This PDF file contains the front matter associated with SPIE Proceedings Volume 9883, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Our intuitive understanding of light has its foundation in the ray approximation and is intimately connected with our vision: as far as our eyes are concerned light behaves like a stream of particles. Here we look inside the wavelength and study the properties of plasmonic structures with dimensions of just a few nanometres: a tenth or even a hundredth of the wavelength of visible light, where the ray picture fails utterly. In this talk we show how the new concept of transformation optics that manipulates electric and magnetic field lines rather than rays can provide an equally intuitive understanding of sub wavelength phenomena and at the same time be an exact description at the level of Maxwell’s equations. The concepts are applied to a number of plasmonic structures

The use of plasmonic effects over a broad range of electromagnetic spectrum has been a challenge over the first few decades of research due to limited number of available materials. Recently, the efforts in the area has been concentrated on identifying and examining new material classes as the building blocks for optical technologies over a broader electromagnetic spectrum. Transition metal nitrides attract attention as plasmonic materials in the visible and infrared spectral regions with optical properties resembling gold. As refractory materials, nitrides can withstand heat induced physical phenomena as well as aggressive chemical environment. Adjustable dielectric permittivity of plasmonic nitrides allow fine tuning of optical properties for selected applications. In addition to favorable optical, physical and chemical properties; transition metal nitrides provide CMOS- and bio-compatibility. In this talk, novel designs and concepts based on refractory plasmonic materials for infrared applications will be presented. Additionally, light confinement at the nanoscale with refractory plasmonic antennas, spectral engineering of absorption and emission with metamaterials, and the use of colloidal solutions for a variety of applications will be discussed.

An extended Malus’ Law for the well-known Polarizer-Analyzer Mounting (PAM) is analytically obtained and investigated. The PAM is composed of two perfectly parallel Metallic Linear Polarizers (MLP), with subwavelength periodic pattern composed of rectangular holes. Our analytical theory especially highlights the influence of multiple reflections between the two MLPs which leads to an extended and tunable Malus Law. We demonstrate that the classical Malus Law (obtained for dichroic polarizers) is modulated by a factor which also depends on the angular difference between both MLP axes. In our analysis, the Malus’ law is studied at the resonance wavelengths. Due to the interactions between the two MLP, the modulation factor is tuned by the optical distance between them which makes substantial variations of the Malus Law. We mention that, for each reflections, the light is re-polarized according to the orientation of the MLP. This tunable Malus’ Law provides an original tool for ultrasensitive detection in the terahertz or microwave regime. For example, one can use an ultra-narrow angle Malus’ Law as a hyper-sensitive device to analyze with a high accuracy the electro-optical response of a material sandwiched between polarizer and analyzer. We theoretically propose one PAM designed to detect a refractive index variation as small as 10−5. Finally, we extend the theory, which takes the form of an extended Jones formalism, to a large number of stacked MLP. It is applied to achieve many polarization manipulation processes as total polarization conversion with tunable spectral bandwidth, for instance.

Two electrooptical effects in a system consisting of subwavelength aluminum gratings and a nematic liquid crystal (LC) layer are discussed. The aluminum gratings produced by a focused ion beam lithography act as interdigitated electrodes, which allows application of an electric field to a very thin fraction of LC layer contacting the grating. The first of the electrooptical effects is associated with an enhanced TE-polarized light transmission of the gratings and the surface induced twist deformation in the bulk of the LC layer, whereas the second one is caused by an influence of the electrically driven LC surface layer on the plasmonic resonance and the related dip of the TM-polarized grating transmission. Besides the different polarizations, the two effects have dramatically different response times. In the case of the plasmonic effect, the measured response time is found to be of 20 - 30 microseconds that is three orders of magnitude faster compared to the switching based on the surface induced twist effect.

