JP2010072151A - Video display apparatus and head mount display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To uniformly illuminate an LCD 13 by suppressing occurrence of aberration while achieving size and weight reduction of apparatus, and to provide a wider angle of field for observation. <P>SOLUTION: Light from a light source 11 is guided to a transmission type LCD 13 via an illuminating optical system 12. Since the LCD 13 is a transmission type, the optical power of an observing optical system is increased by shortening the lens back of the observing optical system. This enables the wider angle of view for observation. Since an optical path from the light source 11 to the LCD 13 is bent by reflecting twice two reflection faces (illuminating mirrors 31 and 32) of the illuminating optical system 12, the illuminating optical system 12 is constituted compactly, and the apparatus is reduced in size and weight. While the incident angle of light-source light to the first reflecting face is decreased, optical power is imparted to the illuminating optical system 12, and occurrence of aberration is suppressed. The LCD 13 is uniformly illuminated thereby. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image display device that provides an observer with an image displayed on a display element as a virtual image, and a head mounted display (hereinafter also referred to as an HMD) including the image display device.

  Conventionally, as display devices that allow an observer to observe a virtual image of an image displayed on a display element (for example, LCD), there are those disclosed in Patent Documents 1 and 2, for example. The display device (view finder) of Patent Document 1 guides light emitted from a light source to an LCD via an illumination optical system including a mirror and a lens, and transmits image light from the LCD to an observer's pupil via an magnifying lens. It is configured to lead to. Further, the display device (observation optical system) of Patent Document 2 reflects light from a light source twice by an illumination prism and guides it to a reflective LCD, and transmits image light from the LCD to the observation optical system (eyepiece prism). Through the observer's pupil.

JP-A-5-95499 JP 2001-33729 A

  However, as in Patent Document 1, if the reflection by the illumination optical system is only one time by the mirror, the optical path of the light incident on the LCD cannot be folded compactly while ensuring a long optical path. Cause trouble. In addition, when the reflection by the mirror is performed only once, aberrations are generated and unevenness in the intensity of the illumination light of the LCD is likely to occur. However, since the lens of the illumination optical system is a transmissive optical element, it has optical power. However, it is difficult to correct aberrations well, and the LCD cannot be illuminated uniformly.

  Further, in a configuration in which a reflective LCD is used and an illumination prism is disposed between the LCD and the observation optical system as in Patent Document 2, the LCD is disposed away from the observation optical system. It is necessary to ensure a large lens back of the observation optical system. For this reason, the optical power of the observation optical system cannot be increased, and the observation field angle when observing the image at the optical pupil position cannot be widened.

  The present invention has been made to solve the above-mentioned problems, and its object is to uniformly illuminate the LCD while suppressing the occurrence of aberrations while reducing the size and weight of the apparatus. Another object of the present invention is to provide a video display device capable of realizing a wide observation angle of view and a head-mounted display using the video display device.

  An image display device according to the present invention includes a light source, a display element that modulates incident light to display an image, an illumination optical system that guides light from the light source to the display element, and guides image light from the display element to an optical pupil. An image display apparatus including an observation optical system, wherein the display element is a transmission type, and the illumination optical system includes two reflecting surfaces that reflect light from a light source twice and guide the display element to the display element. And having positive optical power.

  According to said structure, the light from a light source is guide | induced to a display element via an illumination optical system. The light incident on the display element is modulated there and emitted as image light, and is guided to the optical pupil via the observation optical system. Therefore, at the position of the optical pupil, the observer can observe the virtual image of the image displayed on the display element.

  Here, since the display element is a transmission type, the lens back of the observation optical system is shortened, and the display element is arranged near the observation optical system (near the surface on which the image light from the display element is incident). Can be adopted. Thereby, the optical power of the observation optical system can be increased, and the observation angle of view can be widened.

  The light from the light source is guided to the display element by being reflected twice by the two reflecting surfaces of the illumination optical system. Thus, the optical path from the light source to the display element can be secured long, and the optical path can be folded in a compact manner, and the illumination optical system can be made compact to reduce the size and weight of the apparatus. Furthermore, it is possible to give the illumination optical system optical power while reducing the incident angle of the light source light to the first reflection surface as compared with the case where the illumination optical system has one reflection surface. As a result, the occurrence of aberration can be suppressed and the display element can be illuminated uniformly.

  Moreover, since the illumination optical system has a positive optical power as a whole, it can illuminate the display element by collecting the light from the light source, and allows the observer to observe a bright image. .

  In the video display device of the present invention, the two reflecting surfaces of the illumination optical system are sequentially reflected by the light path from the light source toward the first reflecting surface and the first and second reflecting surfaces. It is desirable that the second light-reflecting surface and the optical path of light traveling toward the display element intersect with each other.

  In this case, the illumination optical system can be reliably configured compactly. In addition, the illumination optical system can be provided with optical power while reliably reducing the incident angle of the light source light on the first reflecting surface, suppressing the occurrence of aberrations and uniformly illuminating the display element. You can definitely get it.

  In the video display device of the present invention, it is desirable that the illumination optical system is hollow. In this case, the illumination optical system is lighter than a configuration having a prism, for example. Further, since there is no internal reflection as occurs in the prism, unnecessary light is not generated and flare does not occur.

  In the video display device of the present invention, the positive optical power of the illumination optical system may be generated by reflection. Since chromatic aberration does not occur in reflection, it is possible to obtain a good optical performance by giving a large positive optical power to the illumination optical system (a display element can be illuminated brightly and uniformly).

  In the image display device of the present invention, the optical pupil formed by the observation optical system is formed smaller in one direction than the other in two directions orthogonal to each other. A configuration in which the light is reflected once and condensed in the other direction may be used.

  In this configuration, the optical pupil is formed smaller in the other direction than in one direction, and the light flux (width) incident on the optical pupil is smaller in the other direction than in the one direction. Since the illumination optical system reflects incident light twice and condenses it in the other direction, that is, in the direction with a small luminous flux (width), it is possible to make the apparatus more compact and allow a viewer to observe a bright image. it can.

  In the video display device of the present invention, the light source and the optical pupil are arranged in a conjugate manner in the other direction, and the video display device diffuses light from the light source in the one direction. The structure which has further may be sufficient.

  Since the light source and the optical pupil are arranged in a conjugate manner in the other direction in which the optical pupil is smaller, the light use efficiency from the light source is high in the other direction, and a bright image can be observed by the observer. In addition, since the light from the light source is diffused in one direction by the one-way diffusion plate, the observer can easily observe the image in one direction where the optical pupil is large.

  In the video display device of the present invention, the light source includes a pair of light emitting diodes that emit light of each color of red, green, and blue, and optically connects the center of the display area of the display element and the center of the optical pupil. When the axis is an optical axis, the pair of light emitting diodes are arranged side by side in the diffusion direction of the unidirectional diffusion plate, and are arranged symmetrically with respect to the plane including the optical axis of the observation optical system. It may be.

  Since each RGB LED is arranged side by side in the diffusing direction of the unidirectional diffuser plate (the one direction of the optical pupil), it is possible to prevent color unevenness from being observed by mixing the colors in the one direction where the optical pupil is large. Can do. The pair of RGB LEDs are arranged symmetrically with respect to the plane including the optical axis of the observation optical system, so that the centers of gravity of the light intensities of the respective colors coincide on the symmetry plane. Thereby, an image with little color unevenness at the center of the optical pupil can be provided to the observer as a high-quality image with little aberration.

  In the video display device of the present invention, the illumination optical system includes a diffusion plate that diffuses light from the light source by unevenness on the surface, and the diffusion plate includes a first reflection surface from the light source side. It may be arranged in the optical path between the second reflection surface, and the second reflection surface from the light source side may have a positive optical power.

