This PDF file contains the front matter associated with SPIE Proceedings Volume 9546 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

We present optimized aperiodic structures for use as broadband, broad-angle thermal emitters which are capable of drastically increasing the efficiency of tungsten lightbulbs. These aperiodic multilayer structures designed with alternating layers of tungsten and air or tungsten and silicon carbide on top of a tungsten substrate exhibit broadband emittance peaked around the center of the visible wavelength range. We investigate the properties of these structures for use as lightbulb filaments, and compare their performance with conventional lightbulbs. We find that these structures greatly enhance the emittance over the visible wavelength range, while also increasing the overall efficiency of the bulb.

We investigate the possibility to selectively reflect certain wavelengths while maintaining the optical properties on other spectral ranges. This is of particular interest for transparent materials, which for specific applications may require high reflectivity at pre-determined frequencies. Although there exist currently techniques such as coatings to produce selective reflection, this work focuses on new approaches for mass production of polyethylene sheets which incorporate either additives or surface patterning for selective reflection between 8 to 13 μ m. Typical additives used to produce a greenhouse effect in plastics include particles such as clays, silica or hydroxide materials. However, the absorption of thermal radiation is less efficient than the decrease of emissivity as it can be compared with the inclusion of Lambertian materials. Photonic band gap engineering by the periodic structuring of metamaterials is known in nature for producing the vivid bright colors in certain organisms via strong wavelength-selective reflection. Research to artificially engineer such structures has mainly focused on wavelengths in the visible and near infrared. However few studies to date have been carried out to investigate the properties of metastructures in the mid infrared range even though the patterning of microstructure is easier to achieve. We present preliminary results on the diffuse reflectivity using FDTD simulations and analyze the technical feasibility of these approaches.

In this work we report room temperature (RT) continuous wave (c.w.) lasing at 1.3 μm in photonic crystal microcavities with a single layer of self-assembled InAsSb quantum dots (QDs) embedded in a photonic crystal microcavity. The laser exhibited ultra–low power threshold (860 nW) and high efficiency (β=0.85), thus operating in the near thresholdless regime. The results open up a wide range of opportunities for room temperature applications of ultra–low threshold lasers, such as integrated photonic circuitry or high sensitivity biosensors.

Disordered optical fibers show novel waveguiding properties that can be used for various device applications, such as beam-multiplexed optical communications and endoscopic image transport. The quality of the transported image is shown to be comparable with or better than some of the best commercially available multicore image fibers with less pixelation and higher contrast. Progress and results, as well as ongoing efforts on the design, fabrication, and characterization of the disordered optical fibers will be discussed.

Hyperuniform disordered photonic structures/solids (HUDS) are a new class of photonic solids, which display large, isotropic photonic band gaps (PBG) comparable in size to the ones found in photonic crystals (PC). The existence of large band gaps in HUDS contradicts the long-standing intuition that Bragg scattering and long- range translational order is required in PBG formation, and demonstrates that interactions between Mie-like local resonances and multiple scattering can induce on their own PBGs. HUDS combine advantages of both isotropy due to disorder (absence of long range two-point correlations) and controlled scattering properties from uniform local topology due to hyperuniformity (constrained disorder). In this paper we review the photonic properties of HUDS including the origin of PBGs and potential applications. We address technologically realisable designs of HUDS including localisation of light in point-defect-like optical cavities and the guiding of light in free-form PC waveguide analogues. We show that HUDS are a promising general-purpose design platform for integrated optical micro-circuitry, including active devices such as optical microcavity lasers and modulators.

Nanoscale integration of materials in three dimensions is critical for the realization of a number of highly functional optical metamaterials. Starting with structures enabled via eutectic solidification and holographic lithography, our team is applying unique template-based and post-synthetic materials transformations in conjunction with powerful computational design tools to develop the scientific underpinnings of, and to produce, 3D metamaterials derived from directionally solidified eutectics. Our approach involves close interactions among computational design, photonic theory, eutectic materials development, template fabrication, materials chemistry, and optical characterization.

Intersubband transitions in n-doped semiconductor heterostructures allow one to quantum-engineer one of the largest known nonlinear response in condensed matter systems but only for the electric field polarized normal to semiconductor layer. By coupling of a quantum-engineered multi-quantum-well semiconductor layer with electromagnetically-engineered plasmonic elements we may produce ultrathin metasurfaces with giant nonlinear response. Here we experimentally demonstrate metasurfaces designed for second harmonic generation at λ≈9.9 μm with a record-high nonlinear response for condensed-matter systems in infrared/visible spectral range, up to 1.17×10⁶ pm/V. The practical impact of the nonlinear metasurfaces proposed here may be extended to a variety of fields, including THz generation and detection, phase conjugation, and other nonlinear optical processes.

Recently, there has been a flurry of research in the field of alternative plasmonic materials, but for telecommunication applications, CMOS compatible materials titanium nitride and doped zinc oxides are among the most promising materials currently available. TiN is a gold-like ceramic with a permittivity cross-over near 500nm. In addition, TiN can attain ultra-thin, ultra-smooth epitaxial films on substrates such as c-sapphire, MgO, and silicon. Partnering TiN with CMOS compatible silicon nitride enables a fully solid state waveguide which is able to achieve a propagation length greater than 1cm for a ~8μm mode size at 1.55μm. Utilizing doped zinc oxide films as a dynamic material, high performance modulators can also be realized due to the low-loss achieved by the TiN/Si3N4 waveguide. Simply by placing a thin layer of aluminum doped zinc oxide (AZO) on top of the waveguide structure, a modulator with very low insertion loss is achieved. Our recent work has investigated optical tuning of AZO films by the pump-probe method, demonstrating a change in the refractive index of -0.17+0.25i at 1.3μm with an ultrafast response of 1ps. Assuming this change in the refractive index for the AZO film, a modulation of ~0.7dB/μm is possible in the structure with ~0.5dB insertion loss and an operational speed of 1THz. Further optimization of the design is expected to lead to an increased modulation depth without sacrificing insertion loss or speed. Consequently, nanophotonic technologies are reaching a critical point where many applications including telecom, medicine, and quantum science can see practical systems which provide new functionalities.

