TIR prism and projection type video display device

Abstract

To provide a TIR prism capable of restricting intrusion of reflectance into an imaging optical system due to a lens surface of a projection optical system, and to provide a projection type video display device comprising the TIR prism.SOLUTION: A TIR prism comprises: a first prism on a side of a light modulation element; a second prism on a side of a projection optical system; and a third prism between the first prism and the second prism. A first prism surface of the first prism and a second prism surface of the second prism are disposed opposite each other via the third prism. The third prism includes: a third prism surface disposed opposite the first prism surface with a gap parallel to the first prism surface thereinbetween; and a fourth prism surface disposed opposite the second prism surface with a gap parallel to the second prism surface thereinbetween. The first prism surface causes total reflection to illumination light and leads it to the light modulation element, and transmits projection light. The second prism surface transmits projection light and causes total reflection to a portion of external light being incident having transmitted the projection optical system. The portion of light is transmitted through a first region in an entrance pupil of the projection optical system and is incident on the second prism surface, and projection light is incident on a second region in the entrance pupil.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a TIR prism and a projection-type image display device including the same. [Background technology]

[0002] Conventionally, a projection type image display device has an imaging optical system inside the main body, and may project an image onto a projection target such as a screen or a building, while guiding external light from the projection target to the imaging optical system to capture an image. In a projection type image display device, the quality of the captured image may be degraded due to the influence of light reflected by the lens surface of the projection optical system.

[0003] Patent document 1 discloses a projection type display device that shares a projection lens during projection and imaging, and that can block some of the light emitted from an illumination optical system from leaking into a light receiving optical system that has an imaging element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication WO2017 / 183249A1 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a TIR prism and a projection-type image display device that can prevent light reflected by a lens surface of a projection optical system from entering an imaging optical system. [Means for solving the problem]

[0006] In order to achieve the above object, a TIR prism according to an embodiment of the present disclosure is a TIR prism that is disposed between a light modulation element and a projection optical system, guides illumination light to the light modulation element, and emits projection light generated by reflection of the illumination light at the light modulation element forward along a projection optical axis to the projection optical system, the TIR prism including a first prism on the light modulation element side, a second prism on the projection optical system side, and a third prism disposed between the first prism and the second prism, the first prism surface of the first prism and the second prism surface of the second prism being disposed opposite each other via the third prism, The projection optical system has a third prism surface disposed opposite the projection optical system across a gap parallel to the projection optical system surface, and a fourth prism surface disposed opposite the second prism surface across a gap parallel to the projection optical system surface, and the first prism surface totally reflects the illumination light to guide it to the light modulation element and transmits the projection light, and the second prism surface transmits the projection light and totally reflects a portion of external light that has passed through the projection optical system backward along the projection optical axis and entered the projection optical system, and the portion of the light passes through a first region in an entrance pupil of the projection optical system and enters the second prism surface, and the projection light exiting the second prism is entered into a second region different from the first region in the entrance pupil. Effect of the Invention

[0007] According to the present disclosure, it is possible to provide a TIR prism and a projection-type image display device that suppresses the intrusion of light reflected by a lens surface of a projection optical system into an imaging optical system. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an overall configuration of a projection-type image display device according to a first embodiment of the present disclosure. [Diagram 2] FIG. 1 is a perspective view showing a configuration of a TIR prism of a projection type image display device according to a first embodiment; [Figure 3A] FIG. 1 is a cross-sectional view of a TIR prism according to a first embodiment, illustrating the propagation of light incident thereon after passing through different regions in an entrance pupil of a projection optical system, within the TIR prism; [Figure 3B] FIG. 2 illustrates different regions of the entrance pupil of a projection system. [Figure 4]FIG. 1 is a cross-sectional view of a TIR prism according to a first embodiment, showing the propagation of projection light within the TIR prism; [Diagram 5] FIG. 1 is a cross-sectional view of a TIR prism according to a first embodiment, showing propagation of external light within the TIR prism; [Figure 6] FIG. 1 is a diagram showing light propagation in a projection imaging optical system according to a first embodiment. [Figure 7] FIG. 11 is a schematic diagram showing an overall configuration of a projection-type image display device according to a second embodiment of the present disclosure. [Figure 8] FIG. 1 is a diagram showing the propagation of light in a projection imaging optical system of a conventional projection type image display device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] According to a first aspect of the present disclosure, a TIR prism is disposed between a light modulation element and a projection optical system, guides illumination light to the light modulation element, and emits projection light generated by reflection of the illumination light at the light modulation element forward along a projection optical axis to the projection optical system, the TIR prism including a first prism on the light modulation element side, a second prism on the projection optical system side, and a third prism disposed between the first prism and the second prism, the first prism surface of the first prism and the second prism surface of the second prism are disposed opposite each other via the third prism, and the third prism is disposed opposite to the first prism surface across a gap parallel to the first prism surface. and a fourth prism surface disposed opposite the second prism surface across a gap parallel to the first prism surface, wherein the first prism surface totally reflects illumination light to guide it to a light modulation element and transmits the projection light, and the second prism surface transmits the projection light and totally reflects a portion of external light that has passed through the projection optical system backward along the projection optical axis and is incident thereon, the portion of the light passing through a first region in an entrance pupil of the projection optical system to be incident on the second prism surface, and the projection light exiting the second prism surface is incident on a second region in the entrance pupil which is different from the first region.

[0010] According to this aspect, it is possible to prevent light reflected by the lens surface of the projection optical system from entering the imaging optical system.

[0011] According to a second aspect of the present disclosure, there is provided a TIR prism as described in the first aspect, in which, of light having a wavelength at the long wavelength end of the projection light and passing through the projection optical system and propagating backward, light that has passed through a first region is incident on a second prism surface at an angle equal to or greater than the critical angle of total reflection, and light that has passed through the second region is incident on the second prism surface at an angle smaller than the critical angle of total reflection.

