U.S. patent application number 12/595250 was filed with the patent office on 2010-06-17 for beam-shaping device.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONICS N.V.. Invention is credited to Siebe Tjek De Zwart, Rifat Ata Mustafa Hikmet, Thomas Caspar Kraan, Marcellinus Petrus Carolus Michael Krijn, Leon Hendrikus Christiaan Kusters, Ties Van Bommel, Oscar Hendrikus Willemsen.
Application Number | 20100149444 12/595250 |
Document ID | / |
Family ID | 39673439 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100149444 |
Kind Code |
A1 |
Hikmet; Rifat Ata Mustafa ;
et al. |
June 17, 2010 |
BEAM-SHAPING DEVICE
Abstract
A beam shaping device (1; 31) comprising first (3; 33) and
second (4; 37) optically transparent substrates, a liquid crystal
layer (2; 36) sandwiched there between, and first (5; 34) and
second (6; 35) electrodes arranged on a side of the liquid crystal
layer (2; 36) facing the first substrate (3; 34). The beam shaping
device (1; 31) is controllable between beam-shaping states, each
permitting passage of light through the beam-shaping device in a
direction perpendicular thereto. The beam shaping device (1; 31) is
configured in such a way that application of a voltage (V) across
the first (5; 34) and second (6; 35) electrodes results in an
electric field having a portion essentially parallel to the liquid
crystal layer (2; 36) in a segment thereof between neighboring
portions of the electrodes (5, 6; 34; 35) and extending
substantially from the first substrate (3; 34) to the second (4;
35) substrate. In this way a relatively high refractive index
gradient can be obtained across short distances, which enables a
very efficient beam shaping. The electric field can be achieved by
utilizing electrodes provided on one side of the liquid crystal
layer, in a so-called in-plane configuration. The device can be
used in an autostereoscopic display device, for switching between
2D and 3D modes.
Inventors: |
Hikmet; Rifat Ata Mustafa;
(Eindhoven, NL) ; Van Bommel; Ties; (Eindhoven,
NL) ; Kraan; Thomas Caspar; (Eindhoven, NL) ;
Kusters; Leon Hendrikus Christiaan; (Oirlo, NL) ; De
Zwart; Siebe Tjek; (Eindhoven, NL) ; Willemsen; Oscar
Hendrikus; (Eindhoven, NL) ; Krijn; Marcellinus
Petrus Carolus Michael; (Eindhoven, NL) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3001
BRIARCLIFF MANOR
NY
10510
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONICS
N.V.
EINDHOVEN
NL
|
Family ID: |
39673439 |
Appl. No.: |
12/595250 |
Filed: |
April 14, 2008 |
PCT Filed: |
April 14, 2008 |
PCT NO: |
PCT/IB2008/051401 |
371 Date: |
December 10, 2009 |
Current U.S.
Class: |
349/15 ; 349/122;
349/139; 349/33; 349/36; 349/69; 349/74 |
Current CPC
Class: |
G02F 1/29 20130101; H04N
13/359 20180501; G02B 30/26 20200101; G02F 1/134363 20130101 |
Class at
Publication: |
349/15 ; 349/139;
349/74; 349/69; 349/122; 349/36; 349/33 |
International
Class: |
G02F 1/133 20060101
G02F001/133; G02F 1/1343 20060101 G02F001/1343; G02F 1/1347
20060101 G02F001/1347; G02F 1/13357 20060101 G02F001/13357; G02F
1/1333 20060101 G02F001/1333; G02F 1/1335 20060101
G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 17, 2007 |
EP |
07106290.5 |
Jun 1, 2007 |
EP |
07109465.0 |
Claims
1. A beam shaping device (1; 31) comprising first (3; 33) and
second (4; 37) optically transparent substrates, a liquid crystal
layer (2; 36) sandwiched there between, and first (5; 34) and
second (6; 35) electrodes arranged on a side of said liquid crystal
layer (2; 36) facing said first substrate (3; 34), wherein said
beam shaping device (1; 31) is controllable between beam-shaping
states, each permitting passage of light through said beam-shaping
device in a direction perpendicular thereto, characterized in that
said beam shaping device (1; 31) is configured in such a way that
application of a voltage (V) across said first (5; 34) and second
(6; 35) electrodes results in an electric field including a portion
essentially parallel to said liquid crystal layer (2; 36) in a
segment thereof between neighboring portions of said electrodes (5,
6; 34; 35) and extending substantially from said first substrate
(3; 34) to said second (4; 35) substrate.
2. A beam shaping device (1; 31) according to claim 1, wherein said
first electrode (5; 34) comprises a first set (42a) of essentially
parallel first electrode conductor lines, and said second electrode
(6; 35) comprises a first set (42b) of essentially parallel second
electrode conductor lines, said first and second electrodes (5, 6;
34, 35) being arranged such that at least one conductor pair
including neighboring first and second electrode conductor lines is
formed.
3. A beam shaping device (31) according to claim 2, wherein said
first electrode (34) further comprises a second set (43a) of
essentially parallel first electrode conductor lines, and said
second electrode (35) comprises a second set (43b) of essentially
parallel second electrode conductor lines, said first and second
electrodes being arranged such that at least one conductor pair
including neighboring first and second electrode conductor lines is
formed.
4. A beam shaping device (31) according to claim 3, wherein said
second sets (43a, b) of conductor lines are arranged at an angle
with respect to said first sets (42a, b) of conductor lines.
5. A beam shaping device (50) according to claim 2 further
comprising a third electrode (52) having at least one third
electrode conductor line, and a fourth electrode (54) having at
least one fourth electrode conductor line, arranged on an opposite
side of said liquid crystal layer (2) with respect to said first
(51) and second (53) electrodes.
6. A beam shaping device (50) according to claim 5, wherein said
third (52) and fourth (54) electrodes are arranged such that each
of said third and fourth electrode conductor lines is essentially
perpendicular with a corresponding one of said first (51) and
second (53) electrode conductor lines.
7. A beam shaping device (1) according to claim 1, wherein said
liquid crystal layer (2) is homeotropically aligned when not
subjected to an electric field.
8. A beam shaping device (1) according to claim 1, wherein said
liquid crystal layer (2) has a planar uniaxial alignment such that
liquid crystal molecules comprised in said liquid crystal layer are
perpendicular to an adjacent conductor line when not subjected to
an electric field.
9. A beam shaping arrangement (20; 30) comprising first (21; 31)
and second (22; 32) beam shaping devices according to claim 1
arranged in a stacked structure.
10. A beam shaping arrangement (30) according to claim 9, wherein
said first (31) and second (32) beam shaping devices are oriented
in relation to each other such that at least a portion of first
(34) and second (35) electrodes comprised in said first beam
shaping device (31) are perpendicular to a corresponding portion of
first (40) and second (41) electrodes comprised in said second beam
shaping device (32).
11. A beam shaping arrangement (20) according to claim 9,
comprising a further optical member (23) adapted to alter a
polarization state of a light beam passing through said
beam-shaping arrangement (20).
12. A lighting device comprising a beam shaping device according to
claim 1, and a light-source, such as a light-emitting diode or a
semiconductor laser, arranged such that a light beam emitted by
said light-source passes through said beam shaping device.
13. A device as claimed in claim 1, wherein the beam shaping device
further comprises a layer between the first and second electrodes
and the liquid crystal layer.
14. A device as claimed in claim 13, wherein the distance between
the neighboring portions of said electrodes wires is p, the
thickness of the layer is d.sub.solid, the permittivity of a
substrate in contact with the liquid crystal layer is
.epsilon..sub.sub and the component of the permittivity of the
liquid crystal material parallel to the extraordinary axis is
.epsilon..sub.LC, and wherein: 0.7.ltoreq.a1<12, in which
a1=.epsilon..sub.LC.times.d.sub.solid/p.
15. A device as claimed in claim 14, wherein 0.9<a2<3.6, in
which a2=.epsilon..sub.LC/.epsilon..sub.sub.
16. A device as claimed in claim 1, further comprising a conductor
layer on the opposite side of the liquid crystal layer to the first
and second electrodes.
17. A device as claimed in claim 16, further comprising a second
insultator layer on the opposite side of the liquid crystal layer
to the electrodes, the second insulator layer having a thickness
d.sub.ground, wherein: 0.9<b1<14.4 and 0.4<b2<6.4, in
which b1=.epsilon..sub.LC.times.d.sub.solid/p and
b2=.epsilon..sub.LC.times.d.sub.ground/p.
18. A device as claimed in claim 16, further comprising control
means for applying a variable voltage to the conductor layer.
19. A device as claimed in claim 18, wherein the control means is
adapted to: apply a first ac voltage to the first electrode; and
apply a second ac voltage to the second electrode.
20. A device as claimed in claim 19, wherein the first and second
ac voltages are in antiphase with the same frequency, and wherein
the variable voltage has a different phase or higher frequency.
21. A device as claimed in claim 16, further comprising control
means for applying a dc voltage to the conductor layer, and wherein
the control means is adapted to: apply a first ac voltage to the
first electrode; and apply a second ac voltage to the second
electrode.
22. A device as claimed in claim 21, wherein the first and second
ac voltages each comprise first and second superposed components,
the first components of the first and second voltages being in
antiphase with the same frequency, and the second components being
the same and having a different phase or higher frequency.
23. A device as claimed in claim 1, further comprising an opaque
layer in the region of the electrodes and aligned with a region of
lowest beam shaping effect, the opaque layer being opaque at least
when the device is driven in the lensing mode.
