This PDF file contains the front matter associated with SPIE Proceedings Volume 9756, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

We introduce and develop design, fabrication and characterization methodology for engineering the effective refractive index of a composite dielectric planar surface created by controlling the density of deeply subwavelength low index nanoholes (e.g., air) in a high index dielectric layer (e.g., Si). The nanoscale properties of a composite dielectric layer allows for full control of the optical wavefront phase by designing arbitrary space-variant refractive index profiles. We present the composite dielectric metasurface microlens exploiting symmetric design to achieve polarization invariant impulse response, and use asymmetric design to demonstrate polarization sensitive impulse response of the lens. This composite dielectric layers lenses were fabricated by patterning nanohole distributions on a dielectric surface and etching to submicron depths. Our dielectric microlens with asymmetric distribution of n_eff (n_eff x ≠ n_{eff y}) demonstrates a graded index lens with polarization dependent focusing with of 32um and 22 um for linearly x- and y-polarized light, respectively operating at a wavelength of λ = 1550nm. We also show numerically and demonstrate experimentally achromatic performance of the devices operating in the wavelength range of 1500nm - 1900nm with FWHM of the focal spots of about 4um. Namely, we have constructed a graded index lens that can overcome diffraction effects even when aperture/wavelength (D/λ) is smaller than 40. The demonstrated novel approach to engineer dielectric composite nanosurfaces has the potential to realize arbitrary phase functions with minimal insertion loss, submicron thickness and miniaturization to reduce element size and weight, and may have a significant impact on numerous miniature imaging systems applications.

We experimentally demonstrate the spatial and spectral control of the thermal emission of a gold mirror in the infrared thanks to plasmonic nano-antennas made of Metal-Insulator-Metal patches. Six juxtaposed arrays of antennas with various geometries were realized on a sample in the same technological process. Their emissivity was characterized thanks to a dedicated bench, based on the combination of a Fourier transform infrared spectrometer and a high resolution infrared camera. We show that these arrays are infrared emitters that exhibit a near unity monochromatic and omnidirectional emissivity in the [3 - 5] μm spectral band.

Metasurfaces are boundaries between two media that are engineered to induce an abrupt phase shift in propagating light over a distance comparable to the wavelength of the light. Metasurface applications exploit this rapid phase shift to allow for precise control of wavefronts. The phase gradient is used to compute the angle at which light is refracted using the generalized Snell’s Law. [1] In practice, refractive metasurfaces are designed using a relatively small number of phaseshifting elements such that the phase gradient is discrete rather than continuous. Designing such a metasurface requires finding phase-shifting elements that cover a full range of phases (a phase range) from 0 to 360 degrees. We demonstrate an analytical technique to calculate the refraction angle due to multiple metasurfaces arranged in series without needing to account for the effect of each individual metasurface. The phase gradients of refractive metasurfaces in series may be summed to obtain the phase gradient of a single equivalent refractive metasurface. This result is relevant to any application that requires a system with multiple metasurfaces, such as biomedical imaging [2], wavefront correctors [3], and beam shaping [4].

Conventionally, all-optical switching devices made out from bulk silicon and other semiconductors are limited by free-carrier relaxation time which spans from picoseconds to microseconds. In this work, we discuss the possibility to suppress the undesired long free-carrier relaxation in subwavelength dielectric nanostructures exhibiting localized magnetic Mie resonances. Numerical calculations show the unsymmetrical modification of the transmittance spectra of the nanodisks due the free carriers photo-injection. Such a spectral dependance allows to control temporal response of the nanostructure by varying the laser pulse spectum.

Optomechanical crystal is a combination of both photonic and phononic crystal. It simultaneously confines light and mechanical motion and results in strong photon-phonon interaction, which provides a new approach to deplete phonons and realize on-chip quantum ground state. It is promising for both fundamental science and technological applications, such as mesoscopic quantum mechanics, sensing, transducing, and so on. Here high optomechanical coupling rate and efficiency are crucial, which dependents on the optical-mechanical mode-overlap and the mechanical frequency (phonon frequency), respectively. However, in the conventional optomechanical-crystal based on the same periodical structure, it is very difficult to obtain large optical-mechanical mode-overlap and high phonon frequency simultaneously. We proposed and demonstrated nanobeam cavities based on hetero optomechanical crystals with two types of periodic structure. The optical and mechanical modes can be separately confined by two types of periodic structures. Due to the design flexibility in the hetero structure, the optical field and the strain field can be designed to be concentrated inside the optomechanical cavities and resemble each other with an enhanced overlap, as well as high phonon frequency. A high optomechanical coupling rate of 1.3 MHz and a high phonon frequency of 5.9 GHz are predicted theoretically. The proposed cavities are fabricated as cantilevers on silicon-on-insulator chips. The measurement results indicate that a mechanical frequency as high as 5.66 GHz is obtained in ambient environment, which is the highest frequency demonstrated in one-dimensional optomechanical crystal structure.

