Image projection device

Abstract

To provide an image projector which can increase the usage efficiency of irradiation light and can suppress the rise of the temperature of an image display unit.SOLUTION: An image projector (100) includes: a light source (10) for irradiating irradiation light; a polarization conversion element (30) for converting the irradiation light to a polarization direction along a first direction and emitting the irradiation light as backlight; a polarization maintenance diffusion unit (50) for diffusing and transmitting the backlight while maintaining the direction of polarization of the backlight; and an image display unit (60) for receiving entrance of the backlight having passed through the polarization maintenance diffusion unit (50), from the back surface, and emitting image light from the display surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image projection device.

Background Art

[0002] Conventionally, as a device for displaying various information in a vehicle, an instrument panel that lights up icons has been used. Also, along with an increase in the amount of information to be displayed, proposals have been made to embed an image display device in the instrument panel or to configure the entire instrument panel with an image display device.

[0003] However, since the instrument panel is located below the front glass (windshield) of the vehicle, in order for passengers such as the driver to visually recognize the information displayed on the instrument panel, it is necessary to move the line of sight downward during driving, which is not preferable. Therefore, an image projection device such as a head-up display (hereinafter referred to as HUD: Head Up Display) has been proposed that projects an image onto the front glass so that information can be read when the passenger visually recognizes the front of the vehicle. (For example, refer to Patent Documents 1 and 2).

[0004] The image projection devices of Patent Documents 1 and 2 irradiate irradiation light including an image with an image irradiation unit, reflect the irradiation light with a free-form surface mirror or the like, and cause an image to be formed in space through a display unit such as a windshield and reach the position of the passenger's viewpoint. As a result, the passenger can recognize that an image is displayed at the imaging position in the depth direction by the irradiation light incident on the viewpoint.

[0005] In such a conventional image projection device, a projection image is displayed using an image display unit such as a liquid crystal display device, and irradiation light is irradiated from the back side of the image display unit to project image light. Therefore, it has also been proposed to arrange a light distribution lens and a light diffusion sheet between the light source and the image display unit to irradiate the image display unit with light uniformly from the light source.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-119248 [Patent Document 2] Japanese Patent Publication No. 2019-119262 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, when a light diffusion sheet is used to uniformly illuminate the image, the diffused light reaches the image display unit unpolarized. Since the image display unit of liquid crystal displays and the like transmits only polarization in a specific direction, if unpolarized light is incident, polarization in directions other than the specific direction is not used for image projection, reducing the efficiency of light utilization. In addition, since the untransmitted light is absorbed by the image display unit, the temperature of the image display unit may rise, potentially negatively impacting the product's lifespan. In particular, HUD devices project image light through a windshield and display a virtual image superimposed on the background outside the vehicle, so the amount of light emitted from the light source is much stronger than that of monitor devices that directly view the display screen, and the effects of temperature rise are greater.

[0008] Therefore, the present invention has been made in view of the above-mentioned conventional problems, and aims to provide an image projection device that can improve the utilization efficiency of irradiated light and suppress the temperature rise of the image display unit. [Means for solving the problem]

[0009] To solve the above problems, the image projection apparatus of the present invention comprises a light source that emits illumination light, a polarization conversion element that converts the illumination light into a polarization direction along a first direction and emits it as backlight light, a polarization-maintaining diffusion section that diffuses and transmits the backlight light while maintaining its polarization direction, and an image display section into which the backlight light that has passed through the polarization-maintaining diffusion section is incident from the back and emits image light from the display surface. The polarization conversion element comprises a half-wave plate, a reflector, and a reflective polarizing portion, and the half-wave plate, the reflector, and the reflective polarizing portion are held on a substantially plate-shaped thin substrate made of a light-transmitting material, and the thin substrate comprises a first thin substrate and a second thin substrate, the half-wave plate and the reflective polarizing portion are held on the surface or back surface of the first thin substrate, and the reflector is held on the surface of the second thin substrate.

[0010] In the image projection apparatus of the present invention, the polarization conversion element converts the irradiated light into backlight light polarized along a first direction, and the polarization-maintaining diffusion unit diffuses it while maintaining its polarization. This reduces the amount of light absorbed by the image display unit, improves the utilization efficiency of the irradiated light, and suppresses the temperature rise of the image display unit.

[0011] Furthermore, in one aspect of the present invention, the longitudinal length of the image display unit is L, and the polarization-maintaining diffusion unit is arranged within a range of L / 10 from the back surface of the image display unit.

[0014] Furthermore, in one aspect of the present invention, the second thin substrate is curved so that the reflector is a concave reflector.

[0015] Furthermore, in one aspect of the present invention, the reflective polarizing portion reflects polarization in the first direction and transmits polarization in a second direction perpendicular to the first direction.

