JPH11326821A - Virtual image observation optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly correct optical aberration generated due to eccentricity of an optical element having a refractive power with respect to a principal ray, secure a degree of freedom in layout of optical components, and reduce the size of an apparatus configuration. Is possible. SOLUTION: A reflection type blaze having a lens 16 for forming a virtual image of a display image of an LCD (liquid crystal display) 6 decentered with respect to a principal ray from the LCD 6 and having an aspherical asymmetrical rotationally symmetric phase adding function. With the de hologram 15,
An aberration generated by eccentricity of the lens 16 with respect to the LCD 6 is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a virtual image observation optical system for observing a virtual image of a display image of an image display device.

[0002]

2. Description of the Related Art Hitherto, a virtual image observation optical system for observing a virtual image of a display image of an image display device has been proposed. Many conventional virtual image observation optical systems are coaxial (rotationally symmetric) in order to suppress an increase in aberration.

For example, as shown in FIG. 17, there has been proposed a virtual image observation optical system having two refraction lenses 107 and 108. As the refractive lenses 107 and 108, plastic aspherical lenses are often used for weight reduction. In this virtual image observation optical system,
First, the video signal 101 is an LCD (Liquid Crystal Display)
The signal is input to the driving circuit 102. This LCD drive circuit 10
2 outputs a cold-cathode tube voltage (backlight voltage) 103 and a drive signal 104 for driving the liquid crystal display, which are supplied to the backlight 105 and the LCD (liquid crystal display) 106. Here, the backlight 105 uses the cold cathode tube 5a as a light source, and the LCD 106
Irradiate the side with light of uniform brightness. This cold cathode tube 5a and L
A diffusion plate 5b for controlling the diffusion angle of the light emitted from the cold cathode tube 5a is provided between the light source and the CD 106.

As the LCD 106 as an image display device, for example, a 0.55-inch transmissive liquid crystal display can be used. The LCD 106 displays an image based on the drive signal, and modulates and transmits a light beam emitted from the backlight 105. The luminous flux transmitted through the LCD 106 in this manner is transmitted to the refraction lenses 107
08, the refracting power for forming a virtual image is given and guided to the pupil 109 of the observer.

Further, as shown in FIG. 18, a virtual image observation optical system constituted by using a concave mirror has been proposed. As the concave mirror of this virtual image observation optical system, a mirror having a reflective film deposited on a plastic aspherical substrate is often used, similarly to the refractive lenses 107 and 108 of the virtual image observation optical system shown in FIG. In this virtual image observation optical system,
First, the video signal 101 is input to the LCD drive circuit 102. The LCD drive circuit 102 outputs a cold-cathode tube voltage 103 and a drive signal 104, which are supplied to the backlight 105 and the LCD 106. Here, the backlight 105 uses the cold-cathode tube 5a as a light source and irradiates the LCD 106 with light of uniform luminance. Between the cold cathode tube 5a and the LCD 106, the cold cathode tube 5a
There is provided a diffusion plate 5b for controlling the diffusion angle of the light emitted by the light source. The LCD 106 displays an image based on the drive signal, and modulates and transmits a light beam emitted from the backlight 105.

[0006] The light beam transmitted through the LCD 106 in this manner is transmitted to the polarizing beam splitter 1 as a light beam splitting device.
It is incident on 10. A part of the total amount of light incident on the polarizing beam splitter 110 passes through the polarizing beam splitter 110, and the rest is reflected by the polarizing beam splitting film 111 on the polarizing beam splitter 110, and is reflected on the aspherical half mirror substrate 113. Incident on the aspherical half mirror film 112 of FIG. The light beam incident on the aspherical half mirror film 112 is partially reflected, and is again reflected by the polarization beam splitter 110.
To the polarization beam splitter 1
The light passes through 10 and enters the pupil 109 of the observer. On the other hand, a part of the background light beam traveling from the back side of the aspherical half mirror substrate 113 is partially
13 and the pupil 1 through the polarizing beam splitter 110
09.

In the case of this virtual image observation optical system, the occurrence of coma and chromatic aberration of magnification is smaller than that of the optical system using a refractive lens as shown in FIG. Can be.

Further, as shown in FIG. 19, in the eccentric concave mirror type virtual image observation optical system, similarly to the above-described virtual image observation optical system, the light beam transmitted through the LCD 106 is reflected on the eccentrically arranged concave mirror 114 by reflection. An optical path that is reflected by the film 115 and guided to the pupil 109 is formed. This virtual image observation optical system has a small number of optical components,
It can be configured to be small and lightweight.

[0009]

In the above-mentioned conventional coaxial (rotationally symmetric) virtual image observation optical system as described above, the layout of optical components is limited, and the size of the entire optical system can be reduced. difficult. In other words, in the case of the virtual image observation optical system shown in FIG. 17, it is very difficult to correct aberration when the viewing angle and the irradiation pupil are increased, and when the angle of view exceeds 20 °, it is difficult to correct coma around the screen. Further, since the optical system is configured linearly, there is a disadvantage that the entire length of the optical system becomes long. With a rotationally symmetric virtual image observation optical system, it is difficult to achieve downsizing while securing a wide angle of view.