24. A device as claimed in claim 23, comprising an analyzer on the
opposite side of the liquid crystal layer to the first and second
electrodes, and the analyzer being configured such that in the
lensing mode of the device, light traveling through the device and
exiting the LC layer at the side of the analyzer at the position of
electrodes is blocked at least partially by the analyzer.
25. A switchable autostereoscopic display device comprising: a
display panel having an array of display pixel elements for
producing a display, the display pixel elements being arranged in
rows and columns; and an imaging arrangement which directs the
output from different pixel elements to different spatial positions
to enable a stereoscopic image to be viewed, arranged such that
display pixel outputs for both eyes of a viewer are simultaneously
directed, wherein the imaging arrangement is electrically
switchable between a 2D mode and a 3D mode and comprises a beam
shaping device as claimed in claim 1.
26. A method of controlling a beam shaping device (1; 31), the beam
shaping device comprising first (3; 33) and second (4; 37)
optically transparent substrates, a liquid crystal layer (2; 36)
sandwiched there between, and first (5; 34) and second (6; 35)
electrodes arranged on a side of said liquid crystal layer (2; 36)
facing said first substrate (3; 34), wherein the method comprises:
controlling the beam shaping device between beam-shaping states,
each permitting passage of light through said beam-shaping device
in a direction perpendicular thereto by applying a voltage (V)
across said first (5; 34) and second (6; 35) electrodes thereby to
generate an electric field including a portion essentially parallel
to said liquid crystal layer (2; 36) in a segment thereof between
neighboring portions of said electrodes (5, 6; 34; 35) and
extending substantially from said first substrate (3; 34) to said
second (4; 35) substrate.
27. A method as claimed in claim 26, wherein the beam shaping
device further comprises a conductor layer on the opposite side of
the liquid crystal layer to the electrodes, and the method further
comprises applying a first ac voltage to the first electrode and
applying a second ac voltage to the second electrode.
28. A method as claimed in claim 27 further comprising applying a
variable voltage to the conductor layer, and wherein the first and
second ac voltages are in antiphase with the same frequency, and
wherein the variable voltage has a different phase or higher
frequency.
29. A method as claimed in claim 27, further comprising applying a
dc voltage to the conductor layer, and wherein the first and second
ac voltages each comprise first and second superposed components,
the first components of the first and second voltages being in
antiphase with the same frequency, and the second components being
the same and having a different phase or higher frequency.
30. A method as claimed in claim 26, wherein the beam shaping
device further comprises a conductor layer on the opposite side of
the liquid crystal layer to the electrodes, and the method further
comprises applying, within a time unit, a voltage to the conductor
layer that is different from the average voltage applied to
neighboring first and second electrodes.
31. A method as claimed in claim 26 for controlling the lens
function of a lens of an autostereoscopic display device.
Description
TECHNICAL FIELD
[0001] The present invention relates to a beam shaping device which
is controllable between beam-shaping states, each permitting
passage of light through the beam-shaping device in a direction
perpendicular thereto.
BACKGROUND OF THE INVENTION
[0002] Active beam shaping is useful for various applications
ranging from general lighting to special lighting applications,
such as a video flash in which the zoom function of the camera is
coupled to the beam width control function of an active optical
element. Liquid crystal optics would appear to be suitable for this
purpose. The alignment orientation of liquid crystal molecules in a
liquid crystal cell can be controlled by applying an electric field
thereto. This reorientation of the liquid crystal molecules results
in a refractive index gradient, which leads to a light ray passing
through the liquid crystal cell being redirected. Hereby, the
direction and/or shape of a light beam can be controlled
electrically.
[0003] One application of beam shaping devices of particular
interest is in the field of autostereoscopic display devices, which
include a display panel having an array of display pixels for
producing a display and an imaging arrangement for directing
different views to different spatial positions. It is well known to
use an array of elongate lenticular elements which are provided
extending parallel to one another and overlying the display pixel
array as the imaging arrangement, and the display pixels are
observed through these lenticular elements.
[0004] In an arrangement in which, for example, each lenticule is
associated with two columns of display pixels, the display pixels
in each column provide a vertical slice of a respective two
dimensional sub-image. The lenticular sheet directs these two
slices and corresponding slices from the display pixel columns
associated with the other lenticules, to the left and right eyes of
a user positioned in front of the sheet, so that the user observes
a single stereoscopic image. The sheet of lenticular elements thus
provides a light output directing function.
[0005] In other arrangements, each lenticule is associated with a
group of four or more adjacent display pixels in the row direction.
Corresponding columns of display pixels in each group are arranged
appropriately to provide a vertical slice from a respective two
dimensional sub-image. As a user's head is moved from left to
right, a series of successive, different, stereoscopic views are
perceived creating, for example, a look-around impression.
[0006] The above described device provides an effective three
dimensional display. However, it will be appreciated that, in order
to provide stereoscopic views, there is a necessary sacrifice in
the horizontal resolution of the device. This sacrifice in
resolution is unacceptable for certain applications, such as the
display of small text characters for viewing from short distances.
For this reason, it has been proposed to provide a display device
that is switchable between a two-dimensional mode and a
three-dimensional (stereoscopic) mode.
[0007] One way to implement this is to provide an electrically
switchable lenticular array. In the two-dimensional mode, the
lenticular elements of the switchable device operate in a "pass
through" mode, i.e. they act in the same way as would a planar
sheet of optically transparent material. The resulting display has
a high resolution, equal to the native resolution of the display
panel, which is suitable for the display of small text characters
from short viewing distances. The two-dimensional display mode
cannot, of course, provide a stereoscopic image.
[0008] In the three-dimensional mode, the lenticular elements of
the switchable device provide a light output directing function, as
described above. The resulting display is capable of providing
stereoscopic images, but has the inevitable resolution loss
mentioned above.
[0009] In order to provide switchable display modes, the lenticular
elements of the switchable device can be formed as a beam shaping
arrangement of an electro-optic material, such as a liquid crystal
material, having a refractive index that is switchable between two
values. The device is then switched between the modes by applying
an appropriate electrical potential to planar electrodes provided
above and below the lenticular elements. The electrical potential
alters the refractive index of the lenticular elements in relation
to that of an adjacent optically transparent layer.
[0010] A more detailed description of the structure and operation
of the switchable device can be found in U.S. Pat. No.
6,069,650.
[0011] The known use of switchable liquid crystal materials for
switchable 2D/3D displays uses a replica technique to form the lens
shapes, which are then filled with liquid crystal material. This
process is not compatible with the other processing steps
associated with the LCD fabrication process, and therefore adds
significantly to the cost of producing the display device.
[0012] A more general example of liquid crystal optics is disclosed
in JP 07-043656, where a light beam coupler is arranged to align a
light beam to a selected optical fiber and to adjust the beam spot
size. In the coupler, a liquid crystal layer is provided between
transparent substrates. One of the substrates is provided with a
ground plane, and the other substrate is provided with a number of
individually controllable electrodes. By varying the potential of
the electrodes in relation to the ground plane a light beam passing
through the coupler is aligned to hit a selected optical fiber.
[0013] Although being capable of deflecting a light beam a short
distance, the device disclosed in JP 07-043656 appears unsuitable
for more macroscopic beam shaping applications, where a large beam
divergence and/or convergence is typically desired.
SUMMARY OF THE INVENTION
[0014] In view of the above-mentioned and other drawbacks of the
prior art, a general object of the present invention is to provide
an improved beam shaping device, in particular a beam shaping
device capable of more efficiently diverging and/or converging a
light beam.
[0015] According to the present invention, these and other objects
are achieved through a beam shaping device comprising first and
second optically transparent substrates, a liquid crystal layer
sandwiched there between, and first and second electrodes arranged
on a side of the liquid crystal layer facing the first substrate,
wherein the beam shaping device is controllable between
beam-shaping states, each permitting passage of light through the
beam-shaping device in a direction perpendicular to the liquid
crystal layer, wherein the beam shaping device is configured in
such a way that application of a voltage across the first and
second electrodes results in an electric field including a portion
essentially parallel to the liquid crystal layer in a segment
thereof between neighboring portions of the electrodes and
extending substantially from the first substrate to the second
substrate.
[0016] The liquid crystal layer may comprise any kind of liquid
crystal molecules, and may be in any one of its phases. The nematic
phase is, however, preferred due to its relatively low viscosity as
compared with other liquid crystal phases such as the smectic
phase. In this way shorter switching times can be obtained. The
liquid crystal layer may further comprise a liquid crystal
composite containing polymers.
[0017] By an "optically transparent" medium should be understood a
medium which permits at least partial transmission of light
(electromagnetic radiation including the visible spectrum, infrared
and ultra violet light).
[0018] The optically transparent substrates may be rigid or
flexible and may, for example by made of glass or a suitable
plastic material, such as poly-methyl methacrylate (PMMA)
[0019] The electrodes may be formed either on the surface of the
substrate or embedded in the substrate. They may be formed in any
electrically conductive material, preferably, however, in an
optically transparent conductive material, such as indium tin oxide
(ITO) or indium zinc oxide (IZO).
[0020] As is well known from the theory of inhomogeneous optical
materials, a ray of light encountering a refractive index gradient
will bend towards a region with a higher refractive index. In a
liquid crystal layer, the refractive index, and thereby the bending
of a ray of light, can be controlled by reorienting the liquid
crystal molecules comprised in the liquid crystal layer by
application of an electric field.
