U.S. patent application number 16/220995 was filed with the patent office on 2020-01-23 for diffractive waveplate lenses and applications.
The applicant listed for this patent is Beam Engineering for Advanced Measurements Co., U.S. Government as Represented by the Secretary of the Army. Invention is credited to Brian Kimball, David E. Roberts, Svetlana Serak, Diane Steeves, Anna Tabirian, Nelson V. Tabirian, Olena Uskova.
Application Number | 20200025986 16/220995 |
Document ID | / |
Family ID | 54321920 |
Filed Date | 2020-01-23 |
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United States Patent
Application |
20200025986 |
Kind Code |
A1 |
Tabirian; Nelson V. ; et
al. |
January 23, 2020 |
DIFFRACTIVE WAVEPLATE LENSES AND APPLICATIONS
Abstract
Methods, systems and devices for diffractive waveplate lens and
mirror systems allowing electronically focusing light at different
focal planes. The system can be incorporated into a variety of
optical schemes for providing electrical control of transmission.
In another embodiment, the system comprises diffractive waveplates
of different functionality to provide a system for controlling not
only focusing but other propagation properties of light including
direction, phase profile, and intensity distribution.
Inventors: |
Tabirian; Nelson V.; (Winter
Park, FL) ; Serak; Svetlana; (Oviedo, FL) ;
Uskova; Olena; (Winter Park, FL) ; Roberts; David
E.; (Apopka, FL) ; Tabirian; Anna; (Winter
Park, FL) ; Steeves; Diane; (Franklin, MA) ;
Kimball; Brian; (Shrewsbury, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Beam Engineering for Advanced Measurements Co.
U.S. Government as Represented by the Secretary of the
Army |
Orlando
Natick |
FL
MA |
US
US |
|
|
Family ID: |
54321920 |
Appl. No.: |
16/220995 |
Filed: |
December 14, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14688425 |
Apr 16, 2015 |
10191191 |
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16220995 |
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14688197 |
Apr 16, 2015 |
10274650 |
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14688425 |
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13916627 |
Jun 13, 2013 |
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14688197 |
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12697083 |
Jan 29, 2010 |
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13916627 |
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61980062 |
Apr 16, 2014 |
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61980062 |
Apr 16, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 5/001 20130101;
G02B 27/4205 20130101; G02B 27/4211 20130101; A61F 2/1618 20130101;
G02B 27/4216 20130101; G02B 6/3592 20130101; G02C 2202/20 20130101;
G02B 5/1828 20130101; G02C 2202/16 20130101; G02B 5/1833 20130101;
A61F 2/1654 20130101; G02C 7/12 20130101; G02C 7/086 20130101; G02C
7/061 20130101; G02C 7/022 20130101; G02B 3/0081 20130101; G02B
27/4261 20130101; G02B 3/10 20130101; G02B 6/024 20130101; G02C
7/10 20130101; G02B 6/3534 20130101; G02B 5/3083 20130101 |
International
Class: |
G02B 5/18 20060101
G02B005/18; G02C 7/02 20060101 G02C007/02; G02C 7/06 20060101
G02C007/06; G02C 7/12 20060101 G02C007/12; A61F 2/16 20060101
A61F002/16; G02B 3/10 20060101 G02B003/10; G02C 7/08 20060101
G02C007/08; G02B 5/30 20060101 G02B005/30; G02B 27/42 20060101
G02B027/42; G02B 5/00 20060101 G02B005/00; G02B 6/024 20060101
G02B006/024; G02B 6/35 20060101 G02B006/35; G02B 3/00 20060101
G02B003/00 |
Goverment Interests
GOVERNMENT LICENSE RIGHTS
[0002] This invention was made with government support under
Contract No. W911QY-12-C-0016. The government has certain rights in
this invention.
Claims
1. An optical system comprising: a light source; a flat mirror
having a quarter wave plate deposited on the flat mirror; one or
more diffractive waveplates with switchable optical power for
receiving the light from the light source, said one or more
diffractive wave plates are selected from a group consisting of
cylindrical diffractive waveplate lenses, cycloidal diffractive
waveplates, axial diffractive waveplates, axicon diffractive
waveplates, beam shaping diffractive waveplates, and arrays of
diffractive waveplates; and a switching device for selectively
switching the optical power of said diffractive waveplates to
provide an electrically controlled diffraction property in
reflected light; a flat mirror to provide an electrically
controlled diffraction property in reflected light; and at least
one quarter waveplate deposited on the flat mirror.
2. The optical system as in claim 1 wherein said light source is
fiber coupled.
3. The optical system as in claim 1, wherein said diffractive
waveplates have an optical axis orientation that is modulated in
one or both transverse directions parallel to a substrate.
4. The optical system as in claim 1 wherein said switching devices
for selectively switching the optical power of said diffractive
waveplate system include variable phase retardation plates.
5. The optical system as in claim 1 wherein said one or more
diffractive waveplates are deposited on a surface of at least one
of the variable phase retardation plates.
6. (canceled)
7. The optical system as in claim 1 wherein said diffractive
waveplate lenses are cylindrical.
8. The optical system as in claim 1, wherein a cylinder axes in
alternating diffractive waveplate lenses are rotated with respect
to each other.
9. An optical imaging system with multiple focal lengths
comprising: a generally unpolarized and non-monochromatic light
source; one or more diffractive waveplates with switchable optical
power for receiving the light from the generally unpolarized and
non-monochromatic light source, said one or more diffractive wave
plates are selected from a group consisting of diffractive
waveplate lenses, cycloidal diffractive waveplates, axial
diffractive waveplates, axicon diffractive waveplates, beam shaping
diffractive waveplates, and arrays of diffractive waveplates; a
substrate in the optical imaging system; and switching devices for
selectively switching the optical power of said one or more
diffractive waveplates.
10. The optical imaging system as in claim 11 wherein said
switching devices for selectively switching the optical power of
said diffractive waveplate lens system include variable phase
retardation plates.
11. (canceled)
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. patent
application Ser. No. 14/688,425 filed Apr. 16, 2015, now allowed,
which claims the benefit of priority to U.S. Provisional
Application Ser. No. 61/980,062 filed Apr. 16, 2014, and this
application is a Continuation-In-Part of U.S. patent application
Ser. No. 14/688,197 filed Apr. 16, 2015, which claims the benefit
of priority to U.S. Provisional Patent Application Ser. No.
61/980,062 filed Apr. 16, 2014, and U.S. patent application Ser.
