This PDF file contains the front matter associated with SPIE Proceedings Volume 8269, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Spin-symmetry breaking in nanoscale structures caused by spin-orbit interaction, leading to a new branch in optics - spinoptics is presented. The spin-based effects offer an unprecedented ability to control light and its polarization state in nanometer-scale optical devices, thereby facilitating a variety of applications related to nano-photonics. The direct observation of optical spin-Hall effect that appears when a wave carrying spin angular momentum (AM) interacts with plasmonic nanostructures is introduced. A plasmonic nanostructure exhibits a crucial role of an AM selection rule in a light-surface plasmon scattering process. A spin-dependent dispersion splitting was obtained in a structure consisting of a coupled thermal antenna array. The observed effects inspire one to investigate other spin-based plasmonic effects and to propose a new generation of optical elements for nano-photonic applications.

We report on recent design and fabrication of Kagome type hollow-core photonic crystal fiber (HC-PCF) for the purpose of high power fast laser beam transportation. The fabricated seven-cell three-ring hypocycloid-shaped large core fiber exhibits an up-to-date lowest attenuation (among all Kagome fibers) of 40dB/km over a broadband transmission centered at 1500nm. We show that the large core size, low attenuation, broadband transmission, single modedness, low dispersion and relatively low banding loss makes it an ideal host for high power laser beam transportation. By filling the fiber with helium gas, a 74μJ, 850fs and 40kHz repetition rate ultra-short pulse at 1550nm has been faithfully delivered with little propagation pulse distortion. Compression of a 105μJ laser pulse from 850fs to 300fs has been achieved by operating the fiber in ambient air.

We propose and design a broadband optical resonator fashioned from two types of waveguides: one sustaining a positive-index mode with a positive phase velocity and another sustaining a negative-index mode with a negative phase velocity. The former has a wavelength that decreases as a function of frequency, while the latter has a wavelength that increases as a function of frequency. Because frequency-dependent wavelength increases in one waveguide component of the resonator are compensated by wavelength decreases in the other component, the resonator can potentially support a continuum of standing wave patterns that all satisfy the same resonance condition, effectively widening the frequency range over which resonance is achievable. We have tailored the geometry of the resonator so that the net phase accrued within the resonator is nearly constant over a large portion of the visible frequency range, and, as shown through FDTD simulations and analytical calculations, a broadband optical resonance is achieved.

Modulation of the Purcell effect by controlling both the Q-factor and detuning in a quantum-dot-nanocavity coupled system was investigated. The Q-factor and detunings are controlled independently by using a nanocavity, a waveguide and a reflector formed in a two-dimensional photonic crystal slab, in combination with a newly developed nitrogen adsorption/desorption technique that enables local control of the refractive index. We investigated analytically and experimentally how the density of states of cavity mode is modulated, and we experimentally clarified how the emission of a quantum dot on resonance with a cavity is modulated. We observed that the emission of a quantum dot via a cavity mode was increased by 3.3 times when the Q-factor was changed from 3,500 to 6,900 while keeping the detuning fixed. The dependence of the Purcell effect on the Q-factor was directly observed.

In this paper, we discuss anomalous and enhanced nonlinear effects available when combining nonlinear optical materials with plasmonic metamaterials. Narrow periodic apertures filled with Kerr nonlinear materials are carved in a plasmonic screen. Large field enhancement confined inside each slit may be obtained, in particular when we operate at the cut-off of this array of plasmonic channels. This ensures a significant boosting of nonlinear optical effects, leading to strong optical bistable performance. New exciting venues for applications are opened with the aforementioned novel nonlinear devices.

The word "magic" is usually associated with movies, fiction, children stories, etc. but seldom with the natural sciences. Recent advances in metamaterials have changed this notion, in which we can now speak of "almost magical" properties that scientists could only dream about only a decade ago. In this article, we review some of the recent "almost magical" progress in the field of meta-materials.

