U.S. patent application number 11/581193 was filed with the patent office on 2009-08-20 for radiation modulation by reflection from controlled composite material.
Invention is credited to Alexandre Bratkovski, Shih-Yuan Wang.
Application Number | 20090208217 11/581193 |
Document ID | / |
Family ID | 40910174 |
Filed Date | 2009-08-20 |
United States Patent
Application |
20090208217 |
Kind Code |
A1 |
Wang; Shih-Yuan ; et
al. |
August 20, 2009 |
RADIATION MODULATION BY REFLECTION FROM CONTROLLED COMPOSITE
MATERIAL
Abstract
Modulation of electromagnetic radiation is described in which an
incident radiation beam is directed toward a surface of a composite
material and at least partially reflects to form a reflected
radiation beam. The composite material comprises an arrangement of
electromagnetically reactive cells of small dimension relative to a
wavelength of the incident radiation beam, and exhibits at least
one of a negative effective permeability and a negative effective
permittivity for at least one frequency. A modulation signal is
applied to the composite material to cause a variation in at least
one of the effective permeability and the effective permittivity,
at least one characteristic of the reflected radiation beam being
modulated according to the modulation signal.
Inventors: |
Wang; Shih-Yuan; (Palo Alto,
CA) ; Bratkovski; Alexandre; (Palo Alto, CA) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD, INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
40910174 |
Appl. No.: |
11/581193 |
Filed: |
October 12, 2006 |
Current U.S.
Class: |
398/83 ;
359/240 |
Current CPC
Class: |
G02F 2203/585 20130101;
G02F 1/31 20130101; H01Q 3/44 20130101; H01Q 15/0086 20130101; G02F
2202/42 20130101; G02F 2203/15 20130101 |
Class at
Publication: |
398/83 ;
359/240 |
International
Class: |
H04J 14/02 20060101
H04J014/02; G02F 1/01 20060101 G02F001/01 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] This invention was made with Government support under
Agreement No. HR0011-05-3-0002, awarded by DARPA. The Government
has certain rights in the invention.
Claims
1. A method for modulating electromagnetic radiation, comprising:
directing an incident radiation beam toward a surface of a
composite material, the composite material having an arrangement of
electromagnetically reactive cells of small dimension relative to a
wavelength of the incident radiation beam, at least one of an
effective permeability and an effective permittivity of the
composite material being negative for at least one frequency;
receiving a reflected radiation beam resulting from at least
partial reflection of the incident radiation beam from said
surface; applying a modulation signal at a first value, the
reflected radiation beam having an intensity that is a first
percentage of an intensity of the incident radiation beam; and
applying a modulation signal at a second value such that at least
one of said effective permeability and said effective permittivity
are more negative than at said first value of said modulation
signal, the intensity of the reflected radiation beam being a
second percentage of the incident radiation beam intensity less
than said first percentage at said second value of said modulation
signal.
2. The method of claim 1, wherein said at least one characteristic
of the reflected radiation beam that is modulated comprises at
least one of phase, amplitude, polarization, and spectral content,
wherein said at least one frequency of the incident radiation beam
comprises one of a microwave frequency, an infrared frequency, and
an optical frequency, and wherein said modulation signal comprises
at least one of an optical signal and an electrical signal that
alters at least one of an inductive property and a capacitive
property of each of said arrangement of electromagnetically
reactive cells.
3. (canceled)
4. A method for modulating electromagnetic radiation, comprising:
directing an incident radiation beam toward a surface of a
composite material, the composite material having an arrangement of
electromagnetically reactive cells of small dimension relative to a
wavelength of the incident radiation beam, at least one of an
effective permeability and an effective permittivity of the
composite material being negative for at least one frequency;
receiving a reflected radiation beam resulting from at least
partial reflection of the incident radiation beam from said
surface; applying the modulation signal at a first value such that
both said effective permeability and said effective permittivity
are positive, the incident radiation beam primarily reflecting at
said surface, the reflected radiation beam having an intensity that
is a relatively high percentage of an intensity of the incident
radiation beam; and applying the modulation signal at a second
value such that at least one of said effective permeability and
said effective permittivity are negative, the incident radiation
beam primarily refracting into the composite material, the
intensity of the reflected radiation beam being a relatively low
percentage of the incident radiation beam intensity.
5. The method of claim 4, a refracted radiation beam being formed
from said refraction of said incident radiation beam into the
composite material for said second value of said modulation signal,
further comprising: dynamically varying the modulation signal
between said first and second values; receiving said reflected
radiation beam at a first receiving location; and receiving said
refracted radiation beam at a second receiving location spatially
distinct from said first receiving location.