In the virtual image observation optical system shown in FIG. 18 using a concave mirror, the loss of the amount of light caused by passing twice through the aspherical half mirror is large, and when the observation angle of view exceeds 30 °, it is generated by the concave mirror. There is a problem that it becomes difficult to correct the field curvature. In addition, there is a problem that the entire optical system is increased in size with an increase in the angle of view due to the polarization beam splitter disposed at an angle of 45 °.

On the other hand, in a non-coaxial virtual image observation optical system, the degree of freedom in the layout of optical components can be increased. However, the virtual image observation optical system shown in FIG. 19 generates an enormous eccentric aberration due to reflection on the decentered concave mirror, and is not practically usable. Therefore, in the non-coaxial virtual image observation optical system, in order to reduce the eccentric aberration generated due to the eccentricity of the optical components, a plurality of toric surfaces and anamorphic surfaces and the like are required, as a result, The size of the optical system cannot be reduced. In the case of an optical system in which eccentric aberration is corrected by using a free-form surface, the shape becomes complicated, and a see-through function for observing a light beam behind a concave mirror cannot be realized as it is.

Accordingly, the present invention has been proposed in view of the above situation, and optical aberrations generated due to the eccentricity of a refracting optical element with respect to a principal ray are corrected favorably. An object of the present invention is to provide a virtual image observation optical system in which the degree of freedom of component layout is ensured and the device configuration can be reduced in size.

[0013]

In order to solve the above-mentioned problems, a virtual image observation optical system according to the present invention comprises an image display device,
At least one optical element for image formation which is arranged eccentrically with respect to a principal ray emitted from the image display device and has a refractive power for forming a virtual image of a display image of the image display device, and an aspherical non-rotationally symmetric phase A reflective diffractive optical element having an additional function, wherein the reflective diffractive optical element reduces optical aberrations caused by the imaging optical element being decentered with respect to the principal ray emitted from the image display device. It is characterized in that it is reduced by the aspherical and non-rotationally symmetric phase adding function.

In the virtual image observation optical system according to the present invention, the imaging optical element may form a virtual image of a display image of the image display device in cooperation with the reflection type diffractive optical element.

The virtual image observation optical system according to the present invention comprises:
An image display device, having a refractive power and an aspherical non-rotationally symmetric phase adding function for forming a virtual image of a display image of the image display device eccentrically installed with respect to a principal ray emitted from the image display device. A reflection type diffractive optical element having an aspherical asymmetrical rotationally symmetric phase adding function to reduce optical aberration caused by eccentricity with respect to a chief ray emitted from the image display device. It is assumed that.

In the virtual image observation optical system according to the present invention, a light beam splitting element may be provided between the image display device and the reflection type diffractive optical element. The angle formed by the center perpendicular of the diffraction surface of the reflection type diffractive optical element and the center perpendicular of the light beam splitting element is 40 ° or less, or the angle formed by the center perpendicular of the image display device and the center normal of the light beam splitting element. 4
By setting the angle to 0 ° or less, it is possible to display a good virtual image while reducing the size of the device configuration.

Further, in the present invention, a Lippmann volume hologram element or a reflection blazed hologram can be used as the reflection type diffraction optical element. As the image display device, an electro-luminescence image display device, a field-emission image display device, or a liquid crystal image display device can be used. As the light source of the backlight of the liquid crystal image display device, a light emitting diode or a semiconductor laser can be used.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the virtual image observation optical system according to the present invention comprises an LCD (liquid crystal display) 6 as an image display device, a reflective blazed hologram 15 as a reflective diffractive optical element, and an image forming apparatus. Eyepiece 1 to be an optical element for use
6 are provided.

The reflection type blazed hologram 15 is shown in FIG.
As shown in FIG. 7, a pit surface 15b having a saw-tooth (blaze) shape is formed on a hologram substrate 15a by a technique such as photoresist, and a diffraction phenomenon is caused by giving a spatial phase modulation to reflected light. It is. The sawtooth shape of the play surface 15b is λ per tooth.
An optical path difference of （(分 wavelength) is obtained, and an optical path difference of λ is generated in a round trip (double path) due to reflection. By forming the sawtooth shape on the hologram substrate 15a in an aspherical and rotationally symmetric manner, it becomes possible to add an aspherical and rotationally symmetric phase difference to the reflected wavefront of the reflective blazed hologram 15. The light use efficiency of the reflective blazed hologram 15 is high, and the efficiency of the first-order diffracted wave may reach about 90% in some cases.

In this virtual image observation optical system,
As shown in FIG. 1, a video signal 1 is input to an LCD driver 2 which is a circuit for driving an LCD 6. From the LCD driver 2, an LED current 3 for lighting an LED (light emitting diode) and a drive signal 4 for driving the LCD 6 are output and input to the backlight 5 and the LCD 6.

The backlight 5 has, as a light source, an LED array 5a in which a so-called chip-size LED having a light emission center wavelength of 525 nm is mounted in a total of eight rows of two rows and four columns. On the LCD 6 side of the LED array 5a,
A diffusion plate 5b is provided to make the luminance of the irradiation light from the LED array 5a uniform and to control the diffusion angle.
The diffusion angle from the LED array 5a is about 10 ° at a half-value angle.

As the LCD 6, for example, a 0.55-inch transmissive liquid crystal display can be used. In the LCD 6, an image signal, which is an electric signal, is converted into an image, and light emitted from the backlight 5 passing through the LCD 6 is modulated according to the image. The light beam transmitted through the LCD 6 is incident on the reflective blazed hologram 15. From this LCD 6, the reflection type blazed hologram 1
The angle of incidence on 5 is about 50 °.