In terms of the effective medium theory, we develop a novel technique for designing nanostructured metamaterials (photonic crystals) with predetermined dielectric and optical properties over a frequency band. The technique is based on materials' architecture and reduces to the design of one-dimensional or two-dimensional nanostructured metal-dielectric composites with a specified graded geometry. As particular examples, we show how to tailor the materials with epsilonnear- zero (ENZ), ultralow-refractive-index (ULRI), and refractive index-near-unity (RINU) over a frequency band using a fitting procedure. The quality of fitting is discussed by the example of RINU metamaterials.

It has been shown that light localization can occur within disordered and random dielectric lattices. The presence and nature of localized light within these dielectric layouts is examined through the rotational order symmetry present within both the field profile and the dielectric. A Fourier-Bessel expansion algorithm using exponentials and Bessel functions as basis functions is employed to decompose the dielectric layout and localized light field profiles. Selecting the coordinate origin for the expansion to coincide with the localized light's field center demonstrates that a relationship exists between the rotational order in the localized light and the dielectric layout.

Photonic band gaps (PBGs) are highly sensitive to lattice geometry and dielectric contrast. Here, we report theoretical and experimental confirmation of PBGs in photonic crystals (PhCs) with increasing levels of structural isotropy. These structures are: a standard 6-fold hexagonal lattice, a locally 12-fold Archimedean-like crystal, a true quasicrystal generated by non-random Stampfli inflation, and a biomimetic crystal based on Fibonacci phyllotaxis. Experimental transmission spectra were obtained at microwave frequencies using high-index alumina (ε = 9.61) rods. The results were compared to FDTD-calculated transmission spectra and PWE-calculated band diagrams. Wide and deep (> 60dB) primary TM gaps present in all high-index samples are related to reciprocal space vectors with the strongest Fourier coefficients. Their mid-gap frequencies are largely independent of the lattice geometry for comparable fill factors, whereas the gap ratios shrink monotonically as structural isotropy increases.

We observe from simulations that a doubly resonant structure can exhibit spectral behavior analogous to electromagnetically induced transparency, as well as superscattering, depending on the excitation. We develop a coupled-mode theory that explains this behavior in terms of the orthogonality of the radiation patterns of the eigenmodes. These results provide insight in the general electromagnetic properties of photonic nanostructures and metamaterials.

Central to the idea of metamaterials is the concept of dynamic homogenization which seeks to define frequency dependent effective properties for Bloch wave propagation. While the theory of static effective property calculations goes back about 60 years, progress in the actual calculation of dynamic effective properties for periodic composites has been made only very recently. Here we discuss the explicit form of the effective dynamic constitutive equations. We elaborate upon the existence and emergence of coupling in the dynamic constitutive relation and further symmetries of the effective tensors.

We consider two-dimensional phononic crystals formed from silicon and voids, and present optimized unit-cell designs for the following modes of elastic wave propagation: (1) out-of-plane, (2) in-plane, (3) combined out-of- plane and in-plane, and (4) flexural (on the basis of Mindlin plate theory). To feasibly search through an excessively large design space (~10⁴⁰ possible realizations) we develop a specialized genetic algorithm and utilize it in conjunction with the reduced Bloch mode expansion method for fast band-structure calculations. Focusing on high-symmetry plain-strain square lattices, we report unit-cell designs exhibiting record values of normalized band-gap size for all four categories. For the case of combined polarizations, we reveal a smoothened design with a normalized band-gap size exceeding 60%. For the thin-plate problem, a manufacturable design is presented with a normalized band gap in excess of 57%.

In micromechanical resonators, energy loss via anchors into the substrates decreases quality factors. To eliminate the anchor loss, a phononic band-gap structure is proposed and employed. In this paper, we investigate the elastic wave propagation in phononic crystal strips, cut from a silicon phononic crystal slab consisting of square-lattice vacuum holes, by analyzing the dispersion relations, acoustic eignemodes, and transmission properties. The phononic crystal strips are applied to devise the anchor-loss free micromechanical resonators and enhance resonator performances. The phononic crystal strips are found to have frequency forbidden bands and are introduced to eliminate the anchor loss in the bar-type and ring-type resonators. Numerical analysis shows that the phononic crystal strips can effectively suppress the acoustic energy leak and increase the stored energy inside the resonators. Realization of a high quality factor micromechanical resonator with minimized anchor loss is expected.