6. The method of claim 1, said incident radiation beam comprising a
first frequency and a second frequency, the method further
comprising applying the modulation signal at a first value that
causes (i) said effective permeability and effective permittivity
to both be positive at said first frequency such that said incident
radiation beam at said first frequency is significantly reflected,
and that causes (ii) at least one of said effective permeability
and effective permittivity to be negative at said second frequency
such that said incident radiation beam at said second frequency is
reflected by a substantially lesser amount than at said first
frequency.
7. The method of claim 1, said incident radiation beam comprising a
plurality of frequencies, the method further comprising applying
the modulation signal at one of a plurality of values that causes
(i) said effective permeability and effective permittivity to both
be positive for a first subset of said frequencies such that said
incident radiation beam for the first subset of frequencies is
significantly reflected, and that causes (ii) at least one of said
effective permeability and effective permittivity to be negative
for a second subset of said frequencies non-overlapping with said
first subset such that said incident radiation beam at said second
subset of said frequencies is reflected by a substantially lesser
amount than at said first subset of frequencies.
8. The method of claim 7, said composite material forming a part of
a first device having an input port receiving said incident
radiation beam and an output port outputting said reflected
radiation beam, the method further comprising: directing the
reflected radiation beam toward an input port of a first of a
plurality of additional devices similar to said first device and
having respective input and output ports in radiative communication
with each other; and directing a plurality of additional respective
incident radiation beams toward respective ones of said input ports
for providing add-drop multiplexing for said incident radiation
beams.
9. The method of claim 1, said incident radiation beam comprising a
first polarization and a second polarization, said arrangement of
electromagnetically reactive cells being anisotropic such that said
at least one negative effective permeability and negative effective
permittivity are obtainable for said first polarization and not
obtainable for said second polarization, the method further
comprising: applying said modulation signal at a first value such
that both said effective permeability and said effective
permittivity are positive for said first polarization, the incident
radiation beam primarily reflecting at said surface for both said
first and second polarizations and the reflected radiation beam
comprising both said first and second polarizations; applying said
modulation signal at a second value such that at least one of said
effective permeability and said effective permittivity are negative
for said first polarization, the incident radiation beam primarily
refracting into the composite material for said first polarization,
wherein said reflected radiation beam comprises primarily said
second polarization and said refracted radiation beam comprises
primarily said first polarization; receiving said reflected
radiation beam at a first receiving location; and receiving said
refracted radiation beam at a second receiving location spatially
distinct from said first receiving location.
10. The method of claim 1, further comprising: applying said
modulation signal at a first value, the reflected radiation beam
having a first phase shift relative to said incident radiation
beam; and applying said modulation signal at a second value such
that at least one of said effective permeability and said effective
permittivity are more negative than at said first value of said
modulation signal, the reflected radiation beam having a second
phase shift relative to said incident radiation beam.
11. The method of claim 10, said composite material being a first
composite material, said incident radiation beam being a first
incident radiation beam, said reflected radiation beam being a
first reflected radiation beam, said modulation signal being a
first modulation signal, the method further comprising: splitting
an input carrier beam into two beams comprising said first incident
radiation beam and a second incident radiation beam, said first
incident radiation beam being incident upon the surface of said
first composite material; directing said second incident radiation
beam toward a surface of a second composite material substantially
similar to said first composite material, a second reflected
radiation beam resulting from at least partial reflection of the
second incident radiation beam from said surface of the second
composite material; applying a second modulation signal at third
and fourth values to said second composite material to cause said
second reflected radiation beam to have third and fourth phase
shifts, respectively, relative to said second incident radiation
beam; and combining said first and second reflected radiation beams
to form an output radiation beam that is a modulated version of
said input carrier beam as modulated according to said first and
second modulation signals.
12. A device for modulating radiation, comprising a composite
material formed by an arrangement of electromagnetically reactive
cells of small dimension relative to a wavelength of an incident
radiation beam, the composite material having a surface from which
the incident radiation beam at least partially reflects to result
in a reflected radiation beam and the composite material can be
operated such that the incident beam at least partially refracts to
result in a refracted radiation beam, the composite material having
at least one of a negative effective permeability and a negative
effective permittivity for at least one frequency, wherein at least
one of an inductive property and a capacitive property of said
electromagnetically reactive cells is controlled by application of
a modulation signal such that at least one characteristic of the
reflected radiation beam and/or refracted radiation beam are
modulated according to said modulation signal.
13. The device of claim 12, wherein said at least one
characteristic of the reflected radiation beam that is modulated
comprises at least one of phase, amplitude, polarization, and
spectral content, wherein said at least one frequency of the
incident radiation beam comprises one of a microwave frequency, an
infrared frequency, and an optical frequency, and wherein said
modulation signal comprises at least one of an optical signal and
an electrical signal.
