JP7607205B2 - Prism group and projection type image display device - Google Patents

Description

The present disclosure relates to a prism group and a projection-type image display device equipped with the same.

Conventionally, there has been known a projection type image display device that has an image sensor inside the main body and is equipped with both a projection optical system that projects projection light onto a projection target, and an image capturing optical system that forms an image on the image sensor using light from the projection target as external light. Such a projection type image display device has the function of projecting an image onto the projection target and capturing an image of the projected image. For example, one described in Patent Document 1 is known as an example of this type of projection type image display device.

The projector (projection type image display device) described in Patent Document 1 is provided with a TIR prism that guides illumination light from a light source to a light modulation element and outputs light reflected by the light modulation element to a projection optical system. Light emitted from a light-emitting element enters the TIR prism through a projection lens, is reflected by the reflecting surface of the TIR prism, and is imaged on an imaging element.

JP 2013-218262 A

In the projector described in Patent Document 1, a TIR prism is used as an optical path branching element for illumination light, projection light, and imaging light. In the configuration of this projector, the imaging optical system is arranged in a direction inclined with respect to the projection optical axis to extract the imaging light. In such an arrangement, it may be difficult to incorporate the imaging optical system inside the projector device, resulting in a problem of the device becoming large. In addition, in the configuration of the projector in Patent Document 1, if an optical component such as a mirror is provided outside the TIR prism to bend the optical path of the imaging light, it is difficult to miniaturize the device due to the spread of the light beam. Therefore, there has been a demand for a projection type image display device that is easier to miniaturize than before.

Therefore, the object of the present disclosure is to solve the above-mentioned problems by providing a prism group that makes it easy to incorporate an imaging optical system into a projection-type image display device and makes it easy to miniaturize the projection-type image display device, and a projection-type image display device equipped with the same.

In order to achieve the above-mentioned objective, the prism group according to the present disclosure comprises a TIR prism and an imaging light reflecting prism, and the TIR prism reflects illumination light supplied by an illumination optical system and guides it to an optical modulation element, and transmits projection light generated by reflection at the optical modulation element and outputs it along the projection optical axis to the projection optical system on the forward side of the projection optical axis, and further reflects imaging light, which is at least a part of external light incident from the projection optical system and propagating in a direction opposite to the forward side of the projection optical axis, and guides it to the imaging light reflecting prism, and the imaging light reflecting prism is configured to internally reflect the imaging light incident from the TIR prism and guide it to the imaging element along the imaging optical axis in a plane substantially perpendicular to the projection optical axis.

According to the prism group according to one aspect of the present disclosure, the imaging optical system can be easily incorporated inside the projection-type image display device, making it easier to miniaturize the projection-type image display device.

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; 2 is a diagram showing the layout of the inside of the projection type image display device of FIG. 1 as viewed from the projection optical system side. FIG. 2 is a perspective view illustrating a configuration of a prism group according to an embodiment of the present disclosure. FIG. 2 is a cross-sectional view of a prism group according to an embodiment of the present disclosure. 10A and 10B are diagrams illustrating an example of the reflection characteristics of a visible partial reflection coating in a group of prisms according to an embodiment of the present disclosure. 10A and 10B are diagrams illustrating an example of the reflection characteristics of an infrared partial reflection coating in a prism group according to an embodiment of the present disclosure. 2 is a diagram showing an example of a spectrum of projection light incident on the projection optical system of FIG. 1 . 11 is a cross-sectional view of a prism group according to a first modified example of the embodiment of the present disclosure. FIG. FIG. 11 is a cross-sectional view of a prism group according to a second modified example of the embodiment of the present disclosure. 9A and 9B are cross-sectional views showing reflection of DMD-OFF light in a prism group according to a first modified example of an embodiment of the present disclosure (FIG. 9A) and a prism group according to a second modified example (FIG. 9B). 1A to 1C are diagrams illustrating how imaging light is propagated through a group of prisms according to an embodiment of the present disclosure. 1A to 1C are diagrams illustrating how imaging light is propagated through a group of prisms according to an embodiment of the present disclosure. FIG. 11 is a schematic diagram illustrating a configuration of a projection imaging optical system of a projection type image display device according to a second embodiment of the present disclosure.

According to a first aspect of the present disclosure, a prism group is provided that includes a TIR prism and an imaging light reflecting prism, in which the TIR prism reflects illumination light supplied by an illumination optical system and guides it to a light modulation element, and transmits projection light generated by reflection at the light modulation element and outputs it along the projection optical axis to the projection optical system on the forward side of the projection optical axis, and further reflects imaging light, which is at least a portion of external light incident from the projection optical system and propagating in a direction opposite to the forward side of the projection optical axis, and guides it to the imaging light reflecting prism, which internally reflects the imaging light incident from the TIR prism and guides it to the imaging element along the imaging optical axis in a plane substantially perpendicular to the projection optical axis.

According to this aspect, the imaging optical system can be easily incorporated into the projection-type image display device, making it easier to miniaturize the projection-type image display device.

According to a second aspect of the present disclosure, there is provided a prism group as described in the first aspect, in which the TIR prism includes a first prism and a second prism arranged in sequence along the projection optical axis from the front side of the projection optical axis, an illumination light reflecting surface of the second prism from which the illumination light is reflected and a projection light incident surface of the first prism into which the projection light is incident are arranged opposite each other with a parallel gap between them, the imaging light reflecting prism has an imaging light incident surface through which the imaging light from the TIR prism passes and is arranged adjacent to the first prism via the imaging light incident surface, the imaging light is internally reflected multiple times within the TIR prism and the imaging light reflecting prism, and the imaging optical axis is located in a direction or near the longitudinal axis along which the imaging light passes through the TIR prism and the imaging light reflecting prism.

According to a third aspect of the present disclosure, there is provided a prism group as described in the second aspect, in which the imaging light reflecting prism is integrally configured with the first prism at the imaging light incident surface.