Sub-diffractional confinement of light has led to advancements in imaging, metamaterials, nano-manufacturing, plasmonics, and other fields. One potential route to sub-diffractional confinement is via stimulated surface phonon polaritons (SPhPs). SPhPs couple infrared photons with optical phonons and consequently their lifetimes can be longer than surface plasmon polaritons (SPPs), whose lifetimes are dominated by electron scattering events. Thus, materials capable of generating SPhPs are of general interest to study. SPhPs are activated by photons with energies near the Reststrahlen band of semiconductors such as SiC. In this work we examine aspects of carrier dynamics by photo-injecting electrons into the SiC conduction band using a pulsed 355 nm laser and probe the resulting dynamics near the Reststrahlen band using a tunable CO2 laser. The fluence of the pump laser was varied to provide photo-injection levels ranging from ~1x10^17 to 1x10^19 free carriers. Probing the excited-state dynamics near the blue-edge of the Reststrahlen band resulted in complex transient behavior, showing both positive and negative changes in transient reflectance depending on the level of photo-injected carriers and probe energy. Numerical calculations of the SiC reflectance spectra with different doping levels were done to simulate the initial photo-injection level provided by the transient experiment. The computed spectra and the experimentally measured excited spectra for different photo-injection levels were compared and resulted in qualitative agreement.

There is a continual need to explore new and promising dynamic materials to power next-generation switchable devices. In recent years, transparent conducting oxides have been shown to be vital materials for such systems, allowing for both optical and electrical tunability. Using a pump-probe technique, we investigate the optical tunability of CMOS-compatible, highly aluminum doped zinc oxide (AZO) thin films. The sample was pumped at 325 nm and probed with a weak beam at 1.3 μm to determine the timescale and magnitude of the changes by altering the temporal delay between the pulses with a delay line. For an incident fluence of 3.9 mJ/cm2 a change of 40% in reflection and 30% (max 6.3dB/μm modulation depth) in transmission is observed which is fully recovered within 1ps. Using a computational model, the experimental results were fitted for the given fluence allowing the recombination time and induced carrier density to be extracted. For a fluence of 3.9 mJ/cm2 the average excess carrier density within the material is 0.7×10^20cm-3 and the recombination time is 88fs. The ultrafast temporal response is the result of Auger recombination due to the extremely high carrier concentration present in our films, ~10^21 cm^-3. By measuring and fitting the results at several incident fluence levels, the recombination time versus carrier density was determined and fitted with an Auger model resulting in an Auger coefficient of C = 1.03×10^20cm6/sec. Consequently, AZO is shown to be a unique, promising, and CMOS-compatible material for high performance dynamic devices in the near future.

A wide range of mechanisms is available for achieving rapid optical responsivity in material components. Amongst them, some of the most promising for potential device applications are those associated with an ultrafast response and a short cycle time. These twin criteria for photoresponsive action substantially favor optical, over most other, forms of response such as those fundamentally associated with photothermal, photochemical or optomechanical processes. The engagement of nonlinear mechanisms to actively control the characteristics of optical materials is not new. Indeed, it has been known for over fifty years that polarization effects of this nature occur in the optical Kerr effect – although in fluid media the involvement of a molecular reorientation mechanism leads to a significant response time. It has more recently emerged that there are other, less familiar forms of optical nonlinearity that can provide a means for one beam of light to instantly influence another. In particular, major material properties such as absorptivity or emissivity can be subjected to instant and highly localized control by the transmission of light with an off-resonant wavelength. This presentation introduces and compares the key electrodynamic mechanisms, discussing the features that suggest the most attractive possibilities for exploitation. The most significant of such mechanistic features include the off-resonant activation of optical emission, the control of excited-state lifetimes, the access of dark states, the inhibition or re-direction of exciton migration, and a coupling of stimulated emission with coherent scattering. It is shown that these offer a variety of new possibilities for ultrafast optical switching and transistor action, ultimately providing all-optical control with nanoscale precision.

The impact of quantum technology will be profound and far-reaching: secure communication networks for consumers, corporations and government; precision sensors for biomedical technology and environmental monitoring; quantum simulators for the design of new materials, pharmaceuticals and clean energy devices; and ultra-powerful quantum computers for addressing otherwise impossibly large datasets for machine learning and artificial intelligence applications. However, engineering quantum systems and controlling them is an immense technological challenge: they are inherently fragile; and information extracted from a quantum system necessarily disturbs the system itself. Of the various approaches to quantum technologies, photons are particularly appealing for their low-noise properties and ease of manipulation at the single qubit level. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability. We will described our latest progress in generating, manipulating and interacting single photons in waveguide circuits on silicon chips.

A central goal of quantum information science is the entanglement of multiple quantum memories that can be individually controlled. Here, we discuss progress towards photonic integrated circuits designed to enable efficient optical interactions between multiple spin qubits in nitrogen vacancy (NV) centers in diamond. We describe NV-nanocavity systems in the strong Purcell regime with optical quality factors approaching 10,000 and electron spin coherence times exceeding 200 μs; implantation of NVs with nanometer-scale apertures, including into cavity field maxima; hybrid on-chip networks for integration of multiple functional NV-cavity systems; and scalable integration of superconducting nanowire single photon detectors on-chip.

We present a novel photonic crystal waveguide, engineered to support broadband modes with circular in-plane polarization. We show experimental evidence that for single-photon emitters with circular dipoles these waveguides act as near-lossless unidirectional photonic reservoirs, where the emission direction is given by the helicity of the dipole. This directional coupling has a strong effect on the scattering of single photons transmitted through the system and we discuss how counter-propagating photons acquire a relative phase of π. Combining this effect with photonic structures that can map a phase to a propagation path, we show how one can create nonreciprocal photonic elements.

