JP2003185977A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display device constituted so that the roughness of an image can be satisfactorily reduced, and also, an image of high resolution can be imparted. <P>SOLUTION: As for the image display device provided with an image display element 1 wherein many pixels having a prescribed aperture are two- dimensionally and regularly arranged, a phase type diffraction grating 3 and an observation optical system 2, provided that L denotes a distance (length as calculated on an air basis) from the display surface of the image display element 1 to the phase type diffraction grating 3, (f) denotes the focal distance of the observation optical system 2, and (m) denotes magnification, the following inequality is satisfied; f>L≥0.2/m<SP>2</SP>[m]...(10). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device, and more particularly to an image display device such as an electronic viewfinder.

[0002]

2. Description of the Related Art A dot matrix type image display element represented by a liquid crystal display element (LCD) displays an image by modulating pixels arranged two-dimensionally.
The higher the pixel density of this display element, the finer the image to be displayed and the sharpness increases, but the difficulty in manufacturing also increases and the cost increases. If an inexpensive display element having a low pixel density is used, the gaps between the pixels are conspicuous and a rough image quality is observed.

On the other hand, as a device for enlarging and displaying an image of an image display element by an optical system, a projector or an HM
D (head-mounted image display device) can be given. When the inexpensive display element described above is used in these devices, the image is enlarged and the gap portion of the pixel is also enlarged, so that the roughness becomes more conspicuous and the image being displayed is felt to be original. The image will have a low texture.

Therefore, a method has been proposed in which an optical filter is provided between the image display element and the eyeball of the observer to separate one pixel into a plurality of pixels, thereby reducing the roughness of the pixel.

For example, there is an image display device having a structure in which a plurality of quartz crystals are stacked between a liquid crystal display element and an observer as shown in FIG.

Further, other conventional types include Japanese Patent No. 2,883,492 and Japanese Patent No. 2,980,268. The image display device has a configuration in which a two-dimensional lattice pattern is installed between a liquid crystal display element and an observer.

Further, JP-A-5-307174, in which an optical low-pass filter is arranged on the front surface of the image display device,
Japanese Patent Application Laid-Open No. 8-122709 and US Pat.
719, 588, etc.

[0008]

However, as shown in FIG.
It is very expensive to use a crystal such as quartz as an optical filter, and moreover, because multiple crystals are used to support two-dimensional display, the optical filter becomes thick and the device itself becomes large. To do.

When the optical filter is composed of a phase type diffraction grating, in order to reduce the roughness of the pixel, the MTF (Modu) at the Nyquist limit of the optical filter is reduced.
(Lation Transfer Function)
Is set low. This reduces the graininess, but since the MTF of the spatial frequency near the Nyquist limit becomes low, a blurred image will be observed. On the contrary, if the MTF at the Nyquist limit is set to be high, the MTF in the vicinity of that frequency is high, and high resolution display can be performed.
Roughness cannot be reduced sufficiently.

Further, the phase type diffraction grating has a different diffraction angle depending on the wavelength, and the MT of the optical filter at each wavelength corresponding to RGB, which is the basis of the color display of the image display device.
F changes. However, in the conventional technology,
There is no consideration for the MTF of optical filters for different wavelengths.

Further, the phase type diffraction grating has the function of an optical low pass filter, but at the same time, the pixels of the display element and the phase type diffraction grating interfere with each other to cause moire fringes. Since the moire fringes have a period of several times the pixel pitch or more, large fringes are overlapped on the display image and the image is significantly deteriorated. As a method of making the moire fringes less visible, JP-A-5-307174 and Japanese Patent No. 2,88
No. 3,492, there is a method in which the grating pitch of the phase type diffraction grating is set to be equal to or less than the pixel pitch of the display element. However, since the diffraction grating pitch and the diffraction angle are in inverse proportion to each other, when the diffraction grating pitch is small, the diffraction angle becomes large and the pixel diffusion amount becomes large. Along with this, the region where the MTF of the optical filter is reduced shifts to the low frequency side, so that the MTF at low spatial frequencies is also reduced, and the image becomes blurred overall.

Further, since the image display device observes the image display element through such an optical filter, when a filter for adhering foreign matter, mixing in foreign matter, and decreasing transmittance is used,
The observer observes the foreign matter other than the image information and the image with reduced transmittance. However, in the prior art,
There is no description about problems when incorporated as a device.

The present invention has been made in view of such problems of the prior art, and an object thereof is to provide an image display device which sufficiently reduces the roughness of an image and gives an image with high resolution. It is to be.

[0014]

An image display device of the present invention that achieves the above object is an image display device in which a large number of pixels having a certain aperture are regularly arranged in two dimensions, and a phase type diffraction grating. And an observation optical system, the distance (air conversion length) from the display surface of the image display element to the phase type diffraction grating is L, and the focal length of the observation optical system is f. When the ratio is m, the relationship of f> L ≧ 0.2 / m ² [m] (10) is satisfied.

Another image display device of the present invention comprises an image display element in which a large number of pixels having a certain aperture are regularly arranged in a two-dimensional manner, a phase type diffraction grating, and an observation optical system. In the image display device, the grating pitch P of the phase type diffraction grating is relative to the light beam diameter W on the phase type diffraction grating of the light beam emitted from the center of the image display element and entering the observation optical system. , 2 ≦ W / P ≦ 50 (11) are satisfied.

Hereinafter, the reason why the above structure is adopted and the operation thereof will be described.

