U.S. patent application number 11/444222 was filed with the patent office on 2009-06-04 for nanoparticle coupled to waveguide.
Invention is credited to Raymond G. Beausoleil, Marco Fiorentino, Charles Santori, Sean Spillane.
Application Number | 20090140275 11/444222 |
Document ID | / |
Family ID | 38801969 |
Filed Date | 2009-06-04 |
United States Patent
Application |
20090140275 |
Kind Code |
A1 |
Santori; Charles ; et
al. |
June 4, 2009 |
NANOPARTICLE COUPLED TO WAVEGUIDE
Abstract
A nanoparticle is able to emit single photons. A waveguide is
coupled to the nanoparticle and able to receive the single photons.
A backreflector is optically coupled to the waveguide and
configured to reflect the single photons toward the waveguide.
Inventors: |
Santori; Charles; (Palo
Alto, CA) ; Spillane; Sean; (Palo Alto, CA) ;
Beausoleil; Raymond G.; (Palo Alto, CA) ; Fiorentino;
Marco; (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: |
38801969 |
Appl. No.: |
11/444222 |
Filed: |
May 31, 2006 |
Current U.S.
Class: |
257/98 ;
257/E33.068; 977/774; 977/950 |
Current CPC
Class: |
G02B 6/0229 20130101;
B82Y 30/00 20130101; G02B 6/02366 20130101; B82Y 10/00 20130101;
B82Y 20/00 20130101; G02B 6/4202 20130101; G02B 6/02328 20130101;
G02B 6/423 20130101; G02B 2006/1213 20130101 |
Class at
Publication: |
257/98 ; 977/774;
257/E33.068; 977/950 |
International
Class: |
H01L 33/00 20060101
H01L033/00 |
Claims
1. A device comprising: an individually addressed nanoparticle for
emitting single photons; a photonic crystal fiber waveguide for
receiving the single photons the waveguide optically coupled to the
nanoparticle at an endface of the waveguide not treated to increase
reflection, the waveguide endface disposed adjacent to the
nanoparticle; and a single backreflector optically coupled to the
waveguide and configured to reflect at least some of the single
photons toward the waveguide, the backreflector disposed adjacent
to the nanoparticle and the waveguide endface; wherein the
nanoparticle is placed on one of the backreflector and the
waveguide.
2. The device as set forth in claim 1, wherein the nanoparticle
comprises a quantum dot.
3. The device as set forth in claim 1, wherein the nanoparticle
comprises a nanocrystal.
4. The device as set forth in claim 1, wherein the backreflector
comprises a Bragg reflector.
5-6. (canceled)
7. The device as set forth in claim 1, wherein the nanoparticle is
placed within a substrate, and the waveguide is aligned with the
nanoparticle using an alignment recess etched in the substrate.
8. (canceled)
9. The device as set forth in claim 1, wherein the nanoparticle is
joined to the backreflector.
10. The device as set forth in claim 1, wherein the nanoparticle is
joined to the waveguide.
11. The device as set forth in claim 1, wherein the nanoparticle is
positioned on the waveguide, and the backreflector is layered over
the waveguide and the nanoparticle.
12. The device as set forth in claim 1, wherein the backreflector
is at least partially transparent at an excitation frequency for
exciting the nanoparticle.
13. The device as set forth in claim 12, further comprising: an
optical fiber coupled to the backreflector, and able to direct a
pulse through the backreflector toward the nanoparticle at the
excitation frequency.
14. The device as set forth in claim 12, further comprising: a lens
optically coupled to the backreflector, and able to direct a pulse
through the backreflector toward the nanoparticle at the excitation
frequency.
15. A method for suppressing leaky modes in photon transmission,
comprising: optically coupling an individually addressed
nanoparticle to a photonic crystal fiber waveguide endface not
treated to increase reflection disposed adjacent to the
nanoparticle, and optically coupling a single backreflector to the
endface of the waveguide behind the nanoparticle and adjacent to
the nanoparticle and the waveguide endface: wherein the
nanoparticle is placed on one of the backreflector and the
waveguide.
16. The method of claim 15 wherein coupling a nanoparticle
comprises placing the nanoparticle at an airhole passage of the
waveguide.
17. The method of claim 15 further comprising: exciting the
nanoparticle to emit a single photon, reflecting the single photon
toward the waveguide, and guiding the photon through the
waveguide.
18. The method of claim 17 wherein exciting the nanoparticle
further comprises directing an optical pulse through the waveguide
toward the nanoparticle.