Invited by Stavroula Foteinopoulou

Plasmonics is a potential route to new and improved optical devices. Many predict that sub wavelength optical systems will be essential in the development of future integrated circuits, offering the only viable way of simultaneously increasing speed and reducing power consumption. Realising this potential will be contingent on the ability to exploit plasmonic effects within the framework of the established semiconductor industry and to this end we present III-V (GaAs) based surface plasmon laser platform capable of effective laser light generation in highly focussed regions of space. Our design utilises a suspended slab of GaAs with a metallic slot printed on top. Here, hybridisation between the plasmonic mode of the slot and the photonic mode of the slab leads to the formation of a mode with confinement and loss that can be adjusted through variation of the slot width alone. As in previous designs the use of a hybrid mode provides strong confinement with relatively low losses, however the ability to print the metal slot removes the randomness associated with device fabrication and the requirement for etching that can deteriorate the semiconductor’s properties. The deterministic fabrication process and the use of bulk GaAs for gain make the device prime for practical implementation.

To study the light-matter interaction between plasmonic systems and gain media, numerous theoretical and numerical methods have been proposed. Among them, because of its accurate treatment of the quantum property of gain media, the time domain (TD) multi-physics approach is viewed as the most powerful method, especially for analysis of transient dynamics. Even though the finite difference, finite-volume and finite element TD methods can be readily coupled to a multi-level atomic system through auxiliary differential equations, for each of them however there is limited information on accurate TD kinetic parameters fitted with experimental measurements. In this work, we develop a multi-physics time domain model to inspect our most recent lasing experiment with a silver nanohole array. We use a classical finite difference time-domain (FDTD) model coupled to the rate equations of a 4-level gain system. To retrieve kinetic energy parameters for accurate modeling, we first fit 1-D simulations with pump-probe experiments studying Rhodamine-101 (R-101) dye embedded in epoxy on an indium tin oxide silica substrate. The retrieved parameters are then fed into a 3-D model to study the lasing behavior of the R-101-coated nanohole array. The simulated emission intensity shows a clear lasing effect, which is in good agreement with the experimental measurements. By tracing the population inversion and polarization dynamics, the amplification and lasing regimes inside the nanohole cavity can be clearly distinguished. With the help of our systematic approach, we can further improve understanding of the time-resolved physics of active plasmonic nanostructures with gain.

The concept of parity-time (PT) symmetry exploits the interplay between the material loss and gain to attain novel optical phenomena such as exceptional point and unidirectional light propagation. Here we experimentally demonstrate a PT symmetry breaking laser that allows unique control of the resonant modes. In contrast to conventional ring cavity lasers with multiple competing modes, our on-chip InGaAsP/InP based PT microring laser exhibits intrinsic single-mode lasing regardless of the gain spectral bandwidth. Thresholdless parity-time symmetry breaking due to the rotationally symmetric structure leads to stable single-mode operation at the specific whispering gallery mode order.

We introduce a new family of spectral singularities with highly directional response in parity-time (PT) symmetric cavities. These spectral singularities support modes with infinite reflection from one side and zero reflection from the other side of the cavity, results in simultaneous unidirectional laser and unidirectional reflectionless parity-time symmetric cavity. Such unidirectional spectral singularities emerge from resonance trapping induced by the interplay between parity-time symmetry and Fano resonances. 

Going beyond traditional cavity-concepts, recently conceived nanolasers employ plasmonic resonances for feedback, allowing them to concentrate light into mode volumes that are no longer limited by diffraction [1]. The use of localized surface plasmon resonances as cold-cavity modes, however, is only one route to lasing on subwavelength scales. Lasing, in fact, does not require modes predefined by geometry but merely a feedback mechanism [2]. Here we demonstrate that the concept of dispersion-less stopped-light [3] allows by combination of nanoplasmonics with quantum gain materials [4] stopped-light lasing in hybrid nanoplasmonic heterostructures. Thereby, photons are trapped and amplified in space just at the point of their emission. It will be discussed that, at the stopped-light point, a stable lasing mode can form over a finite region of gain material due to the arising local (cavity-free) feedback in the form of a sub-wavelength optical vortex. We discuss the remarkable spatio-temporal dynamics of nanoplasmonic stopped-light lasing is studied on the basis of a Maxwell-Bloch Langevin approach [4]. Moreover, a new rate-equation framework is shown to grasp the particular physics of stopped-light lasing involving [4]. The observed high-β characteristics and picosecond relaxation oscillations of cavity-free stopped-light lasing can potentially allow for the design of thresholdless plasmonic laser diodes that can be modulated with THz speeds. References [1] O Hess and KL Tsakmakidis, Science 339, 654 (2013). [2] J M Hamm and O Hess, Science 340, 1298 (2013). [3] KL Tsakmakidis, TW Pickering, JM Hamm, AF Page and O Hess, Phys Rev Lett 112, 167401 (2014). [4] T Pickering, J M Hamm, A F Page, S Wuestner and O Hess, Nature Communications 5, 4971 (2014).

Multicarrier dynamics in colloidal quantum dots (QDs) are normally controlled by nonradiative Auger recombination wherein the energy of an electron-hole pair is converted not into a photon but instead transferred to a third carrier (an electron or a hole). Auger decay is extremely fast in QDs (time scales of tens-to-hundreds of picoseconds) due to both close proximity between interacting charges and elimination of restrictions imposed by translational momentum conservation. Photoluminescence (PL) quenching by nonradiative Auger processes complicates realization of applications that require high emissivity of multicarrier states such as light-emitting diodes (LEDs) and lasers. Therefore, the development of “Auger-recombination-free” QDs is an important current challenge in the field of colloidal nanostructures. Previous single-dot spectroscopic studies have indicated a significant spread in Auger lifetimes across an ensemble of nominally identical QDs. It has been speculated that in addition to dot-to-dot variation in physical dimensions, this spread is contributed to by variations in the structure of the QD interface, which controls the shape of the confinement potential. Here we directly evaluate the effect of the composition of the core-shell interface on single- and multi-exciton dynamics via side-by-side measurements of individual core-shell CdSe/CdS nanocrystals with a sharp vs. smooth (graded) interface. We observe that while having essentially no effect on single-exciton decay, the interfacial alloy layer leads to a systematic increase in the biexciton lifetime indicating suppression of Auger recombination. We demonstrate that using QDs with “engineered interfaces” we can considerably improve the performance of QD LEDs and lasers.