[0012] According to a third aspect of the present disclosure, there is provided a TIR prism as described in the first or second aspect, wherein the first prism has a fifth prism surface onto which the illumination light is incident and a sixth prism surface that transmits the illumination light totally reflected at the first prism surface and outputs it to the light modulation element, and the second prism has a seventh prism surface that outputs the projection light to the projection optical system and receives external light, and an eighth prism surface that transmits and outputs a portion of the light totally reflected at the second prism surface, and the illumination light is incident on the fifth prism surface at an adjusted angle so that the projection light output from the seventh prism surface is input to a second region of the entrance pupil.

[0013] According to a fourth aspect of the present disclosure, there is provided a TIR prism as described in any one of the first to third aspects, wherein a portion of the light totally reflected at the second prism surface forms an image within the second prism, and the eighth prism surface is arranged parallel to the surface on which the image is formed.

[0014] According to a fifth aspect of the present disclosure, there is provided a projection type image display device comprising: an illumination optical system that supplies illumination light; one or more light modulation elements that modulate the illumination light in accordance with a video signal to generate projection light; a prism member including a TIR prism described in any one of the first to fourth aspects; a projection optical system that transmits the projection light that has passed through the prism member through a second region and projects it forward onto a projection object to display an image; and an imaging optical system that receives and forms an image from a portion of external light that passes through the projection optical system backward from the projection object and enters the prism member, the portion passing through the first region of the projection optical system and being totally reflected within the TIR prism.

[0015] Any of the above-described various embodiments may be appropriately combined to achieve the effects of each of the embodiments.

[0016] Hereinafter, the embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of already well-known matters or duplicate explanation of substantially the same configuration may be omitted. This is to avoid the following explanation becoming unnecessarily redundant and to facilitate understanding by those skilled in the art.

[0017] A TIR prism and a projection-type image display device according to an embodiment of the present disclosure will be described with reference to Figures 1 to 8. The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims. In addition, in each drawing, each element is exaggerated for ease of explanation.

[0018] As projection type image display devices that apply a TIR prism according to an embodiment of the present disclosure, a single-panel projection type image display device having one light modulation element (embodiment 1) and a three-panel projection type image display device having three light modulation elements (embodiment 2) are described.

[0019] (Embodiment 1) <Projection-type image display device> The overall configuration of the projection-type image display device 600 according to the first embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing the overall configuration of the projection-type image display device 600 according to the first embodiment of the present disclosure, and shows the overall configuration of the projection-type image display device 600 on the XZ plane. Note that the projection-type image display device according to the embodiment of the present disclosure may be, for example, a high-brightness type projector used for projection mapping, or may be a low-brightness type projector for home use.

[0020] A projection-type image display device 600 in FIG. 1 includes an illumination optical system 200 that supplies illumination light, and a projection / imaging optical system 500 that has both a projection function and an imaging function.

[0021] <Configuration of illumination optical system> The illumination optical system 200 includes a light source unit 20, afocal lenses 31 and 32, a diffusion plate 41, a λ / 4 plate 42, condenser lenses 33, 34, and 35, a dichroic mirror 45, a rod integrator 46, a phosphor wheel 50, a color wheel 60, and lenses 73, 74, and 75 that constitute an illumination light relay optical system. The illumination optical system 200 can supply illumination light in the visible range.

[0022] In the illumination optical system 200, the light source unit 20 can be configured, for example, by a plurality of semiconductor lasers (LD) or light emitting diodes (LED). In this embodiment, for example, a semiconductor laser element 21 that emits blue light can be used. The blue light emitted from the semiconductor laser element 21 is used as the projection light and is also used as the excitation light for exciting the phosphor of the phosphor wheel 50. The blue light emitted from the semiconductor laser element 21 is emitted in the illustrated −X direction, collimated by the collimating lens 22, and then focused by the afocal lenses 31 and 32, transmitted through the diffusion plate 41, and incident on the dichroic mirror 45.

[0023] In this embodiment, the light emitted from light source unit 20 is, for example, S-polarized blue light, and dichroic mirror 45 reflects the S-polarized blue light and can transmit P-polarized blue light and other colored light. The blue light reflected by dichroic mirror 45 travels approximately in the -Z direction, passes through λ / 4 plate 42, and is collected by lenses 33 and 44 to enter phosphor wheel 50, where it excites the phosphors in phosphor wheel 50 to emit light.

[0024] By rotating, different segments of the phosphor layer of the phosphor wheel 50 are excited by the incident blue light, and can generate fluorescence including, for example, emission component light in a yellow region and emission component light in a green region. In addition, a part of the blue light that has passed through the λ / 4 plate 42 is reflected by the phosphor wheel 50 and passes through the λ / 4 plate 42 again to become P-polarized blue component light, which is transmitted through the dichroic mirror 45. The blue component light and emission component light of each color region that have passed through the dichroic mirror 45 proceed in approximately the +Z direction along the illumination optical axis Os, and enter the color wheel 60 via the condenser lens 35.

[0025] Color wheel 60 is controlled to rotate synchronously with phosphor wheel 50, and splits the incident light according to the transmission characteristics of the different segments. The light generated by phosphor wheel 50 and color wheel 60, which rotate synchronously, enters rod integrator 46 and is homogenized there so that component light of each color gamut, including red, green, blue, yellow, etc., is emitted in a time-division manner.

[0026] In this embodiment, in the projection imaging optical system 500 of the projection type image display device 600, the projection light Lp emitted from the TIR prism 300 can be incident on a predetermined area of ​​the entrance pupil of the projection optical system 420. To make the projection light Lp incident on a predetermined area of ​​the entrance pupil of the projection optical system 420, for example, the angle of the illumination light incident surface of the TIR prism 300 may be adjusted to adjust the angle at which the projection light Lp is emitted, but this is not limited to this, and it can also be realized by making the illumination light Ls incident on the TIR prism 300 at the adjusted angle. In this embodiment, the arrangement of the light modulation element 400 of the existing device is utilized, and the illumination light Ls is made incident on the TIR prism 300 at the adjusted angle, so that the projection light Lp can be incident on a predetermined area of ​​the entrance pupil of the projection optical system 420. The area of ​​the entrance pupil where the projection light Lp enters the projection optical system 420 will be described in detail later.