No. 14/688,197 filed Apr. 16, 2015 is a Continuation-In-Part of
U.S. patent application Ser. No. 13/916,627 filed Jun. 13, 2013,
Abandoned, which is a Continuation of U.S. patent application Ser.
No. 12/697,083 filed Jan. 29, 2010, Abandoned. The entire
disclosure of the application listed in this paragraph is
incorporated herein by specific reference thereto.
FIELD OF INVENTION
[0003] This invention relates to optical lenses, the method of
their fabrication, applications of the lenses, and applications of
combinations of said lenses with application of said lenses
including imaging optics and systems, astronomy, displays,
polarizers, optical communication and other areas of laser and
photonics technology.
BACKGROUND AND PRIOR ART
[0004] The present invention is in the technical field of optics.
More particularly, the present invention is in the technical field
of lenses. Lenses are commonly made by shaping an optical material
such as glass. The weight of such lenses increases strongly with
diameter making them expensive and prohibitively heavy for
applications requiring large area. Also, the quality of a lens
typically decreases with increasing size. To achieve desired
features such as high-quality imaging, conventional lenses
sometimes have curved surfaces that are non-spherical. The need to
grind and polish conventional lenses with non-spherical surfaces
can make such lenses extremely expensive. Segmented lenses such as
Fresnel lenses are relatively thin, however, the structural
discontinuities result in severe aberrations. Uses of holographic
lenses are limited by the compromise of efficiency, spectral
bandwidth and dispersion. Thus, there is a need for lenses that
could be obtained in the form of thin film structurally continuous
coatings on a variety of substrates.
[0005] Thus, the need exists for solutions to the above problems
with the prior art.
SUMMARY OF THE INVENTION
[0006] The objective of the present invention is providing a lens
with continuous thin film structure whose properties can be changed
in a useful way by application of an electrical potential to the
lens.
[0007] The second objective of the present invention is providing a
combination of lenses with spherically symmetric continuous thin
film structure such that the properties of the individual lenses
are changed by means of the application of an electrical potential,
in such a way that the combination of lenses allows the focal
position of an imaging system to be adjusted among a multiplicity
of possible focal positions.
[0008] The third objective of the present invention is providing
combinations of lenses, each with a continuous thin film structure,
such that one or more of the lenses are controlled by means of the
application of an electrical potential, and such that by means of
electrical switching of these lenses, coupling between optical
fibers can be turned on or off.
[0009] The fourth objective of the present invention is providing a
variable attenuator of electromagnetic radiation using an
electrically-controlled thin-film structure.
[0010] Many of the exemplary applications have been described
herein with terms such as "light" being used to describe the
electromagnetic radiation that is acted upon by the disclosed
diffractive waveplate lenses. The term "light" in this context
should not be taken to restrict the scope of the disclosed
embodiments to only those in which the electromagnetic radiation
acted upon or manipulated by the diffractive waveplate lenses is in
the visible region of the spectrum. As will be evident to those
skilled in the art, the exemplary embodiments disclosed here, in
addition to being applicable in the visible region of the spectrum,
are equally applicable to the microwave, infrared, ultraviolet, and
X-ray regions of the spectrum. Exceptions to this generalization
are the applications relating to human vision, for which operation
in the visible region of the spectrum is required.
[0011] The design and function of the optical lenses of the present
invention have not been suggested, anticipated or rendered obvious
by any of the prior art references.
[0012] Further objects and advantages of this invention will be
apparent from the following detailed description of the presently
preferred embodiments which are illustrated schematically in the
accompanying drawings.
BRIEF DESCRIPTION OF THE FIGURES
[0013] FIG. 1A shows spatial distribution of optical axis
orientation in spherical diffractive waveplate lenses of one
sign.
[0014] FIG. 1B shows spatial distribution of optical axis
orientation in spherical diffractive waveplate lenses of an
opposite sign.
[0015] FIG. 2A shows a representation of a spherical diffractive
waveplate lens with continuous alignment lines of anisotropy axis
of the birefringent material.
[0016] FIG. 2B shows spherical diffractive waveplate lenses of
opposite signs in description with continuous alignment lines.
[0017] FIG. 3 shows a diffractive waveplate lenses viewed from
opposite sides.
[0018] FIG. 4A shows polarization properties of focusing and
defocusing of a right-hand circular polarized beam by a diffractive
waveplate lens, respectively.
[0019] FIG. 4B shows polarization properties of focusing and
defocusing a left-hand circular polarized beam by a diffractive
waveplate lens, respectively.
[0020] FIG. 5A shows the structure of a cylindrical diffractive
waveplate lens of one handedness.
[0021] FIG. 5B shows the structure of a cylindrical diffractive
waveplate lens of opposite handedness.
[0022] FIG. 6A shows a lens with spherical aberration focusing
light to a large focal spot.
[0023] FIG. 6B shows a lens, with spherical aberration corrected,
focusing light to a small focal spot.
[0024] FIG. 6C shows a multilayer system of diffractive waveplate
lenses of varying spatial frequency of optical axis orientation and
different area.
[0025] FIG. 6D shows a lens with aberrations corrected with a
diffractive waveplate coating.
[0026] FIG. 7 shows a pair of diffractive diffractive waveplate
lenses focusing light to the same spot for right hand circular
(RHC) polarization as well as left hand circular (LHC)
polarization.
[0027] FIG. 8 shows a system of a triplet of diffractive
diffractive waveplate lenses focusing light to the same spot for
light of RHC polarization or LHC polarization, said system having
the same effective focal length for either polarization.
[0028] FIG. 9A shows a conventional glass lens focusing light in
the red region of the spectrum to a small focal spot.
[0029] FIG. 9B shows the paths of rays of light in the red region
of the spectrum, and light in the blue region of the spectrum, near
the focus of a glass lens, illustrating the fact that light with
different wavelengths is focused to different axial locations by
the glass lens.
[0030] FIG. 10A shows a combination of one glass lens and three
diffractive waveplate lenses focusing light in the red region of
the spectrum to a small focal spot.
[0031] FIG. 10B shows the paths of rays of light in the red region
of the spectrum, and light in the blue region of the spectrum, near
the focus of the combination of one glass lens and three
diffractive waveplate lenses, illustrating the fact that light with
different wavelengths is focused to the same axial location by said
combination of lenses.
[0032] FIG. 11A shows the focusing of a collimated beam of light by
an electrically switchable diffractive waveplate lens, with the
lens in the active state (electric field off).
