Based on the phase transition of vanadium dioxide(VO2), an ultra-broadband tunable terahertz metamaterial absorber is proposed. The absorber consists of bilayer VO2 square ring arrays with different sizes, which are completely wrapped in Topas and placed on gold substrate. The simulation results show that the absorption greater than 90% has frequencies ranging from 1.63 THz to 12.39 THz, which provides an absorption frequency bandwidth of 10.76 THz, and a relative bandwidth of 153.5%. By changing the electrical conductivity of VO2, the absorption intensity can be dynamically adjusted between 4.4% and 99.9%. The physical mechanism of complete absorption is elucidated by the impedance matching theory and field distribution. The proposed absorber has demonstrated its properties of polarization insensitivity and wide-angle absorption, and therefore has a variety of application prospects in the terahertz range, such as stealth, modulation, and sensing.
The optical sensor based on lossy mode resonance can overcome the limitations of traditional surface plasmon resonance sensors and work under TE and TM polarized light. In this paper, an LMR sensor theoretical model with the configuration of prism/matching layer/lossy layer/sensing layer is proposed, which is based on the principle of attenuated total reflection. By using TiO2 film as the lossy layer and LiF film as the matching layer, the resonance signal under angle interrogation is effectively improved. One of the advantages of the proposed sensor is that the detection range and detection accuracy are dynamically adjustable, which provides additional degrees of freedom in the design and use of the device. The structural parameters (film thickness, layer refractive index) affecting the resonance signal have been investigated based on the electric field distribution at resonance and the coupled mode theory. The LMR signal under TE and TM polarization can be switched by changing the thickness ratio of the matching layer and the lossy layer. All possible combinations of film thicknesses are given as a reference for the design of the LMR prism sensor based on TiO2 film. Under proper thickness combination, the proposed sensor is capable of detecting the medium with refractive index ranging from 1.32 ∼ 1.47, with a sensitivity range of 34 ∼ 148 °/RIU under angle interrogation and a maximum value of 192 RIU−1 for FOM under TM polarization. We hope these investigations can prove the advantages of LMR prism sensors and provide guidance for the experimental implementation of LMR prism sensors in the future.
Self-referenced refractive index sensors allow more accurate measurements and reduce the influence of extraneous factors. This work proposed a high-sensitivity, self-referenced surface plasmon resonance sensor with Na grating and Au-ZnS composite grating. When Transverse Magnetic-polarized light is incident into the prism, three surface plasmon resonances are excited at the interface of Na-MgF2 grating and Au-ZnS grating. The first one is treated as the reference angle, the second and third are forward and backward surface plasmon resonance, respectively. Using the angular modulation, the single-dip sensitivities are 329.41 deg/RIU and 788.24 deg/RIU in the range of 1.330-1.347. To further improve the performance of the sensor, the double-dips method is adopted, and the average sensitivity in the range of 1.330-1.347 is 1117.65 deg/RIU, while the maximum reaches 4390 deg/RIU. Due to high sensitivity, a good figure of merit can be obtained even with a larger full width at half maximum of 3.30°. This proposed sensor provides potential application in the research of biomolecular detection and chemical testing.
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