We design and numerically investigate an all-dielectric metamaterial, consisting of silicon ring and disk with a missing wedge-shaped slice lying on a silica substrate that realizes multiple switching based on toroidal and trapped dipole magnetic responses. Such two responses can be dynamically switched on and off simultaneously only through changing polarization of incident light, and the direction of toroidal dipole can be rotated 90 deg in two separate frequency regimes. Further, the maximum values of amplitude modulation depth around magnetic responses almost reach 100%, respectively. Multiple switching based on such magnetic responses shows potential applications in active filters, sensors, and switching.

Cadmium sulfide (CdS) nanoparticles (NPs) with europium (Eu) and ytterbium (Yb) dopant concentrations in the range of 1% to 4% were efficiently obtained through a co-precipitation approach in the presence of air at room temperature. Structural, morphological and optical characteristics of CdS  :  Eu^3  + and CdS  :  Yb^3  + NPs were explored by x-ray diffraction, Fourier transform-Raman, ultraviolet-visible absorption spectroscopy, and photoluminescence studies. The realized CdS  :  Eu^3  + NPs (3%) demonstrate the best luminescence with three emission peaks at 470 nm (2.63 eV), 590 nm (2.1 eV), and 616 nm (2.01 eV) that correlates to the excitonic emission of CdS NPs.

Advanced photonic nanostructures have enabled the maximization of synthetic chiroptic activities. The unique structuring of these building blocks has empowered chiral selective interactions with electromagnetic waves in plasmonic structures and dielectric media. Given the repertoire of optimized chiral surfaces in the literature and the ubiquity of chirality in the organic realm, the natural direction to consider is the operation of these devices in larger optical systems much like their chiral organic counterparts. Here, we recapitulate advances in active and nonlinear chiral metamaterials. Many of the results, such as the magneto-chiral anisotropy and third-harmonic Rayleigh scattering optical activity, are relatively unknown members of the more conventional family of tuning methodology and nonlinear processes. We believe that they are poised to play an instrumental role in designing advanced chiroptic systems for applications in biochemistry, valleytronics, spintronics, and chiral quantum optics.

The effects of grating structure on the performance of PTB7  :  PC₇₀BM organic solar cells (OSCs) are considered. First, an OSC with a flat antireflection coating (ARC) is studied, and the effects of grating structures inside the active area of this solar cell are investigated. It is conceivable to increase the short circuit current density (J_SC) of solar cells using dissimilar gratings. Nonetheless, there are essential limitations that constrain usage of this method inside the OSCs. Conducting optimization processes based on particle swarm optimization algorithm, it is found that the highest achievable J_SC for three-grating structure is only 3.2% higher than the single structure grating. Consequently, we have used the grating structure inside the ARC layer of the solar cell. It is observed that using the Gaussian grating ARC layer could increase the overall J_SC of the solar cell by 21.1%, which is omnidirectional, as well.

Compact, multimode, silicon waveguide bends are essential building blocks for high-density, integrated-optics, mode-division-multiplexing (MDM) circuits. However, sharp, multimode, silicon waveguide bends can typically introduce considerable insertion losses and inter-mode crosstalk. Significant efforts have been made to realize compact and high performance multimode silicon waveguide bends, but most of those designs either require complicated fabrication processes or are not really compact. We show that the transmission performances of a regular, ultra-sharp, multimode, silicon waveguide bend can be drastically improved by directly optimizing its topology. The optimization can be efficiently accomplished by using an adjoint-based inverse design. Through this design strategy, we realize a three-mode, silicon waveguide bend that is ultra-compact, with a small radius of 5.5  μm, while having ultra-low average insertion losses of 0.023, 0.046, and 0.068 dB and small average mode crosstalk of −26, −27, and −27  dB for the input modes of TE_{0  −  2} (TE = transverse electric), respectively, in the wavelength range 1500 to 1600 nm. Also, the waveguide bend can be fabricated through a single electron-beam lithography step. The significant advantages in size and performance of the current waveguide bend show the great potential of the proposed inverse design strategy for designing multimode waveguide bends for MDM systems.

