The reflection and transmission of plane waves by a homogeneous anisotropic dielectric slab—as represented by a columnar thin film—with topologically insulating surface states was theoretically investigated. Copolarized and cross-polarized reflectances and transmittances were calculated by solving the associated boundary-value problem. Numerical calculations revealed that all four reflectances and all four transmittances were asymmetric with respect to reversal of projection of the propagation direction of the incident plane wave on the illuminated surface of the slab. This left/right reflection and transmission asymmetry arises due to the combined effects of the slab’s anisotropy and surface states.

Using a traditional sol-gel deposition technique, we successfully fabricated aluminum-doped zinc oxide (AZO) and gallium-doped zinc oxide (GZO) thin films on glass substrates. Employing a plasma treatment method as the postannealing process, we produced thin-film transparent conductive electrodes exhibiting excellent optical and electrical properties, with transmittance greater than 90% across the entire visible spectrum and the near-infrared range, as well as good sheet resistance under 200  Ω/sq. More importantly, to improve the resilience of our fabricated thin-film samples at elevated temperatures and in humid environments, we deposited a layer of reduced graphene oxide (rGO) as protective overcoating. The stability of our composite AZO/rGO and GZO/rGO samples improved substantially compared to that of their counterparts with no rGO coating.

Plasmonic nanostructures enable considerable control and manipulation of light at the subwavelength scale and are promising for demonstration of optical metamaterials with enhanced spectral response. In this paper, we introduce a generation of terahertz bandpass filters that exploit the characteristics of subwavelength plasmonic nanoparticles. The design procedure is discussed based on a well-known complementary split ring resonator with a resonant feature at the THz region (∼1.5  THz), and it has been shown that device design based on plasmonic nanoparticles can conquer the poor off-resonance selectivity limit of common THz filters and exhibit higher transmission response, faster roll-off, and almost ripple-free operation. A much larger coupling capacitance for nanoparticles in the touching condition can modify the resonance wavelength, and localized hot spots enhance the device sensitivity for special applications. The effect of plasmonic nanoparticle size on the filtering characteristics is also discussed. A simple fabrication procedure based on discontinuous islandized surface morphology of thin metallic films on a dielectric has been proposed for demonstration of the THz filters introduced here.

An exposure method is proposed to test the focusing properties of subwavelength photon sieves. To solve the problems caused by the subwavelength photon sieves (such as short focal length and small focal spot size), a grating moiré fringe phase detection technique and a microcontact sensor with lead zirconium titanate (PZT) stepping hybrid technique are used in the experimental setup. The focusing properties of the subwavelength photon sieves are tested by this setup. The results show that the focal length and the focal spot size are close to the designed value. Finally, the intensity distribution of the focal spot is proposed. This research result will be beneficial for understanding the focusing properties of subwavelength photon sieves, will help us to improve the imaging quality, and will provide a good experimental basis for practical applications in the nanolithography field.

We propose and simulate numerically a permittivity-tunable metamaterial channel, which is composed of alternating layers of graphene and silica. The real part of the permittivity of the proposed metamaterial can be tuned from a positive value to a negative one for a broadband width. Furthermore, optical waves can pass through the metamaterial channel only when its permittivity is tuned to zero. Inspired by this intriguing property of the graphene–silica metamaterial, three basic electro-optical logic gates, including NOT, NOR, and NAND gates, were proposed and numerically investigated by using the finite element method. Taking advantage of the permittivity-tunable property of graphene, the working wavelength of the proposed electro-optical logic gates can be actively controlled by tuning the external voltage applied on the graphene–silica metamaterial. These tunable and ultracompact electro-optical logic gates could benefit the development of nanoscale optical devices for highly integrated photonic circuits.

