"Recent advances in metasurface flat optics" was recorded at Photonics West 2020 in San Francisco, California.

The efficient harvesting of electromagnetic (EM) waves by sub-wavelength nanostructures can result in perfect light absorption in the narrow or broad frequency range. In recent years, the concept of lithography-free planar light perfect absorbers has attracted much attention in different parts of the EM spectrum, owing to their ease of fabrication and high functionality. In this talk, we will review the material and architecture requirements for the realization of light perfect absorption using these multilayer metamaterial designs from ultraviolet (UV) to far-infrared (FIR) wavelength regimes. We will summarize our latest studies on the use of metamaterial designs for energy conversion, filtering, and sensing applications using lithography-free light perfect absorbers. We will also discuss the progress, challenges, and outlook of this field to outline its future direction.

Nonreciprocal transmission is the fundamental process behind unidirectional wave propagation phenomena. In our work, a compact and practical parity-time (PT) symmetric metamaterial is designed based on two Silicon Carbide (SiC) media separated by an air gap and photonically doped with gain and loss defects. We demonstrate that an exceptional point (EP) is formed in this PT-symmetric system when SiC operates as a practical epsilon-near-zero (ENZ) material and by taking into account its moderate optical loss. Furthermore and even more importantly, strong self-induced nonreciprocal transmission is excited due to the nonlinear Kerr effect at a frequency slightly shifted off the EP but without breaking the PT-symmetric phase. The transmittance from one direction is exactly unity while the transmittance from the other direction is decreased to very low values, achieving very high optical isolation. The proposed active nonlinear metamaterial overcomes the fundamental physical bounds on nonreciprocity compared with a passive nonlinear nonreciprocal resonator. The strong self-induced nonreciprocal transmission arises from the extreme asymmetric field distribution achieved upon excitation from opposite incident directions. The significant enhancement of the electric field in the defects effectively decreases the required optical power to trigger the presented nonlinear response. This work can have a plethora of applications, such as nonreciprocal ultrathin coatings for the protection of sources or other sensitive equipment from external pulsed signals, circulators, and isolators.

We propose and demonstrate low-refractive-index particles with all-dielectric metamaterial shell which lead to formation of high intensity photonic nanojets. We show that the extra degree of freedom because of the anisotropy of the shell gives rise to an increase in the photonic jet intensity inside the metamaterial shell without a need to increase the size of the particle. The anisotropy of the shell can also control the spectral and spatial location of the Mie-type multipolar resonances to achieve the desired scattering. In experiments, the metamaterial shell is composed of strong nonlinear materials leading to enhanced nonlinear wavelength conversion at nanoscale.

Topologically phases, characterized by topological invariants of bulk energy bands, provide remarkable capability to robustly control the propagation of electrons, photons, and phonons. The recently reported higher-order topological insulators (HOTIs) have shown that not only surface and edge states, but also localized corner states can be topologically protected. So far, most realizations of photonic HOTIs are based on lumped circuit components or bulky structures (assume infinite height) with confining metallic plates, which are not suitable for practical integrated photonics applications. Here, we show possible HOTIs’ metasurface designs using patterned flat plasmonic sheets as well as thin slabs of all-dielectric photonic crystals based on square and kagome lattices. The structures support both gapped one-dimensional edge states and in-gap zero-dimensional corner states. The non-trivial topology of the bands is characterized by 2D Zak phase (bulk polarization) and the presence of the topological modes is determined in a dimensional hierarchy according to bulk-edge-corner correspondence. The higher-order phases can be understood as the result of the interplay of localization mechanisms along two dimensions. Topological transitions are realized by tweaking the arrangement of the constituent atoms of the unit cell, which changes the intra/inter-cell coupling strengths and the symmetry of the lattice/interface. Our work opens the door for robust localized cavity as well as guided edge modes on scalable, integrated photonic platforms, which feature improved control of light-matter interactions. Additionally, since the proposed structures are open-boundary, this allows for greater degree of flexibility and direct experimental studies of classical topological states using near-field scanning technique.

