High-efficiency and ultrathin crystalline silicon solar cells (SCs) with a frequency upconversion (UC) layer and an array of silver nanohemispheres were presented. The light-trapping performances of SCs embedded with different volume ratios and radii of Ag nanohemispheres were systematically studied by finite-element analysis. The simulation results show that the short-circuit current density of the SCs and the light-field intensity in the UC layer can be significantly improved by adjusting the structural parameters of Ag nanohemispheres. The short-circuit current density of the structured SCs have been improved by 16.48% and the light-field intensity in the UC layer has been increased by 2.65 times compared to that of planar SCs. Additionally, the UC effects on the power conversion efficiency of the SCs were also investigated. The presented model will serve as the basis for further preparations of high-efficiency ultrathin crystalline SCs.

Thin film solar cells, which are the second generation of solar cells, have recently attracted much attention due to their low cost and abundance of fabrication materials. But due to the reduction in the thickness of the absorber layer in this generation to <0.5 μm, the amount of absorption is greatly reduced and the short circuit current density (J_sh) decreased due to the reduction of the light path length in the semiconductor. Therefore, light trapping is challenging in this generation to compensate for the reduced short circuit current. In this work, crystalline and amorphous silicon thin film solar cells, which are types of thin film solar cells have been investigated. In this study, using silver metal gratings with triangular and rectangular shapes on the back electrode of the solar cell, we investigated the effect of the grating structure on increasing absorption of the solar cell. Crystalline silicon (c-Si) and amorphous silicon (a-Si) have been used as absorber layer material due to their unique characteristics, such as low cost, abundance, and well established. The results show that by applying the optimal structure of grating in crystalline silicon solar cells, compared with the simple solar cell, the efficiency and short current of the cell increased from 8.87% and 16.81 (mA / cm²) to 13.34% and 24.78 (mA / cm²), respectively. And for the solar cell with amorphous silicon absorber layer, this increase in efficiency and short circuit current has reached from 14.75% and 28.74 (mA / cm²) to 15.22% and 29.6 (mA / cm²), respectively. This increase in electrical parameters of solar cells illustrates the positive effects of back grating structures in improvement of solar cell performance.

Hybrid plasmonic waveguides (HPWs) are capable of supporting subwavelength optical modes. In a composite HPW (CHPW), the propagation loss can be minimized by adjusting the geometrical parameters of its component layers to reduce field flux inside its lossy metal layer. A ring resonator-based plasmonic sensor based on a waveguide structure of suspended CHPW (SCHPW) is designed for gas sensing applications. SCHPWs are applied for the introduced sensor’s 200-nm-wide bus waveguide and 1-μm-radius ring resonator. The operational parameters of the sensor, such as sensitivity and figure of merit (FOM), are investigated in the near-infrared region using a three-dimensional finite-difference time-domain method. For two considered resonances of the proposed sensor, sensitivities of 236.2 and 270 nm / RIU with FOMs of 67.4 and 37.5 RIU ^{− 1} are achieved, respectively. Additionally, for the proposed sensor, a straightforward mechanism for sensing the mass density of the polarizable hydrogen gas is introduced using the theoretical index–density relation of Lorentz–Lorenz. The mass density sensitivities of 358.2 and 409.3 nm / ( g / cm³ ) are achieved for the two considered resonances for the hydrogen gas at the range of 0 to 0.05 g / cm³.

We proposed an all-optical plasmonic switch based on metal-insulator-metal structures. We used the intrinsic nonlinear properties of gold to implement the switch. The proposed switch consists of a bus waveguide side coupled with a pair of asymmetric vertical cavities. We obtained the transmission spectrum of the structure for low input intensities. The results showed that a sharp dip occurs at the wavelength of 860 nm. Due to the nonlinear properties of gold and the nonlinear Kerr effects, the proposed switch has a high transmission ratio of about 0.8 mW / μm² and a low threshold power of 0.07 mW / μm². The threshold power of the structure with and without using the gold nanostructure shows a reduction of 50%. The result showed that the proposed switch has the potential to be applied in the plasmonic integration circuits.

Temporally periodic physical vapor deposition (TP-PVD) is commonly used to fabricate Bragg mirrors on planar surfaces. These devices are notionally of infinite transverse extent and homogeneity, but they have periodically nonhomogeneous electromagnetic constitutions in the thickness direction. Undertaking TP-PVD in two different formats, we found that the Bragg phenomenon can be avoided in certain thin-film applications by undertaking TP-PVD on surfaces roughened randomly on the scale of the wavelength.