[0016] Furthermore, in one aspect of the present invention, the reflective polarizing portion transmits polarization in the first direction, It reflects polarization in a second direction that is perpendicular to the first direction. Furthermore, in order to solve the above problems, the image projection apparatus of the present invention comprises a light source that emits illumination light, a polarization conversion element that converts the illumination light into a polarization direction along a first direction and emits it as backlight light, a polarization-maintaining diffusion section that diffuses and transmits the backlight light while maintaining its polarization direction, a lens disposed between the polarization conversion element and the polarization-maintaining diffusion section, and an image display section into which the backlight light that has passed through the polarization-maintaining diffusion section is incident from the back and emits image light from the display surface, wherein the polarization-maintaining diffusion section is in the form of a sheet. Furthermore, in one aspect of the present invention, the polarization-maintaining diffusion unit maintains the polarization state at the time of incidence at more than 50% on an energy basis. [Effects of the Invention]

[0017] The present invention provides an image projection device that can improve the utilization efficiency of the irradiated light and suppress the temperature rise of the image display unit. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1(a) is a schematic diagram illustrating the outline of the image projection device 100 according to the first embodiment, where Figure 1(a) is a schematic cross-sectional view along the longitudinal direction and Figure 1(b) is a schematic cross-sectional view along the width direction. [Figure 2] This is a schematic diagram illustrating the outline of the image projection device 100 according to the second embodiment, and is a schematic cross-sectional view along the width direction. [Figure 3]It is a diagram showing a configuration example of the polarization conversion element 30 used in the image projection apparatus 100 according to the third embodiment. Fig. 3(a) shows an example in which the light source 10 is arranged along the light irradiation direction, and Fig. 3(b) shows an example in which the light source 10 is arranged in a lateral direction with respect to the light irradiation direction. [Figure 4] It is a diagram showing a configuration example of the polarization conversion element 30 used in the image projection apparatus 100 according to the fourth embodiment. Fig. 4(a) shows an example in which the light source 10 is arranged along the light irradiation direction, and Fig. 4(b) shows an example in which the light source 10 is arranged in a lateral direction with respect to the light irradiation direction. [Figure 5] It is a diagram showing a configuration example of the polarization conversion element 30 used in the image projection apparatus 100 according to the fifth embodiment. Fig. 5(a) shows an example in which the light source 10 is arranged along the light irradiation direction, and Fig. 5(b) shows an example in which the light source 10 is arranged in a lateral direction with respect to the light irradiation direction. [Figure 6] It is a diagram showing a configuration example of the polarization conversion element 30 used in the image projection apparatus 100 according to the sixth embodiment. Fig. 6(a) shows an example in which the light source 10 is arranged along the light irradiation direction, and Fig. 6(b) shows an example in which the light source 10 is arranged in a lateral direction with respect to the light irradiation direction. [Figure 7] It is a diagram showing a configuration example of the polarization conversion element 30 used in the image projection apparatus 100 according to the seventh embodiment. Fig. 7(a) shows an example in which the light transmitted through the reflective polarizing section 36 is incident on the half-wave plate 34, and Fig. 7(b) shows an example in which the light reflected by the mirror 37 is incident on the half-wave plate 34.

Embodiments for Carrying Out the Invention

[0019] (First Embodiment) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and redundant explanations will be omitted as appropriate. In the following description, a form in which the image projection device 100 according to the present invention is applied to a HUD mounted on a vehicle or the like will be exemplified and described. FIG. 1 is a schematic diagram for explaining the outline of the image projection device 100 according to the present embodiment, FIG. 1(a) is a schematic cross-sectional view along the longitudinal direction, and FIG. 1(b) is a schematic cross-sectional view along the width direction. As shown in FIG. 1, the image projection device 100 includes a light source 10, a first lens 20, a polarization conversion element 30, a second lens 40, a polarization-maintaining diffuser 50, and an image display unit 60.

[0020] The light source 10 is a member that irradiates the image display unit 60 with irradiation light through the first lens 20, the polarization conversion element 30, the second lens 40, and the polarization-maintaining diffuser 50. The light source 10 is, for example, a semiconductor light-emitting element such as an LED (Light Emitting Diode), and is arranged in a predetermined direction (the horizontal direction in FIG. 1(a)). The emission color of the light source 10 is not particularly limited, but in the present embodiment, it is white as an example. In the present embodiment, the number of arrays of the light source 10 is one row, but it may be two rows or more. Further, the light source 10 is not limited to an LED, and may be a semiconductor laser, an organic EL (Electro Luminescence) element, or the like.

[0021] The first lens 20 is an optical component positioned in the light emission direction of the multiple light sources 10, which focuses the light emitted from the light sources 10 and emits it as, for example, parallel light or light that is close to parallel light (hereinafter, both are collectively referred to as "approximately parallel light"). As shown in Figure 1, the first lens 20 is extended along the direction of arrangement of the multiple light sources 10 (X-axis direction). In this embodiment, as an example of the first lens 20, a TIR (Total Internal Reflection) lens is used, which has a refractive section in the center that refracts light and reflective sections on both sides of the refractive section that reflect light (not shown). In Figure 1, the shape of the first lens 20 is shown as being extended in the direction of arrangement of the light sources 10, but multiple collimating lenses may be provided for each light source 10. Furthermore, as long as the light from the light sources 10 can be made into approximately parallel light, it is not limited to lenses, and a combination of a reflector and a lens or a configuration in which the reflector alone can produce approximately parallel light may also be adopted.

