U.S. patent application number 11/398376 was filed with the patent office on 2007-10-11 for forming spectral filters.
Invention is credited to Charles R. III Barker, Barret Lippey.
Application Number | 20070236809 11/398376 |
Document ID | / |
Family ID | 38421492 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070236809 |
Kind Code |
A1 |
Lippey; Barret ; et
al. |
October 11, 2007 |
Forming spectral filters
Abstract
A lens bears a plurality of roll-coated layers to pass, to one
eye of a viewer, a first image, in a first band of wavelengths,
that is appropriate for 3D viewing of a stereoscopic image.
Inventors: |
Lippey; Barret; (Belmont,
MA) ; Barker; Charles R. III; (Framingham,
MA) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Family ID: |
38421492 |
Appl. No.: |
11/398376 |
Filed: |
April 5, 2006 |
Current U.S.
Class: |
359/722 ;
348/E13.026 |
Current CPC
Class: |
G02B 5/285 20130101;
G02C 7/00 20130101; H04N 13/324 20180501; H04N 13/334 20180501;
G02B 30/00 20200101; H04N 13/30 20180501; H04N 2213/008 20130101;
G02B 30/23 20200101 |
Class at
Publication: |
359/722 |
International
Class: |
G02B 13/00 20060101
G02B013/00 |
Claims
1. An apparatus comprising a lens bearing a plurality of
roll-coated layers to pass, to one eye of a viewer, a first image,
in a first band of wavelengths, that is appropriate for 3D viewing
of a stereoscopic image.
2. The apparatus of claim 1 in which the lens comprises layers
adhered to a substrate in a roll-coating process and having optical
properties and thicknesses such that the combination of the layers
transmits light within the first band of wavelengths and does not
transmit light within a second band of wavelengths.
3. The apparatus of claim 2 in which the optical properties and
thicknesses of the layers are such that the combination of the
layers transmits light with a third and fourth band of wavelengths
and does not transmit light within a fifth and sixth band of
wavelengths.
4. The apparatus of claim 1 also comprising a second lens bearing a
roll-coated layer to pass, to a second eye of a viewer, a second
image, in a second band of wavelengths, that is complementary to
the first image for 3D viewing of the stereoscopic image.
5. The apparatus of claim 1 in which the first band of wavelengths
comprises a band of wavelengths around 435 nm.
6. The apparatus of claim 2 in which the first band of wavelengths
comprises a band of wavelengths around 435 nm, and the second band
of wavelengths comprises a band of wavelengths around 475 nm.
7. The apparatus of claim 3 in which the first band of wavelengths
comprises a band of wavelengths around 435 nm, the second band of
wavelengths comprises a band of wavelengths around 475 nm, the
third band of wavelengths comprises a band of wavelengths around
510 nm, the fourth band of wavelengths comprises a band of
wavelengths around 610 nm, the fifth band of wavelengths comprises
a band of wavelengths around 550 nm, and the sixth band of
wavelengths comprises a band of wavelengths around 660 nm.
8. The apparatus of claim 1 in which the lens comprises a substrate
sheet having curvature, the roll-coated layer having a generally
uniform thickness normal to the sheet at points along the
curvature, the curvature being such that when the lens is
positioned near a person's face, points along a surface of the
lens, in one plane, are a relatively uniform distance from the eye
of the viewer.
9. The apparatus of claim 1 in which the lens comprises a substrate
sheet having curvature, the roll-coated layer having a generally
uniform thickness normal to the sheet at points along the
curvature, the curvature having a radius of curvature such that
when the lens is positioned near a person's face, the radius is
approximately equal to the distance between the coating and the
center of the eye.
10. The apparatus of claim 9 in which the radius of curvature is
between about 1/2 inch and 4 inches.
11. A set of glasses comprising a frame to hold two lenses, a first
lens including a roll-coated filter to pass light in a first set of
bands of wavelengths and reflect light in a second set of bands of
wavelengths, and a second lens including a roll-coated filter to
pass light in a portion of the second set of bands of wavelengths
and reflect light in a portion of the first set of wavelengths.
12. An apparatus comprising glasses to view a stereoscopic image,
the glasses comprising a first lens bearing a roll-coated optical
layer to pass, to one eye of a viewer, a first image that is
appropriate for 3D viewing of the stereoscopic image, and a second
lens bearing a roll-coated optical layer to pass, to a second eye
of a viewer, a second image that is complementary to the first
image for 3D viewing of the stereoscopic image.
