JP2008033040A - Rear projection display device - Google Patents

Abstract

Provided is a rear projection display device that realizes a large screen and a thin device with a simple device configuration.
A rear projection display device 100 includes a light source 1 that directly modulates and emits a laser beam, an optical element 2 that converts the laser beam emitted from the light source 1 into a substantially parallel beam, and a conversion performed by the optical element 2. A scanning unit 3 that scans so that the substantially parallel light beam is incident on the screen 5; and a screen light guide plate 4 that diffracts and reflects the laser beam scanned by the scanning unit 3 and causes the laser beam to enter the screen 5. The screen light guide plate 4 is provided with a reflective holographic optical element 42 that diffracts and reflects the laser beam so that the laser beam is incident on the surface substantially perpendicularly to the screen 5.
[Selection] Figure 1A

Description

  The present invention relates to a rear projection display device that scans light rays and projects an image from the back of a screen.

  In recent years, rear projection display devices have attracted attention as display devices next to liquid crystal television devices and plasma television devices, and have rapidly become popular because they are much cheaper than rear projection plasma television devices. ing.

  The rear projection display device has been shifted from a conventional CRT (Cathode Ray Tube) method to a method using a micro display such as an LCD (Liquid Crystal Display), and is comparable to a display of a liquid crystal television device or a plasma television device. High image quality can be realized.

  In this rear projection type display device, as with other display devices, there is a rapidly increasing need for a larger screen and a thinner device.

  However, the conventional rear projection display device has a problem that the size occupied by the enlargement projection optical system, particularly the size in the depth direction with respect to the screen becomes large.

  In order to solve this problem, for example, Patent Document 1 proposes a technique for reducing the size in the depth direction of the rear projection display device by projecting image light obliquely on a screen. Further, for example, Patent Document 2 includes a projection optical system that projects an image of a panel display surface onto a screen surface, and a planar mirror system that bends an optical path from the projection optical system to the screen surface, and the planar mirror system is at least There is described a technology of a rear projection display device that has two plane reflection surfaces, one of which faces the screen surface and is arranged so as to reflect light twice.

JP-A-5-165095 JP 2001-235799 A

  However, in a conventional rear projection display device designed to achieve a reduction in thickness, for example, image light projected on a screen is distorted or high-temperature heat is generated as the optical system becomes more complex. Many problems have arisen with the thinning of the apparatus.

  The present invention has been proposed in view of such a conventional situation, and an object of the present invention is to provide a rear projection display device that realizes a large screen and a thin device with a simple device configuration. To do.

  In order to achieve the above-described object, the present invention provides a light source that emits a light beam and an optical that converts the light beam emitted from the light source into a substantially parallel light beam in a rear projection display device that projects an image from the back of a screen. An element, scanning means for scanning so that substantially parallel light rays converted by the optical element are incident on the screen, and a light guide plate for diffracting and reflecting the light rays scanned by the scanning means and causing the light rays to enter the screen. The light guide plate is provided with a diffractive optical element that diffracts and reflects the light beam so that the light beam is incident substantially perpendicularly to the screen.

  According to the present invention, a large-screen and thin rear projection display device can be realized with a simple device configuration.

  In addition, according to the present invention, the angle of light incident on the screen can be made substantially vertical at any position on the screen, and the viewing angle characteristics on the screen can be made uniform on the screen screen. Can achieve uniform image quality.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.

  FIG. 1A is a diagram showing an internal configuration of a rear projection display device 100 according to the first embodiment to which the present invention is applied. The rear projection display device 100 includes a light source 1, an optical element 2 including a light beam shaping optical element 21 and a light beam conversion optical element 22, a scanning unit 3, a screen light guide plate 4, and a screen 5. Configured.

  The screen light guide plate 4 is provided with a reflective holographic optical element 42 capable of causing light rays to enter the surface 5 of the plane plate 41 substantially perpendicularly to the screen 5.

