High frequency optical switch and method of manufacturing the same

Abstract

To provide an optical switch and a modulator device, usable for terahertz data communication speed.SOLUTION: A device comprises: a configured optically transmissive substrate through which electromagnetic radiation is propagated; and a metamaterial arrangement optically coupled to the substrate. The metamaterial arrangement includes: at least one layer of metamaterial particles optically coupled to at least some portion of the optically transmissive substrate; and at least one nanomesh layer made of at least one electrically conducting material placed over at least some portion of at least one metamaterial layer. At least one nanomesh layer is configured to discharge electrons into at least one metamaterial layer in response to electromagnetic or electric signals applied to the metamaterial arrangement. At least one metamaterial layer is configured to change from an optically opaque state into an optically transparent state when receiving the discharged electrons, thereby at least partially altering electromagnetic radiation passing through the substrate.SELECTED DRAWING: Figure 4B

Description

[Technical Field]

[0001] The present invention is generally in the field of optical switches that can be used for high frequency optical wave modulation. [Background technology]

[0002] There is a continually increasing demand for bandwidth in data communications services, required to meet the rapidly growing demands primarily driven by the widespread use of smartphones, social media, video streaming, and big data. As data centers reach maturity and larger data communication pipes become available, the 10 Gb / s technology currently in widespread use will now be required to handle the enormous amounts of data flowing over communications networks. Indeed, several service providers (PVs) are moving to higher bit-rate equipment and increasing bandwidth toward the 40 Gb / s and 100 Gb / s range per wavelength.

[0003] The International Telecommunications Union (ITU) divides the relevant electromagnetic microwave spectrum range from 1530 to 1566 nm (also known as the C-band, where optical fiber exhibits the lowest losses) into fixed 50 GHz spectrum slots. However, this proposed channel spacing is likely not suitable for bit rates greater than 100 Gb / s. Therefore, the technology needs a more flexible grid paradigm that can meet the needs of future bandwidth demands.

[0004] In fact, even if a sufficiently wide spectrum is available, high data rate signals are becoming increasingly difficult to transmit over long distances with high spectral efficiency. Therefore, it is beneficial for transceivers to adapt to the actual network conditions and data rates for each given traffic demand in order to maximize spectral efficiency. The demands of increasing spectral efficiency, expanding content providers, building new data centers, and developing peer relationships between providers drive uncertainty and heterogeneity in demand across the network. Therefore, there is a need for flexible and adaptable networks with flexible transceivers and network elements that can adapt to the ongoing and increasing data traffic demands in practice.

[0005] It has been recognized that high-speed switching and modulation are major obstacles for increased bandwidth communications at bit rates greater than 100 Gb / s and in the terahertz. The obstacles and limitations for ultra-high speed communications can be attributed to RF, optical, switching, and terahertz limitations associated with the network infrastructures in use today, as described below.

[0006] The RF limitation (microwave spectrum) is primarily due to the difficulty of fabricating electronic devices that can be configured to operate substantially above the hundreds of gigahertz frequency range. This difficulty is partly a result of the inherent requirement for very short carrier transit times in semiconductor active regions and the low power generated by the devices, which must have small active areas with minimized capacitance.

[0007] Optical limitations are encountered in that interband diode lasers are primarily designed to operate at visible and near-infrared frequencies. However, the generation of optical signals by radiative recombination of conduction-band electrons and valence-band holes across the band gap of the active semiconductor material does not appear to be easily extendable into the mid-infrared or longer wavelength ranges because suitably narrow band gap semiconductors are not available.

[0008] Switching limitations are also encountered, for example, in that controlling light transmission through materials in the electrical field is not suitable for long wavelengths, e.g., in or near the terahertz region of the optical spectrum, because the switching difference between on / off states is too weak and slow to be achieved by solid-state electronics.

[0009] The terahertz limit stems from the lack of active terahertz frequency sources with good resolution.

[0010] Some solutions in the patent literature are briefly discussed below.

[0011] Patent document 1 describes a transmission arrangement for transmitting data on at least one carrier wave in the terahertz range. The transmission arrangement comprises a transmitter, a receiving means, and an optical transmission system for transmitting a light beam. The transmitter and receiving means are adapted to wirelessly transfer data by means of a carrier wave modulated in the terahertz range of the transmitter. The carrier wave is generated using difference frequency mixing of two light beams generated by one or two light sources.

[0012] The technique and device described in Patent Document 2 is based on an optical resonator made of nonlinear optical material and nonlinear wave mixing to generate RF or microwave resonance and optically coupled signals.

[0013] Patent document 3 describes an optical communication device and technique that induces coupling between differentially polarized whispering gallery modes based on harmonic single sidebands (SSBs) in whispering gallery mode resonators formed in electro-optical materials.

[0014] The optical modulation system described in Patent Document 4 includes a metamaterial structure configured to receive and process input optical signals at at least one operating wavelength, the metamaterial structure changing between a transmittable state and a non-transmittable state for one or more optical signals at one or more operating wavelengths in response to an external stimulus applied to the metamaterial structure. The external stimulus source is coupled to the metamaterial structure and configured to change the metamaterial structure between the transmittable state and the non-transmittable state by applying selected stimulus pulses to the metamaterial structure. The optical modulation system processes the input optical signal and outputs a modulated optical signal that modulates in accordance with the selected pulses applied to the metamaterial structure.

[0015] The above description introduces various aspects of technology in relation to and intended to facilitate a better understanding of various aspects of the present disclosure. Note that the reference to any prior art described in this application is not an admission or suggestion that this prior art forms part of the common general knowledge in any jurisdiction, or that this prior art should be considered relevant and / or reasonably expected to be understood as integrated with other pieces of prior art by those skilled in the art. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] European Patent No. 2876824 [Patent Document 2] U.S. Patent No. 8,111,722 [Patent Document 3] U.S. Patent No. 8,159,736 [Patent Document 4] U.S. Patent No. 8,655,189 Summary of the Invention [Problem to be solved by the invention]

[0017] The subject matter disclosed herein aims to provide techniques and implementations for long wavelength optical modulation near and / or in the terahertz region of the optical spectrum (at and above 100 Gb / s, 400 Gb / s, and in the terahertz bit rate region) to achieve very high bit rates. The embodiments disclosed herein are suitable for implementing optical modulation in solid-state / chip devices configured to operate at room temperature. These embodiments can provide the flexibility and data rates necessary for scalable and adaptive networks, and are therefore attractive for use in new data centers currently being built using, for example, flattened (east-west) topologies.