[0022] The polarization conversion element 30 is an optical component positioned on the light-emitting side of the first lens 20 that converts unpolarized irradiated light into a polarized direction along a specific direction (first direction) and emits it as backlight light. The specific configuration of the polarization conversion element 30 is not limited, but Figure 1(b) shows an example that includes a prism 31, a reflective polarizing section 32, a reflector 33, and a half-wave plate 34.

[0023] The prism 31 is a component made of a light-transmitting material such as glass. In the example shown in Figure 1(b), the surface facing the light source 10 is the light incident surface, and the surface opposite the light incident surface is the light output surface. Between the light incident surface and the light output surface of the prism 31, a reflective polarizing section 32 and a reflector 33 are provided, each inclined at 45 degrees with respect to the light incident surface and the light output surface, respectively. In addition, a half-wave plate 34 is provided on a part of the light output surface of the prism 31.

[0024] The reflective polarizing element 32 is an optical element that transmits polarization in a predetermined direction and reflects polarization perpendicular to that predetermined direction. In the example shown in Figure 1(b), since the light from the light source 10 is incident on half of the prism 31, the reflective polarizing element 32 is positioned on the half into which the incident light is incident. The polarization direction transmitted by the reflective polarizing element 32 is not limited and must ultimately be matched to the polarization direction required for the backlight light that is irradiated onto the image display unit 60. For example, in Figure 1(b), it may transmit polarization in the lateral direction (e.g., p-polarization) and reflect polarization in the direction perpendicular to the paper plane (e.g., s-polarization).

[0025] The reflector 33 is an optical element that reflects incident light. In the example shown in Figure 1(b), it is provided on the half of the prism 31 that is not incident to the irradiated light. The reflector 33 is also positioned at a 45-degree angle to the light incident surface and light exit surface of the prism 31, similar to the reflective polarizing section 32, so that the reflector 33 and the reflective polarizing section 32 are approximately parallel.

[0026] The half-wave plate 34 is an optical component positioned on half of the light-emitting surface of the prism 31 and composed of a birefringent material with different refractive indices in the slow and fast axes. The half-wave plate 34 is designed so that a phase difference of half the wavelength of light occurs between the slow and fast axes by the time the incident light is emitted. Furthermore, the slow and fast axes of the half-wave plate 34 are positioned at a 45-degree angle to the polarization direction of the irradiated light that has passed through the reflective polarizing unit 32. Therefore, the polarization of the irradiated light that has passed through the half-wave plate 34 is rotated by 90 degrees in plane. As a result, the light that has passed through the reflective polarizing unit 32 and the half-wave plate 34, and the light that has been reflected by the reflective polarizing unit 32 and the half-wave plate 34, are irradiated as backlight light with the same polarization direction in a predetermined direction. Figure 1(b) shows an example where the half-wave plate 34 is placed on the side where the prism 31 is provided. However, it may also be placed on the side where the reflector 33 is provided, so that the light reflected by the reflector 33 is incident on the half-wave plate 34. Furthermore, the half-wave plate 34 does not need to have a phase difference of exactly 50% with respect to the wavelength of light; as long as it produces a phase difference close to 50%, it can perform the function of rotating the polarization direction in-plane.

[0027] The second lens 40 controls the luminous flux so that the backlight light irradiated via the polarization conversion element 30 uniformly illuminates the entire illumination area. Therefore, the shape and polarity of the second lens 40 are selected to suit this purpose, but in this embodiment, a concave lens is used as an example of the second lens 40. If the entire illumination area is to be uniformly illuminated by the first lens 20 alone, the second lens 40 may be omitted. The first lens 20 and the second lens 40 are formed of, for example, a resin such as acrylic resin, glass, etc. The first lens 20 and the second lens 40 work together to guide the light emitted from the light source 10 to the illumination area of ​​the image display unit 60. In this embodiment, the illumination area is, for example, the back surface (the surface on the light source 10 side) of the polarization-maintaining diffusion unit 50. However, the location of the illumination area can be determined by considering the specifications of the light source device, etc., and may be, for example, the back surface of the image display unit 60.

[0028] The polarization-maintaining diffusion section 50 is an optical component positioned on the back side of the image display section 60 that diffuses and transmits the backlight light converted by the polarization conversion element 30 while maintaining its polarization direction. The polarization-maintaining diffusion section 50 diffuses the highly directional light deflected by the first lens 20 and the second lens 40 and emits it to the image display section 60, functioning to illuminate the image display section 60 more uniformly. The polarization-maintaining diffusion section 50 may diffuse only the light polarized in the first direction while maintaining its polarization, or it may diffuse the light while maintaining its polarization in all directions. The specific configuration of the polarization-maintaining diffusion section 50 is not limited, but as an example, a product name: HH120 sheet manufactured by Lintec Corporation can be used.

[0029] The image display unit 60 functions as a spatial light modulation unit that receives backlight light transmitted through the polarization-maintaining diffusion unit 50 from the back and emits light modulated by image information from the output surface. The specific configuration of the image display unit 60 is not limited, but as an example, a transmissive liquid crystal display device that transmits light incident from the back and emits it from the front can be used. In a transmissive liquid crystal display device, only polarization in a predetermined direction incident on the back side is transmitted, so the polarization direction in the polarization conversion element 30 and the polarization-maintaining diffusion unit 50 is made to match that predetermined direction.