14. The device of claim 12, further comprising: a first input port
for receiving the incident radiation beam and directing the
incident radiation beam to said surface of the composite material;
a second input port for receiving the modulation signal and
applying the modulation signal to said electromagnetically reactive
cells; and a first output port for receiving the reflected
radiation beam from said surface of said composite material, said
composite material being configured such that both said effective
permeability and effective permittivity are positive for a first
value of said modulation signal to cause said incident radiation
beam to reflect from said surface, said composite material further
being configured such that at least one of said effective
permeability and effective permittivity are negative for a second
value of said modulation signal such that at least a portion of
said incident radiation beam is refracted into said composite
material, wherein said reflected radiation beam has a greater
intensity for said first modulation signal value than for said
second modulation signal value, whereby said device is operable as
an intensity modulator according to said values of said modulation
signal.
15. The device of claim 14, further comprising a second output port
positioned to receive the refracted radiation beam, whereby said
device is operable as a two-way switch according to said values of
said modulation signal.
16. The device of claim 12, said incident radiation beam comprising
a first frequency and a second frequency, said composite material
being configured such that, for a first modulation signal value,
both said effective permeability and effective permittivity are
positive for said first frequency and at least one of said
effective permeability and effective permittivity is negative for
said second frequency, whereas for a second modulation signal
value, both said effective permeability and effective permittivity
are positive for said second frequency and at least one of said
effective permeability and effective permittivity is negative for
said first frequency, the device further comprising: a through port
positioned to receive the reflected radiation beam, said surface
primarily reflecting the incident radiation beam at frequencies for
which both of said effective permeability and effective
permittivity are positive; and a drop port positioned to receive a
refracted beam resulting from a refraction of the incident
radiation beam into the composite material, said surface primarily
refracting the incident radiation beam into the composite material
at frequencies for which at least one of said effective
permeability and effective permittivity are negative, whereby said
device is operable as a channel dropping device that is tunable
according to said modulation signal value.
17. The device of claim 12, further comprising: a first input port
for receiving the incident radiation beam and directing the
incident radiation beam to said surface of the composite material;
a second input port for receiving the modulation signal and
applying the modulation signal to said electromagnetically reactive
cells; and a first output port for receiving the reflected
radiation beam from said surface of said composite material, said
composite material having a resonance frequency at which both of
said effective permeability and effective permittivity are
negative, wherein for a first carrier frequency of said incident
radiation near said resonant frequency, said reflected radiation
beam has a first phase shift relative to said incident radiation
beam for a first value of said modulation signal and a second phase
shift relative to said incident radiation beam for a second value
of said modulation signal, whereby said device is operable as a
phase modulator at said first carrier frequency according to said
modulation signal.
18. A tunable add-drop multiplexer for adding channels to a
radiation beam and removing channels from the radiation beam,
comprising: a plurality of add-drop stages disposed in serial
radiative communication relative to the radiation beam, each
add-drop stage being configured to drop a channel at a drop
frequency and to pass at least one channel at a pass frequency
different than said drop frequency, each add-drop stage comprising
a composite material formed by an arrangement of
electromagnetically reactive cells of small dimension relative to a
wavelength of the radiation beam, the composite material having
both a positive effective permeability and a positive effective
permittivity at said pass frequency and having at least one of a
negative effective permeability and a negative effective
permittivity at said drop frequency, said composite material having
a surface that passes said at least one channel at said pass
frequency by reflection therefrom and that drops said drop channel
at said drop frequency by refraction thereinto; and for each
add-drop stage, a modulation signal application device for applying
a modulation signal to said composite material that varies said
drop frequency by varying at least one of a capacitive property and
inductive property of said arrangement of electromagnetically
reactive cells.
19. The tunable add-drop multiplexer of claim 18, wherein said drop
frequency and pass frequency are each in one of a microwave
frequency range, an infrared frequency range, and an optical
frequency range.
20. The tunable add-drop multiplexer of claim 18, wherein said
modulation signal comprises at least one of an optical signal and
an electrical signal.
21. The tunable add-drop multiplexer of claim 18, wherein said
composite material exhibits both said negative effective
permeability and said negative effective permittivity at said drop
frequency.
