U.S. patent application number 17/226265 was filed with the patent office on 2021-07-29 for optical system.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Gilles J. Benoit, Rolf W. Biernath, Guanglei Du, Sherie A. Kristie, Christopher A. McLaughlin, John A. Wheatley.
Application Number | 20210231851 17/226265 |
Document ID | / |
Family ID | 1000005507710 |
Filed Date | 2021-07-29 |
United States Patent
Application |
20210231851 |
Kind Code |
A1 |
Wheatley; John A. ; et
al. |
July 29, 2021 |
OPTICAL SYSTEM
Abstract
An optical system includes an oriented polymeric multilayer
optical film having a first reflection band, and a light source
configured to produce light in an output band and/or a sensor
configured to receive light in an input band. The light source
and/or sensor is in optical communication with the oriented
polymeric multilayer optical film. In some cases, the first
reflection band overlaps the input and/or output band at normal
incidence, but not at an oblique incidence angle. In some cases,
the first reflection band overlaps the input and/or output band at
an oblique incidence angle, but not at normal incidence. The
optical system can further include a non-birefringent optical
filter having a first blocking band where the first blocking band
overlaps the first reflection band for at least one of normal
incidence or an oblique incidence angle.
Inventors: |
Wheatley; John A.;
(Stillwater, MN) ; Du; Guanglei; (New York,
NY) ; Benoit; Gilles J.; (Minneapolis, MN) ;
Biernath; Rolf W.; (Wyoming, MN) ; McLaughlin;
Christopher A.; (Lino Lakes, MN) ; Kristie; Sherie
A.; (Hudson, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St.Paul |
MN |
US |
|
|
Family ID: |
1000005507710 |
Appl. No.: |
17/226265 |
Filed: |
April 9, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16309187 |
Dec 12, 2018 |
11009637 |
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PCT/US2017/040290 |
Jun 30, 2017 |
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17226265 |
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62361246 |
Jul 12, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 5/305 20130101;
B32B 7/12 20130101; B32B 2551/00 20130101; B32B 2307/412 20130101;
G02B 26/06 20130101; G02B 5/0816 20130101; G02B 5/285 20130101;
G02B 5/26 20130101; G02B 5/22 20130101; B32B 27/36 20130101; G02B
5/287 20130101; G02B 5/0825 20130101; B32B 2255/26 20130101; G02B
5/0841 20130101 |
International
Class: |
G02B 5/28 20060101
G02B005/28; G02B 5/08 20060101 G02B005/08; G02B 5/22 20060101
G02B005/22; G02B 5/26 20060101 G02B005/26; G02B 5/30 20060101
G02B005/30 |
Claims
1. An optical system comprising: an oriented polymeric multilayer
optical film having a first reflection band; a non-birefringent
optical filter having a first blocking band, the first blocking
band overlapping the first reflection band for at least one of
normal incidence or an oblique incidence angle; and a light source
configured to produce light in an output band, the light source in
optical communication with the oriented polymeric multilayer
optical film and with the non-birefringent optical filter, wherein
either: the first reflection band overlaps the output band at
normal incidence, but not at the oblique incidence angle; or the
first reflection band overlaps the output band at the oblique
incidence angle, but not at normal incidence.
2. The optical system of claim 1, wherein the first reflection band
overlaps the output band at normal incidence, but not at the
oblique incidence angle.
3. The optical system of claim 1, wherein the first reflection band
overlaps the output band at the oblique incidence angle, but not at
normal incidence.
4. The optical system of claim 1, wherein the oblique incidence
angle is 60 degrees.
5. The optical system of claim 1, wherein the first blocking band
is entirely contained in the first reflection band at normal
incidence and is not is entirely contained in the first reflection
band at the oblique incidence angle.
6. The optical system of claim 1, wherein the first reflection band
and the first blocking band do not overlap at normal incidence and
do overlap at the oblique incidence angle.
7. The optical system of claim 1, wherein the output band has a
full-width at half-maximum of no more than 40 nm.
8. The optical system of claim 1 further comprising a sensor in
optical communication with the oriented polymeric multilayer
optical film, the non-birefringent optical filter, and the light
source.
9. An optical system comprising: an oriented polymeric multilayer
optical film having a first reflection band; a non-birefringent
optical filter having a first blocking band, the first blocking
band overlapping the first reflection band for at least one of
normal incidence or an oblique incidence angle; and a sensor
configured to receive light in an input band, the sensor in optical
communication with the oriented polymeric multilayer optical film
and with the non-birefringent optical filter, wherein either: the
first reflection band overlaps the input band at normal incidence,
but not at the oblique incidence angle; or the first reflection
band overlaps the input band at the oblique incidence angle, but
not at normal incidence.
10. The optical system of claim 9, wherein the first reflection
band overlaps the input band at normal incidence, but not at the
oblique incidence angle.
11. The optical system of claim 9, wherein the first reflection
band overlaps the input band at the oblique incidence angle, but
not at normal incidence.
12. The optical system of claim 9, wherein the oblique incidence
angle is 60 degrees.
13. The optical system of claim 9, wherein the first blocking band
is entirely contained in the first reflection band at normal
incidence and is not is entirely contained in the first reflection
band at the oblique incidence angle.
14. The optical system of claim 9, wherein the first reflection
band and the first blocking band do not overlap at normal incidence
and do overlap at the oblique incidence angle.
15. The optical system of claim 9, wherein the input band has a
full-width at half-maximum of no more than 40 nm.
16. A method of modifying a first reflection band of an oriented
polymeric multilayer optical film, the method comprising: providing
the oriented polymeric multilayer optical film having the first
reflection band, the first reflection band having a band edge at a
first wavelength at normal incidence; determining a desired normal
incidence band edge wavelength; selecting a non-birefringent
optical filter having a first blocking band, the first blocking
band having the desired normal incidence band edge wavelength and
including the first wavelength at normal incidence; and positioning
the non-birefringent reflector in optical communication with the
oriented polymeric multilayer optical film.
17. The method of claim 16, wherein the non-birefringent optical
filter is a non-birefringent reflector and the first blocking band
is a second reflection band, and wherein selecting the
non-birefringent optical filter comprises selecting different first
and second materials such that a stack of alternating layers of the
first and second materials provides the second reflection band.
18. The method of claim 17, wherein the positioning step comprises
depositing the stack of alternating layers directly onto the
oriented polymeric multilayer optical film.
19. The method of claim 18, wherein the depositing step comprises
depositing the stack of alternating layers through a mask resulting
in a spatially variant non-birefringent reflector.
20. The method of claim 18, wherein the depositing step comprises
one or more of atomic layer deposition, sputtering, chemical vapor
deposition, and layer-by-layer self-assembly.
Description
BACKGROUND
[0001] Optical filters can be utilized to selectively transmit
light of different wavelengths or different polarizations. Optical
filters are useful in a variety of optical systems such as detector
systems.
SUMMARY
[0002] In some aspects of the present description, an optical stack
including an oriented polymeric multilayer optical film and a first
non-birefringent optical filter disposed adjacent the multilayer
optical film is provided. The oriented polymeric multilayer optical
film has a first reflection band with a first band edge having a
variation across a length or a width of the multilayer optical
film. The first band edge, at normal incidence, has a design
wavelength .lamda. and a characteristic deviation about the design
wavelength .DELTA.. The first non-birefringent optical filter has a
first blocking band which, at normal incidence, comprises
wavelengths between .lamda.-.DELTA./2 and .lamda.+.DELTA./2. At
normal incidence, the first reflection band includes a wavelength
range having a width of at least .DELTA. that is outside of the
first blocking band.
[0003] In some aspects of the present description, an optical stack
including an oriented polymeric multilayer optical film and a first
non-birefringent optical filter disposed adjacent the multilayer
optical film is provided. The oriented polymeric multilayer optical
film has a first reflection band with a first band edge at normal
incidence at an undesired band edge wavelength. The first
non-birefringent optical filter has a first blocking band which, at
normal incidence, comprises the undesired band edge wavelength and
has a second band edge at a first desired band edge wavelength.
[0004] In some aspects of the present description, an optical stack
including an oriented polymeric multilayer optical film and a first
non-birefringent optical filter disposed adjacent the multilayer
optical film is provided. The oriented polymeric multilayer optical
film has a first reflection band having a first band width at
normal incidence and having a first band edge that has a first
shift between normal incidence and an incidence angle of 60
degrees. The first non-birefringent optical filter has a first
blocking band having a second band width at normal incidence and
having a second band edge that has a second shift between normal
incidence and an incidence angle of 60 degrees. The first shift is
different from the second shift.
[0005] In some aspects of the present description, an optical
system including the optical stack is provided. The optical system
includes one or both of a light source and a sensor in optical
communication with the optical stack.
[0006] In some aspects of the present description, an optical
system including an oriented polymeric multilayer optical film
having a first reflection band with a first band edge, and a light
source in optical communication with the oriented polymeric
multilayer optical film is provided. The light source is configured
to produce light in an output band. In some cases, the first
reflection band overlaps the output band at normal incidence, but
not at an oblique incidence angle. In some cases, the first
reflection band overlaps the output band at an oblique incidence
angle, but not at normal incidence.
[0007] In some aspects of the present description, an optical
system including an oriented polymeric multilayer optical film
having a first reflection band with a first band edge, and a sensor
in optical communication with the oriented polymeric multilayer
optical film is provided. The sensor is configured to receive light
in an input band. In some cases, the first reflection band overlaps
the input band at normal incidence, but not at an oblique incidence
angle. In some cases, the first reflection band overlaps the input
band at an oblique incidence angle, but not at normal
incidence.