Complex 3D nanophotonic devices demand robust methods for the design and rapid prototyping of heterogeneous material structures with sub-100 nm resolution. Here we present an automated optical tweezer platform for assembling nanoparticles of multiple materials. In pursuit of higher throughput, we have demonstrated record nanoparticle manipulation speeds >150 um/s. To design structures, we use a coupled dipole model that is orders of magnitude faster than commercial tools. In developing this method, we have found that a longstanding practice of basing a metallic nanoparticle’s dipole moment on its skin depth is significantly less accurate than calculations based on full particle volume.

A range of color quantification methods are developed and applied to characterize the structural color of thin film photonic crystals known as polymer opals. Order is progressively induced within these engineered nanostructures, and three-dimensional reflectivity measurements allow for the ‘scattering cone’ to be located and analyzed. Reported are observations that demonstrate how the chromatic properties of resultant structural color change as functions of both viewing angle and sample ordering. These measurements are mapped to a CIE 1931 color space, from which chromaticity metrics are readily extracted. The hue of structural coloration is shown to tune towards longer wavelengths by progressively improved structural order, and an improvement in color saturation can be observed as order is induced. In understanding how structural color can be quantified and manipulated, large-area photonic structures have potential for application as coatings and sensors, as well as smart fabrics and many other optical devices.

We present system-level models for ideal and realistic metasurfaces that can be used in designing metasurface optical systems. We show that ideal gradient metasurfaces have spatially varying field transmission amplitudes that can exceed one and discuss its effect on the modulation transfer function of metalenses. We introduce a general model for non-ideal metasurfaces based on the discrete-space impulse response concept. The new model takes into account reflections and undesired diffractions from metasurfaces and enables accurate black-box models that can be incorporated into design tools. We also present examples of its applications in analyzing optical systems composed of cascaded metasurface components.

Metasurfaces are known as a powerful tool for complex wavefront shaping. However, two-dimensional metasurface systems of nanoparticles exhibit only a weak spatial asymmetry perpendicular to the surface and therefore have mostly reciprocal optical transmission features. To influence this reciprocity, we present a metasurface design principle for nonreciprocal polarization encryption of holograms. Our approach is based on a two-layer plasmonic metasurface design that introduces a local asymmetry and allows full phase and amplitude control of the transmitted light. We experimentally show that our pixel-by-pixel encoded Fourier-hologram appears in a particular linear cross-polarization channel, while it is disappearing in the reverse propagation direction.

This Conference Presentation, "Deep-learning-based design of Fano resonant HfO2 metasurfaces for full color generation," was recorded at Photonics West 2020 held in San Francisco, California, United States.

Metasurfaces consisting of periodically arranged plasmonic nanoparticles could become a promising platform for optical filtering and nonlinear experiments. However, due to the high absorption loss of noble metals e.g. gold, the localized surface plasmon resonances (LSPR) of individual nanoparticles exhibit very low quality factors (Q ~ order of 10), which is not suitable for practical usage. Here, we experimentally demonstrate a plasmonic metasurface with ultra-high-Q (above 1000) surface lattice resonances (SLRs) around the optical telecommunication wavelength of 1550 nm by optimizing the LSPR of rectangular gold nanoparticles and the overall array size.

Nano-architected materials have the potential to be adopted in several areas including photonic devices and structural materials. We present a 3D interference lithography technique with dielectric metasurfaces at visible wavelengths that allows patterning of thick epoxide films over areas on the order of 10 cm^2 with 100 nm resolution. By leveraging the ability of the metasurface to control the amplitude and phase of a wavefront, complex near-field 3D interference patterns can be designed. Pyrolysis of 3D patterned SU-8 produces a carbon-based material with sub-100 nm features and enhanced mechanical properties.

We present a new class of grating-integrated microdisk resonators that directly and efficiently couple to free space and can be excited by top illumination. We discuss the theory and design of such devices and present characterization results of 1530-nm-resonators with 0.8 µm to 1.2 µm radii, which are fabricated using amorphous silicon on glass. A 1.2-µm-radius resonator has a measured Q of ~16,000 and is efficiently excited by top illumination as evidenced by an observed thermally-induced bistability threshold of 0.7 mW. The small footprint and ease of coupling enable dense resonator arrays for applications in free space and flat optics.

