U.S. patent application number 13/935219 was filed with the patent office on 2015-01-08 for optical body with fresnel-rendering of complex topographical surface.
The applicant listed for this patent is 3M Innovative Properties Company. Invention is credited to Michael F. Weber.
Application Number | 20150009572 13/935219 |
Document ID | / |
Family ID | 52112510 |
Filed Date | 2015-01-08 |
United States Patent
Application |
20150009572 |
Kind Code |
A1 |
Weber; Michael F. |
January 8, 2015 |
OPTICAL BODY WITH FRESNEL-RENDERING OF COMPLEX TOPOGRAPHICAL
SURFACE
Abstract
An optical film or other optical body has a structured surface
comprising Fresnel prisms. The Fresnel prisms define a complex
topography. For example, a first and second Fresnel prism may have
elongated first and second plan view shapes that form a "wye"
(Y-shaped) feature. Alternatively or in addition, the Fresnel
prisms may be arranged such that slopes of the Fresnel prisms
define one or more saddle points. Furthermore, one or more of the
Fresnel prisms may have prism shapes in plan view that include
undulating portions, and the Fresnel prisms may be arranged in a
slope sequence that defines one or more inflection points. The
Fresnel prisms may be refractive or reflective, and they may
provide the structured surface with a 3-dimensional appearance.
Inventors: |
Weber; Michael F.;
(Shoreview, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M Innovative Properties Company |
St. Paul |
MN |
US |
|
|
Family ID: |
52112510 |
Appl. No.: |
13/935219 |
Filed: |
July 3, 2013 |
Current U.S.
Class: |
359/625 |
Current CPC
Class: |
G02B 5/09 20130101; G02B
5/32 20130101; G02B 5/045 20130101; G02B 3/08 20130101 |
Class at
Publication: |
359/625 |
International
Class: |
G02B 5/04 20060101
G02B005/04 |
Claims
1. An optical body comprising a structured surface comprising a
plurality of Fresnel prisms comprising a first and second Fresnel
prism; wherein the first and second Fresnel prisms have elongated
first and second plan view shapes respectively, and in a first
region the first and second shapes follow paths that track each
other; wherein in a second region the first and second shapes
follow paths that diverge from each other; and wherein the
plurality of Fresnel prisms also comprises a third Fresnel prism,
and wherein the third Fresnel prism is not present in the first
region but is disposed between the first and second Fresnel prisms
in the second region.
2. (canceled)
3. The optical body of claim 1, wherein the third Fresnel prism has
a third plan view shape that is concave in the second region.
4. The optical body of claim 3, wherein the third plan view shape
is U-shaped.
5. The optical body of claim 1, wherein in the first region the
first and second shapes follow paths that are parallel to each
other.
6. The optical body of claim 1, wherein in the first region the
first and second shapes follow paths that are adjacent to each
other.
7. The optical body of claim 1, wherein the Fresnel prisms are
light transmissive and refractive.
8. The optical body of claim 1, wherein the Fresnel prisms are
reflective.
9. The optical body of claim 1, wherein the structured surface
provides a 3-dimensional appearance.
10. The optical body of claim 1, wherein the first Fresnel prism
has a slope and/or width that changes along a length of the first
Fresnel prism.
11. The optical body of claim 1, wherein the structured surface is
formed in a first material layer, and wherein the optical body
limber comprises a planarizing layer in mating contact with the
structured surface.
12. The optical body of claim 11, wherein the planarizing layer
comprises a nanovoided material.
13. The optical body of claim 11, wherein the structured surface is
formed in a first material layer, and wherein the optical body
further comprises an indicia layer attached directly or indirectly
to the first material layer.
14. The optical body of claim 1, wherein the first and second
Fresnel prisms form a wye.
15. An optical body comprising a structured surface comprising a
plurality of Fresnel prisms, wherein at least some of the Fresnel
prisms are configured to form a wye, wherein the plurality of
Fresnel prisms includes a first and second Fresnel prism having
first and second plan view shapes respectively, and in a first
region the first and second shapes follow paths that track each
other, and in a second region the first and second shapes follow
paths that diverge from each other.
16. (canceled)
17. An optical body comprising a structured surface comprising a
plurality of Fresnel prisms, wherein the Fresnel prisms are
configured such that slopes of the Fresnel prisms define at least a
first saddle point, wherein the slopes of the Fresnel prisms form a
first slope sequence along a first cross-sectional plane that
intersects the first saddle point, and a second slope sequence
alone a second cross-sectional plane that intersects the first
saddle point, the first slope sequence being concave and the second
slope sequence being convex.
18. (canceled)
19. The optical body of claim 17, wherein the slopes of the Fresnel
prisms define a plurality of saddle points which includes the first
saddle point.
20. The optical body of claim 17, wherein the plurality of saddle
points are in a regular repeating array.
21. The optical body of claim 17, wherein the Fresnel prisms are
light transmissive and refractive.
22. The optical body of claim 17, wherein the Fresnel prisms are
reflective.
23. The optical body of claim 17, wherein the structured surface
provides a 3-dimensional appearance.
24. The optical body of claim 17, wherein the plurality of Fresnel
prisms includes a first Fresnel prism having a slope and/or width
that changes along a length of such first Fresnel prism.
25. The optical body of claim 17, wherein the structured surface is
formed in a first material layer, and wherein the optical body
further comprises a planarizing layer in mating contact with the
structured surface.
26. The optical body of claim 25, wherein the planarizing layer
comprises a nanovoided material.
27. The optical body of claim 25, wherein the structured surface is
formed in a first material layer, and wherein the optical body
further comprises an indicia layer attached directly or indirectly
to the first material layer.
28. An optical body comprising a structured surface comprising a
plurality of Fresnel prisms comprising a first Fresnel prism;
wherein the Fresnel prisms are arranged in a slope sequence, the
slope sequence defining one or more inflection points; wherein the
first Fresnel prism has a first prism shape in plan view that
includes an undulating portion; and wherein the structured surface
is firmed in a first material layer, and wherein the optical body
further comprises a planarizing layer in mating contact with the
structured surface.
29. The optical body of claim 28, wherein the first Fresnel prism
has a slope and/or a width that changes along a length of the first
Fresnel prism.
30. The optical body of claim 29, wherein the first Fresnel prism
has a slope that changes along, the length of the first Fresnel
prism.
31. The optical body of claim 29, wherein the first Fresnel prism
has a width that changes along the length of the first Fresnel
prism.
32. The optical body of claim 28, wherein the Fresnel prisms are
light transmissive and refractive.
33. The optical body of claim 28, wherein the Fresnel prisms are
reflective.
34. The optical body of claim 28, wherein the structured surface
provides a 3-dimensional appearance.
35. (canceled)
36. The optical body of claim 28, wherein the planarizing layer
comprises a nanovoided material.
37. An optical body comprising a structured surface comprising a
plurality of Fresnel prisms comprising a first Fresnel prism;
wherein the Fresnel prisms are arranged in a slope sequence, the
slope sequence defining one or more inflection points; wherein the
first Fresnel prism has a first prism shape in plan view that
includes an undulating portion; and wherein the structured surface
is formed in a first material layer, and wherein the optical body
further comprises an indicia layer attached directly or indirectly
to the first material layer.
38. The optical body of claim 28, wherein the undulating portion of
the first prism shape comprises an inflection point.
39. An optical body comprising a structured surface comprising a
plurality of Fresnel prisms comprising a first Fresnel prism, the
first Fresnel prism having a first prism shape in plan view that
includes an inflection point, wherein the Fresnel prisms are
arranged in a slope sequence in a cross sectional plane, the slope
sequence defining one or more inflection points.
40. (canceled)
41. The optical body of claim 39, wherein the first prism shape
undulates and includes a plurality of inflection points.
Description
FIELD
[0001] The present disclosure relates to, among other things,
refractive and reflective optical films and related optical bodies
having a structured surface comprising Fresnel prisms. The
disclosure also relates to articles and systems incorporating such
optical bodies, and methods of making and using such optical
bodies.
BACKGROUND
[0002] About 200 years ago, French physicist Augustin-Jean Fresnel
is said to have developed thinner, lighter lenses for use in early
19th century lighthouses. We refer to these lenses today as Fresnel
lenses. Since that time, Fresnel lenses have been used in a
multitude of applications to provide focusing of light in a thinner
and lighter form than could be provided by a bulk optical lens. It
was also found that curved mirrors could be replaced by analogous
thin, faceted constructions by making the facets reflective. Such
mirrors are referred to as Fresnel mirrors.
BRIEF SUMMARY
[0003] We have developed a family of optical films and other
optical bodies that extend the basic principles of Fresnel lenses
and Fresnel mirrors to more complex topographical surfaces. Like
conventional Fresnel lenses and Fresnel mirrors, these new optical
bodies have structured surfaces on which are formed Fresnel prisms.
However, the Fresnel prisms of the new optical bodies are shaped,
configured, and/or arranged in ways that are unlike any
conventional Fresnel lenses or Fresnel mirrors we are aware of.
[0004] For example, the Fresnel prisms of the disclosed optical
bodies may be configured to represent a rendering of a non-flat
"topographical reference surface" ("TRS") whose topography is more
complex than, for example, a simple spherical dome or a simple
spherical depression. The structured surface of Fresnel prisms may
be said to be a "rendering" of the TRS because, ignoring
discontinuities or other anomalies that occur along the edges of
the Fresnel prisms, the facets of the prisms may have directional
slopes that collectively approximate the spatial distribution of
directional slopes across the surface of the TRS. A "directional
slope" in this regard refers to a vector quantity that has both a
magnitude, e.g., an angular measure of the slope relative to a
reference plane or axis, and a direction; the directional slope at
any given point on the facet of a Fresnel prism or on another
surface of interest may be completely characterized by the local
surface normal vector at the given point. We refer to the
"rendering" as a "Fresnel-rendering" because the rendering maps the
surface of the TRS onto a structured surface comprising Fresnel
prism facets, where the angled facets of the Fresnel prisms are
oriented to have the same or similar directional slopes as the
directional slopes at corresponding points on the TRS, while the
actual heights of at least some of the Fresnel prism facets are
less than the actual heights at corresponding points on the TRS,
such that the overall height or thickness of the structured surface
is typically much less than that of the TRS. Due to the fact that
the structured surface has a spatial distribution of directional
slopes that is the same as, or similar to, the spatial distribution
of directional slopes for the TRS, the structured surface refracts
and/or reflects light in a manner similar to how the TRS would (or
does) refract/reflect light. As a result, an observer of the
optical body with its structured surface, whether in transmitted or
reflected light, perceives the optical body as having the
3-dimensional shape of the TRS.
[0005] The TRS need not be a real physical surface, and
furthermore, it is not in general required that the structured
surface comprising the Fresnel prisms be derived from its
associated TRS. Nevertheless, it can be useful and enlightening to
associate or compare the structured surface of an optical body with
a TRS that has the same or similar spatial distribution of
directional slopes, since the structured surface of the optical
body refracts and/or reflects incident light in a manner that is
similar to how such a corresponding TRS would (or does) refract or
reflect incident light, and since the optical body, by virtue of
its structured surface, may have a 3-dimensional appearance similar
to the 3-dimensional appearance of the TRS.
[0006] As mentioned above, the TRS may have a complex topography.