Optical properties, reflectance and transmittance, of couple inverse conical helix sculptured thin films are investigated using a combination of local homogenization and transfer-matrix method and are compared with a normal chiral one. Varying radius, the major conical helix characteristic, contributes to circular Bragg phenomenon (CBP) in a limited range of wavelengths, not continuously but discretely. These discrete high-reflection regimes in the proposed structure are narrower in comparison to those in fixed-radius structures. The effect of engineering structural parameters, including radius variations and loops making the structure, on peaks’ quantity and intensity and on bandwidth of spectrum in which the CBP occurs have been investigated.

Considering the effects of linear polarization, modulation instability (MI) in silicon on insulator (SOI) waveguides is studied. Impacts of differential group delay, group velocity dispersion, third-order dispersion, and linear loss on gain and frequency of MI, in linearly polarized radiations, are presented theoretically. Fully numerical simulations are performed to verify calculations as well. The results demonstrate strong MI in the normal dispersion regime of SOI waveguides compared to silica fibers with much higher frequencies.

Cadmium sulfide (CdS) colloidal nanocrystals have been synthesized by a chemical reaction route. Polyvinyl alcohol was employed to modify the surface of CdS nanocrystals and improved their optical properties. The prepared nanoparticles were characterized using techniques such as x-ray powder diffraction, UV–VIS absorption, and photoluminescence spectroscopy. The prepared sample displays a strong and narrow green emission peak centered at 519 nm that has not been reported before and it is longer than the onset of absorption of ∼512  nm for bulk CdS. Several weak emission peaks appeared at wavelengths 490, 506, 521, and 543 nm, too. These two important characteristics of the prepared sample are due to the strong band-edge emission of CdS nanocrystals. The obtained results confirm that the prepared CdS nanocrystals have potential for opto-electronic applications.

We have investigated on a tunable graphene-based hybrid plasmonic terahertz waveguide with ultra-long-ranged propagation length at the frequency of 3 THz by using a finite-element method. The proposed structure consists of five graphene sheets, a curved semiconductor layer as a low-index material at the top of an air gap spacer, and gallium arsenide as a high-index material. The most important characteristic of this hybrid structure is its tunable, long-ranged propagation length. By tuning the waveguide dimensions, we can have a very long propagation length ranging from 20 to 15,000  μm, which is approximately 10 times higher than that in recently proposed structures. Moreover, we will show that with this increase in the propagation length, the normalized mode area does not change significantly and remains between 0.03% and 0.04%, indicating that this structure also poses a tight energy confinement.

The formation of gold–silver alloy nanoparticles (Au–Ag alloy NPs) by a two-step process with a pulsed Nd:YAG laser without any additives is presented. Mixtures of Au and Ag colloidal suspensions were separately obtained by 1064-nm laser ablation of metallic targets immersed in ethanol. Subsequently, the as-mixed colloidal suspensions were reirradiated by laser-induced heating at the second-harmonic generation (532 nm) for different irradiation periods of time. The absorption spectra and morphology of the colloidal alloys were studied as a function of exposure time to laser irradiation. Transmission electron microscopy revealed the formation of monodispersed spherical nanoparticles with a homogeneous size distribution in all the synthesized samples. UV–vis and photoluminescence spectroscopy measurements were also employed to characterize the changes in the light absorption and emission of N719 dye solution with different concentrations of Au–Ag colloidal alloys, respectively. The localized surface plasmon resonance (LSPR) of Au–Ag alloy NPs enhanced the absorption and fluorescence peak of the dye solution. The mixture of dye molecules with a higher concentration of alloy NPs exhibited an additional coupling of dipole moments with the LSPR, thereby contributing to the improvement of the optical properties of the mixture.

This contribution reports on the synthesis and the main physical properties of europium oxide nanocrystals synthesized for the first time by a completely green physical–chemistry process using Aspalathus linearis’ leaves natural extract as an effective chelating agent. The structural and optical properties of such biosynthesized nanocrystals were investigated by electron microscopy, selective electron diffraction, energy dispersive spectroscopy, x-rays diffraction, Raman and x-rays photoelectron spectroscopies, as well as room-temperature photoluminescence. The luminescence properties of such cubic nanocrystals with a 16.5 nm average size were characterized by an intense red emission centered at 614.8 nm (⁵D₀−⁷F₃) with an average time decay of 7.808  μs.