22. A Mach-Zehnder apparatus for modulating an incident radiation
beam, comprising: a radiation splitter that splits the incident
radiation beam into a plurality of substantially equal split beams
and directs each split beam along a distinct propagation path; a
plurality of phase modulators positioned along respective ones of
said distinct propagation paths, each of said phase modulators
comprising a composite material modulating the phase of the split
beam by reflection from a surface thereof, the composite material
comprising an arrangement of electromagnetically reactive cells of
small dimension relative to a wavelength of the incident radiation
beam, the composite material having at least one of a negative
effective permeability and a negative effective permittivity at a
frequency of said split beam; for each of said phase modulators, a
modulation signal application device for applying a modulation
signal that varies at least one of a capacitive property and
inductive property of said arrangement of electromagnetically
reactive cells to correspondingly vary the phase of the split beam;
and a radiation combiner that combines said plurality of
phase-modulated split beams into an output radiation beam.
23. The Mach-Zehnder apparatus of claim 22, wherein said phase
modulators are operative in one of a microwave frequency range, an
infrared frequency range, and an optical frequency range.
24. The Mach-Zehnder apparatus of claim 22, wherein said modulation
signal comprises at least one of an optical signal and an
electrical signal.
Description
FIELD
[0002] This patent specification relates to the modulation of
electromagnetic radiation, with particular applicability to
electromagnetic radiation in the microwave and/or optical frequency
ranges.
BACKGROUND
[0003] Devices for modulating electromagnetic radiation represent
fundamental building blocks for many technological endeavors.
Modulation refers to the variation of a property in an
electromagnetic wave or signal, such as amplitude, frequency,
phase, spectral content, or any other measurable characteristic. In
addition to dynamic modulation processes that are operable in real
time relative to a period of the radiation, modulation further
refers to the tuning or adjustment, whether it be static or
dynamic, of a system or device that varies any such measurable
characteristic of the radiation.
[0004] For frequencies in the microwave range, modulation is often
achieved in solid state devices by variation of inputs and/or
operating parameters for electrical components such as
heterojunction bipolar transistors, metal-semiconductor field
effect transistors, and Gunn diodes, and/or in vacuum tube based
devices such as magnetrons, klystrons, and traveling wave tubes, in
each case in conjunction with associated passive electrical
components. For optical frequencies, modulation is often achieved
using devices based on electrooptic and/or magnetooptic materials
such as calcite, quartz, and lithium niobate that change their
refractive index responsive to applied control signals, the
materials being arranged into Mach-Zehnder interferometers (MZIs)
or similar devices converting induced phase changes into amplitude
changes by interference effects. Other electrooptical modulators
include electroabsorption modulators variably absorbing the
incident signal according to an applied electric field, and
acoustic wave modulators using high-frequency sound traveling
within a crystal or a planar wave guide to deflect light from one
place to another.
[0005] For each of the above schemes, practical issues arise in
regard to one or more of modulation speed, dynamic range, spectral
range of operation, noise performance, channel selectivity, device
cost, heat dissipation, device size, tunability, and device power
consumption. It would be desirable to increase the number of device
solutions available for any particular radiation modulation
requirement, and/or to provide for improved radiation modulation
with respect to one or more of the above practical issues. Other
issues arise as would be apparent to one skilled in the art in view
of the present disclosure.
SUMMARY
[0006] In one embodiment, a method for modulating electromagnetic
radiation is provided, comprising directing an incident radiation
beam toward a surface of a composite material, the composite
material having an arrangement of electromagnetically reactive
cells of small dimension relative to a wavelength of the incident
radiation beam. At least one of an effective permeability and an
effective permittivity of the composite material is negative for at
least one frequency. The method further includes receiving a
reflected radiation beam resulting from at least partial reflection
of the incident radiation beam from the surface, and applying a
modulation signal to the composite material to cause a variation in
at least one of the effective permeability and the effective
permittivity. At least one characteristic of the reflected
radiation beam is thereby modulated according to the modulation
signal.
[0007] Also provided is a device for modulating radiation,
comprising a composite material formed by an arrangement of
electromagnetically reactive cells of small dimension relative to a
wavelength of an incident radiation beam. The composite material
has a surface from which the incident radiation beam at least
partially reflects to result in a reflected radiation beam. The
composite material has at least one of a negative effective
permeability and a negative effective permittivity for at least one
frequency. At least one of an inductive property and a capacitive
property of the electromagnetically reactive cells is controlled by
application of a modulation signal such that at least one
characteristic of the reflected radiation beam is modulated
according to the modulation signal.