Optical metasurfaces have developed as a breakthrough concept for advanced wave-front. Key to these “designer metasurfaces”[1] is that they provide full 360 degree phase coverage and that their local phase can be precisely controlled. The local control of phase, amplitude and polarization on an optically thin plane will lead to a new class of flat optical components in the areas of integrated optics, flat displays, energy harvesting and mid-infrared photonics, with increased performance and functionality. However, reflection and/or absorption losses as well as low polarization-conversion efficiencies pose a fundamental obstacle for achieving high transmission efficiencies that are required for practical applications. A promising way to overcome these limitations is the use of metamaterial Huygens’ surfaces [2-4], i.e., reflection-less surfaces that can also provide full 360 degree phase coverage in transmission. Plasmonic implementations of Huygens’ surfaces for microwave [2] and the mid-infrared spectral range [3], where the intrinsic losses of the metals are negligible, have been suggested, however, these designs cannot be transferred to near-infrared or even visible frequencies because of the high dissipative losses of plasmonic structures at optical frequencies. Here, we demonstrate the first holographic metasurface utilizing the concept of all-dielectric Huygens’ surfaces thereby achieving record transmission efficiencies of approximately 82% at 1477nm wavelength. Our low-loss Huygens’ surface is realized by two-dimensional subwavelength arrays of loss-less silicon nanodisks with both electric and magnetic dipole resonances [4]. By controlling the intrinsic properties of the resonances, i.e. their relative electric and magnetic polarizabilities, quality factors and spectral position, we can design silicon nanodisks to behave as near-ideal Huygens’ particles. This allows us to realize all-dielectric Huygens’ surfaces providing full 360 degree phase coverage that lack dissipative losses and also suppress unwanted reflections without relying on cross-polarization schemes that additionally suffer from polarization-conversion losses. We now use such Huygens’ surfaces in order to create a highly-efficient phase masks for the generation of optical holograms. By varying only one geometrical parameter, namely the lattice periodicity that can be controlled easily during the fabrication process we can effectively generate arbitrary hologram images from a 4-level phase discretization. In order to design the arrangement of the pixels in the metasurfaces, we calculate the phase mask required for a hologram generating the letters ‘hv’ in the hologram plane. In the next step the Huygens’ hologram is fabricated on a back-side polished SOI wafer by electron-beam lithography followed by a reactive-ion etching process. Then, we measure the phase of the generated hologram using a home-built Mach-Zehnder interferometer and perform a phase retrieval process to compare the experimental phase with the designed phase. Finally, we record the holographic image in the hologram plane and demonstrate that the device functionality is completely polarization insensitive with a transmission efficiency of 82%, in contrast to all the earlier works utilizing geometric phase. References [1] Yu et al., Nat. Mater. 13, 139 (2014). [2] Pfeiffer et al., Phys. Rev. Lett. 110, 197401 (2013). [3] Monticone et al., Phys. Rev. Lett. 110, 203903 (2013). [4] Decker et al., Adv. Opt. Mater. 3, 813 (2015).

The design of a metamaterial-based absorber for use in a MEMS-based mid-IR microspectrometer is reported. The microspectrometer consists of a LVOF that is aligned with an array of thermopile detectors, which is fabricated on a SiN membrane and coated with the absorber. Special emphasis is put on the CMOS compatible fabrication, which results in an absorber design based on Al disc resonators and an Al background plane that are separated by an SiO2 layer. Wideband operation over the 3-4 μm spectral range is achieved by staggered tuning of four Al disk resonators in one 1.5 x 1.5 μm² unit cell, using four different values of the radius of the Al disk between 0.50 μm and 0.63 μm and an SiO₂ layer thickness of 150 nm. Simulations reveal an average absorption of about 95% with a ±4% ripple at normal incidence, which reduces to about 80% absorption at a 20° incidence angle. The influence of material choice and dimensions on a single absorption peak was studied and the magnetic polariton was identified as the underlying mechanism of absorption.

Metals exhibit strong and fast nonlinearities making metallic, plasmonic, structures very promising for ultrafast all-optical applications at low light intensities. Combining metallic nanostructures in metamaterials provides additional functionalities via prospect of precise engineering of spectral response and dispersion. From this point of view, hyperbolic metamaterials, in particular those based on plasmonic nanorod arrays, provide wealth of exciting possibilities in nonlinear optics offering designed linear and nonlinear properties, polarization control, spontaneous emission control and many others. Experiments and modeling have already demonstrated very strong Kerr-nonlinear response and its ultrafast recovery due to the nonlocal nature of the plasmonic mode of the metamaterial, so that small changes in the permittivity of the metallic component under the excitation modify the nonlocal response that in turn leads to strong changes of the metamaterial transmission. In this talk, we will discuss experimental studies and numerical modeling of second- and third-order nonlinear optical processes in hyperbolic metamaterials based on metallic nanorods and other plasmonic systems where coupling between the resonances plays important role in defining nonlinear response. Second-harmonic generation and ultrafast Kerr-type nonlinearity originating from metallic component of the metamaterial will be considered, including nonlinear magneto-optical effects. Nonlinear optical response of stand-alone as well as integrated metamaterial components will be presented. Some of the examples to be discussed include nonlinear polarization control, nonlinear metamaterial integrated in silicon photonic circuitry and second-harmonic generation, including magneto-optical effects.

Metamaterials with high optical activity (OA) and circular dichroism (CD) are desired for various prospective applications ranging from circular light polarizing to enhanced chiral sensing and biosensing. Modern techniques allow fabricating subwavelength arrays of holes of complex chiral shapes that exhibit extreme optical chirality: their OA and CD take the whole range of possible values in the visible. In order to understand the nature of extreme chirality, we performed the electromagnetic finite difference time domain simulations for the hole shapes resolved by atomic force microscopy. The analysis of the simulation data allowed us to develop an analytical chiral coupled-mode model that nicely fits the results and explains the extreme chirality as determined by the Fano-type transmission resonance due to the interference of a weak background channel and a resonant plasmon channel. The model shows critical importance of the dissipation losses, the hole shape symmetry and chirality. In a planar 2D-chiral hole array, the mirror asymmetry can be induced by the difference of dielectric materials adjacent to the array sides and even their weak deviation results in remarkably strong OA and CD. We note that such deviations can arise due to the dielectric nonlinearity and discuss how 2D-chiral metamaterials in symmetric environment can acquire optical chirality due to the nonlinear symmetry breaking.

