U.S. patent application number 09/726131 was filed with the patent office on 2002-05-30 for color filtering and absorbing total internal reflection image display.
Invention is credited to Mossman, Michele Ann, Whitehead, Lorne A..
Application Number | 20020063963 09/726131 |
Document ID | / |
Family ID | 24917369 |
Filed Date | 2002-05-30 |
United States Patent
Application |
20020063963 |
Kind Code |
A1 |
Whitehead, Lorne A. ; et
al. |
May 30, 2002 |
COLOR FILTERING AND ABSORBING TOTAL INTERNAL REFLECTION IMAGE
DISPLAY
Abstract
A color image display having a spatially uniform distribution of
at least two different "types" of prism structure. The first type
consists of a prism, a color filter associated with one of the
prism's facets and two color absorbing control members, each of
which can be biased away from or into optical contact with one of
the prism's other two facets. The color filter has a first spectral
absorption characteristic, and the control members have second and
third spectral absorption characteristics respectively. The second
type of prism structure consists of a second prism, a color filter
associated with one of the second prism's facets and at least one
color absorbing control member which can be biased away from or
into optical contact with one of the second prism's other two
facets. The second prism's color filter and control member have
fourth and fifth spectral absorption characteristics respectively.
The spectral absorption characteristics are selected such that, for
any selected set comprising proximate ones of each of the two types
of prism structure, controlled movement of the members between
particular selected combinations of their possible respective
positions causes the set as a whole to reflect light which has an
average spectral reflectance characteristic corresponding to any
one of three independent colors, with no one of the independent
colors being obtainable by mixing any other two of the independent
colors.
Inventors: |
Whitehead, Lorne A.;
(Vancouver, CA) ; Mossman, Michele Ann;
(Vancouver, CA) |
Correspondence
Address: |
OYEN, WIGGS, GREEN & MUTALA
480 - THE STATION
601 WEST CORDOVA STREET
VANCOUVER
BC
V6B 1G1
CA
|
Family ID: |
24917369 |
Appl. No.: |
09/726131 |
Filed: |
November 30, 2000 |
Current U.S.
Class: |
359/619 ;
359/625 |
Current CPC
Class: |
G02F 1/167 20130101;
G02F 1/195 20130101; G02F 1/1677 20190101; G02B 5/045 20130101;
G02B 26/02 20130101; G02F 2203/026 20130101 |
Class at
Publication: |
359/619 ;
359/625 |
International
Class: |
G02B 027/10 |
Claims
What is claimed is:
1. Color display apparatus comprising a spatially uniform
distribution of at least first and second types of prism structure,
wherein: (a) said first type of prism structure further comprises:
(i) a first prism; (ii) a first color filter positioned to filter
light incident upon a first facet of said first prism, said first
color filter having a first selected spectral absorption
characteristic; (iii) a first member having a second selected
spectral absorption characteristic, said first member movable with
respect to a second facet of said first prism between: (1) a first
position in which said first member is in optical contact with said
second facet, producing a first absorptive state in which total
internal reflection of light rays at said second facet is reduced
as a function of wavelength in accordance with said second selected
spectral absorption characteristic; (2) a second position in which
said first member is not in optical contact with said second facet,
producing a first reflective state in which light incident upon
said second facet is totally internally reflected toward a third
facet of said first prism; (iv) a second member having a third
selected spectral absorption characteristic, said first member
movable with respect to said third facet of said first prism
between: (1) a third position in which said second member is in
optical contact with said third facet, producing a second
absorptive state in which total internal reflection of light rays
at said third facet is reduced as a function of wavelength in
accordance with said third selected spectral absorption
characteristic; (2) a fourth position in which said second member
is not in optical contact with said third facet, producing a second
reflective state in which light incident upon said third facet is
totally internally reflected toward and through said first color
filter; (b) said second type of prism structure further comprises:
(i) a second prism; (ii) a second color filter positioned to filter
light incident upon a first facet of said second prism, said second
color filter having a fourth selected spectral absorption
characteristic; (iii) a third member having a fifth selected
spectral absorption characteristic, said third member movable with
respect to a second facet of said second prism between: (1) a fifth
position in which said third member is in optical contact with said
second facet of said second prism, producing a third absorptive
state in which total internal reflection of light rays at said
second facet of said second prism is reduced as a function of
wavelength in accordance with said fifth selected spectral
absorption characteristic; (2) a sixth position in which said third
member is not in optical contact with said second facet of said
second prism, producing a third reflective state in which light
incident upon said second facet of said second prism is totally
internally reflected at said second facet of said second prism; (c)
said spectral absorption characteristics are selected such that,
for any selected set comprising proximate ones of all of said types
of prism structure, controlled movement of said members between
particular selected combinations of said respective positions
causes said set to reflect light having an average spectral
reflectance characteristic corresponding to any one of three
independent colors; and, (d) no one of said independent colors is
obtainable by mixing any other two of said independent colors.
2. Color display apparatus as defined in claim 1, wherein: (a) each
one of said first types of prism structure is longitudinally
adjacent to one of said second types of prism structure; and, (b)
each one of said second types of prism structure is longitudinally
adjacent to one of said first types of prism structure.
3. Color display apparatus as defined in claim 1, wherein: (a) said
second type of prism structure further comprises: (i) a fourth
member having a sixth selected spectral absorption characteristic,
said fourth member movable with respect to a third facet of said
second prism between: (1) a seventh position in which said fourth
member is in optical contact with said third facet of said second
prism, producing a fourth absorptive state in which total internal
reflection of light rays at said third facet of said second prism
is reduced as a function of wavelength in accordance with said
sixth selected spectral absorption characteristic; (2) an eighth
position in which said fourth member is not in optical contact with
said third facet of said second prism, producing a fourth
reflective state in which light incident upon said third facet of
said second prism is totally internally reflected toward and
through said second color filter; (b) said spatially uniform
distribution further comprises a third type of prism structure,
said third type of prism structure further comprising: (i) a third
prism; (ii) a third color filter positioned to filter light
incident upon a first facet of said third prism, said third color
filter having a seventh selected spectral absorption
characteristic; (iii) a fifth member having an eighth selected
spectral absorption characteristic, said fifth member movable with
respect to a second facet of said third prism between: (1) a ninth
position in which said fifth member is in optical contact with said
second facet of said third prism, producing a fifth absorptive
state in which total internal reflection of light rays at said
second facet of said third prism is reduced as a function of
wavelength in accordance with said eighth selected spectral
absorption characteristic; (2) a tenth position in which said fifth
member is not in optical contact with said second facet of said
third prism, producing a fifth reflective state in which light
incident upon said second facet of said third prism is totally
internally reflected toward a third facet of said third prism; (iv)
a sixth member having a ninth selected spectral absorption
characteristic, said sixth member movable with respect to a third
facet of said third prism between: (1) an eleventh position in
which said sixth member is in optical contact with said third facet
of said third prism, producing a sixth absorptive state in which
total internal reflection of light rays at said third facet of said
third prism is reduced as a function of wavelength in accordance
with said ninth selected spectral absorption characteristic; and,
(2) a twelfth position in which said sixth member is not in optical
contact with said third facet of said third prism, producing a
sixth reflective state in which light incident upon said third
facet of said third prism is totally internally reflected toward
and through said third color filter.
4. Color display apparatus as defined in claim 3, wherein said
first spectral characteristic further comprises a first primary
color, said fourth spectral characteristic further comprises a
second primary color, and said seventh spectral characteristic
further comprises a third primary color.
5. Color display apparatus as defined in claim 4, wherein said
first, second and third primary colors are subtractive primary
colors.
6. Color display apparatus as defined in claim 4, wherein said
second spectral characteristic further comprises said second
primary color, said third spectral characteristic further comprises
said third primary color, said fifth spectral characteristic
further comprises said third primary color, said sixth spectral
characteristic further comprises said first primary color, said
eighth spectral characteristic further comprises said first primary
color, and said ninth spectral characteristic further comprises
said second primary color.
7. Color display apparatus as defined in claim 1, wherein: (a) said
first member further comprises a first plurality of absorptive
particles suspended in an electrophoretic medium contacting said
second facet of said first prism; (b) said second member further
comprises a second plurality of absorptive particles suspended in
an electrophoretic medium contacting said third facet of said first
prism; and, (c) said third member further comprises a third
plurality of absorptive particles suspended in an electrophoretic
medium contacting said second facet of said second prism.
8. Color display apparatus as defined in claim 3, wherein: (a) said
first member further comprises a first plurality of absorptive
particles suspended in an electrophoretic medium contacting said
second facet of said first prism; (b) said second member further
comprises a second plurality of absorptive particles suspended in
an electrophoretic medium contacting said third facet of said first
prism; (c) said third member further comprises a third plurality of
absorptive particles suspended in an electrophoretic medium
contacting said second facet of said second prism; (d) said fourth
member further comprises a fourth plurality of absorptive particles
suspended in an electrophoretic medium contacting said third facet
of said second prism; (e) said fifth member further comprises a
fifth plurality of absorptive particles suspended in an
electrophoretic medium contacting said second facet of said third
prism; and, (f) said sixth member further comprises a sixth
plurality of absorptive particles suspended in an electrophoretic
medium contacting said third facet of said third prism.
9. Color display apparatus as defined in claim 3, wherein: (a) said
first member and said sixth member of another one of said third
type of prism structure adjacent to said first type of prism
structure together comprise a first plurality of absorptive
particles suspended in an electrophoretic medium contacting said
second facet of said first prism; (b) said second member and said
third member together comprise a second plurality of absorptive
particles suspended in an electrophoretic medium contacting said
third facet of said first prism and contacting said second facet of
said second prism; and, (c) said fourth member and said fifth
member together comprise a third plurality of absorptive particles
suspended in an electrophoretic medium contacting said third facet
of said second prism and contacting said second facet of said third
prism.
10. Color display apparatus as defined in claim 1, wherein said
first, second and third members each further comprise a deformable
elastomeric member.
11. Color display apparatus as defined in claim 3, wherein said
first, second, third, fourth, fifth and sixth members each further
comprise a deformable elastomeric member.
12. Color display apparatus as defined in claim 11, wherein said
second member and said third member together comprise one of said
deformable elastomeric members and fourth member and said fifth
member together comprise another one of said deformable elastomeric
members.
13. Color display apparatus as defined in claim 1, wherein said
first facets of said first and second prisms collectively comprise
a viewing surface, said apparatus further comprising: (a) a
substrate extending substantially parallel to said viewing surface;
(b) a first electrode on said second and third facets of each of
said first and second prisms; (c) a second electrode on said
substrate adjacent said second facet of said first prism; (d) a
third electrode on said substrate adjacent said third facet of said
first prism; (e) a fourth electrode on said substrate adjacent said
second facet of said second prism; said apparatus further
comprising a voltage source for selectably applying: (i) a first
voltage potential between said first and second electrodes to move
said first member into said first position; (ii) a second voltage
potential between said first and second electrodes to move said
first member into said second position; (iii) a third voltage
potential between said first and third electrodes to move said
second member into said third position; (iv) a fourth voltage
potential between said first and third electrodes to move said
second member into said fourth position; (v) a fifth voltage
potential between said first and fourth electrodes to move said
third member into said fifth position; and, (vi) a sixth voltage
potential between said first and fourth electrodes to move said
third member into said sixth position.
14. Color display apparatus as defined in claim 3, wherein said
first facets of said first, second and third prisms collectively
comprise a viewing surface, said apparatus further comprising: (a)
a substrate extending substantially parallel to said viewing
surface; (b) a first electrode on said second and third facets of
each of said first, second and third prisms; (c) a second electrode
on said substrate adjacent said second facet of said first prism;
(d) a third electrode on said substrate adjacent said third facet
of said first prism; (e) a fourth electrode on said substrate
adjacent said second facet of said second prism; (f) a fifth
electrode on said substrate adjacent said third facet of said
second prism; (g) a sixth electrode on said substrate adjacent said
second facet of said third prism; (h) a seventh electrode on said
substrate adjacent said third facet of said third prism; said
apparatus further comprising a voltage source for selectably
applying: (i) a first voltage potential between said first and
second electrodes to move said first member into said first
position; (ii) a second voltage potential between said first and
second electrodes to move said first member into said second
position; (iii) a third voltage potential between said first and
third electrodes to move said second member into said third
position; (iv) a fourth voltage potential between said first and
third electrodes to move said second member into said fourth
position; (v) a fifth voltage potential between said first and
fourth electrodes to move said third member into said fifth
position; (vi) a sixth voltage potential between said first and
fourth electrodes to move said third member into said sixth
position; (vii) a seventh voltage potential between said first and
fifth electrodes to move said fourth member into said seventh
position; (viii) an eighth voltage potential between said first and
sixth electrodes to move said fifth member into said ninth
position; and, (ix) a tenth voltage potential between said first
and seventh electrodes to move said sixth member into said eleventh
position.
15. Color display apparatus as defined in claim 1, wherein said
color filters are formed on said first facets of said respective
prisms.