[0027] In this embodiment, for example, by configuring the exit surface 46a of the rod integrator 46 to have a predetermined angle, the light rays of the illumination light Ls are emitted from the center of the illumination optical axis Os toward the upper side (the +X side in the figure) as conceptually illustrated. This allows the illumination light Ls to be incident on the TIR prism 300 at an adjusted angle without reducing the light intensity of the illumination light Ls introduced into the projection imaging optical system 500.

[0028] The present disclosure is not limited to a method for making the illumination light Ls enter the TIR prism 300 at an adjusted angle. For example, instead of providing an angle on the exit surface 46a of the rod integrator 46, a mask element may be provided to block a portion of the illumination light Ls emitted from the rod integrator 46, thereby adjusting the angle of the illumination light Ls entering the TIR prism 300, or the angle of the illumination light Ls entering the TIR prism 300 may be adjusted by adjusting the arrangement of the optical system that guides the light from the light source unit 20 to the rod integrator 46.

[0029] The light emitted from the rod integrator 46 passes through lenses 73, 74, and 75 that constitute the illumination light relay optical system, and then is emitted from the illumination optical system 200, becoming white illumination light Ls on a time average, and entering the projection imaging optical system 500 at an adjusted angle.

[0030] <Configuration of the projection imaging optical system> The projection imaging optical system generates projection light in accordance with a video signal, emits the generated projection light forward along a projection optical axis, and displays an image by enlarging and projecting it onto a projection object, and also guides external light that enters backward from the projection object along the projection optical axis to the imaging optical system to capture an image.

[0031] In this embodiment, the projection imaging optical system 500 includes a TIR prism 300, a light modulation element 400, a projection optical system 420, an imaging optical system 440, and an imaging element 450. Also, in this embodiment, as shown in the figure, the projection imaging optical system 500 emits projection light Lp in the +X direction along a projection optical axis Op and projects the projection light Lp on an object to be projected 550 in an enlarged manner to display an image, and at the same time emits imaging light Lm, which is a part of the external light Lo, in the approximately +Z direction along the imaging optical axis Om and introduces the imaging light Lm into the imaging element 450 to capture an image.

[0032] In the projection imaging optical system 500, the TIR prism 300 uses total reflection to deflect the illumination light Ls incident in approximately the +Z direction, and guides it to the light modulation element 400 located on the -X side. The configuration of the TIR prism 300 will be described in detail later.

[0033] The light modulation element 400 can be configured using a DMD (Digital Mirror Device). The light modulation element 400 modulates component light of each color gamut included in the illumination light Ls based on a video signal, and distributes it to DMD-ON light that becomes projection light Lp for each pixel, or DMD-OFF light Lf that becomes unnecessary light. The projection light Lp for projection is emitted in the +X direction along the projection optical axis Op, and the DMD-OFF light Lf is deflected from the projection optical axis Op and removed.

[0034] The projection light Lp passes through the TIR prism 300 and propagates along the projection optical axis Op to the projection optical system 420. A plurality of lens elements included in the projection optical system 420 enlarges and projects the projection light Lp onto a projection target 550 such as a screen to display an image.

[0035] On the other hand, an image of the projection object 550 can be captured by the imaging element 450 built in the projection imaging optical system 500 using external light Lo propagating from the projection object 550 in the −X direction shown in the figure.

[0036] As shown in the figure, external light Lo propagates in the −X direction along the projection optical axis Op, and enters the TIR prism 300 via the projection optical system 420. In the present embodiment, a portion of the external light Lo is totally reflected within the TIR prism 300, and is introduced as imaging light Lm along the imaging optical axis Om into the imaging optical system 440.

[0037] The imaging optical system 440 can be composed of a plurality of optical components, and in this embodiment, for example, can be composed of an imaging optical system composed of a plurality of lens elements. The imaging light Lm incident along the imaging optical axis Om can be imaged by the imaging optical system 440 at the imaging element 450. Note that the present disclosure does not limit the imaging magnification of the imaging optical system, and the imaging optical system 440 may be a reduction optical system, a unity magnification optical system, or a magnification optical system. The imaging element 450 can be composed of a solid-state imaging element such as a CCD image sensor or a CMOS image sensor, and converts the received imaging light Lm into an electrical image signal.

[0038] (Light propagation in a conventional projection imaging optical system) Next, the influence on imaging caused by light reflected by the lens surface of the projection optical system in a conventional projection imaging optical system will be described with reference to Fig. 8. Fig. 8 is a diagram showing the propagation of light in a projection imaging optical system 500C of a conventional projection type image display device. In the projection imaging optical system 500C in Fig. 8, elements similar to those in the projection imaging optical system 500 in Fig. 1 are denoted by the same reference numerals, and detailed descriptions thereof will be omitted.

[0039] 8, the projection imaging optical system 500C includes a TIR prism 300C, a light modulation element 400, a projection optical system 420, an imaging optical system 440, and an imaging element 450. The projection light Lpc is emitted by the light modulation element 400, propagates in the +X direction along the projection optical axis Op, and is emitted to a projection target (not shown) after passing through the TIR prism 300C and the multiple lens elements L21, L22, and L23 of the projection optical system 420 in order. On the other hand, the external light Lo from the projection target propagates in the -X direction along the projection optical axis Op, passes through the projection optical system 420, and enters the TIR prism 300C.

[0040] The TIR prism 300C is composed of a prism 310C on the side of the light modulation element 400 (-X side in the figure) and a prism 320C on the side of the projection optical system 420 (+X side in the figure), and the prism surface 311c of the prism 310C and the prism surface 321c of the prism 320C are arranged to face each other with a parallel gap provided, and an air gap is formed between the prism surface 311c and the prism surface 321c. Due to this air gap, illumination light (not shown) incident through the prism surface 312c of the prism 310C is totally reflected by the prism surface 311c, and can be transmitted through the prism surface 313c and incident on the light modulation element 400.

[0041] The external light Lo transmitted through the projection optical system 420 passes through the upper prism surface 322c of the prism 320C and reaches the prism surface 321c. The prism surface 321c is coated with a partial reflection film, and a part of the incident external light Lo is reflected by the partial reflection film to form the imaging light Lmc. The imaging light Lmc is further reflected by the upper prism surface 322c to form an intermediate image Mdc in the prism 320C, and then transmits through the prism surface 323c to be emitted. A part of the emitted external light Lo travels along the imaging optical axis Omc, transmits through the lenses L41, L42, and L43 of the imaging optical system in order, and forms an image at the imaging element 450.

