JPH09304725A - Video display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a video display device where color slurring is little and which has a large pupil while eliminating trouble such as ghost caused by unnecessary light by changing diffraction efficiency according to a spot on the grating surface of a diffraction grating. SOLUTION: This device is provided with a video display means displaying a video, and an ocular optical system forming the image of the video on the retina of a user. In such a case, a 1st diffraction means 1 and a 2nd diffraction means 2 are arranged in an optical path where an exit pupil is formed by the video display means and the ocular optical system, and the 2nd diffraction means 2 is provided with plural areas having different diffraction efficiency characteristic along the diffraction surface. It is conceivable that the diffraction efficiency characteristic is continuously changed on the diffraction surface or it is constituted of a center part where the diffraction efficiency of zero-order light is high and a peripheral part where the diffraction efficiency of zero-order light is low.

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 a head-mounted image display device having a large exit pupil diameter while using a compact optical system.

[0002]

2. Description of the Related Art The applicant of the present application has proposed in Japanese Patent Laid-Open No. 7-72422 a method of enlarging the exit pupil diameter of an eyepiece optical system such as a head-mounted image display device by using two diffraction gratings. That is, in a video display device having a liquid crystal display element and an eyepiece for projecting a display image thereof on a user's retina, a first diffraction grating is provided in an optical path between the eyepiece and an exit pupil formed by the eyepiece. And a second diffraction grating are provided, and the first diffraction grating and the second diffraction grating are arranged so that the diffraction angle of the second diffraction grating with respect to each wavelength of the image substantially matches the diffraction angle of the first diffraction grating. When configured, the exit pupil is divided and a large pupil is obtained. In the case of Japanese Patent Laid-Open No. 7-72422, the angle of view of the displayed image is intended to be 30 °, and the wide angle of view is not taken into consideration.

[0003]

However, when the angle of view of the displayed image becomes wider, in the method of enlarging the pupil diameter immediately before the eyeball utilizing this diffraction, there is a color shift peculiar to the diffraction phenomenon. Phenomena become apparent. This is because the diffraction efficiency of a normal diffraction grating has wavelength dependence, so when viewing a full-color image using three colors of red, green, and blue through the diffraction grating, the colors change in the central part and the peripheral part. It is a phenomenon that it does. Actually, as shown in FIG. 15, the first diffraction grating 1 causes only the + 1st-order light and the −1st-order light to be generated, and the second diffraction grating 2 causes the −first-order light and the −third-order light having the same diffraction angle. A method in which only the first-order light is generated and only the ± first-order lights are used without generating the zero-order light is as follows.

For example, as shown in FIG. 16, a pair of two one-dimensional diffraction gratings 1 and 2 for the vertical and horizontal directions is used to separate and expand the pupil into four, as shown in FIG. However, as shown in the figure, when the angle of view is wide in this pupil, color shift due to diffraction becomes noticeable, and the position of the pupil differs depending on the wavelength. If an observer's pupil is placed in this pupil and an image is observed, a colored image will be seen.

Therefore, the unevenness of the surface of the diffraction grating is configured to generate 0th-order light, and the central pupil that is divided and formed is formed of 0th-order light. It can be made to have little color shift. That is, as shown in FIG. 18, the first diffraction grating 1
Causes the + 1st order light, the 0th order light and the −1st order light to be generated, and the second diffraction grating 2 generates the −1st order light, the 0th order light and the −1st order light, which are as shown in the figure. Then, a pupil is formed by the 0th order light in the center.

However, in practice, the method of generating the 0th order light to form the pupil as shown in FIG. 18 has the following problems. In FIG. 18, the pupils are divided and formed in the one-dimensional direction, but if the arrangement is such that one pair in the vertical direction and one pair in the horizontal direction are divided and formed in the two-dimensional direction, nine pupils as shown in FIG. Is completed. At this time, of the nine pupils divided and formed, the central pupil is the pupil due to the 0th-order light, so there is no positional deviation due to the wavelength at the pupil position regardless of the center or the periphery in the image. That is, the incident angle dependency of the pupil position is constant regardless of the wavelength. When observing an image, the observer often tends to observe the vicinity of the center of the image. Therefore, the central pupil is a pupil which is relatively likely to enter the pupil when the observer observes the image. The fact that the central pupil has no positional deviation due to the wavelength means that the image can be observed without being colored when the image is observed with this pupil. In addition, the pupil can be formed by nine diffracted lights, so that there is an advantage that the pupil expansion rate is large. In order to create the central pupil with less color shift, the first diffracting means 1 and the second diffracting means 2 need to have surface shapes that generate 0th order light.