16. Color display apparatus as defined in claim 1, wherein said
color filters are formed within said first facets of said
respective prisms.
17. Color display apparatus as defined in claim 3, wherein said
color filters are formed on said first facets of said respective
prisms.
18. Color display apparatus as defined in claim 3, wherein said
color filters are formed within said first facets of said
respective prisms.
19. Color display apparatus as defined in claim 7, wherein said
electrophoretic medium is Fluorinert.
20. Color display apparatus as defined in claim 8, wherein said
electrophoretic medium is Fluorinert.
21. Color display apparatus as defined in claim 1, wherein said
prisms are formed of zinc sulphide.
22. Color display apparatus as defined in claim 3, wherein said
prisms are formed of zinc sulphide.
23. Color display apparatus as defined in claim 10, wherein said
elastomer members have stiff surfaces.
24. Color display apparatus as defined in claim 11, wherein said
elastomer members have stiff surfaces.
25. Color display apparatus as defined in claim 7, wherein: (a)
said first plurality of absorptive particles suspended in said
electrophoretic medium are confined within a first channel formed
adjacent said second facet of said first prism; (b) said second
plurality of absorptive particles suspended in said electrophoretic
medium are confined within a second channel formed adjacent said
third facet of said first prism; and, (c) said third plurality of
absorptive particles suspended in said electrophoretic medium are
confined within a third channel formed adjacent said second facet
of said second prism.
26. Color display apparatus as defined in claim 8, wherein: (a)
said first and said sixth plurality of absorptive particles
suspended in said electrophoretic medium are confined together
within a first channel formed adjacent said second facet of said
first prism and adjacent said third facet of said third prism of
another one of said third type of prism structure adjacent to said
first type of prism structure; (b) said second and said third
plurality of absorptive particles suspended in said electrophoretic
medium are confined together within a second channel formed
adjacent said third facet of said first prism and adjacent said
second facet of said second prism; and, (c) said fourth and said
fifth plurality of absorptive particles suspended in said
electrophoretic medium are confined together within a third channel
formed adjacent said second facet of said third prism and adjacent
said second facet of said third prism.
27. Color display apparatus as defined in claim 7, wherein: (a)
said first plurality of absorptive particles suspended in said
electrophoretic medium are distributed among and confined within a
first plurality of compartments formed along and adjacent said
second facet of said first prism; (b) said second plurality of
absorptive particles suspended in said electrophoretic medium are
distributed among and confined within a second plurality of
compartments formed along and adjacent said third facet of said
first prism; and, (c) said third plurality of absorptive particles
suspended in said electrophoretic medium are distributed among and
confined within a third plurality of compartments formed along and
adjacent said second facet of said second prism.
28. Color display apparatus as defined in claim 8, wherein: (a)
said first and sixth plurality of absorptive particles suspended in
said electrophoretic medium are distributed among and confined
together within a first plurality of compartments formed along and
adjacent said second facet of said first prism and adjacent said
third facet of said third prism of another one of said third type
of prism structure adjacent to said first type of prism structure;
(b) said second and third plurality of absorptive particles
suspended in said electrophoretic medium are distributed among and
confined together within a second plurality of compartments formed
along and adjacent said third facet of said first prism and along
and adjacent said second facet of said second prism; and, (c) said
fourth and fifth plurality of absorptive particles suspended in
said electrophoretic medium are distributed among and confined
together within a third plurality of compartments formed along and
adjacent said second facet of said third prism and along and
adjacent said second facet of said third prism.
29. A color image display method, comprising filtering and totally
internally reflecting light at each one of a plurality of at least
first and second types of spatially uniform distributed locations,
said method further comprising: (a) at each one of said first type
of said locations: (i) filtering incident light through a first
facet of a first prism to absorb a first selected spectral
component of said incident light and reflect toward a second facet
of said first prism a first light ray lacking said first spectral
component; (ii) selectably absorbing a second selected spectral
component of said first light ray at said second facet of said
first prism and totally internally reflecting toward a third facet
of said first prism a second light ray lacking said first spectral
component and selectably lacking said second spectral component;
(iii) selectably absorbing a third selected spectral component of
said second light ray at said third facet of said first prism and
totally internally reflecting toward and through said first facet
of said first prism a third light ray lacking said first spectral
component and selectably lacking said second spectral component and
selectably lacking said third spectral component; (b) at each one
of said second type of said locations: (i) filtering said incident
light through a first facet of a second prism to absorb a fourth
selected spectral component of said incident light and reflect
toward a second facet of said second prism a fourth light ray
lacking said fourth spectral component; (ii) selectably absorbing a
fifth selected spectral component of said fourth light ray at
either one or both of: (1) said second facet of said second prism;
(2) a third facet of said second prism; to produce a fifth light
ray lacking said fourth spectral component and selectably lacking
said fifth spectral component; (iii) at said second facet of said
second prism, totally internally reflecting said either one of said
fourth or fifth light rays toward said third facet of said second
prism; (iv) at said third facet of said second prism, totally
internally reflecting said fifth light ray toward and through said
first facet of said second prism; wherein: (v) said spectral
components are selected such that, for any selected set comprising
proximate ones of all of said types of locations, particular
selected combinations of said selectably absorbing of said spectral
components causes said set to reflect light having an average
spectral reflectance characteristic corresponding to any one of
three independent colors; and, (vi) no one of said independent
colors is obtainable by mixing any other two of said independent
colors.
30. A method as defined in claim 29, wherein: (a) said fifth
selected spectral component of said fourth light ray is selectably
absorbed at said second facet of said second prism and totally
internally reflecting toward said third facet of said second prism
as said fifth light ray; (b) said spatially uniform distributed
locations further comprising a third type of location; said method
further comprising: (i) selectably absorbing a sixth selected
spectral component of said fifth light ray at said third facet of
said second prism and totally internally reflecting toward and
through said first facet of said second prism a sixth light ray
lacking said fourth spectral component and selectably lacking said
fifth spectral component and selectably lacking said sixth spectral
component; (c) at each one of said third type of said locations:
(i) filtering said incident light through a first facet of a third
prism to absorb a seventh selected spectral component of said
incident light and reflect toward a second facet of said third
prism a seventh light ray lacking said seventh spectral component;
(ii) selectably absorbing an eighth selected spectral component of
said seventh light ray at said second facet of said third prism and
totally internally reflecting toward a third facet of said third
prism an eighth light ray lacking said seventh spectral component
and selectably lacking said eighth spectral component; and, (iii)
selectably absorbing a ninth selected spectral component of said
eighth light ray at said third facet of said third prism and
totally internally reflecting toward and through said first facet
of said third prism a ninth light ray lacking said seventh spectral
component and selectably lacking said eighth spectral component and
selectably lacking said ninth spectral component.
31. A method as defined in claim 30, wherein said first spectral
component further comprises a first primary color, said fourth
spectral component further comprises a second primary color, and
said seventh spectral component further comprises a third primary
color.
32. A method as defined in claim 31, wherein said first, second and
third primary colors are subtractive primary colors.
33. A method as defined in claim 32, wherein said second spectral
component further comprises said second primary color, said third
spectral component further comprises said third primary color, said
fifth spectral component further comprises said third primary
color, said sixth spectral component further comprises said first
primary color, said eighth spectral component further comprises
said first primary color, and said ninth spectral component further
comprises said second primary color.
34. A method as defined in claim 29, wherein: (a) said selectably
absorbing said second selected spectral component further comprises
electrophoretically moving a first plurality of absorptive
particles into optical contact with said second facet of said first
prism; (b) said selectably absorbing said third selected spectral
component further comprises electrophoretically moving a second
plurality of absorptive particles into optical contact with said
third facet of said first prism; and, (c) said selectably absorbing
said fifth selected spectral component further comprises
electrophoretically moving a third plurality of absorptive
particles into optical contact with said second facet of said
second prism.
35. A method as defined in claim 30, wherein: (a) said selectably
absorbing said second selected spectral component further comprises
electrophoretically moving a first plurality of absorptive
particles into optical contact with said second facet of said first
prism; (b) said selectably absorbing said third selected spectral
component further comprises electrophoretically moving a second
plurality of absorptive particles into optical contact with said
third facet of said first prism; (c) said selectably absorbing said
fifth selected spectral component further comprises
electrophoretically moving a third plurality of absorptive
particles into optical contact with said second facet of said
second prism; (d) said selectably absorbing said sixth selected
spectral component further comprises electrophoretically moving a
fourth plurality of absorptive particles into optical contact with
said second facet of said second prism; (e) said selectably
absorbing said eighth selected spectral component further comprises
electrophoretically moving a fifth plurality of absorptive
particles into optical contact with said second facet of said third
prism; and, (f) said selectably absorbing said ninth selected
spectral component further comprises electrophoretically moving a
sixth plurality of absorptive particles into optical contact with
said second facet of said third prism.
36. A method as defined in claim 29, wherein: (a) said selectably
absorbing said second selected spectral component further comprises
moving a first elastomeric member into optical contact with said
second facet of said first prism; (b) said selectably absorbing
said third selected spectral component further comprises moving a
second elastomeric member into optical contact with said third
facet of said first prism; and, (c) said selectably absorbing said
fifth selected spectral component further comprises moving a third
elastomeric member into optical contact with said second facet of
said second prism.
37. A method as defined in claim 30, wherein: (a) said selectably
absorbing said second selected spectral component further comprises
moving a first elastomeric member into optical contact with said
second facet of said first prism; (b) said selectably absorbing
said third selected spectral component further comprises moving a
second elastomeric member into optical contact with said third
facet of said first prism; (c) said selectably absorbing said fifth
selected spectral component further comprises moving a third
elastomeric member into optical contact with said second facet of
said second prism; (d) said selectably absorbing said sixth
selected spectral component further comprises moving a fourth
elastomeric member into optical contact with said second facet of
said second prism; (e) said selectably absorbing said eighth
selected spectral component further comprises moving a fifth
elastomeric member into optical contact with said second facet of
said second prism; and, (f) said selectably absorbing said ninth
selected spectral component further comprises moving a sixth
elastomeric member into optical contact with said second facet of
said third prism.
38. A method as defined in claim 34, further comprising: (a)
forming a first channel adjacent said second facet of said first
prism, placing an electrophoretic medium in said first channel, and
suspending said first plurality of absorptive particles in said
electrophoretic medium within said first channel; (b) forming a
second channel adjacent said third facet of said first prism,
placing an electrophoretic medium in said second channel, and
suspending said second plurality of absorptive particles in said
electrophoretic medium within said second channel; and, (c) forming
a third channel adjacent said second facet of said second prism,
placing an electrophoretic medium in said third channel, and
suspending said third plurality of absorptive particles in said
electrophoretic medium within said third channel.
39. A method as defined in claim 35, further comprising: (a)
forming a first channel adjacent said second facet of said first
prism and adjacent said third facet of said third prism, placing an
electrophoretic medium in said first channel, and suspending said
first and sixth plurality of absorptive particles together in said
electrophoretic medium within said first channel; (b) forming a
second channel adjacent said third facet of said first prism and
adjacent said second facet of said second prism, placing an
electrophoretic medium in said second channel, and suspending said
second and said third plurality of absorptive particles together in
said electrophoretic medium within said second channel; and, (c)
forming a third channel adjacent said third facet of said second
prism and adjacent said second facet of said third prism, placing
an electrophoretic medium in said third channel, and suspending
said fourth and said fifth plurality of absorptive particles
together in said electrophoretic medium within said third
channel.
40. A method as defined in claim 34, further comprising: (a)
forming a first plurality of compartments along and adjacent said
second facet of said first prism, placing an electrophoretic medium
in each of said first plurality of compartments, and suspending
said first plurality of absorptive particles in said
electrophoretic medium within each of said first plurality of
compartments; (b) forming a second plurality of compartments along
and adjacent said third facet of said second prism, placing an
electrophoretic medium in each of said second plurality of
compartments, and suspending said second plurality of absorptive
particles in said electrophoretic medium within each of said second
plurality of compartments; and, (c) forming a third plurality of
compartments along and adjacent said second facet of said second
prism, placing an electrophoretic medium in each of said third
plurality of compartments, and suspending said third plurality of
absorptive particles in said electrophoretic medium within each of
said third plurality of compartments.
41. A method as defined in claim 35, further comprising: (a)
forming a first plurality of compartments along and adjacent said
second facet of said first prism and along and adjacent said third
facet of said third prism, placing an electrophoretic medium in
each of said first plurality of compartments, and suspending said
first and sixth plurality of absorptive particles together in said
electrophoretic medium within each of said first plurality of
compartments; (b) forming a second plurality of compartments along
and adjacent said third facet of said second prism and along and
adjacent said second facet of said second prism, placing an
electrophoretic medium in each of said second plurality of
compartments, and suspending said second and third plurality of
absorptive particles together in said electrophoretic medium within
each of said second plurality of compartments; and, (c) forming a
third plurality of compartments along and adjacent said third facet
of said second prism and along and adjacent said second facet of
said third prism, placing an electrophoretic medium in each of said
third plurality of compartments, and suspending said fourth and
fifth plurality of absorptive particles together in said
electrophoretic medium within each of said third plurality of
compartments.
