This PDF file contains the front matter associated with SPIE Proceedings Volume 10112, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Design of the resonant optical response of ultrathin two-dimensional materials and heterostructures is enabling scientific exploration of new materials phenomena. As an example, demonstrate near-unity, broadband absorbing optoelectronic devices using sub-15 nm thick transition metal dichalcogenides (TMDCs) of molybdenum andtungsten as van der Waals semiconductor active layers. Specifically, we report that near-unity light absorption is possible in extremely thin (<15 nm) van der Waals semiconductor structures by coupling to strongly damped optical modes of semiconductor/metal heterostructures. We further fabricate Schottky junction devices using these highly absorbing heterostructures and characterize their optoelectronic performance. Our work addresses one of the key criteria to enable TMDCs as potential candidates to achieve high optoelectronic efficiency. We also report mid-infrared spectroscopy measurements of an electrostatically gated topological insulator, in which we observe several percent modulation of transmittance and reflectance of (Bi1-xSbx)2Te3 films as gating shifts the Fermi level. Infrared transmittance measurements of gated (Bi1-xSbx)2Te₃ films were enabled by use of an epitaxial lift-off method for large-area transfer of TI films from the infrared-absorbing SrTiO3 growth substrates to thermal oxidized silicon substrates. We combine these optical experiments with transport measurements and angle-resolved photoemission spectroscopy to identify the observed spectral modulation as a gate-driven transfer of spectral weight between both bulk and topological surface channels and interband and intraband channels. We develop a model for the complex permittivity of gated (Bi₁-xSbx)₂Te3, and find a good match to our experimental data. These results open the path for layered topological insulator materials as a new candidate for tunable infrared optics and highlight the possibility of switching topological optoelectronic phenomena between bulk and spin-polarized surface regimes.

Plasmonic metasurfaces enhance light-matter interaction by focusing light into extremely subwavelength dimensions. These carefully designed structures have been used in extremely thin optical component which can mold the wavefront, with exciting applications in optical lenses, beam steering, and biosensing applications. Adding dynamic tunability to these devices opens up the possibility for new application in single pixel detection and 3D imaging as well as optical modulators and switches. However the existing approaches for designing active optical devices in infrared, are either slow or have small refractive index change. Integrating plasmonic metasurfaces with single-layer graphene (SLG) opens exciting opportunities for developing active plasmonic devices because the amplitude and phase of the transmitted and reflected light can be rapidly modulated by injecting charge carriers into graphene using field-effect gating. I will describe our recent experimental results demonstrating strong phase modulation of mid-infrared light. The phase shifting due to electric gating of the SLG was measured using a Michelson interferometer, and further utilized to demonstrate an electrically controlled (i.e. no moving parts) interferometry capable of measuring distances with sub-micron accuracy. Because of the potentially nanosecond-scale measurement time, active metasurfaces represent a promising platform for ultra-fast standoff detection. Finally, we demonstrate that, by the judicious choice of a strongly anisotropic metasurface, the graphene-controlled phase shift of light can be rendered polarization-dependent, thereby modulating the polarization state (e.g., the ellipticity) of the reflected light. These results pave the way for novel high-speed graphene-based optical devices and sensors such as polarimeters, ellipsometers, and frequency modulators.

Moving media have recently attracted attention for their ability to break reciprocity without magnetic materials. By spinning air in an acoustic cavity, it was recently shown that it is possible to realize an acoustic circulator [R. Fleury, D. Sounas, A. Alù, Science 343, 516 (2014)], with applications for sonars and medical imaging devices. Similarly, by effectively imparting angular momentum to microwave and optical resonators through spatiotemporal modulation, it is possible to induce strong non-reciprocity, with groundbreaking applications in the design of full-duplex communication systems [N. Estep, D. Sounas, J. Soric, A. Alù, Nature Physics 10, 923 (2014)]. Here we show that the non-relativistic Fresnel-Fizeau effect at the basis of these mechanisms can be boosted in epsilon-near-zero (ENZ) media, due to their small intrinsic refractive index. This is a different scenario than resonant structures, where the Fresnel-Fizeau effect is boosted by the effectively large wave-matter interaction distance, even for large intrinsic refractive index for the moving medium. Our results open a new venue to use zero-index metamaterials, and can become practically important in the realization of non-reciprocal imaging systems with built-in isolation and protection from reflections.

Solid state quantum emitters are prime candidates to realize fast on-demand single-photon sources. The improvement in photon emission and collection efficiencies for quantum emitters, such as nitrogen-vacancy (NV) centers in diamond, can be achieved by using a near-field coupling to nanophotonic structures. Plasmonic metamaterial structures with hyperbolic dispersion have been previously demonstrated to significantly increase the fluorescence decay rates from NV centers. However, the electromagnetic waves propagating inside the metamaterial must be outcoupled before they succumb to ohmic losses. We propose a nano-grooved hyperbolic metamaterial that improves the collection efficiency from a nanodiamond-based NV center by a factor of 4.3 compared to the case of coupling to a flat metamaterial. Our design can be utilized to achieve highly efficient and fast single-photon sources based on a variety of quantum emitters.

Hyperbolic Meta-Materials (HMMs) are anisotropic materials with permittivity tensor that has both positive and negative eigenvalues. Here we report that by using a type II HMM as cladding material, a waveguide which only supports higher order modes can be achieved, while the lower order modes become leaky and are absorbed in the HMM cladding. This counter-intuitive property can lead to novel application in optical communication and photonic integrated circuit. The loss in our HMM-Insulator-HMM (HIH) waveguide is smaller than that of similar guided mode in a Metal-Insulator-Metal (MIM) waveguide.