[0008] In some aspects of the present description, a method of
modifying a first reflection band of an oriented polymeric
multilayer optical film is provided. The method includes the steps
of providing the oriented polymeric multilayer optical film having
the first reflection band, the first reflection band having a band
edge at a first wavelength at normal incidence; determining a
desired normal incidence band edge wavelength; selecting a
non-birefringent optical filter having a first blocking band, the
first blocking band having the desired normal incidence band edge
wavelength and including the first wavelength at normal incidence;
and positioning the non-birefringent reflector in optical
communication with the oriented polymeric multilayer optical
film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIGS. 1A-1D are schematic cross-sectional views of optical
stacks;
[0010] FIG. 2 is a schematic cross-sectional view of an optical
stack having a spatially variant layer;
[0011] FIG. 3A is a plot of transmittance at normal incidence
through an oriented polymeric multilayer optical film as a function
of wavelength;
[0012] FIG. 3B is a plot of transmittance at normal incidence
through the oriented polymeric multilayer optical film of FIG. 3A
and through a non-birefringent optical filter as a function of
wavelength;
[0013] FIG. 3C is a plot of transmittance at normal incidence
through the oriented polymeric multilayer optical film of FIG. 3A
and through one or two non-birefringent optical filters as a
function of wavelength;
[0014] FIG. 3D is schematic illustration of an overall blocking
band of an optical stack at normal incidence;
[0015] FIGS. 4A-7B are plots of transmittance as a function of
wavelength for reflection bands and absorbing bands of optical
stacks;
[0016] FIG. 8 is a graph illustrating the concept of full-width at
half-maximum;
[0017] FIG. 9 is a schematic cross-sectional view of an optical
filter;
[0018] FIGS. 10A-10C are schematic illustrations of optical
systems; and
[0019] FIGS. 11-18 are plots of percent transmission versus
wavelength for optical filters.
DETAILED DESCRIPTION
[0020] In the following description, reference is made to the
accompanying drawings that forms a part hereof and in which various
embodiments are shown by way of illustration. The drawings are not
necessarily to scale. It is to be understood that other embodiments
are contemplated and may be made without departing from the scope
or spirit of the present disclosure. The following detailed
description, therefore, is not to be taken in a limiting sense.
[0021] Oriented polymeric multilayer optical films are useful in a
wide variety of applications such as reflective polarizers or
mirrors in backlight systems and optical filters in detector
systems. Such films can be designed to have reflection bands in a
wide variety of wavelength ranges depending on the intended
application.
[0022] Oriented polymeric multilayer optical films having a
reflection band often exhibit variation in one or both band edges
of the reflection band. This variation can be objectionable is some
applications. According to the present description, it has been
found that utilizing an optical stack that includes both an
oriented (and thus birefringent) polymeric multilayer optical film
and a non-birefringent optical filter can provide a substantially
reduced (e.g., by at least 60 percent, or by at least 70 percent,
or by at least 80 percent) band edge variation compared to the
oriented polymeric multilayer optical film alone while providing a
wide blocking band (e.g., a reflection band) that would not be
easily obtained with a non-birefringent optical filter alone.
[0023] The combination of the oriented polymeric multilayer optical
film and the non-birefringent optical filter results in an overall
blocking band for the optical stack. The oriented polymeric
multilayer optical film is typically a reflector for one or both of
two orthogonal polarization states. The non-birefringent optical
filter has a blocking band that can be a reflection band (e.g.,
utilizing alternating non-birefringent layers having different
refractive indices) or an absorbing band (e.g., utilizing dyes or
pigments which absorb in a desired wavelength range). In some
embodiments, the non-birefringent optical filter is reflective and
the overall blocking band is a reflection band, and in some
embodiments the non-birefringent optical filter is absorptive and
the overall blocking band is absorptive in some wavelengths and
reflective at other wavelengths.
[0024] In some embodiments, the optical stacks of the present
description have an overall blocking band which has a designed
shift with incidence angle. Such optical stacks can create an angle
selective element for certain wavelengths that can be used to
provide an angle limited reception zone for a sensor, to provide a
limited angle of emission for a light source, or to provide a
limited angle of view for a marker, for example.
[0025] The optical stacks of the present description further
provide a way to produce a customized blocking band without
incurring the expense of producing a custom designed oriented
polymeric multilayer optical film. The non-birefringent filter (or
filters) can be selected to have a blocking band which overlaps a
band edge (or both band edges) of a reflection band of an oriented
polymeric multilayer optical film and which extends in to a desired
band edge to provide a customized blocking band.
[0026] FIG. 1A is a schematic cross-sectional view of optical stack
100 including first and second layers 110 and 114. One of the first
and second layers 110 and 114 is an oriented polymeric multilayer
optical film and the other of the first and second layers 110 and
114 is a non-birefringent optical filter. Light 140 is incident on
the first layer 110 and the second layer 114 at normal incidence,
while light 142 is incident on the first layer 110 at an oblique
incidence angle of a (angle between light ray and normal vector to
the first layer 110). The light 140 or 142 may be transmitted first
through the oriented polymeric multilayer optical film and then
through the non-birefringent optical filter, or the light 140 or
142 may be transmitted first through the non-birefringent optical
filter and then through the oriented polymeric multilayer optical
film. The first and second layers 110 and 114 may be disposed
immediately adjacent each other as illustrated in FIG. 1A, or an
air gap or an intermediate layer may be disposed between the first
and second layers as illustrated in FIGS. 1B and 1C,
respectively.
[0027] The wavelength of a band edge of a reflection band or of a
blocking band of interference filters typically depends on
incidence angle .alpha. and typically shifts to lower wavelengths
with increasing incidence angles. Incidence angle or angle of
incidence refers to the angle between an incident light ray and a
normal to the surface on which the light ray is incident (e.g.,
oblique incidence angle .alpha. of light 142). Normal incidence
refers to a zero incidence angle. Properties of reflection bands or
blocking bands, such as band edge wavelengths, may be specified at
normal incidence or at an oblique incidence angle. The oblique
incidence angle used in comparing shifts of reflection or blocking
bands from the corresponding bands at normal incidence can be
selected to be 45 degrees or 60 degrees, for example.
[0028] The oriented polymeric multilayer optical film may be a
mirror film or a reflective polarizer film, for example. The
oriented polymeric multilayer optical film has a first reflection
band having a first band edge (e.g., left band edge) and may also
have a second band edge (e.g., right band edge). The oriented
polymeric multilayer optical film may also have a second reflection
band (e.g., a higher order harmonic of the first reflection band).
In some embodiments, the oriented polymeric multilayer optical film
is a comb filter having a plurality of reflection bands with pass
bands between the reflection bands. The oriented polymeric
multilayer optical film and the non-birefringent optical filter can
be made using any of the techniques described elsewhere herein.
[0029] The non-birefringent optical filter can be any filter in
which the optically active layer(s) have isotropic refractive
indices. Examples include interference filters having a plurality
of alternating layers of differing isotropic refractive indices, as
described further elsewhere herein, and include filters having an
absorbing layer (e.g., dye or pigment layer) with isotropic complex
refractive indices. Isotropic dyes or pigments may be considered a
non-birefringent optical filter even if the dyes or pigments are
disposed on or in an oriented substrate. Non-isotropic dyes or
pigments, such as the iodine layer in an iodine stained polyvinyl
alcohol absorbing polarizer, are not non-birefringent optical
filters, as used herein, since the iodine molecules are oriented
and provide a birefringent complex refractive index that is
different in the x- and y-directions (referring to the x-y-z
coordinate system of FIG. 1A).
[0030] The wavelength ranges of the reflection and blocking bands
can be selected based in the intended application. In some
embodiments, one or all of the band edges are located, at normal
incidence, in a range of 300 nm, or 400 nm to 2500 nm, or 2000 nm,
or 1200 nm, or 900 nm, or 700 nm.
[0031] FIG. 1B is a schematic cross-sectional view of optical stack
100b including first and second layers 110b and 114b with an air
gap therebetween. One of the first and second layers 110b and 114b
is an oriented polymeric multilayer optical film and the other of
the first and second layers 110b and 114b is a first
non-birefringent optical filter.
[0032] FIG. 1C is a schematic cross-sectional view of optical stack
100c including first, second and third layers 110c, 114c and 116c.
One of the first, second and third layers 110c, 114c and 116c is an
oriented polymeric multilayer optical film and a different one of
the first, second and third layers 110c, 114c and 116c is a first
non-birefringent optical filter. The remaining layer may be an
adhesive layer, for example, and/or may be a second
non-birefringent optical filter (e.g., a dyed adhesive layer). In
some embodiments, first layer 110c is an oriented polymeric
multilayer optical film, second layer 114c is a first
non-birefringent optical filter, and third layer 116c is an
intermediate layer. In some embodiments, the intermediate layer is
an adhesive layer, and in some embodiments, the intermediate layer
includes one or more dyes or pigments which may include one or more
polarizing dyes or pigments. In some embodiments, the intermediate
layer is an oriented polymeric layer such as oriented polyethylene
terephthalate (PET).
[0033] FIG. 1D is a schematic cross-sectional view of optical stack
100d including first and second layers 110d and 114d. One of the
first and second layers 110d and 114d is an oriented polymeric
multilayer optical film and the other of the first and second
layers 110d and 114d is a first non-birefringent optical filter.