Recently stacked metamaterial structures coupled to a conductive plane have been investigated and have been shown to exhibit the same properties as stacked structures with double the layers, due to dipole mirror coupling. Here we study a system of stacked subwavelength metallic grating layers coupled to a metal film and show that this system not only supports the localized modes of a doubly layered structure, but also, for non-normal incidence, supports modes that exhibit a clear propagation and in one case a simultaneous localization of the electromagnetic field in the region between the metal film and the first grating layer. Furthermore we show that this hybridized propagating mode, excited for any N number of periodic layers, is further influenced as it couples with the highest energy localized mode of the periodic layered stack. Additionally it is found that the localized modes of the structure can be spectrally positioned in a directly adjacent manner, resulting in wideband absorption that can effectively be tuned by varying the grating film spacing.

We investigate experimentally metallic nanoparticle composites fabricated by bottom-up techniques as potential candidates for optical metamaterials. Depending on the plasmonic resonances sustained by individual NPs and their nanoscale organization into larger meta-atoms, various properties might emerge. Here, the focus of our contribution is on the fabrication and optical characterization of silver NP clusters with a spherical shape. We start with the characterisation of the "bulk" dielectric constants of silver NP inks by spectroscopic ellipsometry for different nanoparticle densities (i.e from strongly diluted dispersions to solid randomly packed films). The inks are then used to prepare spherical nanoparticle clusters by an oil-in water emulsion technique. The study of their optical properties demonstrates their ability to support Mie resonances in the visible. These resonances are associated with the excitation of a magnetic dipole, which constitutes a prerequisite to the realization of metamaterials with negative permeability.

In order to better understand how to improve the performance of a superlens, structural and geometrical arrangements of meta-atoms are investigated. Each meta-atom (i.e. the unit element composing a metamaterial) in our study is an asymmetric 3D "S"-shaped resonator. This structure radiates an enhanced scattered field at several possible resonant frequencies, some of which are out of phase with the incident wave. We retrieve the effective parameters of different metamaterials and discuss the role of meta-atom symmetries and dimensions in affecting the effective refractive index of a metamaterial slab. Relative locations and orientations of individual meta-atoms are investigated to provide desired properties with low loss despite the inevitable finite size of each meta-atom. The results presented provide insights for designing superlenses, resonant antennas, and other potential applications.

Composite materials based on plasmonic nanoparticles allow building metamaterials with very large effective permittivity (positive or negative) or ε-near-zero; moreover, if clustered or combined with other nanoparticles, it is possible to generate also effective magnetic permeability (positive or negative), and an ad-hoc design would result in the generation of double negative materials, and therefore backward wave propagation. However, losses are usually significant and affect the metamaterial performance. In this work, we report on the possibility of adopting fluorescent dye molecules or quantum dots, optically pumped, embedded into the dielectric cores of the employed nanoshell particles, and provide loss-compensation in ordered 3D periodic arrays at optical frequencies. Each spherical nanoshell is modeled as an electric dipole. We consider nanoparticles with gold and silver shells. We then find the modes with complex wavenumber in the metamaterial, and describe the composite material in terms of homogenized effective material parameters (refractive index and permittivity). Furthermore, in case of loss-compensation, we compare the results obtained from modal analysis with the ones computed by using two different homogenization methods: (i) Maxwell Garnett homogenization theory and (ii) Nicholson-Ross-Weir retrieval method. We show the design of two ε-near-zero metamaterials with low losses by simulating gain material made of dyes or quantum dots with realistic parameters. A brief discussion about the employment of the two kinds of active gain materials adopted here is given in the end.