However, when the diffraction grating generates 0th-order light, another phenomenon is brought up. In general, when the surface shape is configured so that the 0th order light is generated, the diffraction efficiency of the ± 2nd order light is not low. By forming the surface shape so as to generate the 0th-order light, the unnecessary light in which the 0th-order light and the 2nd-order light are involved becomes more prominent. In particular, unnecessary light that is involved in the secondary light is a light flux group that is more likely to enter the pupil at the pupil position.

That is, as the diffraction efficiency of the 0th order light and the ± 2nd order light becomes higher, the following unnecessary light becomes remarkable.
For simplicity, only one dimension (horizontal direction) will be described.
FIG. 20 is a diagram showing how a light beam is diffracted by two diffraction gratings 1 and 2 in a pair. In the figure, for example, (1, -2) means that the first diffraction grating 1 is the first-order diffraction light and the second diffraction grating 2 is the -second-order diffraction light. In the figure,
The luminous flux emitted from the image display element is divided into a center of the image display element (FIG. (A)) and the periphery of the image display element (FIG. (B)) to form a ray diagram. In these ray diagrams, (1,
Light fluxes such as -2) secondary light and (-1, 2) secondary light are unnecessary light closest to the eyes. These luminous fluxes are unnecessary light that newly stands out when the surface shape is such that the 0th-order light is generated. Even if the ± 2nd-order diffraction efficiency is not high, the ± 1st-order diffraction efficiency is Because it is expensive, (1, -2) next light,
The energy value of the (-1, 2) next light is at a level that cannot be ignored.

Further, it is these light fluxes emitted from the periphery of the image that are likely to enter the eye. This is because, for the (1, -2) th order light, when the incident angle of the light beam emitted from the periphery of the image on the first diffraction grating 1 becomes tight, in other words, when the angle of view becomes wide, This is because it has the property of approaching the exit pupil position. This is because when the incident angle becomes tight, as shown in FIG. 21, the values of the angles Θ _A and Θ _B of the ± 1st order light with respect to the 0th order light are substantially the same regardless of the incident angle, and therefore the second diffraction grating Distance A between + 1st order light and 0th order light on 2
Is larger than the distance B between the −1st order light and the 0th order light. Therefore, unnecessary light of the (1, -2) th order in the case of ambient light easily approaches the normal pupil position and easily enters the eye (in the figure, the luminous flux of the peripheral part of the image is the pupil by the unnecessary light of the (1, -2) th order). Will move to the left in the figure.). As described above, the 0th-order light is used in order to make the color shift inconspicuous, but this causes unnecessary light that is easily visible to the eyes.

The present invention has been made in order to avoid the above-mentioned undesired phenomenon in the case of a wide angle of view, which is related to the prior art. The purpose of the present invention is to cope with the case of a wide angle of view. By changing the diffraction efficiency depending on the location on the lattice plane of (1), it is possible to solve the problem of ghost due to unnecessary light and realize an image display device such as a liquid crystal display device with a large pupil with little color shift.

There is no particular limitation on the diffracting means in the present invention, and any known means can be applied.

[0012]

According to the present invention, there is provided an image display apparatus for displaying an image, comprising:
In an image display device having an eyepiece optical system for forming an image on the retina of the user, a first diffractive unit and a second diffractive unit are provided in an optical path forming an exit pupil by the image display unit and the eyepiece optical system. A diffractive means is provided, and the second diffractive means has a plurality of regions having different diffraction efficiency characteristics along the diffractive surface.

In this case, the diffraction efficiency characteristic of the second diffraction means may be changed continuously on the diffraction surface.

Further, it is desirable that the second diffracting means is composed of a central portion where the diffraction efficiency of 0th order light is high and a peripheral portion where the diffraction efficiency of 0th order light is low.

In the present invention, since the diffraction efficiency characteristic differs depending on the region on the diffraction surface of the diffractive means, it is possible to change the diffraction order to be used or suppress the diffraction efficiency of an unnecessary diffraction order, and it is possible to reduce the diffraction efficiency. By suppressing coloring and suppressing generation of unnecessary light, the diffractive means can be made suitable for the situation of use.