Optical stack 100d is curved about one axis (the x-axis) or about
two orthogonal axes (the x-axis and the y-axis). Optical stack 100d
can be formed using a thermoforming process or an in-mold forming
process. In some embodiments, first and second layers 110d and 114d
are formed as separate layers which are subsequent formed (e.g.,
thermoformed) into the curved shape illustrated in FIG. 1D. In some
embodiments, an in-mold process is used where the oriented
polymeric multilayer optical film is prepared and placed into a
mold and a material with a wavelength selective dye or pigment is
injected into the mold to form the non-birefringent optical filter.
Additional layers may be formed between the oriented polymeric
multilayer optical film and the non-birefringent optical filter. In
some embodiments, the in-mold forming results in an oriented
polymeric multilayer optical film curved about at least one axis
(e.g., curved about two orthogonal axes). In other embodiments, the
in-mold forming results in a flat oriented polymeric multilayer
optical film.
[0034] FIG. 2 is a schematic cross-sectional view of optical stack
200 including first and second layers 210 and 214. One of the first
and second layers 210 and 214 is an oriented polymeric multilayer
optical film and the other of the first and second layers 210 and
214 is a non-birefringent optical filter. The first layer 210 is
spatially variant and includes holes or discontinuities 218. In
some embodiments, first layer 210 is an oriented polymeric
multilayer optical film and holes or discontinuities 218 are holes
through the oriented polymeric multilayer optical film that can be
formed by die cutting, for example. In some embodiments, first
layer 210 is a non-birefringent optical filter and holes or
discontinuities 218 are discontinuities which can be formed by
using a mask in depositing the non-birefringent optical filter. For
example, the non-birefringent optical filter can be formed by
depositing an absorbing material or depositing a reflective stack
of alternating layers onto a substrate or directly onto the
oriented polymeric multilayer optical film. The depositing can be
done through a mask resulting in a patterned non-birefringent
optical filter. The depositing can include printing or spraying an
absorbing material, or sputtering or vapor depositing a reflective
stack of alternating layers, for example. In some embodiments,
first layer 210 is a non-birefringent optical filter that is
discontinuous across a length or a width of the non-birefringent
optical filter.
[0035] In some embodiments, an optical stack includes an oriented
polymeric multilayer optical film having a reflection band with a
first band edge having a variation across a length or a width of
the multilayer optical film, and a first non-birefringent optical
filter having a blocking band and being disposed adjacent the
multilayer optical film. Such reflection and blocking bands are
schematically illustrated in FIGS. 3A-3D.
[0036] FIG. 3A is a plot of transmittance at normal incidence
through an oriented polymeric multilayer optical film as a function
of wavelength and provides a schematic illustration of a first
reflection band 352 of the oriented polymeric multilayer optical
film. First reflection band 352 exhibits a variation across a
length or a width (for example, the length of the film may be the
dimension along the y-direction and the width of the film may be
the dimension along the x-direction, referring to the x-y-z
coordinate system illustrated in FIGS. 1A-2) of the multilayer
optical film indicated in the figure by the dashed lines. First
reflection band 352 has first and second band edges 354 and 356
having design or nominal wavelengths of .lamda..sub.1 and
.lamda..sub.2, respectively, and characteristic deviations about
the design wavelengths of .DELTA..sub.1 and .DELTA..sub.2,
respectively. Unless specified differently, the characteristic
deviations .DELTA..sub.1 and .DELTA..sub.2 refer to the standard
deviation of the first and second band edge wavelengths,
respectively, about the design or nominal wavelengths .lamda..sub.1
and .lamda..sub.2, respectively.
[0037] FIG. 3B is a plot of transmittance at normal incidence
through the oriented polymeric multilayer optical film of FIG. 3A
and through a non-birefringent optical filter as a function of
wavelength, and provides a schematic illustration of a first
blocking band 362 of the non-birefringent optical filter. The first
blocking band 362, which can be an absorbing band or a reflection
band, has first and second band edges 364 and 366, respectively.
The first band edge 364 is at a wavelength lower than
.lamda..sub.1-.DELTA..sub.1/2, and the second band edge 366 is at a
wavelength higher than .lamda..sub.1+.DELTA..sub.1/2. The first
reflection band 352 includes a wavelength range 358 which has a
width of at least .DELTA..sub.1 that is outside of the first
blocking band 362. The wavelength range 358 identified in FIG. 3B
extends from the second band edge 366 to the design or nominal
wavelength .lamda..sub.2.
[0038] FIG. 3C is a plot of transmittance at normal incidence
through the oriented polymeric multilayer optical film of FIG. 3A
and through one or two non-birefringent optical filters as a
function of wavelength, and provides a schematic illustration of
first and second blocking bands 362a and 362b of the one or two
non-birefringent optical filters. In some embodiments, two distinct
non-birefringent optical filters are used with one filter providing
the first blocking band 362a and the other filter used to provide
the second blocking band 362b. In some embodiments, more than two
non-birefringent optical filters are included in the optical stack.
For example, in some applications it may be desired to block light
in one or more wavelength ranges outside of the ranges of any of
the bands 352, 362a and 362b. In some embodiments, a single
non-birefringent optical filter having two or more blocking bands
are used to provide both the first blocking band 362a and the
second blocking band 362b. For example, the first and second
blocking bands 362a and 362b may be reflection bands which are
different order harmonics provided by alternating non-birefringent
first and second layers. For example, the second blocking band 362b
may be a primary reflection band and the first blocking band 362a
may be a second order harmonic of the second blocking band
362b.
[0039] FIG. 3D is schematic illustration of an overall blocking
band 367 provided by the combination of the first reflection band
352 and the first and second blocking bands 362a and 362b
illustrated in FIG. 3C. In some embodiments, the optical filter
includes one but not both of the first and second blocking bands
362a and 362b. In some embodiments, the first non-birefringent
optical filter is a non-birefringent reflector and the overall
blocking band 367 is an overall reflection band. The overall
blocking band 367 has a third band width 368 at normal incidence
which is greater than the first band width
(.lamda..sub.2-.lamda..sub.1) of the first reflection band 352 at
normal incidence. In some embodiments, the overall blocking band
367 has a third band width 368 at normal incidence which is greater
than the first band width (.lamda..sub.2-.lamda..sub.1) of the
first reflection band 352 at normal incidence by a factor of at
least 1.3 or at least 1.5. The overall blocking band 367 has first
and second band edges 364d and 366d established primarily by the
first band edge 364a of the first blocking band 362a and the second
band edge 366b of the second blocking band 362b. As described
further elsewhere herein, in some embodiments, one or both of first
and second band edges 364d and 366d has a shift between normal
incidence and an oblique incidence angle (e.g., 45 or 60 degrees)
that is equal to the corresponding shift in the first band edge
364a or the second band edge 366b. The shift between normal
incidence normal incidence and the oblique incidence angle of one
or both of first and second band edges 364d and 366d may be
different from a corresponding shift in the first and second band
edges 354 and 356 of the first reflection band 352.
[0040] In some embodiments, an optical stack includes an oriented
polymeric multilayer optical film having a first reflection band
(e.g., reflection band 352) with a first band edge (e.g., band edge
354 or band edge 356) having a variation across a length or a width
of the multilayer optical film, and a first non-birefringent
optical filter disposed adjacent the multilayer optical film. The
first band edge, at normal incidence, has a design wavelength
.lamda. (e.g., wavelength .lamda..sub.1 or .lamda..sub.2 depicted
in FIG. 3A) and a characteristic deviation about the design
wavelength .DELTA. (e.g., wavelength .DELTA..sub.1 or .DELTA..sub.2
depicted in FIG. 3A). The first non-birefringent optical filter has
a first blocking band (e.g., blocking band 362 depicted in FIG. 3B
or blocking band 362b depicted in FIG. 3C), the first blocking
band, at normal incidence, including wavelengths between
.lamda.-.DELTA./2 and .lamda.+.DELTA./2. At normal incidence, the
first reflection band includes a wavelength range having a width
(e.g., the width of the wavelength range 358 depicted in FIG. 3B)
of at least .DELTA. that is outside of the first blocking band.
[0041] FIG. 4A is a schematic illustration of a first reflection
band 452 of an oriented polymeric multilayer optical film and a
first blocking band 462 of a non-birefringent optical filter, both
at normal incidence. The first reflection band 452 has first and
second band edges 454 and 456 at normal incidence at wavelengths of
.lamda..sub.1 and .lamda..sub.2, respectively, and the first
blocking band has first and second band edges 464 and 466 at normal
incidence at wavelengths of .lamda..sub.3 and .lamda..sub.4,
respectively.
[0042] In some cases, the band edge 454 is at an undesired
wavelength and the blocking band 462 is utilized to extend the
wavelengths blocked by the optical stack to a desired band edge
wavelength corresponding to the first band edge 464. In some
embodiments, an optical stack includes an oriented polymeric
multilayer optical film (e.g., first layer 110) and a first
non-birefringent optical filter (e.g., second layer 114) adjacent
the multilayer optical film. The oriented polymeric multilayer
optical film has a first reflection band 452 with a first band edge
454 at normal incidence at an undesired band edge wavelength
.lamda..sub.1. The first non-birefringent optical filter has a
first blocking band 462 which, at normal incidence, includes the
undesired band edge wavelength .lamda..sub.1 and has a second band
edge 466 at a first desired band edge wavelength .lamda..sub.3.