Poly (methyl methacrylate) (PMMA) thin film (TF) was employed on TiO₂ nanowires (NWs) to fabricate organic–inorganic hybrid UV photodetector (PD), and its properties were studied and compared with bare TiO₂ NW-based PD. A maximum photoresponsivity of 20×10−³ A/W and a maximum external quantum efficiency of ∼3.15% were observed in the UV region at 370 nm (∼3.35  eV). Enhanced photon absorption was observed in the hybrid detector. The TF of PMMA, which is a π-conjugated polymer, increased the carrier lifetime and reduced recombination rate. The PMMA TF:TiO₂ NWs hybrid UV detector shows excellent rectification, and light current/dark current ratio was measured to be ∼1.46 times in comparison to bare TiO₂ NWs photodetector in the reverse bias condition from −1 to −10  V.

A surface plasmon resonance (SPR) sensor hybridized with self-assembled metallic nanoparticles is proposed and experimentally demonstrated. The measured sensitivity of the proposed SPR sensor is 110.77  deg/RIU, while that of a conventional SPR sensor is 84.75  deg/RIU. The enhanced sensitivity is attributed to the strong localized surface plasmons and the increased surface interaction area by the nanoparticles. Angle variation measurement, which is an easy detection method using bulk optics, is possible with this structure because a supplementary metallic thin film layer on the nanoparticles leads to utilization of the sensitive variation of the strong localized field by the change of the refractive index. Furthermore, the proposed structure can be fabricated with a very simple three-step nonlithographic process.

We report the rise in temperature in various liquid media adjacent to a trapped bead. A nonheating laser at 780 nm has been used to optically trap a 500-nm radius polystyrene bead, while a simultaneous irradiation with a copropagating 1560-nm high-repetition-rate femtosecond laser led to temperature rise in various trapping media. Vibrational combination band of the hydroxyl group in the trapping media resulted in high absorption of 1560-nm laser. This, in turn, gave us control over the trapping media temperature at the focus of the optical trap.

This work aims to reveal the strong influence of TiO₂ nanostructures on the light absorption property of TiO₂ and perovskite mixture. Three TiO₂ nanostructures, i.e., nanoparticles (S1), ultrapure nanorods (S2), and ultrasmall nanorods (S3), were studied: S1 was selected as a baseline; S2 and S3 were synthesized from S1 by using modified hydrothermal processes. Mesoporous TiO₂ thin films were spin-coated from solutions containing these TiO₂ nanorods and nanoparticles (S1 as baseline). Organic–inorganic hybrid perovskite CH₃NH₃PbI₃ was then incorporated into these mesoporous TiO₂ thin films. Optical absorption results showed that the perovskite mixture with ultrasmall TiO₂ nanostructures (S3) has significantly higher optical absorption coefficient. Finite-difference time domain models were built based on three distinct nanostructures of TiO₂ and CH₃NH₃PbI₃ mixtures fabricated (S1 to S3) to understand their optical absorption properties. Our work is promising to fabricate TiO₂ nanostructures, as a backbone structure, for a series of applications including photovoltaics and photodetection.

We theoretically investigate the optical force exerted on a Mie dielectric particle in the evanescent field of a graphene-based resonance multilayer structure using the arbitrary beam theory and the theory of multilayer films. The resonance structure consists of several thin films including a dielectric film (MgF₂), a metal film (silver or gold), and several graphene layers which are located on a prism base. The effects of the metal film thickness and the number of graphene layers on the optical force are numerically investigated. The thickness of the metal layer and the number of graphene layers are optimized to reach the highest optical force. The numerical results show that an optimized composition of graphene and gold leads to a higher optical force compared to that of the graphene and silver. The optical force was enhanced resonantly by four orders of magnitude for the resonance structure containing graphene and a gold film and by three orders of magnitude for the structure containing graphene and a silver film compared to other similar resonance structures. We hope that the results presented in this paper can provide an excellent means of improving the optical manipulation of particles and enable the provision of effective optical tweezers, micromotors, and microaccelelators.

