 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is a continuation-in-part of the pending patent application
entitled "Optical Waveguide Display System" filed Apr. 12, 1989 and which
has U.S. Pat. Ser. No. 337,141 (still pending). The parent application
describes how to switch guided light out of an optical waveguide. Images
are formed by systematically switching light out of many parallel
waveguides arranged, side-by-side, on a substrate.
2. Prior Art
The prior application details how to switch (tap) guided light out from a
waveguide core with sound. Sound is generated by separate transducers
oriented alongside the length of a waveguide. Sound waves interact with
guided light via the acousto-optic effect. Changes in the waveguide
refractive index create light emitting regions at different locations
where individual transducers are placed along the length of the waveguide.
By using many transducers, and many parallel waveguides, images can be
formed on a viewing screen.
Recently, research has revealed a number of limitations inherent in the
acousto-optic display method. First, acoustic taps have high electrical
drive power requirements because sound must be continuously generated to
operate the tap. Typically, sound from a transducer propagates
perpindicularly to the direction of light flow through a waveguide core.
This sound passes through the waveguide core and is absorbed by material
on the other side of the waveguide. Sound traveling beyond the waveguide
core does not interact with guided light. Consequently, since most of the
acoustic energy travels into non-core regions, sound must continuously be
generated by the transducer to operate the tap. This is wasteful, hence
the energy requirements of acoustic taps are high.
Second, optical waveguide displays have low resolutions due to the long
acousto-optic tap interaction lengths that are needed to efficiently
switch light out of the waveguide. The interaction length is the distance
light must travel through a waveguide tap before exiting from the core.
The screen resolution, as described in the prior application, is
determined by the number of consecutive taps which can be placed along the
length of a single waveguide. Thus, the longer the tap interaction length,
the fewer the number of taps which can be arranged along a given length of
waveguide. The acousto-optic tap interaction length is presently estimated
to be.apprxeq.10 cm.
The third major disadvantage to acousto-optic taps is the small degree with
which sound can change the waveguide refractive index. Sound can induce
refractive index changes in silicon dioxide and other commonly used
waveguide materials on the order of .DELTA.n.apprxeq.10.sup.-5. Because
this refractive index change is extremely small, waveguides must be
specially designed so waveguide taps can function with small acousto-optic
effects.
Waveguides suitable for use in conjunction with acousto-optic taps are
constructed by making the cladding layer surrounding the core very thin. A
thin cladding layer allows the evanescent field of core guided light to
interact with materials outside the cladding. A small refractive index
change in a thin cladding waveguide shifts the evanescent field of the
guided light out beyond the cladding. Once outside the cladding, guided
light is scattered, or refracted, so it can be seen by a viewer.
Presently, the light guiding ability of a thin cladding waveguide changes
when it is exposed to different temperature conditions. A thin cladding
waveguide which guides light well at a low temperature will have an
increased attenuation at higher temperatures. This increased attenuation
is caused by the large refractive index change induced by the thermo-optic
effect. For example, a temperature difference in glass of only 20.degree.
C. causes a change in .DELTA.n>10.sup.-5. This thermo-optic refractive
index change is larger than the highest attainable acousto-optic
refractive index change. Consequently, a thin-cladding waveguide used in
conjunction with acoustic taps is very sensitive to thermal conditions and
can only operate in an environment where the temperature is carefully
controlled.
Art related to this invention is disclosed by M. Gottlieb and G.B. Brandt,
"Temperature sensing in optical fibers using cladding and jacket loss
effects", Applied Optics, Vol. 20, No. 22, Nov. 15, 1981, pp. 3867-3873;
M. Gottlieb et. al "Measurement of Temperature with Optical Fibers", ISA
Transactions, Vol. 19, No. 4, pp. 55-62; J. R. Hill et. al., "Synthesis
and Use of Acrylate Polymers for Non-linear Optics", Organic Materials for
Non-linear Optics, Royal Society of Chemistry - Dalton Division, Oxford,
29-30 June 1988, pp. 405-411; J. R. Hill et. al., "Demonstration of the
linear electro-optic effect in a thermopoled polymer film", J. Appl.