According to a fourth aspect of the present disclosure, there is provided a prism group as described in the second aspect, in which the imaging light reflecting prism and the first prism are arranged separately across a parallel gap on the imaging light incident surface.

According to a fifth aspect of the present disclosure, there is provided a prism group according to any one of the second to fourth aspects, in which the TIR prism further includes a third prism disposed between the first prism and the second prism, the third prism having a first prism surface and a second prism surface that forms an angle with the first prism surface, the first prism surface and the projection light entrance surface of the first prism are joined, and the second prism surface and the illumination light reflection surface of the second prism are disposed opposite each other with a parallel gap therebetween.

According to a sixth aspect of the present disclosure, there is provided a prism group described in any one of the second to fifth aspects, in which the projection light incident surface is coated with a visible range partial reflective coating, and the visible range partial reflective coating has a reflectance of 2% or more and 15% or less for light in the visible range to reflect imaging light.

According to a seventh aspect of the present disclosure, there is provided a prism group described in any one of the second to fifth aspects, in which the projection light incident surface is coated with an infrared partial reflective coating, and the infrared partial reflective coating has a reflectivity of 50% or more for light in the infrared range and reflects imaging light.

According to an eighth aspect of the present disclosure, there is provided a prism group described in any one of the first to seventh aspects, in which the imaging light reflecting prism has an internal reflecting surface, the imaging light is internally reflected at the internal reflecting surface, and the internal reflecting surface has a concave shape facing the direction in which the imaging light is internally reflected.

According to a ninth aspect of the present disclosure, there is provided a prism group as described in the eighth aspect, in which the imaging light forms an intermediate image within the imaging light reflecting prism, and the intermediate image is focused at the position of the imaging element, the intermediate image being positioned away from the internal reflecting surface.

According to a tenth aspect of the present disclosure, there is provided a prism group described in any one of the first to ninth aspects, in which the imaging light reflecting prism has an imaging light exit surface, the imaging light is transmitted through the imaging light exit surface and exits to the imaging element, and the imaging light exit surface has a convex shape facing the direction in which the imaging light is exited to the imaging element.

According to an eleventh aspect of the present disclosure, there is provided a projection type image display device comprising: an illumination optical system that supplies illumination light in the visible range; a prism member including a prism group described in any one of the first to tenth aspects; one or more light modulation elements that spatially modulate the light supplied by the illumination optical system and guided by the prism member to enter the projection light and generate projection light corresponding to image information; a projection optical system that enlarges and projects the projection light transmitted through the TIR prism to display an image; and an imaging element that receives the imaging light output by the imaging light reflecting prism and converts it into an electrical image signal.

Any of the various embodiments described above can be combined as appropriate to achieve the effects of each.

Below, 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 explanations of matters that are already well known or duplicate explanations of substantially identical configurations may be omitted. This is to avoid the following explanation becoming unnecessarily redundant and to make it easier for those skilled in the art to understand.

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.

<Embodiment>
Hereinafter, a prism group according to an embodiment of the present disclosure and a projection-type image display device including the same will be described with reference to Figures 1 to 12. As specific examples of a projection-type image display device to which a prism group according to the present disclosure is applied, a single-panel projection-type image display device including one light modulation element (Example 1) and a three-panel projection-type image display device including three light modulation elements (Example 2) will be described.

(Configuration of the projection type image display device 600 according to the first embodiment)
Hereinafter, the configuration of the projection-type image display device 600 of Example 1 according to the embodiment of the present disclosure will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram showing the overall configuration of the projection-type image display device 600 of Example 1 according to the embodiment of the present disclosure. Also, (a) and (b) of FIG. 1 are schematic diagrams showing the overall configuration of the projection-type image display device 600 in the illustrated X-Z plane. (c) of FIG. 1 is a schematic diagram showing the prism group 300 and the imaging optical system 440, etc., seen from the left side of (a) of FIG. 1, that is, the +Z side of (a) of FIG. 1 toward the -Z direction. 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 that may be used for projection mapping, or may be a low-brightness type projector for home use.

1 includes an illumination optical system 200 that supplies illumination light, and a projection imaging optical system 500. 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.

<Illumination optical system>
In the illumination optical system 200, the light source unit 20 is composed of, for example, a plurality of semiconductor lasers (LD) or light emitting diodes (LED). In this embodiment, a semiconductor laser element 21 that emits blue light can be used. The blue light emitted from the semiconductor laser element 21 has a wavelength of about 455 nm and is used as image light and also as 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 collimator 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.

In this embodiment, the light emitted from the light source unit 20 is, for example, S-polarized blue light, and the dichroic mirror 45 reflects the S-polarized blue light and can transmit the P-polarized blue light and other colored light. The blue light reflected by the dichroic mirror 45 travels in approximately the -Z direction, passes through the λ/4 plate 42, and is collected by the condenser lenses 33 and 34 before entering the phosphor wheel 50, where it excites the phosphors in the phosphor wheel 50 to emit light.

As the phosphor wheel 50 rotates, different segments of the phosphor layer are excited by the incident blue light, and can generate fluorescence containing, for example, yellow and green light components. In addition, a portion of the blue light that passes 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 passes through the dichroic mirror 45. The blue component light and the light component lights of each color range that pass through the dichroic mirror 45 travel in approximately the Z direction and enter the color wheel 60 via the condenser lens 35.

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

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, and becomes white light illumination light Ls on a time average, and enters the projection imaging optical system 500.

<Projection imaging optical system>
Next, the projection imaging optical system 500 includes a prism group 300, a light modulation element 400, a projection optical system 420, an imaging optical system 440, and an imaging element 450. In this embodiment, the imaging optical system 440 and the imaging element 450 are disposed on a YZ plane that is approximately perpendicular to the projection optical axis Oa1 in the X direction shown in the figure, and imaging light Li is incident on the imaging element 450 along the imaging optical axis Ob1 in the +Y direction (shown in FIG. 1C).