Description
TECHNICAL FIELD
[0001] A reflective display device in which total internal
reflection is twice controllably frustrated at an interface between
materials having different refractive indices and in which
subtractive color filtration is employed to yield full color
images.
BACKGROUND
[0002] U.S. Pat. No. 5,959,777 (the '777 patent, which is
incorporated herein by reference) titled "Passive High Efficiency
Variable Reflectivity Image Display Device" and issued Sep. 28,
1999 discloses a multiple pixel image display device. Each pixel
has at least one element having a reflective state in which
incident light undergoes total internal reflection ("TIR"), and
having a non-reflective state in which TIR is prevented (i.e.
"frustrated"). Such prevention is achieved by modifying the
evanescent wave associated with TIR. Specifically, a member is
positioned adjacent the element and deformed between first and
second positions. In the first position, a gap remains between the
member and the element to allow the evanescent wave to have the
usual characteristics for TIR. In the second position, the member
is in optical contact with the element (that is, the gap thickness
is substantially less than an optical wavelength), substantially
interfering with the evanescent wave, thus preventing TIR.
[0003] U.S. Pat. No. 5,999,307 (the '307 patent, which is
incorporated herein by reference) titled "Method and Apparatus for
Controllable Frustration of Total Internal Reflection" and issued
Dec. 7, 1999 discloses controllable switching of a TIR interface by
means of an electronically actuated, micro-structured, elastomer
member to controllably deform the member into optical contact with
the interface, within a continuously variable range of optical
contact values, to produce the non-reflective state.
[0004] U.S. Pat. No. 6,064,784 (the '784 patent, which is
incorporated herein by reference) titled "Electrophoretic, Dual
Refraction Frustration of Total Internal Reflection in High
Efficiency Variable Reflectivity Image Displays" and issued May 16,
2000 discloses that an electrophoretic medium can be used to
controllably frustrate TIR in an image display device employing
prismatic reflective surfaces. "Electrophoresis" is a well known
phenomenon whereby a charged species (i.e. particles, ions or
molecules) moves through a medium due to the influence of an
applied electric field.
[0005] U.S. patent application Ser. No. 09/324,103 (the '103
application, which is incorporated herein by reference) filed Jun.
2, 1999 and titled "Electrophoretic, High Index and Phase
Transition Control of Total Internal Reflection in High Efficiency
Variable Reflectivity Image Displays", discloses usage of charged
particles suspended in a medium to electrophoretically control TIR
at a retro-reflective surface on a high refractive index material;
usage of a prismatic structure to redirect ambient light from an
overhead light source toward a display image and then from the
image to the viewing region in front of the image, yielding a high
contrast reflective display; usage of a transparent planar
waveguide to frontlight a color display; control of TIR at a
retro-reflective surface by means of a vapour-liquid phase
transition; and, control of TIR by changing the absorption
coefficient of a material using electrical, chemical and/or
electrochemical methods.
[0006] U.S. patent application Ser. No. 09/449,756 (the '756
application, which is incorporated herein by reference) filed Nov.
26, 1999 and titled "Optical Switching by Controllable Frustration
of Total Internal Reflection" discloses an optical switch for
controllably switching a TIR interface between reflective and
non-reflective states. In one embodiment, the switch has a
stiff-surfaced elastomer dielectric. A separator maintains a gap
between the TIR interface and the dielectric's surface. Variation
of a voltage applied between electrodes on the interface and the
dielectric's surface moves the stiffened surface portion into or
away from optical contact with the TIR interface. In another
embodiment, the optical switch incorporates a cell containing a
fluid. One side of the cell forms a light incident interface. A
membrane is suspended in the fluid. One pair of electrodes is
applied to opposite sides of the membrane; and, another electrode
pair is applied to the side of the cell forming the interface and
to the cell's opposite side, A variable voltage potential is
applied between selected ones of the electrodes. Application of the
voltage potential between selected ones of the membrane and cell
electrodes moves the membrane into optical contact with the
interface, producing the non-reflective state at the interface.
Application of the voltage potential between other selected ones of
the membrane and cell electrodes moves the membrane away from
optical contact with the interface, producing the reflective state
at the interface.
[0007] U.S. patent application Ser. No. 09/585,552 (the '552
application , which is incorporated herein by reference) filed Jun.
2, 2000 and titled "Enhanced Effective Refractive Index Total
Internal Reflection Image Display", discloses an image display with
parallel, macroscopically planar, structured surface, non-light
absorptive light deflecting and reflecting portions which are
longitudinally symmetrical in mutually perpendicular directions,
both of which are perpendicular to the preferred viewing direction.
A liquid containing a plurality of movable members contacts the
light reflecting portion. A controller applies an electromagnetic
force to selectively move the members into an evanescent wave
region adjacent the light reflecting portion to frustrate TIR of
light rays at selected points on the light reflecting portion. The
structured surfaces on the light deflecting portion deflect light
rays incident in the preferred viewing direction toward the light
reflecting portion by imparting to the rays a directional component
in the direction of longitudinal symmetry of the light reflecting
portion. The structured surfaces on the light reflecting portion
totally internally reflect the deflected light rays toward the
light deflecting portion at points other than the selected points
at which TIR is frustrated. Then, the structured surfaces on the
light deflecting portion again deflect the totally internally
reflected light rays, cancelling the directional component
therefrom, such that the deflected totally internally reflected
light rays emerge from the display in a direction substantially
parallel to the preferred viewing direction.
[0008] The present invention improves upon the prior art by
facilitating production of color displays.
SUMMARY OF INVENTION
[0009] The invention provides a color display having a spatially
uniform distribution of at least first and second types of prism
structure. The first type of prism structure consists of a first
prism and a first color filter positioned to filter light incident
upon a first facet (i.e. base) of the first prism. The first color
filter has a first selected spectral absorption characteristic. A
first member having a second selected spectral absorption
characteristic is movable with respect to a second facet of the
first prism between a first position in which the first member is
in optical contact with the second facet, producing a first
absorptive state in which total internal reflection of light rays
at the second facet is reduced as a function of wavelength in
accordance with the second selected spectral absorption
characteristic, and a second position in which the first member is
not in optical contact with the second facet, producing a first
reflective state in which light incident upon the second facet is
totally internally reflected toward a third facet of the first
prism. A second member having a third selected spectral absorption
characteristic is movable with respect to the third facet of the
first prism between a third position in which the second member is
in optical contact with the third facet, producing a second
absorptive state in which total internal reflection of light rays
at the third facet is reduced as a function of wavelength in
accordance with the third selected spectral absorption
characteristic, and a fourth position in which the second member is
not in optical contact with the third facet, producing a second
reflective state in which light incident upon the third facet is
totally internally reflected toward and through the first color
filter.
[0010] The second type of prism structure consists of a second
prism and a second color filter positioned to filter light incident
upon a first facet (i.e. base) of the second prism. The second
color filter has a fourth selected spectral absorption
characteristic. A third member having a fifth selected spectral
absorption characteristic is movable with respect to a second facet
of the second prism between a fifth position in which the third
member is in optical contact with the second facet of the second
prism, producing a third absorptive state in which total internal
reflection of light rays at the second facet of the second prism is
reduced as a function of wavelength in accordance with the fifth
selected spectral absorption characteristic, and a sixth position
in which the third member is not in optical contact with the second
facet of the second prism, producing a third reflective state in
which light incident upon the second facet of the second prism is
totally internally reflected at the second facet of the second
prism.
[0011] The spectral absorption characteristics are selected such
that, for any selected set comprising proximate ones of all of the
types of prism structure included in the display, controlled
movement of the members between particular selected combinations of
their possible respective positions causes the set to reflect light
which has an average spectral reflectance characteristic
corresponding to any one of three independent colors, with no one
of the independent colors being obtainable by mixing any other two
of the independent colors.
[0012] Advantageously, the second type of prism structure also has
a fourth member having a sixth selected spectral absorption
characteristic. The fourth member is movable with respect to a
third facet of the second prism between a seventh position in which
the fourth member is in optical contact with the third facet of the
second prism, producing a fourth absorptive state in which total
internal reflection of light rays at the third facet of the second
prism is reduced as a function of wavelength in accordance with the
sixth selected spectral absorption characteristic, and an eighth
position in which the fourth member is not in optical contact with
the third facet of the second prism, producing a fourth reflective
state in which light incident upon the third facet of the second
prism is totally internally reflected toward and through the second
color filter.
[0013] The spatially uniform distribution preferably includes a
third type of prism structure consisting of a third prism and a
third color filter positioned to filter light incident upon a first
facet (i.e. base) of the third prism. The third color filter has a
seventh selected spectral absorption characteristic. A fifth member
having an eighth selected spectral absorption characteristic is
movable with respect to a second facet of the third prism between a
ninth position in which the fifth member is in optical contact with
the second facet of the third prism, producing a fifth absorptive
state in which total internal reflection of light rays at the
second facet of the third prism is reduced as a function of
wavelength in accordance with the eighth selected spectral
absorption characteristic, and a tenth position in which the fifth
member is not in optical contact with the second facet of the third
prism, producing a fifth reflective state in which light incident
upon the second facet of the third prism is totally internally
reflected toward a third facet of the third prism. A sixth member
having a ninth selected spectral absorption characteristic, the
sixth member movable with respect to a third facet of the third
prism between an eleventh position in which the sixth member is in
optical contact with the third facet of the third prism, producing
a sixth absorptive state in which total internal reflection of
light rays at the third facet of the third prism is reduced as a
function of wavelength in accordance with the ninth selected
spectral absorption characteristic, and a twelfth position in which
the sixth member is not in optical contact with the third facet of
the third prism, producing a sixth reflective state in which light
incident upon the third facet of the third prism is totally
internally reflected toward and through the third color filter.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1A is a fragmented cross-sectional view, on a greatly
enlarged scale, of a portion of a color image display having a
filter with different color segments atop a reflective, high
refractive index prismatic material. FIG. 1B depicts an alternate
embodiment in which the color filter is embedded within the
prismatic material.
[0015] FIG. 2A is similar to FIG. 1B and shows an electrode
structure for selectably and controllably moving a colored,
flexible control element between a first position in which a gap
remains between the element and the longitudinally opposed facets
of two prisms adjacent to the element, and a second position in
which the element is in optical contact with the longitudinally
opposed facets of the two prisms.
[0016] FIG. 2B is similar to FIG. 1B and shows an electrode
structure for selectably and controllably electrophoretically
moving a group of colored absorptive particles between a first
position in which a gap remains between the particle group and the
longitudinally opposed facets of two prisms adjacent to the
particle group, and a second position in which the particle group
is in optical contact with the longitudinally opposed facets of the
two prisms.
[0017] FIG. 2C is a fragmented cross-sectional view, on a greatly
enlarged scale, of a portion of a color image display formed by
interleaving two different filter-prism-control member structures;
and shows an electrode structure for selectably and controllably
moving a colored control member between a first position in which a
gap remains between the member and an adjacent prism facet, and a
second position in which the member is in optical contact with the
adjacent prism facet.
[0018] FIG. 3A schematically shows a FIG. 1A type display with FIG.
2A type control elements actuated to display the color white. FIGS.
3B-3H show the FIG. 3A structure actuated to display the colors
yellow, magenta, Cyan, red, green, blue and black respectively.
[0019] FIG. 4A is a fragmented, pictorial illustration, on a
greatly enlarged scale, of a prismatic sheet material. FIG. 4B
shows the FIG. 4A sheet, with each channel between each
longitudinally adjacent prism facet pair partitioned at spaced
intervals to form a multiplicity of compartments along each such
channel.
[0020] FIG. 5A is a fragmented, pictorial illustration, on a
greatly enlarged scale, of a portion of a display combining the
FIG. 1A prismatic material and external color filter with the FIG.
2B segmented electrode and colored absorptive particle group
structure. FIG. 5B is a fragmented, pictorial illustration, on a
greatly enlarged scale, of a portion of a display combining the
FIG. 1B prismatic material and embedded color filter with the FIG.
2B segmented electrode and subtractive colored absorptive particle
group structure.
DESCRIPTION
[0021] FIG. 1A depicts a portion of an image display in which a
sheet 10 of high refractive index prismatic material is positioned
with its flat viewing surface 12 outward and its prism-bearing
surface 14 inward. Prisms 16A, 16B, 16C forming surface 14 may have
any one of a wide range of prism or near-prism shapes, the only
requirement being that the prisms be capable of totally internally
reflecting incident light rays unless TIR is frustrated as
hereinafter explained. Viewing surface 12 coincides with the flat
base (or "first facet") portions of each of prisms 16A, 16B, 16C
and of many other prisms (not shown) which extend longitudinally
parallel to prisms 16A, 16B, 16C on either side thereof as viewed
in FIG. 1A. Each one of prisms 16A, 16B, 16C, etc. is symmetrical
about its longitudinal axis over the entire length of the prism
(i.e. the cross-sectional shape of each prism does not vary as a
function of length along the prism's longitudinal axis).
