Optical and Quantum Electronics最新文献

Metamaterial absorption can be realized at extremely long wavelengths and across a broad range of frequencies for spectroscopic applications. Among these, terahertz (THz) spectroscopy has gained increasing adoption for sensing applications due to its distinctive optical characteristics. This study proposes and numerically investigates a perfect absorber (PA) in THz spectroscopy, comprising a periodic array of indium antimonide (InSb), a reflector, and a dielectric substrate. Numerical outcomes indicate that the PA is able to obtain 99.9% absorption at 1.748 THz under the surrounding temperature (T = 295 K) and exhibits a Q-factor of approximately 26.4. To interpret the underlying physics of the proposed PA, impedance matching theory, the spatial distribution of the electric field, and power loss density are discussed. The proposed structure demonstrates exceptional stability across a broad spectrum of incidence angles. Furthermore, it delivers simultaneous high sensing performance. The surrounding temperature significantly affects the optical properties of InSb, resulting in a temperature sensitivity of 11.38 GHz/K. The suggested PA can be useful in refractive index (RI) sensing due to its higher sensitivity and greater Q-factor. It has an RI sensitivity of roughly 1452 GHz/RIU. Therefore, the designed tunable THz PA can be extensively employed in sensing, detection, and other associated optoelectronic devices because of its enhanced sensing performances.

In this study, we propose a micro neutron star-like gravity model to explain the phenomenon of superluminal response in quantum entanglement experiments. In our model, measurements of the spin state of one electron may cause that electron to emit ultralong-wavelength photons to inform another entangled electron. Therefore, one electron will be connected to another electron through the Coulomb interaction of ultra-low energy photons. The scattering of ultra-long wavelength light can be ignored, and only the super-strong gravity around the atomic nucleus is considered. In this model, the ultra-long wavelength light close to the atomic nucleus is mainly affected by the super-strong gravitational field of each atomic nucleus, and the time passing through each atomic nucleus will be shortened by Δt on average, and a superluminal response is finally observed. Our model does not violate special relativity but discusses the measurements between different reference coordinates within the framework of general relativity.

In this study, calcium antimony fluoroborate (CAFB) glass matrices were designed with single doping of Tb³⁺ (CAFBTb), Sm³⁺ (CAFBSm), and co-doping of Tb³⁺/Sm³⁺ (CAFBTbSm) ions using the procedure of melt quenching. The structural characteristics of the titled glasses were examined with the help of diffraction profiles. Under appropriate n-UV excitation wavelengths, all the prepared CAFBTb glasses demonstrate an intense green (542 nm) emission related to the ⁵D₄ → ⁷F₅ transition, in which the intensity of the emission peak consistently rises with the Tb³⁺ ion content till 2.5 mol%. In CAFBSm glasses, a prominent orangish-red emission peak has been observed around 598 nm (⁴G_5/2 → ⁶H_7/2 transition) at 402 nm excitation. Furthermore, a gradual decrease in the emission intensities of Tb³⁺ bands and an increase in the emission intensities of Sm³⁺ were observed simultaneously in the CAFBTbSm glasses with increasing activator concentration. This behaviour suggests the occurrence of an energy transfer (ET) process from donor (Tb³⁺) to acceptor (Sm³⁺) ions. This mechanism of transferring energy from Tb³⁺ to Sm³⁺ was proved to be an interaction of dipole-dipole (d-d) via employing Dexter and Reisfeld’s theoretical model. The colour tunability of the CAFBTbSm glasses could be adjusted from the green to the white domain via greenish yellow under 378 nm excitation and by varying the amount of the activator ion concentrations. Under n-UV excitation, the PL lifetime analysis indicates a bi-exponential decay behaviour in the co-doped glasses. Additionally, the emission intensity of the prepared CAFBTbSm glasses was maintained at 88.22% of the initial emission intensity at 25 °C when measured at 100 °C, signifying that these glasses possess exceptional thermal stability and relatively higher activation energy. All the aforementioned findings authorised the feasibility of the titled CAFBTbSm glasses for potential usage in the realm of optoelectronic device applications, especially for white light emitting diode (w-LED) applications.

Lead-free double halide perovskites, specifically Cs₂TlAX₆ (A = As, Sb; X = Cl, Br, I), offer key advantages over lead-based versions, including strong optical absorption, high structural and thermal stability, superior carrier mobility, tunable band gaps, non-toxicity, and cost-effectiveness. Their mechanical, electrical, optical, and thermal properties were investigated using DFT with the PBE functional under ambient and hydrostatic pressures. Stability was confirmed through formation enthalpy, tolerance factor, and elastic constants. Pugh’s and Poisson’s ratios suggest these compounds are generally ductile (except Cs₂TlAsBr₆), with pressure-enhanced machinability, reduced friction, and increased plastic strain. Band structure analysis using the GGA-PBE approximation shows the direct band gap semiconducting nature of Cs₂TlAX₆ (A = As, Sb; X = Cl, Br, I), where the band gap values are ranging from 0.957 to 1.697 eV. However, the TB-mBJ functional efficiently moderates the GGA-PBE underestimation, yielding refined band gaps between 1.22 and 2.17 eV—values which are more efficient solar applications. Pressure-induced band gap tuning highlights potential for optoelectronic device applications. Their narrow band gaps and strong absorption make them suitable for solar cells, while high infrared reflectivity and low thermal conductivity indicate potential as thermal barrier coatings (TBCs).