The capabilities of modern precision nanofabrication and the wide choice of materials [plasmonic metals, high-index dielectrics, phase change materials (PCM), and 2D materials] make the inverse design of nanophotonic structures such as metasurfaces increasingly difficult. Deep learning is becoming increasingly relevant for nanophotonics inverse design. Although deep learning design methodologies are becoming increasingly sophisticated, the problem of the simultaneous inverse design of structure and material has not received much attention. In this contribution, we propose a deep learning-based inverse design methodology for simultaneous material choice and device geometry optimization. To demonstrate the utility of the proposed method, we consider the topical problem of active metasurface design using PCMs. We consider a set of four commonly used PCMs in both fully amorphous and crystalline material phases for the material choice and an arbitrarily specifiable polygonal meta-atom shape for the geometry part, which leads to a vast structure/material design space. We find that a suitably designed deep neural network can achieve good optical spectrum prediction capability in an ample design space. Furthermore, we show that this forward model has a sufficiently high predictive ability to be used in a surrogate-optimization setup resulting in the inverse design of active metasurfaces of switchable functionality.

The optical absorption properties of the two-dimensional (2D) MoSi₂N₄ monolayer is often a focus of research. By semi doping Cr and W at M sites, the influence of M-site atoms on the optical absorption properties of MA₂Z₄ series materials was investigated. The results show that the atomic layer spacing of 2D materials has some changes after the semi doping of the Cr and W elements, but the entire crystal structure is not significantly different. The semi doping of Cr atoms makes the MoSi₂N₄ monolayer have an additional absorption peak, the highest absorption peak of the Mo_0.5Cr_0.5Si₂N₄ monolayer has a large red shift corresponding to the wavelength, and the width of the absorption peak is also greatly improved. The semi doping of W element results in a red shift of the strongest absorption peak and an increase of the maximum absorption intensity of the Mo_0.5W_0.5Si₂N₄ monolayer.

A non-volatile flexible-grid wavelength-selective switch (NVFGWSS) based on subwavelength-grating-Ge₂Sb₂Te₅ (GST)-assisted silicon microring resonators (MRRs) is proposed. By controlling the state of the subwavelength grating GST and the phase shifter, the transmission spectra of the designed subwavelength-grating-GST-assisted silicon MRRs are combined, and thus tunable bandwidths (BWs) are generated as required. A comprehensive analysis of the presented subwavelength-grating-GST-assisted silicon MRRs and the corresponding NVFGWSS is given. Numerical simulations reveal that, for the designed module comprising a subwavelength-grating-GST-assisted silicon MMR and an ellipse-based crossing waveguide, its maximum crosstalk (CT) and insertion loss are −18.08 and 0.50 dB, respectively. For the designed NVFGWSS, as the channel spacing is 0.8 nm, the in-band ripple and CT are <0.895 and −13.006 dB, respectively, and the 3-dB BW changes from 0.51 to 3.2 nm.

The nanocomposite, poly(3-hexylthiophene-2,5-diyl) (P₃HT)–graphene/molybdenum disulfide (MoS₂), was for the first time fabricated by the pulse laser ablation (PLA) method with different numbers of laser pulses deposited onto a porous silicon (PSi) substrate using the drop-casting technique. Nanocrystalline PSi films are prepared by electrochemical etching of a P-type silicon wafer. The optical properties, transmission electron microscope (TEM), and photodetector properties were studied. Optical measurements confirmed that the energy gap decreases from 2.03 to 1.87 eV with the increasing number of laser pulses for graphene and MoS₂. This decrease in the energy gap was attributed to the increase in graphene and its combination with molybdenum. Due to the higher electrical conductivity of the hybrid material, the MoS₂ leads to reduce the band gap. From the TEM images, it was found that the average size of the particles was between 3.1 and 20.8 nm depending on increasing the number of laser pulses for both graphene and MoS₂ with hemispherical particle shapes. The Ag / PSi / P₃HT − G / MoS₂ / Ag photodetector was fabricated for all samples prepared to characterize the effect of laser pulses number for graphene and MoS₂ on the photodetector performance. The maximum value of the specific response, specific detection, and quantum efficiency was 0.35 A / W, 5.1 × 10¹² cm Hz^1/2 W ^{− 1}, and 49.2% at 900 nm due to the absorption edge of silicon around 0.23 A / W, 3.3 × 10¹² cm Hz^1/2 W ^{− 1}, and 38.9% at 760 nm due to the absorption edge of P₃HT − G / MoS₂ NPS. The results indicate that the PLA method successfully fabricated the P₃HT − G / MoS₂ nanocomposites and that the resulting product exhibited high values in responsivity, detectivity, and quantum efficiency. Additionally, it appears that the nanocomposites may have enhanced the same parameters of the PSi photodetector.