Lithium niobate (LN) is a well-understood and heavily used optical material with a variety of useful properties such as its linear electro-optic effect, chi(2) nonlinearity, and piezoelectric effect. However, LN is a difficult material to etch and patterning high quality optical devices is challenging. Here we present results on the design and fabrication of a photonic crystal cavity made in a hybrid silicon-on-lithium-niobate material system. This material system takes advantage of the useful properties of LN, while simultaneously leveraging expertise in silicon etching and removing the need to pattern LN. These devices use the index contrast between silicon and LN to guide and confine optical resonances in a thin film of silicon bonded on top of LN. The photonic crystals have optical wavelength scale mode volumes and simulated quality factors greater than 10^6, with measured quality factors above 10^5. Due to the electro-optic effect in LN, these devices exhibit coupling between the optical resonance frequency and the electric field of adjacent electrodes. We show that such a system can yield a simulated electro-optic coupling rate of 0.6 GHz/V (4 pm/V). We expect resonators of this type to have a wide range of applications, including achieving large coupling to isolated rare-earth ions (such as Er3+) at telecom frequencies, efficient three-wave mixing in resonant silicon devices, and sensitive acousto- and electro-optic modulation.

We use a plane wave expansion method to define parameters for the fabrication of 3-dimensional (3D) core-shell photonic crystals (PhCs) with lattice geometries that are capable of all-angle negative refraction (AANR) in the midinfrared centered around 8.0 μm. We discuss the dependence of the AANR frequency range on the volume fraction of solid within the lattice and on the ratio of the low index core material to the high index shell material. Following the constraints set by simulations, we fabricate two types of nanolattice PhCs: (1) polymer core-germanium shell and (2) amorphous carbon core-germanium shell to enable experimental observation of 3D negative refraction and related dispersion phenomena at infrared and eventually optical frequencies.

Theoretical studies are presented of the electromagnetic fields in one dimensional photonic crystal coatings deposited on interfaces and mirrors. The coatings are finite photonic crystal arrays of a Kerr nonlinear dielectric medium alternating with a linear dielectric medium and exhibit a series of electromagnetic transmission pass and stop frequency bands. The pass and stop bands are related to the underlying photonic crystal structure of the coatings. Within the coatings high field intensities occur in the pass bands and low field intensities occur in the stop bands. In addition, certain high field intensity excitations arising solely from the Kerr nonlinearity occur at certain stop band frequencies. The origins and nature of these stop band excitations are discussed and the enhanced fields associated with them are studied with regards to the Kerr nonlinearity. A mapping is presented of the nature of the excitations generated in the coating within the parameter space of the linear and nonlinear components of the Kerr media dielectric. The field enhancements of the stop band excitations are studied and the optimum conditions for field enhancement within a coating determined. The nature of the wave functions of the modes excited within the stop bands is studied as a function of the stop band frequency intervals in which they occur. Discussions are made of the significance of these results to field enhancement due to nonlinearity, surface enhanced Raman spectroscopy, and in the generation of second harmonics at mirror surfaces and interfaces.

Flat optical devices based on lithographically patterned sub-wavelength dielectric nano-structures provide precise control over optical wavefronts, and thus promise to revolutionize the field of free-space optics. I discuss our work on high contrast transmitarrays and reflectarrays composed of silicon nano-posts located on top of low index substrates like silica glass or transparent polymers. Complete control of both phase and polarization is achieved at the level of single nano-post, which enables control of the optical wavefront with sub-wavelength spatial resolution. Using this nano-post platform, we demonstrate lenses, waveplates, polarizers, arbitrary beam splitters and holograms. Devices that provide multiple functionalities, like simultaneous polarization beam splitting and focusing are implemented. By embedding the metasurfaces in flexible substrates, conformal optical devices that decouple the geometrical shape and optical function are shown. Multiple flat optical elements are integrated in optical systems such as planar retro-reflectors and Fourier lens systems with applications in ultra-compact imaging systems. Applications in microscopy and the prospects for tunable devices are discussed.

Using immersion lenses is a common approach to enhance the resolving power in various fields of optics such as microscopy and lithography. However, conventional immersion lenses are bulky, high-cost and are typically designed for only a few specific immersion liquids. The development of meta-surfaces provides a promising approach to manipulate light in a compact configuration, enabling many optical devices such as polarizers, waveplates and lenses. These are mainly focused in the near-infrared or the long-wavelength region of the visible spectrum due to fabrication challenges and intrinsic losses of materials used. Here, we demonstrate oil immersion planar lenses with a numerical aperture of 1.1 at visible wavelengths. The lenses provide diffraction-limited focal spots with Strehl ratios higher than 0.9 and 0.8 at their design wavelengths of 532 nm and 405 nm, respectively. Fabrication is based on an atomic-layer deposition (ALD) of TiO2. The loss of TiO2 in the visible is negligible and the surface roughness is well-controlled due to the precise monolayer growth of the TiO2 film. By applying the lens (designed at 532 nm) in a confocal scanning microscopy setup, we are able to achieve high-quality images with sub-wavelength resolution. It should be noted that this lens can be efficiently tailored for any liquid. We demonstrate another design for water-immersion lenses, which are highly applicable to super-resolution bio-imaging applications. The compactness and design flexibility of this platform is highly promising for widespread applications in imaging and spectroscopy.