[0043] In some embodiments, a method of modifying a first
reflection band of an oriented polymeric multilayer optical film is
provided. The method includes the steps of: providing the oriented
polymeric multilayer optical film (e.g., first layer 110) having
the first reflection band 452, the first reflection band 452 having
a band edge 454 at a first wavelength .lamda..sub.1 at normal
incidence; determining a desired normal incidence band edge
wavelength .lamda..sub.3; selecting a non-birefringent optical
filter (e.g., second layer 114) having a first blocking band 462,
the first blocking band 462 having the desired normal incidence
band edge wavelength .lamda..sub.3 and including the first
wavelength .lamda..sub.1 at normal incidence; and positioning the
non-birefringent reflector in optical communication with the
oriented polymeric multilayer optical film. The term "optical
communication" as applied to two objects means that light can be
transmitted from one to the other either directly or indirectly
using optical methods (for example, reflection, diffraction,
refraction).
[0044] The shifts of the band edges of the reflection and blocking
bands depend on the construction of the optical stack (e.g., on the
refractive indices uses in the non-birefringent optical filter as
described further elsewhere herein). FIGS. 4B and 4C shows the
reflection and blocking bands at an oblique angle of incidence for
two different embodiments which provide the normal incidence
reflection and blocking bands illustrated in FIG. 4A.
[0045] FIG. 4B is a schematic illustration of a first reflection
band 452b (corresponding to first reflection band 452) and a first
blocking band 462b (corresponding to first blocking band 462) at an
oblique incidence angle. The first and second band edges 454b and
456b of the first reflection band 452b have shifted from
wavelengths of .lamda..sub.1 and .lamda..sub.2 to wavelengths of
.lamda.'.sub.1 and .lamda.'.sub.2, respectively, and the first and
second band edges 464b and 466b of the first blocking band 462b has
shifted from wavelengths of .lamda..sub.3 and .lamda..sub.4 to
wavelengths of .lamda.'.sub.3 and .lamda.'.sub.4, respectively. The
shift from .lamda..sub.i to .lamda.'.sub.i (i.e., the absolute
value of the difference in .lamda..sub.i and .lamda.'.sub.i) for
any i from 1 to 4, may the same or different (e.g., the shifts may
differ by a factor of at least 1.3 or at least 1.5) from any other
shift.
[0046] FIG. 4C is a schematic illustration of a first reflection
band 452c (corresponding to first reflection band 452) and a first
blocking band 462c (corresponding to first blocking band 462) at an
oblique incidence angle in an embodiment where the optical stack
has the reflection and blocking bands 452 and 462, respectively,
illustrated in FIG. 4A at normal incidence, but has differing
shifts from the embodiment of FIG. 4B. The first and second band
edges 454c and 456c of the first reflection band 452c have shifted
from wavelengths of .lamda..sub.1 and .lamda..sub.2 to wavelengths
of .lamda.''.sub.1 and .lamda.''.sub.2, respectively, and the first
and second band edges 464c and 466c of the first blocking band 462c
has shifted from wavelengths of .lamda..sub.3 and .lamda..sub.4 to
wavelengths of .lamda.''.sub.3 and .lamda.''.sub.4, respectively. A
passband has opened between .lamda.''.sub.4 and .lamda.''.sub.1. In
the embodiment illustrated in FIG. 4B, the first reflection band
452b and the first blocking band 462b overlap at both normal and
oblique incidence, while in the embodiment illustrated in FIG. 4C,
the first reflection band 452c and the first blocking band 462c
overlap at normal incidence but not at the oblique angle of
incidence. In other embodiments, the first reflection band and the
first blocking band overlap at the oblique angle of incidence but
not at normal incidence.
[0047] The shift of band edge with incidence angle can be
controlled by the selection of materials used in the oriented
polymeric multilayer optical film and in the non-birefringent
optical filter. For example, the refractive indices of alternating
layers in the oriented polymeric multilayer optical film can be
adjusted to adjust how rapidly the band edge(s) of the reflection
band of the multilayer optical film shifts with incidence angle.
Higher refractive indices result in lower band edge shifts due to
refraction bending the light rays closer to the normal direction
which results in a shorter path length through the layer. In some
embodiments, the non-birefringent optical filter includes a
plurality of alternating layers (e.g., of the form . . . ABABABA .
. . ) as described further elsewhere herein. The alternating layers
can be alternating inorganic layers (both A and B inorganic),
alternating polymeric layers (both A and B polymeric), or a
polymeric layer alternating with an inorganic layer (one of A and B
inorganic and the other polymeric). In some embodiments, lower
refractive index materials are used for the non-birefringent
optical filter than for the oriented polymeric multilayer optical
film and the blocking band of the non-birefringent optical filter
shifts more rapidly with incidence angle than the reflection band
of the oriented polymeric multilayer optical film. Utilizing an
inorganic material for at least one of A and B allows a higher
refractive index material to be used than what is typically
available for oriented polymeric layers. This allows a
non-birefringent optical filter to be constructed which has a band
shift smaller than that of the oriented polymeric multilayer
optical film.
[0048] In some embodiments, an optical stack includes an oriented
polymeric multilayer optical film having a first reflection band
(e.g., reflection band 452 or 453b) having a first band width
(.lamda..sub.2-.lamda..sub.1) at normal incidence and having a
first band edge (e.g., band edge 454 or 454b) that has a first
shift (e.g., .lamda..sub.1-.lamda.'.sub.1) between normal incidence
and an incidence angle of 60 degrees. The optical stack also
includes a first non-birefringent optical filter having a first
blocking band (e.g., blocking band 462 or 462b) having a second
band width (.lamda..sub.4-.lamda..sub.3) at normal incidence and
having a second band edge (e.g., band edge 464 or 464b) that has a
second shift (e.g., .lamda..sub.3-.lamda.'.sub.3) between normal
incidence and an incidence angle of 60 degrees. In some
embodiments, the first band width is different from the second band
width, and the first shift is different from the second shift. For
example, the first band width may be greater than the second band
width and the first shift may be greater than the second shift. In
this case, the optical stack can provide the wide bandwidth of an
oriented polymeric multilayer optical film with the low shift of
band edge with incidence angle provided by a non-birefringent
interference filter, for example. In some embodiments, the first
band width is at least 1.3 or 1.5 times the second band width. In
some embodiments, the first shift is at least 1.3 or 1.5 times the
second shift. In some embodiments, the first blocking band is an
absorbing band that has little or no shift with incidence
angle.
[0049] In some embodiments, the non-birefringent blocking filter
includes two blocking bands or two non-birefringent blocking
filters each including a blocking band is provided. One or both of
the blocking bands may overlap with a band edge of the oriented
polymeric multilayer optical film at normal incidence. This is
illustrated in FIG. 5 which is a schematic illustration of a first
reflection band 552 of an oriented polymeric multilayer optical
film and first and second blocking bands 562a and 562b of one or
two non-birefringent optical filters, all at normal incidence. In
some embodiments, the first reflection band 552 and the first and
second blocking bands 562a and 562b shift with incidence angle such
that both of the first and second blocking bands 562a and 562b
overlap with band edges of the first reflection band 552 at an
oblique incidence angle (e.g., 45 or 60 degrees). In other
embodiments, the first reflection band 552 and the first and second
blocking bands 562a and 562b shift with incidence angle such that
one or both of the first and second blocking bands 562a and 562b do
not overlap with band edges of the first reflection band 552 at an
oblique incidence angle (e.g., 45 or 60 degrees). In still other
embodiments, one or both of the first and second blocking bands
562a and 562b do not overlap with a band edge of the first
reflection band 552 at normal incidence, but do overlap with a band
edge of the first reflection band 552 at an oblique incidence
angle.
[0050] FIGS. 6A-6B schematically illustrates first reflection band
652 and first blocking band 662 which overlap at normal incidence
(shown in FIG. 6A) and which do not overlap at an oblique incidence
angle (shown in FIG. 6B). The first reflection band 652 has band
edges at .lamda..sub.1 and .lamda..sub.2 at normal incidence and at
.lamda.'.sub.1 and .lamda.'.sub.2, respectively, at the oblique
incidence angle. The first blocking band 662 has band edges at
.lamda..sub.3 and .lamda..sub.4 at normal incidence and at
.lamda.'.sub.3 and .lamda.'.sub.4, respectively, at the oblique
incidence angle. A passband is present between .lamda.'.sub.2 and
.lamda.'.sub.3 at the oblique incidence angle. The oblique
incidence angle may be 45 degrees or 60 degrees, for example.
[0051] FIGS. 7A-7B schematically illustrates first reflection band
752 and first blocking band 762 which do not overlap at normal
incidence (shown in FIG. 7A) and which do overlap at an oblique
incidence angle (shown in FIG. 7B). The first reflection band 752
has band edges at .lamda..sub.1 and .lamda..sub.2 at normal
incidence and at .lamda.'.sub.1 and .lamda.'.sub.2, respectively,
at the oblique incidence angle. The first blocking band 762 has
band edges at .lamda..sub.3 and .lamda..sub.4 at normal incidence
and at .lamda.'.sub.3 and .lamda.'.sub.4, respectively, at the
oblique incidence angle. A passband is present between
.lamda..sub.4 and .lamda..sub.1 at normal incidence which is not
present at the oblique incidence angle. The oblique incidence angle
may be 45 degrees or 60 degrees, for example.
[0052] Band shift patterns different from those shown in FIGS.