In the projection imaging optical system 500, the prism group 300 is composed of a TIR (Total Internal Reflection) prism 310 (internal total reflection prism) and an imaging light reflecting prism 350. In this embodiment, the TIR prism 310 is composed of a first prism 320 and a second prism 330, which are substantially triangular prisms, joined together with a small gap between them. The TIR prism 310 uses total reflection to deflect the incident illumination light Ls and guide it to the light modulation element 400. The imaging light reflecting prism 350 is disposed adjacent to the TIR prism 310. The imaging light reflecting prism 350 and the TIR prism 310 may be configured separately (FIG. 7) or integrally (FIGS. 4 and 8). 1, the imaging light reflecting prism 350 and the TIR prism 310 are shown in a separate configuration. The imaging light reflecting prism 350 further reflects and deflects the imaging light Li that is reflected by the TIR prism 310 and enters the imaging light Li, and guides the imaging light Li to the imaging element 450. The configuration of the prism group 300 will be described in detail later.

The light modulation element 400 uses a DMD (Digital Mirror Device), which modulates the component light of each color gamut contained in the illumination light Ls based on a video signal and distributes it to DMD-ON light (on light) or DMD-OFF light Lf (off light) that becomes the projection light Lp for each pixel. The projection light Lp for projection is emitted in the +X direction along the projection optical axis Oa1, and the DMD-OFF light Lf is deflected from the projection optical axis Oa1 and removed.

The projection light Lp passes through the TIR prism 310, is output from the projection light exit surface 321, and is propagated along the projection optical axis Oa1 to the projection optical system 420. The lens group LGp included in the projection optical system 420 enlarges and projects the projection light Lp onto a projection target such as a screen 430 to display an image.

On the other hand, the projected image can be captured by the imaging element 450 built into the projection imaging optical system 500 using imaging light Li, which is at least a part of the external light Le reflected from the screen 430 in the illustrated -X direction.

As shown in the figure, external light Le enters from the projection optical system 420, propagates in the -X direction along the projection optical axis Oa1, and enters the projection light exit surface 321 on the projection optical system side of the first prism 320 of the TIR prism 310. Within the TIR prism 310, imaging light Li, which is at least a part of the external light Le, is internally reflected and deflected and enters the imaging light reflecting prism 350. The imaging light Li that enters the imaging light reflecting prism 350 is further internally reflected and deflected within the imaging light reflecting prism 350, and is emitted from the imaging light exit surface 353 of the imaging light reflecting prism 350 along the imaging optical axis Ob1 and is introduced into the imaging optical system 440 in the +Y direction shown in the figure.

The imaging optical system 440 can be composed of multiple optical components, and in this embodiment, can be composed of a relay optical system consisting of multiple lenses. The imaging light Li emitted from the imaging light emission surface 353 and propagated along the imaging optical axis Ob1 in the +Y direction can be imaged on the imaging element 450 by the imaging optical system 440. Note that this disclosure does not limit the magnification of the image formed by the imaging optical system, and the imaging optical system 440 may be a reduced imaging optical system, or a unity or enlarged imaging 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 Li into an electrical image signal.

<Internal layout of the projection type image display device>
Next, the internal layout of the projection-type image display device 600 according to the embodiment of the present disclosure will be described with reference to Fig. 2. Fig. 2 is a layout diagram of the internal layout of the projection-type image display device 600 of Fig. 1 as viewed from the projection optical system side. However, Fig. 1 shows an example of a configuration in which the imaging optical system 440 and the imaging element 450 are arranged on the -Y side of the prism group 300, while Fig. 2 shows an example of a configuration in which the imaging optical system 440 and the imaging element 450 are arranged on the -Y side of the prism group 300.

1, that is, when viewed from the top of FIG. 1 toward the -X direction, inside the housing 600A of the projection type image display device 600, the prism group 300 is located below the lens group LGp of the projection optical system 420, and the light modulation element 400 is located approximately at the center of the lens group LGp. The illumination light Ls emitted from the illumination optical system 200 is deflected by the folding mirror 47, and passes through the relay lens group 48 and enters the prism group 300 in the approximately +Z direction shown in the figure along the longitudinal axis Ob2 of the prism group 300 that passes through the TIR prism 310 and the imaging light reflecting prism 350.

DMD-ON light (projection light Lp, not shown in Figure 2) from the light modulation element 400 is emitted in the +X direction shown, and DMD-OFF light Lf is deflected in a direction near the longitudinal axis Ob2 of the prism group 300.

Since designing the lens group LGp to have a short back focus allows for a smaller and less costly device, the projection optical system 420 and the projection light exit surface 321 of the prism group 300 on the projection optical system side are configured as close as possible without interfering with each other. Therefore, in the illustrated X direction, which is the exit direction of the projection light Lp, there is little space inside the housing 600A, and the arrangement of optical components, etc. is limited in design.

As described above, in the projection type image display device 600 according to the present disclosure, the imaging light Li, which is at least a part of the external light Le incident from the projection optical system in the illustrated -X direction, can be deflected by being internally reflected multiple times within the prism group 300, and introduced into the imaging element 450 along the imaging optical axis Ob1 in the Y-Z plane substantially perpendicular to the projection optical axis Oa1. This allows the imaging optical system 440 to be easily incorporated into the device without interfering with the projection optical system 420, and the projection optical system provided in a conventional projection type image display device can be used in the projection type image display device without having to be changed. This makes it possible to improve or expand the functionality of the device at low cost.

In addition, by deflecting the imaging light Li through multiple internal reflections inside the prism group 300, the air-equivalent length of the imaging light propagation can be shortened, and by suppressing the spread of the light beam, it is possible to reduce the aperture and thickness of the lenses in the imaging optical system. This makes it easier to reduce the size of the projection-type image display device than ever before.

