Nanowire Antenna Research Articles

(Invited) Shape Engineering of Nanostructured III-V Semiconductor Lasers

Group III-V semiconductors have revolutionised electronics and optoelectronics due to their superior physical and optoelectronic properties including high carrier mobility, direct bandgap and band structure engineering capability. Reducing the device size to nanoscale brings many unique properties, such as large surface-area-to-volume ratio, high aspect ratio, carriers and photons confinement effect. These nanostructures have already been demonstrated for potential applications in light emitters, photodetectors, solar cells and for photoelectrochemical water splitting. However, to date most efforts on the growth of these nanostructures have been limited to nanowires.In this talk, we demonstrate selective area growth of III-V nanostructures, showing the possibility of obtaining other functional nanostructures, beyond the limitation of rod-like geometry. We demonstrate that by changing the pattern design on the mask and growth conditions, we are able to grow and control the shapes to form nanostructures such as membranes, flowers, rings, spirals, stars, ellipses etc. These shape-engineered nanostructures open up possibilities of new applications based on devices with novel geometries.In particular, we will show the results of our InP micro-ring lasers which have excellent cavity due to the atomically flat facets. Micro-disk and micro-ring lasers are light emitting devices that operate in the whispering gallery mode. They are important components for integrated photonics applications as light from can these devices can be efficiently coupled to on-chip waveguides. By coupling the micro-ring laser to a nanowire antenna, we further demonstrate that we can tune the emission directionality to the device.

Nanowire dimer optical antenna brightens the surface defects of silicon

Abstract Plasmonic hot spots located between metallic dimer nanostructures have been utilized comprehensively to achieve efficient light emission. However, different from the enhancement occurred in the plasmonic hot spot, the investigation of light emission off the hot spot on submicron scale remains challenge. In this work, we have constructed a plasmonic nanowire dimer (NWD) system to brighten the light emission of the surface defects of silicon off the hot spot on the submicron scale. The NWD can trap light through plasmonic gap, then, the excited emitter on the submicron scale can radiate light efficiently by coupling with the dipole gap plasmonic mode. Furthermore, the coupling of dipole plasmonic mode with the emitters can be tuned by changing the gap size, and then photoluminescence emission was drastically enhanced up to 126 folds. Theoretical simulations reveal the photoluminescence enhancement arises from the combination of the NWD’s high radiation efficiency, Purcell enhancement, efficient redirection of the emitted photoluminescence and the excitation enhancement. In this study, the photoluminescence signal can be effectively enhanced by placing nano-antenna patch on the detected low-quantum-efficiency emitters, which may open up a pathway toward controlling plasmonic gap mode enhanced light emission off the hot spot on submicron scale.

Thermoresponsive Transient Radio Frequency Antennas: Toward Triggered Wireless Transient Circuits

AbstractWhile implantable medical devices offer tremendous potential for treating a myriad of diseases and disorders, there are many situations in which such devices are only needed for short time periods, with extended presence or surgical removal leading to a host of undesired complications. To address this concern, researchers are working to develop implantable circuitry that eventually disintegrates. Prior work in this area leveraged known bioresorbable materials, but the lifetime of circuits formed from such materials is determined upon fabrication, and on‐demand, triggered disintegration is not possible. To better match the lifetime of an implanted device to the status of the condition it is monitoring or treating, it would be advantageous to be able to noninvasively trigger disintegration at a particular time, avoiding situations in which the device lifetime is either too short or too long. Thus, to enable implantable circuitry with wireless capabilities that can disintegrate upon external stimuli, thermoresponsive transient RF antennas are formed that exhibit stable wireless response in warm aqueous environments but disintegrate and irreversibly lose functionality when cooled below a critical temperature. Antennas are formed by embedding patterned networks of silver nanowires in a thermoresponsive polymeric binder, which maintains network conductivity in warm solution but disintegrates and releases the nanowires when solution temperature drops. Mild sintering enhances electrical properties of the conductive nanowire network and antenna response while maintaining the capability for disintegration. To reduce the undesired effects of swelling, devices are sandwiched between two parylene films. These thermoresponsive transient devices represent an important step toward the realization of wireless medical implants whose disintegration can be triggered at any time by an external cooling stimulus.