As described above, the reflection-type blazed hologram 15 is formed with a blazed surface so as to have an aspherical asymmetrical rotationally symmetric phase adding function. Therefore, the wavefront reflected by the blazed hologram 15 is no longer a superposition of spherical waves like an incident wavefront, but has an aspherical, non-rotationally symmetric wavefront shape. The aspherical and rotationally symmetric phase difference is determined so as to reduce the eccentric aberration caused by passing through the eyepiece 16 arranged eccentrically with respect to the subsequently incident principal ray. The light beam emitted from the eyepiece 16 is guided to the pupil 11 of the observer.

In the case where the reflection type blazed hologram 15 is used, it is desirable to use a light source having a spectrum width of an emission wavelength as narrow as possible. One of the sawtooth-shaped teeth of the phrase surface 15b is formed so as to have an optical path difference of exactly λ / 2. Therefore, when another wavelength is incident, a desired reflected wavefront cannot be obtained, and noise is not obtained. This is because there is a possibility that

As shown in FIG. 3, the virtual image observation optical system according to the present invention can be constituted by using an image display device 6, an aspheric concave mirror 17, and a Lippmann volume hologram 10.

As a hologram material in the Lippman volume hologram 10, a photopolymer, dichromate gelatin, or the like can be considered. When the object light and the reference light enter the Lippman volume hologram 10, as shown in FIG. 4, interference fringes in a stripe pattern appear, and the refractive index is modulated. In the case of a typical photopolymer, the central refractive index n and the refractive index modulation Δn after the heat treatment are respectively n = 1.
52, Δn = 0.06. As shown in FIG. 4, it can be seen that the interference fringes of the Lippmann volume hologram are substantially in the thickness direction of the material. This can be realized by making two light beams enter from the front side and the back side of the hologram surface when printing the hologram.

Regarding the phenomenon in the Lippmann volume hologram 10, when the incident angle to the interference fringes is θ1, what kind of reflection angle θ2 is the scattered light from each interference fringe layer.
It is only necessary to consider whether each other is the most powerful. This is 2
There are two conditions. First, as shown in FIG. 5, it is necessary that two different scattering components on a certain layer reinforce each other. If the distance between two points is L, then Lsin
θ1−Lsinθ2 = mλ. In order for this to hold for any L, it is sufficient that the identity is about L. That is, θ1 = θ2 (Equation 1) Next, as shown in FIG. 6, in order that the scattering components of the two different layers reinforce each other, dcosθ1 + dcosθ2 = mλ (Expression 2) From Expressions 1 and 2, 2d cos θ1 = λ (Bragg diffraction condition), and it can be said that Bragg diffraction is specular reflection having wavelength selectivity or angle selectivity. By recording such interference fringes on the Lippmann volume hologram in an aspherical and non-rotationally symmetric manner, it becomes possible to deflect a light beam of a certain wavelength λ incident on the Lippman volume hologram in an arbitrary direction and reflect it. A spherically non-rotationally symmetric phase difference can be added.

In the non-coaxial virtual image observation optical system shown in FIG. 3, the operation until the image display device 6 displays an image is the same as that described with reference to FIG. The light beam emitted from the image display device 6 is incident on an aspheric concave mirror 17 which is arranged eccentrically. Since the aspherical concave mirror 17 bears a part of the refractive power of the entire optical system, an eccentric aberration occurs here. The luminous flux reflected by the aspheric concave mirror 17 passes through a HOE (holographic optical element) substrate 9 and is decentered and arranged on the Lippman volume hologram 1.
Incident at 0. Since the Lippmann volume hologram 10 also has a refracting power, an aberration occurs due to eccentricity. However, the Lippman volume hologram 10 is formed with an interference fringe that adds an aspherical non-rotationally symmetric phase to the wavefront so as to reduce the eccentric aberration generated by the aspherical concave mirror 17 and the Lippman volume hologram 10.
The reflected wavefront guided to 1 has reduced eccentric aberration, and the observer can observe a good virtual image of the displayed image.

As in the embodiment shown in FIG. 3, the advantage of using a plurality of optical elements having a refracting power for forming a virtual image is that the refracting power is shared by a plurality of surfaces.
The point is that the amount of generation of aberration can be reduced. In addition, since the diffractive optical element has a refractive power and does not generate a field curvature aberration in principle, it can be made flatter than a display image as compared with a case where all refractive powers depend on a concave mirror.

Here, the Lippmann volume hologram 10
Since only the light of a specific wavelength λ is diffracted and other spectra are transmitted, if the HOE substrate 9 is transparent and does not have a large refractive power, the observer can see the background through the Lippman volume hologram 10. The image is clearly visible. The spectral width (wavelength width at which the intensity of the diffracted light is reduced to half) used for diffraction in the Lippman volume hologram 10 is 20 μm in thickness of the photosensitive agent and 500 nm in wavelength.
In this case, since it is about 10 nm, a very bright background image can be obtained.