Optical chirality has been recently suggested to complement the physically relevant conserved quantities of the well-known Maxwell's equations. This time-even pseudoscalar is expected to provide further insight in polarization phenomena of electrodynamics such as spectroscopy of chiral molecules. Previously, the corresponding continuity equation was stated for homogeneous lossless media only. We extend the underlying theory to arbitrary setups and analyse piecewise-constant material distributions in particular. Our implementation in a Finite Element Method framework is applied to illustrative examples in order to introduce this novel tool for the analysis of time-harmonic simulations of nano-optical devices.

Utilizing the inverse design engineering method of topology optimization, we have realized high-performing all-silicon ultra-compact polarization beam splitters. We show that the device footprint of the polarization beam splitter can be as compact as ~2 μm² while performing experimentally with a polarization splitting loss lower than ~0.82 dB and an extinction ratio larger than ~15 dB in the C-band. We investigate the device performance as a function of the device length and find a lower length above which the performance only increases incrementally. Imposing a minimum feature size constraint in the optimization is shown to affect the performance negatively and reveals the necessity for light to scatter on a sub-wavelength scale to obtain functionalities in compact photonic devices.

Optical nano-antennas have been the focus of intense research recently due to their ability to manipulate electromagnetic radiation on a subwavelength scale, and there is major interest in such devices for a wide variety of applications in photonics, sensing, and imaging. Significant effort has been put into developing highly compact, novel, next-generation light sources, which have great potential in realizing efficient sub-wavelength single photon sources and enhanced biological and chemical sensors. We have developed a number of innovative optical antenna designs including elements of chiral metasurfaces for enabling circularly polarized emission from quantum sources, new designs derived from Radio Frequency (RF) elements for quantum source enhancement and directionality, and nanostructures for investigating plasmonic dark-modes that have the ability to significantly reduce the Q-factor of nano-antennas. A challenge, however, remains the development of a scalable nanofabrication technology. The capacity to mass-produce nano-antennas will have a considerable impact on the commercial viability of these devices, and greatly improve research throughput. Here we present recent progress in the development of scalable fabrication strategies for producing of nano-antennas and antenna arrays, along with slot based plasmonic optical devices.

We have studied an influence of Tamm plasmon-polaritons (TPPs) excitation on the nonlinear-optical response of one-dimensional photonic crystal/metal structures. It was shown that in case when the fundamental radiation is in resonance with the TPP, second-harmonic generation in the sample is enhanced over two times of magnitude in comparison with a bare metal film. Using methods of nonlinear transfer matrices it was demonstrated that the third-order nonlinear response of a metal/dielectric heterostructure, when both fundamental and third-harmonic radiation are in resonance with the first- and third-order TPPs respectively, can be enhanced via two mechanisms: fundamental field localization and optical harmonic resonant tunneling. The overall enhancement of the third harmonic generation in that case can exceed three orders of magnitude in comparison with the non-resonant case.

