JPH0192718A - Display method for correcting chromatic aberration generated by diffraction grating optical element, and executing image display by diffraction grating optical element - Google Patents

Abstract

PURPOSE:To always observe a distinct image even when a position of a pupil is varied by utilizing a dispersing action of a transparent refractive optical element, giving an incident angle difference and an optical path length difference to a diffraction grating optical element with respect to light beams of each wavelength of a luminous flux having prescribed wavelength width and suppressing a chromatic aberration generated by the diffraction grating optical element. CONSTITUTION:An axial chromatic aberration caused by a color dispersion generated by a diffraction grating optical element 10 is negated by an effect of a color dispersion tending in the reverse direction generated by a triangular prism 41. Also, there is a misalignment in the optical axis direction of aberration formed by a light beam 20 of wavelength lambdaB generated by the diffraction grating optical element 10. It is correct by a misalignment of a virtual image formed position in the tendency reverse to the diffraction grating optical element 10, caused by a refractive index difference and an optical path length difference between the light beam 20 of wavelength lambdaA and the light beam 21 of wavelength lambdaB generated in the triangular prism 41. In such a way, the axial chromatic aberration generated by the diffraction grating optical element 10 is corrected roughly satisfactorily. Therefore, even when a pupil position has moved in the direction being orthogonal to the optical axis, a distinct image can be observed.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a display method for displaying images using a diffraction grating optical element such as a hologram element, and in particular, to correct chromatic aberration occurring in the diffraction grating optical element to obtain a good image. This invention relates to a display method for displaying information.

[Prior art]

Conventionally, so-called head-up display devices (ζ) have been used to display information within the field of view while the operator of an aircraft or vehicle directs his or her eyes forward, allowing the operator to observe objects in front of him and the displayed information in a superimposed state. Hereinafter referred to as HOD), various technologies have been proposed.

The HUD disclosed in U.S. Pat. An image is formed by focusing with a reflective element.

When the wavelength width of the used light beam is narrow as in the HUD shown in each of the above patents, the chromatic aberration generated in a diffraction grating optical element such as a hologram reflection element is extremely small and poses no problem in practice.

However, when displaying images using a diffraction grating optical element, if the display is made multi-colored, or if ordinary inexpensive fluorescent tubes are used as the display device, chromatic aberrations caused by the diffraction grating optical element may cause problems. The colors of the displayed image are blurred or the displayed image is blurred.

One method to solve this problem is published in Japanese Patent Application Laid-open No. 61-3541.
It is disclosed in Publication No. 6.

FIG. 5 is an explanatory diagram showing the HUD disclosed in the above-mentioned publication.

In the figure, 1 is the display surface of a fluorescent tube, etc., and it shows blue, green,
Wavelength λ3 corresponding to red. λ6. Generates light of λ8. 2
is a display hologram element which forms information displayed on the display surface 1 as a virtual image 10. Reference numeral 3 denotes a chromatic aberration correcting hologram element that receives light from the display surface 1 and directs it toward the display hologram element 2. 9 indicates the observer's eye, which corresponds to the entrance pupil of the optical system shown in FIG.

The wavelength λ8°λ0. emitted from a predetermined object point on the display surface 1. λ
The lights enter the correction hologram element 3, are diffracted in different directions due to the difference in wavelength, and then enter the display hologram 2, respectively.

Then, it is reflected and diffracted by the display hologram and enters the entrance pupil 9. At this time, the display hologram 2 also has a wavelength of λ8 due to the difference in wavelength. Since the light of λ6°λ8 is diffracted in different directions, the wavelength λ. ,λ. , λ3 appear to be approximately the same when observed from the position of the pupil 9- shown in the figure. (Position of virtual image 10) However, in the chromatic aberration correction method as shown in FIG. When moving in the orthogonal direction, each wavelength λゎ, λ0 .
The displayed image due to the light of λ□ is observed to be shifted. Therefore,
If the observation position needs to be moved left and right over a range of up to 250 mm, such as a car driver, the HUD disclosed in the above-mentioned publication cannot always display a clear image.