13. Glasses, to view a 3D frame or video presentation, comprising a
supporting structure, and a pair of curved lenses, each lens
bearing layers having a substantially constant thickness normal to
a surface of the lens, the layers configured to filter images of
the presentation projected in two non-overlapping bands of
wavelengths of light as they are viewed through the lenses, to
produce a 3D impression for a viewer the lenses each having a
radius of curvature between about 1/2 inch and 4 inches.
14. An apparatus comprising a first lens including roll-coated
layers of materials selected to transmit light having a first set
of wavelengths, and a second lens including roll-coated layers of
materials selected to transmit light having a second set of
wavelengths.
15. An apparatus comprising a lens to pass, to one eye of a viewer,
a first image, in a first wavelength, that is appropriate for 3D
viewing of a stereoscopic image the lens having a curvature such
that when the apparatus is positioned near the viewer's face,
points along the surfaces of the lens, in at least one plane, are a
relatively uniform distance from the viewer's eye.
16. The apparatus of claim 15 also comprising a second lens to
pass, to a second eye of the viewer, a second image, in a second
wavelength, that is complementary to the first image for 3D viewing
of the stereoscopic image, the second lens having a curvature such
that when the apparatus is positioned near the viewer's face,
points along the surfaces of the lens, in one plane, are a
relatively uniform distance from the viewer's second eye.
17. The apparatus of claim 15 in which the lens comprises a
substrate sheet and a layer having stress, in which the curvature
of the lens is a result of the stress.
18. An apparatus comprising a lens to pass, to one eye of a viewer,
a first image, in a first band of wavelengths, that is appropriate
for 3D viewing of a stereoscopic image the lens having a curvature
with a radius of curvature such that when the apparatus is
positioned near the viewer's face, the radius is approximately
equal to the distance between the coating and the center of the
eye.
19. The apparatus of claim 18 also comprising a second lens to
pass, to a second eye of the viewer, a second image, in a second
wavelength, that is complementary to the first image for 3D viewing
of the stereoscopic image, the second lens having a curvature with
a radius of curvature such that when the apparatus is positioned
near the viewer's face, the radius equals the distance between the
coating and the center of the second eye.
20. The apparatus of claim 18 in which the lens comprises a
substrate sheet and a layer having a stress, in which the curvature
of the lens is a result of the stress.
21. The apparatus of claim 18 in which the radius of curvature is
between about 1/2 inch and 4 inches.
22. The apparatus of claim 19 in which the first and second lenses
are arranged so that when worn by a viewer while viewing a
projection on a domed screen, light from any point on the dome
passes through each lens at an angle of incidence near
perpendicular to the surface of the lens.
23. A method comprising roll-coating alternating layers of at least
a first and second material having different optical properties
onto a substrate, roll-coating alternating layers of at least the
first and second materials onto a second substrate, thicknesses of
the layers having been selected so that in combination, the layers
on the first substrate will transmit light having a first set of
wavelengths and not transmit light having a second set of
wavelengths, and the layers on the second substrate will transmit
light having the second set of wavelengths and not transmit light
having the first set of wavelengths, removing a portion of each of
the first and second coated substrates, and assembling the portions
into a frame configured to position the portions, one near each eye
of a wearer when the frame is worn on the head of the wearer.
24. The method of claim 23 in which the first material is Silicon
Dioxide (SiO.sub.2).
25. The method of claim 23 in which the second material is Niobium
Pentoxide (Nb.sub.2O.sub.5), Titanium Dioxide (TiO.sub.2) or
Tantalum Pentoxide (Ta.sub.2O.sub.5).
26. The method of claim 23 in which a property of at least one
layers has been selected so that the combination of the layers has
a stress, in which the stress causes the substrate to exhibit a
curvature.
27. The method of claim 23 in which the curvature is selected such
that when the substrate is placed in the vicinity of a human eye
the substrate maintains a uniform distance, in at least one plane,
from the eye.
28. The method of claim 23 in which the curvature is selected such
that when the substrate is placed in the vicinity of a human eye, a
radius of curvature equals the distance between the coating and the
center of the eye.
29. The method of claim 23 also comprising cutting a first piece
from the first coated substrate to form a first lens, cutting a
second piece from the second coated substrate to form a second
lens, and arranging the first and second lenses to form a set of
glasses.
