Projection-type image display device

Abstract

To provide a projection type video display device that can reduce stray light to an image pickup device.SOLUTION: A projection type video display device of the present disclosure comprises: a video light emitting section; a projection lens unit; a light path separation prism that has a first prism, a second prism, and a polarization separation film; a narrow band phase difference plate; and an image pickup device that picks up an image of external light through the projection lens unit and the light path separation prism. The polarization separation film transmits light in a first polarization state being any one of a P-polarization and an S-polarization and reflects light in a second polarization state being the other of the P-polarization and the S-polarization. The video light is incident on the light path separation prism from a first surface of the first prism, transmits through the polarization separation film, emits from a third surface of the second prism, and is incident on the projection lens unit. The external light is emitted from the projection lens unit and is incident on the light path separation prism from the third surface of the second prism, and the polarization separation film reflects light in the second polarization state of the external light. The external light is internally totally reflected on the third surface of the second prism, emitted from a fifth surface, and received by the image pickup device.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a projection-type video display device including an imaging element.

Background Art

[0002] A projection-type video display device that projects an image onto a projection object such as a screen or a building is known. In a conventional projection-type video display device, in order to confirm the positional relationship (distortion) between the projection object and the projected image, the image projected onto the projection object is photographed, and the projection position is adjusted based on the photographed image. This has been studied.

[0003] Therefore, a projection-type video display device incorporating an imaging element has been studied. For example, Patent Document 1 discloses a projector that shares the optical path of video light and the optical path of imaging light by guiding at least a part of the combined light from a color combining element to a projection optical system and guiding at least a part of the reflected light from the projection optical system to an imaging element using an optical path separation element.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The projector described in Patent Document 1 still has room for improvement in reducing stray light to the imaging element.

[0006] The present disclosure provides a projection-type video display device capable of reducing stray light to an imaging element.

Means for Solving the Problems

[0007] The projection type video display device according to the present disclosure includes a video light emitting unit that emits video light, a projection lens unit that enlarges and projects the video light incident from the video light emitting unit onto a projection target, and external light including the video light reflected by the projection target enters, a first prism disposed between the video light emitting unit and the projection lens unit, having a first surface perpendicular to the optical axis of the video light disposed on the video light emitting unit side, and a second surface intersecting the first surface, and disposed on the second surface side of the first prism, a second prism having a third surface perpendicular to the optical axis disposed on the projection lens unit side, a fourth surface intersecting the third surface and facing the second surface, and a fifth surface intersecting the third surface and the fourth surface, and a polarization separation film disposed between the second surface of the first prism and the fourth surface of the second prism, an optical path separation prism having a narrow-band retardation plate disposed between the video light emitting unit and the optical path separation prism, which aligns the video light in a first polarization state of either P-polarized light or S-polarized light, and an imaging element disposed facing the fifth surface of the second prism, imaging external light through the projection lens unit and the optical path separation prism, the polarization separation film transmits light in the first polarization state and reflects light in a second polarization state of either P-polarized light or S-polarized light, the video light enters the optical path separation prism from the first surface, passes through the polarization separation film, exits from the third surface, and enters the projection lens unit, the external light exits from the projection lens unit, enters the optical path separation prism from the third surface, reflects the light in the second polarization state of the external light with the polarization separation film, undergoes total internal reflection at the third surface, exits from the fifth surface, and is received by the imaging element.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide a projection type video display device capable of reducing stray light to the imaging element.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] (Background Leading to the Present Disclosure) There is known a projection type video display device that projects a video onto a projection object such as a screen or a building. In the projection type video display device, in order to confirm the positional relationship between the projection object and the projected video, the video projected onto the projection object may be photographed. In this case, based on the photographed image, the projection position of the video is finely adjusted.

[0011] When the projection type video display device and the image sensor that photographs the projected video are separate bodies, since the angle of view adjustment is complicated, a projection type video display device incorporating the image sensor has been developed. In the projection type video display device incorporating the image sensor, by sharing the optical axes of the respective optical paths of the video light emitted from the projection type video display device and the optical path for imaging the light reflected from the projection object, the angle of view adjustment can be omitted.

[0012] For example, the projector described in Patent Document 1 also functions as an imaging device that images a subject on a screen including a projection optical system, a projection image, and a support. That is, in the projector described in Patent Document 1, an optical path branching element guides at least a part of the combined light from the color combining element to the projection optical system, and guides at least a part of the reflected light from the projection optical system to the imaging element.