Surface acoustic waves (SAWs) with a strong enough piezoelectric field can capture and transport electrons and holes. The presence of SAWs and their photo-generated carriers’ transport properties in the GaAs/AlGaAs quantum well (QW) is a potential scheme to achieve single photon sources and single photon detectors. We numerically solve the system of coupled Schrödinger and Poisson equations and the carriers’ radiative lifetime. A finite difference method of two-dimensional was developed as a conventional approach to the theoretical understanding of the presence in the QW through Python programs. The features of carriers’ radiative lifetime are discussed as functions of the SAW wavelengths and SAW amplitudes. The spatial separation and radiative lifetime extension of the electrons and holes in the SAW-driven QW was explained by the method.

A long-wave infrared (LWIR) on-chip gas sensor based on subwavelength grating waveguide is proposed. By optimizing the grating structural parameters, the corresponding slow-light region is overlapped with the absorption spectrum of methane, which can greatly improve the light–gas interaction to achieve excellent sensing performance. The presented waveguide gas sensor is designed to operate at the wavelength of 7.70 μm, which corresponds to the methane absorption peak in the LWIR and exhibits a high slow-light enhancement factor of 7.514. The related sensitivity and limit of detection are, respectively, 26.54393 and 0.1327 ppm.

The advent of nanotechnology has led to the inevitable need for miniaturization in optoelectronic devices. To achieve this goal, materials with low thickness, conductivity, and transparency, as well as a larger active area, must be developed. Experiments have proven that the opto-electrical properties of transition metal dichalcogenides (TMD)/graphene combinations are highly tunable. On the other hand, a notable feature of light when reflecting from an interface is its spatial and angular displacements. The “lateral shift” in the incident plane, referred to as the Goos–Hanchen (GH) shift, has garnered significant interest among researchers owing to its extensive range of applications. In our work, an atomically thin TMD/graphene/TMD sandwich heterostructure is proposed, and its spatial and angular GH shifts are investigated. The theoretical analysis includes various TMD materials such as MoSe₂, MoS₂, WSe₂, and WS₂. A detailed study of the effects of wavelength, polarization, incident angle, and number of TMD layers in symmetric and asymmetric structures suggests that this hybrid can serve as an ultrathin broadband tunable sensor in optical devices.

To monitor the health of agricultural soil, lead (Pb^{2 +} ) ion measurement is essential. The various sensors for lead ion detection reported in the literature earlier are either expensive or have complicated designs. This inspired us to propose a fiber optic sensor that is simple in design, less expensive, and more efficient. A photonic crystal fiber (PCF)-unclad single mode fiber (SMF)-PCF hybrid configuration makes up the suggested sensor, and the sensing mechanism is based on a synergistic application of surface plasmon resonance and interferometry. It is shown that the suggested structure is easy to use for Pb^{2 +} ion detection, in addition to other advantages in limit of detection (LOD) and sensitivity. The proposed structure is optimized to attain a LOD of 8.32 mg / kg, which is much less than the permissible limit of Pb^{2 +} ions permitted in healthy agricultural soil, i.e., 100 to 400 mg / kg. Additionally, a polymer that is attached atop the gold layer and to which only Pb^{2 +} ions can adhere ensures the sensor’s specificity. To the best of our knowledge, our proposed optical fiber-based sensor design and approach adopted to detect lead ions in agricultural soil are the first of their kind.

To find more simple and universal method to realize the topological photonic crystals (PCs), we use the fold effect of bands of PCs and the Su–Schrieffer–Heeger model. Through the change of structure parameters, a lattice can undergo the transformation from topologically trivial to nontrivial states. The fold effect of bands leads to the multiple topological edge bands, which increase the band width of topological states. Furthermore, the topological corner states can be formed in the designed structure.

Publisher’s note corrects a typographical error in a figure.