This is a list of reviewers who served the Journal of Nanophotonics in 2021.

The thermal evaporation of Cu₂ZnSnS₄ (CZTS) nanoparticles synthesized by changing the sulfur ratio in the precursor solution was used to investigate the critical role of sulfur concentration in the photoelectrochemical (PEC) water splitting reactions of the CZTS photocathode. X-ray diffraction, transmission electron microscopy, UV–visible spectroscopy, impedance spectroscopy, capacity measurement, and PEC performance measurement were used to investigate the effect of precursor sulfur concentration on the structural, morphological, optical, and PEC performance of films. The half-cell solar-to-hydrogen efficiency of CZTS photoelectrodes increased as the sulfur content increased. The power conversion efficiency of the CZTS cathode constructed with CZTS nanoparticles synthesized with a 0.8 to 1.0 M precursor sulfur concentration was 0.32% at 0 V versus RHE under AM 1.5 illumination. The increase in crystallite size and charge carrier concentration is observed with increasing precursor sulfur concentration, and the maximum crystallite size and charge carrier concentration are observed at 1.0 M sulfur concentration. By carefully adjusting the crystallite size and thus the charge carrier concentration of the CZTS material, the PEC water splitting efficiency of the CZTS photocathode can be improved.

The synthesis and characterization of gadolinium-based micro- and nanophosphors are reported. These materials were synthesized by solvent evaporation technique and microwave-assisted solvothermal method, respectively. According to scanning electron microscopy measurements, Gd₂O₃ and Gd(OH)₃ phosphors have lamellar and nanorods structures, respectively. Their luminescent properties are generated by the presence of Tb^3  + ions, which produced light emission at 484, 542, 583, and 621 nm due to the D₄5  →  F₆7, F₅7, F₄7, and F₃7 interlevel transitions within Tb^3  + electronic energy states. These phosphors were embedded into two polymers, polymethyl methacrylate and polystyrene, and their luminescent properties were transferred to polymeric films. In addition, in this case, films can be activated under lower excitation energy than powder phosphors because an energy transfer from polymers to Tb^3  + ions exists. The obtained results reveal that gadolinium-based micro- and nanophosphors are candidates for manufacturing luminescent materials in industrial and biological applications as well.

A typical prism-coupled surface-plasmon-resonance biosensor comprises a metal thin film in contact with a solution containing an analyte to be sensed. The metal film also acts as a binding surface for bioreceptor molecules to capture and concentrate the analyte molecules of interest. We investigated the use of a porous, anisotropic, periodically non-homogeneous material called a chiral sculptured thin film (CSTF) grown on top of the metal film to confine the solution in its pores. The efficacy of a basic plasmonic sensor was compared with those of two types of sensors containing a CSTF, one type having a metal-nanoparticle layer at a distance of one period from the metal film and the other without that layer. The chosen analyte was Immunoglobulin G and the chosen bioreceptor was Protein A. Measurements were made over a wide angular range rather than over a small range tied to the excitation of a surface-plasmon-polariton wave, and the collected data were used to train a machine-learning algorithm called a support vector machine for classification. We concluded that the metal/CSTF sensor with a metal-nanoparticle layer performs best, the metal-nanoparticle layer being crucial to its better performance.

At present, a high-order, reconfigurable photonic signal processor is very difficult to implement. A simple, reconfigurable photonic N-differentiator and integrator based on a unit of the dual-ring coupled Mach–Zehnder interferometer (DRMZI) is proposed first. The reconfigurability is achieved only by controlling the thermo-optic phase shifter (TO-PS) on the two improved micro-ring resonators. The device presents a wide fine-tunable differentiation order range from 0.2  ≤  N  ≤  1.7 reconfigured as a 2  ×  2 differentiator after being optimized the TO-PS and the tunable couplers (TC). If it is reconfigured as an integrator, a first-order photonic temporal integrator with 16.1 GHz 3-dB bandwidth and integration time window 38.4 ps is achieved in our design. The 4  ×  4 port DRMZI differential unit can be cascaded into k-stage to realize 0.2  ×  k  ≤  N  ≤  1.7  ×  k order differential function, theoretically approaching any large order. At the same time, the differential signals can be successfully routed to different output ports by reconfiguring the optical path in the structure. The simulation results have shown that a two-stage 4  ×  4 photonic temporal differentiator can perform more than two order differential operations, e.g., N  =  2.4. Our research can provide a reference for chip-level large-scale integrated photonic processors.