Description
BACKGROUND
[0001] This description relates to forming spectral filters.
[0002] Stereoscopic projection, commonly called three-dimensional
(3D) projecting, delivers slightly different images to each eye of
a viewer, which gives the illusion of depth when the viewer's brain
assembles the two images into a single scene.
[0003] In a polarization-based 3D projection system, two projectors
are used, one for each eye, and polarizing filters are used to
polarize the light from each projector orthogonally to the other.
The viewer wears glasses with corresponding polarizing filters, so
that each eye receives only light projected from the corresponding
projector.
[0004] In anaglyphic projection, the two images are each
color-shifted, one into the red end of the visible spectrum and one
into the blue end. The viewer wears glasses with red and blue
filters, one for each eye, so that each eye sees only the image
shifted into the corresponding color. The viewer's brain
reassembles the two images into a single reduced-color image with
the illusion of depth. Such a system also works with still images,
which can be printed with the two color-shifted images
overlaid.
[0005] A third approach projects alternating images for each eye,
and glasses, for example with LCD shutters, actively block the view
of the eye opposite the image currently being projected.
SUMMARY
[0006] In general, in one aspect, a lens bears a plurality of
roll-coated layers to pass, to one eye of a viewer, a first image,
in a first band of wavelengths, that is appropriate for 3D viewing
of a stereoscopic image.
[0007] Implementations may include one or more of the following
features. The lens includes layers adhered to a substrate in a
roll-coating process and having optical properties and thicknesses
such that the combination of the layers transmits light within the
first band of wavelengths and does not transmit light within a
second band of wavelengths. The optical properties and thicknesses
of the layers are such that the combination of the layers transmits
light with a third and fourth band of wavelengths and combination
of the layers transmits light with a third and fourth band of
wavelengths and does not transmit light within a fifth and sixth
band of wavelengths. A second lens bears a roll-coated layer to
pass, to a second eye of a viewer, a second image, in a second band
of wavelengths, that is complementary to the first image for 3D
viewing of the stereoscopic image. The first band of wavelengths
includes a band of wavelengths around 435 mn. The second band of
wavelengths includes a band of wavelengths around 475 nm. The third
band of wavelengths includes a band of wavelengths around 510 nm,
the fourth band of wavelengths includes a band of wavelengths
around 610 nm, the fifth band of wavelengths includes a band of
wavelengths around 550 nm, and the sixth band of wavelengths
includes a band of wavelengths around 660 nm.
[0008] The lens includes a substrate sheet having curvature, the
roll-coated layer having a generally uniform thickness normal to
the sheet at points along the curvature. The curvature is such that
when the lens is positioned near a person's face, points along a
surface of the lens, in one plane, are a relatively uniform
distance from the eye of the viewer. The curvature has a radius of
curvature such that when the lens is positioned near a person's
face, the radius is approximately equal to the distance between the
coating and the center of the eye. The radius of curvature is
between about 1/2 inch and 4 inches.
[0009] In general, in one aspect, a set of glasses includes a frame
to hold two lenses. A first lens includes a roll-coated filter to
pass light in a first set of bands of wavelengths and reflect light
in a second set of bands of wavelengths. A second lens includes a
roll-coated filter to pass light in a portion of the second set of
bands of wavelengths and reflect light in a portion of the first
set of wavelengths.
[0010] In general, in one aspect, glasses to view a stereoscopic
image include a first lens bearing a roll-coated optical layer to
pass, to one eye of a viewer, a first image that is appropriate for
3D viewing of the stereoscopic image. A second lens bears a
roll-coated optical layer to pass, to a second eye of a viewer, a
second image that is complementary to the first image for 3D
viewing of the stereoscopic image.
[0011] In general, in one aspect, glasses to view a 3D frame or
video presentation include a supporting structure and a pair of
curved lenses. Each lens bears layers having a substantially
constant thickness normal to a surface of the lens. The layers are
configured to filter images of the presentation projected in two
non-overlapping bands of wavelengths of light as they are viewed
through the lenses, to produce a 3D impression for a viewer the
lenses each having a radius of curvature between about 1/2 inch and
4 inches.
[0012] In general, in one aspect, a first lens includes roll-coated
layers of materials selected to transmit light having a first set
of wavelengths, and a second lens includes roll-coated layers of
materials selected to transmit light having a second set of
wavelengths.