[0022] Sheet 10 may, for example, be a thin layer of zinc sulfide
(ZnS, n.apprxeq.2.4), titanium dioxide (TiO.sub.2, n.apprxeq.2.5),
niobium pentoxide (NbO.sub.5, n.apprxeq.2.3) or zirconium oxide
(ZrO, n.apprxeq.2.1). Although higher refractive index materials
are generally preferred, sheet 10 may alternatively be formed of a
lower refractive index material such as polycarbonate
(n.apprxeq.1.6) if a multiple layered prismatic geometry is used,
as described in the '784 patent, to enhance the refractive index
mismatch at the TIR interface. Prisms 16A, 16B, 16C may be formed
on surface 14 by machining an initially flat sheet to generate the
prisms; or, by depositing high refractive index material via
sputtering or evaporation techniques into a machined mould
constituting a physical "negative" of the desired prismatic surface
10. Prisms 16A, 16B, 16C need only be about 2 microns deep, and
sheet 10 need only be sufficiently thick (i.e. 5-10 microns) to
facilitate provision of a generally but not perfectly flat
frontward surface 12. If sheet 10 is insufficiently thick to be
self-supporting, an additional transparent sheet (not shown) can be
affixed to flat surface 12 to provide the necessary support. Any
such additional sheet should be designed to minimize refraction of
incident light rays and thus minimize the impact of such additional
sheet on the optical characteristics of the device, as hereinafter
explained. If a lower refractive index material such as
polycarbonate is used, sheet 10 may be formed using well-known
polycarbonate micro-replication techniques.
[0023] A subtractive color filter 18A having a repetitively
adjacent yellow segment F.sub.Y, magenta segment F.sub.M, Cyan
segment F.sub.C structure is applied atop outward viewing surface
12. This can for example be achieved by applying to outward viewing
surface 12 a thin layer of a suitably colored adhesive having a
refractive index substantially similar to that of sheet 10. The
adhesive layer should be sufficiently thin and sufficiently
transparent that it does not cause substantial deflection of either
incoming or outgoing light rays, and such that it does not
contribute substantially to the overall thickness of sheet 10. Care
is taken to orient yellow segment F.sub.Y so that, when viewed
along a notional axis (not shown) perpendicular to surface 12 and
intersecting the apex of prism 16A, yellow segment F.sub.Y covers
substantially the entire base portion of prism 16A without covering
substantial portions of either of the prisms adjacent thereto.
Similarly, magenta segment F.sub.M is oriented so that, when viewed
along a notional axis (not shown) perpendicular to surface 12 and
intersecting the apex of prism 16B, magenta segment F.sub.M covers
substantially the entire base portion of prism 16B without covering
substantial portions of either of prisms 16A or 16C; and, Cyan
segment F.sub.C is oriented so that, when viewed along a notional
axis (not shown) perpendicular to surface 12 and intersecting the
apex of prism 16C, Cyan segment F.sub.C covers substantially the
entire base portion of prism 16C without covering substantial
portions of either of the prisms adjacent thereto.
[0024] FIG. 1B depicts a portion of an alternate image display in
which subtractive color filter 18B (again having a repetitively
adjacent yellow segment F.sub.Y, magenta segment F.sub.M, Cyan
segment F.sub.C structure) is embedded within sheet 10 to more
precisely orient segments F.sub.Y, F.sub.M, F.sub.C over the bases
of prisms 16A, 16B, 16C respectively, as aforesaid. This can for
example be achieved by printing segments F.sub.Y, F.sub.M, F.sub.C
as a continuously repeated pattern of suitably colored stripes on a
Mylar.TM. sheet using conventional photographic printing
techniques, then using micro-replication techniques to cast prisms
16A, 16B, 16C on the Mylar.TM. sheet atop the printed filter
segments.
[0025] FIG. 2A shows sheet 10 and its internally embedded F.sub.Y,
F.sub.M, F.sub.C segmented subtractive color filter 18B supported
adjacent a substrate 20 which extends parallel to flat viewing
surface 12. Although FIG. 2A depicts a gap between substrate 20 and
the apices of prisms 16A, 16B, 16C no such gap is required and it
may in some cases be more convenient to manufacture the FIG. 2A
apparatus with the prisms' apices contacting and/or bonded to
substrate 20. A first, transparent electrode 22 is deposited on and
extends continuously over substantially the entirety of inward
prism-bearing surface 14. A plurality of discrete electrode
segments 24, 26, 28, 30 are respectively deposited on substrate 20.
Care is taken to orient electrode segment 24 so that it extends
adjacent and parallel to the leftward (as viewed in FIG. 2A) facet
of prism 16A. Similarly, electrode segment 26 extends adjacent and
parallel to the rightward facet of prism 16A; and, adjacent and
parallel to the leftward facet of prism 16B. Electrode segment 28
extends adjacent and parallel to the rightward facet of prism 16B;
and, adjacent and parallel to the leftward facet of prism 16C.
Electrode segment 30 extends adjacent and parallel to the rightward
facet of prism 16C.
[0026] A flexible, Cyan colored movable control element C.sub.C is
fixed to substrate 20 above electrode segment 26. As depicted in
FIG. 2A, control element C.sub.C is in a non-actuated state in
which control element C.sub.C is retracted toward substrate 20,
away from the rightward facet of prism 16A and away from the
longitudinally adjacent leftward facet of prism 16B, leaving a gap
between control element C.sub.C and the prism facets. This can be
achieved by forming control element C.sub.C of an electrically
conductive (or flexible conductor-bearing) elastomer material which
can be controllably electronically actuated to deform the material
into optical contact with the prism facets, and which regains its
original shape when such electronic actuation is discontinued.
Specifically, a first voltage potential is applied between
electrodes 22, 26 to produce an electrostatic force which biases
control element C.sub.C toward substrate 20 in the aforementioned
non-actuated retracted state, leaving a gap between control element
C.sub.C and the longitudinally adjacent right-ward, leftward facets
of prisms 16A, 16B respectively, as seen in FIG. 2A. A second
voltage potential is applied between electrodes 22, 26 to produce
an electrostatic force which biases control element C.sub.C toward
sheet 10, placing control element C.sub.C in optical (but not
electrical) contact with the adjacent rightward, leftward facets of
prisms 16A, 16B respectively. In either case, control element
C.sub.C can be maintained at ground potential. Avoidance of
electrical contact between control element C.sub.C and electrode 22
can be achieved by applying a thin, transparent layer of
electrically insulating material to the control element, or to
electrode 22, or both.
[0027] A similarly shaped and sized, but yellow colored flexible,
deformable control element C.sub.Y is fixed to substrate 20 above
electrode segment 28, between the rightward facet of prism 16B and
the longitudinally adjacent leftward facet of prism 16C.
Application of the first voltage potential between electrodes 22,
28 biases (retracts) control element C.sub.Y toward substrate 20,
leaving a gap between control element C.sub.Y and the adjacent
rightward, leftward facets of prisms 16B, 16C respectively.
Application of the second voltage potential between electrodes 22,
28 biases control element C.sub.Y toward sheet 10, placing control
element C.sub.Y in optical contact with the longitudinally adjacent
rightward, leftward facets of prisms 16B, 16C respectively, as seen
in FIG. 2A.
[0028] Similarly shaped and sized, but magenta colored flexible,
deformable control elements C.sub.M are fixed to substrate 20 above
electrode segments 24, 30 respectively. The leftward control
element C.sub.M is positioned between the leftward facet of prism
16A and the longitudinally adjacent rightward facet of the
(partially shown) prism to the left of prism 16A. The rightward
control element C.sub.M is positioned between the rightward facet
of prism 16C and the longitudinally adjacent leftward facet of the
(partially shown) prism to the right of prism 16C. Application of
the first voltage potential between electrodes 22, 24 biases
leftward control element C.sub.M toward substrate 20, leaving a gap
between leftward control element C.sub.M and the adjacent leftward
facet of prism 16A. Application of the second voltage potential
between electrodes 22, 24 biases leftward control element C.sub.M
toward sheet 10, placing leftward control element C.sub.M in
optical contact with the adjacent leftward facet of prism 16A, as
seen in FIG. 2A. Application of the first voltage potential between
electrodes 22, 30 biases rightward control element C.sub.M toward
substrate 20, leaving a gap between rightward control element
C.sub.M and the adjacent rightward facet of prism 16C. Application
of the second voltage potential between electrodes 22, 30 biases
rightward control element C.sub.M toward sheet 10, placing
rightward control element C.sub.M in optical contact with the
adjacent rightward facet of prism 16C, as seen in FIG. 2A. The
optical characteristics of substrate 20 are relatively unimportant;
substrate 20 need only serve as a suitable mounting support for
electrode segments 24, 26, 28, 30 and for control elements C.sub.C,
C.sub.Y, C.sub.M.
[0029] FIG. 2B shows sheet 10 and its internally embedded F.sub.Y,
F.sub.M, F.sub.C segmented subtractive color filter 18B supported
adjacent a substrate 32 which extends parallel to flat viewing
surface 12 and is bonded to the apices of prisms 16A, 16B, 16C
creating a plurality of prism-shaped channels 34A, 34B, 34C, 34D
between the adjacent facets of prisms 16A, 16B, 16C, the rightward
facet of the (partially shown) prism to the left of prism 16A and
the leftward facet of the (partially shown) prism to the right of
prism 16C. As in the FIG. 2A embodiment, a first, transparent
electrode 22 is deposited on and extends continuously over
substantially the entirety of inward prism-bearing surface 14. A
plurality of discrete electrode segments 24, 26, 28, 30 are
respectively deposited on substrate 20. Care is taken to orient
electrode segment 24 so that it extends within channel 34A adjacent
and parallel to the leftward (as viewed in FIG. 2B) facet of prism
16A. Similarly, electrode segment 26 extends within channel 34B
adjacent and parallel to the rightward facet of prism 16A; and,
adjacent and parallel to the leftward facet of prism 16B. Electrode
segment 28 extends within channel 34C adjacent and parallel to the
rightward facet of prism 16B; and, adjacent and parallel to the
leftward facet of prism 16C. Electrode segment 30 extends within
channel 34D adjacent and parallel to the rightward facet of prism
16C.
[0030] An electrophoresis medium is confined within each one of
channels 34A, 34B, 34C, 34D such that the electrophoresis medium in
channel 34A contacts the leftward facet of prism 16A, the
electrophoresis medium in channel 34B contacts the rightward facet
of prism 16A and the leftward facet of prism 16B, the
electrophoresis medium in channel 34C contacts the rightward facet
of prism 16B and the leftward facet of prism 16C, and the
electrophoresis medium in channel 34D contacts the rightward facet
of prism 16C. The electrophoresis medium is preferably a low
refractive index, low viscosity, electrically insulating liquid
such as Fluorinert.TM. Electronic Liquid F.sub.C-72
(n.apprxeq.1.25) or F.sub.C-75 (n.apprxeq.1.27) heat transfer media
available from 3M, St. Paul, Minn. A Fluorinert:ZnS TIR interface
is thus formed (assuming ZnS is used to form sheet 10).
[0031] The electrophoresis medium within channel 34A contains a
finely dispersed suspension of light absorptive magenta colored
particles P.sub.M such as dyed silica (n.apprxeq.1.44) particles,
latex (n.apprxeq.1.5) particles, pigment (n variable) particles,
etc. As used herein in reference to particles or control elements,
the term "light absorptive" includes particles (or control
elements) which are either light absorptive, or which are both
light absorptive and light scattering, but does not include
particles (or control elements) having only a light scattering
characteristic with no light absorption characteristic. The optical
characteristics of substrate 32 are relatively unimportant; sheet
32 need only form channels 34A, 34B, 34C, 34D for containment of
the electrophoresis medium and particles. The electrophoresis
medium within channel 34B contains a finely dispersed suspension of
light absorptive Cyan colored particles P.sub.C;the electrophoresis
medium within channel 34C contains a finely dispersed suspension of
light absorptive yellow colored particles P.sub.Y and the
electrophoresis medium within channel 34D contains a finely
dispersed suspension of light absorptive magenta colored particles
P.sub.M.
[0032] The FIG. 2B embodiment facilitates frustration of TIR
without the need for mechanical movement of control elements as in
the FIG. 2A embodiment, without the need for maintenance of a gap
(i.e. a region of non-optical contact between the control elements
and inward prism-bearing surface 14) whenever TIR is not to be
frustrated, and without the need for precisely matching flat
surfaces at the TIR interface (i.e. on the facets of prisms 16A,
16B, 16C). Mechanical frustration of TIR is best accomplished at a
flat surface, since it is easier to achieve optical contact at a
flat surface. It is comparatively difficult to mechanically
frustrate TIR at a prismatic surface, due to the difficulty in
attaining the required matching alignment accurately between the
prismatic surface and the part which is to be mechanically moved
into and out of optical contact with the prismatic surface.
