Experimentation with obliquely incident light established that all four circular reflectances of a chiral sculptured thin film backed by a metallic mirror contain strong evidence of the circular Bragg phenomenon. When the mirror is removed, strong evidence of that phenomenon is found only in the spectrum of the copolarized and cohanded reflectance.

We present previously unreported properties of the organic molecular dye compound, 2,3,7,8-tetracyano-5,10-dimethyl-5,10-dihydrodipyrazino[2,3-b:2’,3’-e]pyrazine (DMTC-pyrazine) (CAS Reg. No. 150960-11-5), including photophysical properties with particular emphasis on optical waveguiding. We show that DMTC-pyrazine can self-assemble into monoclinic crystals that are thermally stable over 300°C. Through shape-engineering, optimized growth conditions produced high yields of nanofiber (aspect ratio >6) crystals. No photobleaching of this dye was observed in air even after hours of on-resonant illumination. Excitation of photoluminescence within the DMTC-pyrazine nanofibers propagates in tightly confined guided modes (up to 25  μm). The finesse, end-facet reflectance, and group refractive index of nanofiber DMTC-pyrazine Fabry-Pérot cavities are reported.

Artificial neural network and simulated annealing are applied to obtain optimized design parameters of skewed omega-shaped metamaterial unit cells for providing left-handed material (LHM) with a negative refractive index. The implemented numerical and experimental methods provide evidence for the validity and practicality of the technique. Simulation, with optimized parameters, using CST Microwave Studio, shows that skewed LHMs are low-loss materials.

We design, fabricate, and characterize a frequency-selective surface (FSS) with directional thermal emission and absorption for long-wave infrared wavelengths. The FSS consists of an array of patch antennas connected by microstrips, the ensemble of which supports leaky-wave-type modes with forward and backward propagating branches. The branches are designed to intersect at 9.8  μm and have a broadside beam with 20-deg full width at half maximum at this wavelength. The absorption along these branches is near unity. Measurement of the hemispherical directional reflectometer shows good agreement with simulation. The ability to control the spectral and directional emittance/absorptance profiles of surfaces has significant applications for radiation heat transfer and sensing.

Layered HNbWO₆ nanosheet aggregation (e-HNbWO₆) has been assembled by HNbWO₆ nanosheet via an exfoliation-restaking route. The as-prepared samples are characterized by means of powder x-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy, laser Raman spectroscopy, ultraviolet-vis diffuse reflectance spectroscopy, and N₂ adsorption-desorption isotherms. The photocatalytic performances of the as-prepared samples are evaluated by degradation of methylene blue (MB). The results revealed that e-HNbWO₆ has a specific surface area of about 156.5  m² g⁻¹, and exhibits a relatively excellent photocatalytic performance for degradation of MB under UV light.

We present the theoretical results of the optimization of lossy mode resonance sensors at visible wavelengths. Both angular and spectral interrogations are carried out for absorbing indium tin oxide (ITO) films placed on glass prism. The inclusion of a low-index layer between the prism and the lossy (ITO) layer can produce an efficient refractive index sensor for bio/chemical applications. Further increase in sensitivity can be achieved by changing the index of the prism. It is shown that the sensitivity has strong dependence on the index of prism. Sensitivities as high as 4670  nm/RIU for spectral mode and 67  deg/RIU for angular mode with small values of full width at half maximum (FWHM) can be achieved. Dependence of sensitivity and FWHM on refractive index and thickness of low-index matching layer is also investigated.

We demonstrate an inverted low bandgap semitransparent organic solar cell with improved absorption as well as reasonable transparency perception based on a nanopatterned MoO₃/Ag/MoO₃ (MAM) multilayer film as the transparent anode under illumination from the MAM side. The integrated absorption efficiency of the active layer at normal hybrid-polarized incidence considering an AM 1.5G solar spectrum is up to 51.69%, increased by 18.53% as compared to that of the equivalent planar device (43.61%) and reaching 77.3% of that of the corresponding opaque nanopatterned device (66.90%). Detailed investigations reveal that the excitation of plasmonic waveguide modes (at transverse magnetic polarization) and photonic modes (at transverse electric polarization) are responsible for the observed enhancement in absorption. Importantly, the proposed device exhibits an average transmittance of up to 28.4% and an average transparency perception of 26.3% for the human eyes under hybrid-polarized light illumination along with a good color rendering property. Additionally, our proposal works very well over a fairly wide angular range.

Modern technology allows the fabrication of antennas with a characteristic size comparable to the electromagnetic wavelength in the optical region. This has led to the development of new technologies using nanoscale rectifying antennas (rectennas) for solar energy conversion and sensing of terahertz, infrared, and visible radiation. For example, a rectenna array can collect incident radiation from an emitting source and the resulting conversion efficiency and operating characteristics of the device will depend on the spatial and temporal coherence properties of the absorbed radiation. For solar radiation, the intercepted radiation by a micro- or nanoscale array of devices has a relatively narrow spatial and angular distribution. Using the Van Cittert–Zernike theorem, we show that the coherence length (or radius) of solar radiation on an antenna array is, or can be, tens of times larger than the characteristic wavelength of the solar spectrum, i.e., the thermal wavelength, λ_T=2πℏc/(k_BT), which for T=5000  K is about 3 μm. Such an effect is advantageous, making possible the rectification of solar radiation with nanoscale rectenna arrays, whose size is commensurate with the coherence length. Furthermore, we examine the blackbody radiation emitted from an array of antennas at temperature T, which can be quasicoherent and lead to a modified self-image, analogous to the Talbot-Lau self-imaging process but with thermal rather than monochromatic radiation. The self-emitted thermal radiation may be important as a nondestructive means for quality control of the array.

Photonic crystal waveguide (PCW), due to its large bandwidth, small size, and diversified design of the waveguide structures, represents a breakthrough in the field of optical buffer. Here, a nested structure is designed to improve delay-bandwidth product with ferrite magnetic fluid infiltrated photonic crystal coupled-cavity waveguides. Specifically, three types of coupled cavities, i.e., horizontal-, vertical-, and cross-defect cavity are studied with different concentrations of magnetic fluid. Overall, this aspect of the work is interesting from the perspective of coupled defect waveguides design, which is different from previous line-defect waveguides. Plane wave expansion simulations on the slow light property of the three PCWs reveal that the group velocities are all three orders of magnitude smaller than the speed of light in vacuum and that the corresponding normalized delay-bandwidth product (NDBP) values are all <0.35, with 0.41 being the highest value achieved in vertical-defect coupled cavity. Interestingly, the quality factor (Q), normalized bandwidth (Δω), and NDBP can be readily tuned by varying the concentrations of magnetic fluid. Moreover, all the three coupled-cavity waveguides can be reconfigured, which accordingly changes the corresponding slow light property. Compared to previous works, the results of this work have further improved the slow light property in slow light devices and realized the tunable slow light.

Knowledge of temperatures at the nanoscale is essential for studying and controlling the heat-induced local thermal responses. The temperature rise of a heated nanoparticle (NP) near the interface of two kinds of media with different thermal conductivities is numerically investigated. We find that the temperature rise becomes size independent if it is scaled by the temperature rise in the case where the particle-interface distance is zero and the distance is scaled by the equivalent radius of the NP. This universal scaling behavior can be understood with the principle of dimensional homogeneity. An empirical equation is retrieved to predict the actual particle temperature at a given position. Our results may benefit precise control of heat at the nanoscale with applications in plasmonic absorbers, immunotargeted photothermal cancer cell killing, etc.

Colloidal nanoparticles are attractive optical materials for their low threshold nonlinear response and thus all-optical, nondestructive features which are important in biomedical optics and optical processing. We develop a theoretical scheme based on numerical solution of Nonlinear Schrödinger Equation and nonideal gas model of nonlinearity to investigate temporal analysis of optical bistability (OB) and modulation instability in colloidal nanoparticles. Our scheme determines the dependence of a nanosuspension system dynamic state on characteristic/control parameters including external feedback depth, nanosuspension length, and the initial density of nanoparticles as well as the optical input power. We show that these parameters are intensely correlated. We also indicate that the nonlinear response of nanosuspension may be saturated over a threshold of input power, and thus an unexpected procedure of system evolution toward stability rather than transition to chaos will occur. Consequently, provided that internal feedback is present inside the nanosuspension controlling chaos will be attainable by simply adjusting the optical input power as the control parameter in contrast to the other chaos control methods which require external injection. Finally, we propose an approach which gives a measure of switching time to optimize OB. The optimum results are obtained for the lowest taken values of characteristic/control parameters.

