U.S. patent application number 10/751488 was filed with the patent office on 2004-07-22 for display.
This patent application is currently assigned to HEWLETT-PACKARD CO.. Invention is credited to Klein, Susanne.
Application Number | 20040141105 10/751488 |
Document ID | / |
Family ID | 9909867 |
Filed Date | 2004-07-22 |
United States Patent
Application |
20040141105 |
Kind Code |
A1 |
Klein, Susanne |
July 22, 2004 |
Display
Abstract
The present invention relates to display, in particular to a
liquid crystal display illuminated by ambient light. The display
has a display area, and a light guide system for providing light to
the display area, the light guide system comprising: a planar light
guiding layer comprised of liquid crystal material and having a
light emitting surface and a plurality of side faces disposed
around the light emitting surface; a plurality of light pipes, each
light pipe having a collector end for collecting ambient light and
an output end, the output ends being arranged along the side faces
of the light guiding layer so as to introduce the collected light
into the guiding medium. The output ends of the light pipes are
distributed evenly along each side face of the light guiding layer
so as to provide homogeneous illumination to the display area.
Inventors: |
Klein, Susanne; (Bristol,
GB) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD
INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Assignee: |
HEWLETT-PACKARD CO.
|
Family ID: |
9909867 |
Appl. No.: |
10/751488 |
Filed: |
January 6, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10751488 |
Jan 6, 2004 |
|
|
|
10083505 |
Feb 27, 2002 |
|
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Current U.S.
Class: |
349/65 |
Current CPC
Class: |
G02B 6/0006 20130101;
G02B 6/0028 20130101; G02F 1/133618 20210101; Y10S 385/901
20130101; G02F 1/133615 20130101; G02F 1/133626 20210101 |
Class at
Publication: |
349/065 |
International
Class: |
G02F 001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 2001 |
GB |
0105206.7 |
Claims
What is claimed is:
1. A display comprising: a display area; and a light guide for
providing light to the display area, the light guide comprising: a
planar light guiding medium formed of liquid crystal material and
having a light emitting surface and one or more side faces disposed
around the light emitting surface; a plurality of light pipes, each
light pipe having a collector end for collecting light and an
output end, the output ends being arranged along the side faces so
as to introduce the collected light into the guiding medium;
wherein the output ends of the light pipes are distributed along
the or each side face.
2. A display as claimed in claim 1, wherein the collector ends of
the light pipes are distributed over a light collecting area and
wherein the position of the collector ends on the light collecting
area is scrambled relative to the position of the corresponding
output ends on the side faces of the light guiding medium.
3. A display as claimed in claim 1, wherein the light guiding
medium has a planar back surface, and wherein a reflecting layer is
provided on the back surface of the light guiding medium.
4. A display as claimed in claim 1, wherein: means are provided for
applying an electrical signal to the guiding medium in one or more
localised areas; and, the guiding medium is responsive to the
electrical signal such that the optical properties of the optical
medium are changed in each localised area where the electrical
signal is applied, with the result that in the localised areas
where the electrical signal is applied, light travelling along the
guiding medium exits the guiding medium through the light emitting
surface, and where the electrical signal is not applied, light
within the light guiding medium is channelled therealong.
5. A display as claimed in claim 4, wherein a quarter wave plate is
provided at the output of each light pipe.
6. A display as claimed in claim 1, wherein the light pipes are
formed from optic fibres.
7. A display comprising: a display area; a light guide for
providing light to the display area; and a plurality of electrodes
for addressing localised areas of the liquid crystal light guide,
wherein: the light guide comprises a planar light guiding medium
formed of liquid crystal material having a light emitting surface
and one or more side faces disposed around the light emitting
surface, a plurality of light pipes, each light pipe having a
collector end for collecting light and an output end, the output
ends being arranged along the side faces so as to introduce the
collected light into the guiding medium, wherein the output ends of
the light pipes are distributed along the or each side face; the
plurality of electrodes are adapted to apply a switching electric
field across the guiding medium at said localised areas such that
the optical properties of the optical medium are changed where the
switching electric field is applied such as to cause light
traveling along the guiding medium to exit the guiding medium
through the light emitting surface, whereas if the switching field
is not applied, light within the light guiding medium is channeled
therealong.
