U.S. patent application number 14/638234 was filed with the patent office on 2015-08-27 for display method and display apparatus.
The applicant listed for this patent is OLYMPUS CORPORATION. Invention is credited to Yoshiaki Horikawa.
Application Number | 20150241844 14/638234 |
Document ID | / |
Family ID | 50236862 |
Filed Date | 2015-08-27 |
United States Patent
Application |
20150241844 |
Kind Code |
A1 |
Horikawa; Yoshiaki |
August 27, 2015 |
Display Method and Display Apparatus
Abstract
A display method lets a display beam to propagate in a
transparent substrate while internally reflected repeatedly and
lets the display beam partly emit out of the transparent substrate
every time the display beam is internally reflected, thereby
emitting display beams from almost entirety of a surface of the
transparent substrate. The display beam is produced
holographically. A display apparatus includes a spatial phase
modulator that produces a display beam, a transparent substrate in
which the display beam is internally reflected repeatedly to
propagate in it, and a splitter that lets the display beam partly
emit out of the transparent substrate every time the display beam
is internally reflected.
Inventors: |
Horikawa; Yoshiaki; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OLYMPUS CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
50236862 |
Appl. No.: |
14/638234 |
Filed: |
March 4, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2013/060911 |
Apr 11, 2013 |
|
|
|
14638234 |
|
|
|
|
Current U.S.
Class: |
359/11 ; 359/34;
359/558 |
Current CPC
Class: |
G03H 2225/31 20130101;
G03H 2222/20 20130101; G03H 1/0808 20130101; G03H 2225/32 20130101;
G03H 2222/53 20130101; G03H 1/2294 20130101; G03H 1/12 20130101;
G03H 2223/16 20130101; G02F 1/133504 20130101; G03H 2222/46
20130101; G03H 2222/52 20130101; G03H 2223/23 20130101; G02B 5/32
20130101; G03H 2222/54 20130101; G02B 27/1086 20130101; G03H 1/2205
20130101 |
International
Class: |
G03H 1/12 20060101
G03H001/12; G02B 27/10 20060101 G02B027/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 5, 2012 |
JP |
2012-194964 |
Claims
1. A display method comprising: letting a display beam to propagate
in a transparent substrate while internally reflected repeatedly;
and letting the display beam partly emit out of the transparent
substrate every time the display beam is internally reflected,
thereby emitting the display beams from almost entirety of a
surface of the transparent substrate, wherein the display beam is
produced holographically.
2. A display apparatus according to claim 1, wherein the coherence
length of the display beam is shorter than the distance through
which the display beam propagates by one internal reflection.
3. A display apparatus according to claim 2, wherein the display
beam emitting out of the transparent substrate displays a virtual
image at infinity.
4. A display apparatus comprising: a spatial phase modulator that
produces a display beam; a transparent substrate in which the
display beam is internally reflected repeatedly to propagate in it;
and a splitter that lets the display beam partly emit out of the
transparent substrate every time the display beam is internally
reflected.
5. A display apparatus according to claim 4, wherein the spatial
phase modulator produces the display beam holographically.
6. A display apparatus according to claim 5, wherein the apparatus
uses two transparent substrates.
7. A display apparatus according to claim 5, wherein the spatial
phase modulator is arranged in such a way that the condition that
zero-order light produced by the spatial phase modulator is
transmitted through the transparent substrate and first order-light
is totally reflected by the transparent substrate is met.
8. A display apparatus according to claim 7, wherein a convergent
beam is made incident on the spatial phase modulator, and the
apparatus is provided with a trap that traps the zero order
light.
9. A display apparatus according to claim 5, wherein the coherence
length of the display beam is shorter than the distance through
which the display beam propagates by one internal reflection.
10. A display apparatus according to claim 5, wherein the splitter
comprises a diffraction grating.
11. A display apparatus according to claim 10, wherein the
diffraction grating comprises a volume hologram.
12. A display apparatus comprising: a spatial phase modulator that
produces a display beam holographically; a first transparent
substrate and a second transparent substrate in which the display
beam is internally reflected repeatedly to propagate in them; a
splitter that lets the display beam partly enter the second
transparent substrate every time the display beam is internally
reflected in the first transparent substrate; and a splitter that
lets the display beam partly emit out of the second transparent
substrate every time the display beam is internally reflected in
the second transparent substrate, wherein the coherence length of
the display beam is shorter than the distance through which the
display beam propagates by one internal reflection.
13. A display apparatus comprising: a light source; a transparent
substrate having a first transmitting surface and a second
transmitting surface; a spatial phase modulator arranged between
the light source and the second transmitting surface; and a
splitter arranged between the first transmitting surface and the
second transmitting surface, wherein when the transparent substrate
is seen from the light source side, the spatial phase modulator and
the splitter are arranged side by side.
14. A display apparatus according to claim 13, further comprising
another spatial phase modulator arranged in an optical path from
the light source to the spatial phase modulator.
15. A display apparatus according to claim 13, wherein the light
source is in contact with the first transmitting surface.
16. A display apparatus according to claim 13, further comprising a
lens arranged in an optical path from the light source to the
spatial phase modulator.
17. A display method comprising: causing a display beam to be
reflected; amplitude-splitting the reflected display beam, thereby
producing a beam travelling in the direction same as the travelling
direction of the reflected display beam and a beam travelling in a
direction different from the travelling direction of the reflected
display beam; and performing the reflecting and the
amplitude-splitting repeatedly, wherein the display beam is a beam
produced by diffraction.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation application of
PCT/JP2013/060911 filed on Apr. 11, 2013 and claims a benefit of
priority from the prior Japanese Patent Application No. 2012-194964
filed on Sep. 5, 2012; the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a display apparatus and
display method.
[0004] 2. Description of the Related Art
[0005] In recent years, there has been developed an image display
apparatus adapted to form a virtual image of a display screen in
front of a viewer. In this image display apparatus, a display beam
is internally reflected repeatedly in a transparent substrate to
propagate in the substrate. Every time the display beam is
internally reflected, a portion of the display beam is emitted out
of the substrate. Thus, the display beam is emitted from almost the
entire surface of the substrate in this image display apparatus
(Japanese Patent Publication No. 4605152).
[0006] More specifically, in this image display apparatus, the
display beam is emitted from a display screen of a liquid crystal
display element. The display beam emitted from the display screen
is converted into a parallel beam by an objective lens to enter the
transparent substrate. The display beam is internally reflected
repeatedly in the transparent substrate to propagate in the
substrate. Every time the display beam is internally reflected, the
display beam partly is emitted out of the substrate. Since display
beams emit out of the substrate at multiple locations in this way,
the display beams are emitted from the entire surface of the
transparent substrate. Consequently, the diameter of the overall
display beams emitting out of the transparent substrate is larger
than the diameter of the beam incident on the transparent
substrate.
[0007] In order for the viewer to see a virtual image of the
display screen, it is necessary for the display beam emitted from
the transparent substrate to enter his/her eye. In the image
display apparatus described above, the diameter of the display beam
emitting out of the transparent substrate is large. Consequently,
the allowable range of alignment of the eye with the display beam
(or the transparent substrate) is larger than that in the case
where the diameter of the display beam is small. Therefore, the
viewer can observe the virtual image more easily.
[0008] Moreover, the display beam emitting from the transparent
substrate is a parallel beam. This allows the viewer to observe a
virtual image located in rear of the transparent substrate.
Furthermore, since the display beam has a large diameter, it is not
necessary for the viewer to locate his/her eye close to the display
apparatus. In connection with the above, the location in rear of
the transparent substrate refers to a location on the opposite or
far side of the transparent substrate to the location of the
viewer.
SUMMARY OF THE INVENTION
[0009] To solve the above object and to achieve the object, a
display method according to the present invention comprises:
[0010] letting a display beam to propagate in a transparent
substrate while internally reflected repeatedly; and
[0011] letting the display beam partly emit out of the transparent
substrate every time the display beam is internally reflected,
thereby emitting display beams from almost entirety of a surface of
the transparent substrate,
[0012] wherein the display beam is produced holographically.