The structured surface that corresponds to such a TRS would
typically also have a similar complex topography, but would also
include discontinuities or other anomalies that occur along the
edges of the Fresnel prisms. For example, the TRS and structured
surface may have one or more Y-shaped topographical feature in plan
view, such a feature referred to herein as a "wye". Alternatively
or in addition, the TRS and structured surface may have one or more
topographical saddle point. Alternatively or in addition, the TRS
and structured surface may have features that undulate in plan view
and that have a slope sequence along a cross-sectional plane of
interest that defines one or more inflection points.
[0007] The present application thus describes, among other things,
optical bodies that include a structured surface comprising a
plurality of Fresnel prisms comprising a first and second Fresnel
prism, where the first and second Fresnel prisms have elongated
first and second plan view shapes respectively, and in a first
region the first and second shapes follow paths that track each
other, and where in a second region the first and second shapes
follow paths that diverge from each other.
[0008] The plurality of Fresnel prisms may also comprise a third
Fresnel prism, and the third Fresnel prism may not be present in
the first region but may be disposed between the first and second
Fresnel prisms in the second region. The third Fresnel prism may
have a third plan view shape that is concave in the second region.
The third plan view shape may be U-shaped. In the first region, the
first and second shapes may follow paths that are parallel to each
other. In the first region, the first and second shapes may follow
paths that are adjacent to each other. The first Fresnel prism may
have a slope and/or width that changes along a length of the first
Fresnel prism. The first and second Fresnel prisms may form a
wye.
[0009] The present application also discloses optical bodies that
comprise a structured surface comprising a plurality of Fresnel
prisms, wherein at least some (e.g. at least two or at least three)
of the Fresnel prisms are configured to form a wye. The plurality
of Fresnel prisms may include a first and second Fresnel prism
having first and second plan view shapes respectively, and in a
first region the first and second shapes may follow paths that
track each other, and in a second region the first and second
shapes may follow paths that diverge from each other.
[0010] The present application also discloses optical bodies that
comprise a structured surface comprising a plurality of Fresnel
prisms, wherein the Fresnel prisms are configured such that slopes
of the Fresnel prisms define at least a first saddle point.
[0011] The slopes of the Fresnel prisms may form a first slope
sequence along a first cross-sectional plane that intersects the
first saddle point, and a second slope sequence along a second
cross-sectional plane that intersects the first saddle point, the
first slope sequence being concave and the second slope sequence
being convex. The slopes of the Fresnel prisms may define a
plurality of saddle points which includes the first saddle point.
The plurality of saddle points may be in a regular repeating
array.
[0012] We also disclose optical bodies that comprise a structured
surface comprising a plurality of Fresnel prisms comprising a first
Fresnel prism, where the Fresnel prisms are arranged in a slope
sequence, the slope sequence defining one or more inflection
points, and where the first Fresnel prism has a first prism shape
in plan view that includes an undulating portion. The first Fresnel
prism may have a slope and/or a width that changes along a length
of the first Fresnel prism. The undulating portion of the first
prism shape may comprise an inflection point.
[0013] We also disclose optical bodies that comprise a structured
surface comprising a plurality of Fresnel prisms comprising a first
Fresnel prism, the first Fresnel prism having a first prism shape
in plan view that includes an inflection point. The Fresnel prisms
may be arranged in a slope sequence in a cross sectional plane, the
slope sequence defining one or more inflection points. The first
prism shape may undulate and include a plurality of inflection
points.
[0014] In any of the disclosed optical bodies: Fresnel prisms may
be light transmissive and refractive; the Fresnel prisms may be
reflective; the structured surface may provide a 3-dimensional
appearance; the plurality of Fresnel prisms may include a first
Fresnel prism having a slope and/or width that changes along a
length of such first Fresnel prism; the structured surface may be
formed in a first material layer, and the optical body may further
comprise a planarizing layer in mating contact with the structured
surface, and the planarizing layer may comprise a nanovoided
material; the structured surface may be formed in a first material
layer, and the optical body may further comprise an indicia layer
attached directly or indirectly to the first material layer.
[0015] Related methods, systems, and articles are also
discussed.
[0016] These and other aspects of the present application will be
apparent from the detailed description below. In no event, however,
should the above summaries be construed as limitations on the
claimed subject matter, which subject matter is defined solely by
the attached claims, as may be amended during prosecution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The disclosure may be more completely understood in
connection with the accompanying drawings, in which:
[0018] FIG. 1 is a block diagram showing one possible relationship
between a topographical reference surface (TRS) and a corresponding
Fresnel-rendered structured surface;
[0019] FIG. 2A is a photograph of a piece of flame maple (wood),
the photograph showing both the grain and the figure of the
wood;
[0020] FIG. 2B is the same photograph as FIG. 2A, but with black
lines superimposed on the photograph to identify some wye features
of the wood;
[0021] FIG. 3 is a schematic plan view of a topographical reference
surface (TRS) having a wye feature in the form of a Y-shaped
ridge;
[0022] FIGS. 3A and 3B are schematic cross-sectional views through
cut lines 3A-3A and 3B-3B of FIG. 3;
[0023] FIG. 4 is a schematic plan view of a structured surface
corresponding to the TRS of FIG. 3, the structured surface
comprising Fresnel prisms that define a wye-feature corresponding
to the wye-feature of FIG. 3;
[0024] FIGS. 4A and 4B are schematic cross-sectional views through
cut lines 4A-4A and 4B-4B of FIG. 4;
[0025] FIG. 4C is an enlarged view of FIG. 4, where arrows
representing surface normal vectors are superimposed on several of
the Fresnel prisms to illustrate how the directional slope changes
as a function of position in the plane of the film;
[0026] FIG. 5 is a schematic view, partially in cross-section and
partially in perspective view, of a portion of a film or other
optical body with a structured surface comprising Fresnel
prisms;
[0027] FIG. 6 is a schematic plan view of another topographical
reference surface (TRS) having a wye feature in the form of a
Y-shaped ridge;
[0028] FIGS. 6A and 6B are schematic cross-sectional views through
cut lines 6A-6A and 6B-6B of FIG. 6;
[0029] FIG. 7 is a schematic plan view of a structured surface
corresponding to the TRS of FIG. 6, the structured surface
comprising Fresnel prisms that define a wye-feature corresponding
to the wye-feature of FIG. 6;
[0030] FIGS. 7A and 7B are schematic cross-sectional views through
cut lines 7A-7A and 7B-7B of FIG. 7;
[0031] FIG. 8 is a schematic perspective view of a topographical
reference surface (TRS) having saddle points and inflection
points;
[0032] FIG. 8A is a schematic plan view of the TRS of FIG. 8, where
contour lines are superimposed to show the topography, and
localized peaks, localized valleys, and saddle points are also
labeled;
[0033] FIG. 9 is a schematic plan view of a structured surface
corresponding to a portion of the TRS of FIG. 8, and FIG. 9A is a
close-up schematic plan view of a portion of the surface in FIG. 9
in the vicinity of a saddle point, where arrows representing
surface normal vectors are superimposed on several of the Fresnel
prisms to illustrate how the directional slope changes as a
function of position;
[0034] FIGS. 9B, 9D, and 9F are schematic cross-sectional views
through cut lines 9B-9B, 9D-9D, and 9F-9F respectively in FIG.
9;
[0035] FIGS. 9C, 9E, and 9G are graphs that show the slope
sequences of the (non-vertical) facets that make up the structured
surfaces of FIGS. 9B, 9D, and 9F, respectively;
[0036] FIG. 10 is a schematic plan view of a portion of a
structured surface in an alternative embodiment to that of FIGS. 9
and 9A;
[0037] FIG. 11 is a schematic perspective view of a topographical
reference surface (TRS) having features that undulate in plan view
and having a slope sequence that defines one or more inflection
points;
[0038] FIG. 11A is a schematic side or cross-sectional view of the
TRS of FIG. 11 in the x-z plane;
[0039] FIG. 12 is a schematic plan view of a structured surface
corresponding to the TRS of FIG. 11;
[0040] FIG. 12A is a schematic cross-sectional view through cut
line 12A-12A of FIG. 12, and FIG. 12B is a graph showing the slope
sequences of the facets that make up the structured surface of FIG.
12A;
[0041] FIG. 13 is a schematic perspective view of another
topographical reference surface (TRS) having features that undulate
in plan view and having a slope sequence that defines one or more
inflection points; and
[0042] FIG. 14 is a schematic plan view of a structured surface
corresponding to the TRS of FIG. 13, the structured surface
comprising Fresnel prisms that undulate in plan view and have a
slope sequence that defines multiple inflection points.
[0043] The schematic drawings presented herein are not necessarily
to scale; however, graphs are assumed to have accurate scales
unless otherwise indicated. Like numbers used in the figures refer
to like elements.
DETAILED DESCRIPTION
[0044] As mentioned above, we disclose herein inter alia optical
articles such as optical films or the like in which a structured
surface is shaped, formed, or otherwise configured to have Fresnel
prisms formed therein. The structured surface (in particular,
non-vertical facets of the structured surface) defines a complex
topography. The structured surface may be considered to comprise a
Fresnel-rendering of a non-flat topographical reference surface
(TRS) which has the same or similar complex topography. The complex
topography may include "wye" features, saddle points, inflection
points in a slope sequence, undulating shapes in plan view,
inflection points in plan view, and combinations thereof.
[0045] In FIG. 1, we see a block diagram that shows one possible
relationship between a TRS and a corresponding Fresnel-rendered
structured surface. In this case, a TRS of interest is selected,
designed, or otherwise provided in box 110. The TRS has a complex
topography. As such, the TRS may for example have one or more wye
feature, saddle point, inflection point, or undulating shape, or
combinations thereof. In box 112, the TRS is characterized with the
use of contour lines. A contour line is a locus of points on the
surface whose perpendicular distance from a reference plane (e.g.,
whose height above the reference plane) is a constant. Families or
sets of contour lines may be defined by selecting a series of
distinct heights or constants, with each contour line in the set
being associated with a given one of the distinct heights or
constants. In general, any given contour line need not be strictly
"linear", i.e., need not be straight, but in some cases one or more
of the contour lines, or portions thereof, may be straight. After
the contour lines are defined for the TRS, they can then be used to
transform the TRS into a structured surface, as indicated at box
114. In one version of this transformation, each pair of adjacent
contour lines on the TRS can have identical or substantially
identical counterpart lines on the structured surface, but on the
structured surface, those lines define the opposite edges or
boundaries of a single Fresnel prism, and between those lines is
the inclined facet of that Fresnel prism. The inclined facet has a
slope or curvature which may vary along the length or path of the
Fresnel prism (although for some Fresnel prisms the slope or
curvature may be constant) that matches or substantially matches
the slope or curvature of the portion of the TRS at corresponding
points between the adjacent contour lines at issue.
[0046] The resulting structured surface may be said to be a
Fresnel-rendering of the TRS. This is because, on the one hand, the
spatial distribution of directional slopes of the structured
surface, which is determined substantially by the directional
slopes of the inclined facets of the Fresnel prisms, is the same as
or similar to the spatial distribution of directional slopes of the
TRS. On the other hand, unlike the TRS, the structured surface is
segmented, grooved, or otherwise subdivided into a plurality of
Fresnel prisms. The overall height or thickness of the structured
surface is thus typically much less than that of the TRS, just as
the thickness of a conventional Fresnel lens is much less than the
thickness of the bulk optic lens which it mimics.