Plasmonic nano-structured array sensors have been highlighted by their tremendously promising applications, such as the surface plasmon resonance (SPR) optical biosensors. In this paper, within the visible spectrum region, the optical transmission properties of a metallic thin film deposited over dielectric films of various refraction indices are investigated. With finite difference time domain (FDTD) method, we investigate the optical transmission spectra of such plasmonic structures based on both nano-holes and nano-disc arrays. This investigation includes monitoring the modification in both the transmission resonance wavelengths and peak transmittance. The results of this study provide a better understanding of the interaction between light and plasmonic nano-hole and nano-disc arrays. It shows that the changing the shapes of the nano-holes can affect the resonance wavelengths and the intensity of transmitted spectra and alter its resonance peak transmittance values. We found that the interaction coupling between the localized plasmons (LSP) and the propagating surface plasmons (PSP) can be tuned to boost the performance of the optical sensor.

The effect of circularly polarized beaming excited by traveling surface plasmons, via chiral metasurface is experimentally studied. Here we show that the propagation direction of the plasmonic wave, evanescently excited on the thin gold film affects the handedness of the scattered beam polarization. Nanostructured metasurface leads to excitation of localized plasmonic modes whose relative spatial orientation induces overall spin-orbit interaction. This effect is analogical to the rack-and-pinion gear: the rotational motion into the linear motion converter. From the practical point of view, the observed effect can be utilized in integrated optical circuits for communication systems, cyber security and sensing.

Metamaterials have a number of interesting and potentially useful applications in a variety of fields, such as chemical and biological sensing, enhancement of spontaneous emission, nonlinear optics and as substrates for use in surface enhanced Raman spectroscopy (SERS). However, to date the low-wavelength cutoff for the majority of work at the higher frequency end of the spectrum has been determined by use of the coinage metals, which intrinsically prohibit their implementation below a vacuum wavelength of approximately 500nm for gold and 350nm for silver. Producing nanostructured plasmonic media that exhibit metamaterial functionalities in the ultraviolet will have a number of benefits. Not only will working in a new range of the electromagnetic spectrum allow for higher energy photons to be controlled, but a number of other benefits arise from the behaviour of different materials in the ultraviolet. For instance, many biological molecules, including DNA, exhibit fluorescence in the UV range, allowing for label-free detection and analysis of biological material; the intrinsic electronic absorption can be used to increase this label-free bio-sensitivity as well as enable the possibility of SE(R)RS, a process further enhanced by the frequency dependence on the efficiency of this scattering process. Here, we demonstrate the fabrication and characterisation of metamaterials operating in the deep-near UV. By using alternatives to the coinage metals, including aluminium and gallium, we have measured optical responses in the system down to approximately 200 nm. Sample preparation utilises a self-assembly method, allowing for the production of macroscopic-sized assemblies (> 1 cm2) of nanometric elements (radius ~ 25 nm, separation ~ 100 nm). Careful control of the fabrication conditions allows fine control of the structural parameters, which in turn allows tunability of the optical properties over a wide range of wavelengths (> 200 nm). The structures produced include gallium nanorods, oriented with their long axis perpendicular to the substrate and having a sub-wavelength interrod distance, fabricated via oxygen- and water-free electrodeposition into nanoporous anodised alumina (AAO), and aluminium nanohole arrays fabricated using AAO as a mask for ion milling, with elements at the same nanometric size scale. Both systems have been optically characterised across the UV and visible wavelength ranges and compared with numerical modelling in order to analyse and describe their behaviour.

Raman scattering in disc-shaped graphite nanostructures, etched out of bulk HOPG, are investigated using an excitation wavelength of 532 nm at different laser power. The G-band is fitted using two Lorentzian functions, GL and GH. The difference of Raman shift between the two Lorentzian functions increase with laser power as a consequence of selective absorption and heating of the discs. Further, the G-band from the nanostructured HOPG reveal a Raman enhancement (RE) of ~2.2 and ~1.5 for the components associated with the discs (GL) and the supporting substrate (GH), respectively. The quantitative agreement between the experimental results and performed finite difference time domain calculations make possible to conclude that electromagnetic energy penetrates considerably into the discs from the circular periphery probably due to multiple scattering. In addition, the dependence of RE of the GL component on the laser power is attributed to a temperature dependent electron-phonon coupling.

We numerically analyzed a proposed gold nanoblock as an element of a phase gradient metasurface working in the visible and near-infrared regime. In contrast to previous designs in the literature, these elements work under offresonance condition which leads to significantly reduced absorbing losses and improved conversion efficiency, also in this way a broadband operation is achieved. We show that when the excitation field is in the direction of the (short) width of the nanoblock, a condition required so that it works off resonance, by changing the width of nanoblock we can reach up to 2π phase retardation in reflection. We then use this property to design a polarization beam splitter.

A problem of maximization of the radiative heat transfer (at a given wavelength) between a body and its environment is considered theoretically. It is shown that the spectral density of the radiative heat flux is maximized under the formulated conjugate impedance matching condition, in which case the spectral density of radiated power can exceed the black body limit, resulting in a super-Planckian heat exchange at characteristic distances significantly greater than the wavelength. It is demonstrated that the material parameters of the optimal emitters can be deduced from the known material parameters of the environment and represented by closed-form relations, thus, enabling a way for physical realization of such far-field super-Planckian emitters.