  By disposing the diffusion plate in the optical path between the first reflection surface and the second reflection surface, the diffusion plate is disposed at a position far from both the light source and the display element. By disposing the diffusion plate at a position far from the light source, the display element can be illuminated with uniform light with reduced luminance unevenness. In addition, when the light source is composed of, for example, LEDs that emit light of each color of RGB, color mixing at the diffusion plate is good, and color unevenness can be reduced. On the other hand, the diffusion plate is arranged at a position far from the display element, and the second reflecting surface has optical power, so that a virtual image generated by the unevenness of the diffusion plate is difficult to be observed simultaneously with the virtual image of the image, It is possible to observe high-quality images.

  In the video display device of the present invention, the observation optical system includes a volume phase type reflection hologram optical element, and an optical axis is an axis that optically connects the center of the display area of the display element and the center of the optical pupil. Then, the hologram optical element diffracts and reflects image light incident obliquely from the display element and guides it to the optical pupil, and the optical axis incident surface of the hologram optical element is parallel to the other direction of the optical pupil. It may be.

  The optical axis incident surface of the hologram optical element refers to a plane including the optical axis of incident light and the optical axis of outgoing light with respect to the hologram optical element. In the direction parallel to the optical axis incident surface, the wavelength selectivity of the hologram optical element is large (the diffraction wavelength shift due to the incident angle shift is large), and color unevenness is likely to occur. However, by making the optical axis incident surface parallel to the other direction in which the optical pupil is small (the direction in which the light flux width is small), the range of change of the diffraction wavelength in that direction can be narrowed, and color unevenness in that direction Can be reduced.

  In the video display device of the present invention, the hologram optical element may be a combiner that simultaneously guides the video light from the display element and the light from the outside to the observer's pupil.

  In this case, the observer can observe the display image of the display element and the external image simultaneously through the hologram optical element. In addition, the volume phase type reflection type hologram optical element has a narrow half-value wavelength width of diffraction efficiency, so it has a high external light transmittance and a bright external image can be observed. The image can be observed with high visibility.

  In the video display device of the present invention, the light source is composed of a light emitting diode, and it is desirable that the peak wavelength of diffraction efficiency of the hologram optical element and the intensity peak wavelength of the light emitting diode substantially coincide. In this case, the light from the LED can be efficiently diffracted by the hologram optical element, and the observer can observe a brighter image that is easy to see even when superimposed on the external image.

  In the video display device of the present invention, the observation optical system first reflects the video light from the display element to the observer's pupil while transmitting the external light to the observer's pupil. The structure which has a transparent substrate may be sufficient.

  By using such a first transparent substrate, the display image of the display element can be observed, but the transmittance of external light is increased, so that a bright external image can be observed in a wide viewing range. In addition, the first transparent substrate can be thinned to reduce the size and weight of the device.

  In the video display device of the present invention, it is desirable that the observation optical system has a second transparent substrate for canceling refraction of external light on the first transparent substrate. In this case, distortion can be prevented from occurring in the external image observed by the observer through the observation optical system. In addition, a bright external image can be observed in a wider viewing range via the observation optical system.

  The head-mounted display of the present invention includes the above-described video display device of the present invention and support means for supporting the video display device in front of an observer's eyes. In this configuration, since the video display device is supported by the support means, the observer can observe the video provided from the video display device in a hands-free manner. In addition, since the video display device is small and light, the observer can comfortably wear the HMD, and further, it is possible to observe the outside image with see-through without burden even when the HMD is always worn.

  According to the present invention, since the transmissive display element is used, the lens back of the observation optical system can be shortened to increase its optical power, and the observation angle of view can be widened. In addition, since the illumination optical system bends the optical path from the light source to the display element by means of two reflecting surfaces, the illumination optical system can be made compact to reduce the size and weight of the device and suppress the occurrence of aberrations. The element can be illuminated uniformly. Furthermore, since the illumination optical system has a positive optical power as a whole, the light from the light source can be condensed to illuminate the display element, and a bright image can be observed by the observer.

[Embodiment 1]
An embodiment of the present invention will be described below with reference to the drawings.

(1. Configuration of HMD)
2A is a plan view showing a schematic configuration of the HMD according to the present embodiment, FIG. 2B is a side view of the HMD, and FIG. 2C is a front view of the HMD. is there. The HMD has two video display devices 1 and 1 and support means 2 for supporting them, and as a whole has an appearance like general glasses.

  The video display devices 1 and 1 allow an observer to observe an external image in a see-through manner, display an image, and provide the image as a virtual image to the observer, corresponding to the right and left eyes of the observer. Is provided. In the video display devices 1 and 1, portions corresponding to the right eye lens and the left eye lens of the glasses are configured by bonding an eyepiece prism 21 and a deflection prism 22 (both see FIG. 3), which will be described later. The detailed configuration of the video display devices 1 and 1 will be described later.

  The support means 2 supports the video display devices 1 and 1 in front of the right and left eyes of the observer, and includes a bridge 3, a frame 4, a temple 5, a nose pad 6, a cable 7, and the like. And a translucent plate 8. The nose pad 6 and the translucent plate 8 are supported by the bridge 3. The frame 4, the temple 5 and the nose pad 6 are provided as a pair on the left and right sides, and are respectively composed of a right frame 4R, a left frame 4L, a right temple 5R, a left temple 5L, a right nose pad 6R, and a left nose pad 6L. .

  The bridge 3 connects the left and right video display devices 1. The right temple 5R is rotatably supported by the right frame 4R, and is connected to the video display device 1 for the right eye (on the side opposite to the connection side to the bridge 3) via the right frame 4R. Yes. Similarly, the left temple 5L is rotatably supported by the left frame 4L, and the left-eye image display device 1 is connected to the left frame 4L (on the side opposite to the connection side to the bridge 3). It is connected.

  The cable 7 is a wiring for supplying an external signal (for example, a video signal, a control signal) and power to the video display devices 1 and 1 in parallel, and is provided along the right temple 5R, the right frame 4R, and the bridge 3. Yes. The translucent plate 8 is an external light transmittance control means for controlling the transmittance of external light (light of an external image), and is located in front of the image display devices 1 and 1 (on the side opposite to the observer). Yes. The translucent plate 8 may be provided as necessary.

  When the observer uses the HMD, the right temple 5R and the left temple 5L are brought into contact with the right and left heads of the observer, and the nose pad 6 is put on the nose of the observer so as to wear general glasses. The HMD is attached to the observer's head. In this state, when the video is displayed on the video display devices 1 and 1, the observer can observe each display video on the video display devices 1 and 1 as a virtual image with the right eye and the left eye, respectively. -An external image can be observed through 1 through see-through.

  At this time, if the external light transmittance is set to be low, for example, 50% or less in the semi-transparent plate 8, it becomes easier for the observer to observe the display image of the video display device 1, 1, and conversely, the external light transmission. If the rate is set as high as, for example, 50% or more, the observer can easily observe the external image. Therefore, the external light transmittance of the translucent plate 8 may be set as appropriate in consideration of ease of observation and balance of the display image and the external image of the image display device 1.

  In the present embodiment, the HMD includes the two video display devices 1. 1. However, the HMD may include only one video display device 1. In this case, the video display device 1 is arranged in front of the right or left eye of the observer so that the display video is viewed with one eye.

(2. Configuration of video display device)
Next, a detailed configuration of the video display device 1 • 1 will be described. Since the left and right video display apparatuses 1 and 1 have the same configuration, the configuration of one video display apparatus 1 will be described below.