Membrane or film gain mediums have attracted great attention for their good thermal performances and light field manipulation properties, which are helpful for the power scaling of a laser. A membrane laser enabled on the waveguide grating structure is proposed and this design is flexible to manipulate optical properties by controlling the photonic density of states. Lasing behavior is theoretically analyzed based on the four-level rate equations. Results show that pump absorption is enhanced by about 35 times, which leads to improved laser efficiency. When the laser mode overlaps the resonant guided mode, the Purcell factor achieves 212, leading to enhanced emission rate, as well as an apparent decrease of relaxation oscillating amplitude and time delay. The present work offers a preliminary design and lasing behavior analysis of the vertical external surface-emission laser enabled on the waveguide grating structure.

Classical Drude model has long been employed to study the plasma behavior of metals. The model has also been used for semiconductors to obtain the expressions for plasma frequency and carrier-induced changes in refractive index and absorption in terms of effective mass, transport relaxation time, and mobility of the carriers. However, these expressions remain invalid for semiconductors in which carriers occupy different valleys, as in strained SiGe alloys, GeSn alloys, and even in GaAs or InP under high electric field. We modify Drude equations for occupancy of two valleys by electrons and show deviations from standard textbook expressions. The conditions for recovering known expressions are then established. To illustrate, we consider unstrained GeSn alloys over the range 0  <  x  <  0.2 in which L and Γ conduction band valleys cross positions at x  =  0.08 resulting in a crossover from indirect to direct nature of the band gap. A comparison is made between the present values with values obtained previously.

TiO₂  /  SiO₂ nanocomposites were synthesized by DC reactive magnetron cosputtering technique using different O₂  :  Ar gas mixing ratios. The structural and spectroscopic characteristics of the synthesized samples were introduced using x-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and UV-visible spectroscopy. The XRD results revealed that all nanocomposite samples were polycrystalline. The functional groups of these samples were identified by FTIR. The UV-visible spectra of these samples showed an absorption edge at 450 nm. The results of photodegradation of organic and water pollutants under UV irradiation suggest that the photocatalytic activity of TiO₂  /  SiO₂ nanocomposite is highly improved as compared with that of TiO₂ nanophotocatalyst.

We propose a structure for a tunable multi-channel optical filter based on a one-dimensional quasicrystal made up of ZnSe (layer H) and ZnS (layer L) layers organized following the Octonacci sequence. The fourth stage of the sequence, S₄, is considered here with initial conditions S₁  =  L and S₂  =  H giving the multi-layered system a structure of HLHHHLH. The transmittance spectrum of the s-polarized (transverse electric mode) light is obtained analytically by employing a theoretical calculation based on the transfer matrix method. For normally incident waves, four output signals are transmitted out from the structure. The transmitted signals move to shorter wavelengths as the angle of incidence increases up to 89 deg. At this angle of incidence, the output signals exhibit narrow, sharp, and well-defined resonant peaks. On the other hand, the resonant peaks shift to longer wavelengths as the ambient temperature increases from room temperature to 500°C. The obtained results reveal that the proposed structure could be used as an efficient multi-channel optical filter. The overall dimension of the proposed structure is about 569 nm, which practically makes the filter easily integrated into photonic circuits.

We present a theoretical investigation of enhanced supercontinuum (SC) generation in a lead silicate photonic crystal fiber with the aid of tan-hyperbolic Gaussian pulses of peak power of 100 W, pulse duration of 50 fs, and pumped at a 1550-nm wavelength. It is observed that the generated spectra are asymmetric and composed of oscillatory structures. The span of the spectra increases, extending more toward the longer wavelength region with the increase of the tan-hyperbolic factor Ω₀. The SC spectrum for Ω₀  =  1.50 is found to be about 1.4 times wider than its Gaussian counterpart. This work may have potential applications in photonic and optoelectronic devices.

Silicon (Si) and zinc oxide (ZnO)-based heterojunctions are optoelectronic devices that promise to provide good photonic performance. The n-ZnO  /  p-Si structure is investigated using two-dimensional numerical simulation by ATLAS Silvaco software. This study investigated the effects of p-Si substrate parameters, such as thickness, acceptor concentration, and minority carrier lifetime, on the photonic performances of n-ZnO  /  p-Si heterojunction, taking into account the interface states and defects in the ZnO emitter layer for a real simulated structure. The simulation results showed that the optimal parameters that allow for better photonic performance are a p-Si thickness of 250  μm, an acceptor concentration of 6  ×  10¹⁵  cm^−  3, and a minority carrier lifetime of 10^−  3  s. The obtained photovoltaic parameters are short circuit current density of J_SC  =  38.9  mA  /  cm², open circuit voltage of V_OC  =  0.54  V, fill factor (FF) of FF  =  59  %  , and conversion efficiency of η  =  12.36  %  .