However, a liquid electrophoretic medium easily flows to surround
reflective prism-bearing surface 14, thus eliminating the alignment
difficulty and rendering practical the usage of a prismatic
micro-structured surface as the TIR interface.
[0033] Before further explaining the operation of the FIG. 2B
embodiment, it is useful to review some well known color theory
principles. The CIE chromaticity coordinate system is used to
define any desired color hue as a mixture of appropriate
intensities of three primary colors X, Y, Z in an appropriate
ratio. For example, a desired color Q can be obtained by mixing an
intensity a of color X, an intensity b of color Y, and an intensity
c of color Z. This is represented mathematically as Q=aX+bY+cZ. X,
Y, Z can be thought of as respectively representing the three
mutually perpendicular color intensity (chromaticity) axes of a
chromaticity coordinate system, defining a color "volume" within
which all possible colors can be located. The aforementioned color
Q is defined by the coordinates (a,b,c) within this volume.
Although it is often convenient to use either the primary additive
colors red (R), green (G) and blue (B); or, the primary subtractive
colors Cyan (C), magenta (M), yellow (Y) as the color intensity
(chromaticity) axes of a chromaticity coordinate system, many other
axial colors can be used to define different chromaticity
coordinate systems capable of representing all possible colors. It
is only necessary to ensure that no one of the three selected axial
colors can be obtained by mixing the other two selected axial
colors. By moving a color absorptive member through a range of
optical contact or near optical contact positions relative to a
prism facet, one may vary the relative color intensity of light
rays reflected (as hereinafter explained) at that facet, thereby
generating any desired average reflectance spectrum (corresponding
to any desired CIE chromaticity coordinates) over the surface of a
selected subset of prismatic elements. Accordingly, although the
present invention is hereinafter primarily described in terms of
the primary subtractive colors Cyan, magenta, and yellow; and, in
terms of the primary additive colors red, green and blue; persons
skilled in the art will understand that any CIE chromaticity
coordinate system can be used to implement the invention.
[0034] It is also convenient to recollect that, when mixed together
in equal amounts of equal intensity proportions, the primary
subtractive colors Cyan, magenta, and yellow yield the color black.
The term "subtractive" implies that a material of a given color
absorbs light of a given wavelength (i.e. color), and reflects all
others. For example, a magenta colored material absorbs green light
while reflecting red and blue light; a Cyan colored material
absorbs red light while reflecting green and blue light; and, a
yellow colored material absorbs blue light while reflecting red and
green light. When mixed together in equal amounts of equal
intensity proportions, the primary additive colors red, green and
blue yield the color white. The term "additive" implies that
different combinations of red, green and blue wavelengths (i.e.
colors) yield other colors. If equal amounts of equal intensity
proportions of only the two primary colors red and green are mixed
together the resultant color appears yellow. Similarly, a mixture
of equal amounts of equal intensity proportions of red and blue
yields the color magenta; and, a mixture of equal amounts of equal
intensity proportions of green and blue yields the color Cyan. The
color black corresponds to a complete absence of any colors.
[0035] The embodiments of FIGS. 2A and 2B have three different
"types" of prism structures. Each of the three types consists of a
prism, a color filter with a first selected spectral absorption
characteristic (i.e. absorption as a function of wavelength)
associated with a first facet (i.e. base) of the prism, a first
control member with a second selected spectral absorption
characteristic associated with a second facet of the prism, and a
second control member with a third selected spectral absorption
characteristic associated with a third facet of the prism. There is
no essential relationship between the spectral absorption
characteristics selected for any one of the three types of prism
structure and those selected for either of the other two types of
prism structures. One need only ensure that the spectral absorption
characteristics are selected such that, for any selected set
comprising proximate ones of all three types of prism structure,
controlled movement of the members between particular selected
combinations of their possible respective positions causes the set
as a whole to reflect light which has an average spectral
reflectance characteristic corresponding to any one of three
independent colors. "Independent" means that no one of the three
colors is obtainable by mixing any other two of the three colors.
"Proximate" means that all of the prism structures in the set are
sufficiently close to one another that the human eye does not
distinguish light rays exiting from any one prism structure in the
set apart from light rays exiting from any other prism structure in
the set. A large number of each of the three types of prism
structures are interleaved to provide a spatially uniform
distribution of all three types in any selected macroscopic portion
of the display.
[0036] Prism 16A shown in FIGS. 2A and 2B is accordingly exemplary
of a "first" type of prism structure having a color filter F.sub.Y
with a yellow spectral absorption characteristic, a control member
(element) C.sub.M (or particles P.sub.M) with a magenta spectral
absorption characteristic, and a control member (element) C.sub.C
(or particles P.sub.C) with a Cyan spectral absorption
characteristic. Similarly, prism 16B shown in FIGS. 2A and 2B is a
"second" type of prism structure having a color filter F.sub.M with
a magenta spectral absorption characteristic, a control member
(element) C.sub.C (or particles P.sub.C) with a Cyan spectral
absorption characteristic, and a control member (element) C.sub.Y
(or particles P.sub.Y) with a yellow spectral absorption
characteristic; and, prism 16C shown in FIGS. 2A and 2B is a
"third" type of prism structure having a color filter F.sub.C with
a Cyan spectral absorption characteristic, a control member
(element) C.sub.Y (or particles P.sub.Y) with a yellow spectral
absorption characteristic, and a control member (element) C.sub.M
(or particles P.sub.M) with a magenta spectral absorption
characteristic.
[0037] It will accordingly be understood, with reference to FIGS.
1A and 1B, that yellow filter segment F.sub.Y absorbs incident blue
light while allowing only incident red or green light to pass
through yellow filter segment F.sub.Y into prism 16A; magenta
filter segment F.sub.M absorbs incident green light while allowing
only incident red or blue light to pass through magenta filter
segment F.sub.M into prism 16B; and, Cyan filter segment F.sub.C
absorbs incident red light while allowing only incident green or
blue light to pass through Cyan filter segment F.sub.C into prism
16C.
[0038] Turning now to FIG. 2B, if a first voltage potential is
applied across the electrophoretic medium in channel 34A (i.e.
between electrodes 22, 24) the magenta colored particles P.sub.M
suspended in the electrophoretic medium in channel 34A are
electrophoretically moved to within about 0.25 micron of the TIR
interface at the leftward facet of prism 16A (i.e. inside the
evanescent wave region, as is illustrated for particles P.sub.M in
channel 34A in FIG. 2B). As previously explained, yellow filter
segment F.sub.Y allows only red or green light to pass into prism
16A; and, a magenta colored material absorbs green light while
reflecting red and blue light. Accordingly, when
electrophoretically moved as aforesaid, magenta colored particles
P.sub.M in channel 34A absorb green light at the leftward facet of
prism 16A by causing a refractive index mismatch for green light at
the TIR interface, but without causing a mismatch for red light.
Green light rays are therefore absorbed as they strike particles
P.sub.M inside the evanescent wave region of the TIR interface at
the leftward facet of prism 16A, whereas red light rays are
unaffected and are totally internally reflected toward the
rightward facet of prism 16A. If a second voltage potential is
applied across the electrophoretic medium in channel 34A the
magenta colored particles P.sub.M in channel 34A are
electrophoretically moved away from the TIR interface at the
leftward facet of prism 16A, thus allowing both red and green light
rays which pass through yellow filter segment F.sub.Y to be totally
internally reflected at the TIR interface toward the rightward
facet of prism 16A.
[0039] If a third voltage potential is applied across the
electrophoretic medium in channel 34B (i.e. between electrodes 22,
26) the Cyan colored particles Pc suspended in the electrophoretic
medium in channel 34B are electrophoretically moved to within about
0.25 micron of the TIR interfaces at the rightward facet of prism
16A and at the leftward facet of prism 16B. As explained in the
preceding paragraph, yellow filter segment F.sub.Y atop prism 16A
and selective electrophoretic movement of magenta colored particles
P.sub.M in channel 34A ensures that only red light rays or a
combination of both red and green light rays are totally internally
reflected toward the rightward facet of prism 16A. As was also
previously explained, a Cyan colored material absorbs red light
while reflecting green and blue light. Accordingly, when Cyan
colored particles P.sub.C are electrophoretically moved inside the
evanescent wave region of the TIR interface at the rightward facet
of prism 16A, any red light rays reaching that interface are
absorbed, whereas any green light rays reaching that interface are
totally internally reflected toward and through yellow filter
segment F.sub.Y, which passes green light rays as previously
explained.
[0040] It is well known to persons familiar with optical ray
tracing techniques that the above described ray paths are
reversible. For example, instead of first encountering the leftward
facet of prism 16A, red or green light rays passing through yellow
filter segment F.sub.Y may instead first encounter the rightward
facet of prism 16A. In such case, and if the Cyan colored particles
P.sub.C in channel 34B are electrophoretically moved inside the
evanescent wave region of the TIR interface at the rightward facet
of prism 16A, then any red light rays reaching that interface are
absorbed, whereas any green light rays reaching that interface are
totally internally reflected toward the leftward facet of prism
16A. If the Cyan colored particles P.sub.C in channel 34B are not
electrophoretically moved to within about 0.25 micron of the TIR
interface at the rightward facet of prism 16A then the red light
rays are also totally internally reflected toward leftward facet of
prism 16A. If the magenta colored particles PM in channel 34A are
electrophoretically moved inside the evanescent wave region of the
TIR interface at the leftward facet of prism 16A, then any green
light rays reaching that interface are absorbed, whereas any red
light rays reaching that interface are totally internally reflected
toward and exit through yellow filter segment F.sub.Y. If the
magenta colored particles P.sub.M in channel 34A are not
electrophoretically moved to within about 0.25 micron of the TIR
interface at the leftward facet of prism 16A, then the green light
rays are also totally internally reflected toward and exit through
yellow filter segment F.sub.Y. Persons skilled in the art will
understand that similar principles of reversibility apply to all of
the ray paths described herein (including the claims); and, that
the invention defined by the accompanying claims in not restricted
to any particular light ray direction.
[0041] If a fourth voltage potential is applied across the
electrophoretic medium in channel 34B the Cyan colored particles
P.sub.C suspended in the electrophoretic medium in channel 34B are
electrophoretically moved away from the TIR interface at the
rightward facet of prism 16A (as is illustrated for particles
P.sub.C in channel 34B in FIG. 2B), thus allowing both red and
green light rays which pass yellow filter segment F.sub.Y and which
are totally internally reflected by the TIR interface at the
leftward facet of prism 16A to be further totally internally
reflected by the TIR interface at the rightward facet of prism 16A
toward and through yellow filter segment F.sub.Y, which passes both
red and green light rays as previously explained.
[0042] Now consider the situation in which Cyan colored particles
P.sub.C in channel 34B are electrophoretically moved as aforesaid
inside the evanescent wave region of the TIR interface at the
leftward facet of prism 16B. As previously explained, magenta
filter segment F.sub.M allows only red or blue light to pass into
prism 16B; and, a Cyan colored material absorbs red light while
reflecting green and blue light. Accordingly, when
electrophoretically moved as aforesaid, Cyan colored particles
P.sub.C in channel 34B absorb red light at the leftward facet of
prism 16B by causing a refractive index mismatch for red light at
the TIR interface, but without causing a mismatch for blue light.
Red light rays are therefore absorbed as they strike particles
P.sub.C inside the evanescent wave region of the TIR interface at
the leftward facet of prism 16B, whereas blue light rays are
unaffected and are totally internally reflected toward the
rightward facet of prism 16B. When the fourth voltage potential is
applied across the electrophoretic medium in channel 34B the Cyan
colored particles P.sub.C in channel 34B are electrophoretically
moved away from the TIR interface at the leftward facet of prism
16B, thus allowing both red and blue light rays which pass magenta
filter segment F.sub.M to be totally internally reflected at the
TIR interface toward the rightward facet of prism 16B.
[0043] If a fifth voltage potential is applied across the
electrophoretic medium in channel 34C (i.e. between electrodes 22,
28) the yellow colored particles P.sub.Y suspended in the
electrophoretic medium in channel 34C are electrophoretically moved
to within about 0.25 micron of the TIR interfaces at the rightward
facet of prism 16B and at the leftward facet of prism 16C (as is
illustrated for particles P.sub.Y in channel 34C in FIG. 2B). As
previously explained, magenta filter segment F.sub.M atop prism 16B
and selective electrophoretic movement of Cyan colored particles
P.sub.C in channel 34B ensures that only red light rays or a
combination of both red and blue light rays are totally internally
reflected toward the rightward facet of prism 16B. As was also
previously explained, a yellow colored material absorbs blue light
while reflecting red and green light. Accordingly, when yellow
colored particles P.sub.Y are electrophoretically moved inside the
evanescent wave region of the TIR interface at the rightward facet
of prism 16B, any blue light rays reaching that interface are
absorbed, whereas any red light rays reaching that interface are
totally internally reflected toward and through magenta filter
segment F.sub.M, which passes red light rays as previously
explained.