Electromagnetic (EM) wave detection over a large spectrum has recently attracted significant amount of attention. Traditional electronic EM wave sensors use large metallic probes which distort the field to be measured and also have strict limitations on the detectable RF bandwidth. To address these problems, integrated photonic EM wave sensors have been developed to provide high sensitivity and broad bandwidth. Previously we demonstrated a compact, broadband, and sensitive integrated photonic EM wave sensor, consisting of an organic electro-optic (EO) polymer refilled silicon slot photonic crystal waveguide (PCW) modulator integrated with a gold bowtie antenna, to detect the X band of the electromagnetic spectrum. However, due to the relative large RC constant of the silicon PCW, such EM wave sensors can only work up to tens of GHz. In this work, we present a detailed design and discussion of a new generation of EM wave sensors based on EO polymer refilled plasmonic slot waveguides in conjunction with bowtie antennas to cover a wider electromagnetic spectrum from 1 GHz up to 10THz, including the range of microwave, millimeter wave and even terahertz waves. This antennacoupled plasmonic-organic hybrid (POH) structure is designed to provide an ultra-small RC constant, a large overlap between plasmonic mode and RF field, and strong electric field enhancement, as well as negligible field perturbation. A taper is designed to bridge silicon strip waveguide to plasmonic slot waveguide. Simulation results show that our device can have an EM wave sensing ability up to 10 THz. To the best of our knowledge, this is the first POH device for photonic terahertz wave detection.

Distinguishing contributions of physical and optical characteristics, and their interactions, to complicated features observed in spectra of nanocomposite plasmonic systems slows their implementation in optoelectronics. Use of vacuum, effective medium, or analytic approximations to compute such contributions are insufficient outside the visible spectrum (e.g., in energy harvesting) or for interfaces with complex dielectrics (e.g., semiconductors). This work synthesized discrete dipole computation of local physical/optical interaction with coupled dipole approximation of far-field Fano coupling to precisely distinguish effects of locally discontinuous dielectric environment and structural inhomogeneity on complicated spectra from a square lattice of gold nanospheres supported by complex dielectric substrates. Experimental spectra decomposition of resonant energies/bandwidths elucidated indium tin oxide affected surfaced plasmon resonance while silica affected diffractive coupled resonance features. Energy transport during plasmon decay was examined for each substrate under a variety of physical support configurations with the gold nanospheres. The compact, multi-scale approach can be adapted to arbitrary nanoantenna shapes (e.g., nanorings) interacting with various dielectrics (e.g., dichalcogenides). It offers >10⁴-fold reduction in computation time over existing descriptions to accelerate the design and implementation of functional plasmonic systems.

This paper presents the preliminary experimental studies of the influences of structural parameters, including the fill factor, device size, lattice, and nanoaperture shape, on the far-field optical transmission properties through the finite-sized two-dimensional periodic arrays of metallic nanoapertures. Both the lensing effect and the Talbot effect are observed, characterized and analyzed. Light intensity patterns of Talbot revivals at various Talbot distances containing abundant subwavelength hotspots are obtained, and the average size of the hotspots are derived and compared. Some concluding remarks are given to provide an important technological reference for the design and application of such devices according to the current experimental results.

We demonstrate tunable, polarization-dependent, dual-color plasmonic filters based upon arrays of asymmetric cross-shaped nano-apertures. Acting as individual color emitting nano-pixels, each aperture can selectively transmit one of 2 colors, switched by controlling the polarization of white-light incident on the rear of each pixel. By tuning the dimensions of the pixels we build a polarization sensitive color palette at resolutions far beyond the diffraction limit. Using this switchable color palette we are able to generate complex optical surfaces encoded with dual color and information states; allowing us to embed two color images within the same unit area, using the same set of nanoapertures.

A highly selective plasmonic demultiplexer based on a plasmonic slot waveguide platform is proposed. The structure is optimized as an add drop multiplexer/demultiplexer. The optimal design is targeting minimum FWHM. The device is optimal quad multiplexer/demultiplexer has FWHM of 9.8 nm for each channel with a high output transmission near the 1550 nm. The proposed structure is simple, can be easily fabricated. Extended optimization was performed that enabled the multiplexed signal to have FWHM of 8.16 nm with peak power of 30 % near the 1300 nm. The structure can be utilized for double channel multiplexing applications and more by doing the needed optimization for such high scalability.

