JP2000155286A - Video display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the picture element array pattern of a picture display element inconspicuous by using an optical filter. SOLUTION: As for a video display device having a picture display means 2 displaying a picture and an eyepiece optical system 3 projecting the picture on the retina of a user, a first diffracting means 11 and a second diffracting means 12 are provided in an optical path between the picture display means 2 and an exit pupil formed by the eyepiece optical system 3, and when the grating pitches of diffracting means are respectively set as d1 and d2, the relation of 0<|fl(d2-d1)/d1 d2|<=2L is satisfied. Then, (f) means the focal distance of the eyepiece optical system and λ means an incident wavelength and L means the cycle of the picture element of the picture display means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video display device, and more particularly to a video display device in which pixels are arranged in a mesh pattern such as a liquid crystal display device.
An optical filter for optically erasing the pixel pattern to improve image quality when the two-dimensional display element is enlarged and projected;
The present invention relates to a video display device such as a head mounted video display device having the same.

[0002]

2. Description of the Related Art Helmet-type and goggle-type head-mounted image display devices are being developed for the purpose of virtual reality or for enabling one person to enjoy a large-screen image. .

[0003] Such a head-mounted image display device generally projects an image displayed on a two-dimensional display element such as a liquid crystal display element on a user's retina in an enlarged manner using an eyepiece optical system. (For example, JP-A-4-170512).

A liquid crystal display (LCD) or the like used as the two-dimensional display element is an element in which a plurality of pixels are arranged in a discontinuous mesh. Therefore, if the total number of pixels constituting the image display means is small, the gaps between the pixels are conspicuous when the image is enlarged and projected using the eyepiece optical system, and a mesh-like array pattern is observed by the user. In order to increase the resolution of the video display device by making the gap between the pixels inconspicuous, it is necessary to increase the number of pixels. However, due to the problem of the production yield of the two-dimensional display element, the number of pixels is increased or the gap between the pixels is increased. It is not easy to make it small.

Therefore, conventionally, an optical filter composed of a diffraction grating or a birefringent plate is provided on the front of an image display device such as a liquid crystal display device, and each pixel is divided into a plurality of pixels to form a mesh-like pixel array pattern. Japanese Patent Application Laid-Open No. 3-148622 and Japanese Patent Application Laid-Open No.
No. 114475.

[0006]

However, when a diffraction grating is used as an optical filter, the optimum pitch of the diffraction grating is uniquely determined by the location of the optical filter. It becomes difficult to reduce moire when it occurs. In particular, JP-A-3-148622 and JP-A-63-1144.
In the case where the diffraction grating is arranged in front of the image display device as in the case of No. 75, a moire image becomes conspicuous when the depth of focus of the eyepiece optical system is reduced.

In particular, when the size of the image display device is reduced, the space between the eyepiece optical system and the image display element is narrowed, so that the place where the optical filter is arranged is limited. Therefore, the pitch of the diffraction grating cannot be largely changed. It will be difficult. In addition, since it is near the image plane, there is also a problem that the lattice pattern of the diffraction grating itself and the attached dust can be seen.

As a method of not disposing the optical filter in front of the image display device, there is a method of disposing an optical filter between an eyepiece optical system and an exit pupil formed by the eyepiece optical system. In this case, since the optical path length from the image display element to the optical filter becomes longer, it is necessary to reduce the diffraction angle of the optical filter. Therefore, the pitch of the diffraction grating of the optical filter becomes large, but at this time, there is a problem that image distortion is observed corresponding to the periodic interval of the diffraction grating.

On the other hand, when a birefringent plate is used as an optical filter, the number of birefringent plates must be increased in order to increase the number of separations since the number of separations by the birefringent plate is two. However, since the birefringent plate is expensive, increasing the number of sheets increases the cost. Further, there is a problem that the thickness of the entire optical filter is increased and the entire image display device is enlarged.

The present invention has been made in view of such problems of the prior art, and has as its object to realize an image display device in which the pixel arrangement pattern of an image display element is made inconspicuous by using an optical filter. That is.

