This PDF file contains the front matter associated with SPIE Proceedings Volume 10927, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Almost two decades have passed since the realization of complete 3D photonic crystals at optical wavelengths. During these years, the manipulation of photons by photonic crystals has progressed tremendously. For example, the concept of confining photons to a very small modal volume has been established and nanocavity Q-factors have exceeded ten million, enabling platforms for strong light-matter interaction and quantum information processing. Photonic crystals allow even a broad-area manipulation of photons, by which semiconductor lasers with a very bright, narrow-divergence beam and various functionalities including 2D beam steering have been realized. Such lasers are promising for applications in light-detection and ranging (LiDAR) and direct material processing, which are important for the forthcoming Society 5.0. Photonic crystals also enable thermal emission control, by which the issues of conventional thermal emission devices such as their extremely broad emission spectra and slow response speed have been fixed, and a renovation of thermal emission devices has been achieved. In this plenary talk, we will review such progress of photonic crystals including their social applications.

The pursuit of resonators with ultra-high coherence has led to intense study of “dissipation dilution”, where the stiffness of a material is effectively increased without added loss. Interestingly, the paradigm has to date relied on weak strain produced during material synthesis—the use of geometric strain engineering techniques, capable of producing local stresses near the material yield strength, remains largely unexplored. We show that geometric strain combined with soft-clamping can produce exceptionally high Q mechanical oscillators. Loss due to curvature at the clamping points has been a major limiting factor in engineering of high Q mechanical oscillators. Soft-clamped resonators recently developed by Tsaturyan et al. bypass this limitation by localizing the mode away from the clamping points. We adapt their technique to 1D nanobeams. By corrugating the width of the nanobeam, we create a bandgap in the mechanical mode spectrum. A defect in the center of the beam allows a localized mode to exist in the bandgap. Then, by tapering the overall width of the nanobeam, we increase the stress in the center of the beam to near the yield strength. This combined strategy produces picogram-mass flexural modes with room-temperature Q factors as high as 800 million and Qf products of 10^15 Hz—both unprecedented for a mechanical oscillator of any size. Additionally, strain-engineering allows us to tune the frequency of the ultra-high Q mode from 1-6 MHz while retaining Qf products above 10^14 Hz. The extremely low dissipation and low effective mass of these devices make them promising for performing cavity quantum optomechanics.

Supersymmetric transformations aim to relate boson and fermions, two different species of particles, and their interactions. In quantum mechanics, the mathematical framework of SUSY can be used to design isospectral potentials. By virtue of the isomorphism between Schrodinger and wave equations, one can use such transformations for designing novel optical systems. In this talk, we review the recent developments in the general area of supersymmetric optics and photonics. We will also discuss the possibility of generating high brightness coherent light in supersymmetric laser arrays.

Strong Coulomb interactions in 2D materials results in a wide variety of correlated many body states. In this talk we present optical spectroscopy results and theoretical results on strongly correlated electron states in Landau levels in bi-layer graphene and on trions and trion-polaritons in transition metal dichalcogenides. Our results show a rich variety of features exhibited by these correlated states in 2D materials. In the case of Landau levels, we observe valley-dependent optical transitions that violate the conventional optical selection rules. At low magnetic fields, the oscillator strengths of forbidden transitions are as large as those of the allowed transitions. Moreover, we can tune the relative oscillator strength by tuning the bandgap of bilayer graphene. Our findings provide new insights into the interplay between magnetic field, band structure and many-body interactions in tunable semiconductor systems, and the experimental technique paves the way to studying symmetry-broken states and low energy magneto-optical properties of novel materials. In the case of trions and trion-polaritons, despite the nomenclature, our results show that the actual quantum states are many body states involving at least four or five particles. A trion state in n-doped 2D materials consists of two electrons, one valence band hole, and one conduction band hole. The conduction band hole is weakly bound to the other three particles. However, inside an optical microcavity the hole becomes strongly bound to the other three particles because of strong light-matter interaction. Our results shed new light on the nature of trions and trion-polaritons in 2D materials. We will discuss the connections of our models with the recently proposed exciton-polaron picture of trions.

Alloying of transition-metal dichalcogenides (TMDs) has mostly been explored for rudimentary applications such as bandgap tuning and defect healing. To achieve more complex functionalities, we developed a modified approach based on specially-controlled alloying of atomically-thin TMDs [1, 2]. In this talk, we will discuss application of this modified technique for the synthesis of TMD lateral heterostructures with arbitrary shapes, arbitrary dimensions, and arbitrary band alignments. In addition, via accurate optical and electrical characterizations, we will discuss the prospect of these lateral heterostructures for applications in opto-electronic devices at nanoscale. [1] H. Taghinejad et. al., “Strain relaxation via formation of cracks in compositionally-modulated two-dimensional semiconductor alloys,” Nature 2D Materials and Applications 3, 10 (2018). [2] H. Taghinejad et. al., “Defect-Mediated Alloying of Monolayer Transition-Metal Dichalcogenides,” Submitted (2018).

One of the most fundamental mysteries is the homochirality of living organisms on the Earth. Scientists have spent endless efforts in understanding the origin of the enantiomeric excess, in which a magneto-chiral effect is believed to play a role. However, this magneto-chiral effect observed so far is very weak in diamagnetic bulk crystals under a strong magnetic field, synthetic chiral molecules with magnetic components in solutions, or thin-film chiral magnets and metamaterials. Recently, atomically flat two-dimensional materials have emerged with intriguing properties such as optical anisotropy, two-dimensional ferromagnetism, and valley pseudospins. Here, we report the observation of giant magneto-chiral dichroism in atomically thin van der Waals crystals. We found such giant magneto-chiral dichroism originated from two unique physical processes. The parity-inversion symmetry breaking induces a large chirality, and time-reversal symmetry breaking results in strong magnetic moments. Such an approach offers rich physics with the interplay of the magnetism, chirality, and valley pseudospins in a unified manner. The observed giant magneto-chiral effect may further our understanding of the enantiomeric excess that is important for photochemical reactions, asymmetric synthesizes, and drug delivery.

Polaritonic materials that support epsilon-near-zero (ENZ) modes offer the opportunity to design light-matter interactions at the nanoscale through phenomena like resonant perfect absorption and extreme sub-wavelength light concentration. To date, the utility of ENZ modes is limited in propagating polaritonic systems by a relatively flat spectral dispersion, which gives ENZ modes small group velocities and therefore short propagation lengths. Here we overcome this constraint by coupling ENZ modes to surface plasmon polariton (SPP) modes in doped cadmium oxide ENZ-on-SPP bilayers. What results is a strongly coupled hybrid mode, characterized by strong anti-crossing and a large spectral splitting on the order of 1/3 of the mode frequency. The resonant frequencies, dispersion, and coupling of these polaritonic-hybrid-epsilon-near-zero (PH-ENZ) modes are controlled by tailoring the modal oscillator strength and the ENZ-SPP spectral overlap. As cadmium oxide supports polaritons over a wide range of carrier concentrations without excessive losses, strong coupling effects can potentially be utilized for actively tunable strong coupling at the nanoscale. PH-ENZ modes ultimately leverage the most desirable characteristics of both ENZ and SPP modes through simultaneous strong interior field confinement and mode propagation. As a result, this system could see applications in sub-diffraction modulators using carrier injection schemes, or narrow linewidth thermal emitters working in the 3-5µm spectral window.