Bifocal and multifocal lenses allowing the incoming light to be focused at different focal spots can be applied in imaging, optical communication, and medical applications. In this study, we aim to solve the problems of multifocal lens design by using multilayer Pancharatnam-Berry (P-B) phase architecture. First, we will answer the fundamental question of what will happen when two layers of P-B phase elements are superimposed on each other. We show that a diffraction order with a phase shift equal to the rotation angle difference of the two layers can be observed. Based on this, we designed a multilayer metalens with arbitrary control of focal spot location and relative intensity.

This Conference Presentation, "Sample-efficient machine-learning method for designing photonic nanostructures," was recorded at Photonics West 2020 held in San Francisco, California, United States.

We present subwavelength chiral metasurfaces with freeform geometries obtained from an inverse design algorithm. These metasurfaces possess simultaneously a desired transmission, reflection and absorption spectrum at the wavelength of interest, a feature which is difficult to achieve for regular metasurfaces comprised of discrete shapes due to the limited degrees of freedom in the design. These absorptive metasurfaces could potentially be useful in display technologies by eliminating reflected ambient light, while transmitting the desired image. They have the potential to surpass the performance of traditional circular polarization analyzers and filters.

We demonstrate a novel moiré chiral metamaterial (MCM) with actively tunable and reversible optical chirality, which is enabled by the tunable Fano coupling and a solvent-controllable dielectric spacer in the MCM. Using an ultrathin MCM that is only 1/5 of the working wavelength in thickness, we have achieved the active spectral shift over more than one full width at half maximum and the sign inversion of the circular dichroism spectra. We have further applied the plasmon-enhanced chiral near-fields in the MCM to actively modulate the valley excitons in a monolayer semiconductor. With the large and controllable tunability in both far-field and near-field chiroptical responses, our metamaterials are promising for applications in chiral light modulators, ultrasensitive solvent sensors, and active valleytronic devices.

The search for full control of amplitude and phase of the electromagnetic field from planar surfaces is of high interest for the development of highly integrated photonic systems and at optical devices. A hybrid dielectric plasmonic resonant waveguide grating which enables highly wavelength-selective first order diffraction in a multimode light guide is reported. Measurements show a narrowband peak in the first order of diffraction at resonance, while the undesired transmitted signal is strongly suppressed at other wavelengths as well as in the zeroth diffraction order. Another hybrid resonant waveguide grating is reported and shows a bandwidth of 20nm in the zeroth order of transmission. Overall, this work shows the promising use of hybrid structures for taking the best features of both plasmonic and dielectric grating resonances for designing highly integrated optical devices such as spectrometers or optical security features.

Single, double and triple superimposed surface relief gratings were sequentially laser-inscribed on azobenzene molecular glass films using a Lloyd’s mirror interferometer. The single gratings had a unidirectional sinusoidal profile, the double gratings had two orthogonal grating vectors, and the triple gratings had three grating vectors separated by 30 degrees. These gratings were coated with silver so that surface plasmons can be generated. The purpose of this study is to understand how photons, which have been converted to a plasmon by a first grating, can be re-emitted again, with a different light polarization, by a second in-plane superimposed grating having a different grating vector orientation.

In this study, we implemented a densely packed subwavelength-scale nanocone array, inspired by the morphology of motheye, using a direct printing method. Then, we fabricated triple-deck hierarchical photoanodes on motheye templates through successive deposition of Au, SnO2, and BiVO4 layers. The fabricated motheye structure exhibits a gradual refractive index change, which is excellent for lowering the reflection of high refractive index materials. Also, the synergy between the light trapping effects of the nanocone array and the gap-plasmon structure (reflector/spacer/antenna) maximized the absorption of incident solar light. Due to this enhancement, a current density of 1.481 mA/cm2 was obtained with a thin layer of BiVO4 (200 nm), which is 3.39 times higher than that obtained from a non-patterned structure (reference). Our results could be used for many promising candidate materials for photoanode and optoelectronic devices.