As shown in FIG. 1, when observing a virtual image magnified by the observation optical system 2, the image display element 1 which is an observation object is arranged near the front focus position of the observation optical system 2. Therefore, an object near the image display element 1 is directly observed in an enlarged manner. In the case of the present invention, the image display device 1
The phase-type diffraction grating 3 is provided near the display surface of No. 1 to improve the image quality of the image display element 1. In that case, if the position where the phase type diffraction grating 3 is arranged is within the range of the adjustment force of the human eye E, if foreign matter such as dust adheres to the phase type diffraction grating 3, it is enlarged. I can see it.

Assuming that the far point distance of the human eye is D _f (m) and the near point distance is D _n (m), the adjusting force B (m ^-1 ) of the human eye is
Is given by the following equation.

[0019]     B = 1 / D_n-1 / D_f                                ... (1) As shown in Fig. 2, the near distance depends on the human age.
Very different. Assuming an observer in his 20s to 50s,
Point distance is about -10 to -2D (diopter: m ^-1), D
_n= 10 to 500 mm, and the far point distance is D_f=
In the case of ∞, the adjustment power is 10-2D (diopter: m^-1)
Becomes

In the image display device for observing the small image display element 1 as an enlarged virtual image as in the present invention,
It is considered that the image display elements 1 are placed near the front focus position of the observation optical system 2 and arranged so that the position of the eye E is near the rear focus position of the observation optical system 2.
In this case, the image on the image display element 1 is observed as a virtual image magnified by the observation optical system 2, and in this case, as shown in FIG.
As shown in, the angle u ′ at which the virtual image of the image display element 1 is seen
(FIG. 3 (b)) and the distance (250
The ratio of the angle u (FIG. 3A) expected in mm) is defined as the enlargement ratio m. When expressed by a formula, m = tan (u ′) / tan (u) (2) Further, the enlargement ratio m is given by m = 250 / f ′ ... (3), where f ′ (represented by mm) is the rear focal length of the observation optical system 2.

Next, the depth of focus on the image display element 1 side in the observation optical system 2 of the image display device is obtained. As shown in FIG. 4, the far point distance D _f and the near point distance D _n of the human eye E are both distances from the front principal point which is the entrance pupil of the eye E. Therefore, the distances measured from the front focal position F ′ of the image display element corresponding to D _f and D _n are respectively d _f , d _n , the front focal length of the observation optical system 2 is f, and the rear focal length is f ′. Then, the _{d n -d f = -f · f} '(1 / D f -1 / D n) ··· (4). When the enlargement ratio is shown according to the equation (3), m = D _f / f ′ ... (5). Assuming that the refractive indices of the image display surface side and the image side of the observation optical system 2 are n and n ′, f = −n ′ / n · f ′ (6) Equation (4) is changed to Equation (5), 6) is modified to obtain d _n −d _f = n ′ / n · f ′ ² · (1 / D _f −1 / D _n ) = n ′ / n · (D _f / m) ² · (1 _{/ D f -1 / D n)} ··· (7) the image display device 1 side of the depth of focus by adjusting power of the eye [delta] = d
_{If f- dn} , the far point distance D _f is ∞, and δ = n ′ / n · (D _n / m) ² · B = n ′ / n · D _n / m ² (8) is there. Since both the display surface side and the image side are air, n = n '=
It becomes 1.

In general, when an image is observed near a near point, the details of an object can be clearly seen, but the eyes are strained, and there is a risk of getting tired if the eyes are viewed for a long time. The distance that looks good without getting too tired is farther than the near point. In the twenties, if the observation distance is about 200 mm or more, fatigue does not occur so much. Therefore, _assuming that the near point distance in the above equation is D _n = 0.2, δ is δ = 0.2 / m ² ( 9).

Here, the air-equivalent long distance from the display surface of the image display element 1 to the phase type diffraction grating 3 is L (air-equivalent length).
When set to be larger than 0.2 / m ² (δ), dust and the like adhering to the phase type diffraction grating 3 have a diopter side that is on the negative side of the accommodation power of the eye E of the observer. Can be suppressed and the influence on the observed image can be suppressed. Further, in order to prevent the phase type diffraction grating 3 from interfering with the observation optical system 2, it is desirable that the phase type diffraction grating 3 is located closer to the image display element than the principal point of the observation optical system 2.

Therefore, by setting the air-converted long distance L to be f> L ≧ 0.2 / m ² [m] (10), the observer can observe a good image with less influence of dust and the like. It will be possible.

For example, assuming that the magnification ratio m of the observation optical system 2 is 5 times and 25 times, substituting it into the equation (10), 5 times: L ≧ 8 (mm) 25 times: L ≧ 0.32 (mm ). If the phase-type diffraction grating 3 is arranged in this range, the adhered matter such as dust is on the negative side of the accommodation power of the observer's eye E, so that it is difficult to focus the adhered matter and the observed image is affected. Few.

When the phase type diffraction grating 3 is arranged between the image display element 1 and the observer's eye E in order to improve the image quality by the phase type diffraction grating 3, with respect to the grating pitch of the phase type diffraction grating 3. A sufficiently large luminous flux diameter is a necessary condition for achieving uniform image quality on the entire observation screen. When the distance from the image display element 1 to the phase type diffraction grating 3 is short, the diffraction angle is large and the grating pitch is small, so that the number of the phase type diffraction grating 3 in the light flux does not matter. However, when the distance from the image display element 1 to the phase type diffraction grating 3 is long, it is necessary to reduce the diffraction angle of the phase type diffraction grating 3 (in consideration of the backward ray tracing, different diffraction of the phase type diffraction grating 3 is considered). In order to form an image by shifting the pixels by a half pitch in the order, the diffraction angle becomes smaller as the distance from the image display element 1 to the phase type diffraction grating 3 increases), and the grating pitch of the phase type diffraction grating 3 becomes larger. ,
In some cases, it may be difficult to satisfy the condition that the luminous flux diameter is sufficiently larger than the grating pitch of the phase type diffraction grating 3.