We demonstrate the generation of single photons as well as pairs of entangled photons with quantum dots in semiconducting nanowires, we show applications to quantum optics including generation, manipulation and detection of light at the nanoscale.

Thick-shell or “giant” core/shell nanocrystal quantum dots (gQDs) are efficient and stable emitters. Their characteristic properties of non-blinking and non-photobleaching emission, as well as suppressed non-radiative Auger recombination and minimal self-reabsorption (due to a large effective Stokes shift) make them relevant to both single-emitter and many-emitter applications, e.g., live-cell single-molecule tracking in the biosciences and down-conversion phosphors for solid-state lighting. Here, I will discuss how gQDs are also ideal “building blocks” for achieving additive functionalities through synthesis and modified emission properties through integration with fabricated photonic structures. gQDs have been synthetically incorporated into the interior of a gold shell, resulting in “plasmonic gQDs” that exhibit efficient photoluminescence combined with efficient photothermal transduction and thermometry. Furthermore, through direct patterning of gQDs into all-dielectric antennas, we show an approach for realizing emitter-antenna couples (toward controlling the motion of photons) that is both deterministic and reproducible.

Various sizes of CdSe quantum dots have been fabricated on the surface of the monodisperse silica spheres and five diffe rent photoluminescence (PL) peaks are observed from the CdSe quantum dots. The monodisperse silica spheres were syn thesized with Stöber synthetic method. The surface of the spheres was modified with 100:1 ratio of phenylpropyltrimeth oxysilane (PTMS) and mercaptopropyltrimethoxysilane (MPTMS). The MPTMS works as a covalent bond formation wi th CdSe quantum dots, and the PTMS acts as a separating quantum dots to prevent PL quenching by neighboring quantu m dots. The Fourier transform infrared (FTIR) spectrum of the surface modified spheres (SMSiO₂) shows strong absorpti on peak at 2852 and 2953 cm^-1 representing the characteristic absorption of –CH or -CH2. The FTIR absorption peak at 1 741 cm^-1 represents the characteristic absorption of CdSe quantum dots. The field emission scanning electron microscope image shows the average diameter of the spheres ranging approximately 418 nm. The ultraviolet-visible transmittance s pectrum shows stop band at 880 nm. The PL spectrum shows five different emission bands at 434, 451, 468, 492 and 545 nm, which indicates the formation of several different sizes of CdSe quantum dots.

Meta{surfaces or 2D metamaterials are generally seen as a device able to control the far-field behavior of light. Several studies have shown the possibility of controlling the polarization state, the directivity, the light-by-light manipulation or the generation of second harmonic signal. However, because of their resonant properties, meta{ surfaces also have interesting properties in the near-field. In the present work, a meta{surface made of a set of parallel line distributed dipoles was studied. The coupling of a quantum emitter with the photonic surface modes supported by the meta{surface is investigated.

Coherent coupling between an optical-transition and confined optical mode, when sufficiently strong, gives rise to new modes separated by the vacuum Rabi splitting. Such systems have been investigated for electronic-state transitions, however, only very recently have vibrational transitions been considered. Here, we bring strong polaritonic-coupling in cavities from the visible into the infrared where a new range of static and dynamic vibrational processes await investigation. First, we experimentally and numerically describe coupling between a Fabry-Perot cavity and carbonyl stretch (~1730 cm 1) in poly-methylmethacrylate. As is requisite for “strong coupling”, the measured vacuum Rabi splitting of 132 cm 1 is much larger than the full width of the cavity (34 cm-1) and the inhomogeneously broadened carbonyl-stretch (24 cm-1). Agreement with classical theories providea evidence that the mixed-states are relatively immune to inhomogeneous broadening. Next, we investigate strong and weak coupling regimes through examination of cavities loaded with varying concentrations of urethane. Rabi splittings increases from 0 to ~104 cm-1 with concentrations from 0-20 vol% and are in excellent agreement to an analytical description using no fitting parameters. Ultra-fast pump-probe measurements reveal transient absorption signals over a frequency range well-separated from the vibrational band as well as modifications of energy relaxation times. Finally, we demonstrate coupling to liquids using the C-O stretching band (~1985 cm-1) of Mo(CO)6 in an aqueous solution. Opening the field of polaritonic coupling to vibrational species promises to be a rich arena amenable to a wide variety of infrared-active bonds that can be studied statically and dynamically.

Transition metal dichalcogenides (TMDs) have emerged as an attractive class of two-dimensional (2D) semiconductors that show unprecedented strength in its interaction with light. Here we will discuss our recent work on embedding such a 2D TMD layer of molybdenum disulphide in a dielectric microcavity showing the forming of strongly coupled half-light half-matter quasiparticles called microcavity polaritons. Realizing strong coupling at room temperature in a disorder free landscape such as 2D materials offers a practical and attractive route to realizing devices such as switches and logic gates that exploit the benefits of the half-light half-matter composition of the polaritons.