[0030] In the image projection device 100 described above, the illumination light emitted from the light source 10 is unpolarized, with no limit on the polarization direction. The illumination light emitted from the light source 10 is incident on the first lens 20, collimated, and then incident on the incident surface of the polarization conversion element 30. Of the illumination light incident on the polarization conversion element 30, a portion is transmitted through the reflective polarization unit 32, and another portion is reflected in the direction of the reflector 33. Here, the polarization of the illumination light reflected by the reflective polarization unit 32 is polarized in the first direction through which the image display unit 60 passes. In addition, the polarization of the illumination light transmitted through the reflective polarization unit 32 is polarized in a second direction that is almost perpendicular to the first direction.

[0031] The irradiated light that passes through the reflective polarizing section 32 is incident on the half-wave plate 34, where its polarization direction is rotated by 90 degrees, and it is irradiated onto the second lens 40 as backlight light polarized in the first direction. In addition, the irradiated light that reaches the reflector 33 is reflected and irradiates the second lens 40 as backlight light polarized in the first direction. The backlight light that reaches the second lens 40 has its light distribution adjusted and reaches the polarization-maintaining diffusion section 50.

[0032] In the polarization-maintaining diffusion section 50, the backlight light polarized in the first direction is diffused and transmitted as light polarized in the first direction while maintaining its polarization direction. As a result, the back of the image display section 60 is uniformly illuminated with backlight light polarized in the first direction. Maintaining the polarization direction means that the polarization state at the time of incidence is maintained at more than 50% on an energy basis before and after passing through the polarization-maintaining diffusion section 50, and it is more preferable that it is maintained at 90% or more.

[0033] As shown in Figures 1(a) and 1(b), when the polarization-maintaining diffusion unit 50 is attached to the back of the image display unit 60, almost all of the diffused backlight light can be incident on the image display unit 60. Alternatively, a gap may be provided between the image display unit 60 and the polarization-maintaining diffusion unit 50. In this case, even if some of the backlight light is absorbed by the polarization-maintaining diffusion unit 50 or the image display unit 60 and the temperature rises, the gap prevents heat from being transferred between the two, thereby suppressing adverse effects due to heat. Here, as shown in Figure 1(a), if the length in the longitudinal direction (left-right direction in the figure) of the image display unit 60 is the active area length L, it is preferable that the polarization-maintaining diffusion unit 50 is positioned within a range of L / 10 or less from the back of the image display unit 60. If the distance between the image display unit 60 and the polarization-maintaining diffusion unit 50 is greater than L / 10, the proportion of the diffused backlight light that reaches outside the range of the image display unit 60 increases, and the light utilization efficiency decreases.

[0034] Furthermore, the distance between the second lens 40 and the polarization-maintaining diffusion unit 50 is preferably in the range of L / 16 or more of the active area length L, and more preferably in the range of L / 8 or more. Here, if the effective area is defined as the range through which light that reaches the passenger's viewpoint is transmitted, the distance between the second lens 40 and the polarization-maintaining diffusion unit 50 is the longest distance between their effective areas. If the distance between the second lens 40 and the polarization-maintaining diffusion unit 50 is less than L / 16, it becomes difficult to adjust the brightness unevenness and light distribution of the virtual image.

[0035] In a head-up display (HUD), the image projection device 100 is housed, for example, in the vehicle's dashboard. The image from the image projection device 100 is projected through the windshield or the like to form a virtual image. The light emitted from the image projection device 100 is reflected by a flat mirror or a free-form mirror as needed and guided to the driver's eyes through the windshield for visibility.

[0036] As described above, in the image projection device 100 of this embodiment, the light emitted from the light source 10 is converted into backlight light polarized in a first direction by the polarization conversion element 30, and the polarization-maintaining diffusion unit 50 diffuses the backlight light while maintaining the polarization in the first direction. Since the polarization direction of the backlight light reaching the image display unit 60 matches the polarization direction used for image display in the image display unit 60, the amount of polarization component in the second direction that is absorbed by the image display unit 60 is small, improving the efficiency of light utilization and suppressing the temperature rise of the image display unit 60.

[0037] (Second Embodiment) Next, a second embodiment of the present invention will be described with reference to Figure 2. Content that overlaps with the first embodiment will be omitted from the explanation. Figure 2 is a schematic diagram illustrating the outline of the image projection device 100 according to this embodiment, and is a schematic cross-sectional view along the width direction. In this embodiment, the arrangement of the light source 10 and the first lens 20, and the polarization control in the polarization conversion element 30 differ from the first embodiment. As shown in Figure 2, the image projection device 100 includes a light source 10, a first lens 20, a polarization conversion element 30, a second lens 40, a polarization maintenance diffusion unit 50, and an image display unit 60. As shown in Figure 2, in the image projection device 100 of this embodiment, the light incident surface and the light output surface of the polarization conversion element 30 are almost perpendicular. Therefore, the direction of propagation of the illumination light irradiated from the light source 10 and the first lens 20 is perpendicular to the direction of propagation of the backlight light irradiated from the polarization conversion element 30.