[0044] If a sixth voltage potential is applied across the
electrophoretic medium in channel 34C the yellow colored particles
P.sub.Y suspended in the electrophoretic medium in channel 34C are
electrophoretically moved away from the TIR interface at the
rightward facet of prism 16B, thus allowing both red and blue light
rays which pass magenta filter segment F.sub.M and which are
totally internally reflected by the TIR interface at the leftward
facet of prism 16B to be further totally internally reflected by
the TIR interface at the rightward facet of prism 16B toward and
through magenta filter segment F.sub.M, which passes both red and
blue light rays as previously explained.
[0045] Now consider the situation in which yellow colored particles
P.sub.Y in channel 34C are electrophoretically moved as aforesaid
inside the evanescent wave region of the TIR interface at the
leftward facet of prism 16C. As previously explained, Cyan filter
segment F.sub.C allows only green or blue light to pass into prism
16C; and, a yellow colored material absorbs blue light while
reflecting red and green light. Accordingly, when
electrophoretically moved as aforesaid, yellow colored particles
P.sub.Y in channel 34C absorb blue light at the leftward facet of
prism 16C by causing a refractive index mismatch for blue light at
the TIR interface, but without causing a mismatch for green light.
Blue light rays are therefore absorbed as they strike particles
P.sub.Y inside the evanescent wave region of the TIR interface at
the leftward facet of prism 16C, whereas green light rays are
unaffected and are totally internally reflected toward the
rightward facet of prism 16C. When the sixth voltage potential is
applied across the electrophoretic medium in channel 34C the yellow
colored particles P.sub.Y in channel 34C are electrophoretically
moved away from the TIR interface at the leftward facet of prism
16C, thus allowing both green and blue light rays which pass Cyan
filter segment F.sub.C to be totally internally reflected at the
TIR interface toward the rightward facet of prism 16C.
[0046] If a seventh voltage potential is applied across the
electro-phoretic medium in channel 34D (i.e. between electrodes 22,
30) the magenta colored particles PM suspended in the
electrophoretic medium in channel 34D are electrophoretically moved
to within about 0.25 micron of the TIR interface at the rightward
facet of prism 16C (as is illustrated for particles P.sub.M in
channel 34D in FIG. 2B). As previously explained, Cyan filter
segment F.sub.C atop prism 16C and selective electrophoretic
movement of yellow colored particles P.sub.Y in channel 34C ensures
that only green light rays or a combination of both green and blue
light rays are totally internally reflected toward the rightward
facet of prism 16C. As was also previously explained, a magenta
colored material absorbs green light while reflecting red and blue
light. Accordingly, when magenta colored particles PM are
electrophoretically moved inside the evanescent wave region of the
TIR interface at the rightward facet of prism 16C, any green light
rays reaching that interface are absorbed, whereas any blue light
rays reaching that interface are totally internally reflected
toward and through the Cyan filter segment F.sub.C atop prism 16C,
which passes blue light rays as previously explained.
[0047] If an eighth voltage potential is applied across the
electrophoretic medium in channel 34D the magenta colored particles
P.sub.M suspended in the electrophoretic medium in channel 34D are
electrophoretically moved away from the TIR interface at the
rightward facet of prism 16C, thus allowing both green and blue
light rays which pass the Cyan filter segment F.sub.C atop prism
16C and which are totally internally reflected by the TIR interface
at the leftward facet of prism 16C to be further totally internally
reflected by the TIR interface at the rightward facet of prism 16C
toward and through the Cyan filter segment F.sub.C atop prism 16C,
which passes both green and blue light rays as previously
explained.
[0048] FIGS. 3A-3H illustrate the foregoing, with I.sub.R, I.sub.G,
I.sub.B representing incident red, green and blue light rays
respectively; and, R.sub.R, R.sub.G, R.sub.B respectively
representing red, green and blue light rays which undergo total
internal reflection twice and exit in a direction substantially
opposite to the direction of the incident light rays. For clarity,
FIGS. 3A-3H do not show any electrodes; Cyan, yellow and magenta
colored control elements C.sub.C, C.sub.Y, C.sub.M are shown
instead of electrophoretically movable subtractive colored
particles; and, the subtractive filter incorporating yellow,
magenta and Cyan filter segments F.sub.Y, F.sub.M, F.sub.C is shown
atop prisms 16A, 16B, 16C respectively rather than being embedded
therein. Persons skilled in the art will however understand that
one could substitute an electrophoresis medium containing Cyan,
yellow and magenta colored particles P.sub.C, P.sub.Y, P.sub.M for
control elements C.sub.C, C.sub.y, C.sub.M respectively; and/or
embed yellow, magenta and Cyan filter segments F.sub.Y, F.sub.M,
F.sub.C within prisms 16A, 16B, 16C respectively as previously
explained.
[0049] More particularly, FIG. 3A depicts the situation in which
the color white is displayed by biasing all of the control elements
C.sub.C, C.sub.Y, C.sub.M away from the TIR interface. The color
white is displayed because equal proportions of the colors red,
green and blue exit. Specifically, the yellow filter segment
F.sub.Y atop prism 16A absorbs blue incident light rays I.sub.B and
passes both red and green incident light rays I.sub.R, I.sub.G
which undergo total internal reflection twice within prism 16A and
exit through yellow filter segment F.sub.Y as rays R.sub.R, R.sub.G
respectively. The magenta filter segment F.sub.M atop prism 16B
absorbs green incident light rays I.sub.G and passes both red and
blue incident light rays I.sub.R, I.sub.B which undergo total
internal reflection twice within prism 16B and exit through magenta
filter segment F.sub.M as rays R.sub.R, R.sub.B respectively. The
Cyan filter segment F.sub.C atop prism 16C absorbs red incident
light rays I.sub.R and passes both green and blue incident light
rays I.sub.G, I.sub.B which undergo total internal reflection twice
within prism 16C and exit through Cyan filter segment F.sub.C as
rays R.sub.G, R.sub.B respectively.
[0050] FIG. 3B depicts the situation in which the color yellow is
displayed by biasing the yellow control element C.sub.Y into
optical contact with the TIR interfaces at the rightward facet of
prism 16B and leftward facet of prism 16C, with the Cyan and
magenta control elements C.sup.C, C.sub.M being biased away from
the TIR interface. The color yellow is displayed because equal
proportions of the colors red and green exit. Specifically, the
yellow filter segment F.sub.Y atop prism 16A absorbs blue incident
light rays I.sub.B and passes both red and green incident light
rays I.sub.R, I.sub.G which undergo total internal reflection twice
within prism 16A and exit through yellow filter segment F.sub.Y as
rays R.sub.R, R.sub.G respectively. The magenta filter segment
F.sub.M atop prism 16B absorbs green incident light rays I.sub.G
and passes both red and blue incident light rays I.sub.R, I.sub.B;
both of which are totally internally reflected at the leftward
facet of prism 16B toward the rightward facet of prism 16B. The
yellow control element C.sub.Y biased against the rightward facet
of prism 16B absorbs the reflected blue light rays but totally
internally reflects the reflected red light rays toward and through
magenta filter segment F.sub.M as rays R.sub.R. The Cyan filter
segment F.sub.C atop prism 16C absorbs red incident light rays
I.sub.R and passes both green and blue incident light rays I.sub.G,
I.sub.B toward the leftward facet of prism 16C. The yellow control
element C.sub.Y biased against the leftward facet of prism 16C
absorbs the blue light rays but totally internally reflects the
green light rays toward the rightward facet of prism 16C where the
reflected green light rays again undergo total internal reflection
toward and exit through Cyan filter segment F.sub.C as rays
R.sub.G
[0051] FIG. 3C depicts the situation in which the color magenta is
displayed by biasing the leftward magenta control element C.sub.M
into optical contact with the TIR interface at the leftward facet
of prism 16A, and biasing the rightward magenta control element
C.sub.M into optical contact with the TIR interface at the
rightward facet of prism 16C, with the yellow and Cyan control
elements C.sub.Y, C.sub.C being biased away from the TIR interface.
The color magenta is displayed because equal proportions of the
colors red and blue exit. Specifically, the yellow filter segment
F.sub.Y atop prism 16A absorbs blue incident light rays I.sub.B and
passes both red and green incident light rays I.sub.R, I.sub.G
toward the leftward facet of prism 16A. The leftward magenta
control element C.sub.M biased against the leftward facet of prism
16A absorbs the green light rays but totally internally reflects
the red light rays toward the rightward facet of prism 16A where
the reflected red light rays again undergo total internal
reflection toward and exit through yellow filter segment F.sub.Y as
rays R.sub.R. The magenta filter segment F.sub.M atop prism 16B
absorbs green incident light rays I.sub.G and passes both red and
blue incident light rays I.sub.R, I.sub.B; both of which undergo
total internal reflection twice within prism 16B and exit through
magenta filter segment F.sub.M as rays R.sub.R, R.sub.B
respectively. The Cyan filter segment F.sub.C atop prism 16C
absorbs red incident light rays I.sub.R and passes both green and
blue incident light rays I.sub.G, I.sub.B; both of which are
totally internally reflected at the leftward facet of prism 16C
toward the rightward facet of prism 16C. The rightward magenta
control element C.sub.M biased against the rightward facet of prism
16C absorbs the green light rays but totally internally reflects
the blue light rays toward and through Cyan filter segment F.sub.C
as rays R.sub.B.
[0052] FIG. 3D depicts the situation in which the color Cyan is
displayed by biasing the Cyan control element C.sub.C into optical
contact with the TIR interfaces at the rightward facet of prism 16A
and leftward facet of prism 16B, with the yellow and magenta
control elements C.sub.Y, C.sub.M being biased away from the TIR
interface. The color Cyan is displayed because equal proportions of
the colors green and blue exit. Specifically, the yellow filter
segment F.sub.Y atop prism 16A absorbs blue incident light rays
I.sub.B and passes both red and green incident light rays I.sub.R,
I.sub.G; both of which are totally internally reflected at the
leftward facet of prism 16A toward the rightward facet of prism
16A. The Cyan control element C.sub.C biased against the rightward
facet of prism 16A absorbs the reflected red light rays but totally
internally reflects the reflected green light rays toward and
through yellow filter segment F.sub.Y as rays R.sub.G. The magenta
filter segment F.sub.M atop prism 16B absorbs green incident light
rays I.sub.G and passes both red and blue incident light rays
I.sub.R, I.sub.B toward the leftward facet of prism 16B. The Cyan
control element C.sub.C biased against the leftward facet of prism
16B absorbs the red light rays but totally internally reflects the
blue light rays the rightward facet of prism 16B where the
reflected blue light rays again undergo total internal reflection
toward and exit through magenta filter segment F.sub.M as rays
R.sub.B. The Cyan filter segment F.sub.C atop prism 16C absorbs red
incident light rays I.sub.R and passes both green and blue incident
light rays I.sub.G, I.sub.B which undergo total internal reflection
twice within prism 16C and exit through Cyan filter segment F.sub.C
as rays R.sub.G, R.sub.B respectively.
[0053] FIG. 3E depicts the situation in which the color red is
displayed by biasing the leftward magenta control element C.sub.M
into optical contact with the TIR interface at the leftward facet
of prism 16A, and biasing the rightward magenta control element
C.sub.M into optical contact with the TIR interface at the
rightward facet of prism 16C, and biasing the yellow control
element C.sub.Y into optical contact with the TIR interfaces at the
rightward facet of prism 16B and leftward facet of prism 16C, with
the Cyan control element C.sub.C being biased away from the TIR
interface. The color red is displayed because only red light rays
exit. Specifically, the yellow filter segment F.sub.Y atop prism
16A absorbs blue incident light rays I.sub.B and passes both red
and green incident light rays I.sub.R, I.sub.G toward the leftward
facet of prism 16A. The leftward magenta control element C.sub.M
biased against the leftward facet of prism 16A absorbs the green
light rays but totally internally reflects the red light rays
toward the rightward facet of prism 16A where the reflected red
light rays again undergo total internal reflection toward and exit
through yellow filter segment F.sub.Y as rays R.sub.R. The magenta
filter segment F.sub.M atop prism 16B absorbs green incident light
rays I.sub.G and passes both red and blue incident light rays
I.sub.R, I.sub.B; both of which are totally internally reflected at
the leftward facet of prism 16B toward the rightward facet of prism
16B. The yellow control element C.sub.Y biased against the
rightward facet of prism 16B absorbs the reflected blue light rays
but totally internally reflects the reflected red light rays toward
and through magenta filter segment F.sub.M as rays R.sub.R. The
Cyan filter segment F.sub.C atop prism 16C absorbs red incident
light rays I.sub.R and passes both green and blue incident light
rays I.sub.G, I.sub.B toward the rightward facet of prism 16C. The
yellow control element C.sub.Y biased against the leftward facet of
prism 16C absorbs the blue light rays but totally internally
reflects the green light rays toward the rightward facet of prism
16C. The rightward magenta control element C.sub.M biased against
the rightward facet of prism 16C absorbs the green light rays, so
no light rays exit through Cyan filter segment F.sub.C.