We have recently developed a computational approach to inverse-design photonics based on desired performance, with fabrication constraints and structure robustness incorporated in design process. Our approach performs physics guided search through the full parameter space until an optimal solution is reached. Resulting device designs are non-intuitive, but are fabricable using standard techniques, resistant to temperature variations of hundreds of degrees, typical fabrication errors, and they outperform state of the art counterparts by orders of magnitide in footprint, efficiency and stability. This is completely different from conventional approach to design photonics, which is almost always performed by brute-force or intuition-guided tuning of a few parameters of known structures, until satisfactory performance is achieved, and which almost always leads to sub-optimal designs. Apart from integrated photonics, our approach is also applicable to any other optical and quantum optical devices and systems. We illustrate this with a number of demonstrated photonic devices and circuits in silicon and in diamond.

(Invited talk, with invitation from the Conference Chair)

We leverage a dimensionality reduction approach to develop a novel inverse design platform applicable to a wide class of optical nanoantennas. The proposed dimensionality reduction technique uses a high level of correlation (in frequency and space domains) in the propagation of electromagnetic waves to considerably reduce the dimensionality of the response space of the problem. In addition, the correlation that often exists among the effects of design parameters on the response of the structure (i.e., selecting more design parameters than needed for uniquely identifying a structure for a given input-output relation) is used to reduce the dimensionality of the design space. In addition to the considerable mitigation of computation time and complexity, the two key features of dimensionality reduction, i.e., : 1) the ability to train a NN and later use it for a large class of problems, and 2) the possibility of analytically relating the reduced design space to the original design space to obtain valuable intuitive information about the roles of each design parameter in the overall performance of the nanostructure, highlight the superiority of the proposed approach. This is in contrast to existing analysis and optimization techniques, which require an intensive repetition of the simulations for each design problem without providing an intuitive understanding of the roles of design parameters. As a proof of concept, we apply this approach to a nanoscale structural color recently emerged as a promising candidate to organic colors in the printing technology. To circumvent the high absorption loss and efficiency of plasmonic color generators, we harness the fundamental dipolar Mie resonances of an array of asymmetric titanium dioxide elliptical nanopillars. We will further experimentally demonstrate such an optimized polarization-sensitive all-dielectric significantly enhance the resolution, saturation, and hue of color palettes. Such a novel inverse design approach highlights the performance of machine learning based approaches in developing highly-efficient metastructures.

Optical modes in subwavelength-scale nanostructures are hard to reach from conventional far-field optics because they mainly exist in the form of near-field. Here, we propose an experimental method that can map out the near-field optical modes of any arbitrary nanostructures. We set up a far- to near-field transmission matrix system by using near-field scanning optical microscope and wavefront shaping of incident wave. By applying the singular value decomposition of the measured transmission matrix, we could identify symmetric and antisymmetric modes of a pair of nano-antenna whose width and separation are well below the diffraction limit. Our method will help designing complex functional nanostructures by providing the experimental means of understanding their optical response.

Propagation of electromagnetic (EM) wave through a meta-material having anisotropic permittivity and permeability tensors is simulated through Finite Difference Time Domain (FDTD) simulations using a technique of transformation optics. Details of the algorithm used in the simulation are given here. Using the simulation code developed, a two-dimensional dual-purpose polarization-sensitive meta-material is designed and demonstrated. Such a material can perform two independent tasks simultaneously for Transverse Electric (TE) and Transverse Magnetic (TM) polarization. All-dielectric design for TM polarization is also proposed and demonstrated to reduce the constrains on physical realization of such materials.

We propose and theoretically analyze a scheme that demonstrates generation of enhanced optical harmonics by employing time-variant resonators. We show that the amplitude and phase format of the excitation, as well as the time evolution of the resonator, can be optimized to yield the strongest nonlinear response. We find the conditions for an efficient synthesis of electromagnetic signals that surpass the cavity bandwidth, and discuss a potential experimental realization of this concept.

We review the physics of bound states in the continuum and their applications in meta-optics and metasurfaces. First, we discuss strong coupling between modes of a single subwavelength high-index dielectric resonator and analyse the mode transformation and Fano resonances when resonator’s aspect ratio varies. We demonstrate that strong mode coupling results in resonances with high quality factors, which are related to the physics of bound states in the continuum when the radiative losses are almost suppressed due to the Friedrich–Wintgen scenario of destructive interference. Our theoretical findings are confirmed by microwave and optical experiments for the scattering of high-index subwavelength resonators with a tunable aspect ratio. The proposed mechanism of the strong mode coupling in single subwavelength high-index resonators accompanied by resonances with high quality factor helps to extend substantially functionalities of all-dielectric nanophotonics that opens new horizons for active and passive nanoscale metadevices. Next, we discuss how bound states in the continuum can appear in metasurfaces. We reveal that metasurfaces created by seemingly different lattices of (dielectric or metallic) meta-atoms with broken in-plane symmetry can support sharp high-Q resonances that originate from the physics of bound states in the continuum. We demonstrate a direct link between the bound states in the continuum and the Fano resonances, and discuss a general theory of such metasurfaces, suggesting the way for smart engineering of resonances for many applications in nanophotonics and meta-optics.

The effective multipole decomposition approach is applied to study the optical features of the silicon metasurface in the near-infrared. The spectral regions of perfect transmission and reflection have been analyzed using the Cartesian multipole decomposition. It is shown that transmission peaks appear due to the mutual interaction of multipole moments up to the third order, while reflection peaks are due to the dominant contribution of one of the multipole moments. The results of this work can be broadly applied to design novel metasurfaces, sensors, and optical filters.

We discuss the possibility of controlling energy storage, wireless power transfer, reflection and transmission using coherent excitation of complex eigenstates in metastructures, opening new venues in the quest to control and manipulate light in integrated structures. In particular, we show that it is possible to engage complex zeros of a lossless cavity to mimic absorption and induce storage and release of energy, and efficient power transfer. We also connect these concepts with embedded eigenstates and few-photon optoelectronic devices. Our results open new opportunities for optoelectronic memories and switches operating at very low energy.