[0013] In general, in one aspect, a lens passes, to one eye of a
viewer, a first image, in a first wavelength, that is appropriate
for 3D viewing of a stereoscopic image.
[0014] Implementations may include one or more of the following
features. A second lens passes, to a second eye of the viewer, a
second image, in a second wavelength, that is complementary to the
first image for 3D viewing of the stereoscopic image. The lens
includes a substrate sheet and a layer having stress, in which the
curvature of the lens is a result of the stress. The first and
second lenses are arranged so that when worn by a viewer while
viewing a projection on a domed screen, light from any point on the
dome passes through each lens at an angle of incidence near
perpendicular to the surface of the lens.
[0015] In general, in one aspect, alternating layers of at least a
first and second material having different optical properties are
roll-coated onto a substrate. Alternating layers of at least the
first and second materials are roll-coated onto a second substrate.
Thicknesses of the layers are selected so that in combination, the
layers on the first substrate will transmit light having a first
set of wavelengths and not transmit light having a second set of
wavelengths, and the layers on the second substrate will transmit
light having the second set of wavelengths and not transmit light
having the first set of wavelengths. A portion of each of the first
and second coated substrates is removed, and the portions are
assembled into a frame configured to position the portions, one
near each eye of a wearer when the frame is worn on the head of the
wearer.
[0016] Implementations may include one or more of the following
features. The first material is Silicon Dioxide (SiO2). The second
material is Niobium Pentoxide (Nb2O5), Titanium Dioxide (TiO2) or
Tantalum Pentoxide (Ta2O5). A property of at least one layers is
selected so that the combination of the layers has a stress, in
which the stress substrate to form a first lens, a second piece is
cut from the second coated substrate to form a second lens, and the
first and second lenses are arranged to form a set of glasses.
[0017] Advantages include the ability to manufacture lenses for a
large number of glasses in a single process and for low per-item
cost. Lenses can be curved to properly filter the complete field of
view of the wearer.
[0018] Other features and advantages will be apparent from the
description and from the claims.
DESCRIPTION
[0019] FIG. 1 is a block diagram of a projector.
[0020] FIGS. 2A-2G and 6 are spectral graphs.
[0021] FIG. 3 is a block diagram of a roll-coating machine.
[0022] FIG. 4 is a table describing a coating design.
[0023] FIG. 5A is a sectional top view of glasses on a wearer's
head.
[0024] FIGS. 5B and 5F are perspective view of glasses on a
wearer's head.
[0025] FIGS. 5C and 5D are sectional plan views of lenses and
eyes.
[0026] FIG. 5E is a sectional side view of glasses on a wearer's
head.
[0027] FIG. 6 shows calculation of crosstalk for right eye image,
left-eye lens
[0028] FIG. 7 is a perspective view of a lens and an eye.
[0029] In a typical digital projection system, for example system
100 in FIG. 1, a full-color image is created by generating three
single-color component images that are simultaneously or
sequentially projected to resolve into a single, full-color image
when viewed by the audience. A single imaging device 102, produces
the component images based on an incoming video stream 103 using
light received from a color wheel 104 that rotates red, green, and
blue filters into the path of light 106 projected from a
spread-spectrum (white) light source 108, producing colored light
106C. In some examples, the light sources include a bulb 116, a
reflector 118, and a homogenizing device 120. The homogenizing
device 120, for example, a light pipe, makes sure that the light
reaching the color wheel 104 is uniform in brightness and color.
The imaging device 102 could be a reflective device, such as a DLP
light valve, or a transmissive device, such as an LCD panel (with
appropriate changes to the layout of the projection system
100).
[0030] The filtered and imaged light 1061 is then focused by a lens
110 onto a projection screen 112, to be seen by a viewer 114. As
long as the imaging source 102 and color wheel 104 switch between
component images and colors at the proper rate, the viewer 114 will
perceive a single, full-color image. For example, to produce a full
color image at 30 frames per second (fps), the imaging device must
produce at least 90 single-color frames per second. The actual rate
will depend on the frame-rate of the source material, the number of
color segments in the wheel 104, and the rate at which the wheel
spins. For example, some projectors have more than three segments
and spin the wheel 2, 4, or 8 times faster than the minimum needed,
according to the number of segments. In some examples, three
separate colored light sources are used or three imaging devices
are used, one for each color. Each of these approaches can be
combined with the others in various ways, for example, to project
all three color components simultaneously.