A design of two-dimensional hybrid photonic crystal fiber (PCF) with elliptical and circular air holes and its analyses for large flattened dispersion and high birefringence is presented. The PCF has hexagonal layout with triangular lattice. There are five rings around the solid core. The inner three rings around the core have elliptical air holes while the outer two rings have circular air holes. Three such layouts are designed, analyzed, and compared with the layout having only circular air hole using full-vector finite difference time domain method. The layout with hybrid structure having combined elliptical and circular air hole gives a large flattened dispersion of the order of 4.88  ps/nm/km for the wavelength range of 1.2 to 1.8  μm and magnitude of modal birefringence is 1.238×10⁻³ at 1.55-μm wavelength.

A chemical route was used to synthesize highly stable CdS colloidal nanocrystals. Different characterization techniques, such as UV-Vis, photoluminescence, and time-resolved photoluminescence spectroscopy, were used to study the optical properties of synthesized sample. A strong and narrow green emission peak centered at 532 nm with 40-nm full widths at half maximum and 57.2% quantum efficiency was recorded. The absorption cross section at the first absorption peak is about 11.69×10−¹⁶  cm² that has not been reported before. Variation in optical properties, such as emission peak intensity and full widths at half maximum of emission peak, was evaluated with various long-term measurements (after 1 year). Obtained results confirm that the prepared CdS nanocrystals can be employed as green source material.

The cross section for photoabsorption by a semiconductor quantum dot has been calculated with the previously obtained densities of electrons in the surface traps, conduction electrons, and electrons in unionized impurities. It has been found that the total photoabsorption cross section has two characteristic maxima corresponding to absorption by conduction electrons and by electrons in traps in the bulk of the quantum dot. The contribution of electrons in traps on the surface of the quantum dot is small and manifests itself only in a relatively short-wavelength range of the spectrum.

We studied the limits of optical reflectance to detect plasmonic nanoparticles (NPs) embedded in air and supported by a glass substrate, in an internal reflection configuration. We used a recently derived multiple-scattering model for the coherent reflectance of a disordered monolayer of particles supported on a flat surface to calculate the sensitivity of optical reflectance variations to the presence of plasmonic NPs. We considered gold and silver NPs with radii up to 50 nm and studied the sensitivity as a function of the angle of incidence, wavelength, particle size, and polarization of light. Using our own measurements of noise, we estimated the minimum detectable surface-coverage by the particles. The highest sensitivity is found around the critical angle between the glass substrate and air, for transverse-magnetic polarization, and at wavelengths of light near the plasmon resonance of the particles. We provide estimates of the minimum number of particles per unit area detectable from reflectivity variations and set the basis for single particle detection.

Surface-enhanced Raman spectroscopy (SERS) has emerged as one of the thrust research areas that could find potential applications in bio and chemical sensing. We developed colloidal SERS active substrate with excellent sensitivity and high reproducibility using silver nanocube (AgNC) synthesized via the solvothermal method. Finite-difference time-domain simulation was carried out in detail to visualize dipole generation in the nanocube during localized surface plasmon resonance and to locate the respective hot spots in AgNC responsible for the huge Raman enhancement. The prediction is verified by the SERS analysis of the synthesized nanocubes using Rhodamine 6G molecule. An excellent sensitivity with a detection limit of 10⁻¹⁷  M and a very high enhancement factor of 1.2×10⁸ confirms the “hot spots” in the nanocube. SERS activity is also carried out for crystal violet and for food adulterant Sudan I molecule. Finally, label-free DNA detection is performed to demonstrate the versatility of SERS as a potential biosensor.