As explained above, in the conventional HUD display method using a diffraction grating optical element such as a hologram element, it is difficult to observe a clear image unless the pupil position is limited.

[Summary of the invention]

The present invention has been made in view of the above conventional problems, and an object of the present invention is to satisfactorily correct the Hosotchi chromatic aberration occurring in the diffraction grating optical element, and to move the pupil position in a direction perpendicular to the optical axis. An object of the present invention is to provide a display method for displaying an image using a diffraction grating optical element, which allows a clear image to be observed even when the image is displayed.

In order to achieve the above object, the display method of the present invention makes a light beam of a predetermined wavelength width containing image information to be displayed incident on a diffraction grating optical element, and the image is projected onto a predetermined image plane by the diffraction grating optical element. When forming and displaying, a refractive optical element having a predetermined dispersion characteristic is disposed in the optical path of the light beam up to the diffraction grating optical element, and each of the light beams is The present invention is characterized in that an optical path length difference and an incident angle difference to the diffraction grating optical element are given to the light of the wavelength components, and chromatic aberration occurring in the diffraction grating optical element is corrected to display an image.

Further features and effects of the present invention are specifically described in the Examples below.

〔Example〕

FIG. 1 shows an embodiment of the display method according to the present invention.
It is a schematic block diagram of D.

In the figure, reference numeral 10 is a diffraction grating optical element for image display, and a transparent transparent element on which a volume phase hologram 2 and a volume phase hologram 2 made using a sensitive material such as PVC (polyvinylcarbazole) are supported. It consists of a substrate 5.

The diffraction grating optical element 10 is arranged at a predetermined angle with respect to the optical axis X. Reference numeral 1 denotes a display surface of a fluorescent tube or the like that forms an image, and this display surface 1 may be a display surface of another display means such as a liquid crystal display, or a mask on which a predetermined display pattern is drawn. Reference numeral 41 denotes a triangular prism made of a transparent optical member with an antireflection film formed on the light input/output surface, and is placed in the optical path of the light beam from the display surface 1 to the diffraction grating optical element.

Further, the optical member constituting the triangular prism 41 is made of glass, acrylic resin, etc. Instead of the triangular prism 41, other forms of prisms or lens elements can be used as in other embodiments to be described later. be.

The reflection (diffraction) efficiency of the diffraction grating optical element 10 is 15 to 30
%, the imaging light flux from the display surface 1 is reflected and diffracted in the direction @9, and the light from the object in front existing in the direction of arrow A is transmitted and directed toward the pupil 9. Moreover, its optical function is equivalent to a positive lens or a concave mirror.

Therefore, an observer coincident with the pupil 9 will see the diffraction grating optical element 1
The enlarged virtual image of display information on the display surface 1 formed in the direction of arrow A and the object existing in the direction of arrow A are observed in a superimposed state.

Note that the lights 20, 21, 22, and 23 shown in FIG.
The wavelengths λ□(20,22), λ emitted from the same position of
This figure shows the chief ray of light with a wavelength λ (21°23) different from 9, and only the chief ray of the axial imaging light beam in the optical system of FIG. 1 is depicted for convenience.

The light beam containing display information from the display surface 1 has a predetermined wavelength width,
For example, it has a half-value width of 1100 nm, and the narrower half-value width of the diffraction grating optical element 10 is limited to, for example, 10 to 40 nm. As mentioned above, light 22 and 23 having different wavelengths λ8°λ from the display surface 1 are shown in FIG.

In addition, here, the relationship λ, >λ is established.

Wavelength λ8 emitted from display surface 1. The light beams 22 and 23 of λ8 are obliquely incident on the light incident side slope of the triangular prism 41, respectively, and are respectively refracted by the slope and propagate through the triangular prism 41.

The light 22.23 with wavelengths λ, , λ is refracted again at the light exit side slope of the triangular prism 41 and exits from the triangular prism 41 as light 20.21.

At this time, the light 23 with the wavelength λ8 has a shorter wavelength than the light 22- with the wavelength λ6, so the light 23 with the wavelength λ has the wavelength λ.