[0033] FIG. 11B shows the lack of focusing of a collimated beam of
light by an electrically switchable diffractive waveplate lens,
with the lens in the passive state (electric field on).
[0034] FIG. 12A shows the focusing of a collimated beam of light by
a combination of a conventional refractive lens and two
electrically switchable lenses, with both diffractive waveplate
lenses in the active state (electric field off).
[0035] FIG. 12B shows the focusing of a collimated beam of light by
a combination of a conventional refractive lens and two
electrically switchable lenses, with the first diffractive
waveplate lens in the passive state (electric field on), and the
second diffractive waveplate lens in the active state (electric
field off).
[0036] FIG. 12C shows the focusing of a collimated beam of light by
a combination of a conventional refractive lens and two
electrically switchable lenses, with the second diffractive
waveplate lens in the passive state (electric field on), and the
first diffractive waveplate lens in the active state (electric
field off).
[0037] FIG. 12D shows the focusing of a collimated beam of light by
a combination of a conventional refractive lens and two
electrically switchable lenses, with both diffractive waveplate
lenses in the passive state (electric field on).
[0038] FIG. 13A shows the focusing of the output of an optical
fiber into the input of another optical fiber by means of a
combination of three electrically switchable diffractive waveplate
lenses, with all three lenses in the active state (electric field
oft).
[0039] FIG. 13B shows the absence of focusing of the output of an
optical fiber into the input of another optical fiber by means of a
combination of three electrically switchable diffractive waveplate
lenses, with all three lenses in the passive state (electric field
on).
[0040] FIG. 13C shows the tip of an optical fiber outputting both
focused and defocused beams with the proportion between them being
set by a polarization control element at the input of the
fiber.
[0041] FIG. 14A shows a system of diffractive waveplates
interspaced with polarization control elements for switching the
focus of the beam to different spots in space.
[0042] FIG. 14B shows a switchable system comprising variety of
diffractive waveplate structures.
[0043] FIG. 14C shows a system for switching the orientation of a
light beam intensity distribution with cylindrical diffractive
waveplates.
[0044] FIG. 15 shows a diffractive waveplate lens deposited on one
of the substrates of the switchable phase retarder.
[0045] FIG. 16 shows a flat mirror comprising a switchable phase
retarder and a diffractive waveplate lens.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] Before explaining the disclosed embodiments of the present
invention in detail it is to be understood that the invention is
not limited in its applications to the details of the particular
arrangements shown since the invention is capable of other
embodiments. Also, the terminology used herein is for the purpose
of description and not of limitation.
[0047] In the Summary above and in the Detailed Description of
Preferred Embodiments and in the accompanying drawings, reference
is made to particular features (including method steps) of the
invention. It is to be understood that the disclosure of the
invention in this specification includes all possible combinations
of such particular features. For example, w here a particular
feature is disclosed in the context of a particular aspect or
embodiment of the invention, that feature can also be used, to the
extent possible, in combination with and/or in the context of other
particular aspects and embodiments of the invention, and in the
invention generally.
[0048] In this section, some embodiments of the invention will be
described more fully with reference to the accompanying drawings,
in which preferred embodiments of the invention are shown. This
invention may, however, be embodied in many different forms and
should not be construed as limited to the embodiments set forth
herein. Rather, these embodiments are provided so that this
disclosure will be thorough and complete, and will convey the scope
of the invention to those skilled in the art. Like numbers refer to
like elements throughout, and prime notation is used to indicate
similar elements in alternative embodiments.
[0049] A list of components will now be described. [0050] 101 left
hand thin film diffractive waveplate lens [0051] 102 right hand
thin film diffractive waveplate lens [0052] 201 continuous lines
[0053] 300 plane [0054] 301 observer [0055] 302 observer [0056] 400
component/element [0057] 410 right-hand circular polarized (RHCP)
light beam [0058] 411 defocused RHCP light beam [0059] 412 focused
RHCP light beam [0060] 420 left-hand circular polarized (LHCP)
light beam [0061] 421 defocused (LHCP) light beam [0062] 422
focused LHCP beam [0063] 430 DWL layer [0064] 440 substrate [0065]
601 collimated lens beams [0066] 602 lens [0067] 603 focal region
[0068] 612 aspheric lens [0069] 613 focal region [0070] 614
diffractive waveplate lens [0071] 615 diffractive waveplate lens
[0072] 616 diffractive waveplate lens [0073] 617 incoming beam
[0074] 618 conventional lens [0075] 619 diffractive waveplate lens
[0076] 620 focal region [0077] 701 collimated beam [0078] 702
optical system axis [0079] 703 right-hand circular polarized beam
[0080] 704 left-hand circular polarized beam [0081] 711 diffractive
waveplate lens [0082] 712 diffractive waveplate lens [0083] 721
focal region [0084] 801 diffractive waveplate lens [0085] 802
diffractive waveplate lens [0086] 803 diffractive waveplate lens
[0087] 804 cone of light [0088] 805 focal point [0089] 901
collimated beam [0090] 902 optical system axis [0091] 903 spherical
lens [0092] 904 RHCP component [0093] 905 LHCP red beam [0094] 906
focal point [0095] 907 RHCP component of blue light [0096] 908 LHCP
component of blue light [0097] 909 focal point [0098] 1001
diffractive waveplate lens [0099] 1002 diffractive waveplate lens
[0100] 1003 diffractive waveplate lens [0101] 1010 focal point
[0102] 1101 collimated light beam [0103] 1102 optical system axis
[0104] 1103 diffractive waveplate lens [0105] 1104 focal point
[0106] 1120 non-diffracted collimated beam [0107] 1105 focused beam
[0108] 1120 non-diffractive collimated beam [0109] 1201 beam [0110]
1202 axis [0111] 1203 lens [0112] 1204 diffractive waveplate lens
[0113] 1205 diffractive waveplate lens [0114] 1210 focal plane
[0115] 1220 focal plane [0116] 1230 focal plane [0117] 1240 focal
plane [0118] 1301 fiber optic [0119] 1302 tip of 1301 [0120] 1303
light cone [0121] 1304 diffractive waveplate lens [0122] 1305
diffractive waveplate lens [0123] 1306 diffractive waveplate lens
[0124] 1307 converging cone [0125] 1308 tip of 1309 [0126] 1309
fiber optic [0127] 1310 beam block [0128] 1311 diverging beam
[0129] 1320 fiber optic [0130] 1321 diffractive waveplate lens
[0131] 1322 defocused beam [0132] 1323 focused beam [0133] 1401
diffractive waveplate lens [0134] 1402 diffractive waveplate lens
[0135] 1403 diffractive waveplate lens [0136] 1404 polarization
switching components [0137] 1405 cycloidal diffractive waveplate
[0138] 1406 vector vortex waveplate [0139] 1407 cylindrical
diffractive waveplate lens [0140] 1408 cylindrical diffractive
waveplate lens [0141] 1409 polarization switching components
(switchable phase retardation layer) [0142] 1410 polarization
switching components (switchable phase retardation layer) [0143]
1411 cylindrical diffractive waveplate lens [0144] 1412 cylindrical
diffractive waveplate lens [0145] 1501 electrodes for application
of electric field [0146] 1502 substrate [0147] 1503 substrate
[0148] 1504 electro-optical material [0149] 1505 diffractive
waveplate film [0150] 1602 diffractive waveplate film [0151] 1603
variable phase retardation film [0152] 1604 mirror [0153] 1605
focused beam
Glossary of Terms
[0154] Diffractive waveplates (DWs): A birefringent film with
anisotropy axis orientation modulated in the plane of the film.