This communication focused on the design development of a low-loss, patch size enhancement and a wideband four-element monopole antenna for Ka-band and millimetre wave (mm-wave) communications. This study presents the 4-patch duplication antenna, which has frequency reconfigurability via two PIN diodes and frequency sensitivity via one varactor diode. The proposed technology provides an alternative to tediously built antenna arrays. A small Rogers RT Duroid 5880 (0.508 mm) makes the antenna low-loss. The affect of varactor biasing on tuning linearity, stability, and repeatability have been studied. Excellent impedance matching at 32.5 GHz is achieved with this patch-size enhancement approach. One-element antennas without slots have a peak gain of 6.79 dBi at 32.5 GHz, while slot antenna have 7.02 dBi. The improved four-element array antenna increases the gain to 8.32 dBi. Gain is further improved to 9.81 dBi with the digital modes of PIN diodes. The measured reflections ((:{text{S}}_{11})) and radiation properties were found to be consistent with the simulations. The suggested antenna performs well between 26 GHz and 40 GHz, as evidenced by its − 10 dB bandwidth and results. The observed data showed that the proposed design is suitable for mm-wave and 5G sub-6 GHz frequency range 2 (FR2), and beyond applications.

This study presents a dynamically reconfigurable anisotropic graphene-based metamaterial absorber operating across the 0.5–4.7 THz range. The unit-cell design, composed of two orthogonal pairs of graphene ribbons, produces direction- and polarization-dependent electromagnetic responses. Numerical simulations using CST Studio Suite, complemented by an equivalent circuit model (ECM) analyzed in MATLAB, reveal the transverse electric (TE) and transverse magnetic (TM) resonances. At a Fermi energy of 0.6 eV, the absorber demonstrates high tunability and pronounced linear dichroism (LD) up to 99.1%. The structure supports four TE and two TM high-absorption resonances, achieving absorption rates above 94.5% and 82%, with peak values of 99.68% (TE) and 99.92% (TM). These distinct TE/TM spectral fingerprints offer strong potential for polarization-sensitive THz devices, photonic platforms, and Frequency-Encoded Secure Identification (FESID) applications.

The CdS nanocrystallite films prepared by thermal deposition are characterized by different morphological and optical methods. The nonlinear optical absorption of 1030 nm and 515 nm, 200 fs radiation in the films is determined. The competition of saturable absorption and two-photon absorption is shown in the case of the variation of the pulse energies of the visible and infrared radiation. We show the overlap of the positive and negative nonlinear absorption in different energy ranges of the probe pulses. The saturated intensities of the CdS film are determined to be 1.7 × 10¹² W cm⁻² in the case of 1030 nm probe pulses and 1.3 × 10¹¹ W cm⁻² in the case of 515 nm probe pulses. The two-photon absorption coefficient in the case of 1030 nm pulses is calculated to be 4.7 × 10⁻⁸ cm W⁻¹. The two-photon absorption coefficient in the case of 515 nm probe pulses is determined to be 8 × 10⁻⁸ cm W⁻¹.

Optical loss is a significant factor that limits the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Light-trapping structures and metal plasmons have been found to enhance light absorption in PSCs, thus improving PCE. In this study, two different types of CH₃NH₃PbI₃ PSCs, incorporating an array of ellipsoidal Ag nanoparticles (NPs) within the active layer and an ITO moth-eye grating on the top surface, were designed. The impact of variations in the shape and position the Ag NPs, as well as the inclusion of the ITO moth-eye grating, on light absorption, was thoroughly investigated. The maximum photocurrent density and PCE reach 25.89 mA/cm², 23.77% which is 1.24 times larger than that of the planar reference. The combination of embedded Ag NPs and the ITO antireflection layer causes this synergistic effect. These findings have the potential to design and prepare high-efficiency PSCs.

In this article, two different circular-lattice photonic crystal fiber (PCF) based on chalcogenide (ChG) compositions (Ge(_{11.5})As(_{24})Se(_{64.5}) and Ge(_{15})Sb(_{15})Se(_{70}) respectively) are proposed and their performance for supercontinuum (SC) generation are numerically investigated. Both of the structures generate broad SC spectra with high coherence when pumped by a 5 kW, 50 fs hyperbolic secant pulse at 2.5 (upmu )m wavelength and at the same time exhibit strong localization for core-mode with very low confinement loss. In our numerical studies, four unique combinations of the proposed PCF structures and the ChG core compositions were rigorously examined, yielding SC bandwidths having the widest wavelength up to 10.68 (upmu )m and the narrowest wavelength spanning limited to 3.43 (upmu )m. While exhibiting excellent structural tolerance, one particular case among the four combinations also demonstrates the highest spectral flatness in the generated supercontinuum.

We have designed a two-dimensional hexagonal photonic crystal sensor to detect Cu²⁺ ions in aqueous solutions using a simulation-based approach. The sensor structure consists of air-filled cylindrical holes arranged in a hexagonal lattice within a TiO₂ dielectric background, which acts as the high-refractive-index material. The optical behavior of the sensor is analyzed using the finite element method in COMSOL Multiphysics. A central defect was introduced into the hexagonal unit cells whose refractive index varies according to the concentration of Cu²⁺ ions. The design is optimized with a cylinder radius ((r)) of 70 nm, a pitch ((p)) of 150 nm, and a lattice constant ((a)) of 550 nm to achieve resonance in the infrared region. This structural design results in an observable resonance peak shift within the photonic band gap region. The sensor achieves a sensitivity of 38.22 nm/RIU, a high quality-factor of 28,354.02, and a figure of merit of 733.33 RIU⁻¹. Due to its high performance and compact structure, this sensor offers a practical and efficient solution for heavy metal ion detection in photonic sensing applications.