  For example, as shown in FIGS. 1A, 1B, and 1C, the reflective holographic optical element 42 causes a laser beam to be incident on the screen 5 substantially perpendicularly at any position in the height direction of the screen light guide plate 4. As described above, when the hologram layer is exposed, for example, the incident angle of the reference light incident on the hologram layer is changed depending on the position of the hologram layer.

  Thereby, in the rear projection display device 100, the laser beam can be incident substantially perpendicularly to the screen 5 at any position in the height direction of the screen light guide plate 4. Details of the reflective holographic optical element 42 will be described later.

  FIG. 2 is a diagram showing a system configuration of the rear projection display device 100. The rear projection type display device 100 inputs various video signals by being connected to a video signal generator 101 such as a video player, a video camera, a video recorder, a broadcast tuner, and the Internet. The rear projection display device 100 includes a video signal processing unit 100A that performs signal processing of the video signal input from the video signal generating device 101, a light source driving unit 100B that drives the light source 1 based on the video signal, and the video And a scanning drive unit 100C that drives the scanning unit 3 based on the signal.

  The light source 1 directly modulates a semiconductor laser to obtain a laser beam that is modulated light. The light source 1 emits a laser beam of a semiconductor laser modulated with an arbitrary divergence angle. In the light source 1, since the divergence angle of the laser beam of the semiconductor laser is different between the horizontal direction and the vertical direction, the cross section of the beam bundle is elliptical.

  The light source 1 may be a gas laser, a solid-state laser, a light emitting diode or the like in addition to the semiconductor laser. Moreover, although the optical element 2 is provided with a cylindrical lens and a convex lens, it is not restricted to these, For example, you may provide a prism.

  The laser beam emitted from the light source 1 is incident on the light beam shaping optical element 21, and the cross section of the light beam is shaped from an ellipse to a circle. The laser beam with the cross section of the light beam shaped is incident on the light beam conversion optical element 22 and converted into a substantially parallel light beam having a diameter of the cross section of the light beam of 1 mm or less. The substantially parallel light beam emitted from the light beam converting optical element 22 is reflected by the scanning unit 3.

  The scanning unit 3 includes a reflecting mirror 31A, a scanning driving unit 31B that scans the reflecting mirror 31A so that the laser beam is incident in the vertical direction of the screen 5, a reflecting mirror 32A, and the laser beam is the horizontal direction of the screen. And a scanning drive unit 32B that scans the reflecting mirror 32A so as to be incident on. Here, the scan driver 31B and the scan driver 32B correspond to the scan driver 100C. Note that the scanning unit 3 may include, for example, a prism or the like instead of the reflecting mirror.

  The screen light guide plate 4 diffracts and reflects the laser beam scanned by the scanning unit 3 and causes the laser beam to enter the upper, lower, left, and right directions of the screen 5.

  An image is displayed on the screen 5 based on the scanning of the laser beam by the scanning unit 3.

  As shown in FIG. 3, the screen light guide plate 4 is configured by providing a reflective holographic optical element 42 as a diffractive optical element that diffracts and reflects a laser beam in an arbitrary direction on the surface of a flat plate 41 made of glass, for example. Is done. In the first embodiment to which the present invention is applied, a Lippmann hologram is used as the reflective holographic optical element 42. The Lippmann hologram is also called a volume hologram, and is a hologram recorded three-dimensionally on a relatively thick and transparent photosensitive material, and is usually produced by making object light and reference light incident from opposite directions. Further, since the Lippmann hologram has a thickness sufficiently larger than the wavelength of light, it has selectivity with respect to the wavelength and angle of incident light when diffracting and reflecting the incident light.

  The reflective holographic optical element 42 is formed by laminating a film layer 42A, a hologram layer 42B, and a film layer 42C in this order.

