The optical processes of plasmonic quenching of rhodamine 6G (R6G) molecules fluorescence in polyvinyl alcohol dielectric films formed on rough silver (Ag) surfaces were researched. The depth of penetration of the surface plasmon field into the dielectric film with R6G molecules is calculated. The angular and spectral-kinetic characteristics of dye molecules fluorescence decay on rough Ag surfaces are determined.

This guest editorial summarizes the Special Section on Nanoscience and Biomaterials in Photonics.

A theoretical study of a cylindrical anisotropic optical fiber filled inhomogeneously by an anisotropic metamaterial is carried out. Nanoporous alumina microtubes obtained recently by acid anodization techniques are physical manifestations of such optical waveguides. In these microtubes, the nanopores are aligned radially outward and the nanopore diameters vary radially, rendering the system inhomogeneous. By considering the radial variation of the nanopore size, a local permittivity tensor is obtained by a Maxwell-Garnett homogenization theory. The cylindrically anisotropic and inhomogeneously filled fiber is shown to support propagating modes of hybrid polarization character (EH or HE modes). The salient feature of this system is that the modal fields are extremely confined near the center of the waveguide due to the refractive inhomogeneity. The anisotropy plays a relatively minor role in the localization. The easy control over the dielectric anisotropy and the inhomogeneity made possible in the nanoporous alumina fiber makes it an attractive candidate for nanophotonic applications.

We established a procedure to develop a localized surface plasmon resonance (LSPR) optical sensor platform for immunoassay. Computational simulations, focused on the assessment of the LSPR spectrum and spatial distribution of the electromagnetic field enhancement near the metallic nanoparticle, were used to engineer a nanostructured-sensing platform. Crucial parameters that rule the LSPR sensor performance, as bulk and molecular sensitivity, were evaluated, guiding the development of the optical platform. An LSPR surface-based platform composed of silver nanospheres adhered on a glass slide and functionalized with monoclonal anti-Candida antibodies of the IgG class was fabricated. Molecular biosensing was demonstrated by the identification of Candida albicans antigen. In particular, C. albicans is the most common species involved in a variety of hospital yeast infections. The developed sensing platform was able to identify C. albicans antigen concentration as low as 50  ng  /  mL, indicating the viability of exploring LSPR effect on C. albicans antigen biosensor. Moreover, this work provides insight on the LSPR behavior due to the adsorption of molecules layer on a nanoparticle surface, establishing a paradigm on engineering LSPR biosensor.

The functionalization of the nanoparticle’s (NP) surface is one method for tuning their overall properties to fit targeted applications. We developed a nanosensor based on the specific supramolecular interactions between ß-cyclodextrin (ßCD) nanocavities and organic molecules of biological interests using the metal-enhanced fluorescence effect (MEF) as the detection signal. We grafted ßCD, a typical macrocyclic host molecule that interacts specifically with different organic molecules and changes their physical properties (such as their fluorescence emission intensity), on gold NPs. To evaluate this nanosensor and the effect of the metallic core, we worked with a typical organic molecule, Rhodamine B (RhB), that has a strong association constant with ßCD (5700  M^−  1) and is well-known to be quenched in the presence of cyclodextrins (CDs). The results show that, by grafting ßCD on gold NPs, it is possible to increase the sensitivity of RhB detection by 70%, 80%, and 294% when compared with solutions in (1) a phosphate buffer, (2) with ßCD, and (3) with Au NPs, respectively. These results show that the use of a supramolecular system attached to a metallic NP can interact specifically with a dye to enhance its fluorescence emission through the MEF effect. Moreover, this type of nanosystem can overcome the quenching of the signal by the matrix, such in the case of RhB with CDs. Eventually, this concept could be extended to other dyes with different quenching effects. For this reason, this type of nanosensor system could be used in the future to protect and enhance the dye emission of fluorophores in different biological media.

Deoxyribonucleic acid (DNA)-based functional materials containing luminescent molecules have attracted widespread attention as opto-electronic materials. In this study, luminescence properties of DNA/chiral Ru(phen)3^2  + complexes were investigated. The DNA/chiral Ru(phen)3^2  + complexes showed an enantioselective enhancement of luminescence. The DNA  /  Δ-Ru(phen)3^2  + complex showed a higher luminescence intensity and longer luminescence lifetime than the DNA  /  Λ-Ru(phen)3^2  + complex. Binding modes between DNA and Δ-  /  Λ-Ru(phen)3^2  + are discussed in terms of optical properties. The study shows that Δ-Ru(phen)3^2  + preferentially intercalates to form a more stable DNA complex than Λ-Ru(phen)3^2  +, leading to enantioselective luminescence enhancement.