[0054] FIG. 3F depicts the situation in which the color green is
displayed by biasing the Cyan control element C.sub.C into optical
contact with the TIR interfaces at the rightward facet of prism 16A
and leftward facet of prism 16B, and biasing the yellow control
element C.sub.Y into optical contact with the TIR interfaces at the
rightward facet of prism 16B and leftward facet of prism 16C, with
the leftward and rightward magenta control elements C.sub.M being
biased away from the TIR interface. The color green is displayed
because only green light rays exit. Specifically, the yellow filter
segment F.sub.Y atop prism 16A absorbs blue incident light rays
I.sub.B and passes both red and green incident light rays I.sub.R,
I.sub.G; both of which are totally internally reflected at the
leftward facet of prism 16A toward the rightward facet of prism
16A. The Cyan control element C.sub.C biased against the rightward
facet of prism 16A absorbs the reflected red light rays but totally
internally reflects the reflected green light rays toward and
through yellow filter segment F.sub.Y as rays R.sub.G. The magenta
filter segment F.sub.M atop prism 16B absorbs green incident light
rays I.sub.G and passes both red and blue incident light rays
I.sub.R, I.sub.B toward the leftward facet of prism 16B. The Cyan
control element C.sub.C biased against the leftward facet of prism
16B absorbs the red light rays but totally internally reflects the
blue light rays the rightward facet of prism 16B. The yellow
control element C.sub.Y biased against the rightward facet of prism
16B absorbs the blue light rays, so no light rays exit through
magenta filter segment F.sub.M. The Cyan filter segment F.sub.C
atop prism 16C absorbs red incident light rays I.sub.R and passes
both green and blue incident light rays I.sub.G, I.sub.B toward the
leftward facet of prism 16C. The yellow control element C.sub.Y
biased against the leftward facet of prism 16C absorbs the blue
light rays but totally internally reflects the green light rays
toward the rightward facet of prism 16C where the reflected green
light rays again undergo total internal reflection toward and exit
through Cyan filter segment F.sub.C as rays R.sub.G.
[0055] FIG. 3G depicts the situation in which the color blue is
displayed by biasing the leftward magenta control element C.sub.M
into optical contact with the TIR interface at the leftward facet
of prism 16A, and biasing the rightward magenta control element
C.sub.M into optical contact with the TIR interface at the
rightward facet of prism 16C, and biasing the Cyan control element
C.sub.C into optical contact with the TIR interfaces at the
rightward facet of prism 16A and leftward facet of prism 16B, with
the yellow control element C.sub.Y being biased away from the TIR
interface. The color blue is displayed because only blue light rays
exit. Specifically, the yellow filter segment F.sub.Y atop prism
16A absorbs blue incident light rays I.sub.B and passes both red
and green incident light rays I.sub.R, I.sub.G toward the leftward
facet of prism 16A. The leftward magenta control element C.sub.M
biased against the leftward facet of prism 16A absorbs the green
light rays but totally internally reflects the red light rays
toward the rightward facet of prism 16A. The Cyan control element
C.sub.C biased against the rightward facet of prism 16A absorbs the
red light rays, so no light rays exit through yellow filter segment
F.sub.Y. The magenta filter segment F.sub.M atop prism 16B absorbs
green incident light rays I.sub.G and passes both red and blue
incident light rays I.sub.R, I.sub.B toward the leftward facet of
prism 16B. The Cyan control element C.sub.C biased against the
leftward facet of prism 16B absorbs the red light rays but totally
internally reflects the blue light rays the rightward facet of
prism 16B where the reflected blue light rays again undergo total
internal reflection toward and exit through magenta filter segment
F.sub.M as rays RB. The Cyan filter segment F.sub.C atop prism 16C
absorbs red incident light rays I.sub.R and passes both green and
blue incident light rays I.sub.G, I.sub.B; both of which are
totally internally reflected at the leftward facet of prism 16C
toward the rightward facet of prism 16C. The rightward magenta
control element C.sub.M biased against the rightward facet of prism
16C absorbs the green light rays but totally internally reflects
the blue light rays toward and through Cyan filter segment F.sub.C
as rays R.sub.B.
[0056] FIG. 3H depicts the situation in which the color black is
displayed by biasing the leftward magenta control element C.sub.M
into optical contact with the TIR interface at the leftward facet
of prism 16A, and biasing the rightward magenta control element
C.sub.M into optical contact with the TIR interface at the
rightward facet of prism 16C, and biasing the Cyan control element
C.sub.C into optical contact with the TIR interfaces at the
rightward facet of prism 16A and leftward facet of prism 16B, and
biasing the yellow control element C.sub.Y into optical contact
with the TIR interfaces at the rightward facet of prism 16B and
leftward facet of prism 16C. The color black is displayed because
no light rays exit. Specifically, the yellow filter segment F.sub.Y
atop prism 16A absorbs blue incident light rays I.sub.B and passes
both red and green incident light rays I.sub.R, I.sub.G toward the
leftward facet of prism 16A. The leftward magenta control element
C.sub.M biased against the leftward facet of prism 16A absorbs the
green light rays but totally internally reflects the red light rays
toward the rightward facet of prism 16A. The Cyan control element
C.sub.C biased against the rightward facet of prism 16A absorbs the
red light rays, so no light rays exit through yellow filter segment
F.sub.Y. The magenta filter segment F.sub.M atop prism 16B absorbs
green incident light rays I.sub.G and passes both red and blue
incident light rays I.sub.R, I.sub.B toward the leftward facet of
prism 16B. The Cyan control element C.sub.C biased against the
leftward facet of prism 16B absorbs the red light rays but totally
internally reflects the blue light rays the rightward facet of
prism 16B. The yellow control element C.sub.Y biased against the
rightward facet of prism 16B absorbs the blue light rays, so no
light rays exit through magenta filter segment F.sub.M. The Cyan
filter segment F.sub.C atop prism 16C absorbs red incident light
rays I.sub.R and passes both green and blue incident light rays
I.sub.G, I.sub.B toward the rightward facet of prism 16C. The
yellow control element C.sub.Y biased against the leftward facet of
prism 16C absorbs the blue light rays but totally internally
reflects the green light rays toward the rightward facet of prism
16C. The rightward magenta control element C.sub.M biased against
the rightward facet of prism 16C absorbs the green light rays, so
no light rays exit through Cyan filter segment F.sub.C.
[0057] By selectably varying the voltages applied between electrode
20 and each of electrodes 24, 26, 28, 30 one may vary the extent to
which the respective control elements are biased toward and/or away
from the aforementioned TIR interfaces, thereby varying the extent
of color absorption and/or reflection at each such interface and
thus display any desired color. The apparatus can accordingly be
calibrated to display any particular color in response to a
corresponding particular combination of voltages applied between
electrode 20 and each of electrodes 24, 26, 28, 30. Alternatively,
color absorption can be controlled by means of dithering, which is
a technique used to simulate colors that are not within a currently
available color palette. For example, one may group adjacent
prismatic elements having different reflectivity characteristics
such that the group as a whole produces a color which none of the
individual prismatic elements within the group could produce. A
time-dithering approach can also be used to oscillate one or more
selected control elements into and out of the evanescent wave
region at a selected frequency and duty Cycle, thereby controlling
the amount of time that the control element remains within the
evanescent wave region and thus varying the absorption
characteristic at the TIR interface to produce any desired
color.
[0058] As shown in FIG. 2C, instead of providing a single control
element for each longitudinally adjacent leftward, rightward pair
of prism facets, one may provide a separate control element for
each prism facet, and provide a separate electrode on substrate 20
for each control element. FIG. 2C also shows that useful displays
can be formed with only two different types of "controllable prism
structure", each consisting of a prism, a color filter and two
color absorbing control members. A first type of controllable prism
structure is exemplified by prisms 16A and 16C, which both have a
yellow filter segment F.sub.Y, a Cyan colored control element
C.sub.C beneath the leftward prism facet, and a magenta colored
control element C.sub.M beneath the rightward prism facet. A second
type of controllable prism structure is exemplified by prism 16B,
the prism to the left of prism 16A, and the prism to the right of
prism 16C, all of which have a blue filter segment F.sub.B, a first
black colored control element C.sub.K1 beneath the leftward prism
facet, and a second black colored control element C.sub.K2 beneath
the rightward prism facet. It will be understood that a large
number of the two types of controllable prism structures are
interleaved to provide a spatially uniform distribution of both
types of structure in any selected macroscopic portion of the
display.
[0059] Control element C.sub.C is positioned above electrode
segment 24.sub.R, beneath the leftward (as viewed in FIG. 2C) facet
of prism 16A. Control element C.sub.M is positioned above electrode
segment 26.sub.L, beneath the rightward facet of prism 16A.
Application of a first voltage potential between electrodes 22,
24.sub.R biases (retracts) control element C.sub.C toward substrate
20, leaving a gap between control element C.sub.C and the adjacent
leftward facet of prism 16A, without affecting the prism to the
left of prism 16A. Application of a second voltage potential
between electrodes 22, 24.sub.R biases control element C.sub.C
toward sheet 10, placing control element C.sub.C in optical contact
with the adjacent leftward facet of prism 16A, again without
affecting the prism to the left of prism 16A. Application of the
first voltage potential between electrodes 22, 26.sub.L biases
(retracts) control element C.sub.M toward substrate 20, leaving a
gap between control element C.sub.M and the adjacent rightward
facet of prism 16A, without affecting prism 16B. Application of the
second voltage potential between electrodes 22, 26.sub.L biases
control element C.sub.M toward sheet 10, placing control element
C.sub.M in optical contact with the adjacent rightward facet of
prism 16A, again without affecting prism 16B. Appropriate control
voltages are similarly applied to electrodes 28.sub.R, 30.sub.L to
move control elements C.sub.C, C.sub.M with respect to prism 16C;
and, to electrodes 26.sub.R, 28.sub.L to move control elements
C.sub.K1, C.sub.K2 with respect to prism 16B. As in the case of the
FIG. 2A embodiment, each control element in the FIG. 2C embodiment
may be an electrically conductive (or flexible conductor-bearing)
elastomer material which can be controllably electronically
actuated to deform the material into optical contact with the prism
facets, and which regains its original shape when such electronic
actuation is discontinued.
[0060] In the FIG. 2C display, the first type of controllable prism
structure can be actuated to display any of the colors yellow,
green, red or black. More particularly, the color yellow is
displayed by biasing both control elements C.sub.Y and C.sub.M away
from the respective prism facet TIR interfaces. The color yellow is
displayed because equal proportions of the colors red and green
exit. Specifically, the yellow filter F.sub.Y absorbs blue incident
light rays and passes both red and green incident light rays which
undergo total internal reflection twice within the prism and exit
through blue filter F.sub.B. The color green is displayed if the
Cyan control element C.sub.C is biased into optical contact with
the TIR interface at the leftward prism facet with the magenta
control element C.sub.M being biased away from the TIR interface at
the rightward prism facet. The color green is displayed because
only green light rays exit: the yellow filter F.sub.Y absorbs blue
incident light rays and passes both red and green incident light
rays; the Cyan control element C.sub.C biased against the leftward
prism facet absorbs red light rays, but totally internally reflects
green light rays toward the rightward prism facet which totally
internally reflects the green light rays toward and through blue
filter F.sub.B. The color red is displayed if the Cyan control
element C.sub.C is biased away from the TIR interface at the
leftward prism facet, with the magenta control element C.sub.M
being biased into optical contact with the TIR interface at the
rightward prism facet. The color red is displayed because only red
light rays exit: the yellow filter F.sub.Y absorbs blue incident
light rays and passes both red and green incident light rays, both
of which are totally internally reflected at the leftward prism
facet toward the rightward prism facet; the magenta control element
C.sub.M biased against the rightward prism facet absorbs green
light rays but totally internally reflects red light rays toward
and through blue filter F.sub.B.The color black is displayed by
biasing both control elements C.sub.Y and C.sub.M into optical
contact with the respective prism facet TIR interfaces. The color
black is displayed because no light rays exit: the yellow filter
F.sub.Y absorbs blue incident light rays and passes both red and
green incident light rays; the Cyan control element C.sub.C biased
against the leftward prism facet absorbs red light rays, but
totally internally reflects green light rays toward the rightward
prism facet; the magenta control element C.sub.M biased against the
rightward prism facet absorbs the green light rays, so no light
rays exit through blue filter F.sub.B.