The present work demonstrates the synthesis of a hybrid accepter material containing amino-functionalized graphene oxide (GO) and an inorganic semiconducting material, cadmium selenide (CdSe). First, amino-functionalized graphene was synthesized and then nanocrystals (NCs) of CdSe were in situ grown in the functionalized-(GO) matrix named f-GCdSe. Structural studies such as x-ray diffraction, and a scanning electron microscopic were employed to investigate the growth of CdSe NCs in the graphene matrix. To understand the charge generation and transfer process at the donor/acceptor interface, the absorption, photoluminescence (PL), and transient absorption spectroscopic (TAS) studies have been carried out in poly(3-hexylthiophene) (P3HT)/f-GCdSe thin films. PL quenching in P3HT/f-GCdSe thin film suggests that charge transfer takes place at the donor/acceptor interface. TAS shows higher optical density and long lived free carriers for P3HT/f-GCdSe thin film. These results suggest that f-GCdSe is an excellent electron–acceptor material for organic photovoltaic devices.

Interconnecting layers (ICL) play an important role in regulating the performance of tandem devices. We report the design of a solution-processed ICL that consists of a silver/polymer nanocomposite deposited on the top of a TiO₂ layer. This nanocomposite contains modified poly (3,4-ethylenedioxythiophene) polystyrene sulfonic acid (PEDOT:PSS), and silver nanoparticles (Ag NPs) synthesized by the chemical reduction of silver nitrate in the presence of PEDOT:PSS. Formation of Ag NPs was confirmed by monitoring the plasmon absorption peak characteristics in the UV–visible spectrum of the synthesized nanocomposite. Transmission electron microscopy analysis indicated the presence of spherical silver NPs in a polymer matrix with a mean size of around 20 nm. The sheet resistance of PEDOT:PSS was found to be 2474±35  Ω/sq. It was changed to 445±28  Ω/sq after solvent modification and decreased to 53.31±3.59  Ω/sq after synthesizing silver NPs in the polymer medium. Meanwhile, the transparency of the nanocomposite film deposited on TiO₂ was 89.6%, which is considered appropriate for an interconnecting electrode. We demonstrated that by incorporating a silver/polymer nanocomposite as a hole-transporting layer in contact with TiO₂ as an electron-transporting layer, the ohmic behavior of ICL is enhanced with respect to pristine PEDOT:PSS. P3HT:PCBM-based tandem solar cells based on this solution-processed intermediate electrode represent significantly increased open-circuit voltage (V_oc), reaching close to the sum of the single cells. By incorporating the nanocomposite in the tandem structure, a V_oc of 1.1 V was obtained. This value was almost the sum of the V_oc of two single cells, which was 1.18 V.

A photonic crystal fiber based on surface plasmon resonance (PCF-SPR) sensing of a silver layer is investigated. The sensor has two advantages: polarization independence and less noble metal consumption. The coupling characteristics and sensing performance of the sensor are numerically investigated by the finite-element method employing the COMSOL Multiphysics® software. The optical loss spectrum of the PCF-SPR sensor can be easily tuned by varying the parameters of the structure. The defined amplitude sensitivity is 4398  dB/RIU and spectral sensitivity is 4500  nm/RIU corresponding to resolution of 2.27×10−⁶  RIU and 2.22×10−⁵  RIU, respectively.

This paper presents an ultrafast niobium nitride (NbN) superconducting single-photon detector (SSPD) with an active area of 3×3  μm² that offers better timing performance metrics than the previous SSPD with an active area of 7×7  μm². The improved SSPD demonstrates a record timing jitter (<25  ps), an ultrashort recovery time (<2  ns), an extremely low dark count rate, and a high detection efficiency in a wide spectral range from visible part to near infrared. The record parameters were obtained due to the development of a new technique providing effective optical coupling between a detector with a reduced active area and a standard single-mode telecommunication fiber. The advantages of the new approach are experimentally confirmed by taking electro-optical measurements.

CdSe-based nanocrystal quantum wells (QWs) were synthesized around CdS nanocrystal quantum dots and were bandgap- and strain-engineered to achieve high-efficiency short-wavelength luminescence. Tuning the CdSe QW width in the range of 1.05 to 1.58 nm has led to blue-green light emission, whose quantum yield was improved up to 48% through strain compensation by an optimized ZnS outer shell. The luminescence spectrum can be modified by adding a ZnS inner barrier layer to block charge and exciton transfer between the QW and CdS core. Strain management by adjusting the well and barrier thickness has proven critical in such a complex multilayer quantum system for obtaining high-quality nanocrystals and light emission.

This work thoroughly investigates gold nanowires with various cross-sectional geometries and patterns. The study has determined the effect of the cross section aspect ratio on its maximum optical enhancement. The plasmonic optical enhancement properties of single gold nanowires and an array of three nanowires were investigated using finite element method simulations. The results indicate a significant dependence of the optical enhancement on both the thickness and width of the nanowires. From the simulation data, an equation for each geometry (single and triple array) was found that relates the dimensions and incident wavelength to the optical enhancement. These relationships can be a valuable resource while designing nanowires to optimize the dimensions and provide the maximum possible optical enhancement.

Green emission lines, in addition to the blue and the red, were observed upon 980 nm excitation in yttrium oxide (Y₂O₃) nanopowder codoped with Yb³+ and Tm³+, synthesized by the chemical combustion method. Upconversion emission studies suggest that the number and characteristics of the green lines are influenced by the annealing temperature as well as by the Yb³+/Tm³+ concentration ratio, opening possibilities for new customized applications. The chromaticity properties of the upconversion spectra were quantified by the Commission Internationale de l’éclairage coordinate analysis.

A compact silicon-based polarization demultiplexer (P-DEMUX) is proposed by using a microring resonator, where the metal-loaded strip waveguides are used as the bus channels. The modal characteristics of transverse electric (TE) modes for the hybrid plasmonic waveguides are analogous to those for the strip dielectric ones, while those of transverse magnetic (TM) modes show significant differences, leading to strong polarization-dependence. Consequently, the input TE mode can efficiently output from the drop port at the resonant wavelength, while the input TM mode directly outputs from the through port with nearly negligible coupling. The present P-DEMUX can be easily employed to construct an on-chip wavelength/polarization division multiplexing optical transmission system, further increasing the optical interconnect capacity. Results show that a P-DEMUX with a radius of 2.003  μm for the microring is achieved at the wavelength of 1550 nm, where the extinction ratio and insertion loss are, respectively, ∼22.36 (20.09) dB and ∼0.39 (0.84) dB for the TE (TM) mode. In addition, fabrication tolerances to the key structural parameters are investigated and field evolution through the P-DEMUX is also presented.

TiO₂ nanoparticles (NPs) with high-photocatalysis properties both in ultraviolet and visible-light regions were synthesized via a simple sol-gel method, and an aloe leaf extract (ALE) was used as the cap. When the Ti(OC₄H₉)₄∶(CH₃)₂CHOH∶ALE volume ratio was equal to 0.5∶8∶40, the reaction time was 6 h, and crystallization occurred at 80°C for 2 h, the TiO₂NPs had been synthesized. XRD analysis showed that the structure of TiO₂NPs without thermal treatment was anatase. Transmission electron microscopy images confirmed their average size, which was around 5 nm. The products showed an excellent photocatalytic property for methyl orange in the presence of UV and sunlight with the characterization of UV-vis. The photocatalytic activity was optimized by adjusting the amount of TiO₂, the pH value, and the calcination temperature. Results indicated that ALE acted as a cap and nano-TiO₂ could be synthesized without calcination.

The Dirac-like cone dispersion induced by accidental degeneracy is demonstrated in two-dimensional dielectric photonic crystals (PCs) of core-shell rods arranged in square and triangular lattices. The Dirac-like point (DLP) is achieved at the center of the Brillouin zone with a threefold degenerate state having two bands forming a Dirac cone and a third flat band intersecting the cone at the same frequency. This degenerate state is accidental and exists only for particular set of parameters of the PC. These parameters have been adjusted to obtain accidentally induced DLP. When the core region has a higher refractive index than the cladding, the DLP has monopole and dipole field configurations. When the core region has a lower refractive index than the cladding, the DLP is formed by quadrupole and dipole field configurations. The PCs exhibiting Dirac-like dispersion formed by monopole and dipole interactions can be mapped to an effective medium with ϵ and μ equal to zero. The isotropic behavior of DLP formed by monopole and dipole interactions is observed by computing isofrequency contours.

We have demonstrated the significant impacts of grating tapered sidewall profile on the subwavelength grating wideband reflector characteristics when taking into account the practical fabrication process. Two different classes of wideband reflectors, referred to as zero-contrast gratings and high-contrast gratings, are numerically investigated in detail and the distinct differences of the impacts due to a grating tapered sidewall are observed. Our works reveal that this tapered sidewall profile plays a critical role in determining the reflection bandwidth, average reflectance, and the band edge. The results could be widely utilized in applications of a variety of nanophotonic devices and their integration, as well as facilitate the design of the fabrication process on how to control the degree of tapered sidewall profile for the integrated subwavelength grating nanophotonic devices.