[0013] However, in the projector described in Patent Document 1, since the optical path of the video light and the optical path of the imaging light are shared, there is a problem that stray light in the optical path branching element enters the imaging element. If the stray light enters the imaging element, it may affect the captured image.

[0014] Therefore, the present inventor(s) have studied a projection type video display device that prevents stray light in the optical path branching element from entering the imaging element, and have arrived at the following invention.

[0015] Hereinafter, embodiments will be described in detail with appropriate reference to the drawings. However, a more detailed description than necessary may be omitted. For example, a detailed description of well-known matters and a redundant description of substantially the same configuration may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate the understanding of the parties.

[0016] Note that the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

[0017] (Embodiment 1) [1-1. Configuration of Projection Type Video Display Device] With reference to FIG. 1, the projection type video display device 1 according to Embodiment 1 will be described. FIG. 1 is a diagram showing the configuration of the projection type video display device 1 according to Embodiment 1.

[0018] The projection-type image display device 1 uses, as an image forming means, for example, a transmissive panel type liquid crystal display element of an active matrix system in which thin film transistors are formed in an image area. In the active matrix system, for example, a TN (Twisted Nematic) mode or a VA (Vertical Alignment) mode or the like is adopted.

[0019] The light source device 101 is composed of, for example, a blue semiconductor laser 116, a blue solid light source unit 119, lenses 126, 127, a first diffusing plate 128, a first retardation plate 129, a dichroic mirror 130, condenser lenses 131, 132, 138, a quarter-wave plate 139, a diffusing reflection plate 140, and a phosphor wheel 111.

[0020] The light emitted from the light source device 101 is incident on a projection lens unit 61 through an optical system composed of a first lens array plate 20, a second lens array plate 21, a polarization conversion element 22, a superposition lens 23, a dichroic mirror 24 for red reflection, a dichroic mirror 25 for green reflection, reflection mirrors 26, 27, 28, relay lenses 29, 30, field lenses 31, 32, 33, liquid crystal display elements 37, 38, 39, and a color synthesis prism 43 composed of a dichroic mirror for red reflection and a dichroic mirror for blue reflection. The color synthesis prism 43 is, for example, a cross cube prism.

[0021] The white light from the light source device 101 is incident on a first lens array plate 20 composed of a plurality of lens elements. The light beam incident on the first lens array plate 20 is divided into a number of light beams. The number of divided light beams converges on a second lens array plate 21 composed of a plurality of lenses. The lens elements of the first lens array plate 20 have an aperture shape similar to that of the liquid crystal display elements 37, 38, 39. The focal lengths of the lens elements of the second lens array plate 21 are determined so that the first lens array plate 20 and the liquid crystal display elements 37, 38, 39 are in a substantially conjugate relationship. The light emitted from the second lens array plate 21 is incident on the polarization conversion element 22.

[0022] The polarization conversion element 22 is composed of a polarization beam splitter prism and a half-wave plate, and converts natural light from the light source device 101 into light in one polarization direction. Since the fluorescent light is natural light, it is converted to be polarized in one polarization direction. For example, since blue light is incident as S-polarized light, it is converted to P-polarized light. The light from the polarization conversion element 22 is incident on the superimposing lens 23. The superimposing lens 23 is a lens for superimposing and illuminating the light emitted from each lens element of the second lens array plate 21 onto the liquid crystal display elements 37, 38, and 39.

[0023] The light from the superimposing lens 23 is separated into respective color lights of blue, green, and red by the dichroic mirrors 24 for red reflection and 25 for green reflection, which are color separation means. The green light passes through the field lens 31 and is incident on the liquid crystal display element 37. The red light is reflected by the reflection mirror 26, then passes through the field lens 32 and is incident on the liquid crystal display element 38. The blue light passes through and is refracted and reflected by the relay lenses 29 and 30 and the reflection mirrors 27 and 28, passes through the field lens 33, and is incident on the liquid crystal display element 39.

[0024] The three liquid crystal display elements 37, 38, and 39 change the polarization state of the incident light by controlling the applied voltage to the pixels according to the video signal, and modulate the light by combining the respective incident-side polarizing plates and the exit-side polarizing plates arranged on both sides of each of the liquid crystal display elements 37, 38, and 39 so that the transmission axes are orthogonal to form images of green, red, and blue. The respective color lights transmitted through the liquid crystal display elements 37, 38, and 39 are combined by the color synthesis prism 43, where the red and blue color lights are reflected by the dichroic mirror for red reflection and the dichroic mirror for blue reflection respectively, and are combined with the green color light and incident on the projection imaging optical system 51.