[0021] The present invention is based on the realization that a
larger refractive index gradient, and thereby a more efficient beam
shaping can be achieved by forming an electric field in the liquid
crystal layer, which is essentially parallel to the liquid crystal
layer in a region located between adjacent electrodes and
substantially extending throughout the liquid crystal (LC) layer
between the substrates. As liquid crystal molecules tend to follow
the electric field lines, a gradual transition in orientation of
liquid crystal molecules, for example from perpendicular to the LC
layer in the vicinity of the first electrode to parallel to the LC
layer between the first and second electrodes to perpendicular to
the LC layer in the vicinity of the second electrode, can be
achieved between neighboring portions of the electrodes. In this
way a relatively high refractive index gradient can be obtained
across short distances, which enables a very efficient beam
shaping.
[0022] The present inventors have further found that such an
advantageous electric field can be achieved by utilizing electrodes
provided on one side of the LC layer, in a so-called in-plane
configuration.
[0023] Utilizing this configuration, it has been found that very
efficient beam divergence/convergence can be achieved. For example,
experiments have shown that a collimated beam can be diverged to
angles in excess of 60.degree., which is far in excess of what can
be accomplished through prior art arrangements.
[0024] Additionally, a more efficient throughput of light can be
achieved through the present invention, since the electrode on the
second substrate according to the prior art is no longer required.
Since the reflection losses associated with a continuous
transparent electrode layer is typically around 5% at a wavelength
of 500 nm, correspondingly less light is lost using the
configuration according to the present invention.
[0025] The first electrode may advantageously comprise a first set
of essentially parallel first electrode conductor lines, and the
second electrode comprise a first set of essentially parallel
second electrode conductor lines, the first and second electrodes
being arranged such that at least one conductor pair including
neighboring first and second electrode conductor lines is
formed.
[0026] The conductor lines may have any shape, curved, straight,
undulating etc.
[0027] Through this electrode configuration, a large co-operating
beam-shaping area can be achieved, and, thereby, beam-shaping of a
relatively wide beam accomplished. According to one embodiment, the
first and second electrodes may each be comb-shaped and the "teeth"
of these first and second comb-shaped electrodes are interleaved in
such a way that a number of conductor pairs extending in parallel
are formed.
[0028] Moreover, the first electrode may further comprise a second
set of essentially parallel first electrode conductor lines, and
the second electrode may further comprise a second set of
essentially parallel second electrode conductor lines, the first
and second electrodes being arranged such that at least one
conductor pair including neighboring first and second electrode
conductor lines is formed.
[0029] By providing an additional set of mutually essentially
parallel conductor lines, simultaneous beam-shaping in more than
one direction can be provided in an advantageous manner.
[0030] To this end, the second sets of conductor lines may be
arranged at an angle with respect to the first sets of conductor
lines.
[0031] Since the refractive index experienced by a light beam
passing through an LC layer is generally polarization dependent,
typically only one polarization component of a ray of unpolarized
light passing through the beam-shaping device is bent. By
configuring the first and second electrodes in such a way that the
LC molecules are reoriented in different planes of reorientation in
different portions of the beam-shaping device, bending of different
polarization components of incident rays of unpolarized light can
be achieved in those different portions of the beam-shaping
device.
[0032] Additionally, the provision of different sets of conductor
lines being provided with an angle with respect to each other
enables shaping of the beam to a geometry determined by the number
of such sets and their orientations in a plane parallel to the LC
layer.
[0033] Moreover, the different conductor lines may vary in width,
and further electrodes may be provided on the side of the LC-layer
facing the first substrate, in addition to the above-mentioned
first and second electrodes.
[0034] Furthermore, the beam shaping device may comprise a third
electrode having at least one third electrode conductor line, and a
fourth electrode having at least one fourth electrode conductor
line, arranged on an opposite side of the liquid crystal layer with
respect to the first and second electrodes.
[0035] Through the provision of such additional electrodes, the LC
molecules can be reoriented in more complex reorientation patterns,
whereby essentially polarization independent and/or symmetric
beam-shaping can be achieved.
[0036] According to one embodiment, the third and fourth electrodes
may be arranged such that each of the third and fourth electrode
conductor lines is essentially perpendicular with a corresponding
one of said first and second electrode conductor lines.
[0037] According to one embodiment, the liquid crystal layer may be
homeotropically aligned when not subjected to an electric
field.
[0038] When a liquid crystal layer is homeotropically aligned, the
liquid crystal molecules are arranged perpendicularly to the liquid
crystal layer, so that molecule ends are facing the substrates
between which the liquid crystal layer is sandwiched.
[0039] Using this kind of alignment, the liquid crystal molecules
can be controlled to be reoriented in any direction without any
anomalies. According to an alternative embodiment, the liquid
crystal (LC) molecules comprised in the liquid crystal layer may,
in the absence of an electric field acting on the molecules, be
aligned in such a way that the long axis of each LC-molecule is
essentially parallel to the nearest substrate. Furthermore, in
order to prevent the occurrence of an unwanted twist upon
application of a voltage across the electrodes, the LC-molecules
may be oriented in the plane parallel to the nearest substrate such
that the long axis of each LC-molecule is substantially
perpendicular to an adjacent conductor line pair.
[0040] In this case when an electric field is applied, the
LC-molecules are tilted and no twist thereof takes place. Through
this state of initial orientation, all the light in a beam of a
linearly polarized light can be controlled upon application of an
electric field. This is not the case when a twist is
introduced.
[0041] This kind of planar alignment may, for example, be achieved
through so-called rubbing techniques or by photo-alignment. In case
of multiple regions having various electrode patterns or curved
electrodes, these regions should typically be treated individually
during manufacturing to bring about the desired planar
alignment.
[0042] Furthermore, first and second beam-shaping devices according
to the present invention may advantageously be arranged in a
stacked structure to form a beam-shaping arrangement.
[0043] In this manner, the beam shaping characteristics of the
constituent beam shaping devices can be utilized to provide
improved beam shaping.
The first and second beam shaping devices in such a beam-shaping
arrangement may be oriented in relation to each other such that at
least a portion of first and second electrodes comprised in the
first beam shaping device are perpendicular to a corresponding
portion of first and second electrodes comprised in the second beam
shaping device.
[0044] Hereby, an essentially symmetrical beam divergence can be
achieved, utilizing both polarization directions of the incident
light beam to be shaped.
[0045] Furthermore, the beam-shaping arrangement may comprise a
further optical member adapted to alter a polarization state of a
light beam passing through the beam-shaping arrangement.
[0046] Such a further optical member may, for example, be a rotator
for altering the polarization state of the light after passage of
the first beam-shaping device, and before passage of the second
beam-shaping device. Hereby, polarization independent beam-shaping
can be achieved although the LC layer acts on the light beam in a
polarization dependent manner. The rotator may, for example, be
provided in the form of a so-called retardation plate or a liquid
crystal material, such as a liquid crystal polymer. For rotating
linearly polarized light by 90.degree., a so-called half-wave-plate
or a LC-material in a twisted nematic configuration may be
used.
[0047] The beam-shaping device according to the present invention
may, furthermore, advantageously be comprised in a lighting device
further comprising a light-source, such as a light-emitting diode
or a semiconductor laser, arranged in such a way that a light beam
emitted by the light-source passes through the beam shaping
device.
[0048] In particular, such a lighting device may advantageously
include the above-discussed beam-shaping arrangement.
[0049] The beam shaping device may further comprise a layer between
the electrodes and the liquid crystal layer. This can be used to
change the beam shaping (i.e. lens) characteristics, for example
the lens power for a given thickness of structure. If the distance
between the neighboring portions of the electrode wires is p, the
thickness of the layer is d.sub.solid, the permittivity of a
substrate in contact with the liquid crystal layer is
.epsilon..sub.sub and the component of the permittivity of the
liquid crystal material parallel to the extraordinary axis is
.epsilon..sub.LC, then the design can be such that 0.7<a1<12,
in which a1=.epsilon..sub.LC.times.d.sub.solid/p. This defines the
desired thickness of the layer in relation to the wire pitch and
permittivity of the liquid crystal material. The design can also be
such that 0.9<a2<3.6, in which
a2=.epsilon..sub.LC/.epsilon..sub.sub.
[0050] A conductor layer, with or without a second insulator layer,
can be provided on the opposite side of the liquid crystal layer to
the electrodes. This can be used to shape the electric field in the
beam shaping device. The conductor layer can have any shape
desired. It may for example be a non-patterned layer extending over
an entire lens forming portion of the LC layer.
[0051] If present, the second insulator layer can have a thickness
d.sub.ground, wherein 0.9<b1<14.4 and 0.4<b2<6.4, in
which b1=.epsilon..sub.LC.times.d.sub.solid/p and
b2=.epsilon..sub.LC .times.d.sub.ground/p. This defines the
thickness of the layer between the electrodes and the liquid
crystal layer, and the thickness of the insulator layer on the
opposite side, in relation to the wire pitch and permittivity of
the liquid crystal material.
[0052] A control means can apply a variable voltage to the
conductor layer. For example it can apply a first ac voltage to the
first electrode and apply a second ac voltage to the second
electrode, with the first and second ac voltages in antiphase with
the same frequency, and with the variable voltage having a
different phase or higher frequency. The conductor layer is thus
used to alter the electric field in the LC layer, and this can be
used to tune the beam shaping optical performance (rather than
having only on or off control).
[0053] Alternatively, a dc voltage can be applied to the conductor
layer, and the first and second ac voltages can then each comprise
first and second superposed components, the first components of the
first and second voltages being in antiphase with the same
frequency, and the second components being the same and having a
different phase or higher frequency.
