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A Luneburg lens for spin waves
摘要： We report on the theory of a Luneburg lens for forward-volume magnetostatic spin waves and verify its operation via micromagnetic modelling. The lens converts a plane wave to a point source, and vice versa, by a designed graded refractive index, realized by modulating either the thickness or the saturation magnetization in a circular region. We ?nd that the lens enhances the wave amplitude by about 5 times at the lens focus, and 47% of the incident energy arrives in the focal region. A lens with small deviations from the optimal pro?le can still result in good focusing if the index is graded smoothly.
关键词： graded refractive index,Luneburg lens,micromagnetic modelling,spin waves
更新于2025-09-23 15:21:21
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Comparison of holographic setups used in heat and mass transfer measurement
摘要： The authors of the paper deal with measurement of heat and mass transfer for several years and they have frequently used few techniqes for measurement of refractive index distribution based on holographic interferometry. Some of the well known techniques have been modified some and some new ones developped. Every technique could be applied with success in different type of meassurement and obviously every one has set of properties making them unique. We decided to digest few different basic techniques and describe its properties in this paper with the aim to help the reader select the proper one for their measurement. The list of techniques and its properties is not comprehensive but schould serve as a basic orientation in the field.
关键词： holographic interferometry,refractive index distribution,heat and mass transfer,measurement techniques
更新于2025-09-23 15:21:21
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NUMERICAL ESTIMATION OF THE COMPLEX REFRACTIVE INDEXES BY THE ALTITUDE DEPENDING ON WAVE FREQUENCY IN THE IONIZED REGION OF THE EARTH ATMOSPHERE FOR MICROWAVES INFORMATION AND POWER TRANSMISSIONS
摘要： The phase and group refractive indexes of microwaves in the ionosphere region of the earth atmosphere are very important for both the researching theoretical problems and practical problems in wireless information transmission (WIT) and wireless power transmission (WPT). So far, there have been many attempts devoted to discussing and determining characterizations of earth atmosphere’s ionosphere region including the refractive indexes of microwaves concerning their velocities in ionized region, unfortunately due to the complicated features of the ionosphere region leading to research task facing many challenges. Up to recent, there is still a lack of systematic numerical data of complex refractive index by altitude depending on high frequencies of the electromagnetic waves in the ionosphere region. This paper outlines some theoretical analyses and discussions of some theoretical aspects of the complex refractive index in atmosphere’s ionized region more in detail. Based on conductivities data and the complex relative permittivity by altitude determined previously, the numerically estimated data of complex refractive indexes by the altitude from 100 km up to 1000 km at the di?erent frequencies are also shown and discussed.
关键词： wireless information transmission,refractive index,microwaves,ionosphere,wireless power transmission
更新于2025-09-23 15:21:21
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Effect of NiO NPs doping on the structure and optical properties of PVC polymer films
摘要： The goal of this study was to investigate the structure and optical properties of the prepared PVC/NiO nanocomposites. The samples were characterized via XRD, TEM, SEM, and UV–Vis spectrophotometer experimental measurements. The partial crystal structure of PVC/NiO nanocomposites and cubic structure of NiO nanoparticles were explored by X-ray diffraction. SEM exhibited the good distribution of the nanoparticles in PVC films. Linear optical parameters: refractive index and normalized absorption, increased whenever transmission and reflection reduced by adding NiO nanoparticles. Direct and indirect optical band gaps were obtained from Tauc’s formula, and it was found that both direct and indirect optical band gaps decrease as more NiO nanoparticles added. The direct optical band gap decreases from 5.20 to 5.15 eV. The optical conductivity increased by increasing the content of NiO nanoparticles. The dispersion parameters: oscillator energy E0, dispersion energy Ed, and static refractive index, were calculated by using Wemple and DiDominco model. The nonlinear optical susceptibility x(3) and nonlinear refractive index n2 were evaluated from the linear optical parameters using semiempirical relation. The increasing in nonlinear parameters x(3) and n2 suggest the use of PVC/NiO nanocomposites for nonlinear optical applications.