The abstract is not available

Concentrated solar power (CSP) facilities heavily utilize parabolic troughs to collect and concentrate sunlight onto receivers that deliver solar thermal energy to heat engines for generating electricity. However, parabolic troughs are bulky and heavy and result in a large capital investment for CSP plants, thereby making it difficult for CSP technology to be competitive with photovoltaics. We present the design of a planar focusing collector (PFC) with focal length beyond the micron scale. The PFC design is based on the use of a nanostructured silver surface for linearly polarized singlewavelength light. The designed PFC consists of metallic nanogrooves on a dielectric substrate. The geometric properties, namely the width and depth, of a single-unit nanogroove allows for full control of the optical phase at desired spatial coordinates along the nanogroove short-axis for a single wavelength. Moreover, we show numerically that such phase control can be used to construct a phase front that mimics that of a cylindrical lens. In addition, we determine the concentration ratio by comparing the width of our PFC design to the cross-sectional width of its focal spot. We also determine the conversion efficiency at long focal lengths by evaluating the ratio of the collected optical power to the incoming optical power. Finally, we examine the focusing behavior across multiple wavelengths and angles of incidence. Our work shows how nano-optics and plasmonics could contribute to this important area of CSP technology.

Conventional optical elements such as lenses, waveplates and polarizers function by adding phase delays to the propagating light. The thicknesses of these dielectric optical components are much larger than wavelength to accumulate 0-π phase shift. Moreover, spherical aberration and diffraction limit restrict their usage in integrated photonics circuits. Metasurface based lenses change the phase of transmitted and reflected electromagnetic waves significantly at resonance by exciting surface plasmons on the metallic arrays with thickness much lower than the wavelength of the incident light. However, previous demonstrations of plasmonic lens suffer from low transmission efficiency (< 20%) due to the high plasmonic losses. We overcame this shortcoming to some extend by engineering plasmonic coupling and demonstrated a relatively high 75% transmission in the mid infrared spectral domain. In this proposed work, coupled one dimensional array of gold disks with variable diameters have been employed to add varying phases to the transmitted light in order to create the phase front curvature in mid-IR wavelength range needed for the focusing of the incident radiation. The designed nanostructured surface achieves a resolution beyond the diffraction limit in thin-film planar geometry. The focal point, resolution and transmission efficiency can be tuned by various parameters such as period, diameters, and the size of the disks. The confocal measurement method has been performed to measure the far field focal volume of the fabricated lens, which is in good agreement with the theoretical results. Thin-film planar layout and subwavelength resolution mitigate the limitations of conventional optical elements.

We present the electric field-induced tuning of the light transmission in a photonic crystal device. The device, with alternating layers of Silver and Titanium dioxide nanoparticles, shows a shift of around 10 nm for an applied voltage of 10 V. An accumulation of charges at the Silver/TiO₂ interface due to electric field leads to an increase of the number of charges contributing to the plasma frequency in Silver. This results in a blue shift of the Silver plasmon band, with concomitant blue shift of the photonic band gap as a result of the decrease in the Silver dielectric function.

Nanophotonic concepts have have tremendous potential for improving the already high performance of photonic biosensors in terms of versatility and functionality. Here, we introduce a novel silicon photonic sensing geometry based on a chirped guided mode resonance which affords a simple readout without spectrometer. Secondly, we demonstrate the combination of electrochemical and photonic sensing in an entirely new sensing modality.

We demonstrate both theoretically and experimentally that a proper surface modification of a highly scattering material can substantially improve light coupling into turbid medium and increase the photon life-time in this medium. As a practical example, we demonstrate that such amended excitation geometry leads to a factor of 100 improved Raman signal efficiency.

While a wide range of substrate formats have been proposed for surface enhanced Raman scattering (SERS) applications, the challenge remains in designing a reproducible high efficiency SERS substrate [1]. In part, this is due to the disconnect between the local field enhancement spectra and the localized surface plasmon resonance (LSPR) spectra commonly used to characterize SERS substrates [2]. It remains a challenge to directly evaluate the sensor performance. In this work, we report a systematic study of optical coupling in SERS substrates by measuring the sensor performance across the visible and near-infrared spectral range. Using the experimental SERS scattering cross section measurements of two distinct peaks we compute the best-fit curve for the field enhancement. Using the field enhancement profile we calculate the full sensor performance maps for both Stokes and anti-Stokes shifts and evaluate the optimal pump laser wavelengths for SERS spectroscopy application.

We introduce an ultra-compact plasmonic sensor for lab on chip applications. The device utilizes the heavily doped Si for introducing plasmonic effects. The use of heavily doped silicon instead of metals for plasmonic excitation has the advantage of reduced losses and CMOS compatibility. The proposed device has a simple structure, also it can be easily fabricated using the mature CMOS fabrication technology. The device structure is made of a heavily doped silicon layer, on a silicon dioxide substrate, while the silicon layer is etched to form a slot waveguide, and a rectangular cavity. The proposed plasmonic resonator is operational in the mid infrared spectral region. The sensor possesses a high sensitivity of 5000nm/RIU in the mid infrared range.

The development of innovative photonic devices and metamaterials with tailor-made functionalities depends critically on our capability to characterize them and understand the underlying light-matter interactions. Thus, imaging all components of the electromagnetic light field with nanoscale resolution is of paramount importance in this area. Nowadays, the electric and the vertical magnetic field components of light can be measured with sub-wavelength resolution. This is achieved by scanning the sample surface with specific probes in a method known as scanning near-field optical microscopy (SNOM). However, within this toolbox, an unambiguous way of visualizing the horizontal magnetic field component has been missing. We have answered this challenge by demonstrating experimentally that a hollow-pyramid circular aperture probe SNOM can directly image the horizontal magnetic field of light in simple plasmonic antennas – rod, disk and ring. These results are also confirmed by numerical simulations, showing that the probe can be approximated, in the first order, by a magnetic point-dipole source. This approximation substantially reduces the simulation time and complexity and facilitates the otherwise controversial interpretation of near-field images. Further, we use the validated technique to study complex plasmonic antennas and to explore new opportunities for their engineering and characterization. The applicability of this methodology is currently being extended beyond plasmonics structures. Thus, the presented hollow-pyramid circular aperture based SNOM approach complements the existing techniques for imaging the different electromagnetic field components, by providing an opportunity to explore the tangential magnetic field of light with sub-wavelength resolution.