19. The method of claim 17 wherein exciting the nanoparticle
further comprises directing an optical pulse through the
backreflector toward the nanoparticle.
20. A device comprising: individually addressed nanoparticle
quantum photon emitting means for emitting single photons; photonic
crystal fiber photon guiding means for receiving the single
photons, the photon guiding means optically coupled to the emitting
means at an endface of the photon guiding means not treated to
increase reflection, the photon guiding means endface disposed
adjacent to the emitting means; and a single photon reflecting
means optically coupled to the photon guiding means and configured
to reflect at least some of the single photons toward the endface
of the photon guiding means, the photon reflecting means disposed
adjacent to the emitting means and the photon guiding means
endface; wherein the emitting means is placed on one of the photon
reflecting means and the photon guiding means.
21. A device comprising: an individually addressed nanoparticle for
emitting single photons; a photonic crystal fiber waveguide coupled
to the nanoparticle at an endface of the waveguide not treated to
increase reflection and able to receive the single photons; and a
backreflector optically coupled to the waveguide and configured to
reflect at least some of the single photons toward the waveguide;
wherein the nanoparticle is positioned on the waveguide, and the
backreflector is layered over the waveguide and the nanoparticle.
Description
BACKGROUND
[0001] Nanotechnology and quantum information technology are
emerging branches of science that involve the design of extremely
small electronic and optical circuits that are built at the
molecular level. Traditional opto-electronic circuits are
fabricated using semiconductor wafers to form chips. Circuits are
etched into the semiconductor wafers or chips. The etching process
removes material from certain regions or layers of the chips. In
contrast, nanotechnology generally deals with devices built upward
by adding material, often a single atom at a time. This technique
results in a device where every particle could have a purpose.
Thus, extremely small devices, much smaller than devices formed by
etching, are possible. For example, a logic gate could be
constructed from only a few atoms. An electrical conductor can be
built from a "nanowire" that is a single atom thick. A bit of data
could be represented by the presence or absence of a single
proton.
[0002] Quantum information technology provides a new avenue for
creating smaller and potentially more powerful computers.
Scientific theories such as quantum superposition and quantum
entanglement are now being used to explore the possibility of
creating smaller, more powerful computing devices. The development
in this field has led to the use of light particles, or photons, to
convey information. Light can be polarized into various states
(e.g., horizontally polarized, vertically polarized) and can also
exist in various momentum and frequency states. Exploiting these
properties allows a single photon to represent a single quantum bit
of information.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] For the purpose of illustrating the invention, there is
shown in the drawings one exemplary implementation; however, it is
understood that this invention is not limited to the precise
arrangements and instrumentalities shown.
[0004] FIG. 1 illustrates an exploded view of a device comprising
an exemplary nanoparticle coupled to a waveguide and a
backreflector in accordance with an embodiment of the
invention.
[0005] FIG. 2 is a schematic drawing of an exemplary nanoparticle
coupled to a waveguide and a backreflector in accordance with a
further embodiment of the invention.
[0006] FIG. 3 is a schematic drawing of an exemplary nanoparticle
embedded in two-dimensional photonic crystal, coupled to a
waveguide and a backreflector in accordance with an embodiment of
the invention.
[0007] FIG. 4 is a schematic drawing of an exploded view of a
device comprising an exemplary nanoparticle, waveguide and
backreflector coupled to a single-mode optical fiber in accordance
with an exemplary embodiment of the invention.
[0008] FIG. 5 is a schematic drawing of an exploded view of a
device comprising an exemplary nanoparticle, waveguide and
backreflector coupled to a lens in accordance with an exemplary
embodiment of the invention.
DETAILED DESCRIPTION
[0009] The use of quantum bits provides researchers with
significant potential advancements in computing technology. The
ability to understand and utilize the theories of photon
superposition and entanglement to generate information is a new
field around which there is significant interest. However, one
important issue that surrounds potential use of photons as quantum
bits is the need to generate a photon on demand at the location
where it is desired. A second important issue is the ability to
detect and capture the photons; that is, to efficiently collect
light emitted from the photon source. Both of the foregoing
attributes are useful in creating single-photon sources and
nonlinear devices. Some exemplary devices and techniques for
addressing these needs are described in copending and commonly
assigned U.S. patent application Ser. No. 11/149,511, entitled
"Fiber-Coupled Single Photon Source" (Attorney Docket No.