关键词： PVC nanocomposites,Nonlinear refractive index,Optical dispersion,XRD
更新于2025-09-23 15:21:21
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Enhanced optical efficiency and color purity for organic light-emitting diodes by finely optimizing parameters of nanoscale low-refractive index grid
摘要： To extract the confined waveguided light in organic light-emitting diodes (OLEDs), inserting a low refractive index (RI) periodic structure between the anode and organic layer has been widely investigated as a promising technology. However, the periodic-structure-based light extraction applied inside devices has been shown to severely distort spectrum and affect EL characteristics. In this study, a simple light extraction technology using periodic low-RI nanodot array (NDA) as internal light extraction layer has been demonstrated. The NDA was fabricated simply via laser interference lithography (LIL). The structural parameters of periodic pattern, distance, and height were easily controlled by the LIL process. From computational analysis using finite-difference time-domain (FDTD) method, the NDA with 300 nm pitch and 0.3 coverage ratio per unit cell with 60 nm height showed the highest enhancement with spectral-distortion-minimized characteristics. Through both computational and experimental systematic analysis on the structural parameters of low-RI NDA-embedded OLEDs, highly efficient OLEDs have been fabricated. Finally, as representative indicators, hexagonal and rectangular positioned NDA-embedded OLEDs showed highly improved external quantum efficiencies of 2.44 (+29.55%) and 2.77 (+57.38%), respectively. Furthermore, the disadvantage originating from the nanoscale surface roughness on the transparent conductive oxide was minimized.
关键词： organic light-emitting diodes,nanodot array,FDTD simulation,laser interference lithography,light extraction,low refractive index
更新于2025-09-23 15:21:01
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Performance analysis of slot waveguide using aluminum nitride in slot region
摘要： The major obstacle to accomplish an efficient photonic slot waveguide is its comparatively high propagation loss. In the current work, the silicon-on-insulator based slot waveguide with ultra-low propagation loss has been presented using aluminum nitride (AlN) in the slot region. The performance analysis of the slot waveguide has been done by varying the slot gaps from 20 to 240 nm and by varying the arm width from 160 to 340 nm. As compared with the recently reported works based on different slot waveguides, relatively smaller propagation loss of ~ 0.7 dB/cm has been predicted using the AlN based slot waveguide having a slot gap of 120 nm and arm width of 240 nm. Simulation results have demonstrated that the presence of AlN in the slot gap/low-index region, sandwiched between two high-index (silicon) regions, causes the discontinuity of the electric field of quasi-TE mode between the high-index regions. This results in high confinement of light with the smaller propagation loss in the slot region. Along with this, it has also been observed that the presented slot waveguide has the appreciably good propagation length, with low dispersion characteristics. Hence, this kind of analysis can be extended to realize the various optical devices/applications, such as for coupling, sensing, switching, etc.
关键词： Propagation loss,Aluminum nitride,Slot waveguide,Effective refractive index (ERI),Dispersion
更新于2025-09-23 15:21:01
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Straight Long-Range Surface Plasmon Polariton Waveguide Sensor Operating at ??0 = 850 nm
摘要： A bulk refractive index sensor based on a straight long-range surface plasmon polariton (LRSPP) waveguide is theoretically designed. The waveguide sensor consists of an Au stripe that is embedded in ultraviolet sensitive polymer SU-8. The geometric parameters are optimized by finite difference eigenmode method at the optical wavelength of 850 nm. The sensitivity of 196 dB/RIU/mm can be obtained with a 1.5 μm wide, 25 nm thick Au stripe waveguide. Straight LRSPP waveguides are fabricated by a double layer lift-off process. Its optical transmission is characterized to experimentally prove the feasibility of the proposed design. This sensor has potential for the realization of a portable, low-cost refractometer.