Magnetophotonic crystals (MPCs) support Bloch surface waves (BSWs) and waveguided modes (WGMs) propagation. The influence of the BSW on the Faraday effect in the one-dimensional MPCs is studied. The technique of measuring the angle of Faraday rotation in the MPCs in attenuated total internal reflection scheme in Kretschmann configuration is discussed. The spectra of Faraday rotation demonstrate a Fano-shaped resonance near the spectral-angular position of the BSW resonance both for s- and p-polarized incident light. The presence of the feature in the spectrum of p-polarized light can be explained by the Faraday rotation effect and subsequent BSW excitation mutually enhancing each other.

Here we propose a novel broadband absorber with high efficiency by depositing nanometer iridium (Ir) film onto porous anodic alumina (PAA) template so as to increase the optical path length of the incident light for its great absorption property. Distinguished from the narrow band absorber using sub-wavelength resonant dielectric nanostructures and excitation of the propagating surface plasmon (PSP), PAA with nanometer Ir film can present broadband absorption with high efficiency as a result of the superposition of many different plasmon-enhanced absorption peaks by utilizing light funneling. The average absorption is able to achieve as high as 93.4% for 400-1100nm wavelength band and 96.8% for improved structure of quadrangular frustum pyramid array. And not only the hexagonal latticed structures of PAA template but also many similar structures based on grating or holes with square latticed or other latticed mode are able to achieve the broadband absorption with high efficiency. The absorption caused by the Ir metal layer deposited on the bottom of PAA and the funneled light into the alumina absorbed within the Ir film covering the inner sidewalls, both contribute the broadband absorption of the proposed absorber. This novel absorber can be implemented in fields of solar cell, light harvesting, imaging and so forth.

Two-dimensional atomically thin materials, most notably graphene and transition metal dichalcogenides (TMDs), have generated tremendous interest among researchers. The high electron mobility and strong light absorption exhibited by these materials make them attractive for opto-electronic applications. We will present our recent experimental and theoretical work on the ultrafast dynamics of collective excitations, such as excitons, phonons, and plasmons, in these materials for electronic and photonic device applications. We study the dynamics of excitons in 2D materials and optoelectronic devices using ultrafast optical/terahertz pump-probe and correlation spectroscopy. Our experimental work on metal dichalcogenide materials and devices (such as photodetectors) as well as our theoretical results show that defect assisted recombination involving capture of excitons and carriers by Auger scattering is the fastest mechanism for the non-radiative recombination of photoexcited electrons and holes. In particular, the very Coulomb interaction that resulted in the strongly bound excitons in these materials, causes extremely fast capture of the excitons by defects resulting in extremely poor quantum efficiencies in optoelectronic devices. The large sensitivity of device performance to defects is thus fundamental to 2D TMD materials. Defect-passivated 2D materials have demonstrated quantum efficiencies approaching ten percent. Our ultrafast two-pulse photovoltage correlation experiments show that the photoresponse of TMD photodetectors can be very fast making them useful for operation at frequencies in the hundreds of gigahertz range. Our recent experimental work has shown that 2D materials could be very promising for high frequency phononic devices. Our work has shown that mechanical oscillations in these atomically thin membranes can reach terahertz frequencies and are tunable from few tens of gigahertz to almost one terahertz. 2D material membranes can therefore enable MEMs resonator structures with record frequency-quality factor products at these high frequencies. Our ultrafast work in graphene plasmonic structures has revealed enormous potential for graphene based VLSI interconnects in which electrical signals are carried by plasmonic waves with much reduced propagation delays, losses, signal distortions, and cross-talk compared to conventional metal interconnects like copper.

Graphene is a promising two-dimensional material for photo-detection owing to its high mobility, broadband optical absorption, zero band gap nature, and tunable carrier concentration through electrical gating. Despite these unique properties, its 2.3% optical absorption from ultraviolet to infrared wavelengths and short carrier lifetime has limited its usage for practical applications. In this work, we present a broadband, high responsivity, and high speed graphene photodetector. By use of plasmonic nanoantennas, an incident optical field can be strongly concentrated in close proximity to the metallic nanoantennas. This significantly reduces the drift path length of the majority of photo-generated carriers in graphene to the plasmonic nanoantennas that serve as the photodetector contact electrodes. As a result, a large number of the photo-generated carriers can drift to the photodetector contact electrodes despite the short carrier lifetime of graphene, offering high responsivity levels. Moreover, the photodetector is designed to offer high speed operation by minimizing the capacitive parasitics induced by the plasmonic nanoantennas. We demonstrate a broadband photo-detection operation covering the wavelength regime from 800 nm to 1800 nm. We achieve responsivity levels as high as 0.6 A/W at 800 nm, which is close to the theoretical limit of 0.65 A/W. In summary, the combination of the high-responsivity, broad bandwidth, and high-speed performance of the presented plasmonics-enhanced graphene photodetector could find many applications in future optical communication, imaging and sensing systems.

Two-dimensional transition metal dichalcogenide (TMDC) heterostructures provide a unique platform for strong light-matter interaction in a wide wavelength range. Here, we report the formation of high-quality TMDC heterostructures through a dry transfer method along with the study of the detailed physical properties of heterostructures formed between MoS2 and MoSe2 (especially, simultaneous quenching of photoluminescence of both materials in the overlapping region, red shift and broadening of the MoSe2 photoluminescence) will be reported. We also report the formation of a thin tunable diode by depositing metal contacts on TMDCs and the back-gate.

