This guest editorial summarizes the Special Section on Nanoplasmonics for Biosensing and Enhanced Light-Matter Interaction.

Optical absorption enhancement (AE) using coupled optical spacer and plasmonic effects in standard and inverted organic solar cells (OSCs) are demonstrated using the finite-difference time-domain numerical method. The influence of an added zinc oxide (ZnO) optical spacer layer inserted below the active layer in standard architecture is first theoretically investigated while the influence of varying the ZnO cathodic buffer layer thickness in inverted design is studied on AE. Then, the embedding of a square periodic array of core–shell silver–silica nanospheres (Ag@SiO2 NSs) at different positions in standard and inverted OSCs is performed while AE and short-circuit current density (Jsc) are calculated. As a result of previous combined effects, the optimized standard plasmonic OSCs present 15% and 79.45% enhancement in Jsc over the reference with and without ZnO optical spacer layer, respectively, and a 16% increase of AE when Ag@SiO2 NSs are placed on top of the PEDOT:PSS layer. Compared to the inverted OSC reference, the plasmonic OSCs present 26% and 27% enhancement in Jsc and AE, respectively, when the Ag@SiO2 NSs are located on top of the ZnO layer. Furthermore, the spatial position of these NSs in such OSCs is a key parameter for increasing light absorption via enhanced electromagnetic field distribution.

We propose a simple photonic crystal fiber (PCF) biosensor based on the surface plasmon resonance effect. The sensing properties are characterized using the finite element method. Chemically stable gold material is deposited on the outer surface of the PCF to realize the practical sensing approach. The performance of the modeled biosensor is investigated in terms of wavelength sensitivity, amplitude sensitivity, sensor resolution, and linearity of the resonant wavelength with the variation of structural parameters. In the sensing range of 1.33 to 1.37, maximum sensitivities of 4000  nm/RIU and 478  RIU−1 are achieved with the high sensor resolutions of 2.5×10−5 and 2.1×10−5  RIU using wavelength and amplitude interrogation methods, respectively. The designed biosensor will reduce fabrication complexity due to its simple and realistic hexagonal lattice structure. It is anticipated that the proposed biosensor may find possible applications for unknown biological and biochemical analyte detections with a high degree of accuracy.

Single-molecule detection has become a unique and indispensable tool for the study of molecular motions and interactions at the single-molecule level. Unlike ensemble measurement where the information is averaged, single-molecule analysis yields invaluable information on both the individual molecular properties and their microenvironment. Among the various technologies for the detection of single molecules, the detection with optical methods has many advantages in terms of its high sensitivity, electrical passiveness, and robustness. The recent advances in the engineering of either the excitation light or the solution of the molecules have paved the way for enhanced single-molecule detection. We present recent developments and future perspectives for single-molecule detection in the following three regimes: on a dry surface, in solutions at ultralow concentrations, and in solutions at native physiological concentrations.

Gold core–shell nanoparticles were synthesized based on metallic cores, variable silica shell spacers covered with modified fluorescent silica layers. Ultraluminescent properties were obtained based on metal-enhanced fluorescence (MEF). Different silica spacers were synthesized to optimize the MEF enhancement factor (MEF_EF). An optimal MEF_EF was determined equal to 9.5 for shorter silica spacers (d−_SiO2−=10  nm). These nanoparticles were deposed on Escherichia coli bacteria at different concentration levels for Bioimaging generation over their surfaces. The best luminescent nanoparticles were deposed on intermediate and higher bacteria concentrations. In the presence of intermediate bacteria concentrations, the ultraluminescent nanoparticles adsorbed showed an increase of 35% to 45% compared with individual nanoparticles. To modify the surface of individual bacteria, diluted samples of bacteria were used in which a 20% decrease in fluorescence emission was measured. In the presence of higher bacteria concentrations, fewer clear and bright images were obtained. At diluted ultraluminescent nanoparticle concentrations, a decrease in brightness and image detail was observed; and in the absence of nanoparticle deposition, no image was recorded. Accordingly, these ultraluminescent gold core–shell nanoparticles have been shown to be useful as platforms for biodetection and tracking applications.