Engineered mid-infrared absorbers and thermal emitters have recently enabled a variety of applications including passive cooling and acceleration of water condensation. We demonstrate a large-area absorber in the 8-10 μm range based on a lossy medium with an ultra-low refractive index. Our low-index material is a large-area inverse opal film (air holes, silica matrix), which is crack-free on the centimeter scale. Due to the large fraction of air in these structures (more than 70%), their effective refractive index is close to that of air, facilitating an impedance match for a broad range of incidence angles, and requiring no top-down patterning.

Nanostructured GRIN components are optical elements which can have arbitrary refractive index profile while retaining flat-parallel entry and exit facets. They are composed of more than 9000 individually placed glass subwavelength rods made of two types of glass with different refractive indices. They are developed using a standard stack-and-draw method used for fibre drawing. The refractive index profile of the nanostructured GRIN element can be described by the effective refractive index theory when the diameter of the individual rods are sufficiently smaller than the wavelength. In this paper we show that use of glasses designed for high diffusion and high temperatures during drawing process allows to develop parabolic nanostructured GRIN microlenses with rod diameter larger than wavelength. In particular, we have developed a GRIN microlens with diameter of 115 μm composed of 115 rods on diagonal. Our GRIN microlens has a length of 200 μm and a working distance equal to 1.05 mm, with focal spot of 8.5 μm measured for the 658 nm wavelength. We experimentally verified its imaging properties. Image resolution higher than 3.25 μm was measured.

This study is focused on the properties of the diamond lattice before and after implantation. The diamond lattices with nitrogen-vacancy centres have very exciting properties and they can be used in a plethora of applications from quantum sensing to biomarkers. Characteristic transmission, scattering and photoluminescence of diamond lattice with nitrogen-vacancy centres (NV-) were studied through different techniques at different temperatures. The luminescence of the synthesised diamonds was studied at a 532nm excitation wavelength and recorded in the range of 500-1100nm. Since its intensity decreases with decreasing the number of nitrogen-vacancy centres. Also, we analysed the luminescence depend on the functional groups attached to the diamond surface. Raman spectroscopy studies provide interesting results about the phonon confinement effect, structure composition and homogeneity of the material and information about the functional groups attached above the diamond surface. Raman spectra depend on the structure, purity, sp3/sp2 ratio, crystal size and surface chemistry. With increasing sp3 carbon content the intensity of the diamond peak increases, while the D-band in the Raman spectra weakens. Also, we analysed the shifts in the energy and linewidth of the diamond peak in the Raman spectra. The recent development of novel super-resolution imaging techniques coincides with the efforts to synthesize optically bright and stable biomarkers. In the future, we can use the differently doped nanodiamond fluorophores as biomarkers for sensing and bioimaging.

Third-order nonlinearity is the dominant nonlinear response in centrosymmetric materials such as silicon, silicon dioxide and silicon nitride. To enhance light-matter interactions, high Q microresonators can be employed. In this talk, we will discuss the use of third-order nonlinearity in high Q silicon nitride microresonators for several important applications. The first example is focused on the design and demonstration of octave-spanning frequency combs. Optimized dispersion design not only allows us to obtain an octave span of spectrum (1um to 2um), but also enables two harmonically linked dispersive wave emission which is particularly useful for frequency self-referencing. In the second example, we shift our focus from the classical domain to the quantum domain, where quantum states of light and quantum frequency conversion are both achieved by the same third-order nonlinearity of SiN. Specifically, one photon from a quantum-correlated microresonator photon pair source is frequency shifted by four-wave mixing Bragg scattering in a second microresonator, without degrading the level of quantum correlation. With the developed technologies, we demonstrate tunable quantum interference of the initially non-degenerate photons comprising the pair, and observe the quantum beat of single photons as the photon frequencies are tuned across each other. Our work showcases the versatility of the nanophononics for both classical and quantum information processing.

3C-SiC is a large bandgap material with a wide range of applications both in electronics and photonics. Here we demonstrate a low-loss 3C-SiC-on-Oxide (SiCOI) platform over an octave frequency range from visible to near-infrared. A 3C-SiC film is transferred onto an oxide-on-silicon substrate through wafer bonding to form a reliable SiCOI platform suitable for device integration, and the defect-rich transition layer in SiC is removed by chemical mechanical polishing (CMP). With low density of defects and a small root-mean-square (RMS) surface roughness (Rq) of about 1.4 Å in our SiC thin film, we are able to demonstrate record-high intrinsic quality factors of ~250,000 at 1550 nm wavelength and ~85,000 at 770 nm wavelength. Our low-loss SiCOI platform is promising for wideband nonlinear optical applications including second harmonic generation (SHG), four wave mixing (FWM), and Kerr frequency comb.

Topological insulator is a material in which helical conducting states exist on the surface of the bulk insulator. These states can transport electrons or photons at the boundary without any back scattering, even in presence of obstacles enabling to make topological cavities with arbitrary geometries that light can propagate in one direction. Here, we present the demonstration of the first experimental non-reciprocal topological laser that operates at telecommunication wavelengths. The unidirectional stimulated emission from edge states is coupled to a selected waveguide output port with an isolation ratio of 11 dB. Topological cavities are made of hybrid photonic crystals (i.e., two different photonic crystals) with distinct topological phase invariants, which are bonded on a magnetic material of yttrium iron garnet to break the time-reversal symmetry. Our experimental demonstration, paves the way to develop complex nonreciprocal topological devices of arbitrary geometries for integrated and robust generation and transport of light in classical and quantum regimes.

Graphene has extraordinary electro-optic properties and is therefore a promising candidate for monolithic photonic devices such as photodetectors. However, the integration of this atom-thin layer material with bulky photonic components usually results in a weak light-graphene interaction leading to large device lengths limiting electro-optic performance. In contrast, here we demonstrate a plasmonic slot graphene photodetector on silicon-on-insulator platform with high-responsivity given the 5 µm-short device length. We observe that the maximum photocurrent, and hence the highest responsivity, scales inversely with the slot width. Using a dual-lithography step, we realize 15 nm narrow slots that show a 15-times higher responsivity per unit device-length compared to photonic graphene photodetectors. Furthermore, we reveal that the back-gated electrostatics is overshadowed by channel-doping contributions induced by the contacts of this ultra-short channel graphene photodetector. This leads to quasi charge neutrality, which explains both the previously-unseen offset between the maximum photovoltaic-based photocurrent relative to graphene’s Dirac point and the observed non-ambipolar transport. Such micrometer compact and absorption-efficient photodetectors allow for short-carrier pathways in next-generation photonic components, while being an ideal testbed to study short-channel carrier physics in graphene optoelectronics.