Although the transformation algorithm is very well established and implemented, some intriguing questions remain unanswered. 1) In what precise mathematical sense is the transformation optics algorithm ‘exact’? The invariance of Maxwell’s equations is well understood, but in what sense does the same principle not apply to acoustics (say)? 2) Even if the fields are transformed in a way that apparently mimic vacuum perfectly, it is easy to construct very simple examples where the impedance of the transformed medium is no longer isotropic and homogeneous. This would seem to imply a fundamental shortcoming in any claim that electromagnetic cloaking has been reduced to technology. 3) Transformations are known to exist that introduce a discrepancy between the Poynting vector and the wave-vector. Does this distinction carry any physical significance? We have worked extensively on understanding a commonality between transformation theories that operates at the level of rays – being interpreted as geodesics of an appropriate manifold. At this level we now understand that the *key* problem underlying all attempts to unify the transformational approach to disparate areas of physics is how to relate the transformation of the base metric (be it Euclidean for spatial transformation optics, or Minkowskian for spacetime transformation optics) to the medium parameters of a given physical domain (e.g. constitutive parameters for electromagnetism, bulk modulus and mass density for acoustics, diffusion constant and number density for diffusion physics). Another misconception we will seek to address is the notion of the relationship between transformation optics and curvature. Many have indicated that transformation optics evinces similarities with Einstein’s curvature of spacetime. Here we will show emphatically that transformation optics cannot induce curvature. Inducing curvature in an electromagnetic medium requires the equivalent of a gravitational source. We will propose a scheme that achieves this.

Plasmonic metasurfaces, which can be considered as the two-dimensional analog of metal-based metamaterials, have recently attracted considerable attention due to the possibility to fully control the reflected or transmitted light, while featuring relatively low losses even at optical wavelengths and being suitable for planar fabrication techniques. Among all the different design approaches, one particular configuration, consisting of a subwavelength thin dielectric spacer sandwiched between an optically thick metal film and an array of metal nanobricks (also known as nanopatches), has gained awareness from researchers working in practical any frequency regime as its realization only requires on step of lithography, yet with the possibility to fully control the amplitude and phase of the reflected light. At optical wavelengths, the full control of the reflected light is closely associated with gap surface plasmon (GSP) resonances and, hence, the configuration is also known as GSP-based metasurface. In this work, we highlight the connection between the properties of GSP modes and the optical response of GSP-based metasurfaces, particularly discussing the possibility to independently control either the reflection phases for two orthogonal polarizations or both the amplitude and phase of the reflected light for one polarization by proper choice of geometrical and material parameters [1]. Having obtained thorough insight into the optical response of GSP-based metasurfaces, we design and realize at optical and near-infrared wavelengths a broad range of inhomogeneous metasurfaces targeting different applications. For example, we exemplify the control of reflection amplitude by performing plasmonic color printing on a subwavelength scale [2], while full control of reflection phases for orthogonal polarizations are illustrated by the realization of unidirectional polarization-controlled surface plasmon polariton couplers [3] and compact polarimeters [4]. Finally, the simultaneous control of the amplitude and phase of reflected light allow us to perform calculus operations, such as differentiation and integration, on the incident light [5], which signifies the possibility to do optical signal processing using GSP-based metasurfaces. References: 1. A. Pors and S. I. Bozhevolnyi, “Gap plasmon-based phase-amplitude metasurfaces: material constraints”, Opt. Mater. Express 5, 2448-2458 (2015). 2. A. S. Roberts, A. Pors, O. Albrektsen, and S. I. Bozhevolnyi, “Subwavelength plasmonic color printing for ambient use”, Nano Lett. 14, 783-787 (2014). 3. A. Pors, M. G. Nielsen, T. Bernardin, J.-C. Weeber, and S. I. Bozhevolnyi, “Efficient unidirectional polarization-controlled excitation of surface plasmon polaritons”, Light: Sci. Applications 3, e197 (2014). 4. A. Pors, M. G. Nielsen, and S. I. Bozhevolnyi, “Plasmonic metagratings for simultaneous determination of Stokes parameters”, Optica 2, 716-723 (2015). 5. A. Pors, M. G. Nielsen, and S. I. Bozhevolnyi, “Analog computing using reflective plasmonic metasurfaces”, Nano Lett. 15, 791-797 (2015).

By now superresolution imaging using hyperbolic metamaterial (HMM) structures – hyperlenses – has been demonstrated both theoretically and experimentally. The hyperlens operation relies on the fact that HMM allows propagation of waves with very large transverse wavevectors, which would be evanescent in common isotropic media (thus giving rise to the diffraction limit). However, nearly all hyperlenses proposed so far have been suitable only for very strong scatterers – such as holes in a metal film. When weaker scatterers, dielectric objects for example, are imaged then incident light forms a very strong background, and weak scatterers are not visible due to a poor contrast. We propose a so-called dark-field hyperlens, which would be suitable for imaging of weakly scattering objects. By designing parameters of the HMM, we managed to obtain its response in such way that the hyperlens structure exhibits a cut-off for waves with small transverse wavevectors (low-k waves). This allows the structure to filter out the background illumination, which is contained in low-k waves. We numerically demonstrate that our device achieves superresolution imaging while providing the strong contrast for weak dielectric scatterers. These findings hold a great promise for dark-field superresolution, which could be important in real-time dynamic nanoscopy of label-free biological objects for example.