In the framework of dipole approximation, it is shown that the oscillator strengths of transitions as well as the dipole moments for transitions for one-particle electron Coulomb states emerging above the spherical surface quantum dot of metal assume giant values considerably (by two orders of magnitude) exceeding the typical values of the corresponding quantities for dielectrics. It has been established that the giant values of the light absorption cross section in the nanosystems under investigation make it possible to use such nanosystems as strongly absorbing nanomaterials in a wide range of infrared waves with a wavelength that can be varied in a wide range depending on the type of contacting materials.

Over the last few years, there is a growing interest in photoacoustic imaging using nanoparticles techniques due to the improved penetration depth and resolution. Working with such nanoparticles usually requires pulsed laser illumination to generate an acoustic signal in the right frequencies. However, these pulsed lasers are considered expensive and complicated with respect to continuous-wave (CW) illumination. We design and simulate a special nanostructure with overall dimensions of 190×50× (26–34) nm, which blinks with fast temporal periodicity of 20 to 40 ns, under CW illumination and can be used for the generation of acoustic signals. This blinking is done using the enhanced optical absorption of metallic nanoparticles due to localized surface plasmon resonance (SPR) and the thermal expansion to generate heating–cooling cycles of the nanostructure. The CW laser wavelength is adapted to the localized SPR of the metallic nanostructure at the NIR region, which provides maximum penetration depth of light into biological tissues.

This article focuses on optical connectivity and coupling efficiency to and in between waveguides. We present numerical simulation results of our proposed multitaper (MT) high efficiency coupler that indicates low coupling losses and robustness to misalignment coupling errors. We obtained an absolute coupling loss of 0.85-dB coupling into a silicon waveguide and an improvement of 19 dB in vertical misalignment and 13 dB in angular misalignment, compared with existing coupling techniques. We conclude that using the MT, high efficiency coupling can be achieved while the dimensions and geometry can be adjusted and optimized for the specific configuration.

Controlling the spectral characteristics by regulating the geometry of microstructure has become an effective method to meet the requirements of various applications. To mediate the spectral characteristics, metallic subwavelength slits with different structures and color filters consisting of diverse materials were discussed, and then a designed microstructure composed of color filter and metallic slits, which were surrounded by grooves, was put forward for a compatible effect of controlling the spectral characteristics. Afterward, the spectral characteristics of the proposed structure were simulated by finite-difference time-domain method in the wavelength range of 300 to 10,000 nm. Additionally, the effects of geometric parameters on the spectral characteristics were studied. The results show that the presented microstructure can reflect a monochromatic color at the wavelength of 600 nm and its reflectance is ∼40%. The average absorptance near the wavelength of 1060 nm is more than 95%, and the average reflectance in the infrared band exceeds 80%. In conclusion, the compatible spectrum control in three bands (i.e., visible, near-infrared, and mid-infrared) was realized.

Recently, techniques for nanoparticles have rapidly been developed for various fields, such as material science, medical, and biology. In particular, methods of image processing have widely been used to automatically analyze nanoparticles. A technique to automatically segment overlapping nanoparticles with image processing and machine learning is proposed. Here, two tasks are necessary: elimination of image noises and action of the overlapping shapes. For the first task, mean square error and the seed fill algorithm are adopted to remove noises and improve the quality of the original image. For the second task, four steps are needed to segment the overlapping nanoparticles. First, possibility split lines are obtained by connecting the high curvature pixels on the contours. Second, the candidate split lines are classified with a machine learning algorithm. Third, the overlapping regions are detected with the method of density-based spatial clustering of applications with noise (DBSCAN). Finally, the best split lines are selected with a constrained minimum value. We give some experimental examples and compare our technique with two other methods. The results can show the effectiveness of the proposed technique.

Resonant waveguide gratings (RWGs) are thin-film structures, where coupled modes interfere with the diffracted incoming wave and produce strong angular and spectral filtering. The combination of two finite-length and impedance matched RWGs allows the creation of a passive beam steering element, which is compatible with up-scalable fabrication processes. Here, we propose a design method to create large patterns of such elements able to filter, steer, and focus the light from one point source to another. The method is based on ellipsoidal mirrors to choose a system of confocal prolate spheroids where the two focal points are the source point and observation point, respectively. It allows finding the proper orientation and position of each RWG element of the pattern, such that the phase is constructively preserved at the observation point. The design techniques presented here could be implemented in a variety of systems, where large-scale patterns are needed, such as optical security, multifocal or monochromatic lenses, biosensors, and see-through optical combiners for near-eye displays.