The scaling of active photonic devices to deep-submicron length-scales has been hampered by the fundamental law of diffraction and the absence of materials with sufficiently strong electrooptic effects. Here, we demonstrate a solid state electro-optical switching mechanism that can operate in the visible spectral range with an active volume that is well below the free-space diffraction limit and comparable to the size of the smallest active electronic components. . The switching mechanism relies on electrochemically displacing atoms inside the nanometer-scale gap between two crossed metallic wires forming a crosspoint junction. Such junctions afford extreme light concentration and display singular optical behavior upon formation of a conductive channel. We illustrate how this effect can be used to actively tune the resonances of a plasmonic antenna. The tuning mechanism is analyzed using a combination of electrical and optical measurements as well as electron energy loss (EELS) in a scanning transmission electron microscope (STEM).

The development of integrated approaches for optical trapping, based on photonic or plasmonic structures fabricated on a chip, offers several compelling advantages. First, chip-based optical traps enable the trapping platform to be miniaturized. Second, the chip-based configuration lends itself naturally to the incorporation of sensing modalities. Third, optical nanostructures can generate strong near-fields, boosting the trapping performance. In this presentation, works by the author and his team in the field of optical trapping with silicon photonics and with plasmonics are described. We will describe the use of silicon microring resonators for trapping and sensing particles. We will furthermore describe silicon photonics for sorting particles, as well as for sensing proteins. Finally, we will describe experiments in which a silicon photonic crystal cavity trapped a silver nanoparticle on whose surface molecules had been formed. We carried out Raman spectroscopy of these molecules, with the silver nanoparticle held in position via the photonic crystal cavity. Plasmonic nanostructures are compelling for optical trapping due to the large gradient forces they can generate, a consequence of their ability to generate highly confined optical fields. Yet deleterious thermal effects can also occur. We describe the use of a plasmonic nanotweezer with an integrated heat-sink. If time permits, we will also describe recent work in which fluorescence microscopy was used to track the position of a nanoparticle trapped by a double nanohole aperture.

Plasmonic color originating from metallic nanostructures has many advantages over traditional pigmentation based color and have demonstrated sub wavelength resolution, tolerance to high intensity light, and scalability of the structure's optical response with dimensions and surrounding media. The later of these attributes, post-fabrication tunability, is a unique advantage of plasmonic structures that may enable it to reach niche applications. However, previous attempts of plasmonic tuning have yet to span an entire color space with a single nanostructure dimension. Here, we demonstrate a full red-green-blue (RGB) color changing surface enabled by a high birefringent liquid crystal (LC) and with a single nanostructure. This is achieved through the onset of a surface roughness induced polarization dependence and a combination of bulk and surface LC effects which manifest at different voltages. To further show the feasibility of such a system for display applications, we integrate the LC-plasmonic device with an actively addressed thin film transistor array (TFT) to display arbitrary images and video. Such a color changing surface may also find applications in wearables and active camouflage.

Plasmonics have been actively explored for the structural colour printing applications owing to their preferential photon absorption and scattering. To date, many schemes have been demonstrated for the realization of full colour pixels employing various plasmonic geometries. However the quest for a perfect plasmonic geometry that offers pure colour pixels with distinct reflective peaks and high colour saturation combined with low cost and high throughput scalable fabrication is not yet fulfilled. We propose a scheme for generating all colours from violet to red in the visible spectrum with high colour purity and saturation by a clever engineering of concomitant multiple plasmonic resonances in 2D arrays of aluminum based nano antennas. In order to realize vivid full colour pixels, we fabricated 2D arrays of aluminum nano squares raised on top of PMMA nano posts in the back ground of a perforated back reflector by systematically varying the square size (D) and periodicity (P). In the single layer fabrication process the PMMA nano posts were defined by electron beam lithography and subsequently aluminum thin film was deposited by thermal evaporation to form both the nano squares and the fishnet like back reflector. The colour formation is based on the excitation of plasmonic light absorption at two distinct wavelengths leaving a central reflective peak that is coherently scattered by coupling to a strongly radiating dipole resonance. Pure colours both in the RGB and CMY colour schemes with extreme reflective peaks of high quality factor (FWHM of 100nm) across the visible spectrum are demonstrated.

Plasmonic grating structures can be used in many applications such as nanolithography and optical trapping. In this paper, we used plasmonic grating as optical tweezers to trap and manipulate dielectric nano-particles. Different plasmonic grating structures with single, double, and triple slits have been investigated and analyzed. The three configurations are optimized and compared to find the best candidate to trap and manipulate nanoparticles. The three optimized structures results in capability to super focusing and beaming the light effectively beyond the diffraction limit. A high transverse gradient optical force is obtained using the triple slit configuration that managed to significantly enhance the field and its gradient. Therefore, it has been chosen as an efficient optical tweezers. This structure managed to trap sub10nm particles efficiently. The resultant 50KT potential well traps the nano particles stably. The proposed structure is used also to manipulate the nano-particles by simply changing the angle of the incident light. We managed to control the movement of nano particle over an area of (5μm x 5μm) precisely. The proposed structure has the advantage of trapping and manipulating the particles outside the structure (not inside the structure such as the most proposed optical tweezers). As a result, it can be used in many applications such as drug delivery and biomedical analysis.