[0013] A display apparatus according to the present invention
comprises:
[0014] a spatial phase modulator that produces a display beam;
[0015] a transparent substrate in which the display beam is
internally reflected repeatedly to propagate in it; and
[0016] a splitter that lets the display beam partly emit out of the
transparent substrate every time the display beam is internally
reflected.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIGS. 1A and 1B are diagrams showing the basic construction
of an apparatus and how a display beam propagates, where FIG. 1A
shows a case in which a divergent beam is made incident on a
transparent substrate, and FIG. 1B shows a case in which a parallel
beam is made incident on a transparent substrate;
[0018] FIGS. 2A and 2B are diagrams showing a method and apparatus
for producing a display beam holographically, where FIG. 2A is a
diagram showing an ordinary optical system used to observe a
virtual image, and FIG. 2B is a diagram showing an optical system
that produces a display beam holographically;
[0019] FIG. 3 is a block diagram of a process of obtaining a
hologram by computation;
[0020] FIGS. 4A and 4B are diagrams showing a display apparatus
according to a first embodiment, where FIG. 4A shows a case in
which a divergent beam is made incident on a transparent substrate,
and FIG. 4B shows a case in which a parallel beam is made incident
on a transparent substrate;
[0021] FIG. 5 is a diagram showing a display apparatus according to
a second embodiment;
[0022] FIGS. 6A and 6B are diagrams showing a display apparatus
according to a third embodiment, where FIG. 6A shows a case in
which a divergent beam is made incident on a transparent substrate,
and FIG. 6B shows a case in which a parallel beam is made incident
on a transparent substrate;
[0023] FIGS. 7A and 7B are diagrams showing a display apparatus
according to a fourth embodiment, where FIG. 7A is a diagram
showing the construction of a first transparent substrate and how a
display beam propagates, and FIG. 7B is a diagram showing the
construction of a second transparent substrate and how display
beams propagate;
[0024] FIG. 8 is a diagram showing the overall construction of the
display apparatus according to the fourth embodiment;
[0025] FIGS. 9A and 9B are diagrams showing a construction in the
case where a sufficiently large angle of diffraction of a display
beam cannot be provided, where FIG. 9A is a diagram showing the
construction of a first transparent substrate, and FIG. 9B is a
diagram showing the relationship between incident light, diffracted
light, and zero-order light;
[0026] FIGS. 10A and 10B are diagrams showing a display apparatus
according to a fifth embodiment, where FIG. 10A shows a case in
which a reflective spatial phase modulator is used, and FIG. 10B
shows a case in which a transmissive spatial phase modulator is
used;
[0027] FIG. 11 is a diagram showing beams emitted from the display
apparatus of the embodiment, where the optical distances of the
beams are visualized.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Operations and advantageous effects of embodiments according
to some modes of the present invention will be described. The
operations and advantageous effects of the embodiments will be
described as specific illustrative modes. However, the illustrative
modes that will be described are only some examples of the modes
falling within the scope of the present invention, and there are
many variations of these modes. Therefore, the present invention is
not limited to the illustrative modes described in the
following.
[0029] According to a display method of an embodiment, a display
beam produced holographically is caused to be internally reflected
repeatedly in a transparent substrate to propagate in the
transparent substrate, and the internally reflected display beam
partly is emitted out of the transparent substrate for display
every time the display beam is internally reflected. As the display
beam propagates, multiple display beams are emitted from the
transparent substrate. In this way, the display beams are emitted
from almost the entire surface of the transparent substrate.
[0030] In the display method of this embodiment, a display beam is
produced holographically. Therefore, a display method having high
optical performance can be realized with a small and slim
apparatus. Producing a display beam holographically means producing
(or reproducing) a display beam using a hologram.
[0031] According to the display method of this embodiment, as the
display beam propagates, multiple display beams are emitted from
the transparent substrate. A viewer can view an image by seeing one
of the display beams or a plurality of display beams. Therefore,
the display beams can be regarded collectively as a single display
beam having a large diameter. Not only axial display beams
representing the center of a picture but also off-axis display
beams representing a point on the edge of the picture can also be
regarded collectively as a single display beam having a large
diameter. Thus, in the display method of this embodiment, multiple
beams emitted from the transparent substrate are equivalent to a
single display beam having a large diameter emitted from the entire
surface of the transparent substrate. Therefore, the entire surface
of the transparent substrate constitutes an exit pupil, and the
size of the exit pupil is equal to the size of the transparent
substrate. Thus, the size of the pupil is large, as is the case
with a magnifier whose pupil extends over its entirety, and
therefore the viewer can see a virtual image without locating
his/her head near the display apparatus.
[0032] In the display method of this embodiment, the display beams
emitted out of the transparent substrate are beams that display a
virtual image at infinity. In other words, when the viewer sees the
display beams, a virtual image is formed at infinity (at a distant
location). Therefore, each of the plurality of display beams
emitted from the transparent substrate forms, when seen by the
viewer, a virtual image at infinity. Consequently, even if the
viewer's eyes are presbyopic and can be focused only on far points,
the viewer can see display in focus. Moreover, the viewer can see a
virtual image formed at infinity by seeing any one of the display
beams or seeing a plurality of display beams at the same time. The
display beams (which are produced holographically) are parallel
beams.
[0033] The display method of this embodiment causes a display beam
to be reflected, amplitude-splits the reflected display beam to
produce a beam travelling in the direction same as the travelling
direction of the reflected display beam and a beam travelling in a
direction different from the travelling direction of the reflected
display beam, and performs the reflecting and the
amplitude-splitting repeatedly. The display beam may be a beam
produced by diffraction.
[0034] Next, the basic construction of a display apparatus
according to this embodiment will be described. FIGS. 1A and 1B are
diagrams showing the basic construction of the display apparatus of
this embodiment and how a display beam propagates, where FIG. 1A
shows a case in which a divergent beam is made incident on the
transparent substrate, and FIG. 1B shows a case in which a parallel
beam is made incident on the transparent substrate.
[0035] As shown in FIGS. 1A and 1B, the display apparatus of this
embodiment has an LCOS (Liquid Crystal On Silicone, which is a
reflective liquid crystal display device) 3, 3', a transparent
substrate 4, and a diffraction grating 5. The LCOS 3, 3' is an SPM
(Spatial Phase Modulator), which is a hologram display element that
produces a display beam 2 holographically. The LCOS 3, 3' may be
replaced by a transmission liquid crystal display.
[0036] The transparent substrate 4 has a first interface (first
transmitting surface) 4a and a second interface (second
transmitting surface) 4b. The display beam 2 is reflected (total
reflection) on the internal surfaces such as the first interface 4a
and the second interface 4b of the transparent substrate 4, so that
the display beam 2 propagates inside the transparent substrate
4.
[0037] The diffraction grating 5 serves as splitting means. Every
time the display beam 2 is internally reflected, the diffraction
grating 5 lets the beam partly emit out of the transparent
substrate 4. The diffraction grating 5 is arranged at a location
between the first interface 4a and the second interface 4b. The
diffraction grating 5 is arranged in such a way as to be opposed to
the LCOS 3, 3'. The diffraction grating 5 may be composed of a
volume hologram.
[0038] To produce a display beam 2, it is necessary to make
illumination light incident on the LCOS 3, 3'. FIG. 1A shows a case
in which illumination light emitting from a light source (not
shown) is a divergent beam. The divergent beam 1 enters the
transparent substrate through the first interface 4a and is
incident on the LCOS 3 provided on the second interface 4b. The
LCOS 3 is displaying a phase hologram (hologram pattern or phase
pattern), so that the divergent beam 1 incident on the LCOS 3 is
diffracted by the phase hologram (LCOS 3). Consequently, a display
beam 2 is produced holographically by means of the LCOS 3. The
display beam 2 is produced as first-order diffracted light
(first-order light) by the hologram displayed on the LCOS 3. The
zero-order diffracted light (zero-order light) produced by direct
reflection by the LCOS 3 is emitted out of the transparent
substrate 4.
[0039] In the case of the display apparatus shown in FIG. 1A, the
phase hologram displayed on the LCOS 3 is one that produces a
parallel display beam 2 when a divergent beam 1 is incident on it.
The display beam 2 is an axial display beam (i.e. a beam emitting
from the center of the picture). Off-axis display beams (i.e. beams
emitting from points in the picture other than the center) are also
produced holographically by means of the LCOS 3, though the
off-axis display beams are not shown in the drawing.
[0040] On the other hand, FIG. 1B shows a case in which
illumination light emitting from the light source (not shown) is a
parallel beam. The parallel beam 1' enter the transparent substrate
through the first interface 4a and is incident on the LCOS 3'
provided on the second interface 4b. The LCOS 3' is displaying a
phase hologram (hologram pattern or phase pattern), so that the
illumination light incident on the LCOS 3' is diffracted by the
phase hologram (LCOS 3'). Consequently, a display beam 2 is
produced holographically by means of the LCOS 3'. The display beam
2 is produced as first-order diffracted light (first-order light)
by the hologram displayed on the LCOS 3'. The zero-order diffracted
light (zero-order light) produced by direct reflection by the LCOS
3' is emitted out of the transparent substrate 4.