We present polarization dependent multispectral and broadband plasmonic absorbers in the visible spectrum. The spectral characteristics of these structures are tunable over a broad spectrum. Experimental results are verified with the FDTD and RCWA analysis methods. These structures are used as surface enhanced raman spectroscopy(SERS) substrates. Designed structures have resonances that span the Raman Stokes and excitation wavelength. Such structures can be used for energy, LED and other spectroscopy applications.

The plasmonic modes of a nano-antenna formed by a nanoparticle/thin film hybrid system are investigated. Plasmonic nano-antennas are well-known for their capabilities to concentrate electromagnetic wave into extreme small region and couple the emission from active materials in proximity to the antennas into far-field region. Previously, we have shown through direct measurement of emission profile images that the nano-antennas not only enhance Raman emission but also systematically direct inelastic emission to the far-field through the dipole mode. We also showed that high order modes of the hybrid structure can be detected. Here, the higher order plasmonic modes are characterized through imaging, variable angle linearly polarized excitation, and simulation. Through spectral simulation with improved resolution, two distinct modes are found to contribute to the broad band high order mode. One has dipole-like behavior and the other has quadrupole-like behavior. The modes are characterized both through near-field distribution and farfield scattering profiles. The quadrupole-like mode can be excited by both p- and s-polarized light whereas the dipolelike mode is only excited by p-polarized light. These high order modes are not as bright as the dipole mode in the farfield spectrum but have substantial near field enhancement which can be utilized for surface-enhancing spectroscopy and sensing. In addition, characterization of high order modes may serve to clarify the interaction between nano-antenna and active materials and will lead to design rules for applications of active plasmonic structures in integrated optical circuits.

We demonstrate that large area eight-fold symmetric polymeric photonic quasi-crystals can be created by a specifically configured prism via single-exposure holographic lithography. The prism splits an expanded laser beam into five beams and in sequence converge onto a photoresist with a designed incident angle for forming an interference pattern with eight-fold quasi-period. Different from a conventional eight-fold symmetry prism, only five continuous surfaces are used. From group theory, we have verified the feasibility of the particular configuration. And numerical simulations have confirmed that the eight-fold symmetric periodicity can be obtained. Experimental results with the same five beam configuration are in good agreement with the theoretical prediction. The kind of specially designed prism may benefit mass production of large area photonic quasi-crystals by holographic lithography technique.

A subwavelength plasmonic grating with rectangular grooves on the metal surface is an efficient light trapper with designer resonance position and angular bandwidth. In this work, a new method is presented, where the grooves are filled with a dielectric resulting in a large shift of the resonance wavelength. A case study of a gold grating with grooves 18 nm wide and 47 nm deep is presented, where the resonance is shifted from original 720 nm to 960 nm by filling the grooves with an n = 1.4 immersion oil.

Surface enhanced Raman scattering (SERS) can be used to amplify the Raman cross-section of signals by several orders of magnitude, when a mixed photon-Plasmon mode (surface Plasmon polaritons) couples to molecules on a nano textured metallo-dielectric substrate. In this paper we demonstrate a comprehensive 3D computational model based on Rigorous coupled wave analysis (RCWA) for the purpose of analysing propagating and localised surface Plasmon polaritons supported by planar SERS substrates based on periodic array of metal coated inverted pyramidal nanostructures. Although studies ^{[1, 2]} have explored the optical properties of inverted square pyramidal pits using simulation and experimentation, there has yet been no investigation performed on rectangular inverted pyramidal pits. Here we perform 3D modelling and simulation on rectangular pit arrays with aspect ratio 1:1.2 over 400nm thick gold. We investigate the effect of incident polarisation and electric-field density within the pits and show that inverted rectangular pyramidal pit array can be used as highly effective SERS and Plasmonic substrates.