Further, since the diffraction efficiency characteristic continuously changes on the diffraction surface, the pupil is formed by the diffracted light corresponding to the diffraction efficiency at the place where the light flux passes through the diffracting means.
The coloring due to diffraction can be gradually suppressed, or the generation of unnecessary light can be gradually suppressed, so that the diffractive means can be made suitable for the usage situation.

Further, the chromatic aberration due to the diffraction generated by the first diffracting means is made less noticeable by increasing the diffraction efficiency of the 0th order light at the center where the second diffracting means tends to stand out, thereby making the 0th order light inconspicuous. And unnecessary light due to the secondary light can be prevented by lowering the diffraction efficiency of the 0th-order light in the peripheral portion that is easily seen by the second diffraction means, and as a result, the color generated by the first diffraction means. The unnecessary light can be corrected by the second diffracting means.

Further, when the coloring and unnecessary light generated by the first diffracting means are corrected by the second diffracting means, the diffraction efficiency of the 0th order light of the second diffracting means gradually decreases from the central portion to the periphery. By continuously changing so that
The method of dealing with the color shift of unnecessary light is not a two-step method but a continuous method, and it is not a matter of dealing with either one of the problems in this trade-off relationship,
Depending on the situation, it is possible to deal with coloring suitable for the incident angle and unnecessary light.

Further, at the central portion on the second diffraction grating surface, 0
In order to increase the diffraction efficiency of the next-order light, the 0th-order light is
Changing the diffraction angle by configuring the duty ratio of the surface shape of the diffracting means so that the diffraction efficiency of the ± 2nd-order light becomes low, and making the pitch and depth constant with the same configuration as the first diffracting means. Instead, it is possible to effectively suppress the color due to diffraction in the central portion, and to suppress the generation of unnecessary light that tends to enter the peripheral portion.

Further, the diffraction efficiency of the 0th-order light is high at the center on the second diffraction grating surface, and the diffraction efficiency of the 0th-order light and the ± 2nd-order light continuously decreases toward the periphery, so that the diffractive means By changing the duty ratio of the surface shape of the No. 3 and making the pitch and groove depth constant with the same structure as the first diffracting means, the color due to diffraction can be effectively displayed in the image without changing the diffraction angle. It is possible to suppress the color in the center where it is easy to come out, and to suppress the generation of unnecessary light that tends to enter the eyes toward the periphery. The method of dealing with unwanted light and color misregistration is not a two-step procedure but a continuous one, and it is not a matter of dealing with either of the problems in this trade-off relationship, but depending on the situation. It is possible to deal with colors suitable for corners and unnecessary light.

Further, the second diffracting means has a region where the diffraction efficiency of the 0th order light is high and a region where the diffraction efficiency of the 0th order light is low because the uneven shape of the surface changes on the diffractive surface. On the side where the light beam is diffracted from the optical axis of the diffracting means, the region up to D shown by the following equation is the region where the resolution efficiency of the 0th order light is high, and the region outside D is the region where the diffraction efficiency of the 0th order light is low. It is desirable to have it.

D = atan θ ₀ = btan θ _1- (b-
a) tan {sin ⁻¹ (λ / p + sin θ ₁ )} However, when the distance from the optical axis is D, the distance from the second diffracting means to the exit pupil position: a From the first diffracting means to the exit pupil position Distance: b distance between the first diffracting means and the second diffracting means: b-a when the 0th order light of the first diffracting means is incident on a region where the diffraction efficiency of the 0th order light of the second diffracting means is high. Angle of incidence on the first diffracting means: θ ₀ to the first diffracting means when the first order light of the first diffracting means is incident on the region where the diffraction efficiency of the 0 th order light of the second diffracting means is high. Angle of incidence: θ ₁ groove pitch of the first and second diffracting means: p 1 wavelength: λ 2 (see FIG. 8).