[0031] A type of 3D projection is described, for example, in U.S.
Pat. No. 6,283,597. Rather than polarize the images for each eye or
shift each into a completely different color, the individual red,
green, and blue components of each left- and right-eye image are
constrained to a narrow band of that color, different for each eye,
such that filters can be used to allow only the correct image to
reach each eye while still allowing each eye's image to be composed
of all three colors. FIGS. 2A and 2D show example sets of filtered
color bands for two commonly used light sources. Xenon lamps are
commonly used in cinema projection, while UHP (ultra high
performance) mercury arc lamps are commonly used in home
projectors. Images for the left eye are filtered inside the
projector into bands 202L, 204L, and 206L, shown separately in
FIGS. 2B and 2E, while images for the right eye are filtered inside
the projector into bands 202R, 204R, and 206R, shown separately in
FIGS. 2C and 2F. In each graph, the intensity values are normalized
to 100 representing the potential intensity of unfiltered light.
The transmission rates of the filters, independent of light source,
are shown in FIG. 2G Filters in the viewer's glasses transmit the
appropriate bands for each eye, while blocking the bands used for
the other eye. For good image separation, the bands for the left
and right eye should not overlap,
[0032] For this type of projection, a similar projection system to
that shown in FIG. 1 can be used. Instead of the color filter wheel
104 having three colors, it has six, corresponding to the six bands
202L, 204L, 206L, 202R, 204R, and 206R. Alternatively, the
three-color wheel can still be used, with a second filter or set of
filters used to split each color into the two appropriate bands. In
such a system, the image source produces six images per frame,
i.e., red, blue, and green components for each eye. The viewer 114
wears glasses 116 with filters that allow each eye to see the three
bands used for the corresponding image. Such a system has
advantages of providing a full-color stereoscopic image over a
wider viewing angle than systems using polarized light.
[0033] Such projectors are discussed in co-pending application
Two-Dimensional and Three-Dimensional Projecting of Barret Lippey,
filed on the same day as this application, and incorporated here by
reference.
[0034] As mentioned above, to view a three-color 3D projection, the
viewer wears glasses with lenses including filters that allow each
eye to see the three color-bands used for the corresponding image
and not those used for the complementary image meant for the other
eye. One way to produce such a lens uses a batch-coating process to
produce each lens as a distinct unit.
[0035] Roll-coating can produce complex optical filters
inexpensively on thin, flexible substrates. A roll-coating process
involves coating a series of thin layers of different materials on
a substrate. Whereas a batch process typically coats on individual,
small pieces of glass or plastic that are not flexible, the roll
coating process can deposit coatings onto a roll of flexible
plastic web that is continuously passing through the coating
chamber. One substrate material that may be used is PET
(polyethylene terephthalate), because of its strength, low
outgassing, high heat resistance, and low cost. The PET substrate
can be approximately 0.005'' to 0.015'' thick. The width of the
substrate is typically about 1 foot to 6 feet. Other possible
substrate materials include polycarbonate, polymethyl methacrylate
and transparent polyimide. Thin rolls of these polymeric materials
are flexible enough to be bent around a radius of approximately 1''
without stress failure.
[0036] As shown in FIG. 3, a large roll 300 of the plastic film to
be used as a substrate is mounted on one end of the machine. The
substrate 302 is fed through a vacuum lock 304
[0037] As shown in FIG. 3, a large roll 300 of the plastic film to
be used as a substrate is mounted on one end of the machine. The
substrate 302 is fed through a vacuum lock 304 into the coating
chamber 306 which is kept at low pressure. As a transport mechanism
308 moves the substrate 302 through the coating chamber 306, thin
layers of optical materials are sputtered or evaporated onto the
substrate 302 as it passes in front of successive deposition zones
310 with sputter or evaporation targets 312. The substrate 302 is
stretched over a large drum 314 during deposition so that it stays
flat and the heat of deposition can be removed through the drum.
The substrate then passes through another vacuum lock 304 and is
wound onto another roll 316. A new roll 300 can be spliced onto the
end of a previous roll that runs out. The machine may be designed
to be run without stopping until maintenance is needed. Typical
maintenance includes replacing sputter or evaporation targets 312,
cleaning shields 318, and replacing worn-out equipment. For complex
coatings, the substrate 302 may need to be run through the machine
multiple times. Back and forth motion of the substrate through the
deposition zones can be used if the plastic-film transport
mechanism 308 allows it.