[0041] In the case of the display apparatus shown in FIG. 1B, the
phase hologram displayed on the LCOS 3' is one that produces a
parallel display beam 2 when a parallel beams 1' is incident on it.
The display beam 2 is an axial display beam (i.e. a beam emitting
from the center of the picture). Off-axis display beams (i.e. beams
emitting from points in the picture other than the center) are also
produced holographically by means of the LCOS 3', though the
off-axis display beams are not shown in the drawing.
[0042] Besides a divergent beam and a parallel beam, a convergent
beam may be made incident on the LCOS 3, 3'. In the case where a
convergent beam is made incident on the LCOS 3, 3', the LCOS 3, 3'
may be adapted to display a hologram that produces a parallel
display beam when a convergent beam is incident on it.
[0043] A method and apparatus for generating display beams 2
holographically will be described in detail with reference to FIGS.
2A and 2B. FIG. 2A is a diagram showing an ordinary optical system
used to view a virtual image. FIG. 2B is a diagram showing an
optical system used to produce a display beams holographically. The
display beams are beams with which a viewer sees a virtual image
(parallel beams 10, 12 in FIG. 2A).
[0044] The optical system shown in FIG. 2A is composed of a display
device 6 such as an LCD and a lens 7. If the display device 6 is
located at the position of the focal point (front focal point) of
the lens 7, a picture 8 displayed on the display device 6 is
projected to infinity by the lens 7. Solid lines 9 represent a beam
emitting from the center (on the axis) of the display device 6, and
broken lines 11 represent a beam emitting from a point on the edge
(off-axis) of the display device 6. The beam represented by the
solid lines 9 becomes a parallel beam 10 when emitting from the
lens 7. The beam represented by the broken lines 11 also becomes a
parallel beam 12 when emitting from the lens 7.
[0045] The parallel beams 10 and 12 enter the pupil 14 of the
viewer's eye 13. Consequently, the viewer can see an image 15 of
the picture 8. Since the beams 10 and 12 incident on the viewer's
pupil 14 are parallel beams, the viewer sees a virtual image
located in rear of the display apparatus (on the left side of the
display device 6 in FIG. 2A), namely a virtual image located at
infinity. Therefore, even if the viewer's eyes are presbyopic and
can be focused only on far points, the viewer can see the picture 8
in focus.
[0046] FIG. 2B shows an optical system used to holographically
produce parallel beams 10, 12. This optical system is composed of a
coherent light source 16 and an SPM (Spatial Phase Modulator) 17.
An example of the coherent light source 16 is an LD (Laser Diode).
An example of the SPM 17 is an LCOS described above. The SPM 17 is
a hologram display element. Hereinafter, the hologram display
element will be referred to as the SPM.
[0047] A hologram has a hologram pattern. The hologram pattern is
an interference pattern formed by two wave fronts. One of the wave
fronts is one emitting from the lens 7, and the other wave front is
one emitting from the coherent light source 16 in FIG. 2B. The wave
front emitting from the lens 7 (parallel beams 10, 12) contains
information of an image of the picture 8. On the other hand, the
wave front emitting from the coherent light source 16 is a wave
front that forms interference fringes and, at the same time, is
used to produce reproduction light from the hologram.
[0048] The light emitted from the display device 6 is incoherent
light. Consequently, light emitted from the display device 6 and
the wave front emitting from the coherent light source 16 will not
interfere, even if they are superposed. In other word, a hologram
pattern cannot be obtained by superposition. Therefore, in
practice, a hologram (hologram pattern) is obtained by computation.
The hologram obtained by computation is displayed on the SPM 17,
which is illuminated by the coherent light source 16. In this way,
a hologram or parallel beams 10, 12 are reproduced. The display
beam 2 shown in FIGS. 1A and 1B is the parallel beam 10 among the
parallel beams 10 and 12.
[0049] The viewer can view the picture 8 by seeing the parallel
beams 10, 12 that are thus produced holographically. In other
words, the parallel beams 10, 12 enter the pupil 14 of the viewer's
eye 13 to form an image 15.
[0050] In the optical system shown in FIG. 2A, it is necessary for
the lens 7 to project an image of the off-axis portion of the
picture (the portion of the picture displayed in the peripheral or
outer portion of the display device 6) onto the eye 13 with high
resolving power. To this end, the lens 7 is composed of a plurality
of lenses in practice. It is also necessary for the lens 7 to have
a large diameter. For these reasons, if the optical system shown in
FIG. 2A is used in the display apparatus, it is difficult to make
the display apparatus slim and compact.
[0051] Next, preparation of a hologram by computation will be
described in detail. FIG. 3 is a block diagram of a process of
preparing hologram by computation. As shown in FIG. 3, image data
18 is firstly prepared. The image data 18 is data to be input to
the display device 6 in FIG. 2A. The wave front emitting from the
lens 7 is computed by Fourier-transforming the image data 18 by the
Fourier transform 20.
[0052] Since a spatial frequency distribution obtained by Fourier
transform includes a spatial phase distribution as well as a
spatial intensity distribution, it is not possible to create a
phase hologram having a high diffraction efficiency. So random
phase addition 19 is performed before the Fourier transform 20.
Adding (superposing) random phase information to the image data 18
in advance can average the spatial intensity values after the
Fourier transform over the entire spatial frequency plane or can
substantially equalize the spatial intensities. Consequently, it is
possible to form a hologram as a phase hologram having only phase
information.
[0053] Then, correction 21 is performed. The correction 21 is based
on the arrangement of the optical system. For example, in the case
of the optical system shown in FIG. 2B, a hologram (parallel beams
10, 12) is reproduced using a wave front emitting from the coherent
light source 16. It is necessary that this reproduction can produce
accurate display beams 2 (parallel beams 10, 12). Since the wave
front emitted from the coherent light source 16 is a spherical
wave, the correction 21 computes a hologram using information of
this spherical wave. Then the result of computation (hologram
information) is input to SPM driver control 22. A hologram is
displayed on the SPM (or LCOS 3, 3', in FIGS. 1A and 1B) based on
control information supplied by the SPM driver control 22.
[0054] Since the diffraction efficiency of the SPM 17 is
substantially constant, images of bright scenes and images of dark
scenes would have substantially equal brightness. In view of this,
when display beams are produced holographically, it is necessary to
control the quantity of light incident on the SPM 17 in accordance
with the total light quantity of the image. Hence, total light
quantity data of the image data is input to a light source driver
23 to control the intensity of the light source.
[0055] Referring back to FIG. 1A, the display beam 2 emitted from
the LCOS 3 is totally reflected at the first interface 4a of the
transparent substrate 4 and then incident on the diffraction
grating 5. The display beam 2 is partly diffracted by the
diffraction grating 5. The direction of diffraction is normal to
the first interface 4a. The beam diffracted by the diffraction
grating 5 is emitted from the transparent substrate 4 to the
outside to become a display beam 2a.
[0056] The display beam 2 transmitted through the diffraction
grating 5 is totally reflected at the second interface 4b of the
transparent substrate 4 and then passes through the diffraction
grating 5. The display beam 2 having passed through the diffraction
grating 5 is totally reflected at the first interface 4a again and
incident on the diffraction grating 5. The display beam 2 is
partially diffracted by the diffraction grating 5. The direction of
diffraction is normal to the first interface 4a. The beam
diffracted by the diffraction grating 5 is emitted from the
transparent substrate 4 to the outside to become a display beam 2b.
The display beam 2 further propagates in the transparent substrate
4 to produce another display beam 2c in the same manner. With
repetition of the above process, a lot of display beams (2a, 2b,
2c) are emitted from the entire surface of the transparent
substrate 4 (or the first interface 4a).
[0057] The viewer can see a virtual image if at least one of the
display beams 2a, 2b, 2c is incident on his/her eye. In the case,
for example, where the image data 18 is motion video data, the
viewer can see motion video. In the case where the image data is
still image data, the observer can see a still image.
[0058] In the basic configuration of the display apparatus of this
embodiment, the display beam 2 are produced using the LCOS 3.
Therefore, there can be provided a small and slim display apparatus
having high optical performance. A beam made incident on the LCOS 3
may only be axial beams. Therefore, light emitted from the light
source may directly be used as a beam to be incident on the LCOS 3.