[0008] Also provided is a tunable add-drop multiplexer for adding
channels to a radiation beam and removing channels from the
radiation beam. The tunable add-drop multiplexer comprises a
plurality of add-drop stages disposed in serial radiative
communication relative to the radiation beam, each add-drop stage
being configured to drop a channel at a drop frequency and to pass
at least one channel at a pass frequency different than the drop
frequency. Each add-drop stage comprises a composite material
formed by an arrangement of electromagnetically reactive cells of
small dimension relative to a wavelength of the radiation beam, the
composite material having both a positive effective permeability
and a positive effective permittivity at the pass frequency and
having at least one of a negative effective permeability and a
negative effective permittivity at the drop frequency. The
composite material has a surface that passes the at least one
channel at the pass frequency by reflection therefrom and that
drops the drop channel at the drop frequency by refraction
thereinto. The tunable add-drop multiplexer further comprises, for
each add-drop stage, a modulation signal application device for
applying a modulation signal to the composite material that varies
the drop frequency by varying at least one of a capacitive property
and inductive property of the arrangement of electromagnetically
reactive cells.
[0009] Also provided is a Mach-Zehnder apparatus for modulating an
incident radiation beam. The Mach-Zehnder apparatus comprises a
radiation splitter that splits the incident radiation beam into a
plurality of substantially equal split beams and directs each split
beam along a distinct propagation path and a plurality of phase
modulators positioned along respective ones of the distinct
propagation paths. Each of the phase modulators comprises a
composite material modulating the phase of the split beam by
reflection from a surface thereof. The composite material comprises
an arrangement of electromagnetically reactive cells of small
dimension relative to a wavelength of the incident radiation beam,
and has at least one of a negative effective permeability and a
negative effective permittivity at a frequency of the split beam.
The Mach-Zehnder apparatus further comprises, for each of the phase
modulators, a modulation signal application device for applying a
modulation signal that varies at least one of a capacitive property
and inductive property of the arrangement of electromagnetically
reactive cells to correspondingly vary the phase of the split beam.
The Mach-Zehnder apparatus further comprises a radiation combiner
that combines the plurality of phase-modulated split beams into an
output radiation beam.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIGS. 1A-1B illustrate a modulation device according to an
embodiment for different states of a modulation signal;
[0011] FIGS. 2A-2B illustrate a modulation device according to an
embodiment for different states of a modulation signal;
[0012] FIG. 3 illustrates a modulation device according to an
embodiment and related time plots of a modulation signal and an
output intensity signal;
[0013] FIG. 4A illustrates a modulation device according to an
embodiment;
[0014] FIG. 4B illustrates a related time plot of a modulation
signal, and related frequency spectrum plots of an output signal
corresponding to the modulation device of FIG. 4A;
[0015] FIG. 5 illustrates an add-drop multiplexer according to an
embodiment;
[0016] FIG. 6 illustrates a modulation device according to an
embodiment and related time plots of a modulation signal and an
output phase signal;
[0017] FIG. 7 illustrates a Mach-Zehnder interferometer according
to an embodiment; and
[0018] FIGS. 8A-8B illustrate a modulation device according to an
embodiment for different states of a modulation signal.
DETAILED DESCRIPTION
[0019] FIGS. 1A-1B illustrate a modulation device 100 according to
an embodiment, comprising an input 102, a composite material 104
having a surface 103, an output 106, and a modulation signal
application device 108. The input 102 receives an incident
radiation beam IN and directs it toward the surface 103 of the
composite material 104. At least a portion of the radiation
reflects from the surface to form a reflected radiation beam that
is collected at the output 106 for transfer to downstream radiation
processing devices.
[0020] The composite material 104 comprises an arrangement of
electromagnetically reactive cells of small dimension (e.g., 20
percent or less) relative to a wavelength of the incident radiation
beam, and exhibits at least one of a negative effective
permeability and negative effective permittivity for at least one
frequency that is at least in a general spectral neighborhood of
the incident radiation beam IN. The modulation signal application
device 108 applies a modulation signal CTL to the composite
material 104 that alters at least one of a capacitive and inductive
property of the arrangement of electromagnetically reactive cells
such that at least one characteristic of the reflected radiation
beam is modulated according to the modulation signal CTL.
[0021] The composite material 104 can be selected from a variety of
judiciously engineered artificial materials or metamaterials having
a large population of small cells, each cell having one or more
electrical conductors, that begin to oscillate or resonate at
particular frequencies termed resonant frequencies. Resonant cells
are known in the art, and examples of two-dimensional and
three-dimensional resonant cells can be found, for example, in WO
2003/044897 A1 and U.S. Pat. No. 6,791,432 B2. Near such resonant
frequencies, although the individual response of any particular
resonant cell can be quite complicated, the aggregate behavior of
the population of resonating cells can often be described
macroscopically, as if the composite material were a continuous
material, except that the permeability term is replaced by an
effective permeability .mu..sub.eff and the permittivity term is
replaced by an effective permittivity .epsilon..sub.eff. For
particular structures and arrangements of the resonant cells, it
has been found that the propagation of the electromagnetic
radiation is consistent with negative values of the effective
permeability .mu..sub.eff and/or the effective permittivity
.epsilon..sub.eff at or near the resonant frequencies.