  FIG. 3 is a cross-sectional view illustrating a schematic configuration of the video display device 1. The video display device 1 includes a light source 11, an illumination optical system 12, an LCD 13, and an observation optical system 14.

  Here, for convenience of explanation below, directions are defined as follows. First, an axis that optically connects the center of the display area (screen) of the LCD 13 and the center of the optical pupil E formed by the observation optical system 14 is an optical axis. The optical axis direction when the optical path from the light source 11 to the optical pupil E is developed is taken as the Z direction. In addition, a direction perpendicular to an optical axis incident surface of a hologram optical element 23 (to be described later) of the observation optical system 14 is defined as an X direction, and a direction perpendicular to the ZX plane is defined as a Y direction. The optical axis incident surface of the hologram optical element 23 refers to a plane including the optical axis of incident light and the optical axis of reflected light in the hologram optical element 23, that is, the YZ plane. In addition, the observation optical system 14 of the present embodiment is formed symmetrically with respect to the plane including the optical axis, and the optical axis incident surface of the hologram optical element 23 is also a symmetrical plane of the observation optical system 14. Yes.

  Further, the X, Y, and Z directions shown in FIG. 3 roughly indicate directions in the vicinity of the display surface of the LCD 13, and are similarly illustrated in other drawings. In addition, in each of the X, Y, and Z directions, it does not matter whether it is positive or negative.

  The light source 11 includes a plurality of light emitting diodes (LEDs) that emit a plurality of lights having different wavelengths. More specifically, the light source 11 emits light corresponding to the three primary colors, that is, light corresponding to each color of R (red), G (green), and B (blue). The illumination optical system 12 is an optical system that guides the light emitted from the light source 11 to the LCD 13.

  The LCD 13 is a transmissive display element that has a plurality of pixels in a matrix, modulates light incident from the light source 11 via the illumination optical system 12 for each pixel according to image data, and displays an image. In this embodiment, an RGB color filter (wavelength limiting filter) is provided for each pixel.

  The observation optical system 14 is an eyepiece optical system that guides the image light emitted from the LCD 13 to the optical pupil E, and has positive optical power that is axially asymmetric (rotationally asymmetric, non-axisymmetric). The observation optical system 14 includes an eyepiece prism 21, a deflection prism 22, and a hologram optical element 23.

  The eyepiece prism 21 totally reflects the incident light, that is, the image light from the LCD 13, travels in the direction of the hologram optical element 23, guides it to the observer's pupil through the hologram optical element 23, and transmits external light. The first transparent substrate that leads to the observer's pupil is made of, for example, an acrylic resin together with the deflecting prism 22. The eyepiece prism 21 is formed in a shape in which the lower end portion of the parallel plate is thinned into a wedge shape and the upper end portion is thickened. Further, the eyepiece prism 21 is bonded to the deflection prism 22 with an adhesive so as to sandwich the hologram optical element 23 disposed at the lower end portion thereof.

  The deflection prism 22 is configured by a substantially U-shaped parallel plate in plan view, and is integrated with the eyepiece prism 21 when bonded to the lower end portion and both side surface portions (left and right end surfaces) of the eyepiece prism 21. This is a second transparent substrate that is a substantially parallel plate. By joining the deflecting prism 22 to the eyepiece prism 21, it is possible to prevent distortion of the external image observed by the observer through the observation optical system 14.

  That is, for example, when the deflection prism 22 is not joined to the eyepiece prism 21, the light of the external field image is refracted when passing through the wedge-shaped lower end of the eyepiece prism 21, so that the external field image observed through the eyepiece prism 21 Distortion occurs. However, the deflecting prism 22 is joined to the eyepiece prism 21 to form an integral substantially parallel plate, so that the refraction when the light of the external image is transmitted through the wedge-shaped lower end of the eyepiece prism 21 is canceled by the deflecting prism 22. can do. As a result, it is possible to prevent distortion in the external image observed through the see-through.

  The hologram optical element 23 is a volume phase type reflection hologram that diffracts and reflects image light (light having a wavelength corresponding to three primary colors) incident obliquely from the LCD 13 and guides it to the optical pupil E. The hologram optical element 23 has positive optical power that is optically axisymmetric and has the same function as an aspherical concave mirror. Thereby, the degree of freedom of arrangement of each optical member constituting the apparatus can be increased, and the apparatus can be easily reduced in size, and an image with good aberration correction can be provided to the observer.

Next, the operation of the video display device 1 will be described.
Each color light of RGB emitted from the light source 11 enters the LCD 13 through the illumination optical system 12, where it is modulated for each pixel in accordance with the image data and emitted as video light. This image light enters the eyepiece prism 21 of the observation optical system 14 through the surface 21a. The incident video light is totally reflected a plurality of times by two opposing planes (surfaces 21b and 21c) of the eyepiece prism 21, and is guided to the hologram optical element 23 disposed at the lower end of the eyepiece prism 21, where it is reflected and optically received. Guided to pupil E. Therefore, at the position of the optical pupil E, the observer can observe the enlarged virtual image of the color image displayed on the LCD 13.

  On the other hand, the eyepiece prism 21, the deflecting prism 22, and the hologram optical element 23 transmit almost all the light from the outside, so that the observer can observe the outside world image with see-through. The virtual image of the image displayed on the LCD 13 is observed while being overlapped with a part of the external image.

  Thus, in the video display device 1 of the present embodiment, the hologram optical element 23 of the observation optical system 14 is used as a combiner that guides the image light from the LCD and the external light simultaneously to the observer's pupil. The observer can simultaneously observe the image provided from the LCD and the external image via the hologram optical element 23.

  In addition, since the image light is reflected in the eyepiece prism 21 and guided to the eye, the eyepiece prism 21 can be made thin (for example, about 3 mm) as much as a normal spectacle lens, and it is small and light. . Further, since the reflection in the eyepiece prism 21 is total reflection, the observer can observe the external image through the surfaces 21b and 21c of the eyepiece prism 21 without reducing the transmittance of outside light.

  Further, since the deflection prism 22 cancels the refraction of external light at the wedge portion of the eyepiece prism 21, the observer observes the external light through the eyepiece prism 21, the deflection prism 22 and the hologram optical element 23 without distortion. Can do.

  Since the LCD 13 to be used is a transmission type, the lens back of the observation optical system 14 is shortened, and the LCD 13 is disposed in the vicinity of the observation optical system 14, that is, in the vicinity of the surface 21a on which the image light from the LCD 13 is incident. Can do. Thereby, the optical power of the observation optical system 14 can be increased, and the observation angle of view can be widened.

  In the present embodiment, in the eyepiece prism 21 and the deflecting prism 22, the two surfaces that face each other and transmit external light are parallel planes. 14 can also have a function as a correction spectacle lens.

(3. Characteristics of light source and hologram optical element)
Next, the characteristics of the light source 11 and the hologram optical element 23 will be described.
FIG. 4 is an explanatory diagram showing the optical path in the video display device 1 in a developed state. As shown in the figure, the light source 11 is composed of light source groups 11P and 11Q. The light source groups 11P and 11Q are respectively RGB integrated LEDs (Nichia) having light emitting units 11R ₁ , 11G ₁ and 11B ₁ and light emitting units 11R ₂ , 11G ₂ and 11B ₂ that emit light corresponding to RGB colors. Made of chemical). The light emitting units 11R ₁ , 11G ₁ , 11B ₁ and the light emitting units 11R ₂ , 11G ₂ , 11B ₂ are arranged substantially along the X direction. The light source 11 may be a light source group 11P / 11Q configured in one package.