Hyperbolic metamaterial (HMM) has attracted considerable attention owing to several exotic optical properties, including negative refraction, enhanced spontaneous emission, and subwavelength imaging. The hyperbolic dispersion of HMMs increases photonic density of states in a broad bandwidth, leading to enhancement of spontaneous emission. However, the out-coupling of light from HMMs is difficult due to the evanescent character of the high-k modes at the surface. In this study, we implement the full-field numerical calculations based on finite-difference time-domain (FDTD) method to characterize the optical properties of nanowire HMMs embedded in a grating structure. We first examined the power spectrum of the nanowire HMMs. The Purcell factor and the light enhancement are also analyzed. Furthermore, to examine the out-coupling of light by virtue of the periodic structure, the Purcell factor and enhancement of light extraction efficiency of the hybrid structure will be examined and discussed. The analysis result is important toward engineering highly-efficient photonic devices based on HMMs.

Improvement in high-temperature stable spectrally selective absorbers and emitters is integral for the further development of thermophotovoltaic (TPV), lighting and solar thermal applications. However, the high operational temperatures (T>1000oC) required for efficient energy conversion, along with application specific criteria such as the operational range of low bandgap semiconductors, greatly restrict what can be accomplished with natural materials. Motivated by this challenge, we demonstrate the first example of high temperature thermal radiation engineering with metamaterials. By employing the naturally selective thermal excitation of radiative modes that occurs near topological transitions, we show that thermally stable highly selective emissivity features are achieved for temperatures up to 1000°C with low angular dependence in a sub-micron thick refractory tungsten/hafnium dioxide epsilon-near-zero (ENZ) metamaterial. We also investigate the main mechanisms of thermal degradation of the fabricated refractory metamaterial both in terms of optical performance and structural stability using spectral analysis and energy-dispersive X-ray spectroscopy (EDS) techniques. Importantly, we observe chemical stability of the constituent materials for temperatures up to 1000°C and structural stability beyond 1100°C. The scalable fabrication, requiring magnetron sputtering, and thermally robust optical properties of this metamaterial approach are ideally suited to high temperature emitter applications such as lighting or TPV. Our findings provide a first concrete proof of radiative engineering with high temperature topological transition in ENZ metamaterials, and establish a clear path for implementation in TPV energy harvesting applications.

We experimentally demonstrate a multispectral metasurface that exhibits controlled inhomogeneous optical properties leading to a spatial modulation of the emissivity up to the wavelength scale in the infrared. A metasurface made of a non-periodic set of 100 million optical nano-antennas that spatially and spectrally control the emitted light up to the diffraction limit has been realized and studied. Each antenna acts as an independent deep subwavelength emitter for a given polarization and wavelength, and their juxtaposition at the wavelength scale can encode far field multispectral and polarized images.

As a result of the significant attention in searching for alternative plasmonic materials for real-life nanophotonic devices, transparent conducting oxides (TCOs) have been proposed as promising constituent building blocks for telecommunication wavelengths. They are eminently practical materials because they are CMOS-compatible, can be grown on many different types of substrates, patterned by standard fabrication procedures, and integrated with many other standard technologies. Due to the ability of TCO nanostructures to support strong plasmonic resonance in the near infrared (NIR), metasurface devices, such as a quarter wave plate, have been demonstrated whose properties can be easily adjustable with post processing such as thermal annealing. Additionally, TCOs can be used as epsilon near zero (ENZ) materials in the NIR. From our recent study of the behavior of nanoantennae sitting upon a TCO substrate, we found that TCOs serve as an optical insulating media due to the high impedance of TCOs at the ENZ frequency, enabling emission shaping. Finally, the optical properties of TCOs can be varied by optical or electrical means. Current research is focused on studying the ultrafast carrier dynamics in doped zinc oxide films using pump-probe spectroscopy. We have shown that aluminum doped zinc oxide films can achieve a 40% change in reflection with ultrafast dynamics (<1ps) under a small fluence of 3mJ/cm². Consequently, TCOs are shown to be extremely flexible materials, enabling fascinating physics and unique devices for applications in the NIR regime.

Light absorption in ultrathin layer of semiconductor has been considerable interests for many years due to its potential applications in various optical devices. In particular, there have been great efforts to engineer the optical properties of the film for the control of absorption spectrums. Whereas the isotropic thin films have intrinsic optical properties that are fixed by materials’ properties, metafilm that are composed by deep subwavelength nano-building blocks provides significant flexibilities in controlling the optical properties of the designed effective layers. Here, we present the ultrathin semiconductor metafilm absorbers by arranging germanium (Ge) nanobeams in deep subwavelength scale. Resonant properties of high index semiconductor nanobeams play a key role in designing effective optical properties of the film. We demonstrate this in theory and experimental measurements to build a designing rule of efficient, controllable metafilm absorbers. The proposed strategy of engineering optical properties could open up wide range of applications from ultrathin photodetection and solar energy harvesting to the diverse flexible optoelectronics.