[0022] It has been found that externally controlled variations in
the inductive and/or capacitive properties of the resonant cells,
even relatively small controlled variations, can substantially vary
the macroscopic response of such composite materials. This allows
for external control of the effective permeability .mu..sub.eff
and/or the effective permittivity .epsilon..sub.eff, on either a
local or global basis across the composite material, and on either
a timewise static basis or timewise dynamic basis, as dictated by
the applied external controls. Examples of the application of
external controls to composite materials comprising resonant cells
can be found in one or more of the following commonly assigned
applications, each of which are incorporated by reference herein:
US 2006/0044212A1; US2006/0109540A1; U.S. Pat. No. 7,106,494; and
Ser. No. 11/285,910, Attorney Docket No. 200503281-1 filed Nov. 23,
2005.
[0023] By way of example, and not by way of limitation, the
resonant cells can be disposed on a semiconductor substrate having
an electrical carrier population that is externally controlled by
application of a control radiation beam, as described in U.S. Pat.
No. 7,106,494, supra. The presence of carriers (e.g., electrons or
holes) affects the capacitive and/or inductive properties by
amounts sufficient to alter, and optionally to destroy, the
resonance condition so that substantial and useful control of the
effective permeability .mu..sub.eff and/or the effective
permittivity .epsilon..sub.eff is achieved. By way of further
example, the resonant cells can contain optical gain elements, such
as quantum dots, that can vary the effective permeability
.mu..sub.eff and/or the effective permittivity .epsilon..sub.eff
while also providing gain for the radiation beam, as described in
Ser. No. 11/285,910, supra. By way of further example, the resonant
cells can contain split-ring conductive patterns with small
transistor circuits or electromechanical switches extended across
the gaps thereof, with electrical control signals being applied to
partially or fully short out the split-ring conductive element
across the gap, thereby varying a capacitive and/or inductive
property of the resonant cell. In the particular embodiment of
FIGS. 1A-1B, the control signal CTL is an applied to the composite
material as an optical signal. However, any of a variety of other
devices and strategies can be used to modulate the effective
permeability .mu..sub.eff and/or the effective permittivity
.epsilon..sub.eff of the composite material 104 without departing
from the scope of the present teachings.
[0024] As illustrated in FIG. 1A, when both the effective
permeability .mu..sub.eff and the effective permittivity
.epsilon..sub.eff are positive, the incident radiation beam IN will
generally reflect from the surface 103 toward the output 106 in
accordance with known reflection principles, as it would from an
ordinary surface that is fully or partially metallic. The
reflection can be specular or diffuse depending on the particular
surface characteristics, with specular reflection of smoother
surfaces at relatively shallow angles of incidence (e.g., less than
45 degrees) being more preferable as more of the energy will be
collectible at the output 106.
[0025] However, as the effective permeability .mu..sub.eff and/or
the effective permittivity .epsilon..sub.eff approach negative
values, at least some portion of the incident radiation beam IN
begins to refract into the composite material 104 and at least one
characteristic of the reflected radiation beam becomes affected,
such as intensity, phase, frequency, spectral content, or
combinations thereof. According to an embodiment, this behavior is
harnessed to achieve modulation of the incident radiation beam
through modulation of the effective permeability .mu..sub.eff
and/or the effective permittivity .epsilon..sub.eff, which in turn
are modulated by the modulation signal CTL. A rich variety of
modulation schemes are thereby provided, and the modulation can be
digital/switchable in nature (e.g., on/off, left/right, channel
1/channel 2) or can be analog in nature (e.g., by analog variations
in .mu..sub.eff and .epsilon..sub.eff in the negative and/or
positive regimes). Generally speaking, the particular type of
modulation (e.g., phase, intensity, spectral content, etc.) that is
achievable by a particular composite material can be empirically
determined without undue experimentation. Generally speaking,
affectation of the phase, intensity, spectral content, etc., will
be more pronounced for frequencies near the resonant frequency.
Such modulation can be implemented, using different resonant cell
sizes, at a variety of different frequencies ranging from the
microwave regime to the optical regime without departing from the
scope of the present teachings.
[0026] The example of FIGS. 1A-1B represents perhaps the simplest
type of modulation in which the modulation device 100 operates as
an on-off gate for a monochromatic carrier signal that corresponds
to a resonant frequency of the composite material 104. Thus, when
no control radiation is applied (FIG. 1B), the composite material
significantly negatively refracts the incident beam such that the
reflected radiation beam has a relatively low intensity (designated
more simply as OFF in FIG. 1B). When control radiation is applied
(FIG. 1A), the negatively refracting behavior of the composite
material 104 is destroyed such that the reflected radiation beam
has a relatively high intensity (designated more simply as ON in
FIG. 1A).