Different modulation patterns are possible resulting in different
optical functionality, including lens, prism, axicon, etc.
Generally, DWs may possess more than one layer, and the anisotropy
axis may be modulated also in the bulk of the layer.
[0155] Diffractive waveplate lens: A diffractive waveplate with
lens function. It may provide spherical, cylindrical, and other
types of lens action.
[0156] Optical substrate or optical film. A transparent material
providing mechanical support for DWs. It may be glass, quartz,
plastic, or any other material that is at least partially
transparent for the wavelengths of light that propagate through the
DWs. It may possess anti-reflective or anti-scratch functions.
[0157] Switchable Diffractive waveplate: A DW that can be switched
between diffractive and non-diffractive states upon application of
external influences such as electric fields, temperature, optical
radiation, etc. Generally, the switching can take place through
gradual change of diffraction spectrum.
[0158] Variable phase retarder or polarization controller: An
optical component capable of controlling the polarization of light
propagated through it by applying electric fields, changing
temperature, exposure to a light beam, etc. Particularly, it may be
a liquid crystal sandwiched between substrates coated with
transparent electrodes.
[0159] Before explaining the disclosed preferred embodiments of the
present invention in detail it is to be understood that the
invention is not limited in its application to the details of the
particular arrangements shown since the invention is capable of
other embodiments. Also, the terminology used herein is for the
purpose of description and not limitation.
[0160] In the description here of the invention, the term "light"
will often be used to describe the electromagnetic radiation that
interacts with the diffractive waveplate lenses that are subject of
this invention. Although "light" generally means electromagnetic
radiation with a wavelength in the visible region of the
electromagnetic radiation with a wavelength in the visible region
of the electromagnetic spectrum, it should be understood that the
usage of the term "light" in the description is not restrictive, in
the sense of limiting the design and application to diffractive
waveplate lenses that operate only in the visible region of the
spectrum. In general, all the designs and concepts described herein
apply to operation over a wide range of the electromagnetic
spectrum, including the microwave, infrared, visible, ultraviolet,
and X-ray regions. While physical embodiments of diffractive
waveplate lenses are at present advanced for operation in the
visible region of the spectrum, the designs and applications
disclosed here are applicable over all the noted regions of the
electromagnetic spectrum.
[0161] The present invention relates to the design and application
of diffractive waveplate lenses. The term "diffractive waveplate
lens" as used herein describes a thin film of birefringent material
deposited on a transparent structure, for example, a thin flat
substrate of optical material such as glass. This birefringent film
has the property that it retards the phase of light of one linear
polarization by approximately one half wave (pi radians of optical
phase) relative to the light of the other linear polarization. In
diffractive waveplate lenses, the optical axis orientation depends
on the transverse position on the waveplate, i.e. the position in
the two coordinate axes perpendicular to the surface of the
diffractive waveplate lens. In other words, the optical axis
orientation is modulated in one or both of the transverse
directions parallel to the surface of the substrate on which the
active thin film is applied. Lensing action is due to parabolic
profile of optical axis orientation modulation.
[0162] There are two general types of diffractive waveplate lenses
to which the present invention applies. The first type of
diffractive waveplate lens is axially symmetric and is used, for
example, to focus a collimated beam of light to a point in space.
The second type of diffractive waveplate lens is cylindrically
symmetric and is used, for example, to focus a collimated beam of
light to a line segment in space. In m any exam pies below, an
optical system of circular symmetry is used as an example, but in
general, all of the conclusions apply as well to optical systems of
cylindrical symmetry.
[0163] In FIG. 1, the orientation of the anisotropy axis at each
point of the birefringent thin film 101 is indicated by a short
line segments. In the first type of diffractive waveplate lenses to
which the present invention applies, illustrated in FIG. 1A, the
orientation of the anisotropy axis of the birefringent material
comprising the thin film layer depends only on the radial distance
r from a center point. This type of spherical diffractive waveplate
lens is used for applications such as focusing a collimated beam of
light to a point for imaging a distant scene onto a sensor array.
To perform this function, the angle .alpha. that the anisotropy
axis of the birefringent material makes with the coordinate axis is
given by the following equation:
.alpha. = .+-. k 0 4 f r 2 ##EQU00001##
where k.sub.0=2.pi./.lamda. is the wavenumber of the light that is
to be focused by the diffractive waveplate lens, .lamda. is the
wavelength of that radiation, f is the focal length of the
diffractive waveplate lens (DWL), and r is the distance to the
central point.
[0164] The difference in signs in variation of the anisotropy axis
with radius designate lenses of two opposite signs. The difference
in corresponding patterns 101 and 102 in FIG. 1 is even better
visible in representation of the DWL structure by continuous lines
201 as shown in FIG. 2A. DWLs of different signs correspond to the
right- and left-spiraling patterns in FIG. 2B.
[0165] In the preferred embodiment of the present invention, DWLs
of opposite optical axis modulation signs need not be two separate
optical components and is obtained by rotating the DWL around an
axis in the plane of the DWL by 180 degrees. The observers 301 and
302 looking at a given DWL from opposite sides in FIG. 3 see
patterns of opposite sign.