By doing so, the 0th-order light is generated from the center to the periphery in order to suppress the chromatic aberration due to the diffraction in accordance with the display angle of view, and the 0th-order light is generated from the periphery to suppress the unnecessary light. It is possible to determine whether or not to do so, and it is possible to use a diffraction grating suitable for the usage situation.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a conventional Japanese Unexamined Patent Publication No. 7-72.
Similar to No. 422, in a video display device having a video display means and an eyepiece for projecting the displayed video on the user's retina, a first device is provided in the optical path between the eyepiece and the exit pupil formed by the eyepiece. Of the first diffraction grating and the second diffraction grating are provided so that the diffraction angle of the second diffraction grating with respect to each wavelength of the image substantially matches the diffraction angle of the first diffraction grating. It constitutes a diffraction grating. That is, as shown in FIG. 1, for example, the image displayed on the liquid crystal display element 4 is projected as a magnified image on the eyeball of the user by the convex lens 5 of the eyepiece optical system, and the liquid crystal display element 4 is arranged behind it. It is adapted to be illuminated by the illuminated illumination system 3 and to display its display image. And
Between the convex lens 5 of the eyepiece optical system and the exit pupil 6 thereof, two diffraction gratings 1 and 2 having the same grating interval are arranged in parallel so that the grating directions coincide with each other. In this way, the two diffraction gratings 1,
When 2 is arranged, the parallel light transmitted through the convex lens 5 first enters the diffraction grating 1 and is divided into 0th-order light, 1st-order light, and -1st-order light. These lights then enter the diffraction grating 2 having the same grating spacing. These lights are diffracted again and part of them becomes parallel light. As a result, the luminous flux diameter a before entering the diffraction grating 1 is
After emission, the beam diameter is expanded to b. Therefore, the effective pupil diameter is increased.

Then, according to the present invention, in the diffraction gratings 1 and 2 for enlarging the pupil as a pair of two sheets, the pitch of the uneven shape of the surface on the grating plate remains constant, and the duty ratio of the uneven shape is changed. By doing so, it is possible to change the diffraction efficiency depending on the incident angle, improve the problem of wavelength dependence peculiar to the diffraction phenomenon, and make unnecessary light hard to see. Embodiments of the present invention will be described below with reference to the drawings.

[Example 1] As described in the conventional example, coloring due to diffraction at a wide angle of view and countermeasures against unnecessary light are in a conflicting relationship, and it is difficult to achieve both at the same time. Therefore, in order to prevent coloring in the central pupil, which is easily visible, 0
The diffraction grating means is optimized by using the second-order light and not using the 0th-order light in order to prevent the unnecessary light in the vicinity where the unnecessary light easily enters the eyes.

In order to realize the above, the uneven shape on the surface of the diffraction grating is made rectangular. A feature of the rectangular diffraction grating is that the groove depth at which the 0th-order diffraction efficiency is minimized and the groove depth at which the 1st-order diffraction efficiency is maximized are substantially the same. Therefore, if the groove depth of the diffraction grating is set to a groove depth in the vicinity of this, the dependence of the diffraction efficiency on the groove depth for both the 0th order and the 1st order becomes small, and the problem of color misregistration becomes small. Therefore, the allowable range of the manufacturing error in the groove depth becomes large.

Here, in the first diffracting means 1, specifically, the first diffraction grating, the duty ratio of the rectangular shape on the surface is a value that generates 0th order light over the entire area of the grating surface, for example, as shown in FIG. 3 shows that the diffraction efficiency depends on the groove depth.
The groove depth is set to 65 and the groove depth is set to a value such as d ₁ in FIG. Here, d ₁ is a value such as 0.5 to 0.6 μm in a diffraction grating having a pitch of ₁ to 2 μm.
The pitch determines the diffraction angle. In the second diffracting means 2, specifically, the second diffraction grating, the duty ratio of the rectangular shape on the surface is zero-order light near the center in the direction perpendicular to the grating groove direction as shown in FIG. As shown in FIG. 3, the value that occurs, for example, the dependency of the diffraction efficiency on the groove depth is 0.265.
In addition, the groove depth is set to a value such as d ₁ in FIG. 3, and a value that does not generate 0th-order light in the vicinity of the groove, for example, a duty ratio that shows the groove depth dependence of diffraction efficiency in FIG. 0.5
Further, the groove depth is set to a value such as d ₂ in FIG. Here, the duty ratio is the ratio T / P of the length T of the convex portion to the length P of one cycle of the irregularities in the pitch P of the irregularities on the surface, as shown in FIG. The groove depth d ₁ is approximately equal to d ₂ . Note that the diffraction efficiency of the second order is shown in FIG.
Since the diffraction efficiency of the following is low, it is not described.

In this embodiment, as shown in FIG.
The duty ratio of the second diffractive means 2 is different between the center and the periphery, but the pitch of the grating grooves is the same for the first diffractive means 1 and the second diffractive means 2. It remains constant throughout. As a result, the diffraction angles maintain the same relationship in both means, and the (1, -1) th order and (-1, 1)
An image can be viewed without distortion by looking at the pupil formed by the next (0, 0) -th order regular luminous flux.