If the beam diameter of the phase type diffraction grating is not sufficiently large with respect to the grating pitch, when the observer rotates the eyeball and observes the periphery of the display element, the grating number of the diffraction grating with respect to the beam diameter is Since the change becomes large and the diffraction effect changes, the quality of the observed image changes depending on the place where the user is looking. Therefore, it is important to set the grating pitch of the diffraction grating (1 pitch of the unevenness) to P with respect to the beam diameter W of the phase type diffraction grating, and to satisfy the condition of 2 ≦ W / P ≦ 50 (11) .

When the lower limit of 2 of this condition is exceeded, the number of diffraction gratings with respect to the light beam diameter is small and the length between the gratings is large, so that the observer rotates the eyeball to observe the periphery of the display element. In addition, the number of diffraction gratings changes with respect to the diameter of the light flux, and the image quality of the observed image may change depending on the place of viewing. If the value exceeds the upper limit of 50 and becomes larger, the grating pitch of the phase diffraction grating becomes smaller, the diffraction angle becomes larger, and the amount of diffusion of the diffracted image becomes larger accordingly, so that the image may be blurred.

By the way, the phase type diffraction grating 3 has one grating pattern (irregularities) formed by the convex portion and the substrate portion (FIG. 6). Is the minimum necessary condition for forming a diffraction image. More preferably, it is a condition for reproducing stable image quality that there are three or more grating patterns in the light flux diameter W. More preferably, the number of grid patterns is 5 or more is a condition for reproducing more stable image quality.

In the present invention, the phase type diffraction grating may have a shape having two diffraction components. The enlarged image display element is an image display element in which a large number of pixels having a certain opening are arranged two-dimensionally, and unnecessary high-frequency roughness that is not present in an image also exists two-dimensionally. When a diffraction grating having one diffraction direction (referred to as a one-direction diffraction grating) is arranged, diffracted pixels are separated only in a certain direction and interpolation occurs. For example, in the case of an image display element with pixels arranged in a delta array (FIG. 10), the diffraction pattern of the one-way diffraction grating diverges high-order light in the one-dimensional direction centering on the zero-order light, When combined with a one-way diffraction grating whose direction is horizontal or vertical, the observable image separates pixels in the horizontal direction or in the vertical direction only, so the black matrix between the upper and lower pixels or the left and right pixels is not interpolated. , It is observed as an image in which black streaks remain in the horizontal direction or the vertical direction, and the remaining black matrix cannot reduce the high frequency roughness. Therefore, if a diffraction grating having two directions of diffraction (two-direction diffraction grating) is used, the diffraction pattern becomes a pattern having a two-dimensional spread, and pixels are interpolated very efficiently in combination with an image display element. This makes it possible to reduce the two-dimensional high-frequency roughness.

Further, as the phase type diffraction grating 3 having such a shape having two diffractive components, it is possible to have a shape having two diffractive components on one surface as shown in a perspective view in FIG. In the figure, 13 is a phase part. In the case of a phase type diffraction grating having two diffractive components on one surface, only one surface needs to be manufactured and evaluated, the manufacturing time can be reduced, and the cost can be reduced. Further, the other surface can be an optical surface. For example, by giving a positive refracting power, the magnification of the observation optical system can be increased, and the observer can enjoy an image with a large angle of view. Besides, it can be used as an optical surface for aberration correction,
By forming the diffractive optical surface for correcting chromatic aberration, it is possible to achieve a more complete image display device.

Further, as the phase type diffraction grating 3 having such a shape having two diffraction components, as shown in a perspective view of FIG. In the figure, 13a is a front side phase portion, and 13b is a front side phase portion. The diffraction grating has phase parts 13a and 13b.
By changing the grating height of, it is possible to give different diffraction efficiencies and to make different wavelength dependences. Since the pixel separation of the long wavelength (R) is larger than the pixel separation amount of the short wavelength (B), color misregistration occurs. The amount of color misregistration is proportional to the size of the separation amount. It will be blurred. In the case of a two-dimensional diffraction grating, if the optimum separation amount differs in two directions, the magnitude of the color shift amount also changes, and the sense of resolution greatly differs in the two directions. Therefore, the phase type diffraction grating 3 is
As shown in FIG. 8, if one-direction diffraction gratings are formed on the front and back sides, respectively, the grating height can be changed, and the diffraction efficiency of R in the direction in which the amount of color misregistration is large can be reduced to prevent the resolution from being lowered. Is possible. By using the phase type diffraction grating 3 having such a configuration, it is possible to adapt to image display elements of various arrangements without lowering the resolution.

Since the two one-dimensional diffraction gratings are independent diffraction gratings, the angle formed by the two diffraction directions can be freely given to adapt to various image display elements having different pixel pitches and pixel arrangements. It is possible to create a completely new diffraction grating by combining them.

Of course, as shown in FIG. 9, by combining _two one-way diffraction gratings 3 ₁ and 3 ₂ , it is possible to construct a phase type diffraction grating 3 having the same function and effect.

