Massachusetts Institute of Technology
`Ex. 2001
`Part 4 of 4
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`(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT‘ COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property
`_
`_
`Orgamzatton
`lntemational Bureau
`
`(43) International Publication Date
`24 February 2005 (24.02.2005)
`
`\
`
`:
`“,4”-’
`(‘fl
`
`t;
`
`lllllllllllllllllllillillllilllllllllllllllIlillllllllllllllllllflllllillllllllllllllllflll
`
`(10) International Publication Number
`WO 2005101795] A2
`
`(51) International Patent CIasslllcatlon7:
`
`HOIL
`
`(21) Intemntlonnl Application Ntnnber:
`PCT/llS2003/024245
`
`(74) Agent: LIU. Cull‘. Z.; Cooley Godward LLP. 30(1) El
`Camino Real. Five Palo Alto Square, Palo Alto. CA 94306-
`2155 (US).
`
`(22) International Filing Date:
`
`I August 2003 (01.08.2003)
`
`(25) Filing Language:
`
`(26) Publication Language:
`
`English
`
`English
`
`(30) Priority Data:
`I001 [.991
`l0f2l2.005
`l0/212.001
`l0/212.004
`
`2 August 2002 (02.08.2002)
`2 August 2002 (02.08.2002)
`2 August 2002 (02.03.2002)
`2 August 2002 (0’2.08.?.002)
`
`US
`US
`US
`US
`
`Applicant: ULTRADUTS, INC. [US/US]; 486lI Warm
`Springs Blvd.. Fremont. CA 94539 (US).
`
`Inventors: LEE. Howard, Wing, l-loon; 45176 Imnaha
`Court. Fremont. CA 94539 (US). CI-IIN. Alan, Hap‘. I76.
`Brandt Court. Milpitas. CA 95035 (US). PFENNINGER,
`William, Matthew; 3214 Belmont Terrace. Fremont, CA
`94539 (US). KESHAVARZ, Majtd; I688 Omhard Way.
`Pleasanton. CA 94566 (US).
`
`Designated States (national): AE. AG. AL. AM. AT. AU.
`AZ. BA. BB. BG, BR. BY, BZ. CA, CH. CN. CO. CR. CU,
`CZ. DE. DK, DM. DZ. EC. EE. ES, Fl. GB. GD. GE. GH.
`GM, HR. HU. ID. IL. IN. IS. JP. KE. KG. KP. KR. KZ. LC.
`LK. LR. LS. LT, LU. LV, MA. MD. MG, MK, MN. MW.
`MX, MZ. NI, NO. NZ. OM. PG. PH, PL. PI‘. RO, RU, SC.
`SD. SE. SG. SK, SL. SY. TJ. TM, TN. TR. T1‘. TZ. UA.
`UG. UZ. VC. VN. YU. ZA. ZM. ZW.
`
`Designated States (regional): ARIPO patent (GH. GM.
`KE. LS. MW, MZ. SD. SL. SZ. TZ. UG. ZM. ZW).
`Eurasian patent (AM. AZ. BY, KG. KZ, MD, RU. TJ. TM).
`[European patent (AT. BE. BG, CH. CY. CZ. DE. DK. BE.
`ES. I71. FR. GB. GR. HU.
`I13. IT. LU. MC. NL. PT. RO.
`SE. SI. SK. TR). OAPI patent (BF. BJ. CF. CG. CI. CM.
`GA, GN. GQ. Gw, ML. MR. NE. SN. TD. TG).
`
`Published:
`without intentatianal search repon and to be republished
`upon receipt of that report
`
`For rwa-letter code: and other abbreviations. refer to the "Guid-
`ance Nate: on Code: and Abbreviations" appearing at the begin-
`ning of each regular issue ofthe PCT Gazette.