^{A new design of all-normal and near-zero flattened dispersion based on chalcogenide nanophotonic crystal fiber (PCF) has been proposed to generate smooth and ultra-broadband supercontinuum (SC) in the midinfrared (IR) region. With the optimized geometric parameters, the As₂Se₃ nano-PCF has been found to be suitable for two-octave supercontinuum generation (SCG). We designed a nano-PCF having a flat top dispersion curve with a maximum value of −2.3 [ps/(nm km)] and a large nonlinear coefficient equal to 7250 (W km) −1 around the wavelength of 5.24  μm. By numerical simulations, we predict the generation of a very broadband SC in the mid-IR region extending from 2 to 10  μm in only 2-mm fiber lengths by using a femtosecond laser having a full-width at half-maximum of 50 fs and a relatively low energy of E=80  pJ. The generated SC demonstrates perfect coherence property over the entire bandwidth. SC generation extended into the mid-IR spectral region has potential usefulness in a variety of applications requiring a broad and mid-IR spectrum, such as WDM sources, fiber sensing, IR spectroscopy, fiber laser, and optical tomography coherence.}

Multiple p- and s-polarized compound surface-plasmon-polariton (SPP) waves at a fixed frequency can be guided by a structure consisting of a metal layer sandwiched between a homogeneous isotropic dielectric (HID) material and a periodic multilayered isotropic dielectric (PMLID) material. For any thickness of the metal layer, at least one compound SPP wave must exist. It possesses the p-polarization state, and is strongly bound to the metal/HID interface when the metal thickness is large but to both metal/dielectric interfaces when the metal thickness is small. When the metal layer vanishes, this compound SPP wave transmutes into a Tamm wave. Additional compound SPP waves exist, depending on the thickness of the metal layer, the relative permittivity of the HID material, and the period and composition of the PMLID material. Some of these are p-polarized, the others are s-polarized. All of them differ in phase speed, attenuation rate, and field profile, even though all are excitable at the same frequency. The multiplicity and dependence of the number of compound SPP waves on the relative permittivity of the HID material when the metal layer is thin could be useful for optical sensing applications and intrachip plasmonic optical communication.

Random textures have proven to be a better option for light localization and energy harvesting in solar cells. On the other hand, plasmonic structures are significant in localizing the fields into submicron domains. We propose a layered structure design that contains the random dielectric medium with a plasmonic nanopillars array as a back reflector, followed by demonstrating its efficient light trapping ability through simulation means. This structure has shown significant enhancement in the broadband absorption of the light spectrum in the wavelength range UV-IR and a higher extinction in the near-infrared wavelengths. The structure also shows the dependence of reflection on the nanopillar height as well as localization in the nanopillar region. The broadened and red shifted plasmonic nanopillar resonances (transverse and longitudinal) in a high-index medium are shown as the reasons for enhanced broadband absorption.

Surface-patterning technologies have enabled the improvement of currently existing light-emitting diodes (LEDs) and can be used to overcome the issue of low quantum efficiency of green GaN-based LEDs. We have applied nanosphere lithography to fabricate nanopillars on InGaN/GaN quantum-well LEDs. By etching through the active region, it is possible to improve both the light extraction efficiency and, in addition, the internal quantum efficiency through the effects of lattice strain relaxation. Nanopillars of different sizes are fabricated and analyzed using Raman spectroscopy. We have shown that nanopillar LEDs can be significantly improved by applying a combination of ion-damage curing techniques, including thermal and acidic treatment, and have analyzed their effects using x-ray photoelectron spectroscopy.

We have proposed a design for slow light with ultraflat dispersion in a slotted photonic crystal waveguide consisting of a hexagonal arrangement of elliptical air holes on a silicon-on-insulator substrate. The proposed structure has low group velocity and low group velocity dispersion with a wide normalized bandwidth range of 0.0089. The proposed structure can be used as an optical buffer for the storage of a large amount of data due to the large value of the normalized delay bandwidth product equal to 0.634. An optimized structure for a slotted photonic crystal has been analyzed for its applications as both a time and wavelength division demultiplexer. Furthermore, the time delay between two adjacent wavelengths (1550 and 1555 nm) is more than that reported earlier.

We consider the multiphoton dynamics of a quantum system composed of a three-state atom (a qutrit) and a single-mode photonic field in the ultrastrong and deep strong coupling regimes, when the coupling strength is comparable to or larger than the oscillator energy scale. We assume a qutrit to be in a L configuration, where an upper level is coupled to a twofold degenerate lower level. Direct multiphoton resonant transitions revealing generalized Rabi oscillations, collapse, and revivals in atomic excitation probabilities for the ultrastrong couplings are studied. In the deep strong coupling regime, particular emphasis is placed on the ground state of the considered system which strictly exhibits nonclassical properties.

We report the observation of a supercontinuum (SC) in aqueous CdTe/ZnSe quantum dots (QDs) pumped by 800-nm femtosecond laser pulses based on simulations and experiments. For an average nanocrystal of 5.5 nm in size and a weight concentration of 5  mg/mL, the SC generated with a low-input energy range exhibits high optical to optical conversion efficiency. The measured SC spectrum exhibits spectral broadening that is significantly influenced by the nonlinear coefficient of the QDs. This nanoparticles-based SC effect may have special applications for optical coherence imaging and ultrashort pulse compression.

Our present work proposes a systematic geometric model comprising vertical dual silver nanostrips placed on the top of a thin-film amorphous silicon solar cell. In the first layer, cylindrical silver nanostrips are embedded in the antireflection coating and the other one is placed just above it. Combining the two improves the absorption over the wide spectral range. A finite-difference time domain technique has been used to confirm that a vertical dual silver nanostructure improves absorption over a broad spectrum in comparison to a single layer. Size, shape, and interspacing of the nanostructures have been tuned to obtain the preeminent results. This optimized geometry gives a total quantum efficiency of 32.02% under AM1.5G.

Nanopatterns resulting from two-beam interference in single, double, and multiexposures were simulated. Several patterns were experimentally fabricated to compare with the simulated patterns, allowing judgment of the quality of the simulation tool. Experimental and simulation results were consistent for single and double exposures. Photoresist nanofibers attached and detached from the substrate were fabricated with few changes in the development process. Results show that by increasing the number of exposures, a wide variety of patterns with very fine structures and sophisticated geometries can be generated. Fresnel-lens type structures are formed when the number of exposures is increased. These Fresnel-like patterns might have potential use in obtaining radial and azimuthal polarizations and optical vortices in addition to areas such as security patterns and diffractive optical elements.

Tb³⁺-doped glasses are promising materials for green lasers working at a UV-excitation light. It is essential to find a commercially low-cost host with high quantum efficiency in the visible region. We report the preparation and optical characterization of a thermally stable and optically transparent phosphate glass containing silver nanoparticles with nominal composition 57P₂O₅-40(ZnO-PbO)-2Tb₂O₃-1AgNO₃ (mol%) obtained by a melt-quenching technique and subsequent heat-treatments. The glasses are transparent in UV to near-infrared region and are not hygroscopic at ambient environment. The optical absorption and luminescence excitation spectra of the samples with and without silver nanoparticles are identical, and no sign of any silver species is revealed, while the luminescence spectrum is enhanced up to 1.7 times after heat-treating the samples for 15 h. The transmission electron microscopy and selected area diffraction pattern of glasses show the presence of silver nanoparticles with an average size of ∼15  nm and growth at [200] crystallographic direction. The lifetime of the ⁵D₄ state of Tb³⁺ ions decreases from 3.06 to 2.85 ms by increasing the heat-treatment duration, which is indicative of the plasmonic effect of nanoparticles on the radiative rates of Tb³⁺-doped glasses.

Electronic properties and intersub-band optical transition energies are studied in group II to VI wide band gap semiconductors taking into account the geometrical confinement of the core and shell materials. ZnS/CdS, ZnS/CdSe, and CdS/CdSe are some group II to VI core/shell semiconducting materials, which are considered in the present work. The effects of internal electric field, due to spontaneous and piezoelectric polarization, are taken into consideration in the calculations. The dielectric-mismatch effect and the position-dependent effective mass are included in the Hamiltonian. The electronic properties are studied using the variational method and the optical properties are considered using the density matrix approach. All the properties are discussed for various ratios of core and shell radii of the materials in the strong confinement region. The effect of geometrical confinement on the Coulomb interaction energies in the core/shell materials is found. The oscillator strength is computed for these core/shell materials and the optical absorption coefficient as a function of photon energy is investigated in the strong and weak confinement regions. The result shows that the electronic and optical properties are dominant in the strong confinement region.