Phys., Vol. 64, No. 5, Sept. 1, 1988, pp. 2749-2751; E.A. Chandross et.
al., "Photolocking - A new technique for fabricating optical waveguide
circuits", Appl. Phys. Lett., Vol. 24, No. 2, Jan. 15, 1974, pp. 72- 74;
Hilmar Franke, "Optical recording of refractive-index patterns in doped
poly - (methyl methacrylate) films", Applied Optics, Vol. 23, No. 16, Aug.
15, 1984, pp. 2729-2733; Takashi Kurokawa, "Polymer optical circuits for
multimode optical fiber systems", Applied Optics, Vol. 19, No. 18, Sept.
15, 1980, pp. 3124-3129; M. Haruna and J. Koyama, "Thermooptic reflection
and switching in glass", Applied Optics, Vol. 21, No. 19, Oct. 1, 1982,
pp. 3461-3465; Andrew J. Lovinger, "Ferroelectric Polymers", Science, Vol.
220, No. 4602, June 10, 1983, pp. 1115-1121; D. Bosc and P. Grosso,
"Polymer acousto-optic modulator working at 20 Mhz", 2nd International
Conference on Passive Components: Materials, Technologies, Processing,
Paris, France, Nov. 18-20, 1987, pp. 107-112; D. R. Ulrich, "Overview:
Non-linear Optical Organics and Devices", Organic Materials for Non-linear
Optics, Royal Society of Chemistry - Dalton Division, Oxford, June 29-30,
1988, pp. 241-263; Brettle et. al., "Polymeric non-linear optical
waveguides", SPIE Vol. 824 Advances in Nonlinear Polymers and Inorganic
Crystals, Liquid Crystals, and Laser Media (1987 ), pp. 171-177; R. Lytel
et. al., "Advances in organic electro-optic devices", SPIE Vol. 824
Advances in Nonlinear Polymers and Inorganic Crystals, Liquid Crystals,
and Laser Media (1987), pp. 152-161; NCAP Technology Report, Taliq
Corporation, Sunnyvale CA.
SUMMARY OF THE INVENTION
Objects of the Invention
Accordingly, it is an object of this invention to show an improved
electroptic tap for use in optical waveguide display systems.
Another object is to show an improved waveguide tap comprising a long
interaction region and a light reflecting element.
Yet another object is to show a staggered, multi-waveguide, tap-arrangement
method which enables high screen pixel resolutions to be maintained while
using long interaction length taps.
A further object is to show waveguide manufacturing techniques based on
thermo-poling, photolocking, extrusion and preform/furnace fiber drawing.
Another object is to show a Graded Index (GRIN) microlens focusing method
for efficiently guiding light from a source into many waveguide core
elements.
Yet another object is to show how to use broad-spectrum light to produce
color display images in optical waveguide displays.
Still another object is to show a new type of thermo-optic waveguide tap.
These and additional objects, features and advantages of the present
invention will become more obvious from the following description when
taken in connection with the accompanying drawings.
Brief Description
The invention comprises a number of improvements in the individual elements
required to construct an optical waveguide display. For example, a new
long interaction length waveguide tap based on electroptic effects is
detailed. Also, a focusing element which directs light from the source
into the waveguide cores is introduced. Finally, polymer processing
techniques are described which make waveguide displays less expensive to
manufacture. Taken together, these improvements enable large flat panel
screens to be economically produced.
A new type of waveguide tap structure is introduced. In the tap interaction
region, guided light is coupled through the cladding, from the core, into
a second waveguide running alongside the cladding. The second waveguide,
hereinafter referred to as the "supercladding", guides light in a
direction oriented parallel to the core. Light coupled out from the core
travels through the supercladding until it hits a small reflector formed
in the supercladding. The reflector, in turn, directs light out of the
supercladding to the viewer. Thus, light coupled into the supercladding
from the core over a long interaction length appears as a small light
emitting region located at a supercladding reflector.