The light confinement properties of high quality (Q) factor microtoroid whispering-gallery mode (WGM) optical resonators prevent efficient coupling between far-field radiation and the WGM. Instead, light is most commonly evanescently coupled to the WGM using optical fibers that have been tapered to micron-scale thickness. These tapers, however, break easily and are sensitive to environmental vibrations and fluid flow fluctuations. This limits their effectiveness in mass-produced and/or field-portable biochemical sensing applications. Here we present a gold nanorod grating as an experimentally-feasible alternative for robust coupling of free-space light to a microtoroid resonator, and we simulate its performance with a novel finite-element 3D beam envelope method. 3D simulations of the full system are not tractable due to its large size. Previously, simulations of nanostructures on microtoroids have been performed on a thin wedge of the 3D system with perfect electrical conductor (mirror) boundary conditions. While these simulations provided some insight, they do not accurately model typical travelling-wave WGM experiments because they can only simulate standing waves. The standing wave nodes and antinodes significantly alter interactions between the WGM and the nanostructure. In our new method, we use a small wedge domain with custom boundary conditions that accurately simulate the travelling wave and nanophotonic interactions. Using this approach, we have designed and simulated a grating for far-field WGM coupling. With the grating, it is possible to maintain a high Q-factor of 3×10^6. We anticipate that our proposed modeling approach can solve a variety of other nanoparticle-microtoroid coupled systems in the future.

Atom coherence in the cooperative interaction between the atoms and a single photon creates ultrafast spontaneous emission and ultrastrong intensity peaks, namely single-photon superradiance, which has attracted considerable research interest in the recent years. As the investigation for such a single-photon superradiance usually involves only quantum emitters, in this paper we present the cooperative atom-photon interaction in a system including whispering gallery mode resonators, which are one of the most essential components in nanophotonic devices. Here we both analytically and computationally show that the separated atoms on a resonator can obtain cooperative interaction, manifesting superradiant coupling strength, which results in the ultrafast spontaneous emission and ultrastrong intensity peaks. The conditions of such single-photon superradiance are called whispering gallery mode superradiance conditions. Furthermore, the atoms are proved to have cooperative interaction on a cascade of resonators by a renormalization approach.

We discuss the use of photonic crystal slab to accomplish a number of imaging processing tasks, including edge detection, image smoothing, white noise suppression and, suppression or extraction of periodic features. All these tasks involve filtering in the wavevector domain. Image filtering can be implemented electronically. However, in big-data applications requiring real-time and high-throughput image filtering, conventional digital computations become challenging. Nanophotonics-based optical analog computing may overcome this challenge by offering high-throughput low-energy-consumption filtering using compact devices. Here, we show that several types of isotropic two-dimensional image filters can be implemented with a single photonic crystal slab device. Such a device is carefully designed so that the guided resonance near the Γ point exhibits an isotropic band structure. Depending on the light frequency and the choice of transmission or reflection mode, this compact device realizes isotropic high-pass (Laplacian), low-pass, band-reject and band-pass filtering in the wavevector domain. We numerically demonstrate various important image processing tasks enabled by these filters as mentioned above. Our work points to new opportunities in optical analog computing as provided by nanophotonic structures.

A multilayer hyperbolic metamaterial (HMM), fabricated from alternating thin films of metal and dielectric, displays a hyperbolic, anisotropic dispersion relation due to the coupling of excited surface plasmons. The design, fabrication, and characterization of an HMM based on TiO₂ / Cu alternating layers with a metal-to-dielectric fill factor of 67% is presented. The layers were deposited onto glass and silicon substrates using physical vapor deposition (PVD) with an electron beam evaporator and then characterized using ellipsometry. According to the effective medium theory, this design shows an epsilon-near-zero (ENZ) line near the Helium-Neon wavelength of 633 nm. Our experimental measurements are in good agreement with the theoretical predictions.

We characterize engineered nanostructures with sizes smaller than half a wavelength using spectrally resolved interferometry. We analyze the response of the meta-atom of interest, which has a raspberry-like geometry. To identify the origin of the response, the study of individual building blocks, namely individual gold and silica nano-spheres, are first examined in this paper. Due to the fact that the size of the object is smaller than the resolution limit, phase information plays an important role in our analysis.

We report on the fabrication and optical characterization of hyperbolic nanoparticles on a transparent substrate. These nanoparticles enable a separation of ohmic and radiative channels in the visible and near-infrared frequency ranges. The presented architecture opens the pathway towards novel routes to exploit the light to energy conversion channels beyond what is offered by current plasmon-based nanostructures, possibly enabling applications spanning from thermal emission manipulation, theragnostic nano-devices, optical trapping and nano-manipulation, non-linear optical properties, plasmonenhanced molecular spectroscopy, photovoltaics and solar-water treatments, as well as heat-assisted ultra-dense and ultrafast magnetic recording.

Optical quantum technology needs efficient sources for non-classical light. Solid-state emitters provide excellent mode purity, high brightness, and often also stable operation up to room temperature. At the same time the spin of individual impurities can be entangled with emitted photons. Nano-photonic structures can dramatically enhance the photon emission efficiency and thus the yield of quantum information processing tasks involving photons. One example is a node of a quantum repeater network. In this presentation we address the issue of enhanced photon collection from optically active defects in the solid-state such as diamond [1] or two-dimensional material [2]. We briefly introduce the emitters and then describe recent experiments where we couple them to dielectric/plasmonic antennas [3] and to SiO2/Si light collecting structures [4]. References [1] “Fiber-Coupled Diamond Micro-Waveguides toward an Efficient Quantum Interface for Spin Defect Centers”, M. Fujiwara, O. Neitzke, T. Schröder, A. W. Schell, J. Wolters, J. Zheng, S. Mouradian, M. Almoktar, S. Takeuchi, D. Englund, and O. Benson, ACS Omega 2, 7194-7202 (2017) [2] “Photodynamics of quantum emitters in hexagonal boron nitride revealed by low-temperature spectroscopy“, B. Sontheimer, M. Braun, N. Nikolay, N. Sadzak, I. Aharonovich, and Oliver Benson, Phys. Rev B 96, 121202(R) (2017). [3] “Accurate placement of single nano particles on opaque conductive structures“, N. Nikolay, N. Sadzak, A. Dohms, B. Lubotzky, H. Abudayyeh, R. Rapaport, and O. Benson, Appl. Phys. Lett, accepted (2018); arXiv:1807.10605 [4] “Fine-tuning of whispering gallery modes in on-chip silica microdisk resonators within a full spectral range“, R. Henze, C. Pyrlik, A. Thies, J.M. Ward, A. Wicht, O. Benson, Appl. Phys. Lett. 102, 041104 (2013).