A dual band metamaterial absorber is designed for photovoltaic applications. The novelty of the design provides the absorption of the energy in an ultrathin semiconductor layer. Additionally, dependence of the absorption on the geometric dimensions, polarization, and temperature are also discussed. The results for the thermal characterization of the aforementioned design showed that this absorber operates almost independently from the environmental temperature conditions and the polarization of the light. According to the obtained results, the proposed metamaterial absorber can be a good candidate for the photovoltaic energy generation.

Microscopic quantum theory of nonlinear stimulated scattering of two-dimensional (2-D) massless Dirac particles in doped graphene on the Coulomb field of impurity ions at the presence of an external strong coherent electromagnetic radiation is developed. We consider high Fermi energies and low frequencies (actually terahertz radiation) to exclude the valence electrons excitations. The Liouville–von Neumann equation for the density matrix is solved analytically, taking into account the interaction of electrons with the scattering potential in the Born approximation. With the help of this solution, the nonlinear inverse-Bremsstrahlung absorption rate for a grand canonical ensemble of 2-D Dirac fermions is calculated. It is shown that one can achieve the efficient absorption coefficient by this mechanism.

Ceria nanoparticles are studied as optical probe for different types of tiny metallic particles using fluorescence quenching technique. The synthesized ceria nanoparticles are characterized by having formed charged oxygen vacancies, which can be considered as the main receptors for the used tiny metallic particles to be sensed or absorbed. Under near-UV excitation, the visible fluorescent emission intensity is found to be reduced with increasing the concentration of the studied tiny metallic particles in an aqueous solution. To emphasize the optical sensing process, ceria nanoparticles fluorescence lifetime measurements were demonstrated before and after adding the tiny metallic particles. In addition, Stern–Volmer constants, which are considered as an indication for the sensitivity to quenchers, have been calculated for the used ceria nanoparticles and found to be 1.645, and 0.768  M−1 for both lead and iron sensing, respectively. This work could be further helpful as sensitive optical sensors in both biomedical and environmental applications.

Trivalent cerium is an important luminescent center giving light emission in short wavelength region depending on host materials. Sol–gel formed silica glass is an ideal matrix due to its high transparency, robustness, and low-temperature processability, but the emission from cerium in silica matrix is often mixed up with that from defects in the matrix, making it difficult to obtain well-determined characteristics. Bright emission from Ce ions peaking at about 400 nm was observed in sol–gel silica glasses synthesized with aluminum co-dopant. From luminescence decay time, the origin was confirmed to be d−f transition in trivalent Ce. From dependence of emission characteristics and UV absorbance on aluminum concentration, it was found that the co-dopant plays an important role to convert the optically inactive tetravalent ions to emissive trivalent state.

Metastable phase VO2(B) film coated ITO glass was prepared using cyclic potentiometric device utilizing VOSO4 and H2SO4 solution. The optimum conditions for the deposition of the nanostructured VO2(B) film were determined using cathodic peak current density (Ipc) values. Ipc values increase with increasing both VOSO4 and H2SO4 concentrations and then decrease with further increasing the concentrations. Also, monoclinic phase VO2(M)/ITO film was prepared from VO2(B)/ITO film under the effect of annealing temperatures from 550°C to 750°C. Different analyses have been carried out to confirm the chemical, morphological, and crystal structure of the nanostructured VO2(M)/ITO film. From the XRD analysis, the crystallinity increases with the increasing of annealing temperature from 550°C to 750°C. The optical transmittance spectrum was ∼97% for the film annealed at 650°C. Also, the critical thermochromic temperature (Tc) of the optimized film was ∼47.5°C that measured using cooling and heating modes. Finally, the wettability of the VO2(M)/ITO film at different annealing temperature (550°C to 750°C) was studied, in which the contact angle increases from 81 deg to 92 deg with increasing annealing temperatures from 550°C to 750°C, respectively.