We present a general theory for calculating the spontaneous emission (SE) rate and the photoluminescence intensity of a quantum dot (QD) exciton coupled to an arbitrary structured photonic reservoir and a bath of acoustic phonons. We describe a polaron master equation (ME) approach which includes phonon interaction nonperturbatively and assume a weak coupling with the photon reservoir which is valid in the Purcell coupling regime. As examples of structured photonic reservoirs, we choose the cases of a Lorentzian cavity and a slow-light coupled-cavity waveguide. In analogy with a simple atom, the SE rate of a QD is expected to be proportional to the local density of photon states (LDOS) of the structured reservoir at the resonant frequency of a QD exciton. However, using a polaron ME theory, we show how the phonon-dressed SE rate of a QD is determined by a broad bandwidth of the photonic LDOS, in violation of the well known Fermi’s golden rule. This broadband frequency dependence results in rich spontaneous emission enhancement and suppression, manifesting in significant changes in the Purcell factor and photoluminescence intensity as a function of frequency.

Photonic structure plays a significant role in determining the brightness and efficiency of nanoemitter systems. Using photonic crystal slabs it is possible to affect these quantities in various ways. First, positioning a leaky mode near the emission frequency allows more light to be extracted from within the slab. Second, concentrating high electric field intensity near emitter locations significantly enhances the spontaneous emission rate. However, a large body of work has suggested these two contributing factors are in competition, making it difficult to simultaneously achieve high electric field intensity and light extraction. In previous work, we identified one mode in an array of GaN nanorods which exhibited a 25X enhancement in extracted power, relative to a uniform slab. However, the mode was uncoupled to normal radiation and, consequently, produced a sharp dip in extraction efficiency. Here, we improve upon the previous design by investigating a new class of quasi-aperiodic nanorod array structures. Using an inverse design algorithm, we identify one optimized structure which achieves maximum theoretical light extraction while maintaining a high spontaneous emission rate. Overall, the optimized structure achieves a 48% increase in extracted power and a 20-48% increase in external quantum efficiency relative to the previous periodic design.

Photonic and plasmonic resonators are dielectric or metallic optical devices that confine light at a scale smaller than the wavelength. The eigenmodes of the system are obviously powerful and intuitive tools to describe light scattering and light-matter interactions mediated by the resonant structure. However, owing to the presence of energy dissipation (by radiation or absorption), using the eigenmodes of nanoresonators is an open issue that has been partly solved only recently. We have developed a modal formalism that relies on the concept of quasinormal modes with complex eigenfrequencies. The theory is capable of handling any photonic or plasmonic resonator with strong radiation leakage, absorption and material dispersion. The normalization of the quasinormal modes constitutes one of the key points of the modal formalism; only a proper and efficient normalization method can ensure both a good accuracy and a high versatility of the theory. Different methods for normalizing quasinormal modes have been published recently. We benchmark these methods on the generic example of a plasmonic nanoantenna lying over a substrate.

Pseudospin is of central importance in governing many unusual transport properties of graphene and other artificial systems which have pseudospins of 1/2. These unconventional transport properties are manifested in phenomena such as Klein tunneling, and collimation of electron beams in one-dimensional external potentials. Here we show that in certain photonic crystals (PCs) exhibiting conical dispersions at the center of Brillouin zone, the eigenstates near the “Dirac-like point” can be described by an effective spin-orbit Hamiltonian with a pseudospin of 1. This effective Hamiltonian describes within a unified framework the wave propagations in both positive and negative refractive index media which correspond to the upper and lower conical bands respectively. Different from a Berry phase of π for the Dirac cone of pseudospin-1/2 systems, the Berry phase for the Dirac-like cone turns out to be zero from this pseudospin-1 Hamiltonian. In addition, we found that a change of length scale of the PC can shift the Dirac-like cone rigidly up or down in frequency with its group velocity unchanged, hence mimicking a gate voltage in graphene and allowing for a simple mechanism to control the flow of pseudospin-1 photons. As a photonic analogue of electron potential, the length-scale induced Dirac-like point shift is effectively a photonic potential within the effective pseudospin-1 Hamiltonian description. At the interface of two different potentials, the 3-component spinor gives rise to distinct boundary conditions which do not require each component of the wave function to be continuous, leading to new wave transport behaviors as shown in Klein tunneling and supercollimation. For examples, the Klein tunneling of pseudospin-1 photons is much less anisotropic with reference to the incident angle than that of pseudospin-1/2 electrons, and collimation can be more robust with pseudospin-1 than pseudospin-1/2. The special wave transport properties of pseudospin-1 photons, coupled with the discovery that the effective photonic “potential” can be varied by a simple length-scale change, may offer new ways to control photon transport. We will also explore the difference between pseudospin-1 photons and pseudospin-1/2 particles when they encounter disorder.

The concept of symmetry pervades modern physics. Through the conservation laws derived from various symmetries, high-level restrictions and selection rules can be derived for a variety of physical systems without any need for detailed investigations of their specific properties. The spatial symmetries of electric charge distribution on the metamaterial’s surface determine whether the EM resonance is “bright” (radiatively coupled to) or “dark” (radiatively de-coupled from) the EM continuum. As we demonstrate in this talk, other (non-spatial) symmetries and their breaking can also be crucial to determine the properties of EM resonances and enable their mutual coupling, which in turn can give rise to EM Fano interferences. I will consider a meta-surface formed by a two-dimensional array of double-antenna meta-molecules resting on a gyromagnetic ferrite substrate. In conclusion, I will use simple symmetry considerations to predict and numerically demonstrate two phenomena that occur in meta-surfaces when symmetry of the system is reduced by a gyromagnetic substrate: gyromagnetically induced transparency and nonreciprocal Fano interference. These phenomena hold significant promise for practical applications such as the dynamic control of resonant EM interactions using magnetic fields produced by the external currents, mitigation of co-site interference and improving isolation. Spectral positions, radiative lifetimes and quality factors of Fano resonances can be controlled by the magnitude of the external magnetic field. This class of effects may lead to a new generation of tunable and nonreciprocal Fano resonant systems for various applications where strong field enhancement, tunability and nonreciprocity are simultaneously required.