In addition, as shown in FIG. 2, an actual projection type image display device is designed so that, when viewed from the projection optical system, the illumination light Ls entering the prism group 300 is incident from the lower right in the figure, at an angle of 45 degrees to the long side of the housing 600A. This is due to the fact that the rotation axis of the micromirror of the DMD as the light modulation element 400 is tilted at 45 degrees. Therefore, the prism group 300 that guides the illumination light Ls to the light modulation element 400 is also arranged so that the longitudinal axis Ob2 is tilted at about 45 degrees to the long side of the housing 600A. In such an arrangement, as shown in the figure, there is little space on the longitudinal axis Ob2 side of the prism group 300 inside the device. Furthermore, if the imaging optical system is arranged near the direction in which the DMD-OFF light Lf is guided, the influence of stray light due to the DMD-OFF light Lf will be large.

2, in this embodiment, the imaging light Li can be internally reflected multiple times within the prism group 300, so that it can be guided along an imaging optical axis Ob1 that is located in a direction perpendicular to or near the longitudinal axis Ob2 of the prism group 300. This makes it possible to suppress the effects of stray light due to the DMD-OFF light Lf, and to effectively utilize the space inside the device, leading to a further compact device.

2, the imaging optical axis Ob1 is shown as being approximately perpendicular to the longitudinal axis Ob2 of the prism group 300, but the present disclosure is not limited thereto. The imaging optical axis Ob1 may be disposed in a vicinity of a direction perpendicular to the longitudinal axis Ob2 of the prism group 300. Also, as shown in FIGS. 1 and 2, the imaging optical system 440 and the imaging element 450 may be disposed on either side of the prism group 300 along the imaging optical axis Ob1.

<Configuration of Prism Group 300>
The configuration of the prism group 300 of the projection imaging optical system 500 according to the embodiment will be described with reference to Figures 3 and 4. For clarity, each light beam is shown as only the chief ray.

Figure 3 is a perspective view showing a configuration of a prism group 300 according to an embodiment of the present disclosure. Figure 4 is a cross-sectional view of the prism group 300 according to an embodiment of the present disclosure. The prism group 300 in Figure 3 is shown in a configuration in which the imaging light reflecting prism 350 and the TIR prism 310 are integrally formed.

The TIR prism 310 includes a first prism 320 and a second prism 330, each of which has a substantially triangular prism shape. The first prism 320 and the second prism 330 are arranged in order along the projection optical axis Oa1 from the front side (the +X side shown in the figure) of the projection optical axis Oa1. The second prism 330 has an illumination light reflecting surface 331, and the incident illumination light Ls is totally reflected by the illumination light reflecting surface 331 and introduced into the light modulation element 400. The first prism 320 has a projection light incident surface 322 and a projection light exit surface 321 for the projection light Lp that is reflected by the light modulation element 400 and travels in the +X direction. The first prism 320 and the second prism 330 are joined with a parallel gap between the projection light incident surface 322 and the illumination light reflecting surface 331. As a result, the projection light Lp from the light modulation element 400 passes through the second prism 330 and enters the first prism 320, and then passes through the first prism 320 again to be output from the projection light exit surface 321 along the projection optical axis Oa1 to the projection optical system and form an image. The DMD-OFF light Lf passes through the TIR prism 310 in a direction deflected from the projection optical axis Oa1 and is removed.

The imaging light reflecting prism 350 arranged adjacent to the first prism 320 has an imaging light incident surface 351, an internal reflection surface 352, and an imaging light exit surface 353. In this embodiment, the first prism 320 of the TIR prism 310 and the imaging light reflecting prism 350 are integrally formed at the imaging light incident surface 351.

As shown, external light Le incident on the first prism 320 in the -X direction from the projection optical system (not shown in FIG. 3) forms a beam spot S1 on the projection light incident surface 322. The projection light incident surface 322 is coated with a partial reflection coating, and at least a portion of the incident external light Le is internally reflected by the partial reflection coating as imaging light Li, reaches the projection light exit surface 321 and forms a beam spot S2. The imaging light Li is then internally reflected at the projection light exit surface 321, reaches the imaging light incident surface 351 of the imaging light reflecting prism 350, and passes through the imaging light incident surface 351 to enter the imaging light reflecting prism 350.

In the imaging light reflecting prism 350, the imaging light Li forms a beam spot S3 on the internal reflecting surface 352 and is internally reflected, and is then emitted from the imaging light emitting surface 353 along the imaging optical axis Ob1 in the +Y direction shown in the figure, and can be imaged on the imaging element by the imaging optical system 440.

Thus, in this embodiment, the imaging light Li can be internally reflected three times within the prism group 300, and then introduced into the imaging element 450 along the imaging optical axis Ob1 that is in the Y-Z plane substantially perpendicular to the projection optical axis Oa1 and is located in a direction perpendicular to or near the longitudinal axis Ob2 of the prism group 300. Note that the present disclosure does not limit the number of times the imaging light Li is internally reflected within the prism group 300. Also, although not limited thereto, preferably, the imaging light Li may be totally reflected at the projection light exit surface 321 and enter the imaging light reflecting prism 350. This allows the imaging light to be used efficiently.

5A and 5B are diagrams showing examples of the reflection characteristics of a partial reflection coating in a prism group 300 according to an embodiment of the present disclosure. The partial reflection coating applied to the projection light incidence surface 322 may be a visible partial reflection coating (FIG. 5A) or an infrared partial reflection coating (FIG. 5B).

When a visible partial reflective coating is applied, the visible projection light Lp incident on the projection light incident surface 322 from the light modulation element 400 is also partially reflected due to the reflective characteristics of the visible partial reflective coating, resulting in loss of the projection light Lp. In the present embodiment, the visible partial reflective coating shown in FIG. 5A has a reflectance of 2% or more and 15% or less for light in the visible range with wavelengths of 400 nm to 700 nm. This makes it possible to capture an image by incorporating a portion of external light in the visible range as imaging light without significant loss of the projection light Lp. Note that the reflective characteristics of the visible partial reflective coating are not limited to this.