[0054] An opaque layer can be provided in the region of the
electrodes and aligned with a region of lowest beam shaping effect.
The advantage is that lens aberrations, occurring at and in the
vicinity of the first and second electrodes when the device is
driven in the lensing mode can be shielded. This provides an
improved light beam. This opaque layer may be in the form of an
opaque material that is opaque permanently. Alternatively, the
opaque layer may have a switchable opaqueness, i.e. the opaque
layer may become actually opaque upon driving the device in the
lensing mode of the device, while it is not opaque when the device
is not driven in the lensing mode. In this case light throughput is
optimum in the non-lensing mode.
[0055] A device having such a switchable opaque layer may comprise
an analyzer on the opposite side of the liquid crystal layer to the
first and second electrodes, the analyzer being configured such
that in the lensing mode of the device, light traveling through the
device at the position of electrodes is blocked at least partially
by the analyzer, while light traveling through the device at a
lensing location, substantially away from the electrodes, is not
blocked by the analyzer. Thus, for example, within a device, near
and above a first or second electrode the LC directors will be
aligned predominantly perpendicularly to the device or substrate
layers when the device is operated in the lensing mode. Hence, when
polarized light, such as for example linearly polarized light,
travels through the device in the lensing mode, the polarization
will not be changed at these locations. At the same time, at
locations in the LC layer farther from the electrodes and where
lens action is provided by the electrode field lines, the directors
of the LC material will be aligned substantially more parallel to
the substrates. Consequently, the light traveling through the
device may be altered with respect to its polarization such that it
is able to pass the analyzer. Preferably, the setup of LC alignment
and analyzer orientation is such that in the non-lensing mode all
light is allowed to pass the device including analyzer.
[0056] Some of these modifications are of particular interest for
autostereoscopic display devices, in which there is a fixed desired
focal length and fixed desired electrode wire spacing, to create
the desired lens dimensions.
[0057] Thus, the invention also provides a switchable
autostereoscopic display device comprising:
[0058] a display panel having an array of display pixel elements
for producing a display, the display pixel elements being arranged
in rows and columns; and
[0059] an imaging arrangement which directs the output from
different pixel elements to different spatial positions to enable a
stereoscopic image to be viewed, arranged such that display pixel
outputs for both eyes of a viewer are simultaneously directed,
[0060] wherein the imaging arrangement is electrically switchable
between a 2D mode and a 3D mode and comprises a beam shaping device
of the invention.
[0061] The display panel may comprise an array of individually
addressable emissive, transmissive, refractive or diffractive
display pixels. The display panel preferably is a liquid crystal
display panel or a light emitting diode panel.
[0062] The invention also provides a method of controlling a beam
shaping device, the beam shaping device comprising first and second
optically transparent substrates, a liquid crystal layer sandwiched
there between, and first and second electrodes arranged on a side
of said liquid crystal layer facing said first substrate, wherein
the method comprises:
[0063] controlling the beam shaping device between beam-shaping
states, each permitting passage of light through said beam-shaping
device in a direction perpendicular thereto by applying a voltage
across said first and second electrodes thereby to generate an
electric field including a portion essentially parallel to said
liquid crystal layer in a segment thereof between neighboring
portions of said electrodes and extending substantially from said
first substrate to said second substrate.
[0064] The beam shaping device may further comprise a conductor
layer on the opposite side of the liquid crystal layer to the
electrodes, and the method further comprises applying a first ac
voltage to the first electrode and applying a second ac voltage to
the second electrode. A variable voltage can be applied to the
conductor layer, and wherein the first and second ac voltages are
in antiphase with the same frequency, and the variable voltage has
a different phase or higher frequency. Alternatively, a dc voltage
can be applied to the conductor layer, and the first and second ac
voltages each comprise first and second superposed components, the
first components of the first and second voltages being in
antiphase with the same frequency, and the second components being
the same and having a different phase or higher frequency.
[0065] This method is of particular interest for controlling the
lens function of a lens of an autostereoscopic display device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0066] These and other aspects of the present invention will now be
described in more detail, with reference to the appended drawings
showing a currently preferred embodiment of the invention,
wherein:
[0067] FIG. 1a is a perspective view of an exemplary beam-shaping
device according to an embodiment of the present invention;
[0068] FIG. 1b is a cross-section view of the beam-shaping device
in FIG. 1a along the line A-A' when no voltage is applied across
the electrodes;
[0069] FIG. 1c is a cross-section view of the beam-shaping device
in FIG. 1a along the line A-A' when a voltage V is applied across
the electrodes;
[0070] FIG. 2 is a cross-section view of a first beam-shaping
arrangement wherein a retardation plate is sandwiched between two
beam-shaping devices;
[0071] FIG. 3 is a perspective view of a second beam-shaping
arrangement comprising two beam-shaping devices having
complementary electrodes, arranged in a stacked structure;
[0072] FIG. 4 is an exploded view schematically illustrating
another exemplary beam-shaping device according to an embodiment of
the present invention;
[0073] FIGS. 5a-b show various exemplary electrode configurations;
and
[0074] FIGS. 6a-d are diagrams illustrating experiments performed
on a beam-shaping device according to an embodiment of the present
invention.
[0075] FIG. 7 shows a known autostereoscopic display device;
[0076] FIGS. 8 and 9 are used to illustrate how a known switchable
autostereoscopic display device can function;
[0077] FIG. 10 shows the required lens function for an
autostereoscopic display device;
[0078] FIG. 11 is used to explain a problem in selecting dimensions
for the lens elements of an autostereoscopic display device;
[0079] FIGS. 12 and 13 shows the lens properties for the two lens
configurations of FIG. 11;
[0080] FIG. 14 shows a first example of beam shaping apparatus of
the invention for particular use in an autostereoscopic display
device;
[0081] FIG. 15 shows a second example of beam shaping apparatus of
the invention for particular use in an autostereoscopic display
device;
[0082] FIGS. 16 and 17 shows the lens properties for the two lens
configurations of FIGS. 14 and 15 respectively;
[0083] FIG. 18 a third example of beam shaping apparatus of the
invention using an additional electrode layer;
[0084] FIGS. 19 and 20 show how the additional electrode layer in
the arrangement of FIG. 18 can be used to change electrical
fields;
[0085] FIG. 21 is used to explain a control method of the invention
for controlling the lens properties; and
[0086] FIG. 22 shows the lens characteristics for different control
settings of the method explained with reference to FIG. 21.
[0087] FIG. 23a-23c shows a 3D display according to the
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0088] In the following description, the present invention is
described with reference to a beam-shaping device having a
homeotropically aligned liquid crystal layer--the liquid crystal
(LC) molecules comprised in the LC layer are oriented perpendicular
to the substrates when no voltage is applied to the electrodes. It
should be noted that this by no means limits the scope of the
present invention, which is equally applicable to beam-shaping
devices in which the liquid crystal layer is aligned in any other
way, such as a planar orientation in which the LC-molecules are
oriented in a plane parallel with the substrates. In this
orientation, the LC-molecules may be aligned in parallel with or
perpendicular to the electrodes, or have a hybrid orientation where
the LC molecules have a first orientation adjacent to the first
substrate and a second orientation, orthogonal to the first
orientation, adjacent to the second substrate.
[0089] Furthermore, in order not to obscure the present invention
by details not directly related thereto, further layers well known
to a person skilled in the art, such as alignment layers for
aligning the LC-molecules etc have neither been depicted in the
accompanying drawings, nor described in detail herein.
[0090] It should be noted that the drawings are not to scale. To,
however, give an idea of suitable dimensions, it can be said that
the width of a conductor line in the electrodes would typically
range from 1 .mu.m to 20 .mu.m. Furthermore, the conductor lines
are typically spaced apart by 10 .mu.m to 100 .mu.m, and the
thickness of the LC layer is generally between 5 .mu.m and 50
.mu.m.
[0091] In one aspect, the invention relates generally to
beam-shaping devices suitable for many different applications, and
in another aspect, the invention relates more specifically to
additional features which make the use of the beam shaping device
of particular interest for a 2D/3D switchable display device. The
general concepts and design of the beam-shaping device will first
be described, followed by an explanation of the additional features
particularly relevant to the 2D/3D display field (although these
additional features also have more general application).
[0092] FIGS. 1a-c schematically illustrate an exemplary
beam-shaping device according to an embodiment of the present
invention.
[0093] In FIG. 1a, a beam-shaping device 1 is shown, comprising a
homeotropically aligned liquid crystal (LC) layer 2 sandwiched
between first 3 and second 4 transparent substrates. On the first
substrate 3, facing the LC layer 2, first 5 and second 6
comb-shaped transparent electrodes are provided. By applying a
voltage V over these electrodes 5, 6, a collimated light beam 7
incident on the beam-shaping device can be diverged as is
schematically illustrated in FIG. 1a.
[0094] FIG. 1b, which is a cross-section view along the line A-A'
in FIG. 1a, schematically shows the situation where no voltage is
applied across the electrodes 5, 6. Since no voltage is applied, no
electric field is formed, and, consequently, the LC-molecules have
the orientation imposed on them by the alignment layers (not
shown). In the case illustrated in FIG. 1b, the LC-molecules are
homeotropically aligned, and the shape of the incident light beam
7, here represented by three parallel rays 11a-c of light is
unchanged by the passage through the beam-shaping device 1.
[0095] With reference to FIG. 1c which schematically shows the
situation where the voltage V is applied across the electrodes 5,
6, the beam-shaping mechanism utilized by the beam-shaping device
in FIG. 1a will now be described in more detail.
