JP2001157228A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To considerably improve light availability and to solve problems of uneven color and color aberration. SOLUTION: The optical device is provided with a light source, a reflection type holographic optical element and a reflection type optical element that reflects at least part of a luminous flux emitted from the light source. The luminous flux emitted from the light source is made incident onto the reflection type holographic optical element twice or over and the incident angle of the incident luminous flux onto the reflection type holographic optical element is selected to be at least two kinds or over. The presence/absence of production of a diffraction effect depends on number of incident times of the luminous flux onto the reflection type holographic optical element. Employing the reflection type holographic optical element acting like a luminous flux division optical element for the optical system in place of a half mirror and a polarized beam splitter in this way can considerably reduce the wavelength dependence of a reflected light and a transmitted light due to the incident angle without remarkable reduction of the light availability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device having a virtual image observation optical system, and more particularly to a novel optical device utilizing a reflection type holographic optical element.

[0002]

2. Description of the Related Art Conventionally, a virtual image observation optical system for observing a display image of an image display device as a virtual image has been proposed.
Various types of configurations are known.

As an example, FIG. 10 shows a virtual image observation optical system using a half mirror as a light beam splitting element.

This virtual image observation optical system uses a concave mirror as a reflection type optical element, and in many cases, a reflection film is deposited on a plastic concave substrate. The operation is as follows.

First, a video signal is applied to a liquid crystal display (L
CD) driving circuit 101. LCD drive circuit 1
01, a backlight voltage 102 and a liquid crystal display drive signal 103 are output.
04 and the liquid crystal display 105.

[0006] Here, the backlight 104 is a cold cathode tube 1.
The light source 04a is used as a light source, and a diffusion plate 104b is provided on the LCD side to make the illumination brightness uniform and to control the diffusion angle.

Liquid crystal display 10 as an image output device
For 5, a 0.55-inch transmissive liquid crystal display is used. Here, an electric image signal is converted into an actual image, and a light beam emitted from the backlight 104 is modulated. This light beam is subsequently transmitted to a half mirror 1 which is a light beam splitting device.
06. Here, about half of the total light amount passes through the half mirror 106, and the rest is reflected by the half mirror film 107 and enters the concave mirror 108. Most of the light beam incident on the concave mirror 108 is reflected by the reflection film 109 and is incident on the half mirror 106 again, and about half of the light beam is transmitted through the half mirror 106 and incident on the pupil 110.

In the virtual image observation optical system having such a configuration, since the light beam emitted from the image output device (liquid crystal display) 105 passes through the half mirror 106 twice and then enters the pupil 110, the light utilization efficiency of the optical system is lost. Even if there is no light, the light use efficiency is 25% at maximum, and about 20% in practice.

Therefore, the present applicant has already proposed a virtual image observation optical system in which a polarizing beam splitter (PBS) and a quarter-wave plate are combined instead of a half mirror.

FIG. 11 shows an example of a virtual image observation optical system using a polarizing beam splitter as a light beam splitting element.

This virtual image observation optical system uses an aspherical concave half mirror as a reflection type optical element, and further includes a transmission type liquid crystal image output device, a polarizing beam splitter, and a broadband one.
/ 4 wavelength plate. The operation is as follows.

First, a video signal is input to the liquid crystal display drive circuit 121. A backlight voltage 122 and a liquid crystal display drive signal 123 are output from the LCD drive circuit 121 and input to the backlight 124 and the liquid crystal display 125, respectively.

Here, the backlight 124 is a cold cathode tube 1
The light source 24a is used as a light source, and a diffusion plate 124b is provided on the LCD side to make the luminance of irradiation uniform and to control the diffusion angle. Liquid crystal display 125 as an image output device
A 0.55 inch transmissive liquid crystal display is used. Here, the electric image signal is converted into an actual image, and the luminous flux emitted from the backlight 124 is modulated.

As is well known, a light beam emitted from a liquid crystal image output device is converted into linearly polarized light by a polarizing plate. Here, the polarization direction of the light beam emitted from the liquid crystal image output device is set perpendicular to the paper surface. The polarization beam splitter 126 that subsequently enters the polarization beam splitter 126 is
In 7, the polarization component (p-polarized light) in which the polarization direction of the incident light beam is parallel to the incident surface (the surface including the incident light and the reflected light) is 100%.
The near-polarized light component (s-polarized light) that transmits near and has a characteristic of reflecting nearly 100%. That is, the light beam (s-polarized light with respect to the polarizing beam splitting film 127 of the polarizing beam splitter) emitted from the liquid crystal image output device 125 is mostly reflected by the polarizing beam splitting film 127 of the polarizing beam splitter.