Metallic nanostructures have offered not only the exciting opportunity to manipulate light waves in unconventional manners, but also the exciting potential to create customized nonlinear media with tailored high-order effects. Two particularly compelling directions of current interests are active plasmonics, where the optical properties can be purposely manipulated by external stimuli, and nonlinear plasmonics, which enable intensity-dependent frequency conversion of light. By exploring the interaction of these two directions, we leverage the electrical and optical functions simultaneously supported in nanostructured metals and demonstrate electrically-controlled nonlinear processes from plasmonic metamaterials. We show that a variety of nonlinear optical phenomena, including the wave mixing and the optical rectification, can be purposely modulated by applied voltage signals. In addition, electrically-induced and voltage-controlled nonlinear effects facilitate us to demonstrate the backward phase matching in a negative index material, a long standing prediction in nonlinear metamaterials. Other results to be covered in this talk include photon-drag effect in plasmonic metamaterials and ion-assisted nonlinear effects from plasmonic crystals in electrolytes. Our results reveal a grand opportunity to exploit plasmonic metamaterials as self-contained, dynamic electrooptic systems with intrinsically embedded electrical functions and optical nonlinearities for signal generation, information processing, and biochemical sensing. Reference: L. Kang, Y. Cui, S. Lan, S. P. Rodrigues, M. L. Brongersma, and W. Cai, Nature Communications, 5, 4680 (2014). S. P. Rodrigues and W.Cai, Nature Nanotechnology, 10, 387 (2015). S. Lan, L. Kang, D. T. Schoen, S. P. Rodrigues, Y. Cui, M. L. Brongersma, and W. Cai, Nature Materials, 14, 807 (2015). S. Lan, S. P. Rodrigues, Y. Cui, L. Kang, and W. Cai, Nano Letters, 16, 5074 (2016).

Plasmonics involves the interaction of light with metallic structures at the nanoscale, which enables in particular the generation of strong reflection and absorption effects in the visible and near infrared range. The fabrication of plasmonic nanostructures using ultra-violet (UV) imprint and thin metallic coatings is reported. Wafer-scale fabrication and process compatibility with cost-efficient roll-to-roll production are demonstrated, which paves the road towards an industrial implementation. The color, phase, polarization and direction of the transmitted light are controlled by tuning the process parameters and the symmetry of the nanostructures. A family of devices is presented, for which the potential for sensing, filtering, anticounterfeiting and optical security is evaluated.

Nanostructured metals have utilized the strong spatial confinement of surface plasmon polaritons to harness enormous energy densities on their surfaces, and have demonstrated vast potential for the future of nano-optical systems and devices. While the spectral location of the plasmonic resonance can be tailored with relative ease, the control over the spectral linewidth associated with loss represents a more daunting task. In general, plasmonic resonances typically exhibit a spectral linewidth of ~50 nm, limited largely by the combined damping and radiative loss in nanometallic structures. Here, we present one of the sharpest resonance features demonstrated by any plasmonic system reported to date by introducing dark plasmonic modes in diatomic gratings. Each duty cycle of the diatomic grating consists of two nonequivalent metallic stripes, and the asymmetric design leads to the excitation of a dark plasmonic mode under normal incidence. The dark plasmonic mode in our structure, occurring at a prescribed wavelength of ~840 nm, features an ultra-narrow spectral linewidth of about 5 nm, which represents a small fraction of the value commonly seen in typical plasmonic resonances. We leverage the dark plasmonic mode in the metallic nanostructure and demonstrate a resonance enhanced plasmoelectric effect, where the photon-induced electric potential generated in the grating is shown to follow the resonance behavior in the spectral domain. The light concentrating ability of dark plasmonic modes in conjunction with the ultra-sharp resonance feature at a relatively low loss offers a novel route to enhanced light-matter interactions with high spectral sensitivity for diverse applications.

Systematic study of magnetron sputtered silver-indium tin oxide (Ag-ITO) composite films has been carried out by altering the atomic ratio of silver in the co-sputtered films. The optimal micro-structure characteristic with smooth surface and tight junction between silver and ITO particles could be obtained by tuning Ag atomic ratio. Spectroscopic ellipsometry is applied in order to evaluate the plasmonic properties. Real and imaginary permittivity of the films are retrieved utilizing Drude-Lorentz dispersion model. The cross-over wavelength of the films, optimized to as low as around 1130 nm, exhibits high adjustability on the ratio of silver material and RTP process. Much lower imaginary permittivity as well as tunable real permittivity suggest the potentiality of Ag-ITO composite films as substituted plasmonic materials in the near-infrared region.

By completely opening the parameter space in design of nanophotonic circuits, new functionalities and better performance relative to traditional optoelectronics approaches can be achieved. We have recently developed an inverse (objective first) approach to design nanophotonic structures only based on their desired performance. Moreover, constraints including structure robustness, fabrication error, and minimum feature sizes can be incorporated in design, without need to have an optics expert as a designer. Finally, such structures are fully fabricable using modern lithography and nanofabrication techniques. We have also demonstrated devices designed using this approach, including ultra-compact and efficient wavelength splitters on the silicon platform. Beyond integrated photonics, this approach can also be applied to design of quantum photonic circuits.

We study the ring resonator under a dynamic modulation. Each ring resonator supports a set of resonant modes with an equal spacing. We find that the system exhibits a spectral Bloch oscillation along the frequency axis when we introduce a frequency detuning in the modulation frequency. A periodic switching of the detuning brings out a unidirectional translation of the frequency of light. Moreover, in an array of rings, each of which is dynamically modulated with a different phase, we see topologically-protected edge states. Our work points to a new capability for the control of light in the frequency space.

Optical Parity-Time (PT-) symmetric systems support unusual properties when the symmetric coupling between internal modes is broken. We propose a new class of quasiperiodic PT-axisymmetric systems which lead to a simultaneous extraordinary field enhancement and localization at the symmetry center. The effect is based on the asymmetric radial coupling of outward to inward propagating waves of the complex structure. We explore such optical potentials in 1D and 2D combining gain/loss and index modulations, which could have actual realizations in nanophotonic structures. As a direct application, we show how to render a broad aperture vertical-cavity surface-emitting lasers (VCSEL) into a bright and narrow beam source.