An ultra-broadband and polarization-independent metamaterial absorber consisting of a chromium circular-shaped ring resonator embedded in a dielectric layer and a chromium ground plane is numerically investigated in the solar spectrum. Simulation results show that the absorber can obtain the average absorption of 95.5% over most the solar spectrum, near-infrared, and short-wavelength infrared regime (400 to 2500 nm). The absorption mechanism of the ultra-broadband metamaterial absorber originates from the overlapping of two different resonance wavelengths. In particular, the electromagnetic energy is almost completely dissipated in the chromium layer, which makes it independent on the loss of the dielectric layer and widens the range of choices for potential dielectric materials. Our designed absorber has high practical feasibility and appears to be very promising for solar energy harvesting, thermal imaging, and emissivity control applications.

We report the luminescence properties of undoped and 10% Yb³⁺-doped Y₂Si₂O₇ nanopowders under the infrared excitation of 975-nm laser diode. A broadband white light (WL) emission is observed in the undoped powder, and its intensity becomes stronger with increasing excitation power. A blue emission centered at ∼475  nm is observed below the excitation power of ∼2  W in the Yb³⁺-doped sample. The blue emission intensity dependence on the excitation power suggests that this emission is a two-photon absorption process known as the cooperative luminescence of Yb³⁺ ions. When the excitation power is increased above 2 W, a broadband “white” emission extending from blue into the near infrared appears while the blue cooperative emission band of Yb³⁺ ions disappears. The excitation power dependence of the WL intensity at 758 nm is due to a multiphoton process that may be attributed to the thermal radiation mechanism. The International Commission on Illumination coordinates (x,y) for the WL emission in the Yb³⁺-doped Y₂Si₂O₇ nanocrystalline sample is found to be (0.4503, 0.3999) and (0.5035, 0.4096) for 2.005- and 3.68-W excitation powers, respectively. These values lie in the yellowish region and correspond to the color temperature value of 5030 K, with a color rendering index of 85.

We propose a design for a polarization beam splitter based on the phenomenon of a photonic crystal directional coupler. The design consists of a honeycomb lattice arrangement of air holes of different radii in a silicon-on-insulator substrate exhibiting a complete photonic bandgap. The results obtained by the finite-difference time domain method show that the extinction ratio for transverse electric (TE) and transverse magnetic (TM) polarizations is 24.56 and 28.29 dB, respectively, at a wavelength of 1.55  μm. The degree of polarization for TE polarization is 99.29% and for TM polarization is 99.70%. Hence, the proposed design can be efficiently used as a polarization splitter for on-chip integrated devices.

We present a systematic study of tunable, plasmon extinction characteristics of arrays of nanoscale antennas that have potential use as sensors, energy-harvesting devices, catalytic converters, in near-field optical microscopy, and in surface-enhanced spectroscopy. Each device is composed of a palladium triangular-prism antenna and a flat counter-electrode. Arrays of devices are fabricated on silica using electron-beam lithography, followed by atomic-layer deposition of copper. Optical extinction is measured by employing a broadband light source in a confocal, transmission arrangement. We characterize the plasmon resonance behavior by examining the dependence on device length, the gap spacing between the electrodes, material properties, and the device array density, all of which contribute in varying degrees to the measured response. We employ finite-difference time-domain simulations to demonstrate good qualitative agreement between experimental trends and theory and use scanning electron microscopy to correlate plasmonic extinction characteristics with changes in morphology.

We demonstrate an ultracompact integrated silicon-based plasmonic sensor for lab-on-chip applications in the mid-infrared (MIR) spectral range. Our sensor possesses desirable features such as design simplicity and very high sensitivity. The sensor is designed using a platform for plasmonic effects in the MIR using highly doped silicon. This platform is exploited to create a metal-less plasmonic slot waveguide in the MIR range. This plasmonic waveguide is highly sensitive to any environmental change. Full wave electromagnetic simulations were carried out to design and optimize the structure. The proposed sensor covers a large wavelength span in the MIR range. High spectral sensitivity of 5000  nm/RIU was achieved for our sensor device. Further development of the structure was conducted to extend the sensor operation to multigas sensing.