The phase type diffraction grating 3 may have a shape having one diffraction component. When an image display element having a large black matrix portion in the vertical direction of the pixel is used, the pixel can be interpolated by a diffraction image by diffraction in only one direction, and the black matrix frame around the pixel can be felt thin, which is noticeable to the observer. The pixel aperture is effectively improved. Considering the case of enlarging and displaying characters, it may be easier to observe when the diffraction in only one direction is performed because the resolution is high. Further, in the case of the one-way diffraction grating, since only one surface needs to be manufactured and evaluated, the evaluation time can be reduced and the cost can be reduced. Further, by making the other surface flat, manufacturability and assemblability are improved. Further, the other surface can be an optical surface. For example, by giving a positive power, the magnification of the observation optical system can be increased and the observer can enjoy an image with a large angle of view. Besides, by forming an optical surface for aberration correction or forming a diffractive surface for correction of chromatic aberration, an image display device having a higher degree of completion can be achieved.

Further, in the present invention, the phase type diffraction grating may have a shape having three diffraction components. There are various pixel arrangements of the image display element, and among them, there is a type (delta arrangement) in which the pixel arrangement in the vertical direction is shifted by a half pixel as shown in FIG. With the center as the center, the directions of the closest same-color pixels are three directions of arrow A, arrow C, and arrow D. By using a three-way diffraction grating that can interpolate in three directions of such an image display device, it is possible to reduce roughness without significantly lowering the resolution. In particular, the diffracted light in the oblique direction can be divided into horizontal and vertical components, a low pass filter effect can be given to some extent in any direction of the image display element, and the effect of improving the texture of the entire image is great. In the three-way diffraction grating, as shown in FIG. 11, a type in which a diffraction grating having a two-dimensional phase portion 13c on the front side and a one-dimensional phase portion 13d on the back side is formed, or a diffraction grating (phase portion) The same effect can be obtained when the diffraction structure of FIG. 12 in which the periodic structure of 13e exists in three directions and the diffraction pattern in three directions are also used. This effect is suitable for moving images, people, landscapes, and the like in which the texture is important, and those with color gradation.

In the present invention, the phase type diffraction grating 3
It is desirable that the diffractive surface is oriented toward the image display element 1 side. The phase type diffraction grating 3 is shown in FIGS.
As shown in FIG. 12, it is an optical element in which a phase difference is partially provided by the phase portions 13 and 13a to 13e, and a general phase type diffraction grating 3 has a concave and convex shape on one surface thereof to obtain a phase difference of light. Is generated. This phase type diffraction grating 3
If oil or a fingerprint adheres to the concave portion, the diffraction grating that has given a constant phase difference will have a partially different phase difference, resulting in a difference in diffraction intensity. Further, the dirt attached to the phase-type diffraction grating 3 affects the transmittance, resulting in an image that is difficult to observe. Further, if the uneven portion is chipped or damaged, the same effect is exerted. Therefore, when the diffractive surface is directed toward the image display element 1, the diffractive surface is arranged in the lens frame of the image display device, the observer does not have to directly touch the diffraction grating surface, and the uneven portion of the diffractive surface is dusted from the outside. In addition, stains, fingerprints, and oil are prevented from adhering, and the uneven portions are not chipped or scratched, and uniform and good image observation is possible.

By the way, the amount of pixel separation by the phase type diffraction grating 3 is largest in red (R) and smallest in blue (B) according to the relationship between wavelength and diffraction angle. This difference in the pixel separation amount is directly reflected in the resolution, and if the three colors have the same diffraction efficiency, the red separation amount is the largest, so the resolution is lowered. In order to prevent this, it is possible to provide an image display device having less wavelength dependence by appropriately setting the diffraction efficiency.

For that purpose, the diffraction efficiency of the first-order diffracted light is defined as the diffraction efficiency, which is the value obtained by normalizing each of the diffracted lights obtained by irradiating the phase type diffraction grating with monochromatic light by the 0-th order diffracted light.
1. When the colors corresponding to the wavelengths of monochromatic light are blue, green, and red respectively, when distinguishing by (B), (G), and (R) added after the symbol, E1 (R) <E1 ( It is necessary to satisfy the relationship of G) <E1 (B) ... (12). If this relationship is satisfied, the difference in MTF for each color below the Nyquist frequency is reduced, and an image display device with less wavelength dependence can be obtained.

Further, in the phase type diffraction grating 3, the diffractive surface has a substantially rectangular cross section, and its corners may be rounded. The cross-sectional shape of the phase portion is greatly involved in the diffracted light intensity (diffraction image) of the phase type diffraction grating. The intensity of the diffracted light is obtained by converting the cross-sectional shape of the diffraction grating into a phase difference and performing Fourier transform. When considering a rectangular diffraction grating having a rectangular cross section and rounded corners, it is known that the higher-order diffracted light efficiency is smaller in a rectangle having rounded corners than in a rectangle. A phase diffraction grating having a high efficiency of high-order diffracted light causes a high-order light to be strongly generated in the diffraction direction when an observer observes a white object on a black background, which causes deterioration of image quality. Therefore, by manufacturing a rectangular diffraction grating and rounding the corners by polishing or the like, it is possible to reduce the intensity of higher-order diffracted light and obtain good image quality with less scattered light.

Further, in the phase type diffraction grating 3, the diffractive surface has a trapezoidal cross section, and its corners may be rounded. By setting the corners of the cross-sectional shape to obtuse angles and then rounding the corners by polishing or the like, the phase diffraction grating can be manufactured easily, the high-order diffracted light intensity is small, and a better image quality can be obtained.