As shown in FIG. 7, the virtual image observation optical system according to the present invention is configured as a non-coaxial virtual image observation optical system using the image display device 6 and the two Lippmann volume holograms 10a and 10b. You can also. This embodiment is different from the embodiment shown in FIG.
7 is replaced with a Lippman volume hologram. The operation until the image display device 6 displays an image is the same as that in the embodiment described above with reference to FIG. The light flux emitted from the image display device 6 passes through the first HOE substrate 9a and enters the first Lippman volume hologram 10a which is arranged eccentrically. Since the first Lippmann volume hologram 10a functions as an aspherical concave mirror and plays a part in the refractive power of the entire optical system, aberration due to eccentricity occurs here. However, the first Lippman volume hologram 10a has a function of adding an aspherical asymmetrical rotationally symmetric phase to reduce the eccentric aberration while providing the refractive power, and also functions to reduce the eccentric aberration. First Lippman volume hologram 1
The light beam reflected by Oa passes through the first HOE substrate 9a and then enters the eccentrically arranged second Lippman volume hologram 10b. The second Lippman volume hologram 10b also generates an aberration due to eccentricity because it has a refractive power. However, similarly to the first Lippman volume hologram 10a, the second Lippman volume hologram 10b has an aspherical non-rotationally symmetric phase-adding function. And at the same time, acts to reduce eccentric aberration.

As described above, the reflected luminous flux given the refractive power and the aspherical asymmetrical rotationally symmetric phase difference by the two Lippmann volume holograms 10a and 10b is guided to the pupil 11, and the observer can obtain a good display image. A virtual image can be observed.
As in this embodiment, the merit that all the optical elements having the refracting power for forming a virtual image are constituted by diffractive optical elements is that the diffractive optical element does not generate the field curvature aberration in principle (that is, the Petzval sum). Is 0), which is different from the case where refractive power is given by a concave mirror, in that a completely flat image can be displayed. Further, the reason why the shape of each of the HOE substrates 9a and 9b is curved in this embodiment is to prevent the average resolution of the entire angle of view from deteriorating, particularly in the case of a wide-angle optical system.

As described above, the Lippmann volume hologram diffracts only light having a specific wavelength λ and transmits other spectra. Therefore, unless the second HOE substrate 10b is transparent and has a large refractive power. The observer can clearly see the background image. The spectral width (wavelength width at which the intensity of the diffracted light is reduced to half) used for diffraction in the Lippman volume hologram is as follows:
Since the wavelength is about 10 nm when the wavelength is 500 nm, a very bright background image can be obtained.

Further, as shown in FIG. 8, the virtual image observation optical system according to the present invention can be configured as a non-coaxial virtual image observation optical system using the image display device 6 and the Lippman volume hologram 10. In this case, only one Lippmann volume hologram 10 modulates the light beam emitted from the image display device 6, displays a virtual image by the refracting power, and corrects aberration due to eccentricity by adding an aspherical asymmetrical rotationally symmetric phase difference. I do. The structure of the Lippmann volume hologram 10 is very simple because it performs wavelength selective reflection (Bragg diffraction). Obviously, the observer can clearly see the background image unless the HOE substrate 9 is transparent and has a large refractive power.

Further, the virtual image observation optical system according to the present invention comprises:
As shown in FIG. 9, a non-coaxial (eccentric) virtual image observation optical system using a Lippmann volume hologram 10, which is a reflective diffractive optical element, as a reflective optical element can be configured. In this embodiment, the included angle between the display surface of the LCD 6 and the polarizing beam splitter 7 is 40 °, and the included angle between the normal line of the Lippman volume hologram 10 and the display light beam toward the pupil 11 is 35 °. .

In this virtual image observation optical system, a video signal 1 is input to an LCD driver (liquid crystal display driving circuit) 2 as shown in FIG. LCD driver 2
From there, an LED (light emitting diode: light emitting element) lighting current 3 and a drive signal 4 for driving an LCD (liquid crystal display) 6 serving as an image display device are output and input to the backlight 5 and the LCD 6.

The backlight 5 has, as a light source, an LED array 5a in which a total of eight so-called chip-size LEDs having a central emission wavelength of 525 nm are mounted in two rows and four columns. On the LCD 6 side of the LED array 5a,
A diffusion plate 5b is provided to make the luminance of the irradiation light from the LED array 5a uniform and to control the diffusion angle.
The diffusion angle from the LED array 5a is about 10 ° at a half-value angle.

As the LCD (liquid crystal display) 6 serving as an image display device, for example, a transmission type liquid crystal display of 0.55 inches can be used. In the LCD 6, an image signal which is an electric signal is converted into an image,
The light emitted from the backlight 5 passing through the LCD 6 is modulated according to the image. The light beam transmitted through the LCD 6 enters a wedge-shaped polarizing beam splitter 7 serving as a light beam splitting device. The incident angle from the LCD 6 to the wedge-shaped polarizing beam splitter 7 is about 40 °.

In the wedge-shaped polarizing beam splitter 7, a part of the total amount of incident light passes through the wedge-shaped polarizing beam splitter 7, and the rest is a polarized light beam formed on the wedge-shaped polarizing beam splitter 7. HOE (holographic optical element) substrate 9 reflected by the division film 8
Incident on. The wedge opening angle of the wedge-shaped polarizing beam splitter 7 is 1 ° to 5 °, and is 3 ° in the optical system shown in FIG. The HOE substrate 9 is shown in FIG.
As shown in (1), it is formed in a concave cylindrical surface shape with respect to the incident light from the wedge-shaped polarizing beam splitter 7. This H
The luminous flux transmitted through the OE substrate 9 is generated by the Lippman volume hologram 10 formed on the back surface of the HOE substrate 9.
Only light rays in a specific wavelength range are selectively reflected. Here, only light rays in a range of about 10 nm in a full width at half maximum around 525 nm which is the wavelength of the light source are reflected.

