The excitation of the surface-plasmon-polariton (SPP) waves in the prism-coupled configuration is commonly implemented in Turbadar–Kretschmann–Raether (TKR) configuration, where the prism is attached to a metallic thin film and the columnar thin film (CTF) is present on the opposite side of the metallic film. We present the results of excitation of SPP waves in the alternative prism-coupled configuration, that is, the Turbadar–Otto configuration where the prism is affixed to the CTF. Comparison of the Turbadar–Otto and the TKR configuration showed that the absorption peaks in the angular spectrum are narrower and easier to discern in the former than the latter configuration. The computations also showed the usefulness of the Turbadar–Otto configuration for the optical sensing of a fluid infiltrating the void regions of the CTF.

All-optical universal logic gates are theoretically investigated and demonstrated in a single silicon microring resonator due to mode conversion. Mode conversion takes place at the switching speed of 0.2 ps and at ultrahigh quality factor (Q-factor) and requires low power. Simulated results obtained from the finite-difference-time-domain method verified our proposed model. The Q-factor for NOT, NAND, and NOR logic gates is noted as high as around 1500, 1500, and 2400, respectively. The design is simple and silicon-on-insulator compatible.

The amorphous titania species-loaded H₄Nb₆O₁₇ nanoscroll (ATS  @  H₄Nb₆O₁₇-NSc) is obtained by the recombination of its precursors, H₄Nb₆O₁₇ nanoscroll (H₄Nb₆O₁₇-NSc) sol and Ti(OH)₄ sol, under moderate conditions. The physicochemical properties of as-prepared materials are characterized by means of x-ray diffraction, high resolution transmission electron microscope with the energy dispersive spectroscopy, Raman spectroscopy, ultraviolet–vis diffuse reflectance spectra, and N₂ adsorption–desorption isotherm. Methylene blue solution is employed as the degradation material to evaluate the photocatalytic performance of the as-prepared materials under the visible light irradiation. The results show that the amorphous titania species (ATS) are uniformly dispersed on the surface of the nanoscroll. The surface area and pore volume of ATS  @  H₄Nb₆O₁₇-NSc are 190  m²  ·  g^−  1 and 0.41  cm³  ·  g^−  1, respectively. The bandgap energy of H₄Nb₆O₁₇-NSc is decreased, and the photocatalytic performance of it is enhanced after composite with ATS. A strong interaction between ATS and H₄Nb₆O₁₇-NSc surface is detected in the form of chemical bond Nb─O─Ti.

We propose an optimization-free method for creating a two-dimensional (2-D) identical focal spot array with a prescribed number, tunable interval, and controllable position. This can be realized easily by backward focusing of the field radiated from a planar antenna array situated at the foci of two high-numerical-aperture objective lenses. It is demonstrated here that the number of spots in the focal field array is equal to the number of elements in the planar antenna array; the intervals between the two adjacent spots along the x and y directions depend solely on the gaps between the two corresponding elements, and the position for each spot is determined totally by the location of the corresponding element. Furthermore, the intensity distribution of each spot in the 2-D focal array is identical. These kinds of 2-D focal spot arrays with controllable characteristics may find applications in parallel optical micromanipulation, multifocal multiphoton microscopy, and multiparticle parallel acceleration.

Transparent conductive oxides (TCOs) have emerged as materials for nanoscale electro-optic modulators. The free-carrier-induced epsilon-near-zero effect by applying a gate voltage is capable of achieving ultra-strong electro-absorption (EA) effect. As the EA rate has been theoretically proved to be dependent on the mobility of the TCO gate, we experimentally demonstrated a hybrid silicon-plasmonic EA modulator using high-mobility In₂O₃ as the gate. With an ultra-compact active region of only 5-μm long, we achieved a small voltage swing V_pp of only 2 V to obtain an EA rate of 1.2  dB  /  μm, resulting in very high energy efficiency of 110 femto-joule/bit. We also experimentally proved the correlation between the EA rate and the mobility of TCO materials through comparison with indium-tin-oxide gated modulators. In addition, the hybrid EA modulator is capable of covering more than 100-nm optical bandwidth in the telecommunication wavelength window, which is limited by the bandwidth of the grating coupler.

