| Metamaterials is generally defined as a new artificial material which consists of micro-wavelength periodic unit cell. This kind of material has a great potential application in many fields due to their unique electromagnetic properties. In particular, more and more attention has been paid to the investigation of metamaterial functional devices working at Terahertz(THz) frequency. Nowadays, all kinds of functional devices have been designed and fabricated. Those include THz filter, polarizer, modulator, absorber and switching. Compared with conventional devices, THz metamaterial functional devices are easy-to-integrate and light-weight. The dissertation mainly focuses on the theoretical investigation and design approach of metamaterials based THz absorber and optical switching. The major working contents are listed below: 1. A vertical cascaded ultra-broadband THz metamaterial absorber was proposed. An extra absorption peak, which induced by magnetic resonance coupling of each metallic layer, was introduced to enlarge the absorption spectrum. In the frequency range of 2.6-5.7 THz, the absorption spectrum after superposition can keep absorption higher than 90% for the normal incident THz waves. Additionally, the full width of half maximum(FWHM) approximately reaches to 95% with respect to the central frequency. The incident THz power losses at all resonant frequencies were calculated to analysis the generation mechanism of the extra absorption peak. 2. The incident angle dependent and polarization dependent of the absorption spectrum was investigated through numerical simulation. The results show that the absorber can still sustain absorption above 88% within about 2.5 THz frequency range when the incident angle is less than 50o. At the same time, the variation of the polarization angle has a neglectable influence on the absorption magnitude. Thus, the absorber is polarization insensitive. 3. A terahertz metamaterial optical switching based on asymmetric split-ring resonator was designed. By modulating the pump power, the switching can switch between the ON state and OFF state. The influence of the pump power on the carrier density was specifically investigated through theoretical calculation. Besides, the generation and recombination of the carrier was also analyzed.4. In order to analyze the detailed generation mechanism of each resonant peak. The distribution of electric field and surface current at their resonant frequencies were calculated. According to the results, some resonances are generated by the resonant coupling of the LC resonance and high order resonance. Furthermore, two models were used to simply describe the switching progress of ON/OFF state. 5. The study shows that the switching ratio of the switching window, which locates at the frequency range of 1.26 to 1.49 THz, is higher than 10. The position and width of the switching window can be tuned by changing the permittivity and thickness of dielectric layer. The modulation range is about 0.3 THz. In addition, the response time of the THz optical switching can reach to an order of picoseconds. |