A structure for entangled photon generation via polariton-polariton scattering is proposed. We have designed an air-gap planar cavity with embedded quantum wells, in which the photonic modes are in strong coupling regime with excitons of quantum wells. An electrical tuning mechanism is designed by introducing an air-gap layer and an integrated electrical actuator to the distributed Bragg reflector (DBR) mirror structure. Our structure consists of 40 (17) bottom (top) DBRs with 12  GaAs/AlAs (7/3  nm) quantum wells at the antinodes of the electromagnetic field working at 767-nm wavelength. Initial air-gap thickness is 1500 nm. The Q factor and Rabi splitting of the structure are 1742 and 14 meV, respectively. Reflectivity of cavity/air interface is 0.32, and suspended DBR reflectivity is 0.97. Average indices of suspended mirror and cavity are 3.2062 and 3.1901, respectively. According to our simulation results, by changing air-gap thickness from 1000 to 1350 nm, the wavelength tuning range is extended to 30 nm via applying a maximum voltage of 12 V.

Based on numerical experimental techniques, we demonstrate the possibility to control light by light in nonlinear arrays of subwavelength dielectric parallel waveguides. To reach our goal, we work with waveguides of different cross sections: circular and square. Characteristic dimensions of waveguides are in the order of half of the carrier wavelength, and propagation distances are more than hundreds of wavelengths. We show that with the proper selection of parameters it is possible to obtain light self-trapped in a single waveguide that will allow us to study the optical fields’ interaction in the array. The main result that we discuss here is that we can control the light output position for two input beams. The light behavior is a function of the phase difference and incidence angle, as well as the light power at the input of the array.

II-VI colloidal quantum dots (QDs) are ideal for optical sensors thanks to their high fluorescent brightness and good size uniformity. However, embedding colloidal QDs into a glass matrix with the standard sol-gel process leads to the QDs being damaged by the acid catalyst. Here, we report an acid-free sol-gel technique, which proves to be both simple and effective in fabricating silica glass thin films embedded with commercial II-VI colloidal QDs. Octadecylamine ligands are used as a bifunctional aid to not only stabilize the QDs in solution, but also assist the formation of the SiO₂ gel. We demonstrate that high-quality QD-embedded glass thin films can be developed with this technique, and our fluorescent tests indicate that, except for a small blueshift in the emission spectrum, the QDs are very well preserved through the sol-gel process. This method offers a fast and low-cost path towards thin-film QD sensors with good mechanical and thermal stabilities, which are desirable for applications involving highly focused laser beams, such as ultrafast nanophotonics.

We present the design of a photonic crystal fiber which promises to yield very large optical nonlinearity ∼151  W⁻¹  km⁻¹ at 1.55  μm wavelength. The fiber possesses two zero dispersion points whose locations can be tuned by varying the air hole diameter and hole pitch. The fiber dispersion is anomalous between these two zero dispersion points and its value is moderate. The fiber has been used to numerically simulate optical supercontinuum (SC) generation using low power pump pulses of 50 fs duration at a 1.55-μm wavelength. At the end of 15-cm fiber, SC broadening of about 1200 and 1700 nm can be achieved with pulses of 1 and 5 kW peak power, respectively.

The photorefractive effect in metal-insulator-metal (MIM) plasmonic waveguides is modeled and investigated for both symmetric and asymmetric structures. A metal-LiNbO₃-metal nanostructure with different top and bottom metals is proposed as a plasmonic waveguide. Three different metals, aluminum, gold, and silver, are used as the metals of the plasmonic waveguide and the photorefractive effect is investigated in different structures. The interaction between interfering surface plasmonic polariton modes is studied. It is shown that a strong mode can be coupled to a weak mode by means of the photorefractive effect. It is found that compared with conventional symmetric MIM plasmonic waveguides, an asymmetric structure with different metals, silver-LiNbO₃-gold for example, has a higher photorefractive gain and longer propagation distance, and there is a net photorefractive gain. The effect of the crystal thickness and amplitude inputs is also analyzed. It is found that there is an optimum crystal thickness that yields the maximum photorefractive gain.

SiN composite nanostructures (CNs), composed of SiN nanorods and the underlying SiN film, are formed on Si substrate through SiN deposition, nanosphere lithography, and dry etching. The antireflection performance of Si samples decorated by the SiN CNs with different morphology is experimentally investigated. All the SiN CNs decorated Si samples exhibit antireflection over 300 to 1000 nm and a wide view. Their antireflection performance varies with the height of the nanorods (H) and the thickness of the underneath film (T). A reflectivity of less than 10% over 300 to 1000 nm and an incident angle of 8 deg and 65 deg are achieved in the optimal antireflection structures with H=240  nm, T=750  nm and H=500  nm, T=300  nm, respectively. Furthermore, antireflection behavior in the SiN CNs decorated Si sample with H=500  nm, T=300  nm is compared with that in Si samples decorated by 565- and 60-nm thick SiN film. A weighted reflectance of about 5% is achieved in an SiN CNs decorated Si sample in any incident angle, which is much lower than that in any SiN film coated Si sample. Moreover, such a performance is beyond the limitation of interface reflectivity of Si and SiN materials, and should benefit Si solar cells to simultaneously enhance the absorption and surface passivation.

We report the experimental observation of multiple Bragg diffraction that occurs when the tip of the incident wave vector lies on a line joining the L and W points in the Brillouin zone of a face-centered cubic (FCC) photonic crystal. The multiple Bragg diffraction is analyzed for photonic crystals with different lattice constants and refractive index contrasts. Angle-dependent reflectance spectroscopy indicates strong hybridization of diffraction resonances when the tip of the incident wave vector crosses the W point and the multiple Bragg diffraction is seen to be extended over an angular range of 8 deg around the W point. We also observe a new diffraction resonance in the short-wavelength region for wave vectors shifting toward the W point in the hexagonal facet of the FCC Brillouin zone. Each diffraction resonance is fitted using the Bragg’s law for different planes in the FCC photonic crystal taking into account the internal angle between the planes. The diffraction resonances in the multiple Bragg diffraction regime are assigned to FCC crystal planes with Miller indices (111), (200), (1¯11), and (220). Our results have implications for diverse kinds of wave propagations in periodic structures and applications in light emission, sensing, and structural color pigments.

We investigate the dielectric response, the optical conductivity, and the plasmon spectrum of a two-dimensional electron gas with Rashba and Dresselhaus spin–orbit (SO) interaction. Using the self-consistent field approach, we derive expressions for the dispersion relations of the intra- and inter-SO plasmons. We found that the latter is immersed within the continuum of inter-SO single-particle excitations. The intra-SO plasmons remain undamped and almost unaffected by the SO coupling. The longitudinal optical conductivity shows, however, a dependence on the direction of the externally applied potential, caused by the anisotropic splitting of the spin states. In addition to the control through the driving frequency or electrical gating, this new aspect of the optical absorption spectrum might be useful in spintronics applications.

The epitaxially grown system comprising semimetallic ErAs (erbium arsenide) nanoparticles (MNP) and InAs (indium arsenide) single quantum dots (QDs) hold great promise for plasmonic applications. The distinguishing feature of the ErAs-InAs hybrid is that the hybrid separation can be varied and accurately controlled in the molecular-beam epitaxial growth. In order to assess the potential of this system for plasmonic applications, this paper aims to estimate and optimize the expected magnitude of the plasmonic enhancement. We use the Sun–Khurghin theory to estimate the expected absorption and photoluminescence (PL) enhancement. Using a carefully selected set of materials’ parameters as input, we predict about 500-fold plasmonic PL enhancement for this system under resonant conditions.

We report research results with regard to AlGaAs/GaAs structure processing for THz quantum-cascade lasers (QCLs). We focus on the processes of Ti/Au cladding fabrication for metal–metal waveguides and wafer bonding with indium solder. Particular emphasis is placed on optimization of technological parameters for the said processes that result in working devices. A wide range of technological parameters was studied using test structures and the analysis of their electrical, optical, chemical, and mechanical properties performed by electron microscopic techniques, energy dispersive x-ray spectrometry, secondary ion mass spectroscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, and circular transmission line method. On that basis, a set of technological parameters was selected for the fabrication of devices lasing at a maximum temperature of 130 K from AlGaAs/GaAs structures grown by means of molecular beam epitaxy. Their resulting threshold-current densities were on a level of 1.5  kA/cm². Furthermore, initial stage research regarding fabrication of Cu-based claddings is reported as these are theoretically more promising than the Au-based ones with regard to low-loss waveguide fabrication for THz QCLs.