A layered uniaxial dielectric structure is considered. The layers in the structure are distributed according to a one-dimensional fractal set. The resulting fractal metamaterial is homogenized with an original source-driven homogenization approach which is suitable for both numerical and analytical calculations. Due to the fact that the considered metamaterial is nonmagnetic, the only effective parameter which needs to be calculated is the effective permittivity dyadic e(ω, k). The effective permittivity is obtained analytically (by using a transfer matrix approach) and numerically (by using a Finite-Difference Time-Domain solver).

Plasmon rulers are an emerging concept in which the strong near-field coupling of plasmon nanoantenna elements is employed to obtain structural information at the nanoscale. Here, we combine nanoplasmonics and nanomagnetism to conceptualize a magnetoplasmonic dimer nanoantenna that would be able to report nanoscale distances while optimizing its own spatial orientation. The latter constitutes an active operation in which a dynamically optimized optical response per measured unit length allows for the measurement of small and large nanoscale distances with about 2 orders of magnitude higher precision than current state-of-the-art plasmon rulers. We further propose a concept to optically measure the nanoscale response to the controlled application of force with a magnetic field.

In recent years there has been a renewed interest in research into plasmonic metamaterials. This includes new approaches in designing metamaterials that display hyperbolic dispersions and new fabrication techniques which take advantage of the control and uniformity possible with self-assembled, template based fabrication, and which significantly benefit from both low cost and high throughput. These approaches can readily achieve the dimensions required for the development of metamaterials in the visible and near-infra-red spectral ranges where considerable research has already been carried out. Currently, research in the near-UV to deep-UV (DUV) spectral regions (3-6 eV) is attracting increasing excitement due to the huge number of potential applications, including fluorescence enhancement, surface enhanced resonant Raman scattering, high sensitivity bio-sensing and nanoscale photolithography. Here we describe a self-assembled approach for the fabrication of metamaterials based on aluminium nanowires for applications spanning the deep to near-UV spectral range. Optical characterisation of such highly anisotropic UV metamaterials show the resonances which are tunable throughout the deep UV spectrum (200-500 nm) and which exhibit hyperbolic dispersion from the NUV to infra-red frequency range.

We report new 3D hybrid plasmonic nanostructures exhibiting highly sensitive SERS-based sensing performance, utilizing efficient plasmonic light absorption and analyte-enrichment effect. The hybrid plasmonic nanostructures composed of 3D-stacked Ag NWs and NPs separated by a thin hydrophobic dielectric interlayer. A hydrophobic polydimethylsiloxane (PDMS) interlayer provides dielectric nanogap between Ag NWs and NPs, and analyte-enrichment effect due to the inhibition of drop spreading. The 3D hybrid PDMS-interlayered Ag nanostructures showed hydrophobicity with initial contact angle of 137.6°. Utilizing the analyte-enrichment strategy, the PDMS-interlayered Ag nanostructures exhibited an enhanced sensitivity of methylene blue molecules by a factor of 10 (limit of detection, LOD of 1.5 nM), compared to the alumina-separated 3D hybrid Ag nanostructures.

We demonstrate strong light-matter coupling at room temperature in the terahertz (THz) spectral region using 3D meta-atoms with extremely sub-wavelength volumes. Using an air-bridge fabrication scheme, we have implemented sub-wavelength 3D THz micro-resonators that rely on suspended loop antennas connected to semiconductor-filled patch cavities. We have experimentally shown that they possess the functionalities of lumped LC resonators: their frequency response can be adjusted by independently tuning the inductance associated the antenna element or the capacitance provided by the metal-semiconductor-metal cavity. Moreover, the radiation coupling and efficiency can be engineered acting on the design of the loop antenna, similarly to conventional RF antennas. Here we take advantage of this rich playground in the context of cavity electrodynamics/intersubband polaritonics. In the strong light−matter coupling regime, a cavity and a two-level system exchange energy coherently at a characteristic rate called the vacuum Rabi frequency ΩR which is dominant with respect to all other loss mechanisms involved. The signature, in the frequency domain, is the appearance of a splitting between the bare cavity and material system resonances: the new states are called upper and a lower polariton branches. So far, most experimental demonstrations of strong light−matter interaction between an intersubband transition and a deeply sub-wavelength mode in the THz or mid-infrared ranges rely on wavelength-scale or larger resonators such as photonic crystals, diffractive gratings, dielectric micro-cavities or patch cavities. Lately, planar metamaterials have been used to enhance the light-matter interaction and strongly reduce the interaction volume by engineering the electric and magnetic resonances of the individual subwavelength constituents. In this contribution we provide evidence of strong coupling between a THz intersubband transition and an extremely sub-wavelength mode (≈λ/10) within our recently developed 3D meta-atoms. A GaAs/AlGaAs parabolic quantum well is used as semiconductor active core to observe the strong coupling regime up to room temperature, as the structure ensures by design a sufficiently large useful electron population irrespective of temperature. In contrast with the previous metamaterial paradigm, the electrical dipoles responsible for the light-matter excitation are now exactly confined in the capacitive region of each meta-atom. Remarkably, we will show that we can modulate the light-matter interaction solely via the external inductor/antenna element while keeping the interaction volume (i.e. the capacitor size) unvaried. Perspectives about the exploitation of this metamaterial peculiar features (reconfigurability, dynamic tuning, …) for polaritonic devices will be discussed.