By the way, as shown in the examples below,
Specifically, the diffraction efficiency (%) of the first-order diffracted light at a certain wavelength of the phase type diffraction grating is defined as Exy (x is the horizontal direction, y is the vertical direction), and the reference colors of the image display element are blue, green, and red. When the symbols (B), (G), and (R) attached after the symbol are used for discrimination, it is desirable that the following conditional expressions are satisfied.

Red: 70 <E10 (R) <300, 70 <E01 (R) <300 Green: 100 <E10 (G) <700, 100 <E01 (G) <700 Blue: 100 <E10 (B) < 800, 100 <E01 (B) <800 Here, the respective wavelengths are (B) = 442 nm,
(G) = 537 nm and (R) = 636 nm.

When the phase type diffraction grating 3 having such a characteristic is used, the MTF has a cutoff frequency in the vicinity of the Nyquist frequency, the roughness of the image is sufficiently reduced, and an image with a high resolution can be observed. Become.

Further, as shown in the embodiments described later, the following conditional expressions may be concretely established.

Red: 20 <E10 (R) <50, 20 <E01 (R) <50 Green: 30 <E10 (G) <60, 30 <E01 (G) <60 Blue: 30 <E10 (B) < 70, 30 <E01 (B) <70 Here, the respective wavelengths are (B) = 442 nm,
(G) = 537 nm and (R) = 636 nm.

When the phase type diffraction grating 3 having such characteristics is used, the MTF does not have a cutoff frequency in the vicinity of the Nyquist frequency, but similarly, the roughness of the image is sufficiently reduced and an image with a high resolution is obtained. Can be observed.

Further, in the phase type diffraction grating 3 of the present invention, it is desirable that the diffraction direction of at least one grating has an angle with respect to any side of the display surface of the image display element 1. As shown in FIG. 10, when the concept of the axis is introduced in the delta array in which the pixel arrangement in the vertical direction is shifted by about half a pixel,
In 0, line A is the horizontal axis and line B is the vertical axis. However, the same color pixels are lined up diagonally,
Lines C and D that draw an X can be set. By aligning the diffraction direction of the phase type diffraction grating 3 with the line C of the image display element 1, separation pixels can be arranged between pixels of the same color, and a smooth and high-quality image can be obtained. Further, by setting the diffraction direction of the phase type diffraction grating 3 at an angle deviated from the line C, it is possible to uniformly disperse the color pixels on the display surface without emphasizing the axis on the display surface. The optimum angle differs depending on the pixel arrangement, pixel size, and black matrix size of the image display element 1, and it is important to select an angle suitable for the adopted image display element 1.

In the phase type diffraction grating 3 of the present invention, it is desirable that the diffraction directions of at least two gratings have an angle with respect to any side of the display surface of the image display element 1. By arranging two of the diffraction directions of the phase type diffraction grating 3 with respect to the display surface side and aligning them with the lines C and D in FIG. 10, separation pixels can be arranged between pixels of the same color and the display surface axis can be maintained. It is possible to obtain smooth and high-quality images as they are. In addition, by making the diffraction direction at an angle with the lines A to D, it is possible to hide the display surface axis and scatter the pixels on one surface, and an image with reduced roughness can be obtained.

When the lines A to D are angled, it is desirable to shift the angle θ satisfying | θ | ≧ 1 °.

By the way, in the image display device of the present invention, as typically shown in FIG. 1, an eyepiece optical system is arranged as the observation optical system 2 on the exit surface side of the phase type diffraction grating 3.

Further, in the image display apparatus of the present invention, the observation optical system may be not only an eyepiece lens which is a normal coaxial optical system, but also a decentered free-form surface optical system. The image display device of the present invention is a device for displaying a virtual image by enlarging a small image display element with an observation optical system, and it is preferable that the device and the optical system are small in order to enjoy a large screen in a small space. The observation optical system is shown in FIG.
As shown in FIG. 13D, there are various types, but in the coaxial optical system as shown in FIG. 13A, an optical surface (refractive surface) is required to increase the virtual image size while correcting aberrations. It is necessary to increase the number of surfaces, and the optical system becomes large and the device becomes huge. An eccentric free-form surface optical system configured by decentering a refracting surface and a reflecting surface, in particular, FIG.
A decentered prism optical system as shown in FIG.
This problem can be solved by using No. 1-142783). 13A to 13D, reference numeral 4 indicates an exit pupil (eye point). Such a decentered free-form surface optical system can achieve a compact optical system by folding the optical path by decentering the surface, and the generated decentering aberration causes at least one surface shape of the decentered free-form surface optical system to be rotationally asymmetrical. Good correction can be achieved by using a curved surface. By using such a decentered free-form surface optical system, it is possible to reduce the number of optical elements that were required in the past and to achieve a compact optical system.

In the image display apparatus of the present invention, the phase type diffraction grating 3, the image display element 1 and the observation optical system 2 are fixed by an integrated supporting member so that they can be supported on the observer's head, thereby observing. The person can observe the image in any observation posture and observation direction.

In the above structure, the imaging optical system may be arranged in place of the observation optical system, and the image pickup device may be arranged in place of the image display device to be used as an image pickup apparatus. In that case, a decentered free-form surface optical system can be used as the imaging optical system.

[0055]

BEST MODE FOR CARRYING OUT THE INVENTION Several embodiments of the image display device of the present invention will be described below.