Next, this light beam enters a quarter-wave plate 128 whose optical axis is inclined by 45 ° with respect to the polarization direction of this light beam.

The quarter-wave plate 128 is made of a uniaxial birefringent substance (quartz, calcite, etc.), and has a property that the refractive index differs depending on the direction of incident polarized light.
Therefore, for example, when the incident light flux is incident at an angle of 45 ° with respect to the optical axis of the crystal of the quarter-wave plate 128, the component between the component parallel to the optical axis of the incident polarized light and the component perpendicular thereto A phase difference of π / 2 (λ / 4 in optical path length) occurs.

Now, let the linearly polarized light (amplitude A, period T) incident on the quarter-wave plate 128 be E = Asin [2πt / T], and the polarized light component Eo perpendicular to the optical axis is polarized light parallel to the optical axis. Advances by λ / 4 compared to the component Ee [Depending on the magnitude relation between the ordinary ray refractive index (no) and the extraordinary ray refractive index (ne), it is determined whether the phase is advanced or delayed. ], The polarization component Ee parallel to the optical axis and the polarization component Eo perpendicular to the optical axis are Ee = A / √2sin [2πt / T] Eo = A / √2sin2π [t / T + λ / 4 / λ] = A / √2cos [2πt / T], and clockwise circularly polarized light is obtained.

The quarter wave plate 128 used here
Is a film in which two pieces of polycarbonate having a thickness of about 60 μ are bonded together with their optical axes changed, and the wavelength dependence in the visible light region is extremely reduced.

The light beam converted into clockwise circularly polarized light then enters the aspherical concave half mirror 129. Here, a part of the light beam is transmitted through the aspherical concave half mirror 129, and a part is reflected. This reflected light beam is given a refractive power for forming a virtual image of the output image of the image output device 125. In addition, since the traveling direction changes by 180 °, the light is left-handed circularly polarized light. The reflected luminous flux that has become the left-handed circularly polarized light again passes through the quarter-wave plate 128, and becomes a linearly polarized light that is orthogonal to the polarization direction of the linearly polarized light immediately after exiting the polarization beam splitter 126.

The light beam having this linearly polarized light subsequently re-enters the polarizing beam splitter 126. However, most of the light beam is transmitted this time because the polarizing beam splitter 127 of the polarizing beam splitter 126 becomes p-polarized light. . The luminous flux transmitted through the polarizing beam splitter 126 is subsequently applied to the pupil 1
It is led to 30.

When such a configuration is adopted, the practical light utilization efficiency in consideration of the loss is about 60% (when the aspherical concave half mirror 130 is assumed to be an aspherical concave mirror).
Although the efficiency is increased, the incident angle dependence of the polarizing beam splitter is large, and the reflection / transmittance of each wavelength differs depending on the incident angle. As a result, there is a problem that the observed virtual image has color unevenness. In addition, due to the incident angle dependence of the quarter-wave film, when the incident angle increases, the polarization state of the light beam that is incident on the polarizing beam splitter 127 for the second time greatly deviates from p-polarized light, and the amount of transmitted light decreases. There is also a problem.

In addition, as described in Japanese Patent Application Laid-Open No. 9-281430, a virtual image observation optical system using a total reflection prism as a light beam splitting element has been devised.

This is constructed together with an image output device, using one surface of the total reflection prism as a refraction surface and a reflection surface. In this case, since the total reflection is used, the light use efficiency is very high, about 90%. However, in this case, there is a problem that the weight of the entire optical system increases due to the use of the prism as the light beam splitting element. This is a wide angle of view where the size of the optical system increases,
In the case of the wide pupil tolerance specification, it becomes more remarkable. Further, when the exit angle of the light beam from the reflection / refraction surface to the pupil increases, chromatic aberration occurs. At least one of the refraction surface, reflection surface, and reflection / refraction surface of the prism is non-axial because the optical system is decentered. There is also a problem that it is necessary to make the surface symmetrical and processing becomes difficult.

[0024]

As described above, in the case of a virtual image observation optical system using a half mirror as a light beam splitting element, the light beam emitted from the image display device has two half mirrors.
There is a major problem that the light use efficiency is reduced to 25% or less by passing through the light twice.