The light beam reflected by the Lippmann volume hologram 10 passes through the HOE substrate 9 again, enters the wedge-shaped polarizing beam splitter 7, and partially transmits through the wedge-shaped polarizing beam splitter 7 for observation. Incident on the pupil 11 of the person.
On the other hand, the background light beam traveling from the back side of the HOE substrate 9 passes through the Lippman volume hologram 10, the HOE substrate 9 and the wedge-shaped polarizing beam splitter 7, and the pupil 11
Incident on.

At this time, in the spectrum of the light beam that reaches the pupil 11 from the background, a light beam having a wavelength of about 525 nm is reflected by the Lippman volume hologram 10, so that the intensity of the band is substantially inversely proportional to the diffraction efficiency. descend.

Incidentally, in this virtual image observation optical system, aberration is generated because the Lippman volume hologram 10 having a refracting power is a non-coaxial (eccentric) system and is arranged eccentrically. Some of the aberrations due to such decentering can be reduced by introducing interference fringes that realize aspherical and non-coaxial wavefront conversion in the Lippmann volume hologram 10 that is a reflective diffractive optical element. That is, the Lippman volume hologram 10 has an aspherical asymmetric rotationally symmetric phase adding function of reducing the eccentric aberration while providing the refractive power, and also functions to reduce the eccentric aberration. That is, the Lippman volume hologram 10
The wavefront reflected and diffracted by the hologram has an aspherical non-rotationally symmetric phase difference for correcting eccentric aberration at the same time as the refracting power. The wavefront is well corrected for aberrations, and the observer can see a clear virtual image. When the light flux reflected by the Lippmann volume hologram 10 passes through the wedge-shaped polarizing beam splitter 7,
Aberrations such as astigmatism, coma, and distortion are reduced.

Here, the distortion of the wedge-shaped polarizing beam splitter 7 in the case where the opening angle of the wedge is 3 ° and the case where the opening angle is 0 °, that is, in the case of the parallel plate type beam splitter, are shown. When the occurrence states are compared, FIG.
And as shown in FIG. 12, the Lippman volume hologram 1
It can be seen that the light beam reflected by 0 passes through the wedge-type polarizing beam splitter 7 whose wedge opening angle is 3 °, thereby reducing distortion. At this time, a double image due to reflection on the back surface of the wedge-shaped polarizing beam splitter 7, that is, a so-called ghost image is also removed.

The virtual image observation optical system according to the present invention comprises:
As shown in FIGS. 13 and 14, a coaxial (rotationally symmetric) virtual image observation optical system using an aspherical half mirror as a reflection type optical element can be used. The virtual image observation optical system shown in FIG. 13 includes a parallel plate polarizing beam splitter 12 instead of the wedge-shaped polarizing beam splitter.
The virtual image observation optical system shown in FIG. 14 includes a wedge-shaped polarizing beam splitter 7.

In the virtual image observation optical system shown in FIG.
The video signal 1 is input to the LCD driver 2. LCD
From driver 2, cold cathode tube voltage (backlight voltage)
3 and a driver signal 4 for driving the LCD 6 are output,
The data is input to the backlight 5 and the LCD 6.

The backlight 5 uses a cold cathode tube 5a as a light source. On the LCD 6 side of the cold-cathode tube 5a, a diffusion plate 5b is provided in order to make the luminance of the light emitted from the cold-cathode tube 5a uniform and to control the diffusion angle. LCD6
Is, for example, a 0.55 inch transmissive liquid crystal display, which converts an image signal, which is an electric signal, into an image, and modulates a light beam emitted from the backlight 5 according to the image.

The light beam transmitted through the LCD 6 is incident on a parallel plate polarizing beam splitter 12 which is a light beam splitting device. From LCD 6 to parallel plate polarizing beam splitter 1
The angle of incidence on 2 is 45 °. In the parallel plate polarizing beam splitter 12, a part of the total amount of incident light passes through the parallel plate polarizing beam splitter 12, and the rest is a polarized light beam formed on the parallel plate polarizing beam splitter 12. The light is reflected by the division film 8 and enters the aspheric half mirror film 13. This aspherical half mirror film 13 is formed on an aspherical half mirror substrate 14. The aspherical half mirror substrate 14 is formed in a concave cylindrical surface shape with respect to the incident light from the parallel plate polarizing beam splitter 12.

A part of the light beam incident on the aspherical half mirror film 13 is reflected by the aspherical half mirror film 13 and is incident on the parallel plate polarizing beam splitter 12 again. The light passes through the splitter 12 and enters the pupil 11 of the observer. The background light beam traveling from the back side of the aspherical half mirror film 13 passes through the aspherical half mirror substrate 14, the aspherical half mirror film 13, and the parallel plate polarizing beam splitter 12, and
The light enters the pupil 11.

Here, as shown in FIG. 13, the light beam A reflected on the back surface of the parallel plate beam splitter 12 is also
When the light enters the aspherical half mirror film 13 and is reflected by the aspherical half mirror film 13, the light enters the pupil 11. This light beam A is shifted from the light beam reflected by the polarizing light beam splitting film 8 in parallel with the optical axis, and often enters the pupil 11 to form a ghost image. Here, as shown in FIG. 14, if the parallel-plate polarizing beam splitter is replaced with a wedge-type polarizing beam splitter 7, as shown in FIG. Is
It does not reach the pupil 11 and does not form a ghost image.

