A temperature tunable hybrid metamaterial absorber based on vanadium dioxide (VO2) particles is proposed and simulated in the terahertz frequency regime. An absorption peak is achieved at 6.13 THz at room temperature with maximum absorptivity of 97.3%, which is derived from the local surface plasma (LSP) mode resonance. The effect of geometric parameters on the absorption properties is revealed. When the simulated temperature reaches the phase change point of VO2 particles, the original absorption peak is enhanced and converted into an absorption band. Moreover, an absorption peak is achieved. These resonance behaviors are mainly due to the conversion of VO2 particles into new resonators in the proposed metamaterial absorber. LSP modes are supported by these VO2 particles resonance elements. The absorption band and new absorption peak are enhanced and shifted to lower frequencies with the simulated temperature increasing. An LC equivalent circuit model is proposed to understand these resonance absorption behaviors.
As an optical element, diffraction grating is of considerable importance in many research fields. In this paper, Fourier analysis method is used to analyze the Fraunhofer diffraction phenomena of plane and convex holographic gratings under various conditions. Based on the transmittance function, the law of complex amplitude distribution, intensity distribution and spectral distribution on the diffraction screen is derived. For the planar and convex holographic gratings in the spectrometer design, the inherent laws of optical phenomena can be understood more deeply. In particular, the convex holographic gratings are analyzed as a combination of amplitude type plane grating and phase type spherical mirror, rather than being considered separately in most literature.