We study a problem of achieving three-dimensional dynamic localization of light in a dynamically-modulated resonator lattice. An effective gauge potential for photons has been previously shown to exhibit in such lattice. Dynamic localization of light can be achieved by varying the effective gauge potential sinusoidally in time. Furthermore, the rotating wave approximation was used in previous works on such effective gauge potential for photons. Here, we find that the effect of dynamic localization persists even in the regime where the counter-rotating term has to be taken into count.

We demonstrate that a family of metamaterials, with a designed complex permittivity and permeability such that their index of refraction is real, have anomalous scattering features as opposed to their lossless passive counterparts with the same index of refraction.

In photonics and quantum optics, a key challenge facing any technological application has traditionally been the mitigation of optical losses. Recent work has shown that a new class of optical materials, called Parity-Time symmetric materials, that consist of a precisely balanced distribution of loss and gain can be exploited to engineer novel functionalities for propagating and filtering electromagnetic radiation. Here we show a generic property of optical systems that feature an arbitrary distribution of loss and gain, described by non-Hermitian operators, namely that overall lossy optical systems can transiently amplify certain input signals by several orders of magnitude. We present a mathematical framework to analyze the dynamics of wave propagation in media with an arbitrary distribution of loss and gain and construct the initial conditions to engineer such non-Hermitian power amplifiers.

We describe the process of parametric amplification in a directional coupler of quadratically nonlinear and lossy waveguides, which belong to a class of optical systems with spatial parity-time (PT) symmetry in the linear regime. We identify a distinct spectral parity-time anti-symmetry associated with optical parametric interactions, and show that pump-controlled symmetry breaking can facilitate spectrally selective mode amplification in analogy with PT lasers. We also establish a connection between breaking of spectral and spatial mode symmetries, revealing the potential to implement unconventional regimes of spatial light switching through ultrafast control of PT breaking by pump pulses.

Parity-time (PT) symmetric complex structures can exhibit peculiar properties which are otherwise unattainable in traditional Hermitian systems. This is achieved by judiciously involving balanced regions of gain and loss. Here we investigate the scattering properties of PT-symmetric diffraction gratings. The presence of the imaginary potential can modify the light transport properties in their far field. This is an outcome of a local power flow taking place between the gain and loss regions in the near field. We show that for a certain gain/loss contrast, all the negative diffraction orders can be eliminated while the positive diffraction orders can be amplified.

The optical properties of semiconductors are typically considered intrinsic and fixed. I will discuss how the rapid developments in the understanding of high-index semiconductor nano-antennas can be leveraged to create ultrathin semiconductor metafilms with designer absorption spectra. Such metafilms are constructed by placing one or more types of semiconductor antennas into a dense array with subwavelength spacings. As semiconductor antennas are only weakly-interacting and feature absorption cross sections that can exceed their geometrical cross section, very strongly absorbing metafilms can be created whose spectral absorption properties can directly be linked to the resonant properties of the constituent building blocks. The ability to create semiconductor metafilms with custom absorption spectra opens up new design strategies for planar optoelectronic devices and solar cells.

Metals in the plasmonic metamaterial absorbers for photovoltaics constitute undesired resistive heating. However, tailoring the geometric skin depth of metals can minimize resistive losses while maximizing the optical absorbance in the active semiconductors of the photovoltaic device. Considering experimental permittivity data for In_xGa_1-xN, absorbance in the semiconductor layers of the photovoltaic device can reach above 90%. The results here also provides guidance to compare the performance of different semiconductor materials. This skin depth engineering approach can also be applied to other optoelectronic devices, where optimizing the device performance demands minimizing resistive losses and power consumption, such as photodetectors, laser diodes, and light emitting diodes.

We developed a genetic algorithm to achieve optimal absorption of solar radiation in nano-structured thin films of crystalline silicon (c-Si) for applications in photovoltaics. The device includes on the front side a periodic array of inverted pyramids, with conformal passivation layer (a-Si:H or AlO_x) and anti-reflection coating (SiN_x). The device also includes on the back side a passivation layer (a-Si:H) and a flat reflector (ITO and Ag). The geometrical parameters of the inverted pyramids as well as the thickness of the different layers must be adjusted in order to maximize the absorption of solar radiations in the c-Si. The genetic algorithm enables the determination of optimal solutions that lead to high performances by evaluating only a reduced number of parameter combinations. The results achieved by the genetic algorithm for a 40μm thick c-Si lead to short-circuit currents of 37 mA/cm² when a-Si:H is used for the front-side passivation and 39.1 mA/cm² when transparent AlO_x is used instead.

Hot electrons rapidly dissipate their extra free energy, typically into heat. This is the origin of the Shockley-Queisser efficiency limit of the single junction solar cells. An even faster mechanism of electron-plasmon scattering is available in metals. We demonstrate by detailed simulations, that an ultra-thin solar cell with a composite metamaterial/plasmonic collector could yield efficiency exceeding the Shockley-Quasar limit. The composite collector has a double function: firstly, it is designed to participate in efficiently trapping light, and secondly, it is a plasmonic resonator tuned to absorb the energy of hot electrons, thus protecting them from phonon losses.