[0166] This optical asymmetry is described in detail in FIG. 4
wherein the DWL layer 430 is shown on a substrate 440. As an
example, a right-hand circular polarized (RHCP) light beam 410 is
transformed into a defocused left-hand circular polarized (LHCP)
beam 421 when incident from the side of the substrate. Arranging
the component 400 with the substrate facing the incident RHCP beam
results in a focused LHCP beam 422.
[0167] For a LHCP light beam 420 in FIG. 4, the situation is
reversed. The LHCP beam 420 is transformed into a focused RHCP beam
412 when incident from the side of the DWL and it is transformed
into defocused RHCP beam 411 when incident from the side of the
substrate.
[0168] In the second type of diffractive waveplate lenses to which
the present invention applies, illustrated in FIG. 5, the
orientation of the optical axis of the birefringent material
comprising the thin film layer depends only on the linear distance
x from a central axis. This type of cylindrical diffractive
waveplate lens is used for applications such as focusing a beam of
light to a line for imaging light from the sun onto a line of
photovoltaic devices. In the paraxial approximation, the angle
.cndot. that the optical axis of the birefringent material makes
with the coordinate axis is given by the following equation:
.alpha. = .+-. k 0 4 f x 2 ##EQU00002##
where k.sub.0 and f have the same meanings as before, and x is the
distance from the center of the coordinate axis. FIGS. 5 A and B
correspond to patterns of different sign (cylindrical lenses of
different sign).
[0169] One of the problems with conventional lenses is spherical
aberration, illustrated in FIG. 6A and FIG. 6B, in which an
incident collimated beam 601 is focused by a lens 602.
[0170] When a refractive material such as glass formed such that
one or both surfaces closely approximates a section of a sphere,
such as the lens 602, then the resulting structure can be used to
focus light as illustrated in FIG. 6A. However, as is well known in
the art, when focused by a lens constructed in this way, the rays
of light from a distant source are not all brought to the same
focal point. Specifically, such a lens with spherical surfaces will
bring the peripheral rays, the rays at the edge of the beam, to a
focus closer to the lens than the point to which the lens brings
the rays closer to the axis. Hence, the rays in the focal region
603 in FIG. 6A do not all pass through the same point. This
phenomenon is called spherical aberration.
[0171] By means of modifying one of the surfaces of a lens such
that the surface is not spherical (i.e. such that the surface is
aspherical), all incident light in a collimated beam can be brought
to the same focal point, as indicated in FIG. 6B. With an
appropriately designed aspheric lens 612, all the rays in the focal
region 613 pass through the same point. However, fabrication of
such aspheric lenses is often very expensive, and therefore their
use is impractical for many applications.
[0172] A major advantage of diffractive waveplate lenses is that
the focusing effect of aspheric surfaces of arbitrary form can be
produced simply by changing the dependence of optical axis
orientation of the birefringent film with coordinate
.alpha.=ax+bx.sup.2+cx.sup.3+ . . . . For such lenses, unlike the
situation with conventional lenses, the manufacturing expense of a
lens that has no spherical aberration will not be significantly
greater than for a lens that does have spherical aberration.
[0173] Another technique for obtaining nonlinear orientation
modulation pattern comprises stacking layers of diffractive
waveplate lenses with varying modulation patterns and varying
degree of overlap. A system of three such layers, 614, 615, and 616
is shown in FIG. 6C.
[0174] In one of the embodiments shown in FIG. 60, the thin film
diffractive waveplate lens 619 may be deposited on a conventional
lens 618 to correct for aberrations and focus an incoming beam 617
onto the same point in space 620.
[0175] In general, the optical deflection angle resulting from a
light beam propagating through a diffractive waveplate lens depends
on the circular polarization of the light. As a result, if the
focal length of a lens such as the ones illustrated in FIG. 1 is f
for right-hand-circular polarized (RHCP) light as an example, then
the focal length of the same lens for left-hand-circular polarized
(LHCP) light will be -f Therefore, a diffractive waveplate lens
that converges a collimated beam of RHCP light will diverge a beam
of LHCP light. This is illustrated by the action of the diffractive
waveplate lens 711 in FIG. 7, in which an incident collimated beam
701, centered on axis 702, and including both a RHCP component and
a LHCP component, converges the RHCP component 703 and diverges the
LHCP component 704 of the incident beam.
[0176] In many applications, one of the functions of the optical
system is to bring light to a focal point (in the case of an
axially symmetric system) or to a focal line (in the case of a
cylindrically symmetric system). It is often desirable for light of
all polarizations to be brought to the same focal point or focal
line. In the case of diffractive waveplate lenses, for which the
focal length of a single lens for LHCP light is opposite in sign to
the focal length for the same lens for RHCP light, it is possible
to bring light of both polarizations to the same focal point or
focal line by the use of two diffractive waveplate lenses. In the
preferred embodiment the focal lengths of the two lenses are
related as
f 2 = f 1 - d 2 f 1 ##EQU00003##
where the distance between the two lenses d is smaller than the
absolute value of the focal length of the 1.sup.st lens,
d<|f.sub.1|. By that, the back focal length f.sub.BFL of the
system of two lenses, the distance of the focal spot from the
second lens, is determined by equation
f BFL = f 1 2 d - d ##EQU00004##
[0177] For example, the distance between diffractive waveplate lens
711 and diffractive waveplate lens 712 can be 50 mm, the focal
lengths of lenses 711 and 712 for RHCP light 703 can be 70.7 mm and
-35.4 mm, respectively. Therefore, the focal lengths of lenses 711
and 712 for LHCP light 704 are -70.7 mm and 35.4 mm, respectively.
As shown in FIG. 7, this combination of focal lengths and spacings
results in both RHCP light 703 and LHCP light 704 being brought to
the same focal point 721.
[0178] As will be evident to those skilled in the art, if an
optical system brings light of both RHCP and LHC polarization to a
single point or line focus, then it will bring light of any
polarization to the same point or line focus. Therefore FIG. 7
demonstrates the ability with two diffractive waveplate lenses to
bring light in any polarized or unpolarized beam to the same point
or line focus.
[0179] As previously noted, for diffractive waveplate lenses of the
type that is the subject of the present invention, the sign of
focal length for LHC polarized light is opposite to that of the
focal length for RHC polarized light. It was shown by means of FIG.