On the other hand, when an infrared partial reflection coating is applied, as shown in Figure 5B, in this embodiment, the infrared partial reflection coating reflects imaging light with a reflectance of 50% or more for infrared light with a wavelength of 750 nm or more. Note that the reflection characteristics of the infrared partial reflection coating are not limited to this.

Figure 6 is a diagram showing an example of the spectrum of the projection light incident on the projection optical system 420 of Figure 1. As shown in Figure 6, the projection light incident on the projection optical system has a blue light component LB of approximately 440 nm to 470 nm, a green light component LG of 520 nm to 570 nm, and a red (yellow) light component LR (Y) of 590 nm to 650 nm, and does not contain any infrared light components. Therefore, by taking in external light in the infrared range as imaging light and transmitting approximately 100% of the visible range projection light Lp, it is possible to capture images without any loss of projection light. Note that imaging using infrared rays can be used to detect or track motion in places with no light at all, and is used in nighttime photography and night-vision surveillance cameras.

(Prism group 300a according to modification example 1)
Next, modified examples of the prism group 300 will be described with reference to Fig. 7 and Fig. 8. Fig. 7 is a cross-sectional view of a prism group 300a according to a first modified example of the embodiment of the present disclosure, and Fig. 8 is a cross-sectional view of a prism group 300b according to a second modified example of the embodiment of the present disclosure.

The prism group 300a shown in Fig. 7 is composed of a TIR prism 310a and an imaging light reflecting prism 350a, similar to the prism group 300 shown in Fig. 3-4. As shown in the figure, the prism group 300a differs from the prism group 300 in that the imaging light reflecting prism 350a is formed separately from the TIR prism 310a at the imaging light incident surface 351a.

7, in the prism group 300a, the first prism 320a has a prism surface 323a adjacent to the imaging light reflecting prism 350a. The first prism 320a and the imaging light reflecting prism 350a are formed separated by a parallel gap between the prism surface 323a and the imaging light incident surface 351a.

In the prism group 300a, the external light Le incident on the first prism 320a in the -X direction forms a beam spot S1a on the projection light incident surface 322a. Due to the partial reflection coating of the projection light incident surface 322a, at least a part of the incident external light Le is internally reflected as imaging light Lia, reaches the projection light exit surface 321a and forms a beam spot S2a. Next, the imaging light Lia is internally reflected at the projection light exit surface 321a, passes through the prism surface 323a, reaches the imaging light incident surface 351a of the imaging light reflecting prism 350a, passes through, and enters the imaging light reflecting prism 350a. In the imaging light reflecting prism 350a, the imaging light Lia forms a beam spot S3a on the internal reflection surface 352a, is internally reflected at the internal reflection surface 352a, and is then emitted from the imaging light exit surface 353a.

As described above, the projection light Lp passes through the TIR prism and is emitted to the projection optical system. When passing through the TIR prism, heat is generated by the high-energy projection light Lp, so the TIR prism needs to be made of a heat-resistant glass material. In the prism group 300, if the imaging light reflecting prism is formed integrally with the TIR prism, it is affected by heat conduction, so a glass imaging light reflecting prism is necessary. In addition, in order to suppress the occurrence of aberration due to changes in refractive index, it is desirable to make the imaging light reflecting prism 350 from the same glass material as the TIR prism 310. On the other hand, in the prism group 300a shown in FIG. 7, the imaging light reflecting prism 350a is formed separately from the TIR prism 310a, so that heat conduction is suppressed, and it can be made by adopting a glass material or a resin material different from the TIR prism 310a. Therefore, by forming the imaging prism separately from the TIR prism, a high degree of freedom in material selection is possible. Another advantage of resin optical components is that they have excellent processability, making it possible to manufacture prism members having optical surfaces with complex geometric shapes at low cost.

(Prism group 300b according to modification example 2)
The prism group 300b shown in FIG. 8 is composed of a TIR prism 310b, an imaging light reflecting prism 350b, and a third prism 340, and is different from the prism group 300 in that the third prism 340 is included. As shown in the figure, in this embodiment, the first prism 320b and the imaging light reflecting prism 350b of the TIR prism 310b are integrally formed. However, the present disclosure is not limited to this. In the prism group 300b, the first prism 320b and the imaging light reflecting prism 350b of the TIR prism 310b may be formed separately, similar to the prism group 300a shown in FIG. 7.

As shown in FIG. 8, the third prism 340 of the prism group 300b has a first prism surface 341 and a second prism surface 342. The first prism surface 341 is joined to the projection light incident surface 322b of the first prism 320b of the TIR prism 310b. The second prism surface 342 intersects with the first prism surface 341 at an angle. The second prism surface 342 and the illumination light reflecting surface 331b of the second prism 330b of the TIR prism 310b are arranged opposite each other with a parallel gap therebetween. Although not limited thereto, in this embodiment, the third prism 340 has a wedge shape. The first prism surface 341 and the second prism surface 342 preferably form an apex angle A of 2 degrees to 10 degrees, and in this embodiment, form an apex angle A of about 3 degrees.

In the prism group 300b, external light Le incident on the first prism 320b in the -X direction forms a beam spot S1b on the projection light incident surface 322b. Due to the partial reflection coating of the projection light incident surface 322b, at least a part of the incident external light Le is internally reflected as imaging light Lib, reaches the projection light exit surface 321b and forms a beam spot S2b. Next, the imaging light Lib is internally reflected on the projection light exit surface 321b and enters the imaging light reflecting prism 350b. In the imaging light reflecting prism 350b, the imaging light Lib forms a beam spot S3b on the internal reflection surface 352b, and after being internally reflected on the internal reflection surface 352b, is emitted from the imaging light exit surface 353b.

For comparison, Fig. 8 also shows the beam spot S3a formed by the imaging light Lia on the internal reflection surface 352a (not shown) of the imaging light reflecting prism 350a in the prism group 300a shown in Fig. 7. As shown, the beam spot S3b formed by the imaging light Lib in the prism group 300b is smaller than the beam spot S3a, and the center position of the beam spot S3b is closer to the projection optical axis Oa1 side by a distance D than the center position of the beam spot S3a. It can be seen that the propagation optical path of the imaging light Lib in the prism group 300b is shortened compared to the propagation optical path of the imaging light Lia in the prism group 300a.