[0025] [1-2. Configuration of the Projection Imaging Optical System] Referring to FIGS. 2 and 3, the projection imaging optical system 51 will be described. FIG. 2 is a diagram showing the configuration of the projection imaging optical system 51 of the projection type video display device 1 in FIG. 1. FIG. 3 is an enlarged view of the region R1 in FIG. 2. As shown in FIG. 2, the projection imaging optical system 51 includes a video light emitting unit 45, a projection lens unit 61, an optical path separation prism 56, a narrowband retardation plate 52, and an imaging element 75.

[0026] As shown in FIGS. 1 and 2, the video light emitting unit 45 is composed of liquid crystal display elements 37, 38, 39 and a color combining prism 43, and emits video lights Lp and Ls. In the present embodiment, the S-polarized light is polarized light having a vibration plane perpendicular to the paper surface of the drawing, and the P-polarized light is polarized light having a vibration plane parallel to the paper surface of the drawing.

[0027] As shown in FIG. 2, the narrowband retardation plate 52 is disposed between the video light emitting unit 45 and the optical path separation prism 56. The narrowband retardation plate 52 aligns the video lights Lp and Ls emitted from the video light emitting unit 45 to a first polarization state of either P-polarized light or S-polarized light. In the present embodiment, the video lights Ls of S-polarized light and Lp of P-polarized light are emitted from the video light emitting unit 45. The narrowband retardation plate 52, for example, converts the incident video light Ls of S-polarized light into the video light Lp1 of P-polarized light and emits it, and emits the incident video light Lp of P-polarized light as the video light Lp1 of P-polarized light without conversion. That is, in the present embodiment, the P-polarized light is the first polarization state.

[0028] The optical path separation prism 56 has a first prism 53, a second prism 54, and a polarization separation film 55 (see FIG. 3). The optical path separation prism 56 is disposed between the video light emitting unit 45 and the projection lens unit 61.

[0029] The first prism 53 is disposed on the side of the video light emitting unit 45, and has a first surface 53a perpendicular to the optical axes of the video lights Lp and Ls, and a second surface 53b intersecting the first surface 53a. The second surface 53b is disposed on the side of the projection lens unit 61 with respect to the first surface 53a. Also, the inner angle formed by the first surface 53a and the second surface 53b is an acute angle.

[0030] The second prism 54 is disposed on the side of the second surface 53b of the first prism 53. The second prism 54 has a third surface 54a perpendicular to the optical axis disposed on the side of the projection lens unit 61, a fourth surface 54b that intersects the third surface and faces the second surface 53b, and a fifth surface 54c that intersects the third surface 54a and the fourth surface 54b. The fifth surface 54c intersects the third surface 53a and the fourth surface 54b and is disposed on the side opposite to the first prism 53. Also, the internal angle formed by the third surface 54a and the fifth surface 54c is an acute angle.

[0031] As shown in FIG. 3, the polarization separation film 55 is disposed between the second surface 53b of the first prism 53 and the fourth surface 54b of the second prism 54. The polarization separation film 55 transmits light in a first polarization state of either P-polarized light or S-polarized light and reflects light in a second polarization state of the other of P-polarized light and S-polarized light. In the present embodiment, since the first polarization state is P-polarized light, the polarization separation film 55 transmits P-polarized light (first polarization state) and reflects S-polarized light (second polarization state).

[0032] As the polarization separation film 55, for example, a wire grid polarizer or a polarization beam splitter can be used. In the present embodiment, a wire grid polarizer is employed as the polarization separation film 55. Since the wire grid polarizer has high performance with respect to angular characteristics, it is suitable when the angle θ1 (see FIG. 4) formed by the third surface 54a and the fourth surface 54b of the second prism 54 is smaller than 45 degrees, as will be described later.

[0033] Therefore, the P-polarized video light Lp1 incident on the optical path separation prism 56 passes through the polarization separation film 55. On the other hand, the S-polarized video light Ls incident on the optical path separation prism 56 is reflected and its traveling direction is changed. Accordingly, the P-polarized video light Lp1 that is emitted from the video light output unit 45 and passes through the narrow-band retardation plate 52 passes through the optical path separation prism 56 and is emitted toward the projection lens unit 61.

[0034] The projection lens unit 61 enlarges and projects the image light Lp1 incident from the image light emitting unit 45 onto the projection target 200. Further, external light Lu including the image light Lp1 reflected by the projection target 200 enters the projection lens unit 61.

[0035] The P-polarized image light Lp1 emitted from the image light emitting unit 45 and transmitted through the narrow-band retardation plate 52 enters the optical path separation prism 56 from the first surface 53a of the first prism 53. When it enters the optical path separation prism 56, it passes through the polarization separation film 55 and exits the optical path separation prism 56 from the third surface 54a of the second prism 54 and enters the projection lens unit 61.