[0042] In the projection imaging optical system 500C, when the projection light Lp passes through the projection optical system 420, reflected light that propagates backward (in the -X direction in the figure) is generated by reflection on the lens surfaces of the plurality of lens elements L21, L22, L23. Such lens surface reflected light Gc1 is partially reflected by the partial reflection film on the prism surface 321c, and similar to the imaging light Lmc, reflected light Gc2 that exits from the prism 320C along the imaging optical axis Omc is generated. The reflected light Gc2 enters the imaging optical system 440, and a different image formation can be formed on the imaging element 450 from the imaging light Lmc. As a result, the contrast of the image displayed on the imaging element 450 decreases, and a problem of image quality degradation of the imaging occurs. In this specification, the reflected light generated by the reflection of the projection light Lp on the lens surface of the lens element of the projection optical system, for example, Gc1 and Gc2 shown in FIG. 8, is referred to as "ghost light", and the image formation by the ghost light on the imaging element 450 is referred to as a "ghost image". In a conventional projection imaging optical system, when a ghost image is formed on the imaging element 450, the contrast of the imaging decreases, and image quality degradation occurs.

[0043] Also, in a projection type video display device having high brightness, when projection and imaging are performed simultaneously, strong ghost light is generated on the lens surface of the projection optical system by the high-brightness projection light Lp, and when the strong ghost light enters the imaging optical system, a bright ghost image is formed near the imaging, so that a problem of significantly reduced visibility of the imaging occurs. Therefore, in a conventional projection type video display device, when projection and imaging are performed simultaneously, in order to avoid the generation of strong reflected light of the projection light by the lens surface of the projection optical system, the brightness of the projection light is restricted.

[0044] Therefore, the present disclosure configures a TIR prism so as to suppress the intrusion of the reflected light by the lens surface of the projection optical system into the imaging optical system. Thereby, it is possible to suppress the reflected light by the lens surface of the lens element in the projection optical system from entering the imaging optical system, improve the contrast of the imaging, and improve the image quality. Hereinafter, the configuration of the TIR prism according to the present embodiment will be described with reference to FIG. 2.

[0045] <Configuration of TIR Prism> 2 is a perspective view showing a configuration of the TIR prism 300 of the projection type image display device 600 of the first embodiment. As shown in FIG. 2, the TIR prism 300 according to the embodiment of the present disclosure is composed of a prism 310 on the side of the light modulation element 400 (-X side in the figure), a prism 320 on the side of the projection optical system 420 (+X side in the figure), and a prism 330 arranged between the prisms 310 and 320. The prism surface 311 of the prism 310 and the prism surface 321 of the prism 320 are arranged opposite each other via the prism 330. The prism 330 has a prism surface 331 and a prism surface 332, and the prism surface 331 is arranged opposite the prism surface 311 of the prism 310 across a parallel gap, and the prism surface 332 is arranged opposite the prism surface 321 of the prism 320 across a parallel gap. That is, in TIR prism 300 of the present disclosure, an air gap is formed between prism surface 311 and prism surface 331, and an air gap is also formed between prism surface 321 and prism surface 332.

[0046] In this specification, prism 310, prism 320, and prism 330 may be referred to as a "first prism," a "second prism," and a "third prism," respectively. Also, prism surface 311 may be referred to as a "first prism surface," prism surface 321 may be referred to as a "second prism surface," prism surface 331 may be referred to as a "third prism surface," and prism surface 332 may be referred to as a "fourth prism surface." Note that the present disclosure is not limited to the shape of each prism. Each prism constituting TIR prism 300 may have the shape shown in the figure or other shapes. Also, the present disclosure does not limit the prism surface included in each prism. The TIR prism may further include other prism surfaces.

[0047] In this embodiment, illumination light Ls incident on prism surface 312 of prism 310 at an angle adjusted along illumination optical axis Os is totally reflected by prism surface 311 due to an air gap formed between prism surface 311 and prism surface 331, passes through prism surface 313 on the -X side, and enters light modulation element 400. Projection light Lp generated by reflection of illumination light Ls on light modulation element 400 is emitted from light modulation element 400 in the +X direction along projection optical axis Op, passes through TIR prism 300, and enters projection optical system 420. On the other hand, external light Lo propagating in the -X direction from a projection target (not shown) passes through projection optical system 420 and enters prism surface 322 of prism 320 along projection optical axis Op. Imaging light Lm formed by total reflection of a portion of the external light Lo within TIR prism 300 is emitted from prism surface 323 along imaging optical axis Om and enters imaging optical system 440.

[0048] In this specification, prism surface 312 may be referred to as the “fifth prism surface,” prism surface 313 may be referred to as the “sixth prism surface,” prism surface 322 may be referred to as the “seventh prism surface,” and prism surface 323 may be referred to as the “eighth prism surface.” Note that in Fig. 2, projection optical system 420 and imaging optical system 440 are conceptually shown, and the optical components that constitute each of them are omitted.

[0049] The TIR prism 300 of the present disclosure can totally reflect the light propagating in the -X direction and passing through the projection optical system, or transmit the light through the TIR prism 300, depending on the area of ​​the entrance pupil of the projection optical system through which the light passes. This will be described with reference to Figures 3A and 3B. In this specification, the entrance pupil of the projection optical system refers to the area where a bundle of rays effective for imaging enters the projection optical system, among the rays propagating in various directions from or to the projection object. In other words, the entrance pupil of the projection optical system refers to the irradiation area on the lens surface of the lens element of the projection optical system where the bundle of rays passing through the diaphragm portion (not shown in Figure 2, see Figures 4 and 5) of the projection optical system.

[0050] (Light propagation in a TIR prism due to the division of the entrance pupil of a projection optical system) 3A is a cross-sectional view of TIR prism 300 according to embodiment 1, illustrating the propagation of light incident on and passing through different regions in the entrance pupil of projection optical system 420 within TIR prism 300. FIG. 3B is a diagram illustrating different regions in the entrance pupil of projection optical system 420.