In the prism group 300b, the beam spot S3b formed on the internal reflection surface of the imaging light reflecting prism by the imaging light Lib changes in this way because the third prism 340 is provided. As shown in FIG. 8, the second prism 330b is configured such that the illumination light reflecting surface 331b and the bottom surface 332b perpendicular to the projection optical axis Oa1 form an angle α1. The angle α1 is limited by the characteristics of the DMD as the light modulation element 400 and cannot be freely designed. And, since the illumination light reflecting surface 331b and the projection light incident surface 322b are arranged opposite to each other with a parallel gap between them, the reflection angle of the imaging light on the projection light incident surface is also limited. Therefore, by providing the wedge-shaped third prism 340, it is possible to adjust the reflection angle of the imaging light Lib at the projection light incident surface 322b by increasing the angle β between the projection light incident surface 322b and the projection optical axis Oa1 by the apex angle A of the wedge-shaped third prism 340. This makes it possible to shorten the propagation optical path of the imaging light Lib and make the prism group 300b more compact.

Furthermore, by providing a wedge-shaped third prism 340, the effect of stray light within the prism group 300b can be suppressed. This will be described with reference to Figure 9. Figure 9 is a cross-sectional view showing the reflection of DMD-OFF light in a prism group 300a (Figure 9(a)) according to a first modification of the embodiment of the present disclosure and a prism group 300b (Figure 9(b)) according to a second modification.

As shown in FIG. 9, the DMD-OFF light Lf is removed by passing through the TIR prism. At that time, the DMD-OFF light Lf is partially reflected by the visible partial reflection coat at the projection light incidence surface. In the prism group 300a shown in FIG. 9(a), a part of the DMD-OFF light Lf (OFF light Lf1a) reflected at the projection light incidence surface 322a is incident on the light modulation element 400 due to the inclination angle α1 of the projection light incidence surface 322a, and after being reflected by the light modulation element 400, it enters the prism group 300a and becomes stray light. On the other hand, in the prism group 300b shown in FIG. 9(b), the inclination angle α2 of the projection light incidence surface 322b is larger than the inclination angle α1 of the projection light incidence surface 322a by the angle of the apex angle A of the third prism 340. As a result, a portion of the DMD-OFF light Lf (OFF light Lf1b) reflected by the projection light incident surface 322b is removed without entering the light modulation element 400. In this manner, by providing the third prism 340, the inclination angle of the projection light incident surface 322b can be appropriately adjusted, and the influence of stray light in the prism group 300b due to the DMD-OFF light can be suppressed.

(Curvature design of the prism surface of the imaging light reflecting prism)
10 and 11, a case where the internal reflection surface and the imaging light exit surface of the prism group imaging light reflecting prism according to the embodiment of the present disclosure are given a curvature will be described. Fig. 10 is a diagram showing the state of propagation of imaging light by the prism group 300 (Fig. 10(a)) and the prism group 300c (Fig. 10(b)) according to the embodiment of the present disclosure. Fig. 11 is a diagram showing the state of propagation of imaging light by the prism group 300 (Fig. 11(a)) and the prism group 300d (Fig. 11(b)) according to the embodiment of the present disclosure.

As described above, the external light Le forms a beam spot S1 on the projection light entrance surface 322 (see FIGS. 3 and 4), and at least a part of the external light Le is internally reflected as the imaging light Li, reaches the projection light exit surface 321 (see FIGS. 3 and 4) to form a beam spot S2, and is internally reflected and enters the imaging light reflecting prism 350. Furthermore, after forming a beam spot S3 on the internal reflection surface 352 of the imaging light reflecting prism 350 and being internally reflected, it is emitted from the imaging light exit surface 353. As shown in (a) of FIG. 10 and (a) of FIG. 11, in the implementation of the present disclosure, the external light Le reflected from the screen 430 (shown in FIG. 1) and propagating in the -X direction passes through the projection optical system 420 and enters the prism group 300. At this time, the projection optical system 420 focuses the external light Le to form the beam spot S1, and then the imaging light Li, which is at least a part of the external light Le, converges to form the beam spot S2. After entering the imaging light reflecting prism 350, the imaging light Li further converges, and an intermediate image Ms is formed at a position conjugate with the screen 430 with respect to the lens group LGp of the projection optical system 420. In this embodiment, the intermediate image Ms is formed at a position away from the internal reflecting surface 352. After forming the intermediate image Ms, the imaging light Li gradually widens its light flux as it travels toward the internal reflecting surface 352, and forms a beam spot S3 on the internal reflecting surface 352. Then, the imaging light Li is reflected by the internal reflecting surface 352 toward the imaging light exit surface 353, passes through the imaging light exit surface 353 and is emitted, and is imaged on the imaging element 450 by the imaging optical system 440.

In the prism group 300c shown in FIG. 10(b), the same elements as those in the prism group 300 shown in FIG. 10(a) are given the same reference numerals, and the description thereof will be omitted. In this embodiment, in the prism group 300c, the internal reflection surface 352c of the imaging light reflecting prism 350c can be configured to have a concave shape C1 toward the direction in which the imaging light Lic is internally reflected at the internal reflection surface 352c. The concave shape C1 can focus the imaging light reflected as a concave mirror having positive power. In this way, by giving a curvature to the internal reflection surface 352c of the imaging light reflecting prism, the spread of the imaging light Lic in the prism group 300c can be suppressed, and therefore the spread of the light beam of the outgoing imaging light Lic can be regulated. Therefore, the imaging optical system 440c in the latter stage can be configured using optical components with a smaller aperture and thinner optical components than the imaging optical system 440 shown in FIG. 10(a). As a result, as shown in the figure, the propagation optical path length of the imaging light Lic to the imaging element 450 can be shortened by a distance d1 compared to the propagation optical path length of the imaging light Li emitted by the prism group 300. This makes it possible to further compactify the imaging optical system.