[0011]

According to the present invention, there is provided a video display apparatus for displaying an image, comprising:
An image display device having an eyepiece optical system for projecting the image onto a retina of a user, wherein a first eyepiece is provided in an optical path between the image display means and an exit pupil formed by the eyepiece optical system.
Is provided, and when the grating pitches of these diffraction means are d ₁ and d ₂ , respectively, 0 <| fλ (d ₂ −d ₁ ) / d ₁ d ₂ | ≦ 2L It is characterized by having been constituted so as to satisfy.
Here, f is the focal length of the eyepiece optical system, λ is the incident wavelength, L
Is the distance from any pixel of R, G, B to the pixel closest to the reference pixel from the pixels of the same color arranged in the same row and column as the reference pixel. When the array is a square array, R or B pixels are used as a reference.

In this case, the grating pitch d ₁ of the first diffraction means and the grating pitch d ₂ of the second diffraction means are 0.05 mm <d ₁ <0.3 mm 0.05 mm <d ₂ <0. It is desirable to satisfy 3 mm 2.

Hereinafter, the reason why the above configuration is employed in the present invention and the operation thereof will be described. In the present invention, a first diffraction means and a second diffraction means are provided in an optical path between an eyepiece optical system and an exit pupil formed by the eyepiece optical system, and a grating pitch of the first diffraction grating and a second diffraction means are provided. 2 are configured to have different grating pitches.

Light that is perpendicularly incident on the first diffraction means from the display surface is divided into a plurality of diffracted lights by the first diffraction means. At this time, the diffraction angle θ of the diffracted light of the diffraction order m
⁽¹⁾ _m is calculated using the grating pitch d ₁ of the first diffraction means,
It can be expressed by the following equation (1). Here, λ is the incident wavelength.

D ₁ sin θ ⁽¹⁾ _m = mλ (1) Accordingly, the diffraction angle θ ⁽¹⁾ _m is represented by the following equation (1-1).

Sin θ ⁽¹⁾ _m = mλ / d ₁ (1-1) Further, the diffracted light separated by the first diffracting means is again divided into a plurality of diffracted lights by the second diffracting means. Can be

The m-order light diffracted by the ^first diffraction means is incident on the second diffraction means at an incident angle θ ⁽¹⁾ _m and is diffracted again. At this time, if the grating pitch of the second diffraction means is d ₂ , the diffraction angle θ of the diffracted light of the diffraction order M
⁽²⁾ _M can be represented by the following relational expression (2).

D ₂ (sin θ ⁽²⁾ _M −sin θ ^{( 1)} _m ) = Mλ (2) Therefore, from Expressions (1) and (2), the diffraction angle θ ⁽²⁾ _M is given by the following expression (3) ).

Sin θ ⁽²⁾ _M = mλ / d ₁ + Mλ / d ₂ (3) If m = 0 and M = 0 in equation (3), the diffraction angle θ ⁽²⁾
₀ becomes 0. That is, the light beam travels straight without changing the optical path. If m = + 1 and M = -1, the diffraction angle θ ⁽²⁾ ₋₁ can be expressed as in the following equation (3-1).

Θ ⁽²⁾ ₋₁ ≒ sin θ ⁽²⁾ ₋₁ = λ (d ₂ −d ₁ ) / d ₁ d ₂ (3-1) From equation (3-1), Lattice pitch d ₁ , d ₂
When the difference between the grating pitches is reduced, the diffraction angle θ
⁽²⁾ _-1 can be made smaller. Also, (m,
When the combination of (M) is (m, M) = (-1, 1) or (1, -1), the absolute value of the diffraction angle θ ⁽²⁾ becomes the smallest.

At this time, the diffraction angle θ ⁽²⁾ _-1 is given by the following equation (4)
Becomes equal to the diffraction angle of the ± 1st-order diffracted light when only the diffracting means having the grating pitch d ₀ is used.

D ₀ = | d ₁ d ₂ / (d ₂ −d ₁ ) | (4) As described above, by using two pieces of diffraction means, the diffraction angle by the diffraction means having a large grating pitch can be obtained. Approximately equal diffraction angles can be realized with a small grating pitch.

From equation (3), for a light ray whose combination of diffraction orders is (m, M) = (1, −1) or (−1, 1), a reverse light ray is transmitted from the diffraction grating to the image display element. When tracking is performed, each diffracted light is imaged on the image display element, and the position is shifted from the original pixel position. The shift amount Δ can be expressed as Expression (5) using the focal length f of the eyepiece optical system and the diffraction angle θ ₀ .