[0047] As mentioned above, the TRS need not be a real physical
surface, and furthermore, there is no requirement that the
structured surface comprising the Fresnel prisms be derived from
its associated TRS. Nevertheless, it can be useful and enlightening
to associate or compare the structured surface of an optical body
with a TRS that has the same or similar spatial distribution of
directional slopes, since the structured surface of the optical
body refracts and/or reflects incident light in a manner that is
similar to how such a corresponding TRS would (or does) refract or
reflect incident light, and since the optical body, by virtue of
its structured surface, may have a 3-dimensional appearance similar
to the 3-dimensional appearance of the TRS.
[0048] The film or other optical body with the Fresnel-rendered
structured surface may be useful for aesthetic purposes,
utilitarian purposes, or both. For example, a film having a
Fresnel-rendered structured surface may be adhered to a clear
window or shield, e.g. with a layer of optically clear pressure
sensitive adhesive and with the structured surface facing away from
the window and exposed to air, such that sunlight or other light
can still pass through the window/film combination e.g. for
purposes of illumination, but where light is refracted by the
structured surface of the film in an aesthetically pleasing pattern
that also obscures objects on the other side of the window. The
pattern-wise refraction provided by the structured surface of the
film may also give the appearance of a 3-dimensional image which
corresponds to the 3-D appearance of the corresponding TRS. The
facets of the Fresnel prisms may also be metalized, vapor coated,
or the like so that they are reflective rather than refractive, or
they may be partially metalized so that they are partially
refractive (and thus partially transmissive to sunlight or other
light) and partially reflective.
[0049] Some surfaces suitable for use as topographical reference
surfaces with complex topography can be found in nature. Examples
may include a country landscape of rolling hills and valleys, or
undulating patterns created by desert sand dunes, or the wave-like
nature of the figure of certain types of wood such as curly maple,
flame maple, or flame birch. With regard to the last example
involving the figure of wood, the word "figure" is italicized in
the preceding sentence and throughout this document to distinguish
it from the more common meaning of the word "figure", namely, in
reference to drawings, e.g., FIG. 1, FIG. 2, and so forth. Figure
is a characteristic of some particularly desirable and expensive
wood types. It is associated with stripes or other markings that
are distinct from the wood grain, and that shift in appearance with
changes in illumination geometry and/or observation geometry. For
example, a violin or guitar made of a highly figured wood may
exhibit stripes or other markings that appear to shift in position
along the surface of the wood as the instrument is tilted relative
to a given light source and/or observer. The shifting visual effect
of the wood figure gives a 3-dimensional quality to the appearance
of the wood.
[0050] A photograph of a piece of flame maple is shown in FIG. 2A.
From the perspective of the figure, individual wood grain features
can be seen extending generally horizontally, or left to right. In
contrast, light and dark stripes or bands can be seen extending
generally vertically. The vertical stripes or bands seen in the
figure are manifestations of the figure of the wood under the
particular illumination and observation conditions used to take the
photograph. Note that many or most of the vertical stripes or bands
are not simple straight linear features, but follow more
complicated paths. In some cases, portions of these paths can be
seen to undulate in this plan view. In some cases, the paths form
Y-shaped features, which we refer to as wyes or wye features. Some
of these are identified in FIG. 2B. That figure is the same
photograph as FIG. 2A, but black lines have been superimposed
thereon to identify some of the wyes. Such shapes can form the
basis of a non-flat topographical reference surface (TRS) with
complex topography.
[0051] An example of such a TRS is shown in the schematic view of
FIG. 3. In that figure, a surface 310 has a complex topography and
can form the basis for a Fresnel-rendered structured surface. The
surface 310 extends generally parallel to the x-y plane of an x-y-z
Cartesian coordinate system. The surface 310 is assumed to be flat
except for a Y-shaped ridge or protuberance, referred to as a wye
312. Due to the presence of the wye 312, the surface 310 may be
said to be non-flat even though some portions are flat. In an
alternative embodiment, the wye 312 may be a valley or depression
in the surface rather than a protuberance. In still other
embodiments, the surface 310 may be modified such that the wye 312
is surrounded by sloped, curved, undulating, or otherwise non-flat
surfaces rather than flat surfaces. For example, the surface 310
may be a small portion of a much larger surface whose topography
may be designed to emulate the figure of the wood shown in FIGS. 2A
and 2B, such larger surface containing numerous wyes as well as
other complex and/or simple features. The wye 312 has a base
portion 312a which can be considered to split into a first branch
portion 312b and a second branch portion 312c. The wye 312 also has
boundaries 313a, 313b, 313c as shown, which define the plan-view
Y-shape or outline.
[0052] Schematic cross-sectional views of the surface 310 through
cut lines 3A-3A and 3B-3B are shown in FIGS. 3A and 3B,
respectively. In FIG. 3A, the protuberance of the base portion 312a
can be seen in the functional relationship of the z- and
x-coordinates of the surface 310. In FIG. 3B, the protuberances of
the branch portions 312b, 312c can be seen in the same functional
relationship. In the cross-sectional views of FIGS. 3A and 3B, the
slope (or the projection of the slope in the x-z plane) of the
surface 310 can be ascertained at any x-coordinate position by
calculating the slope of the function at that position, i.e.,
slope=dz/dx. Note that in some places the slope is positive, in
some places the slope is negative, and in some places the slope is
zero. A positive slope is one in which the change dz (or .DELTA.z)
in the z-coordinate is positive for a positive change dx (or
.DELTA.x) in the x-coordinate, and a negative slope is one in which
the change dz (or .DELTA.z) in the z-coordinate is negative for a
positive change dx (or .DELTA.x) in the x-coordinate.
[0053] The complex topography of the surface 310 can be mimicked in
a structured surface of Fresnel prisms, using a Fresnel rendering
process such as that described in connection with FIG. 1. First, we
may characterize the surface 310 with a set of contour lines. The
increment of height that distinguishes one contour line from
another can be used to control the degree of coarseness or fineness
that will characterize the structured surface. The smaller the
height increment, the more contour lines will be included in the
pattern, and the smaller the spacing between adjacent contour
lines; the larger the height increment, the fewer contour lines in
the pattern, and the larger the spacing between adjacent contour
lines. In any case, the contour lines can be used as guides to
define Fresnel prisms on the Fresnel-rendered structured surface
corresponding to the surface 310. Such a Fresnel-rendered surface
is shown as structured surface 410 in FIG. 4.
[0054] The structured surface 410 can be considered to be a
transformation of the surface 310, where the transformation
corresponding to the Fresnel-rendering substantially preserves the
directional slope at each (x,y) position, but subdivides the
surface 410 into distinct segments or grooves in the form of
individual Fresnel prisms between which abrupt changes in height
occur, so that the overall height or thickness of the surface 410
is much smaller than that of the surface 310. (The surface 310 may
also or alternatively be considered to be a transformation of the
surface 410.) The transformation can be adapted in numerous ways,
e.g., rather than a 1:1 correspondence of (x,y) coordinates between
surfaces 310 and 410, a scale factor greater than or less than 1
can be used such that the structured surface 410 is magnified or
de-magnified (respectively) relative to the uninterrupted surface
310, or different scale factors can be used in the x- and
y-directions to introduce a distortion of one surface relative to
the other.
[0055] The surface 410 has a wye 412 which is a Fresnel-rendered
representation of the wye 312 of surface 310. Similar to surface
310, the surface 410 may be flat except for the wye 412. Similar to
the wye 312, the wye 412 has a base portion 412a and two branch
portions 412b, 412c. But unlike the wye 312, the wye 412 is
subdivided into distinct Fresnel prisms 416. The faceted surfaces
of the Fresnel prisms 416 are seen in the plan view of FIG. 4, but
the vertical faces of the Fresnel prisms 416 are not. The faceted
surfaces are bounded along opposite edges of each Fresnel prism,
such edges shown as boundary lines 414 in FIG. 4. The boundary
lines 414 curve and meander along paths which define the plan-view
shape and path of each of the Fresnel prisms 416. The boundary
lines 414 may follow paths in the x-y plane that correspond
substantially or exactly to those of contour lines for the wye 312.
That is, a contour map of the wye 312 may have the same or
substantially the same plan view appearance as the wye 412 of FIG.
4, but where the boundary lines 414 would represent contour lines
on an uninterrupted surface rather than the edges or boundaries of
distinct Fresnel prisms. Thus, the contour lines on a contour map
of the uninterrupted surface 310 can form the basis for determining
where to subdivide the surface into individual Fresnel prisms.
Properties and characteristics of contour lines and contour maps
are therefore also applicable to the boundary lines 414 of FIG. 4.
For example, on a contour map, if the spacing between two adjacent
contour lines is variable along the path of the contours, places
where the spacing is small correspond to a more steeply sloped
surface than places where the spacing is larger. Similarly, if the
spacing between two adjacent lines 414 bounding a given Fresnel
prism 416 is variable along the path of the Fresnel prism, the
inclined facet of the Fresnel prism is more steeply sloped in
places where the spacing is small compared to places where the
spacing is larger. Another property of a contour map is that the
gradient of an inclined surface at any point on a contour line is
perpendicular to the contour line at that point. Similarly, the
gradient of the slope at any point on a given Fresnel prism 416 is
perpendicular to the closest boundary line 414 to that point.
[0056] The foregoing paragraph assumes that the adjacent contour
lines are at different heights above the reference plane, i.e.,
that there is a height differential between the adjacent contour
lines. In some cases, e.g. at the uppermost portion of a ridge of
the TRS or at the lowermost portion of a valley of the TRS, two
adjacent contour lines may be at the same height above the
reference plane, i.e., the height differential between these
adjacent contour lines may be zero. The two adjacent boundary lines
414 that correspond to such adjacent contour lines may then form
the boundaries or edges of a flat region on the structured surface
410. Such a flat region, even though it is bounded by two adjacent
lines 414, is not considered to be a Fresnel prism, since it has no
vertical face and its only facet has a zero inclination. An example
of such a region is shown in FIG. 4 as region 415. For such a
region, a widening or narrowing of the space between its boundary
lines 414 is not associated with any increase or decrease in the
magnitude of slope (since the slope is exactly or substantially
zero), and a line drawn perpendicular to any such boundary line 414
does not represent the gradient of the slope, again since the slope
of such region is zero.
[0057] We may refer to the height associated with adjacent boundary
lines 414 as H, this parameter also being the height differential
between adjacent contour lines corresponding to such adjacent lines
414. We may also refer to the spacing between adjacent boundary
lines 414 as W, this parameter also being the (plan view) spacing
between the adjacent contour lines that correspond to such adjacent
lines 414. With these parameters so defined, the Fresnel prisms 416
on the surface 410 are prisms of constant height H and whose width
is the (potentially variable) distance W between the boundary lines
414 at any given location. Furthermore, the magnitude of the slope
of a given prism 416 at that location is H/W. The height H
represents the vertical distance between the corresponding adjacent
contour lines, and is selected to provide for a Fresnel prism 416
of reasonable height for the process used to make them. The surface
of a given Fresnel prism 416 has the same directional slope at a
given point on its inclined facet as that of the corresponding TRS
(surface 310) at that point. For ease of fabrication, the constant
height Fresnel prism approach may be modified e.g. by replacing any
given Fresnel prism with two or more Fresnel prisms of smaller
heights and smaller widths, and/or by replacing two or more
adjacent Fresnel prisms with a single Fresnel prism of greater
height and greater width, e.g. in cases where the constant height
approach produces Fresnel prisms that are unusually wide or
unusually narrow due to the value of the local slope.