Future low-voltage dielectric elastomer transducers (DETs), based on nanometer-thin elastomer membranes, will rely on soft and compliant electrodes with reasonable electrical conductivity and sound adhesion to the elastomer. State-of-the-art adhesion promoters, including nanometer-thin Cr/Ti films, result in defects for applied areal strains larger than 3% and lead to increases in the stiffness of DETs. To generate forces in the Newton range, these low-voltage DETs have to be stacked in thousands of layers. Herein, we present a compliant electrode, which consists of gold bonded covalently to thiol-functionalized polydimethylsiloxane (SH-PDMS) films. The membranes were fabricated using molecular beam deposition and in situ and/or subsequent ultraviolet light (UV) radiation. Peel-off tests demonstrate the expected strong binding of Au to the SH-PDMS network, with this highly stretchable Au/SH-PDMS layer capable of withstanding strains of at least 60%, without losing conductivity. Optical micrographs show signs of cracks for strained pure Au and Au/Cr electrodes but not for the Au/SH-PDMS layer. The mechanical properties and adhesion forces of Au/SH-PDMS were extracted by means of atomic force microscopy (AFM), using a spherical Au tip coated with methyl groups (CH₃). The elastic modulus of   (  12  ±  9  )    MPa increased slightly against the 20-nm-thin Au/PDMS example, but it can be tailored by the cross-linking density of Au/SH-PDMS via the UV irradiation dose. Unloading nanoindentation curves revealed pull-off forces between the CH₃-functionalized AFM tip and the Au/SH-PDMS layer at the time of separation. For Au/SH-PDMS, the spectral distribution of pull-off forces exhibits repulsive forces with the CH₃ groups of the PDMS network as well as adhesive forces resulting from interactions with the nanometer-sized Au clusters. This approach provides the means to bind gold clusters homogenously within the SH-PDMS film. Such compliant electrodes are the prerequisite for fabricating low-voltage DETs that can be stretched by more than 50%.

This article reviews recent advances in nonlinear optical microscopy for biophotonics, including stimulated Raman scattering (SRS), coherent anti-Stokes Raman scattering (CARS), two-photon excited fluorescence (TPEF), second harmonic generation (SHG), and sum frequency generation (SFG). We first introduce the principles and applications of SRS, CARS, TPEF, SHG, and SFG and their individual applications for biophotonics. We then introduce the combination of SRS, CARS, TPEF, SHG, and SFG microscopy for biophotonics. Our review not only summarizes the recent advances in nonlinear optical microscopy but also can deepen the understanding of the combination of these types of nonlinear optical microscopy for biophotonics.

Nanostructured films based on branched gold nanoparticles were obtained by self-assembly method. The possibility of controlling the film thickness in the range of 500 to 800 nm with preservation of their homogeneity and nanoparticle size (D_SEM  =  55  ±  12  nm) was shown. Position of localized surface plasmon resonance in absorption spectra of the film structures at λ_lspr  =  595 to 600 nm is almost independent on the film thickness. The efficient surface-enhanced Raman spectroscopy substrates based on branched gold nanostructures were developed.

As part of the efforts to enhance the near-field scanning optical microscopy and the detection of evanescent waves, a silicon Schottky diode, shaped as a truncated trapezoid photodetector and sharing a subwavelength pin-hole aperture, has been designed and simulated. Using finite elements method and two-dimensional advanced simulations, the detector has been horizontally shifted across a vertically oriented Gaussian beam, which is projected on top of the device. Both electrical and electro-optical simulations have been conducted. These results are promising toward the fabrication of a new generation of photodetector devices.

Opal photonic crystals (PCs), composed of TiO₂ nanoparticles, three-dimensional array were simulated. This paper shows how electronic, dielectric, and optical properties of such PCs depend on the shape of structural elements, their polymorphic modifications, and the parameters of their stacking in the body’s space of metastructure.

We report the growth of gold nanostructured thin films by cylindrical direct current magnetron sputtering at room temperature. The grown gold nanostructures are mostly rod shape with short lengths of <20 nm and show negative optical parameters in the UV–vis region. So far negative permittivity and permeability were only reported for complex artificial structures. In a case of simple structures such as gold nanostructures, the negative optical parameters were only predicted by simulation methods and considered ideal structures. The small size of gold nanoparticles and the thickness of nanostructured thin films could be the reason of negative permittivity and permeability in our case. The optical properties of the samples were defined experimentally by ultraviolet-visible spectroscopy and their quality was assessed through multitechnique characterization using transmission electron microscopy, field emission scanning electron microscopy, x-ray diffraction, and energy dispersed x-ray.