All-Optical Mapping of the Position of Quantum Dots Embedded in a Nanowire Antenna.

Nanowire antennas embedding single quantum dots (QDs) have recently emerged as a versatile solid-state platform for quantum optics. Within the nanowire section, the emitter position simultaneously determines the strength of the light-matter interaction, as well as the coupling to potential decoherence channels. Therefore, to quantitatively understand device performance and guide future optimization, it is highly desirable to map the emitter position with an accuracy much smaller than the waveguide diameter, on the order of a few hundreds of nanometers. We introduce here a nondestructive, all-optical mapping technique that exploits the QD emission into two guided modes with different transverse profiles. These two modes are fed by the same emitter and thus interfere. The resulting intensity pattern, which is highly sensitive to the emitter position, is resolved in the far-field using Fourier microscopy. We demonstrate this technique on a standard microphotoluminescence setup and map the position of individual QDs in a nanowire antenna with a spatial resolution of ±10 nm. This work opens important perspectives for the future development of light-matter interfaces based on nanowire antennas. Beyond single-QD devices, it will also provide a valuable tool for the investigation of collective effects that imply several emitters coupled to an optical waveguide.

Controllable directive radiation from dipole emitter coupled to dielectric nanowire antenna with substrate-mediated tunability

Abstract

Boosting Local Field Enhancement by on-Chip Nanofocusing and Impedance-Matched Plasmonic Antennas.

Strongly confined surface plasmon-polariton modes can be used for efficiently delivering the electromagnetic energy to nanosized volumes by reducing the cross sections of propagating modes far beyond the diffraction limit, that is, by nanofocusing. This process results in significant local-field enhancement that can advantageously be exploited in modern optical nanotechnologies, including signal processing, biochemical sensing, imaging, and spectroscopy. Here, we propose, analyze, and experimentally demonstrate on-chip nanofocusing followed by impedance-matched nanowire antenna excitation in the end-fire geometry at telecom wavelengths. Numerical and experimental evidence of the efficient excitation of dipole and quadrupole (dark) antenna modes are provided, revealing underlying physical mechanisms and analogies with the operation of plane-wave Fabry-Pérot interferometers. The unique combination of efficient nanofocusing and nanoantenna resonant excitation realized in our experiments offers a major boost to the field intensity enhancement up to ∼12000, with the enhanced field being evenly distributed over the gap volume of 30 × 30 × 10 nm(3), and promises thereby a variety of useful on-chip functionalities within sensing, nonlinear spectroscopy and signal processing.

Strain-tunable quantum dot embedded in a nanowire antenna

We demonstrate an elastically-tunable self-assembled quantum dot in a nanowire antenna that emits single photons with resolution-limited spectral linewidths. The single-photon device is comprised of a single quantum dot embedded in a top-down fabricated nanowire waveguide integrated onto a piezoelectric actuator. Non-resonant excitation leads to static (fluctuating) charges likely at the nanowire surface, causing DC Stark shifts (inhomogeneous broadening); for low excitation powers, the effects are not observed and resolution-limited linewidths are obtained. Despite significant strain-field relaxation in the high-aspect-ratio nanowires, we achieve up to 1.2 meV tuning of a dot's transition energy. Single-photon sources with high brightness, resolution-limited linewidths, and wavelength tunability are promising for future quantum technologies.

Impact of surface plasmon polaritons and other waves on the radiation of a dipole emitter close to a metallic nanowire antenna.

The radiation of a dipole emitter close to a metallic nanowire optical antenna is investigated theoretically. By considering the excitation and multiple scattering of surface plasmon polaritons (SPPs) on the antenna and neglecting all other surface waves, we build up an intuitive pure-SPP model to comprehensively describe the radiation of the antenna. The model shows that for antennas with short lengths that support lower orders of resonance, waves other than SPPs contribute considerably to the antenna radiation, while SPPs play a dominant role for other cases. The enhancement of the antenna radiation is shown arising from two contributions, the field directly radiated by the emitter and the field resonantly excited by the surface waves on the antenna.

Tunable plasmon modes in single silver nanowire optical antennas characterized by far-field microscope polarization spectroscopy.