[0058] In an alternative transformation between the TRS and the
Fresnel-rendered structured surface, the height differential H
between adjacent contour lines on the TRS may be changed from one
contour line to the next in such a way that the spacing W between
adjacent contour lines (in plan view) is held constant, or, for
some surface topographies, as constant as reasonably possible. Such
a procedure produces Fresnel prisms on the corresponding
Fresnel-rendered structured surface whose heights H are not the
same, but whose widths W may be the same, or at least similar to
each other. In still other alternatives, both the height
differential H and the width W may be non-uniform, producing on the
structured surface Fresnel prisms of variable height H and width W,
but whose directional slopes at least approximately match the
directional slopes at corresponding locations on the TRS.
[0059] In reference to FIG. 4, three of the Fresnel prisms 416 have
been shaded so that they may be more easily identified and
discussed. The shaded prisms are Fresnel prisms 416a, 416b, and
416c. These prisms have been selected to demonstrate certain
properties and characteristics of the wye 412, although other ones
of the Fresnel prisms 416 could also have been selected for this
purpose. In describing these properties and characteristics, we
also identify two regions of the structured surface 410 in this
plan view: a region 417a, in an area of the base portion 412a of
the wye, and a region 417b, in an area where the branch portions
412b, 412c begin to diverge from the base portion 412a.
[0060] In the region 417a, the Fresnel prisms 416a, 416b follow
paths in plan view (as seen from their respective boundary lines)
that track each other. The paths track each other because, for
example, if one prism follows a straight path at a particular
point, then near that point the other prism also follows a straight
path parallel to the other path, or if one prism follows a curved
path at a particular point, then near that point the other prism
also follows a curved path with the same or similar curvature as
the other path. With this clarification, the prisms 416a, 416b can
be seen to follow paths that track each other in the region 417a.
These paths are not precisely straight in this region, but are
straight enough, and track each other well enough, to be able to
further describe them as being parallel to each other in the
region. Still further, although the prisms 416a, 416b do not share
a common boundary line 414, they are separated from each other in
the region 417a not by any other Fresnel prism 416 but only by a
portion of the flat region 415, and hence, the prisms 416a, 416b
and their respective paths may still be said to be adjacent to each
other in the region 417a.
[0061] In the region 417b, the Fresnel prisms 416a, 416b follow
paths in plan view that diverge from each other. Furthermore, the
Fresnel prism 416c is present or disposed in the region 417b, but
is not present and not disposed in the region 417a. The plan view
path of the Fresnel prism 416c is also concave and U-shaped in the
region 417b. Note in this regard that a Fresnel prism is deemed to
have a plan view shape that is concave, U-shaped, or the like as
long as at least one orientation of the surface can be found in
which the plan view of the Fresnel prism has such shape. Portions
of the plan view paths of the Fresnel prisms 416a, 416b, 416c can
also be seen to undulate.
[0062] Schematic cross-sectional views of the structured surface
410 through cut lines 4A-4A and 4B-4B are shown in FIGS. 4A and 4B,
respectively. In FIG. 4A, the Fresnel prisms 416 (not labeled in
this figure except for the Fresnel prisms 416a and 416b) and the
flat region 415 which make up the base portion 412a can be seen in
the functional relationship of the n- and x-coordinates of the
surface 410. In FIG. 4B, the Fresnel prisms 416 (again not labeled
here except for the Fresnel prisms 416a, 416b, and 416c) and the
flat region 415 which make up the branch portions 412b, 412c can be
seen in the same functional relationship. In the cross-sectional
views of FIGS. 4A and 4B, the slope (or the projection of the slope
in the x-z plane) of the surface 410 can be ascertained at any
x-coordinate position by calculating the slope of the function at
that position, i.e., slope=dz/dx. Note that in some places the
slope is positive, in some places the slope is negative, and in
some places the slope is zero.
[0063] The inclined facets of the Fresnel prisms 416 in FIGS. 4A
and 4B are drawn as being not only inclined or sloped, but also
planar or straight in transverse cross-section. This may be an
approximation of the actual surface topography of the TRS. For
example, the surface of the TRS may be smoothly and continuously
curved over the region of the wye 312, whereas the inclined facet
of a given Fresnel prism 416 may be a planar or simple wedge-like
approximation of the corresponding smoothly curved portion of the
surface of the wye 312. Stated differently, the directional slope
of the Fresnel prism 416 may have a constant or substantially
constant value along any cross-sectional plane that intersects the
Fresnel prism 416 transversely, the constant directional slope
being an approximation of a variable directional slope at a
corresponding portion of the TRS. In an alternative embodiment, the
inclined facet of the given Fresnel prism 416 may have the same
smoothly curved topography as the corresponding portion of the
surface of the wye 312. Stated differently, the directional slope
of the Fresnel prism 416 may vary along any cross-sectional plane
that intersects the Fresnel prism 416 transversely, the variable
directional slope being the same as or similar to the variable
directional slope at a corresponding portion of the TRS.
[0064] Turning now to FIG. 4C, we see there an enlarged view of
FIG. 4, where arrows 419 representing surface normal vectors are
superimposed on the three shaded Fresnel prisms 416a, 416b, 416c.
The arrows 419 illustrate how the directional slope changes as a
function of position across the structured surface 410, e.g. in the
plane of a film embodying such surface. The direction of a given
arrow 419 is parallel to the gradient of the slope at a given point
on a Fresnel prism 416. In accordance with the above discussion,
one can see that the direction of a given arrow 419 at a given
point is substantially perpendicular to the portion of the line 414
that is closest to that point. We have attempted to draw the
lengths of the arrows 419 to be indicative of the steepness of the
slope, with a longer arrow representing a steeper slope than a
shorter arrow. The steeper slopes (longer arrows 419) occur at
places where a given Fresnel prism is narrower (spacing between
adjacent boundary lines 414 is smaller), and shallower slopes
(shorter arrows 419) occur at places where the Fresnel prism is
wider (spacing between adjacent boundary lines 414 is larger). The
arrows 419 are drawn in FIG. 4C only for the prisms 416a, 416b, and
416c, but the reader will understand that similar arrows can be
drawn in the same fashion for the other prisms 416. In the case of
region 415, arrows 419 for that region would simply be dots, i.e.
they would have zero length, because the slope in that region is
zero and the arrows in that region would all be parallel to the
z-axis.
[0065] In FIG. 5 we show a portion of a film or other optical body
502 with a structured surface 510 comprising Fresnel prisms, three
of which are individually labeled 516a, 516b, 516c, and which can
collectively be referred to as Fresnel prisms 516. The structured
surface 510 may be the same as or similar to the structured surface
410, or the same as or similar to other structured surfaces
disclosed herein. The film 502 is shown as having a 2-layer
construction, with a structured layer 506 attached to a flat
carrier layer 504. The structured layer 506 may for example be or
comprise a cured resin material whose structured surface 510 was
obtained by pressing an uncured resin against a drum or other tool
whose structured surface was an inverted version of the structured
surface 510, and then separating the resin from the tool after or
during curing. In alternative embodiments, the film 502 may have
only a single layer, e.g., layers 504 and 506 may combine to form
only one distinguishable layer, or the film 502 may alternatively
have more than two layers. In cases where the Fresnel prisms 516
are reflective, a metal coating or other reflective layer or layers
can be applied to some or all inclined facets of the prisms 516.
Otherwise, in cases where the film 502 is tailored to transmit and
refract light, the film and its constituent layers may be highly
transparent to visible light. The film and its constituent layers
may be substantially water clear, or it or they may be colored or
tinted e.g. with one or more dyes and/or pigments, or by being made
from a material that is naturally clear but colored.
[0066] The view of FIG. 5 shows the cross-sectional shape of each
of the Fresnel prisms 516 in the x-z plane. In this regard, a
Fresnel prism is typically characterized by two facets: a vertical
facet, and an inclined facet. By "vertical facet" we mean a facet
that is perpendicular, or nearly perpendicular, to the plane of the
film (or the plane of the structured surface). An angle formed
between such a facet and the x-y plane may for example be 90
degrees or slightly less, e.g., in a range from 80 to 90 degrees to
provide some relief to allow the film to be more easily separated
from a molding tool. In FIG. 5, surfaces 516a-2, 516b-2, and 516c-2
are examples of vertical facets of Fresnel prisms. By "inclined
facet" we mean a facet that is inclined relative to the plane of
the film or structured surface, but less inclined than the vertical
facet. An angle formed between the inclined facet and the x-y plane
may for example be in a range from 0.01 to 50 degrees, and more
typically is in a range from 0.1 to 40 degrees, but these typical
ranges should not be construed in an unduly limiting fashion. In
FIG. 5, surfaces 516a-1, 516b-1, and 516c-1 are examples of
inclined facets of Fresnel prisms. In some cases, the (putative or
imaginary) vertical facets of back-to-back Fresnel prisms may
coincide with each other and thus disappear, as shown below in
connection with FIGS. 7, 7A, and 7B.
[0067] The inclined facet and the vertical facet meet to form a
ridge along the top of each prism. Examples of such ridges can be
seen as ridge 516a-3 of Fresnel prism 516a, ridge 516b-3 of Fresnel
prism 516b, and ridge 516c-3 of Fresnel prism 516c. The ridges may
be sharp and abrupt, or rounded and gradual. When the structured
surface 510 is viewed from above (in plan view), the ridges have
the appearance of lines that bound the Fresnel prisms, e.g.,
boundary lines 414 in FIG. 4. Due to the vertical or near-vertical
orientation of the vertical facets, these lines typically coincide
or substantially coincide with lines associated with the base of
each prism, i.e., where the vertical facet of one Fresnel prism
meets the inclined facet of an adjacent Fresnel prism, except in
cases where the inclined facet of a Fresnel prism meets a
horizontal surface (e.g. the left-most prism or the right-most
prism in FIG. 4a), or where the inclined facet of one prism meets
the inclined facet of an adjacent prism (see e.g. Fresnel prisms
716a, 716b in FIG. 7A below). One or more of the Fresnel prisms, or
portions thereof, may in some cases be straight, while other
Fresnel prisms or all of the Fresnel prisms, or portions thereof,
may be non-straight, e.g., curved. In FIG. 5, the Fresnel prisms
516 are shown as being curved, i.e., the ridges 516a-3, 516b-3,
516c-3 are curved in the x-y plane, and the plan view paths defined
by the prisms 516 are similarly curved.
[0068] For generality, the Fresnel prisms 516 are shown as having
different heights and widths. Prism 516a has a height Ha and a
width Wa, the prism 516b has a height Hb and a width Wb, and the
prism 516c has a height He and a width Wc. These heights and widths
correspond to respective slopes or angles of inclination, as
indicated by angles .theta.a, .theta.b, .theta.c, respectively.