Δ = ftan θ ₀ ≒ fθ ₀ θ ₀ = | λ (d ₂ −d ₁ ) / d ₁ d ₂ | (5) The image quality is improved by making the pixel array pattern optically inconspicuous. Therefore, it is desirable that the shift amount Δ is equal to or less than the cycle of each pixel of the liquid crystal display element. Therefore, from Equations (3) and (5), in order to make the pixel period inconspicuous, the grating pitches d ₁ and d _{2 of} each diffraction surface are determined by the following Equation (6).
Should be satisfied. Where f is the focal length of the eyepiece optical system,
λ is the incident wavelength, L is based on arbitrary pixels of R, G, B,
It is the distance from the pixels of the same color arranged in the same row and column as the reference pixel to the pixel closest to the reference pixel. However, when the pixel arrangement is a square arrangement, the R or B pixel is Use as a reference.

0 <| fλ (d ₂ −d ₁ ) / d ₁ d ₂ | ≦ 2L (6) As a result, it is possible to realize a video display device in which the pixel array pattern of the image display element is inconspicuous. it can.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image display device according to the present invention will be described based on several embodiments. FIG. 1 is a diagram showing a main part of a head-mounted image display device according to one embodiment. This image display device converts an image displayed on a liquid crystal display element 2 into an enlarged image by a convex lens 3 of an eyepiece optical system. The liquid crystal display device 2 is projected onto a user's eyeball, and is illuminated by an illumination system 1 disposed behind the liquid crystal display device 2, and a display image thereof is projected. Then, based on the present invention, a diffraction grating 11 having a different grating pitch between the convex lens 3 of the eyepiece optical system and the exit pupil formed by the eyepiece optical system,
12 are arranged in parallel.

FIG. 2 shows a pixel pattern of the liquid crystal display element 2. FIG. 1A shows a vertical stripe arrangement, FIG. 2B shows a mosaic arrangement, FIG. 1C shows a square arrangement, and FIG. 1D shows a delta arrangement. In this case, when the cycle Ly in the same row and the cycle Lx in the same row from the reference pixel R are compared, Ly is closer, so this Ly is L in equation (6). In the horizontal stripe arrangement, Lx is L in Expression (6). Further, in the mosaic arrangement of FIG. 2B, when the period Ly in the same column and the period Lx in the same row are compared from the reference pixel R, Lx is closer, so this Lx is L in the equation (6). FIG. 2 (c)
In the square arrangement, the pixel G is arranged about twice as large as the R and B pixels. Therefore, the reference pixel is selected from R and B.
When the R pixel is used as a reference, the cycle Ly in the same row and the cycle L in the same row
When x is compared, Lx is closer, so this Lx is L in equation (6). Further, in the delta arrangement of FIG. 2D, Lx in the figure is L in the equation (6), as in the case of FIGS. 2A to 2C.

Here, in the liquid crystal display element 2, a liquid crystal layer is sandwiched between a common electrode and a pixel electrode, and a color filter composed of three primary colors (R, G, B) corresponding to each pixel electrode is defined above. It has liquid crystal layer portions arranged at a predetermined period L.

The light that has passed through the convex lens 3 from the liquid crystal display element 2 enters the diffraction gratings 11 and 12, and is separated into a plurality of diffracted lights. FIG. 3 shows an example of the diffraction gratings 11 and 12 that can be used here.

FIG. 3 schematically shows an example of the diffraction gratings 11 and 12 which can be used here. FIG. 5A shows a grid having a ring shape, FIG. 5B shows a grid provided in both vertical and horizontal directions, and FIG. 5C shows one grid in a vertical or horizontal direction (in the case of FIG. , Vertical direction), and FIG. 3D shows a honeycomb-shaped diffraction grating in which rows of hexagonal projections (or depressions between hexagons) are arranged vertically or horizontally. At half a pitch apart from each other. In addition, the two diffraction gratings 11 and 12 are, for example, as shown in FIG.
If the diffraction gratings 11 and 1 are integrally formed on the front and back surfaces of the
The distance between the two surfaces can be stably maintained. The diffraction grating 1
The chromatic dispersion of 1 and 12 can be corrected to compensate each other since two diffraction gratings are used. The diffraction grating shown in FIG. 3 may be either a volume type or a phase type.