[0018] Adaptive data centers can be built from block-like network infrastructure units using virtual blocks that can be seamlessly reconfigured. Using blocks that can easily scale as the network moves to the physical network can be flexibly scaled without having to reconfigure the entire backplane. The combination of adaptive transceivers, flexible grids, and highly capable client nodes enables a new "adaptive" networking paradigm, allowing service providers to address an increasing number of nodes in the network without having to overhaul it frequently.

[0019] 100 Gb / s-based transmission systems have recently been available on the market, and because they are compatible with the already deployed 50 GHz ITU grid / channel spacing, there is no need to replace the grid. Both the telecommunications and data communications industries are currently considering standard transmission data rates beyond 100 Gb / s, with much attention focused on 400 Gb / s. Unfortunately, the spectral width occupied by 400 Gb / s in standard modulation formats is too wide to fit into the 50 GHz ITU grid, and forcing it to fit by adopting a high spectral efficiency modulation format would only allow for shorter transmission distances. A fixed grid cannot support bit rates of 400 Gb / s and 1 Tb / s in standard modulation formats if they overlap at least one 50 GHz grid boundary. Therefore, it should be appreciated that the embodiments disclosed herein are useful for implementing data centers designed to meet the continuing increase in bandwidth demand. [Means for solving the problem]

[0020] Embodiments disclosed herein utilize active metamaterials coupled to wave conductors to construct high-performance optical switches, modulators, and / or filters configured to operate at terahertz data transmission rates. In certain embodiments, metamaterials are used to realize efficient thin-film switches, enabling terahertz communications and signal processing applications. Such devices are highly sought after for filtering, switching, and modulating terahertz signals. Switching of terahertz radiation using thin-film devices is hindered because the wavelength of electromagnetic waves at terahertz frequencies is greater than the 300 micrometer range and therefore does not significantly interact with structures much smaller than this wavelength. The use of metamaterials can circumvent this problem.

[0021] As used herein, the terms wave conductor, optical wave conductor, and wave line refer to media and / or elements usable for the transmission of electromagnetic radiation, including, but not limited to, optical waveguides such as those used in optical data communications, optical fibers, and air. Metamaterials are artificially constructed materials fabricated by assembling different, often nanoscale, entities to substitute for the atoms and molecules that would be found in conventional materials, engineered to exhibit properties not inherently exhibited by the underlying material. Metamaterials used in the embodiments disclosed herein typically have electromagnetic properties that are very different from those found in naturally occurring or chemically synthesized materials. Metamaterials used in some of the embodiments are configured to controllably exhibit negative refraction.

[0022] The metamaterials used in some of the embodiments disclosed herein are designed with optical microstructures configured to interact with electromagnetic radiation (light) passing through them. For example, and without limitation, such optical microstructures may be made of materials such as VO2, VO3, WO3, Ti2O3, NiS 2-y Se y , LaCoO3, PrNiO3, Cd2Os2O7, NdNiO3, Tl2Ru2O7, NiS, BaCo 1-y Ni y S2 (where y≦1), Ca 1-y Sr y VO3 (where y≦1), PrRu4Pl2, BaVS3, EuB6, Fe3O4, La 1-y Ca y MnO3 (where y≦1), La 2-2 Sr 1+2 Mn2O7 (where y≦1), Ti4O7, La2NiO4, manganites-type mixed oxides RE x AE 1-xMetal oxide-based materials can be used to construct such structures, such as MnO3 (where RE is a rare earth element such as lanthanum or praseodymium, AE is an alkaline earth element such as calcium, and x≦1), intermetallic compounds (such as NiAl), polymers such as azobenzene-containing polydiacetylenes, polyvinylidene fluoride, polyvinyl acetate, polyphenylene vinyl, polystyrene sulfonate, polyaniline (e.g., polyaniline doped into synthetic opal nanostructures), and nanostructured polymers such as diblock (e.g., poly[styrene b isoprene] or PS-b-PI) and triblock (e.g., rod-coil copolymer, poly[poly(N-isopropylacrylamide) b polyfluorene b poly(N-isopropylacrylamide)]) copolymers.

[0023] Such metamaterials can be used to construct ultrasmall, ultrafast optical switching devices made from vanadium oxide (VO2). The ability of such devices to switch in the terahertz frequency range is much faster than similar switching devices configured to operate at gigahertz frequencies. Using VO2 metamaterials to construct optical switching devices appears particularly attractive because they can be switched between a transmissive (insulating) state and a non-transmissive (conducting) state at terahertz speeds by inducing an electric charge / field, which could be developed to construct transistor-like devices.

[0024] The metamaterial used in one embodiment was made from nanoparticles of VO2 deposited on an optically transparent substrate (glass) and covered with a "nanomesh" of small gold nanoparticles. When this layer structure was irradiated with an electromagnetic pulse from an ultrafast THz source (e.g., any type of THz signal generator, such as, but not limited to, a laser source, any type of THz-transmitting liquid crystal-based device, or a frequency multiplier), thermionic electrons discharged from the gold nanomesh into the VO2 nanoparticle layer were detected within picoseconds (ps, 10 -12The metamaterial changes its phase from an optically opaque (metallic) phase to an optically transparent (semiconducting) phase over a time period in the time domain of 1 / 4 s (seconds). Embodiments disclosed herein utilize the properties of such metamaterials to controllably change between optically opaque and optically transparent states within the PS time frame to realize optical switching devices for communications applications.