Also, instead of the half mirror, PBS and 1
In the case of a virtual image observation optical system in which a 波長 wavelength plate is combined, the light use efficiency is about 60%. However, when the display image is a color image, the image observed due to the wavelength dependency of the PBS and the 波長 wavelength plate is reduced. There is a problem that color unevenness occurs.

Further, in the method of using the total reflection / transmission according to the angle of the incident light beam using the total reflection prism,
At the same time as increasing the weight of the entire optical system, chromatic aberration may occur unless the angle of incidence / emission to the prism is kept small. In addition, since the optical system is an eccentric system, a huge amount of eccentric aberration occurs in a configuration with an ordinary axisymmetric optical surface, and in order to suppress this, a non-axisymmetric optical surface such as a free-form surface must be introduced. However, this leads to an increase in the cost of components constituting the optical system.

An object of the present invention is to provide a novel optical device which can solve the problems of the conventional virtual image observation optical system.

[0028]

In order to achieve the above-mentioned object, an optical apparatus according to the present invention comprises a light source, a reflective holographic optical element, and a part or all of a light beam emitted from the light source. And at least one reflective optical element, the light beam emitted from the light source is incident on the reflective holographic optical element at least twice, and the incident light beam is transmitted to the reflective holographic optical element. At least two types of incident angles are set, and the presence or absence of the diffraction effect differs depending on the number of incident light beams to the reflective holographic optical element.

By using a thick reflection type hologram optical element in the optical system as a light beam splitting optical element instead of a half mirror and a polarizing beam splitter, reflected light and transmitted light depending on the incident angle without significantly lowering the light use efficiency. Is greatly reduced. Also, the entire optical system is configured to be lighter in weight than in the case where a total reflection prism is used and total reflection / transmission is used depending on the angle of the incident light beam, and the incidence / emission angle is the same as when a prism is used. Because there is no restriction, the degree of freedom of design can be increased. Furthermore, when the optical system has an eccentric layout, the reflection type hologram optical element is provided with not only a light beam splitting function but also a non-axisymmetric phase adding function, so that the configuration is made only with a normal axisymmetric optical surface. The generated eccentric aberration can be reduced without introducing a number of toric surfaces, anamorphic surfaces, or complicated free-form surfaces, thereby realizing a small and lightweight non-coaxial optical system.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a specific configuration of an optical device to which the present invention is applied will be described in detail with reference to the drawings.

The optical device of the present invention uses a reflection hologram optical element as a light beam splitting optical element. The reflection holographic optical element of the present invention is a so-called thick hologram, and diffracts and reflects an incident light beam. At this time, it has selectivity with respect to the wavelength of the incident light beam and the incident angle.

The conditions for reproducing this thick hologram are detailed in, for example, "Physics Selection Book 22. Holography" (Junpei Tsujiuchi, Shokabo). For the incident light for reproduction (diffraction), reproduction (diffraction) is performed only at the same wavelength and the same incident angle as the production light beam, and reproduction (diffraction) is performed at other wavelengths or incident angles. Not
Only the zero-order light (that is, the light flux that passes through the hologram without being diffracted) is generated.

However, the actual thickness of the hologram is several μm.
And a thickness of only several tens μm, and there is a certain tolerance in the incident angle. The allowable error Δθ (the angle at which the diffraction efficiency becomes 0) is approximate, and Δθ = −λ (n ² −sin ² [θ]) ^1/2 / (tsin [θ] cos
[Θ]) (λ: wavelength of incident light beam, t: thickness of hologram, n: center refractive index of hologram, θ: incident angle to hologram), for example, λ = 550 nm, t = 10 μm, n =
1.5, θ = 135 ° (reflection hologram), Δ
θ is about 8 ° (16 ° in the entire width).

Regarding the allowable error of the wavelength, Δλ = λ ² / {t (n ± (n ² −sin ² [θ]))} (the double sign of the denominator is-if 0 <θ <90, and 0 < θ <
180 is represented by +), for example, λ = 550 nm,
In the case of t = 10 μm, n = 1.5, θ = 135 ° (reflection type hologram), Δλ is about 11 nm (22 nm in full width).
Becomes

As a criterion that can be regarded as a thick hologram in practice, there is generally the following parameter Q. It is considered that a thin hologram when Q ≒ 0 and a thick hologram when Q >> 0.