Plasmonic materials and metamaterials have been widely utilized to achieve spectral transmission, reflection and absorption filters based on localized or delocalized resonances arising from the interaction of photons with nanoscale patterns. However, the realization of visible-frequency, high-performance, large-area, optical filters based on nanoplasmonic materials is rather challenging due to nanofabrication related problems (cost, fabrication imperfection, surface roughness) and optical losses of metals. Here, we propose and demonstrate large-area perfect absorbers and transmission color filters and photodectors that could overcome the difficulties associated with nanofabrication using a lithography-free approach. Our resonant flat optical design is based on a modified, asymmetric metal-insulator/semiconductor-metal (MI/SM) based Fabry-Perot cavity incorporated with plasmonic, lossy ultra-thin (~ 30 nm) Ag or (~ 5-15 nm) amorphous Si films. We demonstrated a narrow bandwidth (~17 nm) super absorber with 97% maximum absorption with a performance comparable to nanostructure/nanoparticle-based super absorbers. We also investigated transmission filters in which different colors can be obtained by controlling the spacer thickness of silicon dioxide or amorphous silicon. With measured performance of transmission peak intensity reaching 60% and a narrow-band of ~ 40 nm, our color filters exceed the performance of widely studied plasmonic nanohole array based color filters and make a good candidate for large-area narrow-band photodetection devices. Such plasmonic loss incorporated Fabry-Perot cavities using ultra-thin metallic or semiconductor films could suggest active and practical applications in spectrally selective optical (color and absorber) filters, optoelectronic devices with controlled bandwidth such as narrow-band photodetectors, and light-emitting devices.

In this contribution, we explore the generation of light in transformation-optical media. When charged particles move through a transformation-optical material with a speed larger than the phase velocity of light in the medium, Cherenkov light is emitted. We show that the emitted Cherenkov cone can be modified with longitudinal and transverse stretching of the coordinates. Transverse coordinates stretching alters only the dimensions of the cone, whereas longitudinal stretching also changes the apparent velocity of the charged particle. These results demonstrate that the geometric formalism of transformation optics can be used not only for the manipulation of light beam trajectories, but also for controlling the emission of light, here for describing the Cherenkov cone in an arbitrary anisotropic medium. Subsequently, we illustrate this point by designing a radiator for a ring imaging Cherenkov radiator. Cherenkov radiators are used to identify unknown elementary particles by determining their mass from the Cherenkov radiation cone that is emitted as they pass through the detector apparatus. However, at higher particle momentum, the angle of the Cherenkov cone saturates to a value independent of the mass of the generating particle, making it difficult to effectively distinguish between different particles. Using our transformation optics description, we show how the Cherenkov cone and the cut-off can be controlled to yield a radiator medium with enhanced sensitivity for particle identification at higher momentum [Phys. Rev. Lett. 113, 167402 (2014)].

In typical colloidal suspensions, the corresponding optical polarizability is positive, and thus enhanced scattering takes place as optical beams tend to catastrophically collapse during propagation. Recently, light penetration deep inside scattering suspensions has been realized by engineering dielectric or plasmonic nanoparticle polarizibilities. In particular, we have previously demonstrated two types of soft-matter systems with tunable optical nonlinearities - the dielectric and metallic colloidal suspensions, in which the effects of diffraction and scattering were overcome, hence achieving deep penetration of a light needle through the suspension. In this work, we show that waveguides can be established in soft matter systems such as metallic nanosuspensions through the formation of plasmonic resonant solitons. First, we show that, due to plasmonic resonance, a 1064nm laser beam (probe) would not experience appreciable nonlinear self-action while propagating through 4cm cuvette containing the metallic nanosuspension of gold spheres (40nm), whereas a 532nm laser beam (pump) can readily form a spatial soliton due to nonlinear self-trapping. Second, we demonstrate effective guidance of the probe beam, which would otherwise diffract significantly through the nanosuspensions, due to the soliton-induced waveguide from the pump beam. Such guidance was observed when the power of the probe beam was varied from 20mW to 500mW at constant pump beam power, with more pronounced guidance realized from lower to higher probe beam power. Interestingly, due to the presence of the probe beam, the pump beam undergoes self-trapping at an even lower power. These results may bring about the possibility of engineering plasmonic soliton-based waveguides for many applications.

The magneto-optical effect has been used to control the propagation of surface plasmon polaritons in plasmonic waveguides. Here we investigate single-interface metal-dielectric and metal-dielectric-metal plasmonic waveguides in which either the dielectric or the metal is a magneto-optical material. We derive the dispersion relation of these waveguides, and investigate the effect of an externally applied static magnetic field. We find that in metal-dielectric-metal waveguide structures in which the dielectric is a magneto-optical material, the symmetry of the structure prohibits any non-reciprocal propagation in the system. Moreover, the induced change in the propagation constant of the supported modes in the presence of an externally applied static magnetic field is relatively small. In addition, we find that using a magneto-optical metal in a single-interface metal-dielectric plasmonic waveguide results in non-reciprocal propagation of the plasmonic modes along the interface. We also find that in metal-dielectric-metal plasmonic waveguides in which the metal is a magneto-optical material, the propagation constant of the supported modes is dependent on the relative direction of the applied magnetic fields to the upper and lower metal regions. If the applied magnetic fields to the two metal regions are equal and in the same direction, the induced changes in the propagation constants of the modes propagating in the positive and negative directions are the same. On the other hand, if the directions of the applied external magnetic fields are opposite, the propagation constants of the modes propagating in the positive and negative directions are different. We finally investigate Fabry-Perot cavity magneto-optical switches.

The lack of a dipolar second order susceptibility (χ⁽²⁾) in silicon due to its centro-symmetric diamond lattice usually inhibits efficient second order nonlinear optical processes in the silicon bulk. Depositing stressed silicon nitride layers or growing a thermal oxide layer introduces an inhomogeneous strain into the silicon lattice and breaks the centro-symmetry of its crystal structure thereby creating a χ⁽²⁾. This causes enhanced second harmonic generation and was observed in reflection and transmission measurements for wavelengths in the infrared. However strain is not the only means to break the structures symmetry. Fixed charges at the silicon nitride/silicon interface cause a high electric field close to the silicon interface which causes electric-field-induced-second-harmonic (EFISH) contributions too. The combination of both effects leads to χ⁽²⁾ values which are estimated to be of the order as classic χ⁽²⁾ materials like KDP or LiNiO3. This paves the way for the exploitation of other second order nonlinear processes in the area of silicon photonics and is an example how fundamental optical properties of materials can be altered by strain.

