Bullseye Structure Research Articles

Bullseye dielectric cavities for photon collection from a surface-mounted quantum-light-emitter

Coupling light from a point source to a propagating mode is an important problem in nano-photonics and is essential for many applications in quantum optics. Circular “bullseye” cavities, consisting of concentric rings of alternating refractive index, are a promising technology that can achieve near-unity coupling into a first lens. Here we design a bullseye structure suitable for enhancing the emission from dye molecules, 2D materials and nano-diamonds positioned on the surface of these cavities. A periodic design of cavity, meeting the Bragg scattering condition, achieves a Purcell factor of 22.5 and collection efficiency of 80%. We also tackle the more challenging task of designing a cavity for coupling to a low numerical aperture fibre in the near field. Finally, using an iterative procedure, we study how the collection efficiency varies with apodised (non-periodic) rings.

Enhanced Single-Photon Emission from GaN Quantum Dots in Bullseye Structures

We present the design, fabrication, and detailed characterization of a photonic bullseye structure to enhance the single-photon extraction efficiency from self-assembled GaN/AlN quantum dots (QDs) ...

Extremely large near-field enhancements in the vicinity of plasmonic nanoantennas on top of bull’s eye structures exhibiting the extraordinary transmission of light

In this paper, we demonstrate that the optical electromagnetic fields in the vicinity of plasmonic nanoantennas are substantially enhanced on combining the plasmonic nanoantennas with bull’s eye structures (BESs) as compared to those of isolated plasmonic nanoantennas or of isolated bull’s eye structures. The optical electromagnetic fields are transmitted with high field enhancement through the subwavelength apertures of the BESs at the resonance wavelength, owing to the extraordinary transmission (EOT) of light. By hybridization of the two plasmonic nanoresonators (nanoantennas and BESs), optical energy is coupled to the nanoantennas from the light transmitted through the BESs. This coupling of light energy to the nanoantennas in the transmission mode using EOT and strong near-field enhancement in the vicinity of the gap between the nanoantennas integrated with the BESs has been analyzed numerically using the finite difference time domain (FDTD) method. We optimized the geometrical parameters of both BESs and nanoantenna structures for achieving the highest possible near-field enhancement. The resonance wavelength of this combined plasmonic structure can easily be tuned from visible to the near-infrared range by varying the periodicity of the BESs. Employing the proposed hybrid nanostructure consisting of a BES coupled to a plasmonic nanoantenna, an electric field enhancement of more than 1000 (i.e. an intensity enhancement greater than 1 × 106) is achieved for a 10 nm gap between the two arms of the bowtie nanoantenna, of more than 4000 (i.e. an intensity enhancement greater than 1.6 × 107) for a 5 nm gap, and of more than 9000 (i.e. an intensity enhancement greater than 8.1 × 107) for a 2.5 nm gap. These values of electric field enhancement are substantially higher than what have been reported previously. In this paper, we also present a comparison of the near-field enhancements in the vicinity of plasmonic bowtie nanoantennas coupled to different types of plasmonic nanogratings—two-dimensional nanohole arrays in plasmonic thin films, nanoline arrays in plasmonic thin films, or subwavelength apertures in plasmonic thin films surrounded by concentric periodic grooves. Moreover, we provide a comparison of the electric field enhancements in the vicinity of different types of plasmonic nanoantennas coupled to plasmonic nanogratings. The proposed hybrid nanostructure can open new possibilities in different fields such as surface-enhanced Raman scattering (SERS), plasmon-enhanced fluorescence (PEF), optical trapping, and nonlinear optics.

Plasmonic emission of hybrid Au/Ag bullseye nanostructures

Bullseye nanostructures with different central disk diameters and numbers of concentric rings have been fabricated in Au/Ag metallic films on glass substrates by focused ion beam milling. The Au/Ag bimetallic nanoresonator is expected to provide chemical stability and outstanding plasmonic property. A novel hybrid plasmonic emission has been observed by cathodoluminescence in the scanning electron microscope. It is found that the hybrid plasmon amplitude of the bullseye structure highly depends on the excitation position. The plasmonic intensity is the maximum when the beam is located at the edge of the central disk, and it can be tuned by selecting the disk size and the number of grooves. Additionally, the finite element simulation reveals that the bimetallic bullseye structure strongly confines the optical radiation, and the electric field distribution directly relates to the emission wavelength.

Subwavelength metal structures with tunable transmission characteristics by light

Extraordinary optical transmission (EOT) in subwavelength metal structures has been studied widely. Herein, we propose a strategy for tuning the EOT of the bullseye structure. Specifically, the bullseye structure was immersed in a nonlinear medium, and a controlling light was employed to change the refractive index of the medium. At different intensities and distributions of controlling light, the transmission property of signal light in the bullseye structure was simulated. The results show that a variable transmission spectrum in the bullseye structure can be realized. Moreover, the position of the central transmission peak shifts linearly with the increasing intensity of controlling light.

Control of EOT of subwavelength metal bullseye structures by coaxial nano-columns

The bullseye structure is a classic nano-optical structure. This article designs a new bullseye structure with coaxial nano-pillars. We used the time-domain finite difference method (FDTD) to study the EOT of the structure. Studies show that the radius and height of the column have a significant impact on the transmission characteristics. The proper choice of the radius and height of the column will support the maximum transmission intensity. In addition, the bullseye structure has a higher sensitivity to the environmental refractive index. Theoretical analyses show that the enhancement transmission effect of the structure is caused by the interaction between the local surface plasmon and the surface plasmon polarization. This provides a new idea for the development and application of nano-photonic components.