Q = 2πλt / (nΛ ² ) where λ is the wavelength of the incident light beam, t is the thickness of the hologram,
n is the center refractive index of the hologram, Λ is the interval between interference fringes formed in the hologram, Λ = λ / (2 sin [(θs−θr) / 2]) (λ is the hologram manufacturing wavelength, θs and θr are 2 Incident angles of the two hologram production light beams on the hologram).

As described above, in a thick hologram, the wavelength of the incident light beam and the incident angle within a certain tolerance are selectively diffracted, and the other light beams pass through the hologram without being diffracted. By utilizing this property, even light beams emitted from the same light source can be selectively diffracted due to the different angles at which they enter the reflection hologram optical element.

FIGS. 1 and 2 show, as an example of an optical apparatus to which the present invention is applied, non-coaxial virtual image observation using an image output device, an aspherical concave half mirror, and a Lippmann volume hologram as a reflection type holographic optical element. 1 shows an optical system.

This virtual image observation optical system is mainly composed of a liquid crystal display 2 having a backlight 1, a reflection type holographic optical element 3 which is a light beam splitting optical element, and an aspheric concave half mirror 4. A virtual image is observed by the pupil 5.

In this optical device, first, a video signal is input to the liquid crystal display drive circuit 6. The LCD drive circuit 6 outputs an LED (light emitting diode) lighting current 7 and a liquid crystal display drive signal 8, which are input to the backlight 1 and the liquid crystal display 2, respectively.

The backlight 1 has a chip-size LE having a center wavelength of 525 nm as a light source, for example.
An LED array is used in which D1a is mounted on a plane in two rows and four columns, for a total of eight.

A diffusion plate 1b is provided on the LCD side to make the luminance of irradiation uniform and to control the diffusion angle. In this case, the diffusion angle is a half-value angle of about 10 °.

As the liquid crystal display 2 which is an image output device, a 0.55-inch transmission type liquid crystal display is used.
Here, the electric image signal is converted into an actual image, and the luminous flux emitted from the backlight 1 is modulated. This luminous flux
Subsequently, the light enters a reflection type holographic optical element (Lipman volume hologram) 3 functioning as a light beam splitting device. Here, a specific wavelength range (in this case, about 20 nm in full width at half maximum around 525 nm which is the wavelength of the light source)
Is selectively diffracted and reflected by the hologram layer 3a, and has a center wavelength of 525 nm and a full width at half maximum of 30 nm.
About 70% of the light enters the aspherical concave half mirror 4.

The light beam incident on the aspherical concave half mirror 4 is partially transmitted and partially reflected after being provided with a refracting power for forming a virtual image, and is again reflected by a reflection type holographic optical element (Lipman volume hologram). ) 3

In this case, since the incident angle of the reflection type holographic optical element (Lipmann volume hologram) 3 is largely deviated from the diffraction condition, no diffraction phenomenon occurs.
Almost all light beams except for the transmission loss pass through the reflective holographic optical element (Lipman volume hologram) 3 and enter the pupil 5.

On the other hand, the background light beam traveling from the left side of the aspherical concave half mirror 4 passes through the aspherical concave half mirror 4 and the reflection type holographic optical element (Lipman volume hologram) 3 and similarly enters the pupil 5. I do.

Here, the aspherical concave half mirror 4 having optical power is eccentrically arranged, causing aberration. However, the reflection type holographic optical element (Lipmann volume hologram) 3 has a non-rotationally symmetric phase adding function to reduce the decentering aberration.
That is, a non-rotationally symmetric phase difference for correcting eccentric aberration is added to the wavefront diffracted by the reflection type holographic optical element (Lipmann volume hologram) 3, and thereafter the pupil 5 is reflected by the aspherical concave half mirror 4. Is properly corrected for aberration, and the observer can observe a clear virtual image.

In this embodiment, the display is a single color of green, but the reflection type holographic optical element (Lipman volume hologram) 3 is formed by multiplex exposure of one layer hologram with RGB three color lasers as shown in FIG. RGB for backlight
By using a light source including a spectrum, full-color display is also possible. However, in this case, the diffraction efficiency of each of RGB becomes lower than that in the case of monochromatic exposure.

FIG. 3 shows an apparatus for exposing the Lippmann volume hologram 10 for full color display.