`
`(54) Title: QUANTUM DOTS. NANOCOMPOSITE MATERIALS WITH QUANTUM |')(7l‘S. OPTICAI. DEVICES WITH
`QUANTUM DOTS. AND RELATED FABRICATION METHODS
`
`AIII
`7) Abstract: The invention relates to quantum dots. nanncomposite materials with quantum dots. optical devices with quantum
`dots. and related fabrication methods. In one embodiment. a quantum dot comprises a core including a semiconductor material Y
`
`N ¢ 1
`
`-1
`In
`Ox
`l\
`V-1
`o§
`tn
`
`o 2
`
`0
`
`0 selected from the group consisting of Si and (Be. The quantum dot also comprises a shell surrounding the core. The quantum dot
`is substantially defect free such that the quantum dot exhibits photnluminescence with a quantum cfficiency that is greater than 10
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`QUANTUM DOTS, NANOCOMPOSITE MATERIALS VVITII
`
`QUANTUM DOTS, OPTICAL DEVICES WITH QUANTUM DOTS, AND
`
`RELATED FABRICATION METHODS
`
`FIELD OF THE INVENTION
`
`[0001] The invention relates generally to quantum dots. More particularly,
`
`the invention relates to quantum dots, nanocomposite materials with quantum dots,
`
`optical devices with quantum dots, and related fabrication methods.
`
`BACKGROUND OF THE INVENTION
`
`[0002] As telecommunication networks continue to expand their need for
`
`bandwidth, it is becoming increasingly necessary to introduce new technologies to
`
`keep up with growing demands. These technologies should not only facilitate the
`
`need for bandwidth but also be easily incorporated into today’s network
`
`infrastructure. At the same time, they should be flexible and versatile enough to lit
`
`the requirements of the future. While current telecommunication systems comprise a
`
`combination of electronic and optical data§transrnission, there is pressure to move
`
`towards all-optical networks due to the increased bandwidth provided by high bit-
`
`rates and parallel transmission through wavelength division multiplexing.
`
`[0003] Currently, optical networks use light for much of the transmission of
`
`data between nodes in an optical circuit. Optical cross-connects function as switches
`
`in these nodes by routing signals arriving at one input-port to one of a variety of
`
`output-ports. Most current optical cross-connect systems comprise high-speed
`
`electronic cores, which are complex, cumbersome, and expensive. These switches
`
`typically require a light signal to be translated into an electronic signal, which is
`
`switched or routed to an output-port before being reeonverted to a light signal. The
`
`complexity,
`
`size, and expense of such optical-to-electronic~to-optical
`
`(OEO)
`
`components become even more problematic with higher bit-rates and port counts,
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`even as the cost of electronic components decreases, due to cross-talk and RF
`
`transport issues.
`
`[0004] 0130 devices are typically the rate-limiting component in an optical
`network. As such, many options are being considered to reduce the need for both
`
`OEO conversions, as well as electronic-signal processing in optical network
`
`components. This has lead to emphasis being placed on the development of “all~
`
`optical” switching technology, in which optical signals passing through a switch are
`diverted to the appropriate destination without being converted to electronic signals.
`
`[0005] For most current applications, electronically controlled optical cross-
`
`connects with optical-cores can be used as an all-optical switch.
`
`In these devices,
`
`light routing does not require OEO conversion, but operation of the switch is
`
`electronically controlled.
`
`The various all-optical switching technologies that
`
`currently support such systems include electromechanical switches (e.g., MBMS or
`bulk optics), tl1ermo~optic switches (e.g., phase shifi, capillary, or “bubble” , and
`
`In addition, a variety of
`electro-optic switches (e.g., LiNl>O3 or liquid crystal).
`nonlinear optical switches (e.g., semiconductor optical amplifiers) use a light beam,
`
`rather than electronics, to operate the switch.
`
`[0006] Many all-optical switching technologies are relatively slow and are
`
`therefore generally limited to static configuration control. For example, applications
`such as basic fiber/wavelength routing, provisioning, and restoration typically
`
`require switching speeds around lms. These relatively slow all-optical switches,
`
`however, are generally inadequate for fast switching applications such as dynamic
`
`packet switching (~lns), optical modulation (~ 100 ps), header reading in packet
`
`switched networks
`
`(< 25 ps), and all-optical data-processing (<lps).