[0025] One inventive aspect of the presently disclosed subject matter relates to an optical switch device usable for terahertz data communication rates. The device, in one embodiment, includes an optically transmissive substrate configured to propagate electromagnetic radiation and a metamaterial array optically coupled to the substrate. The metamaterial array includes at least one layer of metamaterial particles optically coupled to at least a portion of the optically transmissive substrate, and at least one nanomesh layer of at least one electrically conductive material disposed over at least a portion of the at least one metamaterial layer. The at least one nanomesh layer is configured to discharge electrons into the at least one metamaterial layer in response to an electromagnetic or electrical signal applied to the nanomaterial array, and the at least one nanomaterial layer is configured to change from an optically opaque state to an optically transparent state upon receiving the discharged electrons, thereby at least partially modifying the electromagnetic radiation passing through the substrate.

[0026] Optionally, the optically transmissive substrate is at least a portion of an optical fiber. Alternatively, the optically transmissive substrate is at least a portion of an optical WMG resonator, e.g., a PANDA resonator. In a further alternative, the optically transmissive substrate is a thin film.

[0027] In some embodiments, the substrate has a thickness of about 0.1 to 1 nanometer. Optionally, but preferably in some embodiments, at least one metamaterial layer comprises vanadium oxide. At least one metamaterial layer may be configured to exhibit negative refraction when subjected to discharged electrons.

[0028] The device, in one embodiment, comprises a metal grating formed on a metamaterial array.

[0029] The thickness of the at least one metamaterial particle layer is typically about 0.1 to 1 nanometer, and in some embodiments, the particle size of the at least one metamaterial particle layer is about 1 to 100 nanometers.

[0030] Optionally, but preferably in some embodiments, at least one nanomesh layer is comprised of gold. The thickness of the at least one nanomesh layer is generally about 0.1-1 nanometer. In some embodiments, the particle size of the at least one nanomesh layer is about 20-100 nanometers. The pore size / diameter of the at least one nanomesh layer is, in some embodiments, about 0.1-1 nanometer.

[0031] The optical switch device may have a geometric dimension of about 100-500 nanometers. In certain embodiments, the electromagnetic or electrical signal applied to the metamaterial array is in the RF, microwave, or terahertz frequency range (e.g., in the range of 100 MHz to 40 THz).

[0032] In another inventive aspect, the presently disclosed subject matter is directed to an optical modulator usable for terahertz data communication rates, which may comprise an optical switching device as described above or below, an input wave line configured to introduce input electromagnetic radiation into the optical switching device, and an output wave line configured to transmit output electromagnetic radiation at least partially modified by the optical switching device.

[0033] Another optical modulation assembly usable for terahertz data rates may be realized using an input wave line configured to introduce input electromagnetic radiation into the optical modulation assembly, an optical splitter configured to receive the input electromagnetic radiation from the input wave line, first and second wave lines optically coupled to the optical splitter to receive portions of the electromagnetic radiation from the input wave line and split thereby, at least one optical switch device as described above or below optically coupled to each core of at least one of the first and second wave lines, and an optical combiner optically coupled to the first and second wave lines and combining the electromagnetic radiation received therefrom from the optical splitter and at least partially modified by the at least one optical switch device. The optical modulator may include an output wave line configured to receive the electromagnetic radiation combined by the optical combiner.

[0034] The optical modulator can include first and second optical switch devices coupled to the cores of the first and second undulating lines, respectively. Optionally, in a preferred embodiment, the at least one metamaterial layer comprises vanadium oxide. Optionally, the at least one metamaterial layer is configured to exhibit negative refraction when receiving discharged electrons.

[0035] The modulator, in one embodiment, comprises a metal grating formed on a metamaterial array.

[0036] Yet another inventive aspect of the subject matter of the present application relates to an optical combiner for combining two or more electromagnetic data carrier waves, the combiner comprising: at least one modulated WGM resonator having a metamaterial assembly coated on an inner wall thereof; at least two input lines optically coupled to the at least one modulated WGM resonator for respectively introducing at least one electromagnetic data carrier wave; and at least one output line optically coupled to the at least one modulated WGM modulator for outputting electromagnetic radiation trapped by the at least one modulated WGM modulator and at least partially merging the at least two electromagnetic data carrier waves.

[0037] The metamaterial assembly, in one embodiment, comprises a layer of vanadium oxide nanoparticles, e.g., as described herein. The metamaterial assembly comprises a layer of gold nanomesh coated on a layer of gold, e.g., as described herein. The optical combiner, in one embodiment, comprises at least one auxiliary WGM resonator having a metamaterial assembly coated within an inner wall thereof and optically coupled to the at least one WGM resonator. The at least one auxiliary WGM resonator can be configured to shape electromagnetic radiation trapped inside the at least one WGM resonator in a predefined manner.

[0038] The optical combiner can comprise a grating formed on a metamaterial assembly of at least one WGM resonator, optionally at least one of the WGM resonators being an ellipsoidal shaped resonator.

[0039] In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which features shown in the drawings are meant to illustrate only certain embodiments of the invention, unless otherwise implicitly indicated, and in which like reference symbols are used to indicate corresponding parts. [Brief explanation of the drawings]

[0040] [Figure 1A] 1A-1C are schematic diagrams illustrating the operation of an optical switch according to one possible embodiment, prepared by deposition of a meta-material on a thin film. [Figure 1B] 1A-1C are diagrams illustrating the operation of an optical switch according to one possible embodiment, showing possible implementations of the optical switch; [Figure 1C] 1A-1C are schematic diagrams illustrating the operation of an optical switch according to one possible embodiment, showing time plots of input and output waves forming an interaction in the optical switch; [Figure 2]1A and 1B are schematic diagrams illustrating an optical switch according to an embodiment. [Figure 3] 1A-1C are diagrams illustrating schematic diagrams of possible realizations of optical modulators according to certain embodiments. [Figure 4A] 1A-1C are schematic diagrams of an optical wave modulator utilizing a whispering gallery mode (WGM) resonator, and a possible realization of an optical wave modulator utilizing a ring resonator. [Figure 4B] FIG. 1 is a schematic diagram of an optical wave modulator utilizing whispering gallery mode (WGM) resonators, showing a possible realization of an optical wave modulator utilizing multiple optically coupled WGM resonators and illustrating the proximity required to facilitate crosstalk / signal coupling for WGM modulation. [Figure 5A] FIG. 1 illustrates a data communication system that utilizes optical wave modulators based on WGM resonators to combine data carriers of different frequencies. [Figure 5B] FIG. 1 illustrates a data communication system that utilizes an optical wave modulator based on a WGM resonator to combine data carriers of different frequencies. [Figure 5C] FIG. 1 illustrates a data communication system that utilizes optical wave modulators based on WGM resonators to combine data carriers of different frequencies. DETAILED DESCRIPTION OF THE INVENTION