  The laser beam scanned by the scanning unit 3 enters the reflective holographic optical element 42, and is diffracted and reflected so that only the light beam in a specific wavelength region is incident on the screen 5 by the hologram layer 42B. The Note that the angle at which the light beam enters the screen 5 may not be substantially vertical. In this case, by incorporating a mechanism for adjusting the viewing angle into the screen 5, it is possible to prevent the viewing angle characteristics from being deteriorated.

  The reflective holographic optical element 42 has a thickness of several μm to several tens of μm, but a certain amount of tolerance occurs in the incident angle of the light beam to the reflective holographic optical element 42.

  Generally, the allowable error Δθ of the hologram layer is calculated by the following formula (1).

Δθ = −λ (n ² −sin ² θ) ^1/2 / (tsin θ cos θ) (1)
Here, λ is the wavelength of the incident light beam, t is the thickness of the hologram layer, n is the central refractive index of the hologram layer, and θ is the incident angle to the hologram layer. From Equation (1), Δθ = 8 ° in the case of a reflective holographic optical element.

  In addition, the wavelength tolerance Δλ is calculated by the following equation (2).

Δλ = λ ² / {t (n ± (n ² −sin ² θ))} (2)
In the reflection-type holographic optical element, for example, when λ = 550 nm, t = 10 μm, n = 1.5, and θ = 135 °, Δλ = 11 nm according to the equation (2).

  Generally, when the parameter Q shown in the following formula (3) is a value close to 0, it is regarded as a thin hologram layer, and when it is a value sufficiently larger than 0, it is regarded as a thick hologram layer.

Q = 2πλt / (nΛ ² ) (3)
Here, λ is the wavelength of the incident light beam, t is the thickness of the hologram layer, n is the center refractive index of the hologram layer, and Λ is the interval between the interference fringes formed in the hologram layer. This Λ is calculated by the following formula (4).

Λ = λ / (2sin ((θs−θr) / 2)) (4)
Here, λ is the wavelength of the hologram layer at the time of manufacturing the hologram layer, and θs and θr are the incident angles of the beam bundles at the time of manufacturing the hologram layers s and r, respectively.

  In this way, in a relatively thick hologram layer, a light beam having a wavelength and an incident angle within a certain allowable error range is selectively diffracted, and the other light beam is transmitted without being diffracted. Even light beams emitted from the same light source have different angles of incidence on the reflective holographic optical element 42 and are selectively diffracted by the hologram layer 42B.

  The reflective holographic optical element 42 has a green hologram layer produced by exposure of a SHG laser (second harmonic generation laser) having a wavelength of 532 nm. Thereby, in the rear projection display device 100, the image displayed on the screen 5 is displayed in a single green color.

  Since the reflection type hologram optical element 42 has selectivity at the diffraction wavelength, it is desirable that the spectrum of the laser beam emitted from the light source 1 matches the diffraction wavelength of the reflection type holographic optical element 42.

  In the rear projection display device 100, an image displayed on the screen 5 can be displayed by using a reflection type holographic optical element having a hologram layer produced by exposure of a laser of another color and a laser of another color. Can be displayed in other colors.

  In the rear projection display device 100 according to the first embodiment to which the present invention having the above-described configuration is applied, the depth distance behind the screen can be greatly reduced as compared with the conventional rear projection display device. Become.

  Further, in the rear projection display device 100 according to the first embodiment to which the present invention is applied, since various lasers or light emitting diodes are used as the light source 1, it is possible to reproduce extremely high purity colors even on a large screen. it can.

  Further, in the rear projection display device 100 according to the first embodiment to which the present invention is applied, by using various lasers or light emitting diodes for the light source 1, the spot diameter is reduced in the beam bundle section of the emitted light beam ( Spot size = 1 pixel size), and is displayed as one pixel on the screen 5 without using Newton's imaging relationship, so it is clearer than a plasma display, a liquid crystal display, or a conventional projector displaying fixed pixels. The video can be displayed on the large screen 5.