7 and the associated discussion that despite the difference in
focal length for light of the two possible circular polarizations,
it is possible to focus light of any polarization with a
combination of two diffractive waveplate lenses. However, there may
be some applications that an alternative method may be used to
focus light of both polarizations, using only a single diffractive
waveplate lens and an additional optical element. For example,
instead of using two diffractive waveplate lenses, a single
diffractive waveplate lens combined with a waveplate and a
refractive lens made from a birefringent material could also be
used to perform focusing of light of any polarization. Methods of
combining diffractive waveplate lenses into optical systems that
include such waveplates and birefringent refractive elements will
be evident to anyone skilled in the art of optical design, once the
fundamental characteristics of diffractive waveplate lenses of this
invention are revealed.
[0180] As will be evident to those skilled in the art, the
effective focal length (EFL) of the optical system comprising lens
711 and 712 in FIG. 7 is much different for light of RHC
polarization than it is for light of LHC polarization. In some
applications, it is required that light of all polarizations be
focused with the same EFL. The capability of a combination of three
diffractive waveplate lenses to not only bring light of any
polarization to the same point or line focus, but also to have the
same EFL for light of any polarization, is illustrated in FIG. 8.
As in FIG. 7, in FIG. 8 an incident beam 701 symmetrically disposed
about a system optical axis 702, comprising both a RHCP component
703 and a LHCP component 704, is incident on the optical system.
However, in FIG. 8, the optical system now consists of three lenses
801, 802, and 803, with a spacing of 30 mm between adjacent lenses,
and with focal lengths of 70.7 mm, -35.4 mm, and 45.5 mm,
respectively. As shown in FIG. 8, this combination of three
diffractive waveplate lenses brings both the RHCP component 703 and
the LHCP component 704 of the incident beam to the same focal point
805. While in both FIG. 7 and FIG. 8 both polarization components
of the incident light beam 701 are brought to the same focal point,
the significant difference between the two figures is that in FIG.
8, the cone angle of the cone of light 804 that converges to the
focus 805 is the same for both the RHC component 703 and the LHC
component 304, as must be the case if and only the system EFL is
the same for both components. FIG. 8 therefore demonstrates that
with three diffractive waveplate lenses, light of any polarization
can be brought to the same focal point, with the same EFL.
[0181] Due to the diffractive nature of diffractive waveplate
lenses, the deflection angle for a given grating is a function of
wavelength, in accordance with the well-known transmission grating
diffraction condition, d sin .theta.=m.lamda.. Here d is the
grating spacing, .theta. is the angle through which the grating
deflects the beam, m is the order of diffraction, and .lamda. is
the wavelength. The phase gratings used in diffractive waveplate
lenses are designed to be continuous in nature, eliminating all but
the first orders of diffraction. Also, for illustrative purposes,
it is useful to consider only the paraxial case, in which the angle
.theta. through which the beam is diffracted is small compared with
.pi., in which case sin .theta. can be approximated by .theta.. The
equation above therefore becomes d.theta..apprxeq..lamda.. That is,
in the paraxial approximation, the deflection angle of a ray of
light incident on a local area of a diffractive waveplate lens is
directly proportional to the wavelength of the light. As a direct
consequence, the focal length of the lens is inversely proportional
to wavelength.
[0182] Because of this strong dependence of the focal length of a
diffractive waveplate lens on wavelength, such lenses may be used
to correct for chromatic aberration in optical systems containing
refractive elements. Chromatic aberration, as the expression is
used here, is the dependence of the focal position on wavelength.
Due to the dependence of the index of refraction n of any
dielectric medium on wavelength, every imaging system that employs
such media suffers from chromatic aberration.
[0183] To illustrate the ability of diffractive waveplate lenses to
correct for chromatic aberration, a specific example will be used.
FIG. 9A illustrates an imaging system employing a single refractive
element made with BK7 glass, an optical material available from
Schott Advanced Optics. A collimated beam 901 of white light from a
distant source is incident on spherical lens 903 with aperture
centered on axis 902. Although BK7 is isotropic, and therefore does
not act any differently on RHCP light than it acts on LHCP light,
we will distinguish between these two components of the incident
unpolarized light because later in this discussion, diffractive
waveplate lenses will be considered whose effects differ between
these two polarization components. With only the refractive element
made from BK7 in place, both the RHCP component 904 and the LHCP
component 905 of the red component of the white input beam are
brought to the same focal point 906.
[0184] The BK7 material from which the refractive lens in FIG. 9A
is made has an index of refraction of n=1.515 for red light
(wavelength .lamda.=650 nm) and n=1.526 for blue light (wavelength
.lamda.=450 nm). As a result, the focal length of the lens is
slightly shorter for blue light than it is for red light. This is
shown in FIG. 9B, showing a magnified view of the region near the
focal point. The focal point 909 on the axis 902 of the input beam,
for both the RHCP component of the blue light 907 and the LHCP
component of the blue light 908, is 2.2% closer to the lens than
the focal point 906 for the two polarization components of the red
light.
[0185] For optical systems such as cameras, it is undesirable for
the focal positions at any two wavelengths within the operating
wavelength band to differ significantly. Therefore, chromatic
aberration correction is an important part of the design of such
optical systems. The most coin m on approach to chromatic
aberration correction refractive imaging systems is to include
refractive elements of multiple types, with various indices of
refraction and various dependences of index of refraction on
wavelength. These approaches increase the complexity and cost of
the system. Therefore, there is a need for alternative approach to
chromatic aberration correction.
[0186] FIG. 10A illustrates correction of the chromatic aberration
in a conventional refractive lens by employment of a set of three
diffractive waveplate lenses. As was the case for FIGS. 9A and 9B,
white light collimated beam 901 is incident along an axis 902 onto
the conventional BK7 glass lens 903. FIG. 10A includes three
diffractive waveplate lenses 1001, 1002, and 1003. As is evident
from the figure, the path of red light through the combined system
is slightly different for the RHCP component 904 than it is for the
LHCP component 905, but both of the polarization components of the
red light are brought to the same focal point 1010. The focal
lengths of the lenses shown in the figure for RHCP polarized red
light are 10.00 mm, 14.00 mm, -7.00 mm, and 14.07 mm for lenses
903, 1001, 1002, and 1003, respectively. As noted previously, for
the diffractive waveplate lenses, the focal lengths change sign for
LHC polarized light.