In this case, it is not necessary to provide a lens for beam
conversion, leading to size reduction and slimming of the display
apparatus.
[0059] In the case where a beam made incident on the LCOS 3' is a
parallel beam also, it is sufficient that only a parallel axial
beam be made incident on the LCOS 3'. Therefore, a lens used to
convert a convergent beam or a divergent beam into a parallel beam
can be simple. Consequently, even in the case where a beam made
incident on the LCOS 3' is a parallel beam, slimming and size
reduction of the display apparatus can be achieved.
[0060] Furthermore, in the basic configuration of the display
apparatus of this embodiment, the display beam 2 is produced
holographically by the LCOS 3, 3'. This allows slimming and size
reduction of the display apparatus.
[0061] In the basic construction of the display apparatus of this
embodiment, as the display beam propagates, a plurality of display
beams 2a, 2b, 2c are emitted from the transparent substrate 4. The
viewer can see a virtual image if at least one of the display beams
is incident on the pupil of his/her eye. In the basic construction
of the display apparatus of this embodiment, there are a plurality
of display beams 2a, 2b, 2c, which are equivalent to a display beam
having a large diameter. The display beam includes an axial beam
representing the center of the picture and off-axis beams
representing points on the edge of the picture. The diameters of
both types of display beams are large, and the exit pupil extends
over the entire surface of the transparent substrate from which the
display beams emitted. In consequence, the allowable range of
alignment of the eye with the display beam (or the transparent
substrate 4) is larger than that in the case where the diameter of
the display beam is smaller. Therefore, the viewer can see the
virtual image easily.
[0062] As described above, an LCOS or a transmission liquid crystal
display device is used as the SPM. Alternatively, a deformable
mirror may also be used. Types of deformable mirrors include one
having a plurality of small mirrors, each of which is deflected and
one in which one thin mirror is deformed.
[0063] The display apparatus can be produced, for example, by
firstly forming a recess on a portion of the transparent substrate
4 on which the diffraction grating 5 is to be arranged, then
arranging the diffraction grating 5 in the recess, and thereafter
covering the diffraction grating 5 with a transparent part that
substantially fits the recess. Alternatively the display apparatus
can be produced by forming a slit-like recess parallel to the first
interface 4a on a side surface of the transparent substrate 4, then
inserting the diffraction grating 5 into the recess, and thereafter
covering the side surface with a transparent part or adhesive.
[0064] A display apparatus according to a first embodiment is shown
in FIGS. 4A and 4B. FIG. 4A shows a case in which a divergent beam
is made incident on the transparent substrate, and FIG. 4b shows a
case in which a parallel beam is made incident on the transparent
substrate. In the display apparatus of this embodiment, an LCOS
(reflective liquid crystal display device) 3, 3' is used as an SPM
(spatial phase modulator).
[0065] The display apparatus of this embodiment includes a light
source 24, an LCOS (reflective liquid crystal display device) 3,
3', a transparent substrate 4, and a diffraction grating 5. The
components having the same functions as those in the display
apparatus shown in FIG. 1 are denoted by the same reference
numerals to eliminate description of them.
[0066] The transparent substrate 4 has a first interface (first
transmitting surface) 4a and a second interface (second
transmitting surface) 4b. A display beam 2 is reflected (total
reflection) on the internal surfaces or the first interface 4a and
the second interface 4b of the transparent substrate 4, so that the
display beam 2 propagates inside the transparent substrate 4.
[0067] The LCOS 3, 3' is an SPM (Spatial Phase Modulator), which is
an element that produces a display beam 2. The LCOS 3, 3' is a
hologram display element that produces a display beam 2
holographically. The LCOS 3, 3' is arranged at a location between
the light source 24 and the second interface 4b. More specifically,
the LCOS 3, 3' is provided on the side of the second interface 4b
that is in contact with the air.
[0068] The diffraction grating 5 serves as splitting means. Every
time the display beam 2 is internally reflected, the diffraction
grating 5 lets the beam partly emit out of the transparent
substrate 4. The diffraction grating 5 is arranged at a location
between the first interface 4a and the second interface 4b. The
diffraction grating 5 is arranged in such a way as to be opposed to
the LCOS 3, 3'. The diffraction grating 5 may be composed of a
volume hologram. When the transparent substrate 4 is seen from the
light source 24 side, the LCOS 3, 3' and the diffraction grating 5
are arranged side by side.
[0069] With this structure, a display beam 2 is emitted from the
LCOS 3, 3'. As described above with reference to FIGS. 1A and 1B,
the display beam 2 propagates in the substrate 4, and display beams
2a, 2b, 2c are emitted out of the transparent substrate 4. In the
display apparatus shown in FIG. 4B also, display beams 2b, 2c are
produced, though not illustrated.
[0070] The LCOS 3 shown in FIG. 4A is displaying a hologram (phase
hologram) that produces a parallel display beam 2 when a divergent
beam 1 is made incident on it. Therefore, a divergent beam 1
emitted from the light source 24 may be directly made incident on
the LCOS 3 without any conversion. This consequently allows the
light source 24 to be arranged close to the transparent substrate 4
and the LCOS 3. In the case shown in FIG. 4A, the light source 24
is in contact with the first interface 4a. This enables slimming
and size reduction of the display apparatus.
[0071] The light source 24 may be arranged closer to the second
interface 4b than the first interface 4a. For example, a recess
(cavity) extending from the first interface 4a into the transparent
substrate 4 may be formed, and the light source 24 may be arranged
in that recess. This enables further slimming and size reduction of
the display apparatus. Alternatively, the light source 24 may be
arranged at a location a little away from the first interface 4a
(in the proximity of the first interface 4a) so long as slimming or
size reduction of the display apparatus is not prevented.
[0072] As described above, since the display apparatus shown in
FIG. 4A does not need a lens for beam conversion, slimming and size
reduction of the display apparatus can be achieved.
[0073] On the other hand, the LCOS 3' shown in FIG. 4B is
displaying a hologram that produces a parallel display beam 2 when
a parallel beam 1' is made incident on it. Therefore, a lens 25 is
provided in the optical path from the light source 24 to the LCOS
3'. This lens 25 converts a divergent beam 1 into a parallel beam
1'. In the display apparatus shown in FIG. 4B, the lens 25 provided
in the apparatus makes it difficult to arrange the light source 24
in the proximity of the first interface 4a. Consequently, the
display apparatus shown in FIG. 4B might not be slimmed down or
reduced in size so much as the display apparatus shown in FIG.
4A.
[0074] Nevertheless, it is sufficient in the display apparatus
shown in FIG. 4B that only the axial beam be made incident on the
LCOS 3'. Therefore, the lens 25 can be made simple. For example,
the lens 25 may be constituted by a small number of lenses. A
single lens is adequate as the lens 25 in the display apparatus
shown in FIG. 4B. Aberrations of the lens may be corrected in the
aforementioned correction 21 (FIG. 3). For the above reasons, in
the case where the beam made incident on the LCOS 3' is a parallel
beam also, the display apparatus can be made slimmer and smaller in
size than the conventional display apparatus (shown in FIG.
2A).
[0075] In the display apparatuses shown in FIGS. 4A and 4B, the
LOCS 3, 3' may be arranged to be closer to the first interface 4a
than the second interface 4b (namely, between the first interface
4a and the second interface 4b).
[0076] Hologram information of the hologram to be displayed by the
LCOS 3 is corrected by correction 21 (FIG. 3). With this
correction, an accurate display beam 2 is produced when a divergent
beam 1 is incident on the LCOS 3. Similarly, hologram information
of the hologram to be displayed by the LCOS 3' is also corrected by
correction 21 (FIG. 3). With this correction, an accurate display
beam 2 is produced when a parallel beam 1' is incident on the LCOS
3'.
[0077] In the case of the display apparatus shown in FIG. 4A, the
zero-order light reflected by the LCOS 3 (zero-order diffracted
light) is emitted from the transparent substrate 4 as diverging
light. Therefore, it does not adversely affect the display (or
observation of the virtual image). In the case of the display
apparatus shown in FIG. 4B, zero-order light reflected by the LCOS
3' is emitted from the transparent substrate 4 perpendicularly
without change (i.e. as a parallel beam). Therefore, it does not
adversely affect the display (or observation of the virtual
image).