[0038] In the example shown in Figure 2, the illumination light emitted from the light source 10 is unpolarized, incident on the first lens 20, collimated, and then incident on the incident surface of the polarization conversion element 30. A portion of the illumination light incident on the polarization conversion element 30 passes through the reflective polarization section 32, while another portion is reflected in the direction of the half-wave plate 34. Here, the polarization of the illumination light reflected by the reflective polarization section 32 is polarized in a second direction that is approximately perpendicular to the first direction. Furthermore, the polarization of the illumination light passing through the reflective polarization section 32 is polarized in the first direction through which the image display section 60 passes.

[0039] The illumination light that passes through the reflective polarizing section 32 reaches the reflecting mirror 33, is reflected, and illuminates the second lens 40 as backlight light polarized in the first direction. In addition, the illumination light reflected by the reflective polarizing section 32 is incident on the half-wave plate 34, its polarization direction is rotated by 90 degrees, and illuminates the second lens 40 as backlight light polarized in the first direction.

[0040] In the image projection device 100 of this embodiment, the light emitted from the light source 10 is converted into backlight light polarized in a first direction by the polarization conversion element 30, and the polarization-maintaining diffusion unit 50 diffuses the backlight light while maintaining the polarization in the first direction. Since the polarization direction of the backlight light reaching the image display unit 60 matches the polarization direction used for image display in the image display unit 60, the amount of polarization component in the second direction that is absorbed by the image display unit 60 is small, improving the efficiency of light utilization and suppressing the temperature rise of the image display unit 60.

[0041] (Third embodiment) Next, a third embodiment of the present invention will be described with reference to Figure 3. Content that overlaps with the first embodiment will be omitted from the explanation. In the first embodiment, an example was shown in which a prism 31 was used as the polarization conversion element 30, but this embodiment differs in that thin substrates 35a, 35b, and 35c are used. Figure 3 shows an example of the configuration of the polarization conversion element 30 used in the image projection device 100 according to this embodiment. Figure 3(a) shows an example in which the light source 10 is arranged along the light irradiation direction, and Figure 3(b) shows an example in which the light source 10 is arranged laterally to the light irradiation direction. As shown in Figure 3, the polarization conversion element 30 of this embodiment includes a half-wave plate 34, thin substrates 35a, 35b, and 35c, a reflective polarization section 36, and a reflector 37.

[0042] The half-wave plate 34 is an optical component positioned on half of the light-emitting surface of the prism 31 and composed of a birefringent material with different refractive indices in the slow and fast axes, causing the polarization of the transmitted irradiated light to rotate 90 degrees within the plane. The specific configuration of the half-wave plate 34 is not limited, but it is preferable to use a plate-like or sheet-like material that can be attached to the surface of a thin substrate 35a, 35b, 35c, etc. As an example, an achromatic half-wave plate from Dexerials, Inc. can be used.

[0043] The thin-walled substrates 35a, 35b, and 35c are roughly plate-shaped members made of a light-transmitting material. The materials constituting the thin-walled substrates 35a, 35b, and 35c are not limited and can be glass, acrylic resin, polycarbonate resin, etc., but it is preferable to use retardation-free materials that do not cause a phase difference in transmitted light. Furthermore, the thickness of the thin-walled substrates 35a, 35b, and 35c is not limited and can be, for example, about 0.5 mm to 3.0 mm thick.

[0044] The reflective polarizing portion 36 is an optical component that transmits polarized light in a predetermined direction and reflects polarized light perpendicular to that predetermined direction. The specific configuration of the reflective polarizing portion 36 is not limited, but it is preferable to use a plate-like or sheet-like material that can be attached to the surface of a thin substrate 35a, 35b, 35c, etc. As an example, reflective polarizing film WGF manufactured by Asahi Kasei Corporation or reflective polarizing plate film manufactured by 3M Japan Limited can be used.

[0045] In the example shown in Figures 3(a) and 3(b), the thin substrates 35a and 35b are positioned at an angle of approximately 45 degrees with respect to the direction of backlight irradiation, while the thin substrate 35c is positioned perpendicular to the direction of backlight irradiation. A reflective polarizing portion 36 is attached to and held on the light incident surface side of the thin substrate 35a. A reflector 37 is attached to and held on the surface of the thin substrate 35b facing the thin substrate 35a. A half-wave plate 34 is attached to and held on the light-emitting surface of the thin substrate 35c. Here, an example is shown in which the half-wave plate 34, reflective polarizing portion 36, and reflector 37 are in sheet form and attached to the thin substrates 35a, 35b, and 35c, but they may also be formed directly on the surface of the thin substrates 35a, 35b, and 35c by vapor deposition or the like. Furthermore, the surface to which the half-wave plate 34, the reflective polarizing section 36, and the reflector 37 are attached is not limited to the side shown in Figures 3(a) and (b), but may also be provided on the opposite side of the thin substrate 35a, 35b, and 35c.

[0046] In the polarization conversion element 30 shown in Figure 3(a), the illumination light irradiated from the light source 10 is unpolarized, incident on the first lens 20, collimated, and then incident on the reflective polarizing section 36 provided on the incident surface of the thin substrate 35a. Of the illumination light incident on the reflective polarizing section 36, a portion is transmitted, and another portion is reflected in the direction of the reflector 37. Here, the polarization of the illumination light reflected by the reflective polarizing section 36 is polarized in the first direction through which the image display section 60 passes. In addition, the polarization of the illumination light that passes through the reflective polarizing section 36 is polarized in a second direction that is almost perpendicular to the first direction.