关键词： refractive index sensor,waveguide,surface plasmon polariton,polymer
更新于2025-09-23 15:21:01
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Hybrid nanoparticle layers toward enhanced luminescence of phosphor plates for white LEDs
摘要： MgF2 porous nanoparticle-silica hybrid coating layers were utilized to enhance luminescence efficiency of phosphor plates for white light emitting diodes (wLEDs). Silica and chemically synthesized porous MgF2 nanoparticles were sequentially deposited by spin coating on the phosphor plate with phosphor-in-glass (PiG) configuration. Microscopic investigation the hybrid film suggested intermixing of silica and porous MgF2 nanoparticles. Numerical estimation based on transfer matrix method expected a significant reduction in reflectance and enhancement of transmission spectra by the hybrid coating. In accordance, the photoluminescence intensity of phosphor plates showed a drastic improvement and quantum yield were enhanced from 30% (for bare PiG plate) to 45% (for hybrid layer coated PiG plate). When assembled with blue LEDs, hybrid nanoparticle coating on the PiG phosphor plates improved luminescence efficacy from 40 lm/W to 49 lm/W without deterioration of chromaticity during operation. In addition, mechanical durability of the hybrid thin film was confirmed by abrasion test. Conformal coating of matching layer consisting of porous MgF2 nanoparticles and silica can provide an efficient route to highly luminescent white LEDs with mechanical stability.
关键词： refractive index,phosphor-in-glass,nanoparticles,Luminescence,Hybrid coating
更新于2025-09-23 15:21:01
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Plasmonic Sensing of Refractive Index and Density in Methanol-Ethanol Mixtures at High Pressure
摘要： The localized surface plasmon resonance (LSPR) of gold nanospheres dispersed in methanol-ethanol 4:1 was measured as a function of pressure up to 60 GPa. The LSPR exhibits an intense redshift with pressure in the range of 0-10 GPa, followed by a slower blueshift at higher pressures. This is because an increase in the solvent refractive index with pressure leads to a redshift of the LSPR peak wavelength while an increase in the electron density of the gold nanospheres with pressure leads to a blueshift. Solvent solidification at 10 GPa and associated non-hydrostatic effects have a negligible influence on the LSPR shifts in the case of nanospheres. Here we show that both the LSPR shifts and changes in the nanospheres absorption coefficient can be explained on the basis of Gans’ model, and this enables the solvent refractive index and the density of the solvent to be determined across the hydrostatic pressure range from 0-60 GPa. Interestingly, plasmonic sensing shows no evidence of crystallization or glass phase transitions in MeOH-EtOH (4:1) solvents within the explored pressure range.
关键词： High Pressure,Optical,Hybrid Materials,Methanol-Ethanol Mixtures,Density,Plasmonics,Magnetic,Refractive Index
更新于2025-09-23 15:21:01
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[IEEE 2020 8th International Electrical Engineering Congress (iEECON) - Chiang Mai, Thailand (2020.3.4-2020.3.6)] 2020 8th International Electrical Engineering Congress (iEECON) - Design and Performance Analysis of an Ultra-compact Nano-plasmonic Refractive Index Sensor
摘要： In this paper, a Dielectric-Metal-Dielectric (DMD) plasmonic waveguide coupled with a rectangular slot is proposed and analyzed numerically with the Finite Element Method (FEM) as a refractive index sensor. Different structural parameters are varied to obtain maximum sensitivity of the proposed structure. In this geometry, silver is used as the metal and it is surrounded by Material Under Sensing (MUS) which is dielectric in nature. The linear correlation between both the refractive index and the position of the transmission peaks is used for the detection of the materials. From this simpler geometry, maximum sensitivity is obtained to be 818 nm/RIU; RIU means Refractive Index Unit. Due to the ease in the nanoscale fabrication of the proposed simplistic structure, it can have potential applications in nanoscale optical devices and the nano chip sensors.
关键词： Finite Element Method,Surface Plasmon Polaritons (SPPs),Refractive Index Sensor
更新于2025-09-23 15:21:01