Melasma is an abnormal acquired skin hyperpigmentation disorder, typically on the face, of unknown origin. It is considered a single disease and very little has been found regarding its pathogenesis. Hydroquinone, an aromatic organic molecule, has been considered as the gold standard substance for dermatological melasma treatment. This substance at high concentrations being absorbed by the skin may produce counterproductive disorders, such as blue or brownish-blue colored skin. In recent years, optical techniques based on the interaction of light with biological samples have become innovative methods for medical applications. We used Raman spectroscopy and surface-enhanced Raman spectroscopy (SERS), to evaluate hydroquinone cation radicals in vitro at relatively low concentrations, laying the foundation for future biomedical applications. We present the experimental and simulated Raman signal in the presence of hydroquinone at concentrations as low as 0.1 M, as well as the experimental SERS signal assisted by gold nanorods obtained for the same molecule, which presents an electromagnetic enhancement factor of ∼10⁴.

The possibility of the use of dye extract from the petals of Cassia fistula flowers as natural dye sensitizers for dye-sensitized solar cells (DSSCs) is explored. To analyze the potential of the sensitizers, characterization by methods like current–voltage response, cyclic voltammetry, and electrochemical impedance spectroscopy were utilized. Surface morphology of the TiO₂ film was studied by atomic force microscopy and scanning electron microscopy. Fourier-transform infrared spectroscopy was used to determine the functional groups present in the dye extract. Device sensitized with ethanolic extract of the flower showed maximum photovoltaic conversion efficiency of 0.182%. The acidified water extract-based device showed an enhanced efficiency of 0.125% compared with that based on pure water extract. We discuss the uncomplicated method of extraction of flower pigments and their execution in DSSCs.

Exciton energy, with and without the inclusion of built-in internal fields, as a function of inner dot radius is investigated in a CdO/ZnO quantum dot with the Smorodinsky–Winternitz potential. The internal fields are owing to spontaneous and piezoelectric polarizations existing between the inner core and outer shell materials in the heterostructure. The dielectric mismatch effect is included. Numerical computations are carried out to obtain the exciton energy employing the variational formulism within the single band effective mass approximation. The energy shift owing to spontaneous and piezoelectric polarizations is found to be 172 meV for 20 Å quantum dot radius. The oscillator strength and the radiative lifetime as a function of dot radius are found. The optical matrix elements and the corresponding gain are studied with the constant carrier density. The optical properties are investigated using density matrix method. It is found that the substantial increase of optical gain is estimated with the inclusion of built-in internal fields.

Silver–palladium nanocomposite films are widely used in electronics. They exhibit a photoresponse sensitive to the polarization and direction of a wave vector of an incident beam. We present the results of experimental research of the effect of direct current bias on the pulse shape of the polarization- and wave vector direction-sensitive photocurrent in Ag/Pd nanocomposite films under nanosecond laser excitation at 532 nm. It is established that the direct current bias applied to the film excites an additional component of the photocurrent, independent of the sign of the angle of incidence, the pulse duration of which is much longer than the one of the polarization- and wave vector direction-sensitive photocurrent. It is shown that depending on the sign of the angle of incidence, the direct current bias may decrease or increase the amplitude, pulse duration, and fall time of the total photocurrent pulse. The obtained results show the ability to control the polarization- and orientation-sensitive photocurrent in Ag/Pd nanocomposite films using a dc voltage.