[0047] The illumination light reflected by the reflective polarizing section 36 reaches the reflecting mirror 37, is reflected again, and illuminates the second lens 40 as backlight light polarized in the first direction. In addition, the illumination light that has passed through the reflective polarizing section 36 is incident on the half-wave plate 34, its polarization direction is rotated by 90 degrees, and illuminates the second lens 40 as backlight light polarized in the first direction.

[0048] In the polarization conversion element 30 shown in Figure 3(b), the illumination light irradiated from the light source 10 is unpolarized, incident on the first lens 20, collimated, and then incident on the reflective polarizing section 36 provided on the incident surface of the thin substrate 35a. Of the illumination light incident on the reflective polarizing section 36, a portion is transmitted in the direction of the reflector 37, and another portion is reflected in the direction of the half-wave plate 34. Here, the polarization of the illumination light reflected by the reflective polarizing section 36 is polarized in a second direction that is almost perpendicular to the first direction. In addition, the polarization of the illumination light transmitted through the reflective polarizing section 36 is polarized in the first direction through which the image display section 60 transmits.

[0049] The illumination light that passes through the reflective polarizing section 36 reaches the reflector 37, is reflected, and illuminates the second lens 40 as backlight light polarized in the first direction. In addition, the illumination light reflected by the reflective polarizing section 36 is incident on the half-wave plate 34, its polarization direction is rotated by 90 degrees, and illuminates the second lens 40 as backlight light polarized in the first direction.

[0050] In the polarization conversion element 30 of this embodiment, the half-wave plate 34, reflective polarizing section 36, and reflector 37 are held using thin substrates 35a, 35b, and 35c, and a thick light guide member such as a prism 31 is not used. This makes it possible to reduce the weight of the polarization conversion element 30 and the image projection device 100 using it.

[0051] (Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to Figure 4. Content that overlaps with the first embodiment will be omitted from the explanation. Figure 4 shows an example of the configuration of a polarization conversion element 30 used in the image projection device 100 according to this embodiment. Figure 4(a) shows an example where the light source 10 is arranged along the light irradiation direction, and Figure 4(b) shows an example where the light source 10 is arranged laterally to the light irradiation direction. As shown in Figure 4, the polarization conversion element 30 of this embodiment includes a half-wave plate 34, thin substrates 35a and 35b, a reflective polarization section 36, and a reflector 37.

[0052] As shown in Figures 4(a) and 4(b), in the polarization conversion element 30 of this embodiment, the thin substrates 35a and 35b are arranged at an angle with respect to the direction of backlight emission. Furthermore, a reflective polarizing portion 36 and a half-wave plate 34 are attached to different regions on the surface of the thin substrate 35a facing the thin substrate 35b. A reflector 37 is attached to the surface of the thin substrate 35b facing the thin substrate 35a. The surfaces to which the half-wave plate 34, reflective polarizing portion 36, and reflector 37 are attached are not limited to the sides shown in Figures 4(a) and 4(b), but may also be provided on the opposite sides of the thin substrates 35a and 35b.

[0053] In the polarization conversion element 30 shown in Figure 4(a), the illumination light irradiated from the light source 10 is unpolarized, incident on the first lens 20, collimated, and then incident on the reflective polarizing section 36 provided on the incident surface of the thin substrate 35a. Of the illumination light incident on the reflective polarizing section 36, a portion is transmitted and another portion is reflected in the direction of the reflector 37. Here, the polarization of the illumination light transmitted through the reflective polarizing section 36 is polarized in the first direction through which the image display section 60 is transmitted. Furthermore, the polarization of the illumination light reflected by the reflective polarizing section 36 is polarized in a second direction that is almost perpendicular to the first direction.

[0054] The illumination light that passes through the reflective polarizing section 36 is illuminated onto the second lens 40 as backlight light polarized in the first direction. The illumination light reflected by the reflective polarizing section 36 reaches the reflector 37, is reflected again, and enters the half-wave plate 34. At the half-wave plate 34, the polarization direction of the illumination light is rotated by 90 degrees and illuminated onto the second lens 40 as backlight light polarized in the first direction.

[0055] In the polarization conversion element 30 shown in Figure 4(b), the illumination light irradiated from the light source 10 is unpolarized, incident on the first lens 20, collimated, and then incident on the reflective polarizing section 36 provided on the thin substrate 35a. Of the illumination light incident on the reflective polarizing section 36, a portion is transmitted in the direction of the reflector 37, and another portion is reflected. Here, the polarization of the illumination light reflected by the reflective polarizing section 36 is polarized in the first direction through which the image display section 60 passes. In addition, the polarization of the illumination light transmitted through the reflective polarizing section 36 is polarized in a second direction that is almost perpendicular to the first direction.

[0056] The illumination light that passes through the reflective polarizing section 36 reaches the reflector 37, is reflected, and enters the half-wave plate 34. At the half-wave plate 34, the polarization direction of the illumination light is rotated by 90 degrees and illuminates the second lens 40 as backlight light polarized in the first direction. In addition, the illumination light reflected by the reflective polarizing section 36 illuminates the second lens 40 as backlight light polarized in the first direction.