[0061] In the FIG. 2C display, the second type of controllable
prism structure can be controllably actuated to produce either of
the colors blue or black. More particularly, the color blue is
displayed by biasing both black control elements C.sub.K1, C.sub.K2
away from the respective prism facet TIR interfaces. The color blue
is displayed because only blue light rays exit. Specifically, the
blue filter FB absorbs both red and green incident light rays and
passes only blue incident light rays which undergo total internal
reflection twice within the prism and exit through blue filter
F.sub.B. The color black is displayed if either one or both of the
black control elements C.sub.K1, C.sub.K2 are biased into optical
contact with the respective prism facet TIR interfaces. The color
black is displayed because no light rays exit: the blue filter FB
absorbs both red and green incident light rays and passes only blue
incident light rays which are absorbed by either of the black
control elements C.sub.K1, C.sub.K2, so no light rays exit through
blue filter F.sub.B. In a practical embodiment of the FIG. 2C
display, one need only provide for controllable actuation of black
control elements C.sub.K1, C.sub.K2 between two states; namely, a
"blue" state in which both control elements C.sub.K1, C.sub.K2 are
biased away from the respective prism facet TIR interfaces to
display the color blue; and, a "black" state in which both control
elements C.sub.K1, C.sub.K2 are biased into optical contact with
the respective prism facet TIR interfaces to display the color
black.
[0062] Due to the aforementioned spatially uniform distribution of
both types of controllable prism structure in any selected
macroscopic portion of the FIG. 2C display, the viewer perceives
colors which result from a combination of the colors produced by
the two types of structures. Because the two types of structures
can be controllably actuated as aforesaid to produce the primary
additive colors red, green and blue; and, by using the
aforementioned voltage variation or dithering techniques, one may
vary the color absorption characteristics at the respective TIR
interfaces to produce any desired color.
[0063] The embodiment of FIG. 2C is exemplary of a more general
version of the invention which requires only two different types of
prism structures. As in the case of the embodiment of FIGS. 2A and
2B, the first "type" of prism structure utilized in the more
general version of the invention consists of a prism, a color
filter with a first selected spectral absorption characteristic
(i.e. absorption as a function of wavelength) associated with a
first facet (i.e. base) of the prism, a first control member with a
second selected spectral absorption characteristic associated with
a second facet of the prism, and a second control member with a
third selected spectral absorption characteristic associated with a
third facet of the prism. The second "type" of prism structure
utilized in the more general version of the invention consists of a
prism, a color filter with a fourth selected spectral absorption
characteristic associated with a first facet (i.e. base) of the
prism; and, at least one first control member with a fifth selected
spectral absorption characteristic associated with either a second
or a third, or both second and third facets of the prism. There is
no essential relationship between the spectral absorption
characteristics selected for the first type of prism structure and
those selected for the second type of prism structure. One need
only ensure that the spectral absorption characteristics are
selected such that, for any selected set comprising proximate ones
of each of the two types of prism structure, controlled movement of
the members between particular selected combinations of their
possible respective positions causes the set as a whole to reflect
light which has an average spectral reflectance characteristic
corresponding to any one of three independent colors, with no one
of the independent colors being obtainable by mixing any other two
of the independent colors.
[0064] Because each of the control elements depicted in the FIG. 2A
embodiment is associated with not one but two prisms (i.e. control
element C.sub.C is associated with the rightward facet of prism 16A
and with the leftward facet of prism 16B), it is necessary to
select spectral characteristics for the filter and control elements
associated with any particular prism in the FIG. 2A embodiment such
that none of the spectral characteristics selected for the filter
and control elements associated with a prism adjacent to the
particular prism can be obtained by mixing any two of the spectral
characteristics selected for such adjacent prism. For example,
having selected Cyan for control element C.sub.C associated with
prism 16B, one must not select Cyan for the filter associated with
the adjacent prism 16A since Cyan colored control element C.sub.C
is already associated with the rightward facet of prism 16A.
However this restriction does not apply to the FIG. 2C embodiment,
because the control elements associated with any particular prism
in the FIG. 2C embodiment are not also associated with any adjacent
prism(s).
[0065] FIG. 4A provides an oblique pictorial illustration, on a
greatly enlarged scale, of a sheet of prismatic material 10. By
inverting sheet 10 to place the apices of its prisms in contact
with an adhesive bearing surface of substrate 32 one may form a
display structure (one small portion of which is seen in FIG. 5A)
with channels for containment of electrophoretically suspended
subtractive colored particles P.sub.C, P.sub.Y, P.sub.M. The
electrophoretic medium and particles can be selectively placed
between adjacent prism facets on sheet 10 after it is inverted as
shown in FIG. 4A, but before substrate 32 is adhesively bonded
thereto. Alternatively, sheet 10 can be bonded to substrate 32 as
aforesaid with an edge of sheet 10 (i.e. an edge intersecting the
direction of longitudinal extent of the prisms) being allowed to
extend a small distance beyond the adjacent edge of substrate 32.
Droplets of particle containing electrophoretic media selectively
placed in the extended portion of each channel are then wicked by
capillary pressure into and fill the respective channels. As
another alternative, the channels can be formed by inverting sheet
10, then contacting the prisms' apices with a liquid adhesive and
allowing the adhesive to cure such that it forms a liquid
impermeable barrier bridging the gap between adjacent prisms'
apices and extending almost the full length of the prisms, but
without filling the spaces between adjacent prism facets. Care is
taken to leave a small adhesive-free region along an edge of sheet
10 so that droplets of particle containing electrophoretic media
can subsequently be selectively placed in each channel by means of
capillary pressure, as described above. As a still further
alternative, precision ultrasonic welding techniques can be used to
seal the prisms' apices to substrate 32. Subtractive color filter
18A with its repetitively adjacent yellow, magenta, Cyan segments
F.sub.Y, F.sub.C, F.sub.M can be bonded to the outward surface of
sheet 10 after sheet 10 is bonded to substrate 32 as aforesaid,
care being taken to orient segments F.sub.Y, F.sub.C, F.sub.M over
the prisms as previously explained. Alternatively, before bonding
sheet 10 to substrate 32 as aforesaid, one may first embed
subtractive color filter 18B with its repetitively adjacent yellow,
magenta, Cyan segments F.sub.Y, F.sub.C, F.sub.M within sheet 10 to
form a display structure (one small portion of which is seen in
FIG. 5B) with channels for containment of subtractive colored
particles P.sub.C, P.sub.Y, P.sub.M. Persons skilled in the art
will understand that, in practice, many thousands of parallel,
longitudinally adjacent microscopically sized prisms and channels
are required to form a high resolution display of a size sufficient
for production of reasonably sized images. A large scale, low
resolution image display can be similarly formed, but without
microscopically small prisms.
[0066] As shown in FIG. 4B, each one of the prism-shaped channels
between adjacent prisms formed on prismatic sheet 10 can be
subdivided into a multiplicity of compartments by using
micro-replication casting techniques to form a plurality of
barriers 36 at spaced intervals along each channel. This
facilitates even distribution of subtractive colored particles
P.sub.C, P.sub.Y, P.sub.M within the channels by providing a
substantially equal quantity of Cyan colored particles P.sub.C
within each one of the compartments in a first channel, a
substantially equal quantity of yellow colored particles P.sub.Y
within each one of the compartments in a second channel, a
substantially equal quantity of magenta colored particles P.sub.M
within each one of the compartments in a third channel, etc. The
separate compartments ensure initial uniform distribution of the
particles along each channel and maintain such uniformity by
substantially preventing particles suspended in one compartment
from flowing into adjacent compartments (or channels) over
time.
[0067] An important characteristic of the FIG. 2B embodiment of the
invention is a large refractive index mismatch between sheet 10 and
the electrophoretic medium in channels 34A, 34B, 34C, 34D. As is
explained in the '103 application, if the index mismatch is
insufficient to attain the critical angle at the TIR interface,
then the FIG. 2B embodiment of the invention will not work. In such
case, a pair of prismatic surfaces can be used to ensure that the
incident light rays encounter the TIR interface at the requisite
angle, as is for example described in relation to the FIG. 5
embodiment of the '784 patent.
[0068] Besides having the desired low refractive index, Fluorinerts
are well also suited to use in displays formed in accordance with
the invention because they are good electrical insulators, and they
are inert. Fluorinerts also have low viscosity and high density, so
particles suspended in Fluorinerts can be moved electrophoretically
relatively easily. As noted above, ZnS is a preferred high
refractive index material suitable for use in forming sheet 10. The
sheet is preferably optically clear and has a high refractive index
of approximately 2.4 in the range of visible wavelengths of light.
(By "optically clear", it is meant that a substantial fraction of
light incident on the material at normal incidence will pass
through a selected thickness of the material, with only a small
fraction of such light being absorbed by the material. Diminished
optical clarity is caused by such absorption (typically a
combination of both absorption and scattering), as the light passes
through the material. In the FIG. 2B embodiment of the invention,
sheet 10 need only be approximately 10 microns thick. A material
which is "opaque" in bulk form may nevertheless be "optically
clear" for purposes of the present invention, if a 10 micron
thickness of such material absorbs (or absorbs and scatters) only a
small fraction of normal incident light.) ZnS is also well suited
to use in displays formed in accordance with the invention because
it has low absorption characteristics and consequently high optical
clarity in the aforementioned wavelength range. Further, ZnS is
available in sheet form and can be machined to yield the desired
prismatic microstructure as explained above.
[0069] Application of a voltage across the electrophoretic medium
in channels 34A, 34B, 34C, 34D electrostatically charges particles
P.sub.C, P.sub.Y, P.sub.M, causing them to move into the evanescent
wave region as aforesaid. When particles P.sub.C, P.sub.Y, P.sub.M
move into the evanescent wave region they must be capable of
frustrating TIR at the ZnS:Fluorinert interface for appropriate
light wavelengths (i.e. Cyan colored particles P.sub.C absorb red
light wavelengths, etc., as previously explained) by absorbing the
evanescent wave. Although particles P.sub.C, P.sub.Y, P.sub.M may
be as large as one micron in diameter, the particles' diameter is
preferably significantly sub-optical (i.e. an order of magnitude
smaller than one micron, say 100 nm in diameter) such that a
monolayer of particles at the TIR interface entirely fills the
evanescent wave region. Useful results are obtained if the diameter
of particles P.sub.C, P.sub.Y, P.sub.M is about one micron, but the
image display device's contrast ratio is reduced because the
ability of particles P.sub.C, P.sub.Y, P.sub.M to pack closely
together at the TIR interface is limited by their diameter. More
particularly, near the critical angle, the evanescent wave extends
quite far into the electrophoretic medium in channels 34A, 34B,
34C, 34D, so particles having a diameter of about one micron are
able to absorb the wave and thereby frustrate TIR. But, as the
angle at which incident light rays strike the TIR interface
increases relative to the critical angle, the depth of the
evanescent wave region decreases significantly. Relatively large
(i.e. one micron) diameter particles cannot be packed as closely
into this reduced depth region and accordingly such particles are
unable to frustrate TIR to the desired extent. Smaller diameter
(i.e. 100 nm) particles can however be closely packed into this
reduced depth region and accordingly such particles are able to
frustrate TIR for incident light rays which strike the TIR
interface at angles exceeding the critical angle.
[0070] As previously explained, a small critical angle is preferred
at the TIR interface since this affords a large range of angles
over which TIR may occur. The relatively large ratio of the index
of refraction of ZnS to that of Fluorinert yields a critical angle
of about 32.degree., which is quite small. In the absence of
electrophoretic activity, as is illustrated for channels 34A, 34C
and 34D in FIG. 2B, and further in the absence of subtractive color
filtration as previously explained, an incident light ray which
passes through sheet 10 undergoes TIR at the ZnS:Fluorinert
interface and is retro-reflected as illustrated. This is because
the 45.degree. angle at which the ray encounters a leftward prism
facet at the ZnS:Fluorinert TIR interface exceeds the interface's
32.degree. critical angle. The reflected light ray then encounters
the prism's rightward facet and again undergoes TIR at the second
prism face, because the 45.degree. angle at which the reflected ray
encounters the rightward facet (which also forms part of the
ZnS:Fluorinert TIR interface) exceeds the interface's 32.degree.
critical angle. After twice undergoing TIR as aforesaid the
retro-reflected ray exits through the ZnS:air interface and
emerges, as illustrated, in a direction nearly 180.degree. opposite
to the direction of the original incident ray, thus achieving a
"white" appearance in the reflected light.
[0071] As will be apparent to those skilled in the art in the light
of the foregoing disclosure, many alterations and modifications are
possible in the practice of this invention without departing from
the spirit or scope thereof. For example, yellow, magenta and Cyan
filter segments F.sub.Y, F.sub.M, F.sub.C need not occur in that
specific order in subtractive color filters 18A, 18B. It is only
necessary to select a particular ordering of the subtractive
primary colors yellow, magenta and Cyan and continuously repeat the
subtractive primary colors in the selected order to form filters
18A, 18B; to orient the filter segments as previously described
with respect to the prisms on sheet 10; and, to ensure that a
different subtractive primary color is selected for each of (i) the
filter segment atop a first prism, (ii) the filter segment atop a
second prism immediately adjacent to the first prism, and (iii) the
control element or particles disposed between the first and second
prisms. Accordingly, the scope of the invention is to be construed
in accordance with the substance defined by the following
claims.
* * * * *