On the other hand, the background light beam traveling from the back side of the aspherical half mirror substrate 14 passes through the aspherical half mirror substrate 14, the aspherical half mirror film 13, and the wedge-shaped polarizing beam splitter 7, and becomes pupil. It is incident on 11. Therefore, if the opening angle of the wedge of the wedge-type polarizing beam splitter 7 is too large, the background deviating from the optical axis of the eyeball is observed or the background image looks distorted due to the prism action. Therefore, it is desirable that the opening angle of the wedge of the wedge-type polarizing beam splitter 7 be in the range of 1 ° to 5 °.

In each of the above embodiments, the display is a single color of green. However, as shown in FIG. 15, the Lippman volume hologram 10 is formed by multiple exposure using lasers 18, 19, and 20 of three colors of RGB, and is formed. By using a light source including an RGB spectrum for the light, full color display is also possible.

In such an apparatus for exposing the Lippmann volume hologram 10 for full-color display, a light beam emitted from a red laser (Kr laser, oscillation wavelength 647 nm) 20 is split by a variable beam splitter 34, one of which is dichroic. The light is reflected by the mirrors 24 and 25 and irradiates one surface of the Lippman volume hologram 10 through the modulation element 31, and the other is reflected by the dichroic mirrors 28 and 29 and modulated by the modulation element 3.
The light is radiated to the other surface side of the Lippman volume hologram 10 via the zero and aspherical non-rotationally symmetric wavefront generating optical system 36. Green laser (SHG laser, oscillation wavelength 532 nm)
The light beam emitted from 18 is reflected by a mirror 21 and split by a variable beam splitter 22, one of which is a dichroic mirror 23 and a dichroic mirror 2.
4 and is reflected by the mirror 25 to be modulated.
Illuminates one surface of the Lippman volume hologram 10 through the mirror, the other is reflected by the mirror 26, passes through the dichroic mirror 27 and the dichroic mirror 28, is reflected by the mirror 29, and is modulated by the modulation element 30 and the aspherical non-rotationally symmetric wavefront generating optics. The other side of the Lippmann volume hologram 10 is irradiated via the system 36. The light beam emitted from the blue laser (Ar laser, oscillation wavelength 488 nm) 19 is split by the variable beam splitter 32,
One is reflected by the mirror 33 and the dichroic mirror 23, passes through the dichroic mirror 24, is reflected by the mirror 25, irradiates one surface of the Lippmann volume hologram 10 through the modulation element 31, and the other is reflected by the dichroic mirror 27, The light passes through the dichroic mirror 28, is reflected by the mirror 29, and is radiated to the other surface of the Lippmann volume hologram 10 via the modulation element 30 and the aspherical asymmetric rotational wavefront generating optical system 36.

By colorizing the Lippman volume hologram 10 in this manner, the spectrum is equally missing from the transmitted light from the background and reaches the pupil 11, so that the background color becomes more natural. There is also.

Further, the virtual image observation optical system according to the present invention can be configured in full color using a reflection type liquid crystal display device. That is, in this virtual image observation optical system, a video signal 1 is input to an LCD driver (liquid crystal display drive circuit) 2 as shown in FIG. LC
An LED (light emitting diode:
A light-emitting element 3 lighting current 3 and a drive signal 4 for driving an LCD (liquid crystal display) 6 serving as an image display device are output and input to the light 5 and the LCD 6.

The light 5 includes, as a light source, an LED array 5 in which several so-called chip-size LEDs having emission center wavelengths of 470 nm, 525 nm, and 640 nm are mounted.
a. Further, as the LCD (liquid crystal display) 6 serving as an image display device, for example, a 0.55-inch reflective liquid crystal display can be used. In the LCD 6, an image signal, which is an electric signal, is converted into an image, and a light beam incident on the LCD 6 from the light 5 by the light guide plate 6a is modulated according to the image and reflected. L
The light beam reflected by the CD 6 enters a wedge-shaped polarizing beam splitter 7 serving as a light beam splitting device. In the wedge-shaped polarizing beam splitter 7, a part of the total amount of incident light passes through the wedge-shaped polarizing beam splitter 7,
The rest is reflected by the polarizing beam splitting film 8 formed on the wedge-shaped polarizing beam splitter 7 and enters the HOE (holographic optical element) substrate 9. The HOE substrate 9 is formed in a concave cylindrical shape with respect to the incident light from the wedge-shaped polarizing beam splitter 7. The light beam transmitted through the HOE substrate 9 has a specific wavelength range, that is, the interference fringes in the Lipman volume hologram 10 satisfy the Bragg condition by the Lippman volume hologram 10 formed on the back surface of the HOE substrate 9. Only light rays of a wavelength are selectively reflected. Here, only light rays in a range of about 10 nm in a full width at half maximum centering on the wavelengths of the light sources, 470 nm, 525 nm, and 640 nm, are reflected.