In this talk I give an overview of our recent work on quantum nano-photonic devices based on rare-earth ions. The rare-earth ions exhibit excellent optical and spin coherence properties when embedded in nano-photonic devices. This enables on-chip optical quantum memories, single rare-earth-ion optically addressable quantum bits, and devices for quantum transduction. I will focus on our recent results based on ytterbium 171 in yttrium orthovanadate.

CMOS-compatible light emitters are intensely investigated for integrated active silicon photonic circuits. One of the approaches to achieve on-chip light emitters is the epitaxial growth of Ge(Si) QDs on silicon. Their broad emission in 1.3-1.5 um range is attractive for the telecomm applications. We investigate optical properties of Ge(Si) QD multilayers, that are grown in a thin Si slab on a SOI wafer, by steady-state and time-resolved micro-photoluminescence. We identify Auger recombination as the governing mechanism of carrier dynamics in such heterostructures. Then we demonstrate the possibility of light manipulation at the nanoscale by resonant nanostructures investigating Si nanodisks with embedded Ge(Si) QDs. We show that the Mie resonances of the disks govern the enhancement of the photoluminescent signal from the embedded QDs due to a good spatial overlap of the emitter position with the electric field of Mie modes. Furthermore, we engineer collective Mie-resonances in a nanodisk trimer resulting in an increased Q-factor and an up to 10-fold enhancement of the luminescent signal due to the excitation of anti-symmetric magnetic and electric dipole modes. Using time-resolved measurements we show that the minima of the radiative lifetime coincide with the positions of the Mie resonances for a large variation of disk sizes confirming the impact of the Purcell effect on QD emission rate. Purcell factors at the different Mie-resonances are determined.

The most common approach in standard nanoplasmonics for the analysis of the resonant behavior of light interaction with these nanostructures has been the application of the local-response approximation (LRA), using – depending on the structure complexity and relation between a characteristic dimension and the interacting wavelength – either (quasi)analytic or numerical approaches. Recently, however, as the characteristic dimensions of such structures have scaled down, it has turned out that more complex models based on the nonlocal response (NOR), or even quantum interaction are required for explaining novel effects, e.g. blue spectral shifts, etc. This fact has lately started a rapid increase of interest in developing appropriate nonlocal models. In particular, in our studies, we have concentrated on understanding the interaction and developing a simple model capable of predicting the longitudinal nonlocal response based on the linearized hydrodynamic model, generalizing the standard Abajo’s nonlocal model. Our model is applicable to simple structures, such as a spherical nanoparticle. Within our model, we have also shown and compared several alternatives within the approach, with respect to inclusion of the current “damping”. As the most promising approach, we have found the approach incorporating both radiative and viscosive damping. Here, we have considered the Landau damping, too. We have demonstrated the applicability of our extended model on comparing the extinction cross section predictions of both gold and silver spherical nanoparticles. Using this model, we have systematically studied the relevant components of the electric fields and electric current densities, with respect to nanoparticles immersed in dielectric surrounding media (such as air or water). In parallel, as an alternative (and more general) approach, based on our previous rich experience with Fourier modal methods, we have considered and developed the extension of the rigorous coupled wave analysis technique capable of treating nonlocal response numerically, for more general structures. Also, moving to even smaller characteristic dimensions of studied nanostructures, we have also adopted within our numerical techniques the Quantum corrected model, to estimate the corrections on spectral cross-section dependences, due to quantum electron tunneling effects.

Ceria nanoparticles have been proved to be one of the most promising optical conversion host structures, due to its low-phonon nature and non-stoichiometric structure. In up-conversion, erbium has been extensively used as the main optical center for converting low-photon energy into higher ones. This paper studies the effect of introducing plasmonic nanostructure, such as gold, for enhancing the optical upconversion quantum yield efficiency of erbium-doped-ceria nanoparticles. The numerical results show that the efficiency experienced a significant enhancement as a result of existence of metal nanostructures. In addition, the temperature influence upon the nanocomposite is studied in detail. The numerical calculations show that the temperature change has a remarkable influence on the luminescence parameters and quantum yield efficiency of the up-conversion structure.

Nonlinear plasmonics is a growing field since the power threshold for observable nonlinear light emission of new frequencies can be lowered greatly due to dramatic electromagnetic field confinement. Along another research line, 2D electron gases (2DEGs) formed at interfaces of oxides have been drawing broader attention globally because the metallic constituents can be eliminated, and hence the inherent huge loss associated with uses of metals in plasmonic applications can be circumvented. Once the nonlinear materials are proximal to 2DEGs and surface plasmon polaritons (SPPs) are excited, the electromagnetic field can be strengthened several orders in magnitude. Consequently, the nonlinear processes can take place at a quite low incident light power. Considering much greater dispersion of SPPs, the second order nonlinear processes can be easily realized in terms of meeting phase matching conditions. In this paper, nonuniform 2DEG formed at the interface of a Z-cut Fe doped LiNbO₃ (LN) slab and an indium-tin-oxide (ITO) thin film was analyzed with semi-classical Thomas Fermi screening model, and dispersion of index of refraction was given accordingly. A laser beam at 532 nm and a white light source illuminated the slab from the opposite directions collinearly and a remarkable light emission redistribution was observed with a continuous spectrum of short visible light peaked around 437 nm. Several confirming experimental results with ITO coated Y-cut slabs are presented and phase grating mediated SPP excitation is proposed to explain the related findings, suggesting that second order nonlinear processes strengthened by SPPs are behind the light emission redistribution.

It is two decades since the first reports that the insulator-to-metal transition (IMT) in vanadium dioxide (VO2) occurred on an ultrafast time scale, followed by growing interest in the potential use of this strongly correlated oxide in a variety of switching schemes. At first glance, VO2 would seem to be ideally suited to a variety of applications in electro-optics and all optical switching: The IMT occurs on a sub-picosecond time scale; it is fully reversible and has a large dielectric contrast at wavelengths in the near- to mid-infrared; and the material itself is fully compatible with many optical and electronic materials of interest. However, there are also well-known difficulties, chief among them the fact that the IMT, if fully completed, is accompanied by a structural phase transition (SPT) that requires nanoseconds to return from the rutile, metallic state to the monoclinic insulating ground state – thus essentially limiting switching speeds to time scales similar to those in amorphous-to-crystalline transitions in chalcogenide glasses. Here we discuss the ways in which the very considerable advantages of VO2 as a modulating or threshold switch can be amplified by deploying it appropriately in silicon photonic modulators, switchable metasurfaces, plasmonic heterostructures, and two-dimensional materials that can support phonon polariton optics. We focus particularly on ways of tailoring the physical properties of the VO2 component of a system to meet the requirements of operating in particular wavelength regions, meeting specific threshold requirements and choosing electrical or optical initiation of the IMT.