We report on theoretical analysis and experimental validation of the applicability of the effective medium approximation to deeply subwavelength (period ⩽λ/30) all-dielectric multilayer structures. Following the theoretical prediction of the anomalous breakdown of the effective medium approximation [H. H. Sheinfux et al., Phys. Rev. Lett. 113, 243901 (2014)] we thoroughly elaborate on regimes, when an actual multilayer stack exhibits significantly different properties compared to its homogenized model. Our findings are fully confirmed in the first direct experimental demonstration of the breakdown effect. Multilayer stacks are composed of alternating alumina and titania layers fabricated using atomic layer deposition. For light incident on such multilayers at angles near the total internal reflection, we observe pronounced differences in the reflectance spectra (up to 0.5) for structures with different layers ordering and different but still deeply subwavelength thicknesses. Such big reflectance difference values resulted from the special geometrical configuration with an additional resonator layer underneath the multilayers employed for the enhancement of the effect. Our results are important for the development of new homogenization approaches for metamaterials, high-precision multilayer ellipsometry methods and in a broad range of sensing applications.

Since its first observation in 1947, the Goos-Hänchen effect—an electromagnetic wave phenomenon where a totally reflected beam with finite cross section undergoes a lateral displacement from its position predicted by geometric optics—has been extensively investigated for various types of optical media such as dielectrics, metals and photonic crystals. Given their huge potential for guiding and sensing applications, the search for giant and tunable Goos-Hänchen shifts is still an open question in the field of optics and photonics. Metamaterials allow for unprecedented control over electromagnetic properties and thus provide an interesting platform in this quest for Goos-Hänchen shift enhancement. Over the last few years, the Goos-Hänchen effect has been investigated for specific metamaterial interfaces including graphene-on-dielectric surfaces, negative index materials and epsilon- near-zero materials. In this contribution, we generalize the approach for the investigation of the Goos-Hänchen effect based on the geometric formalism of transformation optics. Although this metamaterial design methodology is generally applied to manipulate the propagation of light through continuous media, we show how it can also be used to describe the reflections arising at the interface between a vacuum region and a transformed region with a metamaterial implementation. Furthermore, we establish an analytical model that relates the magnitude of the Goos-Hänchen shift to the underlying geometry of the transformed medium. This model shows how the dependence of the Goos-Hänchen shift on geometric parameters can be used to dramatically enhance the size of the shift by an appropriate choice of permittivity and permeability tensors. Numerical simulations of a beam with spatial Gaussian profile incident upon metamaterial interfaces verify the model and firmly establish a novel route towards Goos-Hänchen shift engineering using transformation optics.

In this paper, gold asymmetric-split ring resonators (A-SRRs) are used for proteins sensing in the mid-infrared (IR) spectral region. Self-assembled monolayers (SAMs) of octadecanethiol (ODT) in ethanolic solution were deposited on the resonator surfaces to immobilise protein molecules for their detection. Different diameters ASRRs were fabricated on zinc selenide (ZnSe) substrates using electron-beam lithography technique. Their plasmonic responses appear in the mid-IR spectral region and match with the vibrational responses of many organic molecules. After the formation of SAMs layer, one sample was immersed in bovine serum albumin (BSA) solution for proteins adsorption while other sample was immersed in hydroxyl terminated hexa-ethylene glycol (EG6-OH) solution to modify SAMs surfaces to resist immobilisation of proteins. The vibrational responses of these organic molecules, all samples were excited using an incident broadband mid-IR light source and their reflectance spectra were measured at normal incidence using a microscope coupled Fourier Transform Infrared (FTIR) spectrometer. This study highlights the capability of plasmonic structures (A-SRRs) fabricated on transparent and high refractive index ZnSe substrates allows the detection of BSA proteins with enhanced detection in the mid-IR spectral range, demonstrating their potential for a wide range of sensing applications, e.g. in biomedical engineering and food industries.

We report on the first example of a “meta-tip” configuration that integrates a metasurface on the tip of an optical fiber. Our proposed design is based on an inverted-Babinet plasmonic metasurface obtained by patterning (via focused ion beam) a thin gold film deposited on the tip of an optical fiber, so as to realize an array of rectangular aperture nanoantennas with spatially modulated sizes. By properly tuning the resonances of the aperture nanoantennas, abrupt variations can be impressed in the field wavefront and polarization. We fabricated and characterized several proof-of-principle prototypes operating an near-infrared wavelengths, and implementing the beam-steering (with various angles) of the cross-polarized component, as well as the excitation of surface waves. Our results pave the way to the integration of the exceptional field-manipulation capabilities enabled by metasurfaces with the versatility and ubiquity of fiber-optics technological platforms.