Performing far-field microscope polarization spectroscopy and finite element method simulations, we investigated experimentally and theoretically the surface plasmon modes in single Ag nanowire antennas. Our results show that the surface plasmon resonances in the single Ag nanowire antenna can be tuned from the dipole plasmon mode to a higher order plasmon mode, which would result in the emission with different intensities and polarization states, for the semiconductor quantum dots coupled to the nanowire antenna. The fluorescence polarization is changed with different polarized excitation of the 800 nm light beam, while it remains parallel to the Ag nanowire axis at the 400 nm excitation. The 800 nm incident light interacts nonresonantly with the dipole plasmon mode with the polarized excitation parallel to the Ag nanowire axis, while it excites a higher order plasmon mode with the perpendicular excitation. Under excitation of 400 nm, either the parallel or perpendicular excitation can only result in a dipole plasmon mode. In addition, we demonstrate that the single Ag nanowire antenna can work as an energy concentrator for enhancing the two-photon excited fluorescence of semiconductor quantum dots.

Waveguide-coupled nanowire as an optical antenna

We study the optical coupling between a gold nanowire and a silver ion-exchanged waveguide, with special emphasis on the nanowire antenna radiation pattern. We measure the radiation patterns of waveguide-coupled gold nanowires with a height of 70 nm and width of 50 or 150 nm in the 450-700 nm spectral range for TE and TM polarizations. We perform a systematic theoretical study on the wavelength, polarization, nanowire size, and material dependences on the properties of the radiation pattern. We also give some elements concerning absorption and near-field. Experiments and calculations show localized plasmon resonance for the polarization orthogonal to the wire (far-field resonance at 580 nm for the smallest wire and 670 nm for the widest). It is shown that a great variety of radiation patterns can be obtained, together with a high sensitivity to a change of one parameter, particularly near-resonance.

Photoluminescence enhancement of silicon nanocrystals placed in the near field of a silicon nanowire

Semiconductor nanowires have an excellent ability to trap, guide, scatter, or absorb light for specific morphology-dependent resonant optical modes. The electromagnetic field enhancement associated with these modes could be used to modify the luminescence of emitters positioned in the vicinity of the nanowire, in a way similar to plasmonic nanostructures. We show that the photoluminescence of a single plane of silicon nanocrystals in silica, positioned at about 3 nm below the surface, can be enhanced by a factor of 2 to 3 in the presence of a silicon nanowire antenna on the silica surface. This could be the basis of a promising fully complementary metal oxide semiconductor compatible process to improve silicon-based light emitting devices, despite a lower enhancement compared to plasmonic nanostructures. Two-dimensional photoluminescence maps recorded for different polarization configurations (incident electric field parallel or perpendicular to the nanowire axis) exhibit different behaviors and can be related to the electric field intensity distribution in the near-field region of the nanowire, where the active silicon nanocrystal layer is located.

Multipolar radiation of quantum emitters with nanowire optical antennas

Multipolar transitions other than electric dipoles are generally too weak to be observed at optical frequencies in single quantum emitters. For example, fluorescent molecules and quantum dots have dimensions much smaller than the wavelength of light and therefore emit predominantly as electric dipoles. Here we demonstrate controlled emission of a quantum dot into multipolar radiation through selective coupling to a linear nanowire antenna. The antenna resonance tailors the interaction of the quantum dot with light, effectively creating a hybrid nanoscale source beyond the simple Hertz dipole. Our findings establish a basis for the controlled driving of fundamental modes in nanoantennas and metamaterials, for the understanding of the coupling of quantum emitters to nanophotonic devices such as waveguides and nanolasers, and for the development of innovative quantum nano-optics components with properties not found in nature.