A mid-infrared (mid-IR) broadband polarization beam splitter (PBS) based on a gallium sulfide dual core highly birefringent photonic crystal fiber is proposed. The high birefringence and dual core are achieved by introducing two kinds of circular air holes with different diameters into the fiber core. The mode coupling characteristics of the even and odd modes in the proposed dual core PBS are investigated using the finite-difference time-domain method and coupled-mode theory. The numerical simulation results indicate that, when the incident light frequency is 4.5  μm and the PBS length is 277.1  μm, a wide bandwidth of 170 nm (from 4.472 to 6.642  μm) with a polarization extinction ratio (ER) >20  dB is obtained in the mid-IR waveband. The highest ER of 112.8 dB is realized. The designed PBS will find potential applications in mid-IR optical sensing, communication, and imaging systems because of its wide bandwidth and ultrashort length.

We propose a structure comprising a defective one-dimensional planar binary photonic crystal (PC) to realize a demultiplexing operation for dense wavelength division multiplexer (DWDM) transmission systems. The unit cell of the crystal consists of ZnSe and ZnS thin films, and the defective layer is ZnS_xSe_{1  −  x}, (0  ≤  x  ≤  1). Transmittance for the structure was numerically investigated using the transfer matrix method. The selecting mechanism of the output wavelength was based on selecting the appropriate sulfur concentration (x value) in the defective layer of the PC. We used six different sulfur concentrations to demultiplex six different output channels. The line width of the output channels was about 0.13 nm with a quality factor of 12,199. The average crosstalk between the adjacent transmitted channels was about −22.16  dB. The overall dimension of the proposed demultiplexer was about 108.4  μm, which practically makes the demultiplexer easily integrated into photonic circuits. Our results show that the proposed structure has all of the required characteristics to demultiplex the C-band signals with a 0.16 nm separation, which corresponds to the ITU grid for DWDM.

Periodic metallic nanoparticle arrays have a wide range of applications in sensors due to the generation of the plasmonic lattice resonance (PLR). To increase the figure of merit (FOM) of periodic metallic nanoparticle arrays, schemes to reduce full-width at half maximum (FWHM) are necessary. Introducing silicon and dielectric nanopillars under metallic nanoparticles has been suggested as a feasible route to reducing FWHM and thus enhancing FOM. However, many factors may lead to a reduction in FOM. Thus, different factors, such as the diameter and height of metallic nanoparticles, the diameter and height of silicon nanopillars, the height of dielectric nanopillars, and the period of the arrays, should be explored to improve FOM of this structure. We investigate the influences of different structural parameters on FOM of Ag  /  Si  /  SiO₂ nanopillar array sensors. Results show that a larger diameter of the Ag nanopillars widens the FWHM and weakens the FOM. The optimal diameter of Si nanopillars and the optimal height of Ag nanopillars to obtain a high FOM are all 100 nm. The period of larger arrays corresponds to a narrower FWHM and higher FOM. A larger height of Si nanopillars or a larger height of SiO₂ nanopillars decreases the FWHM and increases the FOM. These results are relatively instructive and meaningful for the design of PLR sensors with a high FOM.