  Here, FIG. 5 is an explanatory diagram showing the spectral intensity characteristics of the light source 11, that is, the relationship between the wavelength of the emitted light and the light intensity. The light source 11 emits light in three wavelength bands, for example, 462 ± 12 nm, 525 ± 17 nm, and 635 ± 10 nm with a center wavelength and a light intensity half-value wavelength width. The light intensity on the vertical axis in FIG. 5 is shown as a relative value when the maximum light intensity of B light is 100. The RGB light intensities of the light source 11 are adjusted in consideration of the diffraction efficiency of the hologram optical element 23 and the light transmittance of the LCD 13, thereby enabling white display.

  On the other hand, FIG. 6 is an explanatory diagram showing the wavelength dependence of the diffraction efficiency in the hologram optical element 23. As shown in the figure, the hologram optical element 23 has, for example, 465 ± 5 nm (B light), 521 ± 5 nm (G light), 634 ± 5 nm (R light) at the peak wavelength of diffraction efficiency and the half width of the diffraction efficiency. ) Is diffracted (reflected) in the three wavelength regions. Here, the peak wavelength of diffraction efficiency is the wavelength at which the diffraction efficiency reaches a peak, and the wavelength width at half maximum of the diffraction efficiency is the wavelength width at which the diffraction efficiency is at half the peak of the diffraction efficiency. It is. The diffraction efficiency in FIG. 6 is shown as a relative value when the maximum diffraction efficiency of B light is 100.

  As described above, the hologram optical element 23 is produced so as to diffract only light having a specific incident angle and a specific wavelength, and therefore hardly affects the transmission of external light. Therefore, as described above, the observer can view the external image as usual through the eyepiece prism 21, the hologram optical element 23, and the deflection prism 22.

  In addition, the volume phase type reflection type hologram optical element 23 has a narrow half-value wavelength width of diffraction efficiency, so that it has a high external light transmittance and a bright external image can be observed. An image with high color purity and high visibility can be observed.

  In addition, from the above numerical relationship, it can be said that the peak wavelength of the diffraction efficiency of the hologram optical element 23 and the peak wavelength (center wavelength) of the light intensity emitted from the light source 11 are substantially the same. In such a setting, light in the vicinity of the wavelength at which the light intensity reaches a peak among the light emitted from the light source 11 is efficiently diffracted by the hologram optical element 23, so that it is bright even when superimposed on the external image, An easy-to-view video can be provided to the observer.

(4. Details of illumination optical system)
Next, details of the illumination optical system 12 will be described. FIG. 1 is a cross-sectional view showing a detailed configuration of the illumination optical system 12. The illumination optical system 12 includes illumination mirrors 31 and 32 and a unidirectional diffuser plate 33.

  The illumination mirror 31 is composed of a spherical mirror having a concave reflecting surface and has a positive optical power. The illumination mirror 31 is arranged so that the light source 11 and the optical pupil E are conjugated in cooperation with the observation optical system 14. The illumination mirror 31 is arranged so that the light diffused by the unidirectional diffuser plate 33 after the light from the light source 11 is condensed efficiently forms the optical pupil E. As a result, a bright image can be observed at the position of the optical pupil E. Note that the reflection surface of the illumination mirror 31 constitutes a first reflection surface on which light from the light source 11 incident on the illumination optical system 12 is first reflected in the illumination optical system 12.

  The illumination mirror 32 is composed of a flat mirror having a flat reflecting surface. The reflection surface of the illumination mirror 32 constitutes a second reflection surface in the illumination optical system 12 where the light reflected by the illumination mirror 31 is incident next and reflected.

  The unidirectional diffuser plate 33 is disposed on the front surface of the illumination mirror 32, and diffuses incident light by 40 degrees in the X direction and 0.2 degrees in the Y direction due to surface irregularities. Here, the unidirectional diffuser plate 33 diffuses the incident light when it is transmitted. However, for example, the illumination mirror 32 may be provided with unevenness to diffuse the incident light.

  With such a configuration of the illumination optical system 12, the light from the light source 11 is reflected by the illumination mirror 31 of the illumination optical system 12, enters the illumination mirror 32 via the unidirectional diffusion plate 33, and is reflected there. The reflected light again enters the unidirectional diffusion plate 33 and is diffused there, and then enters the LCD 13. That is, the light from the light source 11 is guided to the LCD 13 by being reflected twice by the two reflecting surfaces of the illumination optical system 12. At this time, the optical path of light traveling from the light source 11 to the illumination mirror 31 and the optical path of light sequentially reflected by the illumination mirror 31 and the illumination mirror 32 and traveling from the illumination mirror 32 to the LCD 13 intersect.

  Thus, since the optical path from the light source 11 to the LCD 13 is bent by the illumination optical system 12, the illumination optical system 12 can be made compact while ensuring a long optical path, and the image display device 1 can be made small and light. Can do.

  Although the illumination mirror 31 has a spherical shape, it is inclined with respect to the optical path (for example, the optical path of the light (principal ray) on the optical axis), and therefore is optically axisymmetric with respect to the illumination mirror 31 in the YZ plane. Power is applied and this causes axially asymmetric aberrations. However, by providing two reflecting surfaces in the illumination optical system 12, the illumination optical system reduces the incident angle of the light from the light source 11 to the illumination mirror 31 (while relaxing the axial asymmetry in the illumination mirror 31). 12 can have optical power. Therefore, it is possible to uniformly illuminate the LCD 13 while suppressing the generation of axially asymmetric aberration. Furthermore, since the illumination optical system 12 has a positive optical power as a whole, the light from the light source 11 can be condensed to illuminate the LCD 13, and a bright image can be observed by an observer. Become.

  Further, since the illumination mirrors 31 and 32 are arranged so that the optical path of light from the light source 11 toward the illumination mirror 31 and the optical path of light from the illumination mirror 32 toward the LCD 13 intersect, the optical path in the illumination optical system 12 Can be folded compactly. Thereby, the effect of the present invention described above, that is, the effect that the image display device 1 can be reduced in size and weight, and the effect that the LCD 13 can be illuminated uniformly while suppressing the occurrence of aberration can be surely obtained.

  Further, the illumination optical system 12 does not have an optical element such as a prism and is hollow. Thereby, the illumination optical system 12 and the video display device 1 can be further reduced in size and weight in addition to the reduction in size and weight by folding the optical path described above. Further, there is no reflection of unnecessary light such as reflection on the inner surface of the prism, and a high-quality image without flare can be observed.

  Further, the positive optical power of the illumination optical system 12 is generated by reflection on the reflective optical element (here, the illumination mirror 31). Unlike transmission, chromatic aberration does not occur in reflection. Therefore, it is possible to obtain good optical performance even when the illumination optical system 12 has a large positive optical power, and the LCD 13 can be illuminated brightly and uniformly. Is possible. In particular, by configuring the illumination mirror 31 with a concave spherical mirror, it is possible to provide greater optical power without causing chromatic aberration, and to realize bright illumination with less color unevenness and brightness unevenness.

  In addition to the concave spherical surface, for example, an aspherical surface, a free-form surface, or a cylindrical surface can be used as the reflecting surface of the illumination mirror 31, and a surface that can realize uniform illumination with less aberrations can also be used. Is possible.

  In addition, the unidirectional diffuser plate 33 is disposed in the optical path between the illumination mirror 31 and the illumination mirror 32, and is disposed at a position far from both the light source 11 and the LCD 13. By disposing the unidirectional diffuser plate 33 at a position far from the light source 11, the LCD 13 can be illuminated with uniform light with reduced luminance unevenness. Further, as in the present embodiment, when the light source 11 is composed of LEDs that emit RGB color lights, the color mixture in the unidirectional diffuser plate 33 is good, and color unevenness can be reduced. Become.

