No abstract

The polarization conversion of electromagnetic waves plays a crucial role in practical application. Here, a tunable multi-mode dual-band high-efficiency and reflection-type polarization converter based on liquid crystal (LC) in the terahertz region is proposed. It is composed of periodic unit structures, each unit of which is constituted by the designed structure, LC mixture and fully reflected gold mirror. It numerically reveals that in the operating bandwidth 1.03–1.53 and 1.27–1.86 THz corresponding to the refractive index of LC mixture ño and ñe, the converter can convert linear-polarized and circular-polarized waves to its corresponding cross-polarizations, whose polarization conversion ratio is larger than 90%. Meanwhile, the proposed converter can realize the conversion from linear-polarized wave to circular-polarized one in dual-band, 1.10–1.25 and 1.92–2.2 THz or 0.93–1.04 and 1.57–1.88 THz corresponding to ño and ñe with axis ratio lower than 3 dB. The insensibility of incident angle is analyzed as well. In addition, the physical mechanism of the polarization conversion is disclosed. The ultra-thin and compactness characteristic of this designed polarization converter are very attractive for a variety of applications in EM measurement, sensing, terahertz technology and 6G communication.

Polarization measurement has been used for many optical applications in science and technology. Herein, we adopt a reliable method to measure the polarization parameters of incident light, including principal axis, chirality and ellipticity based on the superposition of two orthogonal vortex beams with non-integer topological charges (TCs). All three polarization parameters can be measured and analyzed by the interference pattern produced by the superposition of two vortex beams with 1 1 = and 2 = 0.5 . The relationship between the principal axis of polarization and the interference pattern is deduced theoretically. The measurement results agree with the theoretical formulation very well. The advantages of simplicity make this method have a good application prospect in polarization measurement, optical communication, micro-particles manipulation and quantum science.