  In addition, the rear projection display device 100 according to the first embodiment to which the present invention is applied uses a reflective holographic optical element for the screen light guide plate 4 so that the angle of the light beam incident on the screen 5 is changed to the screen 5. The viewing angle characteristics of the screen 5 can be made uniform on the screen screen. As a result, the rear projection display device 100 can achieve uniform image quality at any position on the screen 5.

  In the rear projection display device 100 according to the first embodiment to which the present invention is applied, the image displayed on the screen 5 is monochromatic.

  Therefore, as a second embodiment to which the present invention is applied, a rear projection display device capable of displaying an image on the screen 5 in full color is applied.

  The rear projection display device according to the second embodiment to which the present invention is applied has a screen provided with a reflective holographic optical element 421 having a hologram layer 421B that is multiple-exposed with RGB three-color lasers as shown in FIG. By using the light guide plate 40 and a laser light source that emits a laser beam including an RGB spectrum, a full color display of an image on the screen 5 is possible. In addition, about the structure similar to the screen light-guide plate 4 shown in FIG. 3, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted.

  FIG. 5 is a view showing the exposure apparatus 10 for performing multiple exposure of the hologram layer 421B in the reflective holographic optical element 421. As shown in FIG.

  In the exposure apparatus 10, a red laser emitted from a red laser (Kr laser, wavelength 647 n) light source 111 is divided by a variable beam splitter 114, one of which is reflected by a dichroic mirror 115 and a mirror 116, and passes through a modulation element 117 to be a hologram. One surface of the layer 421B is irradiated as reference light. The red laser beam is reflected by the mirror 118, the dichroic mirror 119, and the mirror 120, and is irradiated as object light on the other surface of the hologram layer 421B through the modulation element 121 and the aspherical non-rotationally symmetric wavefront generating optical system 122. .

  The green laser emitted from the green laser (SHG laser, wavelength 532 nm) light source 112 is reflected by the mirror 123 and divided by the variable beam splitter 124, one of which passes through the dichroic mirror 125 and the dichroic mirror 115 and is reflected by the mirror 116. Then, it passes through the modulation element 117 and is irradiated as a reference light to one surface of the hologram layer 421B. Further, the green laser is reflected by the mirror 126, passes through the dichroic mirror 127 and the dichroic mirror 119, is reflected by the mirror 120, passes through the modulation element 121 and the aspherical non-rotationally symmetric wavefront generating optical system 122, and is added to the hologram layer 421B. One surface is irradiated as object light.

  The blue laser emitted from the blue laser (Ar laser, wavelength 477 nm) light source 113 is divided by the variable beam splitter 128, one of which is reflected by the mirror 129 and the dichroic mirror 125, passes through the dichroic mirror 115, and is reflected by the mirror 116. Then, it passes through the modulation element 117 and is irradiated as a reference light to one surface of the hologram layer 421B. The blue laser beam is reflected by the dichroic mirror 127, transmitted through the dichroic mirror 119, reflected by the mirror 120, passes through the modulation element 121 and the aspherical non-rotationally symmetric wavefront generating optical system 122, and the other surface of the hologram layer 421B. Is irradiated as object light.

  Note that the exposure apparatus 10 may use a spherical non-rotationally symmetric wavefront generating optical system instead of the aspherical non-rotationally symmetric wavefront generating optical system 122.

  In the rear projection display device according to the second embodiment to which the present invention is applied, the hologram layer subjected to multiple exposure by the exposure device 10 is projected onto the screen 5 by irradiating a laser beam including RGB spectrum as reference light. Full color display of video is possible.

  However, in the rear projection display device according to the second embodiment to which the present invention is applied, the diffraction efficiency of each of the RGB three-color lasers in the hologram layer is lower than that in the case where the hologram layer is subjected to monochromatic exposure.

  Therefore, as a third embodiment to which the present invention is applied, a rear projection display in which an image can be displayed in full color on the screen 5 without reducing the diffraction efficiency of each of the RGB three-color lasers in the hologram layer. Apply the device.