As shown in FIG. 5, the observer's pupil diameter changes depending on the brightness of the object to be observed. In the case of the image display device of the present invention, its brightness is determined by the brightness of the image display element and the total efficiency of the optical system, but it is approximately 1 to 500 cd / m ^2.
Therefore, the pupil diameter is expected to be about 2 mm to 5 mm. When the distance from the display element to the phase type diffraction grating is long, the beam diameter of the phase type diffraction grating is approximately the same as the size of the observer's pupil diameter. For example, FIG. 6A shows the light flux on the phase grating when the center is observed with the pitch of the diffraction grating being 1.5 mm and the pupil diameter being 2 mm.
Shown in. The luminous flux entering the pupil has one lattice pattern, but when the observer observes the corner of the screen by rotating the eyeball, the image quality of the observed image will be 1 to 2 lattice patterns. It changes depending on where you are looking.

On the other hand, FIG. 6B shows a case where the center is observed with the diffraction grating pitch being 0.25 mm and the pupil diameter being 2 mm. The light flux diameter W has eight grid patterns, and when the observer rotates the eyeball to observe the periphery of the screen, the grid pattern has eight to nine grid patterns. Since the change in the number of gratings does not affect the diffraction effect, the observer can obtain a good observation image quality up to the periphery of the screen.

FIG. 14 shows a structural example of the image display device according to the present invention. In FIG. 14, the illumination light emitted from the illumination means (backlight) 5 which is a light source is modulated by the image display element 1 made of a transmissive LCD, and passes through an optical low-pass filter made of a phase type diffraction grating 3 to provide an observation optical system. It is incident on 2 and is guided to the observer's eye E.

In the phase type diffraction grating 3, as shown in a plan view of FIG. 15 (a) and a sectional view of FIG. 15 (b), convex portions 13 which are phase portions are regularly arranged on a base material 14. It is a phase diffraction grating made of (Examples 1 and 3). The base material 14 is arranged substantially perpendicular to the optical axis 10. When viewed from the front, the shape of the convex portion of the phase portion 13 is circular as shown in FIG. 15A, and the cross-sectional shape is substantially rectangular. The shape of the phase portion 13 viewed from the front is not limited to a circle, but may be a quadrangle, a quadrangular corner of which is circular, or an ellipse. Further, the sectional shape is not limited to the rectangular shape, and may be a sine wave shape, a trapezoidal shape, or a triangular wave shape. The air-equivalent length from the display surface of the image display element 1 to the grating surface of the phase type diffraction grating 3 is L.

Some examples of the optical low-pass filter including the phase type diffraction grating 3 will be shown below.

First, numerical data of the phase type diffraction grating 3 of the optical low-pass filters of Examples 1 to 6 are shown in Table 1 below.

[0062]

Here, the focal length f of the observation optical system 2 of Example 1 is 20.0 mm, the focal length f of the observation optical system 2 of Example 2 is 16.0 mm, and the focal point of the observation optical system 2 of Example 3 is The distance f is 32.0 mm, the focal length f of the observation optical system 2 of Example 4 is 26.0 mm, the focal length f of the observation optical system 2 of Example 5 is 18.5 mm, and the focal length f of the observation optical system 2 of Example 6 is The focal length f is 22.6 mm, the refractive index n _d = 1.5254 for the d-line of the phase type diffraction grating 3, and the thickness of the phase type diffraction grating 3 of Example 2 is 1.4 mm. The thickness of the phase type diffraction grating 3 of No. 4 is 2.0 mm.

Here, the phase type diffraction grating 3 of Examples 1 to 4
Is a two-dimensional phase grating, and the first and third embodiments are shown in FIG.
As shown in FIG. 8, the two-dimensional diffraction grating is formed on one surface, and Examples 2 and 4 are types in which the one-dimensional diffraction grating is formed on the front surface and the back surface of the filter as shown in FIG. Further, Example 5 is a one-dimensional diffraction grating having a diffraction component only in the X direction (horizontal direction), and Example 6 is Y.
The one-dimensional diffraction grating has a diffraction component only in the direction (vertical direction).

In the third embodiment, the one-dimensional diffraction grating having a diffraction component in the X direction is rotated by 20 ° clockwise from the vertical direction. Therefore, the diffraction direction is rotated by 20 ° clockwise from the horizontal direction. Is rotating. Examples 1, 2, 4
Uses orthogonal two-dimensional diffraction gratings. However, it is possible to rotate the direction of the grating about the optical axis 10 regardless of the one-dimensional diffraction grating and the two-dimensional diffraction grating.

Therefore, the conditional expression (1
The values of L, W / P and 0.2 / m ² for 0) and (11) are as shown in Table 2 below. However, L and W / P are shown as values L _X , L _Y , W / P _X , and W / P _{Y in the X} and Y directions. The values relating to the distance are expressed in mm.

[0067]

Next, Tables 3 to 8 show the relative intensities of the primary light and the secondary light standardized by the 0th light of Examples 1 to 6 above.

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

The MTF curves of Examples 1 to 6 are shown in FIGS. 16 to 17, 18 to 19, and 20 to 2, respectively.
1, FIG. 22 to FIG. 23, FIG. 24, and FIG. 16,
18, 20, 22, and 24 are in the X direction (horizontal direction).
MTF curves of (a) are R (633 nm), (b) are G (543 nm), and (c) are B (422 nm).
It is a curve. In addition, FIG. 17, FIG. 19, FIG. 21, FIG.
FIG. 25 is an MTF curve in the Y direction (vertical direction), where (a) is R (633 nm), (b) is G (543 nm), and (c).
Is an MTF curve of B (422 nm). In addition, the horizontal axis of each figure is a book / mm.