`
`[0007] Currently, devices based on electric field-induced optical changes,
`
`such as the electro—optic effect (a xm effect) and electro-absorption (a 7;“) effect) are
`
`utilized for optical modulation and switching. However, these devices are rapidly
`
`approaching their speed limits, as they rely on fast electronic signals in order to
`
`perform optical processing or modulation, and these electronic signals suffer
`
`increasingly greater losses due to the fundamental limitations of high-speed electrical
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`propagation. Devices based on nonlinear optical phenomena, such as cross-gain
`
`modulation (XGM) in semiconductor optical amplifiers, 762’ based phenomena (e.g.,
`
`difference-frequency mixing (DFM)), and xm (or Kerr) based phenomena (e.g.,
`
`cross-phase modulation (XPM) and four-wave mixing ('FWM)), have the potential to
`
`switch at rates required for packet-switching, optical data processing, and other
`
`future high-speed switching applications. Devices based on such phenomena have
`the potential (depending on the mechanism) for switching speeds approaching‘ (and
`even exceeding) ten terabits per second (10 Tbit/s), or 10 nillioii bits per second. Of
`
`-
`
`these nonlinear optical phenomena, )6” based phenomena have the most flexibility
`
`but currently suffer from a lack of practical materials with both high nonlinearity and
`
`relatively low loss.
`
`[0008] Research involving the development of 75(3) based all-optical devices
`
`has been extensively pursued since the mid-1980s and has primarily focused on
`
`silica fiber-based devices. This is due to the relatively large figure-of-merit (FOM)
`
`for nonlinear optical switching for silica. There are many practical definitions of a
`
`FOM that take into account the many parameters that can be important and relevant
`
`to all-optical switching. One example of such a FOM is defined as -13% , where An
`:
`a -
`
`is the induced refractive index change, a is the linear and nonlinear absorption
`
`coefficient, and 1: is the response time of the material. For this FOM, which is
`
`particularly relevant for resonant optical nonlinearities where light absorption is
`
`used,
`
`the larger the FOM, the better will be the performance of the all—optical
`
`switching. A definition of a FOM useful for nonresonant optical nonlinearities,
`
`Where ideally no or little light absorption occurs, is 27/,0/1, where 7 is the nonlinear
`
`index of refraction, Bis the two-photon absorption coefficient, and 7» is the
`
`wavelength of operafion.
`
`In this case, usefiil all-optical switching typically occurs
`
`when FOM>1.
`
`Due to the low linear and nonlinear
`
`losses of light at
`
`telecommunication wavelengths in silica, the FOM for silica is adequate even though
`
`An and y (Which are related to Re[x_(3).m]) are small.
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`[0009] Many all-optical switching devices have been demonstrated using
`
`silica fiber (e.g., nonlinear directional couplers, nonlinear optical loop mirrors, and
`
`soliton-based switches). Due to the small 7 of silica, however, impractical fiber
`
`lengths
`
`(~1000 kin) are required for
`
`these devices
`
`to operate at
`
`typical
`
`telecommunication powers (~ 10 mW). As a result, there is a great deal of interest in
`
`developing materials with both a large FOM and a large 7 to reduce overall device
`
`sizes and latency. For certain applications, device sizes ~l mm or less are desirable
`
`for integration of multiple devices and to provide insensitivity to temperature
`
`fluctuations and manufacturing fluctuations
`
`(e.g.,
`
`tight
`
`tolerance over
`
`long
`
`_ distances). In addition, low latency is needed as the data rates increase.
`
`[0010]
`
`In addition to large nonlinearities with large FOMs, it is desirable that
`
`commercial optical switching components are low cost and compatible with high-
`
`throughput automated fabrication. Historically, semiconductor processing, used to
`
`make microprocessor chips, has been one of the most cost-efieetive and automated
`
`processes for miniaturization. While this technology is extremely advanced in the
`
`field of microelectronics, it is still in its infancy with respect to optics. For instance,
`for xm based devices, crystalline L1NiO3 carmot be arbitrarily inserted within a
`
`waveguide created by these techniques.
`
`In addition, polymeric nonlinear materials,
`
`which are more easily processed, typically have values for 7;“) that are too low for
`
`efficient switching.