[0036] The image light Lp1 is enlarged by the projection lens unit 61 and projected onto the projection target (screen) 200, and the image Im1 is projected on the screen 200. The external light Lu including the image light Lp1 reflected by the screen 200 exits from the projection lens unit 61 and enters the optical path separation prism 56 from the third surface 54a of the second prism 54. The external light Lu enters the second prism 54 from a direction orthogonal to the third surface 54a of the second prism 54. The external light Lu incident on the optical path separation prism 56 reflects the light in the S polarization (second polarization state) by the polarization separation film 55. The S-polarized light reflected by the polarization separation film 55 travels through the second prism 54 toward the second surface 54a of the second prism 54 and undergoes total internal reflection at the third surface 54a. The light totally reflected at the third surface 54a travels toward the imaging element, exits the second prism 54 from the fifth surface 54c, and is received by the imaging element 75.

[0037] Since the external light Lu undergoes total internal reflection at the third surface 54a of the second prism 54, the optical path length of the external light Lu until it is received by the imaging element 75 can be lengthened. Total internal reflection means that the external light Lu incident on the third surface 54a from inside the second prism 54 does not transmit from the third surface 54a to the outside of the second prism 54 and undergoes total reflection at the third surface 54a. Therefore, it is not necessary to arrange an element for adjusting the optical path length such as a prism spacer. Thus, the projection type image display device 1 can be miniaturized.

[0038] The imaging element 75 is disposed facing the fifth surface 54c of the second prism 54. The imaging element 75 images the external light Lu via the projection lens unit 61 and the optical path separation prism 56. In the present embodiment, the imaging element 75 images the S-polarized light reflected by the polarization separation film 55 among the external light Lu. The imaging element 75 is constituted by, for example, a CMOS sensor or a CCD sensor.

[0039] FIG. 4 is a schematic diagram showing the path of stray light in the optical path separation prism 56 of FIG. 2. With reference to FIG. 4, reduction of the stray light incident on the imaging element 75 will be described.

[0040] As shown in FIG. 4, the P-polarized video light Lp1 incident on the optical path separation prism 56 from the narrow-band retardation plate 52 does not completely pass through the polarization separation film 55 of the optical path separation prism 56, and a part of it is reflected to become stray light Lpt that repeats reflection within the optical path separation prism 56. In the present embodiment, the angle θ1 formed by the third surface 54a and the fourth surface 54b of the second prism 54 is smaller than 45 degrees. For this reason, the angle of the polarization separation film 55 with respect to the optical axis of the video light Lp1 becomes larger than 45 degrees. When the polarization separation film 55 is arranged in this way, the stray light Lpt reflected by the polarization separation film 55 is likely to repeat total reflection inside the first prism 53. Many of the stray light Lpt that has passed through the polarization separation film 55 enter at an angle less than the total reflection angle at the third surface 54a of the second prism 54, and easily pass through the second prism 54 and escape to the projection lens unit 61 side. Therefore, the stray light incident on the imaging element 75 can be significantly reduced.

[0041] [1-3. Effects, etc.] According to the above-described embodiment, since the angle θ1 formed by the third surface 54a and the fourth surface 54b of the second prism 54 is smaller than 45 degrees, the angle of the polarization separation film 55 with respect to the optical axis of the video light Lp1 becomes larger than 45 degrees. When the polarization separation film 55 is arranged in this way, the stray light Lpt reflected by the polarization separation film 55 is likely to repeat total reflection inside the first prism 53, and a projection type video display device capable of reducing the stray light to the imaging element can be provided.

[0042] The external light Lu received by the imaging element 75 is internally totally reflected at the third surface 54a of the second prism 54 of the optical path separation prism 56. Therefore, since the optical path of the external light Lu becomes long, it is not necessary to arrange an element for adjusting the optical path length such as a prism spacer. This contributes to the miniaturization of the projection type image display device 1.

[0043] In addition, since the angle θ1 formed between the third surface 54a and the fourth surface 54b of the second prism 54 is smaller than 45 degrees, the optical path separation prism 56 can be miniaturized, which contributes to the miniaturization of the projection type image display device 1.

[0044] Note that the angle θ1 formed between the third surface 54a and the fourth surface 54b of the second prism 54 is preferably 20 degrees or more and 35 degrees or less. In this case, the total reflection characteristics at the second surface 53b of the first prism 53 of the stray light Lpt can be improved, and furthermore, the stray light Lpt incident on the imaging element 75 can be reduced.