Theoretical analysis and numerical simulations are applied to propose an improved spectrally splitting method in a filter structure, based on aperture-coupled plasmonic slot cavity. By considering the field distribution inside the cavity slot, this structure is benefited from the position of output aperture to split the resonance modes of the cavity. According to the proposed narrow bandpass filter and spectrally splitting mechanism, a two- and three-port power splitters and an ultracompact four-channel multi/demultiplexer are proposed. Our structures are numerically analyzed using the two-dimensional finite-difference time-domain method. Our results can be utilized for construction of nanoplasmonic multiwavelength multi/demultiplexers to be used in nanoplasmonic integrated circuits.

A device is designed for generating the near-field optical vortex (NFOV) using linearly polarized light illumination. This optical vortex generator consists of 18 homogeneous rectangular holes. Each rectangular hole can be modeled as a pair of orthogonal dipoles with π/2 and −π/2 phase differences under 45 deg and −45  deg polarized light illuminations, respectively. The superposition of the surface plasmon polaritons excited by these 18 homogeneous rectangular holes can create an optical vortex at the center of the generator, and the topological charge of the optical vortex can be changed by arranging these rectangular holes in a different trajectory. Both theoretical analysis and numerical simulation are used to investigate the properties of the NFOV generator. The numerical results demonstrate that the NFOV generated by the device is reliable, efficient, and flexible. This NFOV generator can be applied in optical manipulation.

We proposed a six-channel photonic plasmonic biosensor with bimetallic coating of metal oxide, which operates in the infrared region of the spectrum. The outer surface of the channel has been coated with an indium tin oxide (ITO) material layer followed by another coat of Ta2O5 and TiO2 plasmonic material. The study of light-matter interaction in compact and wider region is carried out, and the sensor performance using bimetallic coating of conducting metal oxides is numerically analyzed. Results show that the compact sensor has high sensitivity and easy liquid infiltration governed by pressure and capillary action. Moreover, wavelength sensitivity is numerically investigated for various structural parameters. The proposed sensor design has maximum wavelength sensitivity of 5000  nm/RIU for ITO/TiO2 plasmonic material.

The high-quality and transparent thin-film zinc oxide (ZnO) nanostructures/nanotextures deposited on glass and silicon substrates using pulsed laser deposition (PLD) technique are reported. A solid-state, Nd-YAG laser was used for the PLD process. The films were deposited (i) at room temperature of 25°C (as deposited), (ii) at 150°C, (iii) at 300°C, (iv) at 450°C, and (v) at 600°C and annealed in the vacuum chamber. The depositions were also carried out at different laser repetition rates such as 10 and 5 Hz. UV spectroscopy and photoluminescence (PL) spectroscopy were carried out for optical studies. X-ray diffraction studies were carried out for all samples and analyzed the effects of the laser repetition rate, deposition, and annealing temperatures on the structural properties. Field-emission scanning electron microscope images are recorded for the best-structured samples. The electrical parameters were calibrated using the Hall effect measurement system and the IV characterization was performed using a CHI Electrochemical workstation. The deposition temperature has a significant effect on the microstrain and dislocation density of the ZnO thin film and optical phenomena with various electrical parameters, including the electron mobility, conductivity, and magnetoresistance. These promising results are suitable conditions for nanophotonics applications.

Shrinking the linewidth of resonances induced by multiple coupled resonators is comprehensively analyzed using the coupled-mode theory (CMT) in time. Two types of coupled resonators under investigation are coupled resonator optical waveguides (CROWs) and side-coupled resonators with waveguide (SCREW). We examine the main parameters influencing on the spectral response such as the number of resonators (n) and the phase shift (φ) between two adjacent resonators. For the CROWs geometry consisting of n coupled resonators, we observe the quality (Q) factor of the right- and left-most resonant lineshapes increases n times larger than that of a single resonator. For the SCREW geometry, relying on the phase shift, sharp, and asymmetric resonant lineshape of the high Q factor a narrow linewidth of the spectral response could be achieved. We employ the finite-difference time-domain (FDTD) method to design and simulate two proposed resonators for practical applications. The proposed coupled resonators in silicon-on-insulator (SOI) slotted two-dimensional (2-D) photonic crystals (PhCs) filled and covered with a low refractive index organic material. Slotted PhC waveguides and cavities are designed to enhance the electromagnetic intensity and to confine the light into small cross-sectional area with low refractive index so that efficient optical devices could be achieved. A good agreement between the theoretical CMT analysis and the FDTD simulation is shown as an evidence for our accurate investigation. All-optical switches based on the CROWs in the SOI slotted 2-D PhC waveguide that are filled and covered by a nonlinear organic cladding to overcome the limitations of its well-known intrinsic properties are also presented. From the calculations, we introduce a dependency of the normalized linewidth of the right-most resonance and its switching power of the all-optical switches on number of resonator, n. This result might provide a guideline for all-optical signal processing on a silicon PhC chip design.