The triangular prism 4 has a larger deflection angle than the deflection angle of the light 22.
1. Therefore, the incident angle θ of the light 21 of wavelength λ8 with respect to the light incidence surface of the diffraction grating optical element 10 is smaller than the incidence angle θ6 of the light 21 with wavelength λ6 with respect to the light incidence surface of the diffraction grating optical member 10. (θ, <θA) Light 20. which exits from the triangular prism 41 and enters the diffraction grating optical element 10 at different incident angles θ8.
21 are each reflected and diffracted by the diffraction grating optical element 10 and go toward the pupil 9. The light 20 with a wavelength λ8 is deflected by an angle 180−(θa+θ2) by the diffraction grating optical element 10, and the light 20 with a wavelength λ
The light 21 of , is transmitted at an angle of 180-
Since it is deflected by (θ3 + θ2), each light 20.21
The light paths of the light beams 20.2 and 20.2 face toward the pupil 9 with their optical paths matching.
The positions of the virtual images of the display surface 1 formed on the opposite side of the pupil 9 with respect to the diffraction grating optical element 10 coincide with each other. In FIG. 1, light 20. reflected and diffracted by a diffraction grating optical element 10.
The optical path 21 coincides with the optical axis.

That is, in the display method shown in FIG.
The longer the wavelength, the smaller the refractive index of the optical member constituting the optical member, and the longer the wavelength, the smaller the deflection angle. On the other hand, the diffraction effect of the diffraction grating optical member 41 increases the diffraction angle as the wavelength becomes longer. There are two different cases in which the deflection angle becomes larger.
Using these functions, the axial chromatic aberration due to chromatic dispersion occurring in the diffraction grating optical element 10 is canceled out by the effect of chromatic dispersion occurring in the triangular prism 41 that tends in the opposite direction.

Furthermore, as shown in FIG. 1, the action of the transparent refractive optical element such as the triangular prism 41 is such that light with a short wavelength λ8 has a longer wavelength λ8.
The objective is to have the light reach the diffraction grating optical element 10 through a longer optical path (length) than the light of . Therefore, the position of the virtual image formed by the light 21 of wavelength λ emitted from the triangular prism 41 is closer to the pupil along the optical axis X than the position of the virtual image formed by the light 20 of wavelength λ emitted from the triangular prism 41. There will be one further away from 9.

On the other hand, the diffraction grating optical element 10 has . Therefore, two different wavelengths λ8. In order to form a virtual image of light 20.21 with wavelength λ8 at the same position, the object point of light with shorter wavelength λ must be
It is necessary to form it farther from the object point of the light of wavelength λ9.

In this embodiment, this effect is obtained by the above-mentioned triangular prism 41.

Therefore, according to the display method shown in FIG.
The positional shift in the optical axis direction of the virtual image formed by
This means that the correction is made by the positional shift of the virtual image forming position, which has a tendency opposite to that of the diffraction grating optical element 10, due to the difference in refractive index and the difference in optical path length with respect to the diffraction grating optical element 10.

According to this embodiment, the longitudinal chromatic aberration generated in the diffraction grating optical element 10 is almost well corrected by the above two effects. Therefore, even if the position of the pupil 9 changes in the direction perpendicular to the optical axis do not have.

Furthermore, in this embodiment, a transparent refractive optical element such as the triangular prism 41 is used to correct the chromatic aberration of the display diffraction grating optical element 10, and a transmittance of 95% or more can be easily obtained. Therefore, by effectively using the light from display surface 1,
Able to display bright images.

In the conventional hologram element for correcting chromatic aberration shown in Fig. 5, it is difficult to increase the diffraction efficiency evenly for light of each wavelength (for example, wavelengths λ8, λ0°, λR), and due to the performance of the element, the light utilization ineffective.

Furthermore, problems tend to occur in color reproducibility when displaying images.

However, according to the present invention, which corrects chromatic aberration using a transparent refractive optical element, as described above, the light utilization efficiency is improved, so images can be displayed brighter than before, and clear images with good color reproduction can be displayed. I can do it.