An analysis is presented of k-space coupling of energy from an object into one or more proximal resonant scatterers. The choice of basis function provides insight into coupling mechanisms and efficiency which leads to the design of effective resonant scatterers that can direct energy and/or information associated with high-k evanescent fields away from the object. We discuss the trade-offs between the k-space and ω-space coupling as a function of the Q of the resonant scatterer. At the nanoscale, this has applications for super-Planckian heat removal as well as superresolution imaging.

Anderson localizing optical fibers (ALOF) enable a novel optical waveguiding mechanism; if a narrow beam is scanned across the input facet of the disordered fiber, the output beam follows the transverse position of the incoming wave. Strong transverse disorder induces several localized modes uniformly spread across the transverse structure of the fiber. Each localized mode acts like a transmission channel which carries a narrow input beam along the fiber without transverse expansion. Here, we investigate scaling of transverse size of the localized modes of ALOF with respect to transverse dimensions of the fiber. Probability density function (PDF) of the mode-area is applied and it is shown that PDF converges to a terminal shape at transverse dimensions considerably smaller than the previous experimental implementations. Our analysis turns the formidable numerical task of ALOF simulations into a much simpler problem, because the convergence of mode-area PDF to a terminal shape indicates that a much smaller disordered fiber, compared to previous numerical and experimental implementations, provides all the statistical information required for the precise analysis of the fiber.

We report on electrically modulating and switching the wavy properties of acoustic phonons in nanoscale piezoelectric heterostructures which are strained both from the pseudomorphic growth at the interfaces as well as through external electric fields. In symmetry planes of such structures, the generation and detection of the transverse acoustic modes are forbidden, and only longitudinal acoustic phonons are generated by ultrafast displacive screening of strains. We show that the combined application of lateral and vertical electric fields can not only turn on and off various modes but they can also modulate the amplitudes and frequencies of the modes [1-3]. The role of the electrical controllability of phonons was further demonstrated as changes to the propagation velocities; the electrically polarized TA waves; and the geometrically varying optical sensitivities of phonons. The capability to manipulate the phononic functionalities with electric fields is analogous to that for manipulating photons and electrons in major technological devices and can be a practical route for integrated phononic circuitry. [1] C. S. Kim et al., Appl. Phys. Lett. 100, 101105 (2012). [2] H. Jeong et al., Phys. Rev. Lett. 114, 043603 (2015). [3] H. Jeong et al., Phys. Rev. B (to appear).

We demonstrate for the first time the storage of multiple phase and amplitude levels of an optical signal as coherent acoustic phonons. The storage concept is implemented on-chip with a GHz-bandwidth.

The optical and mechanical properties of silicon and silica glass make the silicon-on-insulator material system a platform natural for photonics and challenging for phononics. High index-contrast enables index-guiding in silicon waveguides on glass, but silicon's relative stiffness and high sound velocity hampers analogous efforts to ``index-guide'' acoustic waves. Waveguide geometry plays fundamentally different roles in the dispersion of mechanical and optical waves, enabling radiation-free waveguiding in high aspect-ratio cantilevers defined in silicon. We fabricate silicon fins, here 80 nm wide in 340 nm SOI, that exhibit low-loss mechanical resonances at 600-700 MHz. We present designs, numerical studies, and the first measurements of release-free optomechanical “fin cavities” in 340 nm SOI. The dispersion of flexural fin mechanical modes is readily engineered by variation of the fin's width. TE and TM optical cavities at telecom frequencies are made with an adjoined nanobeam. Nanobeam geometry independently influences the optics decoupling optical and mechanical design problems. Optical and mechanical modes can be colocalized with a simple cavity where a parabolically curved fin is placed near a photonic crystal waveguide. We simulate and measure optical and mechanical spectra of these devices. Optomechanical interaction rates ranging from low kHz to 500 kHz for the fin cavities are demonstrated. Furthermore, by analyzing the interaction rates we identify the different optical modes of these structures. The demonstrated SOI fin cavities create new opportunities for quantum optomechanical sensing in a truly CMOS-compatible setting.

Multi-mode optomechanical systems have formed the basis of recent proposals and experiments, enabling optical frequency translation and hybridization of near-resonant mechanical modes. An important question is how to control the internal mechanical states of such systems using laser light. Such control enables engineering of effective nonlinearities for phonons, allowing phonon-phonon frequency translation, mechanical entanglement, and precision metrology. On-chip engineered nanostructures are particularly suitable for exploring multi-mode systems. Here, we consider a silicon nanobeam optomechanical crystal with two mechanical modes coupled to a common optical mode. Simulations of the phonon-phonon scattering parameters of the system suggest that large conversion efficiency can be obtained at cryogenic temperatures. We show that remarkably, phonon-phonon conversion efficiency near unity is achievable, even when the loss rate of the intermediate optical mode dominates all other rates in the system by several orders of magnitude. This counter-intuitive phenomenon is the result of a long-lived mechanical dark state of the system that arises in the optical pumping scheme being used. We experimentally demonstrate two GHz frequency mechanical modes, separated by nearly 300 MHz, coupled to a first-order common optical TE mode with vacuum coupling rates of nearly 500 kHz. By optically driving the optomechanical crystal with two tones separated by the mechanical difference frequency we present evidence for optically induced phonon-phonon interactions at room temperature. We will present results of measurements in a cryogenic environment, operating at 4 Kelvin demonstrating improved large phonon-phonon conversion efficiency.