The supercladding/reflector tap structure enables high screen resolutions
to be maintained while using long interaction length taps. To maintain a
high screen resoltion multiple waveguides are placed, side-by-side, next
to each other. Each waveguide still contains a small number of long
interaction length supercladding/reflector taps. However, the reflectors
on separate waveguides are slightly offset, or staggered, to achieve a
higher resolution. The combined effect of many parallel waveguides, each
with their limited number of staggered taps, increases the display
resolution.
Another important innovation is an energy efficient tap design which uses
electro-optic effects. Electro-optic materials change their index of
refraction in an electric field. By using electro-optic materials to
construct the waveguide core, cladding and/or supercladding elements the
amount of power needed to drive the taps, and hence the screen, is
lowered. Non-linear and ferroelectric polymers are presently considered
the best electro-optic waveguide building materials.
An entirely different type of tap based on thermo-optic effects is also
described. Thermo-optic taps comprise a heating element placed in close
proximity to the waveguide core, cladding and supercladding. The heating
element causes the index of refraction in these waveguide layers to change
at different rates. Slight differences in the refractive index rate of
change in separate waveguide layers force light to couple out of the core
and into the supercladding. Thermo-optic taps are simple to fabricate and
have excellent environmental stability.
Improvements in the light-source-to-waveguide-coupling elements are also
presented. Graded Index lenses (GRIN) reduce a collimated beam of light to
a very small size. Multiple GRIN lenses are used to efficiently focus
light from a source into the many waveguide core elements used in the
display.
Finally, plastic waveguide processing techniques are described which enable
large numbers of waveguides to be economically manufactured. Plastics can
be extruded, molded, laminated, etched, doped, drawn, stamped, machined,
thermo-poled and photolocked to form optical waveguides. Optical
waveguides can be mass produced using these manufacturing techniques at a
low cost.
The attainment of the foregoing and related objects, features and
advantages of the invention will be more readily apparent to those skilled
in the art, after review of the following detailed description of the
invention, taken together with the included drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a side view of a waveguide tap showing how light is coupled out
of a core into a supercladding and reflected out to the viewer.
FIG. 1B is a side view of waveguide tap showing how light is coupled out of
a core into a supercladding, reflected back through the waveguide core,
and directed out to the viewer.
FIG. 1C is a side view of a waveguide tap showing how light is coupled out
into two supercladdings placed on each side of a waveguide core, reflected
from the front and reflected back through the waveguide core, and directed
out to the viewer.
FIG. 2A is a schematic view of a single waveguide with multiple short
interaction length taps placed at even intervals along its length.
FIG. 2B is a schematic view of two waveguides with medium interaction
length taps, and staggered reflectors, that when taken in combination,
achieve the same adjacent pixel resolution as shown in FIG. 2A.
FIG. 2C is a schematic view of four waveguides with long interaction length
taps, and staggered reflectors, which achieve the same adjacent pixel
resolution as shown in FIG. 2A.
FIG. 3A is an end view of a ribbon containing multiple supercladding
elements arranged on one side of multiple core elements.
FIG. 3B is an end view of a ribbon containing multiple supercladding
elements arranged on both sides of multiple core elements.
FIG. 4A is an end view of a ribbon containing multiple supercladding
elements arranged on one side of multiple core elements such that the
core, cladding and supercladding elements are isolated from each other.
FIG. 4B is an end view of a ribbon containing multiple supercladding
elements arranged on both sides of the ribbon cores where the core,
cladding and supercladding elements are isolated from each other.
FIG. 5A is the back of a waveguide ribbon which shows the intensity
modulator and tap electrodes.
FIG. 5B is the light emitting side of the same ribbon in FIG. 5 showing the
ground conductors and supercladding reflectors which direct light out from
the waveguides to the viewer.
FIG. 6 is a rear view of a complete display comprising a light source,
multiple ribbons which are folded and spread out side-by-side to cover a
substrate.
FIG. 7A shows a thermo-optic tap element which switches light by heating an
element placed in close proximity to the core, cladding and supercladding
elements.