Depending on the shape of the TRS associated with the structured
surface 510 and the Fresnel rendering selected, in alternative
embodiments, the heights Ha, Hb, He may be the same, and/or the
widths Wa, Wb, We may be the same, and/or the angles of inclination
.theta.a, .theta.b, .theta.c, may be the same, in a limited portion
or region of the structured surface.
[0069] Any of the disclosed embodiments may have a film
construction such as that shown in FIG. 5, i.e. with a structured
layer 506 attached to a flat carrier layer 504 and with the
structured surface 510 exposed to air. Alternatively, any of the
disclosed embodiments may have film constructions that are
modifications of FIG. 5, e.g., if Fresnel mirrors are desired
rather than Fresnel lenses, a metal vapor coat or other thin
reflective layer can be applied to the structured surface. Also, as
mentioned above, the layers 504 and 506 may be combined to form a
single layer. Additional layers and coatings can also be added to
only one side or to both sides of the film construction. For
example, one or more indicia layer may be added to the
construction, where the indicia layer(s) may provide one or more
natural pattern (e.g. an image of simulated wood grain) and/or one
or more geometric pattern (e.g. a repeating array of one or more
geometric shapes) and/or any other suitable pattern or image, e.g.
a pattern or image that combines aesthetically and/or functionally
with the image or pattern provided by the Fresnel-rendered
structured surface.
[0070] Whether the Fresnel prisms 516 are configured as lenses or
as mirrors (or both), to maximize the refractive and/or reflective
power of the prisms 516, the structured surface 510 may be exposed
to air or vacuum. Alternatively, a planarizing layer (i.e., a layer
whose thickness is comparable to the average prism height, or, in
some cases, at least as great as the smallest, the largest, or the
average prism height such that the upper surface of the planarizing
layer is actually or substantially flat, planar, or smooth) may be
provided in mating contact with the structured surface 510, with
the refractive index of the planarizing layer being less than that
of the structured layer 506. Although such a planarizing layer
generally reduces the refractive and reflective power of the prisms
516 relative to air, adequate refractive or reflective power may
still be obtained with a sufficiently low refractive index of the
planarizing layer relative to the structured layer 506. The
refractive index difference between these layers may desirably be
at least about 0.1. For the planarizing layer, ultra low index
(ULI) nanovoided materials discussed in patent application
publications WO 2010/120864 (Hao et al.) and WO 2011/088161 (Wolk
et al.), having refractive indices in a range from about
n.apprxeq.1.15 to n.apprxeq.1.35, may be used.
[0071] A plan view of another TRS with complex topography is shown
in FIG. 6. In this figure, the surface 610 extends generally
parallel to the x-y plane. The surface 610 is assumed to be flat
except for a Y-shaped ridge or protuberance, referred to as a wye
612. The wye 612 is similar to the wye 312 of FIG. 3, but the wye
612 is more symmetrical and has branches that are straight, and the
topographical profiles of each branch more closely approximate
triangles. In an alternative embodiment, the wye 612 may be a
valley or depression in the surface rather than a protuberance.
Still other alternative embodiments, analogous to the alternative
embodiments discussed in connection with FIG. 3, are also
contemplated. The wye 612 has a base portion 612a which can be
considered to split into a first branch portion 612b and a second
branch portion 612c. The wye 612 also has boundaries 613a, 613b,
613c as shown, which define the plan-view Y-shape or outline.
[0072] Schematic cross-sectional views of the surface 610 through
cut lines 6A-6A and 6B-6B are shown in FIGS. 6A and 6B,
respectively. In FIG. 6A, the protuberance of the base portion 612a
can be seen in the functional relationship of the z- and
x-coordinates of the surface 610. In FIG. 6B, the protuberances of
the branch portions 612b, 612c can be seen in the same functional
relationship. In the cross-sectional views of FIGS. 6A and 6B, the
slope (or the projection of the slope in the x-z plane) of the
surface 610 can be ascertained at any x-coordinate position by
calculating the slope of the function at that position, i.e.,
slope=dz/dx. In some places the slope is positive, in some places
the slope is negative, and in some places the slope is zero.
[0073] In like fashion to the discussion above of FIGS. 3 and 4,
the complex topography of the surface 610 can be mimicked in a
structured surface of Fresnel prisms using a Fresnel rendering
process. First, we may characterize the surface 610 with a set of
contour lines. The contour lines can be used as guides to define
Fresnel prisms on the Fresnel-rendered structured surface
corresponding to the surface 610. Such a Fresnel-rendered surface
is shown as structured surface 710 in FIG. 7.
[0074] The structured surface 710 can be considered to be a
transformation of the surface 610, where the transformation
corresponding to the Fresnel-rendering substantially preserves the
directional slope at each (x,y) position, but subdivides the
surface 610 into distinct segments or grooves in the form of
individual Fresnel prisms between which abrupt changes in height
occur, so that the overall height or thickness of the surface 710
is much smaller than that of the surface 610. (The surface 610 may
also or alternatively be considered to be a transformation of the
surface 710.) The transformation can be adapted in numerous ways,
as discussed above in connection with FIGS. 3 and 4.
[0075] The surface 710 has a wye 712 which is a Fresnel-rendered
representation of the wye 612 of surface 610. Similar to surface
610, the surface 710 may be flat except for the wye 712. Similar to
the wye 612, the wye 712 has a base portion 712a and two branch
portions 712b, 712c. Unlike the wye 612, the wye 712 is subdivided
into distinct Fresnel prisms 716. The faceted surfaces of the
Fresnel prisms 716 are seen in the plan view of FIG. 7, but the
vertical faces of the Fresnel prisms 716 are not. The faceted
surfaces are bounded along opposite edges of each Fresnel prism,
such edges shown as boundary lines 714 in FIG. 7. The boundary
lines 714 follow paths which define the plan-view shape and path of
each of the Fresnel prisms 716. The boundary lines 714 may follow
paths in the x-y plane that correspond substantially or exactly to
those of contour lines for the wye 612. That is, a contour map of
the wye 612 may have the same or substantially the same plan view
appearance as the wye 712 of FIG. 7, but where the boundary lines
714 would represent contour lines on an uninterrupted surface
rather than the edges or boundaries of distinct Fresnel prisms.
Thus, the contour lines on a contour map of the uninterrupted
surface 610 can form the basis for determining where to subdivide
the surface into individual Fresnel prisms, as discussed above.
[0076] In the case of FIG. 4, we saw a structured surface 410 that
included a flat region 415 separating the two oppositely inclined
Fresnel prisms 416a, 416b in the base portion 412a of the wye. In
the case of FIG. 7, the structured surface 710 has no corresponding
feature, because the oppositely inclined Fresnel prisms 716a, 716b
are disposed back-to-back in the base portion 712a of the wye 712,
as best seen in FIG. 7A.
[0077] If we refer to the height associated with adjacent boundary
lines 714 as H, and the spacing between adjacent boundary lines 714
as W, the Fresnel prisms 716 on the surface 710 are prisms of
constant height H and whose width is the (potentially variable)
distance W between the boundary lines 714 at any given location.
Furthermore, the magnitude of the slope of a given prism 716 at
that location is H/W. The height H represents the vertical distance
between the corresponding adjacent contour lines, and is selected
to provide for a Fresnel prism 716 of reasonable height for the
process used to make them. The surface of a given Fresnel prism 716
has the same directional slope at a given point on its inclined
facet as that of the corresponding TRS (surface 610) at that point.
For ease of fabrication or for other reasons, the constant height
Fresnel prism approach may be modified or replaced with alternative
approaches or transformations between the TRS and the
Fresnel-rendered structured surface, as described above.
[0078] In reference to FIG. 7, three of the Fresnel prisms 716 have
been shaded so that they may be more easily identified and
discussed. The shaded prisms are Fresnel prisms 716a, 716b, and
716c. These prisms have been selected to demonstrate certain
properties and characteristics of the wye 712, although other ones
of the Fresnel prisms 716 could also have been selected for this
purpose. In describing these properties and characteristics, we
also identify two regions of the structured surface 710 in this
plan view: a region 717a, in an area of the base portion 712a of
the wye, and a region 717b, in an area where the branch portions
712b, 712c begin to diverge from the base portion 712a.
[0079] In the region 717a, the Fresnel prisms 716a, 716b follow
paths in plan view (as seen from their respective boundary lines)
that track each other. The paths track each other because, for
example, if one prism follows a straight path at a particular
point, then near that point the other prism also follows a straight
path parallel to the other path. The prisms 716a, 716b can be seen
to follow paths that track each other in the region 717a. These
paths are substantially straight, and parallel to each other, in
this region. Also, the prisms 716a, 716b are adjacent to each other
in the region 717a.
[0080] In the region 717b, the Fresnel prisms 716a, 716b follow
paths in plan view that diverge from each other. Furthermore, the
Fresnel prism 716c is present or disposed in the region 717b, but
is not present and not disposed in the region 717a. The plan view
path of the Fresnel prism 716c is also concave and U-shaped in the
region 717b.
[0081] Schematic cross-sectional views of the structured surface
710 through cut lines 7A-7A and 7B-7B are shown in FIGS. 7A and 7B,
respectively. In FIG. 7A, the Fresnel prisms 716 (not labeled in
this figure except for the Fresnel prisms 716a and 716b) which make
up the base portion 712a can be seen in the functional relationship
of the z- and x-coordinates of the surface 710. In FIG. 7B, the
Fresnel prisms 716 (again not labeled here except for the Fresnel
prisms 716a, 716b, and 716c) which make up the branch portions
712b, 712c can be seen in the same functional relationship. In the
cross-sectional views of FIGS. 7A and 7B, the slope (or the
projection of the slope in the x-z plane) of the surface 710 can be
ascertained at any x-coordinate position by calculating the slope
of the function at that position, i.e., slope=dz/dx. Note that in
some places the slope is positive, in some places the slope is
negative, and in some places the slope is zero.
[0082] The inclined facets of the Fresnel prisms 716 in FIGS. 7A
and 7B are shown as planar or straight in transverse cross-section,
but they may instead be non-planar, for example, they may be
continuously curved e.g. with a small degree of curvature, but in
any case the orientations of the inclined facets of the Fresnel
prisms may be tailored to approximate the spatial distribution of
the directional slope of the associated TRS (surface 610).
[0083] A perspective view of another TRS with complex topography is
shown in FIG. 8. In this figure, the surface 810 extends generally
parallel to the x-y plane, but it undulates sinusoidally in both
the x-z plane and the y-z plane. Grid lines (one set of lines with
uniform spacing along the x-axis, and another set of lines with
uniform spacing along the y-axis) are drawn on the surface for
illustrative purposes so that the 3-dimensional shape of the
surface can be better visualized. The height or z-coordinate of any
point on the surface 810 is related to the (x,y) coordinates of
such point by the function
z=sin(x)+sin(y).
This function ranges from a maximum of 2 to a minimum of -2. As can
be seen from the figure, the resulting surface 810 provides a
pattern of alternating rounded peak and valley features. The
alternating pattern also defines saddle points and inflection
points. Some of the saddle points are labeled SP in FIG. 8. A
saddle point is a point on a surface at which the surface has
curvatures of opposite polarity along orthogonal cross-sectional
planes. For example, at a given saddle point, the surface 810 may
curve upwardly when cross-sectioned along the x-z plane, but may
curve downwardly when cross-sectioned along the y-z plane, or vice
versa. Stated differently, the surface at, and in the vicinity of,
the given saddle point can be said to be convex (e.g. curving
upwardly) in the x-z plane and concave (e.g. curving downwardly) in
the y-z plane.