Timing resolution (or timing jitter) and time walk are separate parameters associated with a detector’s response time. Studies have been done mostly on the time resolution of various single-photon detectors. As the designer and manufacturer of the ultra-low noise (ƙ-factor) silicon avalanche photodiode the super low K factor (SLiK) single-photon avalanche diode (SPAD), which is used in many single-photon counting applications, we often get inquiries from customers to better understand how this detector behaves under different operating conditions. Hence, here, we will be focusing on the study of these time-related parameters specifically for the SLiK SPAD, as a way to provide the most direct information for users of this detector to help with its use more efficiently and effectively. We will be providing the study data on how these parameters can be affected by temperature (both intrinsic to the detector chip and environmental input based on operating conditions), operating voltage, photon wavelength, as well as light spot size. How these parameters can be optimized and the trade-offs from optimization from the desired performance will be presented?

A design of hydrogenated amorphous silicon (a-Si:H) solar cell (SC) based on one-dimensional subwavelength grating with nonuniform distribution is proposed and optimized using modified hybrid gravitational search algorithm and particle swarm optimization (GSA-PSO). The reported structure consists of nine gratings with different widths, positions, and heights that can enhance the light trapping through the SC. The nonuniform grating positions and geometrical parameters of the proposed design are optimized in terms of absorption, ultimate efficiency, and short circuit current density. The absorption inside the active layer is enhanced by 67.5% over the conventional thin-film SC. Further, the exposed area caused by forward nanotexturing surface is increased. Moreover, the nonuniform grating parameters and distribution support better light absorption than the periodic grating distribution by increasing the optical path length of the incident light through the active layer. Therefore, the suggested SC achieves a broadband absorption improvement. The enhanced absorption in the active layer is reported using three-dimensional finite-difference time-domain method. In addition, the performance of the suggested SC using different active layer materials, i.e., crystalline silicon, a-Si:H, and gallium arsenide is studied. The hydrogenated amorphous silicon-based design shows high ultimate efficiency of 38.73%, short-circuit current density (J_SC) of 34.69  mA  /  cm², open-circuit voltage of 1.0393 V, and power conversion efficiency of 35.4%. The modified GSA-PSO algorithm shows also high potential for the design and optimization of different types of solar cells.

The rigorous coupled-wave approach (RCWA) was implemented to investigate optical absorption in a triple-p-i-n-junction amorphous-silicon solar cell with a two-dimensional (2-D) metallic periodically corrugated backreflector (PCBR). Both total and useful absorptances were computed against the free-space wavelength λ₀ for both s- and p-polarized polarization states. The useful absorptance in each of the three p-i-n junctions was also computed for normal as well as oblique incidence. Furthermore, two canonical boundary-value problems were solved for the prediction of guided-wave modes (GWMs): surface-plasmon-polariton waves and waveguide modes. Use of the doubly periodic PCBR enhanced both useful and total absorptances in comparison with a planar backreflector. The predicted GWMs were correlated with the peaks of the total and useful absorptances. The excitation of GWMs was mostly confined to λ₀  <  700  nm and enhanced absorption. As excitation of certain GWMs could be correlated with the total absorptance but not with the useful absorptance, the useful absorptance should be studied while devising light-trapping strategies.

A midinfrared high birefringence Ge₂₀Sb₁₅Se₆₅-based hexagonal lattice photonic crystal fiber (PCF) with central defect core and dual-rhombic air holes cladding is proposed. The finite difference time-domain method with perfectly matched layer absorption boundary conditions are used to numerically analyze the guided modes of the designed PCF. The properties of this PCF including the birefringence, beat length, dispersion, and nonlinearity are investigated in the 3 to 5  μm midinfrared range. The results show that for the optimized structure parameters of Λ  =  2  μm, D  =  1.7  μm, H  =  1.76, and d  =  0.4  μm, the highest birefringence of 0.1513 and beat length of 33.04  μm are obtained. The maximum nonlinearity coefficients of 3726 and 2585  w^−  1 km^−  1 for x- and y-polarization modes are achieved. The distinctive dispersion is acquired, which is all-normal for x-polarization mode while has single zero dispersion points at 3.96  μm for y-polarization mode. The designed PCF will have broad application in midinfrared optical fiber sensing, nonlinear optics, and precision optical instruments.