FIG. 7B shows a thermo-optic tap element which switches light by heating
the cladding and supercladding elements through the core.
FIG. 8A shows a waveguide ribbon based on the thermo-optic tap shown in
FIG. 7A.
FIG. 8B shows a waveguide ribbon based on the thermo-optic tap shown in
FIG. 7B.
FIG. 9A shows a photolocking process used to manufacture optical waveguide
ribbon.
FIG. 9B shows a thermo-poling process used to manufacture optical waveguide
ribbon.
FIG. 10A shows a side view of a extrusion process used to manufacture
waveguide ribbon.
FIG. 10B shows a front view of the extrusion manufacturing process shown in
FIG. 10A.
FIG. 11 shows a ribbon manufacturing process based on heating and drawing a
ribbon preform containing multiple waveguide elements.
FIG. 12 shows a block diagram of a complete optical waveguide display
system.
DRAWING REFERENCE NUMBERS
1 Optical waveguides
2 Width of a single waveguide
3 All of the waveguides with staggered taps which make up a vertical column
4 Reflector spacing when more than one waveguide is in a column 3
6 Reflector spacing when a single waveguide is used for column 3
8 Tap interaction region (i.e. - where light is coupled from the core into
the super cladding)
10 Reflector region (i.e. - where light is directed out of the
supercladding to the viewer)
12 Direction of light flow through the waveguide
14 Ground
16 DC voltage
18 Signal conductor
20 Ground conductor
21 Ground conductor for intensity modulators
22 Cladding
24 Thin-layer cladding (i.e. - electro-optic material)
25 Waveguide isolation layer (clear optical, metallic or opaque material)
26 Supercladding (i.e. - electro-optic material)
28 Core
30 Direction of light reflected out of supercladding to the viewer
32 Light exiting the end of the waveguides
34 Dark layer to improve screen contrast ratio
36 Intensity modulator ribbon reflector elements
37 Tap conductor element extends to edge of ribbon
38 Staggered tap fingers define a vertical column 3
39 Reflector regions on ribbon direct tap supercladding light to the viewer
40 Interaction region 8 for intensity modulators
41 Intensity modulator spacing
42 Large size bonding pads associated with intensity modulators
43 Intensity modulator electrode
44 Light source
46 White light from source 44
48 Collimating focusing optics
50 Collimated white light
52 Light coloring element
54 Colored light
56 Focusing lens (GRIN) to direct collimated and colored light 54 into the
ribbon cores
58 Focused light entering ribbon stack 60
60 Stack of waveguide ribbons
62 Bend regions where each ribbon in the stack is folded over and arranged
across the substrate
64 Screen substrate
66 Individual ribbons
67 Light exiting the end of the ribbons
68 Clear viewing window in substrate so light can make it from the ribbon
reflectors 39 to the viewer
70 Gap between separate ribbons taps - usually made conductive
72 Heating element
74 Optical buffer for separating thermal heating element 72
76 Substrate material (also cladding)
78 Core
80 Light confined in core
82 Light coupled into supercladding
84 Supercladding
86 Heated region
88 Thin cladding between core and supercladding
90 Electronics to control the intensity modulators
92 Electronics to control the taps
94 Controller which provides information and synchronizes the tap and
intensity modulators to form complete screen images
96 Electrode brushes contacting the ribbon electrodes to pole waveguide
regions into the ribbon
98 Heat
100 Thermo-poled waveguides formed in the plastic sheet
102 Direction ribbon moves through processing machine
104 Direction ribbon on spool rotates
106 Unprocessed ribbon on the spool
108 Ribbon before it encounters the waveguide processing step
110 Photolocking light source to expose waveguide regions in the ribbon
112 Light beams passing through ribbon 108 to expose the waveguide regions
114 Waveguide regions formed by heating the plastic material 108
116 Rollers
118 Extrusion die
120 Melted optical grade plastic or glass
122 Vesicle containing melted optical waveguide material
124 Waveguides formed by extrusion
126 Fiber preforms before heat-drawing
128 Furnace to melt and stretch prefroms
130 Direction preform is passed through the furnace
132 Waveguide preforms being heated, stretched and reduced to a smaller siz
e
DETAILED DESCRIPTION OF THE INVENTION
Waveguide Taps
Turning now to the drawings, more particularly FIGS. 1A-1C, which show side
views of three different long interaction length waveguide taps. The taps
shown in these diagrams employ the electro-optic effect. However, long
interaction length taps based on acousto-optic, thermo-optic and
magneto-optic effects may also be constructed based on the ideas presented
in the following sections. It is strongly intended that long interaction
length taps which use these other effects be included within the scope of
this discussion.