`
`[0011] Presently, there are a variety of approaches being pursued to reduce‘
`
`the size of x“) based all-optical switches. Approaches being considered include
`
`using semiconductor optical amplifiers (SOAs), manufacturing photonic bandgap
`
`structures with nonlinear materials, enhancing nonresonant optical nonlinearities
`using local field effects, and developing new crystalline materials and polymeric
`
`materials with high optical nonlinearities.
`
`[0012] While proof-of-concept for all-optical switches based on SOAs has
`
`been shown, problems with amplified spontaneous emission buildup currently make
`
`cascading many of these switches problematic.
`
`In addition, the materials used for
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`SOAs (typically Inl’) are expensive and create inherent difiiculties with coupling to
`standard silica fibers and waveguides. Photonic bandgap materials are another
`
`promising approach, but manufacturing using the previously proposed materials is
`still beyond current practical capabilities. While enhancing nonlinearities using local
`
`field effects is an interesting approach, enhancement factors of only ~ 10x have been
`
`achieved to date. Finally, new nonlinear crystalline materials have been developed
`
`(e.g. periodically poled LiNbO3 and p-toluene sulphonate (PTS)) but are typically
`expensive and difficult to princess, making incorporation into waveguide devices
`problematic. Nonlinear polymers, with more appealing mechanical properties, have
`also been developed, but problems such as kinks in the polymer chains can limit the
`
`maximum nonlinearity to a value still unsuitable for practical all-optical applications.
`
`In cases where highly nonlinear polymers have been produced (e.g., polyacetylene),
`
`many of the appealing mechanical properties are lost, creating problems similar to
`
`those found in crystalline materials.
`[0013]
`In addition to high nonlinearity and processability, nonlinear
`
`materials desirably should also be low-loss in the wavelength range~of—interest (e.g.,
`
`from absorption or scattering). These materials desirably should also have a linear
`index of refraction that is compatible with the specific architecture of the device in
`
`which they are to be used (e.g., a nonlinear waveguide core should have an index of
`
`refraction higher than the cladding surrounding it). As such, it has been extremely
`
`difficult
`
`to find a practical material" that
`
`simultaneously satisfies various
`
`requirements for a commercial xm based nonlinear device.
`
`[0014] An ideal 75°’ based nonlinear optical material should have a number
`
`of characteristics, which can include the following:
`1.
`Large Re[x(3);ju]
`in the wavelength range-of-interest (Re[x‘3)m,] is directly
`
`related to An and 7).
`
`Low optical losses from single- and multi—photon absorption and/or resonant
`
`and nonresonant scattering in the wavelength range-of-interest.
`
`Ideally, the
`
`photon energies corresponding to the wavelength range-of-interest are such that
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`the two-photon absorption threshold is not met (i.e., the sum of the two photon
`
`energies are lower than the resonance energy), so that two-photon absorption
`
`and higher multi~photon absorptions are negligible.
`
`A rnulti-photon transition near the wavelength range-of-interest such that
`
`resonant and near resonant enhancement of ac“) occurs (but ideally no or little
`
`rnulti—absorption occurs).
`
`A precisely selected linear index of refraction compatible with the desired
`application (e.g., waveguides) and intended device architecture.
`Physical and chemical compatibility with the specific device architecture and
`
`materials with which the material will be used.
`
`The ability to be processed for incorporation into optical devices.
`
`Low cost oflrnanufacturing and incorporating the material.
`[0015] While many materials may have one or more of these desirable
`
`characteristics, at present, no single material comprises a sufficient number of these
`
`. characteristics required for an optimal xm based optical switch.
`
`In fact, besides
`
`SOAs, no commercial devices are currently available, primarily due to a lack of
`
`appropriate nonlinear optical materials.