We propose a method under the effective mass approximation with an original formulation that applies to quantum wells, circular quantum wires, and spherical quantum dots of arbitrary materials with sizes as small as 1 nm. Hundreds of structures are resolved on the second scale on a laptop, allowing for optimization procedures. We demonstrate its capability by confronting bandgap calculations with exhaustive literature data for CdS, CdSe, PbS, and PbSe nanoparticles. Our approach includes a correction of the mass to address the nonparabolicity of the band structure. The correction gives an accuracy comparable to more demanding calculation methods, such as eight-band k·p, tight-binding, or even semiempirical pseudopotential methods. The effect of the correction is shown on the intrasubband optical properties of InGaAs/AlGaAs coupled quantum wells.

Water-soluble cadmium sulfide (CdS) nanoparticles were synthesized through aqueous thermochemical method using thioglycolic acid as a capping agent. The resulting CdS nanoparticles were characterized using x-ray diffraction, field-emission scanning electron microscopy, ultraviolet–visible, and photoluminescence spectroscopy. The CdS prepared has been used as an electron transport layer (ETL) in a polymer light-emitting diode (PLED) with the structure of poly(ethylene terephthalate)/indium tin oxide/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate/poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene/CdS/aluminium (PET/ITO/PEDOT:PSS/MEH-PPV/CdS/Al). The performance of the fabricated device containing CdS nanoparticles as an ETL was compared with the device with the structure of PET/ITO/PEDOT:PSS/MEH-PPV/Al. According to the obtained results, it was shown that the ETL yields a higher current and lower turn-on voltage. The improvement was ascribed to the step barrier theory and hole blocking effect of the CdS layer. These results show that the CdS layer could be very useful in the fabrication of efficient PLEDs.

To understand a terahertz (THz) response of a point contact device, a number of samples based on CdTe/CdMgTe quantum wells grown by a molecular beam epitaxy were investigated at low temperatures and high magnetic fields. The experiments involved magneto-transport, photocurrent, and transmission measurements carried out with monochromatic THz sources or a Fourier spectrometer. Samples of different geometry with and without gate metallization were used. We observed excitations of a two-dimensional electron plasma in the form of optically induced Shubnikov-de Haas oscillations, cyclotron resonance transitions, and magneto-plasmon resonances. A polaron effect was observed at magnetic fields higher than 10 T. A point contact device processed with an electron beam lithography was investigated as a detector of THz radiation. It was shown that the main mechanism responsible for a THz performance of the point contact was excitation of magneto-plasmons with a wavevector defined by geometrical constrictions of the device mesa.

We analyzed the temporal responses of biological cells in the jumping optical tweezers for tugging, wiggling, and stretching the cells in the time-sharing regime with the finite-element method. We showed that the jumping of local stress and local strain is independently omnipresent on the recovery time of the viscoelastic material and the jumping frequency of the load. We demonstrated that the elongation of a three-dimensional (3-D) viscoelastic object under a jumping load cannot be evaluated using the one-dimensional spring-dashpot material model without considering its 3-D structure.

Recently, the principle of flat focusing based on one-dimensionally chirped dielectric mirrors has been proposed and experimentally demonstrated. The flat chirped mirror causes anomalous diffraction of the beam during reflection, opposite to the normal diffraction in free space propagation. The anomalous diffraction compensates the normal diffraction of the beam resulting in focusing after reflection. For a better focusing performance and for a larger near-field focal distance, a stronger anomalous diffraction is required. We show that the anomalous diffraction can be enhanced by introducing a defect layer in the chirped mirror, as the structure becomes similar to a Gires–Tournois interferometer. The focal distance can be substantially increased due to the defect layer. In our specific structure, the focal distance shows an increase from 19 to 39  μm, numerically.

The major challenge for semiconductors to achieve temperatures below 10 K by luminescence upconversion, is that at these lattice temperatures the acoustic phonon component dominates and the scattering rate becomes comparable to the band-to-band radiative transition rate. This problem can be significantly alleviated by employing quantum-confined systems, where relaxation of wave-vector conservation in the confined direction reduces material conductivity by nearly three orders of magnitude. Although previous studies have reported theoretical and experimental analyses of cooling characteristics for bulk semiconductors, the electron band-to-band transition due to photon absorption or photon emission under cooling conditions in quantum-confined semiconductor systems which exhibit quantum effects at the dimensions of several nanometers have not been completely analyzed in conventional theoretical studies. We realized a numerical investigation of optical cooling conditions for a low-dimensional CdS/CdTe multiple-quantum well heterostructure where injected carriers in the active region are quantum mechanically confined in one dimension. Effects of such quantum mechanically confined carriers on photon absorption and photoluminescence (PL) were analyzed under cooling conditions. Most importantly, the CdS/CdTe heterostructure absorption and PL spectra for cooling conditions were defined in terms of the active layer width and number of quantum wells in the complete heterostructure.

An enhancement in photonic band-edge-induced absorption and emission from rhodamine-B dye doped polystyrene pseudo gap photonic crystals is studied. The band-edge-induced enhancement in absorption is achieved by selecting the incident angle of the excitation beam so that the absorption spectrum of the emitter overlaps the photonic band edge. The band-edge-induced enhancement in emission, on the other hand, is possible with and without an enhancement in band-edge-induced absorption, depending on the collection angle of emission. Through a simple set of measurements with suitably chosen angles for excitation and emission, we achieve a maximum enhancement of 70% in emission intensity with band-edge-induced effects over and above the intrinsic emission in the case of self-assembled opals. This is a comprehensive effort to interpret tunable lasing in opals as well as to predict the wavelength of lasing arising as a result of band-edge-induced distributed feedback effects.

We realize near-perfect absorption with a metallic grating and dielectric substrate. The simulation results show that such near-perfect absorption results from the cavity mode resonance and surface plasmonic polaritions excitation. The absorption peaks can be tuned by changing the geometric parameters or refractive indices of the surrounding materials. When the refractive index of the superstratum is smaller than that of the substrate, one can attain near-perfect absorption with a single-layer metallic grating. The simulation results also show that the absorption peak can be tuned by increasing the incidence angle.

We present our results on the linear and nonlinear optical properties of cobalt nanoparticles synthesized by laser ablation in different organic solvents. Transmission electron microscopy and UV-visible absorption were used for the characterization of morphology, size distribution, and optical properties, respectively. Nonlinear scattering and nonlinear absorption are regarded as the processes contributing to the observed optical-limiting behavior in these nanoparticles, which were investigated by performing Z-scan measurements. Due to strong two-photon absorption and nonlinear scattering, cobalt nanoparticles dispersed in chlorobenzene and chloroform exhibit superior optical-limiting threshold when compared with other solvents.

The closeness of the experimental and theoretical values enables the development of an in situ characterization technique to monitor and analyze the production of gold nanoparticles (NPs), overcoming the use of high-end and expensive instrumentation. Gold NPs below the radius size of 10 nm were successfully synthesized in accordance with a few working parameters of pulse laser ablation in a liquid technique. In this report, the size, shape, concentration, and aggregation properties of gold NPs were estimated by the Mie–Gans model based on a reliable and interactive real-time absorption spectroscopy. The major features can be an important means toward determination of efficient process measures, productivity of gold NPs generated, and efficiency of the mass ablation rate. The accuracy in the measurement is confirmed via transmission electron microscopy analysis.

The present study examines the stability and cytotoxicity of two quantum dots (QDs) systems in cell culture medium in the presence and absence of a thin layer of a ZnS shell. The two systems were built from a core, CdSe, and surface modified with glutathione (GSH), named CdSe∼GSH and CdSe/ZnS∼GSH. CdSe/ZnS∼GSH QDs exhibited a high photostability with a pronounced enhancement in photoluminescence in cell culture medium. Both systems showed insignificant reduction in cell viability of HFB-4 and MCF-7 cell lines in the dark. Following 60 min of low laser power exposure (irradiance of 10  mW cm−²), CdSe∼GSH QDs showed a remarkable decrease in cell viability, which may result from the detachment of GSH molecules, whereas CdSe/ZnS∼GSH QDs showed an insignificant decrease either immediately after irradiation or even 2 h post-exposure, which can be attributed to the high affinity between ZnS and GSH coatings. This study demonstrated that a thin layer of ZnS shell played a crucial role in the stability of CdSe/ZnS∼GSH QDs in cell culture medium with an improvement in luminescence efficiency, whereas surface modification with GSH molecules in the presence of ZnS showed no significant cytotoxic effects before or after photoirradiation, which makes this system attractive for several biomedical applications.