FIG. 1A shows light 32 traveling through a waveguide core 28. The tap is
controlled by applying a voltage difference between conductors 20 and 18.
The electric field produced by the voltage difference induces the
electro-optic material in the tap interaction region 8 to change its index
of refraction. Changes in the waveguide refractive index allow light to
exit the core and enter into the supercladding 26.
Light travels through the transparent supercladding until it hits a
reflector. FIGS. 1A-1C show three angled reflector regions 10 formed in
the supercladding. The reflector redirects light out 30 of the
supercladding so it can be observed. The reflector is preferrably formed
by etching a pit in the supercladding. The pit is partially metalized, so
that supercladding light entering the pit is blocked and reflected out of
the supercladding 30. All the light traveling through the supercladding
hits a reflector and is directed out 30 to the viewer. The interaction
length 8 plus the reflector region length 10 equals the total length of a
tap.
FIG. 1B shows light 30 being reflected out through the waveguide core 28
and cladding 22 layers. As in FIG. 1A, light is coupled out into the
supercladding 26 in the interaction region 8. However, instead of being
reflected 30 directly to the viewer, light in the supercladding 26 must
first pass through the cladding 22 and core 28 layers.
FIG. 1C shows a hybrid combination of the taps shown in FIGS. 1A and 1B.
Two supercladdings 26, one on either side of the core, carry light tapped
out in the interaction region 8. By using two supercladdings the
interaction length 8 needed to couple light out from a waveguide core 28
is decreased. Light evanescently interacts more strongly with the
supercladdings 26 because there are two thin-claddings 24 arranged on each
side of the core 28. Reflectors formed in both supercladdings 10 direct
light to the viewer 30.
The preferred core-to-supercladding coupling mechanism uses the evanescent
field of the core guided light. Guided light can interact with materials
placed near the cladding and core via its evanescent field. Evanescent
field interactions allow very slight refractive index changes to
efficiently tap guided light out of the core and into the supercladding.
The supercladding is preferably made of a material with a higher index of
refraction than the core. A high supercladding index of refraction causes
light coupled into the supercladding to be angled away from the core.
Angling light away from the core causes it to be more centrally located in
the middle of the supercladding. This makes it is easier to remove light
at a reflector region 10 since the reflector pit does not need to be
formed as deeply in the supercladding 26 to remove the centrally located
supercladding light.
Either the cladding, core, and/or supercladding may be made of
electro-optic materials. In one embodiment only the cladding 24 is made of
an electro-optic material. A voltage difference 16 applied to the
electrodes causes the electro-optic cladding 24 to increase its index of
refraction. Increasing the cladding refractive index forces guided light
to interact with the supercladding 26. Light is stripped out of the core
and travels through the supercladding 26 until it hits a reflector region
10.
In a different tap embodiment, an electro-optic supercladding 26 can be
made to act as part of a non-electro-optic cladding. In this
configuration, the evanescent field of light in the waveguide core extends
through the cladding into the supercladding. When the tap is "off", the
supercladding has an index of refraction approximately equal to the
cladding. In the "off" state, the supercladding and cladding collectively
act to guide light through the waveguide. In other words, the cladding
alone is not enough to confine and guide light through the waveguide core.
However, when the tap is switched "on" the refractive index of the
electro-optic supercladding increases. This refractive index increase
couples light out from the waveguide core into the supercladding. Light
travels through the electro-optic supercladding until it hits a reflector
30.