[0078] In the display apparatus of this embodiment, the LCOS 3 and
the LCOS 3' are arranged in such a way that the condition that zero
order light is transmitted through the transparent substrate 4 and
first-order light (or the display beam 2) is totally reflected by
the transparent substrate 4 (or the interfaces 4a, 4b) is met.
Therefore, zero-order light does not adversely affect the display
(or observation of the virtual image).
[0079] In the case of the display apparatus of this embodiment
also, since the beams incident on the viewer's eye are parallel
beams, the viewer would see a virtual image located in rear of the
display apparatus or a virtual image at infinity. Therefore, even
if the viewer's eyes are presbyopic and can be focused only on far
points, the viewer can see the picture 8 in focus.
[0080] In the drawings showing the display apparatus of this
embodiment, only the axial display beam 2 is illustrated, and
off-axis beams are not illustrated for the sake of simplicity. It
should naturally be understood that there also are off-axis
beams.
[0081] A display apparatus according to a second embodiment is
shown in FIG. 5. The display apparatus of this embodiment has an
additional LCOS 26 arranged in the optical path from the light
source 24 to the LCOS 3'. Specifically, as shown in FIG. 5, the
LCOS 3' is arranged on the first interface 4a, and the LCOS 26 is
arranged on the second interface 4b. The components having the same
functions as those in the display apparatus according to the first
embodiment are denoted by the same reference numerals to eliminate
description of them.
[0082] The LCOS 3' is displaying a hologram that produces a
parallel display beam 2 when a parallel beam 1' is made incident on
it. On the other hand, the LCOS 26 is displaying a hologram that
produces a parallel beam 1' when a divergent beam 1 is made
incident on it.
[0083] A divergent beam 1 emitted from the light source 24 is
incident on the LCOS 26. The divergent beam 1 is converted into a
parallel beam 1' by the LCOS 26. The parallel beam 1' after the
conversion is emitted from the LCOS 26. The parallel beam 1'
emitting from the LCOS 26 is incident on the LCOS 3'. The LCOS 3'
produces (reproduces) a display beam 2 from the parallel beam 1',
and the display beam 2 is emitted from the LCOS 3'. As described
with reference to FIGS. 1A and 1B, as the display beam 2 propagates
in the transparent substrate 4, display beams 2a, (2b, 2c) are
emitted outside from the transparent substrate 4.
[0084] In the case of the display apparatus shown in FIG. 4B (first
embodiment), it is necessary to provide a lens 25 between the light
source 24 and the first interface 4a. This necessitates the light
source 24 to be located at a position away from the first interface
4a. Consequently, the display apparatus cannot be slimmed down or
reduced in size to a sufficient degree.
[0085] On the other hand, in the case of the display apparatus of
this embodiment, the LCOS 26 having a function like the lens 25 can
be arranged on the second interface 4b. This allows the light
source 24 to be arranged close to the first interface 4a. In
consequence, the display apparatus can be slimmed down and reduced
in size to a degree substantially the same as the display apparatus
shown in FIG. 4A (first embodiment).
[0086] In FIG. 5, when the transparent substrate 4 is seen from the
light source 24 side, the LCOS 3' and the diffraction grating 5
overlap each other. Actually, however, the LCOS 3' and the
diffraction grating 5 are arranged side by side so that display
beam 2a diffracted by the diffraction grating 5 does not pass
through the LCOS 3'.
[0087] In the drawing showing the display apparatus of this
embodiment, only the axial display beam 2 is illustrated, and
off-axis beams are not illustrated for the sake of simplicity. It
should naturally be understood that there also are off-axial beams.
The LCOS 26 may be replaced by an ordinary hologram (or hologram
lens). In that case, it is preferred that the hologram used be a
volume hologram because of its diffraction efficiency.
[0088] A display apparatus according to a third embodiment is shown
in FIGS. 6A and 6B. FIG. 6A shows a case in which a divergent beam
is made incident on the transparent substrate, and FIG. 6B shows a
case in which a parallel beam is made incident on the transparent
substrate. The display apparatus of this embodiment uses an LCD
(transmission liquid crystal display device) as an SPM (spatial
phase modulator).
[0089] The display apparatus of this embodiment has a light source
24, an LCD (transmission liquid crystal display device) 27, 27', a
transparent substrate 4, and a diffraction grating 5. The
components having the same functions as those in the display
apparatus according to the first embodiment are denoted by the same
reference numerals to eliminate description of them.
[0090] The LCD 27, 27' is an SPM (Spatial Phase Modulator), which
is a hologram display element that produces display beams 2
holographically. The LCD 27, 27' is arranged at a location between
the light source 24 and the second interface 4b. More specifically,
the LCD 27, 27' is provided on the side of the second interface 4b
that is in contact with the air.
[0091] In the display apparatus shown in FIG. 6A, a divergent beam
1 emitting from the light source 24 is made incident on the LCD 27.
On the other hand, in the display apparatus shown in FIG. 6B, a
parallel beam 1' emitting from the light source 24 (not shown) is
made incident on the LCD 27'. Moreover, a phase hologram is
displayed on the LCD 27, 27', so that a display beam 2 is produced
as first-order diffracted light (first-order light). As the display
beam 2 propagates in the transparent substrate 4, display beams 2a,
2b, 2c is emitted out of the transparent substrate 4, in the same
manner as in the display apparatus according to the first
embodiment.
[0092] The LCD 27 is displaying a hologram (phase hologram) that
produces a parallel display beam 2 when a divergent beam 1 is made
incident on it. Therefore, a divergent beam 1 emitted from the
light source 24 may be directly made incident on the LCD 27 without
any conversion. This consequently allows the light source 24 to be
arranged close to the transparent substrate 4 and the LCD 27.
Therefore, the display apparatus can be slimmed down or reduced in
size.
[0093] On the other hand, the LCD 27' shown in FIG. 6B is
displaying a hologram that produces a parallel display beam 2 when
a parallel beam 1' is made incident on it. Therefore, it is
necessary to provide a lens (not shown) in the optical path from
the light source 24 to the LCD 27'. However, it is sufficient that
only the axial beam be made incident on the LCD 27'. Therefore, the
lens can be made simple. For example, the lens may be composed of a
small number of lenses. In the case of the display apparatus shown
in FIG. 4B, a single lens is adequate as the aforementioned lens.
Aberrations of the lens may be corrected in the aforementioned
correction 21 (FIG. 3). For the above reasons, in the case where
the beam made incident on the LCD 27' is parallel beam also, the
display apparatus can be made slimmer and smaller in size than the
conventional display apparatus (shown in FIG. 2A).
[0094] In the display apparatuses shown in FIGS. 6A and 6B, the LCD
27, 27' may be arranged at a location a little away from the second
interface 4b so long as slimming or size reduction of the display
apparatus is not prevented. Alternatively, the LCD 27, 27' may be
arranged at a location closer to the first interface 4a than the
second interface 4b (namely, at a location between the first
interface 4a and the second interface 4b). The light source 24 and
the LCD 27, 27' may be arranged on the first interface 4a side.
[0095] Hologram information of a hologram displayed on the LCD 27
is corrected by the correction 21 (FIG. 3), as with in the display
apparatus according to the first embodiment. With this correction,
an accurate display beam 2 is produced when a divergent beam 1 is
incident on the LCD 27. Hologram information of a hologram
displayed on the LCD 27' is also corrected by the correction 21
(FIG. 3) in a similar manner. With this correction, an accurate
display beam 2 is produced when a parallel beam 1' is incident on
the LCD 27'.
[0096] In the case of the display apparatus shown in FIG. 6A,
zero-order light (zero-order diffracted light) transmitted through
the LCD 27 is emitted from the transparent substrate 4 as diverging
light. Therefore, it does not adversely affect the display (or
observation of a virtual image). In the case of the display
apparatus shown in FIG. 6B, zero-order light having passed through
the LCD 27' is emitted from the transparent substrate 4
perpendicularly without change (i.e. as a parallel beam).
Therefore, it does not adversely affect the display (or observation
of the virtual image).
[0097] In the display apparatus according to this embodiment, the
LCD 27 and the LCD 27' are arranged in such a way that the
condition that zero order light is transmitted through the
transparent substrate 4 and first-order light (or display beams 2)
is totally reflected by the transparent substrate 4 (or the
interfaces 4a, 4b) is met. Therefore, zero-order light does not
adversely affect the display (or observation of the virtual
image).