[0051] 3A, the light beam propagating in the -X direction and entering TIR prism 300 includes light rays La, Lb, and Lc that pass through the entrance pupil of projection optical system 420 at various angles and reach TIR prism 300, and light rays La, Lb, and Lc reach prism surface 321 at different angles after being refracted at prism surface 322. In the XZ plane, when the angles of incidence of incident light rays La, Lb, and Lc in the illustrated +Z direction with respect to normal lines Na, Nb, and Nc at prism surface 321 are βa, βb, and βc, respectively, the relationship is βa>βb>βc. That is, in the TIR prism 300 shown in FIG. 3A, when viewed in the XZ plane, for a given incident ray, the ray that passes through the entrance pupil of the projection optical system 420 on the -Z side of the ray enters the prism surface 321 at a larger angle of incidence, and the ray that passes through the entrance pupil of the projection optical system 420 on the +Z side of the ray enters the prism surface 321 at a smaller angle of incidence.

[0052] Since an air gap is formed between prism surface 321 and prism surface 332, light rays that are incident on prism surface 321 at an angle of incidence equal to or greater than the critical angle of total reflection are totally reflected. Specifically, for a given wavelength of light, if the refractive indices of the outside and inside of TIR prism 300 are n1 and n2, respectively, the critical angle of total reflection is sin -1 Therefore, for example, by configuring prism surface 321 so that the angle of incidence of an incident ray is equal to the total reflection critical angle, the ray and all of the rays that have passed through the entrance pupil of projection optical system 420 on the -Z side of the ray can be totally reflected by prism surface 321, and all of the rays that pass through the entrance pupil of projection optical system 420 on the +Z side of the ray can be transmitted through prism surface 321.

[0053] In this way, a boundary is formed in the entrance pupil of the projection optical system 420 by a light ray incident on the prism surface 321 at the critical angle of total reflection, and this boundary divides the entrance pupil of the projection optical system 420 into two regions. The light ray that passes through each region and enters the prism surface 321 of the TIR prism 300 can travel along different propagation paths depending on whether it is total reflection or transmission.

[0054] Fig. 3B shows the area in the entrance pupil of the projection optical system when the angles of incidence βa, βb, and βc of the incident light beams La, Lb, and Lc are equal to the critical angle of total reflection, respectively. As shown in (a) of Fig. 3B, when the angle of incidence βa is equal to the critical angle of total reflection, the incident light beam La shown in Fig. 3A forms an arc-shaped boundary A on the -Z side from the center in the entrance pupil 420a of the projection optical system 420, and the entrance pupil 420a is divided into an area Sa1 (hereinafter referred to as the "total reflection area") where the transmitted light beam is totally reflected by the prism surface 321 in the -Z side area including the boundary A, and an area Sa2 (hereinafter referred to as the "transmission area") where the transmitted light beam is transmitted through the prism surface 321 in the +Z side area of ​​the boundary A. Similarly, as shown in (b) of FIG. 3B, when the incident angle βb is equal to the total reflection critical angle, the entrance pupil 420a is divided into a total reflection region Sb1 in a -Z side area including the boundary B at the center by the incident light beam Lb, and a transmission region Sb2 in a +Z side area of ​​the boundary B. As shown in (c) of FIG. 3B, when the incident angle βc is equal to the total reflection critical angle, the entrance pupil 420a is divided into a total reflection region Sc1 in a -Z side area including an arc-shaped boundary C closer to the +Z side than the center by the incident light beam Lc, and a transmission region Sc2 in a +Z side area of ​​the boundary C. In this specification, the total reflection region may be referred to as the "first region," and the transmission region may be referred to as the "second region."

[0055] Returning to FIG. 3A, the incident light beam that satisfies the total reflection critical condition can be set by adjusting the inclination angle of the prism surface 321. For example, in the configuration example of the TIR prism 300 shown in FIG. 3A, when the surface on which the prism surface 313 is arranged is a horizontal plane parallel to the YZ plane, and the prism surface 321 and the prism surface 313 are arranged at an angle θc, if the TIR prism 300 is configured so that the light beam Lb that is incident parallel to the projection optical axis Op satisfies the total reflection critical condition, the angle θc is an angle equal to the incidence angle βb of the light beam Lb with respect to the prism surface 321, and is the total reflection critical angle. In this case, for example, if the refractive index n1 outside the TIR prism 300 is the refractive index of air, 1.0, and the refractive index n2 inside the TIR prism 300 is the refractive index of SK5 glass, 1.5891, the total reflection critical angle θc is calculated to be about 39 degrees. Prism surfaces 311 and 313 of prism 310 are arranged to form an angle θ2, and when θ2 is configured to be between 30 and 31 degrees, prism 330 is configured so that angle θ1 between prism surfaces 331 and 332 is equal to (θc-θ2), i.e., an angle less than approximately 9 degrees, thereby enabling light ray Lb to be incident on prism surface 321 at an incident angle βb equal to the total reflection critical angle θc.

[0056] 3B(b), boundary B divides entrance pupil 420a of projection optical system 420 into a total reflection region Sb1 on the -Z side and a transmission region Sb2 on the +Z side. Light rays La and Lb passing through total reflection region Sb1 are totally reflected by prism surface 321, form intermediate image Md within prism 320, and then pass through prism surface 323 to exit and enter imaging optical system 440. On the other hand, light ray Lc passing through transmission region Sb2 passes through prism surfaces 321, 332, 331, 311, and 313 in this order, and exits from TIR prism 300.

[0057] The present disclosure is not limited to the size of the total reflection region and the transmission region. By adjusting the inclination angle of the prism surface 321, the boundary between the total reflection region and the transmission region can be adjusted, and the size of the total reflection region and the transmission region can be adjusted, as shown in (a), (b), and (c) of FIG. 3B. In the following description, a configuration in which the entrance pupil 420a is divided into a total reflection region Sb1 and a transmission region Sb2 by the boundary B shown in (b) of FIG. 3B will be described as an example.