High Q optical cavities are employed to realize a coupled cavity system with which to achieve optical signal processing. Photonic crystal (PhC) nanocavities are particularly attractive because they are suitable for integration. However, they usually suffer from low coupling efficiency with optical fiber and poor resonant wavelength controllability. We recently demonstrated cavity mode formation by placing a tapered nanofiber close to a two-dimensional photonic crystal waveguide. The cavity mode couples directly with the nanofiber, which results in a coupling efficiency of 39% with a high Q of over half a million. The cavity is formed due to the modulation of the effective refractive index, which is caused by bringing a nanofiber close to the silicon slab. Precise tuning of the resonant wavelength becomes possible by changing the contact area of the nanofiber. In this study, we demonstrate the coupling and de-coupling of coupled PhC nanocavities formed by a nanofiber placed on a PhC waveguide. The wavelength shift of one of the cavities (mode A) is more sensitive than that of the other cavity (mode B) to a change in the nanofiber contact area. By using this difference, we can tune the resonant wavelength of mode A (Q = 4.6×10⁵) to that of mode B (Q = 6.0×10⁵). Then, a clear anti-crossing with a mode splitting of g/2π = 0.94 GHz is observed, which is the result of the coupling of the two modes. A reconfigurable coupled cavity system was demonstrated.

As they allow the control of light propagation, photonic crystals find many fields of application. Among them, self-assembled 3D-photonic crystals are ordered at the nanometric scale over centrimetric areas. Furthermore, self-assembly allows the design of complexes structures leading, for example, to the controlled disruption of the crystal periodicity (called defect) and the appearance of permitted optical frequency bands within the photonic bandgap. Light frequencies included in the corresponding passband are then localized in the defect allowing manipulation of nano-emitters fluorescence. We present the fabrication and the optical characterization of a heterostructure composed of a sputtered silica layer sandwiched between two silica opals. We show by photoluminescence measurements than this structure strongly modifies the transmitted fluorescence of nanocrystals.

Maxwell solvers based on the hp-adaptive finite element method allow for accurate geometrical modeling and high numerical accuracy. These features are indispensable for the optimization of optical properties or reconstruction of parameters through inverse processes. High computational complexity prohibits the evaluation of the solution for many parameters. We present a reduced basis method (RBM) for the time-harmonic electromagnetic scattering problem allowing to compute solutions for a parameter configuration orders of magnitude faster. The RBM allows to evaluate linear and nonlinear outputs of interest like Fourier transform or the enhancement of the electromagnetic field in milliseconds. We apply the RBM to compute light-scattering off two dimensional photonic crystal structures made of silicon and reconstruct geometrical parameters.

We demonstrate a solar control window film consisting of metallic nanoantennas designed to reflect infrared (IR) light while allowing visible light to pass through. The film consists of a capacitive frequency-selective surface (CFSS) which acts as a band-stop filter, reflecting only light at target wavelengths. The designed CFSS when installed on windows will lower air conditioning costs by reflecting undesired wavelengths of light and thus reduce the amount of heat that enters a building. State-of-the-art commercial solar control films consist of a multilayer stack which is costly (~$13/m² to $40/m²) to manufacture and absorbs IR radiation, causing delamination or glass breakage when attached to windows. Our solar control film consists of a nanostructured metallic layer on a polyethylene terephthalate (PET) substrate that reflects IR radiation instead of absorbing it, solving the delamination problem. The CFSS is also easy to manufacture with roll-to-roll nanoimprint lithography at a cost of <$12/m². We design the CFSS using the COMSOL Wave Optics module to solve for electromagnetic wave propagation in optical media via the finite element method. The simulation domain is reduced to a single unit cell with periodic boundary conditions to account for the symmetries of the planar, periodic CFSS. The design is optimized using parametric sweeps around the various geometric components of the metallic nanoantenna. Our design achieves peak reflection of 80% at 1000 nm and has a broadband IR response that will allow for optimum solar control without significantly affecting the transmission of visible light.

Gyroid is a type of three-dimensional chiral structures and has been found in many insect species. Besides the photonic crystal properties exhibited by gyroid structures, the chirality and gyroid network morphology also provide unique opportunities for manipulating propagation of light. In this work, we present studies based on finite-difference time domain (FDTD) method for analyzing the dispersion relation characteristics of dielectric single gyroid (SG) metamaterials. The band structures, transmission spectrum, dispersion surfaces, equifrequency contours (EFCs) of SG metamaterials are examined. Some interesting wave guiding characteristics, such as negative refraction and collimation, are presented and discussed. We also show how these optical properties are predicted by analyzing the EFCs at different frequencies. These results are crucial for the design of functional devices at optical frequencies based on dielectric single gyroid metamaterials.