In the apparatus shown in FIG. 3, a light beam emitted from a red laser (Kr laser, oscillation frequency 647 nm) 11 is split by a variable beam splitter 14, one of which is reflected by a dichroic mirror 15 and a mirror 16 and modulated. The light is applied to one surface of the Lippmann volume hologram 10 via the element 17. The other is mirror 1
8. The light is reflected by the dichroic mirror 19 and the mirror 20, passes through the modulation element 21 and the aspherical non-rotationally symmetric wavefront generating optical system 22, and irradiates the other surface of the Lippmann volume hologram 10.

Green laser (SHG laser, oscillation frequency 5
The light beam emitted from the (32 nm) 12 is reflected by a mirror 23 and split by a variable beam splitter 24, one of which passes through a dichroic mirror 25 and a dichroic mirror 15, is reflected by a mirror 16, passes through a modulating element 17, and passes through a modulation element 17. The hologram 10 is irradiated on one surface side. The other is reflected by mirror 26,
Dichroic mirror 27 and dichroic mirror 1
9 is reflected by the mirror 20 and is reflected by the mirror 20.
Then, the light is radiated to the other surface side of the Lippman volume hologram 10 via the aspherical and non-rotationally symmetric wavefront generating optical system 22.

Blue laser (Ar laser, oscillation frequency 47
The light beam emitted from the (7 nm) 13 is split by the variable beam splitter 28, one of which is reflected by the mirror 29 and the dichroic mirror 25, transmitted through the dichroic mirror 15, reflected by the mirror 16, passed through the modulation element 17, and passed through the modulation element 17, and is thus a Lippman volume hologram Irradiation is performed on one side of 10. The other is reflected by the dichroic mirror 27, passes through the dichroic mirror 19, and
0 is reflected by the modulation element 21 and passes through the aspherical non-rotationally symmetric wavefront generating optical system 22 and the Lippmann volume hologram 1
0 is irradiated on the other side.

By coloring the volume of the Lippman volume hologram 10 in this manner, the spectrum is uniformly missing from the transmitted light from the RGB and reaches the pupil 5, so that the background color becomes more natural. It also has advantages.

The optical device can be made full color using a reflection type liquid crystal display device.

In this case, as shown in FIG. 4, a light guide plate 31 is arranged on the surface of the liquid crystal display 2 and a light source 32 is arranged on the side surface, and light from the light source 32 is reflected on the surface of the liquid crystal display 2. The light is guided to the reflective holographic optical element 3. The other configuration is the same as that shown in FIG. 1 described above, and the description is omitted here.

Next, as another example of the optical device of the present invention,
As shown in FIG. 5, a non-coaxial virtual image observation optical system using an image output device (liquid crystal display 2), a free-form mirror 33, a reflective holographic optical element 3, and a refractive lens (doublet) 34 will be described.

The operation up to the liquid crystal display 2 is basically the same as that of the example shown in FIG. 1, and a description thereof will be omitted here. However, in the case of this example, the backlight uses LEDs of three colors of RGB.

The light beam emitted from the liquid crystal display 2 subsequently enters the reflective holographic optical element 3 functioning as a light beam splitting device. Here, a specific wavelength range (4
Only light having a full width at half maximum of about 20 nm centered on each of 70 nm, 525 nm, and 640 nm) is selectively diffracted and reflected, and about 70% of the light emitted from the LED is effectively used and enters the free-form mirror 33.

The light beam incident on the free-form surface mirror 33 is given a part of the refracting power for forming a virtual image, is reflected, and enters the reflection type holographic optical element 3 again. However, in this case, since the incident angle of the reflective holographic optical element 3 is greatly deviated from the diffraction condition, no diffraction phenomenon occurs, and almost all light fluxes excluding transmission loss pass through the reflective holographic optical element 3, Subsequently, the light enters the doublet lens 34.

Here, after the refracting power for the virtual image formation is given again, the light beam is guided to the pupil 5.

At this time, the free-form mirror 33 having the optical power is eccentrically arranged, causing aberration.
However, since the free-form surface mirror 33 has a non-rotationally symmetric phase adding function to reduce the eccentric aberration, the light beam that passes through the doublet lens 34 and is guided to the pupil 5 has a good aberration. Has been corrected.

In this embodiment, the hologram layer 3a is provided for each of RGB to improve the diffraction efficiency, and has a three-layer structure of RGB. This configuration is shown in FIG.
And FIG. It is characterized in that the hologram layer for red having a relatively low diffraction efficiency is arranged on the uppermost layer as viewed from the incident light beam, and the hologram layer for edge colors having a relatively high diffraction efficiency is arranged on the lowermost layer as viewed from the incident light beam.