We will also discuss our efforts to explore the optoelectronic properties of MoxW1-xTe2, which are type-II Weyl semimetals, i.e., gapless topological states of matter with broken inversion and/or time reversal symmetry, which exhibit unconventional responses to externally applied fields. We have observed spatially dispersive circular photogalvanic effect (s-CPGE) over a wide spectral range from mid-IR to visible region in these materials. This effect shows exclusively in the Weyl phase and vanishes upon temperature induced topological phase change. Since the photon energy in our experiments leads to interband transitions between different electronic bands, we use the density matrix formalism to describe the photocurrent response under chiral optical excitation and obtain microscopic insights into the observed phenomena. We will discuss how spatially inhomogeneous optical excitation and unique symmetry and band structure of Weyl semimetals produces CPGE in these systems. Implications for studying band topologies in these class of materials via photogalvanic effects will also be discussed. These results provide a new approach to controlling photoresponse by patterning optical fields in certain class of broken-symmetry materials to store, manipulate and transmit information over a wide spectral range.

Metasurfaces control light propagation at the nanoscale for applications in both free-space and surface-confined geometries. However, all recent designs have exhibited concepts using geometrically fixed structures, or used materials with excessive propagation losses, thereby limiting potential applications. Here we show how to overcome these limitations using a reconfigurable hyperbolic metasurface comprising a heterostructure of isotopically enriched hexagonal boron nitride (hBN) in direct contact with a phase-change material (PCM), single crystal vanadium dioxide (VO2). Metallic and dielectric domains in VO2 provide spatially localized changes in the local dielectric environment to tune the wavelength of hyperbolic phonon polaritons (HPhPs) supported in hBN by a factor of 1.6. This contrasts with earlier work using surface phonon polaritons, where propagation could only be observed above a low-loss dielectric phase. We demonstrate the first realization of in-plane HPhP refraction, which obeys Snell’s law and the means for launching, reflecting and transmitting HPhPs at the PCM domain boundaries. To demonstrate practical applications of this platform, we show how hBN could be combined with either VO2 or GeSbTe glasses to make refractive nanophotonic waveguides and lenses. This approach offers control of in-plane HPhP propagation at the nanoscale and exemplifies a reconfigurable framework combining hyperbolic media and PCMs to design new optical functionalities including resonant cavities, beam steering and waveguiding.

Birefringence is a fundamental property of materials that enables optical components such as wave plates and polarizers, and is quantified by the difference between extraordinary and ordinary refractive indices. Solid homogeneous crystals like calcite and rutile are some of the most birefringent materials at visible and near-infrared wavelengths. However, at longer wavelengths (i.e., mid to far infrared) these materials become highly lossy. In the mid infrared, the most birefringent materials that are transparent are significantly less birefringent than their visible counterparts. While structured materials with strong optical anisotropy exist at these wavelengths (i.e., with form birefringence), their utility is limited by fabrication constraints. In the talk, we will report on a rationally designed and synthesized material, barium titanium sulfide (BaTiS3), which has broadband and giant birefringence surpassing that of any known transparent anisotropic crystal throughout the infrared. We will detail our extensive optical characterization to extract the anisotropic complex refractive index spanning the ultraviolet to the mid infrared by combining generalized spectroscopic ellipsometery and polarized reflection and transmission measurements. We report a difference between the ordinary and extraordinary refractive index of up to 0.76 in a mid-infrared region of transparency, more than twice that of rutile in the visible, and show that the unprecedented optical anisotropy extends to the limit of our detection capabilities (16.7 μm). This material also features highly anisotropic Raman scattering, and we are currently working on measuring polarized infrared photoluminescence measurements to provide further insight into the anisotropy of this unique material.

The chiroptical effect is a property that describes distinct response of matter to light with opposite handedness, which is extensively utilized in stereochemistry, analytical chemistry, metamaterials, and spin photonics. Conventionally, metallic nanostructures have been harnessed to generate a strong chiroptical effect with the assistance of surface plasmon resonance, but they usually suffer from low energy efficiency and large photothermal heat generation due to the high ohmic loss of metallic materials, which severely restricts their practical applications. Here we present a dielectric spiral nanoflower with a giant chiroptical effect produced by magnetic resonance. We theoretically predicted the giant chiroptical effect of the spiral nanoflower by numerical simulations and analyzed its underlying physics by combination of a multipole expansion method. Based on the theoretical design, we experimentally fabricated the spiral nanoflower and demonstrated its strong chiroptical effect by characterizing its circular intensity difference (CID). The largest-to-date CID of 35% is demonstrated. The magnetic quadrupole interference within the spiral nanoflower was also clarified by experimentally tailoring its magnetic quadrupole interference. Our work is expected to overcome the limitation of conventional metallic platforms and pave the way toward the development of various highly efficient and thermostable chiroptical devices and applications.

Advanced nanophotonic concepts, such as photonic crystals, metamaterials and metasurfaces, have enabled unique functionalities including, negative refraction, hyperbolic dispersion, optical magnetism, control of quantum emitters, epsilon-near-zero phenomena, and enhanced light-matter interactions. With the recent development of new plasmonic/photonic materials and nano-fabrication techniques, nanophotonic devices are now capable of providing novel solutions to global challenges including world energy consumption, rapid and accurate chemical/biological detection, quantum computing/security, telecom information densities, and space exploration. These problems are inherently complex due to their multi-disciplinary nature, requiring a manifold of stringent constraints in conjunction with optical performance. Topology optimization has emerged as a successful architect for the systematic design of photonic structures and provide solutions for aforementioned the problems. In this talk, we will highlight recent progress in the field of topology optimization for nanophotonics, share our ongoing results and observations, and discuss future research challenges and directions. In particular, we will discuss our progress in developing solar- thermophotovoltaics components using topology optimization. One of the main aspects of our current work is expanding and streamlining conventional meta-device design methodology to a global optimization space by 1) advancing topology optimization via artificial-intelligence-assisted algorithms and 2) by extending the optimization parameter space into materials domain through optical materials development and multiphysics simulations.

We present a technology to fabricate large-area gapped plasmonic structures deterministically with atomic precision, high throughput and high reliability at low cost. The technology is based on collapsible nano-fingers fabricated using nanoimprint lithography and ALD. A pair of metallic nanoparticles is placed on top of two nano-fingers in flexible polymer with high aspect ratio. ALD is then used to coat a thin conformal dielectric layer. By collapsing the pair of nano-fingers, two metallic nanoparticles with dielectric coating contact each other. Therefore, the gap size between two metallic nanoparticles is well defined by twice the thickness of the ALD-coated dielectric layers. As metallic nanoparticles are known to dramatically modify the spontaneous emission of nearby fluorescent molecules and materials, here we examine the role of the gap plasmon resonance on the molecular fluorescence enhancement. Considering quenching effect, the distance between fluorescent molecules and gold nanoparticles should not be too small in order to obtain strongest enhancement. In that sense, to fully exploit plasmonic enhancement on the fluorescent molecules, an appropriate gap size should be kept between the molecule and each metallic nanoparticle, which separates molecules away from the metal to avoid quenching effect. The ALD-defined gap plasmonic nano-finger structure facilitate direct and precise control on the gap size between the molecule and metallic nanoparticle by simply changing ALD film thickness that has atomic precision. This makes collapsible nano-fingers the ideal structure for the optimization of molecular fluorescence enhancement. With the optimally engineered collapsible nano-fingers plasmonic structure, field enhancement and fluorescence quenching at hot spots can be studied in detail, which paves the way for optimal design on strongest plasmonic enhancement of molecular fluorescence.