200406613-1), filed Jun. 10, 2005, the disclosure of which hereby
is incorporated by reference herein.
[0010] FIG. 1 illustrates an exploded view of a device according to
an embodiment of the invention, comprising an exemplary
nanoparticle 110 coupled to a waveguide 150 and a backreflector
130. Nanoparticle 110 is able to emit a photon on demand, and thus
can serve as a photon source.
[0011] An exemplary nanoparticle 110 is a particle with dimensions
smaller than the wavelength of light, that can be made to emit
photons at a desired wavelength at which a device using an
embodiment of the invention will operate. Typically, nanoparticle
110 is approximately 10-100 nm in diameter. Generally, for a
nanoparticle 110 to be useful in a device according to an
embodiment of the invention, the nanoparticle 110 must provide a
single quantum system that can be addressed optically; or if there
are multiple quantum systems, it must be possible to address them
individually through frequency selection.
[0012] In some embodiments, the nanoparticle 110 is grown in a
semiconductor substrate. Group IV, Group III-V, or Group II-VI
semiconductor materials may be used. A typical material may
comprise Si or GaAs.
[0013] An exemplary nanoparticle 110 can be joined to either the
backreflector 130 or to the waveguide 150, or to both. For example,
the nanoparticle 110 can be placed or grown on the backreflector
130, or can be placed or grown on the end of waveguide 150.
Illustrative examples of a suitable nanoparticle 110 include
nanocrystals such as a diamond nanocrystal with nitrogen vacancy
(NV) center, and a semiconductor nanocrystal. In a further
embodiment, nanoparticle 110 can comprise an electrically driven or
optically driven quantum dot. Quantum dots are capable of
generating a single photon when excited by an electrical charge or
an optical laser. Further examples of nanoparticle 110 include a
self-assembled quantum dot placed or grown on the backreflector 130
or in a micropillar on the backreflector 130.
[0014] In the illustrated embodiment, the waveguide 150 is photonic
crystal fiber, which is capable of suppressing leaky modes.
Photonic crystal fiber, referred to as "holey" fiber, comprises a
plurality of airhole passages 160 residing within the fiber.
Examples of suitable photonic crystal fiber may be either solid or
hollow core. In other embodiments, the waveguide 150 can be a
suitable hollow-core bandgap fiber capable of suppressing leaky
modes, e.g., omniguide fiber.
[0015] In one exemplary embodiment, nanoparticle 110 can be
positioned on an end of waveguide 150, such as by growing or
placing the nanoparticle 110 on the end of waveguide 150, and the
backreflector 130 (e.g., a distributed Bragg reflector) can be
grown over the nanoparticle 110 and the end of waveguide 150, thus
forming a layer to seal the nanoparticle 110 to the end of
waveguide 150. In embodiments of the invention, the nanoparticle
110 may be, but need not be, perfectly centered on the end of
waveguide 150. In some embodiments, nanoparticle 110 may be coupled
to an airhole passage 160, such as at an inner edge of the central
airhole passage 160. In some embodiments, nanoparticle 110 is fully
outside of airhole passage 160; in other embodiments, nanoparticle
110 may enter airhole passage 160.
[0016] Backreflector 130 is configured to reflect photons toward
the waveguide 150. An exemplary backreflector 130 comprises a Bragg
reflector (e.g., a distributed Bragg reflector). Bragg reflectors
are known within the art and are used in applications that require
high reflectivity. In some embodiments, backreflector 130 is a
frequency-selective mirror. In further embodiments, backreflector
130 comprises a metallic reflector, e.g., a metallic film.
[0017] To maintain alignment, the waveguide 150, nanoparticle 110,
and backreflector 130 may in some embodiments be secured in place;
for example, using known techniques, such as using an adhesive. The
backreflector 130, in some embodiments, can be mechanically coupled
to the end of waveguide 150, e.g., using glue or epoxy having a
suitably low refractive index.
[0018] The nanoparticle 110 can be triggered to emit a photon; for
example, through pulsed optical excitation, in which the
nanoparticle 110 is optically pumped using a pulse with an
excitation wavelength that is shorter than the emission wavelength
of the nanoparticle 110. In some exemplary embodiments, the
excitation pulse can enter through the backreflector 130 if the
backreflector 130 is partially transparent at the excitation
wavelength; for example, as illustrated in FIGS. 4 and 5.