[0038] The rolls can weigh up to several hundred pounds each and
can be many thousands of feet long. Because roll coating can be
performed continuously without breaking vacuum or needing lengthy
pump-down each time substrates are loaded, the throughput of roll
coating can be much higher than batch processing and the resultant
cost of roll coating can be much lower. After the roll-coating
process, individual pieces are cut out of the substrate and
assembled into glasses. The individual pieces can be used as lenses
themselves, held in place by the frame of the glasses, or they can
be laminated onto more substantial glass or plastic lenses.
[0039] Each of the layers of optical material has certain optical
properties (e.g., alternating layers of high refractive index and
low refractive index), and the combination of the layers is
designed to produce the filtering characteristics desired for a
particular application. In the case of triple bandpass filters for
3D glasses, the goal is to have a high transmission of the bands
for each eye and high rejection of other light, including the bands
used for the opposite eye, as shown in FIGS. 2B and 2C. FIG. 2B
shows the transmission rate in the three bands 202L, 204L, and 206L
used for the left eye, and FIG. 2C shows the transmission rates in
the three bands 202R, 204R, and 206R used for the right eye. The
steep sides of the peaks representing the bands are desirable to
reduce any bleeding over of light from the complementary bands, a
problem referred to as cross-talk.
[0040] An example of a triple bandpass filter design is shown in
FIG. 4. Table 400 lists the materials in column 402 and their
thicknesses in columns 404 and 406. The calculated spectral
performance of the thicknesses listed in column 404, for the left
eye, is the basis of FIG. 2B. By increasing the coating thickness
of every layer by about 8%, the spectral curve of the coating can
be shifted to longer wavelengths to make the corresponding filter
for the right eye, as shown in column 406 and FIG. 2C. The amount
of the shift in wavelength is equal to the amount of increase in
coating thickness, so the amount should be selected to shift each
pass band 202L, 204L, 206L far enough that the shifted bands 202R,
204R, 206R do not overlap the original ones. It has been found that
for good performance, average transmission in the pass-bands 202L,
etc., should be approximately 80% or greater, and the average
transmission in the blocking bands, that is, for wavelengths
outside the pass-bands, should be approximately 0.5% or less. The
slopes of the band edges, e.g., edge 207 in FIG. 2G, between the
points 209, 211 where 20% and 80% of the available light is
transmitted for each pass-band, should be approximately 1% of the
center wavelengths of the respective bands. By slope, we mean the
spacing of the endpoints of a transition band between a pass band
and a stop band as a percentage of the width of the center of the
wavelength band. The wavelength tolerance of each band (that is,
the tolerance by which the wavelength of the center of the
wavelength band may vary) should be less than approximately 2% on
either side of the nominal center wavelength of the band.
[0041] Filters made by this process can be used in both the glasses
worn by a viewer and as the filters within the projector itself,
with appropriate adjustments made for the geometry of the
projector, for example, if light is incident on the filters at some
angle other than zero degrees within the projector.
[0042] In some examples, because the substrate used in the
roll-coating process is a thin flexible sheet of plastic, the
filters used for the glasses can easily be curved into a
cylindrical shape, as shown in FIG. 5A. Once shaped, the filters
can be held in the desired shape by the frame 510 of the glasses
500. Alternatively, they could be laminated onto a glass or plastic
lens having the desired shape. This flexibility provides an
advantage over batch-coated processes, as it allows a uniform
coating over a curved surface, since the surface is kept flat
during the coating process. Roll coating using sputtering or
evaporation is a directional coating process in which the material
being deposited moves in a straight line from the source to the
substrate. This results in a uniform coating on a flat surface with
appropriate masking and process control. Thickness uniformity
should be within about +/-2% to achieve the tolerances on bands
discussed above. Other coating methods, for example chemical vapor
deposition, that can coat highly curved surfaces because they are
non-directional tend to be expensive compared to sputtering or
evaporation. Since roll-coating works with a flexible substrate, it
allows inexpensive directional coating processes to be used to
create curved lenses.