Nanocubes-based patch antennas have been proven to be an interesting alternative to build nanocavities on larger areas and at lower cost than with classical clean room techniques. These nanocavities can support gap plasmons that make such devices suitable for light absorbing applications, both narrow or broadband depending on the size dispersion of the colloidal nanocubes that are used. Recently, a fabrication approach has been proposed that relies on an alkyldithiol self-assembled monolayer as a cavity spacer instead of the dielectric coating that is usually being used. Through this process it has been demonstrated both an enhanced reproducibility of the cavity resonance and a thinning of the cavity below the usual 3 nm limit. These caracteristics make such structures good candidates for nonlocality study because of the high electric field confinement that arises in very narrow gaps. This self assembled monolayer spacer is also an opportunity for incorporating electronic properties within the nanogap. In this perspective, the present work proposes both a synthesis and a two steps self-assembly of a clicked molecular rectifier monolayer to be embedded into nanopatch cavities. This way, this monolayer will act both as a mechanical spacer and a molecular diode, thus combining photonic and electronic properties.

The realization of high-Q optomechanical cavities in silicon photonic crystals enables the coupling of near-infrared photons and GHz-frequency phonons in ultra-small volumes. Such coupling enables myriads of novel phenomena (resolved sideband cooling, optomechanically induced transparency, or phonon lasing) both in the linear and nonlinear regimes. Here, we report recent advances in silicon photonic crystal optomechanical cavities beyond the linear regimes. First, we show that by combining thermal effects, free-carrier-induced refraction and optomechanical coupling is it possible to attain different states in the cavity, ranging from chaos [1] to phonon lasing [2], being easy to switch from one state to another by using an external optical source [3]. We also show that using think mechanical links between adjacent optomechanical cavities enables to synchronize their mechanical motion via weak mechanical coupling [4]. These results can be easily upscaled to more than two cavities and are thus the first step towards realizing integrated networks of synchronized OM oscillators, which promise an enhancement of the performance of single nano-mechanical oscillator systems and enable a novel architecture for neuromorphic computing applications References [1] D. Navarro-Urrios et al.,” Nature Commun. 8, 14965 (2017). [2] D. Navarro-Urrios et al, “A self-stabilized coherent phonon source driven by optical forces,” Sci. Rep. 5, 15733 (2015). [3] J. Maire et al., “Optical modulation of coherent phonon emission in optomechanical cavities,” Arxiv pre-print on https://arxiv.org/abs/1802.01146 [4] M. F. Colombano et al., “Synchronization of optomechanical cavities by mechanical interaction,” submitted.

Nanoscale-engineered optical systems have been thoroughly investigated for a few decades due to their fascinating abilities to confine and enhance electromagnetic fields in very sub-wavelength and have a large number of applications in domains like biosensing, enhanced-Raman spectroscopy, metamaterials, photothermal therapy, and plasmomechanics. In addition, the recent astonishing ability of phononic crystals to control acoustic or elastic waves has been demonstrated. As an elastic wave modulates in time both the shape and the refractive index of the supporting structure, it is possible to influence the optical response of the same system. We propose a subwavelength optomechanical structure that instead relies on a double resonance to achieve strong modulation at near-infrared wavelengths. Precisely, we investigate the coupling between an optical Fano resonant mode and phononic resonances carried within a 2D metamaterial. The latter was designed to exhibit simultaneous phononic and photonic high Q-factor resonances and it is composed of silver slits deposited on a lithium niobate substrate. The phononic properties are first determined and show that several vibration modes can be electrically induced through the specific design of the structure that behaves as an interdigitated transducer. The structure geometries for each mode is then determined over an acoustic period and used to point out the optical transmission modifications when the structure is illuminated at the normal incidence by a linearly polarized plane wave. Original results are obtained for some modes (the first two odd phononic modes) showing a very efficient and non-linear modification of the transmitted intensity. Different operating procedures are then explored by changing the operation optical wavelength value. This study opens the way to the design of a new generation of extremely miniaturized optoacoustic devices.

GaInAsP photonic crystal nanolaser is a tiny semiconductor laser simply fabricated and operated by photopumping. It is applicable to sensing because it changes its lasing characteristics when some media is directly attached to the cavity. We have demonstrated the sensing of liquids and biomolecules with ultrahigh sensitivity. Such sensitivity was first thought to arise from the index of the media. But we found that this device has the ion sensitivity in addition to the conventional index sensitivity. It was confirmed from various evidence of bio-chemical sensing experiments. It achieves a very simple sensing of CRMP2 protein, a candidate biomarker for Alzheimer's disease only by using a pump source and PD to detect the emission intensity change. It was also found that the emission intensity and wavelength are controllable in a photoelectrochemical circuit, which can be a novel laser engineering.

The detection of micro pollutants by new innovative systems is one of the important issues of our society. This study is dedicated to innovative pollutant sensors exploiting the interaction properties between light and original nanostructured materials, in order to create a real jump in performance in terms of detection limit, quantification and sensitivity. The detection of our pesticide is based on the variation of the optical properties of the materials used in the presence of the molecule to be detected. We propose two ways of investigation that are (i) the Surface Plasmon Resonance detection (SPR) in Kretschmann configuration and (2) the use of an original functionalized nano structured organization based on the use of functionalized gold nanoparticles.