[0187] FIG. 10B shows the ability of the lens combination
illustrated in FIG. 10A to correct for chromatic aberration. The
focal positions 906 and 909 for red and blue light, respectively,
before the addition of diffractive waveplate lenses 1001, 1002, and
1003, are shown in FIG. 10B for reference. Light of all four
considered polarization/wavelength combinations is brought to the
same focal point 1010 after the addition of lenses 1001, 1002, and
1003. In FIG. 10B, the paths of the RHC red beam 904, LHC red beam
905, RHC blue beam 907, and LHC blue beam 908 are shown slightly
offset vertically for clarity, but for the considered optical
design, the four beams come to exactly the same focal point
1010.
[0188] In the discussion of FIG. 6 it was noted that by adjusting
the grating spacing in a diffractive waveplate lens, spherical
aberration can be eliminated. In the discussion of FIG. 10 it was
demonstrated that chromatic aberration correction of a refractive
imaging system is possible by the addition of appropriate
diffractive waveplate lenses. Once the mechanism of correcting for
spherical aberration alone, and the mechanism for correcting for
chromatic aberration alone, methods will be evident to those
skilled in the art that allow the use of diffractive waveplate
lenses to be used to simultaneously compensate for both spherical
and chromatic aberration.
Switchable Lens
[0189] It is well known that the optical properties of liquid
crystal based devices can be made to be controllable by means of an
electric field across the medium containing the liquid crystal
material. A common example of this is the LCD (liquid crystal
display) used in computer monitors and television displays.
Diffractive waveplate lenses can be constructed such that the
focusing properties can be turned on and off by means of the
application of an electric potential across the device. An example
of such a device is illustrated in FIG. 11. In FIG. 11A, with no
electric field applied, an incident collimated beam 1101 enters a
diffractive waveplate lens 1103 centered on axis 1102 of the
optical system, and is focused by the lens to focal point 1104. In
FIG. 11B, due to the effect of an applied electric field, the
orientation of the liquid crystal molecules in lens 1103 is changed
in such a way that the beam is no longer focused by the lens, and
the output beam 1120 remains collimated.
1. Electrically Tunable Focusing System
Electrically Tunable Focusing System
[0190] One of the potential applications of such switchable
diffractive waveplate lenses is to provide a purely electronic
means of focusing for an optical imaging system, without the need
to move any optical elements. This would be highly desirable in
some applications because it eliminates the cost, weight, and
reliability issues of mechanical actuators in the focusing system.
One of the m any possible embodiments of such an electronic
focusing system w herein a combination of two electrically
switchable diffractive waveplate lenses is used to provide four
distinct focus positions is illustrated in FIG. 12. FIG. 12A shows
the case in which a beam 1201 is incident on the input aperture
centered along axis 1202, and is focused to a point in focal plane
1210 by a combination of lenses 1203, 1204, and 1205. In FIG. 12A
both of the diffractive waveplate lenses, 1204 and 1205, are turned
on so they both pull the focal position towards the lens system.
FIG. 12B is the same as FIG. 12A except that in FIG. 12B, lens 1205
remains on but lens 1204 has been shut off. This results in the
focal point shifting from focal plane 1210 to focal plane 1220.
FIG. 12C is also the same as FIG. 12A except that in FIG. 12C, lens
1204 remains on but lens 1205 has been shut off. This results in
the focal point shifting from focal plane 1210 to focal plane 1230.
FIG. 12D is also the same as FIG. 12A except that in FIG. 12D, both
lens 1204 and lens 1205 have been shut off. This results in the
focal point shifting from focal plane 1210 to focal plane 1240.
[0191] In the design concept illustrated in FIG. 12A, four
different focal positions are accessible by means of switching two
lenses on and off. This is accomplished by using diffractive
waveplate lenses of different focal power. By this means, in
general, with k switchable lenses, 2k distinct focus positions can
be made accessible, particularly, equally spaced. Each lens may
have twice the focal power of the previous one, for example.
Camera Lens
[0192] An example of uses of electrically switchable diffractive
waveplate lenses of the present invention are camera lenses and
machine vision wherein the contrast reduction due to presence of
defocused beam does not affect required image information obtained
due to focused portion of the beam.
Fiber Illuminator/Focusing Switching System
[0193] An important use of diffractive waveplate lenses in the
current invention are polarization maintaining fibers. As an
example, the diffractive waveplate lens coated at the output facet
of the fiber may allow collimating or focusing the light emerging
from the fiber. Thus, changing the state of polarization of a laser
light injected into a fiber would allow, for example, switching the
light at its output between illuminating state used for imaging and
focused state that may be used for example, for surgery.
Fiber Coupler
[0194] The capability to switch a diffractive waveplate lens from
an active to a passive state makes possible many other applications
in which optical beams are manipulated by a switchable lens. One of
these many applications is the switching on and off of optical
coupling between the output from one optical fiber and the input of
another optical fiber.
[0195] Such optical switching is illustrated in FIG. 13A and FIG.
13B. In FIG. 13A, light from the tip 1302 of optical fiber 1301
expands away from the tip within a light cone 1303 characteristic
of the fiber type. This output light is captured and focused by the
diffractive waveplate lenses 1304, 1305, and 1306. Except for a
small fraction of the light in the converging cone 1307 of the
light beam, all the light is focused into the tip 1308 of a second
optical fiber 1309. A small fraction of the light is blocked
because it impinges on a beam block 1310, but almost all the light
goes around the beam block and reaches fiber tip 1308.
[0196] As indicated in FIG. 13A, due to the specific arrangement of
the diffractive waveplate lenses 1304, 1305, and 1306, light of
both RHC and LHC polarization is captured and focused into fiber
1309. As will be evident to those skilled in the art, the fact that
both RHC and LHC polarized light is captured and focused into fiber
1309 implies that light of any polarization emanating from fiber
tip 1302 will be captured and focused by the lens combination
comprised of lenses 1304, 1305, and 1306.
[0197] Although a specific exemplary arrangement of the lenses is
shown in FIG. 13A, it will be evident to those skilled in the art
that it is in general true that by appropriate selection of lens
spacing and focal lengths, a combination of three lenses can always
be found to couple the radiation from one fiber to another for any
spacing between the fiber tips, and for any wavelength. The
specific arrangement used as an example in FIG. 13A is for a
spacing from fiber tip 1302 to lens 1304 of 1 mm, a spacing between
each adjacent pair of lenses of 0.5 mm, a focal length of
diffractive waveplate lenses 1304 and 1306 of 0.58 mm for RHC
light, and a focal length of diffractive waveplate lens 1305 for
RHC light of -0.43 mm.
[0198] Switching off the coupling from fiber 1301 to fiber 1302 is
accomplished by turning off the three lenses 1304, 1305, and 1306.