8. A light guide for providing light to a display area, comprising:
a planar light guiding medium being of a liquid crystal material
and having a light emitting surface and one or more side faces
disposed around the light emitting surface; a plurality of light
pipes, each light pipe having a collector end for collecting light
and an output end, the output ends being arranged along the side
faces so as to introduce the collected light into the guiding
medium; wherein the output ends of the light pipes are distributed
evenly along the or each side face.
Description
[0001] The present invention relates to display, in particular to a
liquid crystal display illuminated by ambient light.
[0002] Some displays, such as liquid crystal displays, can be lit
by a back light. The back light may need to be powerful,
particularly if the optical efficiency of the display is low.
Therefore, if the back light is part of a lap top computer or other
portable device, a heavy battery may be required to power the back
light, which may be inconvenient.
[0003] Displays are known that operate without a back light by
reflecting ambient light, the reflectivity of the display being
different at different points on the screen, so that reflected
light forms an image. However, a substantial amount of ambient
light incident on the display may be lost due to absorption within
the display. Furthermore, the user of the display may be tempted to
point the display in the direction where the ambient light is
strongest, which will lead to specular reflection of the ambient
light off the display, thereby making the display less
effective.
[0004] Another type of display which uses a planar waveguide to
provide light through a liquid crystal layer is disclosed in a
paper titled "waveguide Based Liquid Crystal Display," by H. Yuan
and P. Palffy-Muhoray, published in Mol. Cryst. Liq. Cryst., 1999,
Vol. 331, pp. 281-288. This uses total internal reflection between
the liquid crystal and one planar substrate that bounds the liquid
crystal, instead of birefringence between crossed polarizers. In
this planar waveguide lit display, one or more light sources must
then be provided to couple light into the waveguide, for example at
the periphery of a display. Light is then guided by the substrate
and then deflected out of activated areas of the liquid crystal.
This provides an efficient optical structure with a high viewing
angle. It may, however, be difficult to provide one or more light
sources around the periphery of the display to illuminate the
waveguide.
[0005] According to one aspect of the present invention, there is
provided a display having a display area, and a light guide for
providing light to the display area, the light guide
comprising:
[0006] a planar light guiding medium having a light emitting
surface and one or more side faces disposed around the light
emitting surface;
[0007] a plurality of light pipes, each light pipe having a
collector end for collecting light and an output end, the output
ends being arranged along the side faces so as to introduce the
collected light into the guiding medium;
[0008] wherein the output ends of the light pipes are distributed
along the or each side face.
[0009] The light pipes may then be distributed according to the
amount of light needed across the display, or in a particular area
of the display. In a preferred embodiment of the invention, the
light pipes are distributed evenly along the or each side face.
[0010] The light guiding medium will channel light therealong but
will allow some light to escape through the light emitting surface
to illuminate the display area. It will be understood that the term
planar light guiding medium will include a medium with some
curvature, provided that the curvature is sufficiently small that
to allow the guiding medium to channel light therein.
[0011] Because the output ends of the light pipes are distributed
evenly along the side faces of the light guiding medium, light will
be emitted from the light emitting surface more evenly. It will be
appreciated that the light pipes outputs need not be distributed at
the same intervals around all the side faces of the light guiding
medium, and that if the light guiding medium is rectangular, the
intervals between light pipe outputs along the long sides may be
different from the intervals along the short sides of the light
guiding medium.
[0012] Preferably, the collector ends of the light pipes will be
distributed in a spaced apart fashion over a light collecting area,
the position of the collector ends on the light collecting area
being scrambled relative to the position of the corresponding
output ends on the side faces of the light guiding medium. Because
of this, if a portion of the light collecting area is obscured, the
light emitted through the light emitting area will be diminished in
a more uniform manner, and the likelihood of a shadow being formed
in the display area will be reduced.
[0013] There may be some short range order between the positions of
the output ends and the positions corresponding light collector
ends. The light pipes may be grouped in pairs, the light output
ends of each pair being adjacent to one another on a side face, and
the collector ends of each pair being adjacent to one another on
the collecting area. However, a group of light pipes with
neighbouring or nearby collector ends will preferably have output
ends that are located on different portions of a side surface or,
on different side surfaces.