A photoanode consisting of hydrothermally synthesized TiO₂ nanotubes (TNT) and TiO₂ nanoparticles (TNP) was designed for efficient charge collection in dye-sensitized solar cells. TNT and TNP films were fabricated on a conductive glass substrate by using electrophoretic deposition and doctor-blade methods, respectively. The TNP, TNT, and TNT/TNP bi-layer electrodes exhibit solar cell efficiencies of 5.3, 7.4, and 9.2%, respectively. Solar cell performance results indicate a higher short-circuit current density (J_sc) for the TNT/TNP bi-layer electrode when compared to a TNT or TNP electrode alone. The open-circuit voltages (V_oc) of TNT/TNP and TNT electrodes are comparable while the V_oc of TNP electrode is inferior to that of the TNT/TNP electrode. Fill factors of TNT/TNP, TNT, and TNP electrodes also exhibit similar behaviors. The enhanced efficiency of the TNT/TNP bi-layer electrode is found to be mainly due to the enhancement of charge collection efficiency, which is confirmed by the charge transport parameters measured by electrochemical impedance spectroscopy (EIS). EIS analyses also revealed that the TNT/TNP incurs smaller charge transport resistances and longer electron life times when compared to those of TNT or TNP electrodes alone. It was demonstrated that the TNT/TNP bi-layer electrode can possess the advantages of both rapid electron transport rate and a high light scattering effect.

Silver (Ag) nanoparticles (NPs) were synthesized and used as an interfacial layer in the photoanode of quantum dot sensitized solar cells (QDSSCs). Two different methods were employed to determine the size and shape of the Ag NPs. Using transmission electron microscopy images and calculations based on Mie theory, a size of 5 nm and a spherical shape were obtained for the sensitized Ag NPs. Then these NPs were applied in a fluorine-doped tin oxide (FTO)/Ag/TiO₂/CdS photoanode structure in the QDSSCs. As an interfacial layer, Ag NPs were dip-coated on FTO between an FTO glass and a TiO₂ layer. A successive ionic layer adsorption and reaction method was used for deposition of CdS quantum dots on the TiO₂ films. A power conversion efficiency of ∼1.45% was obtained for FTO/Ag/TiO₂/CdS cells, which was ∼40% higher than ∼1.05% found for noninterfacial layer FTO/TiO₂/CdS cells. The easier transport of excited electrons and the inhibition of charge recombination due to the application of an Ag NPs layer are concluded to be responsible for the improved performance of the cells and their increased photocurrent.

A nanostructured poly (o-toluidine)/silicon nanowires (NPOT/SiNWs) heterojunction has been fabricated with a low cost and simple techniques, where NPOT has been in situ polymerized upon SiNWs synthesized by chemical etching of a silicon wafer. The morphology of SiNWs before and after deposition of NPOT has been examined by scanning electron microscope (SEM). The chemical composition of NPOT has been investigated by Fourier transform infrared (FTIR), ultraviolet-visible (UV-visible) spectroscopy, and X-ray diffraction (XRD) techniques. NPOT morphology has also been examined by SEM before being deposited on the SiNWs. I-V measurements of the device have been made at room temperature under dark conditions. The heterojunction diode parameters such as turn-on voltage, reverse saturation current (I₀), ideality factor (η), barrier height (Φ_B) and series resistance (R_s) have been determined from the I−V curves using Schottky equations. The device shows promising characteristics as a candidate for producing heterojunction diodes.

The purpose of this study was to explore the use of surface-enhanced Raman spectroscopy (SERS) to image the distribution of epidermal growth factor receptor (EGFR) in cells. To accomplish this task, 30-nm gold nanoparticles (AuNPs) tagged with antibodies to EGFR (10¹²  per mL) were incubated with cells (10⁶  per mL) of the A431 human epidermoid carcinoma and normal human bronchial epithelial cell lines. Using the 632.8-nm excitation line of a He-Ne laser, Raman spectroscopy measurements were performed using a point mapping scheme. Normal cells show little to no enhancement. SERS signals were observed inside the cytoplasm of A431 cells with an overall enhancement of 4 to 7 orders of magnitude. Raman intensity maps of the 1450 and 1583  cm−¹ peaks correlate well with the expected distribution of EGFR and AuNPs, aggregated following uptake by endosomes and lysosomes. Spectral features from tyrosine and tryptophan residues dominate the SERS signals.

A straight hybrid plasmonic waveguide (HPW) with concentric nanoring and nanodisk is numerically investigated based on a three-dimensional finite-difference time-domain method. It shows that the straight HPW and the nanoring with variational geometry parameters possess different coupling efficiencies at the telecommunication wavelengths. With different coupling processes, effective coupling can be achieved which provides a way to achieve optimal transmittance. Under an appropriate geometry parameter regime, the HPW could simultaneously offer a large split ratio and provide subwavelength field confinement and long propagation distance. The wavelength responses show that the HPW has good wavelength toleration around 1550 nm, indicating that it may be employed as an optical device with the desired performance for optical communications.

We derive an equation for the differential cross-section dσ/dΩ of reflected electrons by using Electron Mirror method. The mathematical derivation of differential cross-section equation is based on the Rutherford scattering model as well as the equation of electric potential difference. We describe the interaction of focused electron beams with a polyethylene terephthalate sample using focused ion beam-scanning electron microscope electron mirror image. The electron differential cross-section dσ/dΩ for different working distances h=33, 20, and 10 mm, with a scattering angle θ ranged from 10 deg to 55 deg, incident electrons energies η=500, 750, and 1000 eV, and scanning potential Δφ ranged from 1 to 2 kV has been calculated. According to our findings, the differential cross-section dσ/dΩ of reflected electrons decreases with increasing scattering angle θ and the working distance h and is directly proportional to the difference potential Δφ and the energy of incident electrons η. Distort the electron mirror images with increased Δφ.

Functional optical metamaterials usually consist of absorbing, anisotropic, and often noncentrosymmetric structures of a size that is only a few times smaller than the wavelength of visible light. If the structures were substantially smaller, excitation of higher-order electromagnetic multipoles in them, including magnetic dipoles, would be inefficient. The required non-negligible size of metamolecules, however, makes the material spatially dispersive, so that its optical characteristics depend on the light propagation direction. We consider the possibility to use this usually unwanted effect. We present a theoretical model that allows one to study the interaction of such spatially dispersive metamaterials with optical beams. Applying the model, we show that a strong spatial dispersion, combined with optical anisotropy and absorption, can be used to efficiently control propagational characteristics of optical beams and create new types of optical elements.

This paper presents an investigation of broadband supercontinuum (SC) generation in photonic crystal fibers using cosh-Gaussian optical pulses. It is found that the SC spectra of these cosh-Gaussian pulses are composed of several internal oscillations. The number of the oscillations increases with an increase in the value of the cosh parameter Ω₀. The internal structure of the SC spectra shows an asymmetric behavior, possessing fewer oscillations as we move from the lower to higher wavelength region. Our results indicate that the SC generation dynamics is dominated by self-phase modulation.

A plasmonic sensor based on a metal–insulator–metal waveguide with a side-coupled nanodisk resonator is proposed and numerically investigated using a finite-difference time-domain method. The numerical simulation results indicate that more than one sharp resonance dip appears in the transmission spectrum in the telecommunication regime, and each resonance wavelength has a linear relationship with the refractive index of the dielectric in the resonator. In addition, the sensing characteristics of the structure and the influence of its structural parameters are analyzed in detail by investigating the transmission spectra. As a refractive-index sensor, its sensitivity can reach as high as 1150 nm per refractive index unit near the resonance wavelength of 1550 nm, and its sensing resolution can reach 10−⁶ for a wavelength resolution of 0.01 nm. Furthermore, by employing the relationship between the temperature and the refractive index, the temperature-sensing characteristics of the structure are also discussed. Near the resonance wavelength of 1550 nm, the temperature sensitivity can reach 0.45  nm/°C. The sensor has a compact and simple structure and may find many potential and important applications in optical networks-on-chip and on-chip nanosensors.

This PDF file contains the editorial “Special Section Guest Editorial—Nanostructured Thin Films: Evolving Perspectives” for JNP Vol. 9 Issue 01

The effect of varying the main and local field on the partial discharge characteristics of polypropylene film is studied by analyzing the temporal behavior of partial discharge parameters. In the first set of experiments, keeping the applied voltage constant, the gap spacing is varied altering the applied field. When the gap is relatively small, discharges appear in quick succession deepening the craters in front of the rod tip where space charges are widely distributed, precipitating discharges of wide range of amplitudes. At relatively larger spacing, the discharge behavior is largely controlled by electric field distribution. In the fixed gap experiments, the local field is varied by introducing polymer nanocomposites that have different filler content. For a fixed gap and constant voltage, discharge magnitudes are lower in samples with nanofiller content below the percolation threshold than in the base polymer. The scatter in discharge magnitudes is lower in samples with nanoparticle content below the percolation threshold than in samples with nanofiller content above the threshold. The major conclusion is the maximum advantage of adding nanofillers is gained only when the particle content is below the percolation threshold.