We present analytical and numerical analysis of cylindrical hyperbolic metamaterials (CHMM) for realizing superscattering in the visible region. We show that up-to two-fold enhancement in optical scattering can be achieved for the structures with CHMM, when compared to the homogeneous structures of normal materials. Through numerical calculations, it is demonstrated that whispering gallery like resonance is supported at the superscattering condition. We also employ effective medium approximation models for a comprehensive analysis of mechanism behind the superscattering and whispering gallery mode.

Future quantum optical networks will require an integrated solution to multiplex suitable sources and detectors on a low-loss platform. Here we combined superconducting single-photon detectors with colloidal PbS/CdS quantum dots (QDs) and low-loss silicon nitride passive photonic components to show their combined operation at cryogenic temperatures. Using a planar concave grating spectrometer, we performed wavelength-resolved measurements of the photoluminescence decay of QDs, which were deterministically placed in the gap of plasmonic antennas, in order to improve their emission rate. We observed a Purcell enhancement matching the antenna simulations, with a concurrent increase of the count rate on the superconducting detectors.

Semiconductor quantum dots (QDs) combine high optical activity and the possibility of integration in a myriad of devices. Here, we demonstrate the integration of (Al)GaAs QDs in nanophononic strings and show that the excitonic two-level system of the QD couples to the confined phononic modes in string. For the chosen design the coupling is mediated via the valence band deformation potential and shear strain. Finite element modelling (FEM) shows that the optomechanical coupling parameter γ_om>0.15 meV/nm, exceeding that of vibrating nanowire architectures by one order of magnitude¹.

We present experimental and theoretical demonstrations of quantum-like behavior in phononic structures. This demonstration extends the notion of classical “entanglement” or classical “nonseparability” to the emerging field of phononics, opens the door for acoustic analogues to true quantum system in quantum information processing, since the preparation and control of entangled superposition of states is an essential ingredient for harnessing the second quantum revolution.

Based on our previous static results (cf. Science 358, 1072 (2017)), we have performed experiments on acoustical activity, the mechanical counterpart of optical activity, on 3D chiral micropolar metamaterial beams at ultrasound frequencies (10-200 kHz). We find rotation angles of the incident linear polarization as large as 22 degrees per unit cell. The experiments versus frequency and beam cross section are in excellent agreement with band structure calculations and finite-element calculations for finite-size beams (cf. Nature Commun. 10, 3384 (2019)). Furthermore, we present other metamaterial architectures that approach the fundamental limit of 90 degrees polarization rotation per unit cell (unpublished).

We propose gold micro-grating structures with VO2 filled slots as suitable emitters to achieve enhanced far-field thermal rectification. We numerically calculate the rectification ratio for two different approaches: peak extinction and peak shift. In the peak extinction approach, a change in temperature switches the coupling between a grating surface plasmon mode and far field on and off. In the peak shift approach it causes a shift in its resonant wavelength. In both these approaches, we discuss the effect of tuning the extinction coefficient of metallic and insulating VO2.

The Ge2Sb2Te5 phase-change alloy (GST) is known for its dramatic complex refractive index (and electrical) contrast between its amorphous and crystalline phases. Switching between such phases is also non-volatile and can be achieved on the nanosecond timescale. The combination of GST with the widespread SiN integrated optical waveguide platform led to the proposal of the all-optical integrated phase-change memory, which exploits the interaction of the guided mode evanescent field with a thin layer of GST on the waveguide top surface. The relative simplicity of the architecture allows for its flexible application for data storage, logic gating, arithmetic and neuromorphic computing. Read operation relies on the transmitted signal optical attenuation, due to the GST extinction coefficient. Write/erase operations are performed via the same optical path, with a higher power ad-hoc pulsing scheme, which locally increases the temperature and triggers either the melt-quench process (write) or recrystallization (erase), encoding the information into the GST crystal fraction. Here we investigate the physical mechanisms involved in the write/erase and read processes via computational methods, with the view to explore novel architecture concepts that improve memory speed, energy efficiency and density. We show the achievements of the development of a 3D simulation framework, performing self-consistent calculations for wavepropagation, heat diffusion and phase-transition processes. We illustrate a viable memory optimization route, which adopts sub-wavelength plasmonic dimer nanoantenna structures to harvest the optical energy and maximize light-matter interaction. We calculate both a speed and energy efficiency improvement of around one order of magnitude, with respect to the conventional (non-plasmonic) device architecture.