[0027] FIGS. 2A-2B illustrate a modulation device 200 according to
an embodiment, comprising a composite material 204 having a surface
203 receiving an incident radiation beam from an input 202.
Depending on the state of a modulation signal CTL from a modulation
signal application device 208, the composite material 204 either
reflectively directs the radiation beam toward a first output 206
when both .mu..sub.eff and .epsilon..sub.eff are positive (FIG.
2A), or refractively directs the radiation beam toward a second
output 210 when one or both of .mu..sub.eff and .epsilon..sub.eff
are negative (FIG. 2B). The modulation device 200 is therefore
operable as a switching device.
[0028] FIG. 3 illustrates a modulation device 300 according to an
embodiment and related time plots 314 and 316 of a modulation
signal and an output intensity signal, respectively. The modulation
device 300 comprises a composite material 304 having a surface 303
receiving an incident radiation beam from an input 302. The
composite material 304 reflectively directs the radiation beam
toward an output 306 such that an intensity of the reflected
radiation beam is a controlled percentage of the intensity of the
incident radiation beam that varies according to an analog value of
a modulation signal CTL from a modulation signal application device
308. The modulation device 300 is therefore operable as an analog
intensity modulator. If gain material such as a distribution of
pumped quantum dots is incorporated into the composite material
304, the controlled percentage can be greater than one hundred
percent and the modulation device 300 thus operable as a transistor
amplifier.
[0029] FIG. 4A illustrates a modulation device 400 according to an
embodiment. FIG. 4B illustrates a related frequency plot 413 of an
incident radiation beam, a related time plot 415 of a modulation
signal CTL, and related frequency spectrum plots 416 and 418 of a
reflected radiation beam corresponding to the modulation device 400
of FIG. 4A. The modulation device 400 is similar in structure to
the modulation device 300 of FIG. 3, comprising an input 402, a
composite material 404 having a surface 403, an output 406, and a
modulation signal application device 408, except that the composite
material 404 is configured and controlled such that the spectral
response is modulated (i.e., tuned) by the modulation signal CTL.
For a first time interval (which can range anywhere from
sub-milliseconds to years without departing from the scope of the
present teachings), the composite material 404 primarily reflects
for frequencies f.sub.1, f.sub.3, and f.sub.4 and primarily
refracts for frequency f.sub.2, thereby removing the frequency
f.sub.2 from the reflected radiation beam while maintaining the
frequencies f.sub.1, f.sub.3, and f.sub.4. For a second time
interval (which, again, can range anywhere from sub-milliseconds to
years) the composite material 404 primarily reflects for
frequencies f.sub.1, f.sub.2, and f.sub.4 and primarily refracts
for frequency f.sub.3, thereby removing the frequency f.sub.3 from
the reflected radiation beam while maintaining the frequencies
f.sub.1, f.sub.2, and f.sub.4. The modulation device 400 is thus
operable as a tunable drop filter.
[0030] FIG. 5 illustrates a tunable add-drop multiplexer 500
according to an embodiment that harnesses the tunable drop filter
capability of the modulation device 400 of FIG. 4A. The tunable
add-drop multiplexer 500 comprises several stages 500a, 500b, and
500c, each stage being similar to the modulation device 400 of FIG.
4A and comprising a composite material 504a, 504b, and 504c,
respectively, that is similar to the composite material 404 of FIG.
4A. The stages 500a, 500b, and 500c are placed in serial radiative
communication with each other relative to an input radiation beam
by virtue of partially coated mirrors 552, 554, and 556, which also
add the channel signals ADD1, ADD2, and ADD3 as shown. It is to be
appreciated that many other schemes for placing the stages
500a-500c in serial radiative communication and for adding channels
are within the scope of the present teachings. In operation, each
stage 500a-500c removes a respective channel DROP1, DROP2, and
DROP3 at a respective frequency from a wavelength division
multiplexed radiation beam and replaces that channel with a
respective replacement channel ADD1, ADD2, and ADD3.
Advantageously, the frequencies at which the channels are dropped
are tunable by virtue of the modulation (tuning) signals CTL1,
CTL2, and CTL3 as illustrated.