To explore the optical characteristics and bionic application potentials of the wing scales of the Madagascan sunset moth, the mapping relationship between the micronano structure and the optical response characteristics was established, and the optical stimuli-responsive mechanism of the structure-colored scales was deeply revealed. The multilevel fine structure of structure-colored scales on the forewings of the Madagascan sunset moth was formed by coupling the linear strip surface and the layered cross-section. The layered film structure system of wing scales was similar to a set of bioresponsive nanophotonic crystals, had a sensitive color change response to the external environment changes such as liquid infiltration and incident angle, and had a highly adjustable reflectivity in the near-infrared range. The unique optical characteristics of the wing scales of the Madagascan sunset moth could provide new ideas for the development of adaptive bionic stealth materials and components.

In this research work, a penta core photonic crystal fiber (PCF)-based refractive index (RI) sensor is presented to address the surface plasmon resonance (SPR) phenomenon. The proposed RI sensor (PRIS) model is tested with two material configurations, i.e., gold-indium tin oxide (Au–ITO) and gold–titanium dioxide (Au–TiO₂). Analytes having an RI varying from 1.340 to 1.380 RIU are tested from the PRIS for both material configurations. These configurations are compared with each other based on sensor parameters, such as wavelength sensitivity (WS), amplitude sensitivity (AS), linearity, and sensor resolution (SR). The sensor parameters are investigated for both transverse electric (TM) mode and transverse electric (TE) mode. The proposed sensor with Au–ITO configuration offers a maximum WS of 12,000  nm  /  RIU, AS of 13,640  RIU^−  1, and maximum SR of 8.33  ×  10^−  6  RIU for TM mode. Corresponding to the TE mode maximum WS of 11,000  nm  /  RIU, AS of 12,180  RIU^−  1 and maximum SR of 9.09  ×  10^−  6  RIU are obtained. The proposed sensor with the Au–TiO₂ configuration presents a maximum WS of 12,000  nm  /  RIU, AS of 20,370  RIU^−  1, and maximum SR of 8.33  ×  10^−  6  RIU for the TM mode. Corresponding to the TE mode maximum WS of 13,000  nm  /  RIU, AS of 18,100  RIU^−  1 and maximum SR of 7.69  ×  10^−  6  RIU is obtained. The maximum values of the sensor features are obtained for the analyte with RI 1.375 RIU for both configurations. Finally, a comparison between sensing parameters of plasmonic material ITO and TiO₂ is performed, and optimum material is identified when used with Au for RI sensing.

We demonstrate two ultra-compact high efficiency silicon waveguide crossing devices based on the tapered multimode interference coupler in the entire wavelength range of 1520 to 1580 nm. A parallel waveguide crossing structure for transverse-electric (TE) mode with a footprint of only 1.05  ×  2.6  μm² is designed, which can provide single mode crossing with the insertion loss better than 0.12 dB and the crosstalk lower than −23  dB in the broadband. A polarization-insensitive waveguide crossing with a footprint of only 1.1  ×  2.3  μm² is also designed, which can provide insertion loss lower than 0.54 dB and crosstalk lower than −23  dB for both TE and transverse-magnetic modes. The proposed parallel crossing scheme can efficiently save rooms for building up sophisticated waveguide crossing networks by avoiding the waveguide bending before or after crossing. These devices can have great application potential in the dense photonic integrated systems.

There is an urgent need for high-speed atomic force microscopy (AFM) systems, and chip-AFM on an integrated optical waveguide provides a perfect solution. A differential splitter of double waveguides is introduced as a readout method of an integrated optical waveguide AFM to overcome the non-linear response of a conventional optical waveguide AFM. Results show that an optical waveguide AFM with a 190 nm width and 1  μm height nano-tip shows a good monotonic dependence on the cantilever deflection within a range of   ±  0.4  μm using a differential splitter readout method.