基于谐振环的太赫兹宽带偏振转换器件研究

提出了一个基于谐振环结构的宽带且高效的太赫兹线偏振转换器.该结构由金属-电介质-金属三层构成,位于顶层的是基于开口谐振环的超表面,中间为介质层,底部为金属板.实验结果表明,该结构可以在0.59-1.24 THz频率范围内将线偏振的太赫兹波偏振方向旋转90°,转换率超过80%.通过计算该结构在所研究的频率范围内反射光的偏振角和椭圆角,证实了该结构可以在较宽的频率范围内实现高效的线偏振转换.对该结构在偏振转换率高的频率下表面电流和电场进行仿真,分析了高偏振转换率和宽带的机理.同时,研究了该结构的偏振转换率对入射角以及偏振角的依赖性,结果表明该结构在0°-30°入射角范围内、-10°-10°偏振角范围内均有很好的偏振转换性能.

A broadband polarization converter based on resonant ring in terahertz region

The terahertz polarization converter has potential applications in the field of terahertz spectroscopy and imaging. A broadband and high conversion rate of terahertz linear polarization converter based on the metasurface of resonant ring is proposed. The designed structure consists of three layers, i.e., the top layer, which is a metasurface of resonant ring; the bottom layer, which is a metal film of aluminum; a dielectric layer of polyethylene terephthalate, which is sandwiched in between. In order to obtain the best performance, the simulation and optimization are performed by using CST microwave studio. At the same time, the preparation conditions are also taken into account. The optimized geometric parameters of device are obtained. The samples are prepared by using the photolithography and wet etching. The performance of the designed polarization converter is demonstrated experimentally by using the terahertz time domain spectroscopy. The experimental results show that the proposed device can rotate 90° the polarization state of incident terahertz wave of linear polarization in a frequency range from 0.59 THz to 1.24 THz. The polarization conversion rate is more than 80%. The experimental result is in good agreement with the simulated one. By calculating the polarization angle and elliptical angle of the reflected terahertz wave, it is proved that this device can achieve a high-efficiency linear polarization conversion in a wide frequency range. The distributions of surface currents and electric fields are simulated at the frequency with the high polarization conversion rate. The mechanism of high polarization conversion rate is analyzed based on the distribution of surface currents. The performances of broadband and high conversion rate of the designed structure are derived from the third-order electromagnetic resonance. At the same time, the dependence of the polarization conversion rate on incident angle and polarization angle is stimulated and analyzed. The results show that this device has a good polarization conversion performance in an incidence angle range of 0°-30° and a polarization angle range of-10°-10°.