The area of the second diffracting means 2 from which the 0th-order light is generated and the area of the periphery from which the 0th-order light is not generated depends on how much the pupil is located at the pupil position 6. Set the optimum value depending on whether the range moves.

That is, when observing an image, the range of movement of the pupil is proportional to the size of the angle of view. When the amount of movement of the pupil is large, it is necessary to prevent unnecessary light from entering the range of movement of the pupil at least, so that the surface of the second diffracting means 2 has a concavo-convex shape so that unnecessary peripheral light is not generated. It is necessary to set the duty ratio to a value that does not generate 0th-order light, and that even if it occurs, unnecessary light due to it has a low diffraction efficiency to such a level that there is no obstacle.

As an example of the configuration, in an image having a horizontal angle of view of 45 °, a pupil diameter a of φ2.5 m is provided immediately after the eyepiece lens 5.
The pupil which was m was separated and enlarged into three by the first diffracting means 1 and the second diffracting means 2, and b = about φ6.
I will give you a case that effectively expands to 5 mm. Diffractive means 1,
If the grating groove pitch of 2 is 1.3 μm, the ± 1st-order diffraction angle is about ± 22.6 ° at the central wavelength of 0.5 μm. At this time, the distance between the two diffraction gratings 1 and 2 (see FIG. 8) is 2.5 / tan22.6 ° so that the pupils after separation are in contact with each other. Although it is 6 mm, it is set to 4.5 mm in consideration of overlapping the pupils as shown in FIG. Further, the distance from the second diffracting means 2 to the pupil is set to 23.5 mm.

It is assumed that the grooves of the diffracting means 1 and 2 have a rectangular cross section, and that the 0th order light is generated from the center of the second diffraction grating 2 to the position of length D in FIG. A hatched portion outside the area does not generate 0th-order light or has a low diffraction efficiency. At this time, the arrival positions of the 0th-order ray of the ray of A and the 1st-order ray of the ray of B in the second diffraction grating 2 are areas where the 0th order of the second diffraction grating 2 is generated. The condition is determined so that it becomes a boundary (a position with a distance D from the center) between the area and the area where it does not occur.

From the ray of B, D = 23.5 tan
It can be written as θ ₀ . In addition, the exit angle of the 1st-order diffracted light of B is θ ₁ '
= Sin ⁻¹ (λ / p + sin θ ₁ ). here,
p is the pitch of the diffraction grating 1, which is 1.3 μm. Therefore, in the figure, A = 28 tan θ ₁ , B = 4.
It can be written as 5 tan θ ₁ '. The following equation is derived from D = AB.

D = 23.5 tan θ ₀ = 28 tan θ ₁ −4.5 tan {sin ⁻¹ (λ / 1.
3 + sin θ ₁ )} λ: wavelength At the incident angle of the light flux from the image display element 4, 0th-order light is emitted from the center to 8 °, that is, θ ₀ = 8, and the wavelength λ
= 0.62 μm (red), 18 ° from the center, that is, in order to prevent the 0th-order light from being emitted from the light ray at θ ₁ = 18, D = 3.3 mm from the above equation.
become.

Therefore, the entire surface of the first diffraction grating means 1 and 2
The duty ratio is 0.265 from the center of the second diffraction grating means 2 to 3.3 mm, and the duty ratio is 0.5 from the center of the second diffraction grating means 2 to 3.3 mm from the center. do it.

At this time, the wavelength λ = 0.55 μm (green) and the wavelength λ = 0.44 μm (blue) are θ ₁ =
15, θ ₁ = 13. The unnecessary light that is most likely to enter is the (1, -2) secondary light emitted from the periphery on the long wavelength side. If the above is done, it is 2 when there is no 0th order light.
The diffraction efficiency of the secondary light is also reduced, and the unnecessary light of the (1, -2) secondary light shown by the thick line in FIG. 8 is eliminated. The state of the pupil at this time is shown in FIG. In FIG. 9, when the duty ratio is configured as described above, the pupil of the arrow is the pupil of the (1, -2) th order light emitted from the periphery of 18 ° from the center. The pupil by the (1, -2) th order light from the periphery (outer side) of 18 ° to the half angle of view 22.5 ° of the angle of view of 45 ° comes closer to the normal pupil, but from these 18 ° to 22.5 °. °
Since the pupil of unnecessary light up to is eliminated, it becomes difficult for the unnecessary light to enter the eyes. The incident angle was 22.5 ° from the center position and the incident angle was 22.5 ° (1, −2) due to the unnecessary light.
2) There is no unnecessary pupil due to the next light, and the first thing that comes into the eye is 1.6mm outside of the unnecessary light.
It becomes more difficult for unwanted light to enter the eyes.