Raman scattering is an excellent analysis tool because a wealth of information can be obtained using a single measurement. It can also be configured as a diagnostic tool as a label free sensing method. In that case, enhancing the Raman signal is important to improve the sensitivity and detect low concentrations of analytes. A nanoparticle showing a particular Raman enhancement shows a much higher enhancement when it is on a nanowire. This was also confirmed experimentally. We report on a simple fabrication method of silver nanoparticles and silicon nanowires decorated with these nanoparticles. The nanowires were fabricated using metal assisted chemical etching. The nanoparticles were formed using electrodeposition. Samples were then immersed in Pyridine. An enhancement factor of around 6 to 8×10⁵ was observed for silver nanoparticles alone. By depositing the same nanoparticles on silicon nanowires, the enhancement factor jumped 10-fold to 7×10⁶. Finite Difference Time Domain simulations showed that a range of enhancement factors is possible up to 10⁹.

We are developing a photonic crystal superlens based on negative refraction effect for mid-infrared astronomical telescopes to improve their angular resolution. The superlens will convert incident beams of large F-number to output beams of small F-number without changing image height. Firstly, we designed the superlens by theoretical calculations. We optimized two-dimensional dielectric structures of the superlens by calculating its band structures and iso-frequency contours using Plane-wave expansion (PWE) method. We also studied interface structures of input/output ports of the superlens in order to maximize its transmittance by numerical calculations using Fourier modal method (FMM). Then, wave-propagation simulations through the superlens by Finite-difference time-domain (FDTD) method showed that Full Width Half Maximum (FWHM) of point spread function will be reduced by approximately 15%. Secondly, we are trying to manufacture the superlens using a three-dimensional laser lithography system based on two-photon polymerization process. We also have measured complex refractive indices of SU-8 photoresist around wavelength of 10micron by spectroscopic ellipsometry. The fabrication and optical benchmark of the superlens are currently underway. In this paper, we present experimental results as well as the design process of the superlens.

Surface-enhanced Raman scattering (SERS) is a powerful technique for trace chemical analysis and single molecule detection in the application of biochemical monitoring and food safety due to its ability to enhance the Raman scattering of molecules near the metallic surface or nanostructures. Here, we present a comprehensive study of the SERS enhancement by the periodically nanostructured surface, where the thin film of silver is deposited onto the surface, except the sidewall of posts, of 1-D lamellar gratings with varying pitch to forming metal-dielectric composite nanostructures. By enhancing the localized and surface-propagating mode in the vicinity of the concaves, the SERS signal can be improved by amplifying the intensity of electric field and increasing the optical path length of the incident light. Experimental investigations show that the enhancement factor can be manipulated by varying the polarization of incident light and the pitch size of gratings. To demonstrate the SERS effects of the proposed structures, thin layers of benzoic acid, which is commonly used as a food preservative, are deposited on the SERS substrates by spin-coating a solution of benzoic acid and dried at room temperature. A Confocal Raman microscope with a 532 nm laser source is used to illuminate light and measure the Raman spectrum of benzoic acid. We demonstrate the Raman signal of benzoic acid can be enhanced on the order of 10² on the SERS substrates.

In this study, we propose a drop-out mechanism based on the enhanced interaction between a defect waveguide and defect microcavities in three-dimensional chirped woodpile photonic crystals (WPCs). We first show that light can be gradually slowed down in the defect waveguide (WG), which is obtained by gradually changing the period of the surrounding WPC along the propagation direction. In result, the waveguide mode gradually approaches the band edge region, while this phenomenon has three consequences. First, the Fourier components of propagating wave will be spatially separated as each frequency will reach its zero velocity at different positions. Second, as the wave slows down, it will penetrate deeper into the surrounding cladding, thus increasing the coupling efficiency between the WG and a nearby placed resonator. Third, the high density of states near the band edge result in highly efficient light scattering of a nearby placed resonator, which in turn increases the quality factor of the interaction. Following this idea, the acceptor type cavities, which are tuned to the localized frequencies, are side-coupled to the WG at respective wave localization areas. Furthermore, drop channels have been introduced to read-out the trapped spectra, showing that the targeted frequencies can be detected selectively. Compared to previous studies, our approach has the advantages of low radiation losses, the absence of any reflection feedback and both enhanced quality factor and transmission of the captured light.

We developed a new type of silicon MOSFET Quantum Well transistor, coupling both electronic and optical properties which should overcome the indirect silicon bandgap constraint, and serve as a future light emitting device in the range 0.8-2μm, as part of a new building block in integrated circuits allowing ultra-high speed processors. Such Quantum Well structure enables discrete energy levels for light recombination. Model and simulations of both optical and electric properties are presented pointing out the influence of the channel thickness and the drain voltage on the optical emission spectrum.

We use rigorous scattering matrix simulations to develop a pathway for synthesizing nanopatterns on polymer surfaces. We consider a system in which the polymer surfaces are initially coated with periodic microspheres in a close packed lattice. When such a lattice is irradiated with a laser of desired wavelength and power, the electric field intensity beneath the spheres is enhanced by more than an order of magnitude, generating localized heating that can remove nanometersize volume of the material in a periodic array of nanocavities. The array of glass spheres can be self-assembled on any curved surface, and these spheres can be utilized as an optical lens to focus light energy within the surface. Our simulations show that the depth and size of the nano-cavities depends critically on the size of microspheres.

Nanoscale periodic material design and fabrication are essentially fundamental requirement for basic scientific researches and industrial applications of nanoscience and engineering. Innovative, effective, reproducible, large-area uniform, tunable and robust nanostructure/material syntheses are still challenging. Here, I would like to introduce the novel periodic nanostructural materials particularly with uniformly ordered nanoporous or nanoflower structures, which are fabricated by simple, cost-effective, and high-throughput wet chemical methods. I also report large-area periodic plasmonic nanostructures based on template-based nanolithography. The surface morphology and optical properties are characterized by SEM and UV-vis. spectroscopy. Furthermore, their enhancement factor is evaluated by using SERS signals.