As is clear from the above description, the image display device of the present invention can be configured as follows, for example.

[1] In an image display device provided with an image display element in which a large number of pixels having a certain aperture are regularly arranged in two dimensions, a phase type diffraction grating, and an observation optical system, When the distance from the display surface of the display element to the phase type diffraction grating (air conversion length) is L, the focal length of the observation optical system is f, and the magnification is m, f> L ≧ 0.2 / An image display device characterized by satisfying the relationship of m ² [m] (10).

[2] In the image display device including an image display element in which a large number of pixels having a certain aperture are regularly arranged in a two-dimensional manner, a phase type diffraction grating, and an observation optical system, Light beam diameter W on the phase type diffraction grating of the light beam emitted from the center of the display element and entering the observation optical system.
On the other hand, the image display device characterized in that the grating pitch P of the phase type diffraction grating satisfies the condition of 2 ≦ W / P ≦ 50 (11).

[3] In the image display device including an image display element in which a large number of pixels having a certain aperture are regularly arranged in two dimensions, a phase type diffraction grating, and an observation optical system, When the distance from the display surface of the display element to the phase type diffraction grating (air conversion length) is L, the focal length of the observation optical system is f, and the magnification is m, f> L ≧ 0.2 / m ² [m] (10) is satisfied, and with respect to the light beam diameter W on the phase-type diffraction grating of the light beam that emerges from the center of the image display element and enters the observation optical system. And the grating pitch P of the phase type diffraction grating satisfies the condition of 2 ≦ W / P ≦ 50 (11).

[4] The image display device according to the above 2 or 3, wherein at least two phase portions of the phase type diffraction grating are included in the light flux diameter W.

[5] The phase type diffraction grating has a shape having two diffractive components.
The image display device according to claim 1.

[6] The image display device according to the above item 5, wherein the phase type diffraction grating has a shape having two diffraction components on one surface.

[7] The image display device as described in the above item 5, wherein the phase type diffraction grating has a shape having diffraction components in one direction on the front and back sides, respectively.

[8] As the phase type diffraction grating, one having a periodic diffraction grating in one direction formed on one surface is used.
The image display device according to the above item 5, wherein a diffraction image is formed in two directions by using a surface.

[0085]

[9] The above-mentioned 1 to 4 characterized in that the phase type diffraction grating has a shape having one diffraction component.
The image display device according to claim 1.

[10] The image display device according to any one of items 1 to 4, wherein the phase type diffraction grating has a shape having three diffraction components.

[11] The image display device described in any one of the above items 1 to 10, wherein the phase type diffraction grating has a diffractive surface facing the image display element side.

[12] In the phase-type diffraction grating, the diffraction efficiency of the first-order diffracted light is defined as a value obtained by normalizing each of the diffracted lights obtained by irradiating monochromatic light with the 0-th order diffracted light.
1. When the colors corresponding to the wavelengths of monochromatic light are blue, green, and red respectively, the following conditions must be satisfied when distinguishing by the symbols (B), (G), and (R) added after the symbol. 12. The image display device according to any one of 1 to 11 above.

E1 (R) <E1 (G) <E1 (B) (12) [13] In the phase type diffraction grating, the diffractive surface has a rectangular cross-section, and its corners are formed. 13. The image display device according to any one of 1 to 12 above, wherein the image display device is rounded.

[14] In the phase type diffraction grating, the diffraction action surface is formed in a trapezoidal cross-sectional shape, and the corner portions thereof are rounded, and the phase diffraction grating is rounded. Image display device.

[15] Let the diffraction efficiency (%) of the first-order diffracted light at a certain wavelength of the phase type diffraction grating be Exy (x is the horizontal direction, y is the vertical direction), and the reference color of the image display element is blue. Green and red are added after the symbol (B),
15. The image display device according to any one of 1 to 14 above, wherein the following conditional expressions are satisfied when distinguishing between (G) and (R).

Red: 70 <E10 (R) <300, 70 <E01 (R) <300 Green: 100 <E10 (G) <700, 100 <E01 (G) <700 Blue: 100 <E10 (B) < 800, 100 <E01 (B) <800 Here, the respective wavelengths are (B) = 442 nm,
(G) = 537 nm and (R) = 636 nm.

[16] Let the diffraction efficiency (%) of the first-order diffracted light at a certain wavelength of the phase type diffraction grating be Exy (x is the horizontal direction, y is the vertical direction), and the reference color of the image display element is blue, Green and red are added after the symbol (B),
15. The image display device according to any one of 1 to 14 above, wherein the following conditional expressions are satisfied when distinguishing between (G) and (R).

Red: 20 <E10 (R) <50, 20 <E01 (R) <50 Green: 30 <E10 (G) <60, 30 <E01 (G) <60 Blue: 30 <E10 (B) < 70, 30 <E01 (B) <70 Here, the respective wavelengths are (B) = 442 nm,
(G) = 537 nm and (R) = 636 nm.

[17] In the phase type diffraction grating, the diffraction direction of at least one grating has an angle with respect to any side of the display surface of the image display element. The image display device according to item 1.

[18] In the phase type diffraction grating, the diffraction directions of at least two gratings have an angle with respect to any side of the display surface of the image display element. The image display device according to item 1.

[19] For any of the above sides,
The image display device according to the above 17 or 18, wherein the image display device has an angle θ that satisfies θ | ≧ 1 °.