[0098] In the case of the display apparatus of this embodiment
also, since the beams incident on the viewer's pupil are parallel
beams, the viewer sees a virtual image located in rear of the
display apparatus, namely a virtual image at infinity. Therefore,
even if the viewer's eyes are presbyopic and can be focused only on
far points, the viewer can see the picture 8 in focus.
[0099] An ordinary LCD that displays intensity information may be
used as the LCD 27, 27'. In this case, what is displayed on the LCD
is not a phase hologram but an amplitude hologram, leading to lower
diffraction efficiency.
[0100] In the drawings showing the display apparatus of this
embodiment, only the axial display beam 2 is illustrated, and
off-axis beams are not illustrated for the sake of simplicity. It
should naturally be understood that there also are off-axial
beams.
[0101] A display apparatus according to a fourth embodiment is
shown in FIGS. 7A, 7B, and 8. FIG. 7A is a diagram showing the
construction of a first transparent substrate and how a display
beam propagates. FIG. 7B is a diagram showing the construction of a
second transparent substrate and how display beams propagate. FIG.
8 is a diagram showing the overall construction of the display
apparatus.
[0102] As shown in FIG. 8, the display apparatus of this embodiment
has a first transparent substrate 30 and a second transparent
substrate 36. The first transparent substrate 30 is located on an
end portion of the second transparent substrate 36. The first
transparent substrate 30 is fixed to the second transparent
substrate 36 at this location.
[0103] As shown in FIG. 7A, the first transparent substrate 30
includes an SPM 29, a beam splitter 31, and a diffraction grating
32. As shown in FIG. 7B, the second transparent substrate 36
includes a beam splitter 37, a diffraction grating 38, and a
diffraction grating 39. It is preferred that the diffraction
gratings 32, 38, and 39 be volume holograms.
[0104] The SPM 29 is a spatial phase modulator that produces a
display beam 34 holographically. In the first transparent substrate
30 and the second transparent substrate 36, display beams 34 are
internally reflected repeatedly to propagate. The beam splitter 31
causes the display beam 34 to partially enter the second
transparent substrate 36 every time the display beam 34 is
internally reflected in the first transparent substrate 30. The
beam splitter 37 causes the display beams 34 to partially emit out
of the second transparent substrate 36 every time the display beams
34 are internally reflected in the second transparent substrate
36.
[0105] Details will be described in the following. In FIGS. 7A, 7B,
and 8, in showing the beam (illumination light) incident on the
display apparatus and display beams, only the center ray in the
axial beam is illustrated for the sake of simplicity. In the
following, they are mentioned as beams. As will naturally be
understood, there also are off-axis beams, though not shown in the
drawings.
[0106] As shown in FIGS. 7A and 8, the first transparent substrate
30 is a transparent member having a rectangular outer shape. The
SPM 29, the beam splitter 31, and the diffraction grating 32 are
arranged along the direction of its long side (the X axis
direction). The display beams 34 propagate along the direction of
its long side. The thickness of the first transparent substrate 30
is, for example, 2 to 4 mm.
[0107] The outer shapes of the beam splitter 31 and the diffraction
grating 32 are both rectangular. The beam splitter 31 and the
diffraction grating 32 are arranged in such a way as to be opposed
to each other. The beam splitter 31 is arranged between two
interfaces of the first transparent substrate 30. The diffraction
grating 32 is arranged on one of the interfaces of the first
transparent substrate 30.
[0108] An end of the aforementioned one interface has a cut
portion. The SPM 29 is arranged on an oblique surface of the cut
portion. One of the end faces (on a short side) between the two
interfaces is a slanted surface. A parallel beam 33 is incident on
this slanted surface.
[0109] In the display apparatus of this embodiment, a parallel beam
33 emitting from an LD light source (not shown) is made incident on
the SPM 29. A display beam 34 is produced as first-order light by a
hologram displayed on the SPM 29. The display beam 34 is totally
reflected by an internal surface (interface) of the first
transparent substrate 30. The display beam 34 having been totally
reflected is split by the beam splitter 31 into transmitted light
and reflected light.
[0110] The transmitted light is incident on the diffraction grating
32 provided on the interface of the first transparent substrate 30.
Then, the light is diffracted by the diffraction grating 32 toward
the beam splitter 31. The diffracted light is emitted from the
first transparent substrate 30 perpendicularly as a display beam
34a. The display beam 34a emitting perpendicularly from the first
transparent substrate 30 enters the second transparent substrate 36
(FIG. 7B).
[0111] The reflected light is totally reflected by the internal
surface (interface) of the first transparent substrate again and
incident on the beam splitter 31 again. Then, it is split by the
beam splitter 31 again into transmitted light and reflected
light.
[0112] The transmitted light resulting from the second splitting is
incident on the diffraction grating 32. Then, the light is
diffracted by the diffraction grating 32 toward the beam splitter
31. The diffracted light is emitted from the first transparent
substrate 30 perpendicularly as a display beam 34b. The display
beam 34b emitting perpendicularly from the first transparent
substrate 30 enters on the second transparent substrate 36 (FIG.
7B).
[0113] The reflected light resulting from the second splitting is
totally reflected again by the internal surface (interface) of the
first transparent substrate 30. Thereafter, a display beam 34c is
produced in a similar manner as the display beams 34a and 34b.
[0114] As described above, the display beam 34 is totally reflected
by the internal surface (interface) of the first transparent
substrate 30 repeatedly to propagate in the first transparent
substrate 30. As the display beam 34 propagates, the display beam
34a, the display beam 34b, and the display beam 34c successively
are emitted from the first transparent substrate 30 perpendicularly
and enter the second transparent substrate 36. Here, the number of
emitting beams (34a, 34b, 34c) illustrated is three, for the sake
of simplicity. The number of the beams is not limited to three.
[0115] It is preferable that the diffraction grating 32 be a volume
hologram, which provides a high diffraction efficiency. The
zero-order light 35 regularly reflected by the SPM 29 is not
totally reflected in the first transparent substrate 30 but
directly is emitted out of the first transparent substrate 30. The
zero-order light 35 thus emitting is vanished by a trap unit (not
shown).
[0116] As shown in FIGS. 7B and 8, the second transparent substrate
36 is a transparent member having a substantially rectangular outer
shape. Its length along the X axis direction (short side) is equal
to the length of the long side of the first transparent substrate
30. Its length along the Z axis direction (long side) is longer
than the short side of the first transparent substrate 30. The
outer shape of the second transparent substrate 36 is not limited
to rectangular. The display beams 34 propagate along the Z axis
direction. The thickness of the second transparent substrate 36 is,
for example, 2 to 4 mm.
[0117] As with the diffraction grating 32, the diffraction grating
39 has a rectangular outer shape. It is preferred that the length
of the short side of the diffraction grating 39 be not longer than
the length of the short side of the first transparent substrate 30.
The diffraction grating 39 is arranged on one of the interfaces of
the second transparent substrate 36. The diffraction grating 39 is
arranged at a location at which it is opposed to the diffraction
grating 32.
[0118] The beam splitter 37 and the diffraction grating 38 are both
arranged in a region that does not overlap the diffraction grating
39 (or the first transparent substrate 30). The beam splitter 37
and the diffraction grating 38 are arranged in such a way as to be
opposed to each other. The beam splitter 37 is arranged between the
two interfaces of the second transparent substrate 36. The
diffraction grating 38 is arranged on one of the interfaces of the
second transparent substrate 36 (on the interface on which the
diffraction grating 39 is arranged).
[0119] The display beams 34a, 34b, 34c incident on the second
transparent substrate 36 are diffracted by the diffraction grating
39. The diffracted display beams 34a, 34b, 34c are totally
reflected by the internal surface (interface) of the second
transparent substrate 36 and incident on the beam splitter 37. In
the following, the description will be directed to the display beam
34a.
[0120] The display beam 34a is split by the beam splitter 37 into
transmitted light and reflected light. The transmitted light is
incident on the diffraction grating 38 and diffracted by the
diffraction grating 38 toward the beam splitter 37. The diffracted
light is emitted from the second transparent substrate 36
perpendicularly as a display beam 34d.
[0121] On the other hand, the reflected light is totally reflected
again by the internal surface (interface) of the second transparent
substrate 36 and incident on the beam splitter 37 again. Then, the
light is split by the beam splitter 37 again into transmitted light
and reflected light.
[0122] The transmitted light resulting from the second splitting is
incident on the diffraction grating 38 and diffracted by the
diffraction grating 38 toward the beam splitter 37. The diffracted
light is emitted from the second transparent substrate 36
perpendicularly as a display beam 34e.