  On the other hand, by disposing the unidirectional diffuser plate 33 at a position far from the LCD 13, the virtual image of the unidirectional diffuser plate 114 is not observed at the same time as the virtual image of the display image on the LCD 13, and a high-quality image can be observed. Can do. The virtual image of the unidirectional diffuser plate 33 is an image including a shadow generated due to unevenness on the surface of the unidirectional diffuser plate 33. The above-mentioned shadow appears corresponding to a portion where light is not emitted by total reflection on the light emission surface (uneven surface) when light is incident on the unidirectional diffusion plate 33.

  In the present embodiment, the illumination mirrors 31 and 32 reflect the light from the light source 11 so that the optical path bends in the YZ plane, and collects the light in the Y direction. As will be described later, since the optical pupil E is formed smaller in the Y direction than in the X direction, the light flux width is reduced in the Y direction. Thereby, the illumination mirrors 31 and 32 can be made small, and the illumination optical system 12 and thus the video display device 1 can be made smaller and lighter.

Further, as described above, the light emitting units 11R ₁ , 11G ₁ , 11B ₁ and the light emitting units 11R ₂ , 11G ₂ , 11B ₂ of the light source 11 are arranged substantially along the X direction. It can also be said that the unidirectional diffusion plates 33 are arranged so as to be substantially along the diffusion direction. Thereby, the light radiate | emitted from each LED can be mixed with the diffusion direction of the unidirectional diffusion plate 33, and a favorable color image without a color nonuniformity can be provided to an observer.

(5. About optical pupil)
In the present embodiment, as described above, the positional relationship between the light source 11 and the optical pupil E is substantially conjugate. In the optical pupil E, in the Y direction, the light emitting area of the light emitting portion of the light source 11 (for example, 0.3 mm square) is diffused by 0.2 degrees on the unidirectional diffusion plate 33 and 2 degrees on each pixel of the LCD 13. Due to the degree of diffusion, it is formed slightly larger than the pupil formed at the conjugate image magnification. As a result, the optical pupil E has a half intensity value of 10 mm in the X direction and 2 mm in the Y direction.

  Thus, the optical pupil E has a size of 10 mm, which is larger than the human pupil (about 3 mm) in one direction (X direction), so that the observer can easily observe the image. On the other hand, since the optical pupil E has a size of 2 mm which is smaller than the human pupil in the other direction (Y direction), the light from the light source 11 is condensed on the optical pupil E in the above direction without waste. Thereby, the observer can observe a bright image.

  In the X direction, incident light is greatly diffused by the unidirectional diffuser plate 33, so that an optical conjugate relationship between the light source 11 and the optical pupil E is not established, but a conjugate arrangement, that is, a positional relationship. Is conjugate, the utilization efficiency of light from the light source 11 is increased, and a bright image can be observed.

(6. Effect of reducing color unevenness by setting optical pupil)
As described above, the optical pupil E is set to have a half intensity value of 10 mm in the X direction and 2 mm in the Y direction. That is, the optical pupil E is larger in the X direction, that is, the direction perpendicular to the optical axis incident surface, than in the Y direction, that is, the direction parallel to the optical axis incident surface (YZ plane) of the hologram optical element 23. By setting the size of the optical pupil E in this way, the observer can observe a high-quality image with little color unevenness without being greatly affected by the wavelength characteristics (wavelength selectivity) of the hologram optical element 23. Can do. The reason is as follows.

  First, the relationship between the incident angle and the wavelength selectivity in the hologram optical element 23 will be described. In the hologram optical element 23 having interference fringes that diffract light having an incident angle greater than 0 degrees, the wavelength selectivity is smaller in the direction perpendicular to the optical axis incident surface than in the direction parallel to the optical axis incident surface (incident angle). The diffraction wavelength shift due to the shift is small. In other words, the angle selectivity with respect to the shift of the incident angle to the interference fringes is lower in the direction perpendicular to the optical axis incident surface than in the direction parallel to the optical axis incident surface. This is because, when light is incident on the interference fringes of the hologram optical element 23 with an incident angle, the angle deviation of the incident angle in the optical axis incident surface is directly the angle deviation of the incident angle, and therefore, the diffraction wavelength is not affected. Although the influence is large, the angle deviation in the direction perpendicular to the optical axis incident surface is small as the deviation of the incident angle, and the influence on the diffraction wavelength is small.

  Accordingly, when light having an angle deviated from a predetermined incident angle is incident on the interference fringes of the hologram optical element 23, the angle deviation in the Y direction parallel to the optical axis incidence surface is more likely to occur on the optical axis incidence surface even with the same angle deviation. The diffraction wavelength is greatly shifted from the angle deviation in the vertical X direction (that is, the Y direction parallel to the optical axis incident surface has a large wavelength selectivity).

  Therefore, by forming the optical pupil E small in the Y direction where the change in the diffraction wavelength is large, the range of change in the diffraction wavelength is narrowed, so that color unevenness on the optical pupil E can be reduced. That is, since the optical axis incident surface of the hologram optical element 23 is parallel to the Y direction where the optical pupil E is small, color unevenness in the Y direction can be reduced. Further, even if the optical pupil E is formed large in the X direction perpendicular to the optical axis incident surface, an image with high color purity can be provided to the observer. In addition, although the incident surface of the light outside the optical axis incident surface is not slightly parallel to the optical axis incident surface, as described above, the angle shift in the direction perpendicular to the optical axis incident surface has little influence on the diffraction wavelength. Even if the incident surface is used as a reference, color unevenness does not increase.

  Further, as described above, the hologram optical element 23 is fabricated so as to diffract the image light of each wavelength of 465 ± 5 nm, 521 ± 5 nm, and 634 ± 5 nm at the diffraction efficiency peak and its half-value wavelength width. Thus, since the half-value wavelength width of diffraction efficiency is the same for each color, the longer the wavelength, the greater the angle selectivity (the smaller the angle of incidence angle shift with respect to wavelength change). Therefore, when the RGB wavelength width of the light emitted from the light source 11 is the same, the size of the optical pupil diffracted by the hologram optical element 23 is smaller as the wavelength is longer. The optical pupil E includes the entire optical pupil range of each color.

  On the other hand, the intensity of light emitted from the LED (each light emitting unit) of the light source 11 is generally stronger near the center and weaker toward the periphery. Each light emitting unit is arranged so as to be substantially conjugate with the optical pupil in the Y direction. However, in the X direction, incident light is diffused by the unidirectional diffuser plate 33, so that it is conjugate with the optical pupil. is not. However, the position with the strongest intensity in the optical pupil is almost the same as the conjugate position with each light emitting section when the unidirectional diffuser plate 33 is not provided.

  Therefore, the pupil center of the long wavelength (R light) with the small optical pupil is positioned on the center side of the optical pupil E, and the pupil center of the short wavelength (B light) with the large optical pupil is positioned outside the center of the optical pupil E. By doing so, the intensity difference depending on the pupil position in the optical pupil E can be reduced for each color. As a result, an image with little color unevenness can be provided to the observer over the entire optical pupil E (the pupil center and the periphery of the pupil).

(7. Effect of reducing color unevenness due to the arrangement of each light emitting part of the light source)
As shown in FIG. 4, the light emitting units of the light source groups 11 </ b> P and 11 </ b> Q constituting the light source 11 are arranged substantially along the X direction perpendicular to the optical axis incident surface of the hologram optical element 23. As described above, since the wavelength selectivity of the hologram optical element 23 is lower in the X direction perpendicular to the optical axis incident surface than in the Y direction parallel to the optical axis incident surface, the light emitting units are arranged substantially along this direction. This makes it possible for the observer to observe a high-quality image without color unevenness.