[0045] (Embodiment 2) Referring to FIG. 5, Embodiment 2 will be described. In Embodiment 2, the same reference numerals are given to the same or equivalent configurations as those in Embodiment 1, and the description overlapping with that in Embodiment 1 will be omitted.

[0046] FIG. 5A is a schematic diagram showing an optical path separation prism 156 according to Embodiment 2. FIG. 5B is an enlarged view of the region R1 in FIG. 5A. As shown in FIGS. 5A and 5B, in Embodiment 2, it is different from Embodiment 1 in that a gap Sp is provided between the second surface 153b of the first prism 153 and the fourth surface 154b of the second prism 154. Further, in the present embodiment, it is different from Embodiment 1 in that the polarization separation film 155 is disposed on the fourth surface 54b of the second prism 154.

[0047] As shown in FIGS. 5A and 5B, in this embodiment, a gap Sp is provided between the second surface 153b of the first prism 153 and the fourth surface 154b of the second prism 154. The size of the gap Sp is the distance between the second surface 53b of the first prism 53 and the fourth surface 54b of the second prism 54, and for example, it may be set to 3 μm or more and 10 μm or less. When the size of the gap Sp is larger than 10 μm, the resolution of the video Im1 projected onto the screen 200 may decrease. Also, since the optical path length changes due to refraction, spherical aberration may occur. For this reason, the size of the gap Sp is preferably 3 μm or more and 10 μm or less.

[0048] By providing a gap Sp between the second surface 153b of the first prism 153 and the fourth surface 154b of the second prism 154, the video light Lp1 incident on the optical path separation prism 156 from the first surface 153a is refracted when it exits from the second surface 153b toward the gap Sp. Subsequently, the incident angle θ2 when passing through the polarization separation film 155 and entering the second prism 154 can be made in the vicinity of 45 degrees. The incident angle θ2 indicates the angle of inclination of the light incident in a direction perpendicular to the second surface 153b.

[0049] When a wire grid polarizer is used as the polarization separation film 155, when the incident angle θ2 is in the vicinity of 45 degrees, the transmittance of P-polarized light in the polarization separation film 155 is high. For this reason, by providing a gap Sp between the first prism 153 and the second prism 154, the transmittance of the P-polarized video light Lp1 in the polarization separation film 155 can be increased.

[0050] For example, when BK7, which is a glass material with a refractive index ne = 1.51872, is used as the material of the first prism 153 and the second prism 154, and the angle θ3 formed between the third surface 154a and the fourth surface 154b of the second prism 154 is 27 degrees, the incident angle θ2 of the video light Lp1 on the polarization separation film 155 can be made about 43.6 degrees.

[0051] When using a material with a refractive index ne of about 1.5 to 1.75 as the material of the first prism 153 and the second prism 154, the angle θ3 formed between the third surface 154a and the fourth surface 154b of the second prism 154 is preferably 20 degrees or more and 35 degrees or less. In this case, the incident angle θ2 of the video light Lp1 when it enters the polarization separation film 155 through the first prism 153 can be made close to 45 degrees.

[0052] FIG. 6 is a schematic diagram showing the path of stray light in the optical path separation prism 156 of FIG. 5A. With reference to FIG. 6, reducing the stray light incident on the image sensor 75 in the present embodiment will be described.

[0053] When a gap Sp is provided between the second surface 153b of the first prism 153 and the fourth surface 154b of the second prism 154, the amount of light that is totally reflected by the second surface 153b of the first prism 153 among the stray light Lpt increases. For this reason, the stray light Lpt incident on the second prism 154 is significantly reduced. Therefore, the stray light incident on the image sensor 75 can be significantly reduced.

[0054] According to the above-described embodiment, the stray light incident on the second prism 154 can be reduced. For this reason, the stray light incident on the image sensor 75 can be significantly reduced.

[0055] (Embodiment 3) Embodiment 3 will be described with reference to FIG. 7. In Embodiment 3, the same or equivalent components as those in Embodiment 2 will be described with the same reference numerals. Also, in Embodiment 3, the description overlapping with that in Embodiment 2 will be omitted.

[0056] FIG. 7 is a schematic diagram showing the configuration of the projection imaging optical system 251 according to Embodiment 3. As shown in FIG. 7, Embodiment 3 is different from Embodiment 2 in that the projection imaging optical system 251 includes a quarter-wave plate 257 and a polarizing plate 258.