[0058] (Projection light and external light propagating within a TIR prism) The propagation of the projection light Lp and the external light Lo in the TIR prism of the present disclosure will be described with reference to Figs. 4 and 5. Fig. 4 is a cross-sectional view of the TIR prism 300 according to the first embodiment, showing the propagation of the projection light Lp in the TIR prism. Fig. 5 is a cross-sectional view of the TIR prism 300 according to the first embodiment, showing the propagation of the external light Lo in the TIR prism. Note that the upper part of each of Figs. 4 and 5 shows the total reflection region Sb1 and the transmission region Sb2 in the entrance pupil 420a defined by the bundle of rays passing through the diaphragm portion P of the projection optical system 420, and the light beam Bp of the projection light or the light beam Bo of the external light in the entrance pupil 420a.

[0059] In this embodiment, for example, the TIR prism 300 can be configured so that a ray of light propagating in the -X direction parallel to the projection optical axis Op shown in Fig. 3 as light having a wavelength at the long wavelength end of the projection light is incident on the TIR prism at an angle that satisfies the total reflection critical condition. In this case, the prism surface 321 and the YZ surface of the TIR prism 300 are arranged to form an angle equal to the total reflection critical angle θc, and the total reflection critical angle θc is calculated as θc=sin -13B(b), the entrance pupil 420a is divided into a total reflection region Sb1 on the -Z side including the boundary B, and a transmission region Sb2 on the +Z side of the boundary B. Of the light having a wavelength near the center of the projection light and propagating in the -X direction along the projection optical axis Op, the light beam that has passed through the total reflection region Sb1 at an angle equal to or greater than the total reflection critical angle can be made to enter the prism surface 321, and the light beam that has passed through the transmission region Sb2 at an angle smaller than the total reflection critical angle can be made to enter the prism surface 321.

[0060] 4, illumination light Ls incident on prism surface 312 is totally reflected by prism surface 311, passes through prism surface 313, passes through optical member 411 such as a cover glass, and then enters light modulation element 400. In this embodiment, illumination light Ls is incident on prism surface 312 at an adjusted angle, so that light rays Lp1 and Lp2 of projection light Lp reflected and emitted from light modulation element 400 pass through optical member 411, pass through TIR prism 300, and reach projection optical system 420, when they enter transmission region Sb2 on the +Z side of boundary B in entrance pupil 420a, and light beam Bp of projection light can be transmitted within transmission region Sb2.

[0061] At this time, the DMD-OFF light Lf, which is unnecessary light from the light modulation element 400, is deflected, and the unnecessary light rays Lf1 and Lf2 can be transmitted through the prism surface 322 at the top of the TIR prism 300 and the lateral prism surface 323 as shown in the figure, and can be emitted without entering the projection optical system 420. Furthermore, in this embodiment, the imaging optical system 440 can be arranged such that the lens surface on the entrance side is spaced a distance d from the prism surface 323. This can prevent the unnecessary light rays Lf1 and Lf2 from entering the imaging optical system 440. The distance d can be configured to be, for example, about 10 mm.

[0062] 5, external light Lo passes through the projection optical system 420 and enters the TIR prism 300. A light beam Bo of external light is incident on the entire area of ​​the entrance pupil 420a including the total reflection area Sb1 and the transmission area Sb2, and light rays Lo1, Lo2, Lo3, Lo4, and Lo5 that have passed through the total reflection area Sb1 and light rays Lo6, Lo7, and Lo8 that have passed through the transmission area Sb2 pass through the prism surface 322 and reach the prism surface 321. At this time, light ray Lo5 parallel to the projection optical axis Op enters the prism surface 321 at the total reflection critical angle θc. Among the external light beam Bo, the light rays Lo1, Lo2, Lo3, Lo4, and Lo5 transmitted through the total reflection region Sb1 enter the prism surface 321 at an incident angle equal to or greater than the total reflection critical angle θc. Therefore, a part Bm of the external light beam in the total reflection region Sb1 due to these light rays is totally reflected by the prism surface 321, and forms an intermediate image on the image formation plane Fm in the prism 320. After that, the light rays Lm1, Lm2, Lm3, Lm4, and Lm5 of the imaging light pass through the prism surface 323 and enter the imaging optical system 440. In this embodiment, the prism surface 323 is arranged parallel to the intermediate image formation plane Fm of the part Bm of the totally reflected external light beam. As a result, the light rays Lm1, Lm2, Lm3, Lm4, and Lm5 of the imaging light emitted from the prism surface 323 can be imaged by the imaging optical system 440 at the imaging element (not shown in FIG. 5).

[0063] On the other hand, light rays Lo6, Lo7, and Lo8 transmitted through transmission region Sb2 are incident on prism surface 321 at an angle of incidence smaller than the total reflection critical angle θc, and therefore transmit through prism surface 321 and prism surface 313 before exiting TIR prism 300.

[0064] In this embodiment, the TIR prism 300 is configured based on the total reflection critical angle θc calculated using the wavelength at the long wavelength end of the projection light. This allows the projection light to be incident on the transmission area in the entrance pupil of the projection optical system. However, the present disclosure is not limited to configuring the TIR prism 300 based on the total reflection critical angle θc calculated using the wavelength at the long wavelength end of the projection light. For example, in a projection imaging optical system, when the influence of ghost light is small, the total reflection critical angle θc can be calculated using a wavelength shifted from the long wavelength end of the projection light to the central wavelength side, and the TIR prism 300 can be configured. In this specification, "making the projection light incident on the transmission area in the entrance pupil of the projection optical system" does not only mean making all the light contained in the projection light incident on the transmission area in the entrance pupil of the projection optical system, but also means actually taking into consideration the wavelength distribution of the projection light, adjustment tolerance, etc., and depending on the application, for example, about 80% of the amount of projection light may be incident on the transmission area in the entrance pupil of the projection optical system. In addition, the external light may have a wide wavelength range. In this specification, "transmitting a part of the external light through the total reflection region at the entrance pupil of the projection optical system" takes into consideration the wavelength distribution of the external light, adjustment tolerances, and the like. For example, a part of about 80% of the amount of light of each wavelength contained in the external light can be transmitted through the total reflection region at the entrance pupil of the projection optical system. Preferably, a part of about 90% of the amount of light of each wavelength contained in the external light is transmitted through the total reflection region at the entrance pupil of the projection optical system.