Although the above-described embodiments have been described as having a plurality of regions having different diffraction efficiencies in the second diffraction grating 2, the second diffraction grating 2 has a plurality of regions having different diffraction efficiencies. The first diffractive means 1 instead of the diffractive means 2.
Has no effect. FIG. 10 is a diagram showing an example in which it is the first diffracting means 1 instead of the second diffracting means 2 that has a plurality of regions having different diffraction efficiencies. FIG. 11 is a diagram showing a method of providing a plurality of regions on the second diffraction grating means 2 according to the present invention, and FIG. 12 is a diagram showing a conventional method of not generating zero-order light for two sheets. FIG. 13 is a diagram showing a conventional method for generating zero-order light for two sheets. FIG.
In FIG. 13, a hatched portion is a portion in which 0th-order light is not generated or a portion having low diffraction efficiency of 0th-order light, and a white portion without hatching is a portion in which 0th-order light is generated or diffraction efficiency of 0th-order light. Is the high part. The unnecessary light is shown by the dotted line. Here, (1, 1) order and (-
Unwanted light such as 1 and -1) reaches a position far away from the normal exit pupil position that enters the pupil, and is not taken up or described because there is no problem. In addition,
In each figure, (a) shows light incident from the center of the image display element, and (b) shows light incident from the periphery of the image display element.

In the case where the first diffracting means 1 is provided instead of the second diffracting means 2 having a plurality of regions having different diffraction efficiencies shown in FIG. 10, a color such as (0, 0) in the central light is obtained. Since there is an unmarked pupil, there is no problem in color, but unnecessary light that easily enters the eyes is generated in the ambient light due to the 0th-order light and then the −2nd-order light.

In the method of not generating the 0th-order light in the two sheets shown in FIG. 12, unnecessary light which is easy to enter the center or the periphery is not generated, but there is no (0, 0) th order light in the center light. Since there are no uncolored eyes, the image near the center appears colored when the image is viewed.

FIG. 13 shows a method of generating zero-order light for both two sheets. With this method, although the problem of color is solved in the central light, the 0th-order light and then the −second-order light which are easily noticeable in the ambient light. Unwanted light caused by light has been generated.

The present invention shown in FIG. 11 eliminates the coloring caused by the diffraction and the unnecessary light in the periphery which is easy to see. In the above description, the expression that the 0th-order light is not generated or that it is generated can be replaced with the expression that the 0th-order light has a low diffraction efficiency and the 0th-order light has a high diffraction efficiency depending on the usage conditions.

[Embodiment 2] In Embodiment 1, the 0th-order diffraction efficiency is changed in two steps between the region where the 0th-order light is generated and the region where it is not generated in the second diffraction grating 2.
An example is shown in which the duty ratio is continuously changed from the center to the outside in order to continuously change the intensity of the pupil. In this case, regarding the coloring, since the (0, 0) th order pupil is formed so that there is no coloring in the center, the second diffraction means 2 has the highest diffraction efficiency of the 0th order in the grating near the optical axis. The duty ratio is set so that the diffraction efficiency of the 0th-order becomes lower toward the periphery, and the diffraction efficiency of the 0th-order light is reduced in the pupil of the peripheral light approaching the range of the exit pupil of the normal light.
The diffraction efficiency of ± second-order light is set to a value close to 0. As an example, an example in which the second diffraction grating 2 is divided into regions having different diffraction efficiency characteristics in five steps from the center to the periphery will be given. As shown in FIG. 14, the distance between the first diffraction grating 1 and the second diffraction grating 2 is 4.5 mm, and the distance from the second diffraction grating 2 to the observer's eye is 23.5 mm.
And the angle of view of the image is 45 °. Second diffraction grating 2
The region of is divided as follows. 1.91mm from center
The area of 1st area 21, 1.91mm to 3.64mm
Up to the second region 22, from 3.64 mm to 5.43 mm to the third region 23, from 5.43 mm to 6.21 mm to the fourth region 24, and from 6.21 mm to the periphery to the fifth region 25, a total of 5 Area. These areas 21-25
The duty ratio is gradually reduced from 0.5 toward the center. For example, if the first area 21 is 0.
5, the second region 22 is 0.45, the third region 23 is 0.4,
The fourth region 24 has a value of 0.35, and the fifth region 25 has a value of 0.3. In this case, the pitch is constant throughout the grating. At this time, as shown in FIG. 14, a ray passing through the outermost periphery of the first region 21 is a 0th-order light with an incident angle of 4.65 ° and an incident angle of 1.
It is 0 ° primary light. Hereinafter, similarly, a ray passing through the outermost periphery of the second region 22 is a 0th-order light having an incident angle of 8.8 ° and an incident angle of 15 °.
The primary light having an incident angle of 13 °, the rays passing through the outermost periphery of the third region 23 are the 0th-order light having an incident angle of 13 °, the primary light having an incident angle of 20 °, and the fourth region 24.
The rays passing through the outermost periphery of are the 0th-order light with an incident angle of 14.8 ° and the 1st-order light with an incident angle of 20 °. With this configuration, the diffraction efficiency of the 0th-order light, and thus the 2nd-order light, in the second diffraction grating 2 becomes lower toward the outer region. When the diffraction efficiency there is ranked from the central region to strong, moderately strong, medium, weak, and weak, the coloring due to unnecessary light and diffraction changes stepwise from the center to the periphery as shown in the following table. .