Designing nanoantenna that could strongly and efficiently concentrate incident light into deep subwavelength volumes is a key issue to locally enhance the electric field and thus produce strong light-matter interactions. Many existing designs are inspired by structures widely used in the radiofrequency domain such as bowtie or Yagi-Uda antennas. Here, we rather use an analogy between acoustics and electromagnetism wave equations, in order to adapt the acoustic Helmholtz resonator to optics. This structure is made of a tiny slit above a larger cavity and exhibits several appealing features: total absorption at resonance, absence of harmonic resonance, giant field intensity enhancement in the whole slit volume, angular independence of the Helmholtz resonance [1-3]. We demonstrate experimentally various structures with Helmholtz-like resonances, and we take advantage of the huge field enhancement in the resonator for sensing applications. In particular, we show how this resonator can be used for both surface plasmon resonance sensing (SPR) and surface enhanced infrared absorption (SEIRA), in order to detect and identify molecules. We demonstrate experimentally that the SEIRA signature of 2,4-dinitrotoluene (DNT) is enhanced by several orders of magnitude, leading to reflectivity variations up to 15%. Similar experiments have been done on various nitrosamines molecules, each having its own infrared fingerprint. These results are promising for the use of these Helmholtz-like resonators as specific and sensitive sensor of molecules. [1] P. Chevalier, P. Bouchon, R. Haïdar, and F. Pardo, Appl. Phys. Lett. 105, 071110(2014) [2] P. Chevalier et al, P. Bouchon, J.J Greffet, J.L. Pelouard, R. Haïdar, and F. Pardo, Phys. Rev. B 90, 195412 (2014) [3] P. Chevalier et al., Appl. Phys. Lett. 112, 171110 (2018)

A photon noise limited sub-mm/far-IR cold telescope in space will require detectors with noise equivalent power (NEP) less than 1x10^-19 W/Hz^1/2 for imaging applications and at least an order of magnitude lower for spectroscopic studies. The detector NEP can be reduced by lowering the operation temperature and improving the thermal isolation between the bolometer and a heat bath. We report on the fabrication of membrane isolated transition edge sensor bolometers incorporating compact (<50 μm) thermal isolation beams based on phononic filters. Phononic filters are created by etching quasi-periodic nanoscale structures into supporting thermo-mechanical beams. The cross-sectional dimensions of the etched features are less than the thermal wavelength at the operating temperature, enabling coherent phonon transport to take place in one dimension. The phonon stop-band can be tuned by adjusting the scale of the quasi-periodic structures. Cascading multiple filter stages can increase bandwidth and provide improved thermal isolation similar to the function of a multi-stage electrical filter. We describe the fabrication of AlMn based transition edge sensor bolometers on silicon and silicon nitride membranes isolated by one- and two-dimensional phononic filters. The phononic filters are patterned through electron beam lithography and isolated with deep reactive ion etching.

High-contrast imaging of magnetic domains were performed using magneto-optical Kerr effect enhanced by the plasmon filter. The plasmon filter was prepared by annealing Au thin films deposited on a SiO₂ substrate. Au nanoparticles were formed by deforming the Au thin film. The filter exhibited an intense absorption peak at wavelength around 570 nm. The images were obtained setting the filter onto a magnet surface using a magneto-optical Kerr effect microscopy. The image contrast was evaluated by comparing Coefficient of Variations (CV) which exhibited the variation of the data in luminance histograms of the observed images. As the value of CV increases, the range of the luminance value expressing the image of magnetic domains is increased. The value of CV of the observation image with the plasmon filter was larger than only substrate, indicating that the contrast of the observation image was improved. High-contrast image of magnetic domains was obtained using the plasmon filter.

Understanding the interactions of light with periodic arrays of Si fins is of the utmost importance for nanoelectronics, where laser light is used for the fabrication and metrology of fin field effect transistors (finFETs). However, due to their nanoscale dimensions and periodic arrangement, these structures exhibit complex photonic properties. In this work, we explain theoretically how the reflectance of semi-infinite periodic arrays of Si fins embedded in SiO2 varies with the fin pitch (i.e. spatial periodicity) and fin width. The results are corroborated with band structure calculations, showing that the spectra of both polarizations, parallel (TE) and perpendicular (TM) to the fin sidewalls, can be understood based on the excitation of one waveguide mode. First, we demonstrate that increasing the pitch decreases the reflectance from the arrays, for both polarizations. Moreover, TE spectra resemble that of bulk Si and are much higher as compared to TM, which are similar to the bulk SiO₂ spectrum. The difference is attributed to the fact that TE mode is mostly confined inside the fin, whereas TM is spread in the SiO₂. Subsequently, we show that the reflectance from the arrays increases as a function of the fin width. TE reflectances are again mostly sensitive towards Si dispersion and higher than TM counterparts. Interestingly, for TM illumination a transition from the SiO₂- to Si-like spectra is observed for the fins of increasing width. The transition is caused by the change in the fraction of the electric field propagating inside the fin. The developed insight will facilitate design, fabrication and metrology of optoelectronic, photovoltaic and nanoelectronic devices.

We present a plasmonic switch based on a combination of plasmonic nanoantennas and a phase-change material such as vanadium dioxide (VO₂) that exhibits great potential for switching the near-field around the nanoantenna at ultrafast time-scales. In order to characterize the switch, we employed the FDTD method to calculate the intensity switching ratio in the vicinity of the nanoantennas, i.e. the ratio of the electric-field intensity between the metallic state (On-state) and the semiconductor state (Off-state) of the VO₂ material. The proposed switch exhibits an intensity switching ratio which is much higher as compared to those reported previously.

An ultra-compact TE-Pass polarization filter has been designed using silicon-on-insulator based W1 Photonic crystal (PhC) slab waveguide structure. The proposed filter has been designed by judicial choice of dimensions of the W1 PhC waveguide, so that it can pass only the TE polarized light and block the TM polarized light. A high extinction ratio ≈34 dB, with nearly ≈1.5 dB insertion loss, has been achieved at wavelength 1550 nm in ≈5 μm long device. The simple structure of the device can be fabricated in single step of lithography with the well-established CMOS fabrication technique.

In this paper, a slotted photonic crystal nanobeam cavity (SPCNC) based sensor has been proposed. The design consists of two rows of parabolically tapered holes and a discontinuous periodic slot in between the two rows of holes. The idea behind the discontinuous slot is to confine light tightly in the low refractive index medium of the structure and thereby increase the sensitivity of the sensor. The slot parameters and the radii of the tapered holes are optimized to achieve a very high Q-factor and sensitivity in the order of ~2.1×10⁶ and 512 nm/refractive index unit respectively. Hence, the proposed structure can be considered as an ideal platform for lab-on-chip gas sensors.

The use of electrospun Polycaprolactone (PCL) nanofiber cloth as a functional air filter was tested. As a model for analysis, the filters were exposed to a steady stream of air that was polluted by tobacco smoke. The filters were weighed before and after exposure to find the effectiveness of filtration. The filters were also imaged before and after exposure using x-ray diffraction to show the effectiveness of filtration. The analysis shows that the weight of the filter after filtration was increased by up to 12% by weight with predominantly carbon and oxygen compounds found to be present after filtration. The pores of the filter were also seen to be closed up whether by melting of the fibers or by contaminants. Further research is being done to understand the nature of the filters against tobacco smoke and to see the effectiveness of the sample infiltration of pollen, dust and UV radiation.