In practical power apparatus, the insulation under high electrical stress is exposed to recurrent partial discharge pulses, and the utility of the insulation is largely determined by its resistance to aging by partial discharges. The occurrence of partial discharges is largely governed by a combination of the applied field and the space charges that are generated due to these discharges. Since the space charge profile generated by a time-varying voltage and, thus, the resultant field would be much different from that of a constant ac voltage, this work investigates how the partial discharge characteristics, the resulting erosion, and remnant breakdown strength change when samples are aged with a step voltage profile. Since incorporation of nanofillers in controlled quantities is known to alter the space charge formation and transportation, this work also focuses on understanding the effect of incorporation of different quantities of natural (cloisite 20 A° natural montmorillonite clay) and synthetic (tetrasilisic fluro mica) nanofillers into a pure polypropylene matrix on its partial discharge characteristics and the resulting effect when aged under the application of step voltages. Isotactic polypropylene films with different filler concentrations of natural and synthetic nanofillers were aged. The cumulative effect of the partial discharge behavior was investigated through analysis of the erosion depth produced by these pulses on sample surface and remnant breakdown strengths of aged samples. Results indicate that maximum partial discharge magnitudes become prominently lower in nanofilled samples as compared to that of base polypropylene only when the applied voltage is beyond a certain level. Up to that voltage, the average discharge magnitude is significantly lower in samples whose filler content is below a percolation threshold, but above that voltage, the average magnitude depends on the aspect ratio of the nanofillers. Partial discharge resistance and characteristic breakdown strength increases with increase in filler content in both types of nanofilled samples, but excessive filler content is not effective in enhancing these parameters.

Oxide materials of desired stoichiometry are challenging to make in small quantities. Nanostructured thin films of multiple oxide materials were obtained by using pulsed laser deposition and multiple independent targets consisting of Si, BaTiO₃, and B. Programmable stoichiometry of nanostructured thin films was achieved by synchronizing a 248-nm krypton fluoride excimer laser at an energy of 300  mJ/pulse, a galvanometer mirror system, and the three independent target materials with a background pressure of oxygen. Island growth occurred on a per pulse basis; some 500 pulses are required to deposit 1 nm of material. The number of pulses on each target was programmed with a high degree of precision. Trends in material properties were systematically identified by varying the stoichiometry of multiple nanostructured thin films and comparing the resulting properties measured using in situ spectroscopic ellipsometry, capacitance measurements including relative permittivity and loss, and energy dispersive spectroscopy (EDS). Films were deposited ∼150 to 907 nm thickness, and in situ ellipsometry data were modeled to calculate thickness n and k. A representative atomic force microscopy measurement was also collected. EDS, ellipsometry, and capacitance measurements were all performed on each of the samples, with one sample having a calculated permittivity greater than 20,000 at 1 kHz.

The properties of chiral photonic crystals with a pitch gradient were investigated both experimentally and theoretically. The liquid-crystalline cell was prepared by bringing two cholesteric liquid crystals (CLCs) with different pitches into contact. There are some essential features in the dynamics of diffusion between the two CLCs. The most important feature is the fact that establishing the final equilibrium pitch (for the temperatures below 17°C) takes a long time—roughly 3 months or more—which, in turn, allows us to investigate the nonstandard change in the reflection spectra during the diffusion. The two reflection curves do not directly actually get closer and merge into one peak, as usual, but the left one gradually gets smaller and almost vanishes, and the right one expands. For this reason, a theoretical model of a pitch change was developed and it was seen that this model does not coincide with the classical ideas of the pitch change. It was also assumed that due to the “freezing” effect during the diffusion process, one could have fixed the intermediate states of the pitch gradient.

The paper reports investigation of a rather new type of optical fiber composed of three layers with the outermost region being radially anisotropic liquid crystal material, and the inner two regions as linear, homogeneous, and isotropic dielectrics. As such, the anisotropy remains in the outermost section of fiber. The core–clad interface of the inner dielectric regions is assumed to be loaded with conducting tape helix structure. It has been found that the width of the tape as well as the helix pitch angle are the effective parameters to govern the dispersion characteristics. Taking into account the zero-order guided modes, the effects on confinements due to the amalgamation of birefringence (optical property of liquid crystal) and tape helix pitch (geometrical/structural property of perfect conductor) are reported. The obtained results are compared with the case of a conducting sheath helix loaded liquid crystal fiber structure, and it has been found that the conducting tape helix loadings would be more useful than the sheath helix loaded fibers.

The excitation of multiple surface-plasmon-polariton (SPP) waves and waveguide modes was experimentally demonstrated in a structure fabricated as a one-dimensional photonic crystal (PC) on top of a two-dimensional metal grating. The PC had two periods, each period comprising nine layers of silicon oxynitrides of different compositions. The individual excitations of the SPP waves and waveguide modes were also theoretically predicted using the Floquet theory, surface-multiplasmonics theory, and the transfer–matrix approach for multilayered waveguides. Both the theoretical and experimental results indicate broadband coupling of incident light of either linear polarization state to the guided waves of both types over a broad range of the angle of incidence.

Thanks to progress in material science and nanotechnologies, surfaces and thin films can now be structured at different scales. Photonics components take advantage of this possibility to fulfill still more and more complex functions. They are composed of organic and inorganic materials, dielectrics, semiconductors, and metallic materials, or a mixture of them. Multiscale and chiral structures can be used to control both spectral and spatial distributions of light together with its polarization state. The optical mode density in the near field and in the far field can then be designed in particular by combining more or less resonant structures for the optical waves, associating diffraction, interferences, and anisotropic structures like Fabry–Perot, waveguide, plasmons, and photonic crystals. Artificially nanostructured materials, often called metamaterials, exhibit new properties. Different phenomena, including optical topological insulator and structures for vortex waves transporting angular momentum of photons, are discussed and illustrated. With the development of nanometer size structures, another step is taken toward allowing control of the intimate interaction of optical waves with materials to tune their basic electronic properties and permittivity. Both optical and electronic properties are also strongly dependent on coupling effects and need a global approach.

A traditional high-reflection optical coating was applied to enhance the directional radiation of nanoantennas. A highly reflective multilayer upon the top lateral side of a horizontally lying silver nanorod enhances the forward scattering when an optical wave is incident on the bare bottom side of the nanorod. Enhanced forward scattering can thus be observed from a glancing deposited silver nanorod array (NRA). An effective method for coupling the energy of incident light into a NRA involves arranging the NRA in a prism coupling. The highly efficient light coupling effect over a broadband and a wide range of angles results in extra-strong forward light scattering.

Optical absorption improvement and cost reduction of thin-film solar cells have been long-time issues. These two aims are achieved simultaneously by combining metallic nanoribbons and dielectric gratings at the front side of ultrathin-film amorphous silicon solar cells. Surface-plasmon-polariton waves excited by the nanoribbons at the long wavelength co-operates with Uller-Zenneck waves and cavity resonances excited by the gratings at the short wavelength with little cross-effect, leading to a complementary absorption enhancement of 31% when compared to planar structure. In addition, this design exhibits wide-angle absorption as well as a high fabrication tolerance. Compared to the previous work combining different mechanisms, this design provides fewer fabrication steps and an easier approach. Moreover, the nanoribbons can be used as a transparent conducting electrode for a low-cost alternative to expensive indium tin oxide thin-film.

Nanostructured thin film absorbers embedded with phase-change thermochromic material can provide a large level of absorption tunability in the near-infrared region. Vanadium dioxide was employed as the phase-change material in the designed structures. The optical absorption properties of the designed structures with respect to the geometric and material parameters were systematically investigated using finite-difference time-domain computations. Absorption level of the resonance wavelength in the near-IR region was tuned from the perfect absorption level to a low level (17%) with a high positive dynamic range of near-infrared absorption intensity tunability (83%). Due to the phase transition of vanadium dioxide, the resonance at the near-infrared region is being turned on and turned off actively and reversibly under the thermal bias, thereby rendering these nanostructures suitable for infrared camouflage, emitters, and sensors.

Difficulty in deposition and integration of fragile graphene-like samples for optoelectronic devices may prevent a multiple contact measurement procedure. We employed noncontact and nondestructive transmission and reflection terahertz (THz)-pulsed spectroscopy to investigate not only the electrical conductivity, but also to study the optical properties of one-dimensional and two-dimensional graphene-like samples. The Drude and non-Drude models were applied to observe and compare the ultrafast carrier transport parameters and high mobility characteristic of such high conductance-nanostructured thin films without requirement for postprocess patterning. The diffusive coefficient and nanoscopic characteristic length from noncontact THz measurement enables us to predict the cut-off frequency of such devices in relevant optoelectronic applications in sub-THz and THz frequencies. The results show that the cut-off frequency of the devices increases with a reduction of the channel length.