[0057] The quarter-wave plate 257 is disposed between the optical path separation prism 256 and the projection lens unit 61. The quarter-wave plate 257 converts the image light Lp1 from the first polarization state into circular polarization, and converts the external light Lu from circular polarization into the second polarization state.

[0058] In the present embodiment, the image light Lp1 of P polarization (the first polarization state) incident from the narrow-band retardation plate 52 is converted into circularly polarized image light Lc. The image light Lc emitted from the quarter-wave plate 257 is enlarged by the projection lens unit 61 and projected onto the screen 200.

[0059] The circularly polarized image light Lc1 that constitutes the image Im1 projected on the screen 200 is reflected by the screen 200 and enters the projection lens unit 61. The external light Lc2 reflected by the screen 200 also contains a large amount of circularly polarized components. The external light Lc2 travels from the projection lens unit 61 toward the optical path separation prism 256 and enters the quarter-wave plate 257. The circularly polarized external light Lc2 incident on the quarter-wave plate 257 is converted into S-polarized external light Ls1 and enters the optical path separation prism 256.

[0060] The external light Ls1 incident on the optical path separation prism 256 is reflected by the polarization separation film 255, totally reflected by the third surface 254a of the second prism 254, and enters the imaging device 75.

[0061] The polarizing plate 258 is disposed between the optical path separation prism 256 and the imaging device 75 and allows the external light Ls1 to pass through. In the present embodiment, the polarizing plate 258 transmits the external light Ls1 of S polarization (the second polarization state) and blocks light in polarization states other than S polarization. Therefore, the external light Ls1 emitted from the optical path separation prism 256 toward the imaging device 75 passes through the polarizing plate 258 and enters the imaging device 75, but stray light containing a large amount of P-polarized components in the optical path separation prism 256 is blocked by the polarizing plate. Therefore, the stray light incident on the imaging device 75 can be further reduced, and the image projected on the screen 200 can be imaged with high sensitivity.

[0062] According to the above-described embodiments, stray light incident on the imaging device 75 can be further reduced. In addition, the image projected onto the screen 200 can be imaged with high sensitivity.

[0063] FIG. 8 is a schematic diagram showing the configuration of a projection imaging optical system 251A according to Modification Example 1 of Embodiment 3. FIG. 9 is a schematic diagram showing the optical path in the optical path separation prism 256 of FIG. 8. FIG. 10 is a diagram showing an example of an image captured by the imaging device 75 in Modification Example 1. With reference to FIGS. 8 to 10, Modification Example 1 of Embodiment 3 will be described.

[0064] As shown in FIG. 8, a movable object hm may exist in front of the screen 200. The object hm is, for example, a human or a robot present in front of the screen 200. In this case, a part of the projected video light Lc1 is projected onto the screen 200 as the video Im2, and a part is projected onto the object hm as the video light Im. In the example of FIG. 8, characters are shown as an example of the video Im2 and the video Im3.

[0065] Illumination light Ln1 may be irradiated from the external illumination light source 210 toward this object hm. Alternatively, the object hm may be irradiated with ambient light around the screen 200. The illumination light Ln1 or the ambient light is unpolarized light, and the illumination light Ln2 that irradiates the object hm and is reflected by the object hm passes through the projection lens unit 61 and enters the quarter-wave plate 257.

[0066] As shown in Fig. 9, in the projection imaging optical system 251A of Modification 1, the illumination light Ln2 passes through the quarter-wave plate 257 and is converted into circularly polarized illumination light Lnc. Among the illumination light Lnc, the S-polarized component (illumination light Lns) reflected by the polarization separation film 255 is totally reflected by the third surface 254a of the second prism 254, exits from the fifth surface 254c, and is received by the imaging device 75 through the polarizing plate 258. Note that the S-polarized component of the ambient light is also received by the imaging device 75 in the same manner. Among the circularly polarized illumination light Lnc, the P-polarized component (illumination light Lnp) passes through the polarization separation film 255 and enters the first prism 253. When the illumination light Lns is received by the imaging device 75, as shown in Fig. 10, both the image by the illumination light Lns and the ambient light and the image by the external light Ls1 are captured by the imaging device 75.

[0067] The quarter-wave plate 257 may be detachable. Fig. 11 is a schematic diagram showing the optical path in the optical path separation prism 256 when the quarter-wave plate 257 is removed. Fig. 12 is a diagram showing an example of an image captured by the imaging device 75 when the quarter-wave plate 257 is removed.