[0019] In further embodiments, the excitation pulse can enter
through the side of the waveguide 150, or directly through the
guided mode of the waveguide 150 (e.g., from a second end of the
waveguide 150 that is distal to nanoparticle 110). In some
embodiments, if the excitation wavelength is different from the
spontaneous emission wavelength of the nanoparticle 110, spectral
filtering can be applied later to separate the resulting emitted
photon from the backreflected or scattered excitation pulse. In
further embodiments, excitation pulses can be timed or gated to
distinguish the resulting emitted photon from the backreflected or
scattered excitation pulse.
[0020] Alternatively, a device according to an embodiment of the
invention can serve as a nonlinear device if one or more input
pulses with appropriate temporal profiles are resonant with optical
transitions of the nanoparticle 110. The pulses then interact with
each other through the nonlinearity provided by the nanoparticle
110, allowing for switching or entanglement in the reflected
pulses.
[0021] Referring to FIG. 2, an alternative embodiment for enabling
coupling of a nanoparticle 110 to a waveguide 150 is shown. In some
embodiments, the nanoparticle 110 can be grown in a substrate 200.
Nanoparticle 110 is positioned such that it aligns with or extends
into an airhole passage 160 of the waveguide 150, such as the
central airhole passage 160.
[0022] The airhole passages 160 extend through the waveguide 150,
from a hole at the end of the waveguide 150 coupled to nanoparticle
110 to a corresponding hole at the opposite end of the waveguide
150; however, for clarity of illustration, the intervening portions
of airhole passages 160 are not depicted in FIG. 2.
[0023] Maintaining the desired mechanical positioning relationship
between nanoparticle 110 and waveguide 150 can be difficult. To
overcome this difficulty, the waveguide 150 can be precisely
positioned on the surface of a substrate 200. In some embodiments,
the nanoparticle 110 is grown within a substrate 200 such as
silicon. An indexing hole 140, into which the waveguide 150 can be
positioned, is etched in the substrate 200 surrounding the
nanoparticle 110. By accurately indexing the waveguide 150 to the
location of the nanoparticle 110, the mechanical positioning
between the nanoparticle 110 and the waveguide 150 can be better
maintained and, as a result, the probability of capturing a
generated photon is increased. To maintain the alignment, the
waveguide 150 may be secured in place; for example, by using known
techniques, such as using an adhesive.
[0024] The backreflector 130 is placed or grown beneath the
indexing hole 140. For example, backreflector 130 can comprise a
Bragg reflector at the bottom of the indexing hole 140. In some
embodiments, backreflector 130 can be positioned on a lower side
201 of substrate 200, opposite the end of waveguide 150.
[0025] In the illustrated embodiment, the waveguide 150 is
positioned within the indexing hole 140 such that the nanoparticle
110 extends into a selected airhole passage 160 contained within
the waveguide 150. Using this configuration, the nanoparticle 110
can be precisely positioned relative to the waveguide 150.
Additionally, the coupling efficiency can be improved by means of
mode-matching between the dipole radiation of the nanoparticle 110
and the guided mode of the waveguide 150, coupled with the fact
that photonic crystal fiber typically has a larger numerical
aperture than conventional single mode fiber, such as is commonly
used in the telecommunications industry (e.g., single mode fiber
typically has a numerical aperture ranging from approximately
0.2-0.5 while photonic crystal fiber typically has a numerical
aperture ranging from approximately 0.7-0.9).
[0026] In some instances, the direct coupling process may be
improved by using a configuration as shown in FIG. 3. A
nanoparticle 110 may be embedded into a substrate 300 that
comprises a two dimensional photonic crystal 302. Two dimensional
photonic crystals can provide Bragg reflections and large index
dispersion in a two dimensional plane. At each interface within the
crystal, light is partly reflected and partly transmitted. By using
this property of photonic crystals, the photon emitted by the
nanoparticle 110 can be better mode matched to the fundamental mode
of a waveguide 150. A pattern of holes 309 may be etched into the
two dimensional photonic crystal, which may be used for aligning
the waveguide 150 in a precise mechanical position relative to the
nanoparticle 110.
[0027] Backreflector 130 is placed or grown beneath one or more of
the holes 309. For example, backreflector 130 can comprise a Bragg
reflector at the bottom of a hole 309 that contains nanoparticle
110. In some embodiments, backreflector 130 can be positioned on a
lower side 311 of substrate 300, opposite the end of waveguide
150.
