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Designing photonic materials with complete band gaps by topology optimization
摘要： Photonic materials may exhibit the propagation of electromagnetic waves is totally prohibited. To achieve a complete photonic band gap (CPBG) for transverse magnetic (TM) and transverse electric (TE) modes, the bi-directional evolutionary structure optimization (BESO) method originated from structural design is extended for this purpose. The optimization problem is formulated with maximizing the minimum imaginary part of complex wave vectors for TM and TE modes. According to sensitivity analysis, the material distribution within the primitive unit cell of photonic materials is adjusted step by step so as to enlarge the minimum imaginary part of wave vectors. In doing so, the CPBG at the specific frequency is obtained at the desired frequency, and the optimized structures of photonic materials with novel topological patterns are achieved. Numerical examples demonstrate that the effectiveness of the proposed topology optimization method for opening the CPBGs at various specified frequencies, which is of significance in controlling the propagation of electromagnetic waves of any polarization.
关键词： Topology optimization,Complete band gap,Evanescent waves,Photonic materials
更新于2025-09-23 15:21:01
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Interferometric Evanescent Wave Excitation of a Nanoantenna for Ultrasensitive Displacement and Phase Metrology
摘要： We propose a method for ultrasensitive displacement and phase measurements based on a nanoantenna illuminated with interfering evanescent waves. We show that with a proper nanoantenna design, tiny displacements and relative phase variations can be converted into changes of the scattering direction in the Fourier space. These sensitive changes stem from the strong position dependence of the orientation of the purely imaginary Poynting vector produced in the interference pattern of evanescent waves. Using strongly confined evanescent standing waves, high sensitivity is demonstrated on the nanoantenna’s zero-scattering direction, which varies linearly with displacement over a wide range. With weakly confined evanescent wave interference, even higher sensitivity to tiny displacement or phase changes can be reached near a particular location. The high sensitivity of the proposed method can form the basis for many metrology applications. Furthermore, this concept demonstrates the importance of the imaginary part of the Poynting vector, a property that is related to reactive power and is often ignored in photonics.
关键词： nanoantenna,Poynting vector,evanescent waves,displacement metrology,phase metrology
更新于2025-09-23 15:21:01
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Theoretical assessment of D-shaped optical fiber chemical sensor associated with nanoscale silver strip operating in near-infrared region
摘要： In present work, we propose a surface plasmon resonance based D-shaped fiber for the chemical sensor using nanoscale silver strip deposited over polished surface of single mode fiber. Various parameters of the designed sensors are optimized to achieve the maximum wavelength sensitivity. The sensing properties are investigated using finite element method based on COMSOL Multiphysics. An average wavelength sensitivity of 2100 nm/RIU is obtained for wide range of refractive index (RI) varying between 1.34 and 1.42 and a maximum wavelength and amplitude sensitivity of 3240 nm/RIU and 192 RIU?1 is achieved for RI range varying between 1.38 and 1.42 with 3.08 × 10?5 RIU resolution. The results indicate that our designed sensor perform effectively in high RI range and hence can be used in chemical and biological sensing.
关键词： Nanoscale,Surface plasmon resonance,Refractive index,D-shaped,Evanescent waves
更新于2025-09-23 15:19:57
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Effect of Evanescent Waves on the Dark Current of Thermophotovoltaic Cells
摘要： The output power of thermophotovoltaic (TPV) cells may be greatly increased when the gap between the emitter and cell is reduced to sub-micron distances (near-field regime), at which photon tunneling due to evanescent waves becomes important. Accurate modeling of TPV cells in these conditions is crucial for the design and optimization of near-field TPV systems. The conventional or standard modeling method uses the summation of the dark current and the short-circuit current, while the direct method applies the photon chemical potential. It has been shown that the two methods are linked through a modification of the direct method using Wien’s approximation. By contrasting different modeling approaches, we quantitatively analyze the effects of evanescent waves on the TPV cell performance parameters, especially the dark current, for different emitter and cell materials in the near-field regime. Our results show that the saturation current by radiative recombination is strongly affected by evanescent waves and the bandgap energy. The current-voltage characteristics calculated by different modeling methods are displayed to demonstrate that a constant saturation current typically used in the standard method could cause substantial error in the near-field regime. For a TPV system with an emitter operating at relatively low temperatures, we show that it is necessary to include the photon chemical potential in the computation of the net radiative heat transfer between the emitter and receiver.