With the help of numerical simulations in microscopic nonlinear quantum theory of coherent electromagnetic radiation interaction with a gapped bilayer graphene, we find the optimal values of pump wave intensity, graphene temperature, and energy gap induced by a constant electric field for practically significant third-order harmonic coherent emission. The Liouville-von Neumann equation is treated numerically for the third harmonic generation in multiphoton excitation regime near the Dirac points of the Brillouin zone. We examine the rates of the third harmonic at the particle–hole annihilation in the field of a strong pump wave of linear polarization for practically real/optimal parameters of a considering system. The obtained results show that by choosing the optimal values of the main characteristic parameters, a gapped bilayer graphene can serve as an effective medium for generation of the third harmonic at room temperatures in the terahertz and far-infrared domains.

A reconfigurable dual-passband to single-passband filter based on highly miniaturized ring resonators is presented. The filter is designed for 448 MHz for the first band and 668 MHz for the second band as the central passband frequencies and simulations are used for enhancing the design. The filter is implemented using microstrip technology on a RO3010 substrate with thickness of 1.28 mm. The lower passband can be eliminated by just changing the location of a short. Measurements for the optional eliminated band are in good agreement with the expected values. The transmission is −3  dB at the central frequency for dual-passband configuration and −26  dB for single-passband configuration.

We propose a highly efficient ultra-broadband perfect absorber with a double-layer continuous spacer of SiO₂ and Si based on a simple four-layer structure Al–SiO₂–Si–Ti. The absorber shows an average absorption over 98.1% at 780-nm bandwidth from 440 to 1220 nm, where two successive absorption bands are over 99%, and the absorption peak is up to 99.9%. Highly efficient broadband absorption benefits from the surface plasmon resonance (the propagating surface plasmon resonance and the localized surface plasmon resonance). Comparing the absorbers with different spacers, the proposed perfect absorber can be regarded as the superposition of two triple-layer structure absorbers. The absorber exhibits nearly perfect polarization independence and a wide incident angle up to 40 deg for transverse magnetic polarization and transverse electric polarization. In addition, the absorber is not only simple in structure and cheap in Al and Ti materials but also compatible with complementary metal oxide semiconductor technology, which means low cost and high efficiency. We believe that the proposed absorber has tremendous application prospects in areas such as solar energy, optical imaging, and infrared detection.

A Mach–Zehnder interferometer based on processed hollow-core fiber (HCF) is proposed and experimentally demonstrated for gas pressure sensing. The fiber sensor is fabricated by splicing a segment of HCF between the two coreless fibers. One end of the HCF is processed into an open cavity, which allows gas pressure of the air-core to be equivalent to that of the external environment. Gas pressure change induces refractive index change of the air-core, thus the measurement of gas pressure can be achieved by monitoring wavelength shift of the interference pattern. The proposed fiber sensor exhibits a high gas pressure sensitivity of 9.35  nm  /  MPa in the range from 0.1 to 0.04 MPa and a temperature sensitivity of 30  pm  /    °  C in the range from 30°C to 90°C. Furthermore, the fiber sensor processes the advantages of compactness, low cost, and all-fiber configuration, which makes it suitable for gas pressure measurement.

A reconfigurable structure is valuable for optical applications, and organic material such as proteins can be biased using external voltage for use in designing switchable gates. Our study introduces the structure of a cylindrical nanoparticle chain waveguide with nine elements having a metal–organic–metal structure. This special plasmonic transmission line was developed with an Ag/organic/Ag arrangement for an optical transmission line with switchable attributes over a SiO₂ substrate. It has made possible to design different types of gates (Yes, OR, and AND) for a single-array element through biasing of the organic section at the chain waveguide elements at λ  =  550  nm. The various numbers of active or inactive elements allow us to achieve a transmission line with multivalue quality. In addition, we have developed a more complicated structure based on cross-junction structure as the XOR gate so we can extract various models of the gate by altering the bias network. Moreover, we have demanded “NOT” gates for designing the XOR gate, which is not possible to design directly. Therefore, the Yes gates in the bias network with control bits have been used to provide this characteristic and logical inverter.