The gas concentration can be detected through a parity-time (PT) -symmetry structure. The structure is constructed by placing a resonance cavity between two PT-symmetry Bragg reflectors. The cavity and some specific layers in the structure are filled with the air doped with another gas. The transmittance spectra of the structure are calculated by the transfer matrix method. The peak value of the defect mode is dependent on the concentration of the gas. The sensor detects the gas concentration by the transmittance of the defect mode, instead of the peak wavelength of the defect mode. The defect mode has a large peak value and high Q value because of the amplification effect of the PT-symmetry structure, which apparently enhances the sensor sensitivity.

We propose an ultrasmall channel based on graphene–SiO₂ metamaterial, which is composed of alternating layers of graphene and SiO₂ periodically. By tuning the permittivity of the graphene through the applied voltage, the basic logic gate-controllable channel made by the graphene–SiO₂ metamaterial is able to control the light transmission, which can be used to work as optical logic gate with ultrasmall footprint and large extinction ratio, including the AND, OR, XOR, and XOR logic gates.

We have analytically studied the localized TE surface waves (SWs) in a one-dimensional graphene-based photonic crystal that is capped by a self-defocusing nonlinear layer. Our method is based on the first integral of the nonlinear Helmholtz wave equation. We have investigated the possibility of controlling the dispersion behavior inside the graphene-induced photonic bandgap (GIBG) via two controllable parameters: the intensity of the electromagnetic field at the surface of the nonlinear cap layer and the chemical potential of the graphene. The results showed that the frequency of the SWs inside the GIBG can be controlled by adjusting the intensity of the electromagnetic field and the chemical potential. We also compared the dispersion of the surface modes in GIBG with Bragg bandgap by changing the intensity of field at the surface of the nonlinear cap layer. It was found that the relative frequency variation of the surface modes inside the GIBG is more than the Bragg bandgap.

Silver nanoparticles (Ag NPs) play a significant role in catalysis, biosensor, antibacterial activity, SERS spectroscopy, and photoelectric materials. These prominent applications are strongly dependent on the size and uniformity of Ag NPs. However, a variety of preparation methods such as electrochemical and green synthesis methods are of difficulties to obtain extra-small and uniform Ag NPs due to complex growth environment, which is prone to render anisotropy of nanoparticles thereby limiting the development of Ag NPs. To address the unmet need, tremendous effort has been made synthesizing extra-small Ag NPs with the outstanding monodispersity and remarkable stability in reverse micelles. The efficient and facile method is established employing a high-performance protective agent, i.e., octadecylamine (ODA) with the average diameter of 3.36  ±  1.0  nm. Moreover, by adjusting octadecylamine concentration, the versatile method has the capability of controlling the size of Ag NPs precisely. In addition, the growth mechanism of Ag NPs based on nucleation theory is described schematically, which is of widespread generality to adapt our method for the preparation of other nanoparticles in the similar system. Overall, the promising strategy to the synthesis of extra-small Ag NPs lays a solid foundation for potential applications in wound healing, health care, medical diagnosis, and environmental remediation.

Surface plasmon (SP)-catalyzed reactions of fluorine phenylboronic acid   [  F-PhB(OH)2  ]   to fluorine phenylboronic ester (F-PhB-E) substituted with fluorine have been investigated by surface-enhanced Raman scattering (SERS). Conversion of F-PhB(OH)2 to F-PhB-E is induced by hot electrons from SP decay. The spectral peaks of F-PhB-E of the SERS were also enumerated.

We introduce an integrated polarization detection structure consisting of a photoelectric conversion material, silicon (Si), in the form of a wire grid and an aluminum (Al) wire grid polarizer layer. This structure provides transverse magnetic (TM) polarization absorptivity and an enhanced extinction ratio in the visible spectrum. Finite difference time domain simulations were used to examine the influences of different periods and thicknesses of the Si and Al grid components. The results showed that the absorptivity of TM polarization exceeded 70% in the visible spectrum (a 20% improvement), the absorptivity of transverse electric polarization was reduced by <90  %  , and the extinction ratio improved by a factor of 33. When the incidence angle is over the range of 0 deg to 30 deg, the absorptivity of TM polarization and the extinction ratio perform well, exceeded 60% and 75.