FIG. 5A shows the state of diffracted light when passing through the diffraction grating. By disposing the diffraction gratings 11 and 12, the light is separated into a plurality of diffracted lights. The light shown by the solid line is the diffraction order (m,
M) is a light beam in which (m, M) = (1, −1) and (−1, 1). These diffracted lights have the smallest diffraction angle after passing through the diffraction grating 12.

FIG. 5B shows the diffraction order (m, m) of each of the diffraction gratings 11 and 12 among the plurality of diffracted lights shown in FIG.
(M) is (m, M) = (1, −1) and (−1, 1) when the diffracted light is traced in the reverse direction. At this time, the light flux indicated by the dotted line is formed on the liquid crystal display element 2 at a position shifted from the original pixel position. The shift amount Δ can be expressed by Expression (5) using the focal length f of the eyepiece optical system 3. The shift amount Δ is
If the period is equal to or less than the period of each pixel of the liquid crystal display element 2, the pixel arrangement pattern can be made optically inconspicuous, and the image quality can be improved. For example, when the focal length f is 25 mm and the pixel period L of the liquid crystal display element 2 is 54 μm, in order to set the shift amount Δ = L / 2 for a wavelength of 0.5 μm, the diffraction angle is set to about 0.062 °. It is necessary to At this time, the first grating pitch d ₁ and the second grating pitch d ₂ are:
The combination may be such that (d ₁ , d ₂ ) = (0.1 mm, 0.082 mm) or (0.1 mm, 0.127 mm). However, any other combination of grating pitches may be used as long as conditional expression (5) is satisfied. At this time, if the grating pitch is too large with respect to the pupil diameter, it causes image distortion. Therefore, it is desirable that the grating pitch of each of the diffraction gratings 11 and 12 satisfies the following conditional expression (7).

0.05 mm <d ₁ <0.3 mm 0.05 mm <d ₂ <0.3 mm (7) In FIG. 5, two diffraction gratings are used, but as shown in FIG. In addition, it is also possible to form diffraction grating surfaces on both surfaces of one parallel flat plate.

FIG. 5C shows that the ± first-order light diffracted using one diffraction grating 13 is traced in the reverse direction, and the shift amount on the liquid crystal display element 2 is the shift amount shown in FIG. It is the same as the amount. Compared to the case of FIG.
In order to obtain the same shift amount, the diffraction angle on the diffraction surface must be reduced. Therefore, the grating pitch of the diffraction grating 13 necessarily increases. For example, focal length f = 25 m
m, the pixel period L of the liquid crystal display element 2 is 54 μm. In order to set the shift amount Δ = L / 2 for a wavelength of 0.5 μm with only one diffraction grating, the grating pitch d = 0.4.
It needs to be 6 mm. Therefore, the pupil diameter is φ = 4 m
When the distance is m, the above-mentioned grating pitch is large with respect to the pupil diameter.

In order to reduce the wavelength dependence of the diffraction efficiency, a rectangular diffraction grating with a duty ratio of 0.5 is used as shown in FIG.
As shown in a perspective view in FIG. In the case of FIG. 6, rectangular shapes of the same size are arranged in a checkered pattern on a plane. Then, the grating pitch P _y in the transverse direction of the grating pitch P _x and the vertical direction is not necessarily match. When the groove depth D ₀ is set to around 0.5 μm, no zero-order light is generated with respect to red, green, and blue light.

As another method for reducing the wavelength dependence of the diffraction efficiency, there is a method using a rectangular diffraction grating having a duty ratio of about 0.25. In the case of this diffraction grating, 0
Next light is also used. FIG. 7 shows the dependence of the diffraction efficiency on the groove depth when the duty ratio is 0.265. The rectangular diffraction grating having a duty ratio of 0.265 has a valley of the 0th-order diffraction efficiency and 1
The peaks of the next diffraction efficiency coincide. Although the groove depth at the time of the coincidence varies depending on the wavelength, the zero-order and the first-order curves are in contact with a gentle slope, so that there is little change in efficiency depending on the wavelength. When the groove depth D _{0 is} 0.58 μm, the wavelength dependency becomes smallest. Such a rectangular diffraction grating may be formed one-dimensionally, or may be formed two-dimensionally as shown in FIG.