Ultraviolet (UV) light is widely used in nanofabrication and biomedical fields. However, in order to shape the wavefront of the UV beam, UV light needs to travel a relatively long distance in optical media that usually have strong UV absorptions. Thus the traditional UV lens is inefficient, costly, and easily aging under the radiation. Hopefully, dielectric metalenses represent a promising alternative. We design and numerically study a polarization-insensitive and achromatic metalens at UV spectra from 234 to 274 nm. The metalens consists of 1519 AlN nanopillars and its focal length is about 4.7  μm, with a <4.6  %   alternation over the entire operating bandwidth, whereas the alternation of a chromatic metalens is 24.3%. More importantly, the focal length remains nearly the same (<0.02  %   alternation) for not only linearly polarized light with different polarization angles but also for the left-handed and right-handed circularly polarized light as well. In addition, the designed metalens still has an excellent convergence ability even at 10-deg oblique incidence. This polarized-insensitive and achromatic metalens will greatly promote the development of UV photonic devices and UV nanophotonics.

We propose various optical ring gas sensors. These gas sensors are promising candidates for integrated on-chip sensing. The sensing operation depends on the change in the effective index. We show a detailed study of different sensors utilizing the absorption wavelength of both methane and carbon dioxide gases. These sensors mainly operate at the range of mid-infrared wavelengths because it contains the vibrational resonance of the gases of interest. We provide the details about the dimensions and the material used in our different structures. Moreover, we report sensitivity up to 5938  nm  /  RIU, and the full-width-half maximum (FWHM) and figure of merit (FoM) for all designs are also calculated. We succeeded in squeezing the FWHM to 4.76 nm and increasing the FoM to 1744.72.

A theoretical study is presented to assess the performance of semiconductor superlattice (SL) multipliers as a function of the currently available input power sources. The prime devices that are considered as input power sources are Impatt diodes, InP Gunn devices, SL electron devices, and backward wave oscillator sources. These sources have been successfully designed to deliver input radiation frequencies in the range from 0.1 to 0.5 THz. We discuss the harmonic power generation of both odd and even harmonics by implementing an ansatz solution stemmed from a hybrid approach combining nonequilibrium Green’s functions and the Boltzmann kinetic equation.

This article highlights the studies on precise measurements of energy transfer efficiency in a steady-state method by adopting sample preparation methods. Steady-state and time-resolved fluorescence measurements were employed to evaluate the cadmium telluride (CdTe) quantum dot (QD) photoluminescence quenching induced by the proximal rhodamine 101 dye (Rh 101) molecule via fluorescence resonance energy transfer (FRET). Further, the evaluation of steady-state measurements in comparison with time-resolved measurements was carried out. The FRET parameters, such as spectral overlap, Förster distance, and intermolecular distance for each donor–acceptor pair, were determined and variation of these parameters with respect to the size of the QD is discussed. Further, efforts to understand the optical and carrier relaxation dynamics of CdTe QDs are made using steady-state and time-resolved fluorescence data.

A temperature tunable hybrid metamaterial absorber based on vanadium dioxide (VO₂) particles is proposed and simulated in the terahertz frequency regime. An absorption peak is achieved at 6.13 THz at room temperature with maximum absorptivity of 97.3%, which is derived from the local surface plasma (LSP) mode resonance. The effect of geometric parameters on the absorption properties is revealed. When the simulated temperature reaches the phase change point of VO₂ particles, the original absorption peak is enhanced and converted into an absorption band. Moreover, an absorption peak is achieved. These resonance behaviors are mainly due to the conversion of VO₂ particles into new resonators in the proposed metamaterial absorber. LSP modes are supported by these VO₂ particles resonance elements. The absorption band and new absorption peak are enhanced and shifted to lower frequencies with the simulated temperature increasing. An LC equivalent circuit model is proposed to understand these resonance absorption behaviors.