[0057] In the polarization conversion element 30 of this embodiment, the half-wave plate 34, the reflective polarizing section 36, and the reflector 37 are held using thin substrates 35a and 35b, allowing for further weight reduction. Furthermore, the area, inclination angle, and spacing of the thin substrates 35a and 35b can be freely designed, improving design flexibility. In addition, the optical characteristics of the polarization conversion element 30 can be easily adjusted by changing the attachment positions of the half-wave plate 34, the reflective polarizing section 36, and the reflector 37 on the thin substrates 35a and 35b.

[0058] (Fifth embodiment) Next, a fifth embodiment of the present invention will be described with reference to Figure 5. Content that overlaps with the first embodiment will be omitted from the explanation. Figure 5 shows an example of the configuration of a polarization conversion element 30 used in the image projection device 100 according to this embodiment. Figure 5(a) shows an example where the light source 10 is arranged along the light irradiation direction, and Figure 5(b) shows an example where the light source 10 is arranged laterally to the light irradiation direction. As shown in Figure 5, the polarization conversion element 30 of this embodiment includes a half-wave plate 34, thin substrates 35a and 35b, a reflective polarization section 36, and a reflector 37.

[0059] As shown in Figures 5(a) and 5(b), in the polarization conversion element 30 of this embodiment, the thin substrates 35a and 35b are arranged at an angle with respect to the direction of backlight emission. A reflective polarizing portion 36 is attached to the incident surface of the thin substrate 35a, and a half-wave plate 34 is attached to the surface opposite the reflective polarizing portion 36. A reflector 37 is attached to the surface of the thin substrate 35b facing the thin substrate 35a.

[0060] In the polarization conversion element 30 shown in Figure 5(a), the illumination light irradiated from the light source 10 is unpolarized, incident on the first lens 20, collimated, and then incident on the reflective polarizing section 36 provided on the incident surface of the thin substrate 35a. Of the illumination light incident on the reflective polarizing section 36, a portion is transmitted, and another portion is reflected in the direction of the reflector 37. Here, the polarization of the illumination light transmitted through the reflective polarizing section 36 is polarized in a second direction that is almost perpendicular to the first direction. Furthermore, the polarization of the illumination light reflected by the reflective polarizing section 36 is polarized in the first direction through which the image display section 60 passes.

[0061] The irradiated light that has passed through the reflective polarizing section 36 is incident on the half-wave plate 34. At the half-wave plate 34, the polarization direction of the irradiated light is rotated by 90 degrees and irradiates the second lens 40 as backlight light polarized in the first direction. In addition, the irradiated light reflected by the reflective polarizing section 36 reaches the reflector 37, is reflected again, and irradiates the second lens 40 as backlight light polarized in the first direction.

[0062] In the polarization conversion element 30 shown in Figure 5(b), the illumination light irradiated from the light source 10 is unpolarized, incident on the first lens 20, collimated, and then incident on the reflective polarizing section 36 provided on the incident surface of the thin substrate 35a. Of the illumination light incident on the reflective polarizing section 36, a portion is transmitted in the direction of the reflector 37, and another portion is reflected. Here, the polarization of the illumination light reflected by the reflective polarizing section 36 is polarized in the first direction through which the image display section 60 passes. In addition, the polarization of the illumination light transmitted through the reflective polarizing section 36 is polarized in a second direction that is almost perpendicular to the first direction.

[0063] The irradiated light that has passed through the reflective polarizing section 36 is incident on the half-wave plate 34. At the half-wave plate 34, the polarization direction of the irradiated light is rotated by 90 degrees and converted into light polarized in the first direction before reaching the reflector 37. The irradiated light that reaches the reflector 37 is reflected and irradiates the second lens 40 as backlight light polarized in the first direction. In addition, the irradiated light reflected by the reflective polarizing section 36 irradiates the second lens 40 as backlight light polarized in the first direction.

[0064] In the polarization conversion element 30 of this embodiment, the half-wave plate 34 and the reflective polarizing portion 36 are held using both sides of the thin substrate 35a, which reduces the area of ​​the thin substrate 35a and further reduces the weight. In addition, the area, tilt angle, spacing, etc. of the thin substrates 35a and 35b can be freely designed, which improves the degree of design freedom.

[0065] (Sixth Embodiment) Next, a sixth embodiment of the present invention will be described with reference to Figure 6. Descriptions that overlap with the first and fourth embodiments will be omitted. Figure 6 shows an example of the configuration of a polarization conversion element 30 used in the image projection device 100 according to this embodiment. Figure 6(a) shows an example where the light source 10 is arranged along the light irradiation direction, and Figure 6(b) shows an example where the light source 10 is arranged laterally to the light irradiation direction. As shown in Figure 6, the polarization conversion element 30 of this embodiment includes a half-wave plate 34, thin substrates 35a and 35b, a reflective polarization section 36, and a reflector 37.