FIG. 6 shows an example of a hologram photosensitive film having a three-layer structure. The hologram photosensitive film 40 is, for example, a photosensitive film suitable for producing a color hologram. On the base film 41, a green photosensitive layer GH, a barrier layer 44a, a blue photosensitive layer BH, a barrier layer 44b, and a red The photosensitive layer RH, the barrier layer 44c, the adhesive layer 43, and the cover film 42 are laminated in this order.

Base film 41 and cover film 4
2 is made of polyethylene terephthalate or the like. The thickness of the base film 41 and the cover film 42 is about several tens of μm.
1 has a thickness of 50 μm, and the cover film 42 has a thickness of 25 μm.
The thickness is set to μm. Further, an antireflection layer (AR coat) may be formed on the cover film 42 disposed on the light beam incident side.

The green, blue and red photosensitive layers GH, BH,
RH is a sensitizing dye (photoseisitizing dy)
e), initiator, chain transfer agent (chai
n transfer agent), a monomer, a photopolymer containing a polymer binder and the like. The thicknesses of the green, blue, and red photosensitive layers GH, BH, and RH are approximately several μm to several tens μm, and specifically, for example, each is 15 μm.

The green photosensitive layer GH has a thickness of about 500 to
A sensitizing dye or a reaction initiator is contained so as to have a sufficient sensitivity only in a wavelength band of 550 nm, and the photosensitive layer BH for blue has a sufficient sensitivity only in a wavelength band of about 400 to 480 nm. , A sensitizing dye and a reaction initiator. Also, the red photosensitive layer RH is about 60
A sensitizing dye and a reaction initiator are contained so as to have sufficient sensitivity only in a wavelength band of 0 to 700 nm.

Therefore, the hologram photosensitive film 40
Is exposed to an Ar gas laser having a wavelength of 477 nm, only the blue photosensitive layer BH is exposed, and the other red photosensitive layer RH and green photosensitive layer GH are not exposed. When the hologram photosensitive film 40 is exposed to a laser using the second harmonic of the YAG laser having a wavelength of 532 nm, only the green photosensitive layer GH is exposed, and the other red photosensitive layer RH and blue photosensitive layer are exposed. BH is not exposed. In addition, wavelength 647n
When exposure is performed with a Kr gas laser of m, only the red photosensitive layer RH is exposed, and the other green photosensitive layer GH and blue photosensitive layer BH are not exposed.

By using such a hologram photosensitive film 40, the independent green, blue and red photosensitive layers G can be obtained by a method of simultaneous exposure of multiple wavelengths of red, green and blue or a method of sequential exposure of multiple wavelengths.
Since green, blue, and red interference fringes are recorded on H, BH, and RH, respectively, a color hologram having high diffraction efficiency can be manufactured even with one film.

In the hologram photosensitive film 40, the photosensitive layers are a green photosensitive layer GH, a blue photosensitive layer BH,
The red photosensitive layer RH is laminated in this order. This is because the green photosensitive layer G having high visibility and high diffraction efficiency is obtained.
H is disposed inside the film, that is, at the position farthest from the irradiation direction of the reproduction light, and the red photosensitive layer RH having low visibility and hardly increasing the diffraction efficiency is disposed outside the film, that is, the irradiation direction of the reproduction light. It is because it was arranged at the position closest to the. Green, blue and red photosensitive layers GH, BH, RH
Is arranged in this manner, it is possible to obtain a color hologram in which the visibility and the diffraction efficiency of each color are balanced.

FIG. 7 shows a hologram photosensitive film 50 to which the reproduction light is irradiated from the base film side.

In this case, on the base film 51,
Red photosensitive layer RH, barrier layer 54a, blue photosensitive layer B
H, barrier layer 54b, green photosensitive layer GH, barrier layer 54
c, an adhesive layer 53 and a cover film 52 are laminated in this order.

In the case of this configuration, the base film 51
It is preferable that an antireflection layer (AR coat) is formed on the substrate.

The barrier layers 44a, 44b, 44c,
Numerals 54a, 54b and 54c are for suppressing the movement of the photopolymer molecules between the green, blue and red photosensitive layers GH, BH and RH, and have a thickness of green, blue and red photosensitive layers. The thickness is smaller than the thickness of the layers GH, BH and RH, for example, about 5 μm. If the photopolymer molecules move between the photosensitive layers GH, BH, and RH for each color, the degree of modulation of the refractive index decreases, and high diffraction efficiency cannot be obtained. By providing a barrier layer between the green, blue, and red photosensitive layers GH, BH, and RH, the movement of photopolymer molecules can be suppressed, and high diffraction efficiency can be obtained.