[0041] One or more specific embodiments of the present disclosure will now be described with reference to the drawings, which are to be considered in all respects only as illustrative and not limiting in any way. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described herein. Elements illustrated in the drawings are not necessarily drawn to scale, and their proportions are not critical. Instead, emphasis is placed on clearly illustrating the principles of the present invention so that, once those skilled in the art understand their structure and principles of operation, they will be able to make and use the optical switch / modulators disclosed herein. The present invention may be provided in other specific forms and embodiments without departing from the essential characteristics disclosed herein.

[0042] This document describes optical switches and modulators configured to operate at high frequencies near and within the terahertz frequency range. The optical switches and modulators disclosed herein are configured to controllably change their optical properties, thereby altering the path of electromagnetic radiation passing through a wave-conducting medium (e.g., a fiber optic core) optically coupled to them. In some embodiments, this is achieved by placing a metamaterial on a portion of a wave-conducting medium, such as an optical fiber, to provide optical coupling between the metamaterial and the wave-conducting medium (core), allowing the metamaterial to interact with electromagnetic radiation passing through it. For example, and without limitation, when using an optical fiber, the metamaterial may be applied along a predefined length of the optical fiber that corresponds to a small number of wavelengths (λ) (e.g., at least 4λ) covering a defined angle / arc of the optical fiber covering its entire circumference (360°).

[0043] In some embodiments, an optical switch and / or modulator is coupled to a whispering gallery mode (WGM) optical modulator assembly to modulate light introduced into the optical resonator by an electrical / optical signal applied to the metamaterial. This can be achieved by depositing a metamaterial on a portion of the WGM resonator such that the metamaterial interacts with electromagnetic radiation trapped within the resonator, optically coupling the metamaterial to the wave-conducting medium / core of the resonator. For example, without limitation, if the WGM resonator is a circular / elliptical / ring / torus-shaped resonator type, the metamaterial may be applied on a predefined length of at least four wavelengths along the WGM resonator, covering a defined angle / arc portion of the resonator that covers its entire circumference (360°). However, it should be noted that WGM resonators of different shapes may be used in embodiments of this application as well, for example, 3D spherical shapes, 3D ellipsoidal shapes, or 3D toroidal structures with polygonal cross-sectional shapes (as geometrically obtained by rotating a polygon around a toroidal symmetry axis).

[0044] Optionally and preferably, in certain embodiments, the metamaterial is made from nanoparticles of vanadium-based materials, including but not limited to vanadium oxide (VO2) nanoparticles, although other possible nanomaterials may similarly be used to realize the optical wave switches and / or modulators disclosed herein without departing from the scope or spirit of the present application.

[0045] The optical wave switch / modulator disclosed herein can be configured to interface between nano-networks and micro-networks (THz←→GHz) for biochemical, biomedical, chemical and molecular biology analysis detection.

[0046] For an overview of the features, process steps, and principles of some examples of the present invention, the example optical modulation structure illustrated generally and diagrammatically in the drawings is made of a vanadium-based material intended for use with coherent light, such as that generated by a semiconductor laser device. The metamaterial-based structure is shown as one example implementation illustrating many of the features, processes, and principles used to realize the optical switch / modulator, which are also useful for other applications and can be made in different variations. Thus, although this specification continues with reference to the illustrated examples, it will be understood that the inventions recited in the following claims can be realized in numerous other ways once the principles are understood from the descriptions, illustrations, and drawings provided herein. All such modifications, as well as any other design modifications obvious to those skilled in the art and useful in data communications applications, may be utilized as appropriate and are intended to fall within the scope of this disclosure.

[0047] Studies of the optical phase change of vanadium-based metamaterial nanoparticles, such as VO2, coated with gold nanoparticles and subjected to a THz source have revealed that it is unclear whether this optical phase change can be achieved by the application of electrons, e.g., a controllably variable electric field. In terahertz communications applications, devices should be sensitive to electrons and photons with as low energy and time consumption as possible for activation and recovery. The inventors have discovered that the optical phase change of VO2 works well with electrons (i.e., can be activated by the application of an electric field) and that the injection of hot electrons from gold nanoparticles also induces the conversion with one-fifth to one-tenth the energy required by applying laser light directly onto bare VO2 nanoparticles (the use of gold nanoparticles is 90% more efficient than applying laser light directly onto VO2 nanoparticles). Therefore, it is concluded that the optical switch device disclosed herein can be switched ON and OFF by the application of optical and / or electronic / electric field sources operating at RF, microwave, and terahertz data transmission rates.

[0048] 1A shows a schematic representation of an optical switch device 3 formed on a substrate 3f, which in one embodiment is realized by a thin film. In this non-limiting example, the switch device 3 is made from a layer 3m of nanoparticles optically coupled (e.g., by vapor deposition) to at least some portion of the substrate 3f and having a thickness of about 0.1-1 nanometers, and a nanomesh 3u of gold and / or equivalent (electrically conducting) nanoparticles applied (e.g., by vapor deposition) onto at least some portion of the nanoparticle layer 3m and having a thickness of about 0.1-1 nanometers.

[0049] The particle size of the nanoparticles of the metamaterial 3m is typically in the range of about 1-20 nanometers, but optionally in the range of about 1-100 nanometers. The particle size of the gold nanomesh 3u is typically about 20-200 nanometers, and the dimensions (size) of its pores 3p are about 0.1-1 nanometers. The substrate 3f is made of an optically transparent material, and in some embodiments, it is realized as a thin film made of a material (e.g., ceramic) that provides transparency upon sintering and has a thickness of about 0.1-1 nanometers.