Metasurfaces refer to periodic arrays of thin nano-antennas which are separated by subwavelength length. Due to the strong capability of nano-antenna distributions in phase profile generation, hologram generation using metasurfaces has attracted attention of many researchers. We propose a reflective type hologram by a metasurface composed of Z-shaped nano-antennas. The proposed metasurface renders precise phase modulation with spatially varying orientation, which attributes to the increase of the level of phase distribution. It has different plasmonic resonance mode for the orthogonal linear polarized incidence that makes different phase delay effect for orthogonal input. The metasurface we propose shows phase modulation characteristics over a wide wavelength range between 800 nm and 1,500 nm. Also it achieves high polarization conversion efficiency above 80% in a broad bandwidth. Meta-hologram using the metasurface has opened the possibility of variety of structures and expanded to near-infrared region. We expect our proposal could be applied to the more complicated meta-holograms.

We propose a novel type of dual surface plasmon polariton (SPP) gap nano-antennas which can excite SPPs directionally and switch the direction according to the device temperature. The device consists of a vanadium dioxide (VO2)- insulator-metal resonator and a metal-insulator-metal resonator with slightly different antenna width. Phase of SPPs generated by the VO2 gap antenna changes as the temperature increases, so that interference between SPPs generated from two separated gap antennas makes its launching direction switched. In case of 624 nm wavelength, directional intensity distinction ratios of coupled SPPs are about 1:5 and 7:1 when VO2 is in insulator phase and metallic phase, respectively.

In recent years, the global market for biosensors has continued to increase in combination with their expanding use in areas such as biodefense/detection, home diagnostics, biometric identification, etc. A constant necessity for inexpensive, portable bio-sensing methods, while still remaining simple to understand and operate, is the motivation behind novel concepts and designs. Labeled visible spectrum bio-sensing systems provide instant feedback that is both simple and easy to work with, but are limited by the light intensity thresholds required by the imaging systems. In comparison, label-free bio-sensing systems and other detection modalities like electrochemical, frequency resonance, thermal change, etc., can require additional technical processing steps to convey the final result, increasing the system’s complexity and possibly the time required for analysis. Further decrease in the detection limit can be achieved through the addition of plasmonic structures into labeled bio-sensing systems. Nano-structures that operate in the visible spectrum have feature sizes typically in the order of the operating wavelength, calling for high aspect ratio nanoscale fabrication capabilities. In order to achieve these dimensions, electron beam lithography (EBL) is used due to its accurate feature production. Hydrogen silsesquioxane (HSQ) based electron beam resist is chosen for one of its benefits, which is after exposure to oxygen plasma, the patterned resist cures into silicon dioxide (SiO2). These cured features in conjunction with nanoscale gold particles help in producing a high electric field through dipole generation. In this work, a detailed process flow of the fabrication of square lattice of plasmonic structures comprising of gold coated silicon dioxide pillars designed to operate at 560 nm wavelength and produce an intensity increase of roughly 100 percent will be presented.

The spectral evolution of the degree of linear polarization (P_L) at a scattering angle of 90° is studied numerically for high refractive index (HRI) dielectric spherical nanoparticles. The behaviour of P_L(90°) is analyzed as a function of the refractive index of the surrounding medium and the particle radius. We focus on the spectral region where both electric and magnetic resonances of order not higher than two are located for various semiconductor materials with low absorption. The spectral behavior of P_L(90°) has only a small, linear dependence on nanoparticle size R. This weak dependence makes it experimentally feasible to perform real-time retrievals of both the refractive index of the external medium and the NP size R. From an industrial point of view, pure materials are nonrealistic, since they can only be provided under certain conditions. For this reason, we also study the effect of contaminants on the resonances of silicon NPs by considering the spectral evolution of P_L(90°).

Recent studies show that the spectral behaviour of localized surface plasmon resonances (LPSRs) in metallic nanoparticles suffer from both a redshift and a broadening in the transition from the far- to the near-field regimes. An interpretation of this effect was given in terms of the evanescent and propagating components of the angular spectrum representation of the radiated field. Due to the increasing interest awakened by magnetodielectric materials as a both low-loss material option for nanotechnology applications, and also for their particular scattering properties, here we study the spectral response of a magnetodielectric nanoparticle as a basic element of a dielectric nano-antenna. This study is made by analyzing the changes suffered by the scattered electromagnetic field when propagating from the surface of this dielectric nanostructure to the far-zone in terms of propagating and evanescent plane wave components of the radiated fields.