`
`[0016] A candidate for an appropriate nonlinear optical material
`
`is one
`
`formed using quantum dots. Over the past several years,
`
`there has been an
`
`increasing interest in exploiting the extraordinary properties associated with quantum
`
`dots. As a result of quantum confinement effects, properties of quantum dots can
`
`difier fiom corresponding bulk values. These quantum confinement effects arise
`
`fiom confinement of electrons and holes along three dimensions. For instance,
`
`quantum confinement effects can lead to an increase in energy gap as the size of the
`
`quantum dots is decreased. Consequently, as the size of the quantum dots is
`
`decreased, light emitted by the quantum dots is shifted towards higher energies or
`
`shorter wavelengths. By controlling the size of the quantum dots as well as the
`
`material forming the quantum dots, properties of the quantum dots can be tuned for a
`
`specific applicafion.
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`[0017] Previous attempts at forming quantum dots have largely focused on
`quantum dots of direct band gap semiconductor materials, such as Group II-VI
`
`semiconductor materials.
`
`In contrast
`
`to such direct band gap semiconductor
`
`materials, Group IV semiconductor materials such as Si and Ge have energy gaps,
`
`chemical properties, and other properties that render them more desirable for a
`
`variety of applications. However, previous attempts at forming quantum dots of Si
`
`or Ge have generally sufiered from a number of shortcomings.
`
`In particular,
`
`formation of quantum dots of Si or Ge sometimes involved extreme conditions of
`
`temperature and pressure while suffering from low yields and lack of reproducibility.
`
`And, quantum dots that were produced were generally incapable of exhibiting
`
`adequate levels of photoluminescence that can be tuned over a broad spectral range.
`
`Also, previous attempts have generally been unsuccessfulin producing quantum dots
`
`of Si or Ge that are sufiiciently stable under ambient conditions or that can be made
`
`sufliciently soluble in a variety of matrix materials.
`[0018]
`It is against this background that a need arose to develop the quantum
`
`dots, nanocomposite materials, and optical devices described herein.
`
`SUMMARY OF THE INVENTION
`
`[0019]
`
`In one innovative aspect, the invention relates to a quantum dot.
`
`In
`
`one embodiment,
`
`the quantum dot comprises a core including a semiconductor
`
`material Y selected from the group consisting of Si and Ge. The quantum dot also
`comprises a shell surrounding the core. The quantum dot is substantially defect flee
`
`such that the quantum dot exhibits photoluminescence with a quantum efficiency
`
`that is geater than 10 percent.
`
`[0020]
`
`In another embodiment, the quantum dot comprises a core including a
`
`semiconductor material Y selected from the group consisting of Si and Ge. The
`
`quantum dot also comprises a ligand layer surrounding the core. The ligand layer
`includes a plurality of surface ligands. The quantum dot exhibits photoluminescence
`
`with a quantum efficiency that is greater than 10 percent.
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`[0021]
`
`In another innovafive aspect, the invention relates to a nanocomposite
`
`material.
`
`In one embodiment, the nanocomposite material comprises a plurality of
`
`quantum dots. The plurality of quantum dots includes a semiconductor material Y
`
`selected from the group consisting of Si and Ge, and at least one quantum dot of the
`
`plurality of quantum dots exhibits photoluminescence with a quantum efliciency that
`
`is greater than 10 percent. The nanocomposite material also comprises a plurality of
`
`molecules-coupling the plurality of quantum dots to form one of a linear array, a
`
`two-dimensional array, and a three-dimensional array.
`
`[0022]
`
`In another embodiment,
`
`the nanocomposite material comprises a
`
`plurality of quantum dots arranged in one of a two-dimensional array and a three-
`
`dimensional array.
`
`‘The plurality of quantum dots includes a semiconductor material
`
`Y selected from the group consisting of Si and Ge, and at least one quantum dot of
`
`the plurality of quantum dots exhibits photoluminescence with a quantum efficiency
`
`that is greater than 10 percent.
`
`[0023]
`
`In a further innovative aspect, the invention relates to an optical
`
`device.
`
`In one embodiment, the optical device comprises a waveguide core and a
`
`nanocomposite material optically coupled to the waveguide core.