Voigt wave propagation was investigated in a homogenized composite material (HCM) arising from a porous electro-optic host material infiltrated by a fluid of refractive index n_a. The constitutive parameters of the HCM were estimated using the extended Bruggeman homogenization formalism. Numerical studies revealed that the directions which support Voigt wave propagation in the HCM could be substantially controlled by means of an applied dc electric field. Furthermore, the extent to which this control could be achieved was found to be sensitive to the porosity of the host material, the shapes, sizes, and orientations of the pores, as well as the refractive index n_a. These findings may be particularly significant for potential technological applications of Voigt waves such as in optical sensing.

This PDF file contains the editorial “Special Section Guest Editorial: Nanoplasmonics” for JNP Vol. 9 Issue 01

The use of heavily doped semiconductors to achieve plasma frequencies in the mid-IR has been recently proposed as a promising way to obtain high-quality and tunable plasmonic materials. We introduce a plasmonic platform based on epitaxial n-type Ge grown on standard Si wafers by means of low-energy plasma-enhanced chemical vapor deposition. Due to the large carrier concentration achieved with P dopants and to the compatibility with the existing CMOS technology, SiGe plasmonics hold promises for mid-IR applications in optoelectronics, IR detection, sensing, and light harvesting. As a representative example, we show simulations of mid-IR plasmonic waveguides based on the experimentally retrieved dielectric constants of the grown materials.

The deployment of nanocavities may efficiently enhance the light-matter interaction for photonic components on chip. Three nanoscale cavity designs are investigated, including the one-dimensional (1-D) photonic crystal (PhC) nanobeam cavity, inline waveguide-integrated plasmon cavity, and square plasmon resonator embedded in the 1-D PhC nanobeam cavity (i.e., Combo cavity). The cavity performance, such as quality and Purcell factor, mode volume, and light-matter interaction strength, are evaluated for each structure for comparison. A deep subwavelength mode volume of 0.18 (λ/2n)³ is observed in the Combo cavity, which exhibits an improved Purcell factor up to 428 and a 44 times enhanced interaction strength due to the compressed mode volume compared to the inline plasmon cavity. Thus, the Combo cavity shows promise of becoming a potential building block for active components of next-generation on-chip photonic circuits.

The field of plasmonics has the potential to enable unique applications in the mid-infrared (IR) wavelength range. However, as is the case regardless of wavelength, the choice of plasmonic material has significant implications for the ultimate utility of any plasmonic device or structure. In this manuscript, we review the wide range of available plasmonic and phononic materials for mid-IR wavelengths, looking in particular at transition metal nitrides, transparent conducting oxides, silicides, doped semiconductors, and even newer plasmonic materials such as graphene. We also include in our survey materials with strong mid-IR phonon resonances, such as GaN, GaP, SiC, and the perovskite SrTiO₃, all of which can support plasmon-like modes over limited wavelength ranges. We will discuss the suitability of each of these plasmonic and phononic materials, as well as the more traditional noble metals for a range of structures and applications and will discuss the potential and limitations of alternative plasmonic materials at these IR wavelengths.

Optical constants for evaporated bismuth (Bi) films were measured by ellipsometry and compared with those published for single crystal and melt-cast polycrystalline Bi in the wavelength range of 1 to 40 μm. The bulk plasma frequency ωp and high-frequency limit to the permittivity ε∞ were determined from the long-wave portion of the permittivity spectrum, taking previously published values for the relaxation time τ and effective mass m . This part of the complex permittivity spectrum was confirmed by comparing calculated and measured reflectivity spectra in the far-infrared. Properties of surface polaritons (SPs) in the long-wave infrared were calculated to evaluate the potential of Bi for applications in infrared plasmonics. Measured excitation resonances for SPs on Bi lamellar gratings agree well with calculated resonance spectra based on grating geometry and complex permittivity.

Surface plasmon based photonic (or plasmonic) circuits merge electronics and photonics at the nanoscale, creating the ability to combine the superior technical advantages of photonics and electronics on the same chip. Recent work has demonstrated their remarkable applications in subwavelength optics, data storage and transmission, light harvesting and generation, and microscopy, as well as bioapplications. Plasmonics has become one of the most intensive research subjects in recent years, and much effort has been made to develop novel and efficient waveguiding structures and plasmonic materials. We will first review some major progress in subwavelength plasmonic waveguides and plasmonic materials. Then, focusing on the applications of a class of promising alternative plasmonic materials, transparent conducting oxides, we will introduce some of our up-to-date study, especially on electro-absorption modulators and beam steering.

We propose and optimize two designs of plasmonic lens structures, concentric grooves with a central hole (CGH) and concentric grooves with a central pillar (CGP), based on a traditional structure of concentric grooves (CG). The numerical investigation based on COMSOL Multiphysics is performed to optimize the three kinds of structures by a 355 nm radially polarized laser illumination. It is found that full-width at half maximum (FWHM) is closely related to the size of the center-position, and the field enhancement effect depends on the resonant wavelength of surface plasmon polaritons, permittivity, film thickness, and groove number. Compared to a FWHM of λ/3 (λ is the wavelength of the laser beam) with the conventional CG type, the combination of localized and extended surface plasmons results in CGP and CGH parameters achieving their optimal value with a much smaller spot size of λ/8 and higher intensity enhancement for a variety of the aspect ratios of central pillar and hole. A focused ion beam was used to fabricate the three type nanostructures with high accuracy. The CGH type with a central hole 20.88 nm in diameter and the CGP type with a central pillar 55.45 nm in diameter have been successfully fabricated approximately to their optimization results.

The spectrum filtering behavior of the slit nanoresonator array structure is based on the coupling between the slit resonance and the Wood’s anomaly of grating array, and therefore has angle dependence, which is not desirable for some applications. To achieve an angle-insensitive spectrum filter, such a coupling should be disrupted. We show that reducing the period of the slit array helps decouple these two resonances. Additionally, by enhancing the light confinement inside the slits through either shrinking the slit width or filling the slits with a high-index medium, a narrow transmission peak is maintained at a small period so that an angle-insensitive spectrum filter is achieved.

We theoretically investigate the optical response of ensembles of polarizable metallic nanoparticles (NPs) that form (1) submonolayer films of particles adsorbed on a dielectric substrate, considered as two-dimensional (2-D) systems, and (2) thin three-dimensional (3-D) films, where NPs are embedded in a dielectric matrix. For system (1), the effect of NPs’ distance to the substrate is taken into account. In both cases, we find that short-range clustering leads to a broadening and a spectral shift of the absorption band related to the surface plasmon resonance (SPR) in individual NPs. We show that the clustering can help in achieving spectrally broad SPR bands, especially if NPs aggregate into fractal clusters, which can be interesting for some applications such as surface-enhanced Raman scattering. In particular, submonolayer films on NPs generated using the diffusion-limited aggregation algorithm produce sizable and spectrally broad absorption, which can be tuned to the visible range by choosing an appropriate capping and/or substrate material. Calculated results for thin 3-D films are compared with experimental data obtained for Au/TiO₂ nanocomposite layers produced by reactive cosputtering.

A quantitative comparison of third-order nonlinear optical properties of colloidal gold nanoshells (NSs) and gold nanorods (NRs) in water solutions has been carried out using open- and closed-aperture Z-scan measurements, performed with femtosecond laser pulses over a broad range of wavelengths. Absorption saturation was found to be a dominant effect for all the studied nanoparticles; however, two-photon absorption (2PA) properties were also detected, and were clearly resolved especially at the shortest wavelengths used. The value of the merit factor σ₂/M (2PA cross section scaled by the molecular weight) for the NRs (10×35  nm) at 530 nm is 7.5 (GM·mol/g), while for the NSs it is 1.9 (GM·mol/g) at the same wavelength.

Surface plasmon resonances of optical bowtie nanoantennas with symmetry breaking are studied numerically using the finite-element method. Beginning with both x-axial and y-axial symmetry, bowtie structures are reshaped by varying two parameters (edge lengths and bow angles) to create various symmetries to achieve controllable resonant modes and gap enhancement in the visible and infrared wavelength range. The four edges’ coupling is the main factor contributing to the final fundamental resonances. Double fundamental resonances can be achieved in bowtie structures with x-axial or y-axial symmetry. These properties can guide both the engineering and the fabrication of plasmonic nanoantennas.

A nanoscale optical filter based on metal-insulator-metal waveguides and a Kerr-type nonlinear nanoslot resonator is introduced and numerically investigated by finite-difference time-domain simulations. It is demonstrated that the resonant wavelengths of the nanoslot resonator experience a red shift due to the intensity dependence of the Kerr nonlinear effect. The simulation results reveal that the resonant modes of the proposed filter can be tuned by properly adjusting the input signal intensity without changing the dimensions of the filter structure. The findings of this study are useful for highly integrated optical circuits, for which we have limitations on the dimensions of the filter structure. In addition, the results are suitable for design of integrated optical waveguides and resonators based on the plasmonic effect. A significant advantage of the proposed tunable filter is its ease of fabrication.