[0084] An inflection point is a point on a curve at which the
curvature changes polarity from positive to negative or vice versa.
Stated differently, an inflection point is a point on a curve at
which the second derivative of the curve, or the second derivative
of a function representative of the curve (e.g. a best-fit smoothly
varying function), changes from positive to negative, or vice
versa. The curve on which the inflection point lies may be the
cross-section or profile of the surface along any given
cross-sectional plane that passes through the inflection point and
is perpendicular to the x-y plane.
[0085] A plan view of the surface 810, in the form of a contour
map, is shown in FIG. 8A. In this view, peaks are labeled P,
valleys are labeled V, and the saddle points SP from FIG. 8 are
indicated with black dots. Although the saddle points are all
labeled SP in FIG. 8, there are actually two different classes or
types of saddle points on the surface 810, and thus in FIG. 8A we
label them more specifically as SP1 or SP2. Contour lines 804 are
also drawn on the surface, each contour line being a locus of
points of equal elevation (having the same z-coordinate), and
adjacent contour lines being indicative of a change in elevation,
i.e., a slope or incline of the surface 810. In the vicinity of a
peak P or a valley V, the contour lines 804 approximate concentric
circles. Farther away from the peaks and valleys, the contour lines
still form closed 2-dimensional shapes, but they become more
square- or diamond-shaped and less circle-shaped with increasing
distance from a peak or valley. Halfway between the peaks and the
valleys, the contour lines 804 become straight (in this plan view)
and connect to each other at the saddle points SP1, SP2 to form two
intersecting sets of parallel straight lines. The straight contour
lines are provided with an additional label 804a.
[0086] The undulating surface 810 may be transformed into a
structured surface of Fresnel prisms as described above. An example
of the resulting Fresnel-rendered surface is shown as structured
surface 910 of FIG. 9. Unlike the TRS, the structured surface 910
is segmented, grooved, or otherwise subdivided into a plurality of
Fresnel prisms 916. Because of this segmentation, the overall
height or thickness of the structured surface 910 is less than that
of the TRS, i.e., of the surface 810. The Fresnel prisms are
bounded by boundary lines 914, which may correspond substantially
to the contour lines 804 of FIG. 8 except that in this particular
embodiment the boundary lines 914 are made to have a finer or
closer spacing than the contour lines 804. The inclined surfaces of
the Fresnel prisms 916 are tailored so that the spatial
distribution of directional slopes of the structured surface 910 is
the same as or similar to the spatial distribution of directional
slopes of the TRS. The portions of the structured surface 910
corresponding to the peaks P of the surface 810 are also labeled P,
and the portions of the structured surface 910 corresponding to the
valleys V of the surface 810 are also labeled V. As an
approximation, for manufacturing simplicity, the regions P and V on
surface 910 can be made to be flat rather than slightly curved as
in the case of the counterpart portions P (which are slightly
concave) and V (which are slightly convex) on surface 810. Such
regions are shown as flat portions 915 in FIG. 9.
[0087] Similar to the contour lines 804 in FIG. 8A, the boundary
lines 914 (and the Fresnel prisms 916 which they bound) approximate
concentric circles in the vicinity of the flat portions 915, and
become more square- or diamond-shaped and less circle-shaped with
increasing distance from such portions 915. Halfway between
neighboring flat portions 915, the boundary lines 914 become
straight and connect to each other at points that are highlighted
with black dots in FIG. 9. These black dots correspond to the
saddle points on the surface 810, and are thus likewise labeled SP1
and SP2 for saddle point. The straight boundary lines are provided
with the additional label 914a to differentiate them from the other
boundary lines 914.
[0088] A close-up view of a portion of the surface 910 in the
vicinity of a saddle point SP2 is shown in FIG. 9A. In this view,
boundary lines 914 (including some straight boundary lines 914a),
Fresnel prisms 916, and a saddle point SP2 can be seen. Also
included in this view are arrows that represent surface normal
vectors for the four Fresnel prisms 916 that are adjacent to the
saddle point SP2. These four Fresnel prisms have boundaries that
include the straight boundary lines 914a. The arrows illustrate the
orientation of directional slopes adjacent to the saddle point SP2,
as well as how the directional slope changes along the length or
path of two of the Fresnel prisms 916. In reference to the
perspective of FIG. 9A, the Fresnel prisms 916 immediately above
and below the saddle point SP2 have inclined surfaces near the
saddle point whose surface normal vectors have components in the
x-y plane which point toward the saddle point SP2. Stated
differently, a cross-section of the surface 910 along a plane
parallel to the y-z plane and passing through the saddle point SP2
would show that the inclined surfaces of those Fresnel prisms (near
the saddle point) are both inclined towards the saddle point, thus
producing a convex slope sequence.
[0089] In contrast to this, the Fresnel prisms 916 immediately to
the left and right (in reference to the perspective of FIG. 9A) of
the saddle point SP2 have inclined surfaces near the saddle point
whose surface normal vectors have components in the x-y plane which
point away from the saddle point SP2. Stated differently, a
cross-section of the surface 910 along a plane parallel to the x-z
plane and passing through the saddle point SP2 would show that the
inclined surfaces of those Fresnel prisms (near the saddle point)
are both inclined away from the saddle point, thus producing a
concave slope sequence.
[0090] The inclined surfaces of the Fresnel prisms and their
respective slopes and slope sequences can be better understood in
connection with FIGS. 9B through 9G. FIGS. 9B, 9D, and 9F show
cross-sectional views of the surface 910 through cut lines 9B-9B,
9D-9D, and 9F-9F (see FIG. 9), respectively. Cut line 9B-9B is
parallel to the x-z plane and passes through two saddle points SP2
and one valley V. Cut line 9D-9D is parallel to the y-z plane and
passes through two peaks P and one of same saddle points SP2 as cut
line 9B-9B. Cut line 9F-9F is oblique to the x- and y-axes, and
passes through two peaks P and the valley V of cut line 9B-9B, and
no saddle points. In FIGS. 9B, 9D, and 9F, the Fresnel prisms 916
are labeled and their inclined facets can be plainly seen. The flat
portions 915 associated with both the peaks P and the valleys V can
also be plainly seen. The saddle points are also labeled in FIGS.
9B and 9D in a consistent fashion with FIG. 9.
[0091] Half of the saddle points on the surface 810 (FIGS. 8 and
8A) are characterized by a concave shape (downwardly curved)
parallel to the x-z plane and a convex shape (upwardly curved)
parallel to the y-z plane. Such saddle points, labeled SP2, are
those that are disposed in cross-sectional planes that are parallel
to the x-z plane and that pass through a row of valleys V. The
remaining half of the saddle points SP on the surface 810 are
characterized oppositely, i.e., by a convex shape parallel to the
x-z plane and a concave shape parallel to the y-z plane. Such
saddle points, labeled SP1, are those that are disposed in
cross-sectional planes that are parallel to the x-z plane and that
pass through a row of peaks P. Similarly with regard to the
structured surface 910, half of its saddle points are characterized
by a slope sequence of the Fresnel prism inclined facets that is
concave parallel to the x-z plane and convex parallel to the y-z
plane. These saddle points, labeled SP2, are the ones that are
disposed in cross-sectional planes that are parallel to the x-z
plane and that pass through a row of valleys V. (Two such saddle
points SP2 are shown in the cross-sectional view of FIG. 9B, and
one of these same saddle points SP2 is shown in the cross-sectional
view of FIG. 9D, and depicted in the plan view of FIG. 9A.) The
remaining half of the saddle points on the surface 910 are
characterized by a slope sequence of the Fresnel prism inclined
facets that is convex parallel to the x-z plane and concave
parallel to the y-z plane. These saddle points, labeled SP1, are
the ones that are disposed in cross-sectional planes that are
parallel to the x-z plane and that pass through a row of peaks
P.
[0092] As noted above, the saddle points SP2 appearing in the
cross-sectional views of FIGS. 9B and 9D are of the type whose
slope sequence is concave parallel to the x-z plane (FIG. 9B) and
convex parallel to the y-z plane (FIG. 9D). Thus, in FIG. 9B, the
Fresnel prisms 916 that are adjacent to either one of the depicted
saddle points SP2 have inclined facets that are inclined away from
the saddle point SP2 to produce a concave (downwardly curved)
feature. In contrast, in FIG. 9D, the Fresnel prisms 916 that are
adjacent to the depicted saddle point SP2 (which is the same as the
saddle point SP2 on the right side of FIG. 9B) have inclined facets
that are inclined towards the saddle point SP to produce a convex
(upwardly curved) feature.
[0093] Further information and insight about the orientation and
arrangement of the Fresnel prisms 916 on the structured surface 910
can be seen in FIGS. 9C, 9E, and 9G. These figures plot the first
derivative or slope of the structured surface 910 (ignoring any
vertical facets of Fresnel prisms) as a function of position along
the relevant cross-sectional plane. Thus, FIG. 9C plots such first
derivative information (dz/dx) as a function of position along the
x-direction for the cut line 9B-9B of FIG. 9 (the cross-sectional
view of FIG. 9B). FIG. 9E plots such first derivative information
(dz/dy) as a function of position along the y-direction for the cut
line 9D-9D of FIG. 9 (the cross-sectional view of FIG. 9D). FIG. 9G
plots such first derivative information (dz/dR, where
R=sqrt(x.sup.2+y.sup.2)) as a function of position along a diagonal
direction for the cut line 9F-9F of FIG. 9 (the cross-sectional
view of FIG. 9F). The first derivative information in the graphs of
these FIGS. 9C, 9E, and 9G appears as a sequence of horizontal line
segments, these line segments having a one-to-one correspondence
with the inclined facets of the Fresnel prisms 916 in the
associated cross-sectional profile of the surface 910, as well as
any other non-vertical portions of the surface 910 such as flat
portions 915. The zero slope associated with the flat portions 915
(for the peaks P and the valleys V) can be readily identified in
these figures. In FIGS. 9C and 9E, positions corresponding to
saddle points are indicated with a dashed vertical line labeled
SP2.
[0094] The characteristic of a saddle point wherein the surface has
curvatures of opposite polarity along orthogonal cross-sectional
planes can be appreciated by a comparison of FIGS. 9C and 9E. In
FIG. 9E, the depicted saddle point SP2 is at a location where the
slope along the positive y-direction changes from negative to
positive. In FIG. 9C, this same saddle point SP2 (see the saddle
point at the right side of FIG. 9C) is at a location where the
slope along the positive x-direction changes in the opposite way,
i.e., from positive to negative.
[0095] Second derivative characteristics of the structured surface
910 can also be analyzed. In the case of Fresnel prisms 916 whose
inclined surfaces are straight or planar, their first derivatives
are flat (horizontal) line segments as seen in FIGS. 9C, 9E, and
9G. If the further derivative of those line segments is then
calculated (and ignoring discontinuities between adjacent line
segments), the result will be an uninteresting and uninformative
flat line. In such cases, a more informative second derivative of
the structured surface (in a cross-sectional plane of interest) can
be obtained by replacing the actual first derivative of the
surface, e.g. as shown by the step-wise horizontal line segments in
FIGS. 9C, 9E, and 9G, with a continuous first derivative function
that approximates the original step-wise first derivative function.