[0123] The reflected light resulting from the second splitting is
totally reflected again by the internal surface (interface) of the
second transparent substrate 36. Then, a display beam 34f is
produced in a similar manner as the display beams 34a and 34b.
[0124] As described above, the display beam 34a is totally
reflected by the internal surfaces (interfaces) of the second
transparent substrate 36 repeatedly to propagate in the second
transparent substrate 36. As the display beams 34a propagates, the
display beam 34d, the display beam 34e, and the display beam 34f
successively are emitted from the second transparent substrate 36
perpendicularly. This is also the case with the display beams 34b
and 34c. As shown in FIG. 8, the display beams 34 spread along one
direction 41 of the display apparatus as they propagate in the
first transparent substrate 30 and also spread along another
direction 42 of the display apparatus as they propagate in the
second transparent substrate 36. Consequently, display beams 43 are
emitted from all over the surface 40 of the display apparatus.
[0125] As described above, in the display apparatus of this
embodiment, the SPM 29 is displaying a hologram that produces a
parallel display beam 34 when a parallel beam 33 is incident on it.
Therefore, it is necessary to provide a lens (not shown) in the
optical path from the light source to the SPM 29. Nevertheless, it
is sufficient that only the axial beam be made incident on the SPM
29. Therefore, the lens can be made simple. For example, the lens
may be constituted by a small number of lenses. A single lens is
adequate as this lens in the display apparatus of this embodiment.
Aberrations of the lens may be corrected in the aforementioned
correction 21 (FIG. 3). For the above reasons, even though the beam
made incident on the SPM 29 is a parallel beam, the display
apparatus can be made slimmer and smaller in size than the
conventional display apparatus (shown in FIG. 2A).
[0126] The beams made incident on the SPM 29 may be a divergent
beam. Then, the SPM 29 may be adapted to display a hologram that
produces a parallel display beam 34 when a divergent beam is made
incident on it. With this arrangement, a divergent beam emitted
from the light source may be directly made incident on the SPM 29
without any conversion. This allows the light source to be arranged
close to the transparent substrate 30 and the SPM 29. Therefore,
the display apparatus can be slimmed down or reduced in size.
Alternatively, instead of a divergent beam, a convergent beam may
be made incident on the SPM 29.
[0127] In the display apparatus of this embodiment, as the display
beams propagate, a plurality of display beams 34d, 34e, 34f are
emitted from the second transparent substrate 36. A viewer can view
an image by seeing one of the display beams or a plurality of
display beams. Therefore, the display beams can be regarded
collectively as a single display beam having a large diameter. Not
only axial display beams representing the center of a picture but
also off-axis display beams representing a point on the edge of the
picture can also be regarded collectively as a single display beam
having a large diameter. Thus, in the display method of this
embodiment, multiple beams emitted from the surface 40 of the
display apparatus are equivalent to a single display beam having a
large diameter emitted from the entirety of the surface 40 of the
display apparatus. Therefore, the entirety of the surface 40 of the
display apparatus constitutes an exit pupil, and the size of the
exit pupil is equal to the size of the surface 40 of the display
apparatus. Thus, the size of the pupil is large, as is the case
with a magnifier whose pupil extends over its entirety, and
therefore the viewer can see a virtual image without locating
his/her head near the display apparatus.
[0128] The display beams 34d, 34e, 34f (display beams 43) emitted
out of the second transparent substrate 36 are beams that display a
virtual image at infinity. In other words, when the viewer sees the
display beams, a virtual image is formed at infinity (at a distant
location). Therefore, each of the plurality of display beams
emitted from the second transparent substrate 36 forms, when seen
by the viewer, a virtual image at infinity. Consequently, even if
the viewer's eyes are presbyopic and can be focused only on far
points, the viewer can see display in focus. Moreover, the viewer
can see a virtual image formed at infinity by seeing any one of the
display beams or seeing a plurality of display beams at the same
time. In the first to third embodiments also, two transparent
substrates may be used to provide a display apparatus having
two-dimensional extension.
[0129] In the display apparatus according to this embodiment, the
surface on which the SPM 29 is provided is slanted relative to the
surface on which the diffraction grating 32 is provided (FIG. 7A).
This configuration is effective in cases where it is not possible
to provide a sufficiently large angle of diffraction for the
display beam 34 emitting from the SPM 29. However, in cases where
it is possible to provide a sufficiently large angle of
diffraction, it is not necessary to slant the surface on which the
SPM 29 is provided relative to the surface on which the diffraction
grating 32 is provided. In the latter case, the arrangement the
same as the first to third embodiments may be employed.
[0130] A case in which it is not possible to provide a large angle
of diffraction for the display beam emitting from the SPM will be
described with reference to FIGS. 9A and 9B. FIG. 9A is a diagram
showing the construction of the first transparent substrate, and
FIG. 9B is a diagram showing the relationship between the incident
light, diffracted light, and zero-order light. The components
having the same functions as those shown in FIG. 7A are denoted by
the same reference numerals to eliminate description of them.
[0131] As described above, a hologram is displayed on the SPM
(LCOS, LCD) 44. The hologram is a kind of diffraction grating.
Therefore, the light incident on the SPM 44 (at an angle of
incidence of .theta..sub.R) is diffracted at a angle of diffraction
of .theta..sub.S as shown in FIG. 9B. Consequently, diffracted
light is emitted from the SPM 44. In addition, zero-order light
also is emitted from the SPM 44. The zero-order light is emitted
from the SPM 44 at a angle of reflection of .theta..sub.R.
[0132] The relationship between the angle of incidence
.theta..sub.R, the angle of diffraction .theta..sub.S, and the
pitch d of the diffraction grating is as follows, with .lamda.
being the wavelength of the incident light.
d = .lamda. sin .theta. S - sin .theta. R ( equation 1 )
##EQU00001##
[0133] The SPM 44 is structured as a one-dimensional or
two-dimensional array of small pixels. A hologram is displayed by
the small pixels. Consequently, the size of two small pixels or
twice the pixel pitch corresponds to the pitch d of the diffraction
grating.
[0134] As will be understood from the above equation, if the angle
of incidence .theta..sub.R is fixed, the larger the pitch d of the
diffraction grating is, or the larger the pixel pitch of the SPM 44
is, the smaller the angle of diffraction .theta..sub.S is. Since
the angle of incidence .theta..sub.R is constant, small angles of
diffraction .theta..sub.S lead to difficulty in separating the
reflected light and the diffracted light.
[0135] Hence, when the SPM 44 used has a large pixel pitch, the
surface on which the SPM 44 is provided is slanted relative to the
surface on which the diffraction grating 32 is provided. This helps
separation of the reflected light and the diffracted light.
[0136] By way of example, a specific case in which the display
apparatus has an angle of view of .+-.5.7 degrees will be described
with reference to FIG. 9A. The angle of view of .+-.5.7 degrees is
intended to be suitable for a case in which the display of a mobile
device such as a cellular phone is seen at a distance of distinct
vision. Since the view angle range is 11.4 degrees, in order to
separate a display beam 34 and zero-order light 35, it is necessary
for the display beam 34L (i.e. off-axis principal ray of the
display beam (which is diffracted light or first-order diffracted
light) and the zero-order light to have an angular difference of at
least 12 degrees. When this is the case, the angle formed by the
display beam 34 L (off-axis principal ray of the display beam 34)
and the zero-order light 35 is 0.6 degree, which allows separation
of the zero-order light 35.
[0137] The pixel pitch of the SPM 44 that displays phase
information is 3 .mu.m. Then, the pitch of the diffraction grating
(a state of the hologram) displayed on the SPM 44 is 6 .mu.m. If
the angle of incidence .theta..sub.R is 60 degrees, the angle of
diffraction .theta..sub.S calculated from equation 1 is 72 degrees.
Thus, an angular difference of 12 degrees can be provided, as
needed.
[0138] In this case, in the arrangement shown in FIG. 9A with
specific numerical values, the display beam 34 is incident on the
internal surface (interface) of the transparent substrate 30 at an
angle of incidence of 51.6 degrees, so that the display beam can be
totally reflected to propagate in the transparent substrate 30.
[0139] A display apparatus according to a fifth embodiment is shown
in FIGS. 10A and 10B. FIG. 10A shows a case in which a reflective
spatial phase modulator is used, and FIG. 10B shows a case in which
a transmissive spatial phase modulator is used. The display
apparatus of this embodiment is adapted to trap zero-order light
emitting from the spatial phase modulator. The components having
the same functions as those in the display apparatus according to
the first embodiment are denoted by the same reference numerals to
eliminate description of them. How the display beam 2 propagates
and is emitted from the transparent substrate 4 is the same as the
display apparatus according to the first embodiment.