[0096] As is schematically shown in FIG. 1c, the liquid crystal
(LC) molecules 10a-c comprised in the LC layer 2 are aligned to the
electric field lines between the electrodes 5, 6. Due to this
reorientation, regions of the LC layer 2 having different
refractive indices are formed. In the exemplary case illustrated in
FIG. 1c, the refractive index experienced by a light beam 7 hitting
the beam-shaping device 1 in a direction which is (locally)
perpendicular thereto varies between the ordinary refractive index
n.sub.o resulting from LC molecules 10a oriented perpendicular to
the LC layer 2 and the extraordinary refractive index n.sub.e
resulting from LC molecules 10c oriented in parallel with the LC
layer 2. Light hitting the beam-shaping device 1 between a portion
thereof with "perpendicular" LC-molecules 10a and a portion thereof
with "parallel" LC-molecules 10c will experience an intermediate
refractive index.
[0097] In FIG. 1c, the three rays 12a, b, c representing the linear
polarization component of unpolarized light having a direction of
polarization which is perpendicular to the long axis of the LC
molecules (ordinary rays) pass through the beam-shaping device 1
practically without experiencing a refractive index gradient. Thus
neither of these rays 12a-c has its direction altered significantly
during passage through the LC-layer 2.
[0098] The other polarization component, rays 13a, b, c,
representing light polarized in the plane of the long axis of the
molecules (extraordinary rays) on the other hand experience a
refractive index gradient and are therefore refracted as is
schematically indicated in FIG. 1c.
[0099] Consequently, a maximum of 50% of the light in an
unpolarized light beam 7 is controllable by the beam-shaping device
1 in FIGS. 1a-c.
In the following, three exemplary beam-shaping devices/arrangements
enabling control of substantially all of the light in an
unpolarized light beam will be described with reference to FIGS.
2-4.
[0100] A first exemplary beam-shaping arrangement 20 will be
described with reference to FIG. 2, which is a cross-section view
showing first 21 and second 22 beam-shaping devices as described in
connection with FIGS. 1a-c arranged in a stacked structure with a
retardation plate 23 sandwiched there between.
[0101] Again, three rays 24a-c of unpolarized light will be
followed through the beam-shaping arrangement 20. As described in
connection with FIG. 1b, the extraordinary rays will be influenced
by the first beam shaping device 21 and the ordinary rays will pass
through this beam-shaping device 21 without being influenced. As
the ordinary ray go through the retardation plate 23, which is here
provided in the form of a so-called half wave plate or a LC polymer
in a twisted nematic configuration, the polarization direction is
rotated 90.degree..
[0102] Hence, when entering the second beam-shaping device 22, the
previously unaffected components 25a-c are now polarized in the
same plane as the long axis of the LC-molecules 27 of the second
beam-shaping device 22 and will be deflected in the same manner as
the other polarization components 26a, c were when passing through
the first beam-shaping device 21.
[0103] Hereby, as schematically illustrated in FIG. 2, all of the
unpolarized light passing through the beam-shaping arrangement 20
can be controlled by the beam-shaping arrangement 20.
[0104] In the above examples, the behavior of LC molecules with a
positive dielectric anisotropy is described. It should, however, be
noted that it is also possible to use LC molecules with negative
dielectric anisotropy. In that case the rays 24a-c will be
refracted in an opposite direction compared to what is described
above.
[0105] It should be noted that, in the presently illustrated
examples, the refraction at interfaces between substrates and
LC-layers etc has been disregarded in order to simplify the
illustrations.
[0106] With reference to FIG. 3, a second exemplary beam-shaping
arrangement 30 will now be described.
[0107] In FIG. 3, first 31 and second 32 beam-shaping devices are
shown in a stacked structure. In order from bottom to top of the
stacked structure, the first beam-shaping device 31 has a first
substrate 33, on which first 34 and second 35 electrodes are
provided, an LC-layer 36, and a second substrate 37. In the
presently illustrated embodiment, the second substrate 37 of the
first beam-shaping device 31 is also the first substrate of the
second beam shaping device 32. Obviously, this common substrate 37
could alternatively be provided as two separate substrates. The
second beam-shaping device 32 further has an LC layer 38, and a
second substrate 39 provided with first 40 and second 41
electrodes.
[0108] As can be seen in FIG. 3, each of the electrodes 34, 35, 40,
41 of the beam-shaping arrangement 30 has two sets 42a-b, 43a-b,
44a-b, and 45a-b, respectively of conductor lines. Within each set
42a-b, 43a-b, 44a-b, and 45a-b, the conductor lines are essentially
parallel to each other, and the two sets 42a-b, 43a-b, 44a-b, and
45a-b are provided with an angle of about 45.degree. with respect
to each other.
[0109] Furthermore, the beam-shaping devices 31, 32 are arranged in
relation to each other in such way that the electrodes 34, 35 of
the first beam-shaping device 31 are perpendicular to the
electrodes 40, 41 of the second beam-shaping device 32.
[0110] Through this beam-shaping arrangement 30, an incident
collimated beam can be shaped symmetrically and utilizing both
polarization components of the incident light. Finally, with
reference to FIG. 4, a third exemplary beam-shaping
device/arrangement 50 will be described, which comprises an
LC-layer 2 sandwiched between first 3 and second 4 optically
transparent substrates. On each of the substrates 3, 4, first 51,
52, and second 53, 54 comb-shaped electrodes are provided on the
side 55, 56 of the substrate 3, 4 facing the LC-layer 2.
[0111] As illustrated in FIG. 4, the electrodes 51, 53 on the first
substrate 3 are essentially perpendicular to the electrodes 52, 54
on the second substrate 4. Through this configuration,
three-dimensional re-orientation of the LC-molecules in the
LC-layer can be achieved, which enables polarization-independent
beam-shaping.
In addition to the electrode configurations illustrated in FIG. 1a
and FIG. 3, many other electrode configurations are possible and
may be advantageous depending on the particular application. A few
examples of such additional electrode configurations are
schematically illustrated in FIGS. 5a-b.
[0112] In FIG. 5a, various in-plane configurations with two
electrodes are illustrated, where the conductor lines have
different directions in relation to each other, are non-straight,
etc.
[0113] In FIG. 5b, two examples of configurations with three
in-plane electrodes are schematically shown.
[0114] It should be noted that the variations illustrated in FIGS.
5a-b represent examples only and that many other variations are
apparent to one skilled in the relevant art.
[0115] The person skilled in the art realizes that the present
invention by no means is limited to the preferred embodiments. For
example, the electric field applied across the electrodes may
advantageously be obtained through the application of an
alternating voltage having a frequency above 100 Hz in order to
overcome charging effects. It is also possible to use a pixilated
cell in combination with active matrix addressing.
Experiments
[0116] With reference to FIGS. 6a-d, which are diagram illustrating
how the beam divergence in an experimental setup of a beam-shaping
device according to an embodiment of the present invention varies
with respect to various parameters, a brief description of some of
the experiments carried out will now be provided.
[0117] In all of the Figures, the intensity has been normalized in
order to illustrate the angular distribution. Furthermore, in the
curves showing beams that are only slightly diverged have been
clipped to improve the discernability of the more diverged
beams.
Beam Divergence as a Function of Applied Voltage
[0118] In FIG. 6a, the angular distribution of light following
passage through the beam-shaping device of a collimated beam of
polarized light is shown with respect to the voltage applied to the
electrodes.
[0119] The characteristics of the cell used in the experiment
resulting in the graphs in FIG. 6a are as follows: [0120] Electrode
width: 4 .mu.m [0121] Free Distance between electrodes: 10 m [0122]
Cell gap: 18 .mu.m [0123] Liquid crystal material: BL009 [0124]
Alignment layer polyimide: Nissan 1211, homeotropically aligned (no
rubbing)
[0125] Using this cell configuration, the alternating voltage
applied across the electrodes has been varied between 0 Vrms and 50
Vrms.
[0126] When applying 0 Vrms across the electrodes, no divergence of
the beam is achieved, as illustrated by the curve 61 in FIG. 6a.
When gradually increasing the voltage, the beam is more and more
diverged. When applying 5 Vrms the light is diverged as illustrated
by the curve 62. The curve 63 results from applying 10 Vrms, the
curve 64 results from applying 15 Vrms, and the curves 65 and 66
correspond to a voltage of 20 Vrms and 50 Vrms, respectively.
Beam Divergence as a Function of Free Distance Between
Electrodes
[0127] In FIG. 6b, the angular distribution of light following
passage through the beam-shaping device of a collimated beam of
polarized light is shown with respect to the distance between the
electrodes. The characteristics of the cell used in the experiment
resulting in the graphs in FIG. 6b are as follows: [0128] Electrode
width: 4 .mu.m [0129] Cell gap: 18 .mu.m [0130] Liquid crystal
material: BL009 [0131] Alignment layer polyimide: Nissan 1211,
homeotropically aligned (no rubbing) [0132] Applied voltage: 50
Vrms
[0133] Using this cell configuration, the free distance between the
electrodes has been varied between 10 .mu.m and 30 .mu.m.
[0134] For a given voltage applied across the electrodes, a shorter
distance between the electrodes entails a higher electric field. A
higher electric field leads to a more efficient redirection of the
liquid crystal molecules in the liquid crystal layer, and hence to
a more efficient beam shaping.
[0135] The shortest distance, 10 .mu.m, leads to the largest
divergence, as can be seen in FIG. 6b, where this distance
corresponds to the curve 71. When the distance is increased to 15
.mu.m, the beam divergence is also decreased to have the angular
distribution represented by the curve 72 in FIG. 6b. With a further
increase to 20 .mu.m, the curve 73 is obtained, and the two final
curves 74, 75 in FIG. 6b result from distances between the
electrodes of 25 .mu.m and 30 .mu.m, respectively.