[0050] In one embodiment, metamaterial layer 3m is made of VO nanoparticles, which may have a variety of different shapes. The geometric dimensions of optical switch 3 in one embodiment are on the order of several hundred nanometers in diameter, optionally on the order of 100-500 nanometers, which is significantly smaller than the geometric dimensions of available optical switches, as previously described. Optical switches of this small size (e.g., based on vanadium oxide materials) for terahertz-rate switching speeds can overcome several technical obstacles for terahertz high-speed switching, offering a solution that can transform data storage, data communications, and telecommunications technologies.

[0051] 1B schematically illustrates the structure and operation of an optical switch 10 according to one possible embodiment. In this non-limiting example, a thin layer of metamaterial 3m is deposited on a thin substrate (not shown) and is at least partially covered by a gold mesh (not shown) configured to be exposed to a signal generated by a signal source 8. In one embodiment, the optical switch 10 includes an optical grating 11 formed by parallel metal lines applied over at least some portion or the entire surface of the metamaterial 3m to enhance surface nonlinear processes (e.g., for frequency conversion). The grating 11 is fabricated by mechanical or chemical erosion.

[0052] The distance d between the metal gratings 11 can be configured for phase-matched input radiation 10a at different wavelengths to provide coherent phase-matched output radiation 10b. This distance d is typically set to be substantially shorter than the wavelength of the input radiation 10a (e.g., RF, microwave, terahertz), e.g., about 10 micrometers in one embodiment, thereby ensuring that all input wavelengths of the input radiation 10a pass through the optical switch 10 to provide coherent phase-matched output radiation 10b.

[0053] A signal 8 (electromagnetic light / RF / microwave radiation or electron / electric field) from a signal source 8 applied to the metamaterial 3m of the optical switch 10 causes thermionic emission from the gold particles of the nanomesh into the nanomaterial layer 3m, causing the metamaterial 3m to change from an opaque phase to a transparent phase in a time interval shorter than a picosecond. The phase change of the metamaterial layer 3m can be used to modulate input electromagnetic radiation 10a directed into one side of the device 10 to produce a phase-shifted output of electromagnetic radiation 10b on the other side of the device 10.

[0054] Signal source 8 may be physically coupled to optical switch 10, e.g., using an optical mixer or frequency multiplier, or may be realized by a signal source in close proximity to input electromagnetic radiation 10a prior to application, e.g., using an optical mixer or frequency multiplier (e.g., not in physical contact with switch device 10), and can generate pulsed signals near and / or within the terahertz frequency range, e.g., up to ≧400 GHz and 40 THz. Figure 1C graphically illustrates the resulting phase shift between input electromagnetic radiation 10a and electromagnetic radiation 10b output from optical switch 10, which closely matches the calculation shown by dashed line plot 10c.

[0055] 2 schematically illustrates an optical switch 7 according to one possible embodiment. The optical switch 7 comprises a wave-conducting substrate 7t configured to transmit electromagnetic radiation (EMR) 9d generated by an EMR source 9 (e.g., a laser light generator), a meta-material nanoparticle layer 7u optically coupled to at least a portion of the transmissive substrate 7t, and a nanomesh layer 7v applied over at least a portion of the meta-material layer 7u. The wave-conducting substrate 7t may be configured to transmit the EMR 9d along its length by total internal reflection (TIR), for example, using a suitable optically transmissive material and / or a coated metal plate (not shown).

[0056] A modulation (EMR optical, RF, microwave, terahertz or electrical) signal 8r generated by a signal source 8 and applied to the nanomesh layer 7v is used to switch the metamaterial layer 7u between its optically opaque and transparent phases, correspondingly changing the internal reflection properties of the wave-conducting substrate 7t between optically reflective and non-reflective (or partially reflective) states, thereby modulating the input EMR 9d with the applied modulation signal 8r.

[0057] In one embodiment, the electromagnetic radiation source and / or modulated signal source 8 utilizes the techniques and / or implementations described and illustrated in WO 2007 / 132459 and / or U.S. Pat. No. 9,964,442 of the same applicant, the disclosures of which are incorporated herein. The modulated EMR generated by the apparatus disclosed herein can be detected by state of the art detectors, such as, but not limited to, passive detectors and active detectors.

[0058] In certain embodiments, metamaterials configured to controllably induce negative refraction are used to modulate electromagnetic radiation. For example, in one possible embodiment, the metamaterial is optically coupled to a portion of the transmissive core of an optical fiber or optical resonator, whereby the phase of light passing therethrough is shifted by application of a modulation signal (8r) to a gold nanomesh applied to at least a portion of the metamaterial. Objectives for such optical switches / modulators include high modulation efficiency, low power modulation signals (8r), e.g., voltages, low insertion loss, high ON / OFF speeds, large modulation with "stretched" wavelengths, negligible or controllable frequency chirp, and long lifetime.

[0059] 3 schematically illustrates an optical modulation device 17 according to one possible embodiment. The modulation device 17 includes an input wavy line 22a configured to introduce an input EMR 9d (input A) into the modulator 17, an optical splitter 22p for splitting the input EMR 9d into first and second wavy lines 22f and 22s, respectively, an optical modulator 30 optically coupled to the second wavy line 22s, and an optical combiner 22c for combining the EMR traveling along the first and second wavy lines 22f and 22s into an output wavy line 22b (output C). The optical modulator 30 is configured to controllably modify the EMR passing through the second wavy line 22s in response to a received modulation signal (input b) from a signal source 8, thereby responsively introducing a phase shift. Thus, the EMR from the first and second dashed lines is combined constructively or destructively by optical combiner 22c in response to a modulation signal from signal source 8, thereby optically modulating input EMR 9d. Optical modulator 30 may be implemented utilizing any of the optical switch / modulators described above and below.