The continuous first derivative function may for example be
piecewise linear, and made by simply connecting the centers of each
of the horizontal line segments of the original first derivative
function. Alternatively, the continuous derivative function may be
a smoothly varying curve that accurately or best fits the original
first derivative function. For each of the original first
derivative functions shown in FIGS. 9C, 9E, and 9G, simple
sinusoidal functions can be determined which pass through the
centers of each of the horizontal line segments. These sinusoidal
functions, labeled 920x, 920y, and 920r, respectively, are suitable
for use as continuous first derivative functions (approximations of
their respective original first derivative functions) from which
second derivatives, as well as higher order derivatives, may be
calculated, e.g. for the purpose of identifying inflection
points.
[0096] Numerous modifications and adaptations of the
Fresnel-rendered surface can be made while still substantially
approximating or mimicking the 3-dimensional nature of the TRS as
embodied or encoded in its spatial distribution of directional
slopes. In one such example, the structured surface 910 described
above can be modified selectively in the vicinity of the saddle
points SP so as to remove the sharp corners that can be seen in
plan view for each outermost Fresnel prism 916 in each set of
concentric Fresnel prisms 916 which surround any given peak P or
valley V region (see flat portions 915). Stated differently, the
sharp corners created at the intersections of the straight boundary
lines 914a at the saddle points SP can be eliminated by flattening
or otherwise re-shaping a small portion of the structured surface
910 in the vicinity of each saddle point SP. Such a modification to
the structured surface 910 is shown in FIG. 10, where the modified
structured surface is labeled 910'. Many or most of the features
described above in connection with structured surface 910,
including e.g. the flat portions 915, and most of the Fresnel
prisms 916, and most of the boundary lines 914, may be the same or
substantially the same in the surface 910', and thus are given the
same labels in FIG. 10. The straight boundary lines 914a may also
be mostly preserved in surface 910', except in the vicinity of the
saddle point SP where such lines can be rounded in order to avoid a
sharp corners on the outermost Fresnel prisms 916, these
modifications resulting in the modified boundary lines 914a' and
the modified outermost Fresnel prisms 916' shown in the plan view
of FIG. 10. The rounding of the plan view paths of the Fresnel
prisms 916' and of the boundary lines 914a' introduces a newly
modified portion of the structured surface 910' at which the
(modified) saddle point SP' is located, such newly modified portion
being shown in this particular embodiment as a new flat portion
915'. This modification can be made at one, some, or all of the
original saddle points SP on the original structured surface 910.
By making the modification at all of the saddle points, the
modified structured surface 910' can be devoid of any such sharp
corners, and the tool from which it is replicated can be more
easily manufactured.
[0097] In FIG. 10, arrows are provided in similar fashion to FIG.
9A to represent surface normal vectors for the four Fresnel prisms
916' that are adjacent to the saddle point SP'. These four Fresnel
prisms have boundaries that include the boundary lines 914a'. The
arrows illustrate the orientation of directional slopes adjacent to
the saddle point SP', as well as how the directional slope changes
along the length or path of the four illustrated Fresnel prisms
916'. Similar to FIG. 9A, the saddle point SP' of FIG. 10 has
inclined surfaces of adjacent Fresnel prisms that are inclined
towards the saddle point along a plane parallel to the y-z plane,
producing a convex slope sequence, and the same saddle point SP'
has inclined surfaces of adjacent Fresnel prisms that are inclined
away from the saddle point along a plane parallel to the x-z plane,
producing a concave slope sequence.
[0098] Many 3-dimensional surfaces that occur in nature are not
strictly unidirectional. The ridge of a 3-dimensional surface may
"wander" in the x-y plane, or the ridge may increase or decrease in
elevation along its length. A linear sine wave, or otherwise linear
"tin roof" corrugated surface can be modified to make it more
interesting by tailoring the ridges and valleys to wander in a
sinusoidal or other oscillatory fashion in the x-y plane. A
perspective view of such a surface, which has a complex topography
and which we refer to as a TRS, is shown in FIG. 11. In this
figure, the surface 1110 extends generally parallel to the x-y
plane, but it undulates sinusoidally in the x-z plane, and each
ridge (peak) and valley also wanders in an oscillating fashion in
the x-y plane. Two intersecting sets of uniformly spaced grid lines
are again drawn on the surface for illustrative purposes so that
the 3-dimensional shape of the surface can be better visualized.
For this particular embodiment, the height or z-coordinate of any
point on the surface 1110 is related to the (x,y) coordinates of
such point by the function
z=0.8*sin(x+sin(0.3*y)).
[0099] The resulting surface 1110 actually provides two different
types of inflection points. A first type is associated with the
oscillatory plan-view shape or path of each ridge, valley, or
portion of intermediate elevation. Any such path in plan view
defines points or regions at which the curvature of the path
changes polarity from positive to negative or vice versa, or at
which the second derivative of the path changes from positive to
negative, or vice versa. A second type of inflection point embodied
in the surface 1110 is associated with the shape of the surface
1110 along a given cross-sectional plane. For example, the shape of
the surface 1110 along any cross-sectional plane parallel to the
x-z plane is sinusoidal. FIG. 11A shows the cross-sectional shape
of the surface 1110 along the x-z plane itself. The inflection
points for this curve are labeled IP2. Additional inflection points
of the second type also exist on cross-sections of the surface 1110
along planes that are not parallel to the x-z plane, e.g., along
planes that parallel to the y-z plane, and planes that are
perpendicular to the x-y plane but disposed at oblique angles to
the x-z and y-z planes. All of the first and second types of
inflection points that exist on the TRS (surface 1110) will also
typically exist on the associated Fresnel-rendered structured
surface, to the extent it accurately approximates or mimics the
spatial distribution of directional slopes of the TRS.
[0100] One embodiment of a Fresnel-rendered structured surface 1210
corresponding to the TRS of FIG. 11 is shown schematically in FIG.
12. Unlike the TRS, the structured surface 1210 is segmented,
grooved, or otherwise subdivided into a plurality of Fresnel prisms
1216. Because of this segmentation, the overall height or thickness
of the structured surface 1210 is less than that of the TRS, i.e.,
of the surface 1110. The Fresnel prisms are bounded by boundary
lines 1214, which may correspond substantially to contour lines of
the surface 1110. The inclined surfaces of the Fresnel prisms 1216
are tailored so that the spatial distribution of directional slopes
of the structured surface 1210 is the same as or similar to the
spatial distribution of directional slopes of the TRS. The portions
of the structured surface 1210 corresponding to the peaks P of the
surface 1110 are also labeled P, and the portions of the structured
surface 1210 corresponding to the valleys V of the surface 1110 are
also labeled V. As an approximation, for manufacturing simplicity,
the regions P and V on surface 1210 can be made to be flat rather
than slightly curved as in the case of the counterpart portions P
(which are slightly concave) and V (which are slightly convex) on
surface 1110. Such regions are shown as flat portions 1215 in FIG.
12.
[0101] In the plan view of FIG. 12, it is possible to identify
inflection points associated with the in-plane path or shape of
each prism 1216, which were referred to in the above discussion as
the first type of inflection points. Some of these inflection
points are identified and labeled as IP1 in FIG. 12.
[0102] The inclined surfaces of the Fresnel prisms and their
respective slopes and slope sequences can be better understood in
connection with FIG. 12A, which shows a cross-sectional view of the
surface 1210 through the cut line 12A-12A. In FIG. 12A, the Fresnel
prisms 1216 are labeled and their inclined facets can be plainly
seen. The flat portions 1215 associated with both the peaks P and
the valleys V can also be plainly seen. For the particular cut line
12A-12A selected, the cut line does not pass through any of the
first type of inflection points. However, the surface 1210 in this
cross-sectional plane does define some inflection points of the
second type. These are identified with the labels IP2 in FIG.
12A.
[0103] Further information and insight about the orientation and
arrangement of the Fresnel prisms 1216 on the structured surface
1210 can be seen in FIG. 12B. This figure plots the first
derivative or slope of the structured surface 1210 (ignoring any
vertical facets of Fresnel prisms) as a function of position along
the cross-sectional plane. Thus, FIG. 12B plots such first
derivative information (dz/dx) as a function of position along the
x-direction for the cut line 12A-12A of FIG. 12 (the
cross-sectional view of FIG. 12A). As seen in previous figures, the
first derivative information in the graph of FIG. 12B appears as a
sequence of horizontal line segments, these line segments having a
one-to-one correspondence with the inclined facets of the Fresnel
prisms 1216 in the associated cross-sectional profile of the
surface 1210, as well as any other non-vertical portions of the
surface 1210 such as flat portions 1215. The zero slope associated
with the flat portions 1215 (for the peaks P and the valleys V) can
be readily identified in the figure. In FIGS. 12A and 12B,
positions corresponding to inflection points (of the second type)
are indicated with a dashed vertical line labeled IP2.
[0104] In accordance with the discussion above, the second
derivative characteristics of the structured surface 1210 can also
be analyzed using a continuous first derivative function that
approximates the original step-wise first derivative function shown
in FIG. 12B. The continuous first derivative function may for
example be piecewise linear, or may be a smoothly varying curve
that accurately or best fits the original first derivative
function. For the original first derivative function shown in FIG.
12B, a simple sinusoidal function 1220x can be determined which
passes through the centers of each of the horizontal line segments.
This sinusoidal function is suitable for use as a continuous first
derivative function from which the second derivative, as well as
higher order derivatives, may be calculated, e.g. for the purpose
of identifying inflection points. Note that inflection points
(whether of the first or second type) can of course exist on curves
or functions that undulate in a non-sinusoidal manner.
[0105] As mentioned above, numerous modifications can be made to
the disclosed embodiments. One modification of the TRS 1110 of FIG.
11 is shown in FIG. 13. In FIG. 13, a surface 1310 is shown that is
similar to surface 1110 insofar as it has a complex topography,
with undulating features in plan view and with inflection points of
both the first and second type. The peaks (ridges) and valleys of
the surface 1310 have a similar wavy-appearance in plan view to
those of FIG. 11, but in the case of surface 1310, the height or
elevation of the peaks, as well as the height or elevation of the
valleys, changes along their respective plan-view paths. The
surface 1310 extends generally parallel to the x-y plane, but it
undulates sinusoidally in the x-z plane, and each ridge (peak) and
valley also wanders or undulates in an oscillating fashion in the
x-y plane. Two intersecting sets of uniformly spaced grid lines are
again drawn on the surface for illustrative purposes so that the
3-dimensional shape of the surface can be better visualized. For
this particular embodiment, the height or z-coordinate of any point
on the surface 1310 is related to the (x,y) coordinates of such
point by the function
z = 0.8 * sin ( x + sin ( 0.1 * y ) ) * ( 60 60 + 2.5 y ) ,
##EQU00001##
where the function is plotted in FIG. 13 between the limits of
0.ltoreq.x.ltoreq.20 and 0.ltoreq.y.ltoreq.60.
[0106] This surface 1310 also provides two different types of
inflection points, referred to above as first type and second type.
