We propose a hybrid plasmonic zeolitic imidazolate framework-8 (ZIF-8) nanostructure to achieve near-infrared dual-band sensing of trace amounts of volatile organic compound (VOC) gases via metal-organic framework patch array integrated on metal (Au) film. To achieve dual-band VOC gas sensing, two absorption peaks related to the surface lattice resonance (SLR) and surface plasmon polaritons (SPP) resonance are constructed in this plasmonic structure, to match the near-infrared absorption bands of methane and ethanol gas molecules respectively. For an 80 nm thick Au layer, the height and width of ZIF-8 patch and the gap between ZIF-8 patches are optimized to be 0.86, 0.925, and 0.43 μm. Then, this structure shows an SLR at 1392.64 and a SPP resonance at 1653.72 nm, which have peak intensities of 0.735 and 0.855, and the Q-values of 1435 and 253, respectively. Furthermore, the third resonance peak related to the Fano resonance is investigated and can be considered as a feasible alternative to calibrate the measurement without external references.
We theoretically investigate the characteristics of the multilayered hyperbolic metamaterial (HMM) composed of graphene and discuss the transmission properties from another angle of Fabry–Perot (F–P) resonance analysis. Dispersion characteristics of graphene-dielectric multilayered hyperbolic metamaterials (GDM HMMs) can be adjusted by changing the chemical potential of graphene. Transfer matrix method is improved to adapt the condition of large tangential vectors, and transmission properties are analyzed numerically. Calculated results indicate that dielectric material and graphene codetermine the dispersion properties of the HMMs, and the optical properties can be dynamically adjusted due to the introduction of graphene. Transmission spectra exhibit F–P resonance properties and discussions prove the validity of the F–P cavity theory. However, the transmission characteristics of GDM HMMs are different from the phenomena and laws of the traditional F–P cavity. Further analysis reveals that the mechanism originates from the contribution of graphene and high-k waves in HMMs. We present an innovative perspective for investigating and understanding transmission properties of GDM HMMs and provide references for design of HMMs and other related photonic devices.
The finite-difference time-domain (FDTD) method, which solves time-dependent Maxwell’s curl equations numerically,
has been proved to be a highly efficient technique for numerous applications in electromagnetic. Despite the simplicity
of the FDTD method, this technique suffers from serious limitations in case that substantial computer resource is
required to solve electromagnetic problems with medium or large computational dimensions, for example in high-index
optical devices. In our work, an efficient wavelet-based FDTD model has been implemented and extended in a parallel
computation environment, to analyze high-index optical devices. This model is based on Daubechies compactly
supported orthogonal wavelets and Deslauriers-Dubuc interpolating functions as biorthogonal wavelet bases, and thus is
a very efficient algorithm to solve differential equations numerically. This wavelet-based FDTD model is a
high-spatial-order FDTD indeed. Because of the highly linear numerical dispersion properties of this high-spatial-order
FDTD, the required discretization can be coarser than that required in the standard FDTD method. In our work, this
wavelet-based FDTD model achieved significant reduction in the number of cells, i.e. used memory. Also, as different
segments of the optical device can be computed simultaneously, there was a significant gain in computation time.
Substantially, we achieved speed-up factors higher than 30 in comparisons to using a single processor. Furthermore, the
efficiency of the parallelized computation such as the influence of the discretization and the load sharing between
different processors were analyzed. As a conclusion, this parallel-computing model is promising to analyze more
complicated optical devices with large dimensions.
We present the electromagnetic analysis of Talbot effect with the finite-difference time-domain (FDTD) method. To our knowledge, it is the first time that FDTD method is applied to analyze the performance of a Talbot illuminator. Furthermore, self-imaging performances of a grating with different flaws are analyzed. The FDTD method can be applied to analyze this kind of diffraction. Of course it also can be analyzed with the Fourier transform method. But for this non-period grating, it will be more complex. In addition, the grating employed here is a high-density grating. The Fourier transform method is not rigorous enough. For these reasons, the FDTD method can show the exact near-field distribution of different flaws in a high-density grating, which is impossible to attain with the conventional Fourier transform method.
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