6A-7B are also possible. In some embodiments, the blocking band
partially overlaps the reflection band at normal incidence and
extends to the right of a right band edge of the reflection band at
normal incidence. In this case, the relative shifts of the band
edges can be selected such that the band width of the resulting
overall blocking band of the optical stack narrows with increasing
incidence angle. In some embodiments, the blocking band partially
overlaps the reflection band at normal incidence and extends to the
left of a left band edge of the reflection band at normal
incidence. In this case, the relative shifts of the band edges can
be selected such that the band width of the resulting overall
blocking band of the optical stack widens with incidence angle
and/or opens a passband (e.g., a passband between .lamda.''.sub.4
and .lamda.''.sub.1 is present in FIG. 4C). In some embodiments,
the blocking band at least partially overlaps the reflection band
at normal incidence and does not extend beyond the reflection band
at normal incidence. In this case, the relative shifts of the band
edges can be selected such that the overall blocking band expands
and/or opens a passband (for example the wavelength range from
.lamda.'.sub.2 to .lamda.'.sub.3 depicted in FIG. 6B is a passband
where transmission is allowed; this passband is not present in FIG.
6A). In some embodiments, the blocking band does not overlap the
reflection band at normal incidence and is positioned to the left
of the left band edge of the reflection band. In this case, the
relative shifts of the band edges can be selected such that the
overall blocking band narrows and/or a passband narrows or closes
(for example the wavelength range from .lamda..sub.4 to
.lamda..sub.1 depicted in FIG. 7A is a passband where transmission
is allowed; this passband is closed in FIG. 7B). In some
embodiments, the blocking band does not overlap the reflection band
at normal incidence and is positioned to the right of the right
band edge of the reflection band. In this case, the relative shifts
of the band edges can be selected such that a passband between the
reflection band and the blocking band widens with increasing
incidence angle.
[0053] In some embodiments, the oriented polymeric multilayer
optical film has a plurality of reflection bands. In some
embodiments, the oriented polymeric multilayer optical film is a
comb filter having a plurality of passbands between adjacent
reflection bands. In some embodiments, at least some of the
passbands shift under the blocking band or shift out from under the
blocking band as the angle of incidence varies.
[0054] FIG. 8 is a graph illustrating the concept of full-width at
half-maximum ("FWHM"). The curve 850 represents a function of
wavelength that can correspond to a transmittance, 1 minus a
transmittance, an absorbance, a reflectance, an output spectrum of
a light source, or an input spectrum of a sensor, for example. In
order to quantify relevant features of the curve 850, a baseline
value B of the curve 850, a peak value P of the curve 850, and an
intermediate value H of the curve 850, halfway between P and B are
identified in FIG. 8. The curve 850 intersects with the value H at
the points p1 and p2, whose wavelength values equal the short
wavelength band edge and the long wavelength band edge .lamda.b,
respectively, of the band 869. The short and long wavelength band
edges can be used to calculate two other parameters of interest:
the width (full-width at half-maximum, or "FWHM") of the band 869,
which equals .lamda.b-.lamda.a; and the center wavelength of the
band 869, which equals (.lamda.a+.lamda.b)/2. Note that the center
wavelength may be the same as or different from the peak wavelength
(point p3) of the band 869, depending on how symmetrical or
asymmetrical the curve 850 is.
[0055] In some embodiments, the curve 850 represents 1 minus the
transmittance through a non-birefringent optical filter or through
an oriented polymeric multilayer optical film. In some embodiments,
the curve 850 represents an output band of a light source. In some
embodiments, the curve 850 represents an input band for a sensor.
In embodiments, where curve 850 represents 1 minus a transmittance
of a blocking band or of a reflection band, the value H may be
greater than 0.6 (transmittance no more than 0.4 or 40 percent),
greater than 0.7 (transmittance no more than 0.3 or 30 percent),
greater than 0.8 (transmittance no more than 0.2 or 20 percent), or
greater than 0.9 (transmittance no more than 0.1 or 10 percent).
The value P may be greater than 0.7 (transmittance no more than 0.3
or 30 percent), greater than 0.8 (transmittance no more than 0.2 or
20 percent), or greater than 0.9 (transmittance no more than 0.1 or
10 percent). The value B may be less than 0.5 (transmittance at
least 0.5 or 50 percent), less than 0.4 (transmittance at least 0.6
or 60 percent), less than 0.3 (transmittance at least 0.7 or 70
percent), or less than 0.2 (transmittance at least 0.8 or 80
percent).
[0056] FIG. 9 is a cross-sectional view of filter 913 which
includes a plurality of alternating first layers 957 and second
layers 959. Filter 913 can be an oriented polymeric multilayer
optical film or a non-birefringent optical filter depending on the
selection of the first and second layers 957 and 959. In some
embodiments, the alternating first and second layers 957 and 959
are alternating polymeric layers having different refractive
indices.
[0057] In some embodiments, the alternating first and second layers
957 and 959 are alternating polymeric layers where at least one of
the first and second layers 957 and 959 are oriented polymeric
layers. Such polymeric filters (e.g., mirrors or reflective
polarizers) are generally described in U.S. Pat. No. 5,882,774
(Jonza et al.); U.S. Pat. No. 5,962,114 (Jonza et al.); U.S. Pat.
No. 5,965,247 (Jonza et. al.); U.S. Pat. No. 6,939,499 (Merrill et
al.); U.S. Pat. No. 6,916,440 (Jackson et al.); U.S. Pat. No.
6,949,212 (Merrill et al.); and U.S. Pat. No. 6,936,209 (Jackson et
al.); for example, each of which is hereby incorporated by
reference herein to the extent that it does not contradict the
present description. In brief summary, a polymeric multilayer
optical film can be made by coextruding a plurality of alternating
polymeric layers (e.g., hundreds of layers), uniaxially or
substantially uniaxially stretching the extruded film (e.g., in a
linear or parabolic tenter) to orient the film in the case of a
polarizer or biaxially stretching the film to orient the film in
the case of a mirror.
[0058] In some embodiments, a non-birefringent optical filter used
in an optical stack is formed by depositing an absorbing material
(e.g., by one or more of printing, spraying, and laminating the
absorbing material) onto a separate substrate or directly onto the
oriented polymeric multilayer optical film. If a separate substrate
is used, after depositing the non-birefringent optical filter onto
the substrate, the substrate can optionally be laminated to the
oriented polymeric multilayer optical film.
[0059] In some embodiments, the alternating first and second layers
957 and 959 are alternating non-birefringent layers. The
alternating non-birefringent layers can be deposited onto a
substrate and the substrate positioned adjacent to (and optionally
laminated to) an oriented polymeric multilayer optical film for
form an optical stack, or the alternating non-birefringent layers
can be deposited directly onto an oriented polymeric multilayer
optical film for form an optical stack. In some embodiments, the
alternating non-birefringent layers is deposited using one or more
of atomic layer deposition, sputtering, chemical vapor deposition,
and layer-by-layer self-assembly.
[0060] In some embodiments, the alternating first and second layers
957 and 959 are alternating inorganic layers. In this case, the
filter 913 may be referred to as a dielectric mirror. Such
dielectric mirrors can be made by depositing alternate low and high
index layers of inorganic materials using thin-film deposition
techniques known in the art. For example, alternating layers of
TiO.sub.2 and SiO.sub.2 can be evaporated onto a substrate or onto
an oriented multilayer optical film to provide a reflective
non-birefringent optical filter. Other oxides or metal-doped oxides
can also be used, including, for example, zinc oxide or metal-doped
zinc oxide, and metal-doped silicon oxide. For example, Al-doped
ZnO or Al-doped SiO.sub.x can be used as inorganic layers.
[0061] In other embodiments, one of the alternating first and
second layers 957 and 959 is polymeric and the other of the
alternating first and second layers 957 and 959 is inorganic. For
example, an inorganic second layer 959 can be vapor deposited or
sputtered onto a polymeric first layer 957, then another polymeric
first layer 957 can be coated onto the inorganic second layer 959.
Another inorganic second layer 959 can then be deposited onto the
coated polymeric first layer 957 and the process repeated until a
desired number of layers is formed. The polymeric first layers can
be formed using a vacuum coater similar to the coater described in
U.S. Pat. No. 5,440,446 (Shaw et al.) and U.S. Pat. No. 7,018,713
(Padiyath et al.), both of which are hereby incorporated herein by
reference to the extent that they do not contradict the present
description, to deposit a monomer layer and curing the monomer
layer by exposure to actinic radiation (e.g., ultra-violet
radiation). For example, a stack of alternating layers of cured
acrylate polymer (e.g., having a refractive index in a range of 1.4
to 1.6) and an oxide (e.g., a metal oxide having a refractive index
in a range of 1.8 to 3.0) can be used to provide a reflective
non-birefringent optical filter. The oxide can be a metal-doped
oxide such as Al-doped ZnO. Refractive index can refer to the
refractive index determined at a wavelength of a center of a
desired reflection band or at a standard fixed wavelength such as
550 nm, for example.
[0062] In other embodiments, a filter 913 having alternating
inorganic layers and a different filter 913 having alternating
oriented polymeric layers are placed adjacent each other to form an
optical stack of the present description. The two filters can be
laminated together through an adhesive layer or the inorganic
filter can be deposited layer by layer onto the polymeric filter
using the layer-by-layer self-assembly methods of U.S. Pat. Pub.
No. 2015/0285956 (Schmidt et al.), for example, which is hereby
incorporated herein by reference to the extent that it does not
contradict the present description.
[0063] Whether polymeric or inorganic layers are used, reflection
is provided when a pair of adjacent layers (optical repeat unit)
has a total optical thickness (physical thickness of a layer times
the refractive index of the layer) of half of a wavelength. By
adjusting the thickness of the layers through the stack of the
layers, a desired reflection band or reflection bands can be
provided.