Metamaterials make use of subwavelength building blocks to enhance our control on the propagation of light. To determine the required material properties for a given functionality, i.e., a set of desired light flows inside a metamaterial device, metamaterial designs often rely on a geometrical design tool known as transformation optics. In recent years, applications in integrated photonics motivated several research groups to develop two-dimensional versions of transformation optics capable of routing surface waves along graphene-dielectric and metal-dielectric interfaces. Although guided electromagnetic waves are highly relevant to applications in integrated optics, no consistent transformation-optical framework has so far been developed for slab waveguides. Indeed, the conventional application of transformation optics to dielectric slab waveguides leads to bulky three-dimensional devices with metamaterial implementations both inside and outside of the waveguide’s core. In this contribution, we develop a transformationoptical framework that still results in thin metamaterial waveguide devices consisting of a nonmagnetic metamaterial core of varying thickness [Phys. Rev. B 93.8, 085429 (2016)]. We numerically demonstrate the effectiveness and versatility of our equivalence relations with three crucial functionalities: a beam bender, a beam splitter and a conformal lens. Our devices perform well on a qualitative (comparison of fields) and quantitative (comparison of transmitted power) level compared to their bulky counterparts. As a result, the geometrical toolbox of transformation optics may lead to a plethora of integrated metamaterial devices to route guided waves along optical chips.

The main research efforts in the metamaterials science are focused on achieving negative permittivity and permeability, as well as on effects such as superresolution, subwavelength guiding, enhancement of field localization, nanoantennas etc. At the same time, there is a wide range of interesting problems, beyond the issues of negative refraction. One of them is the problem associated with the excitation of toroidal response in metamaterials and the unusual phenomena associated with such response. In this paper, we demonstrate that, owing to the unique topology of the toroidal dipolar mode, its electric/magnetic field can be spatially confined within sub-wavelength, externally accessible regions of the metamolecules, which makes the toroidal metamaterials a viable platform for sensing, enhancement of light absorption and optical nonlinearities, and, especially, ingredient for qubits and quantum metamaterials. The metamolecules employed in the present study are planar conductive structures consisting of two symmetric split loops. The excited circular currents along the loops lead to a circulating magnetic moment and, as a result, to a toroidal moment. We note that the electric field is strongly localized in the splits of the loops and allows achieving the extremely high Q-factor of such types of resonators.

Optical fibres provide the best solutions for transmitting high speed, large amounts of data with good power efficiency. However such transmission would also need amplification for transmission over large distances. Erbium Doped Fibre Amplifiers(EDFAs) are currently being used for optical amplification. But good amplification is achievable with multiple stages and considerable length of EDFA fibres. In this paper we compare the use of Silver Split Ring Resonators(SRRs) , Gold Nano Rods and Silver Fishnet structures which give metamaterial properties to be used in optical fibres to give better amplification than EDFA based fibres. Metamaterials belong to a new class of materials with negative values for permittivity and permeability. Such materials would exhibit negative refractive index leading to these materials being called as left handed media.If such left handed media have an internal structure made of dimensions much smaller than the wavelength but sufficiently thick to exhibit bulk properties, using other optical domains such as plasmonics, it is possible to control light interactions and propagation. Artificial structures smaller than the wavelength of light can be used to enhance electric and magnetic fields. Surface plasmons can be excited on a metal and this can enhance the electric field at the surface. Our paper proposes the use of this phenomenon of achieving gain at optical frequencies by using SRRs, Fishnet structures , Nano Rods. We compare the performance of these structures and observe that they provide gain which is much more than that provided by EDFAs.

Hyperbolic metamaterials are examined for many applications thanks to the large density of states and extreme confinement of light they provide. For classical hyperbolic metal/dielectric multilayer structures, it was demon- strated that the properties originate from a specific coupling of the surface plasmon polaritons between the metal/dielectric interfaces. We show a similar analysis for 2D hyperbolic arrays of square (or rectangular) silver nanorods in a TiO2 host. In this case the properties derive from a specific coupling of the plasmons carried by the corners of the nanorods. The dispersion can be seen as the coupling of single rods for a through-metal connection of the corners, as the coupling of structures made of four semi-infinite metallic blocks separated by dielectric for a through-dielectric connection, or as the coupling of two semi-infinite rods for a through-metal and through-dielectric situation. For arrays of small square nanorods the elementary structure that explains the dispersion of the array is the single rod, and for arrays of large square nanorods it is four metallic corners. The medium size square nanorod case is more complicated, because the elementary structure can be one of the three basic designs, depending on the frequency and symmetry of the modes. Finally, we show that for arrays of rectangular nanorods the dispersion is explained by coupling of the two coupled rod structure. This work opens the way for a better understanding of a wide class of metamaterials via their elementary excitations.

An asymmetrical H-shaped resonator (ASH) has been designed using gold on a fused silica substrate. The aim is to obtain a high - quality factor at the reflectance resonance peaks in the mid - infrared wavelength of 2 μm to 8 μm. The structures were modelled using the Finite Difference Time Domain (FDTD) Lumerical Solution simulation software by adjusting the parameter of periodic boundary condition on the X and Y-axis and perfectly matched layer (PML) on the Z- axis. The asymmetric structures give double resonance peaks that depend on the arm-length of the structure. The periodicity along the X and Y-axis was varied to tune the width of the resonant peaks in order to obtain the maximum Qfactor. Experimental results broadly confirm the simulations.