[20] The observation optical system is arranged on the exit surface side of the phase type diffraction grating.
20. The image display device according to claim 1.

[21] The image display device according to any one of the above items 1 to 20, wherein the observation optical system is a decentered free-form surface optical system.

[22] The image according to any one of the above items 1 to 21, wherein the phase type diffraction grating, the image display element and the observation optical system are fixed by an integrated support member. Display device.

[23] In any one of the above items 1 to 22, an imaging optical system is arranged in place of the observation optical system,
An image pickup apparatus comprising an image pickup element by disposing an image pickup element instead of the image display element.

[24] The image pickup apparatus as described in the above item 23, wherein the image forming optical system is a decentered free-form surface optical system.

[0103]

As is apparent from the above description, according to the present invention, the roughness of an image is sufficiently reduced, and
It is possible to provide an image display device that gives an image with high resolution.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an image display device of the present invention.

FIG. 2 is a diagram showing a near point distance and a far point distance that change depending on the age of a person.

FIG. 3 is a diagram for explaining a magnification of an observation optical system.

FIG. 4 is a diagram for explaining the depth of focus on the image display element side of the observation optical system.

FIG. 5 is a diagram showing a pupil diameter of an observer which changes depending on the brightness of an object.

FIG. 6 is a diagram showing a combination of irregularities of a phase type diffraction grating included in a light beam diameter passing through a pupil diameter.

FIG. 7 is a perspective view of a phase type diffraction grating having a shape having two diffraction components on one surface.

FIG. 8 is a perspective view of a phase type diffraction grating having a shape in which front and back sides each have a diffraction component in one direction.

FIG. 9 is a perspective view of a phase type diffraction grating formed by combining two one-direction diffraction gratings.

FIG. 10 is a plan view showing a delta arrangement of pixels.

FIG. 11 is a perspective view of a three-direction diffraction grating in which a front side is provided with a diffraction grating including a two-dimensional phase portion and a back side is provided with a diffraction grating including a one-dimensional phase portion.

FIG. 12 is a plan view of a three-way diffraction grating in which a periodic structure of the diffraction grating (phase portion) exists in three directions.

FIG. 13 is a cross-sectional view showing various types of observation optical systems.

FIG. 14 is a diagram showing a configuration example of an image display device according to the present invention.

15 is a plan view and a cross-sectional view of the phase type diffraction grating in FIG.

16 is an MTF curve in the X direction (horizontal direction) of Example 1. FIG.

17 is an MTF curve in the Y direction (vertical direction) of Example 1. FIG.

18 is an MTF curve in the X direction (horizontal direction) of Example 2. FIG.

19 is an MTF curve in the Y direction (vertical direction) of Example 2. FIG.

20 is an MTF curve in the X direction (horizontal direction) of Example 3. FIG.

FIG. 21 is a Y-direction (vertical direction) MTF curve of Example 3;

FIG. 22 is an MTF curve in the X direction (horizontal direction) of Example 4;

23 is an MTF curve in the Y direction (vertical direction) of Example 4. FIG.

FIG. 24 is an MTF curve in the X direction (horizontal direction) of Example 5;

FIG. 25 is an MTF curve in the Y direction (vertical direction) of Example 6.

FIG. 26 is a diagram showing a configuration of an image display device having a configuration in which several crystals are stacked between a conventional liquid crystal display element and an observer.

[Explanation of symbols]

E ... Observer eye 1 ... Image display element 2 ... Observation optical system 3 ... Phase type diffraction grating 3 ₁ , 3 ₂ ... One-way diffraction grating 4 ... Exit pupil (eyepoint) 5 ... Illumination means (backlight) 10 ... Light Shafts 13, 13a, 13b, 13c, 13d ... Phase portion (convex portion) 13e ... Diffraction grating (phase portion) 14 ... Base material

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H049 AA03 AA13 AA50 AA51 AA60                       AA65 AA66                 5C058 AA06 BA25 DA15 EA14

Claims (3)

[Claims] 1. An image display device comprising an image display element in which a large number of pixels having a certain opening are regularly arranged in a two-dimensional manner, a phase type diffraction grating, and an observation optical system, When the distance from the display surface of the element to the phase type diffraction grating (air conversion length) is L, the focal length of the observation optical system is f, and the magnification is m, f> L ≧ 0.2 / m ² [m] An image display device characterized by satisfying the relationship of (10). 2. An image display device comprising an image display device in which a large number of pixels having a certain aperture are regularly arranged in a two-dimensional manner, a phase type diffraction grating, and an observation optical system. The grating pitch P of the phase type diffraction grating is 2 ≦ W / P ≦ 50 with respect to the beam diameter W of the light beam emitted from the center of the element and entering the observation optical system on the phase type diffraction grating. .. An image display device characterized by satisfying the condition (11). 3. An image display device comprising an image display device in which a large number of pixels having a certain aperture are regularly arranged in a two-dimensional manner, a phase type diffraction grating, and an observation optical system, When the distance from the display surface of the element to the phase type diffraction grating (air conversion length) is L, the focal length of the observation optical system is f, and the magnification is m, f> L ≧ 0.2 / m ² [m] ... (10) is satisfied, and with respect to the light beam diameter W on the phase type diffraction grating of the light beam that emerges from the center of the image display element and enters the observation optical system. An image display device characterized in that the grating pitch P of the phase type diffraction grating satisfies the condition of 2 ≦ W / P ≦ 50 (11).