[0064] FIG. 10A is a schematic illustration of optical system 1001a
including light source 1022 and optical filter 1000a. A light ray
1040a is emitted by the light source 1022 and transmitted through
optical filter 1000a. Optical filter 1000a may be any of the
optical stacks of the present description or may be an oriented
polymeric multilayer optical film having a first reflection band
with a first band edge. FIG. 10B is a schematic illustration of
optical system 1001b including sensor 1024 and optical filter
1000b. A light ray 1040b is transmitted through optical filter
1000b and is received by the sensor 1024. Optical filter 1000b may
be any of the optical stacks of the present description or may be
an oriented polymeric multilayer optical film having a first
reflection band with a first band edge. Optical filter 1000b may be
configured to limit light transmitted into the sensor 1024 to a
desired input band for the sensor 1024. In some embodiments, an
optical system includes both a light source and a sensor. For
example, a light source may be included in optical system 1001b
disposed to provide the light ray 1040b which may reflect off of a
marker (e.g., a white tee shirt, reflective tape, markers in a
sign, license plates such as retroreflective license plates, etc.)
before passing through optical filter 1000b or a sensor may be
included in optical system 1000a to receive the light ray 1040a
directly or after the light ray 1040a has reflected off of a
marker, for example. In some embodiments, the optical stacks of the
present description are used to provide angular limitations of
light passing through the filter. For example, an optical stack can
block light emitted by a light source at normal incidence and
transmit light of the same wavelength at an oblique incidence
angle. As another example, an optical stack can transmit light
emitted by a light source at normal incidence and block light of
the same wavelength at an oblique incidence angle.
[0065] FIG. 10C is a schematic illustration of optical system 1001c
which includes the optical systems 1001a and 1001b described in
reference to FIGS. 10A-B and which further includes marker 1030
which is in optical communication with light source 1022 and sensor
1024. Marker 1030 includes reflector 1032 and layer 1034. Reflector
1032 may be or may include one or more of a specular reflector, a
diffuse reflector, a semi-specular reflector, and a retroreflector.
Layer 1034 can be an optical filter suitable for a given
application, for example. In some embodiments, layer 1034 is an
optical stack of the present description, which can be used, for
example, as an angle limiting filter for the marker 1030. In other
embodiments, layer 1034 is omitted.
[0066] Other uses of optical filters in optical systems are
described in co-pending U.S. Pat. App. No. 62/347,776 (Wheatley et
al.) filed on Jun. 9, 2016 and hereby incorporated herein by
reference to the extent that it does not contradict the present
description.
[0067] In some embodiments, an optical system is provided which
includes an optical filter and further includes one or both of a
light source and a sensor in optical communication with the optical
filter. The optical filter may be any of the optical stacks of the
present description or may be an oriented polymeric multilayer
optical film having a first reflection band with a first band edge.
In some embodiments, the optical system includes the light source
which may be configured to produce light in an output band. In some
embodiments, the output band is a narrow band (e.g., a band having
a full-width at half-maximum of no more than 40 nm). In some
embodiments, the light source is a light emitting diode (LED), a
laser, or a laser diode, for example. In some embodiments, the
optical system includes the sensor which may be configured to
receive light in an input band. In some embodiments, the input band
is a narrow band (e.g., a band having a full-width at half-maximum
of no more than 40 nm) which may be established by an optical
bandpass filter disposed at an entrance to the sensor. In some
embodiments, the first reflection band of the optical stack
overlaps the output band and/or the input band at normal incidence,
but not at an oblique incidence angle (e.g., 45 or 60 degrees). For
example, the first reflection band may correspond to reflection
band 652 and the output band and/or the input band may be in a
wavelength range of .lamda..sub.3 to .lamda..sub.4 depicted in FIG.
6A. At normal incidence the range of .lamda..sub.3 to .lamda..sub.4
overlaps the range of .lamda..sub.1 to .lamda..sub.2 and at an
oblique incidence angle, the range of .lamda..sub.3 to
.lamda..sub.4 does not overlap the range of .lamda.'.sub.1 to
.lamda.'.sub.2. In other embodiments, the first reflection band
overlaps the output band and/or the input band an oblique incidence
angle (e.g., 45 or 60 degrees), but not at normal incidence. For
example, the first reflection band may correspond to reflection
band 752 and the output band and/or input band may be in a
wavelength range of .lamda..sub.3 to .lamda..sub.4 depicted in FIG.
7A. At normal incidence the range of .lamda..sub.3 to .lamda..sub.4
does not overlap the range of .lamda..sub.1 to .lamda..sub.2 and at
an oblique incidence angle, the range of .lamda..sub.3 to
.lamda..sub.4 does overlap the range of .lamda.'.sub.1 to
.lamda.'.sub.2. In some embodiments, the optical system includes
both the light source and the sensor where the sensor, the light
source and the optical stack are in optical communication with each
other as described further elsewhere herein.
EXAMPLES
[0068] The examples that follow illustrate means of fabrication and
test results for optical stacks including a coextruded oriented
polymeric multilayer optical film and a non-birefringent optical
filter designed to overlap at least one band edge of the polymeric
multilayer optical film at normal incidence.
Test Methods
[0069] Optical spectra for were measured using a Perkin Elmer
Lambda 900 UV/VIS spectrophotometer.
Preparatory Example 1
[0070] An oriented polymeric multilayer optical film was prepared
as generally described in U.S. Pat. No. 5,882,774 (Jonza et al.).
The film included a single multilayer optical packet comprised of
550 alternating layers of high index layers of polyethylene
naphthalate (PEN) and low index layers of polymethylmethacrylate
(PMMA), and included a protective skin layer of PEN on each side,
for a total of 552 layers. The film was extruded and biaxially
stretched to produce an oriented polymeric multilayer optical film
having the optical spectra shown in FIG. 11 at normal incidence.
The optical spectra shown in FIG. 11 includes data taken from
multiple sections of the film overlaid to demonstrate the result of
process variations. In this example, the optical band edge was at
.about.700 nm and cross-web variation was on the order of 50
nm.
Preparatory Example 2
[0071] An oriented polymeric multilayer optical film was prepared
as described generally for Preparatory Example 1. The film was
extruded and biaxially stretched to produce an oriented polymeric
multilayer optical film having the optical spectra shown in FIG.
12. The optical spectra shown in FIG. 12 includes film data taken
at multiple locations which are overlaid to demonstrate the result
of process variations. The curves labeled C1, C3, C8, C11, C17 and
C24 correspond to crossweb positions across the film a 2.8 inches,
4.7, inches, 13.8 inches, 19.3 inches, 30.3 inches and 43.2 inches
from an end of the film. In this example, the optical band edge was
at .about.800 nm and cross-web variation was on the order of 50
nm.
Example 1
[0072] A non-birefringent band edge correction filter in the form
of a hybrid organic/inorganic interference filter was deposited
using the vacuum deposition procedures generally described in U.S.
Pat. No. 7,018,713 (Padiyath et al.). For the purposes of this
Example, the hybrid filter was deposited onto a PET film substrate
and subsequently laminated onto the multilayer optical film stack
described as Preparatory Example 1 to produce an optical stack.
Alternatively, the hybrid filter could have been directly coated
onto the multilayer optical film stack of Preparatory Example
1.
[0073] The hybrid filter, which was a non-birefringent optical
filter, was designed as a 12 layer stack with high index (n=1.983
at 681 nm) inorganic layers (ZnO:Al) at 98.3 nm thickness
alternating with low index (n=1.488 at 681 nm) organic polymer
layers at 114.4 nm thickness. The optical spectra of this hybrid
non-birefringent correction filter are shown in FIG. 13.
[0074] After lamination of hybrid filter of this Example onto the
oriented polymeric multilayer optical film of Preparatory Example
1, the resulting optical spectra was measured with results
displayed in FIG. 14. The resulting band edge wavelength shifted to
that of the hybrid filter at 660 nm with cross-web variation
reduced from .about.50 nm to less than 5 nm.
Example 2
[0075] The same hybrid filter formed on PET that was used for
Example 1 was laminated onto the oriented polymeric multilayer
optical film of Preparatory Example 2 to produce an optical stack.
The resulting optical spectra was measured with results displayed
in FIG. 15. The curves labeled L1, L3, L8, L11, L17 and L24
correspond to C1, C3, C8, C11, C17 and C24, respectively, of FIG.
12. The resulting measurements showed the band edge wavelength to
shift to that of the hybrid filter at .about.660 nm with cross-web
variation reduced from .about.50 nm to less than 5 nm.
Example 3
[0076] This Example demonstrates the use of an absorptive dye layer
to provide correction to band edge of a multilayer optical film. An
oriented polymeric multilayer optical film was produce as in
Preparatory Example 1 and had the spectra shown in FIG. 16 (and
also shown as curve 1882 in FIG. 18). For this Example, a sample of
1/8'' thick Acrylite 257-0 GP Red (Cyro Corporation) was used as a
non-birefringent optical filter. This material contained a
spectrally sharp absorbing dye in an acrylic host as shown in the
transmission spectrum of FIG. 17 (also shown as curve 1884 in FIG.
18). It absorbs heavily below about 610 nm, and has a sharp
transition to high transmission at higher wavelengths.