[0044] .

The advantage of this embodiment is that the coloring and the emission of unwanted light are continuous rather than two-stage, so either one of the problems in this trade-off relationship is addressed. Instead of doing so, it is possible to deal with colors and unnecessary light suitable for the incident angle depending on the situation. For example, at an angle of view of 45 °, and at an intermediate angle such as an incident angle of 15 °, it is preferable to deal with the color and unnecessary light by a half and a 6: 4 weight.

In the above example, the diffraction grating 2 is divided into five regions 21 to 25 from the center, but if it is divided into smaller regions and can be regarded as substantially continuous, unnecessary light and color misregistration can be continuously dealt with. . However, in reality, changing the duty ratio for each pitch is poor in manufacturability. Therefore, the manufacturability is improved when the duty ratio is divided for each region.

Although the image display apparatus of the present invention has been described based on its principle and embodiments, the present invention is not limited to these embodiments and various modifications can be made. The above-described image display device of the present invention can be configured as follows, for example. [1] In an image display device having an image display means for displaying an image and an eyepiece optical system for forming the image on the retina of a user, an exit pupil is formed by the image display means and the eyepiece optical system. An image display device characterized in that a first diffractive means and a second diffractive means are provided in an optical path, and the second diffractive means has a plurality of regions having different diffraction efficiency characteristics along a diffractive surface.

[2] The image display device according to the above [1], wherein the diffraction efficiency characteristic of the second diffracting means is continuously changed on the diffraction surface.

[3] The second diffracting means is composed of a central portion where the diffraction efficiency of 0th order light is high and a peripheral portion where the diffraction efficiency of 0th order light is low. ] The image display device described.

[4] The image display device according to the above [2], wherein the diffraction efficiency of the 0th-order light of the second diffracting means gradually decreases from the central portion to the periphery.

[5] In the second diffractive means, the pitch and groove depth of the surface irregularities are the same values as those of the first diffractive means over the entire diffractive surface, and the duty ratio of the surface irregularities is at the central portion. The image display device according to the above [1] or [3], characterized in that the diffraction efficiency of 0th-order light is high and the diffraction efficiency of 0th-order light is low in the peripheral portion.

[6] In the second diffractive means, the pitch and the groove depth of the surface unevenness are the same values as those of the first diffractive means over the entire diffraction surface, and the duty ratio of the unevenness of the surface is from the center to the periphery. The image display device according to the above [2] or [4], characterized in that the diffraction efficiency of 0th-order light is continuously reduced over time.