Moreover, in the present embodiment, each light emitting unit is substantially symmetrical with respect to the optical axis incident surface, that is, two light emitting units that emit light of the same color are substantially the same distance from the optical axis incident surface in opposite directions. It is arranged to be located in. More specifically, in the light source group 11P, the light emitting units 11R ₁ , 11G _1, and 11B ₁ are arranged in this order from the optical axis incident surface side toward the outside in the X direction. Also in the light source group 11Q, the light emitting units 11R ₂ , 11G _2, and 11B ₂ are arranged in this order from the optical axis incident surface side toward the outer side in the X direction.

Here, FIG. 7 is an explanatory view showing the relationship between the pupil position in the X direction in the optical pupil E and the light intensity. The light intensity is shown as a relative value for the same color. The curve indicated by _{11R 1 · 11R 2 · 11G 1} · 11G 2 · 11B 1 · 11B 2 in the figure, from the respective light emitting unit _{11R 1 · 11R 2 · 11G 1} · 11G 2 · 11B 1 · 11B 2 It corresponds to the emitted light.

In this way, by arranging the light emitting units approximately symmetrically with respect to the optical axis incident surface for each color, the light intensity of the emitted light from the _two light emitting units (for example, 11R ₁ and 11R ₂ ) for the same color can be obtained. The center of gravity of the combined total light intensity can be positioned in the symmetry plane (in the optical axis incident plane) for each of the RGB colors. That is, the intensity distribution of each color of RGB can be symmetric in the X direction with the symmetry plane as the center. Accordingly, an image with little color unevenness at the center of the optical pupil E can be provided to the observer.

  In particular, since the light emitting units are arranged in the X direction in the order of wavelengths in which the diffusion in the unidirectional diffusion plate 33 is large (the light is diffused as the wavelength is short), the intensity difference of each color on the optical pupil E is further reduced. Thus, color unevenness can be further reduced. That is, an image with high color purity can be provided to the observer.

  Further, due to the angle selectivity of the hologram optical element 23, the longer the wavelength, the smaller the optical pupil. Therefore, as shown in the figure, the longer the wavelength, the greater the intensity difference depending on the pupil position (the optical pupil E). The difference in strength between the center and the edge is large). Therefore, the light emitting units are arranged in such an order that the wavelength of the emitted light becomes shorter from the optical axis incident surface side toward the outside in the X direction, and the position where the light intensity is higher as the wavelength is longer is closer to the center of the optical pupil E. As a result, the utilization efficiency of the light at the optical pupil E can be increased.

  On the other hand, since the optical pupil is larger as the wavelength is shorter, the difference in intensity depending on the pupil position is smaller as the wavelength is shorter. That is, as the wavelength is shorter, the position where the light intensity is higher is further away from the center of the optical pupil E, and the difference in intensity between the peak intensity and the peripheral intensity is reduced. Therefore, the light use efficiency is not significantly reduced. As a result, the intensity difference in the optical pupil E for each color is reduced, and the luminance unevenness (color unevenness) is reduced.

  In the present embodiment, the unidirectional diffuser plate 33 is diffused by 0.2 degrees in the Y direction. However, even if a diffuser of about 3 degrees in the Y direction is used, for example, it is bright and has high image quality. It is possible to observe the video.

  In this embodiment, the LEDs (light sources 11) in which the light emitting units are arranged in a line in the X direction are used, but they are not completely aligned in one direction, for example, 0.5 mm in the vertical direction (Y direction). Even if LEDs are used in which the light emitting portions are displaced from each other, the diffusion effect by the unidirectional diffusion plate 33 can be obtained. At this time, the LEDs may be arranged so that the direction in which more light emitting units are linearly arranged is the X direction.

(8. Variations of illumination optical system)
By the way, the illumination optical system 12 is not limited to the structure of FIG. FIG. 8 is a cross-sectional view schematically showing another configuration example of the illumination optical system 12. The illumination optical system 12 has the same configuration as that of FIG. 1 except that a plano-convex lens 34 having a positive optical power is disposed instead of the illumination mirror 31. The convex-side surface of the plano-convex lens 34 is a spherical surface, and the back surface (plane-side surface) is a reflecting surface (planar mirror).

  The light from the light source 11 is refracted by the convex surface of the plano-convex lens 34, reflected by the reflecting surface, then emitted again through the convex surface and directed to the illumination mirror 32. The light reflected by the illumination mirror 32 is diffused by the unidirectional diffusion plate 33 and then enters the LCD 13 across the optical path of the light from the light source 11 toward the plano-convex lens 34.

  In this configuration, the light from the light source 11 passes through the convex surface of the plano-convex lens 34 twice, so that optical power can be given to the illumination optical system 12 while reducing the occurrence of aberrations, and uniform and bright illumination light is obtained. be able to. Therefore, it is possible to illuminate the LCD 13 with such illumination light and allow the observer to observe a uniform and bright image. The plano-convex lens 34 may be a cylinder lens.

  FIG. 9 is a cross-sectional view showing still another configuration example of the illumination optical system 12. This illumination optical system 12 is the same as FIG. 1 except that an illumination mirror 32 is disposed instead of the illumination mirror 31 as the first reflecting surface, and a free-form surface mirror 35 is disposed as the second reflecting surface. It is the composition. The unidirectional diffusion plate 33 is disposed in front of the illumination mirror 32. The free-form surface mirror 35 is a concave mirror having positive optical power.

  The light from the light source 11 is incident on the illumination mirror 32 through the unidirectional diffuser plate 33 and reflected there, and is incident on the unidirectional diffuser plate 33 again and diffused, and then travels toward the free-form surface mirror 35. The light reflected by the free-form surface mirror 35 enters the LCD 13 across the optical path of the light from the light source 11 toward the illumination mirror 32.

  In this configuration, the light diffused by the unidirectional diffuser plate 33 is condensed by the positive optical power of the free-form curved mirror 35 and enters the LCD 13, so that the virtual image of the unidirectional diffuser plate 33 is observed together with the image of the LCD 13. It becomes difficult to be done. Therefore, it is possible to reduce the diffusivity of the unidirectional diffusion plate 33 and brighten the image. Further, since the optical path of the illumination light is long due to the reflection twice by the illumination mirror 32 and the free-form surface mirror 35 and the distance from the LCD 13 to the unidirectional diffuser plate 33 is long, the RGB illumination light is sufficiently obtained by the unidirectional diffuser plate 33. Color mixing is performed, and luminance unevenness and color unevenness are suppressed.

  FIG. 10 is a cross-sectional view showing still another configuration example of the illumination optical system 12. The illumination optical system 12 is the same as that in FIG. 1 except that an illumination mirror 32 is disposed instead of the illumination mirror 31 as a first reflection surface and a cylinder mirror 36 is disposed as a second reflection surface. It is a configuration. The unidirectional diffusion plate 33 is disposed on the front surface of the cylinder mirror 36.

  The cylinder mirror 36 is a concave mirror having positive optical power that collects incident light only in the Y direction. Since the cylinder mirror 36 does not have optical power in the X direction, the light source 11 and the optical pupil E are not conjugate in the X direction.

  Light from the light source 11 enters the illumination mirror 32, is reflected there, and enters the cylinder mirror 36 via the one-way diffuser plate 33. The light reflected by the cylinder mirror 36 enters the unidirectional diffusion plate 33 again and is diffused there, and then enters the LCD 13 without traversing the light path from the light source 11 toward the illumination mirror 32.