Second-harmonic generation (SHG) from centrosymmetric nanostructures originating from the breaking of inversion symmetry at their surfaces is a well-known phenomenon and is extensively used as a surface probe in nonlinear optical microscopy. In recent years, SHG and its subsequent enhancement using plasmonics has been observed from nanostructures such as sharp metallic tips, nanoantennae and nanodimers. However, the process is still inefficient, its mechanism not well understood, and an improvement is required. In order to achieve a higher conversion efficiency, we investigate experimentally a way to minimize the radiative losses at the fundamental frequency. In the present investigation, we use silver heptamer nanostructures and tune the subradiant mode of the Fano resonance to the fundamental of the pump source, while tuning a higher order multipolar term to the second harmonic and in the process we obtain a significant enhancement of the second harmonic signal. A detailed explanation and analysis of this is provided by considering the contribution and effect of varying different parameters, such as gap size and radius, as well as the overall symmetry of the structure. In fact, recently gold heptamers have been studied and have indeed shown strong hybridization of their constituent resonant primitive plasmonic modes, leading to new hybridized superradiant 'bright' and subradiant 'dark' modes^{1, 2}. The ease of fabrication and possible tunability achievable, make these structures very versatile tools for studying surface SHG in nanostructures.

We present investigations of the propagation length of guided surface plasmon polaritons along Au waveguides on GaAs and their coupling to near surface InGaAs self-assembled quantum dots. Our results reveal surface plasmon propagation lengths ranging from 13.4 ± 1.7 μm to 27.5 ± 1.5 μm as the width of the waveguide increases from 2-5 μm. Experiments performed on active structures containing near surface quantum dots clearly show that the propagating plasmon mode excites the dot, providing a new method to spatially image the surface plasmon mode. We use low temperature confocal microscopy with polarization control in the excitation and detection channel. After excitation, plasmons propagate along the waveguide and are scattered into the far field at the end. By comparing length and width evolution of the waveguide losses we determine the plasmon propagation length to be 27.5 ± 1.5 μm at 830 nm (for a width of 5 μm), reducing to 13.4 ± 1.7 μm for a width of 2 μm. For active structures containing low density InGaAs quantum dots at a precisely controlled distance 7-120 nm from the Au-GaAs interface, we probed the mutual coupling between the quantum dot and plasmon mode. These investigations reveal a unidirectional energy transfer from the propagating surface plasmon to the quantum dot. The exquisite control of the position and shape afforded by lithography combined with near surface QDs promises efficient on-chip generation and guiding of single plasmons for future applications in nanoscale quantum optics operating below the diffraction limit.

Multilayered Ag/Au/Ag/Au and Au/Ag/Au/Ag films with 200 nm of thickness (50 nm for each layer) were evaporated onto BK7 glass substrates. Sequences of slits (around 60-600 nm of width) were milled with a focused gallium ion beam in the films. We have undertaken a series of high-resolution measurements of the optical transmission through the slits. The transmission measurement setup consists of 488.0 nm (for the Ag/Au/Ag/Au film) and 632.8 nm (for the Au/Ag/Au/Ag sample) wavelength light beams from Ar ion and HeNe lasers, respectively, aligned to the optical axis of a microscope. The beam is focused onto the sample surface by a microscope objective in TM polarization (magnetic Hfield component parallel to the long axis of the slits). As well, theoretical estimates investigating the slits optical transmission were performed. The origin of the slits transmission is mainly attributed to plasmonic surface excitations. Based on the present results, it was possible to observe that (1) the transmission increases linearly with increasing slit width, and (2) the transmission of the multilayered structures is augmented in comparison with a single perforated metal film of equal thickness, for a fixed slit width. A very good correspondence between theory and experiment was observed.

We present the effect of structural randomness on the formation of Anderson localization (AL) in random photonic crystals (RPCs) by using a two-dimensional FDTD (Finite-Difference Time-Domain) computational method. The RPC consists of a silicon substrate with an array of air holes aligned in a triangular lattice shape. The structural randomness is introduced by randomly dislocating the positions of air holes. By investigating impulse response of the system, we obtained frequency spectra and Q-factors of long-lived modes. The modal characteristics of the modes as a function of structural randomness in RPCs and optimization of the structural randomness to achieve high photon confinement efficiency are achieved.