`
`The
`
`nanocomposite material includes a plurality of quantum dots. A quantum dot of the
`
`plurality of quantum dots includes a core that includes a semiconductor material
`
`selected from the group consisting of Si and Ge, and the quantum dot exhibits
`
`photoluminescence with a quantum efficiency that is greater than 10 percent. The
`nanocomposite material has a nonlinear index of refiaction 7 that is at least 109
`
`‘cm:/W when irradiated with an activation light having a wavelength 2. between
`
`approximately 3 it 10's cm and 2 X 10" cm.
`
`[0024]
`
`In another embodiment, the optical device comprises a waveguide
`
`core including a portion formed of a nanocomposite material. The nanocomposite
`material includes a matrix material and a plurality of quantum dotgdispersed in the
`
`matrix material. A quantum dot of the plurality of quantum dots includes a core that
`
`includes a semiconductor material selected from the group consisting of Si and Ge.
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`The quantum dot is substantially defect free such that the quantum dot exhibits
`
`photoluminescence with a quantum efficiency that is greater than 10 percent.
`
`[0025]
`
`In a further embodiment, the optical device comprises a film formed
`
`of a nanocomposite material. The nanocomposite material includes a plurality of .
`
`quantum dots. A quantum dot of the plurality of quantum dots includes a core that
`
`includes a semiconductor material selected from the group consisting of Si and Ge,
`
`and the quantum dot exhibits photoluminescence with a quantum efficiency that. is
`
`greater than 10 percent.
`
`[0026]
`
`In a still further innovative aspect, the invention relates to a method
`
`of fonning a quantum dot.
`
`In one embodiment, the method comprises providing a
`
`particle that includes a semiconductor material Y selected from the group consisting
`
`of Si and Ge. The method also comprises applying sound energy and light energy to
`
`the particle to form a quantum dot that exhibits photoluminescence with a quantum
`
`efficiency that is greater than 10 percent. The quantum dot includes a core, and the
`
`core includes Y.
`
`[0027]
`
`In another embodiment, the method comprises reacting, in a reaction
`
`medium maintained at a temperature between approximately -78°C and 300°C, a
`
`source of a semiconductor material Y selected from the group consisting of Si and
`
`Ge with a reducing agent to form a particle that includes a core. The core includes
`
`Y, and the reducing agent is selected from the group consisting of Group IIA metals,
`
`transition metals, and lanthanides. The method also comprises reacting the particle
`
`with a source of surface ligands to form a ligand layer surrounding the core to form a
`
`quantum dot. The ligand layer includes at least one surface ligand.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0028] For a better understanding of the nature and objects of the invention,
`
`reference should be made to the following detailed description taken in conjunction
`
`with the accompanying drawings, in which:
`
`[0029] Figures 1(a), l(b), 1(c), and 1(d) illustrate quantum dots according to
`
`some embodiments of the invention.
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`[0030] Figure 2 illustrates the energy gap of quantum dots fabricated from
`silicon plotted as a function of the size of the quantum dots, according to an
`
`embodiment of the invention.
`
`[0031] Figure 3 illustrates photoluminescence (PL) spectra from six samples
`
`with different sizes of silicon quantum dots, according to an embodiment of the
`
`invention.
`
`[0032] Figure 4(a) illustrates the energy gap of quantum dots fabricated from
`
`germanium plotted as a function of the size of the quantum dots, according to an
`
`embodiment of the invention.
`
`[0033] Figure 4(b) illustrates size-selective photoluminescence (PL) spectra
`
`for different sizes of germanium quantum dots, according to an embodiment of the
`
`invention.
`
`[0034] Figure 5(a) illustrates concentration dependence of the linear index of
`refraction of engineered nonlinear nanocomposite materials doped with silicon and
`
`germanium quantum dots, according to an embodiment of the invention.
`[0035] Figure 50))
`illustrates concentration dependence of the optical
`nonlinearity of engineered nonlinearnanocomposite materials doped with silicon and
`germanium quantum dots, according to an embodiment of the invention.
`[0036] Figures 6(a), 6(b), 6(0), 6(d), 6(e), and 6(1)
`illustrate nonlinear
`directional couplers comprising engineered nonlinear nanocomposite materials,
`
`according to some embodiments of the invention.