Improving solar cell efficiency is a critical research topic. Nowadays, light trapping techniques are a promising way to enhance solar cell performance. A modified nanocone nanowire (NW) is proposed and analyzed for solar cell applications. The suggested NW consists of conical and truncated conical units. The geometrical parameters are studied using a three-dimensional (3-D) finite difference time-domain (FDTD) method to achieve broadband absorption through the reported design and maximize its ultimate efficiency. The analyzed parameters are absorption spectra, ultimate efficiency, and short circuit current density. The numerical results prove that the proposed structure is superior compared with cone, truncated cone, and cylindrical NWs. The reported design achieves an ultimate efficiency of 44.21% with substrate and back reflector. Further, short circuit current density of 36.17  mA  /  cm² is achieved by the suggested NW. The electrical performance analysis of the proposed structure including doping concentration, junction thickness, and Shockley–Read–Hall recombination is also investigated. The electrical simulations show that a power conversion efficiency of 17.21% can be achieved using the proposed NW. The modified nanocone has advantages of broadband absorption enhancement, low cost, and fabrication feasibility.

Quantum dot solar cells (QDSC) have been extensively studied by various researchers for the last 15 years as they have much higher conversion efficiency and it is capable of producing higher short-circuit current density in comparison with the conventional crystalline solar cells. A theoretical study was carried out on the In_xGa_{1  −  x}As  /  GaAs p-i-n QDSC considering absorption spectra of real cubic quantum dots embedded in the intrinsic region. We incorporated the absorption coefficient of the cubic quantum dot ensemble considering finite potential barriers; additionally, here, we considered the nonuniform size distribution described by the Gaussian function. The contributions of the photocurrent density from different regions of the cell were investigated. The photocurrent density of the intrinsic region was studied by varying the height of the quantum dots and by varying the size dispersion factor. Also, the total short-circuit current density and the power conversion efficiency of such photovoltaic devices were calculated, and some significant results were obtained.

Using an oblique linearly polarized laser beam, Goos–Hänchen (GH) and Imbert–Fedorov (IF) reflection shifts of a two-dimensional array of gold nanoparticles (NPs) on water substrate are investigated within the framework of a theoretical model. The dependences of spatial   (  Δ  )   and angular   (  Θ  )   shifts on the angle of radiation, the polarity of light, the size, and concentration of particles have been studied in detail. It is shown that a grazing p-wave light yields to the highest negative amount of GH shifts, while a 45-deg polarization that radiates at 45 deg would maximize IF shifts. The deviations are sensitive to the particle size linearly and decrease using larger NPs except in the angular out-of-plane shift Θ_IF, which has a critical point where its sign and trend change. The curves of Δ_GH, Θ_GH, and Θ_IF for various lattice constant exhibit peaks for a specific arrangement that moves toward smaller values as the particle size increases. On the other hand, Δ_IF always has an additive behavior. Accurate monitoring of these parameters may serve as a precise method to determine thickness and aggregation of nanostructured films.

A compact footprint, low-power consumption, and high-speed operation electro-optical full-adder/full-subtractor based on graphene–silicon electro-optical switches is demonstrated. Each switch consists of a Mach–Zehnder interferometer in which few-layer graphene is embedded in a silicon slot waveguide to construct phase shifters. The presented structure can be used as full-adder and full-subtractor simultaneously. The analysis of various factors such as extinction ratio, power consumption, and operation speed has been presented. As will be shown, the proposed electro-optical switch has a minimum extinction ratio of 36.21 dB, maximum insertion loss about 0.18 dB, high operation speed of 180 GHz, and is able to work with a low applied voltage about 1.4 V. Also, the extinction ratio and insertion loss of the full-adder/full-subtractor are about 30 and 1.5 dB, respectively, for transfer electric modes at telecommunication wavelength of 1.55  μm.

This article corrects an error in the original published paper.