Beam Divergence as a Function of Electrode Width
[0136] In FIG. 6c, the angular distribution of light following
passage through the beam-shaping device of a collimated beam of
polarized light is shown with respect to the electrode width.
[0137] The characteristics of the cell used in the experiment
resulting in the graphs in FIG. 6c are as follows: [0138] Free
distance between electrodes: 12 .mu.m [0139] Cell gap: 18 .mu.m
[0140] Liquid crystal material: BL009 [0141] Alignment layer
polyimide: Nissan 1211, homeotropically aligned (no rubbing) [0142]
Applied voltage: 50 Vrms
[0143] Using this cell configuration, the electrode width has been
varied between 4 .mu.m and 8 .mu.m.
[0144] In FIG. 6c, the curve 81 corresponds to an electrode width
of 4 .mu.m, the curve 82 corresponds to an electrode width of 6
.mu.m, and the curve 83 corresponds to an electrode width of 8
.mu.m.
Beam Divergence as a Function of Cell Gap
[0145] In FIG. 6d, the angular distribution of light following
passage through the beam-shaping device of a collimated beam of
polarized light is shown with respect to the cell gap.
[0146] The characteristics of the cell used in the experiment
resulting in the graphs in FIG. 6d are as follows: [0147] Electrode
width: 4 .mu.m [0148] Free distance between electrodes: 20 .mu.m
[0149] Liquid crystal material: BL009 [0150] Alignment layer
polyimide: Nissan 1211, homeotropically aligned (no rubbing) [0151]
Applied voltage: 50 Vrms
[0152] Using this cell configuration, the cell gap has been varied
between 12 .mu.m and 27 .mu.m.
[0153] Having a larger cell gap, each ray of the beam to be shaped
travels a longer distance through the liquid crystal layer, and can
thus be deflected to a larger degree. The smallest cell gap, 12
.mu.m, leads to the smallest divergence, as can be seen in FIG. 6d,
where this cell gap corresponds to the curve 91. When the cell gap
is increased to 18 .mu.m, the beam divergence is also increased to
have the angular distribution represented by the curve 92 in FIG.
6d. With a further increase of the cell gap to 27 .mu.m, the curve
93 is obtained.
[0154] As mentioned above, beam shaping devices designed in
accordance with the principles of the invention can have particular
application in the field of 2D/3D switchable displays.
[0155] FIG. 7 is a schematic perspective view of a known direct
view autostereoscopic display device 100. The known device 100
comprises a liquid crystal display panel 103 of the active matrix
type that acts as a spatial light modulator to produce the
display.
[0156] The display panel 103 has an orthogonal array of display
pixels 105 arranged in rows and columns. For the sake of clarity,
only a small number of display pixels 105 are shown in the figure.
In practice, the display panel 3 might comprise about one thousand
rows and several thousand columns of display pixels 105.
[0157] The structure of the liquid crystal display panel 103 is
entirely conventional. In particular, the panel 103 comprises a
pair of spaced transparent glass substrates, between which an
aligned twisted nematic or other liquid crystal material is
provided. The substrates carry patterns of transparent indium tin
oxide (ITO) electrodes on their facing surfaces. Polarizing layers
are also provided on the outer surfaces of the substrates.
[0158] Each display pixel 105 can comprise opposing electrodes on
the substrates, with the intervening liquid crystal material there
between. The shape and layout of the display pixels 105 are
determined by the shape and layout of the electrodes. The display
pixels 105 are regularly spaced from one another by gaps.
[0159] Each display pixel 105 is associated with a switching
element, such as a thin film transistor (TFT) or thin film diode
(TFD). The display pixels are operated to produce the display by
providing addressing signals to the switching elements, and
suitable addressing schemes will be known to those skilled in the
art.
[0160] The display panel 103 is illuminated by a light source 107
comprising, in this case, a planar backlight extending over the
area of the display pixel array. Light from the light source 107 is
directed through the display panel 103, with the individual display
pixels 105 being driven to modulate the light and produce the
display.
[0161] The display device 100 also comprises a lenticular sheet
109, arranged over the display side of the display panel 103, which
performs a view forming function. The lenticular sheet 109
comprises a row of lenticular elements 111 extending parallel to
one another, of which only one is shown with exaggerated dimensions
for the sake of clarity.
[0162] The lenticular elements 111 are in the form of convex
cylindrical lenses, and they act as a light output directing means
to provide different images, or views, from the display panel 103
to the eyes of a user positioned in front of the display device
100.
[0163] The autostereoscopic display device 100 shown in FIG. 1 is
capable of providing several different perspective views in
different directions. In particular, each lenticular element 111
overlies a small group of display pixels 105 in each row. The
lenticular element 111 projects each display pixel 105 of a group
in a different direction, so as to form the several different
views. As the user's head moves from left to right, his/her eyes
will receive different ones of the several views, in turn.
[0164] It has been proposed to provide electrically switchable lens
elements, as mentioned above. This enables the display to be
switched between 2D and 3D modes.
[0165] FIGS. 8 and 9 schematically show an array of electrically
switchable lenticular elements 115 which can be employed in the
device shown in FIG. 1. The array comprises a pair of transparent
glass substrates 119, 121, with transparent electrodes 123, 125
formed of indium tin oxide (ITO) provided on their facing surfaces.
An inverse lens structure 127, formed using a replication
technique, is provided between the substrates 119, 121, adjacent to
an upper one of the substrates 119. Liquid crystal material 129 is
also provided between the substrates 119, 121, adjacent to the
lower one of the substrates 121.
[0166] The inverse lens structure 127 causes the liquid crystal
material 129 to assume parallel, elongate lenticular shapes,
between the inverse lens structure 127 and the lower substrate 121,
as shown in cross-section in FIGS. 2 and 3. Surfaces of the inverse
lens structure 127 and the lower substrate 121 that are in contact
with the liquid crystal material are also provided with an
orientation layer (not shown) for orientating the liquid crystal
material.
[0167] FIG. 8 shows the array when no electric potential is applied
to the electrodes 123, 125. In this state, the refractive index of
the liquid crystal material 129 for light of a particular
polarization is substantially higher than that of the inverse lens
array 127, and the lenticular shapes therefore provide a light
output directing function, i.e. a lens action, as illustrated.
[0168] FIG. 9 shows the array when an alternating electric
potential of approximately 50 to 100 volts is applied to the
electrodes 123, 125. In this state, the refractive index of the
liquid crystal material 49 for light of the particular polarization
is substantially the same as that of the inverse lens array 127, so
that the light output directing function of the lenticular shapes
is cancelled, as illustrated. Thus, in this state, the array
effectively acts in a "pass through" mode.
[0169] The skilled person will appreciate that a light polarizing
means must be used in conjunction with the above described array,
since the liquid crystal material is birefringent, with the
refractive index switching only applying to light of a particular
polarization. The light polarizing means may be provided as part of
the display panel or the imaging arrangement of the device.
[0170] Further details of the structure and operation of arrays of
switchable lenticular elements suitable for use in the display
device shown in FIG. 7 can be found in U.S. Pat. No. 6,069,650.
[0171] FIG. 10 shows the principle of operation of a lenticular
type imaging arrangement as described above and shows the backlight
130, display device 134 such as an LCD and the lenticular array
138.
[0172] The manufacture of the device shown in FIGS. 8 and 9 uses
replica lenticulars, which requires equipment that is not standard
in production facilities. The use of a beam shaping device as
described above, having laterally controlled graded index lens
function, thus simplifies the manufacturing process.
[0173] FIG. 1c shows the electric field distribution in the LC
layer resulting from the use of interleaved wires as shown in FIG.
1a. The applied voltage is an alternating current, to counteract
charging effects. The applied voltage is selected to be high enough
to align the LC in the direction of the field. For a
straightforward design there is an optimal ratio between LC layer
thickness and width between electrodes (approximately 1:1.5) for
the best lens action. However, the required width of the lens, in
order to cover a certain amount of pixels for the desired number of
views, and the desired thickness of the LC layer (to obtain the
desired focal depth) often, but not always, hampers or even
excludes this basic design from being used. A thicker layer of LC
results in a lens with a shorter focal length. The main issue is
that the LC layer has to be chosen to be thinner relative to the
electrode pitch than would be optimal for the lens
characteristics.
[0174] FIG. 11a shows schematically the desired ratio between
thickness and electrode spacing, and FIG. 11b shows the electric
field distribution in the structure when the preferred LC layer
thickness is used to provide the desired focal distance in
combination with a typical desired electrode spacing. These values
of thickness and electrode spacing give rise to strong aberrations
in the lens-action. By reducing the thickness of the LC layer in
FIG. 11b to obtain the desired focal length, an optically
inhomogeneous material is replaced with an optically homogeneous
material, giving rise to the lens aberration.
[0175] FIG. 12 shows the lens characteristics (FIG. 12a shows the
refractive index n versus distance x, and FIG. 12b shows the
refractive index gradient ("angle") versus distance x) for the
desired ratio of FIG. 11a. The thickness is 100 .mu.m and the
electrode spacing is 166 .mu.m.