[0060] FIG. 4A schematically illustrates an optical modulator 20 utilizing a ring WGM resonator 28. The ring resonator 28 is optically coupled to an input ray 22a configured to introduce input EMR into the resonator 28 and to an output ray 22b configured to receive output EMR modulated by the resonator 28 from the resonator 28. The ring resonator 28 includes a metamaterial assembly 23 optically coupled to at least a portion of its optically transmissive core. The metamaterial assembly 23 may be coupled at a defined angle / arc portion defined about the center / axis of symmetry of the resonator 28c (defined by angle α) and / or about its circular axis 28r (defined by angle β). Optionally, the metamaterial assembly 23 is optically coupled to the entire transverse circumference (β=360°) of the ring resonator 28.

[0061] Metamaterial assembly 23 comprises a layer 23v of metamaterial (e.g., VO2) nanoparticles applied over at least some portion (or over all) of the walls of the core material of ring resonator 28, and a gold nanomesh 23u applied over at least some portion of metamaterial nanoparticle layer 23v. Nanomesh 23u is configured to receive a modulating (electromagnetic and / or electrical) signal from signal source 8 and responsively change metamaterial nanoparticle layer 23v between its optically transmissive and optically non-transmissive states to modulate the EMR introduced therein by input wave ray 22a.

[0062] 4B schematically illustrates an optical modulation device 40 utilizing multiple optically coupled WGM resonators 41, 42, 43, and 44 configured to bridge the wavelength gap between two input EMR data carriers F1 and F2 of different frequencies (e.g., optical and / or terahertz signals). Modulator 40 includes input wavy lines 45 and 46 configured to introduce EMR carriers F1 and F2, respectively, into main / modulation WGM resonator 41, e.g., by proximity, i.e., optical coupling without physical contact with WGM resonator 41. WGM resonator 41, in one embodiment, is made from a dielectric material, and its inner wall is covered by metamaterial assembly 23, i.e., consisting of a layer of metamaterial nanoparticles (e.g., VO2) covered by an electrically conducting nanomesh (e.g., made of gold).

[0063] The main WGM resonator 41 is configured to trap modulated EMR carriers F1 and F2 propagating along input lines 45 and 46, couple their frequencies from one to the other so that they resonate along the inner wall of the WGM resonator 41 covered by the metamaterial assembly 23, and output EMR radiation through output line 47 optically coupled to the main WGM resonator 41. Thus, the output EMR propagating along output line 47 couples with the modulated EMR carriers to provide output EMR (F1 + F2). This is achieved, in one embodiment, by a grating configured to facilitate a nonlinear process that results in an EMR merging effect due to random surface charging, enabling balanced local states on the surface. In this way, crosstalk / combining between EMR of substantially different wavelengths (e.g., RF and terahertz) is facilitated. A grating (e.g., a metallic grating (not shown)) can be applied to the metamaterial assembly, as shown in FIG. 1B.

[0064] The auxiliary WGM resonators 42, 43, and 44 are made from a dielectric material, and their inner walls are covered by the metamaterial assembly 23. The auxiliary WGM resonators 42, 43, and 44 are optically coupled (by proximity) to the main WGM resonator, but their geometric dimensions are configured to shape the combined EMR trapped inside the main / modulation WGM resonator 41 in the manner previously defined, to introduce a radiation pattern that is used to demodulate the combined signal at a receiver (not shown) receiving the output EMR propagating along output ray 47, for example, by adding an (information-free) pattern to the spectral variations of the carrier and modulated information, which serves to prevent errors in communication.

[0065] In this manner, multiple EMR carriers with different frequencies (e.g., RF, microwave, and / or terahertz) are optically combined into a single EMR carrier and transmitted toward a receiver. While WGM resonators 41, 42, 43, and 44 are shown as ellipsoids in this non-limiting example, other configurations and shapes may be used as well. The dimensions of primary ellipsoidal WGM resonator 41 are typically on the order of 10-150 microns, while the dimensions of secondary ellipsoidal WGM resonators 42, 43, and 44 may generally be smaller than primary / modulation ellipsoid 41 to prevent modulation.

[0066] 5A shows a schematic diagram of an optical data communication system 33 utilizing an optical modulator 17′ configured to receive two modulated signals and combine them into one EMR carrier wave, in this particular, non-limiting example, terahertz carrier waves THz1, THz2, . The optical modulator 17′ may be realized by an array of optical modulation devices (17) shown in FIG. 3A or by an implementation of the WGM resonator-based modulator of FIG. 4A and / or FIG. 4B modified to optically modulate multiple EMR waves THz1, THz2, . . . having different wavelengths.

[0067] The modified optical modulator 17' in this example includes an optical modulator 30 that optically modulates the EMR introduced into each optical modulator 17' with two respective modulation signals in each of the dashed lines 22f and 22s to perform branch modulation, with each branch realizing a separate data channel via its respective optical modulation unit 30. The system 33 includes a first set 39 of optical modulators 17', each configured to receive and modulate, with a phase shift, each EMR carrier THz1, THz2, ... with two modulation signals from the transponder 26. The transponder 26 is configured to generate two modulation signals for each modulator 17' of the first set of optical modulators 39.

[0068] The second set of optical modulators 38 is configured to modulate EMR from a light source (e.g., a laser source) passing through the wavy line 36x. Each optical modulator 17′ of the second set of optical modulators 38 is configured to receive two respective modulated optical signals generated by the optical modulators 17′ of the first set of optical modulators 39 for modulating the EMR in the wavy line 36x. The modulated EMR (referred to as a complex signal) generated by the second set of optical modulators 38 can be emitted by the antenna transmission unit 36, which is configured to emit the complex signal onto the air interface. A tuning unit 37 is optionally used for efficient Shannon correlation to adapt the modulated signal to the bandwidth of the EMR carrier.