[0028] By embedding the nanoparticle 110 in the two dimensional
photonic crystal 302, radiation by the nanoparticle 110 into modes
outside of the waveguide 150 is suppressed. Further, by embedding
the nanoparticle 110 into the two dimensional photonic crystal
substrate 302, such as glass coated with a InGaAs or Si/SiO.sub.2
coating, radiation is prevented from emanating from nanoparticle
110 in most directions. A waveguide 150 can be positioned in close
proximity (e.g., less than one micron) to the nanoparticle 110 to
capture a generated photon.
[0029] FIG. 4 illustrates an exploded view of a device comprising
an exemplary nanoparticle 110, waveguide 150 and backreflector 130
coupled to a single-mode optical fiber 410 in accordance with an
exemplary embodiment of the invention. To provide optical pumping
or optical excitation of the nanoparticle 110 in an embodiment of
the invention, a single-mode optical fiber 410 of arbitrary length
is coupled to a photon source (not shown) at a source end 411.
Photons are transmitted through fiber 410 from the source end 411
to a destination end 412. The fiber 410 can be crafted to
approximately mode-match the mode of the waveguide 150. The fiber
410 may in some embodiments be coupled (e.g., joined or spliced) to
backreflector 130 and waveguide 150; for example, by using known
techniques, such as using an adhesive.
[0030] Backreflector 130 is configured to reflect photons into
waveguide 150, and is at least partially transparent at an
excitation wavelength, so that photons can be transmitted at the
excitation wavelength from the destination end 412 of fiber 410 to
the nanoparticle 110. In the illustrated embodiment, the
nanoparticle 110 can be optically pumped by transmitting a pulse
through the fiber 410 to the nanoparticle 110 with an excitation
wavelength that is shorter than the emission wavelength of the
nanoparticle 110. In some embodiments, the backreflector 130 is a
frequency-selective mirror. In other embodiments, backreflector 130
comprises a metallic reflector. In an illustrative example, a
metallic backreflector 130 may be less than one percent (1%)
transparent at the excitation frequency, but a sufficiently strong
pulse can be provided through fiber 410 that the portion of the
pulse that passes through the metallic backreflector 130 is
sufficient to excite the nanoparticle 110.
[0031] FIG. 5 illustrates an exploded view of a device comprising
an exemplary nanoparticle 110, waveguide 150 and backreflector 130
optically coupled to a lens 520 in accordance with an exemplary
embodiment of the invention. To provide optical pumping or optical
excitation of the nanoparticle 110 in an embodiment of the
invention, the lens 520 is configured to focus an optical beam 510
on the nanoparticle 110. The lens 520, in some embodiments, can be
mounted in an objective (not shown). In further embodiments, the
lens 520 can be part of an optical train or system that includes
multiple lenses, mirrors, and the like for directing and focusing
the beam 510 on the nanoparticle 110.
[0032] Backreflector 130 is configured to reflect photons into
waveguide 150, and is at least partially transparent at an
excitation wavelength, so that photons of the optical beam 510 can
be transmitted at the excitation wavelength through the
backreflector 130 to the nanoparticle 110. In the illustrated
embodiment, the nanoparticle 110 can be optically pumped by
transmitting a pulse through the lens 520 to the nanoparticle 110
with an excitation wavelength that is shorter than the emission
wavelength of the nanoparticle 110. In some embodiments, the
backreflector 130 is a frequency-selective mirror. In other
embodiments, backreflector 130 comprises a metallic reflector. In
an illustrative example, a metallic backreflector 130 may be less
than one percent (1%) transparent at the excitation frequency, but
a sufficiently strong pulse can be transmitted through lens 520
that the portion of the pulse that passes through the metallic
backreflector 130 is sufficient to excite the nanoparticle 110.
[0033] Although several embodiments have been described, features
from different embodiments may be combined. For example, either the
fiber 410 shown in FIG. 4 or the lens 520 shown in FIG. 5 may be
positioned on the side of the backreflector 130 shown in FIGS. 1-3
that is opposite the nanoparticle 110. For example, the lens 520
shown in FIG. 5 may be used to direct optical beam 510 onto the
nanoparticle 110 shown in FIGS. 1-3 from a position, such as a side
position, where the optical beam 510 does not pass through the
backreflector 130 shown in FIGS. 1-3. A variety of modifications to
the embodiments described will be apparent to those skilled in the
art from the disclosure provided herein. Thus, the present
invention may be embodied in other specific forms without departing
from the spirit or essential attributes thereof and, accordingly,
reference should be made to the appended claims, rather than to the
foregoing specification, as indicating the scope of the
invention.
* * * * *