[0065] Next, suppression of intrusion of reflected light from a lens surface of the projection optical system into the imaging optical system in the projection imaging optical system of this embodiment will be described with reference to Fig. 6. Fig. 6 is a diagram showing propagation of light in the projection imaging optical system 500 of the first embodiment. The upper part of Fig. 6 shows a total reflection region Sb1 and a transmission region Sb2 in the entrance pupil 420a of the projection optical system 420, and a light beam Bp of the projection light, a light beam Bo of external light, and a part Bm of the light beam of external light in the entrance pupil 420a.

[0066] As described with reference to Fig. 4 and Fig. 5, in the projection imaging optical system 500 of this embodiment, when a ray of the projection light Lp passes through the TIR prism 300 and reaches the projection optical system 420, it enters the transmission region Sb2 on the +Z side of the boundary B in the entrance pupil 420a, and the light beam Bp of the projection light passes through the transmission region Sb2. On the other hand, the light beam Bo of the external light Lo enters the entire area including the total reflection region Sb1 and the transmission region Sb2 of the entrance pupil 420a. Of the external light beam Bo, a part Bm of the external light beam that passes through the total reflection region Sb1 is totally reflected by the prism surface 321 and forms an intermediate image Md in the prism 320, and then the light beam Lm of the imaging light passes through the prism surface 323 along the imaging optical axis Om and enters the imaging optical system 440, and an image Mc is formed by the imaging element 450.

[0067] When the projection light Lp passes through the projection optical system 420 in the +X direction, ghost light G1 propagating in the -X direction is generated by reflection on the lens surfaces of the lens elements L21, L22, and L23. It is also known that among such ghost light, some that travels in the opposite direction along roughly the same route as the projection light Lp and returns toward the light modulation element 400 forms a stronger ghost image in the imaging element 450.

[0068] In this embodiment, ghost light G1, which travels in the opposite direction along substantially the same route as projection light Lp and returns toward light modulation element 400, transmits through transmission region Sb2 on the +Z side of boundary B in entrance pupil 420a of projection optical system 420, similar to light beam Bp of projection light. Therefore, ghost light G1 enters prism surface 321 of TIR prism 300 at an angle smaller than the total reflection critical angle, and transmits through prism surface 321. Ghost light G1 that has transmitted through prism surface 321 does not enter imaging optical system 440, but transmits through prism surface 323 and is emitted from TIR prism 300.

[0069] In this manner, the projection imaging optical system 500 of the present embodiment is configured to form a total reflection region Sb1 and a transmission region Sb2 in the entrance pupil 420a of the projection optical system 420, and the light beams of the projection light Lp and part of the external light Lo are transmitted through the respective regions, thereby suppressing the light reflected by the lens surface of the projection optical system 420 from entering the imaging optical system 440 and preventing the formation of a ghost image in the imaging element 450. This can improve the image quality of the image, and can improve the brightness of the projection light when projection and imaging are performed simultaneously.

[0070] The reflected light propagating in the -X direction generated by the lens surfaces of the multiple lens elements L21, L22, and L23 may include reflected light G2 that is focused on the over side of the light modulation element 400 (the rear side of the light modulation element 400, the -X side shown in the figure) and reflected light G3 that is focused on the under side of the light modulation element 400 (the front side of the light modulation element 400, the +X side shown in the figure). The reflected light G2 that is focused on the over side of the light modulation element 400 passes through the prism surface 321 and is emitted from the TIR prism 300 without entering the imaging optical system 440. On the other hand, the reflected light G3 that is focused on the under side of the light modulation element 400 is re-reflected by the prism surface 321, and there is a possibility that the re-reflected light G3a passes through the prism surface 323 and enters the imaging optical system 440. Therefore, it is desirable to configure the projection optical system 420 so that the focusing position of the reflected light generated on the lens surfaces of the lens elements L21, L22, and L23 is on the over side of the light modulation element 400. By appropriately designing the lens surfaces of the lens elements L21, L22, and L23 of the projection optical system 420, it is possible to adjust the focusing position of the reflected light to be on the over side of the light modulation element 400. This specification will not provide a detailed description of the design of the lens surfaces of the projection optical system.

[0071] (Embodiment 2) <Projection-type image display device> A projection type image display device according to a second embodiment of the present disclosure will be described with reference to Fig. 7. Fig. 7 is a schematic diagram showing an overall configuration of a projection type image display device 600A according to the second embodiment of the present disclosure. The projection type image display device 600A according to this embodiment is a three-panel projection type image display device, and includes an illumination optical system 200A and a projection imaging optical system 500A. The illumination optical system 200A of the projection type image display device 600A can be configured similarly to the illumination optical system 200 of the projection type image display device 600 shown in Fig. 1, and detailed description thereof will be omitted.

[0072] The projection imaging optical system 500A of the projection type image display device 600A includes a prism member 360. The prism member 360 is configured by a TIR prism 300 according to an embodiment of the present disclosure and a color separation / synthesis prism 380. The TIR prism 300 is disposed on the front side of the color separation / synthesis prism 380, i.e., on the side of the projection optical system 420A. The illumination light LsA from the illumination optical system is incident on the TIR prism 300 at an adjusted angle, is totally reflected, and then passes through the TIR prism 300 to be incident on the color separation / synthesis prism 380.

[0073] The color separation / synthesis prism 380 includes prisms 381, 382, ​​and 383 arranged in order along the projection optical axis Oa from the projection optical system 420A side. The color separation / synthesis prism 380 separates the light of each color gamut contained in the incident illumination light and guides the light to three corresponding light modulation elements 401, 402, and 403. Each light modulation element 401, 402, and 403 modulates the incident light of each color gamut based on a video signal, and reflects the modulated light components of each color gamut back to each of the three prisms of the color separation / synthesis prism 380.

[0074] The color separation / combination prism 380 guides the projection light (DMD-ON light) reflected by the DMD in each prism to the projection optical axis Op, combines the colors again, and emits the combined projection light LpA in the +X direction along the projection optical axis Op. Unnecessary light (DMD-OFF light, not shown) is deflected away from the projection optical axis Op and removed. The projection light LpA is output from the color separation / combination prism 380, passes through the front TIR prism 300, and enters a transmission area (not shown) in the entrance pupil of the projection optical system 420A. The projection light LpA that has passed through the transmission area is enlarged and projected onto the projection target 550A, such as a screen.