A new kind of bowtie related structures, Sierpinski complementary bowtie aperture (SCBA), is proposed for enhancing and confining optical magnetic field. The magnetic field enhancement factor can be improved with the presence of the fractal. Numerical simulation shows that higher iteration of the SCBA is responsible for the variation of the resonant wavelengths. The magnetic field distributions illustrated 10nm above the output plane prove the magnetic intensity is confined in the sub-wavelength scale. Further investigation demonstrates current can be enhanced in the center of the apertures while electric fields are found to be easier to concentrate at the tiny fractal structures. Magnetic intensity distributions at several resonant points in the spectrum of the third-iteration SCBA are also plotted and the longer wavelength region in near infrared is found to be unsuited for confining magnetic field in SCBA due to weak interaction with the fractals.

We report the 3D simulation of a disk-shaped, Moiré-type plasmonic cavity inside a photonic crystal cavity. The simulation consider normal incidence of light over the sample to be analized with a confocal microscope in reflection mode. The plasmonic cavity is made of gold, 250 nm of thickness, whose surface is modulated by a sinusoidal function. The photonic crystal cavity is made in silicon nitride film (150 nm of thickness) over a SiO2 film (500 nm) on a silicon substrate, the overall structure being Si/SiO2/SiN/Au. The simulation results show a three-fold enhancement of the electric field intensity for the plasmonic cavity within the photonic cavity, in comparison with that for the plasmonic cavity without the photonic crystal cavity. The result indicates that the electric field intensities of the photonic crystal cavity modes add to the scattered field of the plasmonic cavity, thus enhancing the electric field just above the plasmonic cavity. A preliminary test of the structure was done with a 300 nm gold film over a silicon substrate, made by focus ion beam (FIB) milling, to show fluorescence enhancement of porphiryn molecules. The structure can be elaborated to serve either as fluorescence enhancement of molecules or as Surface-enhancement Raman scattering (SERS) sensor.

The classical self-imaging effect can be observed for a periodic object with a pitch larger than the diffraction limit of an imaging system. In this paper, we show that the self-imaging effect can be achieved in an indefinite metamaterial even when the period is much smaller than the diffraction limit in both two-dimensional and three-dimensional numerical simulations, where the paraxial approximation is not applied. This is attributed to the evanescent waves, which carry the information about subwavelength features of the object, can be converted into propagating waves and then conveyed to far field by the metamaterial, where the permittivity in the propagation direction is negative while the transverse ones are positive. The indefinite metamaterial can be realized and approximated by a system of thin, alternating multilayer metal and insulator (MMI) stack. As long as the loss of the metamaterial is small enough, deep subwavelength image size can be achieved.

In this paper, we have demonstrated a metallic nano-structured SPR sensor for an improvement of biosensing sensitivity using a metallic nano-structure. Permittivity of metal is calculated with Drude model for analysis. The sensitivity of SPR sensor with metallic nano-structure is 65 degree/RIU, and that of conventional SPR configuration is 54.8 degree/RIU. We have fabricated the random metallic nano-structures on the metallic thin film using the RIE etching process. Moreover, we have analyzed the structure using the finite-difference time-domain method for the exact characteristic.

A multilayer metal-insulator (MMI) stack system is viewed as an anisotropic metamaterial to exhibit plasmonic behavior and a candidate of "metametal". The dispersion of the fundamental super mode propagating along the boundary between an MMI stack and a dielectric coating is theoretically studied and compared to that of surface waves on a single metalinsulator boundary. The conditions to obtain artificial surface plasmon frequency are thoroughly investigated, and the tuning of effective surface plasmon frequency is verified by electromagnetic modeling. The design rules would bring important insights into layer-by-layer metamaterial development related to superlenses, optical lithography, nanosensing and imaging.

Study of structures that demonstrate negative refraction is important in the search for metamaterials suitable for imaging capabilities below the diffraction limit. In this work, we study negative refraction behavior for the third photonic band of two dimensional elliptical rod photonic crystals in a centered rectangular lattice in air background using analysis of the equifrequency contours of this band combined with FDTD simulations. Hyperbolic equifrequency contours on the third photonic band indicate both negative and positive refraction at different angles. FDTD simulations are used to verify negative and positive refraction in the third band and search for potential imaging capabilities. If these behaviors are found, this photonic crystal design could potentially find use in sub-diffraction limit imaging applications.