  In this configuration, the optical path of light from the light source 11 toward the illumination mirror 32 and the optical path of light from the cylinder mirror 36 toward the LCD 13 are not crossed, but the optical path is folded by the illumination optical system 12 as described above. Since the illumination optical system 12 is the same as the other illumination optical systems 12, the illumination optical system 12 can be made compact.

  FIG. 11 is a cross-sectional view showing still another configuration example of the illumination optical system 12. In this illumination optical system 12, a concave mirror 37 is disposed as a first reflecting surface, a convex mirror 38 is disposed as a second reflecting surface, and a unidirectional diffusion plate 33 is disposed on the light incident side of the LCD 13. It is configured. However, the optical power of the entire illumination optical system 12 is positive.

  The light from the light source 11 enters the concave mirror 37, is reflected there, and enters the convex mirror 38. The light reflected by the convex mirror 38 enters the unidirectional diffusion plate 33 across the optical path of the light from the light source 11 toward the concave mirror 37, diffuses there, and then enters the LCD 13.

  In this configuration, since the light beam is reduced by the negative optical power of the convex mirror 38, the positive optical power of the concave mirror 37 can be increased, and the use radiation angle of the light emitted from the light source 11 can be increased. (The utilization efficiency of light emitted from the light source 11 can be increased). As a result, the LCD 13 can be illuminated with bright light, and the display image on the LCD 13 can be observed brightly. Therefore, it is possible to observe a bright image by using a diffusion plate that diffuses incident light in all directions, for example, 30 degrees instead of the one-way diffusion plate 33. At this time, the optical pupil E in the Y direction becomes a large pupil (for example, about 8 mm) as in the X direction, making it easier to observe the image.

  FIG. 12 is a cross-sectional view showing still another configuration example of the illumination optical system 12. The illumination optical system 12 includes a prism 41 and a diffusion plate 42. The prism 41 has an incident surface 41a, a concave reflecting surface 41b as a first reflecting surface, a planar reflecting surface 41c as a second reflecting surface, and an exit surface 41d. The diffusion plate 42 is a diffusion plate that diffuses incident light in all directions at 30 degrees, and is disposed between the exit surface 41 d of the prism 41 and the LCD 13. Since the concave reflecting surface 41b has a positive optical power, the optical power of the entire illumination optical system 12 is positive.

  The light from the light source 11 enters the inside through the incident surface 41a of the prism 41, is sequentially reflected by the concave reflecting surface 41b and the flat reflecting surface 41c, and then travels from the incident surface 41a to the concave reflecting surface 41b. It crosses the optical path and reaches the exit surface 41d. Light emitted from the exit surface 41 d is diffused by the diffusion plate 42 and then enters the LCD 13.

  In this configuration, the optical path of light traveling from the incident surface 41a to the concave reflecting surface 41b and the optical path of light traveling from the planar reflecting surface 41c to the exit surface 41d intersect within the prism 41, thereby reducing axial asymmetry. The illumination optical system 12 can be made compact while maintaining uniform illumination. In addition, since the luminous flux is small in the prism medium, aberration due to reflection can be suppressed.

  The diffusing plate 42 can be replaced with a unidirectional diffusing plate 33. However, when the unidirectional diffuser plate 33 is used, a shadow due to the unevenness of the unidirectional diffuser plate 33 is slightly observed as a virtual image.

  FIG. 13 is a cross-sectional view showing still another configuration example of the illumination optical system 12. The illumination optical system 12 includes a diffusing plate 42 and a prism 43. The prism 43 has an incident surface 43a, a flat reflecting surface 43b as a first reflecting surface, and a concave reflecting surface 43c as a second reflecting surface. The diffusing plate 42 is disposed between the planar reflecting / light emitting surface 43 b of the prism 43 and the LCD 13. Since the concave reflecting surface 43c has a positive optical power, the optical power of the entire illumination optical system 12 is positive.

  The light from the light source 11 enters the inside through the incident surface 43a of the prism 43, is sequentially reflected by the plane reflecting surface / exit surface 43b and the concave reflecting surface 43c, and reaches the plane reflecting surface / exit surface 43b. The light emitted from the plane reflecting / light emitting surface 43 b is diffused by the diffusion plate 42 and then enters the LCD 13.

  In this configuration, a light ray that enters the plane reflecting surface / exit surface 43b from the incident surface 43a and a light ray that travels on the same optical path as the light ray in the prism 43, and is a plane reflecting surface / exit from the concave reflecting surface 43c. The light beam incident on the surface 43b does not intersect, but the optical path is not changed, and the illumination optical system 12 can be configured compactly. In addition, since the luminous flux is small in the prism medium, aberration due to reflection can be suppressed.

  The diffusing plate 42 can be replaced with a unidirectional diffusing plate 33. However, when the unidirectional diffuser plate 33 is used, a shadow due to the unevenness of the unidirectional diffuser plate 33 is slightly observed as a virtual image. Further, total reflection may be used on the planar reflection surface / exit surface 43b of the prism 43, and a mirror coating may be applied to a portion that is not totally reflected.

(9. Other configurations of video display device)
FIG. 14 is a cross-sectional view schematically showing another configuration of the video display device 1. The video display device 1 has the same configuration as the video display device 1 shown in FIG. 3 except that the light source 51 is used instead of the light source 11 and the observation optical system 52 is used instead of the observation optical system 14.

  However, in the video display device 1 of FIG. 14, the illumination optical system 12 includes only the illumination mirrors 31 and 32 and does not include the unidirectional diffuser plate 33. This is because the following white light source is used as the light source 51, and there is no need to mix RGB colors. However, it is of course possible to further widen the optical pupil E in the X direction by providing the unidirectional diffusion plate 33.

  The light source 51 is a white light source (white LED) that emits white light by exciting a phosphor with blue light or ultraviolet light. Here, FIG. 15 is a plan view when the light source 51 is viewed from the LCD 13 side. The light source 51 has a slit-like light emitting region 51 a having a long side in a direction (X direction) perpendicular to the optical axis incident surface of the hologram optical element 23. That is, in the area outside the light emitting area 51a, light transmission is limited by the mask. The size of the light emitting region 51a is, for example, 3 mm in the X direction and is, for example, 1 mm in the Y direction.

  The light source 51 emits white (including light in RGB wavelength ranges corresponding to the three primary colors) in a slit shape from the light emitting region 51a. Since the light source 51 and the optical pupil E are arranged so as to have a substantially conjugate relationship, the optical pupil E is an image of the optical system in which the size of the light emitting region 51a of the light source 51 (X direction: 3 mm, Y direction: 1 mm). As a result of the magnification of 3 times, the size is 9 mm in the X direction and 3 mm in the Y direction, and the pupil is small in one direction.

  The observation optical system 52 is configured by bonding a free-form surface prism 61 having positive optical power that is axisymmetric and a transparent substrate 62. The free-form surface prism 61 has an incident surface 61a for light from the LCD 13, a reflection surface 61b, and a transmission / reflection surface 61c. The transparent substrate 62 is bonded to the transmission / reflection surface 61 c of the free-form surface prism 61. The free-form surface prism 61 and the transparent substrate 62 correspond to the eyepiece prism 21 and the deflecting prism 22 of FIG. 3, respectively, and constitute a first transparent substrate and a second transparent substrate, respectively.

  Light (white light) emitted from the light source 11 is sequentially reflected by the illumination mirrors 31 and 32 of the illumination optical system 12, and then enters the LCD 13, where it is modulated and emitted as image light. This image light is incident on the inside through the incident surface 61a of the free-form surface prism 61 of the observation optical system 52, is totally reflected by the reflecting surface 61b, is reflected by the transmitting / reflecting surface 61c, and is guided to the optical pupil E. . The observer can observe the display image of the LCD 13 as a virtual image by the combined power of each surface of the free-form surface prism 61 by causing the light reaching the optical pupil E to enter the pupil.