We report on optical design and applications of hybrid meso-scale devices and materials that combine optical and thermal management functionalities owing to their tailored resonant interaction with light in visible and infrared frequency bands. We outline a general approach to designing such materials, and discuss two specific applications in detail. One example is a hybrid optical-thermal antenna with sub-wavelength light focusing, which simultaneously enables intensity enhancement at the operating wavelength in the visible and reduction of the operating temperature. The enhancement is achieved via light recycling in the form of whispering-gallery modes trapped in an optical microcavity, while cooling functionality is realized via a combination of reduced optical absorption and radiative cooling. The other example is a fabric that is opaque in the visible range yet highly transparent in the infrared, which allows the human body to efficiently shed energy in the form of thermal emission. Such fabrics can find numerous applications for personal thermal management and for buildings energy efficiency improvement.

Graphene is one of the emerging active nanophotonics materials with optical properties that can be controlled in real time by an applied bias voltage. Different applications from sensing to active nanophotonics have been discussed in the literature recently and the field is still developing especially with an eye on structured and multi-layer graphene. To design new devices there is a need for precise modeling of multivariate and dynamic optical responses of graphene elements in frequency and time domains. Taking into account the complexity that comes along with multiple unknown parameters, including edge effects in nanostructured graphene elements, graphene impurities, imperfections of characterization optics etc., it is hard to build an adequate multivariate model to reach good quantitative agreement with experiment. Here, we present an approach that uses optimization methods to retrieve the optical properties of a given graphene sample from experiment. We show that with these techniques good quantitative agreement with experiments can be achieved; additionally we encapsulate our techniques in an online data-fitting tool. The tool includes several options to precisely fit the conductivity function to a given experiment - general spline approximations and physically meaningful random phase approximation models for frequency domain solvers, along with the relaxed Lorentz oscillator models for confident time domain simulations. A pilot version of our free online tool entitled Photonics2D-Fit (to be staged at nanoHUB.org) is presented.

Enhanced transmission of light through nanostructures has always been of great interest in the field of plasmonics and nanophotonics. With the aid of near-field effects, the transmission of the electromagnetic waves can be enhanced or suppressed. Much of the work on enhanced transmission has been shown to be frequency-selective. However it is possible to increase the transmission over a large frequency range by using graphene, which has shown broadband properties in many applications. Here, we propose enhanced transmission in wire grid gold structure making use of continuous graphene sheets. We use finite-difference time-domain simulations to study the optical properties of this graphene-metal hybrid structure at mid infrared (mid-IR) wavelengths. The grating structure in wire grid gold provides an ideal platform to match the momentum and excite the surface plasmon polaritons (SPPs) in monolayer graphene. Our numerical calculations show that the local electromagnetic field around the graphene is largely enhanced due to surface plasmons. Moreover, with the highly confined SPPs coupling with the incident light, the transmission through the whole structure can be broadly enhanced in the mid infrared region. We also analyze the effect of the spectrum with different periods and gold nanowire widths to evaluate the size effects of the plasmons in graphene. In addition, by tuning the Fermi level, one can control the wavelength range at which the transmission is enhanced. The mechanism of the enhancement will be explained in the calculated electric field distribution. And we will also highlight the opportunities of graphene for applications such as tunable transmission and active photonic modulator.

On-chip nonlinear optics is a thriving research field, which creates transformative opportunities for manipulating classical or quantum signals in small-footprint integrated devices. Since the length scales are short, nonlinear interactions need to be enhanced by exploiting materials with large nonlinearity in combination with high-Q resonators or slowlight structures. This, however, often results in simultaneous enhancement of competing Q2 nonlinear processes, which limit the efficiency and can cause signal distortion. Here, we exploit the frequency dependence of the optical density-of-states near the edge of a photonic bandgap to selectively enhance or inhibit nonlinear interactions on a chip. We demonstrate this concept for one of the strongest nonlinear effects, stimulated Brillouin scattering using a narrow-band one-dimensional photonic bandgap structure: a Bragg grating. The stimluated Brillouin scattering enhancement enables the generation of a 15-line Brillouin frequency comb. In the inhibition case, we achieve stimulated Brillouin scattering free operation at a power level twice the threshold

We present recent results pertaining to pulse reshaping and optical signal processing using optical nonlinearities of silicon-based tapered photonic wires and photonic crystal waveguides. In particular, we show how nonlinearity and dispersion engineering of tapered photonic wires can be employed to generate optical similaritons and achieve more than 10× pulse compression. We also discuss the properties of four-wave mixing pulse amplification and frequency conversion efficiency in long-period Bragg waveguides and photonic crystal waveguides. Finally, the influence of linear and nonlinear optical effects on the transmission bit-error rate in uniform photonic wires and photonic crystal waveguides made of silicon is discussed.

In this article, we have numerically investigated an intense terahertz (THz) pulses generation in gaseous plasma based on the third-order nonlinear effect, four-wave mixing rectification (FWMR). We have proposed that the fundamental fields and second-harmonic field of ultra-short pulse lasers are combined and focused into a very small gas chamber to induce a gaseous plasma, which intense THz pulse is produced. To understand the THz generation process, the first-order multiple-scale perturbation method (MSPM) has been utilized to derive a set of nonlinear coupled-mode equations for interacting fields such as two fundamental fields, a second-harmonic field, and a THz field. Then, we have simulate the intense THz-pulse generation by using split step-beam propagation method (SS-BPM) and calculated output THz intensities. Finally, the output THz intensities generated from induced air, nitrogen, and argon plasma have been compared.

We discuss a soliton mode of laser femtosecond pulse propagation in a layered structure with cubic nonlinear response in certain layers. Soliton under consideration occupies a few layers. It moves across the layers without its shape destroying. Using computer simulation, we investigate the features of soliton reflection from ambient linear and nonlinear medium. Soliton reflection depends in a strong way on the optical properties of boundary layers. However, in any situation a part of soliton leaves the photonic crystal during some time interval.