`[0037] Figures 7(a), 7(b), 7(c), 7(d), 7(6), and 7(i) illustrate an embodiment
`
`of a nonlinear Mach-Zehnder
`
`(MZ)
`
`interferometer comprising an engineered
`
`nonlinear nanocomposite material.
`
`[0038] Figures 8(a), 8(b), 8(c), and 8(d) illustrate an alternative embodiment
`
`of
`
`a nonlinear MZ interferometer
`
`comprising
`
`an
`
`engineered
`
`nonlinear
`
`nanocomposite material.
`[0039] Figure 9 illustrates a figure-of-merit (FOM) for all-optical switching
`
`with an engineered nonlinear nanocomposite material as a function of quantum dot
`
`size, according to an embodiment of the invention.
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`illustrate photoluminescence spectra of
`[0040] Figures 10(a) and lofty)
`silicon quantum dots made in accordance with an embodiment of the invention.
`
`[0041] Figures 1l(a) and l1(b) illustrate photoluminescence spectra of
`
`germanium quantum dots made in accordance with an embodiment ofthe invention.
`
`[0042] Figure 12 illustrates an opfical device comprising an engineered
`
`nonlinear nanocomposite material, according to an embodiment of the invention.
`
`[0043] Figure 13 illustrates a passive directional coupler known in the art.
`
`\
`
`[0044] Figures 14(a),
`
`l4(b),
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`l4(c), and 14(d)
`
`illustrate a simulation of
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`switching
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`in
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`a
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`directional
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`coupler
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`comprising
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`an
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`engineered
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`nonlinear
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`nanocomposite material, according to an embodiment of the invention.
`
`[0045] Figure 15 illustrates a MZ interferometer known in the art.
`
`[0046] Figures 16(a), l6(b), 16(c), l6(d), and l6(e) illustrate a simulation of
`
`switching in a MZI switch comprising an engineered nonlinear nanocomposite
`
`material, according to an embodiment of the invention.
`
`[0047] Figures l7(a), 17(b), l7(c), l7(d), and l7(e) illustrate several possible
`
`embodiments of an optical
`
`transistor comprising an
`
`engineered nonlinear
`
`nanocomposite material.
`
`[0048] Figures l7(f), l7(g), l7(h), and l7(i) illustrate a simulation for an
`
`optical
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`transistor comprising an engineered nonlinear nanocomposite material,
`
`according to an embodiment of the invention.
`
`[0049] Figure 18 illustrates a waveguide Bragg-reflector known in the art.
`
`[0050] Figures 19(3) and l9(b) illustrate an aotivatable nonlinear waveguide
`
`Bragg—reflector comprising an engineered nonlinear nanocomposite material in de-
`
`activated and activated states, according to an embodiment of the invention.
`
`[0051] Figures 20(a) and 20(b) illustrate a tunable nonlinear waveguide
`
`Bragg-reflector in de-activated and activated states, according to an embodiment of
`
`the invention.
`
`[0052] Figures 21(a) and 2l(b) illustrate two preferred embodiments of
`. Reconfigurable Integrated Optical Systems, where lasers are used to induce an index
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`ll
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`increase in order to define transient optical waveguides, according to some
`
`embodiments of the invention.
`
`[0053] Figure 22 illustrates one preferred embodiment of a reconfigurable
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`photonic bandgap integrated optical system.
`
`[0054] Figure 23 illustrates a wavelength converting optical cr0ss~connect
`
`(OXC) subsystem in accordance with an embodiment of the invention.
`
`[0055] Figure 24 illustrates an all—optical TDM multiplexer in accordance
`B
`
`with an embodiment of the invention.
`[0056] Figure 25 illustrates an all-optical TDM demulfiplexer in accordance
`with an embodiment of the invention.
`
`[0057] Figures 26(3), 26(b), 26(c), 26(d), 26(6), and 26(f) illustrate various
`
`configurations for introducing trigger pulses into optical devices, according to some
`
`embodiments of the invention.
`
`[0058] Figures
`
`27(8),
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`27(b),
`
`27(0),
`
`and
`
`27(d)
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`illustrate preferred
`
`embodiments of generic optical devices.