Furthermore, when a refractive optical element such as the triangular prism 41 shown in FIG. 1, which has different refractive powers in the meridional and sagittal directions, is disposed in the optical path, astigmatism occurs due to the difference in refractive power in the two directions. . Therefore, the diffraction grating optical element 10 of this embodiment is manufactured with different refractive powers in the meridional direction and sagittal direction so as to correct the astigmatism generated in the triangular prism 41. Therefore, chromatic aberration correction can be performed in an extremely simple manner, and adverse effects on other aberrations can be largely avoided. Note that since the focal length (refracting power) of the diffraction grating optical element 10 can be controlled independently in the meridional direction and the sagittal direction, no special effort is required to implement this astigmatism correction.

A specific numerical example of the HUD shown in FIG. 1 will be described below.

The apex angle of the triangular prism 41 is 82°, and for ease of explanation, light 20.22 with wavelength λ9 and light 21.2 with wavelength λ8 are used.
It is assumed that the incident angle and the outgoing angle with respect to the triangular prism 41 of No. 3 are equal. This causes the respective lights 20, 22 and 21.
For the 23 sets, an arrangement that satisfies the minimum deflection angle is set.

Here λA = 0, 58756 p m (d line)
.

When λm = 0.54607 μm (e-line) and the material of the triangular prism 41 is BK7 glass, BK7
The refractive index for the wavelength λ is N, = 1.51633. B
The refractive index of K7 for wavelength λ8 is N, = 1.51825
becomes.

Therefore, the angle formed by the light 20 with wavelength λ9 and the light 21 with wavelength λ8 shown in FIG. 1, and the angle formed by the light 22 with wavelength λ6 and the light 2 with wavelength λ8
The angle formed with 3 is 0.76°.

At this time, if the in-plane grating pitch of the light incidence surface of the diffraction grating optical element 10 is 4.41 μm, then the light 22 with the wavelength λ is incident on the diffraction grating optical element 10 at an incident angle θ4=45°.
and light 2 of wavelength λ8 incident at an incident angle θ, = 44.24°
3 are diffracted in directions forming an angle of θ2=35° with respect to the normal to the light incident surface of the diffraction grating optical element 10.

Similarly, if the apex angle of the triangular prism 41 is 76° and polystyrene is selected as the material, N = 1.59160
．． N,=1.59615, θ9=45°, θ,=
44.166, if the in-plane grating pitch of the light incident surface of the diffraction grating optical element 10 is 4.00 μm, the wavelength λ,
The angle θ2 at which the light 22.23 of λ8 exits from the diffraction grating optical element 10 is θ=34.1°.

FIG. 2 is a HUD showing a first modification of the display method of the present invention.
FIG.

In the figure, 42 is a refractive optical element made by partially cutting a rotationally symmetrical spherical convex lens, and only the off-axis part of a normal spherical lens is set as a light passing region, and the light input/output surface is anti-reflective. A film is formed. Further, other symbols in the drawings indicate the same members as those shown in the embodiment of FIG.

In this embodiment, an optical element 42 consisting of a part of a lens is used in place of the triangular prism 41 of the embodiment shown in FIG.
Based on the correction principle described above, chromatic aberration, especially Hosochi chromatic aberration, generated in the diffraction grating optical element 10 is corrected.

Further, according to the HUD of this embodiment, the image on the display surface 1 is once enlarged by the optical element 42 and then further enlarged by the diffraction grating optical element 10.
A virtual image sufficiently enlarged in the direction of the far arrow A of the diffraction grating optical element 10 is formed. At the same time, due to the dispersion effect of the optical element 42 and the difference in refractive power for the color (the optical path length difference that occurs between the wavelengths λ8 and λB of light 20.21), fine particles are generated in the diffraction grating optical element 10. Chromatic aberration is corrected.

In particular, according to the lens action of the optical element 42, Hosochi chromatic aberration,
That is, the position where the virtual image is formed by the light 20 having the wavelength λ8 along the optical axis X direction is made to match the position where the virtual image is formed by the light 21 having the wavelength λ6, and the positional variation in the direction perpendicular to the optical axis of the pupil 9 is prevented. You can always observe clear images regardless of the situation.