[0176] FIG. 13 shows the lens characteristics (again FIG. 13a shows
the refractive index n versus distance x, and FIG. 13b shows the
refractive index gradient ("angle") versus distance x) for the
reduced thickness lens design of FIG. 11b. The thickness is 40
.mu.m and the electrode spacing is 166 .mu.m. FIGS. 12 and 13 are
calculated using an analytical model. The angular distribution as
shown in FIG. 13 not only lacks the desired strength (it is also
far too strong on the edges), but has strong aberrations in the
center as well (the angular distribution should be a straight line
in the ideal case).
[0177] Thus, there is often a problem that the lens has a focal
distance that is too short if a thick LC is used or has too strong
aberrations in the center if a thin LC layer is used.
[0178] A modification is therefore to increase the focal distance
and/or reduce these aberrations to an acceptable level by improving
the basic designs above by using one or two layers of material that
influence the electric field that is generated within the LC
layer.
[0179] FIG. 14 shows a first modification in which the part of the
liquid crystal layer near the wire structure is replaced with a
layer of solid, transparent material.
[0180] The structure of FIG. 14 thus comprises the additional layer
140, the LC layer 142 and the glass layer 144 of the overlying
LCD.
[0181] This layer 140 has no direct effect on the direction of the
light, because the incident beam travels perpendicular to the
replaced layer and there is no gradient in refractive index within
the layer. However, the layer 140 does have an effect on the
electric field distribution in the LC-layer, indirectly influencing
the light traveling through the lens.
[0182] The magnitude of this effect (and the focal length of the
lens) depends on the thickness of the solid layer 140, the
thickness of the LC layer 142, the permittivity of the solid layer
and the parallel permittivity of the LC.
[0183] FIG. 14 shows the electric field lines 145 defining the lens
shape, and the optical paths 146 through the structure.
[0184] A further modification uses an additional layer of
transparent material 150 in contact with a transparent conductor,
such as Indium-Tin-Oxide (ITO), to reduce the lens thickness (and
therefore increase its focal length) by effectively compressing the
electric field, as shown in FIG. 15. The influence of the grounded
layer 150 is that it imposes conditions on the electric field that
are beneficial for the field distribution needed in the layer of
LC. The two layers 140 and 150 are selected such that the
switchable LC layer 142 is positioned in the required region to
implement the lens switching function. The thickness of the layers
depends on the permittivity of each material and the desired focal
length. Notwithstanding the aforementioned, it will be appreciated
by the person skilled in the art that in alternative embodiments,
as for example the one described with respect to FIG. 18, the
layers 140 and/or 150 may be omitted according to need and
design.
[0185] In the aforementioned modifications, the lenses can be made
weaker and with small spherical aberrations. The lenses can be
designed to have a focal length matching the optical path length
from the lens to the pixels.
[0186] FIGS. 16 and 17 show the lens characteristics for two
designs of an actual 10 cm display with 9 views. FIG. 16 is based
on the arrangement of FIG. 14 and FIG. 17 is based on the
arrangement of FIG. 15. The variables plotted correspond to those
in FIGS. 12 and 13. The focal length, equal to the optical
thickness of the different layers, is 1,342 .mu.m in glass (a 615
.mu.m thick glass plate of the display, a 27 .mu.m thick layer of
polymer and a 700 .mu.m thick glass plate of the lens-array
itself). For this 9 view display, the pixel pitch is 37.5 .mu.m and
the lens pitch is 166.36 .mu.m. For the example of FIG. 16, the LC
layer thickness is 13 .mu.m, and the thickness of the additional
layer 140 is 100 .mu.m. For the example of FIG. 17, the LC layer
thickness is 12 .mu.m, the thickness of the additional layer 140 is
61 .mu.m and the thickness of the layer 150 on the ITO ground plane
is 27 .mu.m.
[0187] As can be seen, the shape of the angular distribution for
both designs is comparable to that of the distribution shown in
FIG. 12. Thus, a lens design is obtained with the desired focal
length while keeping the aberrations on an acceptable level.
[0188] For the design shown in FIG. 14 with a single additional
layer, the key variables are the distance between the wires p, the
thickness of the layer 140 of solid material d.sub.solid, the
permittivity of the glass in contact with the LC
.epsilon..sub.glass and the component of the permittivity of the LC
material parallel to the extraordinary axis .epsilon..sub.LC.
[0189] The lens function is improved based on the ratios between
these variables. The key ratios are:
a1=.epsilon..sub.LC.times.d.sub.solid/p
and
a2=.epsilon..sub.LC/.epsilon..sub.glass
[0190] In the calculations used for FIG. 16, a1=3.0 and a2=1.8.
[0191] The thickness of the LC layer, d.sub.LC, depends on the
desired focal length f, the difference between the ordinary and
extra-ordinary index of refraction (.DELTA.n=n.sub.e-n.sub.o) and
the geometry of the design,
d.sub.LC.about.p.sup.2/(f.times..DELTA.n) and will range from
approximately 5 to 100 .mu.m.
[0192] The preferred range for the variable a1 is 0.7<a1<12,
more preferably 1.5<a1<6 and more preferably
2.5<a1<4.
[0193] The preferred range for the variable a2 is
0.9<a2<3.6.
[0194] For the design shown in FIG. 17 using two additional layers,
the key variables are the distance between the wires p, the
thickness of the layer of solid material near the wire-structure
d.sub.w, the thickness of the layer of solid material near the
grounded ITO layer d.sub.ground and the parallel component of the
permittivity of the LC-material .epsilon..sub.LC. The key ratios
are:
b1=.epsilon..sub.LC.times.d.sub.w/p
and
b2=.epsilon..sub.LC.times.d.sub.ground/p.
[0195] In the calculations used for FIG. 17, b1=3.6 and b2=1.6.
[0196] The thickness of the layer LC, d.sub.LC, again depends on
the desired focal length f, the difference between the ordinary and
extra-ordinary index of refraction and the geometry of the design,
and will again range from approximately 5 to 100 .mu.m.
[0197] The preferred ranges for the variables are:
[0198] 0.9<b1<14.4 and 0.4<b2<6.4, or more
preferably
[0199] 0.9<b1<14.4 and 0.8<b2<3.2, or more
preferably
[0200] 1.8<b1<7.2 and 0.4<b2<6.4, or more
preferably
[0201] 1.8<b1<7.2 and 0.8<b2<3.2.
[0202] The examples above show switching between two different
modes, for example between 2D and 3D modes of operation for the
example of an autostereoscopic display device. However, there may
also be advantages in being able to change the strength of the
lens. One way to alter the lens strength is to lower the applied
voltage on the fork structure below a threshold where the behavior
of the liquid crystal molecules is not dominated anymore by the
direction of the electric field. A balance is then formed with the
force as a result of interaction with surrounding molecules. The
disadvantage of this approach is that it depends on the behavior of
the LC and this behavior changes with temperature. Furthermore, the
change in lens characteristics is not easily predicted.
[0203] A further modification of a device described below changes
the lens strength by influencing the direction of the field within
the layer of LC. This modification uses a conducting plate, such as
layer 150 in FIG. 15 (but does not need the layer 140), and applies
an alternating current to the conducting plate in order to change
the electric field and as a result change the strength of the lens.
Additional insulating layers may be provided between the electrode
fork arrangement and the conducting plate as in the example
above.
[0204] FIG. 18 shows a basic structure of an LC layer and an ITO
layer. The thickness of the ITO layer is not shown, and it is
represented as a line. The electric field lines before a potential
is applied to the conductive plate. The fork structure and the
plate 150 are supplied with alternating current. When an
alternating current is applied to the conducting plate, the
electric field starts switching rapidly between the two conditions
shown in FIG. 19. If the frequencies of the applied voltages are
chosen to be sufficiently high compared to the relaxation time of
the liquid crystals (f<<1/.tau..sub.LC) then the LC molecules
will align between the two different electric fields E.sub.1,
E.sub.2 as shown in FIG. 20.
[0205] Depending on the voltage applied to the fork, the voltage
applied on the plate and the position of the LC layer with respect
to the plate and fork, it is possible to change the lens effect
significantly. Some different ways of achieving a variable lens
effect are shown in FIG. 21.
[0206] In FIG. 21, the top three plots are based on using opposing
voltages on the two forks, V.sub.fork,1 and V.sub.fork,2 with a
base frequency f. The electric field for this situation is modified
by applying a voltage to the conducting plate V.sub.plate that
either has a phase-shift compared to the fork signals (signal 210),
an in-phase signal with a frequency f.sub.plate that is twice as
high as the base frequency f (signal 212) or a frequency which is
much higher than the base frequency (signal 214). These three
possibilities are shown in sequence in FIG. 21.
[0207] An alternative embodiment shown in the lower three plots of
FIG. 21 is to keep V.sub.plate equal to zero, by adding a
modulation to the signals on the two forks. The same lens effects
are obtained, as the difference between each fork voltage and the
plate voltage is the same. In this case, each fork signal has
superposed onto it an additional signal which has a phase-shift
compared to the fork signals, or is an in-phase signal with a
frequency f.sub.plate that is twice as high as the base frequency
for a frequency which is much higher than the base frequency.
[0208] FIG. 22 shows different profiles for the angular
distribution for a lens with different amplitudes of the applied
voltage on the plate Vplate. The design and specifications of the
sample used for the analysis are an electrode pitch 166 .mu.m, LC
layer thickness 70 .mu.m, and an additional layer 140 as in FIG. 15
of 82 .mu.m.
[0209] The voltages on the plate are applied at 1 kHz. The power
source for the fork electrodes is based on V.sub.fork=50V with
frequency f.sub.fork=100 Hz. The linear part in the middle of each
measurement gives an indication for the focal length. The focal
lengths for the 0 V; 7:5V; 15 V and 30 V situations are
approximately 140 .mu.m; 85 .mu.m; 190 .mu.m and 1330 .mu.m
respectively.