The resulting optical configuration after the three lenses are
switched off is shown in FIG. 13B. The cone of light 1307 that
emerges from the combination of lenses is now diverging beam 1311
instead of converging, and no light reaches the input tip 1308 of
fiber 1309.
2. Partially Focused Beams
Partially Focused Beams
[0199] The transition of diffractive waveplate lenses such as
lenses 1304, 1305, and 1306 in FIG. 13A and FIG. 13B from the "on"
state (i.e. focusing or defocusing the input beam) to the "off"
state (i.e. passing the beam without deflection) can be converted
into a continuous process, such that an arbitrary and selectable
fraction of the optical power in the beam can be deflected by the
diffractive structure of the diffractive waveplate lens, and the
balance of the optical power in the beam can be passed without
deflection. This is accomplished by applying an electric potential
to the diffractive waveplate lens that results in an optical
retardation of one linear polarization relative to the other of
more than zero retardation (at which no beam deflection occurs),
but less than one-half wave of retardation (at which 100% of the
optical power in the beam is deflected by the diffractive
structure). By appropriately adjusting the magnitude of the applied
electric potential, the fraction of power focused or defocused by
the lens can be adjusted to any value between 0% and 100%. For
example, in the fiber coupling embodiment shown in FIG. 13A and
FIG. 13B, the fraction of the power transferred from fiber 1301 to
fiber 1309 can be varied from 0% to nearly 100%. In other words,
the gradual transition of the lenses from the state in which they
do not deflect the beam at all, to the state in which they deflect
100% of the optical power in the beam, results in a variable
optical attenuator.
[0200] In a preferred embodiment shown in FIG. 13C the diffractive
waveplate lens 1321 is coated at the output facet of a fiber 1320
to split the output beam between focused 1323 and defocused 1322
beams controlled by the polarization of light at the input of the
fiber.
Switching from Non-Focusing to Focusing State
[0201] In one realization of the present invention, the phase
retardation of the lens is chosen to fulfil full-wave condition
wherein diffraction, hence, focusing action of the lens is absent.
Application of an electric field reduces the phase retardation to
half-wave condition thus setting in the lensing action. Instead of
the electric field, s w itching can be induced also by temperature,
light, and other influences that change either the order parameter
or orientation of the liquid crystal diffractive waveplate
lens.
[0202] In another preferred embodiment, the initial non focusing
state is obtained by arrangement of at least two diffractive
waveplate lenses. Switching at least one of the lenses in such a
system transforms it into a focusing state.
Switching Diffractive Waveplate Lens System by Polarization
Modulators
[0203] As an alternative to switching focusing properties of
diffractive waveplate lenses, the focus position of a light beam at
the output of a system of diffractive waveplate lenses can be
controlled by using variable phase retardation plates to switch the
polarization handedness of a beam at the output of diffractive
waveplate lenses as shown in FIG. 14. By switching the handedness
of polarization, the focusing powers of subsequent lenses, 1401,
1402 and 1403, in the example shown in FIG. 14A, can be added or
subtracted from each other focusing an input beam to different
points in space. Moreover, diffractive waveplates of different
functionalities can be combined in series with polarization
switching components 1404. As shown in FIG. 14B, the optical system
can combine, for example, a DW lens 1401, a cycloidal diffractive
waveplate 1405, and vector vortex waveplates 1406 along with
diffractive waveplate lenses, to switch not only focus position,
but propagation direction and the phase profile of the beam as
well.
[0204] In a preferred embodiment, cylindrical diffractive waveplate
lenses can be sequenced with polarization switching components 1404
to obtain a beam of different orientation of ellipticity axis. FIG.
14C shows such an opportunity for a horizontal and vertical
alignment of the beam intensity distribution profile obtained when
focusing with cylindrical lenses. The cylindrical diffractive
waveplate lenses 1407 and 1408 are identical in this embodiment.
The cylindrical diffractive waveplate lenses 1411 and 1412 are also
identical but aligned perpendicular to the orientation of the
lenses 1407 and 1408. Each pair is interspaced with polarization
switching components 1409 and 14010, for example a liquid crystal
switchable phase retardation layer to generate either undiffracted
or diffracted/focused beams.
[0205] In a preferred embodiment, the switchable phase retarder
serves as substrate for the diffractive waveplate film 1505 as
shown in FIG. 15. The switchable phase retarder is comprised of
substrates 1502 and 1503 with transparent electrodes for
application of an electric field 1501, and the electro-optical
material in-between 1504 such as a liquid crystal.
[0206] While all of the exemplary embodiments discussed herein are
of a realization of diffractive waveplate lenses employed in a mode
in which the optical beam is transmitted through the thin film
diffractive waveplate lens and through the underlying substrate, an
alternative embodiment is to apply the thin film diffractive
waveplate lens to a flat mirror as demonstrated in FIG. 16. In this
manner, flat reflective optical elements can be fabricated to have
a wide variety of beam deflecting properties, including the ability
to focus light with a flat reflective optical element. In one of
the preferred embodiments shown in FIG. 16, a flat mirror 1604
comprises a variable phase retardation film 1603 and a diffractive
waveplate lens 1602. A circular polarized collimated light beam
1601 may thus be reflected from the system as a focused beam 1605,
for example.
[0207] The exemplary embodiments described herein have assumed
either explicitly or implicitly that the thin film constituting the
diffractive waveplate lens is applied to the flat surface of a
solid substrate such as glass. Neither the assumption of a solid
substrate, nor the assumption of a flat surface, should be taken as
restrictive in defining the potential embodiments of this
invention. As will be evident to anyone skilled in the art, the
coatings may be applied to curved substrates, and to flexible
substrates. All of the exemplary embodiments described herein could
also be realized with either a curved substrate, a flexible
substrate, or a substrate that is both curved and flexible.
Microwave, Infrared, Ultraviolet, and X-Ray Regions of the
Spectrum
[0208] By merely changing the thickness of the layer, in a
preferred embodiment of current invention, diffractive waveplate
lenses are optimized for use in different parts of the spectrum,
spanning microwave and to short wavelengths.
[0209] While the invention has been described, disclosed,
illustrated and shown in various terms of certain embodiments or
modifications which it has presumed in practice, the scope of the
invention is not intended to be, nor should it be deemed to be,
limited thereby and such other modifications or embodiments as may
be suggested by the teachings herein are particularly reserved
especially as they fall within the breadth and scope of the claims
here appended.
* * * * *