[0077] The Acrylite 257-0 GP Red layer was placed adjacent the
oriented polymeric multilayer optical film to produce an optical
stack which was a notch filter at normal incidence with a passband
1860 having peak transmission at about 640 nm with a full-width
half-maximum of about 55 nm as shown in FIG. 18. Since the absorber
band edge does not shift with incidence angle and the oriented
polymeric multilayer optical film interference filter shifts to
lower wavelengths with increasing incidence angle, the transmission
notch closes quickly as a function of angle. Transmission through
the optical stack was observed to shift from red to black as the
angle of incidence changed from normal to about 30 degrees.
[0078] The following is a list of exemplary embodiments of the
present description,
Embodiment 1 is an optical stack comprising: an oriented polymeric
multilayer optical film having a first reflection band with a first
band edge having a variation across a length or a width of the
multilayer optical film, the first band edge, at normal incidence,
having a design wavelength .lamda. and a characteristic deviation
about the design wavelength .DELTA.; a first non-birefringent
optical filter disposed adjacent the multilayer optical film and
having a first blocking band, the first blocking band, at normal
incidence, comprising wavelengths between .lamda.-.DELTA./2 and
.lamda.+.DELTA./2, wherein, at normal incidence, the first
reflection band includes a wavelength range having a width of at
least .DELTA. that is outside of the first blocking band.
Embodiment 2 is the optical stack of Embodiment 1, wherein the
first non-birefringent optical filter is a non-birefringent
reflector and the first blocking band is a reflection band.
Embodiment 3 is the optical stack of Embodiment 2, wherein the
non-birefringent reflector comprises a plurality of alternating
first and second layers. Embodiment 4 is the optical stack of
Embodiment 3, wherein the first and second layers are inorganic.
Embodiment 5 is the optical stack of Embodiment 4, wherein the
first layer is inorganic and the second is organic. Embodiment 6 is
the optical stack of Embodiment 1, wherein the blocking band is an
absorbing band. Embodiment 7 is the optical stack of Embodiment 1,
wherein the blocking band is a second reflection band. Embodiment 8
is the optical stack of Embodiment 1, further comprising a second
non-birefringent optical filter, the first reflection band having a
second band edge having a second design wavelength at normal
incidence, the second non-birefringent optical filter having a
second blocking band comprising the second design wavelength.
Embodiment 9 is the optical stack of Embodiment 1, wherein the
first non-birefringent optical filter is disposed directly on the
multilayer optical film. Embodiment 10 is the optical stack of
Embodiment 1, wherein an intermediate layer separates the
non-birefringent optical filter and the multilayer optical film.
Embodiment 11 is the optical stack of Embodiment 10, wherein the
intermediate layer is an adhesive layer. Embodiment 12 is the
optical stack of Embodiment 10, wherein the intermediate layer
comprises one or more dyes or pigments. Embodiment 13 is the
optical stack of Embodiment 12, wherein the one or more dyes or
pigments comprises one or more polarizing dyes or pigments.
Embodiment 14 is the optical stack of Embodiment 1, wherein an air
gap separates the non-birefringent optical filter and the
multilayer optical film. Embodiment 15 is the optical stack of
Embodiment 1 being substantially flat. Embodiment 16 is the optical
stack of Embodiment 1 being curved about at least one axis.
Embodiment 17 is the optical stack of Embodiment 16 being curved
about two orthogonal axes. Embodiment 18 is the optical stack of
Embodiment 1, wherein the first non-birefringent optical filter has
a second blocking band. Embodiment 19 is the optical stack of
Embodiment 18, wherein one of the first and second blocking bands
is a first order reflection band and the other of the first and
second blocking bands is a second order reflection band. Embodiment
20 is the optical stack of Embodiment 1, wherein the oriented
polymeric multilayer optical film is a reflective polarizer.
Embodiment 21 is the optical stack of Embodiment 1, wherein the
oriented polymeric multilayer optical film is a mirror film.
Embodiment 22 is the optical stack of Embodiment 1, wherein the
oriented polymeric multilayer optical film is a comb filter.
Embodiment 23 is the optical stack of Embodiment 1, further
comprising a marker in optical communication with the oriented
polymeric multilayer optical film and with the first
non-birefringent optical filter. Embodiment 24 is the optical stack
of Embodiment 23, wherein the marker comprises a specular
reflector, a diffuse reflector, or a semi-specular reflector.
Embodiment 25 is the optical stack of Embodiment 23, wherein the
marker comprises a retroreflector. Embodiment 26 is an optical
stack comprising: an oriented polymeric multilayer optical film
having a first reflection band with a first band edge at normal
incidence at an undesired band edge wavelength; a first
non-birefringent optical filter adjacent the multilayer optical
film and having a first blocking band, the first blocking band, at
normal incidence, comprising the undesired band edge wavelength and
having a second band edge at a first desired band edge wavelength.
Embodiment 27 is the optical stack of Embodiment 26, further
comprising a second non-birefringent optical filter having a second
blocking band, the first reflection band having a third band edge
at normal incidence at a second undesired band edge wavelength, the
second blocking band comprising the second undesired wavelength and
having a fourth band edge at a second desired band edge wavelength.
Embodiment 28 is the optical stack of Embodiment 27, wherein one of
the first and second non-birefringent optical filters is absorbing
and one is reflective. Embodiment 29 is the optical stack of
Embodiment 26, wherein at least one of the non-birefringent optical
filter and the oriented polymeric multilayer optical film is
spatially variant. Embodiment 30 is the optical stack of Embodiment
29, wherein the oriented polymeric multilayer optical film includes
one or more holes therethrough. Embodiment 31 is the optical stack
of Embodiment 29, wherein the non-birefringent optical filter is
discontinuous across a length or a width of the non-birefringent
optical filter. Embodiment 32 is the optical stack of Embodiment
26, wherein the first non-birefringent optical filter is disposed
directly on the multilayer optical film. Embodiment 33 is the
optical stack of Embodiment 26, wherein an intermediate layer
separates the non-birefringent optical filter and the multilayer
optical film. Embodiment 34 is the optical stack of Embodiment 26,
wherein an air gap separates the non-birefringent optical filter
and the multilayer optical film. Embodiment 35 is the optical stack
of Embodiment 26 being substantially flat. Embodiment 36 is the
optical stack of Embodiment 26 being curved about at least one
axis. Embodiment 37 is the optical stack of Embodiment 36 being
curved about two orthogonal axes. Embodiment 38 is the optical
stack of Embodiment 26, wherein the blocking band is an absorbing
band. Embodiment 39 is the optical stack of Embodiment 26, wherein
the blocking band is a second reflection band. Embodiment 40 is the
optical stack of Embodiment 26, wherein the oriented polymeric
multilayer optical film is a reflective polarizer. Embodiment 41 is
the optical stack of Embodiment 26, wherein the oriented polymeric
multilayer optical film is a mirror film. Embodiment 42 is the
optical stack of Embodiment 26, wherein the oriented polymeric
multilayer optical film is a comb filter. Embodiment 43 is the
optical stack of Embodiment 26, further comprising a marker in
optical communication with the oriented polymeric multilayer
optical film and with the first non-birefringent optical filter.
Embodiment 44 is the optical stack of Embodiment 43, wherein the
marker comprises a specular reflector, a diffuse reflector, or a
semi-specular reflector. Embodiment 45 is the optical stack of
Embodiment 43, wherein the marker comprises a retroreflector.
Embodiment 46 is an optical stack comprising: an oriented polymeric
multilayer optical film having a first reflection band having a
first band width at normal incidence and having a first band edge
that has a first shift between normal incidence and an incidence
angle of 60 degrees; a first non-birefringent optical filter
disposed adjacent the oriented polymeric multilayer optical film
and having a first blocking band having a second band width at
normal incidence and having a second band edge that has a second
shift between normal incidence and an incidence angle of 60
degrees, wherein the first shift is different from the second
shift. Embodiment 47 is the optical stack of Embodiment 46, wherein
the first band width is greater than the second band width.
Embodiment 48 is the optical stack of Embodiment 46, wherein the
first band width is at least 1.3 times the second band width.
Embodiment 49 is the optical stack of Embodiment 46, wherein the
first band width is at least 1.5 times the second band width.
Embodiment 50 is the optical stack of Embodiment 46, wherein the
first shift is less than the second shift. Embodiment 51 is the
optical stack of Embodiment 46, wherein the first shift is greater
than the second shift. Embodiment 52 is the optical stack of
Embodiment 46, wherein the first shift is at least 1.3 times the
second shift. Embodiment 53 is the optical stack of Embodiment 46,
wherein the first shift is at least 1.5 times the second shift.
Embodiment 54 is the optical stack of Embodiment 46, wherein the
first band edge is at a first wavelength at normal incidence and
the first blocking band includes the first wavelength at normal
incidence. Embodiment 55 is the optical stack of Embodiment 46,
wherein the first non-birefringent optical filter is a
non-birefringent reflector and the optical stack has an overall
reflection band arising from the first reflection band and the
first blocking band, the overall reflection band having a third
band width at normal incidence and having a third band edge that
has a third shift between normal incidence and an incidence angle
of 60 degrees, the third band width greater than the first band
width, the third shift equal to the second shift. Embodiment 56 is
the optical stack of Embodiment 46, wherein the first blocking band
is entirely contained in the first reflection band at normal
incidence and is not is entirely contained in the first reflection
band at an oblique incidence angle. Embodiment 57 is the optical
stack of Embodiment 56, wherein the oblique incidence angle is 60
degrees. Embodiment 58 is the optical stack of Embodiment 56,
wherein the blocking band extends to the left of the first
reflection band at the oblique incidence angle. Embodiment 59 is
the optical stack of Embodiment 56, wherein the blocking band
extends to the right of the first reflection band at the oblique
incidence angle. Embodiment 60 is the optical stack of Embodiment
46, wherein the first reflection band and the first blocking band
do not overlap at normal incidence and do overlap at an oblique
incidence angle. Embodiment 61 is the optical stack of Embodiment
60, wherein the oblique incidence angle is 60 degrees. Embodiment
62 is the optical stack of Embodiment 60, wherein, at the oblique
incidence angle, the first blocking band overlaps a left band edge
of the first reflection band. Embodiment 63 is the optical stack of
Embodiment 60, wherein, at the oblique incidence angle, the first
blocking band overlaps a right band edge of the first reflection
band. Embodiment 64 is the optical stack of Embodiment 46, wherein
the first reflection band and the first blocking band overlap at
normal incidence and do not overlap at an oblique incidence angle.