Localized surface plasmon resonance, a property characteristic of metal nanoparticles, is a promising technique for the development of low cost, rapid, and portable biosensors for a variety of medical diagnostic applications. In order to meet the demanding detection limits required for many such applications, performance improvements are required. Designing nanoparticle structures to maximize refractive index sensitivity and optimize the electromagnetic field decay length is one approach to achieving better performance. However, experimentally finding the optimal nanoparticle structure, as has been done in the past, is time consuming and costly, and needs to be done for each biomolecule of interest. Instead, simulations can be used to find the optimal nanoparticle design prior to fabrication. In this paper, we present a numerical modeling technique that allows the design of optimal nanoparticles for LSPR biosensors, and report on the effect of the size and shape of gold nanoparticles on the sensitivity and decay length. The results are used to determine the optimal nanoparticle geometry for an LSPR immunosensor for heat shock protein 70, an important protein with applications in medical and wildlife diagnostics. Our simulations show an improvement of 373% in sensor response when using the optimal configuration, showcasing the significant advantages of proper nanoparticle design.

Periodic nanostructure arrays forming electric dipoles or quadrupoles were fabricated with a Focused Gallium Ion Beam on a gold thin film deposited onto an Er³⁺-doped tellurite glass. The nanostructures were vertically illuminated with an Argon Ion laser (488 nm). The Er³⁺ luminescence spectrum was then measured in the far-field. The observed luminescence is elucidated considering the following effects: (i) excitation of the Er³⁺ ions by means of the localized surface plasmon resonance from the electric dipole/quadrupole nanostructures, that produce an improvement of the local field, resulting in an enhanced luminescence, and (ii) the Er³⁺ luminescence spectrum depends on the albedo of the system (electric dipole/quadrupole arrays), for which its resonant properties is strongly affected. In this way, the emission of the Er³⁺ is achieved through the metallic nanostructures. Additional contributions for the observed emission spectrum regarding the influence of physical and geometrical parameters, period of the electric multipole and lattice symmetry have been investigated. The variation of these parameters resulted in a significantly improvement of luminescence spectra.

Plasmonic lenses consisting of convex/concave concentric rings with different periods were milled with a Focused Gallium Ion Beam on a gold thin film deposited onto an Er³⁺-doped tellurite glass. The plasmonic lenses were vertically illuminated with an Argon Ion laser (488 nm) highly focused by means of a 20x objective lens. The focusing mechanism of the plasmonic lenses is explained by using a simple coherent interference model of surface plasmon-polariton generation on the circular grating as a result of the incident field. Particularly, this beam focusing structure has a modulated groove depth (concave/convex). As a result, phase modulation can be accomplished by the groove depth profile, similarly to a nano-slit array with different thicknesses. This focusing allows a high confinement of SPPs which excited the Er³⁺ ions of the substrate. The luminescence spectrum of Er³⁺ ions was then measured in the far-field, where we could verify the excitation yield of the plasmonic lens on the Er³⁺ ions. We analyze the influence of physical and geometrical parameters on the emission spectra, such as the periodicity and depth profile of the rings. The variation of these parameters resulted in considerable changes of the luminescence spectra.

State of art III-V multi-junction solar cells have demonstrated a record high efficiency of 43.5%. However, these cells are only applicable to high concentration systems due to their high cost of substrates and epitaxial growth. We demonstrate thin film flexible nanostructure arrays for III-V solar cell applications. Such nanostructure arrays allow substrate recycling and much thinner epitaxial layer thus could significantly reduce the cost of traditional III-V solar cells. We fabricate the GaAs thin film nanostructure arrays by conformally growing GaAs thin film on nanostructured template followed by epitaxial lift-off. We demonstrate broadband optical absorption enhancement of a film of GaAs nanostructure arrays over a planar thin film with equal thickness. The absorption enhancement is about 300% at long wavelengths due to significant light trapping effect and about 30% at short wavelengths due to antireflection effect from tapered geometry. Optical simulation shows the physical mechanisms of the absorption enhancement. Using thin film nanostructure arrays, the III-V solar system cost could be greatly reduced, leading to low $/W and high kW/kg flexible solar systems.