FIG. 8 shows a non-coaxial virtual image observation optical system using an image output device and two reflective holographic optical elements as still another example of the optical device to which the present invention is applied.

The operation up to the liquid crystal display 2 is basically the same as that of the example shown in FIG. 1, and the description thereof is omitted here. However, in the case of this example, the backlight uses LEDs of three colors of RGB.

The light beam emitted from the liquid crystal display 2 subsequently enters the first reflective holographic optical element 3 functioning as a light beam splitting device. Here, only light rays in a specific wavelength range (about 470 nm, 525 nm, and about 640 nm, each having a full width at half maximum of about 20 nm) are selectively diffracted and reflected, and about 70% of the light emitted from the LED is effectively used. To the reflective holographic optical element 61.

Second Reflective Holographic Optical Element 6
In the hologram layer 61a, one part of the light beam incident on 1 is transmitted, and one part is reflected after being given a refracting power for forming a virtual image, and is incident on the first reflective holographic optical element 3 again. . However, in this case, since the incident angle of the first reflective holographic optical element 3 is greatly deviated from the diffraction condition, no diffraction phenomenon occurs, and almost all light fluxes excluding transmission loss are reflected by the reflective holographic optical element 3. The light is transmitted to the pupil 5.

On the other hand, the background light beam traveling from the left side of the second reflective holographic optical element 61 passes through the second reflective holographic optical element 61 and the first reflective holographic optical element 3. Thereafter, the light similarly enters the pupil 5.

Here, when the second reflection type holographic optical element 61 is arranged eccentrically, aberration occurs. However, since both the first reflective holographic optical element 3 and the second reflective holographic optical element 61 have a non-rotationally symmetric phase adding function of reducing this decentering aberration, the pupil 5 The guided light beam is well corrected for aberration.

In this embodiment, the hologram layers 3a and 61a are each provided with a hologram layer for each of RGB to improve the diffraction efficiency, and have a three-layer structure. The configuration is as shown in FIGS.

FIG. 9 shows an image output device, a projection lens, and a reflective holographic screen (which are integrally formed by a reflective holographic optical element and a diffusion screen) as still another example of the optical device of the present invention. ) And a rear projection type image display device using a reflection mirror.

The light beam emitted from the image output device 71 enters the projection lens 72 and is given a refracting power for forming an image on a screen. As the image output device 71, a CRT,
There are a combination of a transmissive LCD or a reflective LCD with an LED or a laser, and an electroluminescent image output device that is a self-luminous element.

In this embodiment, a transmission type LCD and a laser are used. The light beam emitted from the projection lens 72 subsequently enters a reflective holographic optical element 73 provided on one surface of a holographic screen 74 functioning as a light beam splitting device. The light beam incident on the reflection type holographic optical element 73 is selectively diffracted and reflected only in a specific wavelength range (in this example, about 20 nm in full width at half maximum around 470 nm, 525 nm and 640 nm, respectively), About 80 of the emitted laser light
% Is effectively used and enters the reflection mirror 75. The light beam incident on the reflection mirror 75 is reflected after being given refracting power for image formation, and is incident again on the reflection type holographic screen 74. However, in this case, since the incident angle of the reflection type holographic optical element 73 is greatly deviated from the diffraction condition, no diffraction phenomenon occurs, and almost all light beams except for the transmission loss pass through the reflection type holographic optical element 73.

This light beam is diffused by a diffusion screen provided on the other side of the reflection type holographic screen 74, and this light beam is observed by an observer (not shown). In the case of this example, since laser light is used as the illumination light source of the image display device, it is characterized in that the light use efficiency can be increased as compared with the case where the above-described LED is used.

In the above-described embodiments, it is desirable that the spectrum of the light source be the diffraction wavelength (Bragg wavelength) of the reflection hologram optical element. This is because only a limited spectral width is used as diffracted light due to the diffraction wavelength selectivity of the reflection hologram optical element, which is important for increasing the light use efficiency.