[0014] The light guiding medium will preferably have a planar back
surface, and a reflecting layer may be provided on the back surface
of the light guiding medium, so as to increase the amount of light
emitted through the light emitting surface.
[0015] In a preferred embodiment, means are provided for applying
an electrical signal to the guiding medium in one or more localised
areas, and the guiding medium is responsive to the electrical
signal such that the optical properties of the optical medium are
changed in each localised area where the electrical signal is
applied, with the result that in the localised areas where the
electrical signal is applied, light travelling along the guiding
medium exits the guiding medium through the light emitting surface,
and where the electrical signal is not applied, light within the
light guiding medium is channelled therealong.
[0016] An image can be formed by applying the electrical signal at
the points where the desired image is light, the remaining area of
the display appearing dark.
[0017] The electrical signal will preferably be in the form of a
voltage applied across the guiding medium, but the electrical
signal may superposed on a background voltage level, such that the
electrical signal at a point on the light guiding medium results in
the absence of a voltage being applied at that point.
[0018] The guiding medium may have a refractive index whose value
is changeable between a first value and a second value when an
electrical signal is applied, the guiding medium having an index
matching layer whose refractive index is close to the first value.
In one embodiment, the refractive index of the guiding medium will
be more closely matched to the refractive index of the index
matching layer at a point where an electrical signal is applied,
and light will be emitted through the light emitting layer at that
point. The light guiding medium will preferably be liquid crystal
material, since its refractive index for at least one polarisation
of light can easily be changed by applying an electric field.
[0019] So that the image produced by the screen can be viewed more
easily by a person in front of the screen, a light scattering layer
will preferably be provided between the light emitting surface and
the light guiding layer.
[0020] Since the liquid crystal material will normally be
birefringent, and since the refractive index for only one
polarisation of light may be changed between a fist value and a
second value by the electrical signal, a quarter wave plate or
other polarisation rotating element may be provided at each side
face of the light guiding medium, in order to increase the amount
of light which can be affected by the change in refractive index of
the liquid crystal material. A semi-reflecting mirror will
preferably be provided on the outer surface of each quarter wave
plate, so that light of one polarisation that is internally
incident on a side face will pass through a quarter wave plate a
first time, will be reflected by the semi-reflecting mirror, and
will then pass through the quarter wave plate a second time,
emerging from the quarter wave plate with a second
polarisation.
[0021] The collector ends of at least some of the light pipes may
be secured together in a bunch having a collector face, and means
may be provided for temporarily securing the bunch in an
orientation relative to the display area. If the ambient light from
a particular direction is particularly bright, a user will then be
able to orient the bunch such that the connector ends face in the
direction where the ambient light is bright, thereby increasing the
brightness of the screen. Alternatively, the end of the bunch may
be optically coupled to an electrical light source.
[0022] In a preferred embodiment, the display will be secured in a
casing, and the collector ends will be distributed over at least a
portion of the external surface of the casing. The display may be
secured to the casing of a lap top computer, or other portable
electronic device of the type having a display, such as a mobile
telephone.
[0023] The light pipes will preferably be formed from optic
fibres.
[0024] The invention will now be further described, by way of
example, with reference to the following drawings in which:
[0025] FIG. 1 shows a plan view of a display having optic fibre
with collector ends according to the invention;
[0026] FIG. 2 shows a front view of a laptop computer with the
display of FIG. 1, where the collector ends are distributed over
the external surface of the laptop casing;
[0027] FIG. 3 shows a back view of the laptop computer of FIG.
2;
[0028] FIG. 4 shows a laptop computer with the display of FIG. 1,
where the optic fibres are secured together in a bundle;
[0029] FIG. 5 shows a cross sectional view of the display in FIG. 1
in one embodiment; and,
[0030] FIG. 6 shows a cross sectional view of a portion of the
display in FIG. 1, in another embodiment.
[0031] In FIG. 1, there is shown a display 10 having a display area
12 bounded by four sides 13a, 13b, 13c, 13d. A plurality of optic
fibres 14 are provided for guiding light towards the display area
12. Each fibre 14 has a collector end 18 through which light can
enter the fibre 14 and a light output end 16 through which the
collected light exits the fibre 14.