[7] The first diffractive means has an uneven surface shape for generating 0th-order light over the entire area, and the second diffractive means has a surface uneven shape on the diffractive surface. Accordingly, there is a region where the diffraction efficiency of the 0th-order light is high and a region where the diffraction efficiency of the 0th-order light is low, and a region up to D shown by the following equation is present on the side where the light beam is diffracted from the optical axis of the diffracting means. It is a region where the resolution efficiency of 0th-order light is high, and 0 is outside the D
The image display device according to the above [1], [3] or [5], which is a region where the diffraction efficiency of the next light is low. D = atan θ ₀ = btan θ ₁ − (b−a) tan
{Sin ⁻¹ (λ / p + sin θ ₁ )} However, when the distance from the optical axis is D, the distance from the second diffracting means to the exit pupil position: a the distance from the first diffracting means to the exit pupil position: b Distance between the first diffracting means and the second diffracting means: b-a The first diffracting means when the 0th order light of the first diffracting means is incident on a region where the diffraction efficiency of the 0th order light is high. Angle of incidence on the diffractive means: θ ₀ Minimum incident on the first diffractive means when the first-order light of the first diffractive means is incident on the region where the diffraction efficiency of the 0th-order light of the second diffractive means is high. Angle: θ ₁ Groove pitch of first diffractive means and second diffractive means: p Wavelength: λ

[0054]

As is apparent from the above description, according to the present invention, the second diffractive means is provided with a plurality of regions having different diffraction efficiency characteristics along the diffractive surface so that the diffractive element to be used is diffracted. It is possible to change the order and suppress the diffraction efficiency of unnecessary diffraction orders. Even if the image display device has a wide angle of view, the problem of ghost due to unnecessary light can be solved, and the large pupil with small color misalignment can be solved. A video display device such as a liquid crystal display device can be realized.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an operation of the diffracting means in the image display device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing groove depth dependence of diffraction efficiency of a rectangular diffraction grating having a duty ratio of 0.265.

FIG. 4 is a diagram showing the groove depth dependence of the diffraction efficiency of a rectangular diffraction grating with a duty ratio of 0.5.

FIG. 5 is a diagram for explaining the definition of duty ratio.

FIG. 6 is a diagram showing a duty ratio distribution of the second diffracting means of the first embodiment.

FIG. 7 is a diagram showing a state of a pupil in a specific numerical example of the first embodiment.

FIG. 8 is a ray diagram of diffracted light in a specific numerical example of Example 1.

9 is a diagram showing the appearance of the pupil in the case of FIG. 8;

FIG. 10 is a ray diagram of diffracted light when the first diffracting means has a plurality of regions having different diffraction efficiencies.

FIG. 11 is a ray diagram of diffracted light when the second diffracting means according to the present invention has a plurality of regions having different diffraction efficiencies.

FIG. 12 is a ray diagram of diffracted light in the case where 0th-order light is not generated in both conventional two diffracting means.

FIG. 13 is a ray diagram of diffracted light in the case where both conventional two diffracting means generate 0th-order light.

FIG. 14 is a ray diagram of diffracted light in Example 2.

FIG. 15 is a diagram for explaining a conventional method of using only ± first-order light without generating zero-order light.

16 is a diagram showing a manner of separating and enlarging the pupil into four by using the one-dimensional diffraction grating pair of FIG. 15 in each of the vertical direction and the horizontal direction.

FIG. 17 is a diagram showing a state of a pupil in the arrangement of FIG.

FIG. 18 is a diagram for explaining a conventional method of using 0th-order light together with ± 1st-order light.

FIG. 19 is a diagram showing a state of a pupil in the arrangement of FIG.

FIG. 20 is a ray diagram showing how unnecessary light is generated when the diffraction efficiency of 0th order light and ± 2nd order light is high.

FIG. 21 is a diagram for explaining the positional relationship of unnecessary light that tends to enter the eye with respect to regular light.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st diffraction grating (diffraction means) 2 ... 2nd diffraction grating (diffraction means) 3 ... Illumination system 4 ... Liquid crystal display element 5 ... Convex lens 6 ... Exit pupil 21 ... 1st area 22 ... 2nd area 23 ... Third region 24 ... Fourth region 25 ... Fifth region

Claims (3)

[Claims] 1. An image display device having an image display means for displaying an image and an eyepiece optical system for forming the image on the retina of a user, wherein an exit pupil is formed by the image display means and the eyepiece optical system. An image display characterized in that a first diffractive means and a second diffractive means are provided in an optical path to be formed, and the second diffractive means has a plurality of regions having different diffraction efficiency characteristics along a diffractive surface. apparatus. 2. The image display device according to claim 1, wherein the diffraction efficiency characteristic of the second diffractive means is continuously changed on the diffractive surface. 3. The second diffractive means is composed of a central portion where the diffraction efficiency of 0th order light is high and a peripheral portion where the diffraction efficiency of 0th order light is low. Video display device.