[0066] As shown in Figures 6(a) and 6(b), in the polarization conversion element 30 of this embodiment, the thin substrates 35a and 35b are arranged at an inclination with respect to the direction of backlight emission. A reflective polarizing portion 36 is attached to the surface of the thin substrate 35a facing the thin substrate 35b. A half-wave plate 34 is attached to the surface of the thin substrate 35a opposite to the region where the reflective polarizing portion 36 is provided. A reflector 37 is attached to the surface of the thin substrate 35b facing the thin substrate 35a. The surfaces to which the half-wave plate 34, the reflective polarizing portion 36, and the reflector 37 are attached are not limited to the sides shown in Figures 4(a) and 4(b), but may be provided on the opposite sides of the thin substrates 35a and 35b. The conversion from unpolarized irradiated light to backlight light polarized in the first direction by the polarization conversion element 30 of this embodiment is the same as that described in Figures 4(a) and 4(b) in the fourth embodiment.

[0067] (Seventh Embodiment) Next, a seventh embodiment of the present invention will be described with reference to Figure 7. Details that overlap with the first embodiment will be omitted. This embodiment differs from the fifth and sixth embodiments in that it uses a reflector 37 with a curved reflective surface. Figure 7 shows an example of the configuration of a polarization conversion element 30 used in the image projection device 100 according to this embodiment. Figure 7(a) shows an example where light transmitted through the reflective polarization section 36 is incident on the half-wave plate 34, and Figure 7(b) shows an example where light reflected by the reflector 37 is incident on the half-wave plate 34. As shown in Figure 7, the polarization conversion element 30 of this embodiment includes a half-wave plate 34, thin substrates 35a and 35b, a reflective polarization section 36, and a reflector 37.

[0068] As shown in Figures 7(a) and 7(b), the thin substrate 35b and the reflector 37 have a curved concave shape, and the reflector 37 functions as a concave reflector. The conversion from unpolarized illumination light to backlight light polarized in the first direction by the polarization conversion element 30 shown in Figure 7(a) is the same as that described in Figure 5(a) in the fifth embodiment. Similarly, the conversion from unpolarized illumination light to backlight light polarized in the first direction by the polarization conversion element 30 shown in Figure 7(b) is the same as that described in Figure 6(a) in the sixth embodiment.

[0069] In the polarization conversion element 30, there is a difference in the optical path between the backlight light that is reflected by the reflector 37 and the backlight light that is not reflected by the reflector 37. If the illumination light emitted from the light source 10 and the first lens 20 is not perfectly parallel light but has a certain degree of divergence angle, this difference in optical path may reduce the density of the backlight light that has passed through the reflector 37. However, as shown in Figures 7(a) and 7(b), if a concave reflector is used as the reflector 37, the divergence angle can be corrected by the reflector 37, reducing the density difference with the backlight light that has not passed through the reflector 37 and improving the overall uniformity of the backlight light.

[0070] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of Symbols]

[0071] 100…Image projection device 10…Light source 20…First lens 30…Polarization conversion element 40...Second lens 50…Polarization-maintaining diffusion section 60...Image display section 31...Prism 32,36…Reflective polarizing part 33,37...reflector 34... Half-wave plate 35a, 35b, 35c…thin base material

Claims

1. A light source that emits light, A polarization conversion element that converts the aforementioned irradiated light into a polarization direction along a first direction and emits it as backlight light, A polarization-maintaining diffusion section that diffuses and transmits the backlight light while maintaining its polarization direction, The image display unit includes an image display unit into which the backlight light that has passed through the polarization-maintaining diffusion unit is incident from the back and image light is emitted from the display surface. The polarization conversion element comprises a half-wave plate, a reflector, and a reflective polarizing element. The half-wave plate, the reflector, and the reflective polarizing element are held in a thin, roughly plate-shaped substrate made of a light-transmitting material. The thin-walled substrate comprises a first thin-walled substrate and a second thin-walled substrate. The half-wave plate and the reflective polarizing portion are held on the front or back surface of the first thin substrate. An image projection device characterized in that the reflecting mirror is held on the surface of the second thin substrate.

2. An image projection device according to claim 1, The image projection device is characterized in that the second thin substrate is curved and the reflecting mirror is a concave reflecting mirror.

3. An image projection device according to claim 1, The image projection device is characterized in that the reflective polarizing portion reflects polarization in the first direction and transmits polarization in a second direction perpendicular to the first direction.

4. An image projection device according to claim 1, The image projection device is characterized in that the reflective polarizing portion transmits polarization in the first direction and reflects polarization in a second direction perpendicular to the first direction.

5. A light source that emits illumination light, A polarization conversion element that converts the aforementioned irradiated light into a polarization direction along a first direction and emits it as backlight light, A polarization-maintaining diffusion section that diffuses and transmits the backlight light while maintaining its polarization direction, A lens disposed between the polarization conversion element and the polarization maintenance diffusion unit, The image display unit includes an image display unit into which the backlight light that has passed through the polarization-maintaining diffusion unit is incident from the back and image light is emitted from the display surface. The image projection apparatus is characterized in that the polarization-maintaining diffusion section is in the form of a sheet.

6. An image projection device according to claim 5, The polarization-maintaining diffusion unit is characterized by maintaining the polarization state at the time of incidence at more than 50% on an energy basis.

7. An image projection device according to any one of claims 1 to 6, The longitudinal length of the image display unit is L, An image projection device characterized in that the polarization-maintaining diffusion unit is arranged within a range of L / 10 from the back surface of the image display unit.

Images