[0068] As shown in Fig. 11, when the quarter-wave plate 257 is removed, the S-polarized component (illumination light Lns) of the illumination light Ln2 is reflected by the polarization separation film 255, totally reflected by the third surface 254a of the second prism 254, exits from the fifth surface 254c, and is received by the imaging device 75 through the polarizing plate 258. The S-polarized component of the ambient light is also received by the imaging device 75 in the same manner. On the other hand, since the external light Lp2 reflected by the screen 200 remains P-polarized, it passes through the polarization separation film 255 and is not received by the imaging device 75.

[0069] When the quarter-wave plate 257 is removed, as shown in Fig. 12, an image by the illumination light Lns and the ambient light is captured by the imaging device 75, and the image Im2 projected by the external light Lp2 is not captured. Therefore, the object hm can be imaged without being affected by the projected image. In this case, for example, a person or an object can be detected and synthesized with the projected image to project an image following the person or the object.

[0070] Since the amount of illumination light Ln1 or ambient light is often small, in order to capture an image of a person or object excluding the projected image, it is desirable to prevent stray light generated from the optical path separation prism 256 or the lenses of the projection lens unit 61 from entering the imaging element 75. By attaching and detaching the 1 / 4 wavelength plate 257, an image excluding the projected image can be easily captured.

[0071] (Other embodiments) As described above, the above embodiment has been described as an example of the technology disclosed in this application. However, the technology in this disclosure is not limited to this, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made. In addition, it is also possible to combine the components described in the above embodiment to create a new embodiment.

[0072] In each embodiment, S-polarized and P-polarized image light are used, but the polarization states may be interchanged. For example, the image light output from narrowband retarder 52 may be S-polarized, and the image light incident on image sensor 75 may be P-polarized.

[0073] In each embodiment, the image light output unit 45 includes three liquid crystal display elements as a light modulation unit, but is not limited to this. The image light output unit 45 may include a DMD (digital micromirror device) instead of the liquid crystal display elements. The image light output from the DMD is also polarized by the narrowband retarder 52, so that the same effect as in the embodiment can be obtained.

[0074] As described above, the embodiment has been described as an example of the technology in the present disclosure. For this purpose, the attached drawings and detailed description have been provided. Therefore, among the components described in the attached drawings and detailed description, not only components essential for solving the problem but also components that are not essential for solving the problem in order to exemplify the above technology may be included. Therefore, the fact that these non-essential components are described in the attached drawings or detailed description should not be used to immediately determine that these non-essential components are essential.

[0075] In addition, since the above-described embodiments are for exemplifying the technology in the present disclosure, various changes, replacements, additions, omissions, etc. can be made within the scope of the claims or the equivalent scope thereof.

[0076] (Summary of the Embodiment) (1) The projection-type video display device of the present disclosure includes a video light emitting unit that emits video light, a projection lens unit that enlarges and projects the video light incident from the video light emitting unit onto a projection target and through which external light including the video light reflected by the projection target is incident, a first prism that is disposed between the video light emitting unit and the projection lens unit and has a first surface perpendicular to the optical axis of the video light disposed on the video light emitting unit side and a second surface that intersects the first surface, a second prism that is disposed on the second surface side of the first prism and has a third surface perpendicular to the optical axis disposed on the projection lens unit side, a fourth surface that intersects the third surface and faces the second surface, and a fifth surface that intersects the third surface and the fourth surface, a polarization separation film disposed between the second surface of the first prism and the fourth surface of the second prism, a narrow-band retardation plate disposed between the video light emitting unit and the polarization separation prism that aligns the video light in a first polarization state of either P polarization or S polarization, and an image sensor that is disposed facing the fifth surface of the second prism and captures the external light through the projection lens unit and the polarization separation prism. The polarization separation film transmits light in the first polarization state and reflects light in a second polarization state of either P polarization or S polarization. The video light enters the polarization separation prism from the first surface, passes through the polarization separation film, exits from the third surface, and enters the projection lens unit. The external light exits from the projection lens unit, enters the polarization separation prism from the third surface, reflects the light in the second polarization state of the external light by the polarization separation film, undergoes total internal reflection at the third surface, exits from the fifth surface, and is received by the image sensor.

[0077] With such a configuration, it is possible to provide a projection-type video display device capable of reducing stray light to the image sensor.

[0078] (2) In the projection type image display device of (1), a gap is provided between the second surface of the first prism and the fourth surface of the second prism, and the polarization separation film may be disposed on the fourth surface.

[0079] With such a configuration, stray light incident on the second prism of the optical path separation prism can be significantly reduced. Therefore, the stray light incident on the imaging device can also be significantly reduced.

[0080] (3) In the projection type image display device of (2), the gap may be provided with a size of 3 μm or more and 10 μm or less.