As a next example, a method for preventing a color change by using a diffraction grating having a sine wave with concave and convex shapes will be described. Here, diffraction gratings 11 and 12 having different groove depths are used. FIG. 8 shows the relationship between the diffraction efficiency of the sine wave diffraction grating and the groove depth. Here, D ₁ and D ₂ in the figure are selected as the groove depths of the two diffraction gratings 11 and 12. The following table shows the magnitude of each diffracted light.

[0038]

In this case, in the arrangement shown in FIG. 1, if a sinusoidal diffraction grating having a groove depth D _{1 is used} as the diffraction grating 11 and a diffraction grating 12 having a groove depth D ₂ is used, the diffraction efficiency of D ₁ is reduced. Although the product of the diffraction efficiency of those D ₂ is the final diffraction efficiency, as can be seen the table above, the two diffraction gratings 11, 1
2, the difference in diffraction efficiency depending on the color can be corrected.

Next, a method of processing a ghost image using extra diffracted light will be described. For example, when two diffraction gratings 11 and 12 having the arrangement shown in FIG. 1 are used, two diffraction gratings 11 and 12 are used.
The light that passes through one of them and is diffracted on the other is extra light, which results in a ghost image. FIG. 9 (a)
FIG. 3 is a diagram showing an example of the light, which is light that passes through a first diffraction grating 11 and is diffracted by a second diffraction grating 12. If the diffraction angle φ is smaller than the viewing angle 2θ, the normal image and the ghost image appear on the user's eye as shown in FIG. 9B, and the image quality deteriorates. . To prevent this, the diffraction angle φ should be larger than the viewing angle 2θ. For example, viewing angle 2θ = 30 °, light wavelength λ
= 0.4 μm, the grating pitch d of the diffraction gratings 11 and 12 becomes d <λ / sin 30 ° = 0.8 μm from the relationship of dsin φ = λ, and the grating pitch d of each of the diffraction gratings 11 and 12 is 0. It is understood that it is sufficient if the thickness is 0.8 μm or less. In setting the wavelength, a short wavelength having a small diffraction angle was selected from visible light. If the grating pitch d of the diffraction gratings 11 and 12 is set in this manner, the ghost image can be separated from the normal image as shown in FIG.

By the way, as shown in FIG. 10, in order to completely remove the ghost image existing on the outer periphery of the normal image,
For example, as shown in FIG. 11, a field-of-view selection glass 14 may be arranged on the exit side of the second diffraction grating 12. This view selection glass 14 is “Angle 2” manufactured by Nippon Sheet Glass Co., Ltd.
As in "1" (product name), light with a small incident angle passes through as it is, but light with a large incident angle is scattered and cannot be transmitted. This special glass 14 is arranged between the diffraction grating 12 and the pupil 6 of the eye, and the diffraction angles φ of the diffraction gratings 11 and 12 are
Is set to be larger than the viewing angle 2θ, the unnecessary diffracted light that generates the ghost image is incident on the field-of-view selection glass 14 at an angle larger than the light that generates the normal image, and thus only the unnecessary diffracted light is scattered here. Ghost image can be completely erased.

Another method for removing a ghost image is to increase the distance from the diffraction grating 12 to the pupil plane of the eye. That is, as shown in FIG. 12, the distance W from the diffraction grating 12 to the pupil plane of the eye may be set so that the unnecessary diffraction light indicated by the broken line does not enter the enlarged pupil diameter b. Assuming that the diffraction angle is φ and the pupil diameter before enlargement is a, W should satisfy the following expression.

W ≧ (b + a / 2) / tan φ In this method, the diffraction angle φ does not need to be larger than the viewing angle 2θ.
There is an advantage that 12 can be used.

In the above embodiment, the case where the convex lens 3 is used as the eyepiece optical system is described. However, the type of the eyepiece optical system is not limited to this. A type using a mirror may be used.