Forming only the supercladding out of an electro-optic material has the
advantage that the core and cladding layers can be made from traditional
non-electro-optic waveguide materials. Very low loss non-electro-optic
materials have been developed which are capable of guiding light long
distances, typically 100 meters or more, with little attenuation. On the
other hand, electro-optic waveguide materials presently have optical
losses in the range of 1 dB/cm. If the core and cladding were made of
currently available electro-optic materials, attenuation of light in the
waveguide would be prohibitively high.
To reduce loss, the waveguide is designed so only a small fraction of the
guided evanescent wave extends past the cladding into the electro-optic
supercladding. Most of the light in the waveguide travels through the
non-electro-optic core and cladding. Only the small fraction of guided
light which actually extends into the electro-optic supercladding is more
highly attenuated. Thus, high loss electro-optic materials can still be
used to build display waveguides.
There are other ways to use electro-optic materials to tap light out of
optical waveguides. Diffractive and/or refractive effects may also be
employed. For example, the core can be made of alternating layers of
electro-optic and non-electro-optic materials. (not shown) In the absence
of an electric field, the electro-optic and non-electro-optic layers are
chosen so they have the same index of refraction. However, when an
electric field is applied to the waveguide, an increase in the index of
refraction in the electro-optic core layers causes an irregular core
refractive index. Diffraction and refraction effects caused by this
irregular core refractive index force light to exit into the
supercladding.
It is possible that a single supercladding reflector 10 will not be
sufficient to deflect out all of the light in the supercladding 26. It is
important that the reflector remove all of the light in the supercladding,
otherwise, light will continue through the supercladding and be reflected
at the next reflector. Light leaking between consecutive waveguide
supercladding reflectors distorts the screen image. To prevent light
leakage, multiple reflectors (not shown) may be placed close next to each
other. A plurality of closely spaced reflectors in region 10 will insure
all of the supercladding light is removed and directed to the viewer 30.
Other reflector-like means may also be used to remove supercladding light.
For example, a diffusing material containing small scattering centers may
be used to re-fill a supercladding reflector pit. Light interacting with
the many small scattering centers will be re-directed out of the
supercladding. Other light re-directing means based on lenses, pigments,
and dyes can also be used. In general, anything which scatters, absorbs,
deflects, refracts or blocks supercladding light can be used in a
reflector region 10.
It should be mentioned that long interaction length 8 taps are relatively
tolerant to irregularities encountered during the manufacturing process.
The performance of long interaction length taps degrades gracefully due to
their long length. Interaction lengths 8 typically will vary from 0.1-20
cm. This is much longer than the core and cladding dimensions which will
typically be in the micron range. As a result, small irregularities in
optical materials and the waveguide core and cladding dimensions have
minimal effects on the performance of the waveguide tap.
In FIGS. 1A-1C the ground is 14 is connected to the bottom conductor 20 and
the positive voltage 16, or signal, is connected to the top conductor 18.
The connection of the ground 14 and voltage 16 to conductors 18 and 20 may
be switched if desired. In fact, FIGS. 5 and 6 show layer 18 connected to
ground 14 and layer 20 connected to the signal 16.
Staggered Taps on Multiple Waveguides
FIGS. 2A-2C show a schematic view of optical waveguide taps. The
perspective in FIGS. 2A-2C is that of a viewer looking at the front of the
display screen. If light were actually flowing direction 12 and emitted
from the reflectors 30 shown in FIGS. 2B and 2C it would travel from the
page toward the reader.
As previously mentioned, the small refractive index changes which can be
achieved with acousto-optic, electro-optic and thermo-optic effects
necessitate long tap interaction lengths. Long tap interaction lengths are
needed to efficiently remove light from the waveguide. Short interaction
length 8 taps can not remove enough core light to brightly illuminate
screen pixels.
The total number of taps arranged along the length of a waveguide
determines the resolution along one dimension of the display. Therefore,
long tap interaction lengths 8 result in low screen resolutions.