The light beam reflected by the Lippmann volume hologram 10 passes through the HOE substrate 9 again, enters the wedge-shaped polarizing beam splitter 7, and partially transmits through the wedge-shaped polarizing beam splitter 7 for observation. Incident on the pupil 11 of the person.
On the other hand, the background light beam traveling from the back side of the HOE substrate 9 passes through the Lippman volume hologram 10, the HOE substrate 9 and the wedge-shaped polarizing beam splitter 7, and the pupil 11
Incident on.

At this time, in the spectrum of the light beam reaching the pupil 11 from the background, the wavelength is 470 nm, 525 n
Since the light near m and 640 nm is reflected by the Lippman volume hologram 10, the intensity of this band decreases substantially in inverse proportion to the diffraction efficiency.

Incidentally, the virtual image observation optical system is a non-coaxial (eccentric) system, and aberration is caused by the eccentric arrangement of the Lippman volume hologram 10 having a refractive power. Some of the aberrations due to such decentering can be reduced by introducing interference fringes that realize aspherical and non-coaxial wavefront conversion in the Lippmann volume hologram 10 that is a reflective diffractive optical element. That is, the Lippman volume hologram 10 has an aspherical asymmetric rotationally symmetric phase adding function of reducing the eccentric aberration while providing the refractive power, and also functions to reduce the eccentric aberration.
At the same time, the light beam reflected by the Lippmann volume hologram surface is transmitted through the wedge-shaped polarizing beam splitter 7, so that aberrations such as astigmatism, coma, and distortion can be further reduced. At the same time, a double image due to reflection on the back surface of the beam splitter, that is, a so-called ghost image is also removed.

In the above-described embodiment, even when a Lippman volume hologram is used in an optical system, the emission spectrum of the light source is set to a diffraction wavelength (Bragg wavelength), similarly to the case of a blazed hologram. (For color, three wavelengths of RGB). In other words, the Lippman volume hologram has a wavelength selection function for diffraction, so that it does not cause noise such as a ghost image as in the case of a blazed hologram, but uses only a limited spectral width as diffracted light. In order to increase the efficiency, it is important to make the emission spectrum of the light source a diffraction wavelength.

In all of the above-described embodiments, an LCD (Liquid Crystal Display) is used as an image display device. In addition, an electro-luminescence image display device which is a self-luminous element, Field-
An emission image display device or the like can also be used.

[0062]

As described above, in the virtual image observation optical system according to the present invention, by using a reflection type diffractive optical element, a plurality of toric surfaces, anamorphic surfaces and complicated free-form surfaces can be introduced. In addition, it is possible to reduce aberrations due to eccentricity of optical components, and to provide a small and light non-coaxial virtual image observation optical system.

Further, by making the diffractive optical element share the refracting power, it is possible to realize a good virtual image display with little field curvature aberration. Furthermore, by using a Lippman volume hologram, which has diffraction wavelength selectivity in principle, as a reflection-type diffractive optical element, a see-through function that balances a bright display image and a bright background image without introducing other optical components is provided. It is possible to give.

That is, according to the present invention, the optical aberration generated due to the eccentricity of the optical element having the refractive power with respect to the principal ray is corrected favorably, the degree of freedom of the layout of the optical components is secured, and the size of the apparatus is reduced. It is possible to provide a virtual image observation optical system which can be realized.

[Brief description of the drawings]

FIG. 1 is a plan view showing a first embodiment of the configuration of a virtual image observation optical system according to the present invention.

FIG. 2 is an enlarged plan view showing the shape of a reflective blazed hologram constituting the virtual image observation optical system.

FIG. 3 is a plan view showing a second embodiment of the configuration of the virtual image observation optical system according to the present invention.

FIG. 4 is an enlarged sectional view showing a structure of a Lippmann volume hologram constituting the virtual image observation optical system.

FIG. 5 is a cross-sectional view for explaining a phenomenon (reflection on the surface) in the Lippman volume hologram.

FIG. 6 is a cross-sectional view for explaining a phenomenon (reflection other than the surface) in the Lippman volume hologram.

FIG. 7 is a plan view showing a third embodiment of the configuration of the virtual image observation optical system according to the present invention.

FIG. 8 is a plan view showing a fourth embodiment of the configuration of the virtual image observation optical system according to the present invention.

FIG. 9 is a plan view showing a fifth embodiment of the configuration of the virtual image observation optical system according to the present invention.

10 is a plan view showing the configuration of the virtual image observation optical system shown in FIG.

FIG. 11 is a graph showing distortion (wedge opening angle 0 °) in the virtual image observation optical system.

FIG. 12 is a graph showing distortion (3 ° wedge opening angle) in the virtual image observation optical system.

FIG. 13 is a plan view showing a sixth embodiment of the configuration of the virtual image observation optical system.

FIG. 14 is a plan view showing a seventh embodiment of the configuration of the virtual image observation optical system.

FIG. 15 is a block diagram showing a configuration of an apparatus for performing color exposure on a Lippmann volume hologram constituting the virtual image observation optical system.

FIG. 16 is a plan view showing an eighth embodiment of the configuration of the virtual image observation optical system.

FIG. 17 is a plan view showing a configuration of a conventional virtual image observation optical system.

FIG. 18 is a plan view showing another example of the configuration of the conventional virtual image observation optical system.

FIG. 19 is a plan view showing still another example of the configuration of the conventional virtual image observation optical system.