[0086]

As is clear from the above description, in the present invention, a thick reflection type hologram optical element is used in the optical system as a light beam splitting optical element instead of the half mirror and the polarization beam splitter. It is possible to reduce the wavelength dependence of reflected light and transmitted light depending on the incident angle without significantly lowering the light use efficiency. Also, a total reflection prism is used according to the angle of the incident light beam using a total reflection prism.
The whole optical system can be made lighter than the case of splitting light beams by using transmission.
Since there is no restriction on the injection angle, the degree of freedom in design can be increased.

Further, when the optical system has an eccentric layout, the reflection type hologram optical element is provided not only with a light beam splitting function but also with a function of adding a non-axisymmetric phase, so that only a normal axisymmetric optical surface can be used. It is possible to reduce the decentering aberration generated in the configuration without introducing a toric surface, an anamorphic surface, or a complicated free-form surface of the number of units, thereby providing a small and lightweight non-coaxial optical system. it can.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a configuration example of a non-coaxial virtual image observation optical system.

FIG. 2 is a schematic diagram illustrating a configuration example of a non-coaxial virtual image observation optical system.

FIG. 3 is a schematic diagram illustrating a configuration example of an apparatus that performs color exposure on a Lippman volume hologram.

FIG. 4 is a schematic diagram showing a configuration example of a non-coaxial virtual image observation optical system using a reflection type liquid crystal display device.

FIG. 5 is a schematic diagram showing a configuration example of a non-coaxial virtual image observation optical system using a free-form surface mirror and a refractive lens.

FIG. 6 is a schematic diagram showing an example of a hologram having a three-layer structure.

FIG. 7 is a schematic diagram showing another example of a hologram having a three-layer structure.

FIG. 8 is a schematic diagram showing a configuration example of a non-coaxial virtual image observation optical system using two reflective holographic optical elements.

FIG. 9 is a schematic diagram showing an example of a rear projection type image display device using a reflection type holographic screen.

FIG. 10 is a schematic diagram showing an example of a virtual image observation optical system using a half mirror as an optical splitting element.

FIG. 11 is a schematic diagram illustrating an example of a virtual image observation optical system using a polarization beam splitter as an optical splitting element.

[Explanation of symbols]

Reference Signs List 1 backlight, 2 liquid crystal display, 3 reflection holographic optical element, 3a hologram layer, 4
Aspherical concave half mirror, 5 pupils

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 CA01 CA05 CA06 CA08 CA09 CA17 CA22 CA28 CA30 2H088 EA12 EA16 HA06 HA10 HA17 HA20 HA21 HA22 HA28 MA04 MA06 MA20 5C061 AA29 AB11 AB12 AB14 AB16 AB18 AB24

Claims (14)

[Claims] 1. A light source comprising: a light source; a reflective holographic optical element; and at least one reflective optical element for reflecting a part or all of a light beam emitted from the light source. A reflective holographic optical element, wherein the light flux is incident on the reflective holographic optical element at least twice or more, and the incident angles of the incident light flux on the reflective holographic optical element are set to be at least two or more; An optical device characterized in that the presence or absence of a diffraction effect is different depending on the number of times a light beam is incident on the optical device. 2. The optical device according to claim 1, wherein the reflection holographic optical element has a function of adding a non-axisymmetric phase to an incident wavefront during diffraction. 3. The optical device according to claim 1, wherein the hologram layer of the reflection type holographic optical element is constituted by a plurality of hologram layers having different wavelengths for generating a diffraction effect. 4. The optical device according to claim 1, wherein the reflection type holographic optical element uses a photopolymer as a hologram photosensitive agent. 5. The optical device according to claim 1, wherein the light source is a light emitting diode or a laser. 6. The optical device according to claim 1, wherein the light source is a self-luminous image output device. 7. The optical device according to claim 1, wherein the light source comprises a combination of an image output device, an illumination light source for illuminating the image output device, and an illumination optical system. 8. The optical device according to claim 7, wherein the illumination light source is a light emitting diode or a laser. 9. The optical device according to claim 1, wherein the reflection type optical element is a concave mirror or a concave translucent mirror. 10. The optical device according to claim 1, wherein the reflection type optical element is a free-form surface mirror or a free-form surface translucent mirror. 11. The optical device according to claim 1, wherein the reflection type optical element is a reflection type holographic optical element. 12. The optical device according to claim 1, further comprising a screen for projecting a light beam transmitted through the reflective holographic optical element. 13. The optical device according to claim 12, wherein the screen is a diffusion screen. 14. The optical device according to claim 1, further comprising a lens into which a light beam transmitted through the reflective holographic optical element is incident.