Consequently, there is a tradeoff between the screen resolution and the
tap efficiency, or screen brightness. Long taps remove more light from the
waveguide and are brighter. However, long taps cause the screen resolution
to be low. Short taps increase the screen resolution, but at the expense
of the screen brightness.
FIG. 2A shows a single waveguide with many short interaction length 6 taps.
The only way to increase the resolution of a screen built with the
waveguide shown in FIG. 2A is to decrease the tap interaction length 6.
However, decreasing the tap interaction length 6 will decrease the
efficiency of the taps.
FIGS. 2B and 2C show how to use multiple waveguides to achieve high screen
resolutions with long interaction length taps. FIG. 2B shows two
waveguides 1; each with half the width 2 of the single waveguide width 3
shown in FIG. 2A. The tap interaction length 8 plus the reflector region
length 10 on each waveguide is twice as long as on the single waveguide
shown in FIG. 2A. By staggering the interaction 8 and reflector 10 regions
on two separate waveguides, the adjacent pixel spacing 4 is kept equal to
the short tap interaction length 6 shown in FIG. 2A.
FIG. 2C shows how the tap interaction length increases when four waveguides
are placed side-by-side. The interaction length 8 and reflector region 10
is twice as long as it is in FIG. 2B and four times as long as in FIG. 2A.
Again, all of the light coupled out in the interaction region 8 is
directed out of the waveguide at a reflector 10.
Many more than four parallel waveguides can be placed next to each other to
achieve even longer interaction lengths 8. For example, if each reflector
spacing 4 is 2 mm, each waveguide is 100 uM wide 2, and there are 20
waveguides in a column 3, the interaction 8 and reflector 10 length on
each waveguide will be 40 mm. With these specifications a 500.times.500
element display screen can fit on a 1.times.1 meter substrate 64.
Staggering taps on separate waveguides causes consecutive pixels along the
direction of light flow 12 to be horizontally displaced. Consecutive
pixels in a column 3 have a "jagged" or "staircase" look because they are
placed on separate, adjacent, waveguides. In addition, since the reflector
size 10 gets smaller as more waveguides are placed next to each other,
light emitted 30 from a reflector region 10 will appear as a small,
point-like source.
To smooth the jagged, point-like, reflector appearance a diffusing material
(not shown) may be positioned between the viewer and the reflectors 10. A
diffusing material scatters reflector light and makes a larger light
emitting area. Consequently, instead of a small point source, the
diffusing layer causes reflector light to appear as a large, planar, light
emitting area. Reflector light 30 traveling through the diffusing layer
should exit with a lambertian intensity profile.
Reflector light scattered in the diffusing layer should be confined to a
region with a width which equals all the parallel waveguides 1 in a
column. For example, in FIGS. 2B and 2C, light emitted from a reflector 30
should illuminate an area in the diffusing layer equal to the column width
3. The length of the light diffusing region should equal the adjacent
reflector spacing 4 or 6.
Reflector 30 light in the diffusing layer can be isolated by forming light
barriers in the diffusing material. Light barriers are conveniently formed
by molding, stamping or extruding a diffusing plastic to create optically
separate scattering regions. In this way, screen pixels can be made which
have large, sharply defined, light emitting areas.
Optical Waveguide Ribbon
FIGS. 3A-3B and 4A-4B show cross sections of four different types of
optical waveguide ribbon. FIG. 3A, shows multiple waveguide ribbon cores
28 surrounded by cladding 22. A thin cladding layer 24 is positioned
between the core 28 and the supercladding 26. The core is typically 1-200
uM thick. Light is coupled out of the cores 28, through the thin cladding
24, into the supercladding 26 and travels 30 to the viewer. As previously
mentioned, the light coupling method may use evanescent field coupling,
diffractive or other refractive effects.
A light absorbing material 34 is placed on one side of the ribbon to
increase the screen contrast ratio. The light absorbing material can be
placed on either side of the ribbon depending on how the reflectors 10 are
formed in the supercladding. If the reflector is similar to the one shown
in FIG. 1A, the light absorbing material 34 is placed on the top. If the
tap is similar to the one shown in FIG. 1B, the absorbing layer 34 | | |