[0075] Meanwhile, external light LoA reflected from projection target object 550A in the -X direction in the figure enters via projection optical system 420A, propagates in the -X direction along projection optical axis Op, and enters TIR prism 300. In TIR prism 300, a part of the external light LoA that has passed through a total reflection region (not shown) in the entrance pupil of projection optical system 420A is totally reflected and emitted as imaging light LmA along imaging optical axis Om. The emitted imaging light LmA is introduced into imaging optical system 440A, and is imaged by imaging element 450A through imaging optical system 440A.

[0076] In this way, the projection imaging optical system 500A is configured to form a total reflection area and a transmission area at the entrance pupil of the projection optical system 420A, and the light beams of the projection light LpA and a portion of the external light LoA transmit through each of the areas, thereby preventing the light reflected by the lens surface of the projection optical system 420A from entering the imaging optical system 440A, thereby improving the image quality of the captured image.

[0077] As described above, the above-mentioned embodiments have been described as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited to these, 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 each of the above-mentioned embodiments to create a new embodiment.

[0078] The accompanying drawings and detailed description are provided to explain the embodiments of the present disclosure. Therefore, among the components described in the accompanying drawings and detailed description, not only essential components for solving the problem but also components that are not essential for solving the problem in order to illustrate the above technology may be included. Therefore, the fact that the non-essential components are described in the accompanying drawings or detailed description should not be interpreted as indicating that the non-essential components are essential.

[0079] Although the present disclosure has been fully described in relation to the preferred embodiments with reference to the accompanying drawings, various modifications are possible within the scope of the claims. Such modifications and embodiments obtained by appropriately combining the technical means disclosed in the different embodiments are also included in the technical scope of the present disclosure. [Industrial Applicability]

[0080] The present disclosure is applicable to prisms and various types of projection-type image display devices. [Explanation of symbols]

[0081] 20 Light source unit 21 Semiconductor laser element 22 Collimating lens 31,32 Afocal lenses 33,34,35 Condenser lens 41 Diffuser 42 λ / 4 plate 45 Dichroic Mirror 46 Rod Integrator 50 Phosphor Wheel 60 Color Wheel 73, 74, 75 Lenses constituting the illumination light relay optical system 200,200A Illumination optical system 300 TIR Prism 310,320,330 Prism 311,312,313 Prism surface 321,322,323 Prism surface 331,332 Prism surface 360 Prism Component 380 Color Separation and Synthesis Prism 400, 401, 402, 403 Optical Modulation Device (DMD) 420,420A Projection Optical System 420a Entrance pupil 440,440A Imaging optical system 450,450A image sensor 500,500A Projection imaging optical system 550,550A Screen, Projection Object Ls, LsA Illumination light Lp, LpA Projection light Lo, LoA External light Lm, LmA Imaging light G1, G2, G3, Gc1 Lens surface reflection light, ghost light G3a, Gc2 Re-reflected light, ghost light Lf unnecessary light, DMD-OFF light L21, L22, L23 lens elements L41, L42, L43 lens elements P Projection optical system aperture Sa1,Sb1,Sc1 Total reflection area, 1st area Sa2,Sb2,Sc2 transmission area, second area Op Projection optical axis Om Imaging optical axis Os Illumination optical axis Md intermediate image Mc Imaging 600,600A Projection type image display device

Claims

1. a TIR prism that is disposed between a light modulation element and a projection optical system, guides illumination light to the light modulation element, and emits projection light generated by reflection of the illumination light at the light modulation element forward along a projection optical axis to the projection optical system, a first prism on the side of the light modulation element, a second prism on the side of the projection optical system, and a third prism disposed between the first prism and the second prism, a first prism surface of the first prism and a second prism surface of the second prism are disposed opposite to each other via the third prism, the third prism has a third prism surface arranged to face the first prism surface across a gap parallel thereto, and a fourth prism surface arranged to face the second prism surface across a gap parallel thereto; the first prism surface totally reflects the illumination light and guides it to the light modulation element, and transmits the projection light; the second prism surface transmits the projection light and totally reflects a part of external light that has passed through the projection optical system and entered rearward along the projection optical axis; the part of the light passes through a first region in an entrance pupil of the projection optical system and is incident on the second prism surface, and the projection light exiting the second prism is incident on a second region in the entrance pupil different from the first region. TIR prism.

2. Among the light having a wavelength at the long wavelength end of the projection light and transmitting through the projection optical system in a backward direction, The light transmitted through the first region is incident on the second prism surface at an angle equal to or greater than a critical angle of total reflection; The light transmitted through the second region is incident on the second prism surface at an angle smaller than a total reflection critical angle. The TIR prism of claim 1 .

3. the first prism has a fifth prism surface onto which the illumination light is incident and a sixth prism surface through which the illumination light totally reflected by the first prism surface passes and is output to a light modulation element; the second prism has a seventh prism surface that outputs the projection light to the projection optical system and receives the external light, and an eighth prism surface that transmits and outputs the part of the light totally reflected by the second prism surface, the illumination light is incident on the fifth prism surface at an adjusted angle such that the projection light emerging from the seventh prism surface is incident on the second region of the entrance pupil; The TIR prism according to claim 1 or 2.

4. the part of the light totally reflected by the second prism surface forms an image within the second prism, the eighth prism surface is arranged parallel to the surface on which the image is formed; The TIR prism of claim 3.

5. an illumination optical system for supplying illumination light; one or more light modulation elements that modulate the illumination light in accordance with a video signal to generate projection light; A prism member including the TIR prism according to claim 1 or 2; a projection optical system that transmits the projection light transmitted through the prism member through the second area and projects the projection light forward onto a projection target to display an image; an imaging optical system that receives and forms an image of a portion of external light that passes through the projection optical system backward from the projection target and enters the prism member, the portion passing through the first region of the projection optical system and being totally reflected within the TIR prism; Equipped with Projection type image display device.

Images