关键词： evanescent waves,Dark current,near-field thermophotovoltaic,diode
更新于2025-09-11 14:15:04
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Efficient and quantitative analysis of photon density of states for two-dimensional photonic crystals with omnidirectional light propagation
摘要： Omnidirectional light propagation in two-dimensional (2D) photonic crystals (PCs) has been investigated by extending the formerly developed 2D finite element analysis (FEA) of in-plane light propagation in which the corresponding band structure (BS) and photon density of states (PDOS) of 2D PCs with complex geometry configurations had been calculated more accurately by using an adaptive FEA in real space for both the transverse electric (TE) and transverse magnetic (TM) modes. In this work, by adopting a wave-guiding theory under the consideration of translational symmetry, the omnidirectional PDOS corresponding to both the radiative and evanescent waves can be calculated efficiently based on the in-plane dispersion relations of both TE and TM modes within the irreducible Brillouin zone. We demonstrate that the complete band gaps shown by previous work considering only the radiative modes will be closed by including the contributions of the evanescent modes. These results are of general importance and relevance to the spontaneous emission by an atom or to dipole radiation in 2D periodic structures. In addition, it may serve as an efficient approach to identifying the existence of a complete photonic band gap in a 2D PC instead of using time-consuming three-dimensional BS calculations.
关键词： two-dimensional photonic crystals,radiative and evanescent waves,finite element analysis,photon density of states,omnidirectional light propagation
更新于2025-09-10 09:29:36
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Sum Frequency Generation Vibrational Spectroscopy using Evanescent Waves - towards Probing Irregular and Complex Surfaces of Mesoscopic-scale Materials
摘要： With rapid development of materials science, on-demand techniques are highly needed with the capability to characterize materials in the micrometer and nanometer scales. In this article, we show that, by employing a prism geometry, total internal reflection (TIR) sum frequency generation (SFG) vibrational spectroscopy allows for characterizing mesoscopic materials with irregular or complex surfaces. Four representative examples were presented. First, we reveal that, mechanical grinding can subtly alter the surface molecular structures of original materials. Second, spin coating can substantially change the surface molecular structures of particle samples. Third, surface restructuring of carboxylated multi-walled carbon nanotubes (c-MWCNTs) can happen in response to the surrounding environment. Fourth, surface adsorption and desorption dynamics of toluene on activated charcoal can be traced. Such experiments demonstrate, there are still a broad range of research fields ahead SFG can be directed to, where materials in mesoscopic scales with irregular or complex surfaces can be studied.
关键词： Surface Characterization,Sum Frequency Generation,Vibrational Spectroscopy,Mesoscopic-scale Materials,Evanescent Waves
更新于2025-09-10 09:29:36
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Enzyme Biosensing Based on Zinc Oxide Nanostructures as Active Surface
摘要： Ag/ZnO mesostructures deposited onto substrates different were analysed in order to use ZnO as bioactive surface. This paper presents the results obtained at the eNDE of strips gratings deposited on different substrates used as bioactive surface using the EM sensor with MM lens in order to improve the emphasizing of the evanescent waves appeared when the slits of MSG are filled with immobilized enzymes.
关键词： EM sensor,enzyme biosensing,bioactive surface,evanescent waves,ZnO nanostructures
更新于2025-09-09 09:28:46
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Extreme Asymmetry in Metasurfaces via Evanescent Fields Engineering: Angular-Asymmetric Absorption
摘要： On the quest towards full control over wave propagation, the development of compact devices that allow asymmetric response is a challenge. In this Letter, we introduce a new paradigm for the engineering of asymmetry in planar structures, revealing and exploiting unilateral excitation of evanescent waves. We test the idea with the design and experimental characterization of a metasurface for angular-asymmetric absorption. The results show that the contrast ratio of absorption (the asymmetry level) can be arbitrarily engineered from zero to infinity for waves coming from two oppositely tilted angles. We demonstrate that the revealed asymmetry effects cannot be realized using conventional diffraction gratings, reflectarrays, and phase-gradient metasurfaces. This Letter opens up promising possibilities for wave manipulation via evanescent waves engineering with applications in one-side detection and sensing, angle-encoded steganography, flat nonlinear devices, and shaping the scattering patterns of various objects.
关键词： evanescent waves,metasurfaces,wave manipulation,asymmetric absorption
更新于2025-09-04 15:30:14