For example, the material of the optical element 42 has a refractive index na=1.
Using acrylic with 49+ n@ = 1.49205,
The focal length f for the d-line is fa = 50 mm, the focal length f for the e-line is f = 49.79199 mm, the focal length f of the diffraction grating optical element 10 is f = 1300 mm, and the diffraction grating optical element 10 and the optical element 42 principal point spacing e
with e=46.0mm and two optical elements 10.4
If the combined focal length F of 2 is F=150 mm, the virtual images formed by the d-line and the e-line perfectly match.

In the embodiment shown in FIG. 2, the optical element 42 is made up of a part of a spherical lens, but the optical element 42 is made up of a part of an aspherical lens.
2 may be configured.

FIG. 3 is a schematic configuration diagram of a HUD showing a second modification of the display method of the present invention.

In the figure, 50 is a refractive optical element in which a light reflecting layer 44 is formed on the concave surface of an optical member 43 which is a partially cut meniscus lens with spherical surfaces on both sides, and an antireflection film is formed on the convex surface of the optical member 43. This surface serves as both the light input and exit surface.

Further, other symbols in the drawings indicate the same members as those shown in the embodiments of FIGS. 1 and 2.

In FIG. 3, light 2 with a wavelength λ6°λ from the display surface 1
2.23 enters the optical element 50 from the convex surface of the optical member 43, is refracted, is reflected by the light reflecting layer 44, is refracted again by the convex surface of the optical member 43, and exits. At this time, λ8
>The refraction angle of the light 23 with a short wavelength λ8 of λ6 on the convex surface of the optical member 43 is larger than that of the light 22 with a short wavelength λ8, and the light 23 with a short wavelength λ8. Light of λ8 22.
Since an optical path length difference is given between 23 and 23, the light 2o of wavelength λ6 emitted from the optical element 50 and the light 21 of wavelength λ pass through the diffraction grating optical element 10 based on the same chromatic aberration correction principle as in the previous embodiment. The imaginary and image positions formed through the image coincide.

Therefore, the viewer can always observe a clear and bright image regardless of the positional change of the pupil 9 in the direction perpendicular to the optical axis X.

According to the HUD of this embodiment, since the concave surface of the optical member 43 is reflective, the optical member 43, which is a part of the lens, is used twice in the optical path. Therefore, it is possible to make the optical element 50 thinner and lighter than, for example, the optical element 42 in FIG. 2. Furthermore, as is clear from FIG. 3, the reflective layer 44 has the function of a bending mirror that bends the optical path, and as a result, not only can a small HUD be constructed as a whole, but also the display surface 1 can be This has the advantage that there is no need to display characters etc. with special reversed characters.

Further, in the optical element 50 of this embodiment, the reflective layer 44 is formed on the concave surface of the optical member 43, and this concave surface functions as a convex mirror, but the reflection characteristics of this convex mirror depend on the wavelength according to the law of reflection. isn't it. Therefore, this convex mirror works as a diverging lens with no wavelength dependence. For example, when the optical element 50 is used as an element having the same focal length as the optical element 42 in FIG. It becomes larger than the curvature of the convex surface of 42.

For this reason, as described above, when the wavelength dependence of the refractive power of the optical element 50 is used to correct the chromatic aberration of the diffraction grating optical element 10, the change in focal length due to wavelength, that is, the change in refractive power increases. , the effect on chromatic aberration correction becomes stronger.

FIG. 4 is a HUD showing a third modification of the display method of the present invention.
FIG.

In the figure, reference numeral 60 denotes a refractive optical element composed of a right-angle prism 45 and a reflective layer 46. Of the two mutually orthogonal surfaces of the right-angle prism 45, a reflective layer 4 is formed on the larger surface.
6 is formed as a reflective surface, and the remaining surface is used as a light incident surface. An antireflection film is formed on the light incident surface. On the other hand, the slope of the right-angle prism 45 has the functions of both a front-emission surface and a total reflection surface, and the functions are shared by different parts of the slope. Further, other symbols in the drawings indicate the same members as those shown in the embodiments of FIGS. 1 to 3.