  Also in this video display apparatus 1, since the observation optical system 14 is an axially asymmetric optical system, the degree of freedom of arrangement of each optical member constituting the apparatus can be increased, and the apparatus can be easily reduced in size, and good It is possible to provide an observer with a high-quality image corrected for aberration. Further, since the transparent substrate 62 cancels the refraction of the external light transmitted through the lower end portion of the free curved surface prism 61, the observer can observe the external light through the free curved surface prism 61 and the transparent substrate 62 without distortion.

  The illumination mirror 31 and the observation optical system 52 of the illumination optical system 12 are set so that the light source 51 and the optical pupil E are conjugate. As shown in FIG. 15, the light emitting area 51a of the light source 51 has a small shape in the reflection direction (Y direction) of the illumination mirror 31, so that the illumination optical system 12 including the illumination mirrors 31 and 32 is made smaller. Can do. Furthermore, since the light source 51 and the optical pupil E are conjugate, a bright image can be provided, and the optical pupil E is small in the folding direction (Y direction) of the optical path in the illumination optical system 12, and the luminous flux is small. Therefore, it can be set as a more compact apparatus.

  In this embodiment, a transmissive color LCD provided with a color filter is used as a spatial modulation element. However, each of the RGB light emitting units is driven sequentially to emit light of each color sequentially in a time-sharing manner, and synchronized with this. A time-division type LCD (for example, a ferroelectric liquid crystal display element) that performs modulation corresponding to each color may be used.

  In the present embodiment, the video display device 1 suitable for the HMD has been variously described. However, the video display device 1 of the present embodiment can be applied to other devices such as a head-up display.

  Needless to say, it is possible to realize the video display device 1 and thus the HMD by appropriately combining the various configurations described in the present embodiment.

  The video display device of the present invention can be used for, for example, a head-mounted display or a head-up display.

It is sectional drawing which shows the detailed structure of the illumination optical system applied to the video display apparatus which concerns on one Embodiment of this invention. (A) is a top view which shows the schematic structure of HMD which has the said video display apparatus, (b) is a side view of HMD, (c) is a front view of HMD. It is sectional drawing which shows the schematic structure of the said video display apparatus. It is explanatory drawing which expand | deploys and shows the optical path in the said video display apparatus. It is explanatory drawing which shows the spectral intensity characteristic of the light source of the said video display apparatus. It is explanatory drawing which shows the wavelength dependence of the diffraction efficiency in the hologram optical element of the said video display apparatus. It is explanatory drawing which shows the relationship between the pupil position of the X direction in the optical pupil of the said video display apparatus, and light intensity. It is sectional drawing which shows the other structural example of the said illumination optical system typically. It is sectional drawing which shows typically the example of another structure of the said illumination optical system. It is sectional drawing which shows typically the example of another structure of the said illumination optical system. It is sectional drawing which shows typically the example of another structure of the said illumination optical system. It is sectional drawing which shows typically the example of another structure of the said illumination optical system. It is sectional drawing which shows typically the example of another structure of the said illumination optical system. It is sectional drawing which shows the other structure of the said video display apparatus typically. It is a top view when the light source of the video display apparatus of FIG. 14 is seen from the LCD side.

Explanation of symbols

1 display apparatus 2 supporting means 11 the light source 11R _1, 11G _1, 11B _1-emitting portion (light emitting diode)
11R ₂ , 11G ₂ , 11B ₂ light emitting part (light emitting diode)
12 Illumination optical system 13 LCD (Transmission type display element)
14 Observation optical system 21 Eyepiece prism (first transparent substrate)
22 Deflection prism (second transparent substrate)
23 Hologram optical element 31 Illumination mirror (reflection surface)
32 Illumination mirror (reflective surface)
33 Unidirectional diffuser 34 Plano-convex lens (reflection surface)
35 Free-form surface mirror (reflection surface)
36 Cylinder mirror (reflective surface)
37 Concave mirror (reflective surface)
38 Convex mirror (reflection surface)
41b Concave reflective surface (reflective surface)
41c Flat reflective surface (reflective surface)
43b Plane reflecting surface and exit surface (reflecting surface)
43c Concave reflective surface (reflective surface)
51 Light source 52 Observation optical system 61 Free-form surface prism (first transparent substrate)
62 Transparent substrate (second transparent substrate)
E Optical pupil

Claims (14)

A light source;
A display element that modulates incident light and displays an image;
An illumination optical system for guiding light from the light source to the display element;
An image display device comprising an observation optical system for guiding image light from a display element to an optical pupil,
The display element is a transmissive type,
The image display apparatus, wherein the illumination optical system has two reflection surfaces that reflect light from a light source twice and guide the light to a display element, and has positive optical power.   The two reflecting surfaces of the illumination optical system are sequentially reflected by the light path from the light source toward the first reflecting surface and the first and second reflecting surfaces, and are reflected from the second reflecting surface. The video display device according to claim 1, wherein the video display devices are arranged so as to intersect with an optical path of light traveling toward the display element.   The video display device according to claim 1, wherein the illumination optical system is hollow.   4. The image display device according to claim 1, wherein the positive optical power of the illumination optical system is generated by reflection. The optical pupil formed by the observation optical system is formed to be smaller in the other direction than one direction among the two directions orthogonal to each other,
5. The video display device according to claim 1, wherein the illumination optical system reflects incident light twice and collects the light in the other direction. 6. The light source and the optical pupil are arranged in a conjugate manner in the other direction,
The video display device according to claim 5, further comprising a unidirectional diffuser plate that diffuses light from the light source in the one direction. The light source includes a pair of light emitting diodes that emit red, green, and blue light.
When the axis that optically connects the center of the display area of the display element and the center of the optical pupil is the optical axis,
The pair of light emitting diodes are arranged side by side in the diffusion direction of the unidirectional diffusion plate, and are arranged symmetrically with respect to a plane including the optical axis of the observation optical system. The video display device described in 1. The illumination optical system has a diffusion plate that diffuses light from the light source by unevenness on the surface,
The diffusion plate is disposed in an optical path between the first reflection surface and the second reflection surface from the light source side,
6. The video display device according to claim 1, wherein the second reflecting surface from the light source side has a positive optical power. The observation optical system includes a volume phase reflection hologram optical element,
When the axis that optically connects the center of the display area of the display element and the center of the optical pupil is the optical axis,
The hologram optical element diffracts and reflects image light incident obliquely from the display element and leads it to the optical pupil,
The image display apparatus according to claim 6, wherein an optical axis incident surface of the hologram optical element is parallel to the other direction of the optical pupil.   10. The image display device according to claim 9, wherein the hologram optical element is a combiner that simultaneously guides the image light from the display element and the light from the outside to the pupil of the observer. The light source is composed of a light emitting diode,
The image display device according to claim 9 or 10, wherein a peak wavelength of diffraction efficiency of the hologram optical element and an intensity peak wavelength of the light emitting diode substantially coincide with each other.   The observation optical system includes a first transparent substrate that totally reflects the image light from the display element and guides the light to the observer's pupil while transmitting the external light to the observer's pupil. The video display device according to claim 1, wherein:   13. The video display apparatus according to claim 12, wherein the observation optical system includes a second transparent substrate for canceling refraction of external light on the first transparent substrate. A video display device according to any one of claims 1 to 13,
A head-mounted display comprising support means for supporting the video display device in front of an observer's eyes.

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