`
`[0059] Figures 28(a) and 28(b) illustrate tapered claddings in accordance
`
`with some embodiments of the invention.
`
`[0060] Figures 29(a), 29(b), and 29(c) illustrate three preferred embodiments
`
`of Linear Arrayed Waveguide Devices.
`
`[006]] Figure 30 illustrates all-optical wavelength conversion using an
`
`engineered nonlinear nanocomposite material of an embodiment of the invention.
`
`[0062] Figure 31 illustrates all-optical demultiplexing for TDM systems
`
`using an engineered nonlinear nanocomposite material of an embodiment of the
`
`- invention.
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`[0063] Figure 32 illustrates an all-optical AND logic gate (also wavelength
`
`converter) using an engineered nonlinear nanocomposite material of an embodiment
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`of the invention.
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`DETAILED DESCRIPTION OF THE INVEN'I'ION
`
`Definitions
`
`[0064] The following definitions may apply to some of the elements
`
`described with regard to some embodiments of the invention. These definitions may
`
`likewise be expanded upon herein.
`
`[0065] As used in this specification and the appended claims, the singular
`forms “a”, “an”, and “the” include plural refer’ences- unless the content clearly
`
`dictates otherwise. Thus, for example, reference to “a quantum dot” includes a
`
`mixture of two or more such quantum dots and may include a population of such
`
`quantum dots.
`[0066] “Optional” or “optionally” means that the subsequently described
`
`event or circumstance may or may not occur and that the description includes
`
`instances where the event or circumstance occurs and instances in which it does not.
`
`For example, the phrase “optionally surrounded with a shell" means that the shell
`may or may not be present and that the description includes both the presence and
`
`absence of such a shell.
`
`[0067] Embodiments of the invention relate to a class of novel materials
`comprising quantum dots. As used herein, the terms "quantum dot", “dot”, and
`"nanocrystal" are synonymous and refer to any particle with size dependent
`properties (e.g., chemical, optical, and electrical properties) along three orthogonal
`dimensions. A quantum dot can be differentiated from a quantum wire and a
`
`quantum well, which have size-dependent properties along at most one dimension
`
`and two dimensions, respectively.
`
`It will be appreciated by one of ordinary skill in the art that quantum
`[0068]
`dots can exist in a variety of shapes, including but not limited to spheroids, rods,
`
`disks, pyramids, cubes, and a plurality of other geometric and non-geometric shapes.
`While these shapes can affect the physical, optical, and electronic characteristics of
`
`quantum dots, the specific shape does not bear on the qualification of a particle as a
`
`quantum dot.
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`[0069] For convenience, the size of quantum dots can be described in terms
`
`of a "diameter". In the case of spherically shaped quantum dots, diameter is used as
`
`is commonly understood. For non-spherical quantum dots, the term diameter, unless
`
`otherwise defined, refers to a radius of revolution (e.g., a smallest radius of
`
`revolution) in which the entire non~spherical quantum dot would fit.
`
`[0070] A quantum dot will typically comprise a “core” of one or more first
`
`materials and can optionally be surrounded by a “shell” of a second material. A
`
`quantum dot core surrounded by a‘ shell’is referred to as a “core-shell” quantum dot.
`
`[0071] The term "core" refers to the inner portion of the quantum dot. A
`
`core can substantially include a single homogeneous monoatornic or polyatomic
`
`material. A core can be crystalline, polycrystalline, or amorphous. A core may be
`
`"defect" free or contain a range of defect densities. In this case, "defect" can refer to
`
`any crystal stacking error, vacancy, insertion, or impurity entity (e.g., a dopant)
`placed within the material forming the core. Impurities can be atorrric or molecular.
`[0072] While a core may herein he sometimes referred to as "crystalline", it
`
`will be understood by one of ordinary skill in the art that the surface of the core may
`
`be polycrystalline or amorphous and that this non-crystalline surface may extend a
`measurable depth within the core. The potentially non-crystalline nature of the
`
`“core-surface region” does not change what is described herein as a substantially
`
`crystalline core. The core-surface region optionally contains defects. The core-
`
`surface region will preferably range in d