[Explanation of symbols]

6 LCD, 7 polarizing beam splitter, 9 HOE
Substrate, 10 Lippman volume hologram, 11 pupils, 1
5 reflective blazed holograms, 16 eyepieces,
17 Aspherical concave mirror

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H04N 5/64 511 H04N 5/64 511A 5/66 102 5/66 102Z

Claims (33)

[Claims] 1. An image display device, and at least one image forming device arranged eccentrically with respect to a principal ray emitted from the image display device and having a refractive power for forming a virtual image of a display image of the image display device. An optical element, comprising a reflective diffractive optical element having an aspherical asymmetrical rotationally symmetric phase adding function, wherein the reflective diffractive optical element is configured such that the imaging optical element is directed to a principal ray emitted from the image display device. A virtual image observation optical system characterized in that optical aberrations generated due to decentering are reduced by an aspherical asymmetric rotationally symmetric phase adding function. 2. The virtual image observation optical system according to claim 1, wherein the imaging optical element has at least one refracting surface. 3. The virtual image observation optical system according to claim 1, wherein the imaging optical element has at least one reflecting surface or a semi-permeable film surface. 4. The virtual image observation optical system according to claim 1, wherein the imaging optical element has at least one reflection type diffraction surface. 5. The virtual image observation optical system according to claim 1, wherein the reflection type diffractive optical element is a Lippman volume hologram element. 6. The virtual image observation optical system according to claim 1, wherein the reflection type diffractive optical element is a reflection type blazed hologram. 7. The virtual image observation optical system according to claim 1, wherein the image display device is an electroluminescence image display device. 8. The virtual image observation optical system according to claim 1, wherein the image display device is a field-emission image display device. 9. The virtual image observation optical system according to claim 1, wherein the image display device is a liquid crystal image display device. 10. The virtual image observation optical system according to claim 9, wherein the liquid crystal image display device includes a backlight using a light emitting diode as a light source. 11. The virtual image observation optical system according to claim 9, wherein the liquid crystal image display device includes a backlight using a semiconductor laser as a light source. 12. The virtual image observation optical system according to claim 1, wherein the image display device is a reflection type liquid crystal image display device. 13. An image display device, at least one image forming optical element disposed eccentrically with respect to a chief ray emitted from the image display device, and an aspherical asymmetrical rotationally symmetric phase adding function. A reflective diffractive optical element that forms a virtual image of a display image of the image display device in cooperation with the image forming optical element, wherein the reflective optical element is such that the image forming optical element is the image. An optical system for observing a virtual image, wherein an optical aberration generated due to decentering with respect to a chief ray emitted from a display device is reduced by an aspherical asymmetric rotationally symmetric phase adding function. 14. An image display device, and a refracting power and an aspherical non-rotation, which are installed eccentrically with respect to a principal ray emitted from the image display device, and form a virtual image of a display image of the image display device. A reflective diffractive optical element having a symmetric phase adding function, wherein the reflective diffractive optical element adds an optical aberration generated by decentering to a principal ray emitted from the image display device to an aspherical non-rotational symmetric phase. A virtual image observation optical system characterized by being reduced by function. 15. The virtual image observation optical system according to claim 14, wherein the reflection type diffractive optical element is a Lippman volume hologram element. 16. The virtual image observation optical system according to claim 14, wherein the reflection type diffractive optical element is a reflection type blazed hologram. 17. The image display device according to claim 1, wherein the image display device is an electroluminescence image display device.
4. The virtual image observation optical system according to 4. 18. The image display device according to claim 14, wherein the image display device is a field-emission image display device.
The virtual image observation optical system according to the above. 19. The virtual image observation optical system according to claim 14, wherein the image display device is a liquid crystal image display device. 20. The virtual image observation optical system according to claim 19, wherein the liquid crystal image display device includes a backlight using a light emitting diode as a light source. 21. The virtual image observation optical system according to claim 19, wherein the liquid crystal image display device includes a backlight using a semiconductor laser as a light source. 22. The virtual image observation optical system according to claim 14, wherein the image display device is a reflection type liquid crystal image display device. 23. The virtual image observation optical system according to claim 14, wherein a light beam splitting element is provided between the image display device and the reflection type diffractive optical element. 24. The virtual image observation optical system according to claim 23, wherein the reflection type diffractive optical element is a Lippmann volume hologram element. 25. The virtual image observation optical system according to claim 23, wherein the reflection type diffractive optical element is a reflection type blazed hologram. 26. The image display device according to claim 2, wherein the image display device is an electroluminescence image display device.
3. The virtual image observation optical system according to 3. 27. The image display device according to claim 23, wherein the image display device is a field-emission image display device.
The virtual image observation optical system according to the above. 28. The virtual image observation optical system according to claim 23, wherein the image display device is a liquid crystal image display device. 29. The virtual image observation optical system according to claim 28, wherein the liquid crystal image display device includes a backlight using a light emitting diode as a light source. 30. The virtual image observation optical system according to claim 28, wherein the liquid crystal image display device includes a backlight using a semiconductor laser as a light source. 31. The virtual image observation optical system according to claim 23, wherein the image display device is a reflection type liquid crystal image display device. 32. The virtual image observation optical system according to claim 23, wherein an angle formed by a center perpendicular to a diffraction surface of the reflection type diffractive optical element and a center perpendicular to the light beam splitting element is 40 ° or less. . 33. The virtual image observation optical system according to claim 23, wherein an angle between a center perpendicular of the image display device and a center perpendicular of the light beam splitting element is 40 ° or less.