  In the rear projection display apparatus according to the third embodiment to which the present invention is applied, a reflection type hologram having a dedicated hologram layer for each of RGB in order to maintain the diffraction efficiency of each of the RGB three-color lasers as shown in FIG. The graphic optical element 52 is used as a screen light guide plate.

  FIG. 7 is a diagram illustrating an example of the configuration of the reflective holographic optical element 52.

  As shown in FIG. 7, the reflective holographic optical element 52 includes a base film 52A, a green hologram layer 52B, a barrier layer 52C, a blue hologram layer 52D, a barrier layer 52E, a red hologram layer 52F, a barrier layer 52G, The adhesive layer 52H and the cover film 52I are formed by being laminated in this order. In this way, the reflective holographic optical element 52 has the red hologram layer having a relatively low diffraction efficiency disposed in the uppermost layer and the green hologram layer having a relatively large diffraction efficiency disposed in the lowermost layer. Features.

  The reflective holographic optical element 52 is irradiated with reproduction light from the cover film 52I side.

  The base film 52A and the cover film 52I are made of, for example, polyethylene terephthalate. The base film 52A and the cover film 52I only have to have a thickness of about several tens of μm. In the present embodiment, for example, the base film 52A has a thickness of 50 μm, and the cover film 52I has a thickness of 25 μm. To do. Note that an antireflection layer (AR coating) may be formed on the cover film 52I.

  Each of the green hologram layer 52B, the blue hologram layer 52D, and the red hologram layer 52F is composed of a photopolymer containing a sensitizing dye, a reaction initiator, a chain transfer agent, a monomer, a polymer binder, and the like. . The green hologram layer 52B, the blue hologram layer 52D, and the red hologram layer 52F only have to have a thickness of about several μm to several tens of μm. In this embodiment, for example, the green hologram layer Each of 52B, blue hologram layer 52D, and red hologram layer 52F is 15 μm.

  The green hologram layer 52B contains a sensitizing dye, a reaction initiator and the like so as to have sufficient sensitivity only in a wavelength band of about 500 to 550 nm, and the blue hologram layer 52D has a wavelength of about 400 to 480 nm. A sensitizing dye, a reaction initiator, and the like are contained so as to have sufficient sensitivity only in the band, and the red hologram layer 52F has a sufficient sensitivity only in a wavelength band of about 600 to 700 nm. Contains a reaction initiator and the like.

  Therefore, for example, when the reflective holographic optical element 52 is exposed with an Ar gas laser having a wavelength of 477 nm, only the blue hologram layer 52D is exposed, and the green hologram layer 52B and the red hologram layer 52F are not exposed. For example, when the reflective holographic optical element 52 is exposed with the second harmonic of a YAG laser having a wavelength of 532 nm, only the green hologram layer 52B is exposed, and the blue hologram layer 52D and the red hologram layer 52F are Not sensitive. For example, when the reflective holographic optical element 52 is exposed with a Kr gas laser having a wavelength of 647 nm, only the red hologram layer 52F is exposed, and the green hologram layer 52B and the blue hologram layer 52D are not exposed.

  In the rear projection type display device according to the third embodiment to which the present invention is applied, the green hologram layer 52B and the blue color are respectively used in any of the exposure methods such as red, green and blue multi-wavelength simultaneous exposure and multi-wavelength sequential exposure. Since green, blue and red interference fringes are recorded on the hologram layer 52D for red and the hologram layer 52F for red, respectively, a color hologram having a high diffraction efficiency can be produced while being a single film.

  In this reflection type holographic optical element 52, the hologram layer is laminated in the order of the green hologram layer 52B, the blue hologram layer 52D, and the red hologram layer 52F, which has high visibility and diffraction efficiency. This is because the high green hologram layer 52B is positioned farthest from the reproduction light irradiation direction, and the red hologram layer 52F having low visibility and low diffraction efficiency is positioned closest to the reproduction light irradiation direction. In the reflective holographic optical element 52, a hologram layer is laminated in the order of a green hologram layer 52B, a blue hologram layer 52D, and a red hologram layer 52F, whereby a color hologram in which the visibility and diffraction efficiency of each color are balanced is achieved. It becomes possible.