FIG. 13 is a cross-sectional view showing a case where an eyepiece optical system is constituted by using the eccentric prism 3 'to constitute a head (face) -mounted image display device. The decentered prism 3 ′ constituting the eyepiece optical system has a positive refractive power and includes three curved surfaces 21 to 23. Light emitted from the liquid crystal display element 2 enters the prism from the first surface 21, The light is totally reflected by the third surface 23, and the reflected light is incident on and reflected by the second surface 22. This time, the light is refracted by the third surface 23 and exits the prism.
The light passes through the two diffraction gratings 11 and 12 according to the present invention via the lens 3 "which forms a part of the eyepiece optical system, and reaches the observer's eye E. In this example, the diffraction gratings 11 and 12 have a pixel array pattern. The head (face) with the function to make it inconspicuous
It is also used as the cover window of the wearable image display device. In addition,
In the case where one of the two diffraction gratings 11 and 12 is exposed to the outside in this way, as shown in FIG. It is desirable to arrange the diffraction grating 12 so that the plane faces outward, so as to prevent dust and scratches on the grating surface.

[0046]

As is apparent from the above description, in the present invention, two diffraction gratings are arranged between the image display element and the exit pupil, and the pixel arrangement of the image display element is determined by the difference between the grating pitches. Since the pattern is made inconspicuous, it is not necessary to increase the period interval of each diffraction grating even if the overall diffraction angle is reduced, and the problem of observing image distortion can be avoided. Further, a moire image, a lattice pattern, dust and the like are not seen.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main part of a head mounted image display device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a pixel pattern of a liquid crystal display element.

FIG. 3 is a diagram illustrating an example of a diffraction grating.

FIG. 4 is a diagram showing an example in which two diffraction gratings are formed integrally.

FIG. 5 is a diagram for explaining the operation of the present invention.

FIG. 6 is a perspective view showing a two-dimensional rectangular diffraction grating that can be used in the present invention.

FIG. 7 is a diagram showing the groove depth dependence of the diffraction efficiency of a rectangular diffraction grating having a duty ratio of 0.265.

FIG. 8 is a diagram showing the groove depth dependence of the diffraction efficiency of a sine wave diffraction grating.

FIG. 9 is a diagram illustrating generation of a ghost image.

FIG. 10 is a diagram illustrating a state where a ghost image is separated from a normal image.

FIG. 11 is a fragmentary cross-sectional view showing an arrangement for erasing a ghost image.

FIG. 12 is a main part sectional view showing another arrangement for removing a ghost image.

FIG. 13 is a cross-sectional view of a case where an eyepiece optical system is configured using an eccentric prism and configured as a head (face) -mounted image display device.

FIG. 14 is a diagram showing a desirable arrangement of a grating surface when a diffraction grating is exposed to the outside.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Illumination system 2 ... Liquid crystal display element 3 ... Convex lens 3 '... Eccentric prism 3 "... Lens 6 ... Pupil 10 ... Glass plate 11 ... First diffraction grating 12 ... Second diffraction grating 13 ... Diffraction grating 14 ... Field of view selection Glass 21 ... first surface 22 ... second surface 23 ... third surface

Claims (2)

[Claims] 1. An image display apparatus comprising: an image display means for displaying an image; and an eyepiece optical system for projecting the image onto a user's retina, wherein the image display means includes an emission part formed by the eyepiece optical system. A first diffractive means and a second diffractive means are provided in the optical path between the pupil and the grating pitch of each of the diffractive means.
_1, when the _{d 2, 0 <| fλ (} d 2 -d 1) / d 1 d 2 | image display device characterized by being configured to satisfy ≦ 2L. Here, f is the focal length of the eyepiece optical system, λ is the incident wavelength, and L is any pixel of R, G, and B as a reference, and among pixels of the same color arranged in the same row and column as the reference pixel. , The distance to the pixel closest to the reference pixel, where
When the pixel array is a square array, R or B pixels are used as a reference. Wherein the grating pitch d ₂ of the grating pitch d ₁ and the second diffraction means of said first diffraction _{means, 0.05mm <d 1 <0.3mm 0.05mm} <d 2 <0. The image display device according to claim 1, wherein 3 mm is satisfied.