[0140] In the case of the display apparatus shown in FIG. 10A, a
divergent beam 1 emitted from a light source 24 is converted by a
lens 45 into a convergent beam 46 and made incident on an LCOS 47.
A display beam 2 is produced by a phase hologram displayed on the
LCOS 47.
[0141] In the display apparatus shown in FIG. 10A, a slanted
surface is provided at an end of a first interface 4a. This slanted
surface is slanted toward a second interface 4b. The lens 45 is
arranged on this slanted surface. A slanted surface is also
provided at an end of the second interface 4b. This slanted surface
is slanted toward the first interface 4a. The LCOS 47 is arranged
on this slanted surface.
[0142] A trap 48 is provided at a location from which the slanted
surface extends from the second interface 4b. The trap 48 extends
perpendicularly from the second interface 4b toward the diffraction
grating 5.
[0143] On the other hand, in the case of the display apparatus
shown in FIG. 10B, a divergent beam 1 emitted from a light source
24 is converted by a lens 45 into a convergent beam 46 and made
incident on an LCD 47'. A display beam 2 is produced by a phase
hologram displayed on the LCD 47'.
[0144] In the display apparatus shown in FIG. 10B, the lens 45 is
arranged on the side surface extending between the first interface
4a and the second interface 4b. The LCD 47' is arranged obliquely
between the first interface 4a and the second interface 4b. The LCD
47' is located between the lens 45 and the trap 48.
[0145] The light source 24 is, for example, a semiconductor laser.
The light source 24 emits a divergent beam 1. The divergent beam 1
is converted into a convergent beam 46 by the lens 45. The
convergent beam is incident on the LCOS 47/LCD 47'. The LCOS 47/LCD
47' produces zero-order light and a display beam 2.
[0146] The LCOS 47 used in the display apparatus shown in FIG. 10A
is a reflective SPM. Therefore, zero-order light regularly
reflected by the LCOS 47 travels toward the trap 48. On the other
hand, the LCD 47' used in the display apparatus shown in FIG. 10B
is a transmissive SPM. Therefore, zero-order light that has
straightly passed (or been transmitted) through the LCD 47 travels
toward the trap 48.
[0147] The trap 48 is a component that absorbs or blocks light.
Therefore, the zero-order light incident on the trap 48 is absorbed
or blocked the trap 48. Consequently, the zero-order light does not
adversely affect the display beam 2 (or observation of the virtual
image).
[0148] In the display apparatus of this embodiment, the beam made
incident on the LCOS 47/LCD 47' is a convergent beam 46.
Consequently, the zero-order light emitting from the LCOS 47/LCD
47' is also a convergent beam. Therefore, the zero-order beam does
not diverge while it travels to the trap 48. In consequence, the
zero-order light does not adversely affect the display beam 2. It
is preferred that the beam diameter of the zero-order light at the
location of the trap 48 be smaller than the size of the trap 48. It
is more preferred that the zero-order beam converges to a spot, if
possible.
[0149] The hologram information of the hologram displayed on the
LCOS 47/the LCD 47' is corrected by the correction 21 (FIG. 3).
With this correction, an accurate display beam 2 is produced when
the convergent beam 46 is incident on the LCOS 47/LCD 47'.
[0150] The lens 45 may be integral with the transparent substrate
4. Alternatively, the lens 45 may be replaced by a LCOS or an
ordinary hologram, as is the case with the second embodiment. This
enables slimming and size reduction of the display apparatus.
[0151] In the display apparatus shown in FIG. 10B, the LCD 47' is
integrally provided in the transparent substrate 4. In practice,
however, the LCD 47' is sandwiched between two transparent members,
in an exemplary case. For example, in the structure shown in FIG.
10A, the LCD 47 may be replaced by the LCD 47', and the LCD 47' may
be covered with another transparent member from the side of the LCD
47'.
[0152] FIG. 11 is a diagram showing beams emitted from the display
apparatus of this embodiment, where the optical distances of the
beams are visualized. This will be described in the following
taking the display apparatus according to the fourth embodiment as
an example.
[0153] As shown in FIG. 8, display beams 43 is emitted from the
surface 40 of the second transparent substrate 36 in the display
apparatus. The display beams 43 include display beams 34d, 34e, 34f
shown in FIG. 7B. (It should be understood that a lot of beams
other than these three beams are emitted from the surface 40.) When
the viewer sees the display apparatus as such, a part of the
display beams is incident on the viewer's eye 51, and the viewer
can see the display (i.e. an virtual image).
[0154] FIG. 11 shows display beams emitting from three positions
50a, 50b, 50c. The three display beams include a display beam 34,
an outermost off-axis display beam 34Uo, and an outermost off-axis
display beam 34Lo. The display beam 34 corresponds to a beam
emitting from an axial point (at the center of a picture). The
outermost off-axis display beam 34Uo corresponds to a beam emitting
from an outermost off-axis point (on one edge of the picture). The
outermost off-axis display beam 34Lo corresponds to a beam emitting
from an outermost off-axis point (of the other edge of the
picture).
[0155] The positions 50a, 50b, and 50c represent optical positions
of the SPM 29 (FIG. 8) seen from the viewer. These optical
positions represent the distances from the surface 40 of the second
transparent substrate 36 to the SPM 29.
[0156] The position 50a represents the optical position of the SPM
29 in the case where the display beam 34 is totally reflected in
the second transparent substrate 36 only once and is emitted out of
it. The position 50b represents the optical position of the SPM 29
in the case where the display beam is totally reflected in the
second transparent substrate 36 twice and is emitted out of it. The
position 50c represents the optical position of the SPM 29 in the
case where the display beam is totally reflected in the second
transparent substrate 36 three times and is emitted out of it.
[0157] Here, the difference of two optical positions is represented
by the difference .DELTA. of the optical distances. The difference
.DELTA. of the optical distances is the propagation distance
resulting from one total reflection in the second transparent
substrate 36. More specifically, it is the distance through which
the display beam 34 propagates (or travels) from the beam splitter
37 to the interface and them back from the interface to the beam
splitter 37.
[0158] While three optical positions are illustrated in FIG. 11,
there are optical positions of the SPM 29 as many as the beams
propagating while totally reflected repeatedly in a two dimensional
manner. Typically, display beams emitting from a plurality of
different optical positions of the SPM 29 are incident on the
viewer's pupil.
[0159] The SPM 29 produces display beam 34, the outermost off-axis
display beam 34Lo, and the outermost off-axis display beam 34Uo
holographically with coherent light. Consequently, the display beam
34, the outermost off-axis display beam 34Lo, and the outermost
off-axis display beam 34Uo are also coherent beams. While in the
case shown in FIG. 11, the display beams incident on the viewer's
pupil 51 are mainly display beams (34, 34L, 34U) emitting from the
position 50b, display beams emitting from the positions 50a and/or
50c may also be incident on the pupil 51 if the pupil 51 is located
at a different position.
[0160] As described above, the display beams emitting from the
positions 50a, 50b, and 50c are coherent beams. Consequently, if a
display beam emitting from the position 50b and a display beam
emitting from the position 50a are incident on the viewer's pupil
51, the two beams would interfere, so that the viewer see an
unintended image (virtual image). The unintended image is, for
example, an image having deteriorated image quality.
[0161] In view of the above, it is preferred that the coherence
length of the light source 24 be shorter than the difference
.DELTA. of optical distances. In other words, it is preferred that
the coherence length of the light source 24 be shorter than the
propagation distance resulting from one total reflection in the
second transparent substrate 36. If this is the case, it is
possible to prevent an unintended image from being formed, even if
a plurality of display beams having different optical distances are
incident on the viewer's eye.
[0162] In the display apparatuses according to the above-described
embodiments, an SPM is used to produce display beams
holographically. However, display beams can be produced
holographically without using an SPM. For example, in the case of
still images, it is not necessary to change a hologram pattern.
Therefore, a film on which a hologram pattern is recorded may be
set at the position of the SPM. The film may be replaced by
something having properties that allow recording of a hologram
pattern only once.
[0163] The present invention can provide a display method and
display apparatus having excellent optical performance while being
small and slim.
[0164] The display method and apparatus according to the present
invention is advantageous in that the apparatus can have excellent
optical performance while being small and slim.
* * * * *