The first type is associated with the oscillatory plan-view shape
or path of each ridge, valley, or portion of intermediate
elevation. Any such path in plan view defines points or regions at
which the curvature of the path changes polarity from positive to
negative or vice versa, or at which the second derivative of the
path changes from positive to negative, or vice versa. This
curvature and undulation can be better seen in the plan view of
FIG. 14 of a structured surface 1410 which is a Fresnel-rendering
of the TRS 1310. Unlike the TRS 1310, the structured surface 1410
is segmented, grooved, or otherwise subdivided into a plurality of
Fresnel prisms 1416. Because of this segmentation, the overall
height or thickness of the structured surface 1410 is less than
that of the TRS, i.e., of the surface 1310. The Fresnel prisms are
bounded by boundary lines 1414, which may correspond substantially
to contour lines of the surface 1310. The inclined surfaces of the
Fresnel prisms 1416 are tailored so that the spatial distribution
of directional slopes of the structured surface 1410 is the same as
or similar to the spatial distribution of directional slopes of the
TRS.
[0107] The second type of inflection point embodied in the surface
1310, as well as the surface 1410, is associated with the shapes of
these surfaces along a given cross-sectional plane, e.g., along the
x-z plane. The shape of the surface 1310 along this plane is
sinusoidal, and the slope sequence of the surface 1410 along this
plane also defines a substantially sinusoidal function. As such,
inflection points of the second type (not labeled in FIG. 13 or 14)
will be present in such cross-sectional shapes, in an analogous
fashion to those shown and described in connection with FIGS. 11
through 12B.
[0108] Films and other optical bodies having the disclosed
structured surfaces can be made in any suitable fashion using known
manufacturing techniques. For example, the films and bodies can be
made with structured surface tools, the tool having a negative or
inverted topography relative to that desired in the finished
product. The structured surface layer of such film or body may be
embossed or cast against the structured surface of the tool to
impart the desired geometry of the Fresnel prisms and optional flat
surfaces. The structured surface of the tool and/or the optical
body can be fabricated in any suitable fashion, e.g. by etching,
scribing, and/or other suitable means, such as gray scale
lithography, 3D printing, and/or diamond machining.
[0109] If desired, the inclined facets of some or all of the
Fresnel prisms on the structured surface of the optical body can be
made partially or completely reflective by applying a reflective
material such as a thin coating of aluminum, silver, or other
reflective metal or other material, and thus may transmit and
refract some incident light or no incident light.
[0110] Some or all of the layers of the finished optical body or
film may be polymer-based such that the article, or one or more
components thereof, can be manufactured on a conventional film line
with conventional polymer based materials. Alternatively or in
addition, the article can be made with other known processes and
equipment, and may comprise non-polymeric materials, such as
glasses, ceramics, metals, and/or other suitable materials. Further
discussion of materials is provided below.
[0111] In some embodiments, the disclosed optical bodies can
comprise thin polymer-based layers that are laminated, coextruded,
and/or coated such that the article is self-supporting, flexible,
and conformable to a target surface or object. In this regard, the
disclosed articles may be configured such that a front or back
major surface of the article attaches to a wall or other object of
interest, and light enters and exits through opposite surfaces of
the article, or through a same surface of the article. The
disclosed articles may include additional layers and coatings to
facilitate such applications, including e.g. planarization
layer(s), adhesive layer(s), release liner(s), hard coat(s), and
the like. The disclosed optical bodies can also in some cases be
made with a transparent base film or substrate such that decorative
reflective images or patterns can be viewed from both sides
(opposite sides) of the film. The films can be applied to windows
or similar light-transmissive substrates, such as an interior
office window, so that decorative images or patterns provided by
the Fresnel prisms can be viewed from both sides of the
combination. Different indicia or color films can be applied to
opposing sides of the film such that the window has a distinctly
different appearance from each side. Colored and/or neutral gray
dyes, pigments, and the like can be incorporated into one or more
of the constituent layers (such as an indicia layer) of, or can be
included as an additional colored or tinted layer in, any of the
disclosed film or film stack embodiments, for further visual
effect. A film, film laminate, or other optical body may have only
one major surface that is Fresnel-rendered to provide Fresnel
prisms as described herein, but in other cases two or more major
surfaces of the film, film laminate, or other optical body can be
Fresnel-rendered in that manner. If multiple Fresnel-rendered
structured surfaces are used, they may be on different layers of a
laminate, and they may be identical to each other, or of different
designs or patterns, and they may be aligned with each other or
misaligned. One or more light-diffusing layers or agents can also
be included in any of the disclosed embodiments. Reflective color
films such as multilayer interference films can provide striking
visual effects when combined with the Fresnel lens and mirror
films. Narrow band color mirror films, examples of which can be
found in U.S. Pat. No. 6,531,230 (Weber et al.), "Color Shifting
Film", may be particularly suitable. The disclosed articles may be
made of any suitable materials now known or later developed,
including materials other than polymer-based films. The articles
may include one or more thick and/or rigid and/or brittle component
such that the resulting article is rigid rather than flexible.
[0112] Unless otherwise indicated, all numbers expressing
quantities, measurement of properties, and so forth used in the
specification and claims are to be understood as being modified by
the term "about". Accordingly, unless indicated to the contrary,
the numerical parameters set forth in the specification and claims
are approximations that can vary depending on the desired
properties sought to be obtained by those skilled in the art
utilizing the teachings of the present application. Not as an
attempt to limit the application of the doctrine of equivalents to
the scope of the claims, each numerical parameter should at least
be construed in light of the number of reported significant digits
and by applying ordinary rounding techniques. Notwithstanding that
the numerical ranges and parameters setting forth the broad scope
of the invention are approximations, to the extent any numerical
values are set forth in specific examples described herein, they
are reported as precisely as reasonably possible. Any numerical
value, however, may well contain errors associated with testing or
measurement limitations.
[0113] Any direction referred to herein, such as "top," "bottom,"
"left," "right," "upper," "lower," "above," below," and other
directions and orientations are used for convenience in reference
to the figures and are not to be limiting of an actual device,
article, or system or its use. The devices, articles, and systems
described herein may be used in a variety of directions and
orientations.
[0114] Various modifications and alterations of this invention will
be apparent to those skilled in the art without departing from the
spirit and scope of this invention, and it should be understood
that this invention is not limited to the illustrative embodiments
set forth herein. The reader should assume that features of one
disclosed embodiment can also be applied to all other disclosed
embodiments unless otherwise indicated. It should also be
understood that all U.S. patents, patent application publications,
and other patent and non-patent documents referred to herein are
incorporated by reference, to the extent they do not contradict the
foregoing disclosure.
[0115] This document discloses numerous embodiments, including but
not limited to the following:
Item 1 is an optical body comprising a structured surface
comprising a plurality of Fresnel prisms comprising a first and
second Fresnel prism; [0116] wherein the first and second Fresnel
prisms have elongated first and second plan view shapes
respectively, and in a first region the first and second shapes
follow paths that track each other; and [0117] wherein in a second
region the first and second shapes follow paths that diverge from
each other. Item 2 is the optical body of item 1, wherein the
plurality of Fresnel prisms also comprises a third Fresnel prism,
and wherein the third Fresnel prism is not present in the first
region but is disposed between the first and second Fresnel prisms
in the second region. Item 3 is the optical body of item 2, wherein
the third Fresnel prism has a third plan view shape that is concave
in the second region. Item 4 is the optical body of item 3, wherein
the third plan view shape is U-shaped. Item 5 is the optical body
of item 1, wherein in the first region the first and second shapes
follow paths that are parallel to each other. Item 6 is the optical
body of item 1, wherein in the first region the first and second
shapes follow paths that are adjacent to each other. Item 10 is the
optical body of item 1, wherein the first Fresnel prism has a slope
and/or width that changes along a length of the first Fresnel
prism. Item 14 is the optical body of item 1, wherein the first and
second Fresnel prisms form a wye. Item 15 is an optical body
comprising a structured surface comprising a plurality of Fresnel
prisms, wherein at least some (e.g. at least two or at least three)
of the Fresnel prisms are configured to form a wye. Item 16 is the
optical body of item 15, wherein the plurality of Fresnel prisms
includes a first and second Fresnel prism having first and second
plan view shapes respectively, and in a first region the first and
second shapes follow paths that track each other, and in a second
region the first and second shapes follow paths that diverge from
each other. Item 17 is an optical body comprising a structured
surface comprising a plurality of Fresnel prisms, wherein the
Fresnel prisms are configured such that slopes of the Fresnel
prisms define at least a first saddle point. Item 18 is the optical
body of item 17, wherein the slopes of the Fresnel prisms form a
first slope sequence along a first cross-sectional plane that
intersects the first saddle point, and a second slope sequence
along a second cross-sectional plane that intersects the first
saddle point, the first slope sequence being concave and the second
slope sequence being convex. Item 19 is the optical body of item
17, wherein the slopes of the Fresnel prisms define a plurality of
saddle points which includes the first saddle point. Item 20 is the
optical body of item 17, wherein the plurality of saddle points are
in a regular repeating array. Item 28 is an optical body comprising
a structured surface comprising a plurality of Fresnel prisms
comprising a first Fresnel prism; [0118] wherein the Fresnel prisms
are arranged in a slope sequence, the slope sequence defining one
or more inflection points; and [0119] wherein the first Fresnel
prism has a first prism shape in plan view that includes an
undulating portion. Item 29 is the optical body of item 28, wherein
the first Fresnel prism has a slope and/or a width that changes
along a length of the first Fresnel prism. Item 30 is the optical
body of item 29, wherein the first Fresnel prism has a slope that
changes along the length of the first Fresnel prism. Item 31 is the
optical body of item 29, wherein the first Fresnel prism has a
width that changes along the length of the first Fresnel prism.
Item 38 is the optical body of item 28, wherein the undulating
portion of the first prism shape comprises an inflection point.
Item 39 is an optical body comprising a structured surface
comprising a plurality of Fresnel prisms comprising a first Fresnel
prism, the first Fresnel prism having a first prism shape in plan
view that includes an inflection point. Item 40 is the optical body
of item 39, wherein the Fresnel prisms are arranged in a slope
sequence in a cross sectional plane, the slope sequence defining
one or more inflection points. Item 41 is the optical body of item
39, wherein the first prism shape undulates and includes a
plurality of inflection points. Item 42 is the optical body of any
other numbered item, wherein the Fresnel prisms are light
transmissive and refractive. Item 43 it the optical body of any
other numbered item, wherein the Fresnel prisms are reflective.
Item 44 is the optical body of any other numbered item, wherein the
structured surface provides a 3-dimensional appearance. Item 45 is
the optical body of any other numbered item, wherein the plurality
of Fresnel prisms includes a first Fresnel prism having a slope
and/or width that changes along a length of such first Fresnel
prism. Item 46 is the optical body of any other numbered item,
wherein the structured surface is formed in a first material layer,
and wherein the optical body further comprises a planarizing layer
in mating contact with the structured surface. Item 47 is the
optical body of item 46, wherein the planarizing layer comprises a
nanovoided material. Item 48 is the optical body of any other
numbered item, wherein the structured surface is formed in a first
material layer, and wherein the optical body further comprises an
indicia layer attached directly or indirectly to the first material
layer.
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