red component light. Therefore, of the light incident on the second prism 136, the green component light passes through the surface 135, and the red component light is reflected by the surface 135. The red component light reflected by the surface 135 is guided to the second DMD (51R). The green component light that passes through the surface 135 of the second prism 136 and enters the third prism 137 is guided to the third DMD (51B).

[0045] The component light guided by the first prism 134 and the second prism 136 may be switched, so that the red component light is guided to the first DMD by the first prism 134 and the blue component light is guided to the second DMD by the second prism 136.

[0046] That is, the green component light, the red component light, and the blue component light are light separated by the color separating / combining prism 61 .

[0047] 4, the first prism 134 receives blue image light 2, which is the first modulated light modulated by the first DMD (51B), and guides it to an optical path along the optical axis 8. Similarly to the reference example, the second prism 136 receives red image light 4, which is the second modulated light modulated by the second DMD (51R), and guides it to an optical path along the optical axis 8. The third prism 137 receives green image light 6, which is the third modulated light modulated by the third DMD (51G), and guides it to an optical path along the optical axis 8.

[0048] That is, blue image light 2, red image light 4, and green image light 6 are combined by color separating / combining prism 61 onto the same optical path along optical axis 8 to become image lights 11a, 11b, and 11c.

[0049] <Third Prism> 4, the third prism 137 has a bottom surface 22 facing the third DMD (51G), and a first side surface 24 and a second side surface 26 adjacent to the bottom surface 22. The bottom surface 22 is disposed so as to be perpendicular to the optical axis 8.

[0050] <First aspect> The first side surface 24 is disposed at an angle other than 90 degrees with respect to the bottom surface 22. Specifically, the first side surface 24 is disposed at an angle of φ1 with respect to the perpendicular to the bottom surface 22. When φ1 is a positive value other than 0 degrees, the first side surface 24 is disposed at an obtuse angle with respect to the bottom surface 22.

[0051] The first side surface 24 is configured to reflect the unwanted light 16. The first side surface 24 may be, for example, mirror-finished so as to reflect the unwanted light 16. Alternatively, the unwanted light 16 can be totally reflected by the first side surface 24 if the incident angle θ1 at which the unwanted light 16 is incident on the first side surface 24 is equal to or greater than the critical angle θc.

[0052] Furthermore, the unwanted light 16 reflected by the first side surface 24 is configured to be totally reflected by the bottom surface 22. The conditions under which the unwanted light 16 reflected by the first side surface 24 is totally reflected by the bottom surface 22 will be described below.

[0053] FIG. 5 is a schematic diagram showing the optical path of the unwanted light 16 in FIG. 4 within the third prism 137. Note that, for convenience, FIG. 5 extracts and illustrates only the angular relationships. For example, point C on the optical path ABC is not the actual point where the unwanted light is incident on the bottom surface, but is the point of intersection with the optical axis 8. This allows the line AC to be aligned with the optical axis 8. Point F is the intersection point of the perpendicular line drawn from point B onto line AC parallel to the optical axis 8. Furthermore, for the optical path CD, point E is the intersection point of the perpendicular line drawn from point D onto line AC parallel to the optical axis 8.

[0054] Based on Figure 5, the angle 2α between the unwanted light 16 and the optical axis 8, the angle of incidence θ1 of the unwanted light 16 on the first side surface 24, the angle of incidence θ2 of the unwanted light 16 on the bottom surface 22, the angle φ1 between the first side surface 24 and the normal to the bottom surface 22, and the critical angle θc of the sodium d-line (d1: 589.6 nm, d2: 589.0 nm) within the third prism 137 satisfy the following equations 1 to 3, where θc is the critical angle of the sodium d-line (d1: 589.6 nm, d2: 589.0 nm) within the third prism 137.

[0055] φ1>0 (Formula 1) θ1=90°-2α-φ1>θc (Equation 2) θ2=2α+2φ1>θc (Equation 3) <Second aspect> Alternatively, the unwanted light 16 may be transmitted through the second side surface 26 and guided to the outside of the prism. In this case, the incident angle θ3 of the unwanted light 16 onto the second side surface 26 must be equal to or less than the critical angle θc, as shown in the following formula 4, based on the angle φ2 between the second side surface 26 and the normal to the bottom surface 22 in addition to the above angles.

[0056] θ3=90°-θ2-φ2≦θc (Equation 4) This suppresses heat generation from the prisms 134, 136, and 137 and the light modulation elements 51B, 51R, and 51G. For example, the DMD incident energy equivalent to 30 klm (kilo lumens) is approximately 80 to 90 W, but the intensity of the unwanted light 16 is approximately 10 W, so heat generation can be reduced by approximately 5% to 10%.

[0057] Furthermore, an absorbing plate 28 that absorbs the unwanted light 16 may be provided on the second side surface 26. This makes it possible to suppress the influence of the unwanted light 16 on devices outside the prism.

[0058] The second side surface 26 may be a diffusing surface instead of a mirror surface.