Helix photonic metamaterials are attractive to many applications due to the unique properties of strong circular dichroism and gyrotropy. In this study, the optical properties of metallic helix metamaterial were systematically investigated. Such metamaterial is composed of three-dimensional metallic helical nanowires arranged in a two-dimensional array. 3D finite-difference time-domain (FDTD) method was adopted for simulating the spectral response under the excitation of circularly polarized light. We show that the spectral responses were correlated to the dimensions of the helix structures. Generally, the resonance wavelengths as well as optical properties were determined by the geometrical parameters and the composed materials of the structures. When the dimension scaled down, electromagnetic interactions between helices are pronounced, which consequently affect the optical responses of the structures. The dependency between structure dimension and the corresponding optical properties were discussed and presented in this report.

Metallic nanorod array metamaterials, consisting of nanowires arranged in a two-dimensional array, have exhibited many unique features and attracted much attention recently. Owing to the sensitive nature of the plasmon resonances to changes in geometrical parameters of nanorod arrays, significant shift in resonance wavelengths along with variances in field distribution have been observed. In this study, we characterize the distribution of electric fields and the energy flow in the metallic nanorod metamaterial by finite-difference time-domain (FDTD) method. We show that the direction of energy flow is strongly correlated to the geometrical parameters of nanorod arrays and the wavelength. We estimated the energy flow along a plasmonic waveguide and analyzed the field distribution in a unit cell corresponding to different geometrical parameters and excitation wavelength. The results show that the dominant direction of energy flow is related to the geometrical parameters and the excitation conditions. The reported phenomena for metallic nanorod metamaterials may find numerous applications for guiding structures and sensors.

Alternating stacks of metal and dielectric films with nano-hole arrays, called fishnet structures, control the propagation of electromagnetic waves. In such a structure, changing a dimension or a shape, especially the change in shape of nanoholes, affect propagation constants. In this study, we report the dispersivity of fishnet structures is controllable with different hole shapes, by measuring the interferometric fringe in various wavelengths. Two structures were fabricated, which consist of five alternating stacks of aluminum and silicon dioxide with nano-hole arrays. The holes in one of the structures are circular with diameters of 500nm, and the other are square with 500nm sides. The lattice constant in each case is 1,000nm. Since fishnet structures are wavelength-dependent structures, the variable-wavelength interferometric microscope was set up. The phase shift of the circular hole and the square hole fishnet were about 110 degrees and 85 degrees, respectively, within a tunable wavelength from 1,470nm to 1,545nm. These values were equivalent to a refractive-index-change of 0.8 and 0.6, respectively. From these results, fishnet structures indicate high dispersivity within target wavelengths. The dispersion of fishnet structure can be controlled by the shape of the hole.

The color of scattered light from longitudinal and transverse surface plasmon resonances of individual gold nanorods is used to detect the polarization direction of incident light at the nanoscale. The relative strength of the scattered intensities of the two resonances reflects the relative orientation between the polarization of incident light and the nanorod. The resultant colored spectrum is used as a metric for polarization sensing in a darkfield geometry. This technique is demonstrated in the visible to near infrared region by varying the aspect ratio of the nanorods between 2 and 5 with diameters less than 20 nm. The ability to determine the polarization of light visually at the nanoscale provides an important tool in material science and molecular biology for probing anisotropic material properties at the nanoscale using single nanorods. In contrast to photothermal imaging where laser induced deformation of nanoparticles occur, this bimodal darkfield scattering is non-destructive and internally calibrated. The tunability of the plasmonic bands by varying the aspect ratio is beneficial for the usage of this method over a broad spectral range.