[0081] With such a configuration, the probability of total reflection of stray light on the second surface of the first prism increases, and the stray light incident on the imaging device can be reduced.

[0082] (4) In any one of the projection type image display devices of (1) to (3), the polarization separation film may be a wire grid polarizer.

[0083] With such a configuration, the effect of reducing stray light can be further improved.

[0084] (5) In any one of the projection type image display devices of (1) to (4), the angle formed by the third surface and the fourth surface of the second prism may be 20 degrees or more and 35 degrees or less.

[0085] With such a configuration, the optical path separation prism can be thinned to realize miniaturization of the projection type image display device.

[0086] (6) In any one of the projection type image display devices of (1) to (5), further, a quarter-wave plate disposed between the optical path separation prism and the projection lens unit, which converts image light from the first polarization state to circular polarization and converts external light from circular polarization to the second polarization state, may be provided.

[0087] With such a configuration, external light can be efficiently incident on the imaging device, and the video light projected onto the projection target can be imaged with high sensitivity.

[0088] (7)(6) In the projection type video display device, the quarter-wave plate may be detachably arranged.

[0089] With such a configuration, the quarter-wave plate can be arranged as needed.

[0090] (8) In any one of the projection type video display devices from (1) to (7), further, a polarizing plate that transmits external light may be provided between the optical path separation prism and the imaging device.

[0091] With such a configuration, stray light incident on the imaging device can be further reduced.

Industrial Applicability

[0092] The present disclosure can be used in a projection type video display device that projects video.

Explanation of Signs

[0093] 1 Projection type video display device 45 Video light emission unit 52 Narrow band retardation plate 53, 153, 253 First prism 53a, 153a, 253a First surface 53b, 153b, 253b Second surface 54, 154, 254 Second prism 54a, 154a, 254a Third surface 54b, 154b, 254b Fourth surface 54c, 154c, 254c Fifth surface 55, 155, 255 Polarization separation film 56, 156, 256 Optical path separation prism 61 Projection lens unit 75 Imaging device 257 Retardation plate 258 Polarizer

Claims

1. An image light emitting unit that emits image light; A projection lens unit that enlarges and projects the image light incident from the image light emitting unit onto a projection target, and onto which external light including the image light reflected by the projection target is incident; A first prism disposed between the image light emitting unit and the projection lens unit, having a first surface perpendicular to the optical axis of the image light disposed on the image light emitting unit side, and a second surface intersecting the first surface; and a second prism disposed on the second surface side of the first prism, having a third surface perpendicular to the optical axis disposed on the projection lens unit side, a fourth surface intersecting the third surface and facing the second surface, and a fifth surface intersecting the third surface and the fourth surface; and a polarization separation film disposed between the second surface of the first prism and the fourth surface of the second prism; an optical path separation prism having the above; A narrow-band retardation plate disposed between the image light emitting unit and the optical path separation prism, which aligns the image light in a first polarization state of either P-polarized light or S-polarized light; An imaging element disposed facing the fifth surface of the second prism, which images the external light through the projection lens unit and the optical path separation prism; Comprising: The polarization separation film transmits light in the first polarization state and reflects light in a second polarization state of either P-polarized light or S-polarized light; The image light enters the optical path separation prism from the first surface, passes through the polarization separation film, exits from the third surface, and enters the projection lens unit; The external light exits from the projection lens unit, enters the optical path separation prism from the third surface, reflects the light in the second polarization state of the external light by the polarization separation film, undergoes total internal reflection at the third surface, exits from the fifth surface, and is received by the imaging element; A gap is provided between the second surface of the first prism and the fourth surface of the second prism; The polarization separation film is disposed on the fourth surface; The angle formed by the third surface and the fourth surface is 20 degrees or more and 35 degrees or less; A projection type image display device.

2. The gap is provided with a size of 3 μm or more and 10 μm or less. The projection type image display device according to Claim 1. The projection type image display device according to claim 1.

3. The polarization separation film is a wire grid polarizer. The projection type image display device according to claim 1 or 2. The projection type image display device according to claim 1 or 2.

4. Furthermore, A quarter-wave plate disposed between the optical path separation prism and the projection lens unit, which converts the image light from the first polarization state to circular polarization and converts the external light from circular polarization to the second polarization state. Comprising The projection type image display device according to any one of claims 1 to 3. **Claim 5** The quarter-wave plate is detachably arranged. The projection type image display device according to claim 4. **Claim 6** Furthermore A polarizing plate disposed between the optical path separation prism and the imaging device, which transmits the external light Comprising The projection type image display device according to any one of claims 1 to 5.

Images