Using transparent conducting oxides, such as indium-tin-oxide (ITO), for optical modulation has attracted research interest because of their epsilon-near-zero (ENZ) characteristics at the telecom wavelengths. Utilizing ITO in multilayer structure modulators, optical absorption of the active ITO layer can be electrically modulated over a large spectrum range. Although they show advances over common silicon electro-optical modulators (EOMs), they suffer from high insertion losses (ILs). To reduce ILs and device footprints without sacrificing bandwidth and modulation strength, slot waveguides are promising options because of their high optical confinement. We present the study and design of an electro-optical absorption modulator based on an electrically tuning ITO carrier density inside an MOS structure. The device structure is based on the dielectric slot waveguide with an ITO plasmonic waveguide modulation section. By changing the dimensions, the effective refractive indices for the slot mode and the off-state mode of the plasmonic section can be matched. When applying electric field to the plasmonic section (on-state), carriers are generated at the ITO-dielectric interface that results in changing the layer where the electric field is confined from a transparent layer into a lossy layer. A finite difference time-domain method with perfect matching layer absorbing boundary conditions is taken up to simulate and analyze this design. An extinction ratio of 15.5 dB is achieved for a 10-μm-long modulation section, at the telecommunications wavelength (1.55  μm). This EOM has advantages of simple design, easy fabrication, compact size, compatibility with existing silicon photonics platforms, as well as broadband performance.

Nanomaterial-based electromagnetic microwave absorber composed from epoxy resin loaded with graphene oxides is proposed for performance enhancement of patch antenna array operational in X and Ku bands (8 to 20 GHz). Nanocomposite graphene offers inherent benefits of structural flexibility and small surface to volume density, which enables implantation of the absorber on same quartz substrate along with the antenna array. The variable positioning of the absorber provides the benefit of controlling the antenna radiation pattern, hence demonstrating significant improvement in the performance of antenna array. Initially, the microwave absorber is designed, and its absorption coefficient and reflective properties are validated by placing the absorber in rectangular waveguide. The realization of two-element patch antenna array loaded with the proposed absorber is then performed on high-frequency structural simulator software. The reflection loss of the absorber is observed to be −81.71  dB at 11 GHz and when applied on array, the beamwidth of major lobe is narrowed by 26 deg with reduction in side lobe levels while maintaining pattern symmetry.

In this work, the structural and luminescent properties of Y₂O₃ powders doped with different concentrations of hafnium and the HfO₂ powders doped with different concentrations of yttrium are presented; these samples were also codoped with europium and terbium. The phosphors were obtained by means of the simple evaporation technique and were calcined at 800°C for 2 h. The excitation and emission spectra of the rare earth (RE) codoped samples are interpreted in terms of the characteristic intraelectronic energy levels of the trivalent RE. The emission peak with maximum intensity for the samples containing europium ions occurs at 611 nm when these ions are excited at 243, 245, and 247 nm wavelengths; this emission is related with the D₀5 to F₂7 transition. Terbium codoped samples give a maximum emission intensity at 542 nm when samples are excited with the following wavelengths λ_exc  =  274, 271, and 273 nm, transition taking place between the D₄5 and F₅7 energy levels. The XRD results for similar samples were analyzed, and it was observed that they have a crystalline structure corresponding to a cubic system and a 21.93-nm grain size calculated by means of the Scherrer’s formula and the Williamson–Hall method; SEM analyzes showed spherical agglomerates for HfO₂ samples, whereas Y₂O₃ showed porous laminar structures. Hafnium-doped yttrium oxide showed a combination of these structures as well as the Y₂O₃  :  Hf^3  +  :  Eu^3  + codoped samples. The results for Y₂O₃  :  Hf^3  +, Tb^3  + showed leaflet and lamellar structures not reported before for this kind of material. The CIE diagram shows tone shifts in the red and green region for emissions of RE-doped yttrium oxide and hafnium oxide powders.

A considerable amount of materials in nanophotonics are dispersive, enabling the propagation of the so-called surface plasmons at their interfaces with dielectrics. Hence, a reliable fit of frequency-dependent permittivity functions with an appropriate model is a first-order necessity for the accurate design of nano-optics devices with time-domain numerical methods, such as finite-difference time-domain or discontinuous Galerkin time-domain. We present the necessary ingredients to fit experimental permittivity functions using the simulated annealing method with a generalized second-order dispersion model implemented in the Diogenes software suite. By scanning through different classes of materials, we came up with effective rules of thumb to make the fitting process fast and accurate.

A theoretical analysis of photonic crystal semiconductor optical amplifier (PC-SOA) is presented. The proposed model is based on rate and propagation equations. The analysis is carried out using two input signal regimes of constant and Gaussian waves. To the best of the authors’ knowledge, temporal and spatial variation of picosecond pulses have not been previously investigated in active PC medium. The effect of injection current, group index, and amplifier length variation on the output signal and amplifier gain is investigated. Based on the results, temporal peak shift, chirp, and spectral width increased in low current regime compared to conventional SOAs. It is also demonstrated that short length PC-SOA can be used as a preamplifier in photonic integrated circuits.