[0031] FIG. 6 illustrates a modulation device 600 according to an
embodiment and related time plots 614 and 616 of a modulation
signal and an output phase signal, respectively. The modulation
device 600 is similar in structure to the modulation device 300 of
FIG. 3, comprising an input 602, a composite material 604 having a
surface 603, an output 606, and a modulation signal application
device 608, except that the composite material 604 is configured
and controlled such that the phase of the incident radiation beam
is modulated by the modulation signal CTL. The composite material
604 reflectively directs the radiation beam toward an output 606
such that a phase of the reflected radiation beam relative to the
incident radiation beam varies according to an analog (or digital)
value of a modulation signal CTL. The modulation device 600 is
therefore operable as a phase modulator which, of course, can be
used to modulate frequency as well.
[0032] FIG. 7 illustrates a Mach-Zehnder interferometer (MZI) 702
according to an embodiment that harnesses the phase modulation
capability of the modulation device 600 of FIG. 6, comprising a
radiation splitter 711 that splits the incident radiation beam into
two substantially equal split beams and directs each split beam
along a distinct propagation path toward a respective phase
modulator 700a and 700b, each being similar to the modulation
device 600 of FIG. 6 and comprising composite materials 704a and
704b, respectively. MZI 702 further comprises a radiation combiner
713 that combines the phase-modulated split beams into an output
radiation beam. The phase modulators 700a and 700b are driven by
coordinated control signals CTL1 and CTL2, usually in a push-pull
fashion, to result in an intensity-modulated output which can be
digital or analog in nature.
[0033] FIGS. 8A-8B illustrate a modulation device 800 according to
an embodiment for different states of a modulation signal CTL. The
modulation device 800 is similar in structure to the previously
described modulation devices, comprising an input 802, a composite
material 804 having a surface 803, an output 806, and a modulation
signal application device 808, except that the composite material
804 is anisotropic such that the resonant behavior giving rise to
the negative values for .mu..sub.eff and .epsilon..sub.eff is
obtainable for certain polarizations but not others. This
polarization selective behavior can be used to achieve useful
results.
[0034] For the example of FIGS. 8A-8B, the composite material
comprises alternating layers including layers 810 of split-ring
resonator cells 807 and layers 812 of wire grids. The split-ring
resonator cells 807 are oriented to resonate when the magnetic
field H is along the z-direction, while the wire grid cells are
oriented to resonate when the electric field E is parallel to the
x-y plane. Accordingly, assuming for simplicity that the radiation
beam approaches the surface 803 at a near-glazing angle, radiation
having the polarization P2 will primarily be refracted into the
composite material for a first state of the modulation signal (FIG.
8B), and will be reflected toward the output 806 for a second state
of the modulation signal CTL (FIG. 8A). However, radiation having
the polarization P1 will tend to reflect toward the output 806
regardless of the value of the modulation signal CTL.
[0035] Stated more loosely, radiation having the polarization P2
will tend to "see" the negative values for .mu..sub.eff and
.epsilon..sub.eff while the polarization P1 will tend not to "see"
the negative values for .mu..sub.eff and .epsilon..sub.eff. This
polarization selective behavior can be used advantageously. For
example, the modulation device 800 can be operable as a
polarization-selective switch or, with a second output attached to
capture the refracted radiation, can serve as a controllably
birefringent material. Importantly, although the previously
described embodiments of FIGS. 1-7 are most easily understood in
the context of isotropic composite materials (i.e., radiation
traveling along each of the x, y, and z axes is treated the same),
and are therefore described as such without reference to
polarization for purposes of clarity, it is to be appreciated (i)
that each of the embodiments of FIGS. 1-7 can be implemented with
anisotropic composite materials as well, (ii) that the features and
advantages of polarization selectivity can be incorporated into
each such embodiment, and (iii) that the resultant devices and
methods are all within the scope of the present teachings. As a
general observation, it is to be noted that many typical
negative-index materials tend toward being anisotropic in
practice.
[0036] Whereas many alterations and modifications of the
embodiments will no doubt become apparent to a person of ordinary
skill in the art after having read the foregoing description, it is
to be understood that the particular embodiments shown and
described by way of illustration are in no way intended to be
considered limiting. By way of example, although described supra as
an electrical and/or optical signal in one or more embodiments, the
modulation signal can be mechanical, acoustic, thermal, etc.,
without departing from the scope of the present teachings. By way
of further example, the modulation signals applied to the composite
material are not limited to scalar quantities, such as single
voltages or single control beam intensities, but rather can also
comprise vector or matrix quantities representative of combined
control signals, spatial intensity distributions, or even
holographic modulation signals.
[0037] By way of still further example, although described supra as
being an optical frequency (including infrared, visible, and
ultraviolet) or microwave frequency in one or more embodiments, the
radiation beam being modulated can be at a radio frequency in
contexts such as for large-scale radio telescope arrays, or even in
the x-ray regime, without departing from the scope of the preferred
embodiments. Thus, reference to the details of the described
embodiments are not intended to limit their scope.
* * * * *