[0069] 5B schematically illustrates an optical data communication system 35 including a plurality of optical modulation chip units 50 configured to mix two THz signals of different frequencies, each configured to receive a respective specific band of input EMR 51 (e.g., from an optical / laser source) directed by a focusing prism and distributed by a shifting prism for the creation of multiple channels, and input EMR 52 (e.g., from an optical / laser source) from a combining unit 39 for signal integration, and modulate it into a respective terahertz wave THz1, THz2, ... The optical modulation chip units 50 may be realized by WGR resonators 40 shown in FIG. 4B configured to combine the EMR from the two EMR data carriers to generate respective terahertz output EMRs that combine the two data carriers, as described above.

[0070] Figure 5C schematically illustrates yet another optical data communication system 34 in which a respective optical modulator 17' is optically coupled to a respective optical modulator chip unit 50 of the system 35 shown in Figure 5B. In this non-limiting example, the optical modulator 17' is utilized to combine an RF signal onto an input EMR 51, which is then combined by each optical modulator chip unit 50 with an EMR input carrier 52 from combiner 39 to generate a respective THz channel.

[0071] As described above and below, the optical modulation / switch device of the present application introduces modulation techniques that can operate according to the physical properties of the signals, and optical modulation / switch embodiments can be used to facilitate crosstalk / combining between widely separated wavelengths, for example, in the RF and terahertz bands.

[0072] Optical RF and / or THz is simply one category that includes a wide array of new devices. In certain embodiments, whispering gallery mode (WGM) optical resonators and THz resonators are used to modulate input EMR. Understanding how these devices are fabricated and used is important to appreciate their performance and limitations. Therefore, this portion of this specification introduces this class of resonator sensors (transmitters and receivers) and describes how these devices can be used for THz communication of data in general, and for data centers in particular, as a viable solution for high-speed communication.

[0073] WGM optical resonators exhibit tunability and narrow resonance linewidths, achieving exceptional optical properties that, in some embodiments, were originally developed for their use in long-distance communications, such as modulation devices. They are being developed into valuable tools for investigating nonlinear optical phenomena and quantum electrodynamic principles. In one possible embodiment, WGM optical resonators are used to realize optical communication modulators, as described below. These embodiments can be used, without limitation, in communication, biochemical analysis, biomedical analysis, chemical and molecular bioanalysis, where their extreme sensitivity in these arenas can be exploited to develop analytical and diagnostic tools.

[0074] WGM resonators get their name from the path that resonating light takes as it circulates in the cavity. This path is similar to the one that sound waves take along the curved walls of the circular rooms studied by Lord Rayleigh. In these whispering galleries, two people standing facing a wall on opposite sides of the room can hear each other with just a whisper. These people would not be able to hear each other if they walked backward toward the center of the room. This effect is caused by the smooth, curved walls, which guide sound waves around the perimeter of the room with great efficiency. Sound waves that take any other path to the listener are dissipated, or scattered, along the route.

[0075] WGM optical resonators are dielectric structures that can trap light in a path around a perimeter, similar to that taken by sound waves traveling from one person to another in a whispering gallery. Although Mie and Debye described the resonant natural frequencies of dielectric spheres before Lord Rayleigh's work, the name was not applied to this type of optical resonator until much later.

[0076] Embodiments of the optical switch / modulator disclosed herein can be utilized in modern data networks, e.g., data centers, to provide the scalability and adaptive networking required for cloud-managed applications and data storage. A commonly used metric for determining the energy efficiency of a data center is power usage effectiveness, or PUE. This simple ratio is the total power entering the data center divided by the power used by the IT equipment.

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[0077] Total facility power consists of the power used by IT equipment plus any overhead power consumed by anything (i.e., cooling, lighting, etc.) that does not consider computing or data communications equipment. The ideal PUE value is 1.0 for a hypothetical situation of zero overhead power. The average data center in the United States has a PUE of 2.0, meaning that the facility uses 2 watts of total power (overhead + IT equipment) for every watt delivered to IT equipment. Modern data center energy efficiency is estimated to be roughly 1.2. Some large data center operators, such as Microsoft and Yahoo, publish PUE projections for facilities in development, and Google publishes actual efficiency performance from data centers in operation quarterly.

[0078] Energy efficiency is a key feature for some of the embodiments disclosed herein. The United States Environmental Protection Agency has an Energy Star rating for stand-alone or large data centers. To qualify for the Eco-label, a data center must be in the top quartile of all reported facility energy efficiency. The European Union also has a similar initiative known as the EU Code of Conduct for data centers.

[0079] Often, the first step toward reducing energy use in a data center is to understand how energy is being used in the data center. Many types of analytics exist for measuring data center energy use. Measured aspects include not only the energy used by the IT equipment itself, but also the energy used by data center facility equipment, such as chillers and fans.

[0080] Power is the largest recurring cost to data center users. A power and cooling analysis, also called a thermal assessment, measures the relative temperature in a particular area as well as the cooling system's ability to handle a particular ambient temperature. A power and cooling analysis can help identify hot spots, over-cooled areas that can handle high power usage densities, equipment load breakpoints, the effectiveness of raised floor strategies, and optimal equipment positioning (such as AC equipment) to balance temperatures across the data center. Power and cooling density is a measure of how many square feet the center can cool at its maximum capacity.

[0081] Energy efficiency analyses measure the energy use of data center IT and facility equipment. A typical energy efficiency analysis measures factors such as a data center's power usage effectiveness (PUE) against industry standards, identifies mechanical and electrical sources of inefficiency, and identifies air management metrics.

[0082] To explore the opportunities of the optical switch / modulator disclosed herein for THz data rate data communications, data communications systems such as those disclosed herein can be devised to utilize multi-hop communications, where nodes in the network can communicate with the aid of two or more other nodes that act as relay nodes between the source and destination nodes of the THz communications, with both passive and active repeaters. Using intermediate repeaters between the transmitter and receiver at THz band frequencies has several advantages. As in any wireless communication system, transmission power, and therefore energy consumption, can be reduced by having several intermediate hops between the transmitter and receiver. Additionally, because available bandwidth is the only distance-dependent function, reducing transmission distance results in the availability of much wider bandwidth and, therefore, transmission at much higher bit rates, which can again provide significant energy savings.

[0083] As discussed above, the embodiments disclosed herein can be used to develop new types of photoconductors that are configured to operate based on discharge coupling versus normal conductivity.