Next, in the prism group 300d shown in FIG. 11(b), the same elements as those in the prism group 300 in FIG. 11(a) are given the same reference numerals, and the description thereof will be omitted. In this embodiment, in the prism group 300d, the imaging light exit surface 353d of the imaging light reflecting prism 350d can be configured to have a convex shape C2 in the direction in which the imaging light Lid is emitted to the imaging element 450. The convex shape C2 can focus the imaging light emitted as a convex lens having positive power. In this way, by giving a curvature to the imaging light exit surface 353d of the imaging light reflecting prism, the spread of the light flux of the emitted imaging light Lid can be regulated. Therefore, the imaging optical system 440d in the latter stage can reduce the number of optical system parts compared to the imaging optical system 440 shown in FIG. 10(a). As a result, as shown in the figure, the propagation optical path length of the imaging light Lid to the imaging element 450 can be shortened by a distance d2 compared to the propagation optical path length of the imaging light Li emitted by the prism group 300. This makes it possible to further compactify the imaging optical system.

Although not shown here, the imaging light incident surface 351 of the imaging light reflecting prism can also be given a curvature. By giving a curvature to one or more prism surfaces of the imaging light reflecting prism, the imaging optical system can be made more compact, making it easier to further miniaturize the entire device.

(Configuration of the projection imaging optical system 500A according to the second embodiment)
FIG. 12 is a schematic diagram showing the configuration of a projection imaging optical system 500A of a projection type image display device of Example 2 according to an embodiment of the present disclosure. The projection type image display device according to this embodiment is a three-plate projection type image display device, and includes an illumination optical system and a projection imaging optical system. Since the illumination optical system is already well known, FIG. 12 shows only the projection imaging optical system 500A without showing the illumination optical system. FIG. 12(b) is a schematic diagram showing the configuration of the projection imaging optical system 500A on the illustrated X-Z plane, and FIG. 12(a) is a schematic diagram showing the projection imaging optical system 500A viewed from the left side of FIG. 1(b), that is, from the +Z side of FIG. 12(b) toward the -Z direction.

As shown in FIG. 12, the projection imaging optical system 500A includes a prism member 360. The prism member 360 is composed of a prism group 300A according to an embodiment of the present disclosure and a color separation/synthesis prism 380A. The prism group 300A is located in front of the color separation/synthesis prism 380A (on the projection optical system 420A side). The illumination light LsA of each color gamut from the illumination optical system passes through the TIR prism 310A of the prism group 300A and enters the color separation/synthesis prism 380A.

The color separation/synthesis prism 380A includes prisms 381A, 382A, and 383A arranged in sequence along the projection optical axis Oa1 from the projection optical system 420A side. The color separation/synthesis prism 380A separates the light of each color gamut contained in the incident illumination light and guides it separately to the 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 380A.

The color separation/synthesis prism 380A guides the projection light (DMD-ON light) reflected by the DMD within each prism to the projection optical axis Oa1 to re-combine the colors, and emits the combined projection light LpA in the +X direction along the projection optical axis Oa1. Light that is not to be projected (DMD-OFF light, not shown) is deflected away from the projection optical axis Oa1 and removed. The projection light LpA is output from the color separation/synthesis prism 380A, passes through the TIR prism 310A on the forward side of the projection optical axis Oa1, and is propagated to the projection optical system 420A. The projection optical system 420A enlarges and projects the projection light LpA onto the screen 430A to display an image.

On the other hand, the external light LeA reflected from the screen in the illustrated -X direction enters the projection optical system 420A, propagates in the -X direction along the projection optical axis Oa1, and enters the first prism 320A of the TIR prism 310A. In the first prism 320A, at least a part of the external light LeA is reflected as imaging light LiA, deflected, and enters the imaging light reflecting prism 350A. Next, the imaging light LiA that entered the imaging light reflecting prism 350A is further reflected and deflected in the imaging light reflecting prism 350A, and is emitted from the imaging light exit surface 353A of the imaging light reflecting prism 350A along the imaging optical axis Ob1. The emitted imaging light LiA travels in the illustrated +Y direction, is introduced into the imaging optical system 440A, and is imaged on the imaging element 450A by the imaging optical system 440A.

In this way, the imaging light LiA, which is at least a part of the external light LeA incident from the projection optical system in the illustrated -X direction, can be introduced to the imaging element 450A along the imaging optical axis Ob1 in the Y-Z plane substantially perpendicular to the projection optical axis Oa1 by being reflected multiple times within the prism group 300A. This allows the imaging optical system 440A to be easily incorporated into the device without interfering with the projection optical system 420A, as described above. In addition, by reflecting and deflecting the imaging light LiA inside the prism group 300A, the air-equivalent length of the imaging light propagation can be shortened, making it easier to miniaturize the projection-type image display device.

As described above, the above embodiments have been described as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited to this, and can also be applied to embodiments in which modifications, substitutions, additions, omissions, etc. have been made. It is also possible to combine the components described in each of the above embodiments to create a new embodiment.

Note that the present disclosure does not limit the shape of each prism. For example, each prism constituting the prism group may be approximately triangular prism-shaped or approximately quadrangular prism-shaped, or may have other shapes.

In addition, the present disclosure does not limit the prism surfaces included in each prism. For example, the TIR prism and the imaging light reflecting prism may further include other prism surfaces, and the imaging light may be reflected by the other prism surfaces.

In the above embodiment, the prism surface of the imaging light reflecting prism is described as being concave or convex, but the present disclosure is not limited to this. For example, one or more prism surfaces of the imaging light reflecting prism may be configured to have a free-form curved surface shape.

As described above, the embodiments have been described as examples of the technology in this disclosure. For that purpose, the attached drawings and detailed description have been provided. Therefore, among the components described in the attached drawings and detailed description, not only are there components essential for solving the problem, but there may also be components that are not essential for solving the problem in order to illustrate the above technology. Therefore, just because those non-essential components are described in the attached drawings or detailed description, it should not be immediately determined that those non-essential components are essential.