[0032] In FIGS. 2 and 3, there is shown an electronic device, here
a laptop computer 20 with the display 10 mounted in the casing 22
of the computer 20. The casing 22 has a plurality of apertures 24,
in each of which there is mounted the collector end 18 of an optic
fibre 14. Ambient light incident on the casing 20 of the computer
is directed by the optic fibres 14 onto the display area 12 of the
display 10.
[0033] The collector ends 18 of the fibres 14 are distributed on
the casing 18 such that there is no relationship between the
position of the output ends 16 and the position of the collector
ends 18. Collector ends 18 which lie close together, for example
within the dashed loop 26 in FIG. 3, will have corresponding output
ends 16 which are located on different sides of the display area
12. If the collector ends 18 within the dashed loop are obscured,
for example by a nearby object or a human hand, the light exiting
the display area 12 will be uniformly diminished, rather than a
shadow being formed on the display area 12.
[0034] In an embodiment shown in FIG. 4, at least some of the
fibres 14 are bunched together in a semi-rigid cladding 64
extending from the casing 22. At one end of the cladding 64, the
collector ends 18 form a bunch 70 having a collecting surface 72,
the other end of the cladding 64 being secured to the casing 22. If
the ambient light is strongest in one direction, the collecting
surface 72 can be oriented in that direction in order to increase
the amount of light provided to the display 12, and the semi-rigid
cladding will support the collecting surface 72 in that
orientation.
[0035] In FIG. 5, there is shown, schematically, a cross sectional
view through the display 10. The display 10 has a layer of liquid
crystal (LC) material 30. A plurality of transparent upper address
lines 42 and lower address lines 43 are respectively provided above
and below the LC layer 30 in order to apply an electric field in at
least one localised area of the LC layer 30. An upper planarizing
layer 46 is provided between the upper address lines 42 and the LC
layer 30, and a lower planarizing layer 48 is provided between the
LC layer 30 and the lower address lines 43. A layer of glass 50 is
provided above the upper address lines 42, the outer surface 52 of
the glass layer acting as a light emitting surface.
[0036] Where an electric field is not applied to the LC layer,
light is channelled by the LC layer 30 such that is propagates
along the layer 30 by undergoing multiple total internal
reflections at the interfaces 54, 56 between the LC layer 30 and
the upper and lower planarizing layers 46, 48 respectively. In a
localised region 60 where an electric field is applied by a voltage
across the address lines 42, 43, the refractive index of the LC
layer 30 is changed, such that total internal reflection no longer
occurs at the upper boundary 54 and the lower boundary 56, and in
that localised region 60, light exits the LC layer 30 and reaches
the light emitting surface 52, thereby forming a bright region in
the display area 12. A mirror 62 is provided below the lower
address lines 43 so that light that leaves the LC layer through the
lower boundary 56 is reflected back up, through the LC layer 30,
and through the light emitting surface 52.
[0037] The glass layer 50 and/or the upper planarizing layer 46
will scatter the light passing therethrough, so that at least some
of the light leaving the light emitting surface 52 leaves the
surface in a normal or near normal direction.
[0038] The LC layer 30 has a four side faces 15a, 15b, 15c, 15d,
against each of which there lies a quarter wave plate 44 followed
by a semi-reflective mirror 47. The output end 16 of each fibre
lies against a semi-reflective mirror, facing towards a side face
of the LC layer 30. Light exiting the output end 16 of a fibre 14
first passes through the semi-reflecting mirror 47, and then though
the quarter wave plate 44, and into the LC layer 30.
[0039] Light that has travelled across the LC layer 30 will be
reflected at least in part by a semi-reflected mirror 47, passing
twice through the quarter wave plate 44 before marking a further
pass through the LC layer 30. The quarter wave plate 44 will rotate
the polarisation of the light passing therethrough, in order to
increase the amount of light emitted through the light emitting
surface 52 if the refractive index of the LC layer 30 is only
changeable for one polarisation of light.
[0040] In another embodiment, shown schematically in FIG. 6, the
output end 16 of each fibre 14 passes through an aperture 66 in the
quarter wave plate layer 44, such that light entering the LC layer
30 from the optic fibre 14 does not pass through the quarter wave
plate layer.
[0041] It will be appreciated from the above description that the
present invention provides a simple and compact way of collecting
ambient light in order to illuminate a portable display, thereby
reducing the need for a battery powered light source.
* * * * *