Bright off-axis directional emission with plasmonic corrugations.

In this work, a new plasmonic bulls-eye structure is introduced to efficiently harvest the emitted light from diamond nitrogen vacancy (NV) centers. We show that the presence of a simple metal sub-layer underneath of a conventional bulls-eye antenna, separated by a dielectric layer, results in the spontaneous emission enhancement and increment in out-coupled light intensity. High Purcell factor is accessible in such a structure, which consequently boosts efficiency of the radiated light intensity from the structure. The structure shows considerable enhancement in far-field intensity, about three times higher than that of a one-side corrugated (conventional) optimized structure. In addition, we study for the first time asymmetric structures to steer emitted beams in two-axis. Our results show that spatial off-axial steering over a cone is approachable by introducing optimal asymmetries to grooves and ridges of the structure. The steered light retains a level of intensity even higher than conventional symmetric structures. A high value of directivity of 16 for off-axis steering is reported.

Low-Noise Plasmonic Nanopore Biosensors for Single Molecule Detection at Elevated Temperatures

Advanced single molecular analysis is a key stepping stone for the rapid sensing and characterization of biomolecules. This will only be made possible through the implementation of versatile platforms, with high sensitivities and the precise control of experimental conditions. The presented work details an advancement of this technology, through the development of a low-noise Pyrex/silicon nitride/gold nanopore platform. The nanopore is surrounded by a plasmonic bullseye structure and provides targeted and controllable heating via laser irradiation, which is directed toward the center of the pore. The device architecture is investigated using multiwavelength laser heating experiments and 'individual DNA molecules are detected under controlled heating. The plasmonic features, optimized through numerical simulations, are tuned to the wavelength of incident light, ensuring a platform that provides substantial heating with high signal-to-noise.

Enhanced Terahertz Transmission Through Bullseye Plasmonics Lenses Fabricated Using Micromilling Techniques

Imaging applications at terahertz frequencies are, in general, limited to relatively low spatial resolution due to the effects of diffraction. By using a subwavelength aperture in the near-field, however, it is possible to achieve subwavelength resolution, although low transmission through the aperture limits the sensitivity of this approach. Plasmonic lenses in the form of bullseye structures, which consist of a circular subwavelength aperture surrounded by concentric periodic corrugations, have demonstrated enhanced transmission, thereby increasing the utility of near-field imaging configurations. In this paper, the design, fabrication, and experimental performance of plasmonic lenses optimized for 300 GHz are discussed. While nanofabrication techniques are required for optical applications, microfabrication techniques are sufficient for terahertz applications. The process flow for fabricating a double-sided bullseye structure using a precision micromilling technique is described. Transmission and beam profile measurements using a customized terahertz testbed are presented.

Integrated colloidal quantum dot photodetectors with color-tunable plasmonic nanofocusing lenses

High-sensitivity photodetection is at the heart of many optoelectronic applications, including spectroscopy, imaging, surveillance, remote sensing and medical diagnostics. Achieving the highest possible sensitivity for a given photodetector technology requires the development of ultra-small-footprint detectors, as the noise sources scale with the area of the detector. This must be accomplished while sacrificing neither the optically active area of the detector nor its responsivity. Currently, such designs are based on diffraction-limited approaches using optical lenses. Here, we employ a plasmonic flat-lens bull’s eye structure (BES) to concentrate and focus light into a nanoscale colloidal quantum dot (CQD) photodetector. The plasmonic lenses function as nanofocusing resonant structures that simultaneously offer color selectivity and enhanced sensitivity. Herein, we demonstrate the first CQD photodetector with a nanoscale footprint, the optically active area of which is determined by the BES; this detector represents an exciting opportunity for high-sensitivity sensing.

Effects of small defects, matrix structures and loading conditions on the fatigue strength of ductile cast irons

The fatigue strength of ductile cast iron is influenced by microstructural inhomogeneities (i.e., graphite, casting defects and matrix structures composed of different phases). In particular, the presence of small casting defects such as micro-shrinkage cavity can frequently cause not only significant deterioration but also large scatter in fatigue strength. Therefore, the laboratory fatigue tests with a limited number of small-sized specimens could result in a non-conservative estimation. For such a material, the prediction for the lower bound of the scatter in fatigue strength is essential from a practical perspective. In this study, a novel method is presented to predict the lower bound based upon the information of microstructural inhomogeneities and loading conditions. This method offers such an advantage that the lower bound can be reasonably predicted without conducting time-consuming fatigue tests. The predictive capability of the method was verified by comparing to the experimental results obtained in rotating-bending, torsion and combined tension–torsion fatigue tests of ductile cast irons with ferritic, pearlitic and bulls-eye structures.

Polarization Multiplexed Optical Bullseye Antennas

We present and analyze a novel optical antenna structure in the form of a polarization multiplexed bullseye antenna with a central nanoaperture. By adjusting the parameters of two, orthogonally oriented, partial bullseye structures, the resonance response for each polarization can be tailored to a specific wavelength. Constructing these dual-polarization structures in aluminum, we predict intra-aperture intensity enhancements exceeding 20 at two independent resonance wavelengths spanning the UV–visible spectrum. Moreover, these resonances share significant intra-aperture excitation volumes.