[0084] Emerging wearable nanosensor networks will enable a set of valuable applications in the biomedical and environmental fields. At the same time, the current state of communication technology limits the processing capabilities of future nanomachines, implying that all analysis of collected data will need to be performed on the microdevice. Therefore, to efficiently enable the long-awaited applications of nanonetworks, their seamless integration into existing networking infrastructures is required, leading to the concept of the Internet of Nano Things. In an embodiment of this application, the mutual information exchange potential between already developed micronetworks and emerging nanonetworks is preliminary investigated, albeit in a preliminary manner.

[0085] Yet, solutions to this problem are nontrivial, as existing microwireless networks primarily use carrier-wave-based electromagnetic communication; nanomachines must rely on EM radiation based on ultra-low power pulses or inherently moving objects as information carriers. Therefore, direct interaction between micronetworks and nanonetworks is currently not feasible, forcing the use of spatial gateway nodes. Furthermore, modern solutions for nanocommunications are rapidly improving to enable the construction of large-scale networks on top of existing link-level technologies. Many theoretical questions remain to be addressed to achieve this goal, ranging from the design of appropriate modulation and coding techniques to the mitigation of noise and interference effects. The embodiments disclosed herein also provide a gateway for this field.

[0086] It is noted that combining metamaterial-based switches / modulators (e.g., using VO2 particles to transition between the opaque and transparent states of the metamaterial in the PS time range) with WGM resonators (e.g., PANDA resonant rings) can provide high-speed optical data communication and tailored antennas for a range of applications in fields such as biology, chemistry, materials science, and nanonetworking.

[0087] As described above and shown in the associated drawings, the present application provides optical switches and modulators for terahertz data rates and methods for fabricating same. While specific embodiments of the invention have been described, it is understood that the invention is not limited thereto and that variations will occur to those skilled in the art, particularly in light of the above teachings. As will be appreciated by those skilled in the art, the invention can be embodied in many different ways, utilizing one or more techniques from those described above, without departing from the scope of the appended claims.

Claims

1. 1. A system comprising an optical combiner configured and operable to combine two or more electromagnetic data carrier waves (F1, F2), said optical combiner comprising: at least one optical whispering gallery mode (WGM) resonator (28, 41-44) having a metamaterial array (23) coated on an inner wall portion, the inner wall portion being disposed within a core material of the resonator (28), the metamaterial array having at least one metamaterial layer (23v) applied on a portion of the inner wall portion and at least one nanomesh layer (23u) made of at least one electrically conductive material disposed on at least a portion of the at least one metamaterial layer, the at least one nanomesh layer being configured to discharge electrons into the at least one metamaterial layer in response to an electromagnetic or electric signal (8r) applied to the metamaterial array, thereby changing the metamaterial layer from an optically opaque state to an optically transparent state when receiving the discharged electrons; at least two input waves (22f, 22s; 45, 46) optically coupled to the at least one WGM resonator for respectively introducing at least two electromagnetic data carrier waves; and at least one output wave (22b, 47) optically coupled to the at least one WGM resonator for outputting electromagnetic radiation trapped inside the at least one WGM resonator and at least partially merging the at least two electromagnetic data carrier waves. A system comprising:

2. The system of claim 1 , further comprising an optically transmissive substrate disposed within at least a portion of the optical fiber or disposed within at least a portion of the optical WGM resonator.

3. The system of claim 2 , wherein the optically transmissive substrate is disposed within at least a portion of an optical WGM resonator, which is a type of PANDA resonator.

4. The system of claim 2 , wherein the optically transmissive substrate is a thin film.

5. The system of claim 4 , wherein the optically transmissive substrate has a thickness of about 0.1 nanometers to 1 nanometer.

6. The at least one layer of metamaterial particles has the following characteristics: (i) the at least one metamaterial layer comprises vanadium oxide; (ii) the at least one meta-material layer is configured to exhibit negative refraction when subjected to the discharged electrons; (iii) a metal grating is formed on the metamaterial array; (iv) the thickness of the at least one layer of metamaterial particles is between about 0.1 and 1 nanometers; (v) the particle size of the at least one layer of metamaterial particles is between about 1 and 100 nanometers; The system according to any one of claims 1 to 5, comprising one or more of:

7. The at least one nanomesh layer has the following characteristics: (i) the at least one nanomesh layer is gold; (ii) the thickness of the at least one nanomesh layer is about 0.1 to 1 nanometer; (iii) the particle size of the at least one nanomesh layer is about 20 to 100 nanometers; (iv) the pore size of the at least one nanomesh layer is about 0.1 to 1 nanometer; The system according to any one of claims 1 to 6, comprising one or more of:

8. The system of any one of claims 1 to 7, wherein the electromagnetic or electrical signal applied to the metamaterial array is in the RF, microwave, or terahertz frequency range.

9. The system of claim 8 , wherein the electromagnetic or electrical signal applied to the meta-material array is in the range of 100 MHz to 40 THz.

10. 10. The system of claim 1, wherein the optical combiner comprises at least one auxiliary WGM resonator having the metamaterial array coated on an internal wall and optically coupled to the at least one WGM resonator, the at least one auxiliary WGM resonator configured to shape the electromagnetic radiation trapped inside the at least one WGM resonator in a predefined manner.

11. The system of any one of claims 1 to 10, wherein the optical combiner comprises a plurality of gratings formed on the metamaterial array of the at least one WGM resonator.

12. The system of any one of claims 1 to 11, wherein at least one of the plurality of WGM resonators is an ellipsoidal shaped resonator.

13. 2. The system of claim 1, wherein the at least one WGM resonator traps the two or more electromagnetic data carrier waves present and propagating along the at least two input wave lines, couples the frequencies of the electromagnetic data carrier waves from one to another so that they resonate along an inner wall of the WGM resonator with the metamaterial array covering the inner wall portion of the resonator, and outputs electromagnetic radiation through the at least one output wave line, thereby combining the modulated electromagnetic data carrier waves to provide output electromagnetic radiation.

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