[0059] In the above, as shown in Fig. 4, the case where part of the image light 2 from the first light modulation element 51B passes through the first dichroic surface 139 and becomes unwanted light has been given as an example, but the present invention is not limited to the above case. For example, as shown in Fig. 8, it can be seen that part of the image light 4 from the second light modulation element 51R also follows the same optical path as the unwanted light when reflected by the first dichroic surface 139. Furthermore, it can be seen that part of the image light 6 from the third light modulation element 51G also follows the same optical path as the unwanted light when reflected by the first dichroic surface 139. In other words, there are cases where part of the image light 2, 4, and 6 from any of the first light modulation element 51B, the second light modulation element 51R, and the third light modulation element 51G becomes unwanted light.

[0060] According to the configuration of the image generating unit according to the first embodiment, the unwanted light 16 reflected by the first side surface 24 of the third prism is totally reflected by the bottom surface 22. This prevents the unwanted light 16 from hitting the third light modulation element 51B, and prevents the unwanted light 16 from being absorbed and generating heat.

[0061] <Projection optical system> The projection optical system 70 projects the generated image light 11 onto a screen or the like to form an image.

[0062] <Control unit> The control unit 80 controls the light source unit 20, the light guide optical system 50, the image generation unit 60, and the projection optical system 70.

[0063] In addition, the present disclosure includes appropriate combinations of any of the various embodiments and / or examples described above, and can achieve the effects of each embodiment and / or example. [Industrial Applicability]

[0064] According to a projection-type image display device using the image generation unit and external image generation unit of the present disclosure, even if part of the image light becomes unwanted light and passes through the prism, the unwanted light is not allowed to reach the third light modulation element, and heat generation due to the unwanted light can be suppressed. [Explanation of symbols]

[0065] 1. Light from a light source (illumination light) 1a, 1b, 1c illumination light 2 Blue video light 4 Red image light 6 Green video light 8 Optical axis 9 OFF light 9a, 9b, 9c OFF light 10 Opening 11. Image Light 11a, 11b, 11c Video light 12 Reflective surface 14 Shade 16 unnecessary light 20 Light source section 22 bottom 24 First Aspect 26 The Second Aspect 28 Absorbing plate 50 Light guiding optical system 51B First optical modulation element (first DMD) 51R Second optical modulation element (second DMD) 51G Third optical modulation element (third DMD) 60 Image generation unit 61 Color Separation and Synthesis Prism 70 Projection optical system (projection unit) 100 Projection type image display device 101a First light source unit 101b Second light source unit 102 Separated composite mirror 103, 106, 108, 110, 112, 113, 116, 117, 123, 124, 126 lenses 104, 109, 114, 125 Mirror 105 Diffuser 107 Dichroic Mirror 111 Rod Integrator 115 Top Hat Diffuser 118 Phosphor Wheel 119 Phosphor 122 Rotation axis 128, 129, 134, 136, 137 Prism 130, 131, 133, 135, 139, 144 sides

Claims

1. three light modulation elements including a first light modulation element, a second light modulation element, and a third light modulation element, each of which modulates light based on a video signal to generate video light; a color separation / combination prism including a first prism, a second prism, and a third prism arranged in this order along an optical axis, each of which guides light to the three light modulation elements; Equipped with the third prism faces the third light modulation element and has a bottom surface perpendicular to the optical axis and a first side surface adjacent to the bottom surface; a part of the image light from the first light modulation element is transmitted as unnecessary light through a first dichroic surface between the first prism and the second prism, transmitted through the second prism, and incident on the third prism; the first side surface of the third prism is configured to reflect the unwanted light incident on the third prism toward the bottom surface, The bottom surface of the third prism is configured to totally reflect the unwanted light reflected by the first side surface. Image generation unit.

2. The image generating unit according to claim 1 , wherein the first side surface of the third prism forms an angle other than 90 degrees with respect to the bottom surface.

3. The image generating unit according to claim 2 , wherein the first side surface forms an obtuse angle with respect to the bottom surface.

4. The image generating unit according to claim 1 , wherein the first side surface is mirror-finished.

5. The image generating unit according to claim 1 , which satisfies the following formulas 1 to 3: φ1>0 (Formula 1) θ1=90°-2α-φ1>θc (Formula 2) θ2=2α+2φ1>θc (Formula 3) where: 2α is the angle that the unwanted light makes with the optical axis, θ1 is the incident angle of the unwanted light on the first side surface, θ2 is the angle of incidence of the unwanted light on the bottom surface, φ1 is the angle between the first side surface and the normal to the bottom surface, θc is the critical angle of the sodium d line in the third prism.

6. the third prism further has a second side surface that faces the first side surface with the bottom surface interposed therebetween, The image generating unit according to claim 1 , further comprising an absorbing plate facing the second side surface and absorbing the unnecessary light totally reflected by the bottom surface.

7. a light source unit that generates light; The image generating unit according to any one of claims 1 to 6; a light guiding optical system that guides light from the light source unit to the image generating unit; a projection optical system that projects the image light generated by the image generation unit; A projection-type image display device comprising:

Images