[0043] Curved lenses 502 are positioned in glasses 116 so that they
maintain a uniform distance D along their lengths from the center
of the eyes 504. As shown in FIGS. 5C and 5D, this helps prevent
shifting of the transmitted wavelengths due to a changing angle of
incidence (AOI) 505 (as measured between the incident light and a
normal 507 from the lens 506) as the eyeball rotates to look
through the left or right edges of the glasses. Incident light
508a, 508b, and 508c passes through the lens 502 to the eye at a
relatively low AOI no matter which direction it is coming from. In
relatively flat glasses, e.g., with lens 506, the AOI 505 of light
508a and 508c entering the lens 506 from the sides is high (whether
the viewer rotates his eyes to the side or simply sees it through
his peripheral vision), while the AOI of light 508b entering the
lens 506 from straight ahead is low. This will alter the
frequencies admitted by the filter, as shown in FIG. 6, resulting
in a ghosting and degradation of the 3D effect at the edges of the
viewer's field of view. In some examples, the curvature of the
lenses 502 may not be completely cylindrical, but might have a
variable radius of curvature. The distance between the lens and the
center of the eye should be relatively uniform, as compared to
traditional flat or slightly curved lenses. In general, each lens
should have a curvature centered on the center of the eye and with
a radius of curvature approximately equal to the distance from the
lens to the center of the eye, for example, 1/2 inch for lenses
very close to the eye, or as much as four inches for lenses
situated farther from the eye. Slightly curved traditional lenses
typically have radii of curvature of around twelve inches.
[0044] Graph 600 shows cross-talk resulting from light passing
through a flat lens at two different angles. Line 602 shows that at
0.degree., little of the light projected for the right-eye is
admitted by a left-eye filter in the glasses. Line 604, however,
shows that at 30.degree. AOI, large peaks 606, 608 of blue and
green light are transmitted at specific wavelengths. Comparing the
wavelength of these peaks to the left-eye bands 202L and 204L shown
in FIG. 2B, one sees that, at this angle, the left eye will be
receiving light meant for the right eye. With a curved lens, all
the light reaching the eye has come through the lens at a low AOI
no matter what direction it came from, preventing this
cross-talk.
[0045] Even the thin flexible sheets used in a roll coating process
are not easily curved in two directions at once, so such lenses
will generally be curved in the horizontal plane, as shown in FIGS.
5A-C and 7, such that the up/down direction will still have some
wavelength shift. This choice is made because the vertical range of
eyeball motion (arrows 702, 704) is generally much less than the
horizontal angle (arrows 706, 708). The lenses could be curved in
the vertical direction, as shown in FIGS. 5E and 5D, if the nature
of the projection, for example, made vertical eye movement a
greater concern.
[0046] In some examples, a sputtered coating has compressive stress
that contributes to a built-in curvature in the completed filter
that is relatively low-stress compared to bending a substrate that
starts flat. Depending on the thickness of the substrate and its
material, the built-in curvature can be adjusted to the proper
curvature to maintain low AOI for all horizontal angles of eyeball
motion. Alternatively, the built-in curvature may get the substrate
part-way to the desired shape, so that the additional curvature
that must be added does not stress the coating as much as it would
if the substrate were naturally flat. If the distance between the
filter and the center of the eyeball is 1'', the radius of
curvature of the film should also be 1''. This natural radius can
be achieved with a sputtered coating that is deposited with typical
stress values and a polycarbonate substrate that is approximately
0.008'' thick. A filter with a PET substrate of the same thickness
and the same sputtered coating has a natural radius of
approximately 3'' because it is a stiffer substrate material, but
this material can bent into the 1'' radius without degradation to
the coating. Experimental reduction of the spectral shift was
confirmed for a large range of horizontal eyeball angles by
building glasses based on the PET substrate bent into a 1'' radius.
Other curvatures may be used, for example, giving up some image
quality to allow a more comfortable fit, or to fit over
prescription eye wear.
[0047] The curved lenses enabled by roll-coating the filters may be
particularly advantageous in domed-screen or cylindrical-screen
theaters. For example, domed screens tend to require more eyeball
motion than flat screens, and roll-coated coatings allow easy
curvature of the glasses to reduce ghosting due to crosstalk
between eyes. Domed screens allow objects to approach the viewer
from the left and right in addition to the front, and a curved lens
maintains the illusion of depth even for images in the viewer's
peripheral vision.
[0048] Other implementations are within the scope of the claims.
For example, the filters could be configured to be attached to a
wearer's existing eyeglasses.
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