Light 25 with wavelength λ from display surface 1 and wavelength λ 8 (λ^〉
The light 24 of λ8) is almost perpendicularly incident on the light incident surface of the rectangular prism 45, propagates through the rectangular prism 45, and is totally reflected on the slope (total reflection surface) of the rectangular prism 45.
The light propagates through the right-angle prism 45 again, is reflected by the reflective layer 46, and heads again toward the slope of the right-angle prism 45 (light 22.23). Here, the light 22.23 with mutually different wavelengths λ8°λ8 Both light beams are refracted at different angles by the slope of the prism 45 and exit from the optical element 60 .

The light 20 of wavelength λ emitted from the optical element 60 and the wavelength λ,
The light 21 enters the diffraction grating optical element 1 at different incident angles.
At the same time, each light 20.
21 is given a predetermined optical path length difference. Therefore, as in the previous embodiments, by appropriately setting the configuration and arrangement of the optical element 60, the chromatic aberration generated in the diffraction grating optical element 10 can be corrected, and the light 20 with the wavelength λ6 and the light 21 with the wavelength λ8 can be The positions of virtual images formed through the diffraction grating optical element can be matched.

Therefore, in this embodiment as well, even if the position of the pupil 9 changes in the direction perpendicular to the optical axis, it is possible to always observe a clear and bright image.

Further, according to the HUD of this embodiment, since the incident light is multiple-reflected by total reflection on the slope of the right-angle prism 45 and reflection by the reflection layer 45, it has the same function as the prism shown in FIG. function) can be achieved with a small prism. Furthermore, it is possible to adopt a configuration in which the optical element 60 and the display surface 1 are placed close to each other or in close contact with each other. Therefore, according to the HUD of this embodiment, it is easy to reduce the overall size.

As mentioned above, in each of the modified examples shown in FIGS. 2 to 4,
Since the transparent refractive optical elements 42, 50, and 60 are used as the chromatic aberration correcting elements of the diffraction grating optical element 10, a clear image can be formed using the light from the display surface 1 with extremely high light utilization efficiency.

Further, when the HUD shown in each of the above embodiments is used as an information display element for a vehicle, etc., the diffraction grating optical element 10 is used as embedded in the windshield of the vehicle.

The display formed on the display surface 1 is performed in response to an image signal from an image information generating means (not shown).

Furthermore, although each of the above embodiments uses a diffraction grating optical element in which a volume phase hologram is formed on a substrate, it is also possible to use a phase hologram in which a relief is formed on a substrate, and this relief phase hologram is Good mass production <HUD
Contributes to lower prices.

〔Effect of the invention〕

As described above, according to the display method of the present invention, the difference in incidence angle and the difference in optical path length to the diffraction grating optical element are determined for each wavelength of the light beam having a predetermined wavelength width by utilizing the dispersion effect of the transparent refractive optical element. It is possible to suppress the chromatic aberration that occurs in the diffraction grating optical element.

Therefore, since the light of each wavelength forms an image on the display surface at the same position via the diffraction grating optical element, a clear image can always be observed even if the position of the pupil changes.

Furthermore, compared to conventional chromatic aberration correction methods using hologram elements, etc., the efficiency of light utilization is significantly improved, and the reproducibility of displayed colors is also good.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a head-up display showing an embodiment of the display method of the present invention. 2 to 4 are schematic configuration diagrams of a head-up display showing first and second modified examples of the display method of the present invention. FIG. 5 is a schematic configuration diagram showing a conventional head-up display. 1... Display surface 9... Pupil (observer) 10... Diffraction grating optical element 41.42, 50.60... Refractive optical element for chromatic aberration correction.

Claims (1)

[Claims] When a light beam with a predetermined wavelength width containing image information to be displayed is made incident on a diffraction grating optical element and the image is formed on a predetermined image plane by the diffraction grating optical element and displayed, the diffraction grating optical element of the light beam A refractive optical element having predetermined dispersion characteristics is disposed in the optical path leading to the refractive optical element, and the dispersion generated by the refractive optical element causes the optical path length difference and the diffraction grating optical A display method for displaying an image using a diffraction grating optical element, characterized in that an image is displayed by giving a difference in the angle of incidence to the element and correcting chromatic aberration occurring in the diffraction grating optical element.