  In the rear projection display device according to the third embodiment to which the present invention is applied, a reflective holographic optical element that is irradiated with reproduction light from the base film side may be applied.

  FIG. 8 is a diagram showing an example of the configuration of the reflective holographic optical element 521 irradiated with reproduction light from the base film side.

  The reflective holographic optical element 521 includes a base film 521A, a red hologram layer 521B, a barrier layer 521C, a blue hologram layer 521D, a barrier layer 521E, a green hologram layer 521F, a barrier layer 521G, an adhesive layer 521H, and a cover film 521I. Are formed by stacking in this order.

  In the reflective holographic optical element 521, it is preferable that an antireflection layer (AR coating) is formed on the base film 521A.

  The barrier layers in the reflection-type holographic optical elements 52 and 521 are both for suppressing the movement of photopolymer molecules between hologram layers, and the thickness thereof is thinner than the thickness of each color hologram layer. The thickness is about 5 μm. When the photopolymer molecule moves between the hologram layers for each color, the refractive index modulation is lowered and high diffraction efficiency cannot be obtained. In the reflection type holographic optical elements 52 and 521, by providing such a barrier layer between the hologram layers for each color, the movement of the photopolymer molecules can be suppressed and high diffraction efficiency can be obtained.

  It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

  For example, in the above-described embodiment, the screen light guide plate 4 is configured by providing the reflective holographic optical element 42 on the surface of the flat plate 41 made of glass, for example. As another embodiment, for example, as shown in FIG. 9A, a transmission type hologram layer 62A as shown in FIG. 9B is provided on the surface of a flat reflecting mirror 61. The transmission type holographic optical element 62 may be provided. In the transmissive holographic optical element 62, the laser beam diffracted by the hologram layer 62A is reflected by the reflecting mirror 61 and incident again on the transmissive holographic optical element 62, and then passes through the holographic optical element 62. Is incident on the screen 5.

  Further, for example, in the above-described embodiment, the light source 1 directly modulates and emits the semiconductor laser, but as another embodiment, a modulation element that modulates a laser beam emitted from an unmodulated light source May be further provided. This modulation element may be provided between the light source 1 and the optical element 2 so as to supply a modulated laser beam to the optical element 2, whether inside or outside the optical element 2. It may be arranged at any position.

  Further, for example, as an embodiment different from the above-described embodiment, as shown in FIG. 10, a transmissive holographic optical element manufactured by multiple exposure of a hologram layer 72A on the surface of a reflecting mirror 61, as shown in FIG. 72 may be provided so that the laser beam is diffracted in a plurality of wavelength bands. Here, it is assumed that the transmission type holographic optical element 72 performs multiple exposure of the hologram layer 72A by the same method as described in the second embodiment.

  Further, for example, as an embodiment different from the above-described embodiment, as shown in FIG. 11, each of RGB is dedicated on the surface of the reflecting mirror 61 in order to maintain the diffraction efficiency of each of the RGB lasers. A transmissive holographic optical element 82 having a hologram layer of the above may be used.

  Further, for example, in the above-described embodiment, the screen light guide plate is provided with the holographic optical element on the surface of the flat substrate or the flat reflecting mirror, but the substrate or reflecting mirror provided with the holographic optical element is used. The shape is not limited to a flat surface, and may be any shape such as a concave toric curved surface, a concave spherical surface, or a concave free curved surface with respect to the screen 5.

  Further, for example, in the above-described embodiment, the optical path including the light source 1 and the optical element 2 is arranged in the depth direction behind the screen 5 as shown in FIG. 1, for example. You may make it bend | fold the optical path provided with the light source 1 and the optical element 2 in the paper surface perpendicular direction. Thereby, the depth distance behind the screen 5 is further shortened.