Ultra-thin metalenses promise to miniaturize imaging systems. However, all lenses require an additional propagation length to allow for light to form an image on a detector. We show that by operating directly on the Fourier components of a complex light field, one may develop an optical element that acts to “propagate” light for a distance that is longer than its physically occupied space. We experimentally demonstrate this effect using a 30-mm-long calcite crystal, mimicking an additional 3.5 mm of free-space propagation while preserving the magnification. This work represents an essential step in the miniaturization of all electro-optical systems.

Nanoparticles made of High Refractive Index (HRI) dielectric materials, such as Si, GaP, Ge or other semiconductor compounds have been proposed recently as an alternative to metals, driven by their low-losses and presence of magnetic response in spite of being non-magnetic materials. However, they are known to suffer relatively large losses and absence of magnetic response at optical frequencies. Here, we intend to show a brief overview of our recent research in light scattering by HRI dielectric nanostructures. In particular, we will show how the strong confinement of electromagnetic energy and the outstanding scattering efficiencies of these HRI dielectric structures make them promising candidates to act as basic units for the design of the next generation of nanoantennas that may be able to boost applications such as sensing, light directivity, optical switching, surface enhanced spectroscopies, all-dielectric metamaterials, or non linear phenomena, such as third harmonic generation

A plasmonic device with a self-referenced capability that uses periodic nanostructures has been proposed and analyzed in terms of the spectral response. Aluminum-based periodic nanostructures that scatter incoming radiation towards a thin homogeneous metal layer, are used to excite Surface Plasmons (SP) for normal incident light. The rigorous coupled wave analysis method is used to engineer the periodic nanostructures and evaluation of performance parameters. The sensitivity, figure of merit and reflective amplitude are considered as the main parameters for engineering the device. The electromagnetic field simulations reveal the presence of waveguide mode and two plasmonic modes, namely, SP mode and substrate mode with three different interactions in the device. The shift in SP mode is used to detect the minute changes in the refractive index of the analyte and the number of exciting waveguide modes is used to capture the changes in the thickness of the analyte. The presence of substrate mode adds the self-reference capability to the proposed plasmonic device due to the independence of any change in the refractive index and thickness of the analyte. The proposed device has been engineered to offer a competitive sensitivity of 1000 nm/RIU and figure of merit 300 RIU^-1 with the fabrication constraints taken into account. Since the proposed structures work under normal incidence conditions which makes this design integrable to the end of an optical fiber that can be used both to excite SP and to interrogate the spectral reflectance.

This Conference Presentation, "Vibrant reflective structural colors with lossy metals using grating supermode resonances," was recorded at Photonics West 2020 held in San Francisco, California, United States.

In this research, the finite-difference time-domain (FDTD) simulation technique is employed to analyze the optical characteristics of the following creatures: Morpho menelaus, Euprymna scolopes, Dynastes hercules, Hoplia coerulea, and Paracheirodon innesi. The layered geometries are simulated to decipher the effect on color appearances, including: thickness of the periodic layered structure, spacing between layers and the number of layers. Furthermore, we compare the biological structures of various creatures; research findings suggest that the color appearances may be accounted for by the specific geometrical nanostructure.

On-chip optical isolators constitute an essential building block for photonic integrated circuits. Monolithic magnetooptical isolators on silicon, while featuring unique benefits such as scalable integration and processing, fully passive operation, large dynamic range, and simple device architecture, had been limited by their far inferior performances compared to their bulk counterparts. Here we discuss our recent work combining garnet material development and isolator device design innovation, which leads to a monolithic optical isolator with an unprecedented low insertion loss of 3 dB and an isolation ratio up to 40 dB. To further overcome the bandwidth and polarization limitations, we demonstrated broadband optical isolators capable of operating for both TM and TE modes. These results open up exciting opportunities for scalable integration of nonreciprocal optical devices with chip-scale photonic circuits.