[0210] As can be seen, the amount of change in lens effect depends
on the amplitude of the applied voltage.
[0211] Here before, driving of the first and second electrodes in
conjunction with the conductor layer has been done such that a
symmetrical lens effect is obtained. Thus, for example, with
reference to FIG. 18, the first and second electrodes are given
opposite and equal voltages V1=-V2, respectively, while the
conductor ITO layer 150 is kept at a voltage V3 of 0 V.
Conveniently, for an asymmetric lens effect, V3 is different from
0V. Such a voltage scheme provides asymmetric field line
distribution and a corresponding asymmetric lens effect, i.e. there
is not only a lens effect, but also beam deflection.
[0212] The beam deflection and one possible application in the
field of 3D autostereoscopic displays are illustrated in FIGS. 23a,
23b and 23c. The beam shaping device is part of an autostereoscopic
display 170. The display comprises a standard LC panel 172,
comprising a polarizer 176, a pixel panel 178 and an analyzer 180
held together by glass substrates 182. A backlight (not shown is
present beneath polarizer 176. The LCD display is combined with a
beam shaping device 174 according to the invention which is to
serve as a lenticular array when used in the lensing mode. The beam
shaping device in this case comprises first electrodes 184 and
second electrodes 186 on a substrate 198. On top of that are
present a first insulating layer 188, a thin LC layer 190, a second
insulating layer 192 a transparent conducting layer 194 and a
substrate 196 of an appropriate transparent material. The pattern
of intertwining first and second electrodes on substrate 198 is as
shown in 1a. The electrode on substrate 196 is an unstructured
electrode that preferably covers the complete substrate. The layers
188 and 192 are optional and may serve the functions described here
before for optimization of lens shape. Shown is a 5-view system,
i.e. there are 5 sub-pixels such as pixels 202, 203 and 204,
underneath each lens of the lenticular, each sub-pixel
corresponding to a different view. Like parts in FIGS. 23a, 23b and
23c have like numerals.
[0213] During regular 3D operation of the display, to the first
electrode a voltage V.sub.1 is applied, to the second electrode a
voltage V2 of -V.sub.1 is applied and to the conductive layer a
voltage of V.sub.3=0V is applied, such that the light stemming from
neighboring pixels 200, 202 and 204 all situated under one
cylindrical lens unit present in between two neighboring first and
second electrode fingers is sent into different directions, i.e.
sent into different views in a symmetrical manner as shown in FIG.
23a.
Alternatively, when V.sub.3.noteq.0 V the symmetry of the Field
lines and hence that of the associated lens gets broken. The field
lines will rearrange themselves such that apart from a lens action
also a beam deflection is the result: each view will be deflected
somewhat, as depicted in FIGS. 23b and 23c. The direction of this
deflection changes sign from lens to lens. The direction also
changes sign when changing the sign of voltage V.sub.3. In general
the effect is obtained when V3 differs from the value that is
exactly in between the voltages applied on neighboring first and
second electrodes.
[0214] By alternating V.sub.3 between .DELTA.V and -.DELTA.V in
subsequent image frames, the individual views will be tilted from
left to right and vice versa from frame to frame. This is
equivalent to saying that in effect the lenticular is shifted in a
virtual manner from left to right and vice versa. Consider the
central view 206 for the time being (i.e. the view in a direction
perpendicular to the display): underneath each lens, with the
method of alternating V.sub.3 between .DELTA.V and -.DELTA.V, two
different sub-pixels being 200 or 204, having different colors will
contribute to the central view instead of only one: one sub-pixel
when V.sub.3=.DELTA.V (FIG. 23b) and the other one when
V.sub.3=-.DELTA.V (FIG. 23c). Thus, in a time-sequential manner,
the resolution for each view in the 3D mode of operation is
doubled. For example, in case the frame rate is 100 Hz, the
lenticular could alternate between two positions: the positions are
switched after every 1/100-second. In this manner, the resolution
per view can be doubled.
[0215] Instead of doubling the resolution per view, it is also
possible to triple the resolution per view when the symmetrical
configuration of voltages is also used. In that case the pixel 202
is providing the central view in FIG. 23.
[0216] The demands on the frame rate are not very high. For
example, time-multiplexing by a factor of two in order to double
the resolution per view does not necessarily imply that the frame
rate has to be doubled. In the case of a frame rate of 50 Hz,
images are generated for each of the two positions of the
view-forming element at a frame rate of 25 Hz only. Since the
images that are generated for the two positions are very similar,
in the perception of the viewer the perceived frame rate is still
50 Hz rather than 25 Hz.
[0217] Upon shifting the lenticular, the image content for each
view should be adapted accordingly.
[0218] In roughly the same manner as doubling the resolution per
view, it is also possible to double the number of views by tilting
the views such that new views are created in between the original
views.
[0219] There is one drawback of this GRIN beam shaping device
forming a lenticular on a display, compared with existing
lenticulars, which is that it will reduce the possible contrast for
the display in 3D mode as a result of the relative inactive area at
the edge of the lenses. The contrast may be retained by using an
opaque material where the lens-effect is absent (the lines between
the lenses). In fact, also in general for beam shaping devices,
aberrations of the lens in the LC region at the location of
electrodes will make light beams less perfect. The light stemming
from the imperfect parts of the lens may be shielded by an opaque
layer. This opaque layer can be a printed layer on either
substrate, or a pattern deposited by any suitable technique.
[0220] Alternatively, a layer with switchable opaqueness is
provided. In one embodiment, an analyzer is present in any of the
modifications described here above. The analyzer is situated at the
opposite side of the LC layer to the first and second electrodes
and is linearly polarizing. In the non-lensing mode of the device,
the LC material directors are aligned parallel to the substrates of
the device, but perpendicular with respect to each other on either
side of the LC layer. The latter type of orientation may be
achieved by polyimide alignment layers rubbed in the appropriate
perpendicular directions. Thus in the LC layer a gradual rotation
of the directors from one orientation to the perpendicular
orientation at the other side of the LC layer occurs upon traveling
through the LC layer in a direction perpendicular to the substrate.
The analyzer is then oriented or rotated such that linearly
polarized light, of which the polarization present upon entering of
the LC layer has been rotated by the gradual LC director rotation
after traveling through the LC layer, exiting the device at the
analyzer side is allowed to pass the analyzer, when the device is
in its non-lensing mode. Upon driving the device in its lensing
mode, at the location of and in the vicinity of the electrodes, the
directors will align substantially off parallel and more
perpendicularly to the substrates, and will lose their gradual
screw like arrangement. Therewith the LC layer loses also its
polarization rotating property at these locations such that the
light exiting the LC layer is now blocked by the analyzer at these
locations. Hence, driving the device in lensing mode, makes the
analyzer layer locally opaque for the light traveling through the
device. The locations relate to those where aberrations are the
largest, i.e. near the electrodes.
[0221] The described setup is particularly attractive for
application in lenticulars on pixel panel arrangements that emit
polarized light, such as an LCD display. The person skilled in the
art will then be able to arrange the LC material of the device and
the analyzer rotation such that the effect to be achieved is
obtained.
[0222] In the examples above, the use of two layers to change the
lens characteristics has been explained. The structure may have one
or both of these layers, and there may be other layers in the
structure not mentioned above. The lower layer (140) is for
reducing the lens strength and the upper layer is for compressing
the electric field. These approaches can be used independently to
obtain the desired change in the lens characteristics.
[0223] The first and second solid insulator layers can be a
photoresist. Alternatively, the insulator layers can comprise
laminates and PET foil layers or other organic/polymeric
layers.
[0224] Various modifications will be apparent to those skilled in
the art.
[0225] Summarizing, a beam shaping device (1; 31) comprising first
(3; 33) and second (4; 37) optically transparent substrates, a
liquid crystal layer (2; 36) sandwiched there between, and first
(5; 34) and second (6; 35) electrodes arranged on a side of the
liquid crystal layer (2; 36) facing the first substrate (3; 34).
The beam shaping device (1; 31) is controllable between
beam-shaping states, each permitting passage of light through the
beam-shaping device in a direction perpendicular thereto. The beam
shaping device (1; 31) is configured in such a way that application
of a voltage (V) across the first (5; 34) and second (6; 35)
electrodes results in an electric field having a portion
essentially parallel to the liquid crystal layer (2; 36) in a
segment thereof between neighboring portions of the electrodes (5,
6; 34; 35) and extending substantially from the first substrate (3;
34) to the second (4; 35) substrate. In this way a relatively high
refractive index gradient can be obtained across short distances,
which enables a very efficient beam shaping. The electric field can
be achieved by utilizing electrodes provided on one side of the
liquid crystal layer, in a so-called in-plane configuration. The
device can be used in an autostereoscopic display device, for
switching between 2D and 3D modes.
[0226] It should be noted that the above-mentioned modifications
and embodiments illustrate rather than limit the invention, and at
that those skilled in the art will be able to design many
alternative embodiments without departing from the scope of the
appended claims. In the claims, any reference signs placed between
parentheses shall not be construed as limiting the claim. The word
"comprising" does not exclude the presence of elements or steps
other than those listed in a claim. The word "a" or "an" preceding
an element does not exclude the presence of a plurality of such
elements. In the device claim enumerating several means, several of
these means may be embodied by one and the same item of hardware.
The mere fact that certain measures are recited in mutually
different dependent claims does not indicate that the combination
of these measures cannot be used to advantage.
* * * * *