Although the present disclosure has been fully described in connection with the preferred embodiments with reference to the accompanying drawings, various modifications are possible within the scope of the claims. Such modifications, as well as embodiments obtained by appropriately combining the technical means disclosed in the different embodiments, are also within the technical scope of the present disclosure.

This disclosure is applicable to prisms and to various types of projection-type image display devices.

200 Illumination optical system 20 Light source unit 21 Semiconductor laser element 22 Collimator lens 31, 32 Afocal lens 33, 34, 35 Condenser lens 41 Diffuser plate 42 λ/4 plate 45 Dichroic mirror 46 Rod integrator 50 Phosphor wheel 60 Color wheel 73, 74, 75 Lenses constituting an illumination light relay optical system 47 Mirror 48 Relay lens group 300, 300a, 300b, 300c, 300d, 300A Prism group 310, 310a, 310b, 310A TIR prism 320, 320a, 320b, 320A, 330, 330b, 340, 381A, 382A, 383A Prism 350, 350a, 350b, 350c, 350d, 350A Imaging light reflecting prism 321, 321a, 321b Projection light exit surface 322, 322a, 322b Projection light entrance surface 323a, 341, 342 Prism surface 331, 331b Illumination light reflecting surface 351, 351a Imaging light entrance surface 352, 352a, 352b, 352c Internal reflection surface 353, 353a, 353b, 353d, 353A Imaging light exit surface 360 Prism member 380A Color separation/combining prism 400, 401, 402, 403 Light modulation element (DMD)
420, 420A Projection optical system 430, 430A Screen 440, 440c, 440d, 440A Imaging optical system 450, 450A Imaging element 500, 500A Projection imaging optical system C1 Concave shape C2 Convex shape Ls, LsA Illumination light Lp, LpA Projection light Le, LeA External light Li, Lia, Lib, Lic, Lid, LiA Imaging light S1, S2, S3, S1a, S2a, S3a, S1b, S2b, S3b Beam spot Lf DMD-OFF light Oa1 Projection optical axis Ob1 Imaging optical axis Ob2 Longitudinal axis of prism group Ms Intermediate image 600 Projection type image display device 600A Projection type image display device housing

Claims (11)

A TIR prism and an imaging light reflecting prism are provided,
The TIR prism is
the prism reflects illumination light supplied by an illumination optical system and guides it to a light modulation element, transmits projection light generated by reflection at the light modulation element and outputs it along a projection optical axis to a projection optical system on the forward side of the projection optical axis, and further reflects imaging light, which is at least a part of external light incident from the projection optical system and propagating in a direction opposite to the forward side of the projection optical axis, and guides it to the imaging light reflecting prism;
The imaging light reflecting prism is
The imaging light incident from the TIR prism is internally reflected and guided to an imaging element along an imaging optical axis that is in a plane substantially perpendicular to the projection optical axis.
Prism group. the TIR prism includes a first prism and a second prism arranged in order along the projection optical axis from a front side of the projection optical axis,
an illumination light reflecting surface of the second prism, on which the illumination light is reflected, and a projection light incident surface of the first prism, on which the projection light is incident, are disposed opposite to each other with a parallel gap therebetween;
the imaging light reflecting prism has an imaging light incident surface through which the imaging light from the TIR prism passes, and is disposed adjacent to the first prism via the imaging light incident surface;
the imaging light is internally reflected multiple times within the TIR prism and the imaging light reflecting prism;
the imaging optical axis is located at or near a direction perpendicular to a longitudinal axis along which the imaging light passes through the TIR prism and the imaging light reflecting prism;
The prism group according to claim 1 . the imaging light reflecting prism is integrally formed with the first prism at the imaging light incident surface,
The prism group according to claim 2 . The imaging light reflecting prism and the first prism are arranged on the imaging light incident surface, separated from each other by a parallel gap.
The prism group according to claim 2 . the TIR prism further includes a third prism disposed between the first prism and the second prism;
the third prism has a first prism surface and a second prism surface that forms an angle with the first prism surface, the first prism surface and the projection light incident surface of the first prism are joined together, and the second prism surface and the illumination light reflecting surface of the second prism are disposed opposite each other with a parallel gap therebetween;
The prism group according to claim 2 . The projection light incidence surface is coated with a visible partial reflection coating,
the visible partial reflective coating has a reflectance of 2% or more and 15% or less for light in the visible range and reflects the imaging light;
The prism group according to claim 2 . The projection light incidence surface is coated with an infrared partial reflection coating,
the infrared partial reflective coating has a reflectance of 50% or more for light in the infrared range and reflects the imaging light;
The prism group according to claim 2 . the imaging light reflecting prism has an internal reflective surface;
at least a portion of the imaging light is internally reflected at the internally reflective surface;
The internal reflection surface has a concave shape toward a direction in which the imaging light is internally reflected.
The prism group according to claim 1 . the imaging light forms an intermediate image in the imaging light reflecting prism, and the intermediate image is focused at a position of the imaging element;
the intermediate image is located at a distance from the internal reflective surface;
The prism group according to claim 8. the imaging light reflecting prism has an imaging light exit surface,
the imaging light is transmitted through the imaging light exit surface and exits to the imaging element;
the imaging light exit surface has a convex shape facing a direction in which the imaging light is emitted to the imaging element;
The prism group according to claim 1 . an illumination optical system for supplying illumination light in the visible range;
A prism member including the prism group according to any one of claims 1 to 10;
one or more light modulation elements that spatially modulate the light supplied by the illumination optical system and guided by the prism member to be incident thereon, and generate the projection light according to image information;
a projection optical system that displays an image by enlarging and projecting the projection light that has passed through the TIR prism;
an imaging element that receives the imaging light output by the imaging light reflecting prism and converts the imaging light into an electrical image signal;
Equipped with
Projection type image display device.