It is a figure which shows the internal structure of the rear projection type display apparatus in 1st Embodiment to which this invention is applied. It is a figure which shows the internal structure of the rear projection type display apparatus in 1st Embodiment to which this invention is applied. It is a figure which shows the internal structure of the rear projection type display apparatus in 1st Embodiment to which this invention is applied. It is a figure which shows the system configuration | structure of the rear projection type display apparatus in 1st Embodiment to which this invention is applied. It is a figure which shows the structure of the screen light-guide plate with which the rear projection type display apparatus in 1st Embodiment to which this invention was applied was equipped. It is a figure which shows the structure of the screen light-guide plate with which the rear projection type display apparatus in 2nd Embodiment to which this invention was applied was equipped. It is a figure which shows the exposure apparatus for carrying out multiple exposure of the hologram layer in a reflection type holographic optical element. It is a figure which shows the structure of the screen light-guide plate with which the rear projection type display apparatus in 3rd Embodiment to which this invention was applied was equipped. It is a figure which shows an example of a structure of a reflection type holographic optical element. It is a figure which shows an example of a structure of a reflection type holographic optical element. (A) is a figure which shows the structure of the screen light-guide plate with which the rear projection type display apparatus in another embodiment to which this invention is applied was equipped, (B) is provided in the screen light-guide plate of (A). It is a figure which shows the structure of the obtained transmission type holographic optical element. It is a figure which shows the structure of the screen light-guide plate with which the rear projection type display apparatus in another embodiment to which this invention is applied was equipped. It is a figure which shows the structure of the screen light-guide plate with which the rear projection type display apparatus in another embodiment to which this invention is applied was equipped.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Light source, 2 Optical element, 3 Scan part, 4 Screen light-guide plate, 5 Screen, 21 Light beam shaping optical element, 22 Light beam conversion optical element, 41 Plane version, 42 Reflective holographic optical element

Claims (14)

In a rear projection display device that projects images from the back of the screen,
A light source that emits light rays;
An optical element that converts light emitted from the light source into substantially parallel light;
Scanning means for scanning so that substantially parallel light rays converted by the optical element are incident on the screen;
A light guide plate that diffracts and reflects the light beam scanned by the scanning means and causes the light beam to enter the screen, and
The rear projection display device, wherein the light guide plate is provided with a diffractive optical element that diffracts and reflects the light beam so that the light beam is incident on the surface substantially perpendicularly to the screen.   2. The rear projection display device according to claim 1, wherein the diffractive optical element is a reflective holographic optical element.   3. The rear projection display device according to claim 2, wherein the reflective holographic optical element has a hologram layer produced by multiple exposure with light beams having different wavelengths.   3. The rear projection display device according to claim 2, wherein the reflective holographic optical element has a plurality of hologram layers produced by exposure with light beams having different wavelengths.   2. The rear projection display device according to claim 1, wherein the light source emits light after directly modulating light.   The rear projection display device according to claim 1, further comprising a modulation element that modulates a light beam emitted from the light source.   2. The rear projection display device according to claim 1, wherein a distance from the upper end of the light guide plate to the screen is shorter than a distance from the lower end of the light guide plate to the screen.   2. The rear projection display device according to claim 1, wherein the light guide plate has a flat shape.   2. The rear projection display device according to claim 1, wherein the light guide plate has a concave toric curved surface with respect to the screen.   2. The rear projection display device according to claim 1, wherein the light guide plate has a concave spherical shape with respect to the screen.   2. The rear projection display device according to claim 1, wherein the light guide plate has a concave free-form surface with respect to the screen.   2. The rear projection display device according to claim 1, wherein the light source is a semiconductor laser.   2. The rear projection display device according to claim 1, wherein the light source is a light emitting diode.   2. The rear projection display device according to claim 1, wherein the scanning unit has a reflective surface and drives the reflective surface so as to scan the substantially parallel light beams in the vertical and horizontal directions of the screen.

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