An electrically controllable focal length is proposed for the visible wavelength range. The proposed structure is composed of a graphene sheet placed on a silver grating. The effect of the chemical potential variation of the graphene sheet on the light wave deflection, and hence the focal length of the structure, is investigated. The results of the full-wave simulation analysis based on the finite difference time domain (FDTD) method show that the focal length of the structure varies by approximately 7.82λ through changing the chemical potential of graphene from 0.1 to 1 eV. In addition, a generalized equivalent circuit model is introduced for the analysis of the proposed tunable graphene structure. The achieved results based on the circuit model match well with those based on the FDTD method. The proposed structure has the potential to be used in imaging devices and optical sensors.

Plasmonic devices enable nanophotonics and nanodevices as an alternative to address the miniaturization and diffraction limit problems in photonics devices. An all-optical 2  ×  1 multiplexer (MUX) based on aplasmonic multilayer structure (insulator–metal–insulator) is proposed. The working wavelength is 1550 nm and the design area is (350  nm  ×  250  nm). The proposed device works under the principle of destructive and constructive interference, which happens between inputs and selector signals. The performance of the proposed device is measured by three criteria: transmission, extension ratio, and modulation depth. In transmission signals, an amplifying process occurs; two states are exceeding 100%. The proposed structure dimensions are excellent and optimum according to the value of MD (98.85%). In addition, the operation of the proposed structure is achieved without the need for the control signal, which adds more complicity and degrades the device efficiency. The proposed structure has a major role in building the all-optical arithmetic logic unit, photonics integrated circuits, and THz applications.

We present a simple quad-band terahertz (THz) metamaterial absorber for perfect absorption. Unlike most reported absorbers, the proposed structure achieves perfect absorption based on high-order plasmon resonance, with the absorptivity of the first three peaks all >99.4  %  . First, the resonance absorption mechanism of the absorber involving fundamental resonance mode and high-order resonance mode is analyzed in detail. Next, the sensing performance is also studied by changing the ambient refractive index, the numerical results show that the designed multiband metamaterial absorber is very sensitive to small changes in refractive index, and appears highly sensitive in its sensing performance. In particular, figure of merit of the last absorption peak reaches 26.6, which is far superior to most multiband metamaterial absorbers operating in the THz regime. The proposed simple structure not only greatly simplifies the fabrication, but also is insensitive to the polarization of incident waves. The results show that the quad-band metamaterial absorber has potential applications in sensing, imaging, detection, and other fields.

A plasmonic perfect absorber based on the ring hole and slot waveguide in three different structures is proposed as a sensor and simulated using the three-dimensional finite-difference time-domain numerical method for perpendicular incidence of a plane wave light within 900 to 1900 nm wavelength range. The simulation results show that two resonance peaks emerged in the absorption spectrum of the devices. To investigate the sensing capability of this absorber, the ring holes and slot waveguides on the upper surface of the structures are filled with analytes with different refractive indices. It is observed that the resonance peaks are redshifted with increasing the refractive index of the analyte. The sensitivity of the first and second resonance peaks for structure 1 is 260.7 and 154.4  nm  /  RIU, respectively, for structure 2 are 303.4 and 102.7  nm  /  RIU, respectively, and for structure 3 are 261.9 and 103.2  nm  /  RIU, respectively, which indicates the good ability of the devices to detect analytes with refractive indices close to each other.

We report a programmable phase change medium-based hyperbolic metamaterial (HMM) with emphasis on the optical response characterized by adjusting the electrical constants and/or structural parameters (such as thicknesses and/or filling fraction) of the constituent materials. The investigation reveals broad area of the type I HMM in the visible regime for the device comprising silver and stibnite mediums. The angle- and polarization-insensitive properties of the configuration demonstrate an in-band rejection of over −75  dB, tunable in the range of 0.5723 to 0.639  μm, and an 8-bit encoding bandwidth of 12 nm. Also, the study yields two distinct modulation mechanisms at the incidence angle of 62 deg, viz. a Brewster modulator in the UV regime (which solely depends on the incidence obliquity) and an angle-insensitive reflection modulator in the visible regime—the features that are programmable according to the thermal ambience.