Embodiment 65 is the optical stack of Embodiment 64, wherein the
oblique incidence angle is 60 degrees. Embodiment 66 is the optical
stack of Embodiment 46, wherein the oriented polymeric multilayer
optical film is a reflective polarizer. Embodiment 67 is the
optical stack of Embodiment 46, wherein the oriented polymeric
multilayer optical film is a mirror film. Embodiment 68 is the
optical stack of Embodiment 46, wherein the oriented polymeric
multilayer optical film is a comb filter. Embodiment 69 is the
optical stack of Embodiment 46, further comprising a marker in
optical communication with the oriented polymeric multilayer
optical film and with the first non-birefringent optical filter.
Embodiment 70 is the optical stack of Embodiment 69, wherein the
marker comprises a specular reflector, a diffuse reflector, or a
semi-specular reflector. Embodiment 71 is the optical stack of
Embodiment 69, wherein the marker comprises a retroreflector.
Embodiment 72 is an optical system comprising the optical stack of
any one of the previous Embodiments directed to an optical stack
and further comprising one or both of a light source and a sensor
in optical communication with the optical stack. Embodiment 73 is
the optical system of Embodiment 72 comprising the light source.
Embodiment 74 is the optical system of Embodiment 73, wherein the
light source is configured to produce light in an output band
having a full-width at half-maximum of no more than 40 nm.
Embodiment 75 is the optical system of Embodiment 74, wherein the
first reflection band overlaps the output band at normal incidence,
but not at an oblique incidence angle. Embodiment 76 is the optical
system of Embodiment 74, wherein the first reflection band overlaps
the output band an oblique incidence angle, but not at normal
incidence. Embodiment 77 is the optical system of Embodiment 73
further comprising the sensor, wherein the sensor, the light source
and the optical stack are in optical communication with each other.
Embodiment 78 is an optical system comprising: an oriented
polymeric multilayer optical film having a first reflection band
with a first band edge and a light source configured to produce
light in an output band, the light source in optical communication
with the oriented polymeric multilayer optical film, wherein the
first reflection band overlaps the output band at normal incidence,
but not at an oblique incidence angle. Embodiment 79 is an optical
system comprising: an oriented polymeric multilayer optical film
having a first reflection band with a first band edge and a light
source configured to produce light in an output band, the light
source in optical communication with the oriented polymeric
multilayer optical film, wherein the first reflection band overlaps
the output band at an oblique incidence angle, but not at normal
incidence. Embodiment 80 is the optical system of Embodiment 78 or
79, wherein the oblique incidence angle is 60 degrees. Embodiment
81 is the optical system of Embodiment 78 or 79, wherein the output
band has a full-width at half-maximum of no more than 40 nm.
Embodiment 82 is the optical system of Embodiment 78 or 79, further
comprising a sensor in optical communication with the oriented
polymeric multilayer optical film and with the light source.
Embodiment 83 is an optical system comprising: an oriented
polymeric multilayer optical film having a first reflection band
with a first band edge and a sensor configured to receive light in
an input band, the sensor in optical communication with the
oriented polymeric multilayer optical film, wherein the first
reflection band overlaps the input band at normal incidence, but
not at an oblique incidence angle. Embodiment 84 is an optical
system comprising: an oriented polymeric multilayer optical film
having a first reflection band with a first band edge and a sensor
configured to receive light in an input band, the sensor in optical
communication with the oriented polymeric multilayer optical film,
wherein the first reflection band overlaps the input band at an
oblique incidence angle, but not at normal incidence. Embodiment 85
is the optical system of Embodiment 83 or 84, wherein the oblique
incidence angle is 60 degrees. Embodiment 86 is the optical system
of Embodiment 83 or 84, wherein the output band has a full-width at
half-maximum of no more than 40 nm. Embodiment 87 is the optical
system of Embodiment 83 or 84, further comprising a light source in
optical communication with the oriented polymeric multilayer
optical film and with the sensor. Embodiment 88 is the optical
system of Embodiment 87, wherein the light source is configured to
produce light in an output band having a full-width at half-maximum
of no more than 40 nm. Embodiment 89 is the optical system of
Embodiment 83 or 84, wherein the sensor comprises an optical filter
limiting the light transmitted into the sensor to the input band.
Embodiment 90 is a method of modifying a first reflection band of
an oriented polymeric multilayer optical film, the method
comprising: providing the oriented polymeric multilayer optical
film having the first reflection band, the first reflection band
having a band edge at a first wavelength at normal incidence;
determining a desired normal incidence band edge wavelength;
selecting a non-birefringent optical filter having a first blocking
band, the first blocking band having the desired normal incidence
band edge wavelength and including the first wavelength at normal
incidence; and positioning the non-birefringent reflector in
optical communication with the oriented polymeric multilayer
optical film. Embodiment 91 is the method of Embodiment 90, wherein
the non-birefringent optical filter is a non-birefringent reflector
and the first blocking band is a second reflection band, and
wherein selecting the non-birefringent optical filter comprises
selecting different first and second materials such that a stack of
alternating layers of the first and second materials provides the
second reflection band. Embodiment 92 is the method of Embodiment
91, wherein the positioning step comprises depositing the stack of
alternating layers directly onto the oriented polymeric multilayer
optical film. Embodiment 93 is the method of Embodiment 92, wherein
the depositing step comprises depositing the stack through a mask
resulting in a spatially variant non-birefringent reflector.
Embodiment 94 is the
method of Embodiment 91, wherein positioning step comprises
depositing the stack of alternating layers onto a substrate to form
the non-birefringent reflector and positioning the formed
non-birefringent reflector adjacent to the oriented polymeric
multilayer optical film. Embodiment 95 is the method of any one of
Embodiments 92 to 94, wherein the depositing step comprises one or
more of atomic layer deposition, sputtering, chemical vapor
deposition, and layer-by-layer self-assembly. Embodiment 96 is the
method of Embodiment 94, further comprising laminating the formed
non-birefringent reflector onto the oriented polymeric multilayer
optical film. Embodiment 97 is the method of Embodiment 94, wherein
the formed non-birefringent reflector is positioned adjacent to the
oriented polymeric multilayer optical film with a gap therebetween.
Embodiment 98 is the method of Embodiment 90, further comprising
cutting out portions of the oriented polymeric multilayer optical
film to form a spatially variant multilayer optical film.
Embodiment 99 is the method of Embodiment 90, wherein the
positioning step comprises in-mold forming of the non-birefringent
optical filter adjacent the oriented polymeric multilayer optical
film. Embodiment 100 is the method of Embodiment 99, wherein the
in-mold forming results in a flat oriented polymeric multilayer
optical film. Embodiment 101 is the method of Embodiment 99,
wherein the in-mold forming results in an oriented polymeric
multilayer optical film curved about at least one axis. Embodiment
102 is the method of Embodiment 101, wherein the in-mold formed
oriented polymeric multilayer optical film is curved about two
orthogonal axes. Embodiment 103 is the method of Embodiment 90,
wherein the positioning step comprises one or more of printing,
spraying, and laminating an absorbing material onto a substrate and
disposing the substrate adjacent the oriented polymeric multilayer
optical film. Embodiment 104 is the method of Embodiment 90,
wherein the positioning step comprises one or more of printing,
spraying, and laminating an absorbing material onto the oriented
polymeric multilayer optical film. Embodiment 105 is the optical
system of any one of the previous Embodiments to an optical system
comprising a light source, further comprising a marker in optical
communication with the light source. Embodiment 106 is the optical
system of any one of the previous Embodiments to an optical system
comprising a sensor, further comprising a marker in optical
communication with the sensor. Embodiment 107 is the optical system
of Embodiment 105 or Embodiment 106, wherein the maker comprises an
optical stack according to any one of the previous Embodiments
directed to an optical stack. Embodiment 108 is the optical system
of Embodiment 105 or Embodiment 106, wherein the maker comprises a
specular reflector, a diffuse reflector, or a semi-specular
reflector. Embodiment 109 is the optical system of Embodiment 105
or Embodiment 106, wherein the marker comprises a
retroreflector.
[0079] Descriptions for elements in figures should be understood to
apply equally to corresponding elements in other figures, unless
indicated otherwise. Although specific embodiments have been
illustrated and described herein, it will be appreciated by those
of ordinary skill in the art that a variety of alternate and/or
equivalent implementations can be substituted for the specific
embodiments shown and described without departing from the scope of
the present disclosure. This application is intended to cover any
adaptations or variations of the specific embodiments discussed
herein. Therefore, it is intended that this disclosure be limited
only by the claims and the equivalents thereof
* * * * *