Printed silver nanowire antennas with low signal loss at high-frequency radio

Silver nanowires are printable and conductive, and are believed to be promising materials in the field of printed electronics. However, the resistivity of silver nanowire printed lines is higher than that of metallic particles or flakes even when sintered at high temperatures of 100-400 °C. Therefore, their applications have been limited to the replacement of transparent electrodes made from high-resistivity materials, such as doped metallic oxides, conductive polymers, carbon nanotubes, or graphenes. Here we report that using printed silver nanowire lines, signal losses obtained in the high-frequency radio were lower than those obtained using etched copper foil antennas, because their surfaces were much smoother than those of etched copper foil antennas. This was the case even though the resistivity of silver nanowire lines was 43-71 μΩ cm, which is much higher than that of etched copper foil (2 μΩ cm). When printed silver nanowire antennas were heated at 100 °C, they achieved signal losses that were much lower than those of silver paste antennas comprising microparticles, nanoparticles, and flakes. Furthermore, using a low temperature process, we succeeded in remotely controlling a commercialized radio-controlled car by transmitting a 2.45 GHz signal via a silver nanowire antenna printed on a polyethylene terephthalate film.

Conjugated Polymer/Metal Nanowire Heterostructure Plasmonic Antennas

The spontaneous emission spectrum, polarization direction, and emission lifetime of monolithically coupled poly-(3-hexylthiophene), P3HT, light-emitting nanostructures are modified by gold nanowire antennas. The P3HT nanostructure is integrated onto the end of the gold nanowire antenna, where localized, longitudinal surface plasmon mode fields are strongest. Comprehensive optical characterization and theoretical modeling are employed to demonstrate plasmonic nanoantenna-mediated light emission from P3HT.

Plasmonic Nanowire Antennae: Conjugated Polymer/Metal Nanowire Heterostructure Plasmonic Antennas (Adv. Mater. 11/2010)

A full-wave plasmonic nanowire antenna is excited into resonance by a dipole emitter located within a polythiophene nanoparticle attached to the end of the antenna in work reported by Deirdre O'Carroll and co-workers on p. 1223. The frontispiece shows an electric field intensity cross-section through the nanoparticle-antenna structure.

Solid-state single photon sources: the nanowire antenna

We design several single-photon-sources based on the emission of a quantum dot embedded in a semiconductor (GaAs) nanowire. Through various taper designs, we engineer the nanowire ends to realize efficient metallic-dielectric mirrors and to reduce the divergence of the far-field radiation diagram. Using fully-vectorial calculations and a comprehensive Fabry-Perot model, we show that various realistic nanowire geometries may act as nanoantennas (volume of approximately 0.05 lambda(3)) that assist funnelling the emitted photons into a single monomode channel. Typically, very high extraction efficiencies above 90% are predicted for a collection optics with a numerical aperture NA=0.85. In addition, since no frequency-selective effect is used in our design, this large efficiency is achieved over a remarkably broad spectral range, Deltalambda=70 nm at lambda=950 nm.

Measurement of the Mutual Coherence Function of an Incoherent Infrared Field with a Gold Nano-wire Dipole Antenna Array

The first direct measurement of the mutual coherence function of a spatially incoherent infrared beam was performed at 10.6 μm using a pair of infrared dipole nano-wire antennas that were connected to a common bolometer in the center of the pair by short lengths of coplanar strip transmission line. A spatially incoherent source was constructed by dithering a BaF2 diffuser near the focus of a CO2 laser beam. The distance from the diffuser to the nano-wire antenna pair was held constant while the distance from the focus of the laser beam to the diffuser was varied to control the effective diameter of the source. The measured bolometer signal was proportional to the magnitude of the mutual coherence function at the plane of the antennas. The experimental results were found to match the predicted performance closely. If this technology can be extended to large arrays, a form of synthetic aperture optical imaging based on the Van Cittert-Zernike theorem is possible, similar to that performed at microwave frequencies now by astronomers. This has the potential to greatly increase the angular resolution attainable with optical instruments.

Quantitative theory of nanowire and nanotube antenna performance

We present quantitative predictions of the performance of nanotubes and nanowires as antennas, including the radiation resistance, the input reactance and resistance, and antenna efficiency, as a function of frequency and nanotube length. Particular attention is paid to the quantum capacitance and kinetic inductance. We develop models for both far-field antenna patterns as well as near-field antenna-to-antenna coupling. In so doing, we also develop a circuit model for a transmission line made of two parallel nanotubes, which has applications for nanointerconnect technology. Finally, we derive an analog of Hallen's integral equation appropriate for single-walled carbon nanotube antennas