Rare-earth-doped glass Anderson localizing optical fibers (g-ALOF) have great potential for novel power, coherence, and spectral properties as the gain medium in fiber lasers. We report on our investigation of the optical properties of Yb-doped g-ALOF near the peak absorption wavelength, especially the localization, and lasing- and gain-related parameters. These include the fluorescence lifetime, emission cross-section, absorption cross-section, saturation power, gain, scattering loss, and background absorption. We also elaborate on several new measurement techniques that were required to obtain these parameters, mainly due to the substantial structural difference between g-ALOFs and conventional fibers.

One major hurdle in the progress of hyperbolic metamaterials (HMMs) is their lossy nature due to the metal constituent. In this work, we design a gain-assisted active HMM utilizing the recently emerged, solution-processed perovskite gain material. Our HMM is consisted of MAPbI₃ perovskite and Au subwavelength multi-layer. We theoretically and experimentally investigate the strong emission polarization anisotropy that is unique to HMMs. Our work opens the way towards applications such as high-speed light emission, super resolution imaging and lithography, electro-optical modulators and perfect light absorbers.

The state-of-the-art infrared (IR) photodetectors are either thermal detectors (bolometers) or quantum detectors (photovoltaic and photoconductive detectors). Compared to quantum IR photodetectors, IR bolometers are slower and less sensitive but in turn, they offer lower cost without need for cooling and exotic materials (e.g. HgCdTe). Phonon/photon engineered materials offer interesting routes for enhancing room-temperature IR bolometers. We have recently demonstrated experimentally a nano-thermoelectric bolometer for long-wave IR detection. The technology utilizes efficient thermoelectric transducers based on silicon nanomembranes, which have an enhanced thermoelectric figure of merit arising from the low thermal conductivity stemming from the nano-scale thickness. For the absorption of the IR radiation the nano-thermoelectric bolometer utilizes a nanomembrane based quarter-wave resistive absorber, which is also known as the Salisbury screen. The use of nanomembranes in both the thermoelectric transducer and the absorber results in a very small thermal mass, and thereby high speed for the detector. In this article, we present an analytical model for quarter-wave resistive absorbers (i.e. Salisbury screens). It can be applied both in radio frequency (RF) and optical applications. The results of the analytical model are compared with the ones obtained with the transfer-matrix method using the optical material data available in the literature. We present also a device model of the nano-thermoelectric IR detector and estimate the full performance of this technology.

This Conference Presentation, "Metaphotonics: from backward phase-matching to augmented reality," was recorded at Photonics West 2020 held in San Francisco, California, United States.

Anti-reflective nanostructured surfaces (ARSS) enhance optical transmission through suppression of Fresnel reflection at boundaries between layered media. Previous studies show random ARSS (rARSS) exhibit broadband enhancement in transmission and polarization insensitivity compared to typical optical windows. ZnSe samples with rARSS treatment were characterized (transmittance, reflectance, and angular scatter) in the mid-wave and long-wave infrared (2 - 12 μm) using a spectrophotometer. Five different random nano-roughness antireflective surfaces were tested at: normal incidence transmission and 15° angle of incidence -15 to 45° angle of reflection. The angular reflectance distribution resembles a diffuse dipole radiator, due to a finite elongated beam cross-section at the incident surface. Scattering diagrams with main and side lobes are presented. Comparing specular transmission and reflection with the scattered performance, an accurate determination of the redistribution of incident energy is obtained. Measurements of rms surface roughness using a confocal microscope is presented alongside the scattering data, for assessment of structured surface feature size effects. The results show differences in the scattered intensity, over the wavelength bands of interest, depending on the random topology of the surface. The partial-integrated scatter values were obtained, allowing the comparison of random anti-reflective surfaces to optically flat surfaces.

Nanostructures of high-refractive-index materials such as semiconductors can support Mie resonances due to confinement of light at the nanoscale and have been investigated both theoretically and experimentally for a range of nanophotonic applications. Transition metal dichalcogenides (TMDCs) from the family of van der Waals layered materials have high refractive index and strong optical anisotropy. Recently, it has been shown that due to the tunable optical properties of TMDCs, they possess enormous potential for designing metasurfaces and various ultra-thin optical elements. Periodically arranged nanoantennas of van der Waals layered materials can exhibit strong spectral resonances in the visible and near-infrared frequencies. In this work, we investigate the scattering and transmission properties of a periodic array of disk-shaped nanoantennas of a TMDC material, tungsten disulfide WS2. We show the dependence of the reflection and transmission spectra from the TMDC nanoantenna array and investigate the spectral features for various thicknesses of the supporting layers positioned between the antenna array and glass substrate.

In this talk, we present some of our recent results in electromagnetic scattering, including a non-classical framework demonstrated via far-field scattering from nanophotonic structures, radiation sources via near-field scattering from free electrons, as well as synthetic scattering with non-Abelian gauge fields.

As the known of the Shockley-Queasier limit, over 90% of widely used silicon crystalline based solar cell only achieve 30% theoretical efficiency. To maximize the light-harvesting, the solar cell’s light-trapping structures must be broadband, omnidirectional, and polarization-insensitive. Quasi-random structures emerge as an ideal candidate since they combine the broadband wide-angle absorption enhancement and strong, customizable enhancement for desired wavelength windows. Herein, we demonstrated a kind of designed quasi-random structures, which were designed by topology optimization based on mathematical algorithms and directly fabricated the final products to achieve high efficiency. The best structure (Rudin-Shapiro) could reduce 11% on reflectance and improve 14% short circuit current which led 13% PCE improvement. Meanwhile, the results also exhibited ~10% efficiency improvement in a wide incident angle range (0-65 degree).

We recently reported the fabrication of mid-infrared SOI photonic crystal slabs and confirmed the creation of the Dirac cone by the angle-resolved reflection spectroscopy. We found the Fano-like line shape, which made it difficult to tell the accurate eigenmode frequencies from the reflection peaks. In this presentation, we focus on the selection rule and the line shape of the reflection peaks. The phase shift of the transmitted and reflected waves will also be examined to clarify the correspondence between the eigenmode frequency and the line shape. The results will be compared with available experimental data.

For the subwavelength plasmonic structures, as their characteristic dimensions are scaling down, it has turned out that the local-response approximation is no longer applicable and more complex models based on the nonlocal response (or even quantum interaction), are required for explaining novel effects, e.g. blue spectral shifts of the resonances, etc. Among these approaches, the longitudinal nonlocal response description based on the linear hydrodynamic model represents the starting point. First, we have concentrated on understanding the interaction and developing simple models capable of predicting the nonlocal response, applicable to simple structures, such as spherical nanoparticles or nonlocal thin layers. Also, as an alternative (and more general) approach, we have considered and developed the extension of the rigorous coupled wave analysis (RCWA) technique capable of treating nonlocal response numerically, for more general both periodic and aperiodic (NonLoc(a)RCWA) structures.

Numerical simulation of opto-electric characterization of GaAs/In_0.2Ga_0.8As core-shell nanowire solar cells is presented, using a finite difference time-domain (FDTD) modeling method. The results show that the absorption, external quantum efficiency (EQE) of the NW solar cell strongly depends on NW lengths and diameters, Moreover, the effect of the diameters on the current density-voltage (J-V) of the NW solar cell was calculated.

Construction of complex nanostructures (metasurfaces) became accessible over the past years due to variety of methods like lithography or deposition of nanoparticles. Rapid development of numerical methods for simulation of light interaction with those metasurfaces allow for design of optical elements that act as geometrical phase elements (GPE), mode filters, topological or chiral converters. We report on systematic approach in the designing of such GPE’s using engineered clusters of nanoparticles (meta-atoms) on a substrate. We study in detail optical properties of such nanoclusters and investigate how individual properties of nanoparticles are influencing the collective response of few selected GPE’s.

In this study, the pseudospectral time-domain (PSTD) simulation technique is employed to model light propagation through a virtual chicken cornea tissue model. We construct a collagen-rich stromal layer model and simulate light impinging upon it. The transmittance through the cornea at different wavelengths is acquired. Factors that may affect optical transparency are explored and investigated. Simulation findings of this research may provide essential information that contribute to chicken cornea transparency.

We numerically designed and engineered an isopropanol-silica based photonic crystal fiber for the coherent supercontinuum generation at 1300 nm and 1600 nm for optical coherence tomography. We have adopted the finite element based technique to calculate the effective mode index with its effective mode area of the fundamental mode at different wavelengths. With effective dispersion tailoring techniques, we have optimized the geometrical dimensions of the fiber and obtained the dispersion value as -27.35 ps/nm/km and +25.4 ps/nm/km at 1300 nm and 1600 nm respectively. We have obtained the nonlinear coefficient values at 1300 nm as 21.80 W^-1km^-1 and at 1600 nm as 13.79 W^-1km^-1. The proposed design can be proven an efficient and true fiber model for the generation of highly coherent supercontinuum broadband source.

Electromagnetic induced transparency (EIT) is a quantum phenomenon, featuring strong dispersion at the transparent window in an absorption spectral region. In recent years, EIT-like behaviors have also been discussed in artificial nanostructures, where a transparent window emerges in an otherwise high reflection band. Up to date, many demonstrations are implemented based on all-dielectric metamaterials as the loss can be reduced compared to their metallic counterparts. However, studies are mostly presented based on high-refractive-index dielectrics, in which the choice of materials is limited at optical frequencies. In this study, we present a new strategy that enables handedness-dependent EIT in a lower refractive index dielectric material (n~1.5), which can be more widely implemented in polymer-based fabrication platforms. In the first part of the study, we numerically present the evolution of EIT response in a helix structure from high to low refractive indices. As the refractive index decreases from 3.5 to 1.5, the resonances are less pronounced and the EIT behavior cannot be maintained. Therefore, we show that by properly tailoring the geometrical parameters, the EIT response may emerge again without increasing the refractive index. In the second part of the study, we characterize the effect of substrate on the handedness-dependent EIT response of the helix structure. We show that the EIT performance is severely degraded since the dielectric helix has a refractive index close to the glass substrate. To resolve the issue, we present a rod-supported structure to effectively retrieve the EIT response. As EIT-based devices are widely used for sensors and nonlinear optics, our design which can be implemented on a polymer-based platform may broaden the horizon of applications in sensors and optoelectronics devices.

We have fabricated biaxial hyperbolic metamaterials (BHMMs) using layered structures consisting of titanium dioxide (TiO₂) and copper (Cu). In order to enable the biaxial property, an oblique angle deposition (OAD) technique is applied to deposit the dielectric layer. We have characterized the biaxial hyperbolic dispersion using variable angle spectroscopic ellipsometry (VASE) measurements in the wavelength range 400 nm to 900 nm. A noticeable difference be- tween in-plane permittivity components of the fabricated BHMM is observed to be 0.13 at 633 nm. The experimental characterization results have been in good agreement with the predictions of effective medium approximation (EMA) with an MSE of 18.

Dynamically tunable reflecting Near infrared band-pass filter based on hybrid graphene-nanometallic structure is demonstrated by numerical simulation. The proposed filter is constructed by unit cells with graphene monolayer embedded into the nanometallic grating structure. The gradual transition of graphene monolayer from very thin metal to dielectric play the key role to tune the reflection spectrum of the structure. Its frequency spectrum is also analyzed, which clearly shows a blueshift of passband with increasing graphene Fermi energy. The filter parameters are investigated by varying graphene Fermi energy through external voltage gates. The modulation depth, center frequency, bandwidth and quality factor of the filter could be tuned. We achieved stable modulation depth as high as 0.735, and quality factor as high as 3.4. The center frequency can be tuned in a broad range from 210 to 230 THz and bandwidth tuning from 60 to 95 THz. The effect of nanogap size and environment refractive index is also numerically investigated. These results are very promising for the future use and integration of the proposed filters as a key element of optical communication system and infrared sensing.

This PDF file contains the front matter associated with SPIE